1 \input texinfo @c -*-texinfo-*-
2 @c Copyright (C) 1988-1996, 1998-2012 Free Software Foundation, Inc.
5 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
6 @c of @set vars. However, you can override filename with makeinfo -o.
11 @settitle Debugging with @value{GDBN}
12 @setchapternewpage odd
24 @c readline appendices use @vindex, @findex and @ftable,
25 @c annotate.texi and gdbmi use @findex.
29 @c !!set GDB manual's edition---not the same as GDB version!
30 @c This is updated by GNU Press.
33 @c !!set GDB edit command default editor
36 @c THIS MANUAL REQUIRES TEXINFO 4.0 OR LATER.
38 @c This is a dir.info fragment to support semi-automated addition of
39 @c manuals to an info tree.
40 @dircategory Software development
42 * Gdb: (gdb). The GNU debugger.
46 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996,
47 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
48 Free Software Foundation, Inc.
50 Permission is granted to copy, distribute and/or modify this document
51 under the terms of the GNU Free Documentation License, Version 1.3 or
52 any later version published by the Free Software Foundation; with the
53 Invariant Sections being ``Free Software'' and ``Free Software Needs
54 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
55 and with the Back-Cover Texts as in (a) below.
57 (a) The FSF's Back-Cover Text is: ``You are free to copy and modify
58 this GNU Manual. Buying copies from GNU Press supports the FSF in
59 developing GNU and promoting software freedom.''
63 This file documents the @sc{gnu} debugger @value{GDBN}.
65 This is the @value{EDITION} Edition, of @cite{Debugging with
66 @value{GDBN}: the @sc{gnu} Source-Level Debugger} for @value{GDBN}
67 @ifset VERSION_PACKAGE
68 @value{VERSION_PACKAGE}
70 Version @value{GDBVN}.
76 @title Debugging with @value{GDBN}
77 @subtitle The @sc{gnu} Source-Level Debugger
79 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
80 @ifset VERSION_PACKAGE
82 @subtitle @value{VERSION_PACKAGE}
84 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
88 \hfill (Send bugs and comments on @value{GDBN} to @value{BUGURL}.)\par
89 \hfill {\it Debugging with @value{GDBN}}\par
90 \hfill \TeX{}info \texinfoversion\par
94 @vskip 0pt plus 1filll
95 Published by the Free Software Foundation @*
96 51 Franklin Street, Fifth Floor,
97 Boston, MA 02110-1301, USA@*
98 ISBN 978-0-9831592-3-0 @*
105 @node Top, Summary, (dir), (dir)
107 @top Debugging with @value{GDBN}
109 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
111 This is the @value{EDITION} Edition, for @value{GDBN}
112 @ifset VERSION_PACKAGE
113 @value{VERSION_PACKAGE}
115 Version @value{GDBVN}.
117 Copyright (C) 1988-2010 Free Software Foundation, Inc.
119 This edition of the GDB manual is dedicated to the memory of Fred
120 Fish. Fred was a long-standing contributor to GDB and to Free
121 software in general. We will miss him.
124 * Summary:: Summary of @value{GDBN}
125 * Sample Session:: A sample @value{GDBN} session
127 * Invocation:: Getting in and out of @value{GDBN}
128 * Commands:: @value{GDBN} commands
129 * Running:: Running programs under @value{GDBN}
130 * Stopping:: Stopping and continuing
131 * Reverse Execution:: Running programs backward
132 * Process Record and Replay:: Recording inferior's execution and replaying it
133 * Stack:: Examining the stack
134 * Source:: Examining source files
135 * Data:: Examining data
136 * Optimized Code:: Debugging optimized code
137 * Macros:: Preprocessor Macros
138 * Tracepoints:: Debugging remote targets non-intrusively
139 * Overlays:: Debugging programs that use overlays
141 * Languages:: Using @value{GDBN} with different languages
143 * Symbols:: Examining the symbol table
144 * Altering:: Altering execution
145 * GDB Files:: @value{GDBN} files
146 * Targets:: Specifying a debugging target
147 * Remote Debugging:: Debugging remote programs
148 * Configurations:: Configuration-specific information
149 * Controlling GDB:: Controlling @value{GDBN}
150 * Extending GDB:: Extending @value{GDBN}
151 * Interpreters:: Command Interpreters
152 * TUI:: @value{GDBN} Text User Interface
153 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
154 * GDB/MI:: @value{GDBN}'s Machine Interface.
155 * Annotations:: @value{GDBN}'s annotation interface.
156 * JIT Interface:: Using the JIT debugging interface.
157 * In-Process Agent:: In-Process Agent
159 * GDB Bugs:: Reporting bugs in @value{GDBN}
161 @ifset SYSTEM_READLINE
162 * Command Line Editing: (rluserman). Command Line Editing
163 * Using History Interactively: (history). Using History Interactively
165 @ifclear SYSTEM_READLINE
166 * Command Line Editing:: Command Line Editing
167 * Using History Interactively:: Using History Interactively
169 * In Memoriam:: In Memoriam
170 * Formatting Documentation:: How to format and print @value{GDBN} documentation
171 * Installing GDB:: Installing GDB
172 * Maintenance Commands:: Maintenance Commands
173 * Remote Protocol:: GDB Remote Serial Protocol
174 * Agent Expressions:: The GDB Agent Expression Mechanism
175 * Target Descriptions:: How targets can describe themselves to
177 * Operating System Information:: Getting additional information from
179 * Trace File Format:: GDB trace file format
180 * Index Section Format:: .gdb_index section format
181 * Copying:: GNU General Public License says
182 how you can copy and share GDB
183 * GNU Free Documentation License:: The license for this documentation
192 @unnumbered Summary of @value{GDBN}
194 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
195 going on ``inside'' another program while it executes---or what another
196 program was doing at the moment it crashed.
198 @value{GDBN} can do four main kinds of things (plus other things in support of
199 these) to help you catch bugs in the act:
203 Start your program, specifying anything that might affect its behavior.
206 Make your program stop on specified conditions.
209 Examine what has happened, when your program has stopped.
212 Change things in your program, so you can experiment with correcting the
213 effects of one bug and go on to learn about another.
216 You can use @value{GDBN} to debug programs written in C and C@t{++}.
217 For more information, see @ref{Supported Languages,,Supported Languages}.
218 For more information, see @ref{C,,C and C++}.
220 Support for D is partial. For information on D, see
224 Support for Modula-2 is partial. For information on Modula-2, see
225 @ref{Modula-2,,Modula-2}.
227 Support for OpenCL C is partial. For information on OpenCL C, see
228 @ref{OpenCL C,,OpenCL C}.
231 Debugging Pascal programs which use sets, subranges, file variables, or
232 nested functions does not currently work. @value{GDBN} does not support
233 entering expressions, printing values, or similar features using Pascal
237 @value{GDBN} can be used to debug programs written in Fortran, although
238 it may be necessary to refer to some variables with a trailing
241 @value{GDBN} can be used to debug programs written in Objective-C,
242 using either the Apple/NeXT or the GNU Objective-C runtime.
245 * Free Software:: Freely redistributable software
246 * Contributors:: Contributors to GDB
250 @unnumberedsec Free Software
252 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
253 General Public License
254 (GPL). The GPL gives you the freedom to copy or adapt a licensed
255 program---but every person getting a copy also gets with it the
256 freedom to modify that copy (which means that they must get access to
257 the source code), and the freedom to distribute further copies.
258 Typical software companies use copyrights to limit your freedoms; the
259 Free Software Foundation uses the GPL to preserve these freedoms.
261 Fundamentally, the General Public License is a license which says that
262 you have these freedoms and that you cannot take these freedoms away
265 @unnumberedsec Free Software Needs Free Documentation
267 The biggest deficiency in the free software community today is not in
268 the software---it is the lack of good free documentation that we can
269 include with the free software. Many of our most important
270 programs do not come with free reference manuals and free introductory
271 texts. Documentation is an essential part of any software package;
272 when an important free software package does not come with a free
273 manual and a free tutorial, that is a major gap. We have many such
276 Consider Perl, for instance. The tutorial manuals that people
277 normally use are non-free. How did this come about? Because the
278 authors of those manuals published them with restrictive terms---no
279 copying, no modification, source files not available---which exclude
280 them from the free software world.
282 That wasn't the first time this sort of thing happened, and it was far
283 from the last. Many times we have heard a GNU user eagerly describe a
284 manual that he is writing, his intended contribution to the community,
285 only to learn that he had ruined everything by signing a publication
286 contract to make it non-free.
288 Free documentation, like free software, is a matter of freedom, not
289 price. The problem with the non-free manual is not that publishers
290 charge a price for printed copies---that in itself is fine. (The Free
291 Software Foundation sells printed copies of manuals, too.) The
292 problem is the restrictions on the use of the manual. Free manuals
293 are available in source code form, and give you permission to copy and
294 modify. Non-free manuals do not allow this.
296 The criteria of freedom for a free manual are roughly the same as for
297 free software. Redistribution (including the normal kinds of
298 commercial redistribution) must be permitted, so that the manual can
299 accompany every copy of the program, both on-line and on paper.
301 Permission for modification of the technical content is crucial too.
302 When people modify the software, adding or changing features, if they
303 are conscientious they will change the manual too---so they can
304 provide accurate and clear documentation for the modified program. A
305 manual that leaves you no choice but to write a new manual to document
306 a changed version of the program is not really available to our
309 Some kinds of limits on the way modification is handled are
310 acceptable. For example, requirements to preserve the original
311 author's copyright notice, the distribution terms, or the list of
312 authors, are ok. It is also no problem to require modified versions
313 to include notice that they were modified. Even entire sections that
314 may not be deleted or changed are acceptable, as long as they deal
315 with nontechnical topics (like this one). These kinds of restrictions
316 are acceptable because they don't obstruct the community's normal use
319 However, it must be possible to modify all the @emph{technical}
320 content of the manual, and then distribute the result in all the usual
321 media, through all the usual channels. Otherwise, the restrictions
322 obstruct the use of the manual, it is not free, and we need another
323 manual to replace it.
325 Please spread the word about this issue. Our community continues to
326 lose manuals to proprietary publishing. If we spread the word that
327 free software needs free reference manuals and free tutorials, perhaps
328 the next person who wants to contribute by writing documentation will
329 realize, before it is too late, that only free manuals contribute to
330 the free software community.
332 If you are writing documentation, please insist on publishing it under
333 the GNU Free Documentation License or another free documentation
334 license. Remember that this decision requires your approval---you
335 don't have to let the publisher decide. Some commercial publishers
336 will use a free license if you insist, but they will not propose the
337 option; it is up to you to raise the issue and say firmly that this is
338 what you want. If the publisher you are dealing with refuses, please
339 try other publishers. If you're not sure whether a proposed license
340 is free, write to @email{licensing@@gnu.org}.
342 You can encourage commercial publishers to sell more free, copylefted
343 manuals and tutorials by buying them, and particularly by buying
344 copies from the publishers that paid for their writing or for major
345 improvements. Meanwhile, try to avoid buying non-free documentation
346 at all. Check the distribution terms of a manual before you buy it,
347 and insist that whoever seeks your business must respect your freedom.
348 Check the history of the book, and try to reward the publishers that
349 have paid or pay the authors to work on it.
351 The Free Software Foundation maintains a list of free documentation
352 published by other publishers, at
353 @url{http://www.fsf.org/doc/other-free-books.html}.
356 @unnumberedsec Contributors to @value{GDBN}
358 Richard Stallman was the original author of @value{GDBN}, and of many
359 other @sc{gnu} programs. Many others have contributed to its
360 development. This section attempts to credit major contributors. One
361 of the virtues of free software is that everyone is free to contribute
362 to it; with regret, we cannot actually acknowledge everyone here. The
363 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
364 blow-by-blow account.
366 Changes much prior to version 2.0 are lost in the mists of time.
369 @emph{Plea:} Additions to this section are particularly welcome. If you
370 or your friends (or enemies, to be evenhanded) have been unfairly
371 omitted from this list, we would like to add your names!
374 So that they may not regard their many labors as thankless, we
375 particularly thank those who shepherded @value{GDBN} through major
377 Andrew Cagney (releases 6.3, 6.2, 6.1, 6.0, 5.3, 5.2, 5.1 and 5.0);
378 Jim Blandy (release 4.18);
379 Jason Molenda (release 4.17);
380 Stan Shebs (release 4.14);
381 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
382 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
383 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
384 Jim Kingdon (releases 3.5, 3.4, and 3.3);
385 and Randy Smith (releases 3.2, 3.1, and 3.0).
387 Richard Stallman, assisted at various times by Peter TerMaat, Chris
388 Hanson, and Richard Mlynarik, handled releases through 2.8.
390 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
391 in @value{GDBN}, with significant additional contributions from Per
392 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
393 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
394 much general update work leading to release 3.0).
396 @value{GDBN} uses the BFD subroutine library to examine multiple
397 object-file formats; BFD was a joint project of David V.
398 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
400 David Johnson wrote the original COFF support; Pace Willison did
401 the original support for encapsulated COFF.
403 Brent Benson of Harris Computer Systems contributed DWARF 2 support.
405 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
406 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
408 Jean-Daniel Fekete contributed Sun 386i support.
409 Chris Hanson improved the HP9000 support.
410 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
411 David Johnson contributed Encore Umax support.
412 Jyrki Kuoppala contributed Altos 3068 support.
413 Jeff Law contributed HP PA and SOM support.
414 Keith Packard contributed NS32K support.
415 Doug Rabson contributed Acorn Risc Machine support.
416 Bob Rusk contributed Harris Nighthawk CX-UX support.
417 Chris Smith contributed Convex support (and Fortran debugging).
418 Jonathan Stone contributed Pyramid support.
419 Michael Tiemann contributed SPARC support.
420 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
421 Pace Willison contributed Intel 386 support.
422 Jay Vosburgh contributed Symmetry support.
423 Marko Mlinar contributed OpenRISC 1000 support.
425 Andreas Schwab contributed M68K @sc{gnu}/Linux support.
427 Rich Schaefer and Peter Schauer helped with support of SunOS shared
430 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
431 about several machine instruction sets.
433 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
434 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
435 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
436 and RDI targets, respectively.
438 Brian Fox is the author of the readline libraries providing
439 command-line editing and command history.
441 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
442 Modula-2 support, and contributed the Languages chapter of this manual.
444 Fred Fish wrote most of the support for Unix System Vr4.
445 He also enhanced the command-completion support to cover C@t{++} overloaded
448 Hitachi America (now Renesas America), Ltd. sponsored the support for
449 H8/300, H8/500, and Super-H processors.
451 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
453 Mitsubishi (now Renesas) sponsored the support for D10V, D30V, and M32R/D
456 Toshiba sponsored the support for the TX39 Mips processor.
458 Matsushita sponsored the support for the MN10200 and MN10300 processors.
460 Fujitsu sponsored the support for SPARClite and FR30 processors.
462 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
465 Michael Snyder added support for tracepoints.
467 Stu Grossman wrote gdbserver.
469 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
470 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
472 The following people at the Hewlett-Packard Company contributed
473 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
474 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
475 compiler, and the Text User Interface (nee Terminal User Interface):
476 Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann,
477 Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase
478 provided HP-specific information in this manual.
480 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
481 Robert Hoehne made significant contributions to the DJGPP port.
483 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
484 development since 1991. Cygnus engineers who have worked on @value{GDBN}
485 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
486 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
487 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
488 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
489 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
490 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
491 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
492 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
493 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
494 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
495 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
496 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
497 Zuhn have made contributions both large and small.
499 Andrew Cagney, Fernando Nasser, and Elena Zannoni, while working for
500 Cygnus Solutions, implemented the original @sc{gdb/mi} interface.
502 Jim Blandy added support for preprocessor macros, while working for Red
505 Andrew Cagney designed @value{GDBN}'s architecture vector. Many
506 people including Andrew Cagney, Stephane Carrez, Randolph Chung, Nick
507 Duffek, Richard Henderson, Mark Kettenis, Grace Sainsbury, Kei
508 Sakamoto, Yoshinori Sato, Michael Snyder, Andreas Schwab, Jason
509 Thorpe, Corinna Vinschen, Ulrich Weigand, and Elena Zannoni, helped
510 with the migration of old architectures to this new framework.
512 Andrew Cagney completely re-designed and re-implemented @value{GDBN}'s
513 unwinder framework, this consisting of a fresh new design featuring
514 frame IDs, independent frame sniffers, and the sentinel frame. Mark
515 Kettenis implemented the @sc{dwarf 2} unwinder, Jeff Johnston the
516 libunwind unwinder, and Andrew Cagney the dummy, sentinel, tramp, and
517 trad unwinders. The architecture-specific changes, each involving a
518 complete rewrite of the architecture's frame code, were carried out by
519 Jim Blandy, Joel Brobecker, Kevin Buettner, Andrew Cagney, Stephane
520 Carrez, Randolph Chung, Orjan Friberg, Richard Henderson, Daniel
521 Jacobowitz, Jeff Johnston, Mark Kettenis, Theodore A. Roth, Kei
522 Sakamoto, Yoshinori Sato, Michael Snyder, Corinna Vinschen, and Ulrich
525 Christian Zankel, Ross Morley, Bob Wilson, and Maxim Grigoriev from
526 Tensilica, Inc.@: contributed support for Xtensa processors. Others
527 who have worked on the Xtensa port of @value{GDBN} in the past include
528 Steve Tjiang, John Newlin, and Scott Foehner.
530 Michael Eager and staff of Xilinx, Inc., contributed support for the
531 Xilinx MicroBlaze architecture.
534 @chapter A Sample @value{GDBN} Session
536 You can use this manual at your leisure to read all about @value{GDBN}.
537 However, a handful of commands are enough to get started using the
538 debugger. This chapter illustrates those commands.
541 In this sample session, we emphasize user input like this: @b{input},
542 to make it easier to pick out from the surrounding output.
545 @c FIXME: this example may not be appropriate for some configs, where
546 @c FIXME...primary interest is in remote use.
548 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
549 processor) exhibits the following bug: sometimes, when we change its
550 quote strings from the default, the commands used to capture one macro
551 definition within another stop working. In the following short @code{m4}
552 session, we define a macro @code{foo} which expands to @code{0000}; we
553 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
554 same thing. However, when we change the open quote string to
555 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
556 procedure fails to define a new synonym @code{baz}:
565 @b{define(bar,defn(`foo'))}
569 @b{changequote(<QUOTE>,<UNQUOTE>)}
571 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
574 m4: End of input: 0: fatal error: EOF in string
578 Let us use @value{GDBN} to try to see what is going on.
581 $ @b{@value{GDBP} m4}
582 @c FIXME: this falsifies the exact text played out, to permit smallbook
583 @c FIXME... format to come out better.
584 @value{GDBN} is free software and you are welcome to distribute copies
585 of it under certain conditions; type "show copying" to see
587 There is absolutely no warranty for @value{GDBN}; type "show warranty"
590 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
595 @value{GDBN} reads only enough symbol data to know where to find the
596 rest when needed; as a result, the first prompt comes up very quickly.
597 We now tell @value{GDBN} to use a narrower display width than usual, so
598 that examples fit in this manual.
601 (@value{GDBP}) @b{set width 70}
605 We need to see how the @code{m4} built-in @code{changequote} works.
606 Having looked at the source, we know the relevant subroutine is
607 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
608 @code{break} command.
611 (@value{GDBP}) @b{break m4_changequote}
612 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
616 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
617 control; as long as control does not reach the @code{m4_changequote}
618 subroutine, the program runs as usual:
621 (@value{GDBP}) @b{run}
622 Starting program: /work/Editorial/gdb/gnu/m4/m4
630 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
631 suspends execution of @code{m4}, displaying information about the
632 context where it stops.
635 @b{changequote(<QUOTE>,<UNQUOTE>)}
637 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
639 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
643 Now we use the command @code{n} (@code{next}) to advance execution to
644 the next line of the current function.
648 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
653 @code{set_quotes} looks like a promising subroutine. We can go into it
654 by using the command @code{s} (@code{step}) instead of @code{next}.
655 @code{step} goes to the next line to be executed in @emph{any}
656 subroutine, so it steps into @code{set_quotes}.
660 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
662 530 if (lquote != def_lquote)
666 The display that shows the subroutine where @code{m4} is now
667 suspended (and its arguments) is called a stack frame display. It
668 shows a summary of the stack. We can use the @code{backtrace}
669 command (which can also be spelled @code{bt}), to see where we are
670 in the stack as a whole: the @code{backtrace} command displays a
671 stack frame for each active subroutine.
674 (@value{GDBP}) @b{bt}
675 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
677 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
679 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
680 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
682 #4 0x79dc in expand_input () at macro.c:40
683 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
687 We step through a few more lines to see what happens. The first two
688 times, we can use @samp{s}; the next two times we use @code{n} to avoid
689 falling into the @code{xstrdup} subroutine.
693 0x3b5c 532 if (rquote != def_rquote)
695 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
696 def_lquote : xstrdup(lq);
698 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
701 538 len_lquote = strlen(rquote);
705 The last line displayed looks a little odd; we can examine the variables
706 @code{lquote} and @code{rquote} to see if they are in fact the new left
707 and right quotes we specified. We use the command @code{p}
708 (@code{print}) to see their values.
711 (@value{GDBP}) @b{p lquote}
712 $1 = 0x35d40 "<QUOTE>"
713 (@value{GDBP}) @b{p rquote}
714 $2 = 0x35d50 "<UNQUOTE>"
718 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
719 To look at some context, we can display ten lines of source
720 surrounding the current line with the @code{l} (@code{list}) command.
726 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
728 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
731 538 len_lquote = strlen(rquote);
732 539 len_rquote = strlen(lquote);
739 Let us step past the two lines that set @code{len_lquote} and
740 @code{len_rquote}, and then examine the values of those variables.
744 539 len_rquote = strlen(lquote);
747 (@value{GDBP}) @b{p len_lquote}
749 (@value{GDBP}) @b{p len_rquote}
754 That certainly looks wrong, assuming @code{len_lquote} and
755 @code{len_rquote} are meant to be the lengths of @code{lquote} and
756 @code{rquote} respectively. We can set them to better values using
757 the @code{p} command, since it can print the value of
758 any expression---and that expression can include subroutine calls and
762 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
764 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
769 Is that enough to fix the problem of using the new quotes with the
770 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
771 executing with the @code{c} (@code{continue}) command, and then try the
772 example that caused trouble initially:
778 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
785 Success! The new quotes now work just as well as the default ones. The
786 problem seems to have been just the two typos defining the wrong
787 lengths. We allow @code{m4} exit by giving it an EOF as input:
791 Program exited normally.
795 The message @samp{Program exited normally.} is from @value{GDBN}; it
796 indicates @code{m4} has finished executing. We can end our @value{GDBN}
797 session with the @value{GDBN} @code{quit} command.
800 (@value{GDBP}) @b{quit}
804 @chapter Getting In and Out of @value{GDBN}
806 This chapter discusses how to start @value{GDBN}, and how to get out of it.
810 type @samp{@value{GDBP}} to start @value{GDBN}.
812 type @kbd{quit} or @kbd{Ctrl-d} to exit.
816 * Invoking GDB:: How to start @value{GDBN}
817 * Quitting GDB:: How to quit @value{GDBN}
818 * Shell Commands:: How to use shell commands inside @value{GDBN}
819 * Logging Output:: How to log @value{GDBN}'s output to a file
823 @section Invoking @value{GDBN}
825 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
826 @value{GDBN} reads commands from the terminal until you tell it to exit.
828 You can also run @code{@value{GDBP}} with a variety of arguments and options,
829 to specify more of your debugging environment at the outset.
831 The command-line options described here are designed
832 to cover a variety of situations; in some environments, some of these
833 options may effectively be unavailable.
835 The most usual way to start @value{GDBN} is with one argument,
836 specifying an executable program:
839 @value{GDBP} @var{program}
843 You can also start with both an executable program and a core file
847 @value{GDBP} @var{program} @var{core}
850 You can, instead, specify a process ID as a second argument, if you want
851 to debug a running process:
854 @value{GDBP} @var{program} 1234
858 would attach @value{GDBN} to process @code{1234} (unless you also have a file
859 named @file{1234}; @value{GDBN} does check for a core file first).
861 Taking advantage of the second command-line argument requires a fairly
862 complete operating system; when you use @value{GDBN} as a remote
863 debugger attached to a bare board, there may not be any notion of
864 ``process'', and there is often no way to get a core dump. @value{GDBN}
865 will warn you if it is unable to attach or to read core dumps.
867 You can optionally have @code{@value{GDBP}} pass any arguments after the
868 executable file to the inferior using @code{--args}. This option stops
871 @value{GDBP} --args gcc -O2 -c foo.c
873 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
874 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
876 You can run @code{@value{GDBP}} without printing the front material, which describes
877 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
884 You can further control how @value{GDBN} starts up by using command-line
885 options. @value{GDBN} itself can remind you of the options available.
895 to display all available options and briefly describe their use
896 (@samp{@value{GDBP} -h} is a shorter equivalent).
898 All options and command line arguments you give are processed
899 in sequential order. The order makes a difference when the
900 @samp{-x} option is used.
904 * File Options:: Choosing files
905 * Mode Options:: Choosing modes
906 * Startup:: What @value{GDBN} does during startup
910 @subsection Choosing Files
912 When @value{GDBN} starts, it reads any arguments other than options as
913 specifying an executable file and core file (or process ID). This is
914 the same as if the arguments were specified by the @samp{-se} and
915 @samp{-c} (or @samp{-p}) options respectively. (@value{GDBN} reads the
916 first argument that does not have an associated option flag as
917 equivalent to the @samp{-se} option followed by that argument; and the
918 second argument that does not have an associated option flag, if any, as
919 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
920 If the second argument begins with a decimal digit, @value{GDBN} will
921 first attempt to attach to it as a process, and if that fails, attempt
922 to open it as a corefile. If you have a corefile whose name begins with
923 a digit, you can prevent @value{GDBN} from treating it as a pid by
924 prefixing it with @file{./}, e.g.@: @file{./12345}.
926 If @value{GDBN} has not been configured to included core file support,
927 such as for most embedded targets, then it will complain about a second
928 argument and ignore it.
930 Many options have both long and short forms; both are shown in the
931 following list. @value{GDBN} also recognizes the long forms if you truncate
932 them, so long as enough of the option is present to be unambiguous.
933 (If you prefer, you can flag option arguments with @samp{--} rather
934 than @samp{-}, though we illustrate the more usual convention.)
936 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
937 @c way, both those who look for -foo and --foo in the index, will find
941 @item -symbols @var{file}
943 @cindex @code{--symbols}
945 Read symbol table from file @var{file}.
947 @item -exec @var{file}
949 @cindex @code{--exec}
951 Use file @var{file} as the executable file to execute when appropriate,
952 and for examining pure data in conjunction with a core dump.
956 Read symbol table from file @var{file} and use it as the executable
959 @item -core @var{file}
961 @cindex @code{--core}
963 Use file @var{file} as a core dump to examine.
965 @item -pid @var{number}
966 @itemx -p @var{number}
969 Connect to process ID @var{number}, as with the @code{attach} command.
971 @item -command @var{file}
973 @cindex @code{--command}
975 Execute commands from file @var{file}. The contents of this file is
976 evaluated exactly as the @code{source} command would.
977 @xref{Command Files,, Command files}.
979 @item -eval-command @var{command}
980 @itemx -ex @var{command}
981 @cindex @code{--eval-command}
983 Execute a single @value{GDBN} command.
985 This option may be used multiple times to call multiple commands. It may
986 also be interleaved with @samp{-command} as required.
989 @value{GDBP} -ex 'target sim' -ex 'load' \
990 -x setbreakpoints -ex 'run' a.out
993 @item -init-command @var{file}
994 @itemx -ix @var{file}
995 @cindex @code{--init-command}
997 Execute commands from file @var{file} before loading gdbinit files or the
1001 @item -init-eval-command @var{command}
1002 @itemx -iex @var{command}
1003 @cindex @code{--init-eval-command}
1005 Execute a single @value{GDBN} command before loading gdbinit files or the
1009 @item -directory @var{directory}
1010 @itemx -d @var{directory}
1011 @cindex @code{--directory}
1013 Add @var{directory} to the path to search for source and script files.
1017 @cindex @code{--readnow}
1019 Read each symbol file's entire symbol table immediately, rather than
1020 the default, which is to read it incrementally as it is needed.
1021 This makes startup slower, but makes future operations faster.
1026 @subsection Choosing Modes
1028 You can run @value{GDBN} in various alternative modes---for example, in
1029 batch mode or quiet mode.
1036 Do not execute commands found in any initialization files. Normally,
1037 @value{GDBN} executes the commands in these files after all the command
1038 options and arguments have been processed. @xref{Command Files,,Command
1044 @cindex @code{--quiet}
1045 @cindex @code{--silent}
1047 ``Quiet''. Do not print the introductory and copyright messages. These
1048 messages are also suppressed in batch mode.
1051 @cindex @code{--batch}
1052 Run in batch mode. Exit with status @code{0} after processing all the
1053 command files specified with @samp{-x} (and all commands from
1054 initialization files, if not inhibited with @samp{-n}). Exit with
1055 nonzero status if an error occurs in executing the @value{GDBN} commands
1056 in the command files. Batch mode also disables pagination, sets unlimited
1057 terminal width and height @pxref{Screen Size}, and acts as if @kbd{set confirm
1058 off} were in effect (@pxref{Messages/Warnings}).
1060 Batch mode may be useful for running @value{GDBN} as a filter, for
1061 example to download and run a program on another computer; in order to
1062 make this more useful, the message
1065 Program exited normally.
1069 (which is ordinarily issued whenever a program running under
1070 @value{GDBN} control terminates) is not issued when running in batch
1074 @cindex @code{--batch-silent}
1075 Run in batch mode exactly like @samp{-batch}, but totally silently. All
1076 @value{GDBN} output to @code{stdout} is prevented (@code{stderr} is
1077 unaffected). This is much quieter than @samp{-silent} and would be useless
1078 for an interactive session.
1080 This is particularly useful when using targets that give @samp{Loading section}
1081 messages, for example.
1083 Note that targets that give their output via @value{GDBN}, as opposed to
1084 writing directly to @code{stdout}, will also be made silent.
1086 @item -return-child-result
1087 @cindex @code{--return-child-result}
1088 The return code from @value{GDBN} will be the return code from the child
1089 process (the process being debugged), with the following exceptions:
1093 @value{GDBN} exits abnormally. E.g., due to an incorrect argument or an
1094 internal error. In this case the exit code is the same as it would have been
1095 without @samp{-return-child-result}.
1097 The user quits with an explicit value. E.g., @samp{quit 1}.
1099 The child process never runs, or is not allowed to terminate, in which case
1100 the exit code will be -1.
1103 This option is useful in conjunction with @samp{-batch} or @samp{-batch-silent},
1104 when @value{GDBN} is being used as a remote program loader or simulator
1109 @cindex @code{--nowindows}
1111 ``No windows''. If @value{GDBN} comes with a graphical user interface
1112 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1113 interface. If no GUI is available, this option has no effect.
1117 @cindex @code{--windows}
1119 If @value{GDBN} includes a GUI, then this option requires it to be
1122 @item -cd @var{directory}
1124 Run @value{GDBN} using @var{directory} as its working directory,
1125 instead of the current directory.
1127 @item -data-directory @var{directory}
1128 @cindex @code{--data-directory}
1129 Run @value{GDBN} using @var{directory} as its data directory.
1130 The data directory is where @value{GDBN} searches for its
1131 auxiliary files. @xref{Data Files}.
1135 @cindex @code{--fullname}
1137 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1138 subprocess. It tells @value{GDBN} to output the full file name and line
1139 number in a standard, recognizable fashion each time a stack frame is
1140 displayed (which includes each time your program stops). This
1141 recognizable format looks like two @samp{\032} characters, followed by
1142 the file name, line number and character position separated by colons,
1143 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1144 @samp{\032} characters as a signal to display the source code for the
1148 @cindex @code{--epoch}
1149 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1150 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1151 routines so as to allow Epoch to display values of expressions in a
1154 @item -annotate @var{level}
1155 @cindex @code{--annotate}
1156 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1157 effect is identical to using @samp{set annotate @var{level}}
1158 (@pxref{Annotations}). The annotation @var{level} controls how much
1159 information @value{GDBN} prints together with its prompt, values of
1160 expressions, source lines, and other types of output. Level 0 is the
1161 normal, level 1 is for use when @value{GDBN} is run as a subprocess of
1162 @sc{gnu} Emacs, level 3 is the maximum annotation suitable for programs
1163 that control @value{GDBN}, and level 2 has been deprecated.
1165 The annotation mechanism has largely been superseded by @sc{gdb/mi}
1169 @cindex @code{--args}
1170 Change interpretation of command line so that arguments following the
1171 executable file are passed as command line arguments to the inferior.
1172 This option stops option processing.
1174 @item -baud @var{bps}
1176 @cindex @code{--baud}
1178 Set the line speed (baud rate or bits per second) of any serial
1179 interface used by @value{GDBN} for remote debugging.
1181 @item -l @var{timeout}
1183 Set the timeout (in seconds) of any communication used by @value{GDBN}
1184 for remote debugging.
1186 @item -tty @var{device}
1187 @itemx -t @var{device}
1188 @cindex @code{--tty}
1190 Run using @var{device} for your program's standard input and output.
1191 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1193 @c resolve the situation of these eventually
1195 @cindex @code{--tui}
1196 Activate the @dfn{Text User Interface} when starting. The Text User
1197 Interface manages several text windows on the terminal, showing
1198 source, assembly, registers and @value{GDBN} command outputs
1199 (@pxref{TUI, ,@value{GDBN} Text User Interface}). Do not use this
1200 option if you run @value{GDBN} from Emacs (@pxref{Emacs, ,
1201 Using @value{GDBN} under @sc{gnu} Emacs}).
1204 @c @cindex @code{--xdb}
1205 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1206 @c For information, see the file @file{xdb_trans.html}, which is usually
1207 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1210 @item -interpreter @var{interp}
1211 @cindex @code{--interpreter}
1212 Use the interpreter @var{interp} for interface with the controlling
1213 program or device. This option is meant to be set by programs which
1214 communicate with @value{GDBN} using it as a back end.
1215 @xref{Interpreters, , Command Interpreters}.
1217 @samp{--interpreter=mi} (or @samp{--interpreter=mi2}) causes
1218 @value{GDBN} to use the @dfn{@sc{gdb/mi} interface} (@pxref{GDB/MI, ,
1219 The @sc{gdb/mi} Interface}) included since @value{GDBN} version 6.0. The
1220 previous @sc{gdb/mi} interface, included in @value{GDBN} version 5.3 and
1221 selected with @samp{--interpreter=mi1}, is deprecated. Earlier
1222 @sc{gdb/mi} interfaces are no longer supported.
1225 @cindex @code{--write}
1226 Open the executable and core files for both reading and writing. This
1227 is equivalent to the @samp{set write on} command inside @value{GDBN}
1231 @cindex @code{--statistics}
1232 This option causes @value{GDBN} to print statistics about time and
1233 memory usage after it completes each command and returns to the prompt.
1236 @cindex @code{--version}
1237 This option causes @value{GDBN} to print its version number and
1238 no-warranty blurb, and exit.
1240 @item -use-deprecated-index-sections
1241 @cindex @code{--use-deprecated-index-sections}
1242 This option causes @value{GDBN} to read and use deprecated
1243 @samp{.gdb_index} sections from symbol files. This can speed up
1244 startup, but may result in some functionality being lost.
1245 @xref{Index Section Format}.
1250 @subsection What @value{GDBN} Does During Startup
1251 @cindex @value{GDBN} startup
1253 Here's the description of what @value{GDBN} does during session startup:
1257 Sets up the command interpreter as specified by the command line
1258 (@pxref{Mode Options, interpreter}).
1261 Executes commands and command files specified by the @samp{-iex} and
1262 @samp{-ix} options in their specified order. Usually you should use the
1263 @samp{-ex} and @samp{-x} options instead, but this way you can apply
1264 settings before @value{GDBN} init files get executed and before inferior
1269 Reads the system-wide @dfn{init file} (if @option{--with-system-gdbinit} was
1270 used when building @value{GDBN}; @pxref{System-wide configuration,
1271 ,System-wide configuration and settings}) and executes all the commands in
1275 Reads the init file (if any) in your home directory@footnote{On
1276 DOS/Windows systems, the home directory is the one pointed to by the
1277 @code{HOME} environment variable.} and executes all the commands in
1281 Processes command line options and operands.
1284 Reads and executes the commands from init file (if any) in the current
1285 working directory. This is only done if the current directory is
1286 different from your home directory. Thus, you can have more than one
1287 init file, one generic in your home directory, and another, specific
1288 to the program you are debugging, in the directory where you invoke
1292 If the command line specified a program to debug, or a process to
1293 attach to, or a core file, @value{GDBN} loads any auto-loaded
1294 scripts provided for the program or for its loaded shared libraries.
1295 @xref{Auto-loading}.
1297 If you wish to disable the auto-loading during startup,
1298 you must do something like the following:
1301 $ gdb -iex "set auto-load-scripts off" myprogram
1304 Option @samp{-ex} does not work because the auto-loading is then turned
1308 Executes commands and command files specified by the @samp{-ex} and
1309 @samp{-x} options in their specified order. @xref{Command Files}, for
1310 more details about @value{GDBN} command files.
1313 Reads the command history recorded in the @dfn{history file}.
1314 @xref{Command History}, for more details about the command history and the
1315 files where @value{GDBN} records it.
1318 Init files use the same syntax as @dfn{command files} (@pxref{Command
1319 Files}) and are processed by @value{GDBN} in the same way. The init
1320 file in your home directory can set options (such as @samp{set
1321 complaints}) that affect subsequent processing of command line options
1322 and operands. Init files are not executed if you use the @samp{-nx}
1323 option (@pxref{Mode Options, ,Choosing Modes}).
1325 To display the list of init files loaded by gdb at startup, you
1326 can use @kbd{gdb --help}.
1328 @cindex init file name
1329 @cindex @file{.gdbinit}
1330 @cindex @file{gdb.ini}
1331 The @value{GDBN} init files are normally called @file{.gdbinit}.
1332 The DJGPP port of @value{GDBN} uses the name @file{gdb.ini}, due to
1333 the limitations of file names imposed by DOS filesystems. The Windows
1334 ports of @value{GDBN} use the standard name, but if they find a
1335 @file{gdb.ini} file, they warn you about that and suggest to rename
1336 the file to the standard name.
1340 @section Quitting @value{GDBN}
1341 @cindex exiting @value{GDBN}
1342 @cindex leaving @value{GDBN}
1345 @kindex quit @r{[}@var{expression}@r{]}
1346 @kindex q @r{(@code{quit})}
1347 @item quit @r{[}@var{expression}@r{]}
1349 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1350 @code{q}), or type an end-of-file character (usually @kbd{Ctrl-d}). If you
1351 do not supply @var{expression}, @value{GDBN} will terminate normally;
1352 otherwise it will terminate using the result of @var{expression} as the
1357 An interrupt (often @kbd{Ctrl-c}) does not exit from @value{GDBN}, but rather
1358 terminates the action of any @value{GDBN} command that is in progress and
1359 returns to @value{GDBN} command level. It is safe to type the interrupt
1360 character at any time because @value{GDBN} does not allow it to take effect
1361 until a time when it is safe.
1363 If you have been using @value{GDBN} to control an attached process or
1364 device, you can release it with the @code{detach} command
1365 (@pxref{Attach, ,Debugging an Already-running Process}).
1367 @node Shell Commands
1368 @section Shell Commands
1370 If you need to execute occasional shell commands during your
1371 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1372 just use the @code{shell} command.
1377 @cindex shell escape
1378 @item shell @var{command-string}
1379 @itemx !@var{command-string}
1380 Invoke a standard shell to execute @var{command-string}.
1381 Note that no space is needed between @code{!} and @var{command-string}.
1382 If it exists, the environment variable @code{SHELL} determines which
1383 shell to run. Otherwise @value{GDBN} uses the default shell
1384 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1387 The utility @code{make} is often needed in development environments.
1388 You do not have to use the @code{shell} command for this purpose in
1393 @cindex calling make
1394 @item make @var{make-args}
1395 Execute the @code{make} program with the specified
1396 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1399 @node Logging Output
1400 @section Logging Output
1401 @cindex logging @value{GDBN} output
1402 @cindex save @value{GDBN} output to a file
1404 You may want to save the output of @value{GDBN} commands to a file.
1405 There are several commands to control @value{GDBN}'s logging.
1409 @item set logging on
1411 @item set logging off
1413 @cindex logging file name
1414 @item set logging file @var{file}
1415 Change the name of the current logfile. The default logfile is @file{gdb.txt}.
1416 @item set logging overwrite [on|off]
1417 By default, @value{GDBN} will append to the logfile. Set @code{overwrite} if
1418 you want @code{set logging on} to overwrite the logfile instead.
1419 @item set logging redirect [on|off]
1420 By default, @value{GDBN} output will go to both the terminal and the logfile.
1421 Set @code{redirect} if you want output to go only to the log file.
1422 @kindex show logging
1424 Show the current values of the logging settings.
1428 @chapter @value{GDBN} Commands
1430 You can abbreviate a @value{GDBN} command to the first few letters of the command
1431 name, if that abbreviation is unambiguous; and you can repeat certain
1432 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1433 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1434 show you the alternatives available, if there is more than one possibility).
1437 * Command Syntax:: How to give commands to @value{GDBN}
1438 * Completion:: Command completion
1439 * Help:: How to ask @value{GDBN} for help
1442 @node Command Syntax
1443 @section Command Syntax
1445 A @value{GDBN} command is a single line of input. There is no limit on
1446 how long it can be. It starts with a command name, which is followed by
1447 arguments whose meaning depends on the command name. For example, the
1448 command @code{step} accepts an argument which is the number of times to
1449 step, as in @samp{step 5}. You can also use the @code{step} command
1450 with no arguments. Some commands do not allow any arguments.
1452 @cindex abbreviation
1453 @value{GDBN} command names may always be truncated if that abbreviation is
1454 unambiguous. Other possible command abbreviations are listed in the
1455 documentation for individual commands. In some cases, even ambiguous
1456 abbreviations are allowed; for example, @code{s} is specially defined as
1457 equivalent to @code{step} even though there are other commands whose
1458 names start with @code{s}. You can test abbreviations by using them as
1459 arguments to the @code{help} command.
1461 @cindex repeating commands
1462 @kindex RET @r{(repeat last command)}
1463 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1464 repeat the previous command. Certain commands (for example, @code{run})
1465 will not repeat this way; these are commands whose unintentional
1466 repetition might cause trouble and which you are unlikely to want to
1467 repeat. User-defined commands can disable this feature; see
1468 @ref{Define, dont-repeat}.
1470 The @code{list} and @code{x} commands, when you repeat them with
1471 @key{RET}, construct new arguments rather than repeating
1472 exactly as typed. This permits easy scanning of source or memory.
1474 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1475 output, in a way similar to the common utility @code{more}
1476 (@pxref{Screen Size,,Screen Size}). Since it is easy to press one
1477 @key{RET} too many in this situation, @value{GDBN} disables command
1478 repetition after any command that generates this sort of display.
1480 @kindex # @r{(a comment)}
1482 Any text from a @kbd{#} to the end of the line is a comment; it does
1483 nothing. This is useful mainly in command files (@pxref{Command
1484 Files,,Command Files}).
1486 @cindex repeating command sequences
1487 @kindex Ctrl-o @r{(operate-and-get-next)}
1488 The @kbd{Ctrl-o} binding is useful for repeating a complex sequence of
1489 commands. This command accepts the current line, like @key{RET}, and
1490 then fetches the next line relative to the current line from the history
1494 @section Command Completion
1497 @cindex word completion
1498 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1499 only one possibility; it can also show you what the valid possibilities
1500 are for the next word in a command, at any time. This works for @value{GDBN}
1501 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1503 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1504 of a word. If there is only one possibility, @value{GDBN} fills in the
1505 word, and waits for you to finish the command (or press @key{RET} to
1506 enter it). For example, if you type
1508 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1509 @c complete accuracy in these examples; space introduced for clarity.
1510 @c If texinfo enhancements make it unnecessary, it would be nice to
1511 @c replace " @key" by "@key" in the following...
1513 (@value{GDBP}) info bre @key{TAB}
1517 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1518 the only @code{info} subcommand beginning with @samp{bre}:
1521 (@value{GDBP}) info breakpoints
1525 You can either press @key{RET} at this point, to run the @code{info
1526 breakpoints} command, or backspace and enter something else, if
1527 @samp{breakpoints} does not look like the command you expected. (If you
1528 were sure you wanted @code{info breakpoints} in the first place, you
1529 might as well just type @key{RET} immediately after @samp{info bre},
1530 to exploit command abbreviations rather than command completion).
1532 If there is more than one possibility for the next word when you press
1533 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1534 characters and try again, or just press @key{TAB} a second time;
1535 @value{GDBN} displays all the possible completions for that word. For
1536 example, you might want to set a breakpoint on a subroutine whose name
1537 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1538 just sounds the bell. Typing @key{TAB} again displays all the
1539 function names in your program that begin with those characters, for
1543 (@value{GDBP}) b make_ @key{TAB}
1544 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1545 make_a_section_from_file make_environ
1546 make_abs_section make_function_type
1547 make_blockvector make_pointer_type
1548 make_cleanup make_reference_type
1549 make_command make_symbol_completion_list
1550 (@value{GDBP}) b make_
1554 After displaying the available possibilities, @value{GDBN} copies your
1555 partial input (@samp{b make_} in the example) so you can finish the
1558 If you just want to see the list of alternatives in the first place, you
1559 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1560 means @kbd{@key{META} ?}. You can type this either by holding down a
1561 key designated as the @key{META} shift on your keyboard (if there is
1562 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1564 @cindex quotes in commands
1565 @cindex completion of quoted strings
1566 Sometimes the string you need, while logically a ``word'', may contain
1567 parentheses or other characters that @value{GDBN} normally excludes from
1568 its notion of a word. To permit word completion to work in this
1569 situation, you may enclose words in @code{'} (single quote marks) in
1570 @value{GDBN} commands.
1572 The most likely situation where you might need this is in typing the
1573 name of a C@t{++} function. This is because C@t{++} allows function
1574 overloading (multiple definitions of the same function, distinguished
1575 by argument type). For example, when you want to set a breakpoint you
1576 may need to distinguish whether you mean the version of @code{name}
1577 that takes an @code{int} parameter, @code{name(int)}, or the version
1578 that takes a @code{float} parameter, @code{name(float)}. To use the
1579 word-completion facilities in this situation, type a single quote
1580 @code{'} at the beginning of the function name. This alerts
1581 @value{GDBN} that it may need to consider more information than usual
1582 when you press @key{TAB} or @kbd{M-?} to request word completion:
1585 (@value{GDBP}) b 'bubble( @kbd{M-?}
1586 bubble(double,double) bubble(int,int)
1587 (@value{GDBP}) b 'bubble(
1590 In some cases, @value{GDBN} can tell that completing a name requires using
1591 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1592 completing as much as it can) if you do not type the quote in the first
1596 (@value{GDBP}) b bub @key{TAB}
1597 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1598 (@value{GDBP}) b 'bubble(
1602 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1603 you have not yet started typing the argument list when you ask for
1604 completion on an overloaded symbol.
1606 For more information about overloaded functions, see @ref{C Plus Plus
1607 Expressions, ,C@t{++} Expressions}. You can use the command @code{set
1608 overload-resolution off} to disable overload resolution;
1609 see @ref{Debugging C Plus Plus, ,@value{GDBN} Features for C@t{++}}.
1611 @cindex completion of structure field names
1612 @cindex structure field name completion
1613 @cindex completion of union field names
1614 @cindex union field name completion
1615 When completing in an expression which looks up a field in a
1616 structure, @value{GDBN} also tries@footnote{The completer can be
1617 confused by certain kinds of invalid expressions. Also, it only
1618 examines the static type of the expression, not the dynamic type.} to
1619 limit completions to the field names available in the type of the
1623 (@value{GDBP}) p gdb_stdout.@kbd{M-?}
1624 magic to_fputs to_rewind
1625 to_data to_isatty to_write
1626 to_delete to_put to_write_async_safe
1631 This is because the @code{gdb_stdout} is a variable of the type
1632 @code{struct ui_file} that is defined in @value{GDBN} sources as
1639 ui_file_flush_ftype *to_flush;
1640 ui_file_write_ftype *to_write;
1641 ui_file_write_async_safe_ftype *to_write_async_safe;
1642 ui_file_fputs_ftype *to_fputs;
1643 ui_file_read_ftype *to_read;
1644 ui_file_delete_ftype *to_delete;
1645 ui_file_isatty_ftype *to_isatty;
1646 ui_file_rewind_ftype *to_rewind;
1647 ui_file_put_ftype *to_put;
1654 @section Getting Help
1655 @cindex online documentation
1658 You can always ask @value{GDBN} itself for information on its commands,
1659 using the command @code{help}.
1662 @kindex h @r{(@code{help})}
1665 You can use @code{help} (abbreviated @code{h}) with no arguments to
1666 display a short list of named classes of commands:
1670 List of classes of commands:
1672 aliases -- Aliases of other commands
1673 breakpoints -- Making program stop at certain points
1674 data -- Examining data
1675 files -- Specifying and examining files
1676 internals -- Maintenance commands
1677 obscure -- Obscure features
1678 running -- Running the program
1679 stack -- Examining the stack
1680 status -- Status inquiries
1681 support -- Support facilities
1682 tracepoints -- Tracing of program execution without
1683 stopping the program
1684 user-defined -- User-defined commands
1686 Type "help" followed by a class name for a list of
1687 commands in that class.
1688 Type "help" followed by command name for full
1690 Command name abbreviations are allowed if unambiguous.
1693 @c the above line break eliminates huge line overfull...
1695 @item help @var{class}
1696 Using one of the general help classes as an argument, you can get a
1697 list of the individual commands in that class. For example, here is the
1698 help display for the class @code{status}:
1701 (@value{GDBP}) help status
1706 @c Line break in "show" line falsifies real output, but needed
1707 @c to fit in smallbook page size.
1708 info -- Generic command for showing things
1709 about the program being debugged
1710 show -- Generic command for showing things
1713 Type "help" followed by command name for full
1715 Command name abbreviations are allowed if unambiguous.
1719 @item help @var{command}
1720 With a command name as @code{help} argument, @value{GDBN} displays a
1721 short paragraph on how to use that command.
1724 @item apropos @var{args}
1725 The @code{apropos} command searches through all of the @value{GDBN}
1726 commands, and their documentation, for the regular expression specified in
1727 @var{args}. It prints out all matches found. For example:
1738 alias -- Define a new command that is an alias of an existing command
1739 aliases -- Aliases of other commands
1740 d -- Delete some breakpoints or auto-display expressions
1741 del -- Delete some breakpoints or auto-display expressions
1742 delete -- Delete some breakpoints or auto-display expressions
1747 @item complete @var{args}
1748 The @code{complete @var{args}} command lists all the possible completions
1749 for the beginning of a command. Use @var{args} to specify the beginning of the
1750 command you want completed. For example:
1756 @noindent results in:
1767 @noindent This is intended for use by @sc{gnu} Emacs.
1770 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1771 and @code{show} to inquire about the state of your program, or the state
1772 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1773 manual introduces each of them in the appropriate context. The listings
1774 under @code{info} and under @code{show} in the Index point to
1775 all the sub-commands. @xref{Index}.
1780 @kindex i @r{(@code{info})}
1782 This command (abbreviated @code{i}) is for describing the state of your
1783 program. For example, you can show the arguments passed to a function
1784 with @code{info args}, list the registers currently in use with @code{info
1785 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1786 You can get a complete list of the @code{info} sub-commands with
1787 @w{@code{help info}}.
1791 You can assign the result of an expression to an environment variable with
1792 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1793 @code{set prompt $}.
1797 In contrast to @code{info}, @code{show} is for describing the state of
1798 @value{GDBN} itself.
1799 You can change most of the things you can @code{show}, by using the
1800 related command @code{set}; for example, you can control what number
1801 system is used for displays with @code{set radix}, or simply inquire
1802 which is currently in use with @code{show radix}.
1805 To display all the settable parameters and their current
1806 values, you can use @code{show} with no arguments; you may also use
1807 @code{info set}. Both commands produce the same display.
1808 @c FIXME: "info set" violates the rule that "info" is for state of
1809 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1810 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1814 Here are three miscellaneous @code{show} subcommands, all of which are
1815 exceptional in lacking corresponding @code{set} commands:
1818 @kindex show version
1819 @cindex @value{GDBN} version number
1821 Show what version of @value{GDBN} is running. You should include this
1822 information in @value{GDBN} bug-reports. If multiple versions of
1823 @value{GDBN} are in use at your site, you may need to determine which
1824 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1825 commands are introduced, and old ones may wither away. Also, many
1826 system vendors ship variant versions of @value{GDBN}, and there are
1827 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1828 The version number is the same as the one announced when you start
1831 @kindex show copying
1832 @kindex info copying
1833 @cindex display @value{GDBN} copyright
1836 Display information about permission for copying @value{GDBN}.
1838 @kindex show warranty
1839 @kindex info warranty
1841 @itemx info warranty
1842 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1843 if your version of @value{GDBN} comes with one.
1848 @chapter Running Programs Under @value{GDBN}
1850 When you run a program under @value{GDBN}, you must first generate
1851 debugging information when you compile it.
1853 You may start @value{GDBN} with its arguments, if any, in an environment
1854 of your choice. If you are doing native debugging, you may redirect
1855 your program's input and output, debug an already running process, or
1856 kill a child process.
1859 * Compilation:: Compiling for debugging
1860 * Starting:: Starting your program
1861 * Arguments:: Your program's arguments
1862 * Environment:: Your program's environment
1864 * Working Directory:: Your program's working directory
1865 * Input/Output:: Your program's input and output
1866 * Attach:: Debugging an already-running process
1867 * Kill Process:: Killing the child process
1869 * Inferiors and Programs:: Debugging multiple inferiors and programs
1870 * Threads:: Debugging programs with multiple threads
1871 * Forks:: Debugging forks
1872 * Checkpoint/Restart:: Setting a @emph{bookmark} to return to later
1876 @section Compiling for Debugging
1878 In order to debug a program effectively, you need to generate
1879 debugging information when you compile it. This debugging information
1880 is stored in the object file; it describes the data type of each
1881 variable or function and the correspondence between source line numbers
1882 and addresses in the executable code.
1884 To request debugging information, specify the @samp{-g} option when you run
1887 Programs that are to be shipped to your customers are compiled with
1888 optimizations, using the @samp{-O} compiler option. However, some
1889 compilers are unable to handle the @samp{-g} and @samp{-O} options
1890 together. Using those compilers, you cannot generate optimized
1891 executables containing debugging information.
1893 @value{NGCC}, the @sc{gnu} C/C@t{++} compiler, supports @samp{-g} with or
1894 without @samp{-O}, making it possible to debug optimized code. We
1895 recommend that you @emph{always} use @samp{-g} whenever you compile a
1896 program. You may think your program is correct, but there is no sense
1897 in pushing your luck. For more information, see @ref{Optimized Code}.
1899 Older versions of the @sc{gnu} C compiler permitted a variant option
1900 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1901 format; if your @sc{gnu} C compiler has this option, do not use it.
1903 @value{GDBN} knows about preprocessor macros and can show you their
1904 expansion (@pxref{Macros}). Most compilers do not include information
1905 about preprocessor macros in the debugging information if you specify
1906 the @option{-g} flag alone. Version 3.1 and later of @value{NGCC},
1907 the @sc{gnu} C compiler, provides macro information if you are using
1908 the DWARF debugging format, and specify the option @option{-g3}.
1910 @xref{Debugging Options,,Options for Debugging Your Program or GCC,
1911 gcc.info, Using the @sc{gnu} Compiler Collection (GCC)}, for more
1912 information on @value{NGCC} options affecting debug information.
1914 You will have the best debugging experience if you use the latest
1915 version of the DWARF debugging format that your compiler supports.
1916 DWARF is currently the most expressive and best supported debugging
1917 format in @value{GDBN}.
1921 @section Starting your Program
1927 @kindex r @r{(@code{run})}
1930 Use the @code{run} command to start your program under @value{GDBN}.
1931 You must first specify the program name (except on VxWorks) with an
1932 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1933 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1934 (@pxref{Files, ,Commands to Specify Files}).
1938 If you are running your program in an execution environment that
1939 supports processes, @code{run} creates an inferior process and makes
1940 that process run your program. In some environments without processes,
1941 @code{run} jumps to the start of your program. Other targets,
1942 like @samp{remote}, are always running. If you get an error
1943 message like this one:
1946 The "remote" target does not support "run".
1947 Try "help target" or "continue".
1951 then use @code{continue} to run your program. You may need @code{load}
1952 first (@pxref{load}).
1954 The execution of a program is affected by certain information it
1955 receives from its superior. @value{GDBN} provides ways to specify this
1956 information, which you must do @emph{before} starting your program. (You
1957 can change it after starting your program, but such changes only affect
1958 your program the next time you start it.) This information may be
1959 divided into four categories:
1962 @item The @emph{arguments.}
1963 Specify the arguments to give your program as the arguments of the
1964 @code{run} command. If a shell is available on your target, the shell
1965 is used to pass the arguments, so that you may use normal conventions
1966 (such as wildcard expansion or variable substitution) in describing
1968 In Unix systems, you can control which shell is used with the
1969 @code{SHELL} environment variable.
1970 @xref{Arguments, ,Your Program's Arguments}.
1972 @item The @emph{environment.}
1973 Your program normally inherits its environment from @value{GDBN}, but you can
1974 use the @value{GDBN} commands @code{set environment} and @code{unset
1975 environment} to change parts of the environment that affect
1976 your program. @xref{Environment, ,Your Program's Environment}.
1978 @item The @emph{working directory.}
1979 Your program inherits its working directory from @value{GDBN}. You can set
1980 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1981 @xref{Working Directory, ,Your Program's Working Directory}.
1983 @item The @emph{standard input and output.}
1984 Your program normally uses the same device for standard input and
1985 standard output as @value{GDBN} is using. You can redirect input and output
1986 in the @code{run} command line, or you can use the @code{tty} command to
1987 set a different device for your program.
1988 @xref{Input/Output, ,Your Program's Input and Output}.
1991 @emph{Warning:} While input and output redirection work, you cannot use
1992 pipes to pass the output of the program you are debugging to another
1993 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1997 When you issue the @code{run} command, your program begins to execute
1998 immediately. @xref{Stopping, ,Stopping and Continuing}, for discussion
1999 of how to arrange for your program to stop. Once your program has
2000 stopped, you may call functions in your program, using the @code{print}
2001 or @code{call} commands. @xref{Data, ,Examining Data}.
2003 If the modification time of your symbol file has changed since the last
2004 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
2005 table, and reads it again. When it does this, @value{GDBN} tries to retain
2006 your current breakpoints.
2011 @cindex run to main procedure
2012 The name of the main procedure can vary from language to language.
2013 With C or C@t{++}, the main procedure name is always @code{main}, but
2014 other languages such as Ada do not require a specific name for their
2015 main procedure. The debugger provides a convenient way to start the
2016 execution of the program and to stop at the beginning of the main
2017 procedure, depending on the language used.
2019 The @samp{start} command does the equivalent of setting a temporary
2020 breakpoint at the beginning of the main procedure and then invoking
2021 the @samp{run} command.
2023 @cindex elaboration phase
2024 Some programs contain an @dfn{elaboration} phase where some startup code is
2025 executed before the main procedure is called. This depends on the
2026 languages used to write your program. In C@t{++}, for instance,
2027 constructors for static and global objects are executed before
2028 @code{main} is called. It is therefore possible that the debugger stops
2029 before reaching the main procedure. However, the temporary breakpoint
2030 will remain to halt execution.
2032 Specify the arguments to give to your program as arguments to the
2033 @samp{start} command. These arguments will be given verbatim to the
2034 underlying @samp{run} command. Note that the same arguments will be
2035 reused if no argument is provided during subsequent calls to
2036 @samp{start} or @samp{run}.
2038 It is sometimes necessary to debug the program during elaboration. In
2039 these cases, using the @code{start} command would stop the execution of
2040 your program too late, as the program would have already completed the
2041 elaboration phase. Under these circumstances, insert breakpoints in your
2042 elaboration code before running your program.
2044 @kindex set exec-wrapper
2045 @item set exec-wrapper @var{wrapper}
2046 @itemx show exec-wrapper
2047 @itemx unset exec-wrapper
2048 When @samp{exec-wrapper} is set, the specified wrapper is used to
2049 launch programs for debugging. @value{GDBN} starts your program
2050 with a shell command of the form @kbd{exec @var{wrapper}
2051 @var{program}}. Quoting is added to @var{program} and its
2052 arguments, but not to @var{wrapper}, so you should add quotes if
2053 appropriate for your shell. The wrapper runs until it executes
2054 your program, and then @value{GDBN} takes control.
2056 You can use any program that eventually calls @code{execve} with
2057 its arguments as a wrapper. Several standard Unix utilities do
2058 this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending
2059 with @code{exec "$@@"} will also work.
2061 For example, you can use @code{env} to pass an environment variable to
2062 the debugged program, without setting the variable in your shell's
2066 (@value{GDBP}) set exec-wrapper env 'LD_PRELOAD=libtest.so'
2070 This command is available when debugging locally on most targets, excluding
2071 @sc{djgpp}, Cygwin, MS Windows, and QNX Neutrino.
2073 @kindex set disable-randomization
2074 @item set disable-randomization
2075 @itemx set disable-randomization on
2076 This option (enabled by default in @value{GDBN}) will turn off the native
2077 randomization of the virtual address space of the started program. This option
2078 is useful for multiple debugging sessions to make the execution better
2079 reproducible and memory addresses reusable across debugging sessions.
2081 This feature is implemented only on certain targets, including @sc{gnu}/Linux.
2082 On @sc{gnu}/Linux you can get the same behavior using
2085 (@value{GDBP}) set exec-wrapper setarch `uname -m` -R
2088 @item set disable-randomization off
2089 Leave the behavior of the started executable unchanged. Some bugs rear their
2090 ugly heads only when the program is loaded at certain addresses. If your bug
2091 disappears when you run the program under @value{GDBN}, that might be because
2092 @value{GDBN} by default disables the address randomization on platforms, such
2093 as @sc{gnu}/Linux, which do that for stand-alone programs. Use @kbd{set
2094 disable-randomization off} to try to reproduce such elusive bugs.
2096 On targets where it is available, virtual address space randomization
2097 protects the programs against certain kinds of security attacks. In these
2098 cases the attacker needs to know the exact location of a concrete executable
2099 code. Randomizing its location makes it impossible to inject jumps misusing
2100 a code at its expected addresses.
2102 Prelinking shared libraries provides a startup performance advantage but it
2103 makes addresses in these libraries predictable for privileged processes by
2104 having just unprivileged access at the target system. Reading the shared
2105 library binary gives enough information for assembling the malicious code
2106 misusing it. Still even a prelinked shared library can get loaded at a new
2107 random address just requiring the regular relocation process during the
2108 startup. Shared libraries not already prelinked are always loaded at
2109 a randomly chosen address.
2111 Position independent executables (PIE) contain position independent code
2112 similar to the shared libraries and therefore such executables get loaded at
2113 a randomly chosen address upon startup. PIE executables always load even
2114 already prelinked shared libraries at a random address. You can build such
2115 executable using @command{gcc -fPIE -pie}.
2117 Heap (malloc storage), stack and custom mmap areas are always placed randomly
2118 (as long as the randomization is enabled).
2120 @item show disable-randomization
2121 Show the current setting of the explicit disable of the native randomization of
2122 the virtual address space of the started program.
2127 @section Your Program's Arguments
2129 @cindex arguments (to your program)
2130 The arguments to your program can be specified by the arguments of the
2132 They are passed to a shell, which expands wildcard characters and
2133 performs redirection of I/O, and thence to your program. Your
2134 @code{SHELL} environment variable (if it exists) specifies what shell
2135 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
2136 the default shell (@file{/bin/sh} on Unix).
2138 On non-Unix systems, the program is usually invoked directly by
2139 @value{GDBN}, which emulates I/O redirection via the appropriate system
2140 calls, and the wildcard characters are expanded by the startup code of
2141 the program, not by the shell.
2143 @code{run} with no arguments uses the same arguments used by the previous
2144 @code{run}, or those set by the @code{set args} command.
2149 Specify the arguments to be used the next time your program is run. If
2150 @code{set args} has no arguments, @code{run} executes your program
2151 with no arguments. Once you have run your program with arguments,
2152 using @code{set args} before the next @code{run} is the only way to run
2153 it again without arguments.
2157 Show the arguments to give your program when it is started.
2161 @section Your Program's Environment
2163 @cindex environment (of your program)
2164 The @dfn{environment} consists of a set of environment variables and
2165 their values. Environment variables conventionally record such things as
2166 your user name, your home directory, your terminal type, and your search
2167 path for programs to run. Usually you set up environment variables with
2168 the shell and they are inherited by all the other programs you run. When
2169 debugging, it can be useful to try running your program with a modified
2170 environment without having to start @value{GDBN} over again.
2174 @item path @var{directory}
2175 Add @var{directory} to the front of the @code{PATH} environment variable
2176 (the search path for executables) that will be passed to your program.
2177 The value of @code{PATH} used by @value{GDBN} does not change.
2178 You may specify several directory names, separated by whitespace or by a
2179 system-dependent separator character (@samp{:} on Unix, @samp{;} on
2180 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
2181 is moved to the front, so it is searched sooner.
2183 You can use the string @samp{$cwd} to refer to whatever is the current
2184 working directory at the time @value{GDBN} searches the path. If you
2185 use @samp{.} instead, it refers to the directory where you executed the
2186 @code{path} command. @value{GDBN} replaces @samp{.} in the
2187 @var{directory} argument (with the current path) before adding
2188 @var{directory} to the search path.
2189 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
2190 @c document that, since repeating it would be a no-op.
2194 Display the list of search paths for executables (the @code{PATH}
2195 environment variable).
2197 @kindex show environment
2198 @item show environment @r{[}@var{varname}@r{]}
2199 Print the value of environment variable @var{varname} to be given to
2200 your program when it starts. If you do not supply @var{varname},
2201 print the names and values of all environment variables to be given to
2202 your program. You can abbreviate @code{environment} as @code{env}.
2204 @kindex set environment
2205 @item set environment @var{varname} @r{[}=@var{value}@r{]}
2206 Set environment variable @var{varname} to @var{value}. The value
2207 changes for your program only, not for @value{GDBN} itself. @var{value} may
2208 be any string; the values of environment variables are just strings, and
2209 any interpretation is supplied by your program itself. The @var{value}
2210 parameter is optional; if it is eliminated, the variable is set to a
2212 @c "any string" here does not include leading, trailing
2213 @c blanks. Gnu asks: does anyone care?
2215 For example, this command:
2222 tells the debugged program, when subsequently run, that its user is named
2223 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
2224 are not actually required.)
2226 @kindex unset environment
2227 @item unset environment @var{varname}
2228 Remove variable @var{varname} from the environment to be passed to your
2229 program. This is different from @samp{set env @var{varname} =};
2230 @code{unset environment} removes the variable from the environment,
2231 rather than assigning it an empty value.
2234 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
2236 by your @code{SHELL} environment variable if it exists (or
2237 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
2238 that runs an initialization file---such as @file{.cshrc} for C-shell, or
2239 @file{.bashrc} for BASH---any variables you set in that file affect
2240 your program. You may wish to move setting of environment variables to
2241 files that are only run when you sign on, such as @file{.login} or
2244 @node Working Directory
2245 @section Your Program's Working Directory
2247 @cindex working directory (of your program)
2248 Each time you start your program with @code{run}, it inherits its
2249 working directory from the current working directory of @value{GDBN}.
2250 The @value{GDBN} working directory is initially whatever it inherited
2251 from its parent process (typically the shell), but you can specify a new
2252 working directory in @value{GDBN} with the @code{cd} command.
2254 The @value{GDBN} working directory also serves as a default for the commands
2255 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
2260 @cindex change working directory
2261 @item cd @var{directory}
2262 Set the @value{GDBN} working directory to @var{directory}.
2266 Print the @value{GDBN} working directory.
2269 It is generally impossible to find the current working directory of
2270 the process being debugged (since a program can change its directory
2271 during its run). If you work on a system where @value{GDBN} is
2272 configured with the @file{/proc} support, you can use the @code{info
2273 proc} command (@pxref{SVR4 Process Information}) to find out the
2274 current working directory of the debuggee.
2277 @section Your Program's Input and Output
2282 By default, the program you run under @value{GDBN} does input and output to
2283 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
2284 to its own terminal modes to interact with you, but it records the terminal
2285 modes your program was using and switches back to them when you continue
2286 running your program.
2289 @kindex info terminal
2291 Displays information recorded by @value{GDBN} about the terminal modes your
2295 You can redirect your program's input and/or output using shell
2296 redirection with the @code{run} command. For example,
2303 starts your program, diverting its output to the file @file{outfile}.
2306 @cindex controlling terminal
2307 Another way to specify where your program should do input and output is
2308 with the @code{tty} command. This command accepts a file name as
2309 argument, and causes this file to be the default for future @code{run}
2310 commands. It also resets the controlling terminal for the child
2311 process, for future @code{run} commands. For example,
2318 directs that processes started with subsequent @code{run} commands
2319 default to do input and output on the terminal @file{/dev/ttyb} and have
2320 that as their controlling terminal.
2322 An explicit redirection in @code{run} overrides the @code{tty} command's
2323 effect on the input/output device, but not its effect on the controlling
2326 When you use the @code{tty} command or redirect input in the @code{run}
2327 command, only the input @emph{for your program} is affected. The input
2328 for @value{GDBN} still comes from your terminal. @code{tty} is an alias
2329 for @code{set inferior-tty}.
2331 @cindex inferior tty
2332 @cindex set inferior controlling terminal
2333 You can use the @code{show inferior-tty} command to tell @value{GDBN} to
2334 display the name of the terminal that will be used for future runs of your
2338 @item set inferior-tty /dev/ttyb
2339 @kindex set inferior-tty
2340 Set the tty for the program being debugged to /dev/ttyb.
2342 @item show inferior-tty
2343 @kindex show inferior-tty
2344 Show the current tty for the program being debugged.
2348 @section Debugging an Already-running Process
2353 @item attach @var{process-id}
2354 This command attaches to a running process---one that was started
2355 outside @value{GDBN}. (@code{info files} shows your active
2356 targets.) The command takes as argument a process ID. The usual way to
2357 find out the @var{process-id} of a Unix process is with the @code{ps} utility,
2358 or with the @samp{jobs -l} shell command.
2360 @code{attach} does not repeat if you press @key{RET} a second time after
2361 executing the command.
2364 To use @code{attach}, your program must be running in an environment
2365 which supports processes; for example, @code{attach} does not work for
2366 programs on bare-board targets that lack an operating system. You must
2367 also have permission to send the process a signal.
2369 When you use @code{attach}, the debugger finds the program running in
2370 the process first by looking in the current working directory, then (if
2371 the program is not found) by using the source file search path
2372 (@pxref{Source Path, ,Specifying Source Directories}). You can also use
2373 the @code{file} command to load the program. @xref{Files, ,Commands to
2376 The first thing @value{GDBN} does after arranging to debug the specified
2377 process is to stop it. You can examine and modify an attached process
2378 with all the @value{GDBN} commands that are ordinarily available when
2379 you start processes with @code{run}. You can insert breakpoints; you
2380 can step and continue; you can modify storage. If you would rather the
2381 process continue running, you may use the @code{continue} command after
2382 attaching @value{GDBN} to the process.
2387 When you have finished debugging the attached process, you can use the
2388 @code{detach} command to release it from @value{GDBN} control. Detaching
2389 the process continues its execution. After the @code{detach} command,
2390 that process and @value{GDBN} become completely independent once more, and you
2391 are ready to @code{attach} another process or start one with @code{run}.
2392 @code{detach} does not repeat if you press @key{RET} again after
2393 executing the command.
2396 If you exit @value{GDBN} while you have an attached process, you detach
2397 that process. If you use the @code{run} command, you kill that process.
2398 By default, @value{GDBN} asks for confirmation if you try to do either of these
2399 things; you can control whether or not you need to confirm by using the
2400 @code{set confirm} command (@pxref{Messages/Warnings, ,Optional Warnings and
2404 @section Killing the Child Process
2409 Kill the child process in which your program is running under @value{GDBN}.
2412 This command is useful if you wish to debug a core dump instead of a
2413 running process. @value{GDBN} ignores any core dump file while your program
2416 On some operating systems, a program cannot be executed outside @value{GDBN}
2417 while you have breakpoints set on it inside @value{GDBN}. You can use the
2418 @code{kill} command in this situation to permit running your program
2419 outside the debugger.
2421 The @code{kill} command is also useful if you wish to recompile and
2422 relink your program, since on many systems it is impossible to modify an
2423 executable file while it is running in a process. In this case, when you
2424 next type @code{run}, @value{GDBN} notices that the file has changed, and
2425 reads the symbol table again (while trying to preserve your current
2426 breakpoint settings).
2428 @node Inferiors and Programs
2429 @section Debugging Multiple Inferiors and Programs
2431 @value{GDBN} lets you run and debug multiple programs in a single
2432 session. In addition, @value{GDBN} on some systems may let you run
2433 several programs simultaneously (otherwise you have to exit from one
2434 before starting another). In the most general case, you can have
2435 multiple threads of execution in each of multiple processes, launched
2436 from multiple executables.
2439 @value{GDBN} represents the state of each program execution with an
2440 object called an @dfn{inferior}. An inferior typically corresponds to
2441 a process, but is more general and applies also to targets that do not
2442 have processes. Inferiors may be created before a process runs, and
2443 may be retained after a process exits. Inferiors have unique
2444 identifiers that are different from process ids. Usually each
2445 inferior will also have its own distinct address space, although some
2446 embedded targets may have several inferiors running in different parts
2447 of a single address space. Each inferior may in turn have multiple
2448 threads running in it.
2450 To find out what inferiors exist at any moment, use @w{@code{info
2454 @kindex info inferiors
2455 @item info inferiors
2456 Print a list of all inferiors currently being managed by @value{GDBN}.
2458 @value{GDBN} displays for each inferior (in this order):
2462 the inferior number assigned by @value{GDBN}
2465 the target system's inferior identifier
2468 the name of the executable the inferior is running.
2473 An asterisk @samp{*} preceding the @value{GDBN} inferior number
2474 indicates the current inferior.
2478 @c end table here to get a little more width for example
2481 (@value{GDBP}) info inferiors
2482 Num Description Executable
2483 2 process 2307 hello
2484 * 1 process 3401 goodbye
2487 To switch focus between inferiors, use the @code{inferior} command:
2490 @kindex inferior @var{infno}
2491 @item inferior @var{infno}
2492 Make inferior number @var{infno} the current inferior. The argument
2493 @var{infno} is the inferior number assigned by @value{GDBN}, as shown
2494 in the first field of the @samp{info inferiors} display.
2498 You can get multiple executables into a debugging session via the
2499 @code{add-inferior} and @w{@code{clone-inferior}} commands. On some
2500 systems @value{GDBN} can add inferiors to the debug session
2501 automatically by following calls to @code{fork} and @code{exec}. To
2502 remove inferiors from the debugging session use the
2503 @w{@code{remove-inferiors}} command.
2506 @kindex add-inferior
2507 @item add-inferior [ -copies @var{n} ] [ -exec @var{executable} ]
2508 Adds @var{n} inferiors to be run using @var{executable} as the
2509 executable. @var{n} defaults to 1. If no executable is specified,
2510 the inferiors begins empty, with no program. You can still assign or
2511 change the program assigned to the inferior at any time by using the
2512 @code{file} command with the executable name as its argument.
2514 @kindex clone-inferior
2515 @item clone-inferior [ -copies @var{n} ] [ @var{infno} ]
2516 Adds @var{n} inferiors ready to execute the same program as inferior
2517 @var{infno}. @var{n} defaults to 1. @var{infno} defaults to the
2518 number of the current inferior. This is a convenient command when you
2519 want to run another instance of the inferior you are debugging.
2522 (@value{GDBP}) info inferiors
2523 Num Description Executable
2524 * 1 process 29964 helloworld
2525 (@value{GDBP}) clone-inferior
2528 (@value{GDBP}) info inferiors
2529 Num Description Executable
2531 * 1 process 29964 helloworld
2534 You can now simply switch focus to inferior 2 and run it.
2536 @kindex remove-inferiors
2537 @item remove-inferiors @var{infno}@dots{}
2538 Removes the inferior or inferiors @var{infno}@dots{}. It is not
2539 possible to remove an inferior that is running with this command. For
2540 those, use the @code{kill} or @code{detach} command first.
2544 To quit debugging one of the running inferiors that is not the current
2545 inferior, you can either detach from it by using the @w{@code{detach
2546 inferior}} command (allowing it to run independently), or kill it
2547 using the @w{@code{kill inferiors}} command:
2550 @kindex detach inferiors @var{infno}@dots{}
2551 @item detach inferior @var{infno}@dots{}
2552 Detach from the inferior or inferiors identified by @value{GDBN}
2553 inferior number(s) @var{infno}@dots{}. Note that the inferior's entry
2554 still stays on the list of inferiors shown by @code{info inferiors},
2555 but its Description will show @samp{<null>}.
2557 @kindex kill inferiors @var{infno}@dots{}
2558 @item kill inferiors @var{infno}@dots{}
2559 Kill the inferior or inferiors identified by @value{GDBN} inferior
2560 number(s) @var{infno}@dots{}. Note that the inferior's entry still
2561 stays on the list of inferiors shown by @code{info inferiors}, but its
2562 Description will show @samp{<null>}.
2565 After the successful completion of a command such as @code{detach},
2566 @code{detach inferiors}, @code{kill} or @code{kill inferiors}, or after
2567 a normal process exit, the inferior is still valid and listed with
2568 @code{info inferiors}, ready to be restarted.
2571 To be notified when inferiors are started or exit under @value{GDBN}'s
2572 control use @w{@code{set print inferior-events}}:
2575 @kindex set print inferior-events
2576 @cindex print messages on inferior start and exit
2577 @item set print inferior-events
2578 @itemx set print inferior-events on
2579 @itemx set print inferior-events off
2580 The @code{set print inferior-events} command allows you to enable or
2581 disable printing of messages when @value{GDBN} notices that new
2582 inferiors have started or that inferiors have exited or have been
2583 detached. By default, these messages will not be printed.
2585 @kindex show print inferior-events
2586 @item show print inferior-events
2587 Show whether messages will be printed when @value{GDBN} detects that
2588 inferiors have started, exited or have been detached.
2591 Many commands will work the same with multiple programs as with a
2592 single program: e.g., @code{print myglobal} will simply display the
2593 value of @code{myglobal} in the current inferior.
2596 Occasionaly, when debugging @value{GDBN} itself, it may be useful to
2597 get more info about the relationship of inferiors, programs, address
2598 spaces in a debug session. You can do that with the @w{@code{maint
2599 info program-spaces}} command.
2602 @kindex maint info program-spaces
2603 @item maint info program-spaces
2604 Print a list of all program spaces currently being managed by
2607 @value{GDBN} displays for each program space (in this order):
2611 the program space number assigned by @value{GDBN}
2614 the name of the executable loaded into the program space, with e.g.,
2615 the @code{file} command.
2620 An asterisk @samp{*} preceding the @value{GDBN} program space number
2621 indicates the current program space.
2623 In addition, below each program space line, @value{GDBN} prints extra
2624 information that isn't suitable to display in tabular form. For
2625 example, the list of inferiors bound to the program space.
2628 (@value{GDBP}) maint info program-spaces
2631 Bound inferiors: ID 1 (process 21561)
2635 Here we can see that no inferior is running the program @code{hello},
2636 while @code{process 21561} is running the program @code{goodbye}. On
2637 some targets, it is possible that multiple inferiors are bound to the
2638 same program space. The most common example is that of debugging both
2639 the parent and child processes of a @code{vfork} call. For example,
2642 (@value{GDBP}) maint info program-spaces
2645 Bound inferiors: ID 2 (process 18050), ID 1 (process 18045)
2648 Here, both inferior 2 and inferior 1 are running in the same program
2649 space as a result of inferior 1 having executed a @code{vfork} call.
2653 @section Debugging Programs with Multiple Threads
2655 @cindex threads of execution
2656 @cindex multiple threads
2657 @cindex switching threads
2658 In some operating systems, such as HP-UX and Solaris, a single program
2659 may have more than one @dfn{thread} of execution. The precise semantics
2660 of threads differ from one operating system to another, but in general
2661 the threads of a single program are akin to multiple processes---except
2662 that they share one address space (that is, they can all examine and
2663 modify the same variables). On the other hand, each thread has its own
2664 registers and execution stack, and perhaps private memory.
2666 @value{GDBN} provides these facilities for debugging multi-thread
2670 @item automatic notification of new threads
2671 @item @samp{thread @var{threadno}}, a command to switch among threads
2672 @item @samp{info threads}, a command to inquire about existing threads
2673 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2674 a command to apply a command to a list of threads
2675 @item thread-specific breakpoints
2676 @item @samp{set print thread-events}, which controls printing of
2677 messages on thread start and exit.
2678 @item @samp{set libthread-db-search-path @var{path}}, which lets
2679 the user specify which @code{libthread_db} to use if the default choice
2680 isn't compatible with the program.
2684 @emph{Warning:} These facilities are not yet available on every
2685 @value{GDBN} configuration where the operating system supports threads.
2686 If your @value{GDBN} does not support threads, these commands have no
2687 effect. For example, a system without thread support shows no output
2688 from @samp{info threads}, and always rejects the @code{thread} command,
2692 (@value{GDBP}) info threads
2693 (@value{GDBP}) thread 1
2694 Thread ID 1 not known. Use the "info threads" command to
2695 see the IDs of currently known threads.
2697 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2698 @c doesn't support threads"?
2701 @cindex focus of debugging
2702 @cindex current thread
2703 The @value{GDBN} thread debugging facility allows you to observe all
2704 threads while your program runs---but whenever @value{GDBN} takes
2705 control, one thread in particular is always the focus of debugging.
2706 This thread is called the @dfn{current thread}. Debugging commands show
2707 program information from the perspective of the current thread.
2709 @cindex @code{New} @var{systag} message
2710 @cindex thread identifier (system)
2711 @c FIXME-implementors!! It would be more helpful if the [New...] message
2712 @c included GDB's numeric thread handle, so you could just go to that
2713 @c thread without first checking `info threads'.
2714 Whenever @value{GDBN} detects a new thread in your program, it displays
2715 the target system's identification for the thread with a message in the
2716 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2717 whose form varies depending on the particular system. For example, on
2718 @sc{gnu}/Linux, you might see
2721 [New Thread 0x41e02940 (LWP 25582)]
2725 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2726 the @var{systag} is simply something like @samp{process 368}, with no
2729 @c FIXME!! (1) Does the [New...] message appear even for the very first
2730 @c thread of a program, or does it only appear for the
2731 @c second---i.e.@: when it becomes obvious we have a multithread
2733 @c (2) *Is* there necessarily a first thread always? Or do some
2734 @c multithread systems permit starting a program with multiple
2735 @c threads ab initio?
2737 @cindex thread number
2738 @cindex thread identifier (GDB)
2739 For debugging purposes, @value{GDBN} associates its own thread
2740 number---always a single integer---with each thread in your program.
2743 @kindex info threads
2744 @item info threads @r{[}@var{id}@dots{}@r{]}
2745 Display a summary of all threads currently in your program. Optional
2746 argument @var{id}@dots{} is one or more thread ids separated by spaces, and
2747 means to print information only about the specified thread or threads.
2748 @value{GDBN} displays for each thread (in this order):
2752 the thread number assigned by @value{GDBN}
2755 the target system's thread identifier (@var{systag})
2758 the thread's name, if one is known. A thread can either be named by
2759 the user (see @code{thread name}, below), or, in some cases, by the
2763 the current stack frame summary for that thread
2767 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2768 indicates the current thread.
2772 @c end table here to get a little more width for example
2775 (@value{GDBP}) info threads
2777 3 process 35 thread 27 0x34e5 in sigpause ()
2778 2 process 35 thread 23 0x34e5 in sigpause ()
2779 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2783 On Solaris, you can display more information about user threads with a
2784 Solaris-specific command:
2787 @item maint info sol-threads
2788 @kindex maint info sol-threads
2789 @cindex thread info (Solaris)
2790 Display info on Solaris user threads.
2794 @kindex thread @var{threadno}
2795 @item thread @var{threadno}
2796 Make thread number @var{threadno} the current thread. The command
2797 argument @var{threadno} is the internal @value{GDBN} thread number, as
2798 shown in the first field of the @samp{info threads} display.
2799 @value{GDBN} responds by displaying the system identifier of the thread
2800 you selected, and its current stack frame summary:
2803 (@value{GDBP}) thread 2
2804 [Switching to thread 2 (Thread 0xb7fdab70 (LWP 12747))]
2805 #0 some_function (ignore=0x0) at example.c:8
2806 8 printf ("hello\n");
2810 As with the @samp{[New @dots{}]} message, the form of the text after
2811 @samp{Switching to} depends on your system's conventions for identifying
2814 @vindex $_thread@r{, convenience variable}
2815 The debugger convenience variable @samp{$_thread} contains the number
2816 of the current thread. You may find this useful in writing breakpoint
2817 conditional expressions, command scripts, and so forth. See
2818 @xref{Convenience Vars,, Convenience Variables}, for general
2819 information on convenience variables.
2821 @kindex thread apply
2822 @cindex apply command to several threads
2823 @item thread apply [@var{threadno} | all] @var{command}
2824 The @code{thread apply} command allows you to apply the named
2825 @var{command} to one or more threads. Specify the numbers of the
2826 threads that you want affected with the command argument
2827 @var{threadno}. It can be a single thread number, one of the numbers
2828 shown in the first field of the @samp{info threads} display; or it
2829 could be a range of thread numbers, as in @code{2-4}. To apply a
2830 command to all threads, type @kbd{thread apply all @var{command}}.
2833 @cindex name a thread
2834 @item thread name [@var{name}]
2835 This command assigns a name to the current thread. If no argument is
2836 given, any existing user-specified name is removed. The thread name
2837 appears in the @samp{info threads} display.
2839 On some systems, such as @sc{gnu}/Linux, @value{GDBN} is able to
2840 determine the name of the thread as given by the OS. On these
2841 systems, a name specified with @samp{thread name} will override the
2842 system-give name, and removing the user-specified name will cause
2843 @value{GDBN} to once again display the system-specified name.
2846 @cindex search for a thread
2847 @item thread find [@var{regexp}]
2848 Search for and display thread ids whose name or @var{systag}
2849 matches the supplied regular expression.
2851 As well as being the complement to the @samp{thread name} command,
2852 this command also allows you to identify a thread by its target
2853 @var{systag}. For instance, on @sc{gnu}/Linux, the target @var{systag}
2857 (@value{GDBN}) thread find 26688
2858 Thread 4 has target id 'Thread 0x41e02940 (LWP 26688)'
2859 (@value{GDBN}) info thread 4
2861 4 Thread 0x41e02940 (LWP 26688) 0x00000031ca6cd372 in select ()
2864 @kindex set print thread-events
2865 @cindex print messages on thread start and exit
2866 @item set print thread-events
2867 @itemx set print thread-events on
2868 @itemx set print thread-events off
2869 The @code{set print thread-events} command allows you to enable or
2870 disable printing of messages when @value{GDBN} notices that new threads have
2871 started or that threads have exited. By default, these messages will
2872 be printed if detection of these events is supported by the target.
2873 Note that these messages cannot be disabled on all targets.
2875 @kindex show print thread-events
2876 @item show print thread-events
2877 Show whether messages will be printed when @value{GDBN} detects that threads
2878 have started and exited.
2881 @xref{Thread Stops,,Stopping and Starting Multi-thread Programs}, for
2882 more information about how @value{GDBN} behaves when you stop and start
2883 programs with multiple threads.
2885 @xref{Set Watchpoints,,Setting Watchpoints}, for information about
2886 watchpoints in programs with multiple threads.
2889 @kindex set libthread-db-search-path
2890 @cindex search path for @code{libthread_db}
2891 @item set libthread-db-search-path @r{[}@var{path}@r{]}
2892 If this variable is set, @var{path} is a colon-separated list of
2893 directories @value{GDBN} will use to search for @code{libthread_db}.
2894 If you omit @var{path}, @samp{libthread-db-search-path} will be reset to
2895 its default value (@code{$sdir:$pdir} on @sc{gnu}/Linux and Solaris systems).
2896 Internally, the default value comes from the @code{LIBTHREAD_DB_SEARCH_PATH}
2899 On @sc{gnu}/Linux and Solaris systems, @value{GDBN} uses a ``helper''
2900 @code{libthread_db} library to obtain information about threads in the
2901 inferior process. @value{GDBN} will use @samp{libthread-db-search-path}
2902 to find @code{libthread_db}.
2904 A special entry @samp{$sdir} for @samp{libthread-db-search-path}
2905 refers to the default system directories that are
2906 normally searched for loading shared libraries.
2908 A special entry @samp{$pdir} for @samp{libthread-db-search-path}
2909 refers to the directory from which @code{libpthread}
2910 was loaded in the inferior process.
2912 For any @code{libthread_db} library @value{GDBN} finds in above directories,
2913 @value{GDBN} attempts to initialize it with the current inferior process.
2914 If this initialization fails (which could happen because of a version
2915 mismatch between @code{libthread_db} and @code{libpthread}), @value{GDBN}
2916 will unload @code{libthread_db}, and continue with the next directory.
2917 If none of @code{libthread_db} libraries initialize successfully,
2918 @value{GDBN} will issue a warning and thread debugging will be disabled.
2920 Setting @code{libthread-db-search-path} is currently implemented
2921 only on some platforms.
2923 @kindex show libthread-db-search-path
2924 @item show libthread-db-search-path
2925 Display current libthread_db search path.
2927 @kindex set debug libthread-db
2928 @kindex show debug libthread-db
2929 @cindex debugging @code{libthread_db}
2930 @item set debug libthread-db
2931 @itemx show debug libthread-db
2932 Turns on or off display of @code{libthread_db}-related events.
2933 Use @code{1} to enable, @code{0} to disable.
2937 @section Debugging Forks
2939 @cindex fork, debugging programs which call
2940 @cindex multiple processes
2941 @cindex processes, multiple
2942 On most systems, @value{GDBN} has no special support for debugging
2943 programs which create additional processes using the @code{fork}
2944 function. When a program forks, @value{GDBN} will continue to debug the
2945 parent process and the child process will run unimpeded. If you have
2946 set a breakpoint in any code which the child then executes, the child
2947 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2948 will cause it to terminate.
2950 However, if you want to debug the child process there is a workaround
2951 which isn't too painful. Put a call to @code{sleep} in the code which
2952 the child process executes after the fork. It may be useful to sleep
2953 only if a certain environment variable is set, or a certain file exists,
2954 so that the delay need not occur when you don't want to run @value{GDBN}
2955 on the child. While the child is sleeping, use the @code{ps} program to
2956 get its process ID. Then tell @value{GDBN} (a new invocation of
2957 @value{GDBN} if you are also debugging the parent process) to attach to
2958 the child process (@pxref{Attach}). From that point on you can debug
2959 the child process just like any other process which you attached to.
2961 On some systems, @value{GDBN} provides support for debugging programs that
2962 create additional processes using the @code{fork} or @code{vfork} functions.
2963 Currently, the only platforms with this feature are HP-UX (11.x and later
2964 only?) and @sc{gnu}/Linux (kernel version 2.5.60 and later).
2966 By default, when a program forks, @value{GDBN} will continue to debug
2967 the parent process and the child process will run unimpeded.
2969 If you want to follow the child process instead of the parent process,
2970 use the command @w{@code{set follow-fork-mode}}.
2973 @kindex set follow-fork-mode
2974 @item set follow-fork-mode @var{mode}
2975 Set the debugger response to a program call of @code{fork} or
2976 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2977 process. The @var{mode} argument can be:
2981 The original process is debugged after a fork. The child process runs
2982 unimpeded. This is the default.
2985 The new process is debugged after a fork. The parent process runs
2990 @kindex show follow-fork-mode
2991 @item show follow-fork-mode
2992 Display the current debugger response to a @code{fork} or @code{vfork} call.
2995 @cindex debugging multiple processes
2996 On Linux, if you want to debug both the parent and child processes, use the
2997 command @w{@code{set detach-on-fork}}.
3000 @kindex set detach-on-fork
3001 @item set detach-on-fork @var{mode}
3002 Tells gdb whether to detach one of the processes after a fork, or
3003 retain debugger control over them both.
3007 The child process (or parent process, depending on the value of
3008 @code{follow-fork-mode}) will be detached and allowed to run
3009 independently. This is the default.
3012 Both processes will be held under the control of @value{GDBN}.
3013 One process (child or parent, depending on the value of
3014 @code{follow-fork-mode}) is debugged as usual, while the other
3019 @kindex show detach-on-fork
3020 @item show detach-on-fork
3021 Show whether detach-on-fork mode is on/off.
3024 If you choose to set @samp{detach-on-fork} mode off, then @value{GDBN}
3025 will retain control of all forked processes (including nested forks).
3026 You can list the forked processes under the control of @value{GDBN} by
3027 using the @w{@code{info inferiors}} command, and switch from one fork
3028 to another by using the @code{inferior} command (@pxref{Inferiors and
3029 Programs, ,Debugging Multiple Inferiors and Programs}).
3031 To quit debugging one of the forked processes, you can either detach
3032 from it by using the @w{@code{detach inferiors}} command (allowing it
3033 to run independently), or kill it using the @w{@code{kill inferiors}}
3034 command. @xref{Inferiors and Programs, ,Debugging Multiple Inferiors
3037 If you ask to debug a child process and a @code{vfork} is followed by an
3038 @code{exec}, @value{GDBN} executes the new target up to the first
3039 breakpoint in the new target. If you have a breakpoint set on
3040 @code{main} in your original program, the breakpoint will also be set on
3041 the child process's @code{main}.
3043 On some systems, when a child process is spawned by @code{vfork}, you
3044 cannot debug the child or parent until an @code{exec} call completes.
3046 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
3047 call executes, the new target restarts. To restart the parent
3048 process, use the @code{file} command with the parent executable name
3049 as its argument. By default, after an @code{exec} call executes,
3050 @value{GDBN} discards the symbols of the previous executable image.
3051 You can change this behaviour with the @w{@code{set follow-exec-mode}}
3055 @kindex set follow-exec-mode
3056 @item set follow-exec-mode @var{mode}
3058 Set debugger response to a program call of @code{exec}. An
3059 @code{exec} call replaces the program image of a process.
3061 @code{follow-exec-mode} can be:
3065 @value{GDBN} creates a new inferior and rebinds the process to this
3066 new inferior. The program the process was running before the
3067 @code{exec} call can be restarted afterwards by restarting the
3073 (@value{GDBP}) info inferiors
3075 Id Description Executable
3078 process 12020 is executing new program: prog2
3079 Program exited normally.
3080 (@value{GDBP}) info inferiors
3081 Id Description Executable
3087 @value{GDBN} keeps the process bound to the same inferior. The new
3088 executable image replaces the previous executable loaded in the
3089 inferior. Restarting the inferior after the @code{exec} call, with
3090 e.g., the @code{run} command, restarts the executable the process was
3091 running after the @code{exec} call. This is the default mode.
3096 (@value{GDBP}) info inferiors
3097 Id Description Executable
3100 process 12020 is executing new program: prog2
3101 Program exited normally.
3102 (@value{GDBP}) info inferiors
3103 Id Description Executable
3110 You can use the @code{catch} command to make @value{GDBN} stop whenever
3111 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
3112 Catchpoints, ,Setting Catchpoints}.
3114 @node Checkpoint/Restart
3115 @section Setting a @emph{Bookmark} to Return to Later
3120 @cindex snapshot of a process
3121 @cindex rewind program state
3123 On certain operating systems@footnote{Currently, only
3124 @sc{gnu}/Linux.}, @value{GDBN} is able to save a @dfn{snapshot} of a
3125 program's state, called a @dfn{checkpoint}, and come back to it
3128 Returning to a checkpoint effectively undoes everything that has
3129 happened in the program since the @code{checkpoint} was saved. This
3130 includes changes in memory, registers, and even (within some limits)
3131 system state. Effectively, it is like going back in time to the
3132 moment when the checkpoint was saved.
3134 Thus, if you're stepping thru a program and you think you're
3135 getting close to the point where things go wrong, you can save
3136 a checkpoint. Then, if you accidentally go too far and miss
3137 the critical statement, instead of having to restart your program
3138 from the beginning, you can just go back to the checkpoint and
3139 start again from there.
3141 This can be especially useful if it takes a lot of time or
3142 steps to reach the point where you think the bug occurs.
3144 To use the @code{checkpoint}/@code{restart} method of debugging:
3149 Save a snapshot of the debugged program's current execution state.
3150 The @code{checkpoint} command takes no arguments, but each checkpoint
3151 is assigned a small integer id, similar to a breakpoint id.
3153 @kindex info checkpoints
3154 @item info checkpoints
3155 List the checkpoints that have been saved in the current debugging
3156 session. For each checkpoint, the following information will be
3163 @item Source line, or label
3166 @kindex restart @var{checkpoint-id}
3167 @item restart @var{checkpoint-id}
3168 Restore the program state that was saved as checkpoint number
3169 @var{checkpoint-id}. All program variables, registers, stack frames
3170 etc.@: will be returned to the values that they had when the checkpoint
3171 was saved. In essence, gdb will ``wind back the clock'' to the point
3172 in time when the checkpoint was saved.
3174 Note that breakpoints, @value{GDBN} variables, command history etc.
3175 are not affected by restoring a checkpoint. In general, a checkpoint
3176 only restores things that reside in the program being debugged, not in
3179 @kindex delete checkpoint @var{checkpoint-id}
3180 @item delete checkpoint @var{checkpoint-id}
3181 Delete the previously-saved checkpoint identified by @var{checkpoint-id}.
3185 Returning to a previously saved checkpoint will restore the user state
3186 of the program being debugged, plus a significant subset of the system
3187 (OS) state, including file pointers. It won't ``un-write'' data from
3188 a file, but it will rewind the file pointer to the previous location,
3189 so that the previously written data can be overwritten. For files
3190 opened in read mode, the pointer will also be restored so that the
3191 previously read data can be read again.
3193 Of course, characters that have been sent to a printer (or other
3194 external device) cannot be ``snatched back'', and characters received
3195 from eg.@: a serial device can be removed from internal program buffers,
3196 but they cannot be ``pushed back'' into the serial pipeline, ready to
3197 be received again. Similarly, the actual contents of files that have
3198 been changed cannot be restored (at this time).
3200 However, within those constraints, you actually can ``rewind'' your
3201 program to a previously saved point in time, and begin debugging it
3202 again --- and you can change the course of events so as to debug a
3203 different execution path this time.
3205 @cindex checkpoints and process id
3206 Finally, there is one bit of internal program state that will be
3207 different when you return to a checkpoint --- the program's process
3208 id. Each checkpoint will have a unique process id (or @var{pid}),
3209 and each will be different from the program's original @var{pid}.
3210 If your program has saved a local copy of its process id, this could
3211 potentially pose a problem.
3213 @subsection A Non-obvious Benefit of Using Checkpoints
3215 On some systems such as @sc{gnu}/Linux, address space randomization
3216 is performed on new processes for security reasons. This makes it
3217 difficult or impossible to set a breakpoint, or watchpoint, on an
3218 absolute address if you have to restart the program, since the
3219 absolute location of a symbol will change from one execution to the
3222 A checkpoint, however, is an @emph{identical} copy of a process.
3223 Therefore if you create a checkpoint at (eg.@:) the start of main,
3224 and simply return to that checkpoint instead of restarting the
3225 process, you can avoid the effects of address randomization and
3226 your symbols will all stay in the same place.
3229 @chapter Stopping and Continuing
3231 The principal purposes of using a debugger are so that you can stop your
3232 program before it terminates; or so that, if your program runs into
3233 trouble, you can investigate and find out why.
3235 Inside @value{GDBN}, your program may stop for any of several reasons,
3236 such as a signal, a breakpoint, or reaching a new line after a
3237 @value{GDBN} command such as @code{step}. You may then examine and
3238 change variables, set new breakpoints or remove old ones, and then
3239 continue execution. Usually, the messages shown by @value{GDBN} provide
3240 ample explanation of the status of your program---but you can also
3241 explicitly request this information at any time.
3244 @kindex info program
3246 Display information about the status of your program: whether it is
3247 running or not, what process it is, and why it stopped.
3251 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
3252 * Continuing and Stepping:: Resuming execution
3253 * Skipping Over Functions and Files::
3254 Skipping over functions and files
3256 * Thread Stops:: Stopping and starting multi-thread programs
3260 @section Breakpoints, Watchpoints, and Catchpoints
3263 A @dfn{breakpoint} makes your program stop whenever a certain point in
3264 the program is reached. For each breakpoint, you can add conditions to
3265 control in finer detail whether your program stops. You can set
3266 breakpoints with the @code{break} command and its variants (@pxref{Set
3267 Breaks, ,Setting Breakpoints}), to specify the place where your program
3268 should stop by line number, function name or exact address in the
3271 On some systems, you can set breakpoints in shared libraries before
3272 the executable is run. There is a minor limitation on HP-UX systems:
3273 you must wait until the executable is run in order to set breakpoints
3274 in shared library routines that are not called directly by the program
3275 (for example, routines that are arguments in a @code{pthread_create}
3279 @cindex data breakpoints
3280 @cindex memory tracing
3281 @cindex breakpoint on memory address
3282 @cindex breakpoint on variable modification
3283 A @dfn{watchpoint} is a special breakpoint that stops your program
3284 when the value of an expression changes. The expression may be a value
3285 of a variable, or it could involve values of one or more variables
3286 combined by operators, such as @samp{a + b}. This is sometimes called
3287 @dfn{data breakpoints}. You must use a different command to set
3288 watchpoints (@pxref{Set Watchpoints, ,Setting Watchpoints}), but aside
3289 from that, you can manage a watchpoint like any other breakpoint: you
3290 enable, disable, and delete both breakpoints and watchpoints using the
3293 You can arrange to have values from your program displayed automatically
3294 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
3298 @cindex breakpoint on events
3299 A @dfn{catchpoint} is another special breakpoint that stops your program
3300 when a certain kind of event occurs, such as the throwing of a C@t{++}
3301 exception or the loading of a library. As with watchpoints, you use a
3302 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
3303 Catchpoints}), but aside from that, you can manage a catchpoint like any
3304 other breakpoint. (To stop when your program receives a signal, use the
3305 @code{handle} command; see @ref{Signals, ,Signals}.)
3307 @cindex breakpoint numbers
3308 @cindex numbers for breakpoints
3309 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
3310 catchpoint when you create it; these numbers are successive integers
3311 starting with one. In many of the commands for controlling various
3312 features of breakpoints you use the breakpoint number to say which
3313 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
3314 @dfn{disabled}; if disabled, it has no effect on your program until you
3317 @cindex breakpoint ranges
3318 @cindex ranges of breakpoints
3319 Some @value{GDBN} commands accept a range of breakpoints on which to
3320 operate. A breakpoint range is either a single breakpoint number, like
3321 @samp{5}, or two such numbers, in increasing order, separated by a
3322 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
3323 all breakpoints in that range are operated on.
3326 * Set Breaks:: Setting breakpoints
3327 * Set Watchpoints:: Setting watchpoints
3328 * Set Catchpoints:: Setting catchpoints
3329 * Delete Breaks:: Deleting breakpoints
3330 * Disabling:: Disabling breakpoints
3331 * Conditions:: Break conditions
3332 * Break Commands:: Breakpoint command lists
3333 * Save Breakpoints:: How to save breakpoints in a file
3334 * Error in Breakpoints:: ``Cannot insert breakpoints''
3335 * Breakpoint-related Warnings:: ``Breakpoint address adjusted...''
3339 @subsection Setting Breakpoints
3341 @c FIXME LMB what does GDB do if no code on line of breakpt?
3342 @c consider in particular declaration with/without initialization.
3344 @c FIXME 2 is there stuff on this already? break at fun start, already init?
3347 @kindex b @r{(@code{break})}
3348 @vindex $bpnum@r{, convenience variable}
3349 @cindex latest breakpoint
3350 Breakpoints are set with the @code{break} command (abbreviated
3351 @code{b}). The debugger convenience variable @samp{$bpnum} records the
3352 number of the breakpoint you've set most recently; see @ref{Convenience
3353 Vars,, Convenience Variables}, for a discussion of what you can do with
3354 convenience variables.
3357 @item break @var{location}
3358 Set a breakpoint at the given @var{location}, which can specify a
3359 function name, a line number, or an address of an instruction.
3360 (@xref{Specify Location}, for a list of all the possible ways to
3361 specify a @var{location}.) The breakpoint will stop your program just
3362 before it executes any of the code in the specified @var{location}.
3364 When using source languages that permit overloading of symbols, such as
3365 C@t{++}, a function name may refer to more than one possible place to break.
3366 @xref{Ambiguous Expressions,,Ambiguous Expressions}, for a discussion of
3369 It is also possible to insert a breakpoint that will stop the program
3370 only if a specific thread (@pxref{Thread-Specific Breakpoints})
3371 or a specific task (@pxref{Ada Tasks}) hits that breakpoint.
3374 When called without any arguments, @code{break} sets a breakpoint at
3375 the next instruction to be executed in the selected stack frame
3376 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
3377 innermost, this makes your program stop as soon as control
3378 returns to that frame. This is similar to the effect of a
3379 @code{finish} command in the frame inside the selected frame---except
3380 that @code{finish} does not leave an active breakpoint. If you use
3381 @code{break} without an argument in the innermost frame, @value{GDBN} stops
3382 the next time it reaches the current location; this may be useful
3385 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
3386 least one instruction has been executed. If it did not do this, you
3387 would be unable to proceed past a breakpoint without first disabling the
3388 breakpoint. This rule applies whether or not the breakpoint already
3389 existed when your program stopped.
3391 @item break @dots{} if @var{cond}
3392 Set a breakpoint with condition @var{cond}; evaluate the expression
3393 @var{cond} each time the breakpoint is reached, and stop only if the
3394 value is nonzero---that is, if @var{cond} evaluates as true.
3395 @samp{@dots{}} stands for one of the possible arguments described
3396 above (or no argument) specifying where to break. @xref{Conditions,
3397 ,Break Conditions}, for more information on breakpoint conditions.
3400 @item tbreak @var{args}
3401 Set a breakpoint enabled only for one stop. @var{args} are the
3402 same as for the @code{break} command, and the breakpoint is set in the same
3403 way, but the breakpoint is automatically deleted after the first time your
3404 program stops there. @xref{Disabling, ,Disabling Breakpoints}.
3407 @cindex hardware breakpoints
3408 @item hbreak @var{args}
3409 Set a hardware-assisted breakpoint. @var{args} are the same as for the
3410 @code{break} command and the breakpoint is set in the same way, but the
3411 breakpoint requires hardware support and some target hardware may not
3412 have this support. The main purpose of this is EPROM/ROM code
3413 debugging, so you can set a breakpoint at an instruction without
3414 changing the instruction. This can be used with the new trap-generation
3415 provided by SPARClite DSU and most x86-based targets. These targets
3416 will generate traps when a program accesses some data or instruction
3417 address that is assigned to the debug registers. However the hardware
3418 breakpoint registers can take a limited number of breakpoints. For
3419 example, on the DSU, only two data breakpoints can be set at a time, and
3420 @value{GDBN} will reject this command if more than two are used. Delete
3421 or disable unused hardware breakpoints before setting new ones
3422 (@pxref{Disabling, ,Disabling Breakpoints}).
3423 @xref{Conditions, ,Break Conditions}.
3424 For remote targets, you can restrict the number of hardware
3425 breakpoints @value{GDBN} will use, see @ref{set remote
3426 hardware-breakpoint-limit}.
3429 @item thbreak @var{args}
3430 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
3431 are the same as for the @code{hbreak} command and the breakpoint is set in
3432 the same way. However, like the @code{tbreak} command,
3433 the breakpoint is automatically deleted after the
3434 first time your program stops there. Also, like the @code{hbreak}
3435 command, the breakpoint requires hardware support and some target hardware
3436 may not have this support. @xref{Disabling, ,Disabling Breakpoints}.
3437 See also @ref{Conditions, ,Break Conditions}.
3440 @cindex regular expression
3441 @cindex breakpoints at functions matching a regexp
3442 @cindex set breakpoints in many functions
3443 @item rbreak @var{regex}
3444 Set breakpoints on all functions matching the regular expression
3445 @var{regex}. This command sets an unconditional breakpoint on all
3446 matches, printing a list of all breakpoints it set. Once these
3447 breakpoints are set, they are treated just like the breakpoints set with
3448 the @code{break} command. You can delete them, disable them, or make
3449 them conditional the same way as any other breakpoint.
3451 The syntax of the regular expression is the standard one used with tools
3452 like @file{grep}. Note that this is different from the syntax used by
3453 shells, so for instance @code{foo*} matches all functions that include
3454 an @code{fo} followed by zero or more @code{o}s. There is an implicit
3455 @code{.*} leading and trailing the regular expression you supply, so to
3456 match only functions that begin with @code{foo}, use @code{^foo}.
3458 @cindex non-member C@t{++} functions, set breakpoint in
3459 When debugging C@t{++} programs, @code{rbreak} is useful for setting
3460 breakpoints on overloaded functions that are not members of any special
3463 @cindex set breakpoints on all functions
3464 The @code{rbreak} command can be used to set breakpoints in
3465 @strong{all} the functions in a program, like this:
3468 (@value{GDBP}) rbreak .
3471 @item rbreak @var{file}:@var{regex}
3472 If @code{rbreak} is called with a filename qualification, it limits
3473 the search for functions matching the given regular expression to the
3474 specified @var{file}. This can be used, for example, to set breakpoints on
3475 every function in a given file:
3478 (@value{GDBP}) rbreak file.c:.
3481 The colon separating the filename qualifier from the regex may
3482 optionally be surrounded by spaces.
3484 @kindex info breakpoints
3485 @cindex @code{$_} and @code{info breakpoints}
3486 @item info breakpoints @r{[}@var{n}@dots{}@r{]}
3487 @itemx info break @r{[}@var{n}@dots{}@r{]}
3488 Print a table of all breakpoints, watchpoints, and catchpoints set and
3489 not deleted. Optional argument @var{n} means print information only
3490 about the specified breakpoint(s) (or watchpoint(s) or catchpoint(s)).
3491 For each breakpoint, following columns are printed:
3494 @item Breakpoint Numbers
3496 Breakpoint, watchpoint, or catchpoint.
3498 Whether the breakpoint is marked to be disabled or deleted when hit.
3499 @item Enabled or Disabled
3500 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
3501 that are not enabled.
3503 Where the breakpoint is in your program, as a memory address. For a
3504 pending breakpoint whose address is not yet known, this field will
3505 contain @samp{<PENDING>}. Such breakpoint won't fire until a shared
3506 library that has the symbol or line referred by breakpoint is loaded.
3507 See below for details. A breakpoint with several locations will
3508 have @samp{<MULTIPLE>} in this field---see below for details.
3510 Where the breakpoint is in the source for your program, as a file and
3511 line number. For a pending breakpoint, the original string passed to
3512 the breakpoint command will be listed as it cannot be resolved until
3513 the appropriate shared library is loaded in the future.
3517 If a breakpoint is conditional, there are two evaluation modes: ``host'' and
3518 ``target''. If mode is ``host'', breakpoint condition evaluation is done by
3519 @value{GDBN} on the host's side. If it is ``target'', then the condition
3520 is evaluated by the target. The @code{info break} command shows
3521 the condition on the line following the affected breakpoint, together with
3522 its condition evaluation mode in between parentheses.
3524 Breakpoint commands, if any, are listed after that. A pending breakpoint is
3525 allowed to have a condition specified for it. The condition is not parsed for
3526 validity until a shared library is loaded that allows the pending
3527 breakpoint to resolve to a valid location.
3530 @code{info break} with a breakpoint
3531 number @var{n} as argument lists only that breakpoint. The
3532 convenience variable @code{$_} and the default examining-address for
3533 the @code{x} command are set to the address of the last breakpoint
3534 listed (@pxref{Memory, ,Examining Memory}).
3537 @code{info break} displays a count of the number of times the breakpoint
3538 has been hit. This is especially useful in conjunction with the
3539 @code{ignore} command. You can ignore a large number of breakpoint
3540 hits, look at the breakpoint info to see how many times the breakpoint
3541 was hit, and then run again, ignoring one less than that number. This
3542 will get you quickly to the last hit of that breakpoint.
3545 For a breakpoints with an enable count (xref) greater than 1,
3546 @code{info break} also displays that count.
3550 @value{GDBN} allows you to set any number of breakpoints at the same place in
3551 your program. There is nothing silly or meaningless about this. When
3552 the breakpoints are conditional, this is even useful
3553 (@pxref{Conditions, ,Break Conditions}).
3555 @cindex multiple locations, breakpoints
3556 @cindex breakpoints, multiple locations
3557 It is possible that a breakpoint corresponds to several locations
3558 in your program. Examples of this situation are:
3562 Multiple functions in the program may have the same name.
3565 For a C@t{++} constructor, the @value{NGCC} compiler generates several
3566 instances of the function body, used in different cases.
3569 For a C@t{++} template function, a given line in the function can
3570 correspond to any number of instantiations.
3573 For an inlined function, a given source line can correspond to
3574 several places where that function is inlined.
3577 In all those cases, @value{GDBN} will insert a breakpoint at all
3578 the relevant locations.
3580 A breakpoint with multiple locations is displayed in the breakpoint
3581 table using several rows---one header row, followed by one row for
3582 each breakpoint location. The header row has @samp{<MULTIPLE>} in the
3583 address column. The rows for individual locations contain the actual
3584 addresses for locations, and show the functions to which those
3585 locations belong. The number column for a location is of the form
3586 @var{breakpoint-number}.@var{location-number}.
3591 Num Type Disp Enb Address What
3592 1 breakpoint keep y <MULTIPLE>
3594 breakpoint already hit 1 time
3595 1.1 y 0x080486a2 in void foo<int>() at t.cc:8
3596 1.2 y 0x080486ca in void foo<double>() at t.cc:8
3599 Each location can be individually enabled or disabled by passing
3600 @var{breakpoint-number}.@var{location-number} as argument to the
3601 @code{enable} and @code{disable} commands. Note that you cannot
3602 delete the individual locations from the list, you can only delete the
3603 entire list of locations that belong to their parent breakpoint (with
3604 the @kbd{delete @var{num}} command, where @var{num} is the number of
3605 the parent breakpoint, 1 in the above example). Disabling or enabling
3606 the parent breakpoint (@pxref{Disabling}) affects all of the locations
3607 that belong to that breakpoint.
3609 @cindex pending breakpoints
3610 It's quite common to have a breakpoint inside a shared library.
3611 Shared libraries can be loaded and unloaded explicitly,
3612 and possibly repeatedly, as the program is executed. To support
3613 this use case, @value{GDBN} updates breakpoint locations whenever
3614 any shared library is loaded or unloaded. Typically, you would
3615 set a breakpoint in a shared library at the beginning of your
3616 debugging session, when the library is not loaded, and when the
3617 symbols from the library are not available. When you try to set
3618 breakpoint, @value{GDBN} will ask you if you want to set
3619 a so called @dfn{pending breakpoint}---breakpoint whose address
3620 is not yet resolved.
3622 After the program is run, whenever a new shared library is loaded,
3623 @value{GDBN} reevaluates all the breakpoints. When a newly loaded
3624 shared library contains the symbol or line referred to by some
3625 pending breakpoint, that breakpoint is resolved and becomes an
3626 ordinary breakpoint. When a library is unloaded, all breakpoints
3627 that refer to its symbols or source lines become pending again.
3629 This logic works for breakpoints with multiple locations, too. For
3630 example, if you have a breakpoint in a C@t{++} template function, and
3631 a newly loaded shared library has an instantiation of that template,
3632 a new location is added to the list of locations for the breakpoint.
3634 Except for having unresolved address, pending breakpoints do not
3635 differ from regular breakpoints. You can set conditions or commands,
3636 enable and disable them and perform other breakpoint operations.
3638 @value{GDBN} provides some additional commands for controlling what
3639 happens when the @samp{break} command cannot resolve breakpoint
3640 address specification to an address:
3642 @kindex set breakpoint pending
3643 @kindex show breakpoint pending
3645 @item set breakpoint pending auto
3646 This is the default behavior. When @value{GDBN} cannot find the breakpoint
3647 location, it queries you whether a pending breakpoint should be created.
3649 @item set breakpoint pending on
3650 This indicates that an unrecognized breakpoint location should automatically
3651 result in a pending breakpoint being created.
3653 @item set breakpoint pending off
3654 This indicates that pending breakpoints are not to be created. Any
3655 unrecognized breakpoint location results in an error. This setting does
3656 not affect any pending breakpoints previously created.
3658 @item show breakpoint pending
3659 Show the current behavior setting for creating pending breakpoints.
3662 The settings above only affect the @code{break} command and its
3663 variants. Once breakpoint is set, it will be automatically updated
3664 as shared libraries are loaded and unloaded.
3666 @cindex automatic hardware breakpoints
3667 For some targets, @value{GDBN} can automatically decide if hardware or
3668 software breakpoints should be used, depending on whether the
3669 breakpoint address is read-only or read-write. This applies to
3670 breakpoints set with the @code{break} command as well as to internal
3671 breakpoints set by commands like @code{next} and @code{finish}. For
3672 breakpoints set with @code{hbreak}, @value{GDBN} will always use hardware
3675 You can control this automatic behaviour with the following commands::
3677 @kindex set breakpoint auto-hw
3678 @kindex show breakpoint auto-hw
3680 @item set breakpoint auto-hw on
3681 This is the default behavior. When @value{GDBN} sets a breakpoint, it
3682 will try to use the target memory map to decide if software or hardware
3683 breakpoint must be used.
3685 @item set breakpoint auto-hw off
3686 This indicates @value{GDBN} should not automatically select breakpoint
3687 type. If the target provides a memory map, @value{GDBN} will warn when
3688 trying to set software breakpoint at a read-only address.
3691 @value{GDBN} normally implements breakpoints by replacing the program code
3692 at the breakpoint address with a special instruction, which, when
3693 executed, given control to the debugger. By default, the program
3694 code is so modified only when the program is resumed. As soon as
3695 the program stops, @value{GDBN} restores the original instructions. This
3696 behaviour guards against leaving breakpoints inserted in the
3697 target should gdb abrubptly disconnect. However, with slow remote
3698 targets, inserting and removing breakpoint can reduce the performance.
3699 This behavior can be controlled with the following commands::
3701 @kindex set breakpoint always-inserted
3702 @kindex show breakpoint always-inserted
3704 @item set breakpoint always-inserted off
3705 All breakpoints, including newly added by the user, are inserted in
3706 the target only when the target is resumed. All breakpoints are
3707 removed from the target when it stops.
3709 @item set breakpoint always-inserted on
3710 Causes all breakpoints to be inserted in the target at all times. If
3711 the user adds a new breakpoint, or changes an existing breakpoint, the
3712 breakpoints in the target are updated immediately. A breakpoint is
3713 removed from the target only when breakpoint itself is removed.
3715 @cindex non-stop mode, and @code{breakpoint always-inserted}
3716 @item set breakpoint always-inserted auto
3717 This is the default mode. If @value{GDBN} is controlling the inferior
3718 in non-stop mode (@pxref{Non-Stop Mode}), gdb behaves as if
3719 @code{breakpoint always-inserted} mode is on. If @value{GDBN} is
3720 controlling the inferior in all-stop mode, @value{GDBN} behaves as if
3721 @code{breakpoint always-inserted} mode is off.
3724 @value{GDBN} handles conditional breakpoints by evaluating these conditions
3725 when a breakpoint breaks. If the condition is true, then the process being
3726 debugged stops, otherwise the process is resumed.
3728 If the target supports evaluating conditions on its end, @value{GDBN} may
3729 download the breakpoint, together with its conditions, to it.
3731 This feature can be controlled via the following commands:
3733 @kindex set breakpoint condition-evaluation
3734 @kindex show breakpoint condition-evaluation
3736 @item set breakpoint condition-evaluation host
3737 This option commands @value{GDBN} to evaluate the breakpoint
3738 conditions on the host's side. Unconditional breakpoints are sent to
3739 the target which in turn receives the triggers and reports them back to GDB
3740 for condition evaluation. This is the standard evaluation mode.
3742 @item set breakpoint condition-evaluation target
3743 This option commands @value{GDBN} to download breakpoint conditions
3744 to the target at the moment of their insertion. The target
3745 is responsible for evaluating the conditional expression and reporting
3746 breakpoint stop events back to @value{GDBN} whenever the condition
3747 is true. Due to limitations of target-side evaluation, some conditions
3748 cannot be evaluated there, e.g., conditions that depend on local data
3749 that is only known to the host. Examples include
3750 conditional expressions involving convenience variables, complex types
3751 that cannot be handled by the agent expression parser and expressions
3752 that are too long to be sent over to the target, specially when the
3753 target is a remote system. In these cases, the conditions will be
3754 evaluated by @value{GDBN}.
3756 @item set breakpoint condition-evaluation auto
3757 This is the default mode. If the target supports evaluating breakpoint
3758 conditions on its end, @value{GDBN} will download breakpoint conditions to
3759 the target (limitations mentioned previously apply). If the target does
3760 not support breakpoint condition evaluation, then @value{GDBN} will fallback
3761 to evaluating all these conditions on the host's side.
3765 @cindex negative breakpoint numbers
3766 @cindex internal @value{GDBN} breakpoints
3767 @value{GDBN} itself sometimes sets breakpoints in your program for
3768 special purposes, such as proper handling of @code{longjmp} (in C
3769 programs). These internal breakpoints are assigned negative numbers,
3770 starting with @code{-1}; @samp{info breakpoints} does not display them.
3771 You can see these breakpoints with the @value{GDBN} maintenance command
3772 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
3775 @node Set Watchpoints
3776 @subsection Setting Watchpoints
3778 @cindex setting watchpoints
3779 You can use a watchpoint to stop execution whenever the value of an
3780 expression changes, without having to predict a particular place where
3781 this may happen. (This is sometimes called a @dfn{data breakpoint}.)
3782 The expression may be as simple as the value of a single variable, or
3783 as complex as many variables combined by operators. Examples include:
3787 A reference to the value of a single variable.
3790 An address cast to an appropriate data type. For example,
3791 @samp{*(int *)0x12345678} will watch a 4-byte region at the specified
3792 address (assuming an @code{int} occupies 4 bytes).
3795 An arbitrarily complex expression, such as @samp{a*b + c/d}. The
3796 expression can use any operators valid in the program's native
3797 language (@pxref{Languages}).
3800 You can set a watchpoint on an expression even if the expression can
3801 not be evaluated yet. For instance, you can set a watchpoint on
3802 @samp{*global_ptr} before @samp{global_ptr} is initialized.
3803 @value{GDBN} will stop when your program sets @samp{global_ptr} and
3804 the expression produces a valid value. If the expression becomes
3805 valid in some other way than changing a variable (e.g.@: if the memory
3806 pointed to by @samp{*global_ptr} becomes readable as the result of a
3807 @code{malloc} call), @value{GDBN} may not stop until the next time
3808 the expression changes.
3810 @cindex software watchpoints
3811 @cindex hardware watchpoints
3812 Depending on your system, watchpoints may be implemented in software or
3813 hardware. @value{GDBN} does software watchpointing by single-stepping your
3814 program and testing the variable's value each time, which is hundreds of
3815 times slower than normal execution. (But this may still be worth it, to
3816 catch errors where you have no clue what part of your program is the
3819 On some systems, such as HP-UX, PowerPC, @sc{gnu}/Linux and most other
3820 x86-based targets, @value{GDBN} includes support for hardware
3821 watchpoints, which do not slow down the running of your program.
3825 @item watch @r{[}-l@r{|}-location@r{]} @var{expr} @r{[}thread @var{threadnum}@r{]} @r{[}mask @var{maskvalue}@r{]}
3826 Set a watchpoint for an expression. @value{GDBN} will break when the
3827 expression @var{expr} is written into by the program and its value
3828 changes. The simplest (and the most popular) use of this command is
3829 to watch the value of a single variable:
3832 (@value{GDBP}) watch foo
3835 If the command includes a @code{@r{[}thread @var{threadnum}@r{]}}
3836 argument, @value{GDBN} breaks only when the thread identified by
3837 @var{threadnum} changes the value of @var{expr}. If any other threads
3838 change the value of @var{expr}, @value{GDBN} will not break. Note
3839 that watchpoints restricted to a single thread in this way only work
3840 with Hardware Watchpoints.
3842 Ordinarily a watchpoint respects the scope of variables in @var{expr}
3843 (see below). The @code{-location} argument tells @value{GDBN} to
3844 instead watch the memory referred to by @var{expr}. In this case,
3845 @value{GDBN} will evaluate @var{expr}, take the address of the result,
3846 and watch the memory at that address. The type of the result is used
3847 to determine the size of the watched memory. If the expression's
3848 result does not have an address, then @value{GDBN} will print an
3851 The @code{@r{[}mask @var{maskvalue}@r{]}} argument allows creation
3852 of masked watchpoints, if the current architecture supports this
3853 feature (e.g., PowerPC Embedded architecture, see @ref{PowerPC
3854 Embedded}.) A @dfn{masked watchpoint} specifies a mask in addition
3855 to an address to watch. The mask specifies that some bits of an address
3856 (the bits which are reset in the mask) should be ignored when matching
3857 the address accessed by the inferior against the watchpoint address.
3858 Thus, a masked watchpoint watches many addresses simultaneously---those
3859 addresses whose unmasked bits are identical to the unmasked bits in the
3860 watchpoint address. The @code{mask} argument implies @code{-location}.
3864 (@value{GDBP}) watch foo mask 0xffff00ff
3865 (@value{GDBP}) watch *0xdeadbeef mask 0xffffff00
3869 @item rwatch @r{[}-l@r{|}-location@r{]} @var{expr} @r{[}thread @var{threadnum}@r{]} @r{[}mask @var{maskvalue}@r{]}
3870 Set a watchpoint that will break when the value of @var{expr} is read
3874 @item awatch @r{[}-l@r{|}-location@r{]} @var{expr} @r{[}thread @var{threadnum}@r{]} @r{[}mask @var{maskvalue}@r{]}
3875 Set a watchpoint that will break when @var{expr} is either read from
3876 or written into by the program.
3878 @kindex info watchpoints @r{[}@var{n}@dots{}@r{]}
3879 @item info watchpoints @r{[}@var{n}@dots{}@r{]}
3880 This command prints a list of watchpoints, using the same format as
3881 @code{info break} (@pxref{Set Breaks}).
3884 If you watch for a change in a numerically entered address you need to
3885 dereference it, as the address itself is just a constant number which will
3886 never change. @value{GDBN} refuses to create a watchpoint that watches
3887 a never-changing value:
3890 (@value{GDBP}) watch 0x600850
3891 Cannot watch constant value 0x600850.
3892 (@value{GDBP}) watch *(int *) 0x600850
3893 Watchpoint 1: *(int *) 6293584
3896 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
3897 watchpoints execute very quickly, and the debugger reports a change in
3898 value at the exact instruction where the change occurs. If @value{GDBN}
3899 cannot set a hardware watchpoint, it sets a software watchpoint, which
3900 executes more slowly and reports the change in value at the next
3901 @emph{statement}, not the instruction, after the change occurs.
3903 @cindex use only software watchpoints
3904 You can force @value{GDBN} to use only software watchpoints with the
3905 @kbd{set can-use-hw-watchpoints 0} command. With this variable set to
3906 zero, @value{GDBN} will never try to use hardware watchpoints, even if
3907 the underlying system supports them. (Note that hardware-assisted
3908 watchpoints that were set @emph{before} setting
3909 @code{can-use-hw-watchpoints} to zero will still use the hardware
3910 mechanism of watching expression values.)
3913 @item set can-use-hw-watchpoints
3914 @kindex set can-use-hw-watchpoints
3915 Set whether or not to use hardware watchpoints.
3917 @item show can-use-hw-watchpoints
3918 @kindex show can-use-hw-watchpoints
3919 Show the current mode of using hardware watchpoints.
3922 For remote targets, you can restrict the number of hardware
3923 watchpoints @value{GDBN} will use, see @ref{set remote
3924 hardware-breakpoint-limit}.
3926 When you issue the @code{watch} command, @value{GDBN} reports
3929 Hardware watchpoint @var{num}: @var{expr}
3933 if it was able to set a hardware watchpoint.
3935 Currently, the @code{awatch} and @code{rwatch} commands can only set
3936 hardware watchpoints, because accesses to data that don't change the
3937 value of the watched expression cannot be detected without examining
3938 every instruction as it is being executed, and @value{GDBN} does not do
3939 that currently. If @value{GDBN} finds that it is unable to set a
3940 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
3941 will print a message like this:
3944 Expression cannot be implemented with read/access watchpoint.
3947 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
3948 data type of the watched expression is wider than what a hardware
3949 watchpoint on the target machine can handle. For example, some systems
3950 can only watch regions that are up to 4 bytes wide; on such systems you
3951 cannot set hardware watchpoints for an expression that yields a
3952 double-precision floating-point number (which is typically 8 bytes
3953 wide). As a work-around, it might be possible to break the large region
3954 into a series of smaller ones and watch them with separate watchpoints.
3956 If you set too many hardware watchpoints, @value{GDBN} might be unable
3957 to insert all of them when you resume the execution of your program.
3958 Since the precise number of active watchpoints is unknown until such
3959 time as the program is about to be resumed, @value{GDBN} might not be
3960 able to warn you about this when you set the watchpoints, and the
3961 warning will be printed only when the program is resumed:
3964 Hardware watchpoint @var{num}: Could not insert watchpoint
3968 If this happens, delete or disable some of the watchpoints.
3970 Watching complex expressions that reference many variables can also
3971 exhaust the resources available for hardware-assisted watchpoints.
3972 That's because @value{GDBN} needs to watch every variable in the
3973 expression with separately allocated resources.
3975 If you call a function interactively using @code{print} or @code{call},
3976 any watchpoints you have set will be inactive until @value{GDBN} reaches another
3977 kind of breakpoint or the call completes.
3979 @value{GDBN} automatically deletes watchpoints that watch local
3980 (automatic) variables, or expressions that involve such variables, when
3981 they go out of scope, that is, when the execution leaves the block in
3982 which these variables were defined. In particular, when the program
3983 being debugged terminates, @emph{all} local variables go out of scope,
3984 and so only watchpoints that watch global variables remain set. If you
3985 rerun the program, you will need to set all such watchpoints again. One
3986 way of doing that would be to set a code breakpoint at the entry to the
3987 @code{main} function and when it breaks, set all the watchpoints.
3989 @cindex watchpoints and threads
3990 @cindex threads and watchpoints
3991 In multi-threaded programs, watchpoints will detect changes to the
3992 watched expression from every thread.
3995 @emph{Warning:} In multi-threaded programs, software watchpoints
3996 have only limited usefulness. If @value{GDBN} creates a software
3997 watchpoint, it can only watch the value of an expression @emph{in a
3998 single thread}. If you are confident that the expression can only
3999 change due to the current thread's activity (and if you are also
4000 confident that no other thread can become current), then you can use
4001 software watchpoints as usual. However, @value{GDBN} may not notice
4002 when a non-current thread's activity changes the expression. (Hardware
4003 watchpoints, in contrast, watch an expression in all threads.)
4006 @xref{set remote hardware-watchpoint-limit}.
4008 @node Set Catchpoints
4009 @subsection Setting Catchpoints
4010 @cindex catchpoints, setting
4011 @cindex exception handlers
4012 @cindex event handling
4014 You can use @dfn{catchpoints} to cause the debugger to stop for certain
4015 kinds of program events, such as C@t{++} exceptions or the loading of a
4016 shared library. Use the @code{catch} command to set a catchpoint.
4020 @item catch @var{event}
4021 Stop when @var{event} occurs. @var{event} can be any of the following:
4024 @cindex stop on C@t{++} exceptions
4025 The throwing of a C@t{++} exception.
4028 The catching of a C@t{++} exception.
4031 @cindex Ada exception catching
4032 @cindex catch Ada exceptions
4033 An Ada exception being raised. If an exception name is specified
4034 at the end of the command (eg @code{catch exception Program_Error}),
4035 the debugger will stop only when this specific exception is raised.
4036 Otherwise, the debugger stops execution when any Ada exception is raised.
4038 When inserting an exception catchpoint on a user-defined exception whose
4039 name is identical to one of the exceptions defined by the language, the
4040 fully qualified name must be used as the exception name. Otherwise,
4041 @value{GDBN} will assume that it should stop on the pre-defined exception
4042 rather than the user-defined one. For instance, assuming an exception
4043 called @code{Constraint_Error} is defined in package @code{Pck}, then
4044 the command to use to catch such exceptions is @kbd{catch exception
4045 Pck.Constraint_Error}.
4047 @item exception unhandled
4048 An exception that was raised but is not handled by the program.
4051 A failed Ada assertion.
4054 @cindex break on fork/exec
4055 A call to @code{exec}. This is currently only available for HP-UX
4059 @itemx syscall @r{[}@var{name} @r{|} @var{number}@r{]} @dots{}
4060 @cindex break on a system call.
4061 A call to or return from a system call, a.k.a.@: @dfn{syscall}. A
4062 syscall is a mechanism for application programs to request a service
4063 from the operating system (OS) or one of the OS system services.
4064 @value{GDBN} can catch some or all of the syscalls issued by the
4065 debuggee, and show the related information for each syscall. If no
4066 argument is specified, calls to and returns from all system calls
4069 @var{name} can be any system call name that is valid for the
4070 underlying OS. Just what syscalls are valid depends on the OS. On
4071 GNU and Unix systems, you can find the full list of valid syscall
4072 names on @file{/usr/include/asm/unistd.h}.
4074 @c For MS-Windows, the syscall names and the corresponding numbers
4075 @c can be found, e.g., on this URL:
4076 @c http://www.metasploit.com/users/opcode/syscalls.html
4077 @c but we don't support Windows syscalls yet.
4079 Normally, @value{GDBN} knows in advance which syscalls are valid for
4080 each OS, so you can use the @value{GDBN} command-line completion
4081 facilities (@pxref{Completion,, command completion}) to list the
4084 You may also specify the system call numerically. A syscall's
4085 number is the value passed to the OS's syscall dispatcher to
4086 identify the requested service. When you specify the syscall by its
4087 name, @value{GDBN} uses its database of syscalls to convert the name
4088 into the corresponding numeric code, but using the number directly
4089 may be useful if @value{GDBN}'s database does not have the complete
4090 list of syscalls on your system (e.g., because @value{GDBN} lags
4091 behind the OS upgrades).
4093 The example below illustrates how this command works if you don't provide
4097 (@value{GDBP}) catch syscall
4098 Catchpoint 1 (syscall)
4100 Starting program: /tmp/catch-syscall
4102 Catchpoint 1 (call to syscall 'close'), \
4103 0xffffe424 in __kernel_vsyscall ()
4107 Catchpoint 1 (returned from syscall 'close'), \
4108 0xffffe424 in __kernel_vsyscall ()
4112 Here is an example of catching a system call by name:
4115 (@value{GDBP}) catch syscall chroot
4116 Catchpoint 1 (syscall 'chroot' [61])
4118 Starting program: /tmp/catch-syscall
4120 Catchpoint 1 (call to syscall 'chroot'), \
4121 0xffffe424 in __kernel_vsyscall ()
4125 Catchpoint 1 (returned from syscall 'chroot'), \
4126 0xffffe424 in __kernel_vsyscall ()
4130 An example of specifying a system call numerically. In the case
4131 below, the syscall number has a corresponding entry in the XML
4132 file, so @value{GDBN} finds its name and prints it:
4135 (@value{GDBP}) catch syscall 252
4136 Catchpoint 1 (syscall(s) 'exit_group')
4138 Starting program: /tmp/catch-syscall
4140 Catchpoint 1 (call to syscall 'exit_group'), \
4141 0xffffe424 in __kernel_vsyscall ()
4145 Program exited normally.
4149 However, there can be situations when there is no corresponding name
4150 in XML file for that syscall number. In this case, @value{GDBN} prints
4151 a warning message saying that it was not able to find the syscall name,
4152 but the catchpoint will be set anyway. See the example below:
4155 (@value{GDBP}) catch syscall 764
4156 warning: The number '764' does not represent a known syscall.
4157 Catchpoint 2 (syscall 764)
4161 If you configure @value{GDBN} using the @samp{--without-expat} option,
4162 it will not be able to display syscall names. Also, if your
4163 architecture does not have an XML file describing its system calls,
4164 you will not be able to see the syscall names. It is important to
4165 notice that these two features are used for accessing the syscall
4166 name database. In either case, you will see a warning like this:
4169 (@value{GDBP}) catch syscall
4170 warning: Could not open "syscalls/i386-linux.xml"
4171 warning: Could not load the syscall XML file 'syscalls/i386-linux.xml'.
4172 GDB will not be able to display syscall names.
4173 Catchpoint 1 (syscall)
4177 Of course, the file name will change depending on your architecture and system.
4179 Still using the example above, you can also try to catch a syscall by its
4180 number. In this case, you would see something like:
4183 (@value{GDBP}) catch syscall 252
4184 Catchpoint 1 (syscall(s) 252)
4187 Again, in this case @value{GDBN} would not be able to display syscall's names.
4190 A call to @code{fork}. This is currently only available for HP-UX
4194 A call to @code{vfork}. This is currently only available for HP-UX
4197 @item load @r{[}regexp@r{]}
4198 @itemx unload @r{[}regexp@r{]}
4199 The loading or unloading of a shared library. If @var{regexp} is
4200 given, then the catchpoint will stop only if the regular expression
4201 matches one of the affected libraries.
4205 @item tcatch @var{event}
4206 Set a catchpoint that is enabled only for one stop. The catchpoint is
4207 automatically deleted after the first time the event is caught.
4211 Use the @code{info break} command to list the current catchpoints.
4213 There are currently some limitations to C@t{++} exception handling
4214 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
4218 If you call a function interactively, @value{GDBN} normally returns
4219 control to you when the function has finished executing. If the call
4220 raises an exception, however, the call may bypass the mechanism that
4221 returns control to you and cause your program either to abort or to
4222 simply continue running until it hits a breakpoint, catches a signal
4223 that @value{GDBN} is listening for, or exits. This is the case even if
4224 you set a catchpoint for the exception; catchpoints on exceptions are
4225 disabled within interactive calls.
4228 You cannot raise an exception interactively.
4231 You cannot install an exception handler interactively.
4234 @cindex raise exceptions
4235 Sometimes @code{catch} is not the best way to debug exception handling:
4236 if you need to know exactly where an exception is raised, it is better to
4237 stop @emph{before} the exception handler is called, since that way you
4238 can see the stack before any unwinding takes place. If you set a
4239 breakpoint in an exception handler instead, it may not be easy to find
4240 out where the exception was raised.
4242 To stop just before an exception handler is called, you need some
4243 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
4244 raised by calling a library function named @code{__raise_exception}
4245 which has the following ANSI C interface:
4248 /* @var{addr} is where the exception identifier is stored.
4249 @var{id} is the exception identifier. */
4250 void __raise_exception (void **addr, void *id);
4254 To make the debugger catch all exceptions before any stack
4255 unwinding takes place, set a breakpoint on @code{__raise_exception}
4256 (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Exceptions}).
4258 With a conditional breakpoint (@pxref{Conditions, ,Break Conditions})
4259 that depends on the value of @var{id}, you can stop your program when
4260 a specific exception is raised. You can use multiple conditional
4261 breakpoints to stop your program when any of a number of exceptions are
4266 @subsection Deleting Breakpoints
4268 @cindex clearing breakpoints, watchpoints, catchpoints
4269 @cindex deleting breakpoints, watchpoints, catchpoints
4270 It is often necessary to eliminate a breakpoint, watchpoint, or
4271 catchpoint once it has done its job and you no longer want your program
4272 to stop there. This is called @dfn{deleting} the breakpoint. A
4273 breakpoint that has been deleted no longer exists; it is forgotten.
4275 With the @code{clear} command you can delete breakpoints according to
4276 where they are in your program. With the @code{delete} command you can
4277 delete individual breakpoints, watchpoints, or catchpoints by specifying
4278 their breakpoint numbers.
4280 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
4281 automatically ignores breakpoints on the first instruction to be executed
4282 when you continue execution without changing the execution address.
4287 Delete any breakpoints at the next instruction to be executed in the
4288 selected stack frame (@pxref{Selection, ,Selecting a Frame}). When
4289 the innermost frame is selected, this is a good way to delete a
4290 breakpoint where your program just stopped.
4292 @item clear @var{location}
4293 Delete any breakpoints set at the specified @var{location}.
4294 @xref{Specify Location}, for the various forms of @var{location}; the
4295 most useful ones are listed below:
4298 @item clear @var{function}
4299 @itemx clear @var{filename}:@var{function}
4300 Delete any breakpoints set at entry to the named @var{function}.
4302 @item clear @var{linenum}
4303 @itemx clear @var{filename}:@var{linenum}
4304 Delete any breakpoints set at or within the code of the specified
4305 @var{linenum} of the specified @var{filename}.
4308 @cindex delete breakpoints
4310 @kindex d @r{(@code{delete})}
4311 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
4312 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
4313 ranges specified as arguments. If no argument is specified, delete all
4314 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
4315 confirm off}). You can abbreviate this command as @code{d}.
4319 @subsection Disabling Breakpoints
4321 @cindex enable/disable a breakpoint
4322 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
4323 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
4324 it had been deleted, but remembers the information on the breakpoint so
4325 that you can @dfn{enable} it again later.
4327 You disable and enable breakpoints, watchpoints, and catchpoints with
4328 the @code{enable} and @code{disable} commands, optionally specifying
4329 one or more breakpoint numbers as arguments. Use @code{info break} to
4330 print a list of all breakpoints, watchpoints, and catchpoints if you
4331 do not know which numbers to use.
4333 Disabling and enabling a breakpoint that has multiple locations
4334 affects all of its locations.
4336 A breakpoint, watchpoint, or catchpoint can have any of several
4337 different states of enablement:
4341 Enabled. The breakpoint stops your program. A breakpoint set
4342 with the @code{break} command starts out in this state.
4344 Disabled. The breakpoint has no effect on your program.
4346 Enabled once. The breakpoint stops your program, but then becomes
4349 Enabled for a count. The breakpoint stops your program for the next
4350 N times, then becomes disabled.
4352 Enabled for deletion. The breakpoint stops your program, but
4353 immediately after it does so it is deleted permanently. A breakpoint
4354 set with the @code{tbreak} command starts out in this state.
4357 You can use the following commands to enable or disable breakpoints,
4358 watchpoints, and catchpoints:
4362 @kindex dis @r{(@code{disable})}
4363 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
4364 Disable the specified breakpoints---or all breakpoints, if none are
4365 listed. A disabled breakpoint has no effect but is not forgotten. All
4366 options such as ignore-counts, conditions and commands are remembered in
4367 case the breakpoint is enabled again later. You may abbreviate
4368 @code{disable} as @code{dis}.
4371 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
4372 Enable the specified breakpoints (or all defined breakpoints). They
4373 become effective once again in stopping your program.
4375 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
4376 Enable the specified breakpoints temporarily. @value{GDBN} disables any
4377 of these breakpoints immediately after stopping your program.
4379 @item enable @r{[}breakpoints@r{]} count @var{count} @var{range}@dots{}
4380 Enable the specified breakpoints temporarily. @value{GDBN} records
4381 @var{count} with each of the specified breakpoints, and decrements a
4382 breakpoint's count when it is hit. When any count reaches 0,
4383 @value{GDBN} disables that breakpoint. If a breakpoint has an ignore
4384 count (@pxref{Conditions, ,Break Conditions}), that will be
4385 decremented to 0 before @var{count} is affected.
4387 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
4388 Enable the specified breakpoints to work once, then die. @value{GDBN}
4389 deletes any of these breakpoints as soon as your program stops there.
4390 Breakpoints set by the @code{tbreak} command start out in this state.
4393 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
4394 @c confusing: tbreak is also initially enabled.
4395 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
4396 ,Setting Breakpoints}), breakpoints that you set are initially enabled;
4397 subsequently, they become disabled or enabled only when you use one of
4398 the commands above. (The command @code{until} can set and delete a
4399 breakpoint of its own, but it does not change the state of your other
4400 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
4404 @subsection Break Conditions
4405 @cindex conditional breakpoints
4406 @cindex breakpoint conditions
4408 @c FIXME what is scope of break condition expr? Context where wanted?
4409 @c in particular for a watchpoint?
4410 The simplest sort of breakpoint breaks every time your program reaches a
4411 specified place. You can also specify a @dfn{condition} for a
4412 breakpoint. A condition is just a Boolean expression in your
4413 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
4414 a condition evaluates the expression each time your program reaches it,
4415 and your program stops only if the condition is @emph{true}.
4417 This is the converse of using assertions for program validation; in that
4418 situation, you want to stop when the assertion is violated---that is,
4419 when the condition is false. In C, if you want to test an assertion expressed
4420 by the condition @var{assert}, you should set the condition
4421 @samp{! @var{assert}} on the appropriate breakpoint.
4423 Conditions are also accepted for watchpoints; you may not need them,
4424 since a watchpoint is inspecting the value of an expression anyhow---but
4425 it might be simpler, say, to just set a watchpoint on a variable name,
4426 and specify a condition that tests whether the new value is an interesting
4429 Break conditions can have side effects, and may even call functions in
4430 your program. This can be useful, for example, to activate functions
4431 that log program progress, or to use your own print functions to
4432 format special data structures. The effects are completely predictable
4433 unless there is another enabled breakpoint at the same address. (In
4434 that case, @value{GDBN} might see the other breakpoint first and stop your
4435 program without checking the condition of this one.) Note that
4436 breakpoint commands are usually more convenient and flexible than break
4438 purpose of performing side effects when a breakpoint is reached
4439 (@pxref{Break Commands, ,Breakpoint Command Lists}).
4441 Breakpoint conditions can also be evaluated on the target's side if
4442 the target supports it. Instead of evaluating the conditions locally,
4443 @value{GDBN} encodes the expression into an agent expression
4444 (@pxref{Agent Expressions}) suitable for execution on the target,
4445 independently of @value{GDBN}. Global variables become raw memory
4446 locations, locals become stack accesses, and so forth.
4448 In this case, @value{GDBN} will only be notified of a breakpoint trigger
4449 when its condition evaluates to true. This mechanism may provide faster
4450 response times depending on the performance characteristics of the target
4451 since it does not need to keep @value{GDBN} informed about
4452 every breakpoint trigger, even those with false conditions.
4454 Break conditions can be specified when a breakpoint is set, by using
4455 @samp{if} in the arguments to the @code{break} command. @xref{Set
4456 Breaks, ,Setting Breakpoints}. They can also be changed at any time
4457 with the @code{condition} command.
4459 You can also use the @code{if} keyword with the @code{watch} command.
4460 The @code{catch} command does not recognize the @code{if} keyword;
4461 @code{condition} is the only way to impose a further condition on a
4466 @item condition @var{bnum} @var{expression}
4467 Specify @var{expression} as the break condition for breakpoint,
4468 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
4469 breakpoint @var{bnum} stops your program only if the value of
4470 @var{expression} is true (nonzero, in C). When you use
4471 @code{condition}, @value{GDBN} checks @var{expression} immediately for
4472 syntactic correctness, and to determine whether symbols in it have
4473 referents in the context of your breakpoint. If @var{expression} uses
4474 symbols not referenced in the context of the breakpoint, @value{GDBN}
4475 prints an error message:
4478 No symbol "foo" in current context.
4483 not actually evaluate @var{expression} at the time the @code{condition}
4484 command (or a command that sets a breakpoint with a condition, like
4485 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
4487 @item condition @var{bnum}
4488 Remove the condition from breakpoint number @var{bnum}. It becomes
4489 an ordinary unconditional breakpoint.
4492 @cindex ignore count (of breakpoint)
4493 A special case of a breakpoint condition is to stop only when the
4494 breakpoint has been reached a certain number of times. This is so
4495 useful that there is a special way to do it, using the @dfn{ignore
4496 count} of the breakpoint. Every breakpoint has an ignore count, which
4497 is an integer. Most of the time, the ignore count is zero, and
4498 therefore has no effect. But if your program reaches a breakpoint whose
4499 ignore count is positive, then instead of stopping, it just decrements
4500 the ignore count by one and continues. As a result, if the ignore count
4501 value is @var{n}, the breakpoint does not stop the next @var{n} times
4502 your program reaches it.
4506 @item ignore @var{bnum} @var{count}
4507 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
4508 The next @var{count} times the breakpoint is reached, your program's
4509 execution does not stop; other than to decrement the ignore count, @value{GDBN}
4512 To make the breakpoint stop the next time it is reached, specify
4515 When you use @code{continue} to resume execution of your program from a
4516 breakpoint, you can specify an ignore count directly as an argument to
4517 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
4518 Stepping,,Continuing and Stepping}.
4520 If a breakpoint has a positive ignore count and a condition, the
4521 condition is not checked. Once the ignore count reaches zero,
4522 @value{GDBN} resumes checking the condition.
4524 You could achieve the effect of the ignore count with a condition such
4525 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
4526 is decremented each time. @xref{Convenience Vars, ,Convenience
4530 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
4533 @node Break Commands
4534 @subsection Breakpoint Command Lists
4536 @cindex breakpoint commands
4537 You can give any breakpoint (or watchpoint or catchpoint) a series of
4538 commands to execute when your program stops due to that breakpoint. For
4539 example, you might want to print the values of certain expressions, or
4540 enable other breakpoints.
4544 @kindex end@r{ (breakpoint commands)}
4545 @item commands @r{[}@var{range}@dots{}@r{]}
4546 @itemx @dots{} @var{command-list} @dots{}
4548 Specify a list of commands for the given breakpoints. The commands
4549 themselves appear on the following lines. Type a line containing just
4550 @code{end} to terminate the commands.
4552 To remove all commands from a breakpoint, type @code{commands} and
4553 follow it immediately with @code{end}; that is, give no commands.
4555 With no argument, @code{commands} refers to the last breakpoint,
4556 watchpoint, or catchpoint set (not to the breakpoint most recently
4557 encountered). If the most recent breakpoints were set with a single
4558 command, then the @code{commands} will apply to all the breakpoints
4559 set by that command. This applies to breakpoints set by
4560 @code{rbreak}, and also applies when a single @code{break} command
4561 creates multiple breakpoints (@pxref{Ambiguous Expressions,,Ambiguous
4565 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
4566 disabled within a @var{command-list}.
4568 You can use breakpoint commands to start your program up again. Simply
4569 use the @code{continue} command, or @code{step}, or any other command
4570 that resumes execution.
4572 Any other commands in the command list, after a command that resumes
4573 execution, are ignored. This is because any time you resume execution
4574 (even with a simple @code{next} or @code{step}), you may encounter
4575 another breakpoint---which could have its own command list, leading to
4576 ambiguities about which list to execute.
4579 If the first command you specify in a command list is @code{silent}, the
4580 usual message about stopping at a breakpoint is not printed. This may
4581 be desirable for breakpoints that are to print a specific message and
4582 then continue. If none of the remaining commands print anything, you
4583 see no sign that the breakpoint was reached. @code{silent} is
4584 meaningful only at the beginning of a breakpoint command list.
4586 The commands @code{echo}, @code{output}, and @code{printf} allow you to
4587 print precisely controlled output, and are often useful in silent
4588 breakpoints. @xref{Output, ,Commands for Controlled Output}.
4590 For example, here is how you could use breakpoint commands to print the
4591 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
4597 printf "x is %d\n",x
4602 One application for breakpoint commands is to compensate for one bug so
4603 you can test for another. Put a breakpoint just after the erroneous line
4604 of code, give it a condition to detect the case in which something
4605 erroneous has been done, and give it commands to assign correct values
4606 to any variables that need them. End with the @code{continue} command
4607 so that your program does not stop, and start with the @code{silent}
4608 command so that no output is produced. Here is an example:
4619 @node Save Breakpoints
4620 @subsection How to save breakpoints to a file
4622 To save breakpoint definitions to a file use the @w{@code{save
4623 breakpoints}} command.
4626 @kindex save breakpoints
4627 @cindex save breakpoints to a file for future sessions
4628 @item save breakpoints [@var{filename}]
4629 This command saves all current breakpoint definitions together with
4630 their commands and ignore counts, into a file @file{@var{filename}}
4631 suitable for use in a later debugging session. This includes all
4632 types of breakpoints (breakpoints, watchpoints, catchpoints,
4633 tracepoints). To read the saved breakpoint definitions, use the
4634 @code{source} command (@pxref{Command Files}). Note that watchpoints
4635 with expressions involving local variables may fail to be recreated
4636 because it may not be possible to access the context where the
4637 watchpoint is valid anymore. Because the saved breakpoint definitions
4638 are simply a sequence of @value{GDBN} commands that recreate the
4639 breakpoints, you can edit the file in your favorite editing program,
4640 and remove the breakpoint definitions you're not interested in, or
4641 that can no longer be recreated.
4644 @c @ifclear BARETARGET
4645 @node Error in Breakpoints
4646 @subsection ``Cannot insert breakpoints''
4648 If you request too many active hardware-assisted breakpoints and
4649 watchpoints, you will see this error message:
4651 @c FIXME: the precise wording of this message may change; the relevant
4652 @c source change is not committed yet (Sep 3, 1999).
4654 Stopped; cannot insert breakpoints.
4655 You may have requested too many hardware breakpoints and watchpoints.
4659 This message is printed when you attempt to resume the program, since
4660 only then @value{GDBN} knows exactly how many hardware breakpoints and
4661 watchpoints it needs to insert.
4663 When this message is printed, you need to disable or remove some of the
4664 hardware-assisted breakpoints and watchpoints, and then continue.
4666 @node Breakpoint-related Warnings
4667 @subsection ``Breakpoint address adjusted...''
4668 @cindex breakpoint address adjusted
4670 Some processor architectures place constraints on the addresses at
4671 which breakpoints may be placed. For architectures thus constrained,
4672 @value{GDBN} will attempt to adjust the breakpoint's address to comply
4673 with the constraints dictated by the architecture.
4675 One example of such an architecture is the Fujitsu FR-V. The FR-V is
4676 a VLIW architecture in which a number of RISC-like instructions may be
4677 bundled together for parallel execution. The FR-V architecture
4678 constrains the location of a breakpoint instruction within such a
4679 bundle to the instruction with the lowest address. @value{GDBN}
4680 honors this constraint by adjusting a breakpoint's address to the
4681 first in the bundle.
4683 It is not uncommon for optimized code to have bundles which contain
4684 instructions from different source statements, thus it may happen that
4685 a breakpoint's address will be adjusted from one source statement to
4686 another. Since this adjustment may significantly alter @value{GDBN}'s
4687 breakpoint related behavior from what the user expects, a warning is
4688 printed when the breakpoint is first set and also when the breakpoint
4691 A warning like the one below is printed when setting a breakpoint
4692 that's been subject to address adjustment:
4695 warning: Breakpoint address adjusted from 0x00010414 to 0x00010410.
4698 Such warnings are printed both for user settable and @value{GDBN}'s
4699 internal breakpoints. If you see one of these warnings, you should
4700 verify that a breakpoint set at the adjusted address will have the
4701 desired affect. If not, the breakpoint in question may be removed and
4702 other breakpoints may be set which will have the desired behavior.
4703 E.g., it may be sufficient to place the breakpoint at a later
4704 instruction. A conditional breakpoint may also be useful in some
4705 cases to prevent the breakpoint from triggering too often.
4707 @value{GDBN} will also issue a warning when stopping at one of these
4708 adjusted breakpoints:
4711 warning: Breakpoint 1 address previously adjusted from 0x00010414
4715 When this warning is encountered, it may be too late to take remedial
4716 action except in cases where the breakpoint is hit earlier or more
4717 frequently than expected.
4719 @node Continuing and Stepping
4720 @section Continuing and Stepping
4724 @cindex resuming execution
4725 @dfn{Continuing} means resuming program execution until your program
4726 completes normally. In contrast, @dfn{stepping} means executing just
4727 one more ``step'' of your program, where ``step'' may mean either one
4728 line of source code, or one machine instruction (depending on what
4729 particular command you use). Either when continuing or when stepping,
4730 your program may stop even sooner, due to a breakpoint or a signal. (If
4731 it stops due to a signal, you may want to use @code{handle}, or use
4732 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
4736 @kindex c @r{(@code{continue})}
4737 @kindex fg @r{(resume foreground execution)}
4738 @item continue @r{[}@var{ignore-count}@r{]}
4739 @itemx c @r{[}@var{ignore-count}@r{]}
4740 @itemx fg @r{[}@var{ignore-count}@r{]}
4741 Resume program execution, at the address where your program last stopped;
4742 any breakpoints set at that address are bypassed. The optional argument
4743 @var{ignore-count} allows you to specify a further number of times to
4744 ignore a breakpoint at this location; its effect is like that of
4745 @code{ignore} (@pxref{Conditions, ,Break Conditions}).
4747 The argument @var{ignore-count} is meaningful only when your program
4748 stopped due to a breakpoint. At other times, the argument to
4749 @code{continue} is ignored.
4751 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
4752 debugged program is deemed to be the foreground program) are provided
4753 purely for convenience, and have exactly the same behavior as
4757 To resume execution at a different place, you can use @code{return}
4758 (@pxref{Returning, ,Returning from a Function}) to go back to the
4759 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
4760 Different Address}) to go to an arbitrary location in your program.
4762 A typical technique for using stepping is to set a breakpoint
4763 (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Catchpoints}) at the
4764 beginning of the function or the section of your program where a problem
4765 is believed to lie, run your program until it stops at that breakpoint,
4766 and then step through the suspect area, examining the variables that are
4767 interesting, until you see the problem happen.
4771 @kindex s @r{(@code{step})}
4773 Continue running your program until control reaches a different source
4774 line, then stop it and return control to @value{GDBN}. This command is
4775 abbreviated @code{s}.
4778 @c "without debugging information" is imprecise; actually "without line
4779 @c numbers in the debugging information". (gcc -g1 has debugging info but
4780 @c not line numbers). But it seems complex to try to make that
4781 @c distinction here.
4782 @emph{Warning:} If you use the @code{step} command while control is
4783 within a function that was compiled without debugging information,
4784 execution proceeds until control reaches a function that does have
4785 debugging information. Likewise, it will not step into a function which
4786 is compiled without debugging information. To step through functions
4787 without debugging information, use the @code{stepi} command, described
4791 The @code{step} command only stops at the first instruction of a source
4792 line. This prevents the multiple stops that could otherwise occur in
4793 @code{switch} statements, @code{for} loops, etc. @code{step} continues
4794 to stop if a function that has debugging information is called within
4795 the line. In other words, @code{step} @emph{steps inside} any functions
4796 called within the line.
4798 Also, the @code{step} command only enters a function if there is line
4799 number information for the function. Otherwise it acts like the
4800 @code{next} command. This avoids problems when using @code{cc -gl}
4801 on MIPS machines. Previously, @code{step} entered subroutines if there
4802 was any debugging information about the routine.
4804 @item step @var{count}
4805 Continue running as in @code{step}, but do so @var{count} times. If a
4806 breakpoint is reached, or a signal not related to stepping occurs before
4807 @var{count} steps, stepping stops right away.
4810 @kindex n @r{(@code{next})}
4811 @item next @r{[}@var{count}@r{]}
4812 Continue to the next source line in the current (innermost) stack frame.
4813 This is similar to @code{step}, but function calls that appear within
4814 the line of code are executed without stopping. Execution stops when
4815 control reaches a different line of code at the original stack level
4816 that was executing when you gave the @code{next} command. This command
4817 is abbreviated @code{n}.
4819 An argument @var{count} is a repeat count, as for @code{step}.
4822 @c FIX ME!! Do we delete this, or is there a way it fits in with
4823 @c the following paragraph? --- Vctoria
4825 @c @code{next} within a function that lacks debugging information acts like
4826 @c @code{step}, but any function calls appearing within the code of the
4827 @c function are executed without stopping.
4829 The @code{next} command only stops at the first instruction of a
4830 source line. This prevents multiple stops that could otherwise occur in
4831 @code{switch} statements, @code{for} loops, etc.
4833 @kindex set step-mode
4835 @cindex functions without line info, and stepping
4836 @cindex stepping into functions with no line info
4837 @itemx set step-mode on
4838 The @code{set step-mode on} command causes the @code{step} command to
4839 stop at the first instruction of a function which contains no debug line
4840 information rather than stepping over it.
4842 This is useful in cases where you may be interested in inspecting the
4843 machine instructions of a function which has no symbolic info and do not
4844 want @value{GDBN} to automatically skip over this function.
4846 @item set step-mode off
4847 Causes the @code{step} command to step over any functions which contains no
4848 debug information. This is the default.
4850 @item show step-mode
4851 Show whether @value{GDBN} will stop in or step over functions without
4852 source line debug information.
4855 @kindex fin @r{(@code{finish})}
4857 Continue running until just after function in the selected stack frame
4858 returns. Print the returned value (if any). This command can be
4859 abbreviated as @code{fin}.
4861 Contrast this with the @code{return} command (@pxref{Returning,
4862 ,Returning from a Function}).
4865 @kindex u @r{(@code{until})}
4866 @cindex run until specified location
4869 Continue running until a source line past the current line, in the
4870 current stack frame, is reached. This command is used to avoid single
4871 stepping through a loop more than once. It is like the @code{next}
4872 command, except that when @code{until} encounters a jump, it
4873 automatically continues execution until the program counter is greater
4874 than the address of the jump.
4876 This means that when you reach the end of a loop after single stepping
4877 though it, @code{until} makes your program continue execution until it
4878 exits the loop. In contrast, a @code{next} command at the end of a loop
4879 simply steps back to the beginning of the loop, which forces you to step
4880 through the next iteration.
4882 @code{until} always stops your program if it attempts to exit the current
4885 @code{until} may produce somewhat counterintuitive results if the order
4886 of machine code does not match the order of the source lines. For
4887 example, in the following excerpt from a debugging session, the @code{f}
4888 (@code{frame}) command shows that execution is stopped at line
4889 @code{206}; yet when we use @code{until}, we get to line @code{195}:
4893 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
4895 (@value{GDBP}) until
4896 195 for ( ; argc > 0; NEXTARG) @{
4899 This happened because, for execution efficiency, the compiler had
4900 generated code for the loop closure test at the end, rather than the
4901 start, of the loop---even though the test in a C @code{for}-loop is
4902 written before the body of the loop. The @code{until} command appeared
4903 to step back to the beginning of the loop when it advanced to this
4904 expression; however, it has not really gone to an earlier
4905 statement---not in terms of the actual machine code.
4907 @code{until} with no argument works by means of single
4908 instruction stepping, and hence is slower than @code{until} with an
4911 @item until @var{location}
4912 @itemx u @var{location}
4913 Continue running your program until either the specified location is
4914 reached, or the current stack frame returns. @var{location} is any of
4915 the forms described in @ref{Specify Location}.
4916 This form of the command uses temporary breakpoints, and
4917 hence is quicker than @code{until} without an argument. The specified
4918 location is actually reached only if it is in the current frame. This
4919 implies that @code{until} can be used to skip over recursive function
4920 invocations. For instance in the code below, if the current location is
4921 line @code{96}, issuing @code{until 99} will execute the program up to
4922 line @code{99} in the same invocation of factorial, i.e., after the inner
4923 invocations have returned.
4926 94 int factorial (int value)
4928 96 if (value > 1) @{
4929 97 value *= factorial (value - 1);
4936 @kindex advance @var{location}
4937 @itemx advance @var{location}
4938 Continue running the program up to the given @var{location}. An argument is
4939 required, which should be of one of the forms described in
4940 @ref{Specify Location}.
4941 Execution will also stop upon exit from the current stack
4942 frame. This command is similar to @code{until}, but @code{advance} will
4943 not skip over recursive function calls, and the target location doesn't
4944 have to be in the same frame as the current one.
4948 @kindex si @r{(@code{stepi})}
4950 @itemx stepi @var{arg}
4952 Execute one machine instruction, then stop and return to the debugger.
4954 It is often useful to do @samp{display/i $pc} when stepping by machine
4955 instructions. This makes @value{GDBN} automatically display the next
4956 instruction to be executed, each time your program stops. @xref{Auto
4957 Display,, Automatic Display}.
4959 An argument is a repeat count, as in @code{step}.
4963 @kindex ni @r{(@code{nexti})}
4965 @itemx nexti @var{arg}
4967 Execute one machine instruction, but if it is a function call,
4968 proceed until the function returns.
4970 An argument is a repeat count, as in @code{next}.
4973 @node Skipping Over Functions and Files
4974 @section Skipping Over Functions and Files
4975 @cindex skipping over functions and files
4977 The program you are debugging may contain some functions which are
4978 uninteresting to debug. The @code{skip} comand lets you tell @value{GDBN} to
4979 skip a function or all functions in a file when stepping.
4981 For example, consider the following C function:
4992 Suppose you wish to step into the functions @code{foo} and @code{bar}, but you
4993 are not interested in stepping through @code{boring}. If you run @code{step}
4994 at line 103, you'll enter @code{boring()}, but if you run @code{next}, you'll
4995 step over both @code{foo} and @code{boring}!
4997 One solution is to @code{step} into @code{boring} and use the @code{finish}
4998 command to immediately exit it. But this can become tedious if @code{boring}
4999 is called from many places.
5001 A more flexible solution is to execute @kbd{skip boring}. This instructs
5002 @value{GDBN} never to step into @code{boring}. Now when you execute
5003 @code{step} at line 103, you'll step over @code{boring} and directly into
5006 You can also instruct @value{GDBN} to skip all functions in a file, with, for
5007 example, @code{skip file boring.c}.
5010 @kindex skip function
5011 @item skip @r{[}@var{linespec}@r{]}
5012 @itemx skip function @r{[}@var{linespec}@r{]}
5013 After running this command, the function named by @var{linespec} or the
5014 function containing the line named by @var{linespec} will be skipped over when
5015 stepping. @xref{Specify Location}.
5017 If you do not specify @var{linespec}, the function you're currently debugging
5020 (If you have a function called @code{file} that you want to skip, use
5021 @kbd{skip function file}.)
5024 @item skip file @r{[}@var{filename}@r{]}
5025 After running this command, any function whose source lives in @var{filename}
5026 will be skipped over when stepping.
5028 If you do not specify @var{filename}, functions whose source lives in the file
5029 you're currently debugging will be skipped.
5032 Skips can be listed, deleted, disabled, and enabled, much like breakpoints.
5033 These are the commands for managing your list of skips:
5037 @item info skip @r{[}@var{range}@r{]}
5038 Print details about the specified skip(s). If @var{range} is not specified,
5039 print a table with details about all functions and files marked for skipping.
5040 @code{info skip} prints the following information about each skip:
5044 A number identifying this skip.
5046 The type of this skip, either @samp{function} or @samp{file}.
5047 @item Enabled or Disabled
5048 Enabled skips are marked with @samp{y}. Disabled skips are marked with @samp{n}.
5050 For function skips, this column indicates the address in memory of the function
5051 being skipped. If you've set a function skip on a function which has not yet
5052 been loaded, this field will contain @samp{<PENDING>}. Once a shared library
5053 which has the function is loaded, @code{info skip} will show the function's
5056 For file skips, this field contains the filename being skipped. For functions
5057 skips, this field contains the function name and its line number in the file
5058 where it is defined.
5062 @item skip delete @r{[}@var{range}@r{]}
5063 Delete the specified skip(s). If @var{range} is not specified, delete all
5067 @item skip enable @r{[}@var{range}@r{]}
5068 Enable the specified skip(s). If @var{range} is not specified, enable all
5071 @kindex skip disable
5072 @item skip disable @r{[}@var{range}@r{]}
5073 Disable the specified skip(s). If @var{range} is not specified, disable all
5082 A signal is an asynchronous event that can happen in a program. The
5083 operating system defines the possible kinds of signals, and gives each
5084 kind a name and a number. For example, in Unix @code{SIGINT} is the
5085 signal a program gets when you type an interrupt character (often @kbd{Ctrl-c});
5086 @code{SIGSEGV} is the signal a program gets from referencing a place in
5087 memory far away from all the areas in use; @code{SIGALRM} occurs when
5088 the alarm clock timer goes off (which happens only if your program has
5089 requested an alarm).
5091 @cindex fatal signals
5092 Some signals, including @code{SIGALRM}, are a normal part of the
5093 functioning of your program. Others, such as @code{SIGSEGV}, indicate
5094 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
5095 program has not specified in advance some other way to handle the signal.
5096 @code{SIGINT} does not indicate an error in your program, but it is normally
5097 fatal so it can carry out the purpose of the interrupt: to kill the program.
5099 @value{GDBN} has the ability to detect any occurrence of a signal in your
5100 program. You can tell @value{GDBN} in advance what to do for each kind of
5103 @cindex handling signals
5104 Normally, @value{GDBN} is set up to let the non-erroneous signals like
5105 @code{SIGALRM} be silently passed to your program
5106 (so as not to interfere with their role in the program's functioning)
5107 but to stop your program immediately whenever an error signal happens.
5108 You can change these settings with the @code{handle} command.
5111 @kindex info signals
5115 Print a table of all the kinds of signals and how @value{GDBN} has been told to
5116 handle each one. You can use this to see the signal numbers of all
5117 the defined types of signals.
5119 @item info signals @var{sig}
5120 Similar, but print information only about the specified signal number.
5122 @code{info handle} is an alias for @code{info signals}.
5125 @item handle @var{signal} @r{[}@var{keywords}@dots{}@r{]}
5126 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
5127 can be the number of a signal or its name (with or without the
5128 @samp{SIG} at the beginning); a list of signal numbers of the form
5129 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
5130 known signals. Optional arguments @var{keywords}, described below,
5131 say what change to make.
5135 The keywords allowed by the @code{handle} command can be abbreviated.
5136 Their full names are:
5140 @value{GDBN} should not stop your program when this signal happens. It may
5141 still print a message telling you that the signal has come in.
5144 @value{GDBN} should stop your program when this signal happens. This implies
5145 the @code{print} keyword as well.
5148 @value{GDBN} should print a message when this signal happens.
5151 @value{GDBN} should not mention the occurrence of the signal at all. This
5152 implies the @code{nostop} keyword as well.
5156 @value{GDBN} should allow your program to see this signal; your program
5157 can handle the signal, or else it may terminate if the signal is fatal
5158 and not handled. @code{pass} and @code{noignore} are synonyms.
5162 @value{GDBN} should not allow your program to see this signal.
5163 @code{nopass} and @code{ignore} are synonyms.
5167 When a signal stops your program, the signal is not visible to the
5169 continue. Your program sees the signal then, if @code{pass} is in
5170 effect for the signal in question @emph{at that time}. In other words,
5171 after @value{GDBN} reports a signal, you can use the @code{handle}
5172 command with @code{pass} or @code{nopass} to control whether your
5173 program sees that signal when you continue.
5175 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
5176 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
5177 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
5180 You can also use the @code{signal} command to prevent your program from
5181 seeing a signal, or cause it to see a signal it normally would not see,
5182 or to give it any signal at any time. For example, if your program stopped
5183 due to some sort of memory reference error, you might store correct
5184 values into the erroneous variables and continue, hoping to see more
5185 execution; but your program would probably terminate immediately as
5186 a result of the fatal signal once it saw the signal. To prevent this,
5187 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
5190 @cindex extra signal information
5191 @anchor{extra signal information}
5193 On some targets, @value{GDBN} can inspect extra signal information
5194 associated with the intercepted signal, before it is actually
5195 delivered to the program being debugged. This information is exported
5196 by the convenience variable @code{$_siginfo}, and consists of data
5197 that is passed by the kernel to the signal handler at the time of the
5198 receipt of a signal. The data type of the information itself is
5199 target dependent. You can see the data type using the @code{ptype
5200 $_siginfo} command. On Unix systems, it typically corresponds to the
5201 standard @code{siginfo_t} type, as defined in the @file{signal.h}
5204 Here's an example, on a @sc{gnu}/Linux system, printing the stray
5205 referenced address that raised a segmentation fault.
5209 (@value{GDBP}) continue
5210 Program received signal SIGSEGV, Segmentation fault.
5211 0x0000000000400766 in main ()
5213 (@value{GDBP}) ptype $_siginfo
5220 struct @{...@} _kill;
5221 struct @{...@} _timer;
5223 struct @{...@} _sigchld;
5224 struct @{...@} _sigfault;
5225 struct @{...@} _sigpoll;
5228 (@value{GDBP}) ptype $_siginfo._sifields._sigfault
5232 (@value{GDBP}) p $_siginfo._sifields._sigfault.si_addr
5233 $1 = (void *) 0x7ffff7ff7000
5237 Depending on target support, @code{$_siginfo} may also be writable.
5240 @section Stopping and Starting Multi-thread Programs
5242 @cindex stopped threads
5243 @cindex threads, stopped
5245 @cindex continuing threads
5246 @cindex threads, continuing
5248 @value{GDBN} supports debugging programs with multiple threads
5249 (@pxref{Threads,, Debugging Programs with Multiple Threads}). There
5250 are two modes of controlling execution of your program within the
5251 debugger. In the default mode, referred to as @dfn{all-stop mode},
5252 when any thread in your program stops (for example, at a breakpoint
5253 or while being stepped), all other threads in the program are also stopped by
5254 @value{GDBN}. On some targets, @value{GDBN} also supports
5255 @dfn{non-stop mode}, in which other threads can continue to run freely while
5256 you examine the stopped thread in the debugger.
5259 * All-Stop Mode:: All threads stop when GDB takes control
5260 * Non-Stop Mode:: Other threads continue to execute
5261 * Background Execution:: Running your program asynchronously
5262 * Thread-Specific Breakpoints:: Controlling breakpoints
5263 * Interrupted System Calls:: GDB may interfere with system calls
5264 * Observer Mode:: GDB does not alter program behavior
5268 @subsection All-Stop Mode
5270 @cindex all-stop mode
5272 In all-stop mode, whenever your program stops under @value{GDBN} for any reason,
5273 @emph{all} threads of execution stop, not just the current thread. This
5274 allows you to examine the overall state of the program, including
5275 switching between threads, without worrying that things may change
5278 Conversely, whenever you restart the program, @emph{all} threads start
5279 executing. @emph{This is true even when single-stepping} with commands
5280 like @code{step} or @code{next}.
5282 In particular, @value{GDBN} cannot single-step all threads in lockstep.
5283 Since thread scheduling is up to your debugging target's operating
5284 system (not controlled by @value{GDBN}), other threads may
5285 execute more than one statement while the current thread completes a
5286 single step. Moreover, in general other threads stop in the middle of a
5287 statement, rather than at a clean statement boundary, when the program
5290 You might even find your program stopped in another thread after
5291 continuing or even single-stepping. This happens whenever some other
5292 thread runs into a breakpoint, a signal, or an exception before the
5293 first thread completes whatever you requested.
5295 @cindex automatic thread selection
5296 @cindex switching threads automatically
5297 @cindex threads, automatic switching
5298 Whenever @value{GDBN} stops your program, due to a breakpoint or a
5299 signal, it automatically selects the thread where that breakpoint or
5300 signal happened. @value{GDBN} alerts you to the context switch with a
5301 message such as @samp{[Switching to Thread @var{n}]} to identify the
5304 On some OSes, you can modify @value{GDBN}'s default behavior by
5305 locking the OS scheduler to allow only a single thread to run.
5308 @item set scheduler-locking @var{mode}
5309 @cindex scheduler locking mode
5310 @cindex lock scheduler
5311 Set the scheduler locking mode. If it is @code{off}, then there is no
5312 locking and any thread may run at any time. If @code{on}, then only the
5313 current thread may run when the inferior is resumed. The @code{step}
5314 mode optimizes for single-stepping; it prevents other threads
5315 from preempting the current thread while you are stepping, so that
5316 the focus of debugging does not change unexpectedly.
5317 Other threads only rarely (or never) get a chance to run
5318 when you step. They are more likely to run when you @samp{next} over a
5319 function call, and they are completely free to run when you use commands
5320 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
5321 thread hits a breakpoint during its timeslice, @value{GDBN} does not change
5322 the current thread away from the thread that you are debugging.
5324 @item show scheduler-locking
5325 Display the current scheduler locking mode.
5328 @cindex resume threads of multiple processes simultaneously
5329 By default, when you issue one of the execution commands such as
5330 @code{continue}, @code{next} or @code{step}, @value{GDBN} allows only
5331 threads of the current inferior to run. For example, if @value{GDBN}
5332 is attached to two inferiors, each with two threads, the
5333 @code{continue} command resumes only the two threads of the current
5334 inferior. This is useful, for example, when you debug a program that
5335 forks and you want to hold the parent stopped (so that, for instance,
5336 it doesn't run to exit), while you debug the child. In other
5337 situations, you may not be interested in inspecting the current state
5338 of any of the processes @value{GDBN} is attached to, and you may want
5339 to resume them all until some breakpoint is hit. In the latter case,
5340 you can instruct @value{GDBN} to allow all threads of all the
5341 inferiors to run with the @w{@code{set schedule-multiple}} command.
5344 @kindex set schedule-multiple
5345 @item set schedule-multiple
5346 Set the mode for allowing threads of multiple processes to be resumed
5347 when an execution command is issued. When @code{on}, all threads of
5348 all processes are allowed to run. When @code{off}, only the threads
5349 of the current process are resumed. The default is @code{off}. The
5350 @code{scheduler-locking} mode takes precedence when set to @code{on},
5351 or while you are stepping and set to @code{step}.
5353 @item show schedule-multiple
5354 Display the current mode for resuming the execution of threads of
5359 @subsection Non-Stop Mode
5361 @cindex non-stop mode
5363 @c This section is really only a place-holder, and needs to be expanded
5364 @c with more details.
5366 For some multi-threaded targets, @value{GDBN} supports an optional
5367 mode of operation in which you can examine stopped program threads in
5368 the debugger while other threads continue to execute freely. This
5369 minimizes intrusion when debugging live systems, such as programs
5370 where some threads have real-time constraints or must continue to
5371 respond to external events. This is referred to as @dfn{non-stop} mode.
5373 In non-stop mode, when a thread stops to report a debugging event,
5374 @emph{only} that thread is stopped; @value{GDBN} does not stop other
5375 threads as well, in contrast to the all-stop mode behavior. Additionally,
5376 execution commands such as @code{continue} and @code{step} apply by default
5377 only to the current thread in non-stop mode, rather than all threads as
5378 in all-stop mode. This allows you to control threads explicitly in
5379 ways that are not possible in all-stop mode --- for example, stepping
5380 one thread while allowing others to run freely, stepping
5381 one thread while holding all others stopped, or stepping several threads
5382 independently and simultaneously.
5384 To enter non-stop mode, use this sequence of commands before you run
5385 or attach to your program:
5388 # Enable the async interface.
5391 # If using the CLI, pagination breaks non-stop.
5394 # Finally, turn it on!
5398 You can use these commands to manipulate the non-stop mode setting:
5401 @kindex set non-stop
5402 @item set non-stop on
5403 Enable selection of non-stop mode.
5404 @item set non-stop off
5405 Disable selection of non-stop mode.
5406 @kindex show non-stop
5408 Show the current non-stop enablement setting.
5411 Note these commands only reflect whether non-stop mode is enabled,
5412 not whether the currently-executing program is being run in non-stop mode.
5413 In particular, the @code{set non-stop} preference is only consulted when
5414 @value{GDBN} starts or connects to the target program, and it is generally
5415 not possible to switch modes once debugging has started. Furthermore,
5416 since not all targets support non-stop mode, even when you have enabled
5417 non-stop mode, @value{GDBN} may still fall back to all-stop operation by
5420 In non-stop mode, all execution commands apply only to the current thread
5421 by default. That is, @code{continue} only continues one thread.
5422 To continue all threads, issue @code{continue -a} or @code{c -a}.
5424 You can use @value{GDBN}'s background execution commands
5425 (@pxref{Background Execution}) to run some threads in the background
5426 while you continue to examine or step others from @value{GDBN}.
5427 The MI execution commands (@pxref{GDB/MI Program Execution}) are
5428 always executed asynchronously in non-stop mode.
5430 Suspending execution is done with the @code{interrupt} command when
5431 running in the background, or @kbd{Ctrl-c} during foreground execution.
5432 In all-stop mode, this stops the whole process;
5433 but in non-stop mode the interrupt applies only to the current thread.
5434 To stop the whole program, use @code{interrupt -a}.
5436 Other execution commands do not currently support the @code{-a} option.
5438 In non-stop mode, when a thread stops, @value{GDBN} doesn't automatically make
5439 that thread current, as it does in all-stop mode. This is because the
5440 thread stop notifications are asynchronous with respect to @value{GDBN}'s
5441 command interpreter, and it would be confusing if @value{GDBN} unexpectedly
5442 changed to a different thread just as you entered a command to operate on the
5443 previously current thread.
5445 @node Background Execution
5446 @subsection Background Execution
5448 @cindex foreground execution
5449 @cindex background execution
5450 @cindex asynchronous execution
5451 @cindex execution, foreground, background and asynchronous
5453 @value{GDBN}'s execution commands have two variants: the normal
5454 foreground (synchronous) behavior, and a background
5455 (asynchronous) behavior. In foreground execution, @value{GDBN} waits for
5456 the program to report that some thread has stopped before prompting for
5457 another command. In background execution, @value{GDBN} immediately gives
5458 a command prompt so that you can issue other commands while your program runs.
5460 You need to explicitly enable asynchronous mode before you can use
5461 background execution commands. You can use these commands to
5462 manipulate the asynchronous mode setting:
5465 @kindex set target-async
5466 @item set target-async on
5467 Enable asynchronous mode.
5468 @item set target-async off
5469 Disable asynchronous mode.
5470 @kindex show target-async
5471 @item show target-async
5472 Show the current target-async setting.
5475 If the target doesn't support async mode, @value{GDBN} issues an error
5476 message if you attempt to use the background execution commands.
5478 To specify background execution, add a @code{&} to the command. For example,
5479 the background form of the @code{continue} command is @code{continue&}, or
5480 just @code{c&}. The execution commands that accept background execution
5486 @xref{Starting, , Starting your Program}.
5490 @xref{Attach, , Debugging an Already-running Process}.
5494 @xref{Continuing and Stepping, step}.
5498 @xref{Continuing and Stepping, stepi}.
5502 @xref{Continuing and Stepping, next}.
5506 @xref{Continuing and Stepping, nexti}.
5510 @xref{Continuing and Stepping, continue}.
5514 @xref{Continuing and Stepping, finish}.
5518 @xref{Continuing and Stepping, until}.
5522 Background execution is especially useful in conjunction with non-stop
5523 mode for debugging programs with multiple threads; see @ref{Non-Stop Mode}.
5524 However, you can also use these commands in the normal all-stop mode with
5525 the restriction that you cannot issue another execution command until the
5526 previous one finishes. Examples of commands that are valid in all-stop
5527 mode while the program is running include @code{help} and @code{info break}.
5529 You can interrupt your program while it is running in the background by
5530 using the @code{interrupt} command.
5537 Suspend execution of the running program. In all-stop mode,
5538 @code{interrupt} stops the whole process, but in non-stop mode, it stops
5539 only the current thread. To stop the whole program in non-stop mode,
5540 use @code{interrupt -a}.
5543 @node Thread-Specific Breakpoints
5544 @subsection Thread-Specific Breakpoints
5546 When your program has multiple threads (@pxref{Threads,, Debugging
5547 Programs with Multiple Threads}), you can choose whether to set
5548 breakpoints on all threads, or on a particular thread.
5551 @cindex breakpoints and threads
5552 @cindex thread breakpoints
5553 @kindex break @dots{} thread @var{threadno}
5554 @item break @var{linespec} thread @var{threadno}
5555 @itemx break @var{linespec} thread @var{threadno} if @dots{}
5556 @var{linespec} specifies source lines; there are several ways of
5557 writing them (@pxref{Specify Location}), but the effect is always to
5558 specify some source line.
5560 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
5561 to specify that you only want @value{GDBN} to stop the program when a
5562 particular thread reaches this breakpoint. @var{threadno} is one of the
5563 numeric thread identifiers assigned by @value{GDBN}, shown in the first
5564 column of the @samp{info threads} display.
5566 If you do not specify @samp{thread @var{threadno}} when you set a
5567 breakpoint, the breakpoint applies to @emph{all} threads of your
5570 You can use the @code{thread} qualifier on conditional breakpoints as
5571 well; in this case, place @samp{thread @var{threadno}} before or
5572 after the breakpoint condition, like this:
5575 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
5580 @node Interrupted System Calls
5581 @subsection Interrupted System Calls
5583 @cindex thread breakpoints and system calls
5584 @cindex system calls and thread breakpoints
5585 @cindex premature return from system calls
5586 There is an unfortunate side effect when using @value{GDBN} to debug
5587 multi-threaded programs. If one thread stops for a
5588 breakpoint, or for some other reason, and another thread is blocked in a
5589 system call, then the system call may return prematurely. This is a
5590 consequence of the interaction between multiple threads and the signals
5591 that @value{GDBN} uses to implement breakpoints and other events that
5594 To handle this problem, your program should check the return value of
5595 each system call and react appropriately. This is good programming
5598 For example, do not write code like this:
5604 The call to @code{sleep} will return early if a different thread stops
5605 at a breakpoint or for some other reason.
5607 Instead, write this:
5612 unslept = sleep (unslept);
5615 A system call is allowed to return early, so the system is still
5616 conforming to its specification. But @value{GDBN} does cause your
5617 multi-threaded program to behave differently than it would without
5620 Also, @value{GDBN} uses internal breakpoints in the thread library to
5621 monitor certain events such as thread creation and thread destruction.
5622 When such an event happens, a system call in another thread may return
5623 prematurely, even though your program does not appear to stop.
5626 @subsection Observer Mode
5628 If you want to build on non-stop mode and observe program behavior
5629 without any chance of disruption by @value{GDBN}, you can set
5630 variables to disable all of the debugger's attempts to modify state,
5631 whether by writing memory, inserting breakpoints, etc. These operate
5632 at a low level, intercepting operations from all commands.
5634 When all of these are set to @code{off}, then @value{GDBN} is said to
5635 be @dfn{observer mode}. As a convenience, the variable
5636 @code{observer} can be set to disable these, plus enable non-stop
5639 Note that @value{GDBN} will not prevent you from making nonsensical
5640 combinations of these settings. For instance, if you have enabled
5641 @code{may-insert-breakpoints} but disabled @code{may-write-memory},
5642 then breakpoints that work by writing trap instructions into the code
5643 stream will still not be able to be placed.
5648 @item set observer on
5649 @itemx set observer off
5650 When set to @code{on}, this disables all the permission variables
5651 below (except for @code{insert-fast-tracepoints}), plus enables
5652 non-stop debugging. Setting this to @code{off} switches back to
5653 normal debugging, though remaining in non-stop mode.
5656 Show whether observer mode is on or off.
5658 @kindex may-write-registers
5659 @item set may-write-registers on
5660 @itemx set may-write-registers off
5661 This controls whether @value{GDBN} will attempt to alter the values of
5662 registers, such as with assignment expressions in @code{print}, or the
5663 @code{jump} command. It defaults to @code{on}.
5665 @item show may-write-registers
5666 Show the current permission to write registers.
5668 @kindex may-write-memory
5669 @item set may-write-memory on
5670 @itemx set may-write-memory off
5671 This controls whether @value{GDBN} will attempt to alter the contents
5672 of memory, such as with assignment expressions in @code{print}. It
5673 defaults to @code{on}.
5675 @item show may-write-memory
5676 Show the current permission to write memory.
5678 @kindex may-insert-breakpoints
5679 @item set may-insert-breakpoints on
5680 @itemx set may-insert-breakpoints off
5681 This controls whether @value{GDBN} will attempt to insert breakpoints.
5682 This affects all breakpoints, including internal breakpoints defined
5683 by @value{GDBN}. It defaults to @code{on}.
5685 @item show may-insert-breakpoints
5686 Show the current permission to insert breakpoints.
5688 @kindex may-insert-tracepoints
5689 @item set may-insert-tracepoints on
5690 @itemx set may-insert-tracepoints off
5691 This controls whether @value{GDBN} will attempt to insert (regular)
5692 tracepoints at the beginning of a tracing experiment. It affects only
5693 non-fast tracepoints, fast tracepoints being under the control of
5694 @code{may-insert-fast-tracepoints}. It defaults to @code{on}.
5696 @item show may-insert-tracepoints
5697 Show the current permission to insert tracepoints.
5699 @kindex may-insert-fast-tracepoints
5700 @item set may-insert-fast-tracepoints on
5701 @itemx set may-insert-fast-tracepoints off
5702 This controls whether @value{GDBN} will attempt to insert fast
5703 tracepoints at the beginning of a tracing experiment. It affects only
5704 fast tracepoints, regular (non-fast) tracepoints being under the
5705 control of @code{may-insert-tracepoints}. It defaults to @code{on}.
5707 @item show may-insert-fast-tracepoints
5708 Show the current permission to insert fast tracepoints.
5710 @kindex may-interrupt
5711 @item set may-interrupt on
5712 @itemx set may-interrupt off
5713 This controls whether @value{GDBN} will attempt to interrupt or stop
5714 program execution. When this variable is @code{off}, the
5715 @code{interrupt} command will have no effect, nor will
5716 @kbd{Ctrl-c}. It defaults to @code{on}.
5718 @item show may-interrupt
5719 Show the current permission to interrupt or stop the program.
5723 @node Reverse Execution
5724 @chapter Running programs backward
5725 @cindex reverse execution
5726 @cindex running programs backward
5728 When you are debugging a program, it is not unusual to realize that
5729 you have gone too far, and some event of interest has already happened.
5730 If the target environment supports it, @value{GDBN} can allow you to
5731 ``rewind'' the program by running it backward.
5733 A target environment that supports reverse execution should be able
5734 to ``undo'' the changes in machine state that have taken place as the
5735 program was executing normally. Variables, registers etc.@: should
5736 revert to their previous values. Obviously this requires a great
5737 deal of sophistication on the part of the target environment; not
5738 all target environments can support reverse execution.
5740 When a program is executed in reverse, the instructions that
5741 have most recently been executed are ``un-executed'', in reverse
5742 order. The program counter runs backward, following the previous
5743 thread of execution in reverse. As each instruction is ``un-executed'',
5744 the values of memory and/or registers that were changed by that
5745 instruction are reverted to their previous states. After executing
5746 a piece of source code in reverse, all side effects of that code
5747 should be ``undone'', and all variables should be returned to their
5748 prior values@footnote{
5749 Note that some side effects are easier to undo than others. For instance,
5750 memory and registers are relatively easy, but device I/O is hard. Some
5751 targets may be able undo things like device I/O, and some may not.
5753 The contract between @value{GDBN} and the reverse executing target
5754 requires only that the target do something reasonable when
5755 @value{GDBN} tells it to execute backwards, and then report the
5756 results back to @value{GDBN}. Whatever the target reports back to
5757 @value{GDBN}, @value{GDBN} will report back to the user. @value{GDBN}
5758 assumes that the memory and registers that the target reports are in a
5759 consistant state, but @value{GDBN} accepts whatever it is given.
5762 If you are debugging in a target environment that supports
5763 reverse execution, @value{GDBN} provides the following commands.
5766 @kindex reverse-continue
5767 @kindex rc @r{(@code{reverse-continue})}
5768 @item reverse-continue @r{[}@var{ignore-count}@r{]}
5769 @itemx rc @r{[}@var{ignore-count}@r{]}
5770 Beginning at the point where your program last stopped, start executing
5771 in reverse. Reverse execution will stop for breakpoints and synchronous
5772 exceptions (signals), just like normal execution. Behavior of
5773 asynchronous signals depends on the target environment.
5775 @kindex reverse-step
5776 @kindex rs @r{(@code{step})}
5777 @item reverse-step @r{[}@var{count}@r{]}
5778 Run the program backward until control reaches the start of a
5779 different source line; then stop it, and return control to @value{GDBN}.
5781 Like the @code{step} command, @code{reverse-step} will only stop
5782 at the beginning of a source line. It ``un-executes'' the previously
5783 executed source line. If the previous source line included calls to
5784 debuggable functions, @code{reverse-step} will step (backward) into
5785 the called function, stopping at the beginning of the @emph{last}
5786 statement in the called function (typically a return statement).
5788 Also, as with the @code{step} command, if non-debuggable functions are
5789 called, @code{reverse-step} will run thru them backward without stopping.
5791 @kindex reverse-stepi
5792 @kindex rsi @r{(@code{reverse-stepi})}
5793 @item reverse-stepi @r{[}@var{count}@r{]}
5794 Reverse-execute one machine instruction. Note that the instruction
5795 to be reverse-executed is @emph{not} the one pointed to by the program
5796 counter, but the instruction executed prior to that one. For instance,
5797 if the last instruction was a jump, @code{reverse-stepi} will take you
5798 back from the destination of the jump to the jump instruction itself.
5800 @kindex reverse-next
5801 @kindex rn @r{(@code{reverse-next})}
5802 @item reverse-next @r{[}@var{count}@r{]}
5803 Run backward to the beginning of the previous line executed in
5804 the current (innermost) stack frame. If the line contains function
5805 calls, they will be ``un-executed'' without stopping. Starting from
5806 the first line of a function, @code{reverse-next} will take you back
5807 to the caller of that function, @emph{before} the function was called,
5808 just as the normal @code{next} command would take you from the last
5809 line of a function back to its return to its caller
5810 @footnote{Unless the code is too heavily optimized.}.
5812 @kindex reverse-nexti
5813 @kindex rni @r{(@code{reverse-nexti})}
5814 @item reverse-nexti @r{[}@var{count}@r{]}
5815 Like @code{nexti}, @code{reverse-nexti} executes a single instruction
5816 in reverse, except that called functions are ``un-executed'' atomically.
5817 That is, if the previously executed instruction was a return from
5818 another function, @code{reverse-nexti} will continue to execute
5819 in reverse until the call to that function (from the current stack
5822 @kindex reverse-finish
5823 @item reverse-finish
5824 Just as the @code{finish} command takes you to the point where the
5825 current function returns, @code{reverse-finish} takes you to the point
5826 where it was called. Instead of ending up at the end of the current
5827 function invocation, you end up at the beginning.
5829 @kindex set exec-direction
5830 @item set exec-direction
5831 Set the direction of target execution.
5832 @itemx set exec-direction reverse
5833 @cindex execute forward or backward in time
5834 @value{GDBN} will perform all execution commands in reverse, until the
5835 exec-direction mode is changed to ``forward''. Affected commands include
5836 @code{step, stepi, next, nexti, continue, and finish}. The @code{return}
5837 command cannot be used in reverse mode.
5838 @item set exec-direction forward
5839 @value{GDBN} will perform all execution commands in the normal fashion.
5840 This is the default.
5844 @node Process Record and Replay
5845 @chapter Recording Inferior's Execution and Replaying It
5846 @cindex process record and replay
5847 @cindex recording inferior's execution and replaying it
5849 On some platforms, @value{GDBN} provides a special @dfn{process record
5850 and replay} target that can record a log of the process execution, and
5851 replay it later with both forward and reverse execution commands.
5854 When this target is in use, if the execution log includes the record
5855 for the next instruction, @value{GDBN} will debug in @dfn{replay
5856 mode}. In the replay mode, the inferior does not really execute code
5857 instructions. Instead, all the events that normally happen during
5858 code execution are taken from the execution log. While code is not
5859 really executed in replay mode, the values of registers (including the
5860 program counter register) and the memory of the inferior are still
5861 changed as they normally would. Their contents are taken from the
5865 If the record for the next instruction is not in the execution log,
5866 @value{GDBN} will debug in @dfn{record mode}. In this mode, the
5867 inferior executes normally, and @value{GDBN} records the execution log
5870 The process record and replay target supports reverse execution
5871 (@pxref{Reverse Execution}), even if the platform on which the
5872 inferior runs does not. However, the reverse execution is limited in
5873 this case by the range of the instructions recorded in the execution
5874 log. In other words, reverse execution on platforms that don't
5875 support it directly can only be done in the replay mode.
5877 When debugging in the reverse direction, @value{GDBN} will work in
5878 replay mode as long as the execution log includes the record for the
5879 previous instruction; otherwise, it will work in record mode, if the
5880 platform supports reverse execution, or stop if not.
5882 For architecture environments that support process record and replay,
5883 @value{GDBN} provides the following commands:
5886 @kindex target record
5890 This command starts the process record and replay target. The process
5891 record and replay target can only debug a process that is already
5892 running. Therefore, you need first to start the process with the
5893 @kbd{run} or @kbd{start} commands, and then start the recording with
5894 the @kbd{target record} command.
5896 Both @code{record} and @code{rec} are aliases of @code{target record}.
5898 @cindex displaced stepping, and process record and replay
5899 Displaced stepping (@pxref{Maintenance Commands,, displaced stepping})
5900 will be automatically disabled when process record and replay target
5901 is started. That's because the process record and replay target
5902 doesn't support displaced stepping.
5904 @cindex non-stop mode, and process record and replay
5905 @cindex asynchronous execution, and process record and replay
5906 If the inferior is in the non-stop mode (@pxref{Non-Stop Mode}) or in
5907 the asynchronous execution mode (@pxref{Background Execution}), the
5908 process record and replay target cannot be started because it doesn't
5909 support these two modes.
5914 Stop the process record and replay target. When process record and
5915 replay target stops, the entire execution log will be deleted and the
5916 inferior will either be terminated, or will remain in its final state.
5918 When you stop the process record and replay target in record mode (at
5919 the end of the execution log), the inferior will be stopped at the
5920 next instruction that would have been recorded. In other words, if
5921 you record for a while and then stop recording, the inferior process
5922 will be left in the same state as if the recording never happened.
5924 On the other hand, if the process record and replay target is stopped
5925 while in replay mode (that is, not at the end of the execution log,
5926 but at some earlier point), the inferior process will become ``live''
5927 at that earlier state, and it will then be possible to continue the
5928 usual ``live'' debugging of the process from that state.
5930 When the inferior process exits, or @value{GDBN} detaches from it,
5931 process record and replay target will automatically stop itself.
5934 @item record save @var{filename}
5935 Save the execution log to a file @file{@var{filename}}.
5936 Default filename is @file{gdb_record.@var{process_id}}, where
5937 @var{process_id} is the process ID of the inferior.
5939 @kindex record restore
5940 @item record restore @var{filename}
5941 Restore the execution log from a file @file{@var{filename}}.
5942 File must have been created with @code{record save}.
5944 @kindex set record insn-number-max
5945 @item set record insn-number-max @var{limit}
5946 Set the limit of instructions to be recorded. Default value is 200000.
5948 If @var{limit} is a positive number, then @value{GDBN} will start
5949 deleting instructions from the log once the number of the record
5950 instructions becomes greater than @var{limit}. For every new recorded
5951 instruction, @value{GDBN} will delete the earliest recorded
5952 instruction to keep the number of recorded instructions at the limit.
5953 (Since deleting recorded instructions loses information, @value{GDBN}
5954 lets you control what happens when the limit is reached, by means of
5955 the @code{stop-at-limit} option, described below.)
5957 If @var{limit} is zero, @value{GDBN} will never delete recorded
5958 instructions from the execution log. The number of recorded
5959 instructions is unlimited in this case.
5961 @kindex show record insn-number-max
5962 @item show record insn-number-max
5963 Show the limit of instructions to be recorded.
5965 @kindex set record stop-at-limit
5966 @item set record stop-at-limit
5967 Control the behavior when the number of recorded instructions reaches
5968 the limit. If ON (the default), @value{GDBN} will stop when the limit
5969 is reached for the first time and ask you whether you want to stop the
5970 inferior or continue running it and recording the execution log. If
5971 you decide to continue recording, each new recorded instruction will
5972 cause the oldest one to be deleted.
5974 If this option is OFF, @value{GDBN} will automatically delete the
5975 oldest record to make room for each new one, without asking.
5977 @kindex show record stop-at-limit
5978 @item show record stop-at-limit
5979 Show the current setting of @code{stop-at-limit}.
5981 @kindex set record memory-query
5982 @item set record memory-query
5983 Control the behavior when @value{GDBN} is unable to record memory
5984 changes caused by an instruction. If ON, @value{GDBN} will query
5985 whether to stop the inferior in that case.
5987 If this option is OFF (the default), @value{GDBN} will automatically
5988 ignore the effect of such instructions on memory. Later, when
5989 @value{GDBN} replays this execution log, it will mark the log of this
5990 instruction as not accessible, and it will not affect the replay
5993 @kindex show record memory-query
5994 @item show record memory-query
5995 Show the current setting of @code{memory-query}.
5999 Show various statistics about the state of process record and its
6000 in-memory execution log buffer, including:
6004 Whether in record mode or replay mode.
6006 Lowest recorded instruction number (counting from when the current execution log started recording instructions).
6008 Highest recorded instruction number.
6010 Current instruction about to be replayed (if in replay mode).
6012 Number of instructions contained in the execution log.
6014 Maximum number of instructions that may be contained in the execution log.
6017 @kindex record delete
6020 When record target runs in replay mode (``in the past''), delete the
6021 subsequent execution log and begin to record a new execution log starting
6022 from the current address. This means you will abandon the previously
6023 recorded ``future'' and begin recording a new ``future''.
6028 @chapter Examining the Stack
6030 When your program has stopped, the first thing you need to know is where it
6031 stopped and how it got there.
6034 Each time your program performs a function call, information about the call
6036 That information includes the location of the call in your program,
6037 the arguments of the call,
6038 and the local variables of the function being called.
6039 The information is saved in a block of data called a @dfn{stack frame}.
6040 The stack frames are allocated in a region of memory called the @dfn{call
6043 When your program stops, the @value{GDBN} commands for examining the
6044 stack allow you to see all of this information.
6046 @cindex selected frame
6047 One of the stack frames is @dfn{selected} by @value{GDBN} and many
6048 @value{GDBN} commands refer implicitly to the selected frame. In
6049 particular, whenever you ask @value{GDBN} for the value of a variable in
6050 your program, the value is found in the selected frame. There are
6051 special @value{GDBN} commands to select whichever frame you are
6052 interested in. @xref{Selection, ,Selecting a Frame}.
6054 When your program stops, @value{GDBN} automatically selects the
6055 currently executing frame and describes it briefly, similar to the
6056 @code{frame} command (@pxref{Frame Info, ,Information about a Frame}).
6059 * Frames:: Stack frames
6060 * Backtrace:: Backtraces
6061 * Selection:: Selecting a frame
6062 * Frame Info:: Information on a frame
6067 @section Stack Frames
6069 @cindex frame, definition
6071 The call stack is divided up into contiguous pieces called @dfn{stack
6072 frames}, or @dfn{frames} for short; each frame is the data associated
6073 with one call to one function. The frame contains the arguments given
6074 to the function, the function's local variables, and the address at
6075 which the function is executing.
6077 @cindex initial frame
6078 @cindex outermost frame
6079 @cindex innermost frame
6080 When your program is started, the stack has only one frame, that of the
6081 function @code{main}. This is called the @dfn{initial} frame or the
6082 @dfn{outermost} frame. Each time a function is called, a new frame is
6083 made. Each time a function returns, the frame for that function invocation
6084 is eliminated. If a function is recursive, there can be many frames for
6085 the same function. The frame for the function in which execution is
6086 actually occurring is called the @dfn{innermost} frame. This is the most
6087 recently created of all the stack frames that still exist.
6089 @cindex frame pointer
6090 Inside your program, stack frames are identified by their addresses. A
6091 stack frame consists of many bytes, each of which has its own address; each
6092 kind of computer has a convention for choosing one byte whose
6093 address serves as the address of the frame. Usually this address is kept
6094 in a register called the @dfn{frame pointer register}
6095 (@pxref{Registers, $fp}) while execution is going on in that frame.
6097 @cindex frame number
6098 @value{GDBN} assigns numbers to all existing stack frames, starting with
6099 zero for the innermost frame, one for the frame that called it,
6100 and so on upward. These numbers do not really exist in your program;
6101 they are assigned by @value{GDBN} to give you a way of designating stack
6102 frames in @value{GDBN} commands.
6104 @c The -fomit-frame-pointer below perennially causes hbox overflow
6105 @c underflow problems.
6106 @cindex frameless execution
6107 Some compilers provide a way to compile functions so that they operate
6108 without stack frames. (For example, the @value{NGCC} option
6110 @samp{-fomit-frame-pointer}
6112 generates functions without a frame.)
6113 This is occasionally done with heavily used library functions to save
6114 the frame setup time. @value{GDBN} has limited facilities for dealing
6115 with these function invocations. If the innermost function invocation
6116 has no stack frame, @value{GDBN} nevertheless regards it as though
6117 it had a separate frame, which is numbered zero as usual, allowing
6118 correct tracing of the function call chain. However, @value{GDBN} has
6119 no provision for frameless functions elsewhere in the stack.
6122 @kindex frame@r{, command}
6123 @cindex current stack frame
6124 @item frame @var{args}
6125 The @code{frame} command allows you to move from one stack frame to another,
6126 and to print the stack frame you select. @var{args} may be either the
6127 address of the frame or the stack frame number. Without an argument,
6128 @code{frame} prints the current stack frame.
6130 @kindex select-frame
6131 @cindex selecting frame silently
6133 The @code{select-frame} command allows you to move from one stack frame
6134 to another without printing the frame. This is the silent version of
6142 @cindex call stack traces
6143 A backtrace is a summary of how your program got where it is. It shows one
6144 line per frame, for many frames, starting with the currently executing
6145 frame (frame zero), followed by its caller (frame one), and on up the
6150 @kindex bt @r{(@code{backtrace})}
6153 Print a backtrace of the entire stack: one line per frame for all
6154 frames in the stack.
6156 You can stop the backtrace at any time by typing the system interrupt
6157 character, normally @kbd{Ctrl-c}.
6159 @item backtrace @var{n}
6161 Similar, but print only the innermost @var{n} frames.
6163 @item backtrace -@var{n}
6165 Similar, but print only the outermost @var{n} frames.
6167 @item backtrace full
6169 @itemx bt full @var{n}
6170 @itemx bt full -@var{n}
6171 Print the values of the local variables also. @var{n} specifies the
6172 number of frames to print, as described above.
6177 The names @code{where} and @code{info stack} (abbreviated @code{info s})
6178 are additional aliases for @code{backtrace}.
6180 @cindex multiple threads, backtrace
6181 In a multi-threaded program, @value{GDBN} by default shows the
6182 backtrace only for the current thread. To display the backtrace for
6183 several or all of the threads, use the command @code{thread apply}
6184 (@pxref{Threads, thread apply}). For example, if you type @kbd{thread
6185 apply all backtrace}, @value{GDBN} will display the backtrace for all
6186 the threads; this is handy when you debug a core dump of a
6187 multi-threaded program.
6189 Each line in the backtrace shows the frame number and the function name.
6190 The program counter value is also shown---unless you use @code{set
6191 print address off}. The backtrace also shows the source file name and
6192 line number, as well as the arguments to the function. The program
6193 counter value is omitted if it is at the beginning of the code for that
6196 Here is an example of a backtrace. It was made with the command
6197 @samp{bt 3}, so it shows the innermost three frames.
6201 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
6203 #1 0x6e38 in expand_macro (sym=0x2b600, data=...) at macro.c:242
6204 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
6206 (More stack frames follow...)
6211 The display for frame zero does not begin with a program counter
6212 value, indicating that your program has stopped at the beginning of the
6213 code for line @code{993} of @code{builtin.c}.
6216 The value of parameter @code{data} in frame 1 has been replaced by
6217 @code{@dots{}}. By default, @value{GDBN} prints the value of a parameter
6218 only if it is a scalar (integer, pointer, enumeration, etc). See command
6219 @kbd{set print frame-arguments} in @ref{Print Settings} for more details
6220 on how to configure the way function parameter values are printed.
6222 @cindex optimized out, in backtrace
6223 @cindex function call arguments, optimized out
6224 If your program was compiled with optimizations, some compilers will
6225 optimize away arguments passed to functions if those arguments are
6226 never used after the call. Such optimizations generate code that
6227 passes arguments through registers, but doesn't store those arguments
6228 in the stack frame. @value{GDBN} has no way of displaying such
6229 arguments in stack frames other than the innermost one. Here's what
6230 such a backtrace might look like:
6234 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
6236 #1 0x6e38 in expand_macro (sym=<optimized out>) at macro.c:242
6237 #2 0x6840 in expand_token (obs=0x0, t=<optimized out>, td=0xf7fffb08)
6239 (More stack frames follow...)
6244 The values of arguments that were not saved in their stack frames are
6245 shown as @samp{<optimized out>}.
6247 If you need to display the values of such optimized-out arguments,
6248 either deduce that from other variables whose values depend on the one
6249 you are interested in, or recompile without optimizations.
6251 @cindex backtrace beyond @code{main} function
6252 @cindex program entry point
6253 @cindex startup code, and backtrace
6254 Most programs have a standard user entry point---a place where system
6255 libraries and startup code transition into user code. For C this is
6256 @code{main}@footnote{
6257 Note that embedded programs (the so-called ``free-standing''
6258 environment) are not required to have a @code{main} function as the
6259 entry point. They could even have multiple entry points.}.
6260 When @value{GDBN} finds the entry function in a backtrace
6261 it will terminate the backtrace, to avoid tracing into highly
6262 system-specific (and generally uninteresting) code.
6264 If you need to examine the startup code, or limit the number of levels
6265 in a backtrace, you can change this behavior:
6268 @item set backtrace past-main
6269 @itemx set backtrace past-main on
6270 @kindex set backtrace
6271 Backtraces will continue past the user entry point.
6273 @item set backtrace past-main off
6274 Backtraces will stop when they encounter the user entry point. This is the
6277 @item show backtrace past-main
6278 @kindex show backtrace
6279 Display the current user entry point backtrace policy.
6281 @item set backtrace past-entry
6282 @itemx set backtrace past-entry on
6283 Backtraces will continue past the internal entry point of an application.
6284 This entry point is encoded by the linker when the application is built,
6285 and is likely before the user entry point @code{main} (or equivalent) is called.
6287 @item set backtrace past-entry off
6288 Backtraces will stop when they encounter the internal entry point of an
6289 application. This is the default.
6291 @item show backtrace past-entry
6292 Display the current internal entry point backtrace policy.
6294 @item set backtrace limit @var{n}
6295 @itemx set backtrace limit 0
6296 @cindex backtrace limit
6297 Limit the backtrace to @var{n} levels. A value of zero means
6300 @item show backtrace limit
6301 Display the current limit on backtrace levels.
6305 @section Selecting a Frame
6307 Most commands for examining the stack and other data in your program work on
6308 whichever stack frame is selected at the moment. Here are the commands for
6309 selecting a stack frame; all of them finish by printing a brief description
6310 of the stack frame just selected.
6313 @kindex frame@r{, selecting}
6314 @kindex f @r{(@code{frame})}
6317 Select frame number @var{n}. Recall that frame zero is the innermost
6318 (currently executing) frame, frame one is the frame that called the
6319 innermost one, and so on. The highest-numbered frame is the one for
6322 @item frame @var{addr}
6324 Select the frame at address @var{addr}. This is useful mainly if the
6325 chaining of stack frames has been damaged by a bug, making it
6326 impossible for @value{GDBN} to assign numbers properly to all frames. In
6327 addition, this can be useful when your program has multiple stacks and
6328 switches between them.
6330 On the SPARC architecture, @code{frame} needs two addresses to
6331 select an arbitrary frame: a frame pointer and a stack pointer.
6333 On the MIPS and Alpha architecture, it needs two addresses: a stack
6334 pointer and a program counter.
6336 On the 29k architecture, it needs three addresses: a register stack
6337 pointer, a program counter, and a memory stack pointer.
6341 Move @var{n} frames up the stack. For positive numbers @var{n}, this
6342 advances toward the outermost frame, to higher frame numbers, to frames
6343 that have existed longer. @var{n} defaults to one.
6346 @kindex do @r{(@code{down})}
6348 Move @var{n} frames down the stack. For positive numbers @var{n}, this
6349 advances toward the innermost frame, to lower frame numbers, to frames
6350 that were created more recently. @var{n} defaults to one. You may
6351 abbreviate @code{down} as @code{do}.
6354 All of these commands end by printing two lines of output describing the
6355 frame. The first line shows the frame number, the function name, the
6356 arguments, and the source file and line number of execution in that
6357 frame. The second line shows the text of that source line.
6365 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
6367 10 read_input_file (argv[i]);
6371 After such a printout, the @code{list} command with no arguments
6372 prints ten lines centered on the point of execution in the frame.
6373 You can also edit the program at the point of execution with your favorite
6374 editing program by typing @code{edit}.
6375 @xref{List, ,Printing Source Lines},
6379 @kindex down-silently
6381 @item up-silently @var{n}
6382 @itemx down-silently @var{n}
6383 These two commands are variants of @code{up} and @code{down},
6384 respectively; they differ in that they do their work silently, without
6385 causing display of the new frame. They are intended primarily for use
6386 in @value{GDBN} command scripts, where the output might be unnecessary and
6391 @section Information About a Frame
6393 There are several other commands to print information about the selected
6399 When used without any argument, this command does not change which
6400 frame is selected, but prints a brief description of the currently
6401 selected stack frame. It can be abbreviated @code{f}. With an
6402 argument, this command is used to select a stack frame.
6403 @xref{Selection, ,Selecting a Frame}.
6406 @kindex info f @r{(@code{info frame})}
6409 This command prints a verbose description of the selected stack frame,
6414 the address of the frame
6416 the address of the next frame down (called by this frame)
6418 the address of the next frame up (caller of this frame)
6420 the language in which the source code corresponding to this frame is written
6422 the address of the frame's arguments
6424 the address of the frame's local variables
6426 the program counter saved in it (the address of execution in the caller frame)
6428 which registers were saved in the frame
6431 @noindent The verbose description is useful when
6432 something has gone wrong that has made the stack format fail to fit
6433 the usual conventions.
6435 @item info frame @var{addr}
6436 @itemx info f @var{addr}
6437 Print a verbose description of the frame at address @var{addr}, without
6438 selecting that frame. The selected frame remains unchanged by this
6439 command. This requires the same kind of address (more than one for some
6440 architectures) that you specify in the @code{frame} command.
6441 @xref{Selection, ,Selecting a Frame}.
6445 Print the arguments of the selected frame, each on a separate line.
6449 Print the local variables of the selected frame, each on a separate
6450 line. These are all variables (declared either static or automatic)
6451 accessible at the point of execution of the selected frame.
6457 @chapter Examining Source Files
6459 @value{GDBN} can print parts of your program's source, since the debugging
6460 information recorded in the program tells @value{GDBN} what source files were
6461 used to build it. When your program stops, @value{GDBN} spontaneously prints
6462 the line where it stopped. Likewise, when you select a stack frame
6463 (@pxref{Selection, ,Selecting a Frame}), @value{GDBN} prints the line where
6464 execution in that frame has stopped. You can print other portions of
6465 source files by explicit command.
6467 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
6468 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
6469 @value{GDBN} under @sc{gnu} Emacs}.
6472 * List:: Printing source lines
6473 * Specify Location:: How to specify code locations
6474 * Edit:: Editing source files
6475 * Search:: Searching source files
6476 * Source Path:: Specifying source directories
6477 * Machine Code:: Source and machine code
6481 @section Printing Source Lines
6484 @kindex l @r{(@code{list})}
6485 To print lines from a source file, use the @code{list} command
6486 (abbreviated @code{l}). By default, ten lines are printed.
6487 There are several ways to specify what part of the file you want to
6488 print; see @ref{Specify Location}, for the full list.
6490 Here are the forms of the @code{list} command most commonly used:
6493 @item list @var{linenum}
6494 Print lines centered around line number @var{linenum} in the
6495 current source file.
6497 @item list @var{function}
6498 Print lines centered around the beginning of function
6502 Print more lines. If the last lines printed were printed with a
6503 @code{list} command, this prints lines following the last lines
6504 printed; however, if the last line printed was a solitary line printed
6505 as part of displaying a stack frame (@pxref{Stack, ,Examining the
6506 Stack}), this prints lines centered around that line.
6509 Print lines just before the lines last printed.
6512 @cindex @code{list}, how many lines to display
6513 By default, @value{GDBN} prints ten source lines with any of these forms of
6514 the @code{list} command. You can change this using @code{set listsize}:
6517 @kindex set listsize
6518 @item set listsize @var{count}
6519 Make the @code{list} command display @var{count} source lines (unless
6520 the @code{list} argument explicitly specifies some other number).
6522 @kindex show listsize
6524 Display the number of lines that @code{list} prints.
6527 Repeating a @code{list} command with @key{RET} discards the argument,
6528 so it is equivalent to typing just @code{list}. This is more useful
6529 than listing the same lines again. An exception is made for an
6530 argument of @samp{-}; that argument is preserved in repetition so that
6531 each repetition moves up in the source file.
6533 In general, the @code{list} command expects you to supply zero, one or two
6534 @dfn{linespecs}. Linespecs specify source lines; there are several ways
6535 of writing them (@pxref{Specify Location}), but the effect is always
6536 to specify some source line.
6538 Here is a complete description of the possible arguments for @code{list}:
6541 @item list @var{linespec}
6542 Print lines centered around the line specified by @var{linespec}.
6544 @item list @var{first},@var{last}
6545 Print lines from @var{first} to @var{last}. Both arguments are
6546 linespecs. When a @code{list} command has two linespecs, and the
6547 source file of the second linespec is omitted, this refers to
6548 the same source file as the first linespec.
6550 @item list ,@var{last}
6551 Print lines ending with @var{last}.
6553 @item list @var{first},
6554 Print lines starting with @var{first}.
6557 Print lines just after the lines last printed.
6560 Print lines just before the lines last printed.
6563 As described in the preceding table.
6566 @node Specify Location
6567 @section Specifying a Location
6568 @cindex specifying location
6571 Several @value{GDBN} commands accept arguments that specify a location
6572 of your program's code. Since @value{GDBN} is a source-level
6573 debugger, a location usually specifies some line in the source code;
6574 for that reason, locations are also known as @dfn{linespecs}.
6576 Here are all the different ways of specifying a code location that
6577 @value{GDBN} understands:
6581 Specifies the line number @var{linenum} of the current source file.
6584 @itemx +@var{offset}
6585 Specifies the line @var{offset} lines before or after the @dfn{current
6586 line}. For the @code{list} command, the current line is the last one
6587 printed; for the breakpoint commands, this is the line at which
6588 execution stopped in the currently selected @dfn{stack frame}
6589 (@pxref{Frames, ,Frames}, for a description of stack frames.) When
6590 used as the second of the two linespecs in a @code{list} command,
6591 this specifies the line @var{offset} lines up or down from the first
6594 @item @var{filename}:@var{linenum}
6595 Specifies the line @var{linenum} in the source file @var{filename}.
6596 If @var{filename} is a relative file name, then it will match any
6597 source file name with the same trailing components. For example, if
6598 @var{filename} is @samp{gcc/expr.c}, then it will match source file
6599 name of @file{/build/trunk/gcc/expr.c}, but not
6600 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
6602 @item @var{function}
6603 Specifies the line that begins the body of the function @var{function}.
6604 For example, in C, this is the line with the open brace.
6606 @item @var{function}:@var{label}
6607 Specifies the line where @var{label} appears in @var{function}.
6609 @item @var{filename}:@var{function}
6610 Specifies the line that begins the body of the function @var{function}
6611 in the file @var{filename}. You only need the file name with a
6612 function name to avoid ambiguity when there are identically named
6613 functions in different source files.
6616 Specifies the line at which the label named @var{label} appears.
6617 @value{GDBN} searches for the label in the function corresponding to
6618 the currently selected stack frame. If there is no current selected
6619 stack frame (for instance, if the inferior is not running), then
6620 @value{GDBN} will not search for a label.
6622 @item *@var{address}
6623 Specifies the program address @var{address}. For line-oriented
6624 commands, such as @code{list} and @code{edit}, this specifies a source
6625 line that contains @var{address}. For @code{break} and other
6626 breakpoint oriented commands, this can be used to set breakpoints in
6627 parts of your program which do not have debugging information or
6630 Here @var{address} may be any expression valid in the current working
6631 language (@pxref{Languages, working language}) that specifies a code
6632 address. In addition, as a convenience, @value{GDBN} extends the
6633 semantics of expressions used in locations to cover the situations
6634 that frequently happen during debugging. Here are the various forms
6638 @item @var{expression}
6639 Any expression valid in the current working language.
6641 @item @var{funcaddr}
6642 An address of a function or procedure derived from its name. In C,
6643 C@t{++}, Java, Objective-C, Fortran, minimal, and assembly, this is
6644 simply the function's name @var{function} (and actually a special case
6645 of a valid expression). In Pascal and Modula-2, this is
6646 @code{&@var{function}}. In Ada, this is @code{@var{function}'Address}
6647 (although the Pascal form also works).
6649 This form specifies the address of the function's first instruction,
6650 before the stack frame and arguments have been set up.
6652 @item '@var{filename}'::@var{funcaddr}
6653 Like @var{funcaddr} above, but also specifies the name of the source
6654 file explicitly. This is useful if the name of the function does not
6655 specify the function unambiguously, e.g., if there are several
6656 functions with identical names in different source files.
6663 @section Editing Source Files
6664 @cindex editing source files
6667 @kindex e @r{(@code{edit})}
6668 To edit the lines in a source file, use the @code{edit} command.
6669 The editing program of your choice
6670 is invoked with the current line set to
6671 the active line in the program.
6672 Alternatively, there are several ways to specify what part of the file you
6673 want to print if you want to see other parts of the program:
6676 @item edit @var{location}
6677 Edit the source file specified by @code{location}. Editing starts at
6678 that @var{location}, e.g., at the specified source line of the
6679 specified file. @xref{Specify Location}, for all the possible forms
6680 of the @var{location} argument; here are the forms of the @code{edit}
6681 command most commonly used:
6684 @item edit @var{number}
6685 Edit the current source file with @var{number} as the active line number.
6687 @item edit @var{function}
6688 Edit the file containing @var{function} at the beginning of its definition.
6693 @subsection Choosing your Editor
6694 You can customize @value{GDBN} to use any editor you want
6696 The only restriction is that your editor (say @code{ex}), recognizes the
6697 following command-line syntax:
6699 ex +@var{number} file
6701 The optional numeric value +@var{number} specifies the number of the line in
6702 the file where to start editing.}.
6703 By default, it is @file{@value{EDITOR}}, but you can change this
6704 by setting the environment variable @code{EDITOR} before using
6705 @value{GDBN}. For example, to configure @value{GDBN} to use the
6706 @code{vi} editor, you could use these commands with the @code{sh} shell:
6712 or in the @code{csh} shell,
6714 setenv EDITOR /usr/bin/vi
6719 @section Searching Source Files
6720 @cindex searching source files
6722 There are two commands for searching through the current source file for a
6727 @kindex forward-search
6728 @item forward-search @var{regexp}
6729 @itemx search @var{regexp}
6730 The command @samp{forward-search @var{regexp}} checks each line,
6731 starting with the one following the last line listed, for a match for
6732 @var{regexp}. It lists the line that is found. You can use the
6733 synonym @samp{search @var{regexp}} or abbreviate the command name as
6736 @kindex reverse-search
6737 @item reverse-search @var{regexp}
6738 The command @samp{reverse-search @var{regexp}} checks each line, starting
6739 with the one before the last line listed and going backward, for a match
6740 for @var{regexp}. It lists the line that is found. You can abbreviate
6741 this command as @code{rev}.
6745 @section Specifying Source Directories
6748 @cindex directories for source files
6749 Executable programs sometimes do not record the directories of the source
6750 files from which they were compiled, just the names. Even when they do,
6751 the directories could be moved between the compilation and your debugging
6752 session. @value{GDBN} has a list of directories to search for source files;
6753 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
6754 it tries all the directories in the list, in the order they are present
6755 in the list, until it finds a file with the desired name.
6757 For example, suppose an executable references the file
6758 @file{/usr/src/foo-1.0/lib/foo.c}, and our source path is
6759 @file{/mnt/cross}. The file is first looked up literally; if this
6760 fails, @file{/mnt/cross/usr/src/foo-1.0/lib/foo.c} is tried; if this
6761 fails, @file{/mnt/cross/foo.c} is opened; if this fails, an error
6762 message is printed. @value{GDBN} does not look up the parts of the
6763 source file name, such as @file{/mnt/cross/src/foo-1.0/lib/foo.c}.
6764 Likewise, the subdirectories of the source path are not searched: if
6765 the source path is @file{/mnt/cross}, and the binary refers to
6766 @file{foo.c}, @value{GDBN} would not find it under
6767 @file{/mnt/cross/usr/src/foo-1.0/lib}.
6769 Plain file names, relative file names with leading directories, file
6770 names containing dots, etc.@: are all treated as described above; for
6771 instance, if the source path is @file{/mnt/cross}, and the source file
6772 is recorded as @file{../lib/foo.c}, @value{GDBN} would first try
6773 @file{../lib/foo.c}, then @file{/mnt/cross/../lib/foo.c}, and after
6774 that---@file{/mnt/cross/foo.c}.
6776 Note that the executable search path is @emph{not} used to locate the
6779 Whenever you reset or rearrange the source path, @value{GDBN} clears out
6780 any information it has cached about where source files are found and where
6781 each line is in the file.
6785 When you start @value{GDBN}, its source path includes only @samp{cdir}
6786 and @samp{cwd}, in that order.
6787 To add other directories, use the @code{directory} command.
6789 The search path is used to find both program source files and @value{GDBN}
6790 script files (read using the @samp{-command} option and @samp{source} command).
6792 In addition to the source path, @value{GDBN} provides a set of commands
6793 that manage a list of source path substitution rules. A @dfn{substitution
6794 rule} specifies how to rewrite source directories stored in the program's
6795 debug information in case the sources were moved to a different
6796 directory between compilation and debugging. A rule is made of
6797 two strings, the first specifying what needs to be rewritten in
6798 the path, and the second specifying how it should be rewritten.
6799 In @ref{set substitute-path}, we name these two parts @var{from} and
6800 @var{to} respectively. @value{GDBN} does a simple string replacement
6801 of @var{from} with @var{to} at the start of the directory part of the
6802 source file name, and uses that result instead of the original file
6803 name to look up the sources.
6805 Using the previous example, suppose the @file{foo-1.0} tree has been
6806 moved from @file{/usr/src} to @file{/mnt/cross}, then you can tell
6807 @value{GDBN} to replace @file{/usr/src} in all source path names with
6808 @file{/mnt/cross}. The first lookup will then be
6809 @file{/mnt/cross/foo-1.0/lib/foo.c} in place of the original location
6810 of @file{/usr/src/foo-1.0/lib/foo.c}. To define a source path
6811 substitution rule, use the @code{set substitute-path} command
6812 (@pxref{set substitute-path}).
6814 To avoid unexpected substitution results, a rule is applied only if the
6815 @var{from} part of the directory name ends at a directory separator.
6816 For instance, a rule substituting @file{/usr/source} into
6817 @file{/mnt/cross} will be applied to @file{/usr/source/foo-1.0} but
6818 not to @file{/usr/sourceware/foo-2.0}. And because the substitution
6819 is applied only at the beginning of the directory name, this rule will
6820 not be applied to @file{/root/usr/source/baz.c} either.
6822 In many cases, you can achieve the same result using the @code{directory}
6823 command. However, @code{set substitute-path} can be more efficient in
6824 the case where the sources are organized in a complex tree with multiple
6825 subdirectories. With the @code{directory} command, you need to add each
6826 subdirectory of your project. If you moved the entire tree while
6827 preserving its internal organization, then @code{set substitute-path}
6828 allows you to direct the debugger to all the sources with one single
6831 @code{set substitute-path} is also more than just a shortcut command.
6832 The source path is only used if the file at the original location no
6833 longer exists. On the other hand, @code{set substitute-path} modifies
6834 the debugger behavior to look at the rewritten location instead. So, if
6835 for any reason a source file that is not relevant to your executable is
6836 located at the original location, a substitution rule is the only
6837 method available to point @value{GDBN} at the new location.
6839 @cindex @samp{--with-relocated-sources}
6840 @cindex default source path substitution
6841 You can configure a default source path substitution rule by
6842 configuring @value{GDBN} with the
6843 @samp{--with-relocated-sources=@var{dir}} option. The @var{dir}
6844 should be the name of a directory under @value{GDBN}'s configured
6845 prefix (set with @samp{--prefix} or @samp{--exec-prefix}), and
6846 directory names in debug information under @var{dir} will be adjusted
6847 automatically if the installed @value{GDBN} is moved to a new
6848 location. This is useful if @value{GDBN}, libraries or executables
6849 with debug information and corresponding source code are being moved
6853 @item directory @var{dirname} @dots{}
6854 @item dir @var{dirname} @dots{}
6855 Add directory @var{dirname} to the front of the source path. Several
6856 directory names may be given to this command, separated by @samp{:}
6857 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
6858 part of absolute file names) or
6859 whitespace. You may specify a directory that is already in the source
6860 path; this moves it forward, so @value{GDBN} searches it sooner.
6864 @vindex $cdir@r{, convenience variable}
6865 @vindex $cwd@r{, convenience variable}
6866 @cindex compilation directory
6867 @cindex current directory
6868 @cindex working directory
6869 @cindex directory, current
6870 @cindex directory, compilation
6871 You can use the string @samp{$cdir} to refer to the compilation
6872 directory (if one is recorded), and @samp{$cwd} to refer to the current
6873 working directory. @samp{$cwd} is not the same as @samp{.}---the former
6874 tracks the current working directory as it changes during your @value{GDBN}
6875 session, while the latter is immediately expanded to the current
6876 directory at the time you add an entry to the source path.
6879 Reset the source path to its default value (@samp{$cdir:$cwd} on Unix systems). This requires confirmation.
6881 @c RET-repeat for @code{directory} is explicitly disabled, but since
6882 @c repeating it would be a no-op we do not say that. (thanks to RMS)
6884 @item set directories @var{path-list}
6885 @kindex set directories
6886 Set the source path to @var{path-list}.
6887 @samp{$cdir:$cwd} are added if missing.
6889 @item show directories
6890 @kindex show directories
6891 Print the source path: show which directories it contains.
6893 @anchor{set substitute-path}
6894 @item set substitute-path @var{from} @var{to}
6895 @kindex set substitute-path
6896 Define a source path substitution rule, and add it at the end of the
6897 current list of existing substitution rules. If a rule with the same
6898 @var{from} was already defined, then the old rule is also deleted.
6900 For example, if the file @file{/foo/bar/baz.c} was moved to
6901 @file{/mnt/cross/baz.c}, then the command
6904 (@value{GDBP}) set substitute-path /usr/src /mnt/cross
6908 will tell @value{GDBN} to replace @samp{/usr/src} with
6909 @samp{/mnt/cross}, which will allow @value{GDBN} to find the file
6910 @file{baz.c} even though it was moved.
6912 In the case when more than one substitution rule have been defined,
6913 the rules are evaluated one by one in the order where they have been
6914 defined. The first one matching, if any, is selected to perform
6917 For instance, if we had entered the following commands:
6920 (@value{GDBP}) set substitute-path /usr/src/include /mnt/include
6921 (@value{GDBP}) set substitute-path /usr/src /mnt/src
6925 @value{GDBN} would then rewrite @file{/usr/src/include/defs.h} into
6926 @file{/mnt/include/defs.h} by using the first rule. However, it would
6927 use the second rule to rewrite @file{/usr/src/lib/foo.c} into
6928 @file{/mnt/src/lib/foo.c}.
6931 @item unset substitute-path [path]
6932 @kindex unset substitute-path
6933 If a path is specified, search the current list of substitution rules
6934 for a rule that would rewrite that path. Delete that rule if found.
6935 A warning is emitted by the debugger if no rule could be found.
6937 If no path is specified, then all substitution rules are deleted.
6939 @item show substitute-path [path]
6940 @kindex show substitute-path
6941 If a path is specified, then print the source path substitution rule
6942 which would rewrite that path, if any.
6944 If no path is specified, then print all existing source path substitution
6949 If your source path is cluttered with directories that are no longer of
6950 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
6951 versions of source. You can correct the situation as follows:
6955 Use @code{directory} with no argument to reset the source path to its default value.
6958 Use @code{directory} with suitable arguments to reinstall the
6959 directories you want in the source path. You can add all the
6960 directories in one command.
6964 @section Source and Machine Code
6965 @cindex source line and its code address
6967 You can use the command @code{info line} to map source lines to program
6968 addresses (and vice versa), and the command @code{disassemble} to display
6969 a range of addresses as machine instructions. You can use the command
6970 @code{set disassemble-next-line} to set whether to disassemble next
6971 source line when execution stops. When run under @sc{gnu} Emacs
6972 mode, the @code{info line} command causes the arrow to point to the
6973 line specified. Also, @code{info line} prints addresses in symbolic form as
6978 @item info line @var{linespec}
6979 Print the starting and ending addresses of the compiled code for
6980 source line @var{linespec}. You can specify source lines in any of
6981 the ways documented in @ref{Specify Location}.
6984 For example, we can use @code{info line} to discover the location of
6985 the object code for the first line of function
6986 @code{m4_changequote}:
6988 @c FIXME: I think this example should also show the addresses in
6989 @c symbolic form, as they usually would be displayed.
6991 (@value{GDBP}) info line m4_changequote
6992 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
6996 @cindex code address and its source line
6997 We can also inquire (using @code{*@var{addr}} as the form for
6998 @var{linespec}) what source line covers a particular address:
7000 (@value{GDBP}) info line *0x63ff
7001 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
7004 @cindex @code{$_} and @code{info line}
7005 @cindex @code{x} command, default address
7006 @kindex x@r{(examine), and} info line
7007 After @code{info line}, the default address for the @code{x} command
7008 is changed to the starting address of the line, so that @samp{x/i} is
7009 sufficient to begin examining the machine code (@pxref{Memory,
7010 ,Examining Memory}). Also, this address is saved as the value of the
7011 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
7016 @cindex assembly instructions
7017 @cindex instructions, assembly
7018 @cindex machine instructions
7019 @cindex listing machine instructions
7021 @itemx disassemble /m
7022 @itemx disassemble /r
7023 This specialized command dumps a range of memory as machine
7024 instructions. It can also print mixed source+disassembly by specifying
7025 the @code{/m} modifier and print the raw instructions in hex as well as
7026 in symbolic form by specifying the @code{/r}.
7027 The default memory range is the function surrounding the
7028 program counter of the selected frame. A single argument to this
7029 command is a program counter value; @value{GDBN} dumps the function
7030 surrounding this value. When two arguments are given, they should
7031 be separated by a comma, possibly surrounded by whitespace. The
7032 arguments specify a range of addresses to dump, in one of two forms:
7035 @item @var{start},@var{end}
7036 the addresses from @var{start} (inclusive) to @var{end} (exclusive)
7037 @item @var{start},+@var{length}
7038 the addresses from @var{start} (inclusive) to
7039 @code{@var{start}+@var{length}} (exclusive).
7043 When 2 arguments are specified, the name of the function is also
7044 printed (since there could be several functions in the given range).
7046 The argument(s) can be any expression yielding a numeric value, such as
7047 @samp{0x32c4}, @samp{&main+10} or @samp{$pc - 8}.
7049 If the range of memory being disassembled contains current program counter,
7050 the instruction at that location is shown with a @code{=>} marker.
7053 The following example shows the disassembly of a range of addresses of
7054 HP PA-RISC 2.0 code:
7057 (@value{GDBP}) disas 0x32c4, 0x32e4
7058 Dump of assembler code from 0x32c4 to 0x32e4:
7059 0x32c4 <main+204>: addil 0,dp
7060 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
7061 0x32cc <main+212>: ldil 0x3000,r31
7062 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
7063 0x32d4 <main+220>: ldo 0(r31),rp
7064 0x32d8 <main+224>: addil -0x800,dp
7065 0x32dc <main+228>: ldo 0x588(r1),r26
7066 0x32e0 <main+232>: ldil 0x3000,r31
7067 End of assembler dump.
7070 Here is an example showing mixed source+assembly for Intel x86, when the
7071 program is stopped just after function prologue:
7074 (@value{GDBP}) disas /m main
7075 Dump of assembler code for function main:
7077 0x08048330 <+0>: push %ebp
7078 0x08048331 <+1>: mov %esp,%ebp
7079 0x08048333 <+3>: sub $0x8,%esp
7080 0x08048336 <+6>: and $0xfffffff0,%esp
7081 0x08048339 <+9>: sub $0x10,%esp
7083 6 printf ("Hello.\n");
7084 => 0x0804833c <+12>: movl $0x8048440,(%esp)
7085 0x08048343 <+19>: call 0x8048284 <puts@@plt>
7089 0x08048348 <+24>: mov $0x0,%eax
7090 0x0804834d <+29>: leave
7091 0x0804834e <+30>: ret
7093 End of assembler dump.
7096 Here is another example showing raw instructions in hex for AMD x86-64,
7099 (gdb) disas /r 0x400281,+10
7100 Dump of assembler code from 0x400281 to 0x40028b:
7101 0x0000000000400281: 38 36 cmp %dh,(%rsi)
7102 0x0000000000400283: 2d 36 34 2e 73 sub $0x732e3436,%eax
7103 0x0000000000400288: 6f outsl %ds:(%rsi),(%dx)
7104 0x0000000000400289: 2e 32 00 xor %cs:(%rax),%al
7105 End of assembler dump.
7108 Some architectures have more than one commonly-used set of instruction
7109 mnemonics or other syntax.
7111 For programs that were dynamically linked and use shared libraries,
7112 instructions that call functions or branch to locations in the shared
7113 libraries might show a seemingly bogus location---it's actually a
7114 location of the relocation table. On some architectures, @value{GDBN}
7115 might be able to resolve these to actual function names.
7118 @kindex set disassembly-flavor
7119 @cindex Intel disassembly flavor
7120 @cindex AT&T disassembly flavor
7121 @item set disassembly-flavor @var{instruction-set}
7122 Select the instruction set to use when disassembling the
7123 program via the @code{disassemble} or @code{x/i} commands.
7125 Currently this command is only defined for the Intel x86 family. You
7126 can set @var{instruction-set} to either @code{intel} or @code{att}.
7127 The default is @code{att}, the AT&T flavor used by default by Unix
7128 assemblers for x86-based targets.
7130 @kindex show disassembly-flavor
7131 @item show disassembly-flavor
7132 Show the current setting of the disassembly flavor.
7136 @kindex set disassemble-next-line
7137 @kindex show disassemble-next-line
7138 @item set disassemble-next-line
7139 @itemx show disassemble-next-line
7140 Control whether or not @value{GDBN} will disassemble the next source
7141 line or instruction when execution stops. If ON, @value{GDBN} will
7142 display disassembly of the next source line when execution of the
7143 program being debugged stops. This is @emph{in addition} to
7144 displaying the source line itself, which @value{GDBN} always does if
7145 possible. If the next source line cannot be displayed for some reason
7146 (e.g., if @value{GDBN} cannot find the source file, or there's no line
7147 info in the debug info), @value{GDBN} will display disassembly of the
7148 next @emph{instruction} instead of showing the next source line. If
7149 AUTO, @value{GDBN} will display disassembly of next instruction only
7150 if the source line cannot be displayed. This setting causes
7151 @value{GDBN} to display some feedback when you step through a function
7152 with no line info or whose source file is unavailable. The default is
7153 OFF, which means never display the disassembly of the next line or
7159 @chapter Examining Data
7161 @cindex printing data
7162 @cindex examining data
7165 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
7166 @c document because it is nonstandard... Under Epoch it displays in a
7167 @c different window or something like that.
7168 The usual way to examine data in your program is with the @code{print}
7169 command (abbreviated @code{p}), or its synonym @code{inspect}. It
7170 evaluates and prints the value of an expression of the language your
7171 program is written in (@pxref{Languages, ,Using @value{GDBN} with
7172 Different Languages}). It may also print the expression using a
7173 Python-based pretty-printer (@pxref{Pretty Printing}).
7176 @item print @var{expr}
7177 @itemx print /@var{f} @var{expr}
7178 @var{expr} is an expression (in the source language). By default the
7179 value of @var{expr} is printed in a format appropriate to its data type;
7180 you can choose a different format by specifying @samp{/@var{f}}, where
7181 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
7185 @itemx print /@var{f}
7186 @cindex reprint the last value
7187 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
7188 @dfn{value history}; @pxref{Value History, ,Value History}). This allows you to
7189 conveniently inspect the same value in an alternative format.
7192 A more low-level way of examining data is with the @code{x} command.
7193 It examines data in memory at a specified address and prints it in a
7194 specified format. @xref{Memory, ,Examining Memory}.
7196 If you are interested in information about types, or about how the
7197 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
7198 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
7202 * Expressions:: Expressions
7203 * Ambiguous Expressions:: Ambiguous Expressions
7204 * Variables:: Program variables
7205 * Arrays:: Artificial arrays
7206 * Output Formats:: Output formats
7207 * Memory:: Examining memory
7208 * Auto Display:: Automatic display
7209 * Print Settings:: Print settings
7210 * Pretty Printing:: Python pretty printing
7211 * Value History:: Value history
7212 * Convenience Vars:: Convenience variables
7213 * Registers:: Registers
7214 * Floating Point Hardware:: Floating point hardware
7215 * Vector Unit:: Vector Unit
7216 * OS Information:: Auxiliary data provided by operating system
7217 * Memory Region Attributes:: Memory region attributes
7218 * Dump/Restore Files:: Copy between memory and a file
7219 * Core File Generation:: Cause a program dump its core
7220 * Character Sets:: Debugging programs that use a different
7221 character set than GDB does
7222 * Caching Remote Data:: Data caching for remote targets
7223 * Searching Memory:: Searching memory for a sequence of bytes
7227 @section Expressions
7230 @code{print} and many other @value{GDBN} commands accept an expression and
7231 compute its value. Any kind of constant, variable or operator defined
7232 by the programming language you are using is valid in an expression in
7233 @value{GDBN}. This includes conditional expressions, function calls,
7234 casts, and string constants. It also includes preprocessor macros, if
7235 you compiled your program to include this information; see
7238 @cindex arrays in expressions
7239 @value{GDBN} supports array constants in expressions input by
7240 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
7241 you can use the command @code{print @{1, 2, 3@}} to create an array
7242 of three integers. If you pass an array to a function or assign it
7243 to a program variable, @value{GDBN} copies the array to memory that
7244 is @code{malloc}ed in the target program.
7246 Because C is so widespread, most of the expressions shown in examples in
7247 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
7248 Languages}, for information on how to use expressions in other
7251 In this section, we discuss operators that you can use in @value{GDBN}
7252 expressions regardless of your programming language.
7254 @cindex casts, in expressions
7255 Casts are supported in all languages, not just in C, because it is so
7256 useful to cast a number into a pointer in order to examine a structure
7257 at that address in memory.
7258 @c FIXME: casts supported---Mod2 true?
7260 @value{GDBN} supports these operators, in addition to those common
7261 to programming languages:
7265 @samp{@@} is a binary operator for treating parts of memory as arrays.
7266 @xref{Arrays, ,Artificial Arrays}, for more information.
7269 @samp{::} allows you to specify a variable in terms of the file or
7270 function where it is defined. @xref{Variables, ,Program Variables}.
7272 @cindex @{@var{type}@}
7273 @cindex type casting memory
7274 @cindex memory, viewing as typed object
7275 @cindex casts, to view memory
7276 @item @{@var{type}@} @var{addr}
7277 Refers to an object of type @var{type} stored at address @var{addr} in
7278 memory. @var{addr} may be any expression whose value is an integer or
7279 pointer (but parentheses are required around binary operators, just as in
7280 a cast). This construct is allowed regardless of what kind of data is
7281 normally supposed to reside at @var{addr}.
7284 @node Ambiguous Expressions
7285 @section Ambiguous Expressions
7286 @cindex ambiguous expressions
7288 Expressions can sometimes contain some ambiguous elements. For instance,
7289 some programming languages (notably Ada, C@t{++} and Objective-C) permit
7290 a single function name to be defined several times, for application in
7291 different contexts. This is called @dfn{overloading}. Another example
7292 involving Ada is generics. A @dfn{generic package} is similar to C@t{++}
7293 templates and is typically instantiated several times, resulting in
7294 the same function name being defined in different contexts.
7296 In some cases and depending on the language, it is possible to adjust
7297 the expression to remove the ambiguity. For instance in C@t{++}, you
7298 can specify the signature of the function you want to break on, as in
7299 @kbd{break @var{function}(@var{types})}. In Ada, using the fully
7300 qualified name of your function often makes the expression unambiguous
7303 When an ambiguity that needs to be resolved is detected, the debugger
7304 has the capability to display a menu of numbered choices for each
7305 possibility, and then waits for the selection with the prompt @samp{>}.
7306 The first option is always @samp{[0] cancel}, and typing @kbd{0 @key{RET}}
7307 aborts the current command. If the command in which the expression was
7308 used allows more than one choice to be selected, the next option in the
7309 menu is @samp{[1] all}, and typing @kbd{1 @key{RET}} selects all possible
7312 For example, the following session excerpt shows an attempt to set a
7313 breakpoint at the overloaded symbol @code{String::after}.
7314 We choose three particular definitions of that function name:
7316 @c FIXME! This is likely to change to show arg type lists, at least
7319 (@value{GDBP}) b String::after
7322 [2] file:String.cc; line number:867
7323 [3] file:String.cc; line number:860
7324 [4] file:String.cc; line number:875
7325 [5] file:String.cc; line number:853
7326 [6] file:String.cc; line number:846
7327 [7] file:String.cc; line number:735
7329 Breakpoint 1 at 0xb26c: file String.cc, line 867.
7330 Breakpoint 2 at 0xb344: file String.cc, line 875.
7331 Breakpoint 3 at 0xafcc: file String.cc, line 846.
7332 Multiple breakpoints were set.
7333 Use the "delete" command to delete unwanted
7340 @kindex set multiple-symbols
7341 @item set multiple-symbols @var{mode}
7342 @cindex multiple-symbols menu
7344 This option allows you to adjust the debugger behavior when an expression
7347 By default, @var{mode} is set to @code{all}. If the command with which
7348 the expression is used allows more than one choice, then @value{GDBN}
7349 automatically selects all possible choices. For instance, inserting
7350 a breakpoint on a function using an ambiguous name results in a breakpoint
7351 inserted on each possible match. However, if a unique choice must be made,
7352 then @value{GDBN} uses the menu to help you disambiguate the expression.
7353 For instance, printing the address of an overloaded function will result
7354 in the use of the menu.
7356 When @var{mode} is set to @code{ask}, the debugger always uses the menu
7357 when an ambiguity is detected.
7359 Finally, when @var{mode} is set to @code{cancel}, the debugger reports
7360 an error due to the ambiguity and the command is aborted.
7362 @kindex show multiple-symbols
7363 @item show multiple-symbols
7364 Show the current value of the @code{multiple-symbols} setting.
7368 @section Program Variables
7370 The most common kind of expression to use is the name of a variable
7373 Variables in expressions are understood in the selected stack frame
7374 (@pxref{Selection, ,Selecting a Frame}); they must be either:
7378 global (or file-static)
7385 visible according to the scope rules of the
7386 programming language from the point of execution in that frame
7389 @noindent This means that in the function
7404 you can examine and use the variable @code{a} whenever your program is
7405 executing within the function @code{foo}, but you can only use or
7406 examine the variable @code{b} while your program is executing inside
7407 the block where @code{b} is declared.
7409 @cindex variable name conflict
7410 There is an exception: you can refer to a variable or function whose
7411 scope is a single source file even if the current execution point is not
7412 in this file. But it is possible to have more than one such variable or
7413 function with the same name (in different source files). If that
7414 happens, referring to that name has unpredictable effects. If you wish,
7415 you can specify a static variable in a particular function or file by
7416 using the colon-colon (@code{::}) notation:
7418 @cindex colon-colon, context for variables/functions
7420 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
7421 @cindex @code{::}, context for variables/functions
7424 @var{file}::@var{variable}
7425 @var{function}::@var{variable}
7429 Here @var{file} or @var{function} is the name of the context for the
7430 static @var{variable}. In the case of file names, you can use quotes to
7431 make sure @value{GDBN} parses the file name as a single word---for example,
7432 to print a global value of @code{x} defined in @file{f2.c}:
7435 (@value{GDBP}) p 'f2.c'::x
7438 The @code{::} notation is normally used for referring to
7439 static variables, since you typically disambiguate uses of local variables
7440 in functions by selecting the appropriate frame and using the
7441 simple name of the variable. However, you may also use this notation
7442 to refer to local variables in frames enclosing the selected frame:
7451 process (a); /* Stop here */
7462 For example, if there is a breakpoint at the commented line,
7463 here is what you might see
7464 when the program stops after executing the call @code{bar(0)}:
7469 (@value{GDBP}) p bar::a
7472 #2 0x080483d0 in foo (a=5) at foobar.c:12
7475 (@value{GDBP}) p bar::a
7479 @cindex C@t{++} scope resolution
7480 These uses of @samp{::} are very rarely in conflict with the very similar
7481 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
7482 scope resolution operator in @value{GDBN} expressions.
7483 @c FIXME: Um, so what happens in one of those rare cases where it's in
7486 @cindex wrong values
7487 @cindex variable values, wrong
7488 @cindex function entry/exit, wrong values of variables
7489 @cindex optimized code, wrong values of variables
7491 @emph{Warning:} Occasionally, a local variable may appear to have the
7492 wrong value at certain points in a function---just after entry to a new
7493 scope, and just before exit.
7495 You may see this problem when you are stepping by machine instructions.
7496 This is because, on most machines, it takes more than one instruction to
7497 set up a stack frame (including local variable definitions); if you are
7498 stepping by machine instructions, variables may appear to have the wrong
7499 values until the stack frame is completely built. On exit, it usually
7500 also takes more than one machine instruction to destroy a stack frame;
7501 after you begin stepping through that group of instructions, local
7502 variable definitions may be gone.
7504 This may also happen when the compiler does significant optimizations.
7505 To be sure of always seeing accurate values, turn off all optimization
7508 @cindex ``No symbol "foo" in current context''
7509 Another possible effect of compiler optimizations is to optimize
7510 unused variables out of existence, or assign variables to registers (as
7511 opposed to memory addresses). Depending on the support for such cases
7512 offered by the debug info format used by the compiler, @value{GDBN}
7513 might not be able to display values for such local variables. If that
7514 happens, @value{GDBN} will print a message like this:
7517 No symbol "foo" in current context.
7520 To solve such problems, either recompile without optimizations, or use a
7521 different debug info format, if the compiler supports several such
7522 formats. @xref{Compilation}, for more information on choosing compiler
7523 options. @xref{C, ,C and C@t{++}}, for more information about debug
7524 info formats that are best suited to C@t{++} programs.
7526 If you ask to print an object whose contents are unknown to
7527 @value{GDBN}, e.g., because its data type is not completely specified
7528 by the debug information, @value{GDBN} will say @samp{<incomplete
7529 type>}. @xref{Symbols, incomplete type}, for more about this.
7531 If you append @kbd{@@entry} string to a function parameter name you get its
7532 value at the time the function got called. If the value is not available an
7533 error message is printed. Entry values are available only with some compilers.
7534 Entry values are normally also printed at the function parameter list according
7535 to @ref{set print entry-values}.
7538 Breakpoint 1, d (i=30) at gdb.base/entry-value.c:29
7544 (gdb) print i@@entry
7548 Strings are identified as arrays of @code{char} values without specified
7549 signedness. Arrays of either @code{signed char} or @code{unsigned char} get
7550 printed as arrays of 1 byte sized integers. @code{-fsigned-char} or
7551 @code{-funsigned-char} @value{NGCC} options have no effect as @value{GDBN}
7552 defines literal string type @code{"char"} as @code{char} without a sign.
7557 signed char var1[] = "A";
7560 You get during debugging
7565 $2 = @{65 'A', 0 '\0'@}
7569 @section Artificial Arrays
7571 @cindex artificial array
7573 @kindex @@@r{, referencing memory as an array}
7574 It is often useful to print out several successive objects of the
7575 same type in memory; a section of an array, or an array of
7576 dynamically determined size for which only a pointer exists in the
7579 You can do this by referring to a contiguous span of memory as an
7580 @dfn{artificial array}, using the binary operator @samp{@@}. The left
7581 operand of @samp{@@} should be the first element of the desired array
7582 and be an individual object. The right operand should be the desired length
7583 of the array. The result is an array value whose elements are all of
7584 the type of the left argument. The first element is actually the left
7585 argument; the second element comes from bytes of memory immediately
7586 following those that hold the first element, and so on. Here is an
7587 example. If a program says
7590 int *array = (int *) malloc (len * sizeof (int));
7594 you can print the contents of @code{array} with
7600 The left operand of @samp{@@} must reside in memory. Array values made
7601 with @samp{@@} in this way behave just like other arrays in terms of
7602 subscripting, and are coerced to pointers when used in expressions.
7603 Artificial arrays most often appear in expressions via the value history
7604 (@pxref{Value History, ,Value History}), after printing one out.
7606 Another way to create an artificial array is to use a cast.
7607 This re-interprets a value as if it were an array.
7608 The value need not be in memory:
7610 (@value{GDBP}) p/x (short[2])0x12345678
7611 $1 = @{0x1234, 0x5678@}
7614 As a convenience, if you leave the array length out (as in
7615 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
7616 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
7618 (@value{GDBP}) p/x (short[])0x12345678
7619 $2 = @{0x1234, 0x5678@}
7622 Sometimes the artificial array mechanism is not quite enough; in
7623 moderately complex data structures, the elements of interest may not
7624 actually be adjacent---for example, if you are interested in the values
7625 of pointers in an array. One useful work-around in this situation is
7626 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
7627 Variables}) as a counter in an expression that prints the first
7628 interesting value, and then repeat that expression via @key{RET}. For
7629 instance, suppose you have an array @code{dtab} of pointers to
7630 structures, and you are interested in the values of a field @code{fv}
7631 in each structure. Here is an example of what you might type:
7641 @node Output Formats
7642 @section Output Formats
7644 @cindex formatted output
7645 @cindex output formats
7646 By default, @value{GDBN} prints a value according to its data type. Sometimes
7647 this is not what you want. For example, you might want to print a number
7648 in hex, or a pointer in decimal. Or you might want to view data in memory
7649 at a certain address as a character string or as an instruction. To do
7650 these things, specify an @dfn{output format} when you print a value.
7652 The simplest use of output formats is to say how to print a value
7653 already computed. This is done by starting the arguments of the
7654 @code{print} command with a slash and a format letter. The format
7655 letters supported are:
7659 Regard the bits of the value as an integer, and print the integer in
7663 Print as integer in signed decimal.
7666 Print as integer in unsigned decimal.
7669 Print as integer in octal.
7672 Print as integer in binary. The letter @samp{t} stands for ``two''.
7673 @footnote{@samp{b} cannot be used because these format letters are also
7674 used with the @code{x} command, where @samp{b} stands for ``byte'';
7675 see @ref{Memory,,Examining Memory}.}
7678 @cindex unknown address, locating
7679 @cindex locate address
7680 Print as an address, both absolute in hexadecimal and as an offset from
7681 the nearest preceding symbol. You can use this format used to discover
7682 where (in what function) an unknown address is located:
7685 (@value{GDBP}) p/a 0x54320
7686 $3 = 0x54320 <_initialize_vx+396>
7690 The command @code{info symbol 0x54320} yields similar results.
7691 @xref{Symbols, info symbol}.
7694 Regard as an integer and print it as a character constant. This
7695 prints both the numerical value and its character representation. The
7696 character representation is replaced with the octal escape @samp{\nnn}
7697 for characters outside the 7-bit @sc{ascii} range.
7699 Without this format, @value{GDBN} displays @code{char},
7700 @w{@code{unsigned char}}, and @w{@code{signed char}} data as character
7701 constants. Single-byte members of vectors are displayed as integer
7705 Regard the bits of the value as a floating point number and print
7706 using typical floating point syntax.
7709 @cindex printing strings
7710 @cindex printing byte arrays
7711 Regard as a string, if possible. With this format, pointers to single-byte
7712 data are displayed as null-terminated strings and arrays of single-byte data
7713 are displayed as fixed-length strings. Other values are displayed in their
7716 Without this format, @value{GDBN} displays pointers to and arrays of
7717 @code{char}, @w{@code{unsigned char}}, and @w{@code{signed char}} as
7718 strings. Single-byte members of a vector are displayed as an integer
7722 @cindex raw printing
7723 Print using the @samp{raw} formatting. By default, @value{GDBN} will
7724 use a Python-based pretty-printer, if one is available (@pxref{Pretty
7725 Printing}). This typically results in a higher-level display of the
7726 value's contents. The @samp{r} format bypasses any Python
7727 pretty-printer which might exist.
7730 For example, to print the program counter in hex (@pxref{Registers}), type
7737 Note that no space is required before the slash; this is because command
7738 names in @value{GDBN} cannot contain a slash.
7740 To reprint the last value in the value history with a different format,
7741 you can use the @code{print} command with just a format and no
7742 expression. For example, @samp{p/x} reprints the last value in hex.
7745 @section Examining Memory
7747 You can use the command @code{x} (for ``examine'') to examine memory in
7748 any of several formats, independently of your program's data types.
7750 @cindex examining memory
7752 @kindex x @r{(examine memory)}
7753 @item x/@var{nfu} @var{addr}
7756 Use the @code{x} command to examine memory.
7759 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
7760 much memory to display and how to format it; @var{addr} is an
7761 expression giving the address where you want to start displaying memory.
7762 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
7763 Several commands set convenient defaults for @var{addr}.
7766 @item @var{n}, the repeat count
7767 The repeat count is a decimal integer; the default is 1. It specifies
7768 how much memory (counting by units @var{u}) to display.
7769 @c This really is **decimal**; unaffected by 'set radix' as of GDB
7772 @item @var{f}, the display format
7773 The display format is one of the formats used by @code{print}
7774 (@samp{x}, @samp{d}, @samp{u}, @samp{o}, @samp{t}, @samp{a}, @samp{c},
7775 @samp{f}, @samp{s}), and in addition @samp{i} (for machine instructions).
7776 The default is @samp{x} (hexadecimal) initially. The default changes
7777 each time you use either @code{x} or @code{print}.
7779 @item @var{u}, the unit size
7780 The unit size is any of
7786 Halfwords (two bytes).
7788 Words (four bytes). This is the initial default.
7790 Giant words (eight bytes).
7793 Each time you specify a unit size with @code{x}, that size becomes the
7794 default unit the next time you use @code{x}. For the @samp{i} format,
7795 the unit size is ignored and is normally not written. For the @samp{s} format,
7796 the unit size defaults to @samp{b}, unless it is explicitly given.
7797 Use @kbd{x /hs} to display 16-bit char strings and @kbd{x /ws} to display
7798 32-bit strings. The next use of @kbd{x /s} will again display 8-bit strings.
7799 Note that the results depend on the programming language of the
7800 current compilation unit. If the language is C, the @samp{s}
7801 modifier will use the UTF-16 encoding while @samp{w} will use
7802 UTF-32. The encoding is set by the programming language and cannot
7805 @item @var{addr}, starting display address
7806 @var{addr} is the address where you want @value{GDBN} to begin displaying
7807 memory. The expression need not have a pointer value (though it may);
7808 it is always interpreted as an integer address of a byte of memory.
7809 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
7810 @var{addr} is usually just after the last address examined---but several
7811 other commands also set the default address: @code{info breakpoints} (to
7812 the address of the last breakpoint listed), @code{info line} (to the
7813 starting address of a line), and @code{print} (if you use it to display
7814 a value from memory).
7817 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
7818 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
7819 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
7820 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
7821 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
7823 Since the letters indicating unit sizes are all distinct from the
7824 letters specifying output formats, you do not have to remember whether
7825 unit size or format comes first; either order works. The output
7826 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
7827 (However, the count @var{n} must come first; @samp{wx4} does not work.)
7829 Even though the unit size @var{u} is ignored for the formats @samp{s}
7830 and @samp{i}, you might still want to use a count @var{n}; for example,
7831 @samp{3i} specifies that you want to see three machine instructions,
7832 including any operands. For convenience, especially when used with
7833 the @code{display} command, the @samp{i} format also prints branch delay
7834 slot instructions, if any, beyond the count specified, which immediately
7835 follow the last instruction that is within the count. The command
7836 @code{disassemble} gives an alternative way of inspecting machine
7837 instructions; see @ref{Machine Code,,Source and Machine Code}.
7839 All the defaults for the arguments to @code{x} are designed to make it
7840 easy to continue scanning memory with minimal specifications each time
7841 you use @code{x}. For example, after you have inspected three machine
7842 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
7843 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
7844 the repeat count @var{n} is used again; the other arguments default as
7845 for successive uses of @code{x}.
7847 When examining machine instructions, the instruction at current program
7848 counter is shown with a @code{=>} marker. For example:
7851 (@value{GDBP}) x/5i $pc-6
7852 0x804837f <main+11>: mov %esp,%ebp
7853 0x8048381 <main+13>: push %ecx
7854 0x8048382 <main+14>: sub $0x4,%esp
7855 => 0x8048385 <main+17>: movl $0x8048460,(%esp)
7856 0x804838c <main+24>: call 0x80482d4 <puts@@plt>
7859 @cindex @code{$_}, @code{$__}, and value history
7860 The addresses and contents printed by the @code{x} command are not saved
7861 in the value history because there is often too much of them and they
7862 would get in the way. Instead, @value{GDBN} makes these values available for
7863 subsequent use in expressions as values of the convenience variables
7864 @code{$_} and @code{$__}. After an @code{x} command, the last address
7865 examined is available for use in expressions in the convenience variable
7866 @code{$_}. The contents of that address, as examined, are available in
7867 the convenience variable @code{$__}.
7869 If the @code{x} command has a repeat count, the address and contents saved
7870 are from the last memory unit printed; this is not the same as the last
7871 address printed if several units were printed on the last line of output.
7873 @cindex remote memory comparison
7874 @cindex verify remote memory image
7875 When you are debugging a program running on a remote target machine
7876 (@pxref{Remote Debugging}), you may wish to verify the program's image in the
7877 remote machine's memory against the executable file you downloaded to
7878 the target. The @code{compare-sections} command is provided for such
7882 @kindex compare-sections
7883 @item compare-sections @r{[}@var{section-name}@r{]}
7884 Compare the data of a loadable section @var{section-name} in the
7885 executable file of the program being debugged with the same section in
7886 the remote machine's memory, and report any mismatches. With no
7887 arguments, compares all loadable sections. This command's
7888 availability depends on the target's support for the @code{"qCRC"}
7893 @section Automatic Display
7894 @cindex automatic display
7895 @cindex display of expressions
7897 If you find that you want to print the value of an expression frequently
7898 (to see how it changes), you might want to add it to the @dfn{automatic
7899 display list} so that @value{GDBN} prints its value each time your program stops.
7900 Each expression added to the list is given a number to identify it;
7901 to remove an expression from the list, you specify that number.
7902 The automatic display looks like this:
7906 3: bar[5] = (struct hack *) 0x3804
7910 This display shows item numbers, expressions and their current values. As with
7911 displays you request manually using @code{x} or @code{print}, you can
7912 specify the output format you prefer; in fact, @code{display} decides
7913 whether to use @code{print} or @code{x} depending your format
7914 specification---it uses @code{x} if you specify either the @samp{i}
7915 or @samp{s} format, or a unit size; otherwise it uses @code{print}.
7919 @item display @var{expr}
7920 Add the expression @var{expr} to the list of expressions to display
7921 each time your program stops. @xref{Expressions, ,Expressions}.
7923 @code{display} does not repeat if you press @key{RET} again after using it.
7925 @item display/@var{fmt} @var{expr}
7926 For @var{fmt} specifying only a display format and not a size or
7927 count, add the expression @var{expr} to the auto-display list but
7928 arrange to display it each time in the specified format @var{fmt}.
7929 @xref{Output Formats,,Output Formats}.
7931 @item display/@var{fmt} @var{addr}
7932 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
7933 number of units, add the expression @var{addr} as a memory address to
7934 be examined each time your program stops. Examining means in effect
7935 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining Memory}.
7938 For example, @samp{display/i $pc} can be helpful, to see the machine
7939 instruction about to be executed each time execution stops (@samp{$pc}
7940 is a common name for the program counter; @pxref{Registers, ,Registers}).
7943 @kindex delete display
7945 @item undisplay @var{dnums}@dots{}
7946 @itemx delete display @var{dnums}@dots{}
7947 Remove items from the list of expressions to display. Specify the
7948 numbers of the displays that you want affected with the command
7949 argument @var{dnums}. It can be a single display number, one of the
7950 numbers shown in the first field of the @samp{info display} display;
7951 or it could be a range of display numbers, as in @code{2-4}.
7953 @code{undisplay} does not repeat if you press @key{RET} after using it.
7954 (Otherwise you would just get the error @samp{No display number @dots{}}.)
7956 @kindex disable display
7957 @item disable display @var{dnums}@dots{}
7958 Disable the display of item numbers @var{dnums}. A disabled display
7959 item is not printed automatically, but is not forgotten. It may be
7960 enabled again later. Specify the numbers of the displays that you
7961 want affected with the command argument @var{dnums}. It can be a
7962 single display number, one of the numbers shown in the first field of
7963 the @samp{info display} display; or it could be a range of display
7964 numbers, as in @code{2-4}.
7966 @kindex enable display
7967 @item enable display @var{dnums}@dots{}
7968 Enable display of item numbers @var{dnums}. It becomes effective once
7969 again in auto display of its expression, until you specify otherwise.
7970 Specify the numbers of the displays that you want affected with the
7971 command argument @var{dnums}. It can be a single display number, one
7972 of the numbers shown in the first field of the @samp{info display}
7973 display; or it could be a range of display numbers, as in @code{2-4}.
7976 Display the current values of the expressions on the list, just as is
7977 done when your program stops.
7979 @kindex info display
7981 Print the list of expressions previously set up to display
7982 automatically, each one with its item number, but without showing the
7983 values. This includes disabled expressions, which are marked as such.
7984 It also includes expressions which would not be displayed right now
7985 because they refer to automatic variables not currently available.
7988 @cindex display disabled out of scope
7989 If a display expression refers to local variables, then it does not make
7990 sense outside the lexical context for which it was set up. Such an
7991 expression is disabled when execution enters a context where one of its
7992 variables is not defined. For example, if you give the command
7993 @code{display last_char} while inside a function with an argument
7994 @code{last_char}, @value{GDBN} displays this argument while your program
7995 continues to stop inside that function. When it stops elsewhere---where
7996 there is no variable @code{last_char}---the display is disabled
7997 automatically. The next time your program stops where @code{last_char}
7998 is meaningful, you can enable the display expression once again.
8000 @node Print Settings
8001 @section Print Settings
8003 @cindex format options
8004 @cindex print settings
8005 @value{GDBN} provides the following ways to control how arrays, structures,
8006 and symbols are printed.
8009 These settings are useful for debugging programs in any language:
8013 @item set print address
8014 @itemx set print address on
8015 @cindex print/don't print memory addresses
8016 @value{GDBN} prints memory addresses showing the location of stack
8017 traces, structure values, pointer values, breakpoints, and so forth,
8018 even when it also displays the contents of those addresses. The default
8019 is @code{on}. For example, this is what a stack frame display looks like with
8020 @code{set print address on}:
8025 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
8027 530 if (lquote != def_lquote)
8031 @item set print address off
8032 Do not print addresses when displaying their contents. For example,
8033 this is the same stack frame displayed with @code{set print address off}:
8037 (@value{GDBP}) set print addr off
8039 #0 set_quotes (lq="<<", rq=">>") at input.c:530
8040 530 if (lquote != def_lquote)
8044 You can use @samp{set print address off} to eliminate all machine
8045 dependent displays from the @value{GDBN} interface. For example, with
8046 @code{print address off}, you should get the same text for backtraces on
8047 all machines---whether or not they involve pointer arguments.
8050 @item show print address
8051 Show whether or not addresses are to be printed.
8054 When @value{GDBN} prints a symbolic address, it normally prints the
8055 closest earlier symbol plus an offset. If that symbol does not uniquely
8056 identify the address (for example, it is a name whose scope is a single
8057 source file), you may need to clarify. One way to do this is with
8058 @code{info line}, for example @samp{info line *0x4537}. Alternately,
8059 you can set @value{GDBN} to print the source file and line number when
8060 it prints a symbolic address:
8063 @item set print symbol-filename on
8064 @cindex source file and line of a symbol
8065 @cindex symbol, source file and line
8066 Tell @value{GDBN} to print the source file name and line number of a
8067 symbol in the symbolic form of an address.
8069 @item set print symbol-filename off
8070 Do not print source file name and line number of a symbol. This is the
8073 @item show print symbol-filename
8074 Show whether or not @value{GDBN} will print the source file name and
8075 line number of a symbol in the symbolic form of an address.
8078 Another situation where it is helpful to show symbol filenames and line
8079 numbers is when disassembling code; @value{GDBN} shows you the line
8080 number and source file that corresponds to each instruction.
8082 Also, you may wish to see the symbolic form only if the address being
8083 printed is reasonably close to the closest earlier symbol:
8086 @item set print max-symbolic-offset @var{max-offset}
8087 @cindex maximum value for offset of closest symbol
8088 Tell @value{GDBN} to only display the symbolic form of an address if the
8089 offset between the closest earlier symbol and the address is less than
8090 @var{max-offset}. The default is 0, which tells @value{GDBN}
8091 to always print the symbolic form of an address if any symbol precedes it.
8093 @item show print max-symbolic-offset
8094 Ask how large the maximum offset is that @value{GDBN} prints in a
8098 @cindex wild pointer, interpreting
8099 @cindex pointer, finding referent
8100 If you have a pointer and you are not sure where it points, try
8101 @samp{set print symbol-filename on}. Then you can determine the name
8102 and source file location of the variable where it points, using
8103 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
8104 For example, here @value{GDBN} shows that a variable @code{ptt} points
8105 at another variable @code{t}, defined in @file{hi2.c}:
8108 (@value{GDBP}) set print symbol-filename on
8109 (@value{GDBP}) p/a ptt
8110 $4 = 0xe008 <t in hi2.c>
8114 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
8115 does not show the symbol name and filename of the referent, even with
8116 the appropriate @code{set print} options turned on.
8119 Other settings control how different kinds of objects are printed:
8122 @item set print array
8123 @itemx set print array on
8124 @cindex pretty print arrays
8125 Pretty print arrays. This format is more convenient to read,
8126 but uses more space. The default is off.
8128 @item set print array off
8129 Return to compressed format for arrays.
8131 @item show print array
8132 Show whether compressed or pretty format is selected for displaying
8135 @cindex print array indexes
8136 @item set print array-indexes
8137 @itemx set print array-indexes on
8138 Print the index of each element when displaying arrays. May be more
8139 convenient to locate a given element in the array or quickly find the
8140 index of a given element in that printed array. The default is off.
8142 @item set print array-indexes off
8143 Stop printing element indexes when displaying arrays.
8145 @item show print array-indexes
8146 Show whether the index of each element is printed when displaying
8149 @item set print elements @var{number-of-elements}
8150 @cindex number of array elements to print
8151 @cindex limit on number of printed array elements
8152 Set a limit on how many elements of an array @value{GDBN} will print.
8153 If @value{GDBN} is printing a large array, it stops printing after it has
8154 printed the number of elements set by the @code{set print elements} command.
8155 This limit also applies to the display of strings.
8156 When @value{GDBN} starts, this limit is set to 200.
8157 Setting @var{number-of-elements} to zero means that the printing is unlimited.
8159 @item show print elements
8160 Display the number of elements of a large array that @value{GDBN} will print.
8161 If the number is 0, then the printing is unlimited.
8163 @item set print frame-arguments @var{value}
8164 @kindex set print frame-arguments
8165 @cindex printing frame argument values
8166 @cindex print all frame argument values
8167 @cindex print frame argument values for scalars only
8168 @cindex do not print frame argument values
8169 This command allows to control how the values of arguments are printed
8170 when the debugger prints a frame (@pxref{Frames}). The possible
8175 The values of all arguments are printed.
8178 Print the value of an argument only if it is a scalar. The value of more
8179 complex arguments such as arrays, structures, unions, etc, is replaced
8180 by @code{@dots{}}. This is the default. Here is an example where
8181 only scalar arguments are shown:
8184 #1 0x08048361 in call_me (i=3, s=@dots{}, ss=0xbf8d508c, u=@dots{}, e=green)
8189 None of the argument values are printed. Instead, the value of each argument
8190 is replaced by @code{@dots{}}. In this case, the example above now becomes:
8193 #1 0x08048361 in call_me (i=@dots{}, s=@dots{}, ss=@dots{}, u=@dots{}, e=@dots{})
8198 By default, only scalar arguments are printed. This command can be used
8199 to configure the debugger to print the value of all arguments, regardless
8200 of their type. However, it is often advantageous to not print the value
8201 of more complex parameters. For instance, it reduces the amount of
8202 information printed in each frame, making the backtrace more readable.
8203 Also, it improves performance when displaying Ada frames, because
8204 the computation of large arguments can sometimes be CPU-intensive,
8205 especially in large applications. Setting @code{print frame-arguments}
8206 to @code{scalars} (the default) or @code{none} avoids this computation,
8207 thus speeding up the display of each Ada frame.
8209 @item show print frame-arguments
8210 Show how the value of arguments should be displayed when printing a frame.
8212 @anchor{set print entry-values}
8213 @item set print entry-values @var{value}
8214 @kindex set print entry-values
8215 Set printing of frame argument values at function entry. In some cases
8216 @value{GDBN} can determine the value of function argument which was passed by
8217 the function caller, even if the value was modified inside the called function
8218 and therefore is different. With optimized code, the current value could be
8219 unavailable, but the entry value may still be known.
8221 The default value is @code{default} (see below for its description). Older
8222 @value{GDBN} behaved as with the setting @code{no}. Compilers not supporting
8223 this feature will behave in the @code{default} setting the same way as with the
8226 This functionality is currently supported only by DWARF 2 debugging format and
8227 the compiler has to produce @samp{DW_TAG_GNU_call_site} tags. With
8228 @value{NGCC}, you need to specify @option{-O -g} during compilation, to get
8231 The @var{value} parameter can be one of the following:
8235 Print only actual parameter values, never print values from function entry
8239 #0 different (val=6)
8240 #0 lost (val=<optimized out>)
8242 #0 invalid (val=<optimized out>)
8246 Print only parameter values from function entry point. The actual parameter
8247 values are never printed.
8249 #0 equal (val@@entry=5)
8250 #0 different (val@@entry=5)
8251 #0 lost (val@@entry=5)
8252 #0 born (val@@entry=<optimized out>)
8253 #0 invalid (val@@entry=<optimized out>)
8257 Print only parameter values from function entry point. If value from function
8258 entry point is not known while the actual value is known, print the actual
8259 value for such parameter.
8261 #0 equal (val@@entry=5)
8262 #0 different (val@@entry=5)
8263 #0 lost (val@@entry=5)
8265 #0 invalid (val@@entry=<optimized out>)
8269 Print actual parameter values. If actual parameter value is not known while
8270 value from function entry point is known, print the entry point value for such
8274 #0 different (val=6)
8275 #0 lost (val@@entry=5)
8277 #0 invalid (val=<optimized out>)
8281 Always print both the actual parameter value and its value from function entry
8282 point, even if values of one or both are not available due to compiler
8285 #0 equal (val=5, val@@entry=5)
8286 #0 different (val=6, val@@entry=5)
8287 #0 lost (val=<optimized out>, val@@entry=5)
8288 #0 born (val=10, val@@entry=<optimized out>)
8289 #0 invalid (val=<optimized out>, val@@entry=<optimized out>)
8293 Print the actual parameter value if it is known and also its value from
8294 function entry point if it is known. If neither is known, print for the actual
8295 value @code{<optimized out>}. If not in MI mode (@pxref{GDB/MI}) and if both
8296 values are known and identical, print the shortened
8297 @code{param=param@@entry=VALUE} notation.
8299 #0 equal (val=val@@entry=5)
8300 #0 different (val=6, val@@entry=5)
8301 #0 lost (val@@entry=5)
8303 #0 invalid (val=<optimized out>)
8307 Always print the actual parameter value. Print also its value from function
8308 entry point, but only if it is known. If not in MI mode (@pxref{GDB/MI}) and
8309 if both values are known and identical, print the shortened
8310 @code{param=param@@entry=VALUE} notation.
8312 #0 equal (val=val@@entry=5)
8313 #0 different (val=6, val@@entry=5)
8314 #0 lost (val=<optimized out>, val@@entry=5)
8316 #0 invalid (val=<optimized out>)
8320 For analysis messages on possible failures of frame argument values at function
8321 entry resolution see @ref{set debug entry-values}.
8323 @item show print entry-values
8324 Show the method being used for printing of frame argument values at function
8327 @item set print repeats
8328 @cindex repeated array elements
8329 Set the threshold for suppressing display of repeated array
8330 elements. When the number of consecutive identical elements of an
8331 array exceeds the threshold, @value{GDBN} prints the string
8332 @code{"<repeats @var{n} times>"}, where @var{n} is the number of
8333 identical repetitions, instead of displaying the identical elements
8334 themselves. Setting the threshold to zero will cause all elements to
8335 be individually printed. The default threshold is 10.
8337 @item show print repeats
8338 Display the current threshold for printing repeated identical
8341 @item set print null-stop
8342 @cindex @sc{null} elements in arrays
8343 Cause @value{GDBN} to stop printing the characters of an array when the first
8344 @sc{null} is encountered. This is useful when large arrays actually
8345 contain only short strings.
8348 @item show print null-stop
8349 Show whether @value{GDBN} stops printing an array on the first
8350 @sc{null} character.
8352 @item set print pretty on
8353 @cindex print structures in indented form
8354 @cindex indentation in structure display
8355 Cause @value{GDBN} to print structures in an indented format with one member
8356 per line, like this:
8371 @item set print pretty off
8372 Cause @value{GDBN} to print structures in a compact format, like this:
8376 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
8377 meat = 0x54 "Pork"@}
8382 This is the default format.
8384 @item show print pretty
8385 Show which format @value{GDBN} is using to print structures.
8387 @item set print sevenbit-strings on
8388 @cindex eight-bit characters in strings
8389 @cindex octal escapes in strings
8390 Print using only seven-bit characters; if this option is set,
8391 @value{GDBN} displays any eight-bit characters (in strings or
8392 character values) using the notation @code{\}@var{nnn}. This setting is
8393 best if you are working in English (@sc{ascii}) and you use the
8394 high-order bit of characters as a marker or ``meta'' bit.
8396 @item set print sevenbit-strings off
8397 Print full eight-bit characters. This allows the use of more
8398 international character sets, and is the default.
8400 @item show print sevenbit-strings
8401 Show whether or not @value{GDBN} is printing only seven-bit characters.
8403 @item set print union on
8404 @cindex unions in structures, printing
8405 Tell @value{GDBN} to print unions which are contained in structures
8406 and other unions. This is the default setting.
8408 @item set print union off
8409 Tell @value{GDBN} not to print unions which are contained in
8410 structures and other unions. @value{GDBN} will print @code{"@{...@}"}
8413 @item show print union
8414 Ask @value{GDBN} whether or not it will print unions which are contained in
8415 structures and other unions.
8417 For example, given the declarations
8420 typedef enum @{Tree, Bug@} Species;
8421 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
8422 typedef enum @{Caterpillar, Cocoon, Butterfly@}
8433 struct thing foo = @{Tree, @{Acorn@}@};
8437 with @code{set print union on} in effect @samp{p foo} would print
8440 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
8444 and with @code{set print union off} in effect it would print
8447 $1 = @{it = Tree, form = @{...@}@}
8451 @code{set print union} affects programs written in C-like languages
8457 These settings are of interest when debugging C@t{++} programs:
8460 @cindex demangling C@t{++} names
8461 @item set print demangle
8462 @itemx set print demangle on
8463 Print C@t{++} names in their source form rather than in the encoded
8464 (``mangled'') form passed to the assembler and linker for type-safe
8465 linkage. The default is on.
8467 @item show print demangle
8468 Show whether C@t{++} names are printed in mangled or demangled form.
8470 @item set print asm-demangle
8471 @itemx set print asm-demangle on
8472 Print C@t{++} names in their source form rather than their mangled form, even
8473 in assembler code printouts such as instruction disassemblies.
8476 @item show print asm-demangle
8477 Show whether C@t{++} names in assembly listings are printed in mangled
8480 @cindex C@t{++} symbol decoding style
8481 @cindex symbol decoding style, C@t{++}
8482 @kindex set demangle-style
8483 @item set demangle-style @var{style}
8484 Choose among several encoding schemes used by different compilers to
8485 represent C@t{++} names. The choices for @var{style} are currently:
8489 Allow @value{GDBN} to choose a decoding style by inspecting your program.
8492 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
8493 This is the default.
8496 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
8499 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
8502 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
8503 @strong{Warning:} this setting alone is not sufficient to allow
8504 debugging @code{cfront}-generated executables. @value{GDBN} would
8505 require further enhancement to permit that.
8508 If you omit @var{style}, you will see a list of possible formats.
8510 @item show demangle-style
8511 Display the encoding style currently in use for decoding C@t{++} symbols.
8513 @item set print object
8514 @itemx set print object on
8515 @cindex derived type of an object, printing
8516 @cindex display derived types
8517 When displaying a pointer to an object, identify the @emph{actual}
8518 (derived) type of the object rather than the @emph{declared} type, using
8519 the virtual function table. Note that the virtual function table is
8520 required---this feature can only work for objects that have run-time
8521 type identification; a single virtual method in the object's declared
8524 @item set print object off
8525 Display only the declared type of objects, without reference to the
8526 virtual function table. This is the default setting.
8528 @item show print object
8529 Show whether actual, or declared, object types are displayed.
8531 @item set print static-members
8532 @itemx set print static-members on
8533 @cindex static members of C@t{++} objects
8534 Print static members when displaying a C@t{++} object. The default is on.
8536 @item set print static-members off
8537 Do not print static members when displaying a C@t{++} object.
8539 @item show print static-members
8540 Show whether C@t{++} static members are printed or not.
8542 @item set print pascal_static-members
8543 @itemx set print pascal_static-members on
8544 @cindex static members of Pascal objects
8545 @cindex Pascal objects, static members display
8546 Print static members when displaying a Pascal object. The default is on.
8548 @item set print pascal_static-members off
8549 Do not print static members when displaying a Pascal object.
8551 @item show print pascal_static-members
8552 Show whether Pascal static members are printed or not.
8554 @c These don't work with HP ANSI C++ yet.
8555 @item set print vtbl
8556 @itemx set print vtbl on
8557 @cindex pretty print C@t{++} virtual function tables
8558 @cindex virtual functions (C@t{++}) display
8559 @cindex VTBL display
8560 Pretty print C@t{++} virtual function tables. The default is off.
8561 (The @code{vtbl} commands do not work on programs compiled with the HP
8562 ANSI C@t{++} compiler (@code{aCC}).)
8564 @item set print vtbl off
8565 Do not pretty print C@t{++} virtual function tables.
8567 @item show print vtbl
8568 Show whether C@t{++} virtual function tables are pretty printed, or not.
8571 @node Pretty Printing
8572 @section Pretty Printing
8574 @value{GDBN} provides a mechanism to allow pretty-printing of values using
8575 Python code. It greatly simplifies the display of complex objects. This
8576 mechanism works for both MI and the CLI.
8579 * Pretty-Printer Introduction:: Introduction to pretty-printers
8580 * Pretty-Printer Example:: An example pretty-printer
8581 * Pretty-Printer Commands:: Pretty-printer commands
8584 @node Pretty-Printer Introduction
8585 @subsection Pretty-Printer Introduction
8587 When @value{GDBN} prints a value, it first sees if there is a pretty-printer
8588 registered for the value. If there is then @value{GDBN} invokes the
8589 pretty-printer to print the value. Otherwise the value is printed normally.
8591 Pretty-printers are normally named. This makes them easy to manage.
8592 The @samp{info pretty-printer} command will list all the installed
8593 pretty-printers with their names.
8594 If a pretty-printer can handle multiple data types, then its
8595 @dfn{subprinters} are the printers for the individual data types.
8596 Each such subprinter has its own name.
8597 The format of the name is @var{printer-name};@var{subprinter-name}.
8599 Pretty-printers are installed by @dfn{registering} them with @value{GDBN}.
8600 Typically they are automatically loaded and registered when the corresponding
8601 debug information is loaded, thus making them available without having to
8602 do anything special.
8604 There are three places where a pretty-printer can be registered.
8608 Pretty-printers registered globally are available when debugging
8612 Pretty-printers registered with a program space are available only
8613 when debugging that program.
8614 @xref{Progspaces In Python}, for more details on program spaces in Python.
8617 Pretty-printers registered with an objfile are loaded and unloaded
8618 with the corresponding objfile (e.g., shared library).
8619 @xref{Objfiles In Python}, for more details on objfiles in Python.
8622 @xref{Selecting Pretty-Printers}, for further information on how
8623 pretty-printers are selected,
8625 @xref{Writing a Pretty-Printer}, for implementing pretty printers
8628 @node Pretty-Printer Example
8629 @subsection Pretty-Printer Example
8631 Here is how a C@t{++} @code{std::string} looks without a pretty-printer:
8634 (@value{GDBP}) print s
8636 static npos = 4294967295,
8638 <std::allocator<char>> = @{
8639 <__gnu_cxx::new_allocator<char>> = @{
8640 <No data fields>@}, <No data fields>
8642 members of std::basic_string<char, std::char_traits<char>,
8643 std::allocator<char> >::_Alloc_hider:
8644 _M_p = 0x804a014 "abcd"
8649 With a pretty-printer for @code{std::string} only the contents are printed:
8652 (@value{GDBP}) print s
8656 @node Pretty-Printer Commands
8657 @subsection Pretty-Printer Commands
8658 @cindex pretty-printer commands
8661 @kindex info pretty-printer
8662 @item info pretty-printer [@var{object-regexp} [@var{name-regexp}]]
8663 Print the list of installed pretty-printers.
8664 This includes disabled pretty-printers, which are marked as such.
8666 @var{object-regexp} is a regular expression matching the objects
8667 whose pretty-printers to list.
8668 Objects can be @code{global}, the program space's file
8669 (@pxref{Progspaces In Python}),
8670 and the object files within that program space (@pxref{Objfiles In Python}).
8671 @xref{Selecting Pretty-Printers}, for details on how @value{GDBN}
8672 looks up a printer from these three objects.
8674 @var{name-regexp} is a regular expression matching the name of the printers
8677 @kindex disable pretty-printer
8678 @item disable pretty-printer [@var{object-regexp} [@var{name-regexp}]]
8679 Disable pretty-printers matching @var{object-regexp} and @var{name-regexp}.
8680 A disabled pretty-printer is not forgotten, it may be enabled again later.
8682 @kindex enable pretty-printer
8683 @item enable pretty-printer [@var{object-regexp} [@var{name-regexp}]]
8684 Enable pretty-printers matching @var{object-regexp} and @var{name-regexp}.
8689 Suppose we have three pretty-printers installed: one from library1.so
8690 named @code{foo} that prints objects of type @code{foo}, and
8691 another from library2.so named @code{bar} that prints two types of objects,
8692 @code{bar1} and @code{bar2}.
8695 (gdb) info pretty-printer
8702 (gdb) info pretty-printer library2
8707 (gdb) disable pretty-printer library1
8709 2 of 3 printers enabled
8710 (gdb) info pretty-printer
8717 (gdb) disable pretty-printer library2 bar:bar1
8719 1 of 3 printers enabled
8720 (gdb) info pretty-printer library2
8727 (gdb) disable pretty-printer library2 bar
8729 0 of 3 printers enabled
8730 (gdb) info pretty-printer library2
8739 Note that for @code{bar} the entire printer can be disabled,
8740 as can each individual subprinter.
8743 @section Value History
8745 @cindex value history
8746 @cindex history of values printed by @value{GDBN}
8747 Values printed by the @code{print} command are saved in the @value{GDBN}
8748 @dfn{value history}. This allows you to refer to them in other expressions.
8749 Values are kept until the symbol table is re-read or discarded
8750 (for example with the @code{file} or @code{symbol-file} commands).
8751 When the symbol table changes, the value history is discarded,
8752 since the values may contain pointers back to the types defined in the
8757 @cindex history number
8758 The values printed are given @dfn{history numbers} by which you can
8759 refer to them. These are successive integers starting with one.
8760 @code{print} shows you the history number assigned to a value by
8761 printing @samp{$@var{num} = } before the value; here @var{num} is the
8764 To refer to any previous value, use @samp{$} followed by the value's
8765 history number. The way @code{print} labels its output is designed to
8766 remind you of this. Just @code{$} refers to the most recent value in
8767 the history, and @code{$$} refers to the value before that.
8768 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
8769 is the value just prior to @code{$$}, @code{$$1} is equivalent to
8770 @code{$$}, and @code{$$0} is equivalent to @code{$}.
8772 For example, suppose you have just printed a pointer to a structure and
8773 want to see the contents of the structure. It suffices to type
8779 If you have a chain of structures where the component @code{next} points
8780 to the next one, you can print the contents of the next one with this:
8787 You can print successive links in the chain by repeating this
8788 command---which you can do by just typing @key{RET}.
8790 Note that the history records values, not expressions. If the value of
8791 @code{x} is 4 and you type these commands:
8799 then the value recorded in the value history by the @code{print} command
8800 remains 4 even though the value of @code{x} has changed.
8805 Print the last ten values in the value history, with their item numbers.
8806 This is like @samp{p@ $$9} repeated ten times, except that @code{show
8807 values} does not change the history.
8809 @item show values @var{n}
8810 Print ten history values centered on history item number @var{n}.
8813 Print ten history values just after the values last printed. If no more
8814 values are available, @code{show values +} produces no display.
8817 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
8818 same effect as @samp{show values +}.
8820 @node Convenience Vars
8821 @section Convenience Variables
8823 @cindex convenience variables
8824 @cindex user-defined variables
8825 @value{GDBN} provides @dfn{convenience variables} that you can use within
8826 @value{GDBN} to hold on to a value and refer to it later. These variables
8827 exist entirely within @value{GDBN}; they are not part of your program, and
8828 setting a convenience variable has no direct effect on further execution
8829 of your program. That is why you can use them freely.
8831 Convenience variables are prefixed with @samp{$}. Any name preceded by
8832 @samp{$} can be used for a convenience variable, unless it is one of
8833 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
8834 (Value history references, in contrast, are @emph{numbers} preceded
8835 by @samp{$}. @xref{Value History, ,Value History}.)
8837 You can save a value in a convenience variable with an assignment
8838 expression, just as you would set a variable in your program.
8842 set $foo = *object_ptr
8846 would save in @code{$foo} the value contained in the object pointed to by
8849 Using a convenience variable for the first time creates it, but its
8850 value is @code{void} until you assign a new value. You can alter the
8851 value with another assignment at any time.
8853 Convenience variables have no fixed types. You can assign a convenience
8854 variable any type of value, including structures and arrays, even if
8855 that variable already has a value of a different type. The convenience
8856 variable, when used as an expression, has the type of its current value.
8859 @kindex show convenience
8860 @cindex show all user variables
8861 @item show convenience
8862 Print a list of convenience variables used so far, and their values.
8863 Abbreviated @code{show conv}.
8865 @kindex init-if-undefined
8866 @cindex convenience variables, initializing
8867 @item init-if-undefined $@var{variable} = @var{expression}
8868 Set a convenience variable if it has not already been set. This is useful
8869 for user-defined commands that keep some state. It is similar, in concept,
8870 to using local static variables with initializers in C (except that
8871 convenience variables are global). It can also be used to allow users to
8872 override default values used in a command script.
8874 If the variable is already defined then the expression is not evaluated so
8875 any side-effects do not occur.
8878 One of the ways to use a convenience variable is as a counter to be
8879 incremented or a pointer to be advanced. For example, to print
8880 a field from successive elements of an array of structures:
8884 print bar[$i++]->contents
8888 Repeat that command by typing @key{RET}.
8890 Some convenience variables are created automatically by @value{GDBN} and given
8891 values likely to be useful.
8894 @vindex $_@r{, convenience variable}
8896 The variable @code{$_} is automatically set by the @code{x} command to
8897 the last address examined (@pxref{Memory, ,Examining Memory}). Other
8898 commands which provide a default address for @code{x} to examine also
8899 set @code{$_} to that address; these commands include @code{info line}
8900 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
8901 except when set by the @code{x} command, in which case it is a pointer
8902 to the type of @code{$__}.
8904 @vindex $__@r{, convenience variable}
8906 The variable @code{$__} is automatically set by the @code{x} command
8907 to the value found in the last address examined. Its type is chosen
8908 to match the format in which the data was printed.
8911 @vindex $_exitcode@r{, convenience variable}
8912 The variable @code{$_exitcode} is automatically set to the exit code when
8913 the program being debugged terminates.
8916 @vindex $_sdata@r{, inspect, convenience variable}
8917 The variable @code{$_sdata} contains extra collected static tracepoint
8918 data. @xref{Tracepoint Actions,,Tracepoint Action Lists}. Note that
8919 @code{$_sdata} could be empty, if not inspecting a trace buffer, or
8920 if extra static tracepoint data has not been collected.
8923 @vindex $_siginfo@r{, convenience variable}
8924 The variable @code{$_siginfo} contains extra signal information
8925 (@pxref{extra signal information}). Note that @code{$_siginfo}
8926 could be empty, if the application has not yet received any signals.
8927 For example, it will be empty before you execute the @code{run} command.
8930 @vindex $_tlb@r{, convenience variable}
8931 The variable @code{$_tlb} is automatically set when debugging
8932 applications running on MS-Windows in native mode or connected to
8933 gdbserver that supports the @code{qGetTIBAddr} request.
8934 @xref{General Query Packets}.
8935 This variable contains the address of the thread information block.
8939 On HP-UX systems, if you refer to a function or variable name that
8940 begins with a dollar sign, @value{GDBN} searches for a user or system
8941 name first, before it searches for a convenience variable.
8943 @cindex convenience functions
8944 @value{GDBN} also supplies some @dfn{convenience functions}. These
8945 have a syntax similar to convenience variables. A convenience
8946 function can be used in an expression just like an ordinary function;
8947 however, a convenience function is implemented internally to
8952 @kindex help function
8953 @cindex show all convenience functions
8954 Print a list of all convenience functions.
8961 You can refer to machine register contents, in expressions, as variables
8962 with names starting with @samp{$}. The names of registers are different
8963 for each machine; use @code{info registers} to see the names used on
8967 @kindex info registers
8968 @item info registers
8969 Print the names and values of all registers except floating-point
8970 and vector registers (in the selected stack frame).
8972 @kindex info all-registers
8973 @cindex floating point registers
8974 @item info all-registers
8975 Print the names and values of all registers, including floating-point
8976 and vector registers (in the selected stack frame).
8978 @item info registers @var{regname} @dots{}
8979 Print the @dfn{relativized} value of each specified register @var{regname}.
8980 As discussed in detail below, register values are normally relative to
8981 the selected stack frame. @var{regname} may be any register name valid on
8982 the machine you are using, with or without the initial @samp{$}.
8985 @cindex stack pointer register
8986 @cindex program counter register
8987 @cindex process status register
8988 @cindex frame pointer register
8989 @cindex standard registers
8990 @value{GDBN} has four ``standard'' register names that are available (in
8991 expressions) on most machines---whenever they do not conflict with an
8992 architecture's canonical mnemonics for registers. The register names
8993 @code{$pc} and @code{$sp} are used for the program counter register and
8994 the stack pointer. @code{$fp} is used for a register that contains a
8995 pointer to the current stack frame, and @code{$ps} is used for a
8996 register that contains the processor status. For example,
8997 you could print the program counter in hex with
9004 or print the instruction to be executed next with
9011 or add four to the stack pointer@footnote{This is a way of removing
9012 one word from the stack, on machines where stacks grow downward in
9013 memory (most machines, nowadays). This assumes that the innermost
9014 stack frame is selected; setting @code{$sp} is not allowed when other
9015 stack frames are selected. To pop entire frames off the stack,
9016 regardless of machine architecture, use @code{return};
9017 see @ref{Returning, ,Returning from a Function}.} with
9023 Whenever possible, these four standard register names are available on
9024 your machine even though the machine has different canonical mnemonics,
9025 so long as there is no conflict. The @code{info registers} command
9026 shows the canonical names. For example, on the SPARC, @code{info
9027 registers} displays the processor status register as @code{$psr} but you
9028 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
9029 is an alias for the @sc{eflags} register.
9031 @value{GDBN} always considers the contents of an ordinary register as an
9032 integer when the register is examined in this way. Some machines have
9033 special registers which can hold nothing but floating point; these
9034 registers are considered to have floating point values. There is no way
9035 to refer to the contents of an ordinary register as floating point value
9036 (although you can @emph{print} it as a floating point value with
9037 @samp{print/f $@var{regname}}).
9039 Some registers have distinct ``raw'' and ``virtual'' data formats. This
9040 means that the data format in which the register contents are saved by
9041 the operating system is not the same one that your program normally
9042 sees. For example, the registers of the 68881 floating point
9043 coprocessor are always saved in ``extended'' (raw) format, but all C
9044 programs expect to work with ``double'' (virtual) format. In such
9045 cases, @value{GDBN} normally works with the virtual format only (the format
9046 that makes sense for your program), but the @code{info registers} command
9047 prints the data in both formats.
9049 @cindex SSE registers (x86)
9050 @cindex MMX registers (x86)
9051 Some machines have special registers whose contents can be interpreted
9052 in several different ways. For example, modern x86-based machines
9053 have SSE and MMX registers that can hold several values packed
9054 together in several different formats. @value{GDBN} refers to such
9055 registers in @code{struct} notation:
9058 (@value{GDBP}) print $xmm1
9060 v4_float = @{0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044@},
9061 v2_double = @{9.92129282474342e-303, 2.7585945287983262e-313@},
9062 v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000",
9063 v8_int16 = @{0, 0, 14072, 315, 11, 0, 13, 0@},
9064 v4_int32 = @{0, 20657912, 11, 13@},
9065 v2_int64 = @{88725056443645952, 55834574859@},
9066 uint128 = 0x0000000d0000000b013b36f800000000
9071 To set values of such registers, you need to tell @value{GDBN} which
9072 view of the register you wish to change, as if you were assigning
9073 value to a @code{struct} member:
9076 (@value{GDBP}) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF
9079 Normally, register values are relative to the selected stack frame
9080 (@pxref{Selection, ,Selecting a Frame}). This means that you get the
9081 value that the register would contain if all stack frames farther in
9082 were exited and their saved registers restored. In order to see the
9083 true contents of hardware registers, you must select the innermost
9084 frame (with @samp{frame 0}).
9086 However, @value{GDBN} must deduce where registers are saved, from the machine
9087 code generated by your compiler. If some registers are not saved, or if
9088 @value{GDBN} is unable to locate the saved registers, the selected stack
9089 frame makes no difference.
9091 @node Floating Point Hardware
9092 @section Floating Point Hardware
9093 @cindex floating point
9095 Depending on the configuration, @value{GDBN} may be able to give
9096 you more information about the status of the floating point hardware.
9101 Display hardware-dependent information about the floating
9102 point unit. The exact contents and layout vary depending on the
9103 floating point chip. Currently, @samp{info float} is supported on
9104 the ARM and x86 machines.
9108 @section Vector Unit
9111 Depending on the configuration, @value{GDBN} may be able to give you
9112 more information about the status of the vector unit.
9117 Display information about the vector unit. The exact contents and
9118 layout vary depending on the hardware.
9121 @node OS Information
9122 @section Operating System Auxiliary Information
9123 @cindex OS information
9125 @value{GDBN} provides interfaces to useful OS facilities that can help
9126 you debug your program.
9128 @cindex @code{ptrace} system call
9129 @cindex @code{struct user} contents
9130 When @value{GDBN} runs on a @dfn{Posix system} (such as GNU or Unix
9131 machines), it interfaces with the inferior via the @code{ptrace}
9132 system call. The operating system creates a special sata structure,
9133 called @code{struct user}, for this interface. You can use the
9134 command @code{info udot} to display the contents of this data
9140 Display the contents of the @code{struct user} maintained by the OS
9141 kernel for the program being debugged. @value{GDBN} displays the
9142 contents of @code{struct user} as a list of hex numbers, similar to
9143 the @code{examine} command.
9146 @cindex auxiliary vector
9147 @cindex vector, auxiliary
9148 Some operating systems supply an @dfn{auxiliary vector} to programs at
9149 startup. This is akin to the arguments and environment that you
9150 specify for a program, but contains a system-dependent variety of
9151 binary values that tell system libraries important details about the
9152 hardware, operating system, and process. Each value's purpose is
9153 identified by an integer tag; the meanings are well-known but system-specific.
9154 Depending on the configuration and operating system facilities,
9155 @value{GDBN} may be able to show you this information. For remote
9156 targets, this functionality may further depend on the remote stub's
9157 support of the @samp{qXfer:auxv:read} packet, see
9158 @ref{qXfer auxiliary vector read}.
9163 Display the auxiliary vector of the inferior, which can be either a
9164 live process or a core dump file. @value{GDBN} prints each tag value
9165 numerically, and also shows names and text descriptions for recognized
9166 tags. Some values in the vector are numbers, some bit masks, and some
9167 pointers to strings or other data. @value{GDBN} displays each value in the
9168 most appropriate form for a recognized tag, and in hexadecimal for
9169 an unrecognized tag.
9172 On some targets, @value{GDBN} can access operating-system-specific information
9173 and display it to user, without interpretation. For remote targets,
9174 this functionality depends on the remote stub's support of the
9175 @samp{qXfer:osdata:read} packet, see @ref{qXfer osdata read}.
9180 List the types of OS information available for the target. If the
9181 target does not return a list of possible types, this command will
9184 @kindex info os processes
9185 @item info os processes
9186 Display the list of processes on the target. For each process,
9187 @value{GDBN} prints the process identifier, the name of the user, and
9188 the command corresponding to the process.
9191 @node Memory Region Attributes
9192 @section Memory Region Attributes
9193 @cindex memory region attributes
9195 @dfn{Memory region attributes} allow you to describe special handling
9196 required by regions of your target's memory. @value{GDBN} uses
9197 attributes to determine whether to allow certain types of memory
9198 accesses; whether to use specific width accesses; and whether to cache
9199 target memory. By default the description of memory regions is
9200 fetched from the target (if the current target supports this), but the
9201 user can override the fetched regions.
9203 Defined memory regions can be individually enabled and disabled. When a
9204 memory region is disabled, @value{GDBN} uses the default attributes when
9205 accessing memory in that region. Similarly, if no memory regions have
9206 been defined, @value{GDBN} uses the default attributes when accessing
9209 When a memory region is defined, it is given a number to identify it;
9210 to enable, disable, or remove a memory region, you specify that number.
9214 @item mem @var{lower} @var{upper} @var{attributes}@dots{}
9215 Define a memory region bounded by @var{lower} and @var{upper} with
9216 attributes @var{attributes}@dots{}, and add it to the list of regions
9217 monitored by @value{GDBN}. Note that @var{upper} == 0 is a special
9218 case: it is treated as the target's maximum memory address.
9219 (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
9222 Discard any user changes to the memory regions and use target-supplied
9223 regions, if available, or no regions if the target does not support.
9226 @item delete mem @var{nums}@dots{}
9227 Remove memory regions @var{nums}@dots{} from the list of regions
9228 monitored by @value{GDBN}.
9231 @item disable mem @var{nums}@dots{}
9232 Disable monitoring of memory regions @var{nums}@dots{}.
9233 A disabled memory region is not forgotten.
9234 It may be enabled again later.
9237 @item enable mem @var{nums}@dots{}
9238 Enable monitoring of memory regions @var{nums}@dots{}.
9242 Print a table of all defined memory regions, with the following columns
9246 @item Memory Region Number
9247 @item Enabled or Disabled.
9248 Enabled memory regions are marked with @samp{y}.
9249 Disabled memory regions are marked with @samp{n}.
9252 The address defining the inclusive lower bound of the memory region.
9255 The address defining the exclusive upper bound of the memory region.
9258 The list of attributes set for this memory region.
9263 @subsection Attributes
9265 @subsubsection Memory Access Mode
9266 The access mode attributes set whether @value{GDBN} may make read or
9267 write accesses to a memory region.
9269 While these attributes prevent @value{GDBN} from performing invalid
9270 memory accesses, they do nothing to prevent the target system, I/O DMA,
9271 etc.@: from accessing memory.
9275 Memory is read only.
9277 Memory is write only.
9279 Memory is read/write. This is the default.
9282 @subsubsection Memory Access Size
9283 The access size attribute tells @value{GDBN} to use specific sized
9284 accesses in the memory region. Often memory mapped device registers
9285 require specific sized accesses. If no access size attribute is
9286 specified, @value{GDBN} may use accesses of any size.
9290 Use 8 bit memory accesses.
9292 Use 16 bit memory accesses.
9294 Use 32 bit memory accesses.
9296 Use 64 bit memory accesses.
9299 @c @subsubsection Hardware/Software Breakpoints
9300 @c The hardware/software breakpoint attributes set whether @value{GDBN}
9301 @c will use hardware or software breakpoints for the internal breakpoints
9302 @c used by the step, next, finish, until, etc. commands.
9306 @c Always use hardware breakpoints
9307 @c @item swbreak (default)
9310 @subsubsection Data Cache
9311 The data cache attributes set whether @value{GDBN} will cache target
9312 memory. While this generally improves performance by reducing debug
9313 protocol overhead, it can lead to incorrect results because @value{GDBN}
9314 does not know about volatile variables or memory mapped device
9319 Enable @value{GDBN} to cache target memory.
9321 Disable @value{GDBN} from caching target memory. This is the default.
9324 @subsection Memory Access Checking
9325 @value{GDBN} can be instructed to refuse accesses to memory that is
9326 not explicitly described. This can be useful if accessing such
9327 regions has undesired effects for a specific target, or to provide
9328 better error checking. The following commands control this behaviour.
9331 @kindex set mem inaccessible-by-default
9332 @item set mem inaccessible-by-default [on|off]
9333 If @code{on} is specified, make @value{GDBN} treat memory not
9334 explicitly described by the memory ranges as non-existent and refuse accesses
9335 to such memory. The checks are only performed if there's at least one
9336 memory range defined. If @code{off} is specified, make @value{GDBN}
9337 treat the memory not explicitly described by the memory ranges as RAM.
9338 The default value is @code{on}.
9339 @kindex show mem inaccessible-by-default
9340 @item show mem inaccessible-by-default
9341 Show the current handling of accesses to unknown memory.
9345 @c @subsubsection Memory Write Verification
9346 @c The memory write verification attributes set whether @value{GDBN}
9347 @c will re-reads data after each write to verify the write was successful.
9351 @c @item noverify (default)
9354 @node Dump/Restore Files
9355 @section Copy Between Memory and a File
9356 @cindex dump/restore files
9357 @cindex append data to a file
9358 @cindex dump data to a file
9359 @cindex restore data from a file
9361 You can use the commands @code{dump}, @code{append}, and
9362 @code{restore} to copy data between target memory and a file. The
9363 @code{dump} and @code{append} commands write data to a file, and the
9364 @code{restore} command reads data from a file back into the inferior's
9365 memory. Files may be in binary, Motorola S-record, Intel hex, or
9366 Tektronix Hex format; however, @value{GDBN} can only append to binary
9372 @item dump @r{[}@var{format}@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
9373 @itemx dump @r{[}@var{format}@r{]} value @var{filename} @var{expr}
9374 Dump the contents of memory from @var{start_addr} to @var{end_addr},
9375 or the value of @var{expr}, to @var{filename} in the given format.
9377 The @var{format} parameter may be any one of:
9384 Motorola S-record format.
9386 Tektronix Hex format.
9389 @value{GDBN} uses the same definitions of these formats as the
9390 @sc{gnu} binary utilities, like @samp{objdump} and @samp{objcopy}. If
9391 @var{format} is omitted, @value{GDBN} dumps the data in raw binary
9395 @item append @r{[}binary@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
9396 @itemx append @r{[}binary@r{]} value @var{filename} @var{expr}
9397 Append the contents of memory from @var{start_addr} to @var{end_addr},
9398 or the value of @var{expr}, to the file @var{filename}, in raw binary form.
9399 (@value{GDBN} can only append data to files in raw binary form.)
9402 @item restore @var{filename} @r{[}binary@r{]} @var{bias} @var{start} @var{end}
9403 Restore the contents of file @var{filename} into memory. The
9404 @code{restore} command can automatically recognize any known @sc{bfd}
9405 file format, except for raw binary. To restore a raw binary file you
9406 must specify the optional keyword @code{binary} after the filename.
9408 If @var{bias} is non-zero, its value will be added to the addresses
9409 contained in the file. Binary files always start at address zero, so
9410 they will be restored at address @var{bias}. Other bfd files have
9411 a built-in location; they will be restored at offset @var{bias}
9414 If @var{start} and/or @var{end} are non-zero, then only data between
9415 file offset @var{start} and file offset @var{end} will be restored.
9416 These offsets are relative to the addresses in the file, before
9417 the @var{bias} argument is applied.
9421 @node Core File Generation
9422 @section How to Produce a Core File from Your Program
9423 @cindex dump core from inferior
9425 A @dfn{core file} or @dfn{core dump} is a file that records the memory
9426 image of a running process and its process status (register values
9427 etc.). Its primary use is post-mortem debugging of a program that
9428 crashed while it ran outside a debugger. A program that crashes
9429 automatically produces a core file, unless this feature is disabled by
9430 the user. @xref{Files}, for information on invoking @value{GDBN} in
9431 the post-mortem debugging mode.
9433 Occasionally, you may wish to produce a core file of the program you
9434 are debugging in order to preserve a snapshot of its state.
9435 @value{GDBN} has a special command for that.
9439 @kindex generate-core-file
9440 @item generate-core-file [@var{file}]
9441 @itemx gcore [@var{file}]
9442 Produce a core dump of the inferior process. The optional argument
9443 @var{file} specifies the file name where to put the core dump. If not
9444 specified, the file name defaults to @file{core.@var{pid}}, where
9445 @var{pid} is the inferior process ID.
9447 Note that this command is implemented only for some systems (as of
9448 this writing, @sc{gnu}/Linux, FreeBSD, Solaris, Unixware, and S390).
9451 @node Character Sets
9452 @section Character Sets
9453 @cindex character sets
9455 @cindex translating between character sets
9456 @cindex host character set
9457 @cindex target character set
9459 If the program you are debugging uses a different character set to
9460 represent characters and strings than the one @value{GDBN} uses itself,
9461 @value{GDBN} can automatically translate between the character sets for
9462 you. The character set @value{GDBN} uses we call the @dfn{host
9463 character set}; the one the inferior program uses we call the
9464 @dfn{target character set}.
9466 For example, if you are running @value{GDBN} on a @sc{gnu}/Linux system, which
9467 uses the ISO Latin 1 character set, but you are using @value{GDBN}'s
9468 remote protocol (@pxref{Remote Debugging}) to debug a program
9469 running on an IBM mainframe, which uses the @sc{ebcdic} character set,
9470 then the host character set is Latin-1, and the target character set is
9471 @sc{ebcdic}. If you give @value{GDBN} the command @code{set
9472 target-charset EBCDIC-US}, then @value{GDBN} translates between
9473 @sc{ebcdic} and Latin 1 as you print character or string values, or use
9474 character and string literals in expressions.
9476 @value{GDBN} has no way to automatically recognize which character set
9477 the inferior program uses; you must tell it, using the @code{set
9478 target-charset} command, described below.
9480 Here are the commands for controlling @value{GDBN}'s character set
9484 @item set target-charset @var{charset}
9485 @kindex set target-charset
9486 Set the current target character set to @var{charset}. To display the
9487 list of supported target character sets, type
9488 @kbd{@w{set target-charset @key{TAB}@key{TAB}}}.
9490 @item set host-charset @var{charset}
9491 @kindex set host-charset
9492 Set the current host character set to @var{charset}.
9494 By default, @value{GDBN} uses a host character set appropriate to the
9495 system it is running on; you can override that default using the
9496 @code{set host-charset} command. On some systems, @value{GDBN} cannot
9497 automatically determine the appropriate host character set. In this
9498 case, @value{GDBN} uses @samp{UTF-8}.
9500 @value{GDBN} can only use certain character sets as its host character
9501 set. If you type @kbd{@w{set host-charset @key{TAB}@key{TAB}}},
9502 @value{GDBN} will list the host character sets it supports.
9504 @item set charset @var{charset}
9506 Set the current host and target character sets to @var{charset}. As
9507 above, if you type @kbd{@w{set charset @key{TAB}@key{TAB}}},
9508 @value{GDBN} will list the names of the character sets that can be used
9509 for both host and target.
9512 @kindex show charset
9513 Show the names of the current host and target character sets.
9515 @item show host-charset
9516 @kindex show host-charset
9517 Show the name of the current host character set.
9519 @item show target-charset
9520 @kindex show target-charset
9521 Show the name of the current target character set.
9523 @item set target-wide-charset @var{charset}
9524 @kindex set target-wide-charset
9525 Set the current target's wide character set to @var{charset}. This is
9526 the character set used by the target's @code{wchar_t} type. To
9527 display the list of supported wide character sets, type
9528 @kbd{@w{set target-wide-charset @key{TAB}@key{TAB}}}.
9530 @item show target-wide-charset
9531 @kindex show target-wide-charset
9532 Show the name of the current target's wide character set.
9535 Here is an example of @value{GDBN}'s character set support in action.
9536 Assume that the following source code has been placed in the file
9537 @file{charset-test.c}:
9543 = @{72, 101, 108, 108, 111, 44, 32, 119,
9544 111, 114, 108, 100, 33, 10, 0@};
9545 char ibm1047_hello[]
9546 = @{200, 133, 147, 147, 150, 107, 64, 166,
9547 150, 153, 147, 132, 90, 37, 0@};
9551 printf ("Hello, world!\n");
9555 In this program, @code{ascii_hello} and @code{ibm1047_hello} are arrays
9556 containing the string @samp{Hello, world!} followed by a newline,
9557 encoded in the @sc{ascii} and @sc{ibm1047} character sets.
9559 We compile the program, and invoke the debugger on it:
9562 $ gcc -g charset-test.c -o charset-test
9563 $ gdb -nw charset-test
9564 GNU gdb 2001-12-19-cvs
9565 Copyright 2001 Free Software Foundation, Inc.
9570 We can use the @code{show charset} command to see what character sets
9571 @value{GDBN} is currently using to interpret and display characters and
9575 (@value{GDBP}) show charset
9576 The current host and target character set is `ISO-8859-1'.
9580 For the sake of printing this manual, let's use @sc{ascii} as our
9581 initial character set:
9583 (@value{GDBP}) set charset ASCII
9584 (@value{GDBP}) show charset
9585 The current host and target character set is `ASCII'.
9589 Let's assume that @sc{ascii} is indeed the correct character set for our
9590 host system --- in other words, let's assume that if @value{GDBN} prints
9591 characters using the @sc{ascii} character set, our terminal will display
9592 them properly. Since our current target character set is also
9593 @sc{ascii}, the contents of @code{ascii_hello} print legibly:
9596 (@value{GDBP}) print ascii_hello
9597 $1 = 0x401698 "Hello, world!\n"
9598 (@value{GDBP}) print ascii_hello[0]
9603 @value{GDBN} uses the target character set for character and string
9604 literals you use in expressions:
9607 (@value{GDBP}) print '+'
9612 The @sc{ascii} character set uses the number 43 to encode the @samp{+}
9615 @value{GDBN} relies on the user to tell it which character set the
9616 target program uses. If we print @code{ibm1047_hello} while our target
9617 character set is still @sc{ascii}, we get jibberish:
9620 (@value{GDBP}) print ibm1047_hello
9621 $4 = 0x4016a8 "\310\205\223\223\226k@@\246\226\231\223\204Z%"
9622 (@value{GDBP}) print ibm1047_hello[0]
9627 If we invoke the @code{set target-charset} followed by @key{TAB}@key{TAB},
9628 @value{GDBN} tells us the character sets it supports:
9631 (@value{GDBP}) set target-charset
9632 ASCII EBCDIC-US IBM1047 ISO-8859-1
9633 (@value{GDBP}) set target-charset
9636 We can select @sc{ibm1047} as our target character set, and examine the
9637 program's strings again. Now the @sc{ascii} string is wrong, but
9638 @value{GDBN} translates the contents of @code{ibm1047_hello} from the
9639 target character set, @sc{ibm1047}, to the host character set,
9640 @sc{ascii}, and they display correctly:
9643 (@value{GDBP}) set target-charset IBM1047
9644 (@value{GDBP}) show charset
9645 The current host character set is `ASCII'.
9646 The current target character set is `IBM1047'.
9647 (@value{GDBP}) print ascii_hello
9648 $6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
9649 (@value{GDBP}) print ascii_hello[0]
9651 (@value{GDBP}) print ibm1047_hello
9652 $8 = 0x4016a8 "Hello, world!\n"
9653 (@value{GDBP}) print ibm1047_hello[0]
9658 As above, @value{GDBN} uses the target character set for character and
9659 string literals you use in expressions:
9662 (@value{GDBP}) print '+'
9667 The @sc{ibm1047} character set uses the number 78 to encode the @samp{+}
9670 @node Caching Remote Data
9671 @section Caching Data of Remote Targets
9672 @cindex caching data of remote targets
9674 @value{GDBN} caches data exchanged between the debugger and a
9675 remote target (@pxref{Remote Debugging}). Such caching generally improves
9676 performance, because it reduces the overhead of the remote protocol by
9677 bundling memory reads and writes into large chunks. Unfortunately, simply
9678 caching everything would lead to incorrect results, since @value{GDBN}
9679 does not necessarily know anything about volatile values, memory-mapped I/O
9680 addresses, etc. Furthermore, in non-stop mode (@pxref{Non-Stop Mode})
9681 memory can be changed @emph{while} a gdb command is executing.
9682 Therefore, by default, @value{GDBN} only caches data
9683 known to be on the stack@footnote{In non-stop mode, it is moderately
9684 rare for a running thread to modify the stack of a stopped thread
9685 in a way that would interfere with a backtrace, and caching of
9686 stack reads provides a significant speed up of remote backtraces.}.
9687 Other regions of memory can be explicitly marked as
9688 cacheable; see @pxref{Memory Region Attributes}.
9691 @kindex set remotecache
9692 @item set remotecache on
9693 @itemx set remotecache off
9694 This option no longer does anything; it exists for compatibility
9697 @kindex show remotecache
9698 @item show remotecache
9699 Show the current state of the obsolete remotecache flag.
9701 @kindex set stack-cache
9702 @item set stack-cache on
9703 @itemx set stack-cache off
9704 Enable or disable caching of stack accesses. When @code{ON}, use
9705 caching. By default, this option is @code{ON}.
9707 @kindex show stack-cache
9708 @item show stack-cache
9709 Show the current state of data caching for memory accesses.
9712 @item info dcache @r{[}line@r{]}
9713 Print the information about the data cache performance. The
9714 information displayed includes the dcache width and depth, and for
9715 each cache line, its number, address, and how many times it was
9716 referenced. This command is useful for debugging the data cache
9719 If a line number is specified, the contents of that line will be
9722 @item set dcache size @var{size}
9724 @kindex set dcache size
9725 Set maximum number of entries in dcache (dcache depth above).
9727 @item set dcache line-size @var{line-size}
9728 @cindex dcache line-size
9729 @kindex set dcache line-size
9730 Set number of bytes each dcache entry caches (dcache width above).
9731 Must be a power of 2.
9733 @item show dcache size
9734 @kindex show dcache size
9735 Show maximum number of dcache entries. See also @ref{Caching Remote Data, info dcache}.
9737 @item show dcache line-size
9738 @kindex show dcache line-size
9739 Show default size of dcache lines. See also @ref{Caching Remote Data, info dcache}.
9743 @node Searching Memory
9744 @section Search Memory
9745 @cindex searching memory
9747 Memory can be searched for a particular sequence of bytes with the
9748 @code{find} command.
9752 @item find @r{[}/@var{sn}@r{]} @var{start_addr}, +@var{len}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
9753 @itemx find @r{[}/@var{sn}@r{]} @var{start_addr}, @var{end_addr}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
9754 Search memory for the sequence of bytes specified by @var{val1}, @var{val2},
9755 etc. The search begins at address @var{start_addr} and continues for either
9756 @var{len} bytes or through to @var{end_addr} inclusive.
9759 @var{s} and @var{n} are optional parameters.
9760 They may be specified in either order, apart or together.
9763 @item @var{s}, search query size
9764 The size of each search query value.
9770 halfwords (two bytes)
9774 giant words (eight bytes)
9777 All values are interpreted in the current language.
9778 This means, for example, that if the current source language is C/C@t{++}
9779 then searching for the string ``hello'' includes the trailing '\0'.
9781 If the value size is not specified, it is taken from the
9782 value's type in the current language.
9783 This is useful when one wants to specify the search
9784 pattern as a mixture of types.
9785 Note that this means, for example, that in the case of C-like languages
9786 a search for an untyped 0x42 will search for @samp{(int) 0x42}
9787 which is typically four bytes.
9789 @item @var{n}, maximum number of finds
9790 The maximum number of matches to print. The default is to print all finds.
9793 You can use strings as search values. Quote them with double-quotes
9795 The string value is copied into the search pattern byte by byte,
9796 regardless of the endianness of the target and the size specification.
9798 The address of each match found is printed as well as a count of the
9799 number of matches found.
9801 The address of the last value found is stored in convenience variable
9803 A count of the number of matches is stored in @samp{$numfound}.
9805 For example, if stopped at the @code{printf} in this function:
9811 static char hello[] = "hello-hello";
9812 static struct @{ char c; short s; int i; @}
9813 __attribute__ ((packed)) mixed
9814 = @{ 'c', 0x1234, 0x87654321 @};
9815 printf ("%s\n", hello);
9820 you get during debugging:
9823 (gdb) find &hello[0], +sizeof(hello), "hello"
9824 0x804956d <hello.1620+6>
9826 (gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o'
9827 0x8049567 <hello.1620>
9828 0x804956d <hello.1620+6>
9830 (gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l'
9831 0x8049567 <hello.1620>
9833 (gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321
9834 0x8049560 <mixed.1625>
9836 (gdb) print $numfound
9839 $2 = (void *) 0x8049560
9842 @node Optimized Code
9843 @chapter Debugging Optimized Code
9844 @cindex optimized code, debugging
9845 @cindex debugging optimized code
9847 Almost all compilers support optimization. With optimization
9848 disabled, the compiler generates assembly code that corresponds
9849 directly to your source code, in a simplistic way. As the compiler
9850 applies more powerful optimizations, the generated assembly code
9851 diverges from your original source code. With help from debugging
9852 information generated by the compiler, @value{GDBN} can map from
9853 the running program back to constructs from your original source.
9855 @value{GDBN} is more accurate with optimization disabled. If you
9856 can recompile without optimization, it is easier to follow the
9857 progress of your program during debugging. But, there are many cases
9858 where you may need to debug an optimized version.
9860 When you debug a program compiled with @samp{-g -O}, remember that the
9861 optimizer has rearranged your code; the debugger shows you what is
9862 really there. Do not be too surprised when the execution path does not
9863 exactly match your source file! An extreme example: if you define a
9864 variable, but never use it, @value{GDBN} never sees that
9865 variable---because the compiler optimizes it out of existence.
9867 Some things do not work as well with @samp{-g -O} as with just
9868 @samp{-g}, particularly on machines with instruction scheduling. If in
9869 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
9870 please report it to us as a bug (including a test case!).
9871 @xref{Variables}, for more information about debugging optimized code.
9874 * Inline Functions:: How @value{GDBN} presents inlining
9875 * Tail Call Frames:: @value{GDBN} analysis of jumps to functions
9878 @node Inline Functions
9879 @section Inline Functions
9880 @cindex inline functions, debugging
9882 @dfn{Inlining} is an optimization that inserts a copy of the function
9883 body directly at each call site, instead of jumping to a shared
9884 routine. @value{GDBN} displays inlined functions just like
9885 non-inlined functions. They appear in backtraces. You can view their
9886 arguments and local variables, step into them with @code{step}, skip
9887 them with @code{next}, and escape from them with @code{finish}.
9888 You can check whether a function was inlined by using the
9889 @code{info frame} command.
9891 For @value{GDBN} to support inlined functions, the compiler must
9892 record information about inlining in the debug information ---
9893 @value{NGCC} using the @sc{dwarf 2} format does this, and several
9894 other compilers do also. @value{GDBN} only supports inlined functions
9895 when using @sc{dwarf 2}. Versions of @value{NGCC} before 4.1
9896 do not emit two required attributes (@samp{DW_AT_call_file} and
9897 @samp{DW_AT_call_line}); @value{GDBN} does not display inlined
9898 function calls with earlier versions of @value{NGCC}. It instead
9899 displays the arguments and local variables of inlined functions as
9900 local variables in the caller.
9902 The body of an inlined function is directly included at its call site;
9903 unlike a non-inlined function, there are no instructions devoted to
9904 the call. @value{GDBN} still pretends that the call site and the
9905 start of the inlined function are different instructions. Stepping to
9906 the call site shows the call site, and then stepping again shows
9907 the first line of the inlined function, even though no additional
9908 instructions are executed.
9910 This makes source-level debugging much clearer; you can see both the
9911 context of the call and then the effect of the call. Only stepping by
9912 a single instruction using @code{stepi} or @code{nexti} does not do
9913 this; single instruction steps always show the inlined body.
9915 There are some ways that @value{GDBN} does not pretend that inlined
9916 function calls are the same as normal calls:
9920 Setting breakpoints at the call site of an inlined function may not
9921 work, because the call site does not contain any code. @value{GDBN}
9922 may incorrectly move the breakpoint to the next line of the enclosing
9923 function, after the call. This limitation will be removed in a future
9924 version of @value{GDBN}; until then, set a breakpoint on an earlier line
9925 or inside the inlined function instead.
9928 @value{GDBN} cannot locate the return value of inlined calls after
9929 using the @code{finish} command. This is a limitation of compiler-generated
9930 debugging information; after @code{finish}, you can step to the next line
9931 and print a variable where your program stored the return value.
9935 @node Tail Call Frames
9936 @section Tail Call Frames
9937 @cindex tail call frames, debugging
9939 Function @code{B} can call function @code{C} in its very last statement. In
9940 unoptimized compilation the call of @code{C} is immediately followed by return
9941 instruction at the end of @code{B} code. Optimizing compiler may replace the
9942 call and return in function @code{B} into one jump to function @code{C}
9943 instead. Such use of a jump instruction is called @dfn{tail call}.
9945 During execution of function @code{C}, there will be no indication in the
9946 function call stack frames that it was tail-called from @code{B}. If function
9947 @code{A} regularly calls function @code{B} which tail-calls function @code{C},
9948 then @value{GDBN} will see @code{A} as the caller of @code{C}. However, in
9949 some cases @value{GDBN} can determine that @code{C} was tail-called from
9950 @code{B}, and it will then create fictitious call frame for that, with the
9951 return address set up as if @code{B} called @code{C} normally.
9953 This functionality is currently supported only by DWARF 2 debugging format and
9954 the compiler has to produce @samp{DW_TAG_GNU_call_site} tags. With
9955 @value{NGCC}, you need to specify @option{-O -g} during compilation, to get
9958 @kbd{info frame} command (@pxref{Frame Info}) will indicate the tail call frame
9959 kind by text @code{tail call frame} such as in this sample @value{GDBN} output:
9963 0x40066b <b(int, double)+11>: jmp 0x400640 <c(int, double)>
9965 Stack level 1, frame at 0x7fffffffda30:
9966 rip = 0x40066d in b (amd64-entry-value.cc:59); saved rip 0x4004c5
9967 tail call frame, caller of frame at 0x7fffffffda30
9968 source language c++.
9969 Arglist at unknown address.
9970 Locals at unknown address, Previous frame's sp is 0x7fffffffda30
9973 The detection of all the possible code path executions can find them ambiguous.
9974 There is no execution history stored (possible @ref{Reverse Execution} is never
9975 used for this purpose) and the last known caller could have reached the known
9976 callee by multiple different jump sequences. In such case @value{GDBN} still
9977 tries to show at least all the unambiguous top tail callers and all the
9978 unambiguous bottom tail calees, if any.
9981 @anchor{set debug entry-values}
9982 @item set debug entry-values
9983 @kindex set debug entry-values
9984 When set to on, enables printing of analysis messages for both frame argument
9985 values at function entry and tail calls. It will show all the possible valid
9986 tail calls code paths it has considered. It will also print the intersection
9987 of them with the final unambiguous (possibly partial or even empty) code path
9990 @item show debug entry-values
9991 @kindex show debug entry-values
9992 Show the current state of analysis messages printing for both frame argument
9993 values at function entry and tail calls.
9996 The analysis messages for tail calls can for example show why the virtual tail
9997 call frame for function @code{c} has not been recognized (due to the indirect
9998 reference by variable @code{x}):
10001 static void __attribute__((noinline, noclone)) c (void);
10002 void (*x) (void) = c;
10003 static void __attribute__((noinline, noclone)) a (void) @{ x++; @}
10004 static void __attribute__((noinline, noclone)) c (void) @{ a (); @}
10005 int main (void) @{ x (); return 0; @}
10007 Breakpoint 1, DW_OP_GNU_entry_value resolving cannot find
10008 DW_TAG_GNU_call_site 0x40039a in main
10010 3 static void __attribute__((noinline, noclone)) a (void) @{ x++; @}
10013 #1 0x000000000040039a in main () at t.c:5
10016 Another possibility is an ambiguous virtual tail call frames resolution:
10020 static void __attribute__((noinline, noclone)) f (void) @{ i++; @}
10021 static void __attribute__((noinline, noclone)) e (void) @{ f (); @}
10022 static void __attribute__((noinline, noclone)) d (void) @{ f (); @}
10023 static void __attribute__((noinline, noclone)) c (void) @{ d (); @}
10024 static void __attribute__((noinline, noclone)) b (void)
10025 @{ if (i) c (); else e (); @}
10026 static void __attribute__((noinline, noclone)) a (void) @{ b (); @}
10027 int main (void) @{ a (); return 0; @}
10029 tailcall: initial: 0x4004d2(a) 0x4004ce(b) 0x4004b2(c) 0x4004a2(d)
10030 tailcall: compare: 0x4004d2(a) 0x4004cc(b) 0x400492(e)
10031 tailcall: reduced: 0x4004d2(a) |
10034 #1 0x00000000004004d2 in a () at t.c:8
10035 #2 0x0000000000400395 in main () at t.c:9
10038 @set CALLSEQ1A @code{main@value{ARROW}a@value{ARROW}b@value{ARROW}c@value{ARROW}d@value{ARROW}f}
10039 @set CALLSEQ2A @code{main@value{ARROW}a@value{ARROW}b@value{ARROW}e@value{ARROW}f}
10041 @c Convert CALLSEQ#A to CALLSEQ#B depending on HAVE_MAKEINFO_CLICK.
10042 @ifset HAVE_MAKEINFO_CLICK
10043 @set ARROW @click{}
10044 @set CALLSEQ1B @clicksequence{@value{CALLSEQ1A}}
10045 @set CALLSEQ2B @clicksequence{@value{CALLSEQ2A}}
10047 @ifclear HAVE_MAKEINFO_CLICK
10049 @set CALLSEQ1B @value{CALLSEQ1A}
10050 @set CALLSEQ2B @value{CALLSEQ2A}
10053 Frames #0 and #2 are real, #1 is a virtual tail call frame.
10054 The code can have possible execution paths @value{CALLSEQ1B} or
10055 @value{CALLSEQ2B}, @value{GDBN} cannot find which one from the inferior state.
10057 @code{initial:} state shows some random possible calling sequence @value{GDBN}
10058 has found. It then finds another possible calling sequcen - that one is
10059 prefixed by @code{compare:}. The non-ambiguous intersection of these two is
10060 printed as the @code{reduced:} calling sequence. That one could have many
10061 futher @code{compare:} and @code{reduced:} statements as long as there remain
10062 any non-ambiguous sequence entries.
10064 For the frame of function @code{b} in both cases there are different possible
10065 @code{$pc} values (@code{0x4004cc} or @code{0x4004ce}), therefore this frame is
10066 also ambigous. The only non-ambiguous frame is the one for function @code{a},
10067 therefore this one is displayed to the user while the ambiguous frames are
10070 There can be also reasons why printing of frame argument values at function
10075 static void __attribute__((noinline, noclone)) c (int i) @{ v++; @}
10076 static void __attribute__((noinline, noclone)) a (int i);
10077 static void __attribute__((noinline, noclone)) b (int i) @{ a (i); @}
10078 static void __attribute__((noinline, noclone)) a (int i)
10079 @{ if (i) b (i - 1); else c (0); @}
10080 int main (void) @{ a (5); return 0; @}
10083 #0 c (i=i@@entry=0) at t.c:2
10084 #1 0x0000000000400428 in a (DW_OP_GNU_entry_value resolving has found
10085 function "a" at 0x400420 can call itself via tail calls
10086 i=<optimized out>) at t.c:6
10087 #2 0x000000000040036e in main () at t.c:7
10090 @value{GDBN} cannot find out from the inferior state if and how many times did
10091 function @code{a} call itself (via function @code{b}) as these calls would be
10092 tail calls. Such tail calls would modify thue @code{i} variable, therefore
10093 @value{GDBN} cannot be sure the value it knows would be right - @value{GDBN}
10094 prints @code{<optimized out>} instead.
10097 @chapter C Preprocessor Macros
10099 Some languages, such as C and C@t{++}, provide a way to define and invoke
10100 ``preprocessor macros'' which expand into strings of tokens.
10101 @value{GDBN} can evaluate expressions containing macro invocations, show
10102 the result of macro expansion, and show a macro's definition, including
10103 where it was defined.
10105 You may need to compile your program specially to provide @value{GDBN}
10106 with information about preprocessor macros. Most compilers do not
10107 include macros in their debugging information, even when you compile
10108 with the @option{-g} flag. @xref{Compilation}.
10110 A program may define a macro at one point, remove that definition later,
10111 and then provide a different definition after that. Thus, at different
10112 points in the program, a macro may have different definitions, or have
10113 no definition at all. If there is a current stack frame, @value{GDBN}
10114 uses the macros in scope at that frame's source code line. Otherwise,
10115 @value{GDBN} uses the macros in scope at the current listing location;
10118 Whenever @value{GDBN} evaluates an expression, it always expands any
10119 macro invocations present in the expression. @value{GDBN} also provides
10120 the following commands for working with macros explicitly.
10124 @kindex macro expand
10125 @cindex macro expansion, showing the results of preprocessor
10126 @cindex preprocessor macro expansion, showing the results of
10127 @cindex expanding preprocessor macros
10128 @item macro expand @var{expression}
10129 @itemx macro exp @var{expression}
10130 Show the results of expanding all preprocessor macro invocations in
10131 @var{expression}. Since @value{GDBN} simply expands macros, but does
10132 not parse the result, @var{expression} need not be a valid expression;
10133 it can be any string of tokens.
10136 @item macro expand-once @var{expression}
10137 @itemx macro exp1 @var{expression}
10138 @cindex expand macro once
10139 @i{(This command is not yet implemented.)} Show the results of
10140 expanding those preprocessor macro invocations that appear explicitly in
10141 @var{expression}. Macro invocations appearing in that expansion are
10142 left unchanged. This command allows you to see the effect of a
10143 particular macro more clearly, without being confused by further
10144 expansions. Since @value{GDBN} simply expands macros, but does not
10145 parse the result, @var{expression} need not be a valid expression; it
10146 can be any string of tokens.
10149 @cindex macro definition, showing
10150 @cindex definition of a macro, showing
10151 @cindex macros, from debug info
10152 @item info macro [-a|-all] [--] @var{macro}
10153 Show the current definition or all definitions of the named @var{macro},
10154 and describe the source location or compiler command-line where that
10155 definition was established. The optional double dash is to signify the end of
10156 argument processing and the beginning of @var{macro} for non C-like macros where
10157 the macro may begin with a hyphen.
10159 @kindex info macros
10160 @item info macros @var{linespec}
10161 Show all macro definitions that are in effect at the location specified
10162 by @var{linespec}, and describe the source location or compiler
10163 command-line where those definitions were established.
10165 @kindex macro define
10166 @cindex user-defined macros
10167 @cindex defining macros interactively
10168 @cindex macros, user-defined
10169 @item macro define @var{macro} @var{replacement-list}
10170 @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list}
10171 Introduce a definition for a preprocessor macro named @var{macro},
10172 invocations of which are replaced by the tokens given in
10173 @var{replacement-list}. The first form of this command defines an
10174 ``object-like'' macro, which takes no arguments; the second form
10175 defines a ``function-like'' macro, which takes the arguments given in
10178 A definition introduced by this command is in scope in every
10179 expression evaluated in @value{GDBN}, until it is removed with the
10180 @code{macro undef} command, described below. The definition overrides
10181 all definitions for @var{macro} present in the program being debugged,
10182 as well as any previous user-supplied definition.
10184 @kindex macro undef
10185 @item macro undef @var{macro}
10186 Remove any user-supplied definition for the macro named @var{macro}.
10187 This command only affects definitions provided with the @code{macro
10188 define} command, described above; it cannot remove definitions present
10189 in the program being debugged.
10193 List all the macros defined using the @code{macro define} command.
10196 @cindex macros, example of debugging with
10197 Here is a transcript showing the above commands in action. First, we
10198 show our source files:
10203 #include "sample.h"
10206 #define ADD(x) (M + x)
10211 printf ("Hello, world!\n");
10213 printf ("We're so creative.\n");
10215 printf ("Goodbye, world!\n");
10222 Now, we compile the program using the @sc{gnu} C compiler,
10223 @value{NGCC}. We pass the @option{-gdwarf-2}@footnote{This is the
10224 minimum. Recent versions of @value{NGCC} support @option{-gdwarf-3}
10225 and @option{-gdwarf-4}; we recommend always choosing the most recent
10226 version of DWARF.} @emph{and} @option{-g3} flags to ensure the compiler
10227 includes information about preprocessor macros in the debugging
10231 $ gcc -gdwarf-2 -g3 sample.c -o sample
10235 Now, we start @value{GDBN} on our sample program:
10239 GNU gdb 2002-05-06-cvs
10240 Copyright 2002 Free Software Foundation, Inc.
10241 GDB is free software, @dots{}
10245 We can expand macros and examine their definitions, even when the
10246 program is not running. @value{GDBN} uses the current listing position
10247 to decide which macro definitions are in scope:
10250 (@value{GDBP}) list main
10253 5 #define ADD(x) (M + x)
10258 10 printf ("Hello, world!\n");
10260 12 printf ("We're so creative.\n");
10261 (@value{GDBP}) info macro ADD
10262 Defined at /home/jimb/gdb/macros/play/sample.c:5
10263 #define ADD(x) (M + x)
10264 (@value{GDBP}) info macro Q
10265 Defined at /home/jimb/gdb/macros/play/sample.h:1
10266 included at /home/jimb/gdb/macros/play/sample.c:2
10268 (@value{GDBP}) macro expand ADD(1)
10269 expands to: (42 + 1)
10270 (@value{GDBP}) macro expand-once ADD(1)
10271 expands to: once (M + 1)
10275 In the example above, note that @code{macro expand-once} expands only
10276 the macro invocation explicit in the original text --- the invocation of
10277 @code{ADD} --- but does not expand the invocation of the macro @code{M},
10278 which was introduced by @code{ADD}.
10280 Once the program is running, @value{GDBN} uses the macro definitions in
10281 force at the source line of the current stack frame:
10284 (@value{GDBP}) break main
10285 Breakpoint 1 at 0x8048370: file sample.c, line 10.
10287 Starting program: /home/jimb/gdb/macros/play/sample
10289 Breakpoint 1, main () at sample.c:10
10290 10 printf ("Hello, world!\n");
10294 At line 10, the definition of the macro @code{N} at line 9 is in force:
10297 (@value{GDBP}) info macro N
10298 Defined at /home/jimb/gdb/macros/play/sample.c:9
10300 (@value{GDBP}) macro expand N Q M
10301 expands to: 28 < 42
10302 (@value{GDBP}) print N Q M
10307 As we step over directives that remove @code{N}'s definition, and then
10308 give it a new definition, @value{GDBN} finds the definition (or lack
10309 thereof) in force at each point:
10312 (@value{GDBP}) next
10314 12 printf ("We're so creative.\n");
10315 (@value{GDBP}) info macro N
10316 The symbol `N' has no definition as a C/C++ preprocessor macro
10317 at /home/jimb/gdb/macros/play/sample.c:12
10318 (@value{GDBP}) next
10320 14 printf ("Goodbye, world!\n");
10321 (@value{GDBP}) info macro N
10322 Defined at /home/jimb/gdb/macros/play/sample.c:13
10324 (@value{GDBP}) macro expand N Q M
10325 expands to: 1729 < 42
10326 (@value{GDBP}) print N Q M
10331 In addition to source files, macros can be defined on the compilation command
10332 line using the @option{-D@var{name}=@var{value}} syntax. For macros defined in
10333 such a way, @value{GDBN} displays the location of their definition as line zero
10334 of the source file submitted to the compiler.
10337 (@value{GDBP}) info macro __STDC__
10338 Defined at /home/jimb/gdb/macros/play/sample.c:0
10345 @chapter Tracepoints
10346 @c This chapter is based on the documentation written by Michael
10347 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
10349 @cindex tracepoints
10350 In some applications, it is not feasible for the debugger to interrupt
10351 the program's execution long enough for the developer to learn
10352 anything helpful about its behavior. If the program's correctness
10353 depends on its real-time behavior, delays introduced by a debugger
10354 might cause the program to change its behavior drastically, or perhaps
10355 fail, even when the code itself is correct. It is useful to be able
10356 to observe the program's behavior without interrupting it.
10358 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
10359 specify locations in the program, called @dfn{tracepoints}, and
10360 arbitrary expressions to evaluate when those tracepoints are reached.
10361 Later, using the @code{tfind} command, you can examine the values
10362 those expressions had when the program hit the tracepoints. The
10363 expressions may also denote objects in memory---structures or arrays,
10364 for example---whose values @value{GDBN} should record; while visiting
10365 a particular tracepoint, you may inspect those objects as if they were
10366 in memory at that moment. However, because @value{GDBN} records these
10367 values without interacting with you, it can do so quickly and
10368 unobtrusively, hopefully not disturbing the program's behavior.
10370 The tracepoint facility is currently available only for remote
10371 targets. @xref{Targets}. In addition, your remote target must know
10372 how to collect trace data. This functionality is implemented in the
10373 remote stub; however, none of the stubs distributed with @value{GDBN}
10374 support tracepoints as of this writing. The format of the remote
10375 packets used to implement tracepoints are described in @ref{Tracepoint
10378 It is also possible to get trace data from a file, in a manner reminiscent
10379 of corefiles; you specify the filename, and use @code{tfind} to search
10380 through the file. @xref{Trace Files}, for more details.
10382 This chapter describes the tracepoint commands and features.
10385 * Set Tracepoints::
10386 * Analyze Collected Data::
10387 * Tracepoint Variables::
10391 @node Set Tracepoints
10392 @section Commands to Set Tracepoints
10394 Before running such a @dfn{trace experiment}, an arbitrary number of
10395 tracepoints can be set. A tracepoint is actually a special type of
10396 breakpoint (@pxref{Set Breaks}), so you can manipulate it using
10397 standard breakpoint commands. For instance, as with breakpoints,
10398 tracepoint numbers are successive integers starting from one, and many
10399 of the commands associated with tracepoints take the tracepoint number
10400 as their argument, to identify which tracepoint to work on.
10402 For each tracepoint, you can specify, in advance, some arbitrary set
10403 of data that you want the target to collect in the trace buffer when
10404 it hits that tracepoint. The collected data can include registers,
10405 local variables, or global data. Later, you can use @value{GDBN}
10406 commands to examine the values these data had at the time the
10407 tracepoint was hit.
10409 Tracepoints do not support every breakpoint feature. Ignore counts on
10410 tracepoints have no effect, and tracepoints cannot run @value{GDBN}
10411 commands when they are hit. Tracepoints may not be thread-specific
10414 @cindex fast tracepoints
10415 Some targets may support @dfn{fast tracepoints}, which are inserted in
10416 a different way (such as with a jump instead of a trap), that is
10417 faster but possibly restricted in where they may be installed.
10419 @cindex static tracepoints
10420 @cindex markers, static tracepoints
10421 @cindex probing markers, static tracepoints
10422 Regular and fast tracepoints are dynamic tracing facilities, meaning
10423 that they can be used to insert tracepoints at (almost) any location
10424 in the target. Some targets may also support controlling @dfn{static
10425 tracepoints} from @value{GDBN}. With static tracing, a set of
10426 instrumentation points, also known as @dfn{markers}, are embedded in
10427 the target program, and can be activated or deactivated by name or
10428 address. These are usually placed at locations which facilitate
10429 investigating what the target is actually doing. @value{GDBN}'s
10430 support for static tracing includes being able to list instrumentation
10431 points, and attach them with @value{GDBN} defined high level
10432 tracepoints that expose the whole range of convenience of
10433 @value{GDBN}'s tracepoints support. Namely, support for collecting
10434 registers values and values of global or local (to the instrumentation
10435 point) variables; tracepoint conditions and trace state variables.
10436 The act of installing a @value{GDBN} static tracepoint on an
10437 instrumentation point, or marker, is referred to as @dfn{probing} a
10438 static tracepoint marker.
10440 @code{gdbserver} supports tracepoints on some target systems.
10441 @xref{Server,,Tracepoints support in @code{gdbserver}}.
10443 This section describes commands to set tracepoints and associated
10444 conditions and actions.
10447 * Create and Delete Tracepoints::
10448 * Enable and Disable Tracepoints::
10449 * Tracepoint Passcounts::
10450 * Tracepoint Conditions::
10451 * Trace State Variables::
10452 * Tracepoint Actions::
10453 * Listing Tracepoints::
10454 * Listing Static Tracepoint Markers::
10455 * Starting and Stopping Trace Experiments::
10456 * Tracepoint Restrictions::
10459 @node Create and Delete Tracepoints
10460 @subsection Create and Delete Tracepoints
10463 @cindex set tracepoint
10465 @item trace @var{location}
10466 The @code{trace} command is very similar to the @code{break} command.
10467 Its argument @var{location} can be a source line, a function name, or
10468 an address in the target program. @xref{Specify Location}. The
10469 @code{trace} command defines a tracepoint, which is a point in the
10470 target program where the debugger will briefly stop, collect some
10471 data, and then allow the program to continue. Setting a tracepoint or
10472 changing its actions takes effect immediately if the remote stub
10473 supports the @samp{InstallInTrace} feature (@pxref{install tracepoint
10475 If remote stub doesn't support the @samp{InstallInTrace} feature, all
10476 these changes don't take effect until the next @code{tstart}
10477 command, and once a trace experiment is running, further changes will
10478 not have any effect until the next trace experiment starts. In addition,
10479 @value{GDBN} supports @dfn{pending tracepoints}---tracepoints whose
10480 address is not yet resolved. (This is similar to pending breakpoints.)
10481 Pending tracepoints are not downloaded to the target and not installed
10482 until they are resolved. The resolution of pending tracepoints requires
10483 @value{GDBN} support---when debugging with the remote target, and
10484 @value{GDBN} disconnects from the remote stub (@pxref{disconnected
10485 tracing}), pending tracepoints can not be resolved (and downloaded to
10486 the remote stub) while @value{GDBN} is disconnected.
10488 Here are some examples of using the @code{trace} command:
10491 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
10493 (@value{GDBP}) @b{trace +2} // 2 lines forward
10495 (@value{GDBP}) @b{trace my_function} // first source line of function
10497 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
10499 (@value{GDBP}) @b{trace *0x2117c4} // an address
10503 You can abbreviate @code{trace} as @code{tr}.
10505 @item trace @var{location} if @var{cond}
10506 Set a tracepoint with condition @var{cond}; evaluate the expression
10507 @var{cond} each time the tracepoint is reached, and collect data only
10508 if the value is nonzero---that is, if @var{cond} evaluates as true.
10509 @xref{Tracepoint Conditions, ,Tracepoint Conditions}, for more
10510 information on tracepoint conditions.
10512 @item ftrace @var{location} [ if @var{cond} ]
10513 @cindex set fast tracepoint
10514 @cindex fast tracepoints, setting
10516 The @code{ftrace} command sets a fast tracepoint. For targets that
10517 support them, fast tracepoints will use a more efficient but possibly
10518 less general technique to trigger data collection, such as a jump
10519 instruction instead of a trap, or some sort of hardware support. It
10520 may not be possible to create a fast tracepoint at the desired
10521 location, in which case the command will exit with an explanatory
10524 @value{GDBN} handles arguments to @code{ftrace} exactly as for
10527 On 32-bit x86-architecture systems, fast tracepoints normally need to
10528 be placed at an instruction that is 5 bytes or longer, but can be
10529 placed at 4-byte instructions if the low 64K of memory of the target
10530 program is available to install trampolines. Some Unix-type systems,
10531 such as @sc{gnu}/Linux, exclude low addresses from the program's
10532 address space; but for instance with the Linux kernel it is possible
10533 to let @value{GDBN} use this area by doing a @command{sysctl} command
10534 to set the @code{mmap_min_addr} kernel parameter, as in
10537 sudo sysctl -w vm.mmap_min_addr=32768
10541 which sets the low address to 32K, which leaves plenty of room for
10542 trampolines. The minimum address should be set to a page boundary.
10544 @item strace @var{location} [ if @var{cond} ]
10545 @cindex set static tracepoint
10546 @cindex static tracepoints, setting
10547 @cindex probe static tracepoint marker
10549 The @code{strace} command sets a static tracepoint. For targets that
10550 support it, setting a static tracepoint probes a static
10551 instrumentation point, or marker, found at @var{location}. It may not
10552 be possible to set a static tracepoint at the desired location, in
10553 which case the command will exit with an explanatory message.
10555 @value{GDBN} handles arguments to @code{strace} exactly as for
10556 @code{trace}, with the addition that the user can also specify
10557 @code{-m @var{marker}} as @var{location}. This probes the marker
10558 identified by the @var{marker} string identifier. This identifier
10559 depends on the static tracepoint backend library your program is
10560 using. You can find all the marker identifiers in the @samp{ID} field
10561 of the @code{info static-tracepoint-markers} command output.
10562 @xref{Listing Static Tracepoint Markers,,Listing Static Tracepoint
10563 Markers}. For example, in the following small program using the UST
10569 trace_mark(ust, bar33, "str %s", "FOOBAZ");
10574 the marker id is composed of joining the first two arguments to the
10575 @code{trace_mark} call with a slash, which translates to:
10578 (@value{GDBP}) info static-tracepoint-markers
10579 Cnt Enb ID Address What
10580 1 n ust/bar33 0x0000000000400ddc in main at stexample.c:22
10586 so you may probe the marker above with:
10589 (@value{GDBP}) strace -m ust/bar33
10592 Static tracepoints accept an extra collect action --- @code{collect
10593 $_sdata}. This collects arbitrary user data passed in the probe point
10594 call to the tracing library. In the UST example above, you'll see
10595 that the third argument to @code{trace_mark} is a printf-like format
10596 string. The user data is then the result of running that formating
10597 string against the following arguments. Note that @code{info
10598 static-tracepoint-markers} command output lists that format string in
10599 the @samp{Data:} field.
10601 You can inspect this data when analyzing the trace buffer, by printing
10602 the $_sdata variable like any other variable available to
10603 @value{GDBN}. @xref{Tracepoint Actions,,Tracepoint Action Lists}.
10606 @cindex last tracepoint number
10607 @cindex recent tracepoint number
10608 @cindex tracepoint number
10609 The convenience variable @code{$tpnum} records the tracepoint number
10610 of the most recently set tracepoint.
10612 @kindex delete tracepoint
10613 @cindex tracepoint deletion
10614 @item delete tracepoint @r{[}@var{num}@r{]}
10615 Permanently delete one or more tracepoints. With no argument, the
10616 default is to delete all tracepoints. Note that the regular
10617 @code{delete} command can remove tracepoints also.
10622 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
10624 (@value{GDBP}) @b{delete trace} // remove all tracepoints
10628 You can abbreviate this command as @code{del tr}.
10631 @node Enable and Disable Tracepoints
10632 @subsection Enable and Disable Tracepoints
10634 These commands are deprecated; they are equivalent to plain @code{disable} and @code{enable}.
10637 @kindex disable tracepoint
10638 @item disable tracepoint @r{[}@var{num}@r{]}
10639 Disable tracepoint @var{num}, or all tracepoints if no argument
10640 @var{num} is given. A disabled tracepoint will have no effect during
10641 a trace experiment, but it is not forgotten. You can re-enable
10642 a disabled tracepoint using the @code{enable tracepoint} command.
10643 If the command is issued during a trace experiment and the debug target
10644 has support for disabling tracepoints during a trace experiment, then the
10645 change will be effective immediately. Otherwise, it will be applied to the
10646 next trace experiment.
10648 @kindex enable tracepoint
10649 @item enable tracepoint @r{[}@var{num}@r{]}
10650 Enable tracepoint @var{num}, or all tracepoints. If this command is
10651 issued during a trace experiment and the debug target supports enabling
10652 tracepoints during a trace experiment, then the enabled tracepoints will
10653 become effective immediately. Otherwise, they will become effective the
10654 next time a trace experiment is run.
10657 @node Tracepoint Passcounts
10658 @subsection Tracepoint Passcounts
10662 @cindex tracepoint pass count
10663 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
10664 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
10665 automatically stop a trace experiment. If a tracepoint's passcount is
10666 @var{n}, then the trace experiment will be automatically stopped on
10667 the @var{n}'th time that tracepoint is hit. If the tracepoint number
10668 @var{num} is not specified, the @code{passcount} command sets the
10669 passcount of the most recently defined tracepoint. If no passcount is
10670 given, the trace experiment will run until stopped explicitly by the
10676 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
10677 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
10679 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
10680 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
10681 (@value{GDBP}) @b{trace foo}
10682 (@value{GDBP}) @b{pass 3}
10683 (@value{GDBP}) @b{trace bar}
10684 (@value{GDBP}) @b{pass 2}
10685 (@value{GDBP}) @b{trace baz}
10686 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
10687 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
10688 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
10689 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
10693 @node Tracepoint Conditions
10694 @subsection Tracepoint Conditions
10695 @cindex conditional tracepoints
10696 @cindex tracepoint conditions
10698 The simplest sort of tracepoint collects data every time your program
10699 reaches a specified place. You can also specify a @dfn{condition} for
10700 a tracepoint. A condition is just a Boolean expression in your
10701 programming language (@pxref{Expressions, ,Expressions}). A
10702 tracepoint with a condition evaluates the expression each time your
10703 program reaches it, and data collection happens only if the condition
10706 Tracepoint conditions can be specified when a tracepoint is set, by
10707 using @samp{if} in the arguments to the @code{trace} command.
10708 @xref{Create and Delete Tracepoints, ,Setting Tracepoints}. They can
10709 also be set or changed at any time with the @code{condition} command,
10710 just as with breakpoints.
10712 Unlike breakpoint conditions, @value{GDBN} does not actually evaluate
10713 the conditional expression itself. Instead, @value{GDBN} encodes the
10714 expression into an agent expression (@pxref{Agent Expressions})
10715 suitable for execution on the target, independently of @value{GDBN}.
10716 Global variables become raw memory locations, locals become stack
10717 accesses, and so forth.
10719 For instance, suppose you have a function that is usually called
10720 frequently, but should not be called after an error has occurred. You
10721 could use the following tracepoint command to collect data about calls
10722 of that function that happen while the error code is propagating
10723 through the program; an unconditional tracepoint could end up
10724 collecting thousands of useless trace frames that you would have to
10728 (@value{GDBP}) @kbd{trace normal_operation if errcode > 0}
10731 @node Trace State Variables
10732 @subsection Trace State Variables
10733 @cindex trace state variables
10735 A @dfn{trace state variable} is a special type of variable that is
10736 created and managed by target-side code. The syntax is the same as
10737 that for GDB's convenience variables (a string prefixed with ``$''),
10738 but they are stored on the target. They must be created explicitly,
10739 using a @code{tvariable} command. They are always 64-bit signed
10742 Trace state variables are remembered by @value{GDBN}, and downloaded
10743 to the target along with tracepoint information when the trace
10744 experiment starts. There are no intrinsic limits on the number of
10745 trace state variables, beyond memory limitations of the target.
10747 @cindex convenience variables, and trace state variables
10748 Although trace state variables are managed by the target, you can use
10749 them in print commands and expressions as if they were convenience
10750 variables; @value{GDBN} will get the current value from the target
10751 while the trace experiment is running. Trace state variables share
10752 the same namespace as other ``$'' variables, which means that you
10753 cannot have trace state variables with names like @code{$23} or
10754 @code{$pc}, nor can you have a trace state variable and a convenience
10755 variable with the same name.
10759 @item tvariable $@var{name} [ = @var{expression} ]
10761 The @code{tvariable} command creates a new trace state variable named
10762 @code{$@var{name}}, and optionally gives it an initial value of
10763 @var{expression}. @var{expression} is evaluated when this command is
10764 entered; the result will be converted to an integer if possible,
10765 otherwise @value{GDBN} will report an error. A subsequent
10766 @code{tvariable} command specifying the same name does not create a
10767 variable, but instead assigns the supplied initial value to the
10768 existing variable of that name, overwriting any previous initial
10769 value. The default initial value is 0.
10771 @item info tvariables
10772 @kindex info tvariables
10773 List all the trace state variables along with their initial values.
10774 Their current values may also be displayed, if the trace experiment is
10777 @item delete tvariable @r{[} $@var{name} @dots{} @r{]}
10778 @kindex delete tvariable
10779 Delete the given trace state variables, or all of them if no arguments
10784 @node Tracepoint Actions
10785 @subsection Tracepoint Action Lists
10789 @cindex tracepoint actions
10790 @item actions @r{[}@var{num}@r{]}
10791 This command will prompt for a list of actions to be taken when the
10792 tracepoint is hit. If the tracepoint number @var{num} is not
10793 specified, this command sets the actions for the one that was most
10794 recently defined (so that you can define a tracepoint and then say
10795 @code{actions} without bothering about its number). You specify the
10796 actions themselves on the following lines, one action at a time, and
10797 terminate the actions list with a line containing just @code{end}. So
10798 far, the only defined actions are @code{collect}, @code{teval}, and
10799 @code{while-stepping}.
10801 @code{actions} is actually equivalent to @code{commands} (@pxref{Break
10802 Commands, ,Breakpoint Command Lists}), except that only the defined
10803 actions are allowed; any other @value{GDBN} command is rejected.
10805 @cindex remove actions from a tracepoint
10806 To remove all actions from a tracepoint, type @samp{actions @var{num}}
10807 and follow it immediately with @samp{end}.
10810 (@value{GDBP}) @b{collect @var{data}} // collect some data
10812 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
10814 (@value{GDBP}) @b{end} // signals the end of actions.
10817 In the following example, the action list begins with @code{collect}
10818 commands indicating the things to be collected when the tracepoint is
10819 hit. Then, in order to single-step and collect additional data
10820 following the tracepoint, a @code{while-stepping} command is used,
10821 followed by the list of things to be collected after each step in a
10822 sequence of single steps. The @code{while-stepping} command is
10823 terminated by its own separate @code{end} command. Lastly, the action
10824 list is terminated by an @code{end} command.
10827 (@value{GDBP}) @b{trace foo}
10828 (@value{GDBP}) @b{actions}
10829 Enter actions for tracepoint 1, one per line:
10832 > while-stepping 12
10833 > collect $pc, arr[i]
10838 @kindex collect @r{(tracepoints)}
10839 @item collect@r{[}/@var{mods}@r{]} @var{expr1}, @var{expr2}, @dots{}
10840 Collect values of the given expressions when the tracepoint is hit.
10841 This command accepts a comma-separated list of any valid expressions.
10842 In addition to global, static, or local variables, the following
10843 special arguments are supported:
10847 Collect all registers.
10850 Collect all function arguments.
10853 Collect all local variables.
10856 Collect the return address. This is helpful if you want to see more
10860 @vindex $_sdata@r{, collect}
10861 Collect static tracepoint marker specific data. Only available for
10862 static tracepoints. @xref{Tracepoint Actions,,Tracepoint Action
10863 Lists}. On the UST static tracepoints library backend, an
10864 instrumentation point resembles a @code{printf} function call. The
10865 tracing library is able to collect user specified data formatted to a
10866 character string using the format provided by the programmer that
10867 instrumented the program. Other backends have similar mechanisms.
10868 Here's an example of a UST marker call:
10871 const char master_name[] = "$your_name";
10872 trace_mark(channel1, marker1, "hello %s", master_name)
10875 In this case, collecting @code{$_sdata} collects the string
10876 @samp{hello $yourname}. When analyzing the trace buffer, you can
10877 inspect @samp{$_sdata} like any other variable available to
10881 You can give several consecutive @code{collect} commands, each one
10882 with a single argument, or one @code{collect} command with several
10883 arguments separated by commas; the effect is the same.
10885 The optional @var{mods} changes the usual handling of the arguments.
10886 @code{s} requests that pointers to chars be handled as strings, in
10887 particular collecting the contents of the memory being pointed at, up
10888 to the first zero. The upper bound is by default the value of the
10889 @code{print elements} variable; if @code{s} is followed by a decimal
10890 number, that is the upper bound instead. So for instance
10891 @samp{collect/s25 mystr} collects as many as 25 characters at
10894 The command @code{info scope} (@pxref{Symbols, info scope}) is
10895 particularly useful for figuring out what data to collect.
10897 @kindex teval @r{(tracepoints)}
10898 @item teval @var{expr1}, @var{expr2}, @dots{}
10899 Evaluate the given expressions when the tracepoint is hit. This
10900 command accepts a comma-separated list of expressions. The results
10901 are discarded, so this is mainly useful for assigning values to trace
10902 state variables (@pxref{Trace State Variables}) without adding those
10903 values to the trace buffer, as would be the case if the @code{collect}
10906 @kindex while-stepping @r{(tracepoints)}
10907 @item while-stepping @var{n}
10908 Perform @var{n} single-step instruction traces after the tracepoint,
10909 collecting new data after each step. The @code{while-stepping}
10910 command is followed by the list of what to collect while stepping
10911 (followed by its own @code{end} command):
10914 > while-stepping 12
10915 > collect $regs, myglobal
10921 Note that @code{$pc} is not automatically collected by
10922 @code{while-stepping}; you need to explicitly collect that register if
10923 you need it. You may abbreviate @code{while-stepping} as @code{ws} or
10926 @item set default-collect @var{expr1}, @var{expr2}, @dots{}
10927 @kindex set default-collect
10928 @cindex default collection action
10929 This variable is a list of expressions to collect at each tracepoint
10930 hit. It is effectively an additional @code{collect} action prepended
10931 to every tracepoint action list. The expressions are parsed
10932 individually for each tracepoint, so for instance a variable named
10933 @code{xyz} may be interpreted as a global for one tracepoint, and a
10934 local for another, as appropriate to the tracepoint's location.
10936 @item show default-collect
10937 @kindex show default-collect
10938 Show the list of expressions that are collected by default at each
10943 @node Listing Tracepoints
10944 @subsection Listing Tracepoints
10947 @kindex info tracepoints @r{[}@var{n}@dots{}@r{]}
10948 @kindex info tp @r{[}@var{n}@dots{}@r{]}
10949 @cindex information about tracepoints
10950 @item info tracepoints @r{[}@var{num}@dots{}@r{]}
10951 Display information about the tracepoint @var{num}. If you don't
10952 specify a tracepoint number, displays information about all the
10953 tracepoints defined so far. The format is similar to that used for
10954 @code{info breakpoints}; in fact, @code{info tracepoints} is the same
10955 command, simply restricting itself to tracepoints.
10957 A tracepoint's listing may include additional information specific to
10962 its passcount as given by the @code{passcount @var{n}} command
10966 (@value{GDBP}) @b{info trace}
10967 Num Type Disp Enb Address What
10968 1 tracepoint keep y 0x0804ab57 in foo() at main.cxx:7
10970 collect globfoo, $regs
10979 This command can be abbreviated @code{info tp}.
10982 @node Listing Static Tracepoint Markers
10983 @subsection Listing Static Tracepoint Markers
10986 @kindex info static-tracepoint-markers
10987 @cindex information about static tracepoint markers
10988 @item info static-tracepoint-markers
10989 Display information about all static tracepoint markers defined in the
10992 For each marker, the following columns are printed:
10996 An incrementing counter, output to help readability. This is not a
10999 The marker ID, as reported by the target.
11000 @item Enabled or Disabled
11001 Probed markers are tagged with @samp{y}. @samp{n} identifies marks
11002 that are not enabled.
11004 Where the marker is in your program, as a memory address.
11006 Where the marker is in the source for your program, as a file and line
11007 number. If the debug information included in the program does not
11008 allow @value{GDBN} to locate the source of the marker, this column
11009 will be left blank.
11013 In addition, the following information may be printed for each marker:
11017 User data passed to the tracing library by the marker call. In the
11018 UST backend, this is the format string passed as argument to the
11020 @item Static tracepoints probing the marker
11021 The list of static tracepoints attached to the marker.
11025 (@value{GDBP}) info static-tracepoint-markers
11026 Cnt ID Enb Address What
11027 1 ust/bar2 y 0x0000000000400e1a in main at stexample.c:25
11028 Data: number1 %d number2 %d
11029 Probed by static tracepoints: #2
11030 2 ust/bar33 n 0x0000000000400c87 in main at stexample.c:24
11036 @node Starting and Stopping Trace Experiments
11037 @subsection Starting and Stopping Trace Experiments
11040 @kindex tstart [ @var{notes} ]
11041 @cindex start a new trace experiment
11042 @cindex collected data discarded
11044 This command starts the trace experiment, and begins collecting data.
11045 It has the side effect of discarding all the data collected in the
11046 trace buffer during the previous trace experiment. If any arguments
11047 are supplied, they are taken as a note and stored with the trace
11048 experiment's state. The notes may be arbitrary text, and are
11049 especially useful with disconnected tracing in a multi-user context;
11050 the notes can explain what the trace is doing, supply user contact
11051 information, and so forth.
11053 @kindex tstop [ @var{notes} ]
11054 @cindex stop a running trace experiment
11056 This command stops the trace experiment. If any arguments are
11057 supplied, they are recorded with the experiment as a note. This is
11058 useful if you are stopping a trace started by someone else, for
11059 instance if the trace is interfering with the system's behavior and
11060 needs to be stopped quickly.
11062 @strong{Note}: a trace experiment and data collection may stop
11063 automatically if any tracepoint's passcount is reached
11064 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
11067 @cindex status of trace data collection
11068 @cindex trace experiment, status of
11070 This command displays the status of the current trace data
11074 Here is an example of the commands we described so far:
11077 (@value{GDBP}) @b{trace gdb_c_test}
11078 (@value{GDBP}) @b{actions}
11079 Enter actions for tracepoint #1, one per line.
11080 > collect $regs,$locals,$args
11081 > while-stepping 11
11085 (@value{GDBP}) @b{tstart}
11086 [time passes @dots{}]
11087 (@value{GDBP}) @b{tstop}
11090 @anchor{disconnected tracing}
11091 @cindex disconnected tracing
11092 You can choose to continue running the trace experiment even if
11093 @value{GDBN} disconnects from the target, voluntarily or
11094 involuntarily. For commands such as @code{detach}, the debugger will
11095 ask what you want to do with the trace. But for unexpected
11096 terminations (@value{GDBN} crash, network outage), it would be
11097 unfortunate to lose hard-won trace data, so the variable
11098 @code{disconnected-tracing} lets you decide whether the trace should
11099 continue running without @value{GDBN}.
11102 @item set disconnected-tracing on
11103 @itemx set disconnected-tracing off
11104 @kindex set disconnected-tracing
11105 Choose whether a tracing run should continue to run if @value{GDBN}
11106 has disconnected from the target. Note that @code{detach} or
11107 @code{quit} will ask you directly what to do about a running trace no
11108 matter what this variable's setting, so the variable is mainly useful
11109 for handling unexpected situations, such as loss of the network.
11111 @item show disconnected-tracing
11112 @kindex show disconnected-tracing
11113 Show the current choice for disconnected tracing.
11117 When you reconnect to the target, the trace experiment may or may not
11118 still be running; it might have filled the trace buffer in the
11119 meantime, or stopped for one of the other reasons. If it is running,
11120 it will continue after reconnection.
11122 Upon reconnection, the target will upload information about the
11123 tracepoints in effect. @value{GDBN} will then compare that
11124 information to the set of tracepoints currently defined, and attempt
11125 to match them up, allowing for the possibility that the numbers may
11126 have changed due to creation and deletion in the meantime. If one of
11127 the target's tracepoints does not match any in @value{GDBN}, the
11128 debugger will create a new tracepoint, so that you have a number with
11129 which to specify that tracepoint. This matching-up process is
11130 necessarily heuristic, and it may result in useless tracepoints being
11131 created; you may simply delete them if they are of no use.
11133 @cindex circular trace buffer
11134 If your target agent supports a @dfn{circular trace buffer}, then you
11135 can run a trace experiment indefinitely without filling the trace
11136 buffer; when space runs out, the agent deletes already-collected trace
11137 frames, oldest first, until there is enough room to continue
11138 collecting. This is especially useful if your tracepoints are being
11139 hit too often, and your trace gets terminated prematurely because the
11140 buffer is full. To ask for a circular trace buffer, simply set
11141 @samp{circular-trace-buffer} to on. You can set this at any time,
11142 including during tracing; if the agent can do it, it will change
11143 buffer handling on the fly, otherwise it will not take effect until
11147 @item set circular-trace-buffer on
11148 @itemx set circular-trace-buffer off
11149 @kindex set circular-trace-buffer
11150 Choose whether a tracing run should use a linear or circular buffer
11151 for trace data. A linear buffer will not lose any trace data, but may
11152 fill up prematurely, while a circular buffer will discard old trace
11153 data, but it will have always room for the latest tracepoint hits.
11155 @item show circular-trace-buffer
11156 @kindex show circular-trace-buffer
11157 Show the current choice for the trace buffer. Note that this may not
11158 match the agent's current buffer handling, nor is it guaranteed to
11159 match the setting that might have been in effect during a past run,
11160 for instance if you are looking at frames from a trace file.
11165 @item set trace-user @var{text}
11166 @kindex set trace-user
11168 @item show trace-user
11169 @kindex show trace-user
11171 @item set trace-notes @var{text}
11172 @kindex set trace-notes
11173 Set the trace run's notes.
11175 @item show trace-notes
11176 @kindex show trace-notes
11177 Show the trace run's notes.
11179 @item set trace-stop-notes @var{text}
11180 @kindex set trace-stop-notes
11181 Set the trace run's stop notes. The handling of the note is as for
11182 @code{tstop} arguments; the set command is convenient way to fix a
11183 stop note that is mistaken or incomplete.
11185 @item show trace-stop-notes
11186 @kindex show trace-stop-notes
11187 Show the trace run's stop notes.
11191 @node Tracepoint Restrictions
11192 @subsection Tracepoint Restrictions
11194 @cindex tracepoint restrictions
11195 There are a number of restrictions on the use of tracepoints. As
11196 described above, tracepoint data gathering occurs on the target
11197 without interaction from @value{GDBN}. Thus the full capabilities of
11198 the debugger are not available during data gathering, and then at data
11199 examination time, you will be limited by only having what was
11200 collected. The following items describe some common problems, but it
11201 is not exhaustive, and you may run into additional difficulties not
11207 Tracepoint expressions are intended to gather objects (lvalues). Thus
11208 the full flexibility of GDB's expression evaluator is not available.
11209 You cannot call functions, cast objects to aggregate types, access
11210 convenience variables or modify values (except by assignment to trace
11211 state variables). Some language features may implicitly call
11212 functions (for instance Objective-C fields with accessors), and therefore
11213 cannot be collected either.
11216 Collection of local variables, either individually or in bulk with
11217 @code{$locals} or @code{$args}, during @code{while-stepping} may
11218 behave erratically. The stepping action may enter a new scope (for
11219 instance by stepping into a function), or the location of the variable
11220 may change (for instance it is loaded into a register). The
11221 tracepoint data recorded uses the location information for the
11222 variables that is correct for the tracepoint location. When the
11223 tracepoint is created, it is not possible, in general, to determine
11224 where the steps of a @code{while-stepping} sequence will advance the
11225 program---particularly if a conditional branch is stepped.
11228 Collection of an incompletely-initialized or partially-destroyed object
11229 may result in something that @value{GDBN} cannot display, or displays
11230 in a misleading way.
11233 When @value{GDBN} displays a pointer to character it automatically
11234 dereferences the pointer to also display characters of the string
11235 being pointed to. However, collecting the pointer during tracing does
11236 not automatically collect the string. You need to explicitly
11237 dereference the pointer and provide size information if you want to
11238 collect not only the pointer, but the memory pointed to. For example,
11239 @code{*ptr@@50} can be used to collect the 50 element array pointed to
11243 It is not possible to collect a complete stack backtrace at a
11244 tracepoint. Instead, you may collect the registers and a few hundred
11245 bytes from the stack pointer with something like @code{*(unsigned char *)$esp@@300}
11246 (adjust to use the name of the actual stack pointer register on your
11247 target architecture, and the amount of stack you wish to capture).
11248 Then the @code{backtrace} command will show a partial backtrace when
11249 using a trace frame. The number of stack frames that can be examined
11250 depends on the sizes of the frames in the collected stack. Note that
11251 if you ask for a block so large that it goes past the bottom of the
11252 stack, the target agent may report an error trying to read from an
11256 If you do not collect registers at a tracepoint, @value{GDBN} can
11257 infer that the value of @code{$pc} must be the same as the address of
11258 the tracepoint and use that when you are looking at a trace frame
11259 for that tracepoint. However, this cannot work if the tracepoint has
11260 multiple locations (for instance if it was set in a function that was
11261 inlined), or if it has a @code{while-stepping} loop. In those cases
11262 @value{GDBN} will warn you that it can't infer @code{$pc}, and default
11267 @node Analyze Collected Data
11268 @section Using the Collected Data
11270 After the tracepoint experiment ends, you use @value{GDBN} commands
11271 for examining the trace data. The basic idea is that each tracepoint
11272 collects a trace @dfn{snapshot} every time it is hit and another
11273 snapshot every time it single-steps. All these snapshots are
11274 consecutively numbered from zero and go into a buffer, and you can
11275 examine them later. The way you examine them is to @dfn{focus} on a
11276 specific trace snapshot. When the remote stub is focused on a trace
11277 snapshot, it will respond to all @value{GDBN} requests for memory and
11278 registers by reading from the buffer which belongs to that snapshot,
11279 rather than from @emph{real} memory or registers of the program being
11280 debugged. This means that @strong{all} @value{GDBN} commands
11281 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
11282 behave as if we were currently debugging the program state as it was
11283 when the tracepoint occurred. Any requests for data that are not in
11284 the buffer will fail.
11287 * tfind:: How to select a trace snapshot
11288 * tdump:: How to display all data for a snapshot
11289 * save tracepoints:: How to save tracepoints for a future run
11293 @subsection @code{tfind @var{n}}
11296 @cindex select trace snapshot
11297 @cindex find trace snapshot
11298 The basic command for selecting a trace snapshot from the buffer is
11299 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
11300 counting from zero. If no argument @var{n} is given, the next
11301 snapshot is selected.
11303 Here are the various forms of using the @code{tfind} command.
11307 Find the first snapshot in the buffer. This is a synonym for
11308 @code{tfind 0} (since 0 is the number of the first snapshot).
11311 Stop debugging trace snapshots, resume @emph{live} debugging.
11314 Same as @samp{tfind none}.
11317 No argument means find the next trace snapshot.
11320 Find the previous trace snapshot before the current one. This permits
11321 retracing earlier steps.
11323 @item tfind tracepoint @var{num}
11324 Find the next snapshot associated with tracepoint @var{num}. Search
11325 proceeds forward from the last examined trace snapshot. If no
11326 argument @var{num} is given, it means find the next snapshot collected
11327 for the same tracepoint as the current snapshot.
11329 @item tfind pc @var{addr}
11330 Find the next snapshot associated with the value @var{addr} of the
11331 program counter. Search proceeds forward from the last examined trace
11332 snapshot. If no argument @var{addr} is given, it means find the next
11333 snapshot with the same value of PC as the current snapshot.
11335 @item tfind outside @var{addr1}, @var{addr2}
11336 Find the next snapshot whose PC is outside the given range of
11337 addresses (exclusive).
11339 @item tfind range @var{addr1}, @var{addr2}
11340 Find the next snapshot whose PC is between @var{addr1} and
11341 @var{addr2} (inclusive).
11343 @item tfind line @r{[}@var{file}:@r{]}@var{n}
11344 Find the next snapshot associated with the source line @var{n}. If
11345 the optional argument @var{file} is given, refer to line @var{n} in
11346 that source file. Search proceeds forward from the last examined
11347 trace snapshot. If no argument @var{n} is given, it means find the
11348 next line other than the one currently being examined; thus saying
11349 @code{tfind line} repeatedly can appear to have the same effect as
11350 stepping from line to line in a @emph{live} debugging session.
11353 The default arguments for the @code{tfind} commands are specifically
11354 designed to make it easy to scan through the trace buffer. For
11355 instance, @code{tfind} with no argument selects the next trace
11356 snapshot, and @code{tfind -} with no argument selects the previous
11357 trace snapshot. So, by giving one @code{tfind} command, and then
11358 simply hitting @key{RET} repeatedly you can examine all the trace
11359 snapshots in order. Or, by saying @code{tfind -} and then hitting
11360 @key{RET} repeatedly you can examine the snapshots in reverse order.
11361 The @code{tfind line} command with no argument selects the snapshot
11362 for the next source line executed. The @code{tfind pc} command with
11363 no argument selects the next snapshot with the same program counter
11364 (PC) as the current frame. The @code{tfind tracepoint} command with
11365 no argument selects the next trace snapshot collected by the same
11366 tracepoint as the current one.
11368 In addition to letting you scan through the trace buffer manually,
11369 these commands make it easy to construct @value{GDBN} scripts that
11370 scan through the trace buffer and print out whatever collected data
11371 you are interested in. Thus, if we want to examine the PC, FP, and SP
11372 registers from each trace frame in the buffer, we can say this:
11375 (@value{GDBP}) @b{tfind start}
11376 (@value{GDBP}) @b{while ($trace_frame != -1)}
11377 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
11378 $trace_frame, $pc, $sp, $fp
11382 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
11383 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
11384 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
11385 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
11386 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
11387 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
11388 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
11389 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
11390 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
11391 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
11392 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
11395 Or, if we want to examine the variable @code{X} at each source line in
11399 (@value{GDBP}) @b{tfind start}
11400 (@value{GDBP}) @b{while ($trace_frame != -1)}
11401 > printf "Frame %d, X == %d\n", $trace_frame, X
11411 @subsection @code{tdump}
11413 @cindex dump all data collected at tracepoint
11414 @cindex tracepoint data, display
11416 This command takes no arguments. It prints all the data collected at
11417 the current trace snapshot.
11420 (@value{GDBP}) @b{trace 444}
11421 (@value{GDBP}) @b{actions}
11422 Enter actions for tracepoint #2, one per line:
11423 > collect $regs, $locals, $args, gdb_long_test
11426 (@value{GDBP}) @b{tstart}
11428 (@value{GDBP}) @b{tfind line 444}
11429 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
11431 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
11433 (@value{GDBP}) @b{tdump}
11434 Data collected at tracepoint 2, trace frame 1:
11435 d0 0xc4aa0085 -995491707
11439 d4 0x71aea3d 119204413
11442 d7 0x380035 3670069
11443 a0 0x19e24a 1696330
11444 a1 0x3000668 50333288
11446 a3 0x322000 3284992
11447 a4 0x3000698 50333336
11448 a5 0x1ad3cc 1758156
11449 fp 0x30bf3c 0x30bf3c
11450 sp 0x30bf34 0x30bf34
11452 pc 0x20b2c8 0x20b2c8
11456 p = 0x20e5b4 "gdb-test"
11463 gdb_long_test = 17 '\021'
11468 @code{tdump} works by scanning the tracepoint's current collection
11469 actions and printing the value of each expression listed. So
11470 @code{tdump} can fail, if after a run, you change the tracepoint's
11471 actions to mention variables that were not collected during the run.
11473 Also, for tracepoints with @code{while-stepping} loops, @code{tdump}
11474 uses the collected value of @code{$pc} to distinguish between trace
11475 frames that were collected at the tracepoint hit, and frames that were
11476 collected while stepping. This allows it to correctly choose whether
11477 to display the basic list of collections, or the collections from the
11478 body of the while-stepping loop. However, if @code{$pc} was not collected,
11479 then @code{tdump} will always attempt to dump using the basic collection
11480 list, and may fail if a while-stepping frame does not include all the
11481 same data that is collected at the tracepoint hit.
11482 @c This is getting pretty arcane, example would be good.
11484 @node save tracepoints
11485 @subsection @code{save tracepoints @var{filename}}
11486 @kindex save tracepoints
11487 @kindex save-tracepoints
11488 @cindex save tracepoints for future sessions
11490 This command saves all current tracepoint definitions together with
11491 their actions and passcounts, into a file @file{@var{filename}}
11492 suitable for use in a later debugging session. To read the saved
11493 tracepoint definitions, use the @code{source} command (@pxref{Command
11494 Files}). The @w{@code{save-tracepoints}} command is a deprecated
11495 alias for @w{@code{save tracepoints}}
11497 @node Tracepoint Variables
11498 @section Convenience Variables for Tracepoints
11499 @cindex tracepoint variables
11500 @cindex convenience variables for tracepoints
11503 @vindex $trace_frame
11504 @item (int) $trace_frame
11505 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
11506 snapshot is selected.
11508 @vindex $tracepoint
11509 @item (int) $tracepoint
11510 The tracepoint for the current trace snapshot.
11512 @vindex $trace_line
11513 @item (int) $trace_line
11514 The line number for the current trace snapshot.
11516 @vindex $trace_file
11517 @item (char []) $trace_file
11518 The source file for the current trace snapshot.
11520 @vindex $trace_func
11521 @item (char []) $trace_func
11522 The name of the function containing @code{$tracepoint}.
11525 Note: @code{$trace_file} is not suitable for use in @code{printf},
11526 use @code{output} instead.
11528 Here's a simple example of using these convenience variables for
11529 stepping through all the trace snapshots and printing some of their
11530 data. Note that these are not the same as trace state variables,
11531 which are managed by the target.
11534 (@value{GDBP}) @b{tfind start}
11536 (@value{GDBP}) @b{while $trace_frame != -1}
11537 > output $trace_file
11538 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
11544 @section Using Trace Files
11545 @cindex trace files
11547 In some situations, the target running a trace experiment may no
11548 longer be available; perhaps it crashed, or the hardware was needed
11549 for a different activity. To handle these cases, you can arrange to
11550 dump the trace data into a file, and later use that file as a source
11551 of trace data, via the @code{target tfile} command.
11556 @item tsave [ -r ] @var{filename}
11557 Save the trace data to @var{filename}. By default, this command
11558 assumes that @var{filename} refers to the host filesystem, so if
11559 necessary @value{GDBN} will copy raw trace data up from the target and
11560 then save it. If the target supports it, you can also supply the
11561 optional argument @code{-r} (``remote'') to direct the target to save
11562 the data directly into @var{filename} in its own filesystem, which may be
11563 more efficient if the trace buffer is very large. (Note, however, that
11564 @code{target tfile} can only read from files accessible to the host.)
11566 @kindex target tfile
11568 @item target tfile @var{filename}
11569 Use the file named @var{filename} as a source of trace data. Commands
11570 that examine data work as they do with a live target, but it is not
11571 possible to run any new trace experiments. @code{tstatus} will report
11572 the state of the trace run at the moment the data was saved, as well
11573 as the current trace frame you are examining. @var{filename} must be
11574 on a filesystem accessible to the host.
11579 @chapter Debugging Programs That Use Overlays
11582 If your program is too large to fit completely in your target system's
11583 memory, you can sometimes use @dfn{overlays} to work around this
11584 problem. @value{GDBN} provides some support for debugging programs that
11588 * How Overlays Work:: A general explanation of overlays.
11589 * Overlay Commands:: Managing overlays in @value{GDBN}.
11590 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
11591 mapped by asking the inferior.
11592 * Overlay Sample Program:: A sample program using overlays.
11595 @node How Overlays Work
11596 @section How Overlays Work
11597 @cindex mapped overlays
11598 @cindex unmapped overlays
11599 @cindex load address, overlay's
11600 @cindex mapped address
11601 @cindex overlay area
11603 Suppose you have a computer whose instruction address space is only 64
11604 kilobytes long, but which has much more memory which can be accessed by
11605 other means: special instructions, segment registers, or memory
11606 management hardware, for example. Suppose further that you want to
11607 adapt a program which is larger than 64 kilobytes to run on this system.
11609 One solution is to identify modules of your program which are relatively
11610 independent, and need not call each other directly; call these modules
11611 @dfn{overlays}. Separate the overlays from the main program, and place
11612 their machine code in the larger memory. Place your main program in
11613 instruction memory, but leave at least enough space there to hold the
11614 largest overlay as well.
11616 Now, to call a function located in an overlay, you must first copy that
11617 overlay's machine code from the large memory into the space set aside
11618 for it in the instruction memory, and then jump to its entry point
11621 @c NB: In the below the mapped area's size is greater or equal to the
11622 @c size of all overlays. This is intentional to remind the developer
11623 @c that overlays don't necessarily need to be the same size.
11627 Data Instruction Larger
11628 Address Space Address Space Address Space
11629 +-----------+ +-----------+ +-----------+
11631 +-----------+ +-----------+ +-----------+<-- overlay 1
11632 | program | | main | .----| overlay 1 | load address
11633 | variables | | program | | +-----------+
11634 | and heap | | | | | |
11635 +-----------+ | | | +-----------+<-- overlay 2
11636 | | +-----------+ | | | load address
11637 +-----------+ | | | .-| overlay 2 |
11639 mapped --->+-----------+ | | +-----------+
11640 address | | | | | |
11641 | overlay | <-' | | |
11642 | area | <---' +-----------+<-- overlay 3
11643 | | <---. | | load address
11644 +-----------+ `--| overlay 3 |
11651 @anchor{A code overlay}A code overlay
11655 The diagram (@pxref{A code overlay}) shows a system with separate data
11656 and instruction address spaces. To map an overlay, the program copies
11657 its code from the larger address space to the instruction address space.
11658 Since the overlays shown here all use the same mapped address, only one
11659 may be mapped at a time. For a system with a single address space for
11660 data and instructions, the diagram would be similar, except that the
11661 program variables and heap would share an address space with the main
11662 program and the overlay area.
11664 An overlay loaded into instruction memory and ready for use is called a
11665 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
11666 instruction memory. An overlay not present (or only partially present)
11667 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
11668 is its address in the larger memory. The mapped address is also called
11669 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
11670 called the @dfn{load memory address}, or @dfn{LMA}.
11672 Unfortunately, overlays are not a completely transparent way to adapt a
11673 program to limited instruction memory. They introduce a new set of
11674 global constraints you must keep in mind as you design your program:
11679 Before calling or returning to a function in an overlay, your program
11680 must make sure that overlay is actually mapped. Otherwise, the call or
11681 return will transfer control to the right address, but in the wrong
11682 overlay, and your program will probably crash.
11685 If the process of mapping an overlay is expensive on your system, you
11686 will need to choose your overlays carefully to minimize their effect on
11687 your program's performance.
11690 The executable file you load onto your system must contain each
11691 overlay's instructions, appearing at the overlay's load address, not its
11692 mapped address. However, each overlay's instructions must be relocated
11693 and its symbols defined as if the overlay were at its mapped address.
11694 You can use GNU linker scripts to specify different load and relocation
11695 addresses for pieces of your program; see @ref{Overlay Description,,,
11696 ld.info, Using ld: the GNU linker}.
11699 The procedure for loading executable files onto your system must be able
11700 to load their contents into the larger address space as well as the
11701 instruction and data spaces.
11705 The overlay system described above is rather simple, and could be
11706 improved in many ways:
11711 If your system has suitable bank switch registers or memory management
11712 hardware, you could use those facilities to make an overlay's load area
11713 contents simply appear at their mapped address in instruction space.
11714 This would probably be faster than copying the overlay to its mapped
11715 area in the usual way.
11718 If your overlays are small enough, you could set aside more than one
11719 overlay area, and have more than one overlay mapped at a time.
11722 You can use overlays to manage data, as well as instructions. In
11723 general, data overlays are even less transparent to your design than
11724 code overlays: whereas code overlays only require care when you call or
11725 return to functions, data overlays require care every time you access
11726 the data. Also, if you change the contents of a data overlay, you
11727 must copy its contents back out to its load address before you can copy a
11728 different data overlay into the same mapped area.
11733 @node Overlay Commands
11734 @section Overlay Commands
11736 To use @value{GDBN}'s overlay support, each overlay in your program must
11737 correspond to a separate section of the executable file. The section's
11738 virtual memory address and load memory address must be the overlay's
11739 mapped and load addresses. Identifying overlays with sections allows
11740 @value{GDBN} to determine the appropriate address of a function or
11741 variable, depending on whether the overlay is mapped or not.
11743 @value{GDBN}'s overlay commands all start with the word @code{overlay};
11744 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
11749 Disable @value{GDBN}'s overlay support. When overlay support is
11750 disabled, @value{GDBN} assumes that all functions and variables are
11751 always present at their mapped addresses. By default, @value{GDBN}'s
11752 overlay support is disabled.
11754 @item overlay manual
11755 @cindex manual overlay debugging
11756 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
11757 relies on you to tell it which overlays are mapped, and which are not,
11758 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
11759 commands described below.
11761 @item overlay map-overlay @var{overlay}
11762 @itemx overlay map @var{overlay}
11763 @cindex map an overlay
11764 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
11765 be the name of the object file section containing the overlay. When an
11766 overlay is mapped, @value{GDBN} assumes it can find the overlay's
11767 functions and variables at their mapped addresses. @value{GDBN} assumes
11768 that any other overlays whose mapped ranges overlap that of
11769 @var{overlay} are now unmapped.
11771 @item overlay unmap-overlay @var{overlay}
11772 @itemx overlay unmap @var{overlay}
11773 @cindex unmap an overlay
11774 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
11775 must be the name of the object file section containing the overlay.
11776 When an overlay is unmapped, @value{GDBN} assumes it can find the
11777 overlay's functions and variables at their load addresses.
11780 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
11781 consults a data structure the overlay manager maintains in the inferior
11782 to see which overlays are mapped. For details, see @ref{Automatic
11783 Overlay Debugging}.
11785 @item overlay load-target
11786 @itemx overlay load
11787 @cindex reloading the overlay table
11788 Re-read the overlay table from the inferior. Normally, @value{GDBN}
11789 re-reads the table @value{GDBN} automatically each time the inferior
11790 stops, so this command should only be necessary if you have changed the
11791 overlay mapping yourself using @value{GDBN}. This command is only
11792 useful when using automatic overlay debugging.
11794 @item overlay list-overlays
11795 @itemx overlay list
11796 @cindex listing mapped overlays
11797 Display a list of the overlays currently mapped, along with their mapped
11798 addresses, load addresses, and sizes.
11802 Normally, when @value{GDBN} prints a code address, it includes the name
11803 of the function the address falls in:
11806 (@value{GDBP}) print main
11807 $3 = @{int ()@} 0x11a0 <main>
11810 When overlay debugging is enabled, @value{GDBN} recognizes code in
11811 unmapped overlays, and prints the names of unmapped functions with
11812 asterisks around them. For example, if @code{foo} is a function in an
11813 unmapped overlay, @value{GDBN} prints it this way:
11816 (@value{GDBP}) overlay list
11817 No sections are mapped.
11818 (@value{GDBP}) print foo
11819 $5 = @{int (int)@} 0x100000 <*foo*>
11822 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
11826 (@value{GDBP}) overlay list
11827 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
11828 mapped at 0x1016 - 0x104a
11829 (@value{GDBP}) print foo
11830 $6 = @{int (int)@} 0x1016 <foo>
11833 When overlay debugging is enabled, @value{GDBN} can find the correct
11834 address for functions and variables in an overlay, whether or not the
11835 overlay is mapped. This allows most @value{GDBN} commands, like
11836 @code{break} and @code{disassemble}, to work normally, even on unmapped
11837 code. However, @value{GDBN}'s breakpoint support has some limitations:
11841 @cindex breakpoints in overlays
11842 @cindex overlays, setting breakpoints in
11843 You can set breakpoints in functions in unmapped overlays, as long as
11844 @value{GDBN} can write to the overlay at its load address.
11846 @value{GDBN} can not set hardware or simulator-based breakpoints in
11847 unmapped overlays. However, if you set a breakpoint at the end of your
11848 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
11849 you are using manual overlay management), @value{GDBN} will re-set its
11850 breakpoints properly.
11854 @node Automatic Overlay Debugging
11855 @section Automatic Overlay Debugging
11856 @cindex automatic overlay debugging
11858 @value{GDBN} can automatically track which overlays are mapped and which
11859 are not, given some simple co-operation from the overlay manager in the
11860 inferior. If you enable automatic overlay debugging with the
11861 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
11862 looks in the inferior's memory for certain variables describing the
11863 current state of the overlays.
11865 Here are the variables your overlay manager must define to support
11866 @value{GDBN}'s automatic overlay debugging:
11870 @item @code{_ovly_table}:
11871 This variable must be an array of the following structures:
11876 /* The overlay's mapped address. */
11879 /* The size of the overlay, in bytes. */
11880 unsigned long size;
11882 /* The overlay's load address. */
11885 /* Non-zero if the overlay is currently mapped;
11887 unsigned long mapped;
11891 @item @code{_novlys}:
11892 This variable must be a four-byte signed integer, holding the total
11893 number of elements in @code{_ovly_table}.
11897 To decide whether a particular overlay is mapped or not, @value{GDBN}
11898 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
11899 @code{lma} members equal the VMA and LMA of the overlay's section in the
11900 executable file. When @value{GDBN} finds a matching entry, it consults
11901 the entry's @code{mapped} member to determine whether the overlay is
11904 In addition, your overlay manager may define a function called
11905 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
11906 will silently set a breakpoint there. If the overlay manager then
11907 calls this function whenever it has changed the overlay table, this
11908 will enable @value{GDBN} to accurately keep track of which overlays
11909 are in program memory, and update any breakpoints that may be set
11910 in overlays. This will allow breakpoints to work even if the
11911 overlays are kept in ROM or other non-writable memory while they
11912 are not being executed.
11914 @node Overlay Sample Program
11915 @section Overlay Sample Program
11916 @cindex overlay example program
11918 When linking a program which uses overlays, you must place the overlays
11919 at their load addresses, while relocating them to run at their mapped
11920 addresses. To do this, you must write a linker script (@pxref{Overlay
11921 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
11922 since linker scripts are specific to a particular host system, target
11923 architecture, and target memory layout, this manual cannot provide
11924 portable sample code demonstrating @value{GDBN}'s overlay support.
11926 However, the @value{GDBN} source distribution does contain an overlaid
11927 program, with linker scripts for a few systems, as part of its test
11928 suite. The program consists of the following files from
11929 @file{gdb/testsuite/gdb.base}:
11933 The main program file.
11935 A simple overlay manager, used by @file{overlays.c}.
11940 Overlay modules, loaded and used by @file{overlays.c}.
11943 Linker scripts for linking the test program on the @code{d10v-elf}
11944 and @code{m32r-elf} targets.
11947 You can build the test program using the @code{d10v-elf} GCC
11948 cross-compiler like this:
11951 $ d10v-elf-gcc -g -c overlays.c
11952 $ d10v-elf-gcc -g -c ovlymgr.c
11953 $ d10v-elf-gcc -g -c foo.c
11954 $ d10v-elf-gcc -g -c bar.c
11955 $ d10v-elf-gcc -g -c baz.c
11956 $ d10v-elf-gcc -g -c grbx.c
11957 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
11958 baz.o grbx.o -Wl,-Td10v.ld -o overlays
11961 The build process is identical for any other architecture, except that
11962 you must substitute the appropriate compiler and linker script for the
11963 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
11967 @chapter Using @value{GDBN} with Different Languages
11970 Although programming languages generally have common aspects, they are
11971 rarely expressed in the same manner. For instance, in ANSI C,
11972 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
11973 Modula-2, it is accomplished by @code{p^}. Values can also be
11974 represented (and displayed) differently. Hex numbers in C appear as
11975 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
11977 @cindex working language
11978 Language-specific information is built into @value{GDBN} for some languages,
11979 allowing you to express operations like the above in your program's
11980 native language, and allowing @value{GDBN} to output values in a manner
11981 consistent with the syntax of your program's native language. The
11982 language you use to build expressions is called the @dfn{working
11986 * Setting:: Switching between source languages
11987 * Show:: Displaying the language
11988 * Checks:: Type and range checks
11989 * Supported Languages:: Supported languages
11990 * Unsupported Languages:: Unsupported languages
11994 @section Switching Between Source Languages
11996 There are two ways to control the working language---either have @value{GDBN}
11997 set it automatically, or select it manually yourself. You can use the
11998 @code{set language} command for either purpose. On startup, @value{GDBN}
11999 defaults to setting the language automatically. The working language is
12000 used to determine how expressions you type are interpreted, how values
12003 In addition to the working language, every source file that
12004 @value{GDBN} knows about has its own working language. For some object
12005 file formats, the compiler might indicate which language a particular
12006 source file is in. However, most of the time @value{GDBN} infers the
12007 language from the name of the file. The language of a source file
12008 controls whether C@t{++} names are demangled---this way @code{backtrace} can
12009 show each frame appropriately for its own language. There is no way to
12010 set the language of a source file from within @value{GDBN}, but you can
12011 set the language associated with a filename extension. @xref{Show, ,
12012 Displaying the Language}.
12014 This is most commonly a problem when you use a program, such
12015 as @code{cfront} or @code{f2c}, that generates C but is written in
12016 another language. In that case, make the
12017 program use @code{#line} directives in its C output; that way
12018 @value{GDBN} will know the correct language of the source code of the original
12019 program, and will display that source code, not the generated C code.
12022 * Filenames:: Filename extensions and languages.
12023 * Manually:: Setting the working language manually
12024 * Automatically:: Having @value{GDBN} infer the source language
12028 @subsection List of Filename Extensions and Languages
12030 If a source file name ends in one of the following extensions, then
12031 @value{GDBN} infers that its language is the one indicated.
12049 C@t{++} source file
12055 Objective-C source file
12059 Fortran source file
12062 Modula-2 source file
12066 Assembler source file. This actually behaves almost like C, but
12067 @value{GDBN} does not skip over function prologues when stepping.
12070 In addition, you may set the language associated with a filename
12071 extension. @xref{Show, , Displaying the Language}.
12074 @subsection Setting the Working Language
12076 If you allow @value{GDBN} to set the language automatically,
12077 expressions are interpreted the same way in your debugging session and
12080 @kindex set language
12081 If you wish, you may set the language manually. To do this, issue the
12082 command @samp{set language @var{lang}}, where @var{lang} is the name of
12083 a language, such as
12084 @code{c} or @code{modula-2}.
12085 For a list of the supported languages, type @samp{set language}.
12087 Setting the language manually prevents @value{GDBN} from updating the working
12088 language automatically. This can lead to confusion if you try
12089 to debug a program when the working language is not the same as the
12090 source language, when an expression is acceptable to both
12091 languages---but means different things. For instance, if the current
12092 source file were written in C, and @value{GDBN} was parsing Modula-2, a
12100 might not have the effect you intended. In C, this means to add
12101 @code{b} and @code{c} and place the result in @code{a}. The result
12102 printed would be the value of @code{a}. In Modula-2, this means to compare
12103 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
12105 @node Automatically
12106 @subsection Having @value{GDBN} Infer the Source Language
12108 To have @value{GDBN} set the working language automatically, use
12109 @samp{set language local} or @samp{set language auto}. @value{GDBN}
12110 then infers the working language. That is, when your program stops in a
12111 frame (usually by encountering a breakpoint), @value{GDBN} sets the
12112 working language to the language recorded for the function in that
12113 frame. If the language for a frame is unknown (that is, if the function
12114 or block corresponding to the frame was defined in a source file that
12115 does not have a recognized extension), the current working language is
12116 not changed, and @value{GDBN} issues a warning.
12118 This may not seem necessary for most programs, which are written
12119 entirely in one source language. However, program modules and libraries
12120 written in one source language can be used by a main program written in
12121 a different source language. Using @samp{set language auto} in this
12122 case frees you from having to set the working language manually.
12125 @section Displaying the Language
12127 The following commands help you find out which language is the
12128 working language, and also what language source files were written in.
12131 @item show language
12132 @kindex show language
12133 Display the current working language. This is the
12134 language you can use with commands such as @code{print} to
12135 build and compute expressions that may involve variables in your program.
12138 @kindex info frame@r{, show the source language}
12139 Display the source language for this frame. This language becomes the
12140 working language if you use an identifier from this frame.
12141 @xref{Frame Info, ,Information about a Frame}, to identify the other
12142 information listed here.
12145 @kindex info source@r{, show the source language}
12146 Display the source language of this source file.
12147 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
12148 information listed here.
12151 In unusual circumstances, you may have source files with extensions
12152 not in the standard list. You can then set the extension associated
12153 with a language explicitly:
12156 @item set extension-language @var{ext} @var{language}
12157 @kindex set extension-language
12158 Tell @value{GDBN} that source files with extension @var{ext} are to be
12159 assumed as written in the source language @var{language}.
12161 @item info extensions
12162 @kindex info extensions
12163 List all the filename extensions and the associated languages.
12167 @section Type and Range Checking
12170 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
12171 checking are included, but they do not yet have any effect. This
12172 section documents the intended facilities.
12174 @c FIXME remove warning when type/range code added
12176 Some languages are designed to guard you against making seemingly common
12177 errors through a series of compile- and run-time checks. These include
12178 checking the type of arguments to functions and operators, and making
12179 sure mathematical overflows are caught at run time. Checks such as
12180 these help to ensure a program's correctness once it has been compiled
12181 by eliminating type mismatches, and providing active checks for range
12182 errors when your program is running.
12184 @value{GDBN} can check for conditions like the above if you wish.
12185 Although @value{GDBN} does not check the statements in your program,
12186 it can check expressions entered directly into @value{GDBN} for
12187 evaluation via the @code{print} command, for example. As with the
12188 working language, @value{GDBN} can also decide whether or not to check
12189 automatically based on your program's source language.
12190 @xref{Supported Languages, ,Supported Languages}, for the default
12191 settings of supported languages.
12194 * Type Checking:: An overview of type checking
12195 * Range Checking:: An overview of range checking
12198 @cindex type checking
12199 @cindex checks, type
12200 @node Type Checking
12201 @subsection An Overview of Type Checking
12203 Some languages, such as Modula-2, are strongly typed, meaning that the
12204 arguments to operators and functions have to be of the correct type,
12205 otherwise an error occurs. These checks prevent type mismatch
12206 errors from ever causing any run-time problems. For example,
12214 The second example fails because the @code{CARDINAL} 1 is not
12215 type-compatible with the @code{REAL} 2.3.
12217 For the expressions you use in @value{GDBN} commands, you can tell the
12218 @value{GDBN} type checker to skip checking;
12219 to treat any mismatches as errors and abandon the expression;
12220 or to only issue warnings when type mismatches occur,
12221 but evaluate the expression anyway. When you choose the last of
12222 these, @value{GDBN} evaluates expressions like the second example above, but
12223 also issues a warning.
12225 Even if you turn type checking off, there may be other reasons
12226 related to type that prevent @value{GDBN} from evaluating an expression.
12227 For instance, @value{GDBN} does not know how to add an @code{int} and
12228 a @code{struct foo}. These particular type errors have nothing to do
12229 with the language in use, and usually arise from expressions, such as
12230 the one described above, which make little sense to evaluate anyway.
12232 Each language defines to what degree it is strict about type. For
12233 instance, both Modula-2 and C require the arguments to arithmetical
12234 operators to be numbers. In C, enumerated types and pointers can be
12235 represented as numbers, so that they are valid arguments to mathematical
12236 operators. @xref{Supported Languages, ,Supported Languages}, for further
12237 details on specific languages.
12239 @value{GDBN} provides some additional commands for controlling the type checker:
12241 @kindex set check type
12242 @kindex show check type
12244 @item set check type auto
12245 Set type checking on or off based on the current working language.
12246 @xref{Supported Languages, ,Supported Languages}, for the default settings for
12249 @item set check type on
12250 @itemx set check type off
12251 Set type checking on or off, overriding the default setting for the
12252 current working language. Issue a warning if the setting does not
12253 match the language default. If any type mismatches occur in
12254 evaluating an expression while type checking is on, @value{GDBN} prints a
12255 message and aborts evaluation of the expression.
12257 @item set check type warn
12258 Cause the type checker to issue warnings, but to always attempt to
12259 evaluate the expression. Evaluating the expression may still
12260 be impossible for other reasons. For example, @value{GDBN} cannot add
12261 numbers and structures.
12264 Show the current setting of the type checker, and whether or not @value{GDBN}
12265 is setting it automatically.
12268 @cindex range checking
12269 @cindex checks, range
12270 @node Range Checking
12271 @subsection An Overview of Range Checking
12273 In some languages (such as Modula-2), it is an error to exceed the
12274 bounds of a type; this is enforced with run-time checks. Such range
12275 checking is meant to ensure program correctness by making sure
12276 computations do not overflow, or indices on an array element access do
12277 not exceed the bounds of the array.
12279 For expressions you use in @value{GDBN} commands, you can tell
12280 @value{GDBN} to treat range errors in one of three ways: ignore them,
12281 always treat them as errors and abandon the expression, or issue
12282 warnings but evaluate the expression anyway.
12284 A range error can result from numerical overflow, from exceeding an
12285 array index bound, or when you type a constant that is not a member
12286 of any type. Some languages, however, do not treat overflows as an
12287 error. In many implementations of C, mathematical overflow causes the
12288 result to ``wrap around'' to lower values---for example, if @var{m} is
12289 the largest integer value, and @var{s} is the smallest, then
12292 @var{m} + 1 @result{} @var{s}
12295 This, too, is specific to individual languages, and in some cases
12296 specific to individual compilers or machines. @xref{Supported Languages, ,
12297 Supported Languages}, for further details on specific languages.
12299 @value{GDBN} provides some additional commands for controlling the range checker:
12301 @kindex set check range
12302 @kindex show check range
12304 @item set check range auto
12305 Set range checking on or off based on the current working language.
12306 @xref{Supported Languages, ,Supported Languages}, for the default settings for
12309 @item set check range on
12310 @itemx set check range off
12311 Set range checking on or off, overriding the default setting for the
12312 current working language. A warning is issued if the setting does not
12313 match the language default. If a range error occurs and range checking is on,
12314 then a message is printed and evaluation of the expression is aborted.
12316 @item set check range warn
12317 Output messages when the @value{GDBN} range checker detects a range error,
12318 but attempt to evaluate the expression anyway. Evaluating the
12319 expression may still be impossible for other reasons, such as accessing
12320 memory that the process does not own (a typical example from many Unix
12324 Show the current setting of the range checker, and whether or not it is
12325 being set automatically by @value{GDBN}.
12328 @node Supported Languages
12329 @section Supported Languages
12331 @value{GDBN} supports C, C@t{++}, D, Objective-C, Fortran, Java, OpenCL C, Pascal,
12332 assembly, Modula-2, and Ada.
12333 @c This is false ...
12334 Some @value{GDBN} features may be used in expressions regardless of the
12335 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
12336 and the @samp{@{type@}addr} construct (@pxref{Expressions,
12337 ,Expressions}) can be used with the constructs of any supported
12340 The following sections detail to what degree each source language is
12341 supported by @value{GDBN}. These sections are not meant to be language
12342 tutorials or references, but serve only as a reference guide to what the
12343 @value{GDBN} expression parser accepts, and what input and output
12344 formats should look like for different languages. There are many good
12345 books written on each of these languages; please look to these for a
12346 language reference or tutorial.
12349 * C:: C and C@t{++}
12351 * Objective-C:: Objective-C
12352 * OpenCL C:: OpenCL C
12353 * Fortran:: Fortran
12355 * Modula-2:: Modula-2
12360 @subsection C and C@t{++}
12362 @cindex C and C@t{++}
12363 @cindex expressions in C or C@t{++}
12365 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
12366 to both languages. Whenever this is the case, we discuss those languages
12370 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
12371 @cindex @sc{gnu} C@t{++}
12372 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
12373 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
12374 effectively, you must compile your C@t{++} programs with a supported
12375 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
12376 compiler (@code{aCC}).
12379 * C Operators:: C and C@t{++} operators
12380 * C Constants:: C and C@t{++} constants
12381 * C Plus Plus Expressions:: C@t{++} expressions
12382 * C Defaults:: Default settings for C and C@t{++}
12383 * C Checks:: C and C@t{++} type and range checks
12384 * Debugging C:: @value{GDBN} and C
12385 * Debugging C Plus Plus:: @value{GDBN} features for C@t{++}
12386 * Decimal Floating Point:: Numbers in Decimal Floating Point format
12390 @subsubsection C and C@t{++} Operators
12392 @cindex C and C@t{++} operators
12394 Operators must be defined on values of specific types. For instance,
12395 @code{+} is defined on numbers, but not on structures. Operators are
12396 often defined on groups of types.
12398 For the purposes of C and C@t{++}, the following definitions hold:
12403 @emph{Integral types} include @code{int} with any of its storage-class
12404 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
12407 @emph{Floating-point types} include @code{float}, @code{double}, and
12408 @code{long double} (if supported by the target platform).
12411 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
12414 @emph{Scalar types} include all of the above.
12419 The following operators are supported. They are listed here
12420 in order of increasing precedence:
12424 The comma or sequencing operator. Expressions in a comma-separated list
12425 are evaluated from left to right, with the result of the entire
12426 expression being the last expression evaluated.
12429 Assignment. The value of an assignment expression is the value
12430 assigned. Defined on scalar types.
12433 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
12434 and translated to @w{@code{@var{a} = @var{a op b}}}.
12435 @w{@code{@var{op}=}} and @code{=} have the same precedence.
12436 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
12437 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
12440 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
12441 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
12445 Logical @sc{or}. Defined on integral types.
12448 Logical @sc{and}. Defined on integral types.
12451 Bitwise @sc{or}. Defined on integral types.
12454 Bitwise exclusive-@sc{or}. Defined on integral types.
12457 Bitwise @sc{and}. Defined on integral types.
12460 Equality and inequality. Defined on scalar types. The value of these
12461 expressions is 0 for false and non-zero for true.
12463 @item <@r{, }>@r{, }<=@r{, }>=
12464 Less than, greater than, less than or equal, greater than or equal.
12465 Defined on scalar types. The value of these expressions is 0 for false
12466 and non-zero for true.
12469 left shift, and right shift. Defined on integral types.
12472 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
12475 Addition and subtraction. Defined on integral types, floating-point types and
12478 @item *@r{, }/@r{, }%
12479 Multiplication, division, and modulus. Multiplication and division are
12480 defined on integral and floating-point types. Modulus is defined on
12484 Increment and decrement. When appearing before a variable, the
12485 operation is performed before the variable is used in an expression;
12486 when appearing after it, the variable's value is used before the
12487 operation takes place.
12490 Pointer dereferencing. Defined on pointer types. Same precedence as
12494 Address operator. Defined on variables. Same precedence as @code{++}.
12496 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
12497 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
12498 to examine the address
12499 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
12503 Negative. Defined on integral and floating-point types. Same
12504 precedence as @code{++}.
12507 Logical negation. Defined on integral types. Same precedence as
12511 Bitwise complement operator. Defined on integral types. Same precedence as
12516 Structure member, and pointer-to-structure member. For convenience,
12517 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
12518 pointer based on the stored type information.
12519 Defined on @code{struct} and @code{union} data.
12522 Dereferences of pointers to members.
12525 Array indexing. @code{@var{a}[@var{i}]} is defined as
12526 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
12529 Function parameter list. Same precedence as @code{->}.
12532 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
12533 and @code{class} types.
12536 Doubled colons also represent the @value{GDBN} scope operator
12537 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
12541 If an operator is redefined in the user code, @value{GDBN} usually
12542 attempts to invoke the redefined version instead of using the operator's
12543 predefined meaning.
12546 @subsubsection C and C@t{++} Constants
12548 @cindex C and C@t{++} constants
12550 @value{GDBN} allows you to express the constants of C and C@t{++} in the
12555 Integer constants are a sequence of digits. Octal constants are
12556 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
12557 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
12558 @samp{l}, specifying that the constant should be treated as a
12562 Floating point constants are a sequence of digits, followed by a decimal
12563 point, followed by a sequence of digits, and optionally followed by an
12564 exponent. An exponent is of the form:
12565 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
12566 sequence of digits. The @samp{+} is optional for positive exponents.
12567 A floating-point constant may also end with a letter @samp{f} or
12568 @samp{F}, specifying that the constant should be treated as being of
12569 the @code{float} (as opposed to the default @code{double}) type; or with
12570 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
12574 Enumerated constants consist of enumerated identifiers, or their
12575 integral equivalents.
12578 Character constants are a single character surrounded by single quotes
12579 (@code{'}), or a number---the ordinal value of the corresponding character
12580 (usually its @sc{ascii} value). Within quotes, the single character may
12581 be represented by a letter or by @dfn{escape sequences}, which are of
12582 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
12583 of the character's ordinal value; or of the form @samp{\@var{x}}, where
12584 @samp{@var{x}} is a predefined special character---for example,
12585 @samp{\n} for newline.
12587 Wide character constants can be written by prefixing a character
12588 constant with @samp{L}, as in C. For example, @samp{L'x'} is the wide
12589 form of @samp{x}. The target wide character set is used when
12590 computing the value of this constant (@pxref{Character Sets}).
12593 String constants are a sequence of character constants surrounded by
12594 double quotes (@code{"}). Any valid character constant (as described
12595 above) may appear. Double quotes within the string must be preceded by
12596 a backslash, so for instance @samp{"a\"b'c"} is a string of five
12599 Wide string constants can be written by prefixing a string constant
12600 with @samp{L}, as in C. The target wide character set is used when
12601 computing the value of this constant (@pxref{Character Sets}).
12604 Pointer constants are an integral value. You can also write pointers
12605 to constants using the C operator @samp{&}.
12608 Array constants are comma-separated lists surrounded by braces @samp{@{}
12609 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
12610 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
12611 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
12614 @node C Plus Plus Expressions
12615 @subsubsection C@t{++} Expressions
12617 @cindex expressions in C@t{++}
12618 @value{GDBN} expression handling can interpret most C@t{++} expressions.
12620 @cindex debugging C@t{++} programs
12621 @cindex C@t{++} compilers
12622 @cindex debug formats and C@t{++}
12623 @cindex @value{NGCC} and C@t{++}
12625 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use
12626 the proper compiler and the proper debug format. Currently,
12627 @value{GDBN} works best when debugging C@t{++} code that is compiled
12628 with the most recent version of @value{NGCC} possible. The DWARF
12629 debugging format is preferred; @value{NGCC} defaults to this on most
12630 popular platforms. Other compilers and/or debug formats are likely to
12631 work badly or not at all when using @value{GDBN} to debug C@t{++}
12632 code. @xref{Compilation}.
12637 @cindex member functions
12639 Member function calls are allowed; you can use expressions like
12642 count = aml->GetOriginal(x, y)
12645 @vindex this@r{, inside C@t{++} member functions}
12646 @cindex namespace in C@t{++}
12648 While a member function is active (in the selected stack frame), your
12649 expressions have the same namespace available as the member function;
12650 that is, @value{GDBN} allows implicit references to the class instance
12651 pointer @code{this} following the same rules as C@t{++}. @code{using}
12652 declarations in the current scope are also respected by @value{GDBN}.
12654 @cindex call overloaded functions
12655 @cindex overloaded functions, calling
12656 @cindex type conversions in C@t{++}
12658 You can call overloaded functions; @value{GDBN} resolves the function
12659 call to the right definition, with some restrictions. @value{GDBN} does not
12660 perform overload resolution involving user-defined type conversions,
12661 calls to constructors, or instantiations of templates that do not exist
12662 in the program. It also cannot handle ellipsis argument lists or
12665 It does perform integral conversions and promotions, floating-point
12666 promotions, arithmetic conversions, pointer conversions, conversions of
12667 class objects to base classes, and standard conversions such as those of
12668 functions or arrays to pointers; it requires an exact match on the
12669 number of function arguments.
12671 Overload resolution is always performed, unless you have specified
12672 @code{set overload-resolution off}. @xref{Debugging C Plus Plus,
12673 ,@value{GDBN} Features for C@t{++}}.
12675 You must specify @code{set overload-resolution off} in order to use an
12676 explicit function signature to call an overloaded function, as in
12678 p 'foo(char,int)'('x', 13)
12681 The @value{GDBN} command-completion facility can simplify this;
12682 see @ref{Completion, ,Command Completion}.
12684 @cindex reference declarations
12686 @value{GDBN} understands variables declared as C@t{++} references; you can use
12687 them in expressions just as you do in C@t{++} source---they are automatically
12690 In the parameter list shown when @value{GDBN} displays a frame, the values of
12691 reference variables are not displayed (unlike other variables); this
12692 avoids clutter, since references are often used for large structures.
12693 The @emph{address} of a reference variable is always shown, unless
12694 you have specified @samp{set print address off}.
12697 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
12698 expressions can use it just as expressions in your program do. Since
12699 one scope may be defined in another, you can use @code{::} repeatedly if
12700 necessary, for example in an expression like
12701 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
12702 resolving name scope by reference to source files, in both C and C@t{++}
12703 debugging (@pxref{Variables, ,Program Variables}).
12706 @value{GDBN} performs argument-dependent lookup, following the C@t{++}
12711 @subsubsection C and C@t{++} Defaults
12713 @cindex C and C@t{++} defaults
12715 If you allow @value{GDBN} to set type and range checking automatically, they
12716 both default to @code{off} whenever the working language changes to
12717 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
12718 selects the working language.
12720 If you allow @value{GDBN} to set the language automatically, it
12721 recognizes source files whose names end with @file{.c}, @file{.C}, or
12722 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
12723 these files, it sets the working language to C or C@t{++}.
12724 @xref{Automatically, ,Having @value{GDBN} Infer the Source Language},
12725 for further details.
12727 @c Type checking is (a) primarily motivated by Modula-2, and (b)
12728 @c unimplemented. If (b) changes, it might make sense to let this node
12729 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
12732 @subsubsection C and C@t{++} Type and Range Checks
12734 @cindex C and C@t{++} checks
12736 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
12737 is not used. However, if you turn type checking on, @value{GDBN}
12738 considers two variables type equivalent if:
12742 The two variables are structured and have the same structure, union, or
12746 The two variables have the same type name, or types that have been
12747 declared equivalent through @code{typedef}.
12750 @c leaving this out because neither J Gilmore nor R Pesch understand it.
12753 The two @code{struct}, @code{union}, or @code{enum} variables are
12754 declared in the same declaration. (Note: this may not be true for all C
12759 Range checking, if turned on, is done on mathematical operations. Array
12760 indices are not checked, since they are often used to index a pointer
12761 that is not itself an array.
12764 @subsubsection @value{GDBN} and C
12766 The @code{set print union} and @code{show print union} commands apply to
12767 the @code{union} type. When set to @samp{on}, any @code{union} that is
12768 inside a @code{struct} or @code{class} is also printed. Otherwise, it
12769 appears as @samp{@{...@}}.
12771 The @code{@@} operator aids in the debugging of dynamic arrays, formed
12772 with pointers and a memory allocation function. @xref{Expressions,
12775 @node Debugging C Plus Plus
12776 @subsubsection @value{GDBN} Features for C@t{++}
12778 @cindex commands for C@t{++}
12780 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
12781 designed specifically for use with C@t{++}. Here is a summary:
12784 @cindex break in overloaded functions
12785 @item @r{breakpoint menus}
12786 When you want a breakpoint in a function whose name is overloaded,
12787 @value{GDBN} has the capability to display a menu of possible breakpoint
12788 locations to help you specify which function definition you want.
12789 @xref{Ambiguous Expressions,,Ambiguous Expressions}.
12791 @cindex overloading in C@t{++}
12792 @item rbreak @var{regex}
12793 Setting breakpoints using regular expressions is helpful for setting
12794 breakpoints on overloaded functions that are not members of any special
12796 @xref{Set Breaks, ,Setting Breakpoints}.
12798 @cindex C@t{++} exception handling
12801 Debug C@t{++} exception handling using these commands. @xref{Set
12802 Catchpoints, , Setting Catchpoints}.
12804 @cindex inheritance
12805 @item ptype @var{typename}
12806 Print inheritance relationships as well as other information for type
12808 @xref{Symbols, ,Examining the Symbol Table}.
12810 @item info vtbl @var{expression}.
12811 The @code{info vtbl} command can be used to display the virtual
12812 method tables of the object computed by @var{expression}. This shows
12813 one entry per virtual table; there may be multiple virtual tables when
12814 multiple inheritance is in use.
12816 @cindex C@t{++} symbol display
12817 @item set print demangle
12818 @itemx show print demangle
12819 @itemx set print asm-demangle
12820 @itemx show print asm-demangle
12821 Control whether C@t{++} symbols display in their source form, both when
12822 displaying code as C@t{++} source and when displaying disassemblies.
12823 @xref{Print Settings, ,Print Settings}.
12825 @item set print object
12826 @itemx show print object
12827 Choose whether to print derived (actual) or declared types of objects.
12828 @xref{Print Settings, ,Print Settings}.
12830 @item set print vtbl
12831 @itemx show print vtbl
12832 Control the format for printing virtual function tables.
12833 @xref{Print Settings, ,Print Settings}.
12834 (The @code{vtbl} commands do not work on programs compiled with the HP
12835 ANSI C@t{++} compiler (@code{aCC}).)
12837 @kindex set overload-resolution
12838 @cindex overloaded functions, overload resolution
12839 @item set overload-resolution on
12840 Enable overload resolution for C@t{++} expression evaluation. The default
12841 is on. For overloaded functions, @value{GDBN} evaluates the arguments
12842 and searches for a function whose signature matches the argument types,
12843 using the standard C@t{++} conversion rules (see @ref{C Plus Plus
12844 Expressions, ,C@t{++} Expressions}, for details).
12845 If it cannot find a match, it emits a message.
12847 @item set overload-resolution off
12848 Disable overload resolution for C@t{++} expression evaluation. For
12849 overloaded functions that are not class member functions, @value{GDBN}
12850 chooses the first function of the specified name that it finds in the
12851 symbol table, whether or not its arguments are of the correct type. For
12852 overloaded functions that are class member functions, @value{GDBN}
12853 searches for a function whose signature @emph{exactly} matches the
12856 @kindex show overload-resolution
12857 @item show overload-resolution
12858 Show the current setting of overload resolution.
12860 @item @r{Overloaded symbol names}
12861 You can specify a particular definition of an overloaded symbol, using
12862 the same notation that is used to declare such symbols in C@t{++}: type
12863 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
12864 also use the @value{GDBN} command-line word completion facilities to list the
12865 available choices, or to finish the type list for you.
12866 @xref{Completion,, Command Completion}, for details on how to do this.
12869 @node Decimal Floating Point
12870 @subsubsection Decimal Floating Point format
12871 @cindex decimal floating point format
12873 @value{GDBN} can examine, set and perform computations with numbers in
12874 decimal floating point format, which in the C language correspond to the
12875 @code{_Decimal32}, @code{_Decimal64} and @code{_Decimal128} types as
12876 specified by the extension to support decimal floating-point arithmetic.
12878 There are two encodings in use, depending on the architecture: BID (Binary
12879 Integer Decimal) for x86 and x86-64, and DPD (Densely Packed Decimal) for
12880 PowerPC. @value{GDBN} will use the appropriate encoding for the configured
12883 Because of a limitation in @file{libdecnumber}, the library used by @value{GDBN}
12884 to manipulate decimal floating point numbers, it is not possible to convert
12885 (using a cast, for example) integers wider than 32-bit to decimal float.
12887 In addition, in order to imitate @value{GDBN}'s behaviour with binary floating
12888 point computations, error checking in decimal float operations ignores
12889 underflow, overflow and divide by zero exceptions.
12891 In the PowerPC architecture, @value{GDBN} provides a set of pseudo-registers
12892 to inspect @code{_Decimal128} values stored in floating point registers.
12893 See @ref{PowerPC,,PowerPC} for more details.
12899 @value{GDBN} can be used to debug programs written in D and compiled with
12900 GDC, LDC or DMD compilers. Currently @value{GDBN} supports only one D
12901 specific feature --- dynamic arrays.
12904 @subsection Objective-C
12906 @cindex Objective-C
12907 This section provides information about some commands and command
12908 options that are useful for debugging Objective-C code. See also
12909 @ref{Symbols, info classes}, and @ref{Symbols, info selectors}, for a
12910 few more commands specific to Objective-C support.
12913 * Method Names in Commands::
12914 * The Print Command with Objective-C::
12917 @node Method Names in Commands
12918 @subsubsection Method Names in Commands
12920 The following commands have been extended to accept Objective-C method
12921 names as line specifications:
12923 @kindex clear@r{, and Objective-C}
12924 @kindex break@r{, and Objective-C}
12925 @kindex info line@r{, and Objective-C}
12926 @kindex jump@r{, and Objective-C}
12927 @kindex list@r{, and Objective-C}
12931 @item @code{info line}
12936 A fully qualified Objective-C method name is specified as
12939 -[@var{Class} @var{methodName}]
12942 where the minus sign is used to indicate an instance method and a
12943 plus sign (not shown) is used to indicate a class method. The class
12944 name @var{Class} and method name @var{methodName} are enclosed in
12945 brackets, similar to the way messages are specified in Objective-C
12946 source code. For example, to set a breakpoint at the @code{create}
12947 instance method of class @code{Fruit} in the program currently being
12951 break -[Fruit create]
12954 To list ten program lines around the @code{initialize} class method,
12958 list +[NSText initialize]
12961 In the current version of @value{GDBN}, the plus or minus sign is
12962 required. In future versions of @value{GDBN}, the plus or minus
12963 sign will be optional, but you can use it to narrow the search. It
12964 is also possible to specify just a method name:
12970 You must specify the complete method name, including any colons. If
12971 your program's source files contain more than one @code{create} method,
12972 you'll be presented with a numbered list of classes that implement that
12973 method. Indicate your choice by number, or type @samp{0} to exit if
12976 As another example, to clear a breakpoint established at the
12977 @code{makeKeyAndOrderFront:} method of the @code{NSWindow} class, enter:
12980 clear -[NSWindow makeKeyAndOrderFront:]
12983 @node The Print Command with Objective-C
12984 @subsubsection The Print Command With Objective-C
12985 @cindex Objective-C, print objects
12986 @kindex print-object
12987 @kindex po @r{(@code{print-object})}
12989 The print command has also been extended to accept methods. For example:
12992 print -[@var{object} hash]
12995 @cindex print an Objective-C object description
12996 @cindex @code{_NSPrintForDebugger}, and printing Objective-C objects
12998 will tell @value{GDBN} to send the @code{hash} message to @var{object}
12999 and print the result. Also, an additional command has been added,
13000 @code{print-object} or @code{po} for short, which is meant to print
13001 the description of an object. However, this command may only work
13002 with certain Objective-C libraries that have a particular hook
13003 function, @code{_NSPrintForDebugger}, defined.
13006 @subsection OpenCL C
13009 This section provides information about @value{GDBN}s OpenCL C support.
13012 * OpenCL C Datatypes::
13013 * OpenCL C Expressions::
13014 * OpenCL C Operators::
13017 @node OpenCL C Datatypes
13018 @subsubsection OpenCL C Datatypes
13020 @cindex OpenCL C Datatypes
13021 @value{GDBN} supports the builtin scalar and vector datatypes specified
13022 by OpenCL 1.1. In addition the half- and double-precision floating point
13023 data types of the @code{cl_khr_fp16} and @code{cl_khr_fp64} OpenCL
13024 extensions are also known to @value{GDBN}.
13026 @node OpenCL C Expressions
13027 @subsubsection OpenCL C Expressions
13029 @cindex OpenCL C Expressions
13030 @value{GDBN} supports accesses to vector components including the access as
13031 lvalue where possible. Since OpenCL C is based on C99 most C expressions
13032 supported by @value{GDBN} can be used as well.
13034 @node OpenCL C Operators
13035 @subsubsection OpenCL C Operators
13037 @cindex OpenCL C Operators
13038 @value{GDBN} supports the operators specified by OpenCL 1.1 for scalar and
13042 @subsection Fortran
13043 @cindex Fortran-specific support in @value{GDBN}
13045 @value{GDBN} can be used to debug programs written in Fortran, but it
13046 currently supports only the features of Fortran 77 language.
13048 @cindex trailing underscore, in Fortran symbols
13049 Some Fortran compilers (@sc{gnu} Fortran 77 and Fortran 95 compilers
13050 among them) append an underscore to the names of variables and
13051 functions. When you debug programs compiled by those compilers, you
13052 will need to refer to variables and functions with a trailing
13056 * Fortran Operators:: Fortran operators and expressions
13057 * Fortran Defaults:: Default settings for Fortran
13058 * Special Fortran Commands:: Special @value{GDBN} commands for Fortran
13061 @node Fortran Operators
13062 @subsubsection Fortran Operators and Expressions
13064 @cindex Fortran operators and expressions
13066 Operators must be defined on values of specific types. For instance,
13067 @code{+} is defined on numbers, but not on characters or other non-
13068 arithmetic types. Operators are often defined on groups of types.
13072 The exponentiation operator. It raises the first operand to the power
13076 The range operator. Normally used in the form of array(low:high) to
13077 represent a section of array.
13080 The access component operator. Normally used to access elements in derived
13081 types. Also suitable for unions. As unions aren't part of regular Fortran,
13082 this can only happen when accessing a register that uses a gdbarch-defined
13086 @node Fortran Defaults
13087 @subsubsection Fortran Defaults
13089 @cindex Fortran Defaults
13091 Fortran symbols are usually case-insensitive, so @value{GDBN} by
13092 default uses case-insensitive matches for Fortran symbols. You can
13093 change that with the @samp{set case-insensitive} command, see
13094 @ref{Symbols}, for the details.
13096 @node Special Fortran Commands
13097 @subsubsection Special Fortran Commands
13099 @cindex Special Fortran commands
13101 @value{GDBN} has some commands to support Fortran-specific features,
13102 such as displaying common blocks.
13105 @cindex @code{COMMON} blocks, Fortran
13106 @kindex info common
13107 @item info common @r{[}@var{common-name}@r{]}
13108 This command prints the values contained in the Fortran @code{COMMON}
13109 block whose name is @var{common-name}. With no argument, the names of
13110 all @code{COMMON} blocks visible at the current program location are
13117 @cindex Pascal support in @value{GDBN}, limitations
13118 Debugging Pascal programs which use sets, subranges, file variables, or
13119 nested functions does not currently work. @value{GDBN} does not support
13120 entering expressions, printing values, or similar features using Pascal
13123 The Pascal-specific command @code{set print pascal_static-members}
13124 controls whether static members of Pascal objects are displayed.
13125 @xref{Print Settings, pascal_static-members}.
13128 @subsection Modula-2
13130 @cindex Modula-2, @value{GDBN} support
13132 The extensions made to @value{GDBN} to support Modula-2 only support
13133 output from the @sc{gnu} Modula-2 compiler (which is currently being
13134 developed). Other Modula-2 compilers are not currently supported, and
13135 attempting to debug executables produced by them is most likely
13136 to give an error as @value{GDBN} reads in the executable's symbol
13139 @cindex expressions in Modula-2
13141 * M2 Operators:: Built-in operators
13142 * Built-In Func/Proc:: Built-in functions and procedures
13143 * M2 Constants:: Modula-2 constants
13144 * M2 Types:: Modula-2 types
13145 * M2 Defaults:: Default settings for Modula-2
13146 * Deviations:: Deviations from standard Modula-2
13147 * M2 Checks:: Modula-2 type and range checks
13148 * M2 Scope:: The scope operators @code{::} and @code{.}
13149 * GDB/M2:: @value{GDBN} and Modula-2
13153 @subsubsection Operators
13154 @cindex Modula-2 operators
13156 Operators must be defined on values of specific types. For instance,
13157 @code{+} is defined on numbers, but not on structures. Operators are
13158 often defined on groups of types. For the purposes of Modula-2, the
13159 following definitions hold:
13164 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
13168 @emph{Character types} consist of @code{CHAR} and its subranges.
13171 @emph{Floating-point types} consist of @code{REAL}.
13174 @emph{Pointer types} consist of anything declared as @code{POINTER TO
13178 @emph{Scalar types} consist of all of the above.
13181 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
13184 @emph{Boolean types} consist of @code{BOOLEAN}.
13188 The following operators are supported, and appear in order of
13189 increasing precedence:
13193 Function argument or array index separator.
13196 Assignment. The value of @var{var} @code{:=} @var{value} is
13200 Less than, greater than on integral, floating-point, or enumerated
13204 Less than or equal to, greater than or equal to
13205 on integral, floating-point and enumerated types, or set inclusion on
13206 set types. Same precedence as @code{<}.
13208 @item =@r{, }<>@r{, }#
13209 Equality and two ways of expressing inequality, valid on scalar types.
13210 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
13211 available for inequality, since @code{#} conflicts with the script
13215 Set membership. Defined on set types and the types of their members.
13216 Same precedence as @code{<}.
13219 Boolean disjunction. Defined on boolean types.
13222 Boolean conjunction. Defined on boolean types.
13225 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
13228 Addition and subtraction on integral and floating-point types, or union
13229 and difference on set types.
13232 Multiplication on integral and floating-point types, or set intersection
13236 Division on floating-point types, or symmetric set difference on set
13237 types. Same precedence as @code{*}.
13240 Integer division and remainder. Defined on integral types. Same
13241 precedence as @code{*}.
13244 Negative. Defined on @code{INTEGER} and @code{REAL} data.
13247 Pointer dereferencing. Defined on pointer types.
13250 Boolean negation. Defined on boolean types. Same precedence as
13254 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
13255 precedence as @code{^}.
13258 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
13261 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
13265 @value{GDBN} and Modula-2 scope operators.
13269 @emph{Warning:} Set expressions and their operations are not yet supported, so @value{GDBN}
13270 treats the use of the operator @code{IN}, or the use of operators
13271 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
13272 @code{<=}, and @code{>=} on sets as an error.
13276 @node Built-In Func/Proc
13277 @subsubsection Built-in Functions and Procedures
13278 @cindex Modula-2 built-ins
13280 Modula-2 also makes available several built-in procedures and functions.
13281 In describing these, the following metavariables are used:
13286 represents an @code{ARRAY} variable.
13289 represents a @code{CHAR} constant or variable.
13292 represents a variable or constant of integral type.
13295 represents an identifier that belongs to a set. Generally used in the
13296 same function with the metavariable @var{s}. The type of @var{s} should
13297 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
13300 represents a variable or constant of integral or floating-point type.
13303 represents a variable or constant of floating-point type.
13309 represents a variable.
13312 represents a variable or constant of one of many types. See the
13313 explanation of the function for details.
13316 All Modula-2 built-in procedures also return a result, described below.
13320 Returns the absolute value of @var{n}.
13323 If @var{c} is a lower case letter, it returns its upper case
13324 equivalent, otherwise it returns its argument.
13327 Returns the character whose ordinal value is @var{i}.
13330 Decrements the value in the variable @var{v} by one. Returns the new value.
13332 @item DEC(@var{v},@var{i})
13333 Decrements the value in the variable @var{v} by @var{i}. Returns the
13336 @item EXCL(@var{m},@var{s})
13337 Removes the element @var{m} from the set @var{s}. Returns the new
13340 @item FLOAT(@var{i})
13341 Returns the floating point equivalent of the integer @var{i}.
13343 @item HIGH(@var{a})
13344 Returns the index of the last member of @var{a}.
13347 Increments the value in the variable @var{v} by one. Returns the new value.
13349 @item INC(@var{v},@var{i})
13350 Increments the value in the variable @var{v} by @var{i}. Returns the
13353 @item INCL(@var{m},@var{s})
13354 Adds the element @var{m} to the set @var{s} if it is not already
13355 there. Returns the new set.
13358 Returns the maximum value of the type @var{t}.
13361 Returns the minimum value of the type @var{t}.
13364 Returns boolean TRUE if @var{i} is an odd number.
13367 Returns the ordinal value of its argument. For example, the ordinal
13368 value of a character is its @sc{ascii} value (on machines supporting the
13369 @sc{ascii} character set). @var{x} must be of an ordered type, which include
13370 integral, character and enumerated types.
13372 @item SIZE(@var{x})
13373 Returns the size of its argument. @var{x} can be a variable or a type.
13375 @item TRUNC(@var{r})
13376 Returns the integral part of @var{r}.
13378 @item TSIZE(@var{x})
13379 Returns the size of its argument. @var{x} can be a variable or a type.
13381 @item VAL(@var{t},@var{i})
13382 Returns the member of the type @var{t} whose ordinal value is @var{i}.
13386 @emph{Warning:} Sets and their operations are not yet supported, so
13387 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
13391 @cindex Modula-2 constants
13393 @subsubsection Constants
13395 @value{GDBN} allows you to express the constants of Modula-2 in the following
13401 Integer constants are simply a sequence of digits. When used in an
13402 expression, a constant is interpreted to be type-compatible with the
13403 rest of the expression. Hexadecimal integers are specified by a
13404 trailing @samp{H}, and octal integers by a trailing @samp{B}.
13407 Floating point constants appear as a sequence of digits, followed by a
13408 decimal point and another sequence of digits. An optional exponent can
13409 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
13410 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
13411 digits of the floating point constant must be valid decimal (base 10)
13415 Character constants consist of a single character enclosed by a pair of
13416 like quotes, either single (@code{'}) or double (@code{"}). They may
13417 also be expressed by their ordinal value (their @sc{ascii} value, usually)
13418 followed by a @samp{C}.
13421 String constants consist of a sequence of characters enclosed by a
13422 pair of like quotes, either single (@code{'}) or double (@code{"}).
13423 Escape sequences in the style of C are also allowed. @xref{C
13424 Constants, ,C and C@t{++} Constants}, for a brief explanation of escape
13428 Enumerated constants consist of an enumerated identifier.
13431 Boolean constants consist of the identifiers @code{TRUE} and
13435 Pointer constants consist of integral values only.
13438 Set constants are not yet supported.
13442 @subsubsection Modula-2 Types
13443 @cindex Modula-2 types
13445 Currently @value{GDBN} can print the following data types in Modula-2
13446 syntax: array types, record types, set types, pointer types, procedure
13447 types, enumerated types, subrange types and base types. You can also
13448 print the contents of variables declared using these type.
13449 This section gives a number of simple source code examples together with
13450 sample @value{GDBN} sessions.
13452 The first example contains the following section of code:
13461 and you can request @value{GDBN} to interrogate the type and value of
13462 @code{r} and @code{s}.
13465 (@value{GDBP}) print s
13467 (@value{GDBP}) ptype s
13469 (@value{GDBP}) print r
13471 (@value{GDBP}) ptype r
13476 Likewise if your source code declares @code{s} as:
13480 s: SET ['A'..'Z'] ;
13484 then you may query the type of @code{s} by:
13487 (@value{GDBP}) ptype s
13488 type = SET ['A'..'Z']
13492 Note that at present you cannot interactively manipulate set
13493 expressions using the debugger.
13495 The following example shows how you might declare an array in Modula-2
13496 and how you can interact with @value{GDBN} to print its type and contents:
13500 s: ARRAY [-10..10] OF CHAR ;
13504 (@value{GDBP}) ptype s
13505 ARRAY [-10..10] OF CHAR
13508 Note that the array handling is not yet complete and although the type
13509 is printed correctly, expression handling still assumes that all
13510 arrays have a lower bound of zero and not @code{-10} as in the example
13513 Here are some more type related Modula-2 examples:
13517 colour = (blue, red, yellow, green) ;
13518 t = [blue..yellow] ;
13526 The @value{GDBN} interaction shows how you can query the data type
13527 and value of a variable.
13530 (@value{GDBP}) print s
13532 (@value{GDBP}) ptype t
13533 type = [blue..yellow]
13537 In this example a Modula-2 array is declared and its contents
13538 displayed. Observe that the contents are written in the same way as
13539 their @code{C} counterparts.
13543 s: ARRAY [1..5] OF CARDINAL ;
13549 (@value{GDBP}) print s
13550 $1 = @{1, 0, 0, 0, 0@}
13551 (@value{GDBP}) ptype s
13552 type = ARRAY [1..5] OF CARDINAL
13555 The Modula-2 language interface to @value{GDBN} also understands
13556 pointer types as shown in this example:
13560 s: POINTER TO ARRAY [1..5] OF CARDINAL ;
13567 and you can request that @value{GDBN} describes the type of @code{s}.
13570 (@value{GDBP}) ptype s
13571 type = POINTER TO ARRAY [1..5] OF CARDINAL
13574 @value{GDBN} handles compound types as we can see in this example.
13575 Here we combine array types, record types, pointer types and subrange
13586 myarray = ARRAY myrange OF CARDINAL ;
13587 myrange = [-2..2] ;
13589 s: POINTER TO ARRAY myrange OF foo ;
13593 and you can ask @value{GDBN} to describe the type of @code{s} as shown
13597 (@value{GDBP}) ptype s
13598 type = POINTER TO ARRAY [-2..2] OF foo = RECORD
13601 f3 : ARRAY [-2..2] OF CARDINAL;
13606 @subsubsection Modula-2 Defaults
13607 @cindex Modula-2 defaults
13609 If type and range checking are set automatically by @value{GDBN}, they
13610 both default to @code{on} whenever the working language changes to
13611 Modula-2. This happens regardless of whether you or @value{GDBN}
13612 selected the working language.
13614 If you allow @value{GDBN} to set the language automatically, then entering
13615 code compiled from a file whose name ends with @file{.mod} sets the
13616 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN}
13617 Infer the Source Language}, for further details.
13620 @subsubsection Deviations from Standard Modula-2
13621 @cindex Modula-2, deviations from
13623 A few changes have been made to make Modula-2 programs easier to debug.
13624 This is done primarily via loosening its type strictness:
13628 Unlike in standard Modula-2, pointer constants can be formed by
13629 integers. This allows you to modify pointer variables during
13630 debugging. (In standard Modula-2, the actual address contained in a
13631 pointer variable is hidden from you; it can only be modified
13632 through direct assignment to another pointer variable or expression that
13633 returned a pointer.)
13636 C escape sequences can be used in strings and characters to represent
13637 non-printable characters. @value{GDBN} prints out strings with these
13638 escape sequences embedded. Single non-printable characters are
13639 printed using the @samp{CHR(@var{nnn})} format.
13642 The assignment operator (@code{:=}) returns the value of its right-hand
13646 All built-in procedures both modify @emph{and} return their argument.
13650 @subsubsection Modula-2 Type and Range Checks
13651 @cindex Modula-2 checks
13654 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
13657 @c FIXME remove warning when type/range checks added
13659 @value{GDBN} considers two Modula-2 variables type equivalent if:
13663 They are of types that have been declared equivalent via a @code{TYPE
13664 @var{t1} = @var{t2}} statement
13667 They have been declared on the same line. (Note: This is true of the
13668 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
13671 As long as type checking is enabled, any attempt to combine variables
13672 whose types are not equivalent is an error.
13674 Range checking is done on all mathematical operations, assignment, array
13675 index bounds, and all built-in functions and procedures.
13678 @subsubsection The Scope Operators @code{::} and @code{.}
13680 @cindex @code{.}, Modula-2 scope operator
13681 @cindex colon, doubled as scope operator
13683 @vindex colon-colon@r{, in Modula-2}
13684 @c Info cannot handle :: but TeX can.
13687 @vindex ::@r{, in Modula-2}
13690 There are a few subtle differences between the Modula-2 scope operator
13691 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
13696 @var{module} . @var{id}
13697 @var{scope} :: @var{id}
13701 where @var{scope} is the name of a module or a procedure,
13702 @var{module} the name of a module, and @var{id} is any declared
13703 identifier within your program, except another module.
13705 Using the @code{::} operator makes @value{GDBN} search the scope
13706 specified by @var{scope} for the identifier @var{id}. If it is not
13707 found in the specified scope, then @value{GDBN} searches all scopes
13708 enclosing the one specified by @var{scope}.
13710 Using the @code{.} operator makes @value{GDBN} search the current scope for
13711 the identifier specified by @var{id} that was imported from the
13712 definition module specified by @var{module}. With this operator, it is
13713 an error if the identifier @var{id} was not imported from definition
13714 module @var{module}, or if @var{id} is not an identifier in
13718 @subsubsection @value{GDBN} and Modula-2
13720 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
13721 Five subcommands of @code{set print} and @code{show print} apply
13722 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
13723 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
13724 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
13725 analogue in Modula-2.
13727 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
13728 with any language, is not useful with Modula-2. Its
13729 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
13730 created in Modula-2 as they can in C or C@t{++}. However, because an
13731 address can be specified by an integral constant, the construct
13732 @samp{@{@var{type}@}@var{adrexp}} is still useful.
13734 @cindex @code{#} in Modula-2
13735 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
13736 interpreted as the beginning of a comment. Use @code{<>} instead.
13742 The extensions made to @value{GDBN} for Ada only support
13743 output from the @sc{gnu} Ada (GNAT) compiler.
13744 Other Ada compilers are not currently supported, and
13745 attempting to debug executables produced by them is most likely
13749 @cindex expressions in Ada
13751 * Ada Mode Intro:: General remarks on the Ada syntax
13752 and semantics supported by Ada mode
13754 * Omissions from Ada:: Restrictions on the Ada expression syntax.
13755 * Additions to Ada:: Extensions of the Ada expression syntax.
13756 * Stopping Before Main Program:: Debugging the program during elaboration.
13757 * Ada Tasks:: Listing and setting breakpoints in tasks.
13758 * Ada Tasks and Core Files:: Tasking Support when Debugging Core Files
13759 * Ravenscar Profile:: Tasking Support when using the Ravenscar
13761 * Ada Glitches:: Known peculiarities of Ada mode.
13764 @node Ada Mode Intro
13765 @subsubsection Introduction
13766 @cindex Ada mode, general
13768 The Ada mode of @value{GDBN} supports a fairly large subset of Ada expression
13769 syntax, with some extensions.
13770 The philosophy behind the design of this subset is
13774 That @value{GDBN} should provide basic literals and access to operations for
13775 arithmetic, dereferencing, field selection, indexing, and subprogram calls,
13776 leaving more sophisticated computations to subprograms written into the
13777 program (which therefore may be called from @value{GDBN}).
13780 That type safety and strict adherence to Ada language restrictions
13781 are not particularly important to the @value{GDBN} user.
13784 That brevity is important to the @value{GDBN} user.
13787 Thus, for brevity, the debugger acts as if all names declared in
13788 user-written packages are directly visible, even if they are not visible
13789 according to Ada rules, thus making it unnecessary to fully qualify most
13790 names with their packages, regardless of context. Where this causes
13791 ambiguity, @value{GDBN} asks the user's intent.
13793 The debugger will start in Ada mode if it detects an Ada main program.
13794 As for other languages, it will enter Ada mode when stopped in a program that
13795 was translated from an Ada source file.
13797 While in Ada mode, you may use `@t{--}' for comments. This is useful
13798 mostly for documenting command files. The standard @value{GDBN} comment
13799 (@samp{#}) still works at the beginning of a line in Ada mode, but not in the
13800 middle (to allow based literals).
13802 The debugger supports limited overloading. Given a subprogram call in which
13803 the function symbol has multiple definitions, it will use the number of
13804 actual parameters and some information about their types to attempt to narrow
13805 the set of definitions. It also makes very limited use of context, preferring
13806 procedures to functions in the context of the @code{call} command, and
13807 functions to procedures elsewhere.
13809 @node Omissions from Ada
13810 @subsubsection Omissions from Ada
13811 @cindex Ada, omissions from
13813 Here are the notable omissions from the subset:
13817 Only a subset of the attributes are supported:
13821 @t{'First}, @t{'Last}, and @t{'Length}
13822 on array objects (not on types and subtypes).
13825 @t{'Min} and @t{'Max}.
13828 @t{'Pos} and @t{'Val}.
13834 @t{'Range} on array objects (not subtypes), but only as the right
13835 operand of the membership (@code{in}) operator.
13838 @t{'Access}, @t{'Unchecked_Access}, and
13839 @t{'Unrestricted_Access} (a GNAT extension).
13847 @code{Characters.Latin_1} are not available and
13848 concatenation is not implemented. Thus, escape characters in strings are
13849 not currently available.
13852 Equality tests (@samp{=} and @samp{/=}) on arrays test for bitwise
13853 equality of representations. They will generally work correctly
13854 for strings and arrays whose elements have integer or enumeration types.
13855 They may not work correctly for arrays whose element
13856 types have user-defined equality, for arrays of real values
13857 (in particular, IEEE-conformant floating point, because of negative
13858 zeroes and NaNs), and for arrays whose elements contain unused bits with
13859 indeterminate values.
13862 The other component-by-component array operations (@code{and}, @code{or},
13863 @code{xor}, @code{not}, and relational tests other than equality)
13864 are not implemented.
13867 @cindex array aggregates (Ada)
13868 @cindex record aggregates (Ada)
13869 @cindex aggregates (Ada)
13870 There is limited support for array and record aggregates. They are
13871 permitted only on the right sides of assignments, as in these examples:
13874 (@value{GDBP}) set An_Array := (1, 2, 3, 4, 5, 6)
13875 (@value{GDBP}) set An_Array := (1, others => 0)
13876 (@value{GDBP}) set An_Array := (0|4 => 1, 1..3 => 2, 5 => 6)
13877 (@value{GDBP}) set A_2D_Array := ((1, 2, 3), (4, 5, 6), (7, 8, 9))
13878 (@value{GDBP}) set A_Record := (1, "Peter", True);
13879 (@value{GDBP}) set A_Record := (Name => "Peter", Id => 1, Alive => True)
13883 discriminant's value by assigning an aggregate has an
13884 undefined effect if that discriminant is used within the record.
13885 However, you can first modify discriminants by directly assigning to
13886 them (which normally would not be allowed in Ada), and then performing an
13887 aggregate assignment. For example, given a variable @code{A_Rec}
13888 declared to have a type such as:
13891 type Rec (Len : Small_Integer := 0) is record
13893 Vals : IntArray (1 .. Len);
13897 you can assign a value with a different size of @code{Vals} with two
13901 (@value{GDBP}) set A_Rec.Len := 4
13902 (@value{GDBP}) set A_Rec := (Id => 42, Vals => (1, 2, 3, 4))
13905 As this example also illustrates, @value{GDBN} is very loose about the usual
13906 rules concerning aggregates. You may leave out some of the
13907 components of an array or record aggregate (such as the @code{Len}
13908 component in the assignment to @code{A_Rec} above); they will retain their
13909 original values upon assignment. You may freely use dynamic values as
13910 indices in component associations. You may even use overlapping or
13911 redundant component associations, although which component values are
13912 assigned in such cases is not defined.
13915 Calls to dispatching subprograms are not implemented.
13918 The overloading algorithm is much more limited (i.e., less selective)
13919 than that of real Ada. It makes only limited use of the context in
13920 which a subexpression appears to resolve its meaning, and it is much
13921 looser in its rules for allowing type matches. As a result, some
13922 function calls will be ambiguous, and the user will be asked to choose
13923 the proper resolution.
13926 The @code{new} operator is not implemented.
13929 Entry calls are not implemented.
13932 Aside from printing, arithmetic operations on the native VAX floating-point
13933 formats are not supported.
13936 It is not possible to slice a packed array.
13939 The names @code{True} and @code{False}, when not part of a qualified name,
13940 are interpreted as if implicitly prefixed by @code{Standard}, regardless of
13942 Should your program
13943 redefine these names in a package or procedure (at best a dubious practice),
13944 you will have to use fully qualified names to access their new definitions.
13947 @node Additions to Ada
13948 @subsubsection Additions to Ada
13949 @cindex Ada, deviations from
13951 As it does for other languages, @value{GDBN} makes certain generic
13952 extensions to Ada (@pxref{Expressions}):
13956 If the expression @var{E} is a variable residing in memory (typically
13957 a local variable or array element) and @var{N} is a positive integer,
13958 then @code{@var{E}@@@var{N}} displays the values of @var{E} and the
13959 @var{N}-1 adjacent variables following it in memory as an array. In
13960 Ada, this operator is generally not necessary, since its prime use is
13961 in displaying parts of an array, and slicing will usually do this in
13962 Ada. However, there are occasional uses when debugging programs in
13963 which certain debugging information has been optimized away.
13966 @code{@var{B}::@var{var}} means ``the variable named @var{var} that
13967 appears in function or file @var{B}.'' When @var{B} is a file name,
13968 you must typically surround it in single quotes.
13971 The expression @code{@{@var{type}@} @var{addr}} means ``the variable of type
13972 @var{type} that appears at address @var{addr}.''
13975 A name starting with @samp{$} is a convenience variable
13976 (@pxref{Convenience Vars}) or a machine register (@pxref{Registers}).
13979 In addition, @value{GDBN} provides a few other shortcuts and outright
13980 additions specific to Ada:
13984 The assignment statement is allowed as an expression, returning
13985 its right-hand operand as its value. Thus, you may enter
13988 (@value{GDBP}) set x := y + 3
13989 (@value{GDBP}) print A(tmp := y + 1)
13993 The semicolon is allowed as an ``operator,'' returning as its value
13994 the value of its right-hand operand.
13995 This allows, for example,
13996 complex conditional breaks:
13999 (@value{GDBP}) break f
14000 (@value{GDBP}) condition 1 (report(i); k += 1; A(k) > 100)
14004 Rather than use catenation and symbolic character names to introduce special
14005 characters into strings, one may instead use a special bracket notation,
14006 which is also used to print strings. A sequence of characters of the form
14007 @samp{["@var{XX}"]} within a string or character literal denotes the
14008 (single) character whose numeric encoding is @var{XX} in hexadecimal. The
14009 sequence of characters @samp{["""]} also denotes a single quotation mark
14010 in strings. For example,
14012 "One line.["0a"]Next line.["0a"]"
14015 contains an ASCII newline character (@code{Ada.Characters.Latin_1.LF})
14019 The subtype used as a prefix for the attributes @t{'Pos}, @t{'Min}, and
14020 @t{'Max} is optional (and is ignored in any case). For example, it is valid
14024 (@value{GDBP}) print 'max(x, y)
14028 When printing arrays, @value{GDBN} uses positional notation when the
14029 array has a lower bound of 1, and uses a modified named notation otherwise.
14030 For example, a one-dimensional array of three integers with a lower bound
14031 of 3 might print as
14038 That is, in contrast to valid Ada, only the first component has a @code{=>}
14042 You may abbreviate attributes in expressions with any unique,
14043 multi-character subsequence of
14044 their names (an exact match gets preference).
14045 For example, you may use @t{a'len}, @t{a'gth}, or @t{a'lh}
14046 in place of @t{a'length}.
14049 @cindex quoting Ada internal identifiers
14050 Since Ada is case-insensitive, the debugger normally maps identifiers you type
14051 to lower case. The GNAT compiler uses upper-case characters for
14052 some of its internal identifiers, which are normally of no interest to users.
14053 For the rare occasions when you actually have to look at them,
14054 enclose them in angle brackets to avoid the lower-case mapping.
14057 (@value{GDBP}) print <JMPBUF_SAVE>[0]
14061 Printing an object of class-wide type or dereferencing an
14062 access-to-class-wide value will display all the components of the object's
14063 specific type (as indicated by its run-time tag). Likewise, component
14064 selection on such a value will operate on the specific type of the
14069 @node Stopping Before Main Program
14070 @subsubsection Stopping at the Very Beginning
14072 @cindex breakpointing Ada elaboration code
14073 It is sometimes necessary to debug the program during elaboration, and
14074 before reaching the main procedure.
14075 As defined in the Ada Reference
14076 Manual, the elaboration code is invoked from a procedure called
14077 @code{adainit}. To run your program up to the beginning of
14078 elaboration, simply use the following two commands:
14079 @code{tbreak adainit} and @code{run}.
14082 @subsubsection Extensions for Ada Tasks
14083 @cindex Ada, tasking
14085 Support for Ada tasks is analogous to that for threads (@pxref{Threads}).
14086 @value{GDBN} provides the following task-related commands:
14091 This command shows a list of current Ada tasks, as in the following example:
14098 (@value{GDBP}) info tasks
14099 ID TID P-ID Pri State Name
14100 1 8088000 0 15 Child Activation Wait main_task
14101 2 80a4000 1 15 Accept Statement b
14102 3 809a800 1 15 Child Activation Wait a
14103 * 4 80ae800 3 15 Runnable c
14108 In this listing, the asterisk before the last task indicates it to be the
14109 task currently being inspected.
14113 Represents @value{GDBN}'s internal task number.
14119 The parent's task ID (@value{GDBN}'s internal task number).
14122 The base priority of the task.
14125 Current state of the task.
14129 The task has been created but has not been activated. It cannot be
14133 The task is not blocked for any reason known to Ada. (It may be waiting
14134 for a mutex, though.) It is conceptually "executing" in normal mode.
14137 The task is terminated, in the sense of ARM 9.3 (5). Any dependents
14138 that were waiting on terminate alternatives have been awakened and have
14139 terminated themselves.
14141 @item Child Activation Wait
14142 The task is waiting for created tasks to complete activation.
14144 @item Accept Statement
14145 The task is waiting on an accept or selective wait statement.
14147 @item Waiting on entry call
14148 The task is waiting on an entry call.
14150 @item Async Select Wait
14151 The task is waiting to start the abortable part of an asynchronous
14155 The task is waiting on a select statement with only a delay
14158 @item Child Termination Wait
14159 The task is sleeping having completed a master within itself, and is
14160 waiting for the tasks dependent on that master to become terminated or
14161 waiting on a terminate Phase.
14163 @item Wait Child in Term Alt
14164 The task is sleeping waiting for tasks on terminate alternatives to
14165 finish terminating.
14167 @item Accepting RV with @var{taskno}
14168 The task is accepting a rendez-vous with the task @var{taskno}.
14172 Name of the task in the program.
14176 @kindex info task @var{taskno}
14177 @item info task @var{taskno}
14178 This command shows detailled informations on the specified task, as in
14179 the following example:
14184 (@value{GDBP}) info tasks
14185 ID TID P-ID Pri State Name
14186 1 8077880 0 15 Child Activation Wait main_task
14187 * 2 807c468 1 15 Runnable task_1
14188 (@value{GDBP}) info task 2
14189 Ada Task: 0x807c468
14192 Parent: 1 (main_task)
14198 @kindex task@r{ (Ada)}
14199 @cindex current Ada task ID
14200 This command prints the ID of the current task.
14206 (@value{GDBP}) info tasks
14207 ID TID P-ID Pri State Name
14208 1 8077870 0 15 Child Activation Wait main_task
14209 * 2 807c458 1 15 Runnable t
14210 (@value{GDBP}) task
14211 [Current task is 2]
14214 @item task @var{taskno}
14215 @cindex Ada task switching
14216 This command is like the @code{thread @var{threadno}}
14217 command (@pxref{Threads}). It switches the context of debugging
14218 from the current task to the given task.
14224 (@value{GDBP}) info tasks
14225 ID TID P-ID Pri State Name
14226 1 8077870 0 15 Child Activation Wait main_task
14227 * 2 807c458 1 15 Runnable t
14228 (@value{GDBP}) task 1
14229 [Switching to task 1]
14230 #0 0x8067726 in pthread_cond_wait ()
14232 #0 0x8067726 in pthread_cond_wait ()
14233 #1 0x8056714 in system.os_interface.pthread_cond_wait ()
14234 #2 0x805cb63 in system.task_primitives.operations.sleep ()
14235 #3 0x806153e in system.tasking.stages.activate_tasks ()
14236 #4 0x804aacc in un () at un.adb:5
14239 @item break @var{linespec} task @var{taskno}
14240 @itemx break @var{linespec} task @var{taskno} if @dots{}
14241 @cindex breakpoints and tasks, in Ada
14242 @cindex task breakpoints, in Ada
14243 @kindex break @dots{} task @var{taskno}@r{ (Ada)}
14244 These commands are like the @code{break @dots{} thread @dots{}}
14245 command (@pxref{Thread Stops}).
14246 @var{linespec} specifies source lines, as described
14247 in @ref{Specify Location}.
14249 Use the qualifier @samp{task @var{taskno}} with a breakpoint command
14250 to specify that you only want @value{GDBN} to stop the program when a
14251 particular Ada task reaches this breakpoint. @var{taskno} is one of the
14252 numeric task identifiers assigned by @value{GDBN}, shown in the first
14253 column of the @samp{info tasks} display.
14255 If you do not specify @samp{task @var{taskno}} when you set a
14256 breakpoint, the breakpoint applies to @emph{all} tasks of your
14259 You can use the @code{task} qualifier on conditional breakpoints as
14260 well; in this case, place @samp{task @var{taskno}} before the
14261 breakpoint condition (before the @code{if}).
14269 (@value{GDBP}) info tasks
14270 ID TID P-ID Pri State Name
14271 1 140022020 0 15 Child Activation Wait main_task
14272 2 140045060 1 15 Accept/Select Wait t2
14273 3 140044840 1 15 Runnable t1
14274 * 4 140056040 1 15 Runnable t3
14275 (@value{GDBP}) b 15 task 2
14276 Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15.
14277 (@value{GDBP}) cont
14282 Breakpoint 5, test_task_debug () at test_task_debug.adb:15
14284 (@value{GDBP}) info tasks
14285 ID TID P-ID Pri State Name
14286 1 140022020 0 15 Child Activation Wait main_task
14287 * 2 140045060 1 15 Runnable t2
14288 3 140044840 1 15 Runnable t1
14289 4 140056040 1 15 Delay Sleep t3
14293 @node Ada Tasks and Core Files
14294 @subsubsection Tasking Support when Debugging Core Files
14295 @cindex Ada tasking and core file debugging
14297 When inspecting a core file, as opposed to debugging a live program,
14298 tasking support may be limited or even unavailable, depending on
14299 the platform being used.
14300 For instance, on x86-linux, the list of tasks is available, but task
14301 switching is not supported. On Tru64, however, task switching will work
14304 On certain platforms, including Tru64, the debugger needs to perform some
14305 memory writes in order to provide Ada tasking support. When inspecting
14306 a core file, this means that the core file must be opened with read-write
14307 privileges, using the command @samp{"set write on"} (@pxref{Patching}).
14308 Under these circumstances, you should make a backup copy of the core
14309 file before inspecting it with @value{GDBN}.
14311 @node Ravenscar Profile
14312 @subsubsection Tasking Support when using the Ravenscar Profile
14313 @cindex Ravenscar Profile
14315 The @dfn{Ravenscar Profile} is a subset of the Ada tasking features,
14316 specifically designed for systems with safety-critical real-time
14320 @kindex set ravenscar task-switching on
14321 @cindex task switching with program using Ravenscar Profile
14322 @item set ravenscar task-switching on
14323 Allows task switching when debugging a program that uses the Ravenscar
14324 Profile. This is the default.
14326 @kindex set ravenscar task-switching off
14327 @item set ravenscar task-switching off
14328 Turn off task switching when debugging a program that uses the Ravenscar
14329 Profile. This is mostly intended to disable the code that adds support
14330 for the Ravenscar Profile, in case a bug in either @value{GDBN} or in
14331 the Ravenscar runtime is preventing @value{GDBN} from working properly.
14332 To be effective, this command should be run before the program is started.
14334 @kindex show ravenscar task-switching
14335 @item show ravenscar task-switching
14336 Show whether it is possible to switch from task to task in a program
14337 using the Ravenscar Profile.
14342 @subsubsection Known Peculiarities of Ada Mode
14343 @cindex Ada, problems
14345 Besides the omissions listed previously (@pxref{Omissions from Ada}),
14346 we know of several problems with and limitations of Ada mode in
14348 some of which will be fixed with planned future releases of the debugger
14349 and the GNU Ada compiler.
14353 Static constants that the compiler chooses not to materialize as objects in
14354 storage are invisible to the debugger.
14357 Named parameter associations in function argument lists are ignored (the
14358 argument lists are treated as positional).
14361 Many useful library packages are currently invisible to the debugger.
14364 Fixed-point arithmetic, conversions, input, and output is carried out using
14365 floating-point arithmetic, and may give results that only approximate those on
14369 The GNAT compiler never generates the prefix @code{Standard} for any of
14370 the standard symbols defined by the Ada language. @value{GDBN} knows about
14371 this: it will strip the prefix from names when you use it, and will never
14372 look for a name you have so qualified among local symbols, nor match against
14373 symbols in other packages or subprograms. If you have
14374 defined entities anywhere in your program other than parameters and
14375 local variables whose simple names match names in @code{Standard},
14376 GNAT's lack of qualification here can cause confusion. When this happens,
14377 you can usually resolve the confusion
14378 by qualifying the problematic names with package
14379 @code{Standard} explicitly.
14382 Older versions of the compiler sometimes generate erroneous debugging
14383 information, resulting in the debugger incorrectly printing the value
14384 of affected entities. In some cases, the debugger is able to work
14385 around an issue automatically. In other cases, the debugger is able
14386 to work around the issue, but the work-around has to be specifically
14389 @kindex set ada trust-PAD-over-XVS
14390 @kindex show ada trust-PAD-over-XVS
14393 @item set ada trust-PAD-over-XVS on
14394 Configure GDB to strictly follow the GNAT encoding when computing the
14395 value of Ada entities, particularly when @code{PAD} and @code{PAD___XVS}
14396 types are involved (see @code{ada/exp_dbug.ads} in the GCC sources for
14397 a complete description of the encoding used by the GNAT compiler).
14398 This is the default.
14400 @item set ada trust-PAD-over-XVS off
14401 This is related to the encoding using by the GNAT compiler. If @value{GDBN}
14402 sometimes prints the wrong value for certain entities, changing @code{ada
14403 trust-PAD-over-XVS} to @code{off} activates a work-around which may fix
14404 the issue. It is always safe to set @code{ada trust-PAD-over-XVS} to
14405 @code{off}, but this incurs a slight performance penalty, so it is
14406 recommended to leave this setting to @code{on} unless necessary.
14410 @node Unsupported Languages
14411 @section Unsupported Languages
14413 @cindex unsupported languages
14414 @cindex minimal language
14415 In addition to the other fully-supported programming languages,
14416 @value{GDBN} also provides a pseudo-language, called @code{minimal}.
14417 It does not represent a real programming language, but provides a set
14418 of capabilities close to what the C or assembly languages provide.
14419 This should allow most simple operations to be performed while debugging
14420 an application that uses a language currently not supported by @value{GDBN}.
14422 If the language is set to @code{auto}, @value{GDBN} will automatically
14423 select this language if the current frame corresponds to an unsupported
14427 @chapter Examining the Symbol Table
14429 The commands described in this chapter allow you to inquire about the
14430 symbols (names of variables, functions and types) defined in your
14431 program. This information is inherent in the text of your program and
14432 does not change as your program executes. @value{GDBN} finds it in your
14433 program's symbol table, in the file indicated when you started @value{GDBN}
14434 (@pxref{File Options, ,Choosing Files}), or by one of the
14435 file-management commands (@pxref{Files, ,Commands to Specify Files}).
14437 @cindex symbol names
14438 @cindex names of symbols
14439 @cindex quoting names
14440 Occasionally, you may need to refer to symbols that contain unusual
14441 characters, which @value{GDBN} ordinarily treats as word delimiters. The
14442 most frequent case is in referring to static variables in other
14443 source files (@pxref{Variables,,Program Variables}). File names
14444 are recorded in object files as debugging symbols, but @value{GDBN} would
14445 ordinarily parse a typical file name, like @file{foo.c}, as the three words
14446 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
14447 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
14454 looks up the value of @code{x} in the scope of the file @file{foo.c}.
14457 @cindex case-insensitive symbol names
14458 @cindex case sensitivity in symbol names
14459 @kindex set case-sensitive
14460 @item set case-sensitive on
14461 @itemx set case-sensitive off
14462 @itemx set case-sensitive auto
14463 Normally, when @value{GDBN} looks up symbols, it matches their names
14464 with case sensitivity determined by the current source language.
14465 Occasionally, you may wish to control that. The command @code{set
14466 case-sensitive} lets you do that by specifying @code{on} for
14467 case-sensitive matches or @code{off} for case-insensitive ones. If
14468 you specify @code{auto}, case sensitivity is reset to the default
14469 suitable for the source language. The default is case-sensitive
14470 matches for all languages except for Fortran, for which the default is
14471 case-insensitive matches.
14473 @kindex show case-sensitive
14474 @item show case-sensitive
14475 This command shows the current setting of case sensitivity for symbols
14478 @kindex info address
14479 @cindex address of a symbol
14480 @item info address @var{symbol}
14481 Describe where the data for @var{symbol} is stored. For a register
14482 variable, this says which register it is kept in. For a non-register
14483 local variable, this prints the stack-frame offset at which the variable
14486 Note the contrast with @samp{print &@var{symbol}}, which does not work
14487 at all for a register variable, and for a stack local variable prints
14488 the exact address of the current instantiation of the variable.
14490 @kindex info symbol
14491 @cindex symbol from address
14492 @cindex closest symbol and offset for an address
14493 @item info symbol @var{addr}
14494 Print the name of a symbol which is stored at the address @var{addr}.
14495 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
14496 nearest symbol and an offset from it:
14499 (@value{GDBP}) info symbol 0x54320
14500 _initialize_vx + 396 in section .text
14504 This is the opposite of the @code{info address} command. You can use
14505 it to find out the name of a variable or a function given its address.
14507 For dynamically linked executables, the name of executable or shared
14508 library containing the symbol is also printed:
14511 (@value{GDBP}) info symbol 0x400225
14512 _start + 5 in section .text of /tmp/a.out
14513 (@value{GDBP}) info symbol 0x2aaaac2811cf
14514 __read_nocancel + 6 in section .text of /usr/lib64/libc.so.6
14518 @item whatis [@var{arg}]
14519 Print the data type of @var{arg}, which can be either an expression
14520 or a name of a data type. With no argument, print the data type of
14521 @code{$}, the last value in the value history.
14523 If @var{arg} is an expression (@pxref{Expressions, ,Expressions}), it
14524 is not actually evaluated, and any side-effecting operations (such as
14525 assignments or function calls) inside it do not take place.
14527 If @var{arg} is a variable or an expression, @code{whatis} prints its
14528 literal type as it is used in the source code. If the type was
14529 defined using a @code{typedef}, @code{whatis} will @emph{not} print
14530 the data type underlying the @code{typedef}. If the type of the
14531 variable or the expression is a compound data type, such as
14532 @code{struct} or @code{class}, @code{whatis} never prints their
14533 fields or methods. It just prints the @code{struct}/@code{class}
14534 name (a.k.a.@: its @dfn{tag}). If you want to see the members of
14535 such a compound data type, use @code{ptype}.
14537 If @var{arg} is a type name that was defined using @code{typedef},
14538 @code{whatis} @dfn{unrolls} only one level of that @code{typedef}.
14539 Unrolling means that @code{whatis} will show the underlying type used
14540 in the @code{typedef} declaration of @var{arg}. However, if that
14541 underlying type is also a @code{typedef}, @code{whatis} will not
14544 For C code, the type names may also have the form @samp{class
14545 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
14546 @var{union-tag}} or @samp{enum @var{enum-tag}}.
14549 @item ptype [@var{arg}]
14550 @code{ptype} accepts the same arguments as @code{whatis}, but prints a
14551 detailed description of the type, instead of just the name of the type.
14552 @xref{Expressions, ,Expressions}.
14554 Contrary to @code{whatis}, @code{ptype} always unrolls any
14555 @code{typedef}s in its argument declaration, whether the argument is
14556 a variable, expression, or a data type. This means that @code{ptype}
14557 of a variable or an expression will not print literally its type as
14558 present in the source code---use @code{whatis} for that. @code{typedef}s at
14559 the pointer or reference targets are also unrolled. Only @code{typedef}s of
14560 fields, methods and inner @code{class typedef}s of @code{struct}s,
14561 @code{class}es and @code{union}s are not unrolled even with @code{ptype}.
14563 For example, for this variable declaration:
14566 typedef double real_t;
14567 struct complex @{ real_t real; double imag; @};
14568 typedef struct complex complex_t;
14570 real_t *real_pointer_var;
14574 the two commands give this output:
14578 (@value{GDBP}) whatis var
14580 (@value{GDBP}) ptype var
14581 type = struct complex @{
14585 (@value{GDBP}) whatis complex_t
14586 type = struct complex
14587 (@value{GDBP}) whatis struct complex
14588 type = struct complex
14589 (@value{GDBP}) ptype struct complex
14590 type = struct complex @{
14594 (@value{GDBP}) whatis real_pointer_var
14596 (@value{GDBP}) ptype real_pointer_var
14602 As with @code{whatis}, using @code{ptype} without an argument refers to
14603 the type of @code{$}, the last value in the value history.
14605 @cindex incomplete type
14606 Sometimes, programs use opaque data types or incomplete specifications
14607 of complex data structure. If the debug information included in the
14608 program does not allow @value{GDBN} to display a full declaration of
14609 the data type, it will say @samp{<incomplete type>}. For example,
14610 given these declarations:
14614 struct foo *fooptr;
14618 but no definition for @code{struct foo} itself, @value{GDBN} will say:
14621 (@value{GDBP}) ptype foo
14622 $1 = <incomplete type>
14626 ``Incomplete type'' is C terminology for data types that are not
14627 completely specified.
14630 @item info types @var{regexp}
14632 Print a brief description of all types whose names match the regular
14633 expression @var{regexp} (or all types in your program, if you supply
14634 no argument). Each complete typename is matched as though it were a
14635 complete line; thus, @samp{i type value} gives information on all
14636 types in your program whose names include the string @code{value}, but
14637 @samp{i type ^value$} gives information only on types whose complete
14638 name is @code{value}.
14640 This command differs from @code{ptype} in two ways: first, like
14641 @code{whatis}, it does not print a detailed description; second, it
14642 lists all source files where a type is defined.
14645 @cindex local variables
14646 @item info scope @var{location}
14647 List all the variables local to a particular scope. This command
14648 accepts a @var{location} argument---a function name, a source line, or
14649 an address preceded by a @samp{*}, and prints all the variables local
14650 to the scope defined by that location. (@xref{Specify Location}, for
14651 details about supported forms of @var{location}.) For example:
14654 (@value{GDBP}) @b{info scope command_line_handler}
14655 Scope for command_line_handler:
14656 Symbol rl is an argument at stack/frame offset 8, length 4.
14657 Symbol linebuffer is in static storage at address 0x150a18, length 4.
14658 Symbol linelength is in static storage at address 0x150a1c, length 4.
14659 Symbol p is a local variable in register $esi, length 4.
14660 Symbol p1 is a local variable in register $ebx, length 4.
14661 Symbol nline is a local variable in register $edx, length 4.
14662 Symbol repeat is a local variable at frame offset -8, length 4.
14666 This command is especially useful for determining what data to collect
14667 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
14670 @kindex info source
14672 Show information about the current source file---that is, the source file for
14673 the function containing the current point of execution:
14676 the name of the source file, and the directory containing it,
14678 the directory it was compiled in,
14680 its length, in lines,
14682 which programming language it is written in,
14684 whether the executable includes debugging information for that file, and
14685 if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and
14687 whether the debugging information includes information about
14688 preprocessor macros.
14692 @kindex info sources
14694 Print the names of all source files in your program for which there is
14695 debugging information, organized into two lists: files whose symbols
14696 have already been read, and files whose symbols will be read when needed.
14698 @kindex info functions
14699 @item info functions
14700 Print the names and data types of all defined functions.
14702 @item info functions @var{regexp}
14703 Print the names and data types of all defined functions
14704 whose names contain a match for regular expression @var{regexp}.
14705 Thus, @samp{info fun step} finds all functions whose names
14706 include @code{step}; @samp{info fun ^step} finds those whose names
14707 start with @code{step}. If a function name contains characters
14708 that conflict with the regular expression language (e.g.@:
14709 @samp{operator*()}), they may be quoted with a backslash.
14711 @kindex info variables
14712 @item info variables
14713 Print the names and data types of all variables that are defined
14714 outside of functions (i.e.@: excluding local variables).
14716 @item info variables @var{regexp}
14717 Print the names and data types of all variables (except for local
14718 variables) whose names contain a match for regular expression
14721 @kindex info classes
14722 @cindex Objective-C, classes and selectors
14724 @itemx info classes @var{regexp}
14725 Display all Objective-C classes in your program, or
14726 (with the @var{regexp} argument) all those matching a particular regular
14729 @kindex info selectors
14730 @item info selectors
14731 @itemx info selectors @var{regexp}
14732 Display all Objective-C selectors in your program, or
14733 (with the @var{regexp} argument) all those matching a particular regular
14737 This was never implemented.
14738 @kindex info methods
14740 @itemx info methods @var{regexp}
14741 The @code{info methods} command permits the user to examine all defined
14742 methods within C@t{++} program, or (with the @var{regexp} argument) a
14743 specific set of methods found in the various C@t{++} classes. Many
14744 C@t{++} classes provide a large number of methods. Thus, the output
14745 from the @code{ptype} command can be overwhelming and hard to use. The
14746 @code{info-methods} command filters the methods, printing only those
14747 which match the regular-expression @var{regexp}.
14750 @cindex opaque data types
14751 @kindex set opaque-type-resolution
14752 @item set opaque-type-resolution on
14753 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
14754 declared as a pointer to a @code{struct}, @code{class}, or
14755 @code{union}---for example, @code{struct MyType *}---that is used in one
14756 source file although the full declaration of @code{struct MyType} is in
14757 another source file. The default is on.
14759 A change in the setting of this subcommand will not take effect until
14760 the next time symbols for a file are loaded.
14762 @item set opaque-type-resolution off
14763 Tell @value{GDBN} not to resolve opaque types. In this case, the type
14764 is printed as follows:
14766 @{<no data fields>@}
14769 @kindex show opaque-type-resolution
14770 @item show opaque-type-resolution
14771 Show whether opaque types are resolved or not.
14773 @kindex maint print symbols
14774 @cindex symbol dump
14775 @kindex maint print psymbols
14776 @cindex partial symbol dump
14777 @item maint print symbols @var{filename}
14778 @itemx maint print psymbols @var{filename}
14779 @itemx maint print msymbols @var{filename}
14780 Write a dump of debugging symbol data into the file @var{filename}.
14781 These commands are used to debug the @value{GDBN} symbol-reading code. Only
14782 symbols with debugging data are included. If you use @samp{maint print
14783 symbols}, @value{GDBN} includes all the symbols for which it has already
14784 collected full details: that is, @var{filename} reflects symbols for
14785 only those files whose symbols @value{GDBN} has read. You can use the
14786 command @code{info sources} to find out which files these are. If you
14787 use @samp{maint print psymbols} instead, the dump shows information about
14788 symbols that @value{GDBN} only knows partially---that is, symbols defined in
14789 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
14790 @samp{maint print msymbols} dumps just the minimal symbol information
14791 required for each object file from which @value{GDBN} has read some symbols.
14792 @xref{Files, ,Commands to Specify Files}, for a discussion of how
14793 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
14795 @kindex maint info symtabs
14796 @kindex maint info psymtabs
14797 @cindex listing @value{GDBN}'s internal symbol tables
14798 @cindex symbol tables, listing @value{GDBN}'s internal
14799 @cindex full symbol tables, listing @value{GDBN}'s internal
14800 @cindex partial symbol tables, listing @value{GDBN}'s internal
14801 @item maint info symtabs @r{[} @var{regexp} @r{]}
14802 @itemx maint info psymtabs @r{[} @var{regexp} @r{]}
14804 List the @code{struct symtab} or @code{struct partial_symtab}
14805 structures whose names match @var{regexp}. If @var{regexp} is not
14806 given, list them all. The output includes expressions which you can
14807 copy into a @value{GDBN} debugging this one to examine a particular
14808 structure in more detail. For example:
14811 (@value{GDBP}) maint info psymtabs dwarf2read
14812 @{ objfile /home/gnu/build/gdb/gdb
14813 ((struct objfile *) 0x82e69d0)
14814 @{ psymtab /home/gnu/src/gdb/dwarf2read.c
14815 ((struct partial_symtab *) 0x8474b10)
14818 text addresses 0x814d3c8 -- 0x8158074
14819 globals (* (struct partial_symbol **) 0x8507a08 @@ 9)
14820 statics (* (struct partial_symbol **) 0x40e95b78 @@ 2882)
14821 dependencies (none)
14824 (@value{GDBP}) maint info symtabs
14828 We see that there is one partial symbol table whose filename contains
14829 the string @samp{dwarf2read}, belonging to the @samp{gdb} executable;
14830 and we see that @value{GDBN} has not read in any symtabs yet at all.
14831 If we set a breakpoint on a function, that will cause @value{GDBN} to
14832 read the symtab for the compilation unit containing that function:
14835 (@value{GDBP}) break dwarf2_psymtab_to_symtab
14836 Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c,
14838 (@value{GDBP}) maint info symtabs
14839 @{ objfile /home/gnu/build/gdb/gdb
14840 ((struct objfile *) 0x82e69d0)
14841 @{ symtab /home/gnu/src/gdb/dwarf2read.c
14842 ((struct symtab *) 0x86c1f38)
14845 blockvector ((struct blockvector *) 0x86c1bd0) (primary)
14846 linetable ((struct linetable *) 0x8370fa0)
14847 debugformat DWARF 2
14856 @chapter Altering Execution
14858 Once you think you have found an error in your program, you might want to
14859 find out for certain whether correcting the apparent error would lead to
14860 correct results in the rest of the run. You can find the answer by
14861 experiment, using the @value{GDBN} features for altering execution of the
14864 For example, you can store new values into variables or memory
14865 locations, give your program a signal, restart it at a different
14866 address, or even return prematurely from a function.
14869 * Assignment:: Assignment to variables
14870 * Jumping:: Continuing at a different address
14871 * Signaling:: Giving your program a signal
14872 * Returning:: Returning from a function
14873 * Calling:: Calling your program's functions
14874 * Patching:: Patching your program
14878 @section Assignment to Variables
14881 @cindex setting variables
14882 To alter the value of a variable, evaluate an assignment expression.
14883 @xref{Expressions, ,Expressions}. For example,
14890 stores the value 4 into the variable @code{x}, and then prints the
14891 value of the assignment expression (which is 4).
14892 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
14893 information on operators in supported languages.
14895 @kindex set variable
14896 @cindex variables, setting
14897 If you are not interested in seeing the value of the assignment, use the
14898 @code{set} command instead of the @code{print} command. @code{set} is
14899 really the same as @code{print} except that the expression's value is
14900 not printed and is not put in the value history (@pxref{Value History,
14901 ,Value History}). The expression is evaluated only for its effects.
14903 If the beginning of the argument string of the @code{set} command
14904 appears identical to a @code{set} subcommand, use the @code{set
14905 variable} command instead of just @code{set}. This command is identical
14906 to @code{set} except for its lack of subcommands. For example, if your
14907 program has a variable @code{width}, you get an error if you try to set
14908 a new value with just @samp{set width=13}, because @value{GDBN} has the
14909 command @code{set width}:
14912 (@value{GDBP}) whatis width
14914 (@value{GDBP}) p width
14916 (@value{GDBP}) set width=47
14917 Invalid syntax in expression.
14921 The invalid expression, of course, is @samp{=47}. In
14922 order to actually set the program's variable @code{width}, use
14925 (@value{GDBP}) set var width=47
14928 Because the @code{set} command has many subcommands that can conflict
14929 with the names of program variables, it is a good idea to use the
14930 @code{set variable} command instead of just @code{set}. For example, if
14931 your program has a variable @code{g}, you run into problems if you try
14932 to set a new value with just @samp{set g=4}, because @value{GDBN} has
14933 the command @code{set gnutarget}, abbreviated @code{set g}:
14937 (@value{GDBP}) whatis g
14941 (@value{GDBP}) set g=4
14945 The program being debugged has been started already.
14946 Start it from the beginning? (y or n) y
14947 Starting program: /home/smith/cc_progs/a.out
14948 "/home/smith/cc_progs/a.out": can't open to read symbols:
14949 Invalid bfd target.
14950 (@value{GDBP}) show g
14951 The current BFD target is "=4".
14956 The program variable @code{g} did not change, and you silently set the
14957 @code{gnutarget} to an invalid value. In order to set the variable
14961 (@value{GDBP}) set var g=4
14964 @value{GDBN} allows more implicit conversions in assignments than C; you can
14965 freely store an integer value into a pointer variable or vice versa,
14966 and you can convert any structure to any other structure that is the
14967 same length or shorter.
14968 @comment FIXME: how do structs align/pad in these conversions?
14969 @comment /doc@cygnus.com 18dec1990
14971 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
14972 construct to generate a value of specified type at a specified address
14973 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
14974 to memory location @code{0x83040} as an integer (which implies a certain size
14975 and representation in memory), and
14978 set @{int@}0x83040 = 4
14982 stores the value 4 into that memory location.
14985 @section Continuing at a Different Address
14987 Ordinarily, when you continue your program, you do so at the place where
14988 it stopped, with the @code{continue} command. You can instead continue at
14989 an address of your own choosing, with the following commands:
14993 @item jump @var{linespec}
14994 @itemx jump @var{location}
14995 Resume execution at line @var{linespec} or at address given by
14996 @var{location}. Execution stops again immediately if there is a
14997 breakpoint there. @xref{Specify Location}, for a description of the
14998 different forms of @var{linespec} and @var{location}. It is common
14999 practice to use the @code{tbreak} command in conjunction with
15000 @code{jump}. @xref{Set Breaks, ,Setting Breakpoints}.
15002 The @code{jump} command does not change the current stack frame, or
15003 the stack pointer, or the contents of any memory location or any
15004 register other than the program counter. If line @var{linespec} is in
15005 a different function from the one currently executing, the results may
15006 be bizarre if the two functions expect different patterns of arguments or
15007 of local variables. For this reason, the @code{jump} command requests
15008 confirmation if the specified line is not in the function currently
15009 executing. However, even bizarre results are predictable if you are
15010 well acquainted with the machine-language code of your program.
15013 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
15014 On many systems, you can get much the same effect as the @code{jump}
15015 command by storing a new value into the register @code{$pc}. The
15016 difference is that this does not start your program running; it only
15017 changes the address of where it @emph{will} run when you continue. For
15025 makes the next @code{continue} command or stepping command execute at
15026 address @code{0x485}, rather than at the address where your program stopped.
15027 @xref{Continuing and Stepping, ,Continuing and Stepping}.
15029 The most common occasion to use the @code{jump} command is to back
15030 up---perhaps with more breakpoints set---over a portion of a program
15031 that has already executed, in order to examine its execution in more
15036 @section Giving your Program a Signal
15037 @cindex deliver a signal to a program
15041 @item signal @var{signal}
15042 Resume execution where your program stopped, but immediately give it the
15043 signal @var{signal}. @var{signal} can be the name or the number of a
15044 signal. For example, on many systems @code{signal 2} and @code{signal
15045 SIGINT} are both ways of sending an interrupt signal.
15047 Alternatively, if @var{signal} is zero, continue execution without
15048 giving a signal. This is useful when your program stopped on account of
15049 a signal and would ordinary see the signal when resumed with the
15050 @code{continue} command; @samp{signal 0} causes it to resume without a
15053 @code{signal} does not repeat when you press @key{RET} a second time
15054 after executing the command.
15058 Invoking the @code{signal} command is not the same as invoking the
15059 @code{kill} utility from the shell. Sending a signal with @code{kill}
15060 causes @value{GDBN} to decide what to do with the signal depending on
15061 the signal handling tables (@pxref{Signals}). The @code{signal} command
15062 passes the signal directly to your program.
15066 @section Returning from a Function
15069 @cindex returning from a function
15072 @itemx return @var{expression}
15073 You can cancel execution of a function call with the @code{return}
15074 command. If you give an
15075 @var{expression} argument, its value is used as the function's return
15079 When you use @code{return}, @value{GDBN} discards the selected stack frame
15080 (and all frames within it). You can think of this as making the
15081 discarded frame return prematurely. If you wish to specify a value to
15082 be returned, give that value as the argument to @code{return}.
15084 This pops the selected stack frame (@pxref{Selection, ,Selecting a
15085 Frame}), and any other frames inside of it, leaving its caller as the
15086 innermost remaining frame. That frame becomes selected. The
15087 specified value is stored in the registers used for returning values
15090 The @code{return} command does not resume execution; it leaves the
15091 program stopped in the state that would exist if the function had just
15092 returned. In contrast, the @code{finish} command (@pxref{Continuing
15093 and Stepping, ,Continuing and Stepping}) resumes execution until the
15094 selected stack frame returns naturally.
15096 @value{GDBN} needs to know how the @var{expression} argument should be set for
15097 the inferior. The concrete registers assignment depends on the OS ABI and the
15098 type being returned by the selected stack frame. For example it is common for
15099 OS ABI to return floating point values in FPU registers while integer values in
15100 CPU registers. Still some ABIs return even floating point values in CPU
15101 registers. Larger integer widths (such as @code{long long int}) also have
15102 specific placement rules. @value{GDBN} already knows the OS ABI from its
15103 current target so it needs to find out also the type being returned to make the
15104 assignment into the right register(s).
15106 Normally, the selected stack frame has debug info. @value{GDBN} will always
15107 use the debug info instead of the implicit type of @var{expression} when the
15108 debug info is available. For example, if you type @kbd{return -1}, and the
15109 function in the current stack frame is declared to return a @code{long long
15110 int}, @value{GDBN} transparently converts the implicit @code{int} value of -1
15111 into a @code{long long int}:
15114 Breakpoint 1, func () at gdb.base/return-nodebug.c:29
15116 (@value{GDBP}) return -1
15117 Make func return now? (y or n) y
15118 #0 0x004004f6 in main () at gdb.base/return-nodebug.c:43
15119 43 printf ("result=%lld\n", func ());
15123 However, if the selected stack frame does not have a debug info, e.g., if the
15124 function was compiled without debug info, @value{GDBN} has to find out the type
15125 to return from user. Specifying a different type by mistake may set the value
15126 in different inferior registers than the caller code expects. For example,
15127 typing @kbd{return -1} with its implicit type @code{int} would set only a part
15128 of a @code{long long int} result for a debug info less function (on 32-bit
15129 architectures). Therefore the user is required to specify the return type by
15130 an appropriate cast explicitly:
15133 Breakpoint 2, 0x0040050b in func ()
15134 (@value{GDBP}) return -1
15135 Return value type not available for selected stack frame.
15136 Please use an explicit cast of the value to return.
15137 (@value{GDBP}) return (long long int) -1
15138 Make selected stack frame return now? (y or n) y
15139 #0 0x00400526 in main ()
15144 @section Calling Program Functions
15147 @cindex calling functions
15148 @cindex inferior functions, calling
15149 @item print @var{expr}
15150 Evaluate the expression @var{expr} and display the resulting value.
15151 @var{expr} may include calls to functions in the program being
15155 @item call @var{expr}
15156 Evaluate the expression @var{expr} without displaying @code{void}
15159 You can use this variant of the @code{print} command if you want to
15160 execute a function from your program that does not return anything
15161 (a.k.a.@: @dfn{a void function}), but without cluttering the output
15162 with @code{void} returned values that @value{GDBN} will otherwise
15163 print. If the result is not void, it is printed and saved in the
15167 It is possible for the function you call via the @code{print} or
15168 @code{call} command to generate a signal (e.g., if there's a bug in
15169 the function, or if you passed it incorrect arguments). What happens
15170 in that case is controlled by the @code{set unwindonsignal} command.
15172 Similarly, with a C@t{++} program it is possible for the function you
15173 call via the @code{print} or @code{call} command to generate an
15174 exception that is not handled due to the constraints of the dummy
15175 frame. In this case, any exception that is raised in the frame, but has
15176 an out-of-frame exception handler will not be found. GDB builds a
15177 dummy-frame for the inferior function call, and the unwinder cannot
15178 seek for exception handlers outside of this dummy-frame. What happens
15179 in that case is controlled by the
15180 @code{set unwind-on-terminating-exception} command.
15183 @item set unwindonsignal
15184 @kindex set unwindonsignal
15185 @cindex unwind stack in called functions
15186 @cindex call dummy stack unwinding
15187 Set unwinding of the stack if a signal is received while in a function
15188 that @value{GDBN} called in the program being debugged. If set to on,
15189 @value{GDBN} unwinds the stack it created for the call and restores
15190 the context to what it was before the call. If set to off (the
15191 default), @value{GDBN} stops in the frame where the signal was
15194 @item show unwindonsignal
15195 @kindex show unwindonsignal
15196 Show the current setting of stack unwinding in the functions called by
15199 @item set unwind-on-terminating-exception
15200 @kindex set unwind-on-terminating-exception
15201 @cindex unwind stack in called functions with unhandled exceptions
15202 @cindex call dummy stack unwinding on unhandled exception.
15203 Set unwinding of the stack if a C@t{++} exception is raised, but left
15204 unhandled while in a function that @value{GDBN} called in the program being
15205 debugged. If set to on (the default), @value{GDBN} unwinds the stack
15206 it created for the call and restores the context to what it was before
15207 the call. If set to off, @value{GDBN} the exception is delivered to
15208 the default C@t{++} exception handler and the inferior terminated.
15210 @item show unwind-on-terminating-exception
15211 @kindex show unwind-on-terminating-exception
15212 Show the current setting of stack unwinding in the functions called by
15217 @cindex weak alias functions
15218 Sometimes, a function you wish to call is actually a @dfn{weak alias}
15219 for another function. In such case, @value{GDBN} might not pick up
15220 the type information, including the types of the function arguments,
15221 which causes @value{GDBN} to call the inferior function incorrectly.
15222 As a result, the called function will function erroneously and may
15223 even crash. A solution to that is to use the name of the aliased
15227 @section Patching Programs
15229 @cindex patching binaries
15230 @cindex writing into executables
15231 @cindex writing into corefiles
15233 By default, @value{GDBN} opens the file containing your program's
15234 executable code (or the corefile) read-only. This prevents accidental
15235 alterations to machine code; but it also prevents you from intentionally
15236 patching your program's binary.
15238 If you'd like to be able to patch the binary, you can specify that
15239 explicitly with the @code{set write} command. For example, you might
15240 want to turn on internal debugging flags, or even to make emergency
15246 @itemx set write off
15247 If you specify @samp{set write on}, @value{GDBN} opens executable and
15248 core files for both reading and writing; if you specify @kbd{set write
15249 off} (the default), @value{GDBN} opens them read-only.
15251 If you have already loaded a file, you must load it again (using the
15252 @code{exec-file} or @code{core-file} command) after changing @code{set
15253 write}, for your new setting to take effect.
15257 Display whether executable files and core files are opened for writing
15258 as well as reading.
15262 @chapter @value{GDBN} Files
15264 @value{GDBN} needs to know the file name of the program to be debugged,
15265 both in order to read its symbol table and in order to start your
15266 program. To debug a core dump of a previous run, you must also tell
15267 @value{GDBN} the name of the core dump file.
15270 * Files:: Commands to specify files
15271 * Separate Debug Files:: Debugging information in separate files
15272 * Index Files:: Index files speed up GDB
15273 * Symbol Errors:: Errors reading symbol files
15274 * Data Files:: GDB data files
15278 @section Commands to Specify Files
15280 @cindex symbol table
15281 @cindex core dump file
15283 You may want to specify executable and core dump file names. The usual
15284 way to do this is at start-up time, using the arguments to
15285 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
15286 Out of @value{GDBN}}).
15288 Occasionally it is necessary to change to a different file during a
15289 @value{GDBN} session. Or you may run @value{GDBN} and forget to
15290 specify a file you want to use. Or you are debugging a remote target
15291 via @code{gdbserver} (@pxref{Server, file, Using the @code{gdbserver}
15292 Program}). In these situations the @value{GDBN} commands to specify
15293 new files are useful.
15296 @cindex executable file
15298 @item file @var{filename}
15299 Use @var{filename} as the program to be debugged. It is read for its
15300 symbols and for the contents of pure memory. It is also the program
15301 executed when you use the @code{run} command. If you do not specify a
15302 directory and the file is not found in the @value{GDBN} working directory,
15303 @value{GDBN} uses the environment variable @code{PATH} as a list of
15304 directories to search, just as the shell does when looking for a program
15305 to run. You can change the value of this variable, for both @value{GDBN}
15306 and your program, using the @code{path} command.
15308 @cindex unlinked object files
15309 @cindex patching object files
15310 You can load unlinked object @file{.o} files into @value{GDBN} using
15311 the @code{file} command. You will not be able to ``run'' an object
15312 file, but you can disassemble functions and inspect variables. Also,
15313 if the underlying BFD functionality supports it, you could use
15314 @kbd{gdb -write} to patch object files using this technique. Note
15315 that @value{GDBN} can neither interpret nor modify relocations in this
15316 case, so branches and some initialized variables will appear to go to
15317 the wrong place. But this feature is still handy from time to time.
15320 @code{file} with no argument makes @value{GDBN} discard any information it
15321 has on both executable file and the symbol table.
15324 @item exec-file @r{[} @var{filename} @r{]}
15325 Specify that the program to be run (but not the symbol table) is found
15326 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
15327 if necessary to locate your program. Omitting @var{filename} means to
15328 discard information on the executable file.
15330 @kindex symbol-file
15331 @item symbol-file @r{[} @var{filename} @r{]}
15332 Read symbol table information from file @var{filename}. @code{PATH} is
15333 searched when necessary. Use the @code{file} command to get both symbol
15334 table and program to run from the same file.
15336 @code{symbol-file} with no argument clears out @value{GDBN} information on your
15337 program's symbol table.
15339 The @code{symbol-file} command causes @value{GDBN} to forget the contents of
15340 some breakpoints and auto-display expressions. This is because they may
15341 contain pointers to the internal data recording symbols and data types,
15342 which are part of the old symbol table data being discarded inside
15345 @code{symbol-file} does not repeat if you press @key{RET} again after
15348 When @value{GDBN} is configured for a particular environment, it
15349 understands debugging information in whatever format is the standard
15350 generated for that environment; you may use either a @sc{gnu} compiler, or
15351 other compilers that adhere to the local conventions.
15352 Best results are usually obtained from @sc{gnu} compilers; for example,
15353 using @code{@value{NGCC}} you can generate debugging information for
15356 For most kinds of object files, with the exception of old SVR3 systems
15357 using COFF, the @code{symbol-file} command does not normally read the
15358 symbol table in full right away. Instead, it scans the symbol table
15359 quickly to find which source files and which symbols are present. The
15360 details are read later, one source file at a time, as they are needed.
15362 The purpose of this two-stage reading strategy is to make @value{GDBN}
15363 start up faster. For the most part, it is invisible except for
15364 occasional pauses while the symbol table details for a particular source
15365 file are being read. (The @code{set verbose} command can turn these
15366 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
15367 Warnings and Messages}.)
15369 We have not implemented the two-stage strategy for COFF yet. When the
15370 symbol table is stored in COFF format, @code{symbol-file} reads the
15371 symbol table data in full right away. Note that ``stabs-in-COFF''
15372 still does the two-stage strategy, since the debug info is actually
15376 @cindex reading symbols immediately
15377 @cindex symbols, reading immediately
15378 @item symbol-file @r{[} -readnow @r{]} @var{filename}
15379 @itemx file @r{[} -readnow @r{]} @var{filename}
15380 You can override the @value{GDBN} two-stage strategy for reading symbol
15381 tables by using the @samp{-readnow} option with any of the commands that
15382 load symbol table information, if you want to be sure @value{GDBN} has the
15383 entire symbol table available.
15385 @c FIXME: for now no mention of directories, since this seems to be in
15386 @c flux. 13mar1992 status is that in theory GDB would look either in
15387 @c current dir or in same dir as myprog; but issues like competing
15388 @c GDB's, or clutter in system dirs, mean that in practice right now
15389 @c only current dir is used. FFish says maybe a special GDB hierarchy
15390 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
15394 @item core-file @r{[}@var{filename}@r{]}
15396 Specify the whereabouts of a core dump file to be used as the ``contents
15397 of memory''. Traditionally, core files contain only some parts of the
15398 address space of the process that generated them; @value{GDBN} can access the
15399 executable file itself for other parts.
15401 @code{core-file} with no argument specifies that no core file is
15404 Note that the core file is ignored when your program is actually running
15405 under @value{GDBN}. So, if you have been running your program and you
15406 wish to debug a core file instead, you must kill the subprocess in which
15407 the program is running. To do this, use the @code{kill} command
15408 (@pxref{Kill Process, ,Killing the Child Process}).
15410 @kindex add-symbol-file
15411 @cindex dynamic linking
15412 @item add-symbol-file @var{filename} @var{address}
15413 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]}
15414 @itemx add-symbol-file @var{filename} @var{address} -s @var{section} @var{address} @dots{}
15415 The @code{add-symbol-file} command reads additional symbol table
15416 information from the file @var{filename}. You would use this command
15417 when @var{filename} has been dynamically loaded (by some other means)
15418 into the program that is running. @var{address} should be the memory
15419 address at which the file has been loaded; @value{GDBN} cannot figure
15420 this out for itself. You can additionally specify an arbitrary number
15421 of @samp{-s @var{section} @var{address}} pairs, to give an explicit
15422 section name and base address for that section. You can specify any
15423 @var{address} as an expression.
15425 The symbol table of the file @var{filename} is added to the symbol table
15426 originally read with the @code{symbol-file} command. You can use the
15427 @code{add-symbol-file} command any number of times; the new symbol data
15428 thus read keeps adding to the old. To discard all old symbol data
15429 instead, use the @code{symbol-file} command without any arguments.
15431 @cindex relocatable object files, reading symbols from
15432 @cindex object files, relocatable, reading symbols from
15433 @cindex reading symbols from relocatable object files
15434 @cindex symbols, reading from relocatable object files
15435 @cindex @file{.o} files, reading symbols from
15436 Although @var{filename} is typically a shared library file, an
15437 executable file, or some other object file which has been fully
15438 relocated for loading into a process, you can also load symbolic
15439 information from relocatable @file{.o} files, as long as:
15443 the file's symbolic information refers only to linker symbols defined in
15444 that file, not to symbols defined by other object files,
15446 every section the file's symbolic information refers to has actually
15447 been loaded into the inferior, as it appears in the file, and
15449 you can determine the address at which every section was loaded, and
15450 provide these to the @code{add-symbol-file} command.
15454 Some embedded operating systems, like Sun Chorus and VxWorks, can load
15455 relocatable files into an already running program; such systems
15456 typically make the requirements above easy to meet. However, it's
15457 important to recognize that many native systems use complex link
15458 procedures (@code{.linkonce} section factoring and C@t{++} constructor table
15459 assembly, for example) that make the requirements difficult to meet. In
15460 general, one cannot assume that using @code{add-symbol-file} to read a
15461 relocatable object file's symbolic information will have the same effect
15462 as linking the relocatable object file into the program in the normal
15465 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
15467 @kindex add-symbol-file-from-memory
15468 @cindex @code{syscall DSO}
15469 @cindex load symbols from memory
15470 @item add-symbol-file-from-memory @var{address}
15471 Load symbols from the given @var{address} in a dynamically loaded
15472 object file whose image is mapped directly into the inferior's memory.
15473 For example, the Linux kernel maps a @code{syscall DSO} into each
15474 process's address space; this DSO provides kernel-specific code for
15475 some system calls. The argument can be any expression whose
15476 evaluation yields the address of the file's shared object file header.
15477 For this command to work, you must have used @code{symbol-file} or
15478 @code{exec-file} commands in advance.
15480 @kindex add-shared-symbol-files
15482 @item add-shared-symbol-files @var{library-file}
15483 @itemx assf @var{library-file}
15484 The @code{add-shared-symbol-files} command can currently be used only
15485 in the Cygwin build of @value{GDBN} on MS-Windows OS, where it is an
15486 alias for the @code{dll-symbols} command (@pxref{Cygwin Native}).
15487 @value{GDBN} automatically looks for shared libraries, however if
15488 @value{GDBN} does not find yours, you can invoke
15489 @code{add-shared-symbol-files}. It takes one argument: the shared
15490 library's file name. @code{assf} is a shorthand alias for
15491 @code{add-shared-symbol-files}.
15494 @item section @var{section} @var{addr}
15495 The @code{section} command changes the base address of the named
15496 @var{section} of the exec file to @var{addr}. This can be used if the
15497 exec file does not contain section addresses, (such as in the
15498 @code{a.out} format), or when the addresses specified in the file
15499 itself are wrong. Each section must be changed separately. The
15500 @code{info files} command, described below, lists all the sections and
15504 @kindex info target
15507 @code{info files} and @code{info target} are synonymous; both print the
15508 current target (@pxref{Targets, ,Specifying a Debugging Target}),
15509 including the names of the executable and core dump files currently in
15510 use by @value{GDBN}, and the files from which symbols were loaded. The
15511 command @code{help target} lists all possible targets rather than
15514 @kindex maint info sections
15515 @item maint info sections
15516 Another command that can give you extra information about program sections
15517 is @code{maint info sections}. In addition to the section information
15518 displayed by @code{info files}, this command displays the flags and file
15519 offset of each section in the executable and core dump files. In addition,
15520 @code{maint info sections} provides the following command options (which
15521 may be arbitrarily combined):
15525 Display sections for all loaded object files, including shared libraries.
15526 @item @var{sections}
15527 Display info only for named @var{sections}.
15528 @item @var{section-flags}
15529 Display info only for sections for which @var{section-flags} are true.
15530 The section flags that @value{GDBN} currently knows about are:
15533 Section will have space allocated in the process when loaded.
15534 Set for all sections except those containing debug information.
15536 Section will be loaded from the file into the child process memory.
15537 Set for pre-initialized code and data, clear for @code{.bss} sections.
15539 Section needs to be relocated before loading.
15541 Section cannot be modified by the child process.
15543 Section contains executable code only.
15545 Section contains data only (no executable code).
15547 Section will reside in ROM.
15549 Section contains data for constructor/destructor lists.
15551 Section is not empty.
15553 An instruction to the linker to not output the section.
15554 @item COFF_SHARED_LIBRARY
15555 A notification to the linker that the section contains
15556 COFF shared library information.
15558 Section contains common symbols.
15561 @kindex set trust-readonly-sections
15562 @cindex read-only sections
15563 @item set trust-readonly-sections on
15564 Tell @value{GDBN} that readonly sections in your object file
15565 really are read-only (i.e.@: that their contents will not change).
15566 In that case, @value{GDBN} can fetch values from these sections
15567 out of the object file, rather than from the target program.
15568 For some targets (notably embedded ones), this can be a significant
15569 enhancement to debugging performance.
15571 The default is off.
15573 @item set trust-readonly-sections off
15574 Tell @value{GDBN} not to trust readonly sections. This means that
15575 the contents of the section might change while the program is running,
15576 and must therefore be fetched from the target when needed.
15578 @item show trust-readonly-sections
15579 Show the current setting of trusting readonly sections.
15582 All file-specifying commands allow both absolute and relative file names
15583 as arguments. @value{GDBN} always converts the file name to an absolute file
15584 name and remembers it that way.
15586 @cindex shared libraries
15587 @anchor{Shared Libraries}
15588 @value{GDBN} supports @sc{gnu}/Linux, MS-Windows, HP-UX, SunOS, SVr4, Irix,
15589 and IBM RS/6000 AIX shared libraries.
15591 On MS-Windows @value{GDBN} must be linked with the Expat library to support
15592 shared libraries. @xref{Expat}.
15594 @value{GDBN} automatically loads symbol definitions from shared libraries
15595 when you use the @code{run} command, or when you examine a core file.
15596 (Before you issue the @code{run} command, @value{GDBN} does not understand
15597 references to a function in a shared library, however---unless you are
15598 debugging a core file).
15600 On HP-UX, if the program loads a library explicitly, @value{GDBN}
15601 automatically loads the symbols at the time of the @code{shl_load} call.
15603 @c FIXME: some @value{GDBN} release may permit some refs to undef
15604 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
15605 @c FIXME...lib; check this from time to time when updating manual
15607 There are times, however, when you may wish to not automatically load
15608 symbol definitions from shared libraries, such as when they are
15609 particularly large or there are many of them.
15611 To control the automatic loading of shared library symbols, use the
15615 @kindex set auto-solib-add
15616 @item set auto-solib-add @var{mode}
15617 If @var{mode} is @code{on}, symbols from all shared object libraries
15618 will be loaded automatically when the inferior begins execution, you
15619 attach to an independently started inferior, or when the dynamic linker
15620 informs @value{GDBN} that a new library has been loaded. If @var{mode}
15621 is @code{off}, symbols must be loaded manually, using the
15622 @code{sharedlibrary} command. The default value is @code{on}.
15624 @cindex memory used for symbol tables
15625 If your program uses lots of shared libraries with debug info that
15626 takes large amounts of memory, you can decrease the @value{GDBN}
15627 memory footprint by preventing it from automatically loading the
15628 symbols from shared libraries. To that end, type @kbd{set
15629 auto-solib-add off} before running the inferior, then load each
15630 library whose debug symbols you do need with @kbd{sharedlibrary
15631 @var{regexp}}, where @var{regexp} is a regular expression that matches
15632 the libraries whose symbols you want to be loaded.
15634 @kindex show auto-solib-add
15635 @item show auto-solib-add
15636 Display the current autoloading mode.
15639 @cindex load shared library
15640 To explicitly load shared library symbols, use the @code{sharedlibrary}
15644 @kindex info sharedlibrary
15646 @item info share @var{regex}
15647 @itemx info sharedlibrary @var{regex}
15648 Print the names of the shared libraries which are currently loaded
15649 that match @var{regex}. If @var{regex} is omitted then print
15650 all shared libraries that are loaded.
15652 @kindex sharedlibrary
15654 @item sharedlibrary @var{regex}
15655 @itemx share @var{regex}
15656 Load shared object library symbols for files matching a
15657 Unix regular expression.
15658 As with files loaded automatically, it only loads shared libraries
15659 required by your program for a core file or after typing @code{run}. If
15660 @var{regex} is omitted all shared libraries required by your program are
15663 @item nosharedlibrary
15664 @kindex nosharedlibrary
15665 @cindex unload symbols from shared libraries
15666 Unload all shared object library symbols. This discards all symbols
15667 that have been loaded from all shared libraries. Symbols from shared
15668 libraries that were loaded by explicit user requests are not
15672 Sometimes you may wish that @value{GDBN} stops and gives you control
15673 when any of shared library events happen. The best way to do this is
15674 to use @code{catch load} and @code{catch unload} (@pxref{Set
15677 @value{GDBN} also supports the the @code{set stop-on-solib-events}
15678 command for this. This command exists for historical reasons. It is
15679 less useful than setting a catchpoint, because it does not allow for
15680 conditions or commands as a catchpoint does.
15683 @item set stop-on-solib-events
15684 @kindex set stop-on-solib-events
15685 This command controls whether @value{GDBN} should give you control
15686 when the dynamic linker notifies it about some shared library event.
15687 The most common event of interest is loading or unloading of a new
15690 @item show stop-on-solib-events
15691 @kindex show stop-on-solib-events
15692 Show whether @value{GDBN} stops and gives you control when shared
15693 library events happen.
15696 Shared libraries are also supported in many cross or remote debugging
15697 configurations. @value{GDBN} needs to have access to the target's libraries;
15698 this can be accomplished either by providing copies of the libraries
15699 on the host system, or by asking @value{GDBN} to automatically retrieve the
15700 libraries from the target. If copies of the target libraries are
15701 provided, they need to be the same as the target libraries, although the
15702 copies on the target can be stripped as long as the copies on the host are
15705 @cindex where to look for shared libraries
15706 For remote debugging, you need to tell @value{GDBN} where the target
15707 libraries are, so that it can load the correct copies---otherwise, it
15708 may try to load the host's libraries. @value{GDBN} has two variables
15709 to specify the search directories for target libraries.
15712 @cindex prefix for shared library file names
15713 @cindex system root, alternate
15714 @kindex set solib-absolute-prefix
15715 @kindex set sysroot
15716 @item set sysroot @var{path}
15717 Use @var{path} as the system root for the program being debugged. Any
15718 absolute shared library paths will be prefixed with @var{path}; many
15719 runtime loaders store the absolute paths to the shared library in the
15720 target program's memory. If you use @code{set sysroot} to find shared
15721 libraries, they need to be laid out in the same way that they are on
15722 the target, with e.g.@: a @file{/lib} and @file{/usr/lib} hierarchy
15725 If @var{path} starts with the sequence @file{remote:}, @value{GDBN} will
15726 retrieve the target libraries from the remote system. This is only
15727 supported when using a remote target that supports the @code{remote get}
15728 command (@pxref{File Transfer,,Sending files to a remote system}).
15729 The part of @var{path} following the initial @file{remote:}
15730 (if present) is used as system root prefix on the remote file system.
15731 @footnote{If you want to specify a local system root using a directory
15732 that happens to be named @file{remote:}, you need to use some equivalent
15733 variant of the name like @file{./remote:}.}
15735 For targets with an MS-DOS based filesystem, such as MS-Windows and
15736 SymbianOS, @value{GDBN} tries prefixing a few variants of the target
15737 absolute file name with @var{path}. But first, on Unix hosts,
15738 @value{GDBN} converts all backslash directory separators into forward
15739 slashes, because the backslash is not a directory separator on Unix:
15742 c:\foo\bar.dll @result{} c:/foo/bar.dll
15745 Then, @value{GDBN} attempts prefixing the target file name with
15746 @var{path}, and looks for the resulting file name in the host file
15750 c:/foo/bar.dll @result{} /path/to/sysroot/c:/foo/bar.dll
15753 If that does not find the shared library, @value{GDBN} tries removing
15754 the @samp{:} character from the drive spec, both for convenience, and,
15755 for the case of the host file system not supporting file names with
15759 c:/foo/bar.dll @result{} /path/to/sysroot/c/foo/bar.dll
15762 This makes it possible to have a system root that mirrors a target
15763 with more than one drive. E.g., you may want to setup your local
15764 copies of the target system shared libraries like so (note @samp{c} vs
15768 @file{/path/to/sysroot/c/sys/bin/foo.dll}
15769 @file{/path/to/sysroot/c/sys/bin/bar.dll}
15770 @file{/path/to/sysroot/z/sys/bin/bar.dll}
15774 and point the system root at @file{/path/to/sysroot}, so that
15775 @value{GDBN} can find the correct copies of both
15776 @file{c:\sys\bin\foo.dll}, and @file{z:\sys\bin\bar.dll}.
15778 If that still does not find the shared library, @value{GDBN} tries
15779 removing the whole drive spec from the target file name:
15782 c:/foo/bar.dll @result{} /path/to/sysroot/foo/bar.dll
15785 This last lookup makes it possible to not care about the drive name,
15786 if you don't want or need to.
15788 The @code{set solib-absolute-prefix} command is an alias for @code{set
15791 @cindex default system root
15792 @cindex @samp{--with-sysroot}
15793 You can set the default system root by using the configure-time
15794 @samp{--with-sysroot} option. If the system root is inside
15795 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
15796 @samp{--exec-prefix}), then the default system root will be updated
15797 automatically if the installed @value{GDBN} is moved to a new
15800 @kindex show sysroot
15802 Display the current shared library prefix.
15804 @kindex set solib-search-path
15805 @item set solib-search-path @var{path}
15806 If this variable is set, @var{path} is a colon-separated list of
15807 directories to search for shared libraries. @samp{solib-search-path}
15808 is used after @samp{sysroot} fails to locate the library, or if the
15809 path to the library is relative instead of absolute. If you want to
15810 use @samp{solib-search-path} instead of @samp{sysroot}, be sure to set
15811 @samp{sysroot} to a nonexistent directory to prevent @value{GDBN} from
15812 finding your host's libraries. @samp{sysroot} is preferred; setting
15813 it to a nonexistent directory may interfere with automatic loading
15814 of shared library symbols.
15816 @kindex show solib-search-path
15817 @item show solib-search-path
15818 Display the current shared library search path.
15820 @cindex DOS file-name semantics of file names.
15821 @kindex set target-file-system-kind (unix|dos-based|auto)
15822 @kindex show target-file-system-kind
15823 @item set target-file-system-kind @var{kind}
15824 Set assumed file system kind for target reported file names.
15826 Shared library file names as reported by the target system may not
15827 make sense as is on the system @value{GDBN} is running on. For
15828 example, when remote debugging a target that has MS-DOS based file
15829 system semantics, from a Unix host, the target may be reporting to
15830 @value{GDBN} a list of loaded shared libraries with file names such as
15831 @file{c:\Windows\kernel32.dll}. On Unix hosts, there's no concept of
15832 drive letters, so the @samp{c:\} prefix is not normally understood as
15833 indicating an absolute file name, and neither is the backslash
15834 normally considered a directory separator character. In that case,
15835 the native file system would interpret this whole absolute file name
15836 as a relative file name with no directory components. This would make
15837 it impossible to point @value{GDBN} at a copy of the remote target's
15838 shared libraries on the host using @code{set sysroot}, and impractical
15839 with @code{set solib-search-path}. Setting
15840 @code{target-file-system-kind} to @code{dos-based} tells @value{GDBN}
15841 to interpret such file names similarly to how the target would, and to
15842 map them to file names valid on @value{GDBN}'s native file system
15843 semantics. The value of @var{kind} can be @code{"auto"}, in addition
15844 to one of the supported file system kinds. In that case, @value{GDBN}
15845 tries to determine the appropriate file system variant based on the
15846 current target's operating system (@pxref{ABI, ,Configuring the
15847 Current ABI}). The supported file system settings are:
15851 Instruct @value{GDBN} to assume the target file system is of Unix
15852 kind. Only file names starting the forward slash (@samp{/}) character
15853 are considered absolute, and the directory separator character is also
15857 Instruct @value{GDBN} to assume the target file system is DOS based.
15858 File names starting with either a forward slash, or a drive letter
15859 followed by a colon (e.g., @samp{c:}), are considered absolute, and
15860 both the slash (@samp{/}) and the backslash (@samp{\\}) characters are
15861 considered directory separators.
15864 Instruct @value{GDBN} to use the file system kind associated with the
15865 target operating system (@pxref{ABI, ,Configuring the Current ABI}).
15866 This is the default.
15870 @cindex file name canonicalization
15871 @cindex base name differences
15872 When processing file names provided by the user, @value{GDBN}
15873 frequently needs to compare them to the file names recorded in the
15874 program's debug info. Normally, @value{GDBN} compares just the
15875 @dfn{base names} of the files as strings, which is reasonably fast
15876 even for very large programs. (The base name of a file is the last
15877 portion of its name, after stripping all the leading directories.)
15878 This shortcut in comparison is based upon the assumption that files
15879 cannot have more than one base name. This is usually true, but
15880 references to files that use symlinks or similar filesystem
15881 facilities violate that assumption. If your program records files
15882 using such facilities, or if you provide file names to @value{GDBN}
15883 using symlinks etc., you can set @code{basenames-may-differ} to
15884 @code{true} to instruct @value{GDBN} to completely canonicalize each
15885 pair of file names it needs to compare. This will make file-name
15886 comparisons accurate, but at a price of a significant slowdown.
15889 @item set basenames-may-differ
15890 @kindex set basenames-may-differ
15891 Set whether a source file may have multiple base names.
15893 @item show basenames-may-differ
15894 @kindex show basenames-may-differ
15895 Show whether a source file may have multiple base names.
15898 @node Separate Debug Files
15899 @section Debugging Information in Separate Files
15900 @cindex separate debugging information files
15901 @cindex debugging information in separate files
15902 @cindex @file{.debug} subdirectories
15903 @cindex debugging information directory, global
15904 @cindex global debugging information directory
15905 @cindex build ID, and separate debugging files
15906 @cindex @file{.build-id} directory
15908 @value{GDBN} allows you to put a program's debugging information in a
15909 file separate from the executable itself, in a way that allows
15910 @value{GDBN} to find and load the debugging information automatically.
15911 Since debugging information can be very large---sometimes larger
15912 than the executable code itself---some systems distribute debugging
15913 information for their executables in separate files, which users can
15914 install only when they need to debug a problem.
15916 @value{GDBN} supports two ways of specifying the separate debug info
15921 The executable contains a @dfn{debug link} that specifies the name of
15922 the separate debug info file. The separate debug file's name is
15923 usually @file{@var{executable}.debug}, where @var{executable} is the
15924 name of the corresponding executable file without leading directories
15925 (e.g., @file{ls.debug} for @file{/usr/bin/ls}). In addition, the
15926 debug link specifies a 32-bit @dfn{Cyclic Redundancy Check} (CRC)
15927 checksum for the debug file, which @value{GDBN} uses to validate that
15928 the executable and the debug file came from the same build.
15931 The executable contains a @dfn{build ID}, a unique bit string that is
15932 also present in the corresponding debug info file. (This is supported
15933 only on some operating systems, notably those which use the ELF format
15934 for binary files and the @sc{gnu} Binutils.) For more details about
15935 this feature, see the description of the @option{--build-id}
15936 command-line option in @ref{Options, , Command Line Options, ld.info,
15937 The GNU Linker}. The debug info file's name is not specified
15938 explicitly by the build ID, but can be computed from the build ID, see
15942 Depending on the way the debug info file is specified, @value{GDBN}
15943 uses two different methods of looking for the debug file:
15947 For the ``debug link'' method, @value{GDBN} looks up the named file in
15948 the directory of the executable file, then in a subdirectory of that
15949 directory named @file{.debug}, and finally under the global debug
15950 directory, in a subdirectory whose name is identical to the leading
15951 directories of the executable's absolute file name.
15954 For the ``build ID'' method, @value{GDBN} looks in the
15955 @file{.build-id} subdirectory of the global debug directory for a file
15956 named @file{@var{nn}/@var{nnnnnnnn}.debug}, where @var{nn} are the
15957 first 2 hex characters of the build ID bit string, and @var{nnnnnnnn}
15958 are the rest of the bit string. (Real build ID strings are 32 or more
15959 hex characters, not 10.)
15962 So, for example, suppose you ask @value{GDBN} to debug
15963 @file{/usr/bin/ls}, which has a debug link that specifies the
15964 file @file{ls.debug}, and a build ID whose value in hex is
15965 @code{abcdef1234}. If the global debug directory is
15966 @file{/usr/lib/debug}, then @value{GDBN} will look for the following
15967 debug information files, in the indicated order:
15971 @file{/usr/lib/debug/.build-id/ab/cdef1234.debug}
15973 @file{/usr/bin/ls.debug}
15975 @file{/usr/bin/.debug/ls.debug}
15977 @file{/usr/lib/debug/usr/bin/ls.debug}.
15980 You can set the global debugging info directory's name, and view the
15981 name @value{GDBN} is currently using.
15985 @kindex set debug-file-directory
15986 @item set debug-file-directory @var{directories}
15987 Set the directories which @value{GDBN} searches for separate debugging
15988 information files to @var{directory}. Multiple directory components can be set
15989 concatenating them by a directory separator.
15991 @kindex show debug-file-directory
15992 @item show debug-file-directory
15993 Show the directories @value{GDBN} searches for separate debugging
15998 @cindex @code{.gnu_debuglink} sections
15999 @cindex debug link sections
16000 A debug link is a special section of the executable file named
16001 @code{.gnu_debuglink}. The section must contain:
16005 A filename, with any leading directory components removed, followed by
16008 zero to three bytes of padding, as needed to reach the next four-byte
16009 boundary within the section, and
16011 a four-byte CRC checksum, stored in the same endianness used for the
16012 executable file itself. The checksum is computed on the debugging
16013 information file's full contents by the function given below, passing
16014 zero as the @var{crc} argument.
16017 Any executable file format can carry a debug link, as long as it can
16018 contain a section named @code{.gnu_debuglink} with the contents
16021 @cindex @code{.note.gnu.build-id} sections
16022 @cindex build ID sections
16023 The build ID is a special section in the executable file (and in other
16024 ELF binary files that @value{GDBN} may consider). This section is
16025 often named @code{.note.gnu.build-id}, but that name is not mandatory.
16026 It contains unique identification for the built files---the ID remains
16027 the same across multiple builds of the same build tree. The default
16028 algorithm SHA1 produces 160 bits (40 hexadecimal characters) of the
16029 content for the build ID string. The same section with an identical
16030 value is present in the original built binary with symbols, in its
16031 stripped variant, and in the separate debugging information file.
16033 The debugging information file itself should be an ordinary
16034 executable, containing a full set of linker symbols, sections, and
16035 debugging information. The sections of the debugging information file
16036 should have the same names, addresses, and sizes as the original file,
16037 but they need not contain any data---much like a @code{.bss} section
16038 in an ordinary executable.
16040 The @sc{gnu} binary utilities (Binutils) package includes the
16041 @samp{objcopy} utility that can produce
16042 the separated executable / debugging information file pairs using the
16043 following commands:
16046 @kbd{objcopy --only-keep-debug foo foo.debug}
16051 These commands remove the debugging
16052 information from the executable file @file{foo} and place it in the file
16053 @file{foo.debug}. You can use the first, second or both methods to link the
16058 The debug link method needs the following additional command to also leave
16059 behind a debug link in @file{foo}:
16062 @kbd{objcopy --add-gnu-debuglink=foo.debug foo}
16065 Ulrich Drepper's @file{elfutils} package, starting with version 0.53, contains
16066 a version of the @code{strip} command such that the command @kbd{strip foo -f
16067 foo.debug} has the same functionality as the two @code{objcopy} commands and
16068 the @code{ln -s} command above, together.
16071 Build ID gets embedded into the main executable using @code{ld --build-id} or
16072 the @value{NGCC} counterpart @code{gcc -Wl,--build-id}. Build ID support plus
16073 compatibility fixes for debug files separation are present in @sc{gnu} binary
16074 utilities (Binutils) package since version 2.18.
16079 @cindex CRC algorithm definition
16080 The CRC used in @code{.gnu_debuglink} is the CRC-32 defined in
16081 IEEE 802.3 using the polynomial:
16083 @c TexInfo requires naked braces for multi-digit exponents for Tex
16084 @c output, but this causes HTML output to barf. HTML has to be set using
16085 @c raw commands. So we end up having to specify this equation in 2
16090 <em>x</em><sup>32</sup> + <em>x</em><sup>26</sup> + <em>x</em><sup>23</sup> + <em>x</em><sup>22</sup> + <em>x</em><sup>16</sup> + <em>x</em><sup>12</sup> + <em>x</em><sup>11</sup>
16091 + <em>x</em><sup>10</sup> + <em>x</em><sup>8</sup> + <em>x</em><sup>7</sup> + <em>x</em><sup>5</sup> + <em>x</em><sup>4</sup> + <em>x</em><sup>2</sup> + <em>x</em> + 1
16097 @math{x^{32} + x^{26} + x^{23} + x^{22} + x^{16} + x^{12} + x^{11}}
16098 @math{+ x^{10} + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1}
16102 The function is computed byte at a time, taking the least
16103 significant bit of each byte first. The initial pattern
16104 @code{0xffffffff} is used, to ensure leading zeros affect the CRC and
16105 the final result is inverted to ensure trailing zeros also affect the
16108 @emph{Note:} This is the same CRC polynomial as used in handling the
16109 @dfn{Remote Serial Protocol} @code{qCRC} packet (@pxref{Remote Protocol,
16110 , @value{GDBN} Remote Serial Protocol}). However in the
16111 case of the Remote Serial Protocol, the CRC is computed @emph{most}
16112 significant bit first, and the result is not inverted, so trailing
16113 zeros have no effect on the CRC value.
16115 To complete the description, we show below the code of the function
16116 which produces the CRC used in @code{.gnu_debuglink}. Inverting the
16117 initially supplied @code{crc} argument means that an initial call to
16118 this function passing in zero will start computing the CRC using
16121 @kindex gnu_debuglink_crc32
16124 gnu_debuglink_crc32 (unsigned long crc,
16125 unsigned char *buf, size_t len)
16127 static const unsigned long crc32_table[256] =
16129 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
16130 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
16131 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
16132 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
16133 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
16134 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
16135 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
16136 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
16137 0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
16138 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
16139 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
16140 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
16141 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
16142 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
16143 0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
16144 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
16145 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
16146 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
16147 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
16148 0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
16149 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
16150 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
16151 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
16152 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
16153 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
16154 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
16155 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
16156 0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
16157 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
16158 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
16159 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
16160 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
16161 0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
16162 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
16163 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
16164 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
16165 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
16166 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
16167 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
16168 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
16169 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
16170 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
16171 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
16172 0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
16173 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
16174 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
16175 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
16176 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
16177 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
16178 0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
16179 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
16182 unsigned char *end;
16184 crc = ~crc & 0xffffffff;
16185 for (end = buf + len; buf < end; ++buf)
16186 crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
16187 return ~crc & 0xffffffff;
16192 This computation does not apply to the ``build ID'' method.
16196 @section Index Files Speed Up @value{GDBN}
16197 @cindex index files
16198 @cindex @samp{.gdb_index} section
16200 When @value{GDBN} finds a symbol file, it scans the symbols in the
16201 file in order to construct an internal symbol table. This lets most
16202 @value{GDBN} operations work quickly---at the cost of a delay early
16203 on. For large programs, this delay can be quite lengthy, so
16204 @value{GDBN} provides a way to build an index, which speeds up
16207 The index is stored as a section in the symbol file. @value{GDBN} can
16208 write the index to a file, then you can put it into the symbol file
16209 using @command{objcopy}.
16211 To create an index file, use the @code{save gdb-index} command:
16214 @item save gdb-index @var{directory}
16215 @kindex save gdb-index
16216 Create an index file for each symbol file currently known by
16217 @value{GDBN}. Each file is named after its corresponding symbol file,
16218 with @samp{.gdb-index} appended, and is written into the given
16222 Once you have created an index file you can merge it into your symbol
16223 file, here named @file{symfile}, using @command{objcopy}:
16226 $ objcopy --add-section .gdb_index=symfile.gdb-index \
16227 --set-section-flags .gdb_index=readonly symfile symfile
16230 There are currently some limitation on indices. They only work when
16231 for DWARF debugging information, not stabs. And, they do not
16232 currently work for programs using Ada.
16234 @node Symbol Errors
16235 @section Errors Reading Symbol Files
16237 While reading a symbol file, @value{GDBN} occasionally encounters problems,
16238 such as symbol types it does not recognize, or known bugs in compiler
16239 output. By default, @value{GDBN} does not notify you of such problems, since
16240 they are relatively common and primarily of interest to people
16241 debugging compilers. If you are interested in seeing information
16242 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
16243 only one message about each such type of problem, no matter how many
16244 times the problem occurs; or you can ask @value{GDBN} to print more messages,
16245 to see how many times the problems occur, with the @code{set
16246 complaints} command (@pxref{Messages/Warnings, ,Optional Warnings and
16249 The messages currently printed, and their meanings, include:
16252 @item inner block not inside outer block in @var{symbol}
16254 The symbol information shows where symbol scopes begin and end
16255 (such as at the start of a function or a block of statements). This
16256 error indicates that an inner scope block is not fully contained
16257 in its outer scope blocks.
16259 @value{GDBN} circumvents the problem by treating the inner block as if it had
16260 the same scope as the outer block. In the error message, @var{symbol}
16261 may be shown as ``@code{(don't know)}'' if the outer block is not a
16264 @item block at @var{address} out of order
16266 The symbol information for symbol scope blocks should occur in
16267 order of increasing addresses. This error indicates that it does not
16270 @value{GDBN} does not circumvent this problem, and has trouble
16271 locating symbols in the source file whose symbols it is reading. (You
16272 can often determine what source file is affected by specifying
16273 @code{set verbose on}. @xref{Messages/Warnings, ,Optional Warnings and
16276 @item bad block start address patched
16278 The symbol information for a symbol scope block has a start address
16279 smaller than the address of the preceding source line. This is known
16280 to occur in the SunOS 4.1.1 (and earlier) C compiler.
16282 @value{GDBN} circumvents the problem by treating the symbol scope block as
16283 starting on the previous source line.
16285 @item bad string table offset in symbol @var{n}
16288 Symbol number @var{n} contains a pointer into the string table which is
16289 larger than the size of the string table.
16291 @value{GDBN} circumvents the problem by considering the symbol to have the
16292 name @code{foo}, which may cause other problems if many symbols end up
16295 @item unknown symbol type @code{0x@var{nn}}
16297 The symbol information contains new data types that @value{GDBN} does
16298 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
16299 uncomprehended information, in hexadecimal.
16301 @value{GDBN} circumvents the error by ignoring this symbol information.
16302 This usually allows you to debug your program, though certain symbols
16303 are not accessible. If you encounter such a problem and feel like
16304 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
16305 on @code{complain}, then go up to the function @code{read_dbx_symtab}
16306 and examine @code{*bufp} to see the symbol.
16308 @item stub type has NULL name
16310 @value{GDBN} could not find the full definition for a struct or class.
16312 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
16313 The symbol information for a C@t{++} member function is missing some
16314 information that recent versions of the compiler should have output for
16317 @item info mismatch between compiler and debugger
16319 @value{GDBN} could not parse a type specification output by the compiler.
16324 @section GDB Data Files
16326 @cindex prefix for data files
16327 @value{GDBN} will sometimes read an auxiliary data file. These files
16328 are kept in a directory known as the @dfn{data directory}.
16330 You can set the data directory's name, and view the name @value{GDBN}
16331 is currently using.
16334 @kindex set data-directory
16335 @item set data-directory @var{directory}
16336 Set the directory which @value{GDBN} searches for auxiliary data files
16337 to @var{directory}.
16339 @kindex show data-directory
16340 @item show data-directory
16341 Show the directory @value{GDBN} searches for auxiliary data files.
16344 @cindex default data directory
16345 @cindex @samp{--with-gdb-datadir}
16346 You can set the default data directory by using the configure-time
16347 @samp{--with-gdb-datadir} option. If the data directory is inside
16348 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
16349 @samp{--exec-prefix}), then the default data directory will be updated
16350 automatically if the installed @value{GDBN} is moved to a new
16353 The data directory may also be specified with the
16354 @code{--data-directory} command line option.
16355 @xref{Mode Options}.
16358 @chapter Specifying a Debugging Target
16360 @cindex debugging target
16361 A @dfn{target} is the execution environment occupied by your program.
16363 Often, @value{GDBN} runs in the same host environment as your program;
16364 in that case, the debugging target is specified as a side effect when
16365 you use the @code{file} or @code{core} commands. When you need more
16366 flexibility---for example, running @value{GDBN} on a physically separate
16367 host, or controlling a standalone system over a serial port or a
16368 realtime system over a TCP/IP connection---you can use the @code{target}
16369 command to specify one of the target types configured for @value{GDBN}
16370 (@pxref{Target Commands, ,Commands for Managing Targets}).
16372 @cindex target architecture
16373 It is possible to build @value{GDBN} for several different @dfn{target
16374 architectures}. When @value{GDBN} is built like that, you can choose
16375 one of the available architectures with the @kbd{set architecture}
16379 @kindex set architecture
16380 @kindex show architecture
16381 @item set architecture @var{arch}
16382 This command sets the current target architecture to @var{arch}. The
16383 value of @var{arch} can be @code{"auto"}, in addition to one of the
16384 supported architectures.
16386 @item show architecture
16387 Show the current target architecture.
16389 @item set processor
16391 @kindex set processor
16392 @kindex show processor
16393 These are alias commands for, respectively, @code{set architecture}
16394 and @code{show architecture}.
16398 * Active Targets:: Active targets
16399 * Target Commands:: Commands for managing targets
16400 * Byte Order:: Choosing target byte order
16403 @node Active Targets
16404 @section Active Targets
16406 @cindex stacking targets
16407 @cindex active targets
16408 @cindex multiple targets
16410 There are multiple classes of targets such as: processes, executable files or
16411 recording sessions. Core files belong to the process class, making core file
16412 and process mutually exclusive. Otherwise, @value{GDBN} can work concurrently
16413 on multiple active targets, one in each class. This allows you to (for
16414 example) start a process and inspect its activity, while still having access to
16415 the executable file after the process finishes. Or if you start process
16416 recording (@pxref{Reverse Execution}) and @code{reverse-step} there, you are
16417 presented a virtual layer of the recording target, while the process target
16418 remains stopped at the chronologically last point of the process execution.
16420 Use the @code{core-file} and @code{exec-file} commands to select a new core
16421 file or executable target (@pxref{Files, ,Commands to Specify Files}). To
16422 specify as a target a process that is already running, use the @code{attach}
16423 command (@pxref{Attach, ,Debugging an Already-running Process}).
16425 @node Target Commands
16426 @section Commands for Managing Targets
16429 @item target @var{type} @var{parameters}
16430 Connects the @value{GDBN} host environment to a target machine or
16431 process. A target is typically a protocol for talking to debugging
16432 facilities. You use the argument @var{type} to specify the type or
16433 protocol of the target machine.
16435 Further @var{parameters} are interpreted by the target protocol, but
16436 typically include things like device names or host names to connect
16437 with, process numbers, and baud rates.
16439 The @code{target} command does not repeat if you press @key{RET} again
16440 after executing the command.
16442 @kindex help target
16444 Displays the names of all targets available. To display targets
16445 currently selected, use either @code{info target} or @code{info files}
16446 (@pxref{Files, ,Commands to Specify Files}).
16448 @item help target @var{name}
16449 Describe a particular target, including any parameters necessary to
16452 @kindex set gnutarget
16453 @item set gnutarget @var{args}
16454 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
16455 knows whether it is reading an @dfn{executable},
16456 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
16457 with the @code{set gnutarget} command. Unlike most @code{target} commands,
16458 with @code{gnutarget} the @code{target} refers to a program, not a machine.
16461 @emph{Warning:} To specify a file format with @code{set gnutarget},
16462 you must know the actual BFD name.
16466 @xref{Files, , Commands to Specify Files}.
16468 @kindex show gnutarget
16469 @item show gnutarget
16470 Use the @code{show gnutarget} command to display what file format
16471 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
16472 @value{GDBN} will determine the file format for each file automatically,
16473 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
16476 @cindex common targets
16477 Here are some common targets (available, or not, depending on the GDB
16482 @item target exec @var{program}
16483 @cindex executable file target
16484 An executable file. @samp{target exec @var{program}} is the same as
16485 @samp{exec-file @var{program}}.
16487 @item target core @var{filename}
16488 @cindex core dump file target
16489 A core dump file. @samp{target core @var{filename}} is the same as
16490 @samp{core-file @var{filename}}.
16492 @item target remote @var{medium}
16493 @cindex remote target
16494 A remote system connected to @value{GDBN} via a serial line or network
16495 connection. This command tells @value{GDBN} to use its own remote
16496 protocol over @var{medium} for debugging. @xref{Remote Debugging}.
16498 For example, if you have a board connected to @file{/dev/ttya} on the
16499 machine running @value{GDBN}, you could say:
16502 target remote /dev/ttya
16505 @code{target remote} supports the @code{load} command. This is only
16506 useful if you have some other way of getting the stub to the target
16507 system, and you can put it somewhere in memory where it won't get
16508 clobbered by the download.
16510 @item target sim @r{[}@var{simargs}@r{]} @dots{}
16511 @cindex built-in simulator target
16512 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
16520 works; however, you cannot assume that a specific memory map, device
16521 drivers, or even basic I/O is available, although some simulators do
16522 provide these. For info about any processor-specific simulator details,
16523 see the appropriate section in @ref{Embedded Processors, ,Embedded
16528 Some configurations may include these targets as well:
16532 @item target nrom @var{dev}
16533 @cindex NetROM ROM emulator target
16534 NetROM ROM emulator. This target only supports downloading.
16538 Different targets are available on different configurations of @value{GDBN};
16539 your configuration may have more or fewer targets.
16541 Many remote targets require you to download the executable's code once
16542 you've successfully established a connection. You may wish to control
16543 various aspects of this process.
16548 @kindex set hash@r{, for remote monitors}
16549 @cindex hash mark while downloading
16550 This command controls whether a hash mark @samp{#} is displayed while
16551 downloading a file to the remote monitor. If on, a hash mark is
16552 displayed after each S-record is successfully downloaded to the
16556 @kindex show hash@r{, for remote monitors}
16557 Show the current status of displaying the hash mark.
16559 @item set debug monitor
16560 @kindex set debug monitor
16561 @cindex display remote monitor communications
16562 Enable or disable display of communications messages between
16563 @value{GDBN} and the remote monitor.
16565 @item show debug monitor
16566 @kindex show debug monitor
16567 Show the current status of displaying communications between
16568 @value{GDBN} and the remote monitor.
16573 @kindex load @var{filename}
16574 @item load @var{filename}
16576 Depending on what remote debugging facilities are configured into
16577 @value{GDBN}, the @code{load} command may be available. Where it exists, it
16578 is meant to make @var{filename} (an executable) available for debugging
16579 on the remote system---by downloading, or dynamic linking, for example.
16580 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
16581 the @code{add-symbol-file} command.
16583 If your @value{GDBN} does not have a @code{load} command, attempting to
16584 execute it gets the error message ``@code{You can't do that when your
16585 target is @dots{}}''
16587 The file is loaded at whatever address is specified in the executable.
16588 For some object file formats, you can specify the load address when you
16589 link the program; for other formats, like a.out, the object file format
16590 specifies a fixed address.
16591 @c FIXME! This would be a good place for an xref to the GNU linker doc.
16593 Depending on the remote side capabilities, @value{GDBN} may be able to
16594 load programs into flash memory.
16596 @code{load} does not repeat if you press @key{RET} again after using it.
16600 @section Choosing Target Byte Order
16602 @cindex choosing target byte order
16603 @cindex target byte order
16605 Some types of processors, such as the MIPS, PowerPC, and Renesas SH,
16606 offer the ability to run either big-endian or little-endian byte
16607 orders. Usually the executable or symbol will include a bit to
16608 designate the endian-ness, and you will not need to worry about
16609 which to use. However, you may still find it useful to adjust
16610 @value{GDBN}'s idea of processor endian-ness manually.
16614 @item set endian big
16615 Instruct @value{GDBN} to assume the target is big-endian.
16617 @item set endian little
16618 Instruct @value{GDBN} to assume the target is little-endian.
16620 @item set endian auto
16621 Instruct @value{GDBN} to use the byte order associated with the
16625 Display @value{GDBN}'s current idea of the target byte order.
16629 Note that these commands merely adjust interpretation of symbolic
16630 data on the host, and that they have absolutely no effect on the
16634 @node Remote Debugging
16635 @chapter Debugging Remote Programs
16636 @cindex remote debugging
16638 If you are trying to debug a program running on a machine that cannot run
16639 @value{GDBN} in the usual way, it is often useful to use remote debugging.
16640 For example, you might use remote debugging on an operating system kernel,
16641 or on a small system which does not have a general purpose operating system
16642 powerful enough to run a full-featured debugger.
16644 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
16645 to make this work with particular debugging targets. In addition,
16646 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
16647 but not specific to any particular target system) which you can use if you
16648 write the remote stubs---the code that runs on the remote system to
16649 communicate with @value{GDBN}.
16651 Other remote targets may be available in your
16652 configuration of @value{GDBN}; use @code{help target} to list them.
16655 * Connecting:: Connecting to a remote target
16656 * File Transfer:: Sending files to a remote system
16657 * Server:: Using the gdbserver program
16658 * Remote Configuration:: Remote configuration
16659 * Remote Stub:: Implementing a remote stub
16663 @section Connecting to a Remote Target
16665 On the @value{GDBN} host machine, you will need an unstripped copy of
16666 your program, since @value{GDBN} needs symbol and debugging information.
16667 Start up @value{GDBN} as usual, using the name of the local copy of your
16668 program as the first argument.
16670 @cindex @code{target remote}
16671 @value{GDBN} can communicate with the target over a serial line, or
16672 over an @acronym{IP} network using @acronym{TCP} or @acronym{UDP}. In
16673 each case, @value{GDBN} uses the same protocol for debugging your
16674 program; only the medium carrying the debugging packets varies. The
16675 @code{target remote} command establishes a connection to the target.
16676 Its arguments indicate which medium to use:
16680 @item target remote @var{serial-device}
16681 @cindex serial line, @code{target remote}
16682 Use @var{serial-device} to communicate with the target. For example,
16683 to use a serial line connected to the device named @file{/dev/ttyb}:
16686 target remote /dev/ttyb
16689 If you're using a serial line, you may want to give @value{GDBN} the
16690 @w{@samp{--baud}} option, or use the @code{set remotebaud} command
16691 (@pxref{Remote Configuration, set remotebaud}) before the
16692 @code{target} command.
16694 @item target remote @code{@var{host}:@var{port}}
16695 @itemx target remote @code{tcp:@var{host}:@var{port}}
16696 @cindex @acronym{TCP} port, @code{target remote}
16697 Debug using a @acronym{TCP} connection to @var{port} on @var{host}.
16698 The @var{host} may be either a host name or a numeric @acronym{IP}
16699 address; @var{port} must be a decimal number. The @var{host} could be
16700 the target machine itself, if it is directly connected to the net, or
16701 it might be a terminal server which in turn has a serial line to the
16704 For example, to connect to port 2828 on a terminal server named
16708 target remote manyfarms:2828
16711 If your remote target is actually running on the same machine as your
16712 debugger session (e.g.@: a simulator for your target running on the
16713 same host), you can omit the hostname. For example, to connect to
16714 port 1234 on your local machine:
16717 target remote :1234
16721 Note that the colon is still required here.
16723 @item target remote @code{udp:@var{host}:@var{port}}
16724 @cindex @acronym{UDP} port, @code{target remote}
16725 Debug using @acronym{UDP} packets to @var{port} on @var{host}. For example, to
16726 connect to @acronym{UDP} port 2828 on a terminal server named @code{manyfarms}:
16729 target remote udp:manyfarms:2828
16732 When using a @acronym{UDP} connection for remote debugging, you should
16733 keep in mind that the `U' stands for ``Unreliable''. @acronym{UDP}
16734 can silently drop packets on busy or unreliable networks, which will
16735 cause havoc with your debugging session.
16737 @item target remote | @var{command}
16738 @cindex pipe, @code{target remote} to
16739 Run @var{command} in the background and communicate with it using a
16740 pipe. The @var{command} is a shell command, to be parsed and expanded
16741 by the system's command shell, @code{/bin/sh}; it should expect remote
16742 protocol packets on its standard input, and send replies on its
16743 standard output. You could use this to run a stand-alone simulator
16744 that speaks the remote debugging protocol, to make net connections
16745 using programs like @code{ssh}, or for other similar tricks.
16747 If @var{command} closes its standard output (perhaps by exiting),
16748 @value{GDBN} will try to send it a @code{SIGTERM} signal. (If the
16749 program has already exited, this will have no effect.)
16753 Once the connection has been established, you can use all the usual
16754 commands to examine and change data. The remote program is already
16755 running; you can use @kbd{step} and @kbd{continue}, and you do not
16756 need to use @kbd{run}.
16758 @cindex interrupting remote programs
16759 @cindex remote programs, interrupting
16760 Whenever @value{GDBN} is waiting for the remote program, if you type the
16761 interrupt character (often @kbd{Ctrl-c}), @value{GDBN} attempts to stop the
16762 program. This may or may not succeed, depending in part on the hardware
16763 and the serial drivers the remote system uses. If you type the
16764 interrupt character once again, @value{GDBN} displays this prompt:
16767 Interrupted while waiting for the program.
16768 Give up (and stop debugging it)? (y or n)
16771 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
16772 (If you decide you want to try again later, you can use @samp{target
16773 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
16774 goes back to waiting.
16777 @kindex detach (remote)
16779 When you have finished debugging the remote program, you can use the
16780 @code{detach} command to release it from @value{GDBN} control.
16781 Detaching from the target normally resumes its execution, but the results
16782 will depend on your particular remote stub. After the @code{detach}
16783 command, @value{GDBN} is free to connect to another target.
16787 The @code{disconnect} command behaves like @code{detach}, except that
16788 the target is generally not resumed. It will wait for @value{GDBN}
16789 (this instance or another one) to connect and continue debugging. After
16790 the @code{disconnect} command, @value{GDBN} is again free to connect to
16793 @cindex send command to remote monitor
16794 @cindex extend @value{GDBN} for remote targets
16795 @cindex add new commands for external monitor
16797 @item monitor @var{cmd}
16798 This command allows you to send arbitrary commands directly to the
16799 remote monitor. Since @value{GDBN} doesn't care about the commands it
16800 sends like this, this command is the way to extend @value{GDBN}---you
16801 can add new commands that only the external monitor will understand
16805 @node File Transfer
16806 @section Sending files to a remote system
16807 @cindex remote target, file transfer
16808 @cindex file transfer
16809 @cindex sending files to remote systems
16811 Some remote targets offer the ability to transfer files over the same
16812 connection used to communicate with @value{GDBN}. This is convenient
16813 for targets accessible through other means, e.g.@: @sc{gnu}/Linux systems
16814 running @code{gdbserver} over a network interface. For other targets,
16815 e.g.@: embedded devices with only a single serial port, this may be
16816 the only way to upload or download files.
16818 Not all remote targets support these commands.
16822 @item remote put @var{hostfile} @var{targetfile}
16823 Copy file @var{hostfile} from the host system (the machine running
16824 @value{GDBN}) to @var{targetfile} on the target system.
16827 @item remote get @var{targetfile} @var{hostfile}
16828 Copy file @var{targetfile} from the target system to @var{hostfile}
16829 on the host system.
16831 @kindex remote delete
16832 @item remote delete @var{targetfile}
16833 Delete @var{targetfile} from the target system.
16838 @section Using the @code{gdbserver} Program
16841 @cindex remote connection without stubs
16842 @code{gdbserver} is a control program for Unix-like systems, which
16843 allows you to connect your program with a remote @value{GDBN} via
16844 @code{target remote}---but without linking in the usual debugging stub.
16846 @code{gdbserver} is not a complete replacement for the debugging stubs,
16847 because it requires essentially the same operating-system facilities
16848 that @value{GDBN} itself does. In fact, a system that can run
16849 @code{gdbserver} to connect to a remote @value{GDBN} could also run
16850 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
16851 because it is a much smaller program than @value{GDBN} itself. It is
16852 also easier to port than all of @value{GDBN}, so you may be able to get
16853 started more quickly on a new system by using @code{gdbserver}.
16854 Finally, if you develop code for real-time systems, you may find that
16855 the tradeoffs involved in real-time operation make it more convenient to
16856 do as much development work as possible on another system, for example
16857 by cross-compiling. You can use @code{gdbserver} to make a similar
16858 choice for debugging.
16860 @value{GDBN} and @code{gdbserver} communicate via either a serial line
16861 or a TCP connection, using the standard @value{GDBN} remote serial
16865 @emph{Warning:} @code{gdbserver} does not have any built-in security.
16866 Do not run @code{gdbserver} connected to any public network; a
16867 @value{GDBN} connection to @code{gdbserver} provides access to the
16868 target system with the same privileges as the user running
16872 @subsection Running @code{gdbserver}
16873 @cindex arguments, to @code{gdbserver}
16874 @cindex @code{gdbserver}, command-line arguments
16876 Run @code{gdbserver} on the target system. You need a copy of the
16877 program you want to debug, including any libraries it requires.
16878 @code{gdbserver} does not need your program's symbol table, so you can
16879 strip the program if necessary to save space. @value{GDBN} on the host
16880 system does all the symbol handling.
16882 To use the server, you must tell it how to communicate with @value{GDBN};
16883 the name of your program; and the arguments for your program. The usual
16887 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
16890 @var{comm} is either a device name (to use a serial line), or a TCP
16891 hostname and portnumber, or @code{-} or @code{stdio} to use
16892 stdin/stdout of @code{gdbserver}.
16893 For example, to debug Emacs with the argument
16894 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
16898 target> gdbserver /dev/com1 emacs foo.txt
16901 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
16904 To use a TCP connection instead of a serial line:
16907 target> gdbserver host:2345 emacs foo.txt
16910 The only difference from the previous example is the first argument,
16911 specifying that you are communicating with the host @value{GDBN} via
16912 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
16913 expect a TCP connection from machine @samp{host} to local TCP port 2345.
16914 (Currently, the @samp{host} part is ignored.) You can choose any number
16915 you want for the port number as long as it does not conflict with any
16916 TCP ports already in use on the target system (for example, @code{23} is
16917 reserved for @code{telnet}).@footnote{If you choose a port number that
16918 conflicts with another service, @code{gdbserver} prints an error message
16919 and exits.} You must use the same port number with the host @value{GDBN}
16920 @code{target remote} command.
16922 The @code{stdio} connection is useful when starting @code{gdbserver}
16926 (gdb) target remote | ssh -T hostname gdbserver - hello
16929 The @samp{-T} option to ssh is provided because we don't need a remote pty,
16930 and we don't want escape-character handling. Ssh does this by default when
16931 a command is provided, the flag is provided to make it explicit.
16932 You could elide it if you want to.
16934 Programs started with stdio-connected gdbserver have @file{/dev/null} for
16935 @code{stdin}, and @code{stdout},@code{stderr} are sent back to gdb for
16936 display through a pipe connected to gdbserver.
16937 Both @code{stdout} and @code{stderr} use the same pipe.
16939 @subsubsection Attaching to a Running Program
16940 @cindex attach to a program, @code{gdbserver}
16941 @cindex @option{--attach}, @code{gdbserver} option
16943 On some targets, @code{gdbserver} can also attach to running programs.
16944 This is accomplished via the @code{--attach} argument. The syntax is:
16947 target> gdbserver --attach @var{comm} @var{pid}
16950 @var{pid} is the process ID of a currently running process. It isn't necessary
16951 to point @code{gdbserver} at a binary for the running process.
16954 You can debug processes by name instead of process ID if your target has the
16955 @code{pidof} utility:
16958 target> gdbserver --attach @var{comm} `pidof @var{program}`
16961 In case more than one copy of @var{program} is running, or @var{program}
16962 has multiple threads, most versions of @code{pidof} support the
16963 @code{-s} option to only return the first process ID.
16965 @subsubsection Multi-Process Mode for @code{gdbserver}
16966 @cindex @code{gdbserver}, multiple processes
16967 @cindex multiple processes with @code{gdbserver}
16969 When you connect to @code{gdbserver} using @code{target remote},
16970 @code{gdbserver} debugs the specified program only once. When the
16971 program exits, or you detach from it, @value{GDBN} closes the connection
16972 and @code{gdbserver} exits.
16974 If you connect using @kbd{target extended-remote}, @code{gdbserver}
16975 enters multi-process mode. When the debugged program exits, or you
16976 detach from it, @value{GDBN} stays connected to @code{gdbserver} even
16977 though no program is running. The @code{run} and @code{attach}
16978 commands instruct @code{gdbserver} to run or attach to a new program.
16979 The @code{run} command uses @code{set remote exec-file} (@pxref{set
16980 remote exec-file}) to select the program to run. Command line
16981 arguments are supported, except for wildcard expansion and I/O
16982 redirection (@pxref{Arguments}).
16984 @cindex @option{--multi}, @code{gdbserver} option
16985 To start @code{gdbserver} without supplying an initial command to run
16986 or process ID to attach, use the @option{--multi} command line option.
16987 Then you can connect using @kbd{target extended-remote} and start
16988 the program you want to debug.
16990 In multi-process mode @code{gdbserver} does not automatically exit unless you
16991 use the option @option{--once}. You can terminate it by using
16992 @code{monitor exit} (@pxref{Monitor Commands for gdbserver}). Note that the
16993 conditions under which @code{gdbserver} terminates depend on how @value{GDBN}
16994 connects to it (@kbd{target remote} or @kbd{target extended-remote}). The
16995 @option{--multi} option to @code{gdbserver} has no influence on that.
16997 @subsubsection TCP port allocation lifecycle of @code{gdbserver}
16999 This section applies only when @code{gdbserver} is run to listen on a TCP port.
17001 @code{gdbserver} normally terminates after all of its debugged processes have
17002 terminated in @kbd{target remote} mode. On the other hand, for @kbd{target
17003 extended-remote}, @code{gdbserver} stays running even with no processes left.
17004 @value{GDBN} normally terminates the spawned debugged process on its exit,
17005 which normally also terminates @code{gdbserver} in the @kbd{target remote}
17006 mode. Therefore, when the connection drops unexpectedly, and @value{GDBN}
17007 cannot ask @code{gdbserver} to kill its debugged processes, @code{gdbserver}
17008 stays running even in the @kbd{target remote} mode.
17010 When @code{gdbserver} stays running, @value{GDBN} can connect to it again later.
17011 Such reconnecting is useful for features like @ref{disconnected tracing}. For
17012 completeness, at most one @value{GDBN} can be connected at a time.
17014 @cindex @option{--once}, @code{gdbserver} option
17015 By default, @code{gdbserver} keeps the listening TCP port open, so that
17016 additional connections are possible. However, if you start @code{gdbserver}
17017 with the @option{--once} option, it will stop listening for any further
17018 connection attempts after connecting to the first @value{GDBN} session. This
17019 means no further connections to @code{gdbserver} will be possible after the
17020 first one. It also means @code{gdbserver} will terminate after the first
17021 connection with remote @value{GDBN} has closed, even for unexpectedly closed
17022 connections and even in the @kbd{target extended-remote} mode. The
17023 @option{--once} option allows reusing the same port number for connecting to
17024 multiple instances of @code{gdbserver} running on the same host, since each
17025 instance closes its port after the first connection.
17027 @subsubsection Other Command-Line Arguments for @code{gdbserver}
17029 @cindex @option{--debug}, @code{gdbserver} option
17030 The @option{--debug} option tells @code{gdbserver} to display extra
17031 status information about the debugging process.
17032 @cindex @option{--remote-debug}, @code{gdbserver} option
17033 The @option{--remote-debug} option tells @code{gdbserver} to display
17034 remote protocol debug output. These options are intended for
17035 @code{gdbserver} development and for bug reports to the developers.
17037 @cindex @option{--wrapper}, @code{gdbserver} option
17038 The @option{--wrapper} option specifies a wrapper to launch programs
17039 for debugging. The option should be followed by the name of the
17040 wrapper, then any command-line arguments to pass to the wrapper, then
17041 @kbd{--} indicating the end of the wrapper arguments.
17043 @code{gdbserver} runs the specified wrapper program with a combined
17044 command line including the wrapper arguments, then the name of the
17045 program to debug, then any arguments to the program. The wrapper
17046 runs until it executes your program, and then @value{GDBN} gains control.
17048 You can use any program that eventually calls @code{execve} with
17049 its arguments as a wrapper. Several standard Unix utilities do
17050 this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending
17051 with @code{exec "$@@"} will also work.
17053 For example, you can use @code{env} to pass an environment variable to
17054 the debugged program, without setting the variable in @code{gdbserver}'s
17058 $ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog
17061 @subsection Connecting to @code{gdbserver}
17063 Run @value{GDBN} on the host system.
17065 First make sure you have the necessary symbol files. Load symbols for
17066 your application using the @code{file} command before you connect. Use
17067 @code{set sysroot} to locate target libraries (unless your @value{GDBN}
17068 was compiled with the correct sysroot using @code{--with-sysroot}).
17070 The symbol file and target libraries must exactly match the executable
17071 and libraries on the target, with one exception: the files on the host
17072 system should not be stripped, even if the files on the target system
17073 are. Mismatched or missing files will lead to confusing results
17074 during debugging. On @sc{gnu}/Linux targets, mismatched or missing
17075 files may also prevent @code{gdbserver} from debugging multi-threaded
17078 Connect to your target (@pxref{Connecting,,Connecting to a Remote Target}).
17079 For TCP connections, you must start up @code{gdbserver} prior to using
17080 the @code{target remote} command. Otherwise you may get an error whose
17081 text depends on the host system, but which usually looks something like
17082 @samp{Connection refused}. Don't use the @code{load}
17083 command in @value{GDBN} when using @code{gdbserver}, since the program is
17084 already on the target.
17086 @subsection Monitor Commands for @code{gdbserver}
17087 @cindex monitor commands, for @code{gdbserver}
17088 @anchor{Monitor Commands for gdbserver}
17090 During a @value{GDBN} session using @code{gdbserver}, you can use the
17091 @code{monitor} command to send special requests to @code{gdbserver}.
17092 Here are the available commands.
17096 List the available monitor commands.
17098 @item monitor set debug 0
17099 @itemx monitor set debug 1
17100 Disable or enable general debugging messages.
17102 @item monitor set remote-debug 0
17103 @itemx monitor set remote-debug 1
17104 Disable or enable specific debugging messages associated with the remote
17105 protocol (@pxref{Remote Protocol}).
17107 @item monitor set libthread-db-search-path [PATH]
17108 @cindex gdbserver, search path for @code{libthread_db}
17109 When this command is issued, @var{path} is a colon-separated list of
17110 directories to search for @code{libthread_db} (@pxref{Threads,,set
17111 libthread-db-search-path}). If you omit @var{path},
17112 @samp{libthread-db-search-path} will be reset to its default value.
17114 The special entry @samp{$pdir} for @samp{libthread-db-search-path} is
17115 not supported in @code{gdbserver}.
17118 Tell gdbserver to exit immediately. This command should be followed by
17119 @code{disconnect} to close the debugging session. @code{gdbserver} will
17120 detach from any attached processes and kill any processes it created.
17121 Use @code{monitor exit} to terminate @code{gdbserver} at the end
17122 of a multi-process mode debug session.
17126 @subsection Tracepoints support in @code{gdbserver}
17127 @cindex tracepoints support in @code{gdbserver}
17129 On some targets, @code{gdbserver} supports tracepoints, fast
17130 tracepoints and static tracepoints.
17132 For fast or static tracepoints to work, a special library called the
17133 @dfn{in-process agent} (IPA), must be loaded in the inferior process.
17134 This library is built and distributed as an integral part of
17135 @code{gdbserver}. In addition, support for static tracepoints
17136 requires building the in-process agent library with static tracepoints
17137 support. At present, the UST (LTTng Userspace Tracer,
17138 @url{http://lttng.org/ust}) tracing engine is supported. This support
17139 is automatically available if UST development headers are found in the
17140 standard include path when @code{gdbserver} is built, or if
17141 @code{gdbserver} was explicitly configured using @option{--with-ust}
17142 to point at such headers. You can explicitly disable the support
17143 using @option{--with-ust=no}.
17145 There are several ways to load the in-process agent in your program:
17148 @item Specifying it as dependency at link time
17150 You can link your program dynamically with the in-process agent
17151 library. On most systems, this is accomplished by adding
17152 @code{-linproctrace} to the link command.
17154 @item Using the system's preloading mechanisms
17156 You can force loading the in-process agent at startup time by using
17157 your system's support for preloading shared libraries. Many Unixes
17158 support the concept of preloading user defined libraries. In most
17159 cases, you do that by specifying @code{LD_PRELOAD=libinproctrace.so}
17160 in the environment. See also the description of @code{gdbserver}'s
17161 @option{--wrapper} command line option.
17163 @item Using @value{GDBN} to force loading the agent at run time
17165 On some systems, you can force the inferior to load a shared library,
17166 by calling a dynamic loader function in the inferior that takes care
17167 of dynamically looking up and loading a shared library. On most Unix
17168 systems, the function is @code{dlopen}. You'll use the @code{call}
17169 command for that. For example:
17172 (@value{GDBP}) call dlopen ("libinproctrace.so", ...)
17175 Note that on most Unix systems, for the @code{dlopen} function to be
17176 available, the program needs to be linked with @code{-ldl}.
17179 On systems that have a userspace dynamic loader, like most Unix
17180 systems, when you connect to @code{gdbserver} using @code{target
17181 remote}, you'll find that the program is stopped at the dynamic
17182 loader's entry point, and no shared library has been loaded in the
17183 program's address space yet, including the in-process agent. In that
17184 case, before being able to use any of the fast or static tracepoints
17185 features, you need to let the loader run and load the shared
17186 libraries. The simplest way to do that is to run the program to the
17187 main procedure. E.g., if debugging a C or C@t{++} program, start
17188 @code{gdbserver} like so:
17191 $ gdbserver :9999 myprogram
17194 Start GDB and connect to @code{gdbserver} like so, and run to main:
17198 (@value{GDBP}) target remote myhost:9999
17199 0x00007f215893ba60 in ?? () from /lib64/ld-linux-x86-64.so.2
17200 (@value{GDBP}) b main
17201 (@value{GDBP}) continue
17204 The in-process tracing agent library should now be loaded into the
17205 process; you can confirm it with the @code{info sharedlibrary}
17206 command, which will list @file{libinproctrace.so} as loaded in the
17207 process. You are now ready to install fast tracepoints, list static
17208 tracepoint markers, probe static tracepoints markers, and start
17211 @node Remote Configuration
17212 @section Remote Configuration
17215 @kindex show remote
17216 This section documents the configuration options available when
17217 debugging remote programs. For the options related to the File I/O
17218 extensions of the remote protocol, see @ref{system,
17219 system-call-allowed}.
17222 @item set remoteaddresssize @var{bits}
17223 @cindex address size for remote targets
17224 @cindex bits in remote address
17225 Set the maximum size of address in a memory packet to the specified
17226 number of bits. @value{GDBN} will mask off the address bits above
17227 that number, when it passes addresses to the remote target. The
17228 default value is the number of bits in the target's address.
17230 @item show remoteaddresssize
17231 Show the current value of remote address size in bits.
17233 @item set remotebaud @var{n}
17234 @cindex baud rate for remote targets
17235 Set the baud rate for the remote serial I/O to @var{n} baud. The
17236 value is used to set the speed of the serial port used for debugging
17239 @item show remotebaud
17240 Show the current speed of the remote connection.
17242 @item set remotebreak
17243 @cindex interrupt remote programs
17244 @cindex BREAK signal instead of Ctrl-C
17245 @anchor{set remotebreak}
17246 If set to on, @value{GDBN} sends a @code{BREAK} signal to the remote
17247 when you type @kbd{Ctrl-c} to interrupt the program running
17248 on the remote. If set to off, @value{GDBN} sends the @samp{Ctrl-C}
17249 character instead. The default is off, since most remote systems
17250 expect to see @samp{Ctrl-C} as the interrupt signal.
17252 @item show remotebreak
17253 Show whether @value{GDBN} sends @code{BREAK} or @samp{Ctrl-C} to
17254 interrupt the remote program.
17256 @item set remoteflow on
17257 @itemx set remoteflow off
17258 @kindex set remoteflow
17259 Enable or disable hardware flow control (@code{RTS}/@code{CTS})
17260 on the serial port used to communicate to the remote target.
17262 @item show remoteflow
17263 @kindex show remoteflow
17264 Show the current setting of hardware flow control.
17266 @item set remotelogbase @var{base}
17267 Set the base (a.k.a.@: radix) of logging serial protocol
17268 communications to @var{base}. Supported values of @var{base} are:
17269 @code{ascii}, @code{octal}, and @code{hex}. The default is
17272 @item show remotelogbase
17273 Show the current setting of the radix for logging remote serial
17276 @item set remotelogfile @var{file}
17277 @cindex record serial communications on file
17278 Record remote serial communications on the named @var{file}. The
17279 default is not to record at all.
17281 @item show remotelogfile.
17282 Show the current setting of the file name on which to record the
17283 serial communications.
17285 @item set remotetimeout @var{num}
17286 @cindex timeout for serial communications
17287 @cindex remote timeout
17288 Set the timeout limit to wait for the remote target to respond to
17289 @var{num} seconds. The default is 2 seconds.
17291 @item show remotetimeout
17292 Show the current number of seconds to wait for the remote target
17295 @cindex limit hardware breakpoints and watchpoints
17296 @cindex remote target, limit break- and watchpoints
17297 @anchor{set remote hardware-watchpoint-limit}
17298 @anchor{set remote hardware-breakpoint-limit}
17299 @item set remote hardware-watchpoint-limit @var{limit}
17300 @itemx set remote hardware-breakpoint-limit @var{limit}
17301 Restrict @value{GDBN} to using @var{limit} remote hardware breakpoint or
17302 watchpoints. A limit of -1, the default, is treated as unlimited.
17304 @cindex limit hardware watchpoints length
17305 @cindex remote target, limit watchpoints length
17306 @anchor{set remote hardware-watchpoint-length-limit}
17307 @item set remote hardware-watchpoint-length-limit @var{limit}
17308 Restrict @value{GDBN} to using @var{limit} bytes for the maximum length of
17309 a remote hardware watchpoint. A limit of -1, the default, is treated
17312 @item show remote hardware-watchpoint-length-limit
17313 Show the current limit (in bytes) of the maximum length of
17314 a remote hardware watchpoint.
17316 @item set remote exec-file @var{filename}
17317 @itemx show remote exec-file
17318 @anchor{set remote exec-file}
17319 @cindex executable file, for remote target
17320 Select the file used for @code{run} with @code{target
17321 extended-remote}. This should be set to a filename valid on the
17322 target system. If it is not set, the target will use a default
17323 filename (e.g.@: the last program run).
17325 @item set remote interrupt-sequence
17326 @cindex interrupt remote programs
17327 @cindex select Ctrl-C, BREAK or BREAK-g
17328 Allow the user to select one of @samp{Ctrl-C}, a @code{BREAK} or
17329 @samp{BREAK-g} as the
17330 sequence to the remote target in order to interrupt the execution.
17331 @samp{Ctrl-C} is a default. Some system prefers @code{BREAK} which
17332 is high level of serial line for some certain time.
17333 Linux kernel prefers @samp{BREAK-g}, a.k.a Magic SysRq g.
17334 It is @code{BREAK} signal followed by character @code{g}.
17336 @item show interrupt-sequence
17337 Show which of @samp{Ctrl-C}, @code{BREAK} or @code{BREAK-g}
17338 is sent by @value{GDBN} to interrupt the remote program.
17339 @code{BREAK-g} is BREAK signal followed by @code{g} and
17340 also known as Magic SysRq g.
17342 @item set remote interrupt-on-connect
17343 @cindex send interrupt-sequence on start
17344 Specify whether interrupt-sequence is sent to remote target when
17345 @value{GDBN} connects to it. This is mostly needed when you debug
17346 Linux kernel. Linux kernel expects @code{BREAK} followed by @code{g}
17347 which is known as Magic SysRq g in order to connect @value{GDBN}.
17349 @item show interrupt-on-connect
17350 Show whether interrupt-sequence is sent
17351 to remote target when @value{GDBN} connects to it.
17355 @item set tcp auto-retry on
17356 @cindex auto-retry, for remote TCP target
17357 Enable auto-retry for remote TCP connections. This is useful if the remote
17358 debugging agent is launched in parallel with @value{GDBN}; there is a race
17359 condition because the agent may not become ready to accept the connection
17360 before @value{GDBN} attempts to connect. When auto-retry is
17361 enabled, if the initial attempt to connect fails, @value{GDBN} reattempts
17362 to establish the connection using the timeout specified by
17363 @code{set tcp connect-timeout}.
17365 @item set tcp auto-retry off
17366 Do not auto-retry failed TCP connections.
17368 @item show tcp auto-retry
17369 Show the current auto-retry setting.
17371 @item set tcp connect-timeout @var{seconds}
17372 @cindex connection timeout, for remote TCP target
17373 @cindex timeout, for remote target connection
17374 Set the timeout for establishing a TCP connection to the remote target to
17375 @var{seconds}. The timeout affects both polling to retry failed connections
17376 (enabled by @code{set tcp auto-retry on}) and waiting for connections
17377 that are merely slow to complete, and represents an approximate cumulative
17380 @item show tcp connect-timeout
17381 Show the current connection timeout setting.
17384 @cindex remote packets, enabling and disabling
17385 The @value{GDBN} remote protocol autodetects the packets supported by
17386 your debugging stub. If you need to override the autodetection, you
17387 can use these commands to enable or disable individual packets. Each
17388 packet can be set to @samp{on} (the remote target supports this
17389 packet), @samp{off} (the remote target does not support this packet),
17390 or @samp{auto} (detect remote target support for this packet). They
17391 all default to @samp{auto}. For more information about each packet,
17392 see @ref{Remote Protocol}.
17394 During normal use, you should not have to use any of these commands.
17395 If you do, that may be a bug in your remote debugging stub, or a bug
17396 in @value{GDBN}. You may want to report the problem to the
17397 @value{GDBN} developers.
17399 For each packet @var{name}, the command to enable or disable the
17400 packet is @code{set remote @var{name}-packet}. The available settings
17403 @multitable @columnfractions 0.28 0.32 0.25
17406 @tab Related Features
17408 @item @code{fetch-register}
17410 @tab @code{info registers}
17412 @item @code{set-register}
17416 @item @code{binary-download}
17418 @tab @code{load}, @code{set}
17420 @item @code{read-aux-vector}
17421 @tab @code{qXfer:auxv:read}
17422 @tab @code{info auxv}
17424 @item @code{symbol-lookup}
17425 @tab @code{qSymbol}
17426 @tab Detecting multiple threads
17428 @item @code{attach}
17429 @tab @code{vAttach}
17432 @item @code{verbose-resume}
17434 @tab Stepping or resuming multiple threads
17440 @item @code{software-breakpoint}
17444 @item @code{hardware-breakpoint}
17448 @item @code{write-watchpoint}
17452 @item @code{read-watchpoint}
17456 @item @code{access-watchpoint}
17460 @item @code{target-features}
17461 @tab @code{qXfer:features:read}
17462 @tab @code{set architecture}
17464 @item @code{library-info}
17465 @tab @code{qXfer:libraries:read}
17466 @tab @code{info sharedlibrary}
17468 @item @code{memory-map}
17469 @tab @code{qXfer:memory-map:read}
17470 @tab @code{info mem}
17472 @item @code{read-sdata-object}
17473 @tab @code{qXfer:sdata:read}
17474 @tab @code{print $_sdata}
17476 @item @code{read-spu-object}
17477 @tab @code{qXfer:spu:read}
17478 @tab @code{info spu}
17480 @item @code{write-spu-object}
17481 @tab @code{qXfer:spu:write}
17482 @tab @code{info spu}
17484 @item @code{read-siginfo-object}
17485 @tab @code{qXfer:siginfo:read}
17486 @tab @code{print $_siginfo}
17488 @item @code{write-siginfo-object}
17489 @tab @code{qXfer:siginfo:write}
17490 @tab @code{set $_siginfo}
17492 @item @code{threads}
17493 @tab @code{qXfer:threads:read}
17494 @tab @code{info threads}
17496 @item @code{get-thread-local-@*storage-address}
17497 @tab @code{qGetTLSAddr}
17498 @tab Displaying @code{__thread} variables
17500 @item @code{get-thread-information-block-address}
17501 @tab @code{qGetTIBAddr}
17502 @tab Display MS-Windows Thread Information Block.
17504 @item @code{search-memory}
17505 @tab @code{qSearch:memory}
17508 @item @code{supported-packets}
17509 @tab @code{qSupported}
17510 @tab Remote communications parameters
17512 @item @code{pass-signals}
17513 @tab @code{QPassSignals}
17514 @tab @code{handle @var{signal}}
17516 @item @code{program-signals}
17517 @tab @code{QProgramSignals}
17518 @tab @code{handle @var{signal}}
17520 @item @code{hostio-close-packet}
17521 @tab @code{vFile:close}
17522 @tab @code{remote get}, @code{remote put}
17524 @item @code{hostio-open-packet}
17525 @tab @code{vFile:open}
17526 @tab @code{remote get}, @code{remote put}
17528 @item @code{hostio-pread-packet}
17529 @tab @code{vFile:pread}
17530 @tab @code{remote get}, @code{remote put}
17532 @item @code{hostio-pwrite-packet}
17533 @tab @code{vFile:pwrite}
17534 @tab @code{remote get}, @code{remote put}
17536 @item @code{hostio-unlink-packet}
17537 @tab @code{vFile:unlink}
17538 @tab @code{remote delete}
17540 @item @code{hostio-readlink-packet}
17541 @tab @code{vFile:readlink}
17544 @item @code{noack-packet}
17545 @tab @code{QStartNoAckMode}
17546 @tab Packet acknowledgment
17548 @item @code{osdata}
17549 @tab @code{qXfer:osdata:read}
17550 @tab @code{info os}
17552 @item @code{query-attached}
17553 @tab @code{qAttached}
17554 @tab Querying remote process attach state.
17556 @item @code{traceframe-info}
17557 @tab @code{qXfer:traceframe-info:read}
17558 @tab Traceframe info
17560 @item @code{install-in-trace}
17561 @tab @code{InstallInTrace}
17562 @tab Install tracepoint in tracing
17564 @item @code{disable-randomization}
17565 @tab @code{QDisableRandomization}
17566 @tab @code{set disable-randomization}
17568 @item @code{conditional-breakpoints-packet}
17569 @tab @code{Z0 and Z1}
17570 @tab @code{Support for target-side breakpoint condition evaluation}
17574 @section Implementing a Remote Stub
17576 @cindex debugging stub, example
17577 @cindex remote stub, example
17578 @cindex stub example, remote debugging
17579 The stub files provided with @value{GDBN} implement the target side of the
17580 communication protocol, and the @value{GDBN} side is implemented in the
17581 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
17582 these subroutines to communicate, and ignore the details. (If you're
17583 implementing your own stub file, you can still ignore the details: start
17584 with one of the existing stub files. @file{sparc-stub.c} is the best
17585 organized, and therefore the easiest to read.)
17587 @cindex remote serial debugging, overview
17588 To debug a program running on another machine (the debugging
17589 @dfn{target} machine), you must first arrange for all the usual
17590 prerequisites for the program to run by itself. For example, for a C
17595 A startup routine to set up the C runtime environment; these usually
17596 have a name like @file{crt0}. The startup routine may be supplied by
17597 your hardware supplier, or you may have to write your own.
17600 A C subroutine library to support your program's
17601 subroutine calls, notably managing input and output.
17604 A way of getting your program to the other machine---for example, a
17605 download program. These are often supplied by the hardware
17606 manufacturer, but you may have to write your own from hardware
17610 The next step is to arrange for your program to use a serial port to
17611 communicate with the machine where @value{GDBN} is running (the @dfn{host}
17612 machine). In general terms, the scheme looks like this:
17616 @value{GDBN} already understands how to use this protocol; when everything
17617 else is set up, you can simply use the @samp{target remote} command
17618 (@pxref{Targets,,Specifying a Debugging Target}).
17620 @item On the target,
17621 you must link with your program a few special-purpose subroutines that
17622 implement the @value{GDBN} remote serial protocol. The file containing these
17623 subroutines is called a @dfn{debugging stub}.
17625 On certain remote targets, you can use an auxiliary program
17626 @code{gdbserver} instead of linking a stub into your program.
17627 @xref{Server,,Using the @code{gdbserver} Program}, for details.
17630 The debugging stub is specific to the architecture of the remote
17631 machine; for example, use @file{sparc-stub.c} to debug programs on
17634 @cindex remote serial stub list
17635 These working remote stubs are distributed with @value{GDBN}:
17640 @cindex @file{i386-stub.c}
17643 For Intel 386 and compatible architectures.
17646 @cindex @file{m68k-stub.c}
17647 @cindex Motorola 680x0
17649 For Motorola 680x0 architectures.
17652 @cindex @file{sh-stub.c}
17655 For Renesas SH architectures.
17658 @cindex @file{sparc-stub.c}
17660 For @sc{sparc} architectures.
17662 @item sparcl-stub.c
17663 @cindex @file{sparcl-stub.c}
17666 For Fujitsu @sc{sparclite} architectures.
17670 The @file{README} file in the @value{GDBN} distribution may list other
17671 recently added stubs.
17674 * Stub Contents:: What the stub can do for you
17675 * Bootstrapping:: What you must do for the stub
17676 * Debug Session:: Putting it all together
17679 @node Stub Contents
17680 @subsection What the Stub Can Do for You
17682 @cindex remote serial stub
17683 The debugging stub for your architecture supplies these three
17687 @item set_debug_traps
17688 @findex set_debug_traps
17689 @cindex remote serial stub, initialization
17690 This routine arranges for @code{handle_exception} to run when your
17691 program stops. You must call this subroutine explicitly in your
17692 program's startup code.
17694 @item handle_exception
17695 @findex handle_exception
17696 @cindex remote serial stub, main routine
17697 This is the central workhorse, but your program never calls it
17698 explicitly---the setup code arranges for @code{handle_exception} to
17699 run when a trap is triggered.
17701 @code{handle_exception} takes control when your program stops during
17702 execution (for example, on a breakpoint), and mediates communications
17703 with @value{GDBN} on the host machine. This is where the communications
17704 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
17705 representative on the target machine. It begins by sending summary
17706 information on the state of your program, then continues to execute,
17707 retrieving and transmitting any information @value{GDBN} needs, until you
17708 execute a @value{GDBN} command that makes your program resume; at that point,
17709 @code{handle_exception} returns control to your own code on the target
17713 @cindex @code{breakpoint} subroutine, remote
17714 Use this auxiliary subroutine to make your program contain a
17715 breakpoint. Depending on the particular situation, this may be the only
17716 way for @value{GDBN} to get control. For instance, if your target
17717 machine has some sort of interrupt button, you won't need to call this;
17718 pressing the interrupt button transfers control to
17719 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
17720 simply receiving characters on the serial port may also trigger a trap;
17721 again, in that situation, you don't need to call @code{breakpoint} from
17722 your own program---simply running @samp{target remote} from the host
17723 @value{GDBN} session gets control.
17725 Call @code{breakpoint} if none of these is true, or if you simply want
17726 to make certain your program stops at a predetermined point for the
17727 start of your debugging session.
17730 @node Bootstrapping
17731 @subsection What You Must Do for the Stub
17733 @cindex remote stub, support routines
17734 The debugging stubs that come with @value{GDBN} are set up for a particular
17735 chip architecture, but they have no information about the rest of your
17736 debugging target machine.
17738 First of all you need to tell the stub how to communicate with the
17742 @item int getDebugChar()
17743 @findex getDebugChar
17744 Write this subroutine to read a single character from the serial port.
17745 It may be identical to @code{getchar} for your target system; a
17746 different name is used to allow you to distinguish the two if you wish.
17748 @item void putDebugChar(int)
17749 @findex putDebugChar
17750 Write this subroutine to write a single character to the serial port.
17751 It may be identical to @code{putchar} for your target system; a
17752 different name is used to allow you to distinguish the two if you wish.
17755 @cindex control C, and remote debugging
17756 @cindex interrupting remote targets
17757 If you want @value{GDBN} to be able to stop your program while it is
17758 running, you need to use an interrupt-driven serial driver, and arrange
17759 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
17760 character). That is the character which @value{GDBN} uses to tell the
17761 remote system to stop.
17763 Getting the debugging target to return the proper status to @value{GDBN}
17764 probably requires changes to the standard stub; one quick and dirty way
17765 is to just execute a breakpoint instruction (the ``dirty'' part is that
17766 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
17768 Other routines you need to supply are:
17771 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
17772 @findex exceptionHandler
17773 Write this function to install @var{exception_address} in the exception
17774 handling tables. You need to do this because the stub does not have any
17775 way of knowing what the exception handling tables on your target system
17776 are like (for example, the processor's table might be in @sc{rom},
17777 containing entries which point to a table in @sc{ram}).
17778 @var{exception_number} is the exception number which should be changed;
17779 its meaning is architecture-dependent (for example, different numbers
17780 might represent divide by zero, misaligned access, etc). When this
17781 exception occurs, control should be transferred directly to
17782 @var{exception_address}, and the processor state (stack, registers,
17783 and so on) should be just as it is when a processor exception occurs. So if
17784 you want to use a jump instruction to reach @var{exception_address}, it
17785 should be a simple jump, not a jump to subroutine.
17787 For the 386, @var{exception_address} should be installed as an interrupt
17788 gate so that interrupts are masked while the handler runs. The gate
17789 should be at privilege level 0 (the most privileged level). The
17790 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
17791 help from @code{exceptionHandler}.
17793 @item void flush_i_cache()
17794 @findex flush_i_cache
17795 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
17796 instruction cache, if any, on your target machine. If there is no
17797 instruction cache, this subroutine may be a no-op.
17799 On target machines that have instruction caches, @value{GDBN} requires this
17800 function to make certain that the state of your program is stable.
17804 You must also make sure this library routine is available:
17807 @item void *memset(void *, int, int)
17809 This is the standard library function @code{memset} that sets an area of
17810 memory to a known value. If you have one of the free versions of
17811 @code{libc.a}, @code{memset} can be found there; otherwise, you must
17812 either obtain it from your hardware manufacturer, or write your own.
17815 If you do not use the GNU C compiler, you may need other standard
17816 library subroutines as well; this varies from one stub to another,
17817 but in general the stubs are likely to use any of the common library
17818 subroutines which @code{@value{NGCC}} generates as inline code.
17821 @node Debug Session
17822 @subsection Putting it All Together
17824 @cindex remote serial debugging summary
17825 In summary, when your program is ready to debug, you must follow these
17830 Make sure you have defined the supporting low-level routines
17831 (@pxref{Bootstrapping,,What You Must Do for the Stub}):
17833 @code{getDebugChar}, @code{putDebugChar},
17834 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
17838 Insert these lines in your program's startup code, before the main
17839 procedure is called:
17846 On some machines, when a breakpoint trap is raised, the hardware
17847 automatically makes the PC point to the instruction after the
17848 breakpoint. If your machine doesn't do that, you may need to adjust
17849 @code{handle_exception} to arrange for it to return to the instruction
17850 after the breakpoint on this first invocation, so that your program
17851 doesn't keep hitting the initial breakpoint instead of making
17855 For the 680x0 stub only, you need to provide a variable called
17856 @code{exceptionHook}. Normally you just use:
17859 void (*exceptionHook)() = 0;
17863 but if before calling @code{set_debug_traps}, you set it to point to a
17864 function in your program, that function is called when
17865 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
17866 error). The function indicated by @code{exceptionHook} is called with
17867 one parameter: an @code{int} which is the exception number.
17870 Compile and link together: your program, the @value{GDBN} debugging stub for
17871 your target architecture, and the supporting subroutines.
17874 Make sure you have a serial connection between your target machine and
17875 the @value{GDBN} host, and identify the serial port on the host.
17878 @c The "remote" target now provides a `load' command, so we should
17879 @c document that. FIXME.
17880 Download your program to your target machine (or get it there by
17881 whatever means the manufacturer provides), and start it.
17884 Start @value{GDBN} on the host, and connect to the target
17885 (@pxref{Connecting,,Connecting to a Remote Target}).
17889 @node Configurations
17890 @chapter Configuration-Specific Information
17892 While nearly all @value{GDBN} commands are available for all native and
17893 cross versions of the debugger, there are some exceptions. This chapter
17894 describes things that are only available in certain configurations.
17896 There are three major categories of configurations: native
17897 configurations, where the host and target are the same, embedded
17898 operating system configurations, which are usually the same for several
17899 different processor architectures, and bare embedded processors, which
17900 are quite different from each other.
17905 * Embedded Processors::
17912 This section describes details specific to particular native
17917 * BSD libkvm Interface:: Debugging BSD kernel memory images
17918 * SVR4 Process Information:: SVR4 process information
17919 * DJGPP Native:: Features specific to the DJGPP port
17920 * Cygwin Native:: Features specific to the Cygwin port
17921 * Hurd Native:: Features specific to @sc{gnu} Hurd
17922 * Neutrino:: Features specific to QNX Neutrino
17923 * Darwin:: Features specific to Darwin
17929 On HP-UX systems, if you refer to a function or variable name that
17930 begins with a dollar sign, @value{GDBN} searches for a user or system
17931 name first, before it searches for a convenience variable.
17934 @node BSD libkvm Interface
17935 @subsection BSD libkvm Interface
17938 @cindex kernel memory image
17939 @cindex kernel crash dump
17941 BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory
17942 interface that provides a uniform interface for accessing kernel virtual
17943 memory images, including live systems and crash dumps. @value{GDBN}
17944 uses this interface to allow you to debug live kernels and kernel crash
17945 dumps on many native BSD configurations. This is implemented as a
17946 special @code{kvm} debugging target. For debugging a live system, load
17947 the currently running kernel into @value{GDBN} and connect to the
17951 (@value{GDBP}) @b{target kvm}
17954 For debugging crash dumps, provide the file name of the crash dump as an
17958 (@value{GDBP}) @b{target kvm /var/crash/bsd.0}
17961 Once connected to the @code{kvm} target, the following commands are
17967 Set current context from the @dfn{Process Control Block} (PCB) address.
17970 Set current context from proc address. This command isn't available on
17971 modern FreeBSD systems.
17974 @node SVR4 Process Information
17975 @subsection SVR4 Process Information
17977 @cindex examine process image
17978 @cindex process info via @file{/proc}
17980 Many versions of SVR4 and compatible systems provide a facility called
17981 @samp{/proc} that can be used to examine the image of a running
17982 process using file-system subroutines. If @value{GDBN} is configured
17983 for an operating system with this facility, the command @code{info
17984 proc} is available to report information about the process running
17985 your program, or about any process running on your system. @code{info
17986 proc} works only on SVR4 systems that include the @code{procfs} code.
17987 This includes, as of this writing, @sc{gnu}/Linux, OSF/1 (Digital
17988 Unix), Solaris, Irix, and Unixware, but not HP-UX, for example.
17994 @itemx info proc @var{process-id}
17995 Summarize available information about any running process. If a
17996 process ID is specified by @var{process-id}, display information about
17997 that process; otherwise display information about the program being
17998 debugged. The summary includes the debugged process ID, the command
17999 line used to invoke it, its current working directory, and its
18000 executable file's absolute file name.
18002 On some systems, @var{process-id} can be of the form
18003 @samp{[@var{pid}]/@var{tid}} which specifies a certain thread ID
18004 within a process. If the optional @var{pid} part is missing, it means
18005 a thread from the process being debugged (the leading @samp{/} still
18006 needs to be present, or else @value{GDBN} will interpret the number as
18007 a process ID rather than a thread ID).
18009 @item info proc mappings
18010 @cindex memory address space mappings
18011 Report the memory address space ranges accessible in the program, with
18012 information on whether the process has read, write, or execute access
18013 rights to each range. On @sc{gnu}/Linux systems, each memory range
18014 includes the object file which is mapped to that range, instead of the
18015 memory access rights to that range.
18017 @item info proc stat
18018 @itemx info proc status
18019 @cindex process detailed status information
18020 These subcommands are specific to @sc{gnu}/Linux systems. They show
18021 the process-related information, including the user ID and group ID;
18022 how many threads are there in the process; its virtual memory usage;
18023 the signals that are pending, blocked, and ignored; its TTY; its
18024 consumption of system and user time; its stack size; its @samp{nice}
18025 value; etc. For more information, see the @samp{proc} man page
18026 (type @kbd{man 5 proc} from your shell prompt).
18028 @item info proc all
18029 Show all the information about the process described under all of the
18030 above @code{info proc} subcommands.
18033 @comment These sub-options of 'info proc' were not included when
18034 @comment procfs.c was re-written. Keep their descriptions around
18035 @comment against the day when someone finds the time to put them back in.
18036 @kindex info proc times
18037 @item info proc times
18038 Starting time, user CPU time, and system CPU time for your program and
18041 @kindex info proc id
18043 Report on the process IDs related to your program: its own process ID,
18044 the ID of its parent, the process group ID, and the session ID.
18047 @item set procfs-trace
18048 @kindex set procfs-trace
18049 @cindex @code{procfs} API calls
18050 This command enables and disables tracing of @code{procfs} API calls.
18052 @item show procfs-trace
18053 @kindex show procfs-trace
18054 Show the current state of @code{procfs} API call tracing.
18056 @item set procfs-file @var{file}
18057 @kindex set procfs-file
18058 Tell @value{GDBN} to write @code{procfs} API trace to the named
18059 @var{file}. @value{GDBN} appends the trace info to the previous
18060 contents of the file. The default is to display the trace on the
18063 @item show procfs-file
18064 @kindex show procfs-file
18065 Show the file to which @code{procfs} API trace is written.
18067 @item proc-trace-entry
18068 @itemx proc-trace-exit
18069 @itemx proc-untrace-entry
18070 @itemx proc-untrace-exit
18071 @kindex proc-trace-entry
18072 @kindex proc-trace-exit
18073 @kindex proc-untrace-entry
18074 @kindex proc-untrace-exit
18075 These commands enable and disable tracing of entries into and exits
18076 from the @code{syscall} interface.
18079 @kindex info pidlist
18080 @cindex process list, QNX Neutrino
18081 For QNX Neutrino only, this command displays the list of all the
18082 processes and all the threads within each process.
18085 @kindex info meminfo
18086 @cindex mapinfo list, QNX Neutrino
18087 For QNX Neutrino only, this command displays the list of all mapinfos.
18091 @subsection Features for Debugging @sc{djgpp} Programs
18092 @cindex @sc{djgpp} debugging
18093 @cindex native @sc{djgpp} debugging
18094 @cindex MS-DOS-specific commands
18097 @sc{djgpp} is a port of the @sc{gnu} development tools to MS-DOS and
18098 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
18099 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
18100 top of real-mode DOS systems and their emulations.
18102 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
18103 defines a few commands specific to the @sc{djgpp} port. This
18104 subsection describes those commands.
18109 This is a prefix of @sc{djgpp}-specific commands which print
18110 information about the target system and important OS structures.
18113 @cindex MS-DOS system info
18114 @cindex free memory information (MS-DOS)
18115 @item info dos sysinfo
18116 This command displays assorted information about the underlying
18117 platform: the CPU type and features, the OS version and flavor, the
18118 DPMI version, and the available conventional and DPMI memory.
18123 @cindex segment descriptor tables
18124 @cindex descriptor tables display
18126 @itemx info dos ldt
18127 @itemx info dos idt
18128 These 3 commands display entries from, respectively, Global, Local,
18129 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
18130 tables are data structures which store a descriptor for each segment
18131 that is currently in use. The segment's selector is an index into a
18132 descriptor table; the table entry for that index holds the
18133 descriptor's base address and limit, and its attributes and access
18136 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
18137 segment (used for both data and the stack), and a DOS segment (which
18138 allows access to DOS/BIOS data structures and absolute addresses in
18139 conventional memory). However, the DPMI host will usually define
18140 additional segments in order to support the DPMI environment.
18142 @cindex garbled pointers
18143 These commands allow to display entries from the descriptor tables.
18144 Without an argument, all entries from the specified table are
18145 displayed. An argument, which should be an integer expression, means
18146 display a single entry whose index is given by the argument. For
18147 example, here's a convenient way to display information about the
18148 debugged program's data segment:
18151 @exdent @code{(@value{GDBP}) info dos ldt $ds}
18152 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
18156 This comes in handy when you want to see whether a pointer is outside
18157 the data segment's limit (i.e.@: @dfn{garbled}).
18159 @cindex page tables display (MS-DOS)
18161 @itemx info dos pte
18162 These two commands display entries from, respectively, the Page
18163 Directory and the Page Tables. Page Directories and Page Tables are
18164 data structures which control how virtual memory addresses are mapped
18165 into physical addresses. A Page Table includes an entry for every
18166 page of memory that is mapped into the program's address space; there
18167 may be several Page Tables, each one holding up to 4096 entries. A
18168 Page Directory has up to 4096 entries, one each for every Page Table
18169 that is currently in use.
18171 Without an argument, @kbd{info dos pde} displays the entire Page
18172 Directory, and @kbd{info dos pte} displays all the entries in all of
18173 the Page Tables. An argument, an integer expression, given to the
18174 @kbd{info dos pde} command means display only that entry from the Page
18175 Directory table. An argument given to the @kbd{info dos pte} command
18176 means display entries from a single Page Table, the one pointed to by
18177 the specified entry in the Page Directory.
18179 @cindex direct memory access (DMA) on MS-DOS
18180 These commands are useful when your program uses @dfn{DMA} (Direct
18181 Memory Access), which needs physical addresses to program the DMA
18184 These commands are supported only with some DPMI servers.
18186 @cindex physical address from linear address
18187 @item info dos address-pte @var{addr}
18188 This command displays the Page Table entry for a specified linear
18189 address. The argument @var{addr} is a linear address which should
18190 already have the appropriate segment's base address added to it,
18191 because this command accepts addresses which may belong to @emph{any}
18192 segment. For example, here's how to display the Page Table entry for
18193 the page where a variable @code{i} is stored:
18196 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
18197 @exdent @code{Page Table entry for address 0x11a00d30:}
18198 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
18202 This says that @code{i} is stored at offset @code{0xd30} from the page
18203 whose physical base address is @code{0x02698000}, and shows all the
18204 attributes of that page.
18206 Note that you must cast the addresses of variables to a @code{char *},
18207 since otherwise the value of @code{__djgpp_base_address}, the base
18208 address of all variables and functions in a @sc{djgpp} program, will
18209 be added using the rules of C pointer arithmetics: if @code{i} is
18210 declared an @code{int}, @value{GDBN} will add 4 times the value of
18211 @code{__djgpp_base_address} to the address of @code{i}.
18213 Here's another example, it displays the Page Table entry for the
18217 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
18218 @exdent @code{Page Table entry for address 0x29110:}
18219 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
18223 (The @code{+ 3} offset is because the transfer buffer's address is the
18224 3rd member of the @code{_go32_info_block} structure.) The output
18225 clearly shows that this DPMI server maps the addresses in conventional
18226 memory 1:1, i.e.@: the physical (@code{0x00029000} + @code{0x110}) and
18227 linear (@code{0x29110}) addresses are identical.
18229 This command is supported only with some DPMI servers.
18232 @cindex DOS serial data link, remote debugging
18233 In addition to native debugging, the DJGPP port supports remote
18234 debugging via a serial data link. The following commands are specific
18235 to remote serial debugging in the DJGPP port of @value{GDBN}.
18238 @kindex set com1base
18239 @kindex set com1irq
18240 @kindex set com2base
18241 @kindex set com2irq
18242 @kindex set com3base
18243 @kindex set com3irq
18244 @kindex set com4base
18245 @kindex set com4irq
18246 @item set com1base @var{addr}
18247 This command sets the base I/O port address of the @file{COM1} serial
18250 @item set com1irq @var{irq}
18251 This command sets the @dfn{Interrupt Request} (@code{IRQ}) line to use
18252 for the @file{COM1} serial port.
18254 There are similar commands @samp{set com2base}, @samp{set com3irq},
18255 etc.@: for setting the port address and the @code{IRQ} lines for the
18258 @kindex show com1base
18259 @kindex show com1irq
18260 @kindex show com2base
18261 @kindex show com2irq
18262 @kindex show com3base
18263 @kindex show com3irq
18264 @kindex show com4base
18265 @kindex show com4irq
18266 The related commands @samp{show com1base}, @samp{show com1irq} etc.@:
18267 display the current settings of the base address and the @code{IRQ}
18268 lines used by the COM ports.
18271 @kindex info serial
18272 @cindex DOS serial port status
18273 This command prints the status of the 4 DOS serial ports. For each
18274 port, it prints whether it's active or not, its I/O base address and
18275 IRQ number, whether it uses a 16550-style FIFO, its baudrate, and the
18276 counts of various errors encountered so far.
18280 @node Cygwin Native
18281 @subsection Features for Debugging MS Windows PE Executables
18282 @cindex MS Windows debugging
18283 @cindex native Cygwin debugging
18284 @cindex Cygwin-specific commands
18286 @value{GDBN} supports native debugging of MS Windows programs, including
18287 DLLs with and without symbolic debugging information.
18289 @cindex Ctrl-BREAK, MS-Windows
18290 @cindex interrupt debuggee on MS-Windows
18291 MS-Windows programs that call @code{SetConsoleMode} to switch off the
18292 special meaning of the @samp{Ctrl-C} keystroke cannot be interrupted
18293 by typing @kbd{C-c}. For this reason, @value{GDBN} on MS-Windows
18294 supports @kbd{C-@key{BREAK}} as an alternative interrupt key
18295 sequence, which can be used to interrupt the debuggee even if it
18298 There are various additional Cygwin-specific commands, described in
18299 this section. Working with DLLs that have no debugging symbols is
18300 described in @ref{Non-debug DLL Symbols}.
18305 This is a prefix of MS Windows-specific commands which print
18306 information about the target system and important OS structures.
18308 @item info w32 selector
18309 This command displays information returned by
18310 the Win32 API @code{GetThreadSelectorEntry} function.
18311 It takes an optional argument that is evaluated to
18312 a long value to give the information about this given selector.
18313 Without argument, this command displays information
18314 about the six segment registers.
18316 @item info w32 thread-information-block
18317 This command displays thread specific information stored in the
18318 Thread Information Block (readable on the X86 CPU family using @code{$fs}
18319 selector for 32-bit programs and @code{$gs} for 64-bit programs).
18323 This is a Cygwin-specific alias of @code{info shared}.
18325 @kindex dll-symbols
18327 This command loads symbols from a dll similarly to
18328 add-sym command but without the need to specify a base address.
18330 @kindex set cygwin-exceptions
18331 @cindex debugging the Cygwin DLL
18332 @cindex Cygwin DLL, debugging
18333 @item set cygwin-exceptions @var{mode}
18334 If @var{mode} is @code{on}, @value{GDBN} will break on exceptions that
18335 happen inside the Cygwin DLL. If @var{mode} is @code{off},
18336 @value{GDBN} will delay recognition of exceptions, and may ignore some
18337 exceptions which seem to be caused by internal Cygwin DLL
18338 ``bookkeeping''. This option is meant primarily for debugging the
18339 Cygwin DLL itself; the default value is @code{off} to avoid annoying
18340 @value{GDBN} users with false @code{SIGSEGV} signals.
18342 @kindex show cygwin-exceptions
18343 @item show cygwin-exceptions
18344 Displays whether @value{GDBN} will break on exceptions that happen
18345 inside the Cygwin DLL itself.
18347 @kindex set new-console
18348 @item set new-console @var{mode}
18349 If @var{mode} is @code{on} the debuggee will
18350 be started in a new console on next start.
18351 If @var{mode} is @code{off}, the debuggee will
18352 be started in the same console as the debugger.
18354 @kindex show new-console
18355 @item show new-console
18356 Displays whether a new console is used
18357 when the debuggee is started.
18359 @kindex set new-group
18360 @item set new-group @var{mode}
18361 This boolean value controls whether the debuggee should
18362 start a new group or stay in the same group as the debugger.
18363 This affects the way the Windows OS handles
18366 @kindex show new-group
18367 @item show new-group
18368 Displays current value of new-group boolean.
18370 @kindex set debugevents
18371 @item set debugevents
18372 This boolean value adds debug output concerning kernel events related
18373 to the debuggee seen by the debugger. This includes events that
18374 signal thread and process creation and exit, DLL loading and
18375 unloading, console interrupts, and debugging messages produced by the
18376 Windows @code{OutputDebugString} API call.
18378 @kindex set debugexec
18379 @item set debugexec
18380 This boolean value adds debug output concerning execute events
18381 (such as resume thread) seen by the debugger.
18383 @kindex set debugexceptions
18384 @item set debugexceptions
18385 This boolean value adds debug output concerning exceptions in the
18386 debuggee seen by the debugger.
18388 @kindex set debugmemory
18389 @item set debugmemory
18390 This boolean value adds debug output concerning debuggee memory reads
18391 and writes by the debugger.
18395 This boolean values specifies whether the debuggee is called
18396 via a shell or directly (default value is on).
18400 Displays if the debuggee will be started with a shell.
18405 * Non-debug DLL Symbols:: Support for DLLs without debugging symbols
18408 @node Non-debug DLL Symbols
18409 @subsubsection Support for DLLs without Debugging Symbols
18410 @cindex DLLs with no debugging symbols
18411 @cindex Minimal symbols and DLLs
18413 Very often on windows, some of the DLLs that your program relies on do
18414 not include symbolic debugging information (for example,
18415 @file{kernel32.dll}). When @value{GDBN} doesn't recognize any debugging
18416 symbols in a DLL, it relies on the minimal amount of symbolic
18417 information contained in the DLL's export table. This section
18418 describes working with such symbols, known internally to @value{GDBN} as
18419 ``minimal symbols''.
18421 Note that before the debugged program has started execution, no DLLs
18422 will have been loaded. The easiest way around this problem is simply to
18423 start the program --- either by setting a breakpoint or letting the
18424 program run once to completion. It is also possible to force
18425 @value{GDBN} to load a particular DLL before starting the executable ---
18426 see the shared library information in @ref{Files}, or the
18427 @code{dll-symbols} command in @ref{Cygwin Native}. Currently,
18428 explicitly loading symbols from a DLL with no debugging information will
18429 cause the symbol names to be duplicated in @value{GDBN}'s lookup table,
18430 which may adversely affect symbol lookup performance.
18432 @subsubsection DLL Name Prefixes
18434 In keeping with the naming conventions used by the Microsoft debugging
18435 tools, DLL export symbols are made available with a prefix based on the
18436 DLL name, for instance @code{KERNEL32!CreateFileA}. The plain name is
18437 also entered into the symbol table, so @code{CreateFileA} is often
18438 sufficient. In some cases there will be name clashes within a program
18439 (particularly if the executable itself includes full debugging symbols)
18440 necessitating the use of the fully qualified name when referring to the
18441 contents of the DLL. Use single-quotes around the name to avoid the
18442 exclamation mark (``!'') being interpreted as a language operator.
18444 Note that the internal name of the DLL may be all upper-case, even
18445 though the file name of the DLL is lower-case, or vice-versa. Since
18446 symbols within @value{GDBN} are @emph{case-sensitive} this may cause
18447 some confusion. If in doubt, try the @code{info functions} and
18448 @code{info variables} commands or even @code{maint print msymbols}
18449 (@pxref{Symbols}). Here's an example:
18452 (@value{GDBP}) info function CreateFileA
18453 All functions matching regular expression "CreateFileA":
18455 Non-debugging symbols:
18456 0x77e885f4 CreateFileA
18457 0x77e885f4 KERNEL32!CreateFileA
18461 (@value{GDBP}) info function !
18462 All functions matching regular expression "!":
18464 Non-debugging symbols:
18465 0x6100114c cygwin1!__assert
18466 0x61004034 cygwin1!_dll_crt0@@0
18467 0x61004240 cygwin1!dll_crt0(per_process *)
18471 @subsubsection Working with Minimal Symbols
18473 Symbols extracted from a DLL's export table do not contain very much
18474 type information. All that @value{GDBN} can do is guess whether a symbol
18475 refers to a function or variable depending on the linker section that
18476 contains the symbol. Also note that the actual contents of the memory
18477 contained in a DLL are not available unless the program is running. This
18478 means that you cannot examine the contents of a variable or disassemble
18479 a function within a DLL without a running program.
18481 Variables are generally treated as pointers and dereferenced
18482 automatically. For this reason, it is often necessary to prefix a
18483 variable name with the address-of operator (``&'') and provide explicit
18484 type information in the command. Here's an example of the type of
18488 (@value{GDBP}) print 'cygwin1!__argv'
18493 (@value{GDBP}) x 'cygwin1!__argv'
18494 0x10021610: "\230y\""
18497 And two possible solutions:
18500 (@value{GDBP}) print ((char **)'cygwin1!__argv')[0]
18501 $2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"
18505 (@value{GDBP}) x/2x &'cygwin1!__argv'
18506 0x610c0aa8 <cygwin1!__argv>: 0x10021608 0x00000000
18507 (@value{GDBP}) x/x 0x10021608
18508 0x10021608: 0x0022fd98
18509 (@value{GDBP}) x/s 0x0022fd98
18510 0x22fd98: "/cygdrive/c/mydirectory/myprogram"
18513 Setting a break point within a DLL is possible even before the program
18514 starts execution. However, under these circumstances, @value{GDBN} can't
18515 examine the initial instructions of the function in order to skip the
18516 function's frame set-up code. You can work around this by using ``*&''
18517 to set the breakpoint at a raw memory address:
18520 (@value{GDBP}) break *&'python22!PyOS_Readline'
18521 Breakpoint 1 at 0x1e04eff0
18524 The author of these extensions is not entirely convinced that setting a
18525 break point within a shared DLL like @file{kernel32.dll} is completely
18529 @subsection Commands Specific to @sc{gnu} Hurd Systems
18530 @cindex @sc{gnu} Hurd debugging
18532 This subsection describes @value{GDBN} commands specific to the
18533 @sc{gnu} Hurd native debugging.
18538 @kindex set signals@r{, Hurd command}
18539 @kindex set sigs@r{, Hurd command}
18540 This command toggles the state of inferior signal interception by
18541 @value{GDBN}. Mach exceptions, such as breakpoint traps, are not
18542 affected by this command. @code{sigs} is a shorthand alias for
18547 @kindex show signals@r{, Hurd command}
18548 @kindex show sigs@r{, Hurd command}
18549 Show the current state of intercepting inferior's signals.
18551 @item set signal-thread
18552 @itemx set sigthread
18553 @kindex set signal-thread
18554 @kindex set sigthread
18555 This command tells @value{GDBN} which thread is the @code{libc} signal
18556 thread. That thread is run when a signal is delivered to a running
18557 process. @code{set sigthread} is the shorthand alias of @code{set
18560 @item show signal-thread
18561 @itemx show sigthread
18562 @kindex show signal-thread
18563 @kindex show sigthread
18564 These two commands show which thread will run when the inferior is
18565 delivered a signal.
18568 @kindex set stopped@r{, Hurd command}
18569 This commands tells @value{GDBN} that the inferior process is stopped,
18570 as with the @code{SIGSTOP} signal. The stopped process can be
18571 continued by delivering a signal to it.
18574 @kindex show stopped@r{, Hurd command}
18575 This command shows whether @value{GDBN} thinks the debuggee is
18578 @item set exceptions
18579 @kindex set exceptions@r{, Hurd command}
18580 Use this command to turn off trapping of exceptions in the inferior.
18581 When exception trapping is off, neither breakpoints nor
18582 single-stepping will work. To restore the default, set exception
18585 @item show exceptions
18586 @kindex show exceptions@r{, Hurd command}
18587 Show the current state of trapping exceptions in the inferior.
18589 @item set task pause
18590 @kindex set task@r{, Hurd commands}
18591 @cindex task attributes (@sc{gnu} Hurd)
18592 @cindex pause current task (@sc{gnu} Hurd)
18593 This command toggles task suspension when @value{GDBN} has control.
18594 Setting it to on takes effect immediately, and the task is suspended
18595 whenever @value{GDBN} gets control. Setting it to off will take
18596 effect the next time the inferior is continued. If this option is set
18597 to off, you can use @code{set thread default pause on} or @code{set
18598 thread pause on} (see below) to pause individual threads.
18600 @item show task pause
18601 @kindex show task@r{, Hurd commands}
18602 Show the current state of task suspension.
18604 @item set task detach-suspend-count
18605 @cindex task suspend count
18606 @cindex detach from task, @sc{gnu} Hurd
18607 This command sets the suspend count the task will be left with when
18608 @value{GDBN} detaches from it.
18610 @item show task detach-suspend-count
18611 Show the suspend count the task will be left with when detaching.
18613 @item set task exception-port
18614 @itemx set task excp
18615 @cindex task exception port, @sc{gnu} Hurd
18616 This command sets the task exception port to which @value{GDBN} will
18617 forward exceptions. The argument should be the value of the @dfn{send
18618 rights} of the task. @code{set task excp} is a shorthand alias.
18620 @item set noninvasive
18621 @cindex noninvasive task options
18622 This command switches @value{GDBN} to a mode that is the least
18623 invasive as far as interfering with the inferior is concerned. This
18624 is the same as using @code{set task pause}, @code{set exceptions}, and
18625 @code{set signals} to values opposite to the defaults.
18627 @item info send-rights
18628 @itemx info receive-rights
18629 @itemx info port-rights
18630 @itemx info port-sets
18631 @itemx info dead-names
18634 @cindex send rights, @sc{gnu} Hurd
18635 @cindex receive rights, @sc{gnu} Hurd
18636 @cindex port rights, @sc{gnu} Hurd
18637 @cindex port sets, @sc{gnu} Hurd
18638 @cindex dead names, @sc{gnu} Hurd
18639 These commands display information about, respectively, send rights,
18640 receive rights, port rights, port sets, and dead names of a task.
18641 There are also shorthand aliases: @code{info ports} for @code{info
18642 port-rights} and @code{info psets} for @code{info port-sets}.
18644 @item set thread pause
18645 @kindex set thread@r{, Hurd command}
18646 @cindex thread properties, @sc{gnu} Hurd
18647 @cindex pause current thread (@sc{gnu} Hurd)
18648 This command toggles current thread suspension when @value{GDBN} has
18649 control. Setting it to on takes effect immediately, and the current
18650 thread is suspended whenever @value{GDBN} gets control. Setting it to
18651 off will take effect the next time the inferior is continued.
18652 Normally, this command has no effect, since when @value{GDBN} has
18653 control, the whole task is suspended. However, if you used @code{set
18654 task pause off} (see above), this command comes in handy to suspend
18655 only the current thread.
18657 @item show thread pause
18658 @kindex show thread@r{, Hurd command}
18659 This command shows the state of current thread suspension.
18661 @item set thread run
18662 This command sets whether the current thread is allowed to run.
18664 @item show thread run
18665 Show whether the current thread is allowed to run.
18667 @item set thread detach-suspend-count
18668 @cindex thread suspend count, @sc{gnu} Hurd
18669 @cindex detach from thread, @sc{gnu} Hurd
18670 This command sets the suspend count @value{GDBN} will leave on a
18671 thread when detaching. This number is relative to the suspend count
18672 found by @value{GDBN} when it notices the thread; use @code{set thread
18673 takeover-suspend-count} to force it to an absolute value.
18675 @item show thread detach-suspend-count
18676 Show the suspend count @value{GDBN} will leave on the thread when
18679 @item set thread exception-port
18680 @itemx set thread excp
18681 Set the thread exception port to which to forward exceptions. This
18682 overrides the port set by @code{set task exception-port} (see above).
18683 @code{set thread excp} is the shorthand alias.
18685 @item set thread takeover-suspend-count
18686 Normally, @value{GDBN}'s thread suspend counts are relative to the
18687 value @value{GDBN} finds when it notices each thread. This command
18688 changes the suspend counts to be absolute instead.
18690 @item set thread default
18691 @itemx show thread default
18692 @cindex thread default settings, @sc{gnu} Hurd
18693 Each of the above @code{set thread} commands has a @code{set thread
18694 default} counterpart (e.g., @code{set thread default pause}, @code{set
18695 thread default exception-port}, etc.). The @code{thread default}
18696 variety of commands sets the default thread properties for all
18697 threads; you can then change the properties of individual threads with
18698 the non-default commands.
18703 @subsection QNX Neutrino
18704 @cindex QNX Neutrino
18706 @value{GDBN} provides the following commands specific to the QNX
18710 @item set debug nto-debug
18711 @kindex set debug nto-debug
18712 When set to on, enables debugging messages specific to the QNX
18715 @item show debug nto-debug
18716 @kindex show debug nto-debug
18717 Show the current state of QNX Neutrino messages.
18724 @value{GDBN} provides the following commands specific to the Darwin target:
18727 @item set debug darwin @var{num}
18728 @kindex set debug darwin
18729 When set to a non zero value, enables debugging messages specific to
18730 the Darwin support. Higher values produce more verbose output.
18732 @item show debug darwin
18733 @kindex show debug darwin
18734 Show the current state of Darwin messages.
18736 @item set debug mach-o @var{num}
18737 @kindex set debug mach-o
18738 When set to a non zero value, enables debugging messages while
18739 @value{GDBN} is reading Darwin object files. (@dfn{Mach-O} is the
18740 file format used on Darwin for object and executable files.) Higher
18741 values produce more verbose output. This is a command to diagnose
18742 problems internal to @value{GDBN} and should not be needed in normal
18745 @item show debug mach-o
18746 @kindex show debug mach-o
18747 Show the current state of Mach-O file messages.
18749 @item set mach-exceptions on
18750 @itemx set mach-exceptions off
18751 @kindex set mach-exceptions
18752 On Darwin, faults are first reported as a Mach exception and are then
18753 mapped to a Posix signal. Use this command to turn on trapping of
18754 Mach exceptions in the inferior. This might be sometimes useful to
18755 better understand the cause of a fault. The default is off.
18757 @item show mach-exceptions
18758 @kindex show mach-exceptions
18759 Show the current state of exceptions trapping.
18764 @section Embedded Operating Systems
18766 This section describes configurations involving the debugging of
18767 embedded operating systems that are available for several different
18771 * VxWorks:: Using @value{GDBN} with VxWorks
18774 @value{GDBN} includes the ability to debug programs running on
18775 various real-time operating systems.
18778 @subsection Using @value{GDBN} with VxWorks
18784 @kindex target vxworks
18785 @item target vxworks @var{machinename}
18786 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
18787 is the target system's machine name or IP address.
18791 On VxWorks, @code{load} links @var{filename} dynamically on the
18792 current target system as well as adding its symbols in @value{GDBN}.
18794 @value{GDBN} enables developers to spawn and debug tasks running on networked
18795 VxWorks targets from a Unix host. Already-running tasks spawned from
18796 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
18797 both the Unix host and on the VxWorks target. The program
18798 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
18799 installed with the name @code{vxgdb}, to distinguish it from a
18800 @value{GDBN} for debugging programs on the host itself.)
18803 @item VxWorks-timeout @var{args}
18804 @kindex vxworks-timeout
18805 All VxWorks-based targets now support the option @code{vxworks-timeout}.
18806 This option is set by the user, and @var{args} represents the number of
18807 seconds @value{GDBN} waits for responses to rpc's. You might use this if
18808 your VxWorks target is a slow software simulator or is on the far side
18809 of a thin network line.
18812 The following information on connecting to VxWorks was current when
18813 this manual was produced; newer releases of VxWorks may use revised
18816 @findex INCLUDE_RDB
18817 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
18818 to include the remote debugging interface routines in the VxWorks
18819 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
18820 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
18821 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
18822 source debugging task @code{tRdbTask} when VxWorks is booted. For more
18823 information on configuring and remaking VxWorks, see the manufacturer's
18825 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
18827 Once you have included @file{rdb.a} in your VxWorks system image and set
18828 your Unix execution search path to find @value{GDBN}, you are ready to
18829 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
18830 @code{vxgdb}, depending on your installation).
18832 @value{GDBN} comes up showing the prompt:
18839 * VxWorks Connection:: Connecting to VxWorks
18840 * VxWorks Download:: VxWorks download
18841 * VxWorks Attach:: Running tasks
18844 @node VxWorks Connection
18845 @subsubsection Connecting to VxWorks
18847 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
18848 network. To connect to a target whose host name is ``@code{tt}'', type:
18851 (vxgdb) target vxworks tt
18855 @value{GDBN} displays messages like these:
18858 Attaching remote machine across net...
18863 @value{GDBN} then attempts to read the symbol tables of any object modules
18864 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
18865 these files by searching the directories listed in the command search
18866 path (@pxref{Environment, ,Your Program's Environment}); if it fails
18867 to find an object file, it displays a message such as:
18870 prog.o: No such file or directory.
18873 When this happens, add the appropriate directory to the search path with
18874 the @value{GDBN} command @code{path}, and execute the @code{target}
18877 @node VxWorks Download
18878 @subsubsection VxWorks Download
18880 @cindex download to VxWorks
18881 If you have connected to the VxWorks target and you want to debug an
18882 object that has not yet been loaded, you can use the @value{GDBN}
18883 @code{load} command to download a file from Unix to VxWorks
18884 incrementally. The object file given as an argument to the @code{load}
18885 command is actually opened twice: first by the VxWorks target in order
18886 to download the code, then by @value{GDBN} in order to read the symbol
18887 table. This can lead to problems if the current working directories on
18888 the two systems differ. If both systems have NFS mounted the same
18889 filesystems, you can avoid these problems by using absolute paths.
18890 Otherwise, it is simplest to set the working directory on both systems
18891 to the directory in which the object file resides, and then to reference
18892 the file by its name, without any path. For instance, a program
18893 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
18894 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
18895 program, type this on VxWorks:
18898 -> cd "@var{vxpath}/vw/demo/rdb"
18902 Then, in @value{GDBN}, type:
18905 (vxgdb) cd @var{hostpath}/vw/demo/rdb
18906 (vxgdb) load prog.o
18909 @value{GDBN} displays a response similar to this:
18912 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
18915 You can also use the @code{load} command to reload an object module
18916 after editing and recompiling the corresponding source file. Note that
18917 this makes @value{GDBN} delete all currently-defined breakpoints,
18918 auto-displays, and convenience variables, and to clear the value
18919 history. (This is necessary in order to preserve the integrity of
18920 debugger's data structures that reference the target system's symbol
18923 @node VxWorks Attach
18924 @subsubsection Running Tasks
18926 @cindex running VxWorks tasks
18927 You can also attach to an existing task using the @code{attach} command as
18931 (vxgdb) attach @var{task}
18935 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
18936 or suspended when you attach to it. Running tasks are suspended at
18937 the time of attachment.
18939 @node Embedded Processors
18940 @section Embedded Processors
18942 This section goes into details specific to particular embedded
18945 @cindex send command to simulator
18946 Whenever a specific embedded processor has a simulator, @value{GDBN}
18947 allows to send an arbitrary command to the simulator.
18950 @item sim @var{command}
18951 @kindex sim@r{, a command}
18952 Send an arbitrary @var{command} string to the simulator. Consult the
18953 documentation for the specific simulator in use for information about
18954 acceptable commands.
18960 * M32R/D:: Renesas M32R/D
18961 * M68K:: Motorola M68K
18962 * MicroBlaze:: Xilinx MicroBlaze
18963 * MIPS Embedded:: MIPS Embedded
18964 * OpenRISC 1000:: OpenRisc 1000
18965 * PA:: HP PA Embedded
18966 * PowerPC Embedded:: PowerPC Embedded
18967 * Sparclet:: Tsqware Sparclet
18968 * Sparclite:: Fujitsu Sparclite
18969 * Z8000:: Zilog Z8000
18972 * Super-H:: Renesas Super-H
18981 @item target rdi @var{dev}
18982 ARM Angel monitor, via RDI library interface to ADP protocol. You may
18983 use this target to communicate with both boards running the Angel
18984 monitor, or with the EmbeddedICE JTAG debug device.
18987 @item target rdp @var{dev}
18992 @value{GDBN} provides the following ARM-specific commands:
18995 @item set arm disassembler
18997 This commands selects from a list of disassembly styles. The
18998 @code{"std"} style is the standard style.
19000 @item show arm disassembler
19002 Show the current disassembly style.
19004 @item set arm apcs32
19005 @cindex ARM 32-bit mode
19006 This command toggles ARM operation mode between 32-bit and 26-bit.
19008 @item show arm apcs32
19009 Display the current usage of the ARM 32-bit mode.
19011 @item set arm fpu @var{fputype}
19012 This command sets the ARM floating-point unit (FPU) type. The
19013 argument @var{fputype} can be one of these:
19017 Determine the FPU type by querying the OS ABI.
19019 Software FPU, with mixed-endian doubles on little-endian ARM
19022 GCC-compiled FPA co-processor.
19024 Software FPU with pure-endian doubles.
19030 Show the current type of the FPU.
19033 This command forces @value{GDBN} to use the specified ABI.
19036 Show the currently used ABI.
19038 @item set arm fallback-mode (arm|thumb|auto)
19039 @value{GDBN} uses the symbol table, when available, to determine
19040 whether instructions are ARM or Thumb. This command controls
19041 @value{GDBN}'s default behavior when the symbol table is not
19042 available. The default is @samp{auto}, which causes @value{GDBN} to
19043 use the current execution mode (from the @code{T} bit in the @code{CPSR}
19046 @item show arm fallback-mode
19047 Show the current fallback instruction mode.
19049 @item set arm force-mode (arm|thumb|auto)
19050 This command overrides use of the symbol table to determine whether
19051 instructions are ARM or Thumb. The default is @samp{auto}, which
19052 causes @value{GDBN} to use the symbol table and then the setting
19053 of @samp{set arm fallback-mode}.
19055 @item show arm force-mode
19056 Show the current forced instruction mode.
19058 @item set debug arm
19059 Toggle whether to display ARM-specific debugging messages from the ARM
19060 target support subsystem.
19062 @item show debug arm
19063 Show whether ARM-specific debugging messages are enabled.
19066 The following commands are available when an ARM target is debugged
19067 using the RDI interface:
19070 @item rdilogfile @r{[}@var{file}@r{]}
19072 @cindex ADP (Angel Debugger Protocol) logging
19073 Set the filename for the ADP (Angel Debugger Protocol) packet log.
19074 With an argument, sets the log file to the specified @var{file}. With
19075 no argument, show the current log file name. The default log file is
19078 @item rdilogenable @r{[}@var{arg}@r{]}
19079 @kindex rdilogenable
19080 Control logging of ADP packets. With an argument of 1 or @code{"yes"}
19081 enables logging, with an argument 0 or @code{"no"} disables it. With
19082 no arguments displays the current setting. When logging is enabled,
19083 ADP packets exchanged between @value{GDBN} and the RDI target device
19084 are logged to a file.
19086 @item set rdiromatzero
19087 @kindex set rdiromatzero
19088 @cindex ROM at zero address, RDI
19089 Tell @value{GDBN} whether the target has ROM at address 0. If on,
19090 vector catching is disabled, so that zero address can be used. If off
19091 (the default), vector catching is enabled. For this command to take
19092 effect, it needs to be invoked prior to the @code{target rdi} command.
19094 @item show rdiromatzero
19095 @kindex show rdiromatzero
19096 Show the current setting of ROM at zero address.
19098 @item set rdiheartbeat
19099 @kindex set rdiheartbeat
19100 @cindex RDI heartbeat
19101 Enable or disable RDI heartbeat packets. It is not recommended to
19102 turn on this option, since it confuses ARM and EPI JTAG interface, as
19103 well as the Angel monitor.
19105 @item show rdiheartbeat
19106 @kindex show rdiheartbeat
19107 Show the setting of RDI heartbeat packets.
19111 @item target sim @r{[}@var{simargs}@r{]} @dots{}
19112 The @value{GDBN} ARM simulator accepts the following optional arguments.
19115 @item --swi-support=@var{type}
19116 Tell the simulator which SWI interfaces to support.
19117 @var{type} may be a comma separated list of the following values.
19118 The default value is @code{all}.
19131 @subsection Renesas M32R/D and M32R/SDI
19134 @kindex target m32r
19135 @item target m32r @var{dev}
19136 Renesas M32R/D ROM monitor.
19138 @kindex target m32rsdi
19139 @item target m32rsdi @var{dev}
19140 Renesas M32R SDI server, connected via parallel port to the board.
19143 The following @value{GDBN} commands are specific to the M32R monitor:
19146 @item set download-path @var{path}
19147 @kindex set download-path
19148 @cindex find downloadable @sc{srec} files (M32R)
19149 Set the default path for finding downloadable @sc{srec} files.
19151 @item show download-path
19152 @kindex show download-path
19153 Show the default path for downloadable @sc{srec} files.
19155 @item set board-address @var{addr}
19156 @kindex set board-address
19157 @cindex M32-EVA target board address
19158 Set the IP address for the M32R-EVA target board.
19160 @item show board-address
19161 @kindex show board-address
19162 Show the current IP address of the target board.
19164 @item set server-address @var{addr}
19165 @kindex set server-address
19166 @cindex download server address (M32R)
19167 Set the IP address for the download server, which is the @value{GDBN}'s
19170 @item show server-address
19171 @kindex show server-address
19172 Display the IP address of the download server.
19174 @item upload @r{[}@var{file}@r{]}
19175 @kindex upload@r{, M32R}
19176 Upload the specified @sc{srec} @var{file} via the monitor's Ethernet
19177 upload capability. If no @var{file} argument is given, the current
19178 executable file is uploaded.
19180 @item tload @r{[}@var{file}@r{]}
19181 @kindex tload@r{, M32R}
19182 Test the @code{upload} command.
19185 The following commands are available for M32R/SDI:
19190 @cindex reset SDI connection, M32R
19191 This command resets the SDI connection.
19195 This command shows the SDI connection status.
19198 @kindex debug_chaos
19199 @cindex M32R/Chaos debugging
19200 Instructs the remote that M32R/Chaos debugging is to be used.
19202 @item use_debug_dma
19203 @kindex use_debug_dma
19204 Instructs the remote to use the DEBUG_DMA method of accessing memory.
19207 @kindex use_mon_code
19208 Instructs the remote to use the MON_CODE method of accessing memory.
19211 @kindex use_ib_break
19212 Instructs the remote to set breakpoints by IB break.
19214 @item use_dbt_break
19215 @kindex use_dbt_break
19216 Instructs the remote to set breakpoints by DBT.
19222 The Motorola m68k configuration includes ColdFire support, and a
19223 target command for the following ROM monitor.
19227 @kindex target dbug
19228 @item target dbug @var{dev}
19229 dBUG ROM monitor for Motorola ColdFire.
19234 @subsection MicroBlaze
19235 @cindex Xilinx MicroBlaze
19236 @cindex XMD, Xilinx Microprocessor Debugger
19238 The MicroBlaze is a soft-core processor supported on various Xilinx
19239 FPGAs, such as Spartan or Virtex series. Boards with these processors
19240 usually have JTAG ports which connect to a host system running the Xilinx
19241 Embedded Development Kit (EDK) or Software Development Kit (SDK).
19242 This host system is used to download the configuration bitstream to
19243 the target FPGA. The Xilinx Microprocessor Debugger (XMD) program
19244 communicates with the target board using the JTAG interface and
19245 presents a @code{gdbserver} interface to the board. By default
19246 @code{xmd} uses port @code{1234}. (While it is possible to change
19247 this default port, it requires the use of undocumented @code{xmd}
19248 commands. Contact Xilinx support if you need to do this.)
19250 Use these GDB commands to connect to the MicroBlaze target processor.
19253 @item target remote :1234
19254 Use this command to connect to the target if you are running @value{GDBN}
19255 on the same system as @code{xmd}.
19257 @item target remote @var{xmd-host}:1234
19258 Use this command to connect to the target if it is connected to @code{xmd}
19259 running on a different system named @var{xmd-host}.
19262 Use this command to download a program to the MicroBlaze target.
19264 @item set debug microblaze @var{n}
19265 Enable MicroBlaze-specific debugging messages if non-zero.
19267 @item show debug microblaze @var{n}
19268 Show MicroBlaze-specific debugging level.
19271 @node MIPS Embedded
19272 @subsection MIPS Embedded
19274 @cindex MIPS boards
19275 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
19276 MIPS board attached to a serial line. This is available when
19277 you configure @value{GDBN} with @samp{--target=mips-elf}.
19280 Use these @value{GDBN} commands to specify the connection to your target board:
19283 @item target mips @var{port}
19284 @kindex target mips @var{port}
19285 To run a program on the board, start up @code{@value{GDBP}} with the
19286 name of your program as the argument. To connect to the board, use the
19287 command @samp{target mips @var{port}}, where @var{port} is the name of
19288 the serial port connected to the board. If the program has not already
19289 been downloaded to the board, you may use the @code{load} command to
19290 download it. You can then use all the usual @value{GDBN} commands.
19292 For example, this sequence connects to the target board through a serial
19293 port, and loads and runs a program called @var{prog} through the
19297 host$ @value{GDBP} @var{prog}
19298 @value{GDBN} is free software and @dots{}
19299 (@value{GDBP}) target mips /dev/ttyb
19300 (@value{GDBP}) load @var{prog}
19304 @item target mips @var{hostname}:@var{portnumber}
19305 On some @value{GDBN} host configurations, you can specify a TCP
19306 connection (for instance, to a serial line managed by a terminal
19307 concentrator) instead of a serial port, using the syntax
19308 @samp{@var{hostname}:@var{portnumber}}.
19310 @item target pmon @var{port}
19311 @kindex target pmon @var{port}
19314 @item target ddb @var{port}
19315 @kindex target ddb @var{port}
19316 NEC's DDB variant of PMON for Vr4300.
19318 @item target lsi @var{port}
19319 @kindex target lsi @var{port}
19320 LSI variant of PMON.
19322 @kindex target r3900
19323 @item target r3900 @var{dev}
19324 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
19326 @kindex target array
19327 @item target array @var{dev}
19328 Array Tech LSI33K RAID controller board.
19334 @value{GDBN} also supports these special commands for MIPS targets:
19337 @item set mipsfpu double
19338 @itemx set mipsfpu single
19339 @itemx set mipsfpu none
19340 @itemx set mipsfpu auto
19341 @itemx show mipsfpu
19342 @kindex set mipsfpu
19343 @kindex show mipsfpu
19344 @cindex MIPS remote floating point
19345 @cindex floating point, MIPS remote
19346 If your target board does not support the MIPS floating point
19347 coprocessor, you should use the command @samp{set mipsfpu none} (if you
19348 need this, you may wish to put the command in your @value{GDBN} init
19349 file). This tells @value{GDBN} how to find the return value of
19350 functions which return floating point values. It also allows
19351 @value{GDBN} to avoid saving the floating point registers when calling
19352 functions on the board. If you are using a floating point coprocessor
19353 with only single precision floating point support, as on the @sc{r4650}
19354 processor, use the command @samp{set mipsfpu single}. The default
19355 double precision floating point coprocessor may be selected using
19356 @samp{set mipsfpu double}.
19358 In previous versions the only choices were double precision or no
19359 floating point, so @samp{set mipsfpu on} will select double precision
19360 and @samp{set mipsfpu off} will select no floating point.
19362 As usual, you can inquire about the @code{mipsfpu} variable with
19363 @samp{show mipsfpu}.
19365 @item set timeout @var{seconds}
19366 @itemx set retransmit-timeout @var{seconds}
19367 @itemx show timeout
19368 @itemx show retransmit-timeout
19369 @cindex @code{timeout}, MIPS protocol
19370 @cindex @code{retransmit-timeout}, MIPS protocol
19371 @kindex set timeout
19372 @kindex show timeout
19373 @kindex set retransmit-timeout
19374 @kindex show retransmit-timeout
19375 You can control the timeout used while waiting for a packet, in the MIPS
19376 remote protocol, with the @code{set timeout @var{seconds}} command. The
19377 default is 5 seconds. Similarly, you can control the timeout used while
19378 waiting for an acknowledgment of a packet with the @code{set
19379 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
19380 You can inspect both values with @code{show timeout} and @code{show
19381 retransmit-timeout}. (These commands are @emph{only} available when
19382 @value{GDBN} is configured for @samp{--target=mips-elf}.)
19384 The timeout set by @code{set timeout} does not apply when @value{GDBN}
19385 is waiting for your program to stop. In that case, @value{GDBN} waits
19386 forever because it has no way of knowing how long the program is going
19387 to run before stopping.
19389 @item set syn-garbage-limit @var{num}
19390 @kindex set syn-garbage-limit@r{, MIPS remote}
19391 @cindex synchronize with remote MIPS target
19392 Limit the maximum number of characters @value{GDBN} should ignore when
19393 it tries to synchronize with the remote target. The default is 10
19394 characters. Setting the limit to -1 means there's no limit.
19396 @item show syn-garbage-limit
19397 @kindex show syn-garbage-limit@r{, MIPS remote}
19398 Show the current limit on the number of characters to ignore when
19399 trying to synchronize with the remote system.
19401 @item set monitor-prompt @var{prompt}
19402 @kindex set monitor-prompt@r{, MIPS remote}
19403 @cindex remote monitor prompt
19404 Tell @value{GDBN} to expect the specified @var{prompt} string from the
19405 remote monitor. The default depends on the target:
19415 @item show monitor-prompt
19416 @kindex show monitor-prompt@r{, MIPS remote}
19417 Show the current strings @value{GDBN} expects as the prompt from the
19420 @item set monitor-warnings
19421 @kindex set monitor-warnings@r{, MIPS remote}
19422 Enable or disable monitor warnings about hardware breakpoints. This
19423 has effect only for the @code{lsi} target. When on, @value{GDBN} will
19424 display warning messages whose codes are returned by the @code{lsi}
19425 PMON monitor for breakpoint commands.
19427 @item show monitor-warnings
19428 @kindex show monitor-warnings@r{, MIPS remote}
19429 Show the current setting of printing monitor warnings.
19431 @item pmon @var{command}
19432 @kindex pmon@r{, MIPS remote}
19433 @cindex send PMON command
19434 This command allows sending an arbitrary @var{command} string to the
19435 monitor. The monitor must be in debug mode for this to work.
19438 @node OpenRISC 1000
19439 @subsection OpenRISC 1000
19440 @cindex OpenRISC 1000
19442 @cindex or1k boards
19443 See OR1k Architecture document (@uref{www.opencores.org}) for more information
19444 about platform and commands.
19448 @kindex target jtag
19449 @item target jtag jtag://@var{host}:@var{port}
19451 Connects to remote JTAG server.
19452 JTAG remote server can be either an or1ksim or JTAG server,
19453 connected via parallel port to the board.
19455 Example: @code{target jtag jtag://localhost:9999}
19458 @item or1ksim @var{command}
19459 If connected to @code{or1ksim} OpenRISC 1000 Architectural
19460 Simulator, proprietary commands can be executed.
19462 @kindex info or1k spr
19463 @item info or1k spr
19464 Displays spr groups.
19466 @item info or1k spr @var{group}
19467 @itemx info or1k spr @var{groupno}
19468 Displays register names in selected group.
19470 @item info or1k spr @var{group} @var{register}
19471 @itemx info or1k spr @var{register}
19472 @itemx info or1k spr @var{groupno} @var{registerno}
19473 @itemx info or1k spr @var{registerno}
19474 Shows information about specified spr register.
19477 @item spr @var{group} @var{register} @var{value}
19478 @itemx spr @var{register @var{value}}
19479 @itemx spr @var{groupno} @var{registerno @var{value}}
19480 @itemx spr @var{registerno @var{value}}
19481 Writes @var{value} to specified spr register.
19484 Some implementations of OpenRISC 1000 Architecture also have hardware trace.
19485 It is very similar to @value{GDBN} trace, except it does not interfere with normal
19486 program execution and is thus much faster. Hardware breakpoints/watchpoint
19487 triggers can be set using:
19490 Load effective address/data
19492 Store effective address/data
19494 Access effective address ($SEA or $LEA) or data ($SDATA/$LDATA)
19499 When triggered, it can capture low level data, like: @code{PC}, @code{LSEA},
19500 @code{LDATA}, @code{SDATA}, @code{READSPR}, @code{WRITESPR}, @code{INSTR}.
19502 @code{htrace} commands:
19503 @cindex OpenRISC 1000 htrace
19506 @item hwatch @var{conditional}
19507 Set hardware watchpoint on combination of Load/Store Effective Address(es)
19508 or Data. For example:
19510 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
19512 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
19516 Display information about current HW trace configuration.
19518 @item htrace trigger @var{conditional}
19519 Set starting criteria for HW trace.
19521 @item htrace qualifier @var{conditional}
19522 Set acquisition qualifier for HW trace.
19524 @item htrace stop @var{conditional}
19525 Set HW trace stopping criteria.
19527 @item htrace record [@var{data}]*
19528 Selects the data to be recorded, when qualifier is met and HW trace was
19531 @item htrace enable
19532 @itemx htrace disable
19533 Enables/disables the HW trace.
19535 @item htrace rewind [@var{filename}]
19536 Clears currently recorded trace data.
19538 If filename is specified, new trace file is made and any newly collected data
19539 will be written there.
19541 @item htrace print [@var{start} [@var{len}]]
19542 Prints trace buffer, using current record configuration.
19544 @item htrace mode continuous
19545 Set continuous trace mode.
19547 @item htrace mode suspend
19548 Set suspend trace mode.
19552 @node PowerPC Embedded
19553 @subsection PowerPC Embedded
19555 @cindex DVC register
19556 @value{GDBN} supports using the DVC (Data Value Compare) register to
19557 implement in hardware simple hardware watchpoint conditions of the form:
19560 (@value{GDBP}) watch @var{ADDRESS|VARIABLE} \
19561 if @var{ADDRESS|VARIABLE} == @var{CONSTANT EXPRESSION}
19564 The DVC register will be automatically used when @value{GDBN} detects
19565 such pattern in a condition expression, and the created watchpoint uses one
19566 debug register (either the @code{exact-watchpoints} option is on and the
19567 variable is scalar, or the variable has a length of one byte). This feature
19568 is available in native @value{GDBN} running on a Linux kernel version 2.6.34
19571 When running on PowerPC embedded processors, @value{GDBN} automatically uses
19572 ranged hardware watchpoints, unless the @code{exact-watchpoints} option is on,
19573 in which case watchpoints using only one debug register are created when
19574 watching variables of scalar types.
19576 You can create an artificial array to watch an arbitrary memory
19577 region using one of the following commands (@pxref{Expressions}):
19580 (@value{GDBP}) watch *((char *) @var{address})@@@var{length}
19581 (@value{GDBP}) watch @{char[@var{length}]@} @var{address}
19584 PowerPC embedded processors support masked watchpoints. See the discussion
19585 about the @code{mask} argument in @ref{Set Watchpoints}.
19587 @cindex ranged breakpoint
19588 PowerPC embedded processors support hardware accelerated
19589 @dfn{ranged breakpoints}. A ranged breakpoint stops execution of
19590 the inferior whenever it executes an instruction at any address within
19591 the range it specifies. To set a ranged breakpoint in @value{GDBN},
19592 use the @code{break-range} command.
19594 @value{GDBN} provides the following PowerPC-specific commands:
19597 @kindex break-range
19598 @item break-range @var{start-location}, @var{end-location}
19599 Set a breakpoint for an address range.
19600 @var{start-location} and @var{end-location} can specify a function name,
19601 a line number, an offset of lines from the current line or from the start
19602 location, or an address of an instruction (see @ref{Specify Location},
19603 for a list of all the possible ways to specify a @var{location}.)
19604 The breakpoint will stop execution of the inferior whenever it
19605 executes an instruction at any address within the specified range,
19606 (including @var{start-location} and @var{end-location}.)
19608 @kindex set powerpc
19609 @item set powerpc soft-float
19610 @itemx show powerpc soft-float
19611 Force @value{GDBN} to use (or not use) a software floating point calling
19612 convention. By default, @value{GDBN} selects the calling convention based
19613 on the selected architecture and the provided executable file.
19615 @item set powerpc vector-abi
19616 @itemx show powerpc vector-abi
19617 Force @value{GDBN} to use the specified calling convention for vector
19618 arguments and return values. The valid options are @samp{auto};
19619 @samp{generic}, to avoid vector registers even if they are present;
19620 @samp{altivec}, to use AltiVec registers; and @samp{spe} to use SPE
19621 registers. By default, @value{GDBN} selects the calling convention
19622 based on the selected architecture and the provided executable file.
19624 @item set powerpc exact-watchpoints
19625 @itemx show powerpc exact-watchpoints
19626 Allow @value{GDBN} to use only one debug register when watching a variable
19627 of scalar type, thus assuming that the variable is accessed through the
19628 address of its first byte.
19630 @kindex target dink32
19631 @item target dink32 @var{dev}
19632 DINK32 ROM monitor.
19634 @kindex target ppcbug
19635 @item target ppcbug @var{dev}
19636 @kindex target ppcbug1
19637 @item target ppcbug1 @var{dev}
19638 PPCBUG ROM monitor for PowerPC.
19641 @item target sds @var{dev}
19642 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
19645 @cindex SDS protocol
19646 The following commands specific to the SDS protocol are supported
19650 @item set sdstimeout @var{nsec}
19651 @kindex set sdstimeout
19652 Set the timeout for SDS protocol reads to be @var{nsec} seconds. The
19653 default is 2 seconds.
19655 @item show sdstimeout
19656 @kindex show sdstimeout
19657 Show the current value of the SDS timeout.
19659 @item sds @var{command}
19660 @kindex sds@r{, a command}
19661 Send the specified @var{command} string to the SDS monitor.
19666 @subsection HP PA Embedded
19670 @kindex target op50n
19671 @item target op50n @var{dev}
19672 OP50N monitor, running on an OKI HPPA board.
19674 @kindex target w89k
19675 @item target w89k @var{dev}
19676 W89K monitor, running on a Winbond HPPA board.
19681 @subsection Tsqware Sparclet
19685 @value{GDBN} enables developers to debug tasks running on
19686 Sparclet targets from a Unix host.
19687 @value{GDBN} uses code that runs on
19688 both the Unix host and on the Sparclet target. The program
19689 @code{@value{GDBP}} is installed and executed on the Unix host.
19692 @item remotetimeout @var{args}
19693 @kindex remotetimeout
19694 @value{GDBN} supports the option @code{remotetimeout}.
19695 This option is set by the user, and @var{args} represents the number of
19696 seconds @value{GDBN} waits for responses.
19699 @cindex compiling, on Sparclet
19700 When compiling for debugging, include the options @samp{-g} to get debug
19701 information and @samp{-Ttext} to relocate the program to where you wish to
19702 load it on the target. You may also want to add the options @samp{-n} or
19703 @samp{-N} in order to reduce the size of the sections. Example:
19706 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
19709 You can use @code{objdump} to verify that the addresses are what you intended:
19712 sparclet-aout-objdump --headers --syms prog
19715 @cindex running, on Sparclet
19717 your Unix execution search path to find @value{GDBN}, you are ready to
19718 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
19719 (or @code{sparclet-aout-gdb}, depending on your installation).
19721 @value{GDBN} comes up showing the prompt:
19728 * Sparclet File:: Setting the file to debug
19729 * Sparclet Connection:: Connecting to Sparclet
19730 * Sparclet Download:: Sparclet download
19731 * Sparclet Execution:: Running and debugging
19734 @node Sparclet File
19735 @subsubsection Setting File to Debug
19737 The @value{GDBN} command @code{file} lets you choose with program to debug.
19740 (gdbslet) file prog
19744 @value{GDBN} then attempts to read the symbol table of @file{prog}.
19745 @value{GDBN} locates
19746 the file by searching the directories listed in the command search
19748 If the file was compiled with debug information (option @samp{-g}), source
19749 files will be searched as well.
19750 @value{GDBN} locates
19751 the source files by searching the directories listed in the directory search
19752 path (@pxref{Environment, ,Your Program's Environment}).
19754 to find a file, it displays a message such as:
19757 prog: No such file or directory.
19760 When this happens, add the appropriate directories to the search paths with
19761 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
19762 @code{target} command again.
19764 @node Sparclet Connection
19765 @subsubsection Connecting to Sparclet
19767 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
19768 To connect to a target on serial port ``@code{ttya}'', type:
19771 (gdbslet) target sparclet /dev/ttya
19772 Remote target sparclet connected to /dev/ttya
19773 main () at ../prog.c:3
19777 @value{GDBN} displays messages like these:
19783 @node Sparclet Download
19784 @subsubsection Sparclet Download
19786 @cindex download to Sparclet
19787 Once connected to the Sparclet target,
19788 you can use the @value{GDBN}
19789 @code{load} command to download the file from the host to the target.
19790 The file name and load offset should be given as arguments to the @code{load}
19792 Since the file format is aout, the program must be loaded to the starting
19793 address. You can use @code{objdump} to find out what this value is. The load
19794 offset is an offset which is added to the VMA (virtual memory address)
19795 of each of the file's sections.
19796 For instance, if the program
19797 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
19798 and bss at 0x12010170, in @value{GDBN}, type:
19801 (gdbslet) load prog 0x12010000
19802 Loading section .text, size 0xdb0 vma 0x12010000
19805 If the code is loaded at a different address then what the program was linked
19806 to, you may need to use the @code{section} and @code{add-symbol-file} commands
19807 to tell @value{GDBN} where to map the symbol table.
19809 @node Sparclet Execution
19810 @subsubsection Running and Debugging
19812 @cindex running and debugging Sparclet programs
19813 You can now begin debugging the task using @value{GDBN}'s execution control
19814 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
19815 manual for the list of commands.
19819 Breakpoint 1 at 0x12010000: file prog.c, line 3.
19821 Starting program: prog
19822 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
19823 3 char *symarg = 0;
19825 4 char *execarg = "hello!";
19830 @subsection Fujitsu Sparclite
19834 @kindex target sparclite
19835 @item target sparclite @var{dev}
19836 Fujitsu sparclite boards, used only for the purpose of loading.
19837 You must use an additional command to debug the program.
19838 For example: target remote @var{dev} using @value{GDBN} standard
19844 @subsection Zilog Z8000
19847 @cindex simulator, Z8000
19848 @cindex Zilog Z8000 simulator
19850 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
19853 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
19854 unsegmented variant of the Z8000 architecture) or the Z8001 (the
19855 segmented variant). The simulator recognizes which architecture is
19856 appropriate by inspecting the object code.
19859 @item target sim @var{args}
19861 @kindex target sim@r{, with Z8000}
19862 Debug programs on a simulated CPU. If the simulator supports setup
19863 options, specify them via @var{args}.
19867 After specifying this target, you can debug programs for the simulated
19868 CPU in the same style as programs for your host computer; use the
19869 @code{file} command to load a new program image, the @code{run} command
19870 to run your program, and so on.
19872 As well as making available all the usual machine registers
19873 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
19874 additional items of information as specially named registers:
19879 Counts clock-ticks in the simulator.
19882 Counts instructions run in the simulator.
19885 Execution time in 60ths of a second.
19889 You can refer to these values in @value{GDBN} expressions with the usual
19890 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
19891 conditional breakpoint that suspends only after at least 5000
19892 simulated clock ticks.
19895 @subsection Atmel AVR
19898 When configured for debugging the Atmel AVR, @value{GDBN} supports the
19899 following AVR-specific commands:
19902 @item info io_registers
19903 @kindex info io_registers@r{, AVR}
19904 @cindex I/O registers (Atmel AVR)
19905 This command displays information about the AVR I/O registers. For
19906 each register, @value{GDBN} prints its number and value.
19913 When configured for debugging CRIS, @value{GDBN} provides the
19914 following CRIS-specific commands:
19917 @item set cris-version @var{ver}
19918 @cindex CRIS version
19919 Set the current CRIS version to @var{ver}, either @samp{10} or @samp{32}.
19920 The CRIS version affects register names and sizes. This command is useful in
19921 case autodetection of the CRIS version fails.
19923 @item show cris-version
19924 Show the current CRIS version.
19926 @item set cris-dwarf2-cfi
19927 @cindex DWARF-2 CFI and CRIS
19928 Set the usage of DWARF-2 CFI for CRIS debugging. The default is @samp{on}.
19929 Change to @samp{off} when using @code{gcc-cris} whose version is below
19932 @item show cris-dwarf2-cfi
19933 Show the current state of using DWARF-2 CFI.
19935 @item set cris-mode @var{mode}
19937 Set the current CRIS mode to @var{mode}. It should only be changed when
19938 debugging in guru mode, in which case it should be set to
19939 @samp{guru} (the default is @samp{normal}).
19941 @item show cris-mode
19942 Show the current CRIS mode.
19946 @subsection Renesas Super-H
19949 For the Renesas Super-H processor, @value{GDBN} provides these
19954 @kindex regs@r{, Super-H}
19955 Show the values of all Super-H registers.
19957 @item set sh calling-convention @var{convention}
19958 @kindex set sh calling-convention
19959 Set the calling-convention used when calling functions from @value{GDBN}.
19960 Allowed values are @samp{gcc}, which is the default setting, and @samp{renesas}.
19961 With the @samp{gcc} setting, functions are called using the @value{NGCC} calling
19962 convention. If the DWARF-2 information of the called function specifies
19963 that the function follows the Renesas calling convention, the function
19964 is called using the Renesas calling convention. If the calling convention
19965 is set to @samp{renesas}, the Renesas calling convention is always used,
19966 regardless of the DWARF-2 information. This can be used to override the
19967 default of @samp{gcc} if debug information is missing, or the compiler
19968 does not emit the DWARF-2 calling convention entry for a function.
19970 @item show sh calling-convention
19971 @kindex show sh calling-convention
19972 Show the current calling convention setting.
19977 @node Architectures
19978 @section Architectures
19980 This section describes characteristics of architectures that affect
19981 all uses of @value{GDBN} with the architecture, both native and cross.
19988 * HPPA:: HP PA architecture
19989 * SPU:: Cell Broadband Engine SPU architecture
19994 @subsection x86 Architecture-specific Issues
19997 @item set struct-convention @var{mode}
19998 @kindex set struct-convention
19999 @cindex struct return convention
20000 @cindex struct/union returned in registers
20001 Set the convention used by the inferior to return @code{struct}s and
20002 @code{union}s from functions to @var{mode}. Possible values of
20003 @var{mode} are @code{"pcc"}, @code{"reg"}, and @code{"default"} (the
20004 default). @code{"default"} or @code{"pcc"} means that @code{struct}s
20005 are returned on the stack, while @code{"reg"} means that a
20006 @code{struct} or a @code{union} whose size is 1, 2, 4, or 8 bytes will
20007 be returned in a register.
20009 @item show struct-convention
20010 @kindex show struct-convention
20011 Show the current setting of the convention to return @code{struct}s
20020 @kindex set rstack_high_address
20021 @cindex AMD 29K register stack
20022 @cindex register stack, AMD29K
20023 @item set rstack_high_address @var{address}
20024 On AMD 29000 family processors, registers are saved in a separate
20025 @dfn{register stack}. There is no way for @value{GDBN} to determine the
20026 extent of this stack. Normally, @value{GDBN} just assumes that the
20027 stack is ``large enough''. This may result in @value{GDBN} referencing
20028 memory locations that do not exist. If necessary, you can get around
20029 this problem by specifying the ending address of the register stack with
20030 the @code{set rstack_high_address} command. The argument should be an
20031 address, which you probably want to precede with @samp{0x} to specify in
20034 @kindex show rstack_high_address
20035 @item show rstack_high_address
20036 Display the current limit of the register stack, on AMD 29000 family
20044 See the following section.
20049 @cindex stack on Alpha
20050 @cindex stack on MIPS
20051 @cindex Alpha stack
20053 Alpha- and MIPS-based computers use an unusual stack frame, which
20054 sometimes requires @value{GDBN} to search backward in the object code to
20055 find the beginning of a function.
20057 @cindex response time, MIPS debugging
20058 To improve response time (especially for embedded applications, where
20059 @value{GDBN} may be restricted to a slow serial line for this search)
20060 you may want to limit the size of this search, using one of these
20064 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
20065 @item set heuristic-fence-post @var{limit}
20066 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
20067 search for the beginning of a function. A value of @var{0} (the
20068 default) means there is no limit. However, except for @var{0}, the
20069 larger the limit the more bytes @code{heuristic-fence-post} must search
20070 and therefore the longer it takes to run. You should only need to use
20071 this command when debugging a stripped executable.
20073 @item show heuristic-fence-post
20074 Display the current limit.
20078 These commands are available @emph{only} when @value{GDBN} is configured
20079 for debugging programs on Alpha or MIPS processors.
20081 Several MIPS-specific commands are available when debugging MIPS
20085 @item set mips abi @var{arg}
20086 @kindex set mips abi
20087 @cindex set ABI for MIPS
20088 Tell @value{GDBN} which MIPS ABI is used by the inferior. Possible
20089 values of @var{arg} are:
20093 The default ABI associated with the current binary (this is the
20103 @item show mips abi
20104 @kindex show mips abi
20105 Show the MIPS ABI used by @value{GDBN} to debug the inferior.
20108 @itemx show mipsfpu
20109 @xref{MIPS Embedded, set mipsfpu}.
20111 @item set mips mask-address @var{arg}
20112 @kindex set mips mask-address
20113 @cindex MIPS addresses, masking
20114 This command determines whether the most-significant 32 bits of 64-bit
20115 MIPS addresses are masked off. The argument @var{arg} can be
20116 @samp{on}, @samp{off}, or @samp{auto}. The latter is the default
20117 setting, which lets @value{GDBN} determine the correct value.
20119 @item show mips mask-address
20120 @kindex show mips mask-address
20121 Show whether the upper 32 bits of MIPS addresses are masked off or
20124 @item set remote-mips64-transfers-32bit-regs
20125 @kindex set remote-mips64-transfers-32bit-regs
20126 This command controls compatibility with 64-bit MIPS targets that
20127 transfer data in 32-bit quantities. If you have an old MIPS 64 target
20128 that transfers 32 bits for some registers, like @sc{sr} and @sc{fsr},
20129 and 64 bits for other registers, set this option to @samp{on}.
20131 @item show remote-mips64-transfers-32bit-regs
20132 @kindex show remote-mips64-transfers-32bit-regs
20133 Show the current setting of compatibility with older MIPS 64 targets.
20135 @item set debug mips
20136 @kindex set debug mips
20137 This command turns on and off debugging messages for the MIPS-specific
20138 target code in @value{GDBN}.
20140 @item show debug mips
20141 @kindex show debug mips
20142 Show the current setting of MIPS debugging messages.
20148 @cindex HPPA support
20150 When @value{GDBN} is debugging the HP PA architecture, it provides the
20151 following special commands:
20154 @item set debug hppa
20155 @kindex set debug hppa
20156 This command determines whether HPPA architecture-specific debugging
20157 messages are to be displayed.
20159 @item show debug hppa
20160 Show whether HPPA debugging messages are displayed.
20162 @item maint print unwind @var{address}
20163 @kindex maint print unwind@r{, HPPA}
20164 This command displays the contents of the unwind table entry at the
20165 given @var{address}.
20171 @subsection Cell Broadband Engine SPU architecture
20172 @cindex Cell Broadband Engine
20175 When @value{GDBN} is debugging the Cell Broadband Engine SPU architecture,
20176 it provides the following special commands:
20179 @item info spu event
20181 Display SPU event facility status. Shows current event mask
20182 and pending event status.
20184 @item info spu signal
20185 Display SPU signal notification facility status. Shows pending
20186 signal-control word and signal notification mode of both signal
20187 notification channels.
20189 @item info spu mailbox
20190 Display SPU mailbox facility status. Shows all pending entries,
20191 in order of processing, in each of the SPU Write Outbound,
20192 SPU Write Outbound Interrupt, and SPU Read Inbound mailboxes.
20195 Display MFC DMA status. Shows all pending commands in the MFC
20196 DMA queue. For each entry, opcode, tag, class IDs, effective
20197 and local store addresses and transfer size are shown.
20199 @item info spu proxydma
20200 Display MFC Proxy-DMA status. Shows all pending commands in the MFC
20201 Proxy-DMA queue. For each entry, opcode, tag, class IDs, effective
20202 and local store addresses and transfer size are shown.
20206 When @value{GDBN} is debugging a combined PowerPC/SPU application
20207 on the Cell Broadband Engine, it provides in addition the following
20211 @item set spu stop-on-load @var{arg}
20213 Set whether to stop for new SPE threads. When set to @code{on}, @value{GDBN}
20214 will give control to the user when a new SPE thread enters its @code{main}
20215 function. The default is @code{off}.
20217 @item show spu stop-on-load
20219 Show whether to stop for new SPE threads.
20221 @item set spu auto-flush-cache @var{arg}
20222 Set whether to automatically flush the software-managed cache. When set to
20223 @code{on}, @value{GDBN} will automatically cause the SPE software-managed
20224 cache to be flushed whenever SPE execution stops. This provides a consistent
20225 view of PowerPC memory that is accessed via the cache. If an application
20226 does not use the software-managed cache, this option has no effect.
20228 @item show spu auto-flush-cache
20229 Show whether to automatically flush the software-managed cache.
20234 @subsection PowerPC
20235 @cindex PowerPC architecture
20237 When @value{GDBN} is debugging the PowerPC architecture, it provides a set of
20238 pseudo-registers to enable inspection of 128-bit wide Decimal Floating Point
20239 numbers stored in the floating point registers. These values must be stored
20240 in two consecutive registers, always starting at an even register like
20241 @code{f0} or @code{f2}.
20243 The pseudo-registers go from @code{$dl0} through @code{$dl15}, and are formed
20244 by joining the even/odd register pairs @code{f0} and @code{f1} for @code{$dl0},
20245 @code{f2} and @code{f3} for @code{$dl1} and so on.
20247 For POWER7 processors, @value{GDBN} provides a set of pseudo-registers, the 64-bit
20248 wide Extended Floating Point Registers (@samp{f32} through @samp{f63}).
20251 @node Controlling GDB
20252 @chapter Controlling @value{GDBN}
20254 You can alter the way @value{GDBN} interacts with you by using the
20255 @code{set} command. For commands controlling how @value{GDBN} displays
20256 data, see @ref{Print Settings, ,Print Settings}. Other settings are
20261 * Editing:: Command editing
20262 * Command History:: Command history
20263 * Screen Size:: Screen size
20264 * Numbers:: Numbers
20265 * ABI:: Configuring the current ABI
20266 * Messages/Warnings:: Optional warnings and messages
20267 * Debugging Output:: Optional messages about internal happenings
20268 * Other Misc Settings:: Other Miscellaneous Settings
20276 @value{GDBN} indicates its readiness to read a command by printing a string
20277 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
20278 can change the prompt string with the @code{set prompt} command. For
20279 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
20280 the prompt in one of the @value{GDBN} sessions so that you can always tell
20281 which one you are talking to.
20283 @emph{Note:} @code{set prompt} does not add a space for you after the
20284 prompt you set. This allows you to set a prompt which ends in a space
20285 or a prompt that does not.
20289 @item set prompt @var{newprompt}
20290 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
20292 @kindex show prompt
20294 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
20297 Versions of @value{GDBN} that ship with Python scripting enabled have
20298 prompt extensions. The commands for interacting with these extensions
20302 @kindex set extended-prompt
20303 @item set extended-prompt @var{prompt}
20304 Set an extended prompt that allows for substitutions.
20305 @xref{gdb.prompt}, for a list of escape sequences that can be used for
20306 substitution. Any escape sequences specified as part of the prompt
20307 string are replaced with the corresponding strings each time the prompt
20313 set extended-prompt Current working directory: \w (gdb)
20316 Note that when an extended-prompt is set, it takes control of the
20317 @var{prompt_hook} hook. @xref{prompt_hook}, for further information.
20319 @kindex show extended-prompt
20320 @item show extended-prompt
20321 Prints the extended prompt. Any escape sequences specified as part of
20322 the prompt string with @code{set extended-prompt}, are replaced with the
20323 corresponding strings each time the prompt is displayed.
20327 @section Command Editing
20329 @cindex command line editing
20331 @value{GDBN} reads its input commands via the @dfn{Readline} interface. This
20332 @sc{gnu} library provides consistent behavior for programs which provide a
20333 command line interface to the user. Advantages are @sc{gnu} Emacs-style
20334 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
20335 substitution, and a storage and recall of command history across
20336 debugging sessions.
20338 You may control the behavior of command line editing in @value{GDBN} with the
20339 command @code{set}.
20342 @kindex set editing
20345 @itemx set editing on
20346 Enable command line editing (enabled by default).
20348 @item set editing off
20349 Disable command line editing.
20351 @kindex show editing
20353 Show whether command line editing is enabled.
20356 @ifset SYSTEM_READLINE
20357 @xref{Command Line Editing, , , rluserman, GNU Readline Library},
20359 @ifclear SYSTEM_READLINE
20360 @xref{Command Line Editing},
20362 for more details about the Readline
20363 interface. Users unfamiliar with @sc{gnu} Emacs or @code{vi} are
20364 encouraged to read that chapter.
20366 @node Command History
20367 @section Command History
20368 @cindex command history
20370 @value{GDBN} can keep track of the commands you type during your
20371 debugging sessions, so that you can be certain of precisely what
20372 happened. Use these commands to manage the @value{GDBN} command
20375 @value{GDBN} uses the @sc{gnu} History library, a part of the Readline
20376 package, to provide the history facility.
20377 @ifset SYSTEM_READLINE
20378 @xref{Using History Interactively, , , history, GNU History Library},
20380 @ifclear SYSTEM_READLINE
20381 @xref{Using History Interactively},
20383 for the detailed description of the History library.
20385 To issue a command to @value{GDBN} without affecting certain aspects of
20386 the state which is seen by users, prefix it with @samp{server }
20387 (@pxref{Server Prefix}). This
20388 means that this command will not affect the command history, nor will it
20389 affect @value{GDBN}'s notion of which command to repeat if @key{RET} is
20390 pressed on a line by itself.
20392 @cindex @code{server}, command prefix
20393 The server prefix does not affect the recording of values into the value
20394 history; to print a value without recording it into the value history,
20395 use the @code{output} command instead of the @code{print} command.
20397 Here is the description of @value{GDBN} commands related to command
20401 @cindex history substitution
20402 @cindex history file
20403 @kindex set history filename
20404 @cindex @env{GDBHISTFILE}, environment variable
20405 @item set history filename @var{fname}
20406 Set the name of the @value{GDBN} command history file to @var{fname}.
20407 This is the file where @value{GDBN} reads an initial command history
20408 list, and where it writes the command history from this session when it
20409 exits. You can access this list through history expansion or through
20410 the history command editing characters listed below. This file defaults
20411 to the value of the environment variable @code{GDBHISTFILE}, or to
20412 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
20415 @cindex save command history
20416 @kindex set history save
20417 @item set history save
20418 @itemx set history save on
20419 Record command history in a file, whose name may be specified with the
20420 @code{set history filename} command. By default, this option is disabled.
20422 @item set history save off
20423 Stop recording command history in a file.
20425 @cindex history size
20426 @kindex set history size
20427 @cindex @env{HISTSIZE}, environment variable
20428 @item set history size @var{size}
20429 Set the number of commands which @value{GDBN} keeps in its history list.
20430 This defaults to the value of the environment variable
20431 @code{HISTSIZE}, or to 256 if this variable is not set.
20434 History expansion assigns special meaning to the character @kbd{!}.
20435 @ifset SYSTEM_READLINE
20436 @xref{Event Designators, , , history, GNU History Library},
20438 @ifclear SYSTEM_READLINE
20439 @xref{Event Designators},
20443 @cindex history expansion, turn on/off
20444 Since @kbd{!} is also the logical not operator in C, history expansion
20445 is off by default. If you decide to enable history expansion with the
20446 @code{set history expansion on} command, you may sometimes need to
20447 follow @kbd{!} (when it is used as logical not, in an expression) with
20448 a space or a tab to prevent it from being expanded. The readline
20449 history facilities do not attempt substitution on the strings
20450 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
20452 The commands to control history expansion are:
20455 @item set history expansion on
20456 @itemx set history expansion
20457 @kindex set history expansion
20458 Enable history expansion. History expansion is off by default.
20460 @item set history expansion off
20461 Disable history expansion.
20464 @kindex show history
20466 @itemx show history filename
20467 @itemx show history save
20468 @itemx show history size
20469 @itemx show history expansion
20470 These commands display the state of the @value{GDBN} history parameters.
20471 @code{show history} by itself displays all four states.
20476 @kindex show commands
20477 @cindex show last commands
20478 @cindex display command history
20479 @item show commands
20480 Display the last ten commands in the command history.
20482 @item show commands @var{n}
20483 Print ten commands centered on command number @var{n}.
20485 @item show commands +
20486 Print ten commands just after the commands last printed.
20490 @section Screen Size
20491 @cindex size of screen
20492 @cindex pauses in output
20494 Certain commands to @value{GDBN} may produce large amounts of
20495 information output to the screen. To help you read all of it,
20496 @value{GDBN} pauses and asks you for input at the end of each page of
20497 output. Type @key{RET} when you want to continue the output, or @kbd{q}
20498 to discard the remaining output. Also, the screen width setting
20499 determines when to wrap lines of output. Depending on what is being
20500 printed, @value{GDBN} tries to break the line at a readable place,
20501 rather than simply letting it overflow onto the following line.
20503 Normally @value{GDBN} knows the size of the screen from the terminal
20504 driver software. For example, on Unix @value{GDBN} uses the termcap data base
20505 together with the value of the @code{TERM} environment variable and the
20506 @code{stty rows} and @code{stty cols} settings. If this is not correct,
20507 you can override it with the @code{set height} and @code{set
20514 @kindex show height
20515 @item set height @var{lpp}
20517 @itemx set width @var{cpl}
20519 These @code{set} commands specify a screen height of @var{lpp} lines and
20520 a screen width of @var{cpl} characters. The associated @code{show}
20521 commands display the current settings.
20523 If you specify a height of zero lines, @value{GDBN} does not pause during
20524 output no matter how long the output is. This is useful if output is to a
20525 file or to an editor buffer.
20527 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
20528 from wrapping its output.
20530 @item set pagination on
20531 @itemx set pagination off
20532 @kindex set pagination
20533 Turn the output pagination on or off; the default is on. Turning
20534 pagination off is the alternative to @code{set height 0}. Note that
20535 running @value{GDBN} with the @option{--batch} option (@pxref{Mode
20536 Options, -batch}) also automatically disables pagination.
20538 @item show pagination
20539 @kindex show pagination
20540 Show the current pagination mode.
20545 @cindex number representation
20546 @cindex entering numbers
20548 You can always enter numbers in octal, decimal, or hexadecimal in
20549 @value{GDBN} by the usual conventions: octal numbers begin with
20550 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
20551 begin with @samp{0x}. Numbers that neither begin with @samp{0} or
20552 @samp{0x}, nor end with a @samp{.} are, by default, entered in base
20553 10; likewise, the default display for numbers---when no particular
20554 format is specified---is base 10. You can change the default base for
20555 both input and output with the commands described below.
20558 @kindex set input-radix
20559 @item set input-radix @var{base}
20560 Set the default base for numeric input. Supported choices
20561 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
20562 specified either unambiguously or using the current input radix; for
20566 set input-radix 012
20567 set input-radix 10.
20568 set input-radix 0xa
20572 sets the input base to decimal. On the other hand, @samp{set input-radix 10}
20573 leaves the input radix unchanged, no matter what it was, since
20574 @samp{10}, being without any leading or trailing signs of its base, is
20575 interpreted in the current radix. Thus, if the current radix is 16,
20576 @samp{10} is interpreted in hex, i.e.@: as 16 decimal, which doesn't
20579 @kindex set output-radix
20580 @item set output-radix @var{base}
20581 Set the default base for numeric display. Supported choices
20582 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
20583 specified either unambiguously or using the current input radix.
20585 @kindex show input-radix
20586 @item show input-radix
20587 Display the current default base for numeric input.
20589 @kindex show output-radix
20590 @item show output-radix
20591 Display the current default base for numeric display.
20593 @item set radix @r{[}@var{base}@r{]}
20597 These commands set and show the default base for both input and output
20598 of numbers. @code{set radix} sets the radix of input and output to
20599 the same base; without an argument, it resets the radix back to its
20600 default value of 10.
20605 @section Configuring the Current ABI
20607 @value{GDBN} can determine the @dfn{ABI} (Application Binary Interface) of your
20608 application automatically. However, sometimes you need to override its
20609 conclusions. Use these commands to manage @value{GDBN}'s view of the
20616 One @value{GDBN} configuration can debug binaries for multiple operating
20617 system targets, either via remote debugging or native emulation.
20618 @value{GDBN} will autodetect the @dfn{OS ABI} (Operating System ABI) in use,
20619 but you can override its conclusion using the @code{set osabi} command.
20620 One example where this is useful is in debugging of binaries which use
20621 an alternate C library (e.g.@: @sc{uClibc} for @sc{gnu}/Linux) which does
20622 not have the same identifying marks that the standard C library for your
20627 Show the OS ABI currently in use.
20630 With no argument, show the list of registered available OS ABI's.
20632 @item set osabi @var{abi}
20633 Set the current OS ABI to @var{abi}.
20636 @cindex float promotion
20638 Generally, the way that an argument of type @code{float} is passed to a
20639 function depends on whether the function is prototyped. For a prototyped
20640 (i.e.@: ANSI/ISO style) function, @code{float} arguments are passed unchanged,
20641 according to the architecture's convention for @code{float}. For unprototyped
20642 (i.e.@: K&R style) functions, @code{float} arguments are first promoted to type
20643 @code{double} and then passed.
20645 Unfortunately, some forms of debug information do not reliably indicate whether
20646 a function is prototyped. If @value{GDBN} calls a function that is not marked
20647 as prototyped, it consults @kbd{set coerce-float-to-double}.
20650 @kindex set coerce-float-to-double
20651 @item set coerce-float-to-double
20652 @itemx set coerce-float-to-double on
20653 Arguments of type @code{float} will be promoted to @code{double} when passed
20654 to an unprototyped function. This is the default setting.
20656 @item set coerce-float-to-double off
20657 Arguments of type @code{float} will be passed directly to unprototyped
20660 @kindex show coerce-float-to-double
20661 @item show coerce-float-to-double
20662 Show the current setting of promoting @code{float} to @code{double}.
20666 @kindex show cp-abi
20667 @value{GDBN} needs to know the ABI used for your program's C@t{++}
20668 objects. The correct C@t{++} ABI depends on which C@t{++} compiler was
20669 used to build your application. @value{GDBN} only fully supports
20670 programs with a single C@t{++} ABI; if your program contains code using
20671 multiple C@t{++} ABI's or if @value{GDBN} can not identify your
20672 program's ABI correctly, you can tell @value{GDBN} which ABI to use.
20673 Currently supported ABI's include ``gnu-v2'', for @code{g++} versions
20674 before 3.0, ``gnu-v3'', for @code{g++} versions 3.0 and later, and
20675 ``hpaCC'' for the HP ANSI C@t{++} compiler. Other C@t{++} compilers may
20676 use the ``gnu-v2'' or ``gnu-v3'' ABI's as well. The default setting is
20681 Show the C@t{++} ABI currently in use.
20684 With no argument, show the list of supported C@t{++} ABI's.
20686 @item set cp-abi @var{abi}
20687 @itemx set cp-abi auto
20688 Set the current C@t{++} ABI to @var{abi}, or return to automatic detection.
20691 @node Messages/Warnings
20692 @section Optional Warnings and Messages
20694 @cindex verbose operation
20695 @cindex optional warnings
20696 By default, @value{GDBN} is silent about its inner workings. If you are
20697 running on a slow machine, you may want to use the @code{set verbose}
20698 command. This makes @value{GDBN} tell you when it does a lengthy
20699 internal operation, so you will not think it has crashed.
20701 Currently, the messages controlled by @code{set verbose} are those
20702 which announce that the symbol table for a source file is being read;
20703 see @code{symbol-file} in @ref{Files, ,Commands to Specify Files}.
20706 @kindex set verbose
20707 @item set verbose on
20708 Enables @value{GDBN} output of certain informational messages.
20710 @item set verbose off
20711 Disables @value{GDBN} output of certain informational messages.
20713 @kindex show verbose
20715 Displays whether @code{set verbose} is on or off.
20718 By default, if @value{GDBN} encounters bugs in the symbol table of an
20719 object file, it is silent; but if you are debugging a compiler, you may
20720 find this information useful (@pxref{Symbol Errors, ,Errors Reading
20725 @kindex set complaints
20726 @item set complaints @var{limit}
20727 Permits @value{GDBN} to output @var{limit} complaints about each type of
20728 unusual symbols before becoming silent about the problem. Set
20729 @var{limit} to zero to suppress all complaints; set it to a large number
20730 to prevent complaints from being suppressed.
20732 @kindex show complaints
20733 @item show complaints
20734 Displays how many symbol complaints @value{GDBN} is permitted to produce.
20738 @anchor{confirmation requests}
20739 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
20740 lot of stupid questions to confirm certain commands. For example, if
20741 you try to run a program which is already running:
20745 The program being debugged has been started already.
20746 Start it from the beginning? (y or n)
20749 If you are willing to unflinchingly face the consequences of your own
20750 commands, you can disable this ``feature'':
20754 @kindex set confirm
20756 @cindex confirmation
20757 @cindex stupid questions
20758 @item set confirm off
20759 Disables confirmation requests. Note that running @value{GDBN} with
20760 the @option{--batch} option (@pxref{Mode Options, -batch}) also
20761 automatically disables confirmation requests.
20763 @item set confirm on
20764 Enables confirmation requests (the default).
20766 @kindex show confirm
20768 Displays state of confirmation requests.
20772 @cindex command tracing
20773 If you need to debug user-defined commands or sourced files you may find it
20774 useful to enable @dfn{command tracing}. In this mode each command will be
20775 printed as it is executed, prefixed with one or more @samp{+} symbols, the
20776 quantity denoting the call depth of each command.
20779 @kindex set trace-commands
20780 @cindex command scripts, debugging
20781 @item set trace-commands on
20782 Enable command tracing.
20783 @item set trace-commands off
20784 Disable command tracing.
20785 @item show trace-commands
20786 Display the current state of command tracing.
20789 @node Debugging Output
20790 @section Optional Messages about Internal Happenings
20791 @cindex optional debugging messages
20793 @value{GDBN} has commands that enable optional debugging messages from
20794 various @value{GDBN} subsystems; normally these commands are of
20795 interest to @value{GDBN} maintainers, or when reporting a bug. This
20796 section documents those commands.
20799 @kindex set exec-done-display
20800 @item set exec-done-display
20801 Turns on or off the notification of asynchronous commands'
20802 completion. When on, @value{GDBN} will print a message when an
20803 asynchronous command finishes its execution. The default is off.
20804 @kindex show exec-done-display
20805 @item show exec-done-display
20806 Displays the current setting of asynchronous command completion
20809 @cindex gdbarch debugging info
20810 @cindex architecture debugging info
20811 @item set debug arch
20812 Turns on or off display of gdbarch debugging info. The default is off
20814 @item show debug arch
20815 Displays the current state of displaying gdbarch debugging info.
20816 @item set debug aix-thread
20817 @cindex AIX threads
20818 Display debugging messages about inner workings of the AIX thread
20820 @item show debug aix-thread
20821 Show the current state of AIX thread debugging info display.
20822 @item set debug check-physname
20824 Check the results of the ``physname'' computation. When reading DWARF
20825 debugging information for C@t{++}, @value{GDBN} attempts to compute
20826 each entity's name. @value{GDBN} can do this computation in two
20827 different ways, depending on exactly what information is present.
20828 When enabled, this setting causes @value{GDBN} to compute the names
20829 both ways and display any discrepancies.
20830 @item show debug check-physname
20831 Show the current state of ``physname'' checking.
20832 @item set debug dwarf2-die
20833 @cindex DWARF2 DIEs
20834 Dump DWARF2 DIEs after they are read in.
20835 The value is the number of nesting levels to print.
20836 A value of zero turns off the display.
20837 @item show debug dwarf2-die
20838 Show the current state of DWARF2 DIE debugging.
20839 @item set debug displaced
20840 @cindex displaced stepping debugging info
20841 Turns on or off display of @value{GDBN} debugging info for the
20842 displaced stepping support. The default is off.
20843 @item show debug displaced
20844 Displays the current state of displaying @value{GDBN} debugging info
20845 related to displaced stepping.
20846 @item set debug event
20847 @cindex event debugging info
20848 Turns on or off display of @value{GDBN} event debugging info. The
20850 @item show debug event
20851 Displays the current state of displaying @value{GDBN} event debugging
20853 @item set debug expression
20854 @cindex expression debugging info
20855 Turns on or off display of debugging info about @value{GDBN}
20856 expression parsing. The default is off.
20857 @item show debug expression
20858 Displays the current state of displaying debugging info about
20859 @value{GDBN} expression parsing.
20860 @item set debug frame
20861 @cindex frame debugging info
20862 Turns on or off display of @value{GDBN} frame debugging info. The
20864 @item show debug frame
20865 Displays the current state of displaying @value{GDBN} frame debugging
20867 @item set debug gnu-nat
20868 @cindex @sc{gnu}/Hurd debug messages
20869 Turns on or off debugging messages from the @sc{gnu}/Hurd debug support.
20870 @item show debug gnu-nat
20871 Show the current state of @sc{gnu}/Hurd debugging messages.
20872 @item set debug infrun
20873 @cindex inferior debugging info
20874 Turns on or off display of @value{GDBN} debugging info for running the inferior.
20875 The default is off. @file{infrun.c} contains GDB's runtime state machine used
20876 for implementing operations such as single-stepping the inferior.
20877 @item show debug infrun
20878 Displays the current state of @value{GDBN} inferior debugging.
20879 @item set debug jit
20880 @cindex just-in-time compilation, debugging messages
20881 Turns on or off debugging messages from JIT debug support.
20882 @item show debug jit
20883 Displays the current state of @value{GDBN} JIT debugging.
20884 @item set debug lin-lwp
20885 @cindex @sc{gnu}/Linux LWP debug messages
20886 @cindex Linux lightweight processes
20887 Turns on or off debugging messages from the Linux LWP debug support.
20888 @item show debug lin-lwp
20889 Show the current state of Linux LWP debugging messages.
20890 @item set debug observer
20891 @cindex observer debugging info
20892 Turns on or off display of @value{GDBN} observer debugging. This
20893 includes info such as the notification of observable events.
20894 @item show debug observer
20895 Displays the current state of observer debugging.
20896 @item set debug overload
20897 @cindex C@t{++} overload debugging info
20898 Turns on or off display of @value{GDBN} C@t{++} overload debugging
20899 info. This includes info such as ranking of functions, etc. The default
20901 @item show debug overload
20902 Displays the current state of displaying @value{GDBN} C@t{++} overload
20904 @cindex expression parser, debugging info
20905 @cindex debug expression parser
20906 @item set debug parser
20907 Turns on or off the display of expression parser debugging output.
20908 Internally, this sets the @code{yydebug} variable in the expression
20909 parser. @xref{Tracing, , Tracing Your Parser, bison, Bison}, for
20910 details. The default is off.
20911 @item show debug parser
20912 Show the current state of expression parser debugging.
20913 @cindex packets, reporting on stdout
20914 @cindex serial connections, debugging
20915 @cindex debug remote protocol
20916 @cindex remote protocol debugging
20917 @cindex display remote packets
20918 @item set debug remote
20919 Turns on or off display of reports on all packets sent back and forth across
20920 the serial line to the remote machine. The info is printed on the
20921 @value{GDBN} standard output stream. The default is off.
20922 @item show debug remote
20923 Displays the state of display of remote packets.
20924 @item set debug serial
20925 Turns on or off display of @value{GDBN} serial debugging info. The
20927 @item show debug serial
20928 Displays the current state of displaying @value{GDBN} serial debugging
20930 @item set debug solib-frv
20931 @cindex FR-V shared-library debugging
20932 Turns on or off debugging messages for FR-V shared-library code.
20933 @item show debug solib-frv
20934 Display the current state of FR-V shared-library code debugging
20936 @item set debug target
20937 @cindex target debugging info
20938 Turns on or off display of @value{GDBN} target debugging info. This info
20939 includes what is going on at the target level of GDB, as it happens. The
20940 default is 0. Set it to 1 to track events, and to 2 to also track the
20941 value of large memory transfers. Changes to this flag do not take effect
20942 until the next time you connect to a target or use the @code{run} command.
20943 @item show debug target
20944 Displays the current state of displaying @value{GDBN} target debugging
20946 @item set debug timestamp
20947 @cindex timestampping debugging info
20948 Turns on or off display of timestamps with @value{GDBN} debugging info.
20949 When enabled, seconds and microseconds are displayed before each debugging
20951 @item show debug timestamp
20952 Displays the current state of displaying timestamps with @value{GDBN}
20954 @item set debugvarobj
20955 @cindex variable object debugging info
20956 Turns on or off display of @value{GDBN} variable object debugging
20957 info. The default is off.
20958 @item show debugvarobj
20959 Displays the current state of displaying @value{GDBN} variable object
20961 @item set debug xml
20962 @cindex XML parser debugging
20963 Turns on or off debugging messages for built-in XML parsers.
20964 @item show debug xml
20965 Displays the current state of XML debugging messages.
20968 @node Other Misc Settings
20969 @section Other Miscellaneous Settings
20970 @cindex miscellaneous settings
20973 @kindex set interactive-mode
20974 @item set interactive-mode
20975 If @code{on}, forces @value{GDBN} to assume that GDB was started
20976 in a terminal. In practice, this means that @value{GDBN} should wait
20977 for the user to answer queries generated by commands entered at
20978 the command prompt. If @code{off}, forces @value{GDBN} to operate
20979 in the opposite mode, and it uses the default answers to all queries.
20980 If @code{auto} (the default), @value{GDBN} tries to determine whether
20981 its standard input is a terminal, and works in interactive-mode if it
20982 is, non-interactively otherwise.
20984 In the vast majority of cases, the debugger should be able to guess
20985 correctly which mode should be used. But this setting can be useful
20986 in certain specific cases, such as running a MinGW @value{GDBN}
20987 inside a cygwin window.
20989 @kindex show interactive-mode
20990 @item show interactive-mode
20991 Displays whether the debugger is operating in interactive mode or not.
20994 @node Extending GDB
20995 @chapter Extending @value{GDBN}
20996 @cindex extending GDB
20998 @value{GDBN} provides three mechanisms for extension. The first is based
20999 on composition of @value{GDBN} commands, the second is based on the
21000 Python scripting language, and the third is for defining new aliases of
21003 To facilitate the use of the first two extensions, @value{GDBN} is capable
21004 of evaluating the contents of a file. When doing so, @value{GDBN}
21005 can recognize which scripting language is being used by looking at
21006 the filename extension. Files with an unrecognized filename extension
21007 are always treated as a @value{GDBN} Command Files.
21008 @xref{Command Files,, Command files}.
21010 You can control how @value{GDBN} evaluates these files with the following
21014 @kindex set script-extension
21015 @kindex show script-extension
21016 @item set script-extension off
21017 All scripts are always evaluated as @value{GDBN} Command Files.
21019 @item set script-extension soft
21020 The debugger determines the scripting language based on filename
21021 extension. If this scripting language is supported, @value{GDBN}
21022 evaluates the script using that language. Otherwise, it evaluates
21023 the file as a @value{GDBN} Command File.
21025 @item set script-extension strict
21026 The debugger determines the scripting language based on filename
21027 extension, and evaluates the script using that language. If the
21028 language is not supported, then the evaluation fails.
21030 @item show script-extension
21031 Display the current value of the @code{script-extension} option.
21036 * Sequences:: Canned Sequences of Commands
21037 * Python:: Scripting @value{GDBN} using Python
21038 * Aliases:: Creating new spellings of existing commands
21042 @section Canned Sequences of Commands
21044 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
21045 Command Lists}), @value{GDBN} provides two ways to store sequences of
21046 commands for execution as a unit: user-defined commands and command
21050 * Define:: How to define your own commands
21051 * Hooks:: Hooks for user-defined commands
21052 * Command Files:: How to write scripts of commands to be stored in a file
21053 * Output:: Commands for controlled output
21057 @subsection User-defined Commands
21059 @cindex user-defined command
21060 @cindex arguments, to user-defined commands
21061 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
21062 which you assign a new name as a command. This is done with the
21063 @code{define} command. User commands may accept up to 10 arguments
21064 separated by whitespace. Arguments are accessed within the user command
21065 via @code{$arg0@dots{}$arg9}. A trivial example:
21069 print $arg0 + $arg1 + $arg2
21074 To execute the command use:
21081 This defines the command @code{adder}, which prints the sum of
21082 its three arguments. Note the arguments are text substitutions, so they may
21083 reference variables, use complex expressions, or even perform inferior
21086 @cindex argument count in user-defined commands
21087 @cindex how many arguments (user-defined commands)
21088 In addition, @code{$argc} may be used to find out how many arguments have
21089 been passed. This expands to a number in the range 0@dots{}10.
21094 print $arg0 + $arg1
21097 print $arg0 + $arg1 + $arg2
21105 @item define @var{commandname}
21106 Define a command named @var{commandname}. If there is already a command
21107 by that name, you are asked to confirm that you want to redefine it.
21108 @var{commandname} may be a bare command name consisting of letters,
21109 numbers, dashes, and underscores. It may also start with any predefined
21110 prefix command. For example, @samp{define target my-target} creates
21111 a user-defined @samp{target my-target} command.
21113 The definition of the command is made up of other @value{GDBN} command lines,
21114 which are given following the @code{define} command. The end of these
21115 commands is marked by a line containing @code{end}.
21118 @kindex end@r{ (user-defined commands)}
21119 @item document @var{commandname}
21120 Document the user-defined command @var{commandname}, so that it can be
21121 accessed by @code{help}. The command @var{commandname} must already be
21122 defined. This command reads lines of documentation just as @code{define}
21123 reads the lines of the command definition, ending with @code{end}.
21124 After the @code{document} command is finished, @code{help} on command
21125 @var{commandname} displays the documentation you have written.
21127 You may use the @code{document} command again to change the
21128 documentation of a command. Redefining the command with @code{define}
21129 does not change the documentation.
21131 @kindex dont-repeat
21132 @cindex don't repeat command
21134 Used inside a user-defined command, this tells @value{GDBN} that this
21135 command should not be repeated when the user hits @key{RET}
21136 (@pxref{Command Syntax, repeat last command}).
21138 @kindex help user-defined
21139 @item help user-defined
21140 List all user-defined commands and all python commands defined in class
21141 COMAND_USER. The first line of the documentation or docstring is
21146 @itemx show user @var{commandname}
21147 Display the @value{GDBN} commands used to define @var{commandname} (but
21148 not its documentation). If no @var{commandname} is given, display the
21149 definitions for all user-defined commands.
21150 This does not work for user-defined python commands.
21152 @cindex infinite recursion in user-defined commands
21153 @kindex show max-user-call-depth
21154 @kindex set max-user-call-depth
21155 @item show max-user-call-depth
21156 @itemx set max-user-call-depth
21157 The value of @code{max-user-call-depth} controls how many recursion
21158 levels are allowed in user-defined commands before @value{GDBN} suspects an
21159 infinite recursion and aborts the command.
21160 This does not apply to user-defined python commands.
21163 In addition to the above commands, user-defined commands frequently
21164 use control flow commands, described in @ref{Command Files}.
21166 When user-defined commands are executed, the
21167 commands of the definition are not printed. An error in any command
21168 stops execution of the user-defined command.
21170 If used interactively, commands that would ask for confirmation proceed
21171 without asking when used inside a user-defined command. Many @value{GDBN}
21172 commands that normally print messages to say what they are doing omit the
21173 messages when used in a user-defined command.
21176 @subsection User-defined Command Hooks
21177 @cindex command hooks
21178 @cindex hooks, for commands
21179 @cindex hooks, pre-command
21182 You may define @dfn{hooks}, which are a special kind of user-defined
21183 command. Whenever you run the command @samp{foo}, if the user-defined
21184 command @samp{hook-foo} exists, it is executed (with no arguments)
21185 before that command.
21187 @cindex hooks, post-command
21189 A hook may also be defined which is run after the command you executed.
21190 Whenever you run the command @samp{foo}, if the user-defined command
21191 @samp{hookpost-foo} exists, it is executed (with no arguments) after
21192 that command. Post-execution hooks may exist simultaneously with
21193 pre-execution hooks, for the same command.
21195 It is valid for a hook to call the command which it hooks. If this
21196 occurs, the hook is not re-executed, thereby avoiding infinite recursion.
21198 @c It would be nice if hookpost could be passed a parameter indicating
21199 @c if the command it hooks executed properly or not. FIXME!
21201 @kindex stop@r{, a pseudo-command}
21202 In addition, a pseudo-command, @samp{stop} exists. Defining
21203 (@samp{hook-stop}) makes the associated commands execute every time
21204 execution stops in your program: before breakpoint commands are run,
21205 displays are printed, or the stack frame is printed.
21207 For example, to ignore @code{SIGALRM} signals while
21208 single-stepping, but treat them normally during normal execution,
21213 handle SIGALRM nopass
21217 handle SIGALRM pass
21220 define hook-continue
21221 handle SIGALRM pass
21225 As a further example, to hook at the beginning and end of the @code{echo}
21226 command, and to add extra text to the beginning and end of the message,
21234 define hookpost-echo
21238 (@value{GDBP}) echo Hello World
21239 <<<---Hello World--->>>
21244 You can define a hook for any single-word command in @value{GDBN}, but
21245 not for command aliases; you should define a hook for the basic command
21246 name, e.g.@: @code{backtrace} rather than @code{bt}.
21247 @c FIXME! So how does Joe User discover whether a command is an alias
21249 You can hook a multi-word command by adding @code{hook-} or
21250 @code{hookpost-} to the last word of the command, e.g.@:
21251 @samp{define target hook-remote} to add a hook to @samp{target remote}.
21253 If an error occurs during the execution of your hook, execution of
21254 @value{GDBN} commands stops and @value{GDBN} issues a prompt
21255 (before the command that you actually typed had a chance to run).
21257 If you try to define a hook which does not match any known command, you
21258 get a warning from the @code{define} command.
21260 @node Command Files
21261 @subsection Command Files
21263 @cindex command files
21264 @cindex scripting commands
21265 A command file for @value{GDBN} is a text file made of lines that are
21266 @value{GDBN} commands. Comments (lines starting with @kbd{#}) may
21267 also be included. An empty line in a command file does nothing; it
21268 does not mean to repeat the last command, as it would from the
21271 You can request the execution of a command file with the @code{source}
21272 command. Note that the @code{source} command is also used to evaluate
21273 scripts that are not Command Files. The exact behavior can be configured
21274 using the @code{script-extension} setting.
21275 @xref{Extending GDB,, Extending GDB}.
21279 @cindex execute commands from a file
21280 @item source [-s] [-v] @var{filename}
21281 Execute the command file @var{filename}.
21284 The lines in a command file are generally executed sequentially,
21285 unless the order of execution is changed by one of the
21286 @emph{flow-control commands} described below. The commands are not
21287 printed as they are executed. An error in any command terminates
21288 execution of the command file and control is returned to the console.
21290 @value{GDBN} first searches for @var{filename} in the current directory.
21291 If the file is not found there, and @var{filename} does not specify a
21292 directory, then @value{GDBN} also looks for the file on the source search path
21293 (specified with the @samp{directory} command);
21294 except that @file{$cdir} is not searched because the compilation directory
21295 is not relevant to scripts.
21297 If @code{-s} is specified, then @value{GDBN} searches for @var{filename}
21298 on the search path even if @var{filename} specifies a directory.
21299 The search is done by appending @var{filename} to each element of the
21300 search path. So, for example, if @var{filename} is @file{mylib/myscript}
21301 and the search path contains @file{/home/user} then @value{GDBN} will
21302 look for the script @file{/home/user/mylib/myscript}.
21303 The search is also done if @var{filename} is an absolute path.
21304 For example, if @var{filename} is @file{/tmp/myscript} and
21305 the search path contains @file{/home/user} then @value{GDBN} will
21306 look for the script @file{/home/user/tmp/myscript}.
21307 For DOS-like systems, if @var{filename} contains a drive specification,
21308 it is stripped before concatenation. For example, if @var{filename} is
21309 @file{d:myscript} and the search path contains @file{c:/tmp} then @value{GDBN}
21310 will look for the script @file{c:/tmp/myscript}.
21312 If @code{-v}, for verbose mode, is given then @value{GDBN} displays
21313 each command as it is executed. The option must be given before
21314 @var{filename}, and is interpreted as part of the filename anywhere else.
21316 Commands that would ask for confirmation if used interactively proceed
21317 without asking when used in a command file. Many @value{GDBN} commands that
21318 normally print messages to say what they are doing omit the messages
21319 when called from command files.
21321 @value{GDBN} also accepts command input from standard input. In this
21322 mode, normal output goes to standard output and error output goes to
21323 standard error. Errors in a command file supplied on standard input do
21324 not terminate execution of the command file---execution continues with
21328 gdb < cmds > log 2>&1
21331 (The syntax above will vary depending on the shell used.) This example
21332 will execute commands from the file @file{cmds}. All output and errors
21333 would be directed to @file{log}.
21335 Since commands stored on command files tend to be more general than
21336 commands typed interactively, they frequently need to deal with
21337 complicated situations, such as different or unexpected values of
21338 variables and symbols, changes in how the program being debugged is
21339 built, etc. @value{GDBN} provides a set of flow-control commands to
21340 deal with these complexities. Using these commands, you can write
21341 complex scripts that loop over data structures, execute commands
21342 conditionally, etc.
21349 This command allows to include in your script conditionally executed
21350 commands. The @code{if} command takes a single argument, which is an
21351 expression to evaluate. It is followed by a series of commands that
21352 are executed only if the expression is true (its value is nonzero).
21353 There can then optionally be an @code{else} line, followed by a series
21354 of commands that are only executed if the expression was false. The
21355 end of the list is marked by a line containing @code{end}.
21359 This command allows to write loops. Its syntax is similar to
21360 @code{if}: the command takes a single argument, which is an expression
21361 to evaluate, and must be followed by the commands to execute, one per
21362 line, terminated by an @code{end}. These commands are called the
21363 @dfn{body} of the loop. The commands in the body of @code{while} are
21364 executed repeatedly as long as the expression evaluates to true.
21368 This command exits the @code{while} loop in whose body it is included.
21369 Execution of the script continues after that @code{while}s @code{end}
21372 @kindex loop_continue
21373 @item loop_continue
21374 This command skips the execution of the rest of the body of commands
21375 in the @code{while} loop in whose body it is included. Execution
21376 branches to the beginning of the @code{while} loop, where it evaluates
21377 the controlling expression.
21379 @kindex end@r{ (if/else/while commands)}
21381 Terminate the block of commands that are the body of @code{if},
21382 @code{else}, or @code{while} flow-control commands.
21387 @subsection Commands for Controlled Output
21389 During the execution of a command file or a user-defined command, normal
21390 @value{GDBN} output is suppressed; the only output that appears is what is
21391 explicitly printed by the commands in the definition. This section
21392 describes three commands useful for generating exactly the output you
21397 @item echo @var{text}
21398 @c I do not consider backslash-space a standard C escape sequence
21399 @c because it is not in ANSI.
21400 Print @var{text}. Nonprinting characters can be included in
21401 @var{text} using C escape sequences, such as @samp{\n} to print a
21402 newline. @strong{No newline is printed unless you specify one.}
21403 In addition to the standard C escape sequences, a backslash followed
21404 by a space stands for a space. This is useful for displaying a
21405 string with spaces at the beginning or the end, since leading and
21406 trailing spaces are otherwise trimmed from all arguments.
21407 To print @samp{@w{ }and foo =@w{ }}, use the command
21408 @samp{echo \@w{ }and foo = \@w{ }}.
21410 A backslash at the end of @var{text} can be used, as in C, to continue
21411 the command onto subsequent lines. For example,
21414 echo This is some text\n\
21415 which is continued\n\
21416 onto several lines.\n
21419 produces the same output as
21422 echo This is some text\n
21423 echo which is continued\n
21424 echo onto several lines.\n
21428 @item output @var{expression}
21429 Print the value of @var{expression} and nothing but that value: no
21430 newlines, no @samp{$@var{nn} = }. The value is not entered in the
21431 value history either. @xref{Expressions, ,Expressions}, for more information
21434 @item output/@var{fmt} @var{expression}
21435 Print the value of @var{expression} in format @var{fmt}. You can use
21436 the same formats as for @code{print}. @xref{Output Formats,,Output
21437 Formats}, for more information.
21440 @item printf @var{template}, @var{expressions}@dots{}
21441 Print the values of one or more @var{expressions} under the control of
21442 the string @var{template}. To print several values, make
21443 @var{expressions} be a comma-separated list of individual expressions,
21444 which may be either numbers or pointers. Their values are printed as
21445 specified by @var{template}, exactly as a C program would do by
21446 executing the code below:
21449 printf (@var{template}, @var{expressions}@dots{});
21452 As in @code{C} @code{printf}, ordinary characters in @var{template}
21453 are printed verbatim, while @dfn{conversion specification} introduced
21454 by the @samp{%} character cause subsequent @var{expressions} to be
21455 evaluated, their values converted and formatted according to type and
21456 style information encoded in the conversion specifications, and then
21459 For example, you can print two values in hex like this:
21462 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
21465 @code{printf} supports all the standard @code{C} conversion
21466 specifications, including the flags and modifiers between the @samp{%}
21467 character and the conversion letter, with the following exceptions:
21471 The argument-ordering modifiers, such as @samp{2$}, are not supported.
21474 The modifier @samp{*} is not supported for specifying precision or
21478 The @samp{'} flag (for separation of digits into groups according to
21479 @code{LC_NUMERIC'}) is not supported.
21482 The type modifiers @samp{hh}, @samp{j}, @samp{t}, and @samp{z} are not
21486 The conversion letter @samp{n} (as in @samp{%n}) is not supported.
21489 The conversion letters @samp{a} and @samp{A} are not supported.
21493 Note that the @samp{ll} type modifier is supported only if the
21494 underlying @code{C} implementation used to build @value{GDBN} supports
21495 the @code{long long int} type, and the @samp{L} type modifier is
21496 supported only if @code{long double} type is available.
21498 As in @code{C}, @code{printf} supports simple backslash-escape
21499 sequences, such as @code{\n}, @samp{\t}, @samp{\\}, @samp{\"},
21500 @samp{\a}, and @samp{\f}, that consist of backslash followed by a
21501 single character. Octal and hexadecimal escape sequences are not
21504 Additionally, @code{printf} supports conversion specifications for DFP
21505 (@dfn{Decimal Floating Point}) types using the following length modifiers
21506 together with a floating point specifier.
21511 @samp{H} for printing @code{Decimal32} types.
21514 @samp{D} for printing @code{Decimal64} types.
21517 @samp{DD} for printing @code{Decimal128} types.
21520 If the underlying @code{C} implementation used to build @value{GDBN} has
21521 support for the three length modifiers for DFP types, other modifiers
21522 such as width and precision will also be available for @value{GDBN} to use.
21524 In case there is no such @code{C} support, no additional modifiers will be
21525 available and the value will be printed in the standard way.
21527 Here's an example of printing DFP types using the above conversion letters:
21529 printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl
21533 @item eval @var{template}, @var{expressions}@dots{}
21534 Convert the values of one or more @var{expressions} under the control of
21535 the string @var{template} to a command line, and call it.
21540 @section Scripting @value{GDBN} using Python
21541 @cindex python scripting
21542 @cindex scripting with python
21544 You can script @value{GDBN} using the @uref{http://www.python.org/,
21545 Python programming language}. This feature is available only if
21546 @value{GDBN} was configured using @option{--with-python}.
21548 @cindex python directory
21549 Python scripts used by @value{GDBN} should be installed in
21550 @file{@var{data-directory}/python}, where @var{data-directory} is
21551 the data directory as determined at @value{GDBN} startup (@pxref{Data Files}).
21552 This directory, known as the @dfn{python directory},
21553 is automatically added to the Python Search Path in order to allow
21554 the Python interpreter to locate all scripts installed at this location.
21556 Additionally, @value{GDBN} commands and convenience functions which
21557 are written in Python and are located in the
21558 @file{@var{data-directory}/python/gdb/command} or
21559 @file{@var{data-directory}/python/gdb/function} directories are
21560 automatically imported when @value{GDBN} starts.
21563 * Python Commands:: Accessing Python from @value{GDBN}.
21564 * Python API:: Accessing @value{GDBN} from Python.
21565 * Auto-loading:: Automatically loading Python code.
21566 * Python modules:: Python modules provided by @value{GDBN}.
21569 @node Python Commands
21570 @subsection Python Commands
21571 @cindex python commands
21572 @cindex commands to access python
21574 @value{GDBN} provides one command for accessing the Python interpreter,
21575 and one related setting:
21579 @item python @r{[}@var{code}@r{]}
21580 The @code{python} command can be used to evaluate Python code.
21582 If given an argument, the @code{python} command will evaluate the
21583 argument as a Python command. For example:
21586 (@value{GDBP}) python print 23
21590 If you do not provide an argument to @code{python}, it will act as a
21591 multi-line command, like @code{define}. In this case, the Python
21592 script is made up of subsequent command lines, given after the
21593 @code{python} command. This command list is terminated using a line
21594 containing @code{end}. For example:
21597 (@value{GDBP}) python
21599 End with a line saying just "end".
21605 @kindex set python print-stack
21606 @item set python print-stack
21607 By default, @value{GDBN} will print only the message component of a
21608 Python exception when an error occurs in a Python script. This can be
21609 controlled using @code{set python print-stack}: if @code{full}, then
21610 full Python stack printing is enabled; if @code{none}, then Python stack
21611 and message printing is disabled; if @code{message}, the default, only
21612 the message component of the error is printed.
21615 It is also possible to execute a Python script from the @value{GDBN}
21619 @item source @file{script-name}
21620 The script name must end with @samp{.py} and @value{GDBN} must be configured
21621 to recognize the script language based on filename extension using
21622 the @code{script-extension} setting. @xref{Extending GDB, ,Extending GDB}.
21624 @item python execfile ("script-name")
21625 This method is based on the @code{execfile} Python built-in function,
21626 and thus is always available.
21630 @subsection Python API
21632 @cindex programming in python
21634 @cindex python stdout
21635 @cindex python pagination
21636 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
21637 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
21638 A Python program which outputs to one of these streams may have its
21639 output interrupted by the user (@pxref{Screen Size}). In this
21640 situation, a Python @code{KeyboardInterrupt} exception is thrown.
21643 * Basic Python:: Basic Python Functions.
21644 * Exception Handling:: How Python exceptions are translated.
21645 * Values From Inferior:: Python representation of values.
21646 * Types In Python:: Python representation of types.
21647 * Pretty Printing API:: Pretty-printing values.
21648 * Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
21649 * Writing a Pretty-Printer:: Writing a Pretty-Printer.
21650 * Inferiors In Python:: Python representation of inferiors (processes)
21651 * Events In Python:: Listening for events from @value{GDBN}.
21652 * Threads In Python:: Accessing inferior threads from Python.
21653 * Commands In Python:: Implementing new commands in Python.
21654 * Parameters In Python:: Adding new @value{GDBN} parameters.
21655 * Functions In Python:: Writing new convenience functions.
21656 * Progspaces In Python:: Program spaces.
21657 * Objfiles In Python:: Object files.
21658 * Frames In Python:: Accessing inferior stack frames from Python.
21659 * Blocks In Python:: Accessing frame blocks from Python.
21660 * Symbols In Python:: Python representation of symbols.
21661 * Symbol Tables In Python:: Python representation of symbol tables.
21662 * Lazy Strings In Python:: Python representation of lazy strings.
21663 * Breakpoints In Python:: Manipulating breakpoints using Python.
21664 * Finish Breakpoints in Python:: Setting Breakpoints on function return
21669 @subsubsection Basic Python
21671 @cindex python functions
21672 @cindex python module
21674 @value{GDBN} introduces a new Python module, named @code{gdb}. All
21675 methods and classes added by @value{GDBN} are placed in this module.
21676 @value{GDBN} automatically @code{import}s the @code{gdb} module for
21677 use in all scripts evaluated by the @code{python} command.
21679 @findex gdb.PYTHONDIR
21680 @defvar gdb.PYTHONDIR
21681 A string containing the python directory (@pxref{Python}).
21684 @findex gdb.execute
21685 @defun gdb.execute (command @r{[}, from_tty @r{[}, to_string@r{]]})
21686 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
21687 If a GDB exception happens while @var{command} runs, it is
21688 translated as described in @ref{Exception Handling,,Exception Handling}.
21690 @var{from_tty} specifies whether @value{GDBN} ought to consider this
21691 command as having originated from the user invoking it interactively.
21692 It must be a boolean value. If omitted, it defaults to @code{False}.
21694 By default, any output produced by @var{command} is sent to
21695 @value{GDBN}'s standard output. If the @var{to_string} parameter is
21696 @code{True}, then output will be collected by @code{gdb.execute} and
21697 returned as a string. The default is @code{False}, in which case the
21698 return value is @code{None}. If @var{to_string} is @code{True}, the
21699 @value{GDBN} virtual terminal will be temporarily set to unlimited width
21700 and height, and its pagination will be disabled; @pxref{Screen Size}.
21703 @findex gdb.breakpoints
21704 @defun gdb.breakpoints ()
21705 Return a sequence holding all of @value{GDBN}'s breakpoints.
21706 @xref{Breakpoints In Python}, for more information.
21709 @findex gdb.parameter
21710 @defun gdb.parameter (parameter)
21711 Return the value of a @value{GDBN} parameter. @var{parameter} is a
21712 string naming the parameter to look up; @var{parameter} may contain
21713 spaces if the parameter has a multi-part name. For example,
21714 @samp{print object} is a valid parameter name.
21716 If the named parameter does not exist, this function throws a
21717 @code{gdb.error} (@pxref{Exception Handling}). Otherwise, the
21718 parameter's value is converted to a Python value of the appropriate
21719 type, and returned.
21722 @findex gdb.history
21723 @defun gdb.history (number)
21724 Return a value from @value{GDBN}'s value history (@pxref{Value
21725 History}). @var{number} indicates which history element to return.
21726 If @var{number} is negative, then @value{GDBN} will take its absolute value
21727 and count backward from the last element (i.e., the most recent element) to
21728 find the value to return. If @var{number} is zero, then @value{GDBN} will
21729 return the most recent element. If the element specified by @var{number}
21730 doesn't exist in the value history, a @code{gdb.error} exception will be
21733 If no exception is raised, the return value is always an instance of
21734 @code{gdb.Value} (@pxref{Values From Inferior}).
21737 @findex gdb.parse_and_eval
21738 @defun gdb.parse_and_eval (expression)
21739 Parse @var{expression} as an expression in the current language,
21740 evaluate it, and return the result as a @code{gdb.Value}.
21741 @var{expression} must be a string.
21743 This function can be useful when implementing a new command
21744 (@pxref{Commands In Python}), as it provides a way to parse the
21745 command's argument as an expression. It is also useful simply to
21746 compute values, for example, it is the only way to get the value of a
21747 convenience variable (@pxref{Convenience Vars}) as a @code{gdb.Value}.
21750 @findex gdb.post_event
21751 @defun gdb.post_event (event)
21752 Put @var{event}, a callable object taking no arguments, into
21753 @value{GDBN}'s internal event queue. This callable will be invoked at
21754 some later point, during @value{GDBN}'s event processing. Events
21755 posted using @code{post_event} will be run in the order in which they
21756 were posted; however, there is no way to know when they will be
21757 processed relative to other events inside @value{GDBN}.
21759 @value{GDBN} is not thread-safe. If your Python program uses multiple
21760 threads, you must be careful to only call @value{GDBN}-specific
21761 functions in the main @value{GDBN} thread. @code{post_event} ensures
21765 (@value{GDBP}) python
21769 > def __init__(self, message):
21770 > self.message = message;
21771 > def __call__(self):
21772 > gdb.write(self.message)
21774 >class MyThread1 (threading.Thread):
21776 > gdb.post_event(Writer("Hello "))
21778 >class MyThread2 (threading.Thread):
21780 > gdb.post_event(Writer("World\n"))
21782 >MyThread1().start()
21783 >MyThread2().start()
21785 (@value{GDBP}) Hello World
21790 @defun gdb.write (string @r{[}, stream{]})
21791 Print a string to @value{GDBN}'s paginated output stream. The
21792 optional @var{stream} determines the stream to print to. The default
21793 stream is @value{GDBN}'s standard output stream. Possible stream
21800 @value{GDBN}'s standard output stream.
21805 @value{GDBN}'s standard error stream.
21810 @value{GDBN}'s log stream (@pxref{Logging Output}).
21813 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
21814 call this function and will automatically direct the output to the
21819 @defun gdb.flush ()
21820 Flush the buffer of a @value{GDBN} paginated stream so that the
21821 contents are displayed immediately. @value{GDBN} will flush the
21822 contents of a stream automatically when it encounters a newline in the
21823 buffer. The optional @var{stream} determines the stream to flush. The
21824 default stream is @value{GDBN}'s standard output stream. Possible
21831 @value{GDBN}'s standard output stream.
21836 @value{GDBN}'s standard error stream.
21841 @value{GDBN}'s log stream (@pxref{Logging Output}).
21845 Flushing @code{sys.stdout} or @code{sys.stderr} will automatically
21846 call this function for the relevant stream.
21849 @findex gdb.target_charset
21850 @defun gdb.target_charset ()
21851 Return the name of the current target character set (@pxref{Character
21852 Sets}). This differs from @code{gdb.parameter('target-charset')} in
21853 that @samp{auto} is never returned.
21856 @findex gdb.target_wide_charset
21857 @defun gdb.target_wide_charset ()
21858 Return the name of the current target wide character set
21859 (@pxref{Character Sets}). This differs from
21860 @code{gdb.parameter('target-wide-charset')} in that @samp{auto} is
21864 @findex gdb.solib_name
21865 @defun gdb.solib_name (address)
21866 Return the name of the shared library holding the given @var{address}
21867 as a string, or @code{None}.
21870 @findex gdb.decode_line
21871 @defun gdb.decode_line @r{[}expression@r{]}
21872 Return locations of the line specified by @var{expression}, or of the
21873 current line if no argument was given. This function returns a Python
21874 tuple containing two elements. The first element contains a string
21875 holding any unparsed section of @var{expression} (or @code{None} if
21876 the expression has been fully parsed). The second element contains
21877 either @code{None} or another tuple that contains all the locations
21878 that match the expression represented as @code{gdb.Symtab_and_line}
21879 objects (@pxref{Symbol Tables In Python}). If @var{expression} is
21880 provided, it is decoded the way that @value{GDBN}'s inbuilt
21881 @code{break} or @code{edit} commands do (@pxref{Specify Location}).
21884 @defun gdb.prompt_hook (current_prompt)
21885 @anchor{prompt_hook}
21887 If @var{prompt_hook} is callable, @value{GDBN} will call the method
21888 assigned to this operation before a prompt is displayed by
21891 The parameter @code{current_prompt} contains the current @value{GDBN}
21892 prompt. This method must return a Python string, or @code{None}. If
21893 a string is returned, the @value{GDBN} prompt will be set to that
21894 string. If @code{None} is returned, @value{GDBN} will continue to use
21895 the current prompt.
21897 Some prompts cannot be substituted in @value{GDBN}. Secondary prompts
21898 such as those used by readline for command input, and annotation
21899 related prompts are prohibited from being changed.
21902 @node Exception Handling
21903 @subsubsection Exception Handling
21904 @cindex python exceptions
21905 @cindex exceptions, python
21907 When executing the @code{python} command, Python exceptions
21908 uncaught within the Python code are translated to calls to
21909 @value{GDBN} error-reporting mechanism. If the command that called
21910 @code{python} does not handle the error, @value{GDBN} will
21911 terminate it and print an error message containing the Python
21912 exception name, the associated value, and the Python call stack
21913 backtrace at the point where the exception was raised. Example:
21916 (@value{GDBP}) python print foo
21917 Traceback (most recent call last):
21918 File "<string>", line 1, in <module>
21919 NameError: name 'foo' is not defined
21922 @value{GDBN} errors that happen in @value{GDBN} commands invoked by
21923 Python code are converted to Python exceptions. The type of the
21924 Python exception depends on the error.
21928 This is the base class for most exceptions generated by @value{GDBN}.
21929 It is derived from @code{RuntimeError}, for compatibility with earlier
21930 versions of @value{GDBN}.
21932 If an error occurring in @value{GDBN} does not fit into some more
21933 specific category, then the generated exception will have this type.
21935 @item gdb.MemoryError
21936 This is a subclass of @code{gdb.error} which is thrown when an
21937 operation tried to access invalid memory in the inferior.
21939 @item KeyboardInterrupt
21940 User interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
21941 prompt) is translated to a Python @code{KeyboardInterrupt} exception.
21944 In all cases, your exception handler will see the @value{GDBN} error
21945 message as its value and the Python call stack backtrace at the Python
21946 statement closest to where the @value{GDBN} error occured as the
21949 @findex gdb.GdbError
21950 When implementing @value{GDBN} commands in Python via @code{gdb.Command},
21951 it is useful to be able to throw an exception that doesn't cause a
21952 traceback to be printed. For example, the user may have invoked the
21953 command incorrectly. Use the @code{gdb.GdbError} exception
21954 to handle this case. Example:
21958 >class HelloWorld (gdb.Command):
21959 > """Greet the whole world."""
21960 > def __init__ (self):
21961 > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
21962 > def invoke (self, args, from_tty):
21963 > argv = gdb.string_to_argv (args)
21964 > if len (argv) != 0:
21965 > raise gdb.GdbError ("hello-world takes no arguments")
21966 > print "Hello, World!"
21969 (gdb) hello-world 42
21970 hello-world takes no arguments
21973 @node Values From Inferior
21974 @subsubsection Values From Inferior
21975 @cindex values from inferior, with Python
21976 @cindex python, working with values from inferior
21978 @cindex @code{gdb.Value}
21979 @value{GDBN} provides values it obtains from the inferior program in
21980 an object of type @code{gdb.Value}. @value{GDBN} uses this object
21981 for its internal bookkeeping of the inferior's values, and for
21982 fetching values when necessary.
21984 Inferior values that are simple scalars can be used directly in
21985 Python expressions that are valid for the value's data type. Here's
21986 an example for an integer or floating-point value @code{some_val}:
21993 As result of this, @code{bar} will also be a @code{gdb.Value} object
21994 whose values are of the same type as those of @code{some_val}.
21996 Inferior values that are structures or instances of some class can
21997 be accessed using the Python @dfn{dictionary syntax}. For example, if
21998 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
21999 can access its @code{foo} element with:
22002 bar = some_val['foo']
22005 Again, @code{bar} will also be a @code{gdb.Value} object.
22007 A @code{gdb.Value} that represents a function can be executed via
22008 inferior function call. Any arguments provided to the call must match
22009 the function's prototype, and must be provided in the order specified
22012 For example, @code{some_val} is a @code{gdb.Value} instance
22013 representing a function that takes two integers as arguments. To
22014 execute this function, call it like so:
22017 result = some_val (10,20)
22020 Any values returned from a function call will be stored as a
22023 The following attributes are provided:
22026 @defvar Value.address
22027 If this object is addressable, this read-only attribute holds a
22028 @code{gdb.Value} object representing the address. Otherwise,
22029 this attribute holds @code{None}.
22032 @cindex optimized out value in Python
22033 @defvar Value.is_optimized_out
22034 This read-only boolean attribute is true if the compiler optimized out
22035 this value, thus it is not available for fetching from the inferior.
22039 The type of this @code{gdb.Value}. The value of this attribute is a
22040 @code{gdb.Type} object (@pxref{Types In Python}).
22043 @defvar Value.dynamic_type
22044 The dynamic type of this @code{gdb.Value}. This uses C@t{++} run-time
22045 type information (@acronym{RTTI}) to determine the dynamic type of the
22046 value. If this value is of class type, it will return the class in
22047 which the value is embedded, if any. If this value is of pointer or
22048 reference to a class type, it will compute the dynamic type of the
22049 referenced object, and return a pointer or reference to that type,
22050 respectively. In all other cases, it will return the value's static
22053 Note that this feature will only work when debugging a C@t{++} program
22054 that includes @acronym{RTTI} for the object in question. Otherwise,
22055 it will just return the static type of the value as in @kbd{ptype foo}
22056 (@pxref{Symbols, ptype}).
22059 @defvar Value.is_lazy
22060 The value of this read-only boolean attribute is @code{True} if this
22061 @code{gdb.Value} has not yet been fetched from the inferior.
22062 @value{GDBN} does not fetch values until necessary, for efficiency.
22066 myval = gdb.parse_and_eval ('somevar')
22069 The value of @code{somevar} is not fetched at this time. It will be
22070 fetched when the value is needed, or when the @code{fetch_lazy}
22075 The following methods are provided:
22078 @defun Value.__init__ (@var{val})
22079 Many Python values can be converted directly to a @code{gdb.Value} via
22080 this object initializer. Specifically:
22083 @item Python boolean
22084 A Python boolean is converted to the boolean type from the current
22087 @item Python integer
22088 A Python integer is converted to the C @code{long} type for the
22089 current architecture.
22092 A Python long is converted to the C @code{long long} type for the
22093 current architecture.
22096 A Python float is converted to the C @code{double} type for the
22097 current architecture.
22099 @item Python string
22100 A Python string is converted to a target string, using the current
22103 @item @code{gdb.Value}
22104 If @code{val} is a @code{gdb.Value}, then a copy of the value is made.
22106 @item @code{gdb.LazyString}
22107 If @code{val} is a @code{gdb.LazyString} (@pxref{Lazy Strings In
22108 Python}), then the lazy string's @code{value} method is called, and
22109 its result is used.
22113 @defun Value.cast (type)
22114 Return a new instance of @code{gdb.Value} that is the result of
22115 casting this instance to the type described by @var{type}, which must
22116 be a @code{gdb.Type} object. If the cast cannot be performed for some
22117 reason, this method throws an exception.
22120 @defun Value.dereference ()
22121 For pointer data types, this method returns a new @code{gdb.Value} object
22122 whose contents is the object pointed to by the pointer. For example, if
22123 @code{foo} is a C pointer to an @code{int}, declared in your C program as
22130 then you can use the corresponding @code{gdb.Value} to access what
22131 @code{foo} points to like this:
22134 bar = foo.dereference ()
22137 The result @code{bar} will be a @code{gdb.Value} object holding the
22138 value pointed to by @code{foo}.
22141 @defun Value.dynamic_cast (type)
22142 Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
22143 operator were used. Consult a C@t{++} reference for details.
22146 @defun Value.reinterpret_cast (type)
22147 Like @code{Value.cast}, but works as if the C@t{++} @code{reinterpret_cast}
22148 operator were used. Consult a C@t{++} reference for details.
22151 @defun Value.string (@r{[}encoding@r{[}, errors@r{[}, length@r{]]]})
22152 If this @code{gdb.Value} represents a string, then this method
22153 converts the contents to a Python string. Otherwise, this method will
22154 throw an exception.
22156 Strings are recognized in a language-specific way; whether a given
22157 @code{gdb.Value} represents a string is determined by the current
22160 For C-like languages, a value is a string if it is a pointer to or an
22161 array of characters or ints. The string is assumed to be terminated
22162 by a zero of the appropriate width. However if the optional length
22163 argument is given, the string will be converted to that given length,
22164 ignoring any embedded zeros that the string may contain.
22166 If the optional @var{encoding} argument is given, it must be a string
22167 naming the encoding of the string in the @code{gdb.Value}, such as
22168 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
22169 the same encodings as the corresponding argument to Python's
22170 @code{string.decode} method, and the Python codec machinery will be used
22171 to convert the string. If @var{encoding} is not given, or if
22172 @var{encoding} is the empty string, then either the @code{target-charset}
22173 (@pxref{Character Sets}) will be used, or a language-specific encoding
22174 will be used, if the current language is able to supply one.
22176 The optional @var{errors} argument is the same as the corresponding
22177 argument to Python's @code{string.decode} method.
22179 If the optional @var{length} argument is given, the string will be
22180 fetched and converted to the given length.
22183 @defun Value.lazy_string (@r{[}encoding @r{[}, length@r{]]})
22184 If this @code{gdb.Value} represents a string, then this method
22185 converts the contents to a @code{gdb.LazyString} (@pxref{Lazy Strings
22186 In Python}). Otherwise, this method will throw an exception.
22188 If the optional @var{encoding} argument is given, it must be a string
22189 naming the encoding of the @code{gdb.LazyString}. Some examples are:
22190 @samp{ascii}, @samp{iso-8859-6} or @samp{utf-8}. If the
22191 @var{encoding} argument is an encoding that @value{GDBN} does
22192 recognize, @value{GDBN} will raise an error.
22194 When a lazy string is printed, the @value{GDBN} encoding machinery is
22195 used to convert the string during printing. If the optional
22196 @var{encoding} argument is not provided, or is an empty string,
22197 @value{GDBN} will automatically select the encoding most suitable for
22198 the string type. For further information on encoding in @value{GDBN}
22199 please see @ref{Character Sets}.
22201 If the optional @var{length} argument is given, the string will be
22202 fetched and encoded to the length of characters specified. If
22203 the @var{length} argument is not provided, the string will be fetched
22204 and encoded until a null of appropriate width is found.
22207 @defun Value.fetch_lazy ()
22208 If the @code{gdb.Value} object is currently a lazy value
22209 (@code{gdb.Value.is_lazy} is @code{True}), then the value is
22210 fetched from the inferior. Any errors that occur in the process
22211 will produce a Python exception.
22213 If the @code{gdb.Value} object is not a lazy value, this method
22216 This method does not return a value.
22221 @node Types In Python
22222 @subsubsection Types In Python
22223 @cindex types in Python
22224 @cindex Python, working with types
22227 @value{GDBN} represents types from the inferior using the class
22230 The following type-related functions are available in the @code{gdb}
22233 @findex gdb.lookup_type
22234 @defun gdb.lookup_type (name @r{[}, block@r{]})
22235 This function looks up a type by name. @var{name} is the name of the
22236 type to look up. It must be a string.
22238 If @var{block} is given, then @var{name} is looked up in that scope.
22239 Otherwise, it is searched for globally.
22241 Ordinarily, this function will return an instance of @code{gdb.Type}.
22242 If the named type cannot be found, it will throw an exception.
22245 If the type is a structure or class type, or an enum type, the fields
22246 of that type can be accessed using the Python @dfn{dictionary syntax}.
22247 For example, if @code{some_type} is a @code{gdb.Type} instance holding
22248 a structure type, you can access its @code{foo} field with:
22251 bar = some_type['foo']
22254 @code{bar} will be a @code{gdb.Field} object; see below under the
22255 description of the @code{Type.fields} method for a description of the
22256 @code{gdb.Field} class.
22258 An instance of @code{Type} has the following attributes:
22262 The type code for this type. The type code will be one of the
22263 @code{TYPE_CODE_} constants defined below.
22266 @defvar Type.sizeof
22267 The size of this type, in target @code{char} units. Usually, a
22268 target's @code{char} type will be an 8-bit byte. However, on some
22269 unusual platforms, this type may have a different size.
22273 The tag name for this type. The tag name is the name after
22274 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
22275 languages have this concept. If this type has no tag name, then
22276 @code{None} is returned.
22280 The following methods are provided:
22283 @defun Type.fields ()
22284 For structure and union types, this method returns the fields. Range
22285 types have two fields, the minimum and maximum values. Enum types
22286 have one field per enum constant. Function and method types have one
22287 field per parameter. The base types of C@t{++} classes are also
22288 represented as fields. If the type has no fields, or does not fit
22289 into one of these categories, an empty sequence will be returned.
22291 Each field is a @code{gdb.Field} object, with some pre-defined attributes:
22294 This attribute is not available for @code{static} fields (as in
22295 C@t{++} or Java). For non-@code{static} fields, the value is the bit
22296 position of the field. For @code{enum} fields, the value is the
22297 enumeration member's integer representation.
22300 The name of the field, or @code{None} for anonymous fields.
22303 This is @code{True} if the field is artificial, usually meaning that
22304 it was provided by the compiler and not the user. This attribute is
22305 always provided, and is @code{False} if the field is not artificial.
22307 @item is_base_class
22308 This is @code{True} if the field represents a base class of a C@t{++}
22309 structure. This attribute is always provided, and is @code{False}
22310 if the field is not a base class of the type that is the argument of
22311 @code{fields}, or if that type was not a C@t{++} class.
22314 If the field is packed, or is a bitfield, then this will have a
22315 non-zero value, which is the size of the field in bits. Otherwise,
22316 this will be zero; in this case the field's size is given by its type.
22319 The type of the field. This is usually an instance of @code{Type},
22320 but it can be @code{None} in some situations.
22324 @defun Type.array (@var{n1} @r{[}, @var{n2}@r{]})
22325 Return a new @code{gdb.Type} object which represents an array of this
22326 type. If one argument is given, it is the inclusive upper bound of
22327 the array; in this case the lower bound is zero. If two arguments are
22328 given, the first argument is the lower bound of the array, and the
22329 second argument is the upper bound of the array. An array's length
22330 must not be negative, but the bounds can be.
22333 @defun Type.const ()
22334 Return a new @code{gdb.Type} object which represents a
22335 @code{const}-qualified variant of this type.
22338 @defun Type.volatile ()
22339 Return a new @code{gdb.Type} object which represents a
22340 @code{volatile}-qualified variant of this type.
22343 @defun Type.unqualified ()
22344 Return a new @code{gdb.Type} object which represents an unqualified
22345 variant of this type. That is, the result is neither @code{const} nor
22349 @defun Type.range ()
22350 Return a Python @code{Tuple} object that contains two elements: the
22351 low bound of the argument type and the high bound of that type. If
22352 the type does not have a range, @value{GDBN} will raise a
22353 @code{gdb.error} exception (@pxref{Exception Handling}).
22356 @defun Type.reference ()
22357 Return a new @code{gdb.Type} object which represents a reference to this
22361 @defun Type.pointer ()
22362 Return a new @code{gdb.Type} object which represents a pointer to this
22366 @defun Type.strip_typedefs ()
22367 Return a new @code{gdb.Type} that represents the real type,
22368 after removing all layers of typedefs.
22371 @defun Type.target ()
22372 Return a new @code{gdb.Type} object which represents the target type
22375 For a pointer type, the target type is the type of the pointed-to
22376 object. For an array type (meaning C-like arrays), the target type is
22377 the type of the elements of the array. For a function or method type,
22378 the target type is the type of the return value. For a complex type,
22379 the target type is the type of the elements. For a typedef, the
22380 target type is the aliased type.
22382 If the type does not have a target, this method will throw an
22386 @defun Type.template_argument (n @r{[}, block@r{]})
22387 If this @code{gdb.Type} is an instantiation of a template, this will
22388 return a new @code{gdb.Type} which represents the type of the
22389 @var{n}th template argument.
22391 If this @code{gdb.Type} is not a template type, this will throw an
22392 exception. Ordinarily, only C@t{++} code will have template types.
22394 If @var{block} is given, then @var{name} is looked up in that scope.
22395 Otherwise, it is searched for globally.
22400 Each type has a code, which indicates what category this type falls
22401 into. The available type categories are represented by constants
22402 defined in the @code{gdb} module:
22405 @findex TYPE_CODE_PTR
22406 @findex gdb.TYPE_CODE_PTR
22407 @item gdb.TYPE_CODE_PTR
22408 The type is a pointer.
22410 @findex TYPE_CODE_ARRAY
22411 @findex gdb.TYPE_CODE_ARRAY
22412 @item gdb.TYPE_CODE_ARRAY
22413 The type is an array.
22415 @findex TYPE_CODE_STRUCT
22416 @findex gdb.TYPE_CODE_STRUCT
22417 @item gdb.TYPE_CODE_STRUCT
22418 The type is a structure.
22420 @findex TYPE_CODE_UNION
22421 @findex gdb.TYPE_CODE_UNION
22422 @item gdb.TYPE_CODE_UNION
22423 The type is a union.
22425 @findex TYPE_CODE_ENUM
22426 @findex gdb.TYPE_CODE_ENUM
22427 @item gdb.TYPE_CODE_ENUM
22428 The type is an enum.
22430 @findex TYPE_CODE_FLAGS
22431 @findex gdb.TYPE_CODE_FLAGS
22432 @item gdb.TYPE_CODE_FLAGS
22433 A bit flags type, used for things such as status registers.
22435 @findex TYPE_CODE_FUNC
22436 @findex gdb.TYPE_CODE_FUNC
22437 @item gdb.TYPE_CODE_FUNC
22438 The type is a function.
22440 @findex TYPE_CODE_INT
22441 @findex gdb.TYPE_CODE_INT
22442 @item gdb.TYPE_CODE_INT
22443 The type is an integer type.
22445 @findex TYPE_CODE_FLT
22446 @findex gdb.TYPE_CODE_FLT
22447 @item gdb.TYPE_CODE_FLT
22448 A floating point type.
22450 @findex TYPE_CODE_VOID
22451 @findex gdb.TYPE_CODE_VOID
22452 @item gdb.TYPE_CODE_VOID
22453 The special type @code{void}.
22455 @findex TYPE_CODE_SET
22456 @findex gdb.TYPE_CODE_SET
22457 @item gdb.TYPE_CODE_SET
22460 @findex TYPE_CODE_RANGE
22461 @findex gdb.TYPE_CODE_RANGE
22462 @item gdb.TYPE_CODE_RANGE
22463 A range type, that is, an integer type with bounds.
22465 @findex TYPE_CODE_STRING
22466 @findex gdb.TYPE_CODE_STRING
22467 @item gdb.TYPE_CODE_STRING
22468 A string type. Note that this is only used for certain languages with
22469 language-defined string types; C strings are not represented this way.
22471 @findex TYPE_CODE_BITSTRING
22472 @findex gdb.TYPE_CODE_BITSTRING
22473 @item gdb.TYPE_CODE_BITSTRING
22476 @findex TYPE_CODE_ERROR
22477 @findex gdb.TYPE_CODE_ERROR
22478 @item gdb.TYPE_CODE_ERROR
22479 An unknown or erroneous type.
22481 @findex TYPE_CODE_METHOD
22482 @findex gdb.TYPE_CODE_METHOD
22483 @item gdb.TYPE_CODE_METHOD
22484 A method type, as found in C@t{++} or Java.
22486 @findex TYPE_CODE_METHODPTR
22487 @findex gdb.TYPE_CODE_METHODPTR
22488 @item gdb.TYPE_CODE_METHODPTR
22489 A pointer-to-member-function.
22491 @findex TYPE_CODE_MEMBERPTR
22492 @findex gdb.TYPE_CODE_MEMBERPTR
22493 @item gdb.TYPE_CODE_MEMBERPTR
22494 A pointer-to-member.
22496 @findex TYPE_CODE_REF
22497 @findex gdb.TYPE_CODE_REF
22498 @item gdb.TYPE_CODE_REF
22501 @findex TYPE_CODE_CHAR
22502 @findex gdb.TYPE_CODE_CHAR
22503 @item gdb.TYPE_CODE_CHAR
22506 @findex TYPE_CODE_BOOL
22507 @findex gdb.TYPE_CODE_BOOL
22508 @item gdb.TYPE_CODE_BOOL
22511 @findex TYPE_CODE_COMPLEX
22512 @findex gdb.TYPE_CODE_COMPLEX
22513 @item gdb.TYPE_CODE_COMPLEX
22514 A complex float type.
22516 @findex TYPE_CODE_TYPEDEF
22517 @findex gdb.TYPE_CODE_TYPEDEF
22518 @item gdb.TYPE_CODE_TYPEDEF
22519 A typedef to some other type.
22521 @findex TYPE_CODE_NAMESPACE
22522 @findex gdb.TYPE_CODE_NAMESPACE
22523 @item gdb.TYPE_CODE_NAMESPACE
22524 A C@t{++} namespace.
22526 @findex TYPE_CODE_DECFLOAT
22527 @findex gdb.TYPE_CODE_DECFLOAT
22528 @item gdb.TYPE_CODE_DECFLOAT
22529 A decimal floating point type.
22531 @findex TYPE_CODE_INTERNAL_FUNCTION
22532 @findex gdb.TYPE_CODE_INTERNAL_FUNCTION
22533 @item gdb.TYPE_CODE_INTERNAL_FUNCTION
22534 A function internal to @value{GDBN}. This is the type used to represent
22535 convenience functions.
22538 Further support for types is provided in the @code{gdb.types}
22539 Python module (@pxref{gdb.types}).
22541 @node Pretty Printing API
22542 @subsubsection Pretty Printing API
22544 An example output is provided (@pxref{Pretty Printing}).
22546 A pretty-printer is just an object that holds a value and implements a
22547 specific interface, defined here.
22549 @defun pretty_printer.children (self)
22550 @value{GDBN} will call this method on a pretty-printer to compute the
22551 children of the pretty-printer's value.
22553 This method must return an object conforming to the Python iterator
22554 protocol. Each item returned by the iterator must be a tuple holding
22555 two elements. The first element is the ``name'' of the child; the
22556 second element is the child's value. The value can be any Python
22557 object which is convertible to a @value{GDBN} value.
22559 This method is optional. If it does not exist, @value{GDBN} will act
22560 as though the value has no children.
22563 @defun pretty_printer.display_hint (self)
22564 The CLI may call this method and use its result to change the
22565 formatting of a value. The result will also be supplied to an MI
22566 consumer as a @samp{displayhint} attribute of the variable being
22569 This method is optional. If it does exist, this method must return a
22572 Some display hints are predefined by @value{GDBN}:
22576 Indicate that the object being printed is ``array-like''. The CLI
22577 uses this to respect parameters such as @code{set print elements} and
22578 @code{set print array}.
22581 Indicate that the object being printed is ``map-like'', and that the
22582 children of this value can be assumed to alternate between keys and
22586 Indicate that the object being printed is ``string-like''. If the
22587 printer's @code{to_string} method returns a Python string of some
22588 kind, then @value{GDBN} will call its internal language-specific
22589 string-printing function to format the string. For the CLI this means
22590 adding quotation marks, possibly escaping some characters, respecting
22591 @code{set print elements}, and the like.
22595 @defun pretty_printer.to_string (self)
22596 @value{GDBN} will call this method to display the string
22597 representation of the value passed to the object's constructor.
22599 When printing from the CLI, if the @code{to_string} method exists,
22600 then @value{GDBN} will prepend its result to the values returned by
22601 @code{children}. Exactly how this formatting is done is dependent on
22602 the display hint, and may change as more hints are added. Also,
22603 depending on the print settings (@pxref{Print Settings}), the CLI may
22604 print just the result of @code{to_string} in a stack trace, omitting
22605 the result of @code{children}.
22607 If this method returns a string, it is printed verbatim.
22609 Otherwise, if this method returns an instance of @code{gdb.Value},
22610 then @value{GDBN} prints this value. This may result in a call to
22611 another pretty-printer.
22613 If instead the method returns a Python value which is convertible to a
22614 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
22615 the resulting value. Again, this may result in a call to another
22616 pretty-printer. Python scalars (integers, floats, and booleans) and
22617 strings are convertible to @code{gdb.Value}; other types are not.
22619 Finally, if this method returns @code{None} then no further operations
22620 are peformed in this method and nothing is printed.
22622 If the result is not one of these types, an exception is raised.
22625 @value{GDBN} provides a function which can be used to look up the
22626 default pretty-printer for a @code{gdb.Value}:
22628 @findex gdb.default_visualizer
22629 @defun gdb.default_visualizer (value)
22630 This function takes a @code{gdb.Value} object as an argument. If a
22631 pretty-printer for this value exists, then it is returned. If no such
22632 printer exists, then this returns @code{None}.
22635 @node Selecting Pretty-Printers
22636 @subsubsection Selecting Pretty-Printers
22638 The Python list @code{gdb.pretty_printers} contains an array of
22639 functions or callable objects that have been registered via addition
22640 as a pretty-printer. Printers in this list are called @code{global}
22641 printers, they're available when debugging all inferiors.
22642 Each @code{gdb.Progspace} contains a @code{pretty_printers} attribute.
22643 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
22646 Each function on these lists is passed a single @code{gdb.Value}
22647 argument and should return a pretty-printer object conforming to the
22648 interface definition above (@pxref{Pretty Printing API}). If a function
22649 cannot create a pretty-printer for the value, it should return
22652 @value{GDBN} first checks the @code{pretty_printers} attribute of each
22653 @code{gdb.Objfile} in the current program space and iteratively calls
22654 each enabled lookup routine in the list for that @code{gdb.Objfile}
22655 until it receives a pretty-printer object.
22656 If no pretty-printer is found in the objfile lists, @value{GDBN} then
22657 searches the pretty-printer list of the current program space,
22658 calling each enabled function until an object is returned.
22659 After these lists have been exhausted, it tries the global
22660 @code{gdb.pretty_printers} list, again calling each enabled function until an
22661 object is returned.
22663 The order in which the objfiles are searched is not specified. For a
22664 given list, functions are always invoked from the head of the list,
22665 and iterated over sequentially until the end of the list, or a printer
22666 object is returned.
22668 For various reasons a pretty-printer may not work.
22669 For example, the underlying data structure may have changed and
22670 the pretty-printer is out of date.
22672 The consequences of a broken pretty-printer are severe enough that
22673 @value{GDBN} provides support for enabling and disabling individual
22674 printers. For example, if @code{print frame-arguments} is on,
22675 a backtrace can become highly illegible if any argument is printed
22676 with a broken printer.
22678 Pretty-printers are enabled and disabled by attaching an @code{enabled}
22679 attribute to the registered function or callable object. If this attribute
22680 is present and its value is @code{False}, the printer is disabled, otherwise
22681 the printer is enabled.
22683 @node Writing a Pretty-Printer
22684 @subsubsection Writing a Pretty-Printer
22685 @cindex writing a pretty-printer
22687 A pretty-printer consists of two parts: a lookup function to detect
22688 if the type is supported, and the printer itself.
22690 Here is an example showing how a @code{std::string} printer might be
22691 written. @xref{Pretty Printing API}, for details on the API this class
22695 class StdStringPrinter(object):
22696 "Print a std::string"
22698 def __init__(self, val):
22701 def to_string(self):
22702 return self.val['_M_dataplus']['_M_p']
22704 def display_hint(self):
22708 And here is an example showing how a lookup function for the printer
22709 example above might be written.
22712 def str_lookup_function(val):
22713 lookup_tag = val.type.tag
22714 if lookup_tag == None:
22716 regex = re.compile("^std::basic_string<char,.*>$")
22717 if regex.match(lookup_tag):
22718 return StdStringPrinter(val)
22722 The example lookup function extracts the value's type, and attempts to
22723 match it to a type that it can pretty-print. If it is a type the
22724 printer can pretty-print, it will return a printer object. If not, it
22725 returns @code{None}.
22727 We recommend that you put your core pretty-printers into a Python
22728 package. If your pretty-printers are for use with a library, we
22729 further recommend embedding a version number into the package name.
22730 This practice will enable @value{GDBN} to load multiple versions of
22731 your pretty-printers at the same time, because they will have
22734 You should write auto-loaded code (@pxref{Auto-loading}) such that it
22735 can be evaluated multiple times without changing its meaning. An
22736 ideal auto-load file will consist solely of @code{import}s of your
22737 printer modules, followed by a call to a register pretty-printers with
22738 the current objfile.
22740 Taken as a whole, this approach will scale nicely to multiple
22741 inferiors, each potentially using a different library version.
22742 Embedding a version number in the Python package name will ensure that
22743 @value{GDBN} is able to load both sets of printers simultaneously.
22744 Then, because the search for pretty-printers is done by objfile, and
22745 because your auto-loaded code took care to register your library's
22746 printers with a specific objfile, @value{GDBN} will find the correct
22747 printers for the specific version of the library used by each
22750 To continue the @code{std::string} example (@pxref{Pretty Printing API}),
22751 this code might appear in @code{gdb.libstdcxx.v6}:
22754 def register_printers(objfile):
22755 objfile.pretty_printers.append(str_lookup_function)
22759 And then the corresponding contents of the auto-load file would be:
22762 import gdb.libstdcxx.v6
22763 gdb.libstdcxx.v6.register_printers(gdb.current_objfile())
22766 The previous example illustrates a basic pretty-printer.
22767 There are a few things that can be improved on.
22768 The printer doesn't have a name, making it hard to identify in a
22769 list of installed printers. The lookup function has a name, but
22770 lookup functions can have arbitrary, even identical, names.
22772 Second, the printer only handles one type, whereas a library typically has
22773 several types. One could install a lookup function for each desired type
22774 in the library, but one could also have a single lookup function recognize
22775 several types. The latter is the conventional way this is handled.
22776 If a pretty-printer can handle multiple data types, then its
22777 @dfn{subprinters} are the printers for the individual data types.
22779 The @code{gdb.printing} module provides a formal way of solving these
22780 problems (@pxref{gdb.printing}).
22781 Here is another example that handles multiple types.
22783 These are the types we are going to pretty-print:
22786 struct foo @{ int a, b; @};
22787 struct bar @{ struct foo x, y; @};
22790 Here are the printers:
22794 """Print a foo object."""
22796 def __init__(self, val):
22799 def to_string(self):
22800 return ("a=<" + str(self.val["a"]) +
22801 "> b=<" + str(self.val["b"]) + ">")
22804 """Print a bar object."""
22806 def __init__(self, val):
22809 def to_string(self):
22810 return ("x=<" + str(self.val["x"]) +
22811 "> y=<" + str(self.val["y"]) + ">")
22814 This example doesn't need a lookup function, that is handled by the
22815 @code{gdb.printing} module. Instead a function is provided to build up
22816 the object that handles the lookup.
22819 import gdb.printing
22821 def build_pretty_printer():
22822 pp = gdb.printing.RegexpCollectionPrettyPrinter(
22824 pp.add_printer('foo', '^foo$', fooPrinter)
22825 pp.add_printer('bar', '^bar$', barPrinter)
22829 And here is the autoload support:
22832 import gdb.printing
22834 gdb.printing.register_pretty_printer(
22835 gdb.current_objfile(),
22836 my_library.build_pretty_printer())
22839 Finally, when this printer is loaded into @value{GDBN}, here is the
22840 corresponding output of @samp{info pretty-printer}:
22843 (gdb) info pretty-printer
22850 @node Inferiors In Python
22851 @subsubsection Inferiors In Python
22852 @cindex inferiors in Python
22854 @findex gdb.Inferior
22855 Programs which are being run under @value{GDBN} are called inferiors
22856 (@pxref{Inferiors and Programs}). Python scripts can access
22857 information about and manipulate inferiors controlled by @value{GDBN}
22858 via objects of the @code{gdb.Inferior} class.
22860 The following inferior-related functions are available in the @code{gdb}
22863 @defun gdb.inferiors ()
22864 Return a tuple containing all inferior objects.
22867 @defun gdb.selected_inferior ()
22868 Return an object representing the current inferior.
22871 A @code{gdb.Inferior} object has the following attributes:
22874 @defvar Inferior.num
22875 ID of inferior, as assigned by GDB.
22878 @defvar Inferior.pid
22879 Process ID of the inferior, as assigned by the underlying operating
22883 @defvar Inferior.was_attached
22884 Boolean signaling whether the inferior was created using `attach', or
22885 started by @value{GDBN} itself.
22889 A @code{gdb.Inferior} object has the following methods:
22892 @defun Inferior.is_valid ()
22893 Returns @code{True} if the @code{gdb.Inferior} object is valid,
22894 @code{False} if not. A @code{gdb.Inferior} object will become invalid
22895 if the inferior no longer exists within @value{GDBN}. All other
22896 @code{gdb.Inferior} methods will throw an exception if it is invalid
22897 at the time the method is called.
22900 @defun Inferior.threads ()
22901 This method returns a tuple holding all the threads which are valid
22902 when it is called. If there are no valid threads, the method will
22903 return an empty tuple.
22906 @findex gdb.read_memory
22907 @defun Inferior.read_memory (address, length)
22908 Read @var{length} bytes of memory from the inferior, starting at
22909 @var{address}. Returns a buffer object, which behaves much like an array
22910 or a string. It can be modified and given to the @code{gdb.write_memory}
22914 @findex gdb.write_memory
22915 @defun Inferior.write_memory (address, buffer @r{[}, length@r{]})
22916 Write the contents of @var{buffer} to the inferior, starting at
22917 @var{address}. The @var{buffer} parameter must be a Python object
22918 which supports the buffer protocol, i.e., a string, an array or the
22919 object returned from @code{gdb.read_memory}. If given, @var{length}
22920 determines the number of bytes from @var{buffer} to be written.
22923 @findex gdb.search_memory
22924 @defun Inferior.search_memory (address, length, pattern)
22925 Search a region of the inferior memory starting at @var{address} with
22926 the given @var{length} using the search pattern supplied in
22927 @var{pattern}. The @var{pattern} parameter must be a Python object
22928 which supports the buffer protocol, i.e., a string, an array or the
22929 object returned from @code{gdb.read_memory}. Returns a Python @code{Long}
22930 containing the address where the pattern was found, or @code{None} if
22931 the pattern could not be found.
22935 @node Events In Python
22936 @subsubsection Events In Python
22937 @cindex inferior events in Python
22939 @value{GDBN} provides a general event facility so that Python code can be
22940 notified of various state changes, particularly changes that occur in
22943 An @dfn{event} is just an object that describes some state change. The
22944 type of the object and its attributes will vary depending on the details
22945 of the change. All the existing events are described below.
22947 In order to be notified of an event, you must register an event handler
22948 with an @dfn{event registry}. An event registry is an object in the
22949 @code{gdb.events} module which dispatches particular events. A registry
22950 provides methods to register and unregister event handlers:
22953 @defun EventRegistry.connect (object)
22954 Add the given callable @var{object} to the registry. This object will be
22955 called when an event corresponding to this registry occurs.
22958 @defun EventRegistry.disconnect (object)
22959 Remove the given @var{object} from the registry. Once removed, the object
22960 will no longer receive notifications of events.
22964 Here is an example:
22967 def exit_handler (event):
22968 print "event type: exit"
22969 print "exit code: %d" % (event.exit_code)
22971 gdb.events.exited.connect (exit_handler)
22974 In the above example we connect our handler @code{exit_handler} to the
22975 registry @code{events.exited}. Once connected, @code{exit_handler} gets
22976 called when the inferior exits. The argument @dfn{event} in this example is
22977 of type @code{gdb.ExitedEvent}. As you can see in the example the
22978 @code{ExitedEvent} object has an attribute which indicates the exit code of
22981 The following is a listing of the event registries that are available and
22982 details of the events they emit:
22987 Emits @code{gdb.ThreadEvent}.
22989 Some events can be thread specific when @value{GDBN} is running in non-stop
22990 mode. When represented in Python, these events all extend
22991 @code{gdb.ThreadEvent}. Note, this event is not emitted directly; instead,
22992 events which are emitted by this or other modules might extend this event.
22993 Examples of these events are @code{gdb.BreakpointEvent} and
22994 @code{gdb.ContinueEvent}.
22997 @defvar ThreadEvent.inferior_thread
22998 In non-stop mode this attribute will be set to the specific thread which was
22999 involved in the emitted event. Otherwise, it will be set to @code{None}.
23003 Emits @code{gdb.ContinueEvent} which extends @code{gdb.ThreadEvent}.
23005 This event indicates that the inferior has been continued after a stop. For
23006 inherited attribute refer to @code{gdb.ThreadEvent} above.
23008 @item events.exited
23009 Emits @code{events.ExitedEvent} which indicates that the inferior has exited.
23010 @code{events.ExitedEvent} has two attributes:
23012 @defvar ExitedEvent.exit_code
23013 An integer representing the exit code, if available, which the inferior
23014 has returned. (The exit code could be unavailable if, for example,
23015 @value{GDBN} detaches from the inferior.) If the exit code is unavailable,
23016 the attribute does not exist.
23018 @defvar ExitedEvent inferior
23019 A reference to the inferior which triggered the @code{exited} event.
23024 Emits @code{gdb.StopEvent} which extends @code{gdb.ThreadEvent}.
23026 Indicates that the inferior has stopped. All events emitted by this registry
23027 extend StopEvent. As a child of @code{gdb.ThreadEvent}, @code{gdb.StopEvent}
23028 will indicate the stopped thread when @value{GDBN} is running in non-stop
23029 mode. Refer to @code{gdb.ThreadEvent} above for more details.
23031 Emits @code{gdb.SignalEvent} which extends @code{gdb.StopEvent}.
23033 This event indicates that the inferior or one of its threads has received as
23034 signal. @code{gdb.SignalEvent} has the following attributes:
23037 @defvar SignalEvent.stop_signal
23038 A string representing the signal received by the inferior. A list of possible
23039 signal values can be obtained by running the command @code{info signals} in
23040 the @value{GDBN} command prompt.
23044 Also emits @code{gdb.BreakpointEvent} which extends @code{gdb.StopEvent}.
23046 @code{gdb.BreakpointEvent} event indicates that one or more breakpoints have
23047 been hit, and has the following attributes:
23050 @defvar BreakpointEvent.breakpoints
23051 A sequence containing references to all the breakpoints (type
23052 @code{gdb.Breakpoint}) that were hit.
23053 @xref{Breakpoints In Python}, for details of the @code{gdb.Breakpoint} object.
23055 @defvar BreakpointEvent.breakpoint
23056 A reference to the first breakpoint that was hit.
23057 This function is maintained for backward compatibility and is now deprecated
23058 in favor of the @code{gdb.BreakpointEvent.breakpoints} attribute.
23062 @item events.new_objfile
23063 Emits @code{gdb.NewObjFileEvent} which indicates that a new object file has
23064 been loaded by @value{GDBN}. @code{gdb.NewObjFileEvent} has one attribute:
23067 @defvar NewObjFileEvent.new_objfile
23068 A reference to the object file (@code{gdb.Objfile}) which has been loaded.
23069 @xref{Objfiles In Python}, for details of the @code{gdb.Objfile} object.
23075 @node Threads In Python
23076 @subsubsection Threads In Python
23077 @cindex threads in python
23079 @findex gdb.InferiorThread
23080 Python scripts can access information about, and manipulate inferior threads
23081 controlled by @value{GDBN}, via objects of the @code{gdb.InferiorThread} class.
23083 The following thread-related functions are available in the @code{gdb}
23086 @findex gdb.selected_thread
23087 @defun gdb.selected_thread ()
23088 This function returns the thread object for the selected thread. If there
23089 is no selected thread, this will return @code{None}.
23092 A @code{gdb.InferiorThread} object has the following attributes:
23095 @defvar InferiorThread.name
23096 The name of the thread. If the user specified a name using
23097 @code{thread name}, then this returns that name. Otherwise, if an
23098 OS-supplied name is available, then it is returned. Otherwise, this
23099 returns @code{None}.
23101 This attribute can be assigned to. The new value must be a string
23102 object, which sets the new name, or @code{None}, which removes any
23103 user-specified thread name.
23106 @defvar InferiorThread.num
23107 ID of the thread, as assigned by GDB.
23110 @defvar InferiorThread.ptid
23111 ID of the thread, as assigned by the operating system. This attribute is a
23112 tuple containing three integers. The first is the Process ID (PID); the second
23113 is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID).
23114 Either the LWPID or TID may be 0, which indicates that the operating system
23115 does not use that identifier.
23119 A @code{gdb.InferiorThread} object has the following methods:
23122 @defun InferiorThread.is_valid ()
23123 Returns @code{True} if the @code{gdb.InferiorThread} object is valid,
23124 @code{False} if not. A @code{gdb.InferiorThread} object will become
23125 invalid if the thread exits, or the inferior that the thread belongs
23126 is deleted. All other @code{gdb.InferiorThread} methods will throw an
23127 exception if it is invalid at the time the method is called.
23130 @defun InferiorThread.switch ()
23131 This changes @value{GDBN}'s currently selected thread to the one represented
23135 @defun InferiorThread.is_stopped ()
23136 Return a Boolean indicating whether the thread is stopped.
23139 @defun InferiorThread.is_running ()
23140 Return a Boolean indicating whether the thread is running.
23143 @defun InferiorThread.is_exited ()
23144 Return a Boolean indicating whether the thread is exited.
23148 @node Commands In Python
23149 @subsubsection Commands In Python
23151 @cindex commands in python
23152 @cindex python commands
23153 You can implement new @value{GDBN} CLI commands in Python. A CLI
23154 command is implemented using an instance of the @code{gdb.Command}
23155 class, most commonly using a subclass.
23157 @defun Command.__init__ (name, @var{command_class} @r{[}, @var{completer_class} @r{[}, @var{prefix}@r{]]})
23158 The object initializer for @code{Command} registers the new command
23159 with @value{GDBN}. This initializer is normally invoked from the
23160 subclass' own @code{__init__} method.
23162 @var{name} is the name of the command. If @var{name} consists of
23163 multiple words, then the initial words are looked for as prefix
23164 commands. In this case, if one of the prefix commands does not exist,
23165 an exception is raised.
23167 There is no support for multi-line commands.
23169 @var{command_class} should be one of the @samp{COMMAND_} constants
23170 defined below. This argument tells @value{GDBN} how to categorize the
23171 new command in the help system.
23173 @var{completer_class} is an optional argument. If given, it should be
23174 one of the @samp{COMPLETE_} constants defined below. This argument
23175 tells @value{GDBN} how to perform completion for this command. If not
23176 given, @value{GDBN} will attempt to complete using the object's
23177 @code{complete} method (see below); if no such method is found, an
23178 error will occur when completion is attempted.
23180 @var{prefix} is an optional argument. If @code{True}, then the new
23181 command is a prefix command; sub-commands of this command may be
23184 The help text for the new command is taken from the Python
23185 documentation string for the command's class, if there is one. If no
23186 documentation string is provided, the default value ``This command is
23187 not documented.'' is used.
23190 @cindex don't repeat Python command
23191 @defun Command.dont_repeat ()
23192 By default, a @value{GDBN} command is repeated when the user enters a
23193 blank line at the command prompt. A command can suppress this
23194 behavior by invoking the @code{dont_repeat} method. This is similar
23195 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
23198 @defun Command.invoke (argument, from_tty)
23199 This method is called by @value{GDBN} when this command is invoked.
23201 @var{argument} is a string. It is the argument to the command, after
23202 leading and trailing whitespace has been stripped.
23204 @var{from_tty} is a boolean argument. When true, this means that the
23205 command was entered by the user at the terminal; when false it means
23206 that the command came from elsewhere.
23208 If this method throws an exception, it is turned into a @value{GDBN}
23209 @code{error} call. Otherwise, the return value is ignored.
23211 @findex gdb.string_to_argv
23212 To break @var{argument} up into an argv-like string use
23213 @code{gdb.string_to_argv}. This function behaves identically to
23214 @value{GDBN}'s internal argument lexer @code{buildargv}.
23215 It is recommended to use this for consistency.
23216 Arguments are separated by spaces and may be quoted.
23220 print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
23221 ['1', '2 "3', '4 "5', "6 '7"]
23226 @cindex completion of Python commands
23227 @defun Command.complete (text, word)
23228 This method is called by @value{GDBN} when the user attempts
23229 completion on this command. All forms of completion are handled by
23230 this method, that is, the @key{TAB} and @key{M-?} key bindings
23231 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
23234 The arguments @var{text} and @var{word} are both strings. @var{text}
23235 holds the complete command line up to the cursor's location.
23236 @var{word} holds the last word of the command line; this is computed
23237 using a word-breaking heuristic.
23239 The @code{complete} method can return several values:
23242 If the return value is a sequence, the contents of the sequence are
23243 used as the completions. It is up to @code{complete} to ensure that the
23244 contents actually do complete the word. A zero-length sequence is
23245 allowed, it means that there were no completions available. Only
23246 string elements of the sequence are used; other elements in the
23247 sequence are ignored.
23250 If the return value is one of the @samp{COMPLETE_} constants defined
23251 below, then the corresponding @value{GDBN}-internal completion
23252 function is invoked, and its result is used.
23255 All other results are treated as though there were no available
23260 When a new command is registered, it must be declared as a member of
23261 some general class of commands. This is used to classify top-level
23262 commands in the on-line help system; note that prefix commands are not
23263 listed under their own category but rather that of their top-level
23264 command. The available classifications are represented by constants
23265 defined in the @code{gdb} module:
23268 @findex COMMAND_NONE
23269 @findex gdb.COMMAND_NONE
23270 @item gdb.COMMAND_NONE
23271 The command does not belong to any particular class. A command in
23272 this category will not be displayed in any of the help categories.
23274 @findex COMMAND_RUNNING
23275 @findex gdb.COMMAND_RUNNING
23276 @item gdb.COMMAND_RUNNING
23277 The command is related to running the inferior. For example,
23278 @code{start}, @code{step}, and @code{continue} are in this category.
23279 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
23280 commands in this category.
23282 @findex COMMAND_DATA
23283 @findex gdb.COMMAND_DATA
23284 @item gdb.COMMAND_DATA
23285 The command is related to data or variables. For example,
23286 @code{call}, @code{find}, and @code{print} are in this category. Type
23287 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
23290 @findex COMMAND_STACK
23291 @findex gdb.COMMAND_STACK
23292 @item gdb.COMMAND_STACK
23293 The command has to do with manipulation of the stack. For example,
23294 @code{backtrace}, @code{frame}, and @code{return} are in this
23295 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
23296 list of commands in this category.
23298 @findex COMMAND_FILES
23299 @findex gdb.COMMAND_FILES
23300 @item gdb.COMMAND_FILES
23301 This class is used for file-related commands. For example,
23302 @code{file}, @code{list} and @code{section} are in this category.
23303 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
23304 commands in this category.
23306 @findex COMMAND_SUPPORT
23307 @findex gdb.COMMAND_SUPPORT
23308 @item gdb.COMMAND_SUPPORT
23309 This should be used for ``support facilities'', generally meaning
23310 things that are useful to the user when interacting with @value{GDBN},
23311 but not related to the state of the inferior. For example,
23312 @code{help}, @code{make}, and @code{shell} are in this category. Type
23313 @kbd{help support} at the @value{GDBN} prompt to see a list of
23314 commands in this category.
23316 @findex COMMAND_STATUS
23317 @findex gdb.COMMAND_STATUS
23318 @item gdb.COMMAND_STATUS
23319 The command is an @samp{info}-related command, that is, related to the
23320 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
23321 and @code{show} are in this category. Type @kbd{help status} at the
23322 @value{GDBN} prompt to see a list of commands in this category.
23324 @findex COMMAND_BREAKPOINTS
23325 @findex gdb.COMMAND_BREAKPOINTS
23326 @item gdb.COMMAND_BREAKPOINTS
23327 The command has to do with breakpoints. For example, @code{break},
23328 @code{clear}, and @code{delete} are in this category. Type @kbd{help
23329 breakpoints} at the @value{GDBN} prompt to see a list of commands in
23332 @findex COMMAND_TRACEPOINTS
23333 @findex gdb.COMMAND_TRACEPOINTS
23334 @item gdb.COMMAND_TRACEPOINTS
23335 The command has to do with tracepoints. For example, @code{trace},
23336 @code{actions}, and @code{tfind} are in this category. Type
23337 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
23338 commands in this category.
23340 @findex COMMAND_USER
23341 @findex gdb.COMMAND_USER
23342 @item gdb.COMMAND_USER
23343 The command is a general purpose command for the user, and typically
23344 does not fit in one of the other categories.
23345 Type @kbd{help user-defined} at the @value{GDBN} prompt to see
23346 a list of commands in this category, as well as the list of gdb macros
23347 (@pxref{Sequences}).
23349 @findex COMMAND_OBSCURE
23350 @findex gdb.COMMAND_OBSCURE
23351 @item gdb.COMMAND_OBSCURE
23352 The command is only used in unusual circumstances, or is not of
23353 general interest to users. For example, @code{checkpoint},
23354 @code{fork}, and @code{stop} are in this category. Type @kbd{help
23355 obscure} at the @value{GDBN} prompt to see a list of commands in this
23358 @findex COMMAND_MAINTENANCE
23359 @findex gdb.COMMAND_MAINTENANCE
23360 @item gdb.COMMAND_MAINTENANCE
23361 The command is only useful to @value{GDBN} maintainers. The
23362 @code{maintenance} and @code{flushregs} commands are in this category.
23363 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
23364 commands in this category.
23367 A new command can use a predefined completion function, either by
23368 specifying it via an argument at initialization, or by returning it
23369 from the @code{complete} method. These predefined completion
23370 constants are all defined in the @code{gdb} module:
23373 @findex COMPLETE_NONE
23374 @findex gdb.COMPLETE_NONE
23375 @item gdb.COMPLETE_NONE
23376 This constant means that no completion should be done.
23378 @findex COMPLETE_FILENAME
23379 @findex gdb.COMPLETE_FILENAME
23380 @item gdb.COMPLETE_FILENAME
23381 This constant means that filename completion should be performed.
23383 @findex COMPLETE_LOCATION
23384 @findex gdb.COMPLETE_LOCATION
23385 @item gdb.COMPLETE_LOCATION
23386 This constant means that location completion should be done.
23387 @xref{Specify Location}.
23389 @findex COMPLETE_COMMAND
23390 @findex gdb.COMPLETE_COMMAND
23391 @item gdb.COMPLETE_COMMAND
23392 This constant means that completion should examine @value{GDBN}
23395 @findex COMPLETE_SYMBOL
23396 @findex gdb.COMPLETE_SYMBOL
23397 @item gdb.COMPLETE_SYMBOL
23398 This constant means that completion should be done using symbol names
23402 The following code snippet shows how a trivial CLI command can be
23403 implemented in Python:
23406 class HelloWorld (gdb.Command):
23407 """Greet the whole world."""
23409 def __init__ (self):
23410 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
23412 def invoke (self, arg, from_tty):
23413 print "Hello, World!"
23418 The last line instantiates the class, and is necessary to trigger the
23419 registration of the command with @value{GDBN}. Depending on how the
23420 Python code is read into @value{GDBN}, you may need to import the
23421 @code{gdb} module explicitly.
23423 @node Parameters In Python
23424 @subsubsection Parameters In Python
23426 @cindex parameters in python
23427 @cindex python parameters
23428 @tindex gdb.Parameter
23430 You can implement new @value{GDBN} parameters using Python. A new
23431 parameter is implemented as an instance of the @code{gdb.Parameter}
23434 Parameters are exposed to the user via the @code{set} and
23435 @code{show} commands. @xref{Help}.
23437 There are many parameters that already exist and can be set in
23438 @value{GDBN}. Two examples are: @code{set follow fork} and
23439 @code{set charset}. Setting these parameters influences certain
23440 behavior in @value{GDBN}. Similarly, you can define parameters that
23441 can be used to influence behavior in custom Python scripts and commands.
23443 @defun Parameter.__init__ (name, @var{command-class}, @var{parameter-class} @r{[}, @var{enum-sequence}@r{]})
23444 The object initializer for @code{Parameter} registers the new
23445 parameter with @value{GDBN}. This initializer is normally invoked
23446 from the subclass' own @code{__init__} method.
23448 @var{name} is the name of the new parameter. If @var{name} consists
23449 of multiple words, then the initial words are looked for as prefix
23450 parameters. An example of this can be illustrated with the
23451 @code{set print} set of parameters. If @var{name} is
23452 @code{print foo}, then @code{print} will be searched as the prefix
23453 parameter. In this case the parameter can subsequently be accessed in
23454 @value{GDBN} as @code{set print foo}.
23456 If @var{name} consists of multiple words, and no prefix parameter group
23457 can be found, an exception is raised.
23459 @var{command-class} should be one of the @samp{COMMAND_} constants
23460 (@pxref{Commands In Python}). This argument tells @value{GDBN} how to
23461 categorize the new parameter in the help system.
23463 @var{parameter-class} should be one of the @samp{PARAM_} constants
23464 defined below. This argument tells @value{GDBN} the type of the new
23465 parameter; this information is used for input validation and
23468 If @var{parameter-class} is @code{PARAM_ENUM}, then
23469 @var{enum-sequence} must be a sequence of strings. These strings
23470 represent the possible values for the parameter.
23472 If @var{parameter-class} is not @code{PARAM_ENUM}, then the presence
23473 of a fourth argument will cause an exception to be thrown.
23475 The help text for the new parameter is taken from the Python
23476 documentation string for the parameter's class, if there is one. If
23477 there is no documentation string, a default value is used.
23480 @defvar Parameter.set_doc
23481 If this attribute exists, and is a string, then its value is used as
23482 the help text for this parameter's @code{set} command. The value is
23483 examined when @code{Parameter.__init__} is invoked; subsequent changes
23487 @defvar Parameter.show_doc
23488 If this attribute exists, and is a string, then its value is used as
23489 the help text for this parameter's @code{show} command. The value is
23490 examined when @code{Parameter.__init__} is invoked; subsequent changes
23494 @defvar Parameter.value
23495 The @code{value} attribute holds the underlying value of the
23496 parameter. It can be read and assigned to just as any other
23497 attribute. @value{GDBN} does validation when assignments are made.
23500 There are two methods that should be implemented in any
23501 @code{Parameter} class. These are:
23503 @defun Parameter.get_set_string (self)
23504 @value{GDBN} will call this method when a @var{parameter}'s value has
23505 been changed via the @code{set} API (for example, @kbd{set foo off}).
23506 The @code{value} attribute has already been populated with the new
23507 value and may be used in output. This method must return a string.
23510 @defun Parameter.get_show_string (self, svalue)
23511 @value{GDBN} will call this method when a @var{parameter}'s
23512 @code{show} API has been invoked (for example, @kbd{show foo}). The
23513 argument @code{svalue} receives the string representation of the
23514 current value. This method must return a string.
23517 When a new parameter is defined, its type must be specified. The
23518 available types are represented by constants defined in the @code{gdb}
23522 @findex PARAM_BOOLEAN
23523 @findex gdb.PARAM_BOOLEAN
23524 @item gdb.PARAM_BOOLEAN
23525 The value is a plain boolean. The Python boolean values, @code{True}
23526 and @code{False} are the only valid values.
23528 @findex PARAM_AUTO_BOOLEAN
23529 @findex gdb.PARAM_AUTO_BOOLEAN
23530 @item gdb.PARAM_AUTO_BOOLEAN
23531 The value has three possible states: true, false, and @samp{auto}. In
23532 Python, true and false are represented using boolean constants, and
23533 @samp{auto} is represented using @code{None}.
23535 @findex PARAM_UINTEGER
23536 @findex gdb.PARAM_UINTEGER
23537 @item gdb.PARAM_UINTEGER
23538 The value is an unsigned integer. The value of 0 should be
23539 interpreted to mean ``unlimited''.
23541 @findex PARAM_INTEGER
23542 @findex gdb.PARAM_INTEGER
23543 @item gdb.PARAM_INTEGER
23544 The value is a signed integer. The value of 0 should be interpreted
23545 to mean ``unlimited''.
23547 @findex PARAM_STRING
23548 @findex gdb.PARAM_STRING
23549 @item gdb.PARAM_STRING
23550 The value is a string. When the user modifies the string, any escape
23551 sequences, such as @samp{\t}, @samp{\f}, and octal escapes, are
23552 translated into corresponding characters and encoded into the current
23555 @findex PARAM_STRING_NOESCAPE
23556 @findex gdb.PARAM_STRING_NOESCAPE
23557 @item gdb.PARAM_STRING_NOESCAPE
23558 The value is a string. When the user modifies the string, escapes are
23559 passed through untranslated.
23561 @findex PARAM_OPTIONAL_FILENAME
23562 @findex gdb.PARAM_OPTIONAL_FILENAME
23563 @item gdb.PARAM_OPTIONAL_FILENAME
23564 The value is a either a filename (a string), or @code{None}.
23566 @findex PARAM_FILENAME
23567 @findex gdb.PARAM_FILENAME
23568 @item gdb.PARAM_FILENAME
23569 The value is a filename. This is just like
23570 @code{PARAM_STRING_NOESCAPE}, but uses file names for completion.
23572 @findex PARAM_ZINTEGER
23573 @findex gdb.PARAM_ZINTEGER
23574 @item gdb.PARAM_ZINTEGER
23575 The value is an integer. This is like @code{PARAM_INTEGER}, except 0
23576 is interpreted as itself.
23579 @findex gdb.PARAM_ENUM
23580 @item gdb.PARAM_ENUM
23581 The value is a string, which must be one of a collection string
23582 constants provided when the parameter is created.
23585 @node Functions In Python
23586 @subsubsection Writing new convenience functions
23588 @cindex writing convenience functions
23589 @cindex convenience functions in python
23590 @cindex python convenience functions
23591 @tindex gdb.Function
23593 You can implement new convenience functions (@pxref{Convenience Vars})
23594 in Python. A convenience function is an instance of a subclass of the
23595 class @code{gdb.Function}.
23597 @defun Function.__init__ (name)
23598 The initializer for @code{Function} registers the new function with
23599 @value{GDBN}. The argument @var{name} is the name of the function,
23600 a string. The function will be visible to the user as a convenience
23601 variable of type @code{internal function}, whose name is the same as
23602 the given @var{name}.
23604 The documentation for the new function is taken from the documentation
23605 string for the new class.
23608 @defun Function.invoke (@var{*args})
23609 When a convenience function is evaluated, its arguments are converted
23610 to instances of @code{gdb.Value}, and then the function's
23611 @code{invoke} method is called. Note that @value{GDBN} does not
23612 predetermine the arity of convenience functions. Instead, all
23613 available arguments are passed to @code{invoke}, following the
23614 standard Python calling convention. In particular, a convenience
23615 function can have default values for parameters without ill effect.
23617 The return value of this method is used as its value in the enclosing
23618 expression. If an ordinary Python value is returned, it is converted
23619 to a @code{gdb.Value} following the usual rules.
23622 The following code snippet shows how a trivial convenience function can
23623 be implemented in Python:
23626 class Greet (gdb.Function):
23627 """Return string to greet someone.
23628 Takes a name as argument."""
23630 def __init__ (self):
23631 super (Greet, self).__init__ ("greet")
23633 def invoke (self, name):
23634 return "Hello, %s!" % name.string ()
23639 The last line instantiates the class, and is necessary to trigger the
23640 registration of the function with @value{GDBN}. Depending on how the
23641 Python code is read into @value{GDBN}, you may need to import the
23642 @code{gdb} module explicitly.
23644 @node Progspaces In Python
23645 @subsubsection Program Spaces In Python
23647 @cindex progspaces in python
23648 @tindex gdb.Progspace
23650 A program space, or @dfn{progspace}, represents a symbolic view
23651 of an address space.
23652 It consists of all of the objfiles of the program.
23653 @xref{Objfiles In Python}.
23654 @xref{Inferiors and Programs, program spaces}, for more details
23655 about program spaces.
23657 The following progspace-related functions are available in the
23660 @findex gdb.current_progspace
23661 @defun gdb.current_progspace ()
23662 This function returns the program space of the currently selected inferior.
23663 @xref{Inferiors and Programs}.
23666 @findex gdb.progspaces
23667 @defun gdb.progspaces ()
23668 Return a sequence of all the progspaces currently known to @value{GDBN}.
23671 Each progspace is represented by an instance of the @code{gdb.Progspace}
23674 @defvar Progspace.filename
23675 The file name of the progspace as a string.
23678 @defvar Progspace.pretty_printers
23679 The @code{pretty_printers} attribute is a list of functions. It is
23680 used to look up pretty-printers. A @code{Value} is passed to each
23681 function in order; if the function returns @code{None}, then the
23682 search continues. Otherwise, the return value should be an object
23683 which is used to format the value. @xref{Pretty Printing API}, for more
23687 @node Objfiles In Python
23688 @subsubsection Objfiles In Python
23690 @cindex objfiles in python
23691 @tindex gdb.Objfile
23693 @value{GDBN} loads symbols for an inferior from various
23694 symbol-containing files (@pxref{Files}). These include the primary
23695 executable file, any shared libraries used by the inferior, and any
23696 separate debug info files (@pxref{Separate Debug Files}).
23697 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
23699 The following objfile-related functions are available in the
23702 @findex gdb.current_objfile
23703 @defun gdb.current_objfile ()
23704 When auto-loading a Python script (@pxref{Auto-loading}), @value{GDBN}
23705 sets the ``current objfile'' to the corresponding objfile. This
23706 function returns the current objfile. If there is no current objfile,
23707 this function returns @code{None}.
23710 @findex gdb.objfiles
23711 @defun gdb.objfiles ()
23712 Return a sequence of all the objfiles current known to @value{GDBN}.
23713 @xref{Objfiles In Python}.
23716 Each objfile is represented by an instance of the @code{gdb.Objfile}
23719 @defvar Objfile.filename
23720 The file name of the objfile as a string.
23723 @defvar Objfile.pretty_printers
23724 The @code{pretty_printers} attribute is a list of functions. It is
23725 used to look up pretty-printers. A @code{Value} is passed to each
23726 function in order; if the function returns @code{None}, then the
23727 search continues. Otherwise, the return value should be an object
23728 which is used to format the value. @xref{Pretty Printing API}, for more
23732 A @code{gdb.Objfile} object has the following methods:
23734 @defun Objfile.is_valid ()
23735 Returns @code{True} if the @code{gdb.Objfile} object is valid,
23736 @code{False} if not. A @code{gdb.Objfile} object can become invalid
23737 if the object file it refers to is not loaded in @value{GDBN} any
23738 longer. All other @code{gdb.Objfile} methods will throw an exception
23739 if it is invalid at the time the method is called.
23742 @node Frames In Python
23743 @subsubsection Accessing inferior stack frames from Python.
23745 @cindex frames in python
23746 When the debugged program stops, @value{GDBN} is able to analyze its call
23747 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
23748 represents a frame in the stack. A @code{gdb.Frame} object is only valid
23749 while its corresponding frame exists in the inferior's stack. If you try
23750 to use an invalid frame object, @value{GDBN} will throw a @code{gdb.error}
23751 exception (@pxref{Exception Handling}).
23753 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
23757 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
23761 The following frame-related functions are available in the @code{gdb} module:
23763 @findex gdb.selected_frame
23764 @defun gdb.selected_frame ()
23765 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
23768 @findex gdb.newest_frame
23769 @defun gdb.newest_frame ()
23770 Return the newest frame object for the selected thread.
23773 @defun gdb.frame_stop_reason_string (reason)
23774 Return a string explaining the reason why @value{GDBN} stopped unwinding
23775 frames, as expressed by the given @var{reason} code (an integer, see the
23776 @code{unwind_stop_reason} method further down in this section).
23779 A @code{gdb.Frame} object has the following methods:
23782 @defun Frame.is_valid ()
23783 Returns true if the @code{gdb.Frame} object is valid, false if not.
23784 A frame object can become invalid if the frame it refers to doesn't
23785 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
23786 an exception if it is invalid at the time the method is called.
23789 @defun Frame.name ()
23790 Returns the function name of the frame, or @code{None} if it can't be
23794 @defun Frame.type ()
23795 Returns the type of the frame. The value can be one of:
23797 @item gdb.NORMAL_FRAME
23798 An ordinary stack frame.
23800 @item gdb.DUMMY_FRAME
23801 A fake stack frame that was created by @value{GDBN} when performing an
23802 inferior function call.
23804 @item gdb.INLINE_FRAME
23805 A frame representing an inlined function. The function was inlined
23806 into a @code{gdb.NORMAL_FRAME} that is older than this one.
23808 @item gdb.TAILCALL_FRAME
23809 A frame representing a tail call. @xref{Tail Call Frames}.
23811 @item gdb.SIGTRAMP_FRAME
23812 A signal trampoline frame. This is the frame created by the OS when
23813 it calls into a signal handler.
23815 @item gdb.ARCH_FRAME
23816 A fake stack frame representing a cross-architecture call.
23818 @item gdb.SENTINEL_FRAME
23819 This is like @code{gdb.NORMAL_FRAME}, but it is only used for the
23824 @defun Frame.unwind_stop_reason ()
23825 Return an integer representing the reason why it's not possible to find
23826 more frames toward the outermost frame. Use
23827 @code{gdb.frame_stop_reason_string} to convert the value returned by this
23828 function to a string. The value can be one of:
23831 @item gdb.FRAME_UNWIND_NO_REASON
23832 No particular reason (older frames should be available).
23834 @item gdb.FRAME_UNWIND_NULL_ID
23835 The previous frame's analyzer returns an invalid result.
23837 @item gdb.FRAME_UNWIND_OUTERMOST
23838 This frame is the outermost.
23840 @item gdb.FRAME_UNWIND_UNAVAILABLE
23841 Cannot unwind further, because that would require knowing the
23842 values of registers or memory that have not been collected.
23844 @item gdb.FRAME_UNWIND_INNER_ID
23845 This frame ID looks like it ought to belong to a NEXT frame,
23846 but we got it for a PREV frame. Normally, this is a sign of
23847 unwinder failure. It could also indicate stack corruption.
23849 @item gdb.FRAME_UNWIND_SAME_ID
23850 This frame has the same ID as the previous one. That means
23851 that unwinding further would almost certainly give us another
23852 frame with exactly the same ID, so break the chain. Normally,
23853 this is a sign of unwinder failure. It could also indicate
23856 @item gdb.FRAME_UNWIND_NO_SAVED_PC
23857 The frame unwinder did not find any saved PC, but we needed
23858 one to unwind further.
23860 @item gdb.FRAME_UNWIND_FIRST_ERROR
23861 Any stop reason greater or equal to this value indicates some kind
23862 of error. This special value facilitates writing code that tests
23863 for errors in unwinding in a way that will work correctly even if
23864 the list of the other values is modified in future @value{GDBN}
23865 versions. Using it, you could write:
23867 reason = gdb.selected_frame().unwind_stop_reason ()
23868 reason_str = gdb.frame_stop_reason_string (reason)
23869 if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
23870 print "An error occured: %s" % reason_str
23877 Returns the frame's resume address.
23880 @defun Frame.block ()
23881 Return the frame's code block. @xref{Blocks In Python}.
23884 @defun Frame.function ()
23885 Return the symbol for the function corresponding to this frame.
23886 @xref{Symbols In Python}.
23889 @defun Frame.older ()
23890 Return the frame that called this frame.
23893 @defun Frame.newer ()
23894 Return the frame called by this frame.
23897 @defun Frame.find_sal ()
23898 Return the frame's symtab and line object.
23899 @xref{Symbol Tables In Python}.
23902 @defun Frame.read_var (variable @r{[}, block@r{]})
23903 Return the value of @var{variable} in this frame. If the optional
23904 argument @var{block} is provided, search for the variable from that
23905 block; otherwise start at the frame's current block (which is
23906 determined by the frame's current program counter). @var{variable}
23907 must be a string or a @code{gdb.Symbol} object. @var{block} must be a
23908 @code{gdb.Block} object.
23911 @defun Frame.select ()
23912 Set this frame to be the selected frame. @xref{Stack, ,Examining the
23917 @node Blocks In Python
23918 @subsubsection Accessing frame blocks from Python.
23920 @cindex blocks in python
23923 Within each frame, @value{GDBN} maintains information on each block
23924 stored in that frame. These blocks are organized hierarchically, and
23925 are represented individually in Python as a @code{gdb.Block}.
23926 Please see @ref{Frames In Python}, for a more in-depth discussion on
23927 frames. Furthermore, see @ref{Stack, ,Examining the Stack}, for more
23928 detailed technical information on @value{GDBN}'s book-keeping of the
23931 A @code{gdb.Block} is iterable. The iterator returns the symbols
23932 (@pxref{Symbols In Python}) local to the block.
23934 The following block-related functions are available in the @code{gdb}
23937 @findex gdb.block_for_pc
23938 @defun gdb.block_for_pc (pc)
23939 Return the @code{gdb.Block} containing the given @var{pc} value. If the
23940 block cannot be found for the @var{pc} value specified, the function
23941 will return @code{None}.
23944 A @code{gdb.Block} object has the following methods:
23947 @defun Block.is_valid ()
23948 Returns @code{True} if the @code{gdb.Block} object is valid,
23949 @code{False} if not. A block object can become invalid if the block it
23950 refers to doesn't exist anymore in the inferior. All other
23951 @code{gdb.Block} methods will throw an exception if it is invalid at
23952 the time the method is called. The block's validity is also checked
23953 during iteration over symbols of the block.
23957 A @code{gdb.Block} object has the following attributes:
23960 @defvar Block.start
23961 The start address of the block. This attribute is not writable.
23965 The end address of the block. This attribute is not writable.
23968 @defvar Block.function
23969 The name of the block represented as a @code{gdb.Symbol}. If the
23970 block is not named, then this attribute holds @code{None}. This
23971 attribute is not writable.
23974 @defvar Block.superblock
23975 The block containing this block. If this parent block does not exist,
23976 this attribute holds @code{None}. This attribute is not writable.
23979 @defvar Block.global_block
23980 The global block associated with this block. This attribute is not
23984 @defvar Block.static_block
23985 The static block associated with this block. This attribute is not
23989 @defvar Block.is_global
23990 @code{True} if the @code{gdb.Block} object is a global block,
23991 @code{False} if not. This attribute is not
23995 @defvar Block.is_static
23996 @code{True} if the @code{gdb.Block} object is a static block,
23997 @code{False} if not. This attribute is not writable.
24001 @node Symbols In Python
24002 @subsubsection Python representation of Symbols.
24004 @cindex symbols in python
24007 @value{GDBN} represents every variable, function and type as an
24008 entry in a symbol table. @xref{Symbols, ,Examining the Symbol Table}.
24009 Similarly, Python represents these symbols in @value{GDBN} with the
24010 @code{gdb.Symbol} object.
24012 The following symbol-related functions are available in the @code{gdb}
24015 @findex gdb.lookup_symbol
24016 @defun gdb.lookup_symbol (name @r{[}, block @r{[}, domain@r{]]})
24017 This function searches for a symbol by name. The search scope can be
24018 restricted to the parameters defined in the optional domain and block
24021 @var{name} is the name of the symbol. It must be a string. The
24022 optional @var{block} argument restricts the search to symbols visible
24023 in that @var{block}. The @var{block} argument must be a
24024 @code{gdb.Block} object. If omitted, the block for the current frame
24025 is used. The optional @var{domain} argument restricts
24026 the search to the domain type. The @var{domain} argument must be a
24027 domain constant defined in the @code{gdb} module and described later
24030 The result is a tuple of two elements.
24031 The first element is a @code{gdb.Symbol} object or @code{None} if the symbol
24033 If the symbol is found, the second element is @code{True} if the symbol
24034 is a field of a method's object (e.g., @code{this} in C@t{++}),
24035 otherwise it is @code{False}.
24036 If the symbol is not found, the second element is @code{False}.
24039 @findex gdb.lookup_global_symbol
24040 @defun gdb.lookup_global_symbol (name @r{[}, domain@r{]})
24041 This function searches for a global symbol by name.
24042 The search scope can be restricted to by the domain argument.
24044 @var{name} is the name of the symbol. It must be a string.
24045 The optional @var{domain} argument restricts the search to the domain type.
24046 The @var{domain} argument must be a domain constant defined in the @code{gdb}
24047 module and described later in this chapter.
24049 The result is a @code{gdb.Symbol} object or @code{None} if the symbol
24053 A @code{gdb.Symbol} object has the following attributes:
24056 @defvar Symbol.type
24057 The type of the symbol or @code{None} if no type is recorded.
24058 This attribute is represented as a @code{gdb.Type} object.
24059 @xref{Types In Python}. This attribute is not writable.
24062 @defvar Symbol.symtab
24063 The symbol table in which the symbol appears. This attribute is
24064 represented as a @code{gdb.Symtab} object. @xref{Symbol Tables In
24065 Python}. This attribute is not writable.
24068 @defvar Symbol.line
24069 The line number in the source code at which the symbol was defined.
24070 This is an integer.
24073 @defvar Symbol.name
24074 The name of the symbol as a string. This attribute is not writable.
24077 @defvar Symbol.linkage_name
24078 The name of the symbol, as used by the linker (i.e., may be mangled).
24079 This attribute is not writable.
24082 @defvar Symbol.print_name
24083 The name of the symbol in a form suitable for output. This is either
24084 @code{name} or @code{linkage_name}, depending on whether the user
24085 asked @value{GDBN} to display demangled or mangled names.
24088 @defvar Symbol.addr_class
24089 The address class of the symbol. This classifies how to find the value
24090 of a symbol. Each address class is a constant defined in the
24091 @code{gdb} module and described later in this chapter.
24094 @defvar Symbol.needs_frame
24095 This is @code{True} if evaluating this symbol's value requires a frame
24096 (@pxref{Frames In Python}) and @code{False} otherwise. Typically,
24097 local variables will require a frame, but other symbols will not.
24100 @defvar Symbol.is_argument
24101 @code{True} if the symbol is an argument of a function.
24104 @defvar Symbol.is_constant
24105 @code{True} if the symbol is a constant.
24108 @defvar Symbol.is_function
24109 @code{True} if the symbol is a function or a method.
24112 @defvar Symbol.is_variable
24113 @code{True} if the symbol is a variable.
24117 A @code{gdb.Symbol} object has the following methods:
24120 @defun Symbol.is_valid ()
24121 Returns @code{True} if the @code{gdb.Symbol} object is valid,
24122 @code{False} if not. A @code{gdb.Symbol} object can become invalid if
24123 the symbol it refers to does not exist in @value{GDBN} any longer.
24124 All other @code{gdb.Symbol} methods will throw an exception if it is
24125 invalid at the time the method is called.
24128 @defun Symbol.value (@r{[}frame@r{]})
24129 Compute the value of the symbol, as a @code{gdb.Value}. For
24130 functions, this computes the address of the function, cast to the
24131 appropriate type. If the symbol requires a frame in order to compute
24132 its value, then @var{frame} must be given. If @var{frame} is not
24133 given, or if @var{frame} is invalid, then this method will throw an
24138 The available domain categories in @code{gdb.Symbol} are represented
24139 as constants in the @code{gdb} module:
24142 @findex SYMBOL_UNDEF_DOMAIN
24143 @findex gdb.SYMBOL_UNDEF_DOMAIN
24144 @item gdb.SYMBOL_UNDEF_DOMAIN
24145 This is used when a domain has not been discovered or none of the
24146 following domains apply. This usually indicates an error either
24147 in the symbol information or in @value{GDBN}'s handling of symbols.
24148 @findex SYMBOL_VAR_DOMAIN
24149 @findex gdb.SYMBOL_VAR_DOMAIN
24150 @item gdb.SYMBOL_VAR_DOMAIN
24151 This domain contains variables, function names, typedef names and enum
24153 @findex SYMBOL_STRUCT_DOMAIN
24154 @findex gdb.SYMBOL_STRUCT_DOMAIN
24155 @item gdb.SYMBOL_STRUCT_DOMAIN
24156 This domain holds struct, union and enum type names.
24157 @findex SYMBOL_LABEL_DOMAIN
24158 @findex gdb.SYMBOL_LABEL_DOMAIN
24159 @item gdb.SYMBOL_LABEL_DOMAIN
24160 This domain contains names of labels (for gotos).
24161 @findex SYMBOL_VARIABLES_DOMAIN
24162 @findex gdb.SYMBOL_VARIABLES_DOMAIN
24163 @item gdb.SYMBOL_VARIABLES_DOMAIN
24164 This domain holds a subset of the @code{SYMBOLS_VAR_DOMAIN}; it
24165 contains everything minus functions and types.
24166 @findex SYMBOL_FUNCTIONS_DOMAIN
24167 @findex gdb.SYMBOL_FUNCTIONS_DOMAIN
24168 @item gdb.SYMBOL_FUNCTION_DOMAIN
24169 This domain contains all functions.
24170 @findex SYMBOL_TYPES_DOMAIN
24171 @findex gdb.SYMBOL_TYPES_DOMAIN
24172 @item gdb.SYMBOL_TYPES_DOMAIN
24173 This domain contains all types.
24176 The available address class categories in @code{gdb.Symbol} are represented
24177 as constants in the @code{gdb} module:
24180 @findex SYMBOL_LOC_UNDEF
24181 @findex gdb.SYMBOL_LOC_UNDEF
24182 @item gdb.SYMBOL_LOC_UNDEF
24183 If this is returned by address class, it indicates an error either in
24184 the symbol information or in @value{GDBN}'s handling of symbols.
24185 @findex SYMBOL_LOC_CONST
24186 @findex gdb.SYMBOL_LOC_CONST
24187 @item gdb.SYMBOL_LOC_CONST
24188 Value is constant int.
24189 @findex SYMBOL_LOC_STATIC
24190 @findex gdb.SYMBOL_LOC_STATIC
24191 @item gdb.SYMBOL_LOC_STATIC
24192 Value is at a fixed address.
24193 @findex SYMBOL_LOC_REGISTER
24194 @findex gdb.SYMBOL_LOC_REGISTER
24195 @item gdb.SYMBOL_LOC_REGISTER
24196 Value is in a register.
24197 @findex SYMBOL_LOC_ARG
24198 @findex gdb.SYMBOL_LOC_ARG
24199 @item gdb.SYMBOL_LOC_ARG
24200 Value is an argument. This value is at the offset stored within the
24201 symbol inside the frame's argument list.
24202 @findex SYMBOL_LOC_REF_ARG
24203 @findex gdb.SYMBOL_LOC_REF_ARG
24204 @item gdb.SYMBOL_LOC_REF_ARG
24205 Value address is stored in the frame's argument list. Just like
24206 @code{LOC_ARG} except that the value's address is stored at the
24207 offset, not the value itself.
24208 @findex SYMBOL_LOC_REGPARM_ADDR
24209 @findex gdb.SYMBOL_LOC_REGPARM_ADDR
24210 @item gdb.SYMBOL_LOC_REGPARM_ADDR
24211 Value is a specified register. Just like @code{LOC_REGISTER} except
24212 the register holds the address of the argument instead of the argument
24214 @findex SYMBOL_LOC_LOCAL
24215 @findex gdb.SYMBOL_LOC_LOCAL
24216 @item gdb.SYMBOL_LOC_LOCAL
24217 Value is a local variable.
24218 @findex SYMBOL_LOC_TYPEDEF
24219 @findex gdb.SYMBOL_LOC_TYPEDEF
24220 @item gdb.SYMBOL_LOC_TYPEDEF
24221 Value not used. Symbols in the domain @code{SYMBOL_STRUCT_DOMAIN} all
24223 @findex SYMBOL_LOC_BLOCK
24224 @findex gdb.SYMBOL_LOC_BLOCK
24225 @item gdb.SYMBOL_LOC_BLOCK
24227 @findex SYMBOL_LOC_CONST_BYTES
24228 @findex gdb.SYMBOL_LOC_CONST_BYTES
24229 @item gdb.SYMBOL_LOC_CONST_BYTES
24230 Value is a byte-sequence.
24231 @findex SYMBOL_LOC_UNRESOLVED
24232 @findex gdb.SYMBOL_LOC_UNRESOLVED
24233 @item gdb.SYMBOL_LOC_UNRESOLVED
24234 Value is at a fixed address, but the address of the variable has to be
24235 determined from the minimal symbol table whenever the variable is
24237 @findex SYMBOL_LOC_OPTIMIZED_OUT
24238 @findex gdb.SYMBOL_LOC_OPTIMIZED_OUT
24239 @item gdb.SYMBOL_LOC_OPTIMIZED_OUT
24240 The value does not actually exist in the program.
24241 @findex SYMBOL_LOC_COMPUTED
24242 @findex gdb.SYMBOL_LOC_COMPUTED
24243 @item gdb.SYMBOL_LOC_COMPUTED
24244 The value's address is a computed location.
24247 @node Symbol Tables In Python
24248 @subsubsection Symbol table representation in Python.
24250 @cindex symbol tables in python
24252 @tindex gdb.Symtab_and_line
24254 Access to symbol table data maintained by @value{GDBN} on the inferior
24255 is exposed to Python via two objects: @code{gdb.Symtab_and_line} and
24256 @code{gdb.Symtab}. Symbol table and line data for a frame is returned
24257 from the @code{find_sal} method in @code{gdb.Frame} object.
24258 @xref{Frames In Python}.
24260 For more information on @value{GDBN}'s symbol table management, see
24261 @ref{Symbols, ,Examining the Symbol Table}, for more information.
24263 A @code{gdb.Symtab_and_line} object has the following attributes:
24266 @defvar Symtab_and_line.symtab
24267 The symbol table object (@code{gdb.Symtab}) for this frame.
24268 This attribute is not writable.
24271 @defvar Symtab_and_line.pc
24272 Indicates the current program counter address. This attribute is not
24276 @defvar Symtab_and_line.line
24277 Indicates the current line number for this object. This
24278 attribute is not writable.
24282 A @code{gdb.Symtab_and_line} object has the following methods:
24285 @defun Symtab_and_line.is_valid ()
24286 Returns @code{True} if the @code{gdb.Symtab_and_line} object is valid,
24287 @code{False} if not. A @code{gdb.Symtab_and_line} object can become
24288 invalid if the Symbol table and line object it refers to does not
24289 exist in @value{GDBN} any longer. All other
24290 @code{gdb.Symtab_and_line} methods will throw an exception if it is
24291 invalid at the time the method is called.
24295 A @code{gdb.Symtab} object has the following attributes:
24298 @defvar Symtab.filename
24299 The symbol table's source filename. This attribute is not writable.
24302 @defvar Symtab.objfile
24303 The symbol table's backing object file. @xref{Objfiles In Python}.
24304 This attribute is not writable.
24308 A @code{gdb.Symtab} object has the following methods:
24311 @defun Symtab.is_valid ()
24312 Returns @code{True} if the @code{gdb.Symtab} object is valid,
24313 @code{False} if not. A @code{gdb.Symtab} object can become invalid if
24314 the symbol table it refers to does not exist in @value{GDBN} any
24315 longer. All other @code{gdb.Symtab} methods will throw an exception
24316 if it is invalid at the time the method is called.
24319 @defun Symtab.fullname ()
24320 Return the symbol table's source absolute file name.
24324 @node Breakpoints In Python
24325 @subsubsection Manipulating breakpoints using Python
24327 @cindex breakpoints in python
24328 @tindex gdb.Breakpoint
24330 Python code can manipulate breakpoints via the @code{gdb.Breakpoint}
24333 @defun Breakpoint.__init__ (spec @r{[}, type @r{[}, wp_class @r{[},internal@r{]]]})
24334 Create a new breakpoint. @var{spec} is a string naming the
24335 location of the breakpoint, or an expression that defines a
24336 watchpoint. The contents can be any location recognized by the
24337 @code{break} command, or in the case of a watchpoint, by the @code{watch}
24338 command. The optional @var{type} denotes the breakpoint to create
24339 from the types defined later in this chapter. This argument can be
24340 either: @code{gdb.BP_BREAKPOINT} or @code{gdb.BP_WATCHPOINT}. @var{type}
24341 defaults to @code{gdb.BP_BREAKPOINT}. The optional @var{internal} argument
24342 allows the breakpoint to become invisible to the user. The breakpoint
24343 will neither be reported when created, nor will it be listed in the
24344 output from @code{info breakpoints} (but will be listed with the
24345 @code{maint info breakpoints} command). The optional @var{wp_class}
24346 argument defines the class of watchpoint to create, if @var{type} is
24347 @code{gdb.BP_WATCHPOINT}. If a watchpoint class is not provided, it is
24348 assumed to be a @code{gdb.WP_WRITE} class.
24351 @defun Breakpoint.stop (self)
24352 The @code{gdb.Breakpoint} class can be sub-classed and, in
24353 particular, you may choose to implement the @code{stop} method.
24354 If this method is defined as a sub-class of @code{gdb.Breakpoint},
24355 it will be called when the inferior reaches any location of a
24356 breakpoint which instantiates that sub-class. If the method returns
24357 @code{True}, the inferior will be stopped at the location of the
24358 breakpoint, otherwise the inferior will continue.
24360 If there are multiple breakpoints at the same location with a
24361 @code{stop} method, each one will be called regardless of the
24362 return status of the previous. This ensures that all @code{stop}
24363 methods have a chance to execute at that location. In this scenario
24364 if one of the methods returns @code{True} but the others return
24365 @code{False}, the inferior will still be stopped.
24367 You should not alter the execution state of the inferior (i.e.@:, step,
24368 next, etc.), alter the current frame context (i.e.@:, change the current
24369 active frame), or alter, add or delete any breakpoint. As a general
24370 rule, you should not alter any data within @value{GDBN} or the inferior
24373 Example @code{stop} implementation:
24376 class MyBreakpoint (gdb.Breakpoint):
24378 inf_val = gdb.parse_and_eval("foo")
24385 The available watchpoint types represented by constants are defined in the
24390 @findex gdb.WP_READ
24392 Read only watchpoint.
24395 @findex gdb.WP_WRITE
24397 Write only watchpoint.
24400 @findex gdb.WP_ACCESS
24401 @item gdb.WP_ACCESS
24402 Read/Write watchpoint.
24405 @defun Breakpoint.is_valid ()
24406 Return @code{True} if this @code{Breakpoint} object is valid,
24407 @code{False} otherwise. A @code{Breakpoint} object can become invalid
24408 if the user deletes the breakpoint. In this case, the object still
24409 exists, but the underlying breakpoint does not. In the cases of
24410 watchpoint scope, the watchpoint remains valid even if execution of the
24411 inferior leaves the scope of that watchpoint.
24414 @defun Breakpoint.delete
24415 Permanently deletes the @value{GDBN} breakpoint. This also
24416 invalidates the Python @code{Breakpoint} object. Any further access
24417 to this object's attributes or methods will raise an error.
24420 @defvar Breakpoint.enabled
24421 This attribute is @code{True} if the breakpoint is enabled, and
24422 @code{False} otherwise. This attribute is writable.
24425 @defvar Breakpoint.silent
24426 This attribute is @code{True} if the breakpoint is silent, and
24427 @code{False} otherwise. This attribute is writable.
24429 Note that a breakpoint can also be silent if it has commands and the
24430 first command is @code{silent}. This is not reported by the
24431 @code{silent} attribute.
24434 @defvar Breakpoint.thread
24435 If the breakpoint is thread-specific, this attribute holds the thread
24436 id. If the breakpoint is not thread-specific, this attribute is
24437 @code{None}. This attribute is writable.
24440 @defvar Breakpoint.task
24441 If the breakpoint is Ada task-specific, this attribute holds the Ada task
24442 id. If the breakpoint is not task-specific (or the underlying
24443 language is not Ada), this attribute is @code{None}. This attribute
24447 @defvar Breakpoint.ignore_count
24448 This attribute holds the ignore count for the breakpoint, an integer.
24449 This attribute is writable.
24452 @defvar Breakpoint.number
24453 This attribute holds the breakpoint's number --- the identifier used by
24454 the user to manipulate the breakpoint. This attribute is not writable.
24457 @defvar Breakpoint.type
24458 This attribute holds the breakpoint's type --- the identifier used to
24459 determine the actual breakpoint type or use-case. This attribute is not
24463 @defvar Breakpoint.visible
24464 This attribute tells whether the breakpoint is visible to the user
24465 when set, or when the @samp{info breakpoints} command is run. This
24466 attribute is not writable.
24469 The available types are represented by constants defined in the @code{gdb}
24473 @findex BP_BREAKPOINT
24474 @findex gdb.BP_BREAKPOINT
24475 @item gdb.BP_BREAKPOINT
24476 Normal code breakpoint.
24478 @findex BP_WATCHPOINT
24479 @findex gdb.BP_WATCHPOINT
24480 @item gdb.BP_WATCHPOINT
24481 Watchpoint breakpoint.
24483 @findex BP_HARDWARE_WATCHPOINT
24484 @findex gdb.BP_HARDWARE_WATCHPOINT
24485 @item gdb.BP_HARDWARE_WATCHPOINT
24486 Hardware assisted watchpoint.
24488 @findex BP_READ_WATCHPOINT
24489 @findex gdb.BP_READ_WATCHPOINT
24490 @item gdb.BP_READ_WATCHPOINT
24491 Hardware assisted read watchpoint.
24493 @findex BP_ACCESS_WATCHPOINT
24494 @findex gdb.BP_ACCESS_WATCHPOINT
24495 @item gdb.BP_ACCESS_WATCHPOINT
24496 Hardware assisted access watchpoint.
24499 @defvar Breakpoint.hit_count
24500 This attribute holds the hit count for the breakpoint, an integer.
24501 This attribute is writable, but currently it can only be set to zero.
24504 @defvar Breakpoint.location
24505 This attribute holds the location of the breakpoint, as specified by
24506 the user. It is a string. If the breakpoint does not have a location
24507 (that is, it is a watchpoint) the attribute's value is @code{None}. This
24508 attribute is not writable.
24511 @defvar Breakpoint.expression
24512 This attribute holds a breakpoint expression, as specified by
24513 the user. It is a string. If the breakpoint does not have an
24514 expression (the breakpoint is not a watchpoint) the attribute's value
24515 is @code{None}. This attribute is not writable.
24518 @defvar Breakpoint.condition
24519 This attribute holds the condition of the breakpoint, as specified by
24520 the user. It is a string. If there is no condition, this attribute's
24521 value is @code{None}. This attribute is writable.
24524 @defvar Breakpoint.commands
24525 This attribute holds the commands attached to the breakpoint. If
24526 there are commands, this attribute's value is a string holding all the
24527 commands, separated by newlines. If there are no commands, this
24528 attribute is @code{None}. This attribute is not writable.
24531 @node Finish Breakpoints in Python
24532 @subsubsection Finish Breakpoints
24534 @cindex python finish breakpoints
24535 @tindex gdb.FinishBreakpoint
24537 A finish breakpoint is a temporary breakpoint set at the return address of
24538 a frame, based on the @code{finish} command. @code{gdb.FinishBreakpoint}
24539 extends @code{gdb.Breakpoint}. The underlying breakpoint will be disabled
24540 and deleted when the execution will run out of the breakpoint scope (i.e.@:
24541 @code{Breakpoint.stop} or @code{FinishBreakpoint.out_of_scope} triggered).
24542 Finish breakpoints are thread specific and must be create with the right
24545 @defun FinishBreakpoint.__init__ (@r{[}frame@r{]} @r{[}, internal@r{]})
24546 Create a finish breakpoint at the return address of the @code{gdb.Frame}
24547 object @var{frame}. If @var{frame} is not provided, this defaults to the
24548 newest frame. The optional @var{internal} argument allows the breakpoint to
24549 become invisible to the user. @xref{Breakpoints In Python}, for further
24550 details about this argument.
24553 @defun FinishBreakpoint.out_of_scope (self)
24554 In some circumstances (e.g.@: @code{longjmp}, C@t{++} exceptions, @value{GDBN}
24555 @code{return} command, @dots{}), a function may not properly terminate, and
24556 thus never hit the finish breakpoint. When @value{GDBN} notices such a
24557 situation, the @code{out_of_scope} callback will be triggered.
24559 You may want to sub-class @code{gdb.FinishBreakpoint} and override this
24563 class MyFinishBreakpoint (gdb.FinishBreakpoint)
24565 print "normal finish"
24568 def out_of_scope ():
24569 print "abnormal finish"
24573 @defvar FinishBreakpoint.return_value
24574 When @value{GDBN} is stopped at a finish breakpoint and the frame
24575 used to build the @code{gdb.FinishBreakpoint} object had debug symbols, this
24576 attribute will contain a @code{gdb.Value} object corresponding to the return
24577 value of the function. The value will be @code{None} if the function return
24578 type is @code{void} or if the return value was not computable. This attribute
24582 @node Lazy Strings In Python
24583 @subsubsection Python representation of lazy strings.
24585 @cindex lazy strings in python
24586 @tindex gdb.LazyString
24588 A @dfn{lazy string} is a string whose contents is not retrieved or
24589 encoded until it is needed.
24591 A @code{gdb.LazyString} is represented in @value{GDBN} as an
24592 @code{address} that points to a region of memory, an @code{encoding}
24593 that will be used to encode that region of memory, and a @code{length}
24594 to delimit the region of memory that represents the string. The
24595 difference between a @code{gdb.LazyString} and a string wrapped within
24596 a @code{gdb.Value} is that a @code{gdb.LazyString} will be treated
24597 differently by @value{GDBN} when printing. A @code{gdb.LazyString} is
24598 retrieved and encoded during printing, while a @code{gdb.Value}
24599 wrapping a string is immediately retrieved and encoded on creation.
24601 A @code{gdb.LazyString} object has the following functions:
24603 @defun LazyString.value ()
24604 Convert the @code{gdb.LazyString} to a @code{gdb.Value}. This value
24605 will point to the string in memory, but will lose all the delayed
24606 retrieval, encoding and handling that @value{GDBN} applies to a
24607 @code{gdb.LazyString}.
24610 @defvar LazyString.address
24611 This attribute holds the address of the string. This attribute is not
24615 @defvar LazyString.length
24616 This attribute holds the length of the string in characters. If the
24617 length is -1, then the string will be fetched and encoded up to the
24618 first null of appropriate width. This attribute is not writable.
24621 @defvar LazyString.encoding
24622 This attribute holds the encoding that will be applied to the string
24623 when the string is printed by @value{GDBN}. If the encoding is not
24624 set, or contains an empty string, then @value{GDBN} will select the
24625 most appropriate encoding when the string is printed. This attribute
24629 @defvar LazyString.type
24630 This attribute holds the type that is represented by the lazy string's
24631 type. For a lazy string this will always be a pointer type. To
24632 resolve this to the lazy string's character type, use the type's
24633 @code{target} method. @xref{Types In Python}. This attribute is not
24638 @subsection Auto-loading
24639 @cindex auto-loading, Python
24641 When a new object file is read (for example, due to the @code{file}
24642 command, or because the inferior has loaded a shared library),
24643 @value{GDBN} will look for Python support scripts in several ways:
24644 @file{@var{objfile}-gdb.py} and @code{.debug_gdb_scripts} section.
24647 * objfile-gdb.py file:: The @file{@var{objfile}-gdb.py} file
24648 * .debug_gdb_scripts section:: The @code{.debug_gdb_scripts} section
24649 * Which flavor to choose?::
24652 The auto-loading feature is useful for supplying application-specific
24653 debugging commands and scripts.
24655 Auto-loading can be enabled or disabled,
24656 and the list of auto-loaded scripts can be printed.
24659 @kindex set auto-load-scripts
24660 @item set auto-load-scripts [yes|no]
24661 Enable or disable the auto-loading of Python scripts.
24663 @kindex show auto-load-scripts
24664 @item show auto-load-scripts
24665 Show whether auto-loading of Python scripts is enabled or disabled.
24667 @kindex info auto-load-scripts
24668 @cindex print list of auto-loaded scripts
24669 @item info auto-load-scripts [@var{regexp}]
24670 Print the list of all scripts that @value{GDBN} auto-loaded.
24672 Also printed is the list of scripts that were mentioned in
24673 the @code{.debug_gdb_scripts} section and were not found
24674 (@pxref{.debug_gdb_scripts section}).
24675 This is useful because their names are not printed when @value{GDBN}
24676 tries to load them and fails. There may be many of them, and printing
24677 an error message for each one is problematic.
24679 If @var{regexp} is supplied only scripts with matching names are printed.
24684 (gdb) info auto-load-scripts
24686 Yes py-section-script.py
24687 full name: /tmp/py-section-script.py
24688 Missing my-foo-pretty-printers.py
24692 When reading an auto-loaded file, @value{GDBN} sets the
24693 @dfn{current objfile}. This is available via the @code{gdb.current_objfile}
24694 function (@pxref{Objfiles In Python}). This can be useful for
24695 registering objfile-specific pretty-printers.
24697 @node objfile-gdb.py file
24698 @subsubsection The @file{@var{objfile}-gdb.py} file
24699 @cindex @file{@var{objfile}-gdb.py}
24701 When a new object file is read, @value{GDBN} looks for
24702 a file named @file{@var{objfile}-gdb.py},
24703 where @var{objfile} is the object file's real name, formed by ensuring
24704 that the file name is absolute, following all symlinks, and resolving
24705 @code{.} and @code{..} components. If this file exists and is
24706 readable, @value{GDBN} will evaluate it as a Python script.
24708 If this file does not exist, and if the parameter
24709 @code{debug-file-directory} is set (@pxref{Separate Debug Files}),
24710 then @value{GDBN} will look for @var{real-name} in all of the
24711 directories mentioned in the value of @code{debug-file-directory}.
24713 Finally, if this file does not exist, then @value{GDBN} will look for
24714 a file named @file{@var{data-directory}/auto-load/@var{real-name}}, where
24715 @var{data-directory} is @value{GDBN}'s data directory (available via
24716 @code{show data-directory}, @pxref{Data Files}), and @var{real-name}
24717 is the object file's real name, as described above.
24719 @value{GDBN} does not track which files it has already auto-loaded this way.
24720 @value{GDBN} will load the associated script every time the corresponding
24721 @var{objfile} is opened.
24722 So your @file{-gdb.py} file should be careful to avoid errors if it
24723 is evaluated more than once.
24725 @node .debug_gdb_scripts section
24726 @subsubsection The @code{.debug_gdb_scripts} section
24727 @cindex @code{.debug_gdb_scripts} section
24729 For systems using file formats like ELF and COFF,
24730 when @value{GDBN} loads a new object file
24731 it will look for a special section named @samp{.debug_gdb_scripts}.
24732 If this section exists, its contents is a list of names of scripts to load.
24734 @value{GDBN} will look for each specified script file first in the
24735 current directory and then along the source search path
24736 (@pxref{Source Path, ,Specifying Source Directories}),
24737 except that @file{$cdir} is not searched, since the compilation
24738 directory is not relevant to scripts.
24740 Entries can be placed in section @code{.debug_gdb_scripts} with,
24741 for example, this GCC macro:
24744 /* Note: The "MS" section flags are to remove duplicates. */
24745 #define DEFINE_GDB_SCRIPT(script_name) \
24747 .pushsection \".debug_gdb_scripts\", \"MS\",@@progbits,1\n\
24749 .asciz \"" script_name "\"\n\
24755 Then one can reference the macro in a header or source file like this:
24758 DEFINE_GDB_SCRIPT ("my-app-scripts.py")
24761 The script name may include directories if desired.
24763 If the macro is put in a header, any application or library
24764 using this header will get a reference to the specified script.
24766 @node Which flavor to choose?
24767 @subsubsection Which flavor to choose?
24769 Given the multiple ways of auto-loading Python scripts, it might not always
24770 be clear which one to choose. This section provides some guidance.
24772 Benefits of the @file{-gdb.py} way:
24776 Can be used with file formats that don't support multiple sections.
24779 Ease of finding scripts for public libraries.
24781 Scripts specified in the @code{.debug_gdb_scripts} section are searched for
24782 in the source search path.
24783 For publicly installed libraries, e.g., @file{libstdc++}, there typically
24784 isn't a source directory in which to find the script.
24787 Doesn't require source code additions.
24790 Benefits of the @code{.debug_gdb_scripts} way:
24794 Works with static linking.
24796 Scripts for libraries done the @file{-gdb.py} way require an objfile to
24797 trigger their loading. When an application is statically linked the only
24798 objfile available is the executable, and it is cumbersome to attach all the
24799 scripts from all the input libraries to the executable's @file{-gdb.py} script.
24802 Works with classes that are entirely inlined.
24804 Some classes can be entirely inlined, and thus there may not be an associated
24805 shared library to attach a @file{-gdb.py} script to.
24808 Scripts needn't be copied out of the source tree.
24810 In some circumstances, apps can be built out of large collections of internal
24811 libraries, and the build infrastructure necessary to install the
24812 @file{-gdb.py} scripts in a place where @value{GDBN} can find them is
24813 cumbersome. It may be easier to specify the scripts in the
24814 @code{.debug_gdb_scripts} section as relative paths, and add a path to the
24815 top of the source tree to the source search path.
24818 @node Python modules
24819 @subsection Python modules
24820 @cindex python modules
24822 @value{GDBN} comes with several modules to assist writing Python code.
24825 * gdb.printing:: Building and registering pretty-printers.
24826 * gdb.types:: Utilities for working with types.
24827 * gdb.prompt:: Utilities for prompt value substitution.
24831 @subsubsection gdb.printing
24832 @cindex gdb.printing
24834 This module provides a collection of utilities for working with
24838 @item PrettyPrinter (@var{name}, @var{subprinters}=None)
24839 This class specifies the API that makes @samp{info pretty-printer},
24840 @samp{enable pretty-printer} and @samp{disable pretty-printer} work.
24841 Pretty-printers should generally inherit from this class.
24843 @item SubPrettyPrinter (@var{name})
24844 For printers that handle multiple types, this class specifies the
24845 corresponding API for the subprinters.
24847 @item RegexpCollectionPrettyPrinter (@var{name})
24848 Utility class for handling multiple printers, all recognized via
24849 regular expressions.
24850 @xref{Writing a Pretty-Printer}, for an example.
24852 @item FlagEnumerationPrinter (@var{name})
24853 A pretty-printer which handles printing of @code{enum} values. Unlike
24854 @value{GDBN}'s built-in @code{enum} printing, this printer attempts to
24855 work properly when there is some overlap between the enumeration
24856 constants. @var{name} is the name of the printer and also the name of
24857 the @code{enum} type to look up.
24859 @item register_pretty_printer (@var{obj}, @var{printer}, @var{replace}=False)
24860 Register @var{printer} with the pretty-printer list of @var{obj}.
24861 If @var{replace} is @code{True} then any existing copy of the printer
24862 is replaced. Otherwise a @code{RuntimeError} exception is raised
24863 if a printer with the same name already exists.
24867 @subsubsection gdb.types
24870 This module provides a collection of utilities for working with
24871 @code{gdb.Types} objects.
24874 @item get_basic_type (@var{type})
24875 Return @var{type} with const and volatile qualifiers stripped,
24876 and with typedefs and C@t{++} references converted to the underlying type.
24881 typedef const int const_int;
24883 const_int& foo_ref (foo);
24884 int main () @{ return 0; @}
24891 (gdb) python import gdb.types
24892 (gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
24893 (gdb) python print gdb.types.get_basic_type(foo_ref.type)
24897 @item has_field (@var{type}, @var{field})
24898 Return @code{True} if @var{type}, assumed to be a type with fields
24899 (e.g., a structure or union), has field @var{field}.
24901 @item make_enum_dict (@var{enum_type})
24902 Return a Python @code{dictionary} type produced from @var{enum_type}.
24904 @item deep_items (@var{type})
24905 Returns a Python iterator similar to the standard
24906 @code{gdb.Type.iteritems} method, except that the iterator returned
24907 by @code{deep_items} will recursively traverse anonymous struct or
24908 union fields. For example:
24922 Then in @value{GDBN}:
24924 (@value{GDBP}) python import gdb.types
24925 (@value{GDBP}) python struct_a = gdb.lookup_type("struct A")
24926 (@value{GDBP}) python print struct_a.keys ()
24928 (@value{GDBP}) python print [k for k,v in gdb.types.deep_items(struct_a)]
24929 @{['a', 'b0', 'b1']@}
24935 @subsubsection gdb.prompt
24938 This module provides a method for prompt value-substitution.
24941 @item substitute_prompt (@var{string})
24942 Return @var{string} with escape sequences substituted by values. Some
24943 escape sequences take arguments. You can specify arguments inside
24944 ``@{@}'' immediately following the escape sequence.
24946 The escape sequences you can pass to this function are:
24950 Substitute a backslash.
24952 Substitute an ESC character.
24954 Substitute the selected frame; an argument names a frame parameter.
24956 Substitute a newline.
24958 Substitute a parameter's value; the argument names the parameter.
24960 Substitute a carriage return.
24962 Substitute the selected thread; an argument names a thread parameter.
24964 Substitute the version of GDB.
24966 Substitute the current working directory.
24968 Begin a sequence of non-printing characters. These sequences are
24969 typically used with the ESC character, and are not counted in the string
24970 length. Example: ``\[\e[0;34m\](gdb)\[\e[0m\]'' will return a
24971 blue-colored ``(gdb)'' prompt where the length is five.
24973 End a sequence of non-printing characters.
24979 substitute_prompt (``frame: \f,
24980 print arguments: \p@{print frame-arguments@}'')
24983 @exdent will return the string:
24986 "frame: main, print arguments: scalars"
24991 @section Creating new spellings of existing commands
24992 @cindex aliases for commands
24994 It is often useful to define alternate spellings of existing commands.
24995 For example, if a new @value{GDBN} command defined in Python has
24996 a long name to type, it is handy to have an abbreviated version of it
24997 that involves less typing.
24999 @value{GDBN} itself uses aliases. For example @samp{s} is an alias
25000 of the @samp{step} command even though it is otherwise an ambiguous
25001 abbreviation of other commands like @samp{set} and @samp{show}.
25003 Aliases are also used to provide shortened or more common versions
25004 of multi-word commands. For example, @value{GDBN} provides the
25005 @samp{tty} alias of the @samp{set inferior-tty} command.
25007 You can define a new alias with the @samp{alias} command.
25012 @item alias [-a] [--] @var{ALIAS} = @var{COMMAND}
25016 @var{ALIAS} specifies the name of the new alias.
25017 Each word of @var{ALIAS} must consist of letters, numbers, dashes and
25020 @var{COMMAND} specifies the name of an existing command
25021 that is being aliased.
25023 The @samp{-a} option specifies that the new alias is an abbreviation
25024 of the command. Abbreviations are not shown in command
25025 lists displayed by the @samp{help} command.
25027 The @samp{--} option specifies the end of options,
25028 and is useful when @var{ALIAS} begins with a dash.
25030 Here is a simple example showing how to make an abbreviation
25031 of a command so that there is less to type.
25032 Suppose you were tired of typing @samp{disas}, the current
25033 shortest unambiguous abbreviation of the @samp{disassemble} command
25034 and you wanted an even shorter version named @samp{di}.
25035 The following will accomplish this.
25038 (gdb) alias -a di = disas
25041 Note that aliases are different from user-defined commands.
25042 With a user-defined command, you also need to write documentation
25043 for it with the @samp{document} command.
25044 An alias automatically picks up the documentation of the existing command.
25046 Here is an example where we make @samp{elms} an abbreviation of
25047 @samp{elements} in the @samp{set print elements} command.
25048 This is to show that you can make an abbreviation of any part
25052 (gdb) alias -a set print elms = set print elements
25053 (gdb) alias -a show print elms = show print elements
25054 (gdb) set p elms 20
25056 Limit on string chars or array elements to print is 200.
25059 Note that if you are defining an alias of a @samp{set} command,
25060 and you want to have an alias for the corresponding @samp{show}
25061 command, then you need to define the latter separately.
25063 Unambiguously abbreviated commands are allowed in @var{COMMAND} and
25064 @var{ALIAS}, just as they are normally.
25067 (gdb) alias -a set pr elms = set p ele
25070 Finally, here is an example showing the creation of a one word
25071 alias for a more complex command.
25072 This creates alias @samp{spe} of the command @samp{set print elements}.
25075 (gdb) alias spe = set print elements
25080 @chapter Command Interpreters
25081 @cindex command interpreters
25083 @value{GDBN} supports multiple command interpreters, and some command
25084 infrastructure to allow users or user interface writers to switch
25085 between interpreters or run commands in other interpreters.
25087 @value{GDBN} currently supports two command interpreters, the console
25088 interpreter (sometimes called the command-line interpreter or @sc{cli})
25089 and the machine interface interpreter (or @sc{gdb/mi}). This manual
25090 describes both of these interfaces in great detail.
25092 By default, @value{GDBN} will start with the console interpreter.
25093 However, the user may choose to start @value{GDBN} with another
25094 interpreter by specifying the @option{-i} or @option{--interpreter}
25095 startup options. Defined interpreters include:
25099 @cindex console interpreter
25100 The traditional console or command-line interpreter. This is the most often
25101 used interpreter with @value{GDBN}. With no interpreter specified at runtime,
25102 @value{GDBN} will use this interpreter.
25105 @cindex mi interpreter
25106 The newest @sc{gdb/mi} interface (currently @code{mi2}). Used primarily
25107 by programs wishing to use @value{GDBN} as a backend for a debugger GUI
25108 or an IDE. For more information, see @ref{GDB/MI, ,The @sc{gdb/mi}
25112 @cindex mi2 interpreter
25113 The current @sc{gdb/mi} interface.
25116 @cindex mi1 interpreter
25117 The @sc{gdb/mi} interface included in @value{GDBN} 5.1, 5.2, and 5.3.
25121 @cindex invoke another interpreter
25122 The interpreter being used by @value{GDBN} may not be dynamically
25123 switched at runtime. Although possible, this could lead to a very
25124 precarious situation. Consider an IDE using @sc{gdb/mi}. If a user
25125 enters the command "interpreter-set console" in a console view,
25126 @value{GDBN} would switch to using the console interpreter, rendering
25127 the IDE inoperable!
25129 @kindex interpreter-exec
25130 Although you may only choose a single interpreter at startup, you may execute
25131 commands in any interpreter from the current interpreter using the appropriate
25132 command. If you are running the console interpreter, simply use the
25133 @code{interpreter-exec} command:
25136 interpreter-exec mi "-data-list-register-names"
25139 @sc{gdb/mi} has a similar command, although it is only available in versions of
25140 @value{GDBN} which support @sc{gdb/mi} version 2 (or greater).
25143 @chapter @value{GDBN} Text User Interface
25145 @cindex Text User Interface
25148 * TUI Overview:: TUI overview
25149 * TUI Keys:: TUI key bindings
25150 * TUI Single Key Mode:: TUI single key mode
25151 * TUI Commands:: TUI-specific commands
25152 * TUI Configuration:: TUI configuration variables
25155 The @value{GDBN} Text User Interface (TUI) is a terminal
25156 interface which uses the @code{curses} library to show the source
25157 file, the assembly output, the program registers and @value{GDBN}
25158 commands in separate text windows. The TUI mode is supported only
25159 on platforms where a suitable version of the @code{curses} library
25162 The TUI mode is enabled by default when you invoke @value{GDBN} as
25163 @samp{@value{GDBP} -tui}.
25164 You can also switch in and out of TUI mode while @value{GDBN} runs by
25165 using various TUI commands and key bindings, such as @kbd{C-x C-a}.
25166 @xref{TUI Keys, ,TUI Key Bindings}.
25169 @section TUI Overview
25171 In TUI mode, @value{GDBN} can display several text windows:
25175 This window is the @value{GDBN} command window with the @value{GDBN}
25176 prompt and the @value{GDBN} output. The @value{GDBN} input is still
25177 managed using readline.
25180 The source window shows the source file of the program. The current
25181 line and active breakpoints are displayed in this window.
25184 The assembly window shows the disassembly output of the program.
25187 This window shows the processor registers. Registers are highlighted
25188 when their values change.
25191 The source and assembly windows show the current program position
25192 by highlighting the current line and marking it with a @samp{>} marker.
25193 Breakpoints are indicated with two markers. The first marker
25194 indicates the breakpoint type:
25198 Breakpoint which was hit at least once.
25201 Breakpoint which was never hit.
25204 Hardware breakpoint which was hit at least once.
25207 Hardware breakpoint which was never hit.
25210 The second marker indicates whether the breakpoint is enabled or not:
25214 Breakpoint is enabled.
25217 Breakpoint is disabled.
25220 The source, assembly and register windows are updated when the current
25221 thread changes, when the frame changes, or when the program counter
25224 These windows are not all visible at the same time. The command
25225 window is always visible. The others can be arranged in several
25236 source and assembly,
25239 source and registers, or
25242 assembly and registers.
25245 A status line above the command window shows the following information:
25249 Indicates the current @value{GDBN} target.
25250 (@pxref{Targets, ,Specifying a Debugging Target}).
25253 Gives the current process or thread number.
25254 When no process is being debugged, this field is set to @code{No process}.
25257 Gives the current function name for the selected frame.
25258 The name is demangled if demangling is turned on (@pxref{Print Settings}).
25259 When there is no symbol corresponding to the current program counter,
25260 the string @code{??} is displayed.
25263 Indicates the current line number for the selected frame.
25264 When the current line number is not known, the string @code{??} is displayed.
25267 Indicates the current program counter address.
25271 @section TUI Key Bindings
25272 @cindex TUI key bindings
25274 The TUI installs several key bindings in the readline keymaps
25275 @ifset SYSTEM_READLINE
25276 (@pxref{Command Line Editing, , , rluserman, GNU Readline Library}).
25278 @ifclear SYSTEM_READLINE
25279 (@pxref{Command Line Editing}).
25281 The following key bindings are installed for both TUI mode and the
25282 @value{GDBN} standard mode.
25291 Enter or leave the TUI mode. When leaving the TUI mode,
25292 the curses window management stops and @value{GDBN} operates using
25293 its standard mode, writing on the terminal directly. When reentering
25294 the TUI mode, control is given back to the curses windows.
25295 The screen is then refreshed.
25299 Use a TUI layout with only one window. The layout will
25300 either be @samp{source} or @samp{assembly}. When the TUI mode
25301 is not active, it will switch to the TUI mode.
25303 Think of this key binding as the Emacs @kbd{C-x 1} binding.
25307 Use a TUI layout with at least two windows. When the current
25308 layout already has two windows, the next layout with two windows is used.
25309 When a new layout is chosen, one window will always be common to the
25310 previous layout and the new one.
25312 Think of it as the Emacs @kbd{C-x 2} binding.
25316 Change the active window. The TUI associates several key bindings
25317 (like scrolling and arrow keys) with the active window. This command
25318 gives the focus to the next TUI window.
25320 Think of it as the Emacs @kbd{C-x o} binding.
25324 Switch in and out of the TUI SingleKey mode that binds single
25325 keys to @value{GDBN} commands (@pxref{TUI Single Key Mode}).
25328 The following key bindings only work in the TUI mode:
25333 Scroll the active window one page up.
25337 Scroll the active window one page down.
25341 Scroll the active window one line up.
25345 Scroll the active window one line down.
25349 Scroll the active window one column left.
25353 Scroll the active window one column right.
25357 Refresh the screen.
25360 Because the arrow keys scroll the active window in the TUI mode, they
25361 are not available for their normal use by readline unless the command
25362 window has the focus. When another window is active, you must use
25363 other readline key bindings such as @kbd{C-p}, @kbd{C-n}, @kbd{C-b}
25364 and @kbd{C-f} to control the command window.
25366 @node TUI Single Key Mode
25367 @section TUI Single Key Mode
25368 @cindex TUI single key mode
25370 The TUI also provides a @dfn{SingleKey} mode, which binds several
25371 frequently used @value{GDBN} commands to single keys. Type @kbd{C-x s} to
25372 switch into this mode, where the following key bindings are used:
25375 @kindex c @r{(SingleKey TUI key)}
25379 @kindex d @r{(SingleKey TUI key)}
25383 @kindex f @r{(SingleKey TUI key)}
25387 @kindex n @r{(SingleKey TUI key)}
25391 @kindex q @r{(SingleKey TUI key)}
25393 exit the SingleKey mode.
25395 @kindex r @r{(SingleKey TUI key)}
25399 @kindex s @r{(SingleKey TUI key)}
25403 @kindex u @r{(SingleKey TUI key)}
25407 @kindex v @r{(SingleKey TUI key)}
25411 @kindex w @r{(SingleKey TUI key)}
25416 Other keys temporarily switch to the @value{GDBN} command prompt.
25417 The key that was pressed is inserted in the editing buffer so that
25418 it is possible to type most @value{GDBN} commands without interaction
25419 with the TUI SingleKey mode. Once the command is entered the TUI
25420 SingleKey mode is restored. The only way to permanently leave
25421 this mode is by typing @kbd{q} or @kbd{C-x s}.
25425 @section TUI-specific Commands
25426 @cindex TUI commands
25428 The TUI has specific commands to control the text windows.
25429 These commands are always available, even when @value{GDBN} is not in
25430 the TUI mode. When @value{GDBN} is in the standard mode, most
25431 of these commands will automatically switch to the TUI mode.
25433 Note that if @value{GDBN}'s @code{stdout} is not connected to a
25434 terminal, or @value{GDBN} has been started with the machine interface
25435 interpreter (@pxref{GDB/MI, ,The @sc{gdb/mi} Interface}), most of
25436 these commands will fail with an error, because it would not be
25437 possible or desirable to enable curses window management.
25442 List and give the size of all displayed windows.
25446 Display the next layout.
25449 Display the previous layout.
25452 Display the source window only.
25455 Display the assembly window only.
25458 Display the source and assembly window.
25461 Display the register window together with the source or assembly window.
25465 Make the next window active for scrolling.
25468 Make the previous window active for scrolling.
25471 Make the source window active for scrolling.
25474 Make the assembly window active for scrolling.
25477 Make the register window active for scrolling.
25480 Make the command window active for scrolling.
25484 Refresh the screen. This is similar to typing @kbd{C-L}.
25486 @item tui reg float
25488 Show the floating point registers in the register window.
25490 @item tui reg general
25491 Show the general registers in the register window.
25494 Show the next register group. The list of register groups as well as
25495 their order is target specific. The predefined register groups are the
25496 following: @code{general}, @code{float}, @code{system}, @code{vector},
25497 @code{all}, @code{save}, @code{restore}.
25499 @item tui reg system
25500 Show the system registers in the register window.
25504 Update the source window and the current execution point.
25506 @item winheight @var{name} +@var{count}
25507 @itemx winheight @var{name} -@var{count}
25509 Change the height of the window @var{name} by @var{count}
25510 lines. Positive counts increase the height, while negative counts
25513 @item tabset @var{nchars}
25515 Set the width of tab stops to be @var{nchars} characters.
25518 @node TUI Configuration
25519 @section TUI Configuration Variables
25520 @cindex TUI configuration variables
25522 Several configuration variables control the appearance of TUI windows.
25525 @item set tui border-kind @var{kind}
25526 @kindex set tui border-kind
25527 Select the border appearance for the source, assembly and register windows.
25528 The possible values are the following:
25531 Use a space character to draw the border.
25534 Use @sc{ascii} characters @samp{+}, @samp{-} and @samp{|} to draw the border.
25537 Use the Alternate Character Set to draw the border. The border is
25538 drawn using character line graphics if the terminal supports them.
25541 @item set tui border-mode @var{mode}
25542 @kindex set tui border-mode
25543 @itemx set tui active-border-mode @var{mode}
25544 @kindex set tui active-border-mode
25545 Select the display attributes for the borders of the inactive windows
25546 or the active window. The @var{mode} can be one of the following:
25549 Use normal attributes to display the border.
25555 Use reverse video mode.
25558 Use half bright mode.
25560 @item half-standout
25561 Use half bright and standout mode.
25564 Use extra bright or bold mode.
25566 @item bold-standout
25567 Use extra bright or bold and standout mode.
25572 @chapter Using @value{GDBN} under @sc{gnu} Emacs
25575 @cindex @sc{gnu} Emacs
25576 A special interface allows you to use @sc{gnu} Emacs to view (and
25577 edit) the source files for the program you are debugging with
25580 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
25581 executable file you want to debug as an argument. This command starts
25582 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
25583 created Emacs buffer.
25584 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
25586 Running @value{GDBN} under Emacs can be just like running @value{GDBN} normally except for two
25591 All ``terminal'' input and output goes through an Emacs buffer, called
25594 This applies both to @value{GDBN} commands and their output, and to the input
25595 and output done by the program you are debugging.
25597 This is useful because it means that you can copy the text of previous
25598 commands and input them again; you can even use parts of the output
25601 All the facilities of Emacs' Shell mode are available for interacting
25602 with your program. In particular, you can send signals the usual
25603 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
25607 @value{GDBN} displays source code through Emacs.
25609 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
25610 source file for that frame and puts an arrow (@samp{=>}) at the
25611 left margin of the current line. Emacs uses a separate buffer for
25612 source display, and splits the screen to show both your @value{GDBN} session
25615 Explicit @value{GDBN} @code{list} or search commands still produce output as
25616 usual, but you probably have no reason to use them from Emacs.
25619 We call this @dfn{text command mode}. Emacs 22.1, and later, also uses
25620 a graphical mode, enabled by default, which provides further buffers
25621 that can control the execution and describe the state of your program.
25622 @xref{GDB Graphical Interface,,, Emacs, The @sc{gnu} Emacs Manual}.
25624 If you specify an absolute file name when prompted for the @kbd{M-x
25625 gdb} argument, then Emacs sets your current working directory to where
25626 your program resides. If you only specify the file name, then Emacs
25627 sets your current working directory to the directory associated
25628 with the previous buffer. In this case, @value{GDBN} may find your
25629 program by searching your environment's @code{PATH} variable, but on
25630 some operating systems it might not find the source. So, although the
25631 @value{GDBN} input and output session proceeds normally, the auxiliary
25632 buffer does not display the current source and line of execution.
25634 The initial working directory of @value{GDBN} is printed on the top
25635 line of the GUD buffer and this serves as a default for the commands
25636 that specify files for @value{GDBN} to operate on. @xref{Files,
25637 ,Commands to Specify Files}.
25639 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If you
25640 need to call @value{GDBN} by a different name (for example, if you
25641 keep several configurations around, with different names) you can
25642 customize the Emacs variable @code{gud-gdb-command-name} to run the
25645 In the GUD buffer, you can use these special Emacs commands in
25646 addition to the standard Shell mode commands:
25650 Describe the features of Emacs' GUD Mode.
25653 Execute to another source line, like the @value{GDBN} @code{step} command; also
25654 update the display window to show the current file and location.
25657 Execute to next source line in this function, skipping all function
25658 calls, like the @value{GDBN} @code{next} command. Then update the display window
25659 to show the current file and location.
25662 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
25663 display window accordingly.
25666 Execute until exit from the selected stack frame, like the @value{GDBN}
25667 @code{finish} command.
25670 Continue execution of your program, like the @value{GDBN} @code{continue}
25674 Go up the number of frames indicated by the numeric argument
25675 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
25676 like the @value{GDBN} @code{up} command.
25679 Go down the number of frames indicated by the numeric argument, like the
25680 @value{GDBN} @code{down} command.
25683 In any source file, the Emacs command @kbd{C-x @key{SPC}} (@code{gud-break})
25684 tells @value{GDBN} to set a breakpoint on the source line point is on.
25686 In text command mode, if you type @kbd{M-x speedbar}, Emacs displays a
25687 separate frame which shows a backtrace when the GUD buffer is current.
25688 Move point to any frame in the stack and type @key{RET} to make it
25689 become the current frame and display the associated source in the
25690 source buffer. Alternatively, click @kbd{Mouse-2} to make the
25691 selected frame become the current one. In graphical mode, the
25692 speedbar displays watch expressions.
25694 If you accidentally delete the source-display buffer, an easy way to get
25695 it back is to type the command @code{f} in the @value{GDBN} buffer, to
25696 request a frame display; when you run under Emacs, this recreates
25697 the source buffer if necessary to show you the context of the current
25700 The source files displayed in Emacs are in ordinary Emacs buffers
25701 which are visiting the source files in the usual way. You can edit
25702 the files with these buffers if you wish; but keep in mind that @value{GDBN}
25703 communicates with Emacs in terms of line numbers. If you add or
25704 delete lines from the text, the line numbers that @value{GDBN} knows cease
25705 to correspond properly with the code.
25707 A more detailed description of Emacs' interaction with @value{GDBN} is
25708 given in the Emacs manual (@pxref{Debuggers,,, Emacs, The @sc{gnu}
25711 @c The following dropped because Epoch is nonstandard. Reactivate
25712 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
25714 @kindex Emacs Epoch environment
25718 Version 18 of @sc{gnu} Emacs has a built-in window system
25719 called the @code{epoch}
25720 environment. Users of this environment can use a new command,
25721 @code{inspect} which performs identically to @code{print} except that
25722 each value is printed in its own window.
25727 @chapter The @sc{gdb/mi} Interface
25729 @unnumberedsec Function and Purpose
25731 @cindex @sc{gdb/mi}, its purpose
25732 @sc{gdb/mi} is a line based machine oriented text interface to
25733 @value{GDBN} and is activated by specifying using the
25734 @option{--interpreter} command line option (@pxref{Mode Options}). It
25735 is specifically intended to support the development of systems which
25736 use the debugger as just one small component of a larger system.
25738 This chapter is a specification of the @sc{gdb/mi} interface. It is written
25739 in the form of a reference manual.
25741 Note that @sc{gdb/mi} is still under construction, so some of the
25742 features described below are incomplete and subject to change
25743 (@pxref{GDB/MI Development and Front Ends, , @sc{gdb/mi} Development and Front Ends}).
25745 @unnumberedsec Notation and Terminology
25747 @cindex notational conventions, for @sc{gdb/mi}
25748 This chapter uses the following notation:
25752 @code{|} separates two alternatives.
25755 @code{[ @var{something} ]} indicates that @var{something} is optional:
25756 it may or may not be given.
25759 @code{( @var{group} )*} means that @var{group} inside the parentheses
25760 may repeat zero or more times.
25763 @code{( @var{group} )+} means that @var{group} inside the parentheses
25764 may repeat one or more times.
25767 @code{"@var{string}"} means a literal @var{string}.
25771 @heading Dependencies
25775 * GDB/MI General Design::
25776 * GDB/MI Command Syntax::
25777 * GDB/MI Compatibility with CLI::
25778 * GDB/MI Development and Front Ends::
25779 * GDB/MI Output Records::
25780 * GDB/MI Simple Examples::
25781 * GDB/MI Command Description Format::
25782 * GDB/MI Breakpoint Commands::
25783 * GDB/MI Program Context::
25784 * GDB/MI Thread Commands::
25785 * GDB/MI Ada Tasking Commands::
25786 * GDB/MI Program Execution::
25787 * GDB/MI Stack Manipulation::
25788 * GDB/MI Variable Objects::
25789 * GDB/MI Data Manipulation::
25790 * GDB/MI Tracepoint Commands::
25791 * GDB/MI Symbol Query::
25792 * GDB/MI File Commands::
25794 * GDB/MI Kod Commands::
25795 * GDB/MI Memory Overlay Commands::
25796 * GDB/MI Signal Handling Commands::
25798 * GDB/MI Target Manipulation::
25799 * GDB/MI File Transfer Commands::
25800 * GDB/MI Miscellaneous Commands::
25803 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25804 @node GDB/MI General Design
25805 @section @sc{gdb/mi} General Design
25806 @cindex GDB/MI General Design
25808 Interaction of a @sc{GDB/MI} frontend with @value{GDBN} involves three
25809 parts---commands sent to @value{GDBN}, responses to those commands
25810 and notifications. Each command results in exactly one response,
25811 indicating either successful completion of the command, or an error.
25812 For the commands that do not resume the target, the response contains the
25813 requested information. For the commands that resume the target, the
25814 response only indicates whether the target was successfully resumed.
25815 Notifications is the mechanism for reporting changes in the state of the
25816 target, or in @value{GDBN} state, that cannot conveniently be associated with
25817 a command and reported as part of that command response.
25819 The important examples of notifications are:
25823 Exec notifications. These are used to report changes in
25824 target state---when a target is resumed, or stopped. It would not
25825 be feasible to include this information in response of resuming
25826 commands, because one resume commands can result in multiple events in
25827 different threads. Also, quite some time may pass before any event
25828 happens in the target, while a frontend needs to know whether the resuming
25829 command itself was successfully executed.
25832 Console output, and status notifications. Console output
25833 notifications are used to report output of CLI commands, as well as
25834 diagnostics for other commands. Status notifications are used to
25835 report the progress of a long-running operation. Naturally, including
25836 this information in command response would mean no output is produced
25837 until the command is finished, which is undesirable.
25840 General notifications. Commands may have various side effects on
25841 the @value{GDBN} or target state beyond their official purpose. For example,
25842 a command may change the selected thread. Although such changes can
25843 be included in command response, using notification allows for more
25844 orthogonal frontend design.
25848 There's no guarantee that whenever an MI command reports an error,
25849 @value{GDBN} or the target are in any specific state, and especially,
25850 the state is not reverted to the state before the MI command was
25851 processed. Therefore, whenever an MI command results in an error,
25852 we recommend that the frontend refreshes all the information shown in
25853 the user interface.
25857 * Context management::
25858 * Asynchronous and non-stop modes::
25862 @node Context management
25863 @subsection Context management
25865 In most cases when @value{GDBN} accesses the target, this access is
25866 done in context of a specific thread and frame (@pxref{Frames}).
25867 Often, even when accessing global data, the target requires that a thread
25868 be specified. The CLI interface maintains the selected thread and frame,
25869 and supplies them to target on each command. This is convenient,
25870 because a command line user would not want to specify that information
25871 explicitly on each command, and because user interacts with
25872 @value{GDBN} via a single terminal, so no confusion is possible as
25873 to what thread and frame are the current ones.
25875 In the case of MI, the concept of selected thread and frame is less
25876 useful. First, a frontend can easily remember this information
25877 itself. Second, a graphical frontend can have more than one window,
25878 each one used for debugging a different thread, and the frontend might
25879 want to access additional threads for internal purposes. This
25880 increases the risk that by relying on implicitly selected thread, the
25881 frontend may be operating on a wrong one. Therefore, each MI command
25882 should explicitly specify which thread and frame to operate on. To
25883 make it possible, each MI command accepts the @samp{--thread} and
25884 @samp{--frame} options, the value to each is @value{GDBN} identifier
25885 for thread and frame to operate on.
25887 Usually, each top-level window in a frontend allows the user to select
25888 a thread and a frame, and remembers the user selection for further
25889 operations. However, in some cases @value{GDBN} may suggest that the
25890 current thread be changed. For example, when stopping on a breakpoint
25891 it is reasonable to switch to the thread where breakpoint is hit. For
25892 another example, if the user issues the CLI @samp{thread} command via
25893 the frontend, it is desirable to change the frontend's selected thread to the
25894 one specified by user. @value{GDBN} communicates the suggestion to
25895 change current thread using the @samp{=thread-selected} notification.
25896 No such notification is available for the selected frame at the moment.
25898 Note that historically, MI shares the selected thread with CLI, so
25899 frontends used the @code{-thread-select} to execute commands in the
25900 right context. However, getting this to work right is cumbersome. The
25901 simplest way is for frontend to emit @code{-thread-select} command
25902 before every command. This doubles the number of commands that need
25903 to be sent. The alternative approach is to suppress @code{-thread-select}
25904 if the selected thread in @value{GDBN} is supposed to be identical to the
25905 thread the frontend wants to operate on. However, getting this
25906 optimization right can be tricky. In particular, if the frontend
25907 sends several commands to @value{GDBN}, and one of the commands changes the
25908 selected thread, then the behaviour of subsequent commands will
25909 change. So, a frontend should either wait for response from such
25910 problematic commands, or explicitly add @code{-thread-select} for
25911 all subsequent commands. No frontend is known to do this exactly
25912 right, so it is suggested to just always pass the @samp{--thread} and
25913 @samp{--frame} options.
25915 @node Asynchronous and non-stop modes
25916 @subsection Asynchronous command execution and non-stop mode
25918 On some targets, @value{GDBN} is capable of processing MI commands
25919 even while the target is running. This is called @dfn{asynchronous
25920 command execution} (@pxref{Background Execution}). The frontend may
25921 specify a preferrence for asynchronous execution using the
25922 @code{-gdb-set target-async 1} command, which should be emitted before
25923 either running the executable or attaching to the target. After the
25924 frontend has started the executable or attached to the target, it can
25925 find if asynchronous execution is enabled using the
25926 @code{-list-target-features} command.
25928 Even if @value{GDBN} can accept a command while target is running,
25929 many commands that access the target do not work when the target is
25930 running. Therefore, asynchronous command execution is most useful
25931 when combined with non-stop mode (@pxref{Non-Stop Mode}). Then,
25932 it is possible to examine the state of one thread, while other threads
25935 When a given thread is running, MI commands that try to access the
25936 target in the context of that thread may not work, or may work only on
25937 some targets. In particular, commands that try to operate on thread's
25938 stack will not work, on any target. Commands that read memory, or
25939 modify breakpoints, may work or not work, depending on the target. Note
25940 that even commands that operate on global state, such as @code{print},
25941 @code{set}, and breakpoint commands, still access the target in the
25942 context of a specific thread, so frontend should try to find a
25943 stopped thread and perform the operation on that thread (using the
25944 @samp{--thread} option).
25946 Which commands will work in the context of a running thread is
25947 highly target dependent. However, the two commands
25948 @code{-exec-interrupt}, to stop a thread, and @code{-thread-info},
25949 to find the state of a thread, will always work.
25951 @node Thread groups
25952 @subsection Thread groups
25953 @value{GDBN} may be used to debug several processes at the same time.
25954 On some platfroms, @value{GDBN} may support debugging of several
25955 hardware systems, each one having several cores with several different
25956 processes running on each core. This section describes the MI
25957 mechanism to support such debugging scenarios.
25959 The key observation is that regardless of the structure of the
25960 target, MI can have a global list of threads, because most commands that
25961 accept the @samp{--thread} option do not need to know what process that
25962 thread belongs to. Therefore, it is not necessary to introduce
25963 neither additional @samp{--process} option, nor an notion of the
25964 current process in the MI interface. The only strictly new feature
25965 that is required is the ability to find how the threads are grouped
25968 To allow the user to discover such grouping, and to support arbitrary
25969 hierarchy of machines/cores/processes, MI introduces the concept of a
25970 @dfn{thread group}. Thread group is a collection of threads and other
25971 thread groups. A thread group always has a string identifier, a type,
25972 and may have additional attributes specific to the type. A new
25973 command, @code{-list-thread-groups}, returns the list of top-level
25974 thread groups, which correspond to processes that @value{GDBN} is
25975 debugging at the moment. By passing an identifier of a thread group
25976 to the @code{-list-thread-groups} command, it is possible to obtain
25977 the members of specific thread group.
25979 To allow the user to easily discover processes, and other objects, he
25980 wishes to debug, a concept of @dfn{available thread group} is
25981 introduced. Available thread group is an thread group that
25982 @value{GDBN} is not debugging, but that can be attached to, using the
25983 @code{-target-attach} command. The list of available top-level thread
25984 groups can be obtained using @samp{-list-thread-groups --available}.
25985 In general, the content of a thread group may be only retrieved only
25986 after attaching to that thread group.
25988 Thread groups are related to inferiors (@pxref{Inferiors and
25989 Programs}). Each inferior corresponds to a thread group of a special
25990 type @samp{process}, and some additional operations are permitted on
25991 such thread groups.
25993 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25994 @node GDB/MI Command Syntax
25995 @section @sc{gdb/mi} Command Syntax
25998 * GDB/MI Input Syntax::
25999 * GDB/MI Output Syntax::
26002 @node GDB/MI Input Syntax
26003 @subsection @sc{gdb/mi} Input Syntax
26005 @cindex input syntax for @sc{gdb/mi}
26006 @cindex @sc{gdb/mi}, input syntax
26008 @item @var{command} @expansion{}
26009 @code{@var{cli-command} | @var{mi-command}}
26011 @item @var{cli-command} @expansion{}
26012 @code{[ @var{token} ] @var{cli-command} @var{nl}}, where
26013 @var{cli-command} is any existing @value{GDBN} CLI command.
26015 @item @var{mi-command} @expansion{}
26016 @code{[ @var{token} ] "-" @var{operation} ( " " @var{option} )*
26017 @code{[} " --" @code{]} ( " " @var{parameter} )* @var{nl}}
26019 @item @var{token} @expansion{}
26020 "any sequence of digits"
26022 @item @var{option} @expansion{}
26023 @code{"-" @var{parameter} [ " " @var{parameter} ]}
26025 @item @var{parameter} @expansion{}
26026 @code{@var{non-blank-sequence} | @var{c-string}}
26028 @item @var{operation} @expansion{}
26029 @emph{any of the operations described in this chapter}
26031 @item @var{non-blank-sequence} @expansion{}
26032 @emph{anything, provided it doesn't contain special characters such as
26033 "-", @var{nl}, """ and of course " "}
26035 @item @var{c-string} @expansion{}
26036 @code{""" @var{seven-bit-iso-c-string-content} """}
26038 @item @var{nl} @expansion{}
26047 The CLI commands are still handled by the @sc{mi} interpreter; their
26048 output is described below.
26051 The @code{@var{token}}, when present, is passed back when the command
26055 Some @sc{mi} commands accept optional arguments as part of the parameter
26056 list. Each option is identified by a leading @samp{-} (dash) and may be
26057 followed by an optional argument parameter. Options occur first in the
26058 parameter list and can be delimited from normal parameters using
26059 @samp{--} (this is useful when some parameters begin with a dash).
26066 We want easy access to the existing CLI syntax (for debugging).
26069 We want it to be easy to spot a @sc{mi} operation.
26072 @node GDB/MI Output Syntax
26073 @subsection @sc{gdb/mi} Output Syntax
26075 @cindex output syntax of @sc{gdb/mi}
26076 @cindex @sc{gdb/mi}, output syntax
26077 The output from @sc{gdb/mi} consists of zero or more out-of-band records
26078 followed, optionally, by a single result record. This result record
26079 is for the most recent command. The sequence of output records is
26080 terminated by @samp{(gdb)}.
26082 If an input command was prefixed with a @code{@var{token}} then the
26083 corresponding output for that command will also be prefixed by that same
26087 @item @var{output} @expansion{}
26088 @code{( @var{out-of-band-record} )* [ @var{result-record} ] "(gdb)" @var{nl}}
26090 @item @var{result-record} @expansion{}
26091 @code{ [ @var{token} ] "^" @var{result-class} ( "," @var{result} )* @var{nl}}
26093 @item @var{out-of-band-record} @expansion{}
26094 @code{@var{async-record} | @var{stream-record}}
26096 @item @var{async-record} @expansion{}
26097 @code{@var{exec-async-output} | @var{status-async-output} | @var{notify-async-output}}
26099 @item @var{exec-async-output} @expansion{}
26100 @code{[ @var{token} ] "*" @var{async-output}}
26102 @item @var{status-async-output} @expansion{}
26103 @code{[ @var{token} ] "+" @var{async-output}}
26105 @item @var{notify-async-output} @expansion{}
26106 @code{[ @var{token} ] "=" @var{async-output}}
26108 @item @var{async-output} @expansion{}
26109 @code{@var{async-class} ( "," @var{result} )* @var{nl}}
26111 @item @var{result-class} @expansion{}
26112 @code{"done" | "running" | "connected" | "error" | "exit"}
26114 @item @var{async-class} @expansion{}
26115 @code{"stopped" | @var{others}} (where @var{others} will be added
26116 depending on the needs---this is still in development).
26118 @item @var{result} @expansion{}
26119 @code{ @var{variable} "=" @var{value}}
26121 @item @var{variable} @expansion{}
26122 @code{ @var{string} }
26124 @item @var{value} @expansion{}
26125 @code{ @var{const} | @var{tuple} | @var{list} }
26127 @item @var{const} @expansion{}
26128 @code{@var{c-string}}
26130 @item @var{tuple} @expansion{}
26131 @code{ "@{@}" | "@{" @var{result} ( "," @var{result} )* "@}" }
26133 @item @var{list} @expansion{}
26134 @code{ "[]" | "[" @var{value} ( "," @var{value} )* "]" | "["
26135 @var{result} ( "," @var{result} )* "]" }
26137 @item @var{stream-record} @expansion{}
26138 @code{@var{console-stream-output} | @var{target-stream-output} | @var{log-stream-output}}
26140 @item @var{console-stream-output} @expansion{}
26141 @code{"~" @var{c-string}}
26143 @item @var{target-stream-output} @expansion{}
26144 @code{"@@" @var{c-string}}
26146 @item @var{log-stream-output} @expansion{}
26147 @code{"&" @var{c-string}}
26149 @item @var{nl} @expansion{}
26152 @item @var{token} @expansion{}
26153 @emph{any sequence of digits}.
26161 All output sequences end in a single line containing a period.
26164 The @code{@var{token}} is from the corresponding request. Note that
26165 for all async output, while the token is allowed by the grammar and
26166 may be output by future versions of @value{GDBN} for select async
26167 output messages, it is generally omitted. Frontends should treat
26168 all async output as reporting general changes in the state of the
26169 target and there should be no need to associate async output to any
26173 @cindex status output in @sc{gdb/mi}
26174 @var{status-async-output} contains on-going status information about the
26175 progress of a slow operation. It can be discarded. All status output is
26176 prefixed by @samp{+}.
26179 @cindex async output in @sc{gdb/mi}
26180 @var{exec-async-output} contains asynchronous state change on the target
26181 (stopped, started, disappeared). All async output is prefixed by
26185 @cindex notify output in @sc{gdb/mi}
26186 @var{notify-async-output} contains supplementary information that the
26187 client should handle (e.g., a new breakpoint information). All notify
26188 output is prefixed by @samp{=}.
26191 @cindex console output in @sc{gdb/mi}
26192 @var{console-stream-output} is output that should be displayed as is in the
26193 console. It is the textual response to a CLI command. All the console
26194 output is prefixed by @samp{~}.
26197 @cindex target output in @sc{gdb/mi}
26198 @var{target-stream-output} is the output produced by the target program.
26199 All the target output is prefixed by @samp{@@}.
26202 @cindex log output in @sc{gdb/mi}
26203 @var{log-stream-output} is output text coming from @value{GDBN}'s internals, for
26204 instance messages that should be displayed as part of an error log. All
26205 the log output is prefixed by @samp{&}.
26208 @cindex list output in @sc{gdb/mi}
26209 New @sc{gdb/mi} commands should only output @var{lists} containing
26215 @xref{GDB/MI Stream Records, , @sc{gdb/mi} Stream Records}, for more
26216 details about the various output records.
26218 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26219 @node GDB/MI Compatibility with CLI
26220 @section @sc{gdb/mi} Compatibility with CLI
26222 @cindex compatibility, @sc{gdb/mi} and CLI
26223 @cindex @sc{gdb/mi}, compatibility with CLI
26225 For the developers convenience CLI commands can be entered directly,
26226 but there may be some unexpected behaviour. For example, commands
26227 that query the user will behave as if the user replied yes, breakpoint
26228 command lists are not executed and some CLI commands, such as
26229 @code{if}, @code{when} and @code{define}, prompt for further input with
26230 @samp{>}, which is not valid MI output.
26232 This feature may be removed at some stage in the future and it is
26233 recommended that front ends use the @code{-interpreter-exec} command
26234 (@pxref{-interpreter-exec}).
26236 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26237 @node GDB/MI Development and Front Ends
26238 @section @sc{gdb/mi} Development and Front Ends
26239 @cindex @sc{gdb/mi} development
26241 The application which takes the MI output and presents the state of the
26242 program being debugged to the user is called a @dfn{front end}.
26244 Although @sc{gdb/mi} is still incomplete, it is currently being used
26245 by a variety of front ends to @value{GDBN}. This makes it difficult
26246 to introduce new functionality without breaking existing usage. This
26247 section tries to minimize the problems by describing how the protocol
26250 Some changes in MI need not break a carefully designed front end, and
26251 for these the MI version will remain unchanged. The following is a
26252 list of changes that may occur within one level, so front ends should
26253 parse MI output in a way that can handle them:
26257 New MI commands may be added.
26260 New fields may be added to the output of any MI command.
26263 The range of values for fields with specified values, e.g.,
26264 @code{in_scope} (@pxref{-var-update}) may be extended.
26266 @c The format of field's content e.g type prefix, may change so parse it
26267 @c at your own risk. Yes, in general?
26269 @c The order of fields may change? Shouldn't really matter but it might
26270 @c resolve inconsistencies.
26273 If the changes are likely to break front ends, the MI version level
26274 will be increased by one. This will allow the front end to parse the
26275 output according to the MI version. Apart from mi0, new versions of
26276 @value{GDBN} will not support old versions of MI and it will be the
26277 responsibility of the front end to work with the new one.
26279 @c Starting with mi3, add a new command -mi-version that prints the MI
26282 The best way to avoid unexpected changes in MI that might break your front
26283 end is to make your project known to @value{GDBN} developers and
26284 follow development on @email{gdb@@sourceware.org} and
26285 @email{gdb-patches@@sourceware.org}.
26286 @cindex mailing lists
26288 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26289 @node GDB/MI Output Records
26290 @section @sc{gdb/mi} Output Records
26293 * GDB/MI Result Records::
26294 * GDB/MI Stream Records::
26295 * GDB/MI Async Records::
26296 * GDB/MI Frame Information::
26297 * GDB/MI Thread Information::
26298 * GDB/MI Ada Exception Information::
26301 @node GDB/MI Result Records
26302 @subsection @sc{gdb/mi} Result Records
26304 @cindex result records in @sc{gdb/mi}
26305 @cindex @sc{gdb/mi}, result records
26306 In addition to a number of out-of-band notifications, the response to a
26307 @sc{gdb/mi} command includes one of the following result indications:
26311 @item "^done" [ "," @var{results} ]
26312 The synchronous operation was successful, @code{@var{results}} are the return
26317 This result record is equivalent to @samp{^done}. Historically, it
26318 was output instead of @samp{^done} if the command has resumed the
26319 target. This behaviour is maintained for backward compatibility, but
26320 all frontends should treat @samp{^done} and @samp{^running}
26321 identically and rely on the @samp{*running} output record to determine
26322 which threads are resumed.
26326 @value{GDBN} has connected to a remote target.
26328 @item "^error" "," @var{c-string}
26330 The operation failed. The @code{@var{c-string}} contains the corresponding
26335 @value{GDBN} has terminated.
26339 @node GDB/MI Stream Records
26340 @subsection @sc{gdb/mi} Stream Records
26342 @cindex @sc{gdb/mi}, stream records
26343 @cindex stream records in @sc{gdb/mi}
26344 @value{GDBN} internally maintains a number of output streams: the console, the
26345 target, and the log. The output intended for each of these streams is
26346 funneled through the @sc{gdb/mi} interface using @dfn{stream records}.
26348 Each stream record begins with a unique @dfn{prefix character} which
26349 identifies its stream (@pxref{GDB/MI Output Syntax, , @sc{gdb/mi} Output
26350 Syntax}). In addition to the prefix, each stream record contains a
26351 @code{@var{string-output}}. This is either raw text (with an implicit new
26352 line) or a quoted C string (which does not contain an implicit newline).
26355 @item "~" @var{string-output}
26356 The console output stream contains text that should be displayed in the
26357 CLI console window. It contains the textual responses to CLI commands.
26359 @item "@@" @var{string-output}
26360 The target output stream contains any textual output from the running
26361 target. This is only present when GDB's event loop is truly
26362 asynchronous, which is currently only the case for remote targets.
26364 @item "&" @var{string-output}
26365 The log stream contains debugging messages being produced by @value{GDBN}'s
26369 @node GDB/MI Async Records
26370 @subsection @sc{gdb/mi} Async Records
26372 @cindex async records in @sc{gdb/mi}
26373 @cindex @sc{gdb/mi}, async records
26374 @dfn{Async} records are used to notify the @sc{gdb/mi} client of
26375 additional changes that have occurred. Those changes can either be a
26376 consequence of @sc{gdb/mi} commands (e.g., a breakpoint modified) or a result of
26377 target activity (e.g., target stopped).
26379 The following is the list of possible async records:
26383 @item *running,thread-id="@var{thread}"
26384 The target is now running. The @var{thread} field tells which
26385 specific thread is now running, and can be @samp{all} if all threads
26386 are running. The frontend should assume that no interaction with a
26387 running thread is possible after this notification is produced.
26388 The frontend should not assume that this notification is output
26389 only once for any command. @value{GDBN} may emit this notification
26390 several times, either for different threads, because it cannot resume
26391 all threads together, or even for a single thread, if the thread must
26392 be stepped though some code before letting it run freely.
26394 @item *stopped,reason="@var{reason}",thread-id="@var{id}",stopped-threads="@var{stopped}",core="@var{core}"
26395 The target has stopped. The @var{reason} field can have one of the
26399 @item breakpoint-hit
26400 A breakpoint was reached.
26401 @item watchpoint-trigger
26402 A watchpoint was triggered.
26403 @item read-watchpoint-trigger
26404 A read watchpoint was triggered.
26405 @item access-watchpoint-trigger
26406 An access watchpoint was triggered.
26407 @item function-finished
26408 An -exec-finish or similar CLI command was accomplished.
26409 @item location-reached
26410 An -exec-until or similar CLI command was accomplished.
26411 @item watchpoint-scope
26412 A watchpoint has gone out of scope.
26413 @item end-stepping-range
26414 An -exec-next, -exec-next-instruction, -exec-step, -exec-step-instruction or
26415 similar CLI command was accomplished.
26416 @item exited-signalled
26417 The inferior exited because of a signal.
26419 The inferior exited.
26420 @item exited-normally
26421 The inferior exited normally.
26422 @item signal-received
26423 A signal was received by the inferior.
26425 The inferior has stopped due to a library being loaded or unloaded.
26426 This can happen when @code{stop-on-solib-events} (@pxref{Files}) is
26427 set or when a @code{catch load} or @code{catch unload} catchpoint is
26428 in use (@pxref{Set Catchpoints}).
26430 The inferior has forked. This is reported when @code{catch fork}
26431 (@pxref{Set Catchpoints}) has been used.
26433 The inferior has vforked. This is reported in when @code{catch vfork}
26434 (@pxref{Set Catchpoints}) has been used.
26435 @item syscall-entry
26436 The inferior entered a system call. This is reported when @code{catch
26437 syscall} (@pxref{Set Catchpoints}) has been used.
26438 @item syscall-entry
26439 The inferior returned from a system call. This is reported when
26440 @code{catch syscall} (@pxref{Set Catchpoints}) has been used.
26442 The inferior called @code{exec}. This is reported when @code{catch exec}
26443 (@pxref{Set Catchpoints}) has been used.
26446 The @var{id} field identifies the thread that directly caused the stop
26447 -- for example by hitting a breakpoint. Depending on whether all-stop
26448 mode is in effect (@pxref{All-Stop Mode}), @value{GDBN} may either
26449 stop all threads, or only the thread that directly triggered the stop.
26450 If all threads are stopped, the @var{stopped} field will have the
26451 value of @code{"all"}. Otherwise, the value of the @var{stopped}
26452 field will be a list of thread identifiers. Presently, this list will
26453 always include a single thread, but frontend should be prepared to see
26454 several threads in the list. The @var{core} field reports the
26455 processor core on which the stop event has happened. This field may be absent
26456 if such information is not available.
26458 @item =thread-group-added,id="@var{id}"
26459 @itemx =thread-group-removed,id="@var{id}"
26460 A thread group was either added or removed. The @var{id} field
26461 contains the @value{GDBN} identifier of the thread group. When a thread
26462 group is added, it generally might not be associated with a running
26463 process. When a thread group is removed, its id becomes invalid and
26464 cannot be used in any way.
26466 @item =thread-group-started,id="@var{id}",pid="@var{pid}"
26467 A thread group became associated with a running program,
26468 either because the program was just started or the thread group
26469 was attached to a program. The @var{id} field contains the
26470 @value{GDBN} identifier of the thread group. The @var{pid} field
26471 contains process identifier, specific to the operating system.
26473 @item =thread-group-exited,id="@var{id}"[,exit-code="@var{code}"]
26474 A thread group is no longer associated with a running program,
26475 either because the program has exited, or because it was detached
26476 from. The @var{id} field contains the @value{GDBN} identifier of the
26477 thread group. @var{code} is the exit code of the inferior; it exists
26478 only when the inferior exited with some code.
26480 @item =thread-created,id="@var{id}",group-id="@var{gid}"
26481 @itemx =thread-exited,id="@var{id}",group-id="@var{gid}"
26482 A thread either was created, or has exited. The @var{id} field
26483 contains the @value{GDBN} identifier of the thread. The @var{gid}
26484 field identifies the thread group this thread belongs to.
26486 @item =thread-selected,id="@var{id}"
26487 Informs that the selected thread was changed as result of the last
26488 command. This notification is not emitted as result of @code{-thread-select}
26489 command but is emitted whenever an MI command that is not documented
26490 to change the selected thread actually changes it. In particular,
26491 invoking, directly or indirectly (via user-defined command), the CLI
26492 @code{thread} command, will generate this notification.
26494 We suggest that in response to this notification, front ends
26495 highlight the selected thread and cause subsequent commands to apply to
26498 @item =library-loaded,...
26499 Reports that a new library file was loaded by the program. This
26500 notification has 4 fields---@var{id}, @var{target-name},
26501 @var{host-name}, and @var{symbols-loaded}. The @var{id} field is an
26502 opaque identifier of the library. For remote debugging case,
26503 @var{target-name} and @var{host-name} fields give the name of the
26504 library file on the target, and on the host respectively. For native
26505 debugging, both those fields have the same value. The
26506 @var{symbols-loaded} field is emitted only for backward compatibility
26507 and should not be relied on to convey any useful information. The
26508 @var{thread-group} field, if present, specifies the id of the thread
26509 group in whose context the library was loaded. If the field is
26510 absent, it means the library was loaded in the context of all present
26513 @item =library-unloaded,...
26514 Reports that a library was unloaded by the program. This notification
26515 has 3 fields---@var{id}, @var{target-name} and @var{host-name} with
26516 the same meaning as for the @code{=library-loaded} notification.
26517 The @var{thread-group} field, if present, specifies the id of the
26518 thread group in whose context the library was unloaded. If the field is
26519 absent, it means the library was unloaded in the context of all present
26522 @item =breakpoint-created,bkpt=@{...@}
26523 @itemx =breakpoint-modified,bkpt=@{...@}
26524 @itemx =breakpoint-deleted,bkpt=@{...@}
26525 Reports that a breakpoint was created, modified, or deleted,
26526 respectively. Only user-visible breakpoints are reported to the MI
26529 The @var{bkpt} argument is of the same form as returned by the various
26530 breakpoint commands; @xref{GDB/MI Breakpoint Commands}.
26532 Note that if a breakpoint is emitted in the result record of a
26533 command, then it will not also be emitted in an async record.
26537 @node GDB/MI Frame Information
26538 @subsection @sc{gdb/mi} Frame Information
26540 Response from many MI commands includes an information about stack
26541 frame. This information is a tuple that may have the following
26546 The level of the stack frame. The innermost frame has the level of
26547 zero. This field is always present.
26550 The name of the function corresponding to the frame. This field may
26551 be absent if @value{GDBN} is unable to determine the function name.
26554 The code address for the frame. This field is always present.
26557 The name of the source files that correspond to the frame's code
26558 address. This field may be absent.
26561 The source line corresponding to the frames' code address. This field
26565 The name of the binary file (either executable or shared library) the
26566 corresponds to the frame's code address. This field may be absent.
26570 @node GDB/MI Thread Information
26571 @subsection @sc{gdb/mi} Thread Information
26573 Whenever @value{GDBN} has to report an information about a thread, it
26574 uses a tuple with the following fields:
26578 The numeric id assigned to the thread by @value{GDBN}. This field is
26582 Target-specific string identifying the thread. This field is always present.
26585 Additional information about the thread provided by the target.
26586 It is supposed to be human-readable and not interpreted by the
26587 frontend. This field is optional.
26590 Either @samp{stopped} or @samp{running}, depending on whether the
26591 thread is presently running. This field is always present.
26594 The value of this field is an integer number of the processor core the
26595 thread was last seen on. This field is optional.
26598 @node GDB/MI Ada Exception Information
26599 @subsection @sc{gdb/mi} Ada Exception Information
26601 Whenever a @code{*stopped} record is emitted because the program
26602 stopped after hitting an exception catchpoint (@pxref{Set Catchpoints}),
26603 @value{GDBN} provides the name of the exception that was raised via
26604 the @code{exception-name} field.
26606 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26607 @node GDB/MI Simple Examples
26608 @section Simple Examples of @sc{gdb/mi} Interaction
26609 @cindex @sc{gdb/mi}, simple examples
26611 This subsection presents several simple examples of interaction using
26612 the @sc{gdb/mi} interface. In these examples, @samp{->} means that the
26613 following line is passed to @sc{gdb/mi} as input, while @samp{<-} means
26614 the output received from @sc{gdb/mi}.
26616 Note the line breaks shown in the examples are here only for
26617 readability, they don't appear in the real output.
26619 @subheading Setting a Breakpoint
26621 Setting a breakpoint generates synchronous output which contains detailed
26622 information of the breakpoint.
26625 -> -break-insert main
26626 <- ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
26627 enabled="y",addr="0x08048564",func="main",file="myprog.c",
26628 fullname="/home/nickrob/myprog.c",line="68",times="0"@}
26632 @subheading Program Execution
26634 Program execution generates asynchronous records and MI gives the
26635 reason that execution stopped.
26641 <- *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
26642 frame=@{addr="0x08048564",func="main",
26643 args=[@{name="argc",value="1"@},@{name="argv",value="0xbfc4d4d4"@}],
26644 file="myprog.c",fullname="/home/nickrob/myprog.c",line="68"@}
26649 <- *stopped,reason="exited-normally"
26653 @subheading Quitting @value{GDBN}
26655 Quitting @value{GDBN} just prints the result class @samp{^exit}.
26663 Please note that @samp{^exit} is printed immediately, but it might
26664 take some time for @value{GDBN} to actually exit. During that time, @value{GDBN}
26665 performs necessary cleanups, including killing programs being debugged
26666 or disconnecting from debug hardware, so the frontend should wait till
26667 @value{GDBN} exits and should only forcibly kill @value{GDBN} if it
26668 fails to exit in reasonable time.
26670 @subheading A Bad Command
26672 Here's what happens if you pass a non-existent command:
26676 <- ^error,msg="Undefined MI command: rubbish"
26681 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26682 @node GDB/MI Command Description Format
26683 @section @sc{gdb/mi} Command Description Format
26685 The remaining sections describe blocks of commands. Each block of
26686 commands is laid out in a fashion similar to this section.
26688 @subheading Motivation
26690 The motivation for this collection of commands.
26692 @subheading Introduction
26694 A brief introduction to this collection of commands as a whole.
26696 @subheading Commands
26698 For each command in the block, the following is described:
26700 @subsubheading Synopsis
26703 -command @var{args}@dots{}
26706 @subsubheading Result
26708 @subsubheading @value{GDBN} Command
26710 The corresponding @value{GDBN} CLI command(s), if any.
26712 @subsubheading Example
26714 Example(s) formatted for readability. Some of the described commands have
26715 not been implemented yet and these are labeled N.A.@: (not available).
26718 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26719 @node GDB/MI Breakpoint Commands
26720 @section @sc{gdb/mi} Breakpoint Commands
26722 @cindex breakpoint commands for @sc{gdb/mi}
26723 @cindex @sc{gdb/mi}, breakpoint commands
26724 This section documents @sc{gdb/mi} commands for manipulating
26727 @subheading The @code{-break-after} Command
26728 @findex -break-after
26730 @subsubheading Synopsis
26733 -break-after @var{number} @var{count}
26736 The breakpoint number @var{number} is not in effect until it has been
26737 hit @var{count} times. To see how this is reflected in the output of
26738 the @samp{-break-list} command, see the description of the
26739 @samp{-break-list} command below.
26741 @subsubheading @value{GDBN} Command
26743 The corresponding @value{GDBN} command is @samp{ignore}.
26745 @subsubheading Example
26750 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
26751 enabled="y",addr="0x000100d0",func="main",file="hello.c",
26752 fullname="/home/foo/hello.c",line="5",times="0"@}
26759 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
26760 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
26761 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
26762 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
26763 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
26764 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
26765 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
26766 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
26767 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
26768 line="5",times="0",ignore="3"@}]@}
26773 @subheading The @code{-break-catch} Command
26774 @findex -break-catch
26777 @subheading The @code{-break-commands} Command
26778 @findex -break-commands
26780 @subsubheading Synopsis
26783 -break-commands @var{number} [ @var{command1} ... @var{commandN} ]
26786 Specifies the CLI commands that should be executed when breakpoint
26787 @var{number} is hit. The parameters @var{command1} to @var{commandN}
26788 are the commands. If no command is specified, any previously-set
26789 commands are cleared. @xref{Break Commands}. Typical use of this
26790 functionality is tracing a program, that is, printing of values of
26791 some variables whenever breakpoint is hit and then continuing.
26793 @subsubheading @value{GDBN} Command
26795 The corresponding @value{GDBN} command is @samp{commands}.
26797 @subsubheading Example
26802 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
26803 enabled="y",addr="0x000100d0",func="main",file="hello.c",
26804 fullname="/home/foo/hello.c",line="5",times="0"@}
26806 -break-commands 1 "print v" "continue"
26811 @subheading The @code{-break-condition} Command
26812 @findex -break-condition
26814 @subsubheading Synopsis
26817 -break-condition @var{number} @var{expr}
26820 Breakpoint @var{number} will stop the program only if the condition in
26821 @var{expr} is true. The condition becomes part of the
26822 @samp{-break-list} output (see the description of the @samp{-break-list}
26825 @subsubheading @value{GDBN} Command
26827 The corresponding @value{GDBN} command is @samp{condition}.
26829 @subsubheading Example
26833 -break-condition 1 1
26837 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
26838 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
26839 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
26840 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
26841 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
26842 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
26843 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
26844 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
26845 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
26846 line="5",cond="1",times="0",ignore="3"@}]@}
26850 @subheading The @code{-break-delete} Command
26851 @findex -break-delete
26853 @subsubheading Synopsis
26856 -break-delete ( @var{breakpoint} )+
26859 Delete the breakpoint(s) whose number(s) are specified in the argument
26860 list. This is obviously reflected in the breakpoint list.
26862 @subsubheading @value{GDBN} Command
26864 The corresponding @value{GDBN} command is @samp{delete}.
26866 @subsubheading Example
26874 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
26875 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
26876 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
26877 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
26878 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
26879 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
26880 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
26885 @subheading The @code{-break-disable} Command
26886 @findex -break-disable
26888 @subsubheading Synopsis
26891 -break-disable ( @var{breakpoint} )+
26894 Disable the named @var{breakpoint}(s). The field @samp{enabled} in the
26895 break list is now set to @samp{n} for the named @var{breakpoint}(s).
26897 @subsubheading @value{GDBN} Command
26899 The corresponding @value{GDBN} command is @samp{disable}.
26901 @subsubheading Example
26909 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
26910 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
26911 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
26912 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
26913 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
26914 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
26915 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
26916 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="n",
26917 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
26918 line="5",times="0"@}]@}
26922 @subheading The @code{-break-enable} Command
26923 @findex -break-enable
26925 @subsubheading Synopsis
26928 -break-enable ( @var{breakpoint} )+
26931 Enable (previously disabled) @var{breakpoint}(s).
26933 @subsubheading @value{GDBN} Command
26935 The corresponding @value{GDBN} command is @samp{enable}.
26937 @subsubheading Example
26945 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
26946 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
26947 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
26948 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
26949 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
26950 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
26951 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
26952 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
26953 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
26954 line="5",times="0"@}]@}
26958 @subheading The @code{-break-info} Command
26959 @findex -break-info
26961 @subsubheading Synopsis
26964 -break-info @var{breakpoint}
26968 Get information about a single breakpoint.
26970 @subsubheading @value{GDBN} Command
26972 The corresponding @value{GDBN} command is @samp{info break @var{breakpoint}}.
26974 @subsubheading Example
26977 @subheading The @code{-break-insert} Command
26978 @findex -break-insert
26980 @subsubheading Synopsis
26983 -break-insert [ -t ] [ -h ] [ -f ] [ -d ] [ -a ]
26984 [ -c @var{condition} ] [ -i @var{ignore-count} ]
26985 [ -p @var{thread} ] [ @var{location} ]
26989 If specified, @var{location}, can be one of:
26996 @item filename:linenum
26997 @item filename:function
27001 The possible optional parameters of this command are:
27005 Insert a temporary breakpoint.
27007 Insert a hardware breakpoint.
27008 @item -c @var{condition}
27009 Make the breakpoint conditional on @var{condition}.
27010 @item -i @var{ignore-count}
27011 Initialize the @var{ignore-count}.
27013 If @var{location} cannot be parsed (for example if it
27014 refers to unknown files or functions), create a pending
27015 breakpoint. Without this flag, @value{GDBN} will report
27016 an error, and won't create a breakpoint, if @var{location}
27019 Create a disabled breakpoint.
27021 Create a tracepoint. @xref{Tracepoints}. When this parameter
27022 is used together with @samp{-h}, a fast tracepoint is created.
27025 @subsubheading Result
27027 The result is in the form:
27030 ^done,bkpt=@{number="@var{number}",type="@var{type}",disp="del"|"keep",
27031 enabled="y"|"n",addr="@var{hex}",func="@var{funcname}",file="@var{filename}",
27032 fullname="@var{full_filename}",line="@var{lineno}",[thread="@var{threadno},]
27033 times="@var{times}"@}
27037 where @var{number} is the @value{GDBN} number for this breakpoint,
27038 @var{funcname} is the name of the function where the breakpoint was
27039 inserted, @var{filename} is the name of the source file which contains
27040 this function, @var{lineno} is the source line number within that file
27041 and @var{times} the number of times that the breakpoint has been hit
27042 (always 0 for -break-insert but may be greater for -break-info or -break-list
27043 which use the same output).
27045 Note: this format is open to change.
27046 @c An out-of-band breakpoint instead of part of the result?
27048 @subsubheading @value{GDBN} Command
27050 The corresponding @value{GDBN} commands are @samp{break}, @samp{tbreak},
27051 @samp{hbreak}, @samp{thbreak}, and @samp{rbreak}.
27053 @subsubheading Example
27058 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",
27059 fullname="/home/foo/recursive2.c,line="4",times="0"@}
27061 -break-insert -t foo
27062 ^done,bkpt=@{number="2",addr="0x00010774",file="recursive2.c",
27063 fullname="/home/foo/recursive2.c,line="11",times="0"@}
27066 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
27067 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27068 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27069 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27070 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27071 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27072 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27073 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
27074 addr="0x0001072c", func="main",file="recursive2.c",
27075 fullname="/home/foo/recursive2.c,"line="4",times="0"@},
27076 bkpt=@{number="2",type="breakpoint",disp="del",enabled="y",
27077 addr="0x00010774",func="foo",file="recursive2.c",
27078 fullname="/home/foo/recursive2.c",line="11",times="0"@}]@}
27080 -break-insert -r foo.*
27081 ~int foo(int, int);
27082 ^done,bkpt=@{number="3",addr="0x00010774",file="recursive2.c,
27083 "fullname="/home/foo/recursive2.c",line="11",times="0"@}
27087 @subheading The @code{-break-list} Command
27088 @findex -break-list
27090 @subsubheading Synopsis
27096 Displays the list of inserted breakpoints, showing the following fields:
27100 number of the breakpoint
27102 type of the breakpoint: @samp{breakpoint} or @samp{watchpoint}
27104 should the breakpoint be deleted or disabled when it is hit: @samp{keep}
27107 is the breakpoint enabled or no: @samp{y} or @samp{n}
27109 memory location at which the breakpoint is set
27111 logical location of the breakpoint, expressed by function name, file
27114 number of times the breakpoint has been hit
27117 If there are no breakpoints or watchpoints, the @code{BreakpointTable}
27118 @code{body} field is an empty list.
27120 @subsubheading @value{GDBN} Command
27122 The corresponding @value{GDBN} command is @samp{info break}.
27124 @subsubheading Example
27129 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
27130 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27131 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27132 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27133 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27134 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27135 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27136 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
27137 addr="0x000100d0",func="main",file="hello.c",line="5",times="0"@},
27138 bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
27139 addr="0x00010114",func="foo",file="hello.c",fullname="/home/foo/hello.c",
27140 line="13",times="0"@}]@}
27144 Here's an example of the result when there are no breakpoints:
27149 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
27150 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27151 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27152 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27153 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27154 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27155 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27160 @subheading The @code{-break-passcount} Command
27161 @findex -break-passcount
27163 @subsubheading Synopsis
27166 -break-passcount @var{tracepoint-number} @var{passcount}
27169 Set the passcount for tracepoint @var{tracepoint-number} to
27170 @var{passcount}. If the breakpoint referred to by @var{tracepoint-number}
27171 is not a tracepoint, error is emitted. This corresponds to CLI
27172 command @samp{passcount}.
27174 @subheading The @code{-break-watch} Command
27175 @findex -break-watch
27177 @subsubheading Synopsis
27180 -break-watch [ -a | -r ]
27183 Create a watchpoint. With the @samp{-a} option it will create an
27184 @dfn{access} watchpoint, i.e., a watchpoint that triggers either on a
27185 read from or on a write to the memory location. With the @samp{-r}
27186 option, the watchpoint created is a @dfn{read} watchpoint, i.e., it will
27187 trigger only when the memory location is accessed for reading. Without
27188 either of the options, the watchpoint created is a regular watchpoint,
27189 i.e., it will trigger when the memory location is accessed for writing.
27190 @xref{Set Watchpoints, , Setting Watchpoints}.
27192 Note that @samp{-break-list} will report a single list of watchpoints and
27193 breakpoints inserted.
27195 @subsubheading @value{GDBN} Command
27197 The corresponding @value{GDBN} commands are @samp{watch}, @samp{awatch}, and
27200 @subsubheading Example
27202 Setting a watchpoint on a variable in the @code{main} function:
27207 ^done,wpt=@{number="2",exp="x"@}
27212 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="x"@},
27213 value=@{old="-268439212",new="55"@},
27214 frame=@{func="main",args=[],file="recursive2.c",
27215 fullname="/home/foo/bar/recursive2.c",line="5"@}
27219 Setting a watchpoint on a variable local to a function. @value{GDBN} will stop
27220 the program execution twice: first for the variable changing value, then
27221 for the watchpoint going out of scope.
27226 ^done,wpt=@{number="5",exp="C"@}
27231 *stopped,reason="watchpoint-trigger",
27232 wpt=@{number="5",exp="C"@},value=@{old="-276895068",new="3"@},
27233 frame=@{func="callee4",args=[],
27234 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27235 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
27240 *stopped,reason="watchpoint-scope",wpnum="5",
27241 frame=@{func="callee3",args=[@{name="strarg",
27242 value="0x11940 \"A string argument.\""@}],
27243 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27244 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
27248 Listing breakpoints and watchpoints, at different points in the program
27249 execution. Note that once the watchpoint goes out of scope, it is
27255 ^done,wpt=@{number="2",exp="C"@}
27258 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
27259 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27260 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27261 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27262 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27263 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27264 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27265 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
27266 addr="0x00010734",func="callee4",
27267 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27268 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c"line="8",times="1"@},
27269 bkpt=@{number="2",type="watchpoint",disp="keep",
27270 enabled="y",addr="",what="C",times="0"@}]@}
27275 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="C"@},
27276 value=@{old="-276895068",new="3"@},
27277 frame=@{func="callee4",args=[],
27278 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27279 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
27282 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
27283 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27284 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27285 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27286 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27287 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27288 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27289 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
27290 addr="0x00010734",func="callee4",
27291 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27292 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",times="1"@},
27293 bkpt=@{number="2",type="watchpoint",disp="keep",
27294 enabled="y",addr="",what="C",times="-5"@}]@}
27298 ^done,reason="watchpoint-scope",wpnum="2",
27299 frame=@{func="callee3",args=[@{name="strarg",
27300 value="0x11940 \"A string argument.\""@}],
27301 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27302 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
27305 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
27306 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27307 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27308 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27309 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27310 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27311 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27312 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
27313 addr="0x00010734",func="callee4",
27314 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27315 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",
27320 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27321 @node GDB/MI Program Context
27322 @section @sc{gdb/mi} Program Context
27324 @subheading The @code{-exec-arguments} Command
27325 @findex -exec-arguments
27328 @subsubheading Synopsis
27331 -exec-arguments @var{args}
27334 Set the inferior program arguments, to be used in the next
27337 @subsubheading @value{GDBN} Command
27339 The corresponding @value{GDBN} command is @samp{set args}.
27341 @subsubheading Example
27345 -exec-arguments -v word
27352 @subheading The @code{-exec-show-arguments} Command
27353 @findex -exec-show-arguments
27355 @subsubheading Synopsis
27358 -exec-show-arguments
27361 Print the arguments of the program.
27363 @subsubheading @value{GDBN} Command
27365 The corresponding @value{GDBN} command is @samp{show args}.
27367 @subsubheading Example
27372 @subheading The @code{-environment-cd} Command
27373 @findex -environment-cd
27375 @subsubheading Synopsis
27378 -environment-cd @var{pathdir}
27381 Set @value{GDBN}'s working directory.
27383 @subsubheading @value{GDBN} Command
27385 The corresponding @value{GDBN} command is @samp{cd}.
27387 @subsubheading Example
27391 -environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
27397 @subheading The @code{-environment-directory} Command
27398 @findex -environment-directory
27400 @subsubheading Synopsis
27403 -environment-directory [ -r ] [ @var{pathdir} ]+
27406 Add directories @var{pathdir} to beginning of search path for source files.
27407 If the @samp{-r} option is used, the search path is reset to the default
27408 search path. If directories @var{pathdir} are supplied in addition to the
27409 @samp{-r} option, the search path is first reset and then addition
27411 Multiple directories may be specified, separated by blanks. Specifying
27412 multiple directories in a single command
27413 results in the directories added to the beginning of the
27414 search path in the same order they were presented in the command.
27415 If blanks are needed as
27416 part of a directory name, double-quotes should be used around
27417 the name. In the command output, the path will show up separated
27418 by the system directory-separator character. The directory-separator
27419 character must not be used
27420 in any directory name.
27421 If no directories are specified, the current search path is displayed.
27423 @subsubheading @value{GDBN} Command
27425 The corresponding @value{GDBN} command is @samp{dir}.
27427 @subsubheading Example
27431 -environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
27432 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
27434 -environment-directory ""
27435 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
27437 -environment-directory -r /home/jjohnstn/src/gdb /usr/src
27438 ^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd"
27440 -environment-directory -r
27441 ^done,source-path="$cdir:$cwd"
27446 @subheading The @code{-environment-path} Command
27447 @findex -environment-path
27449 @subsubheading Synopsis
27452 -environment-path [ -r ] [ @var{pathdir} ]+
27455 Add directories @var{pathdir} to beginning of search path for object files.
27456 If the @samp{-r} option is used, the search path is reset to the original
27457 search path that existed at gdb start-up. If directories @var{pathdir} are
27458 supplied in addition to the
27459 @samp{-r} option, the search path is first reset and then addition
27461 Multiple directories may be specified, separated by blanks. Specifying
27462 multiple directories in a single command
27463 results in the directories added to the beginning of the
27464 search path in the same order they were presented in the command.
27465 If blanks are needed as
27466 part of a directory name, double-quotes should be used around
27467 the name. In the command output, the path will show up separated
27468 by the system directory-separator character. The directory-separator
27469 character must not be used
27470 in any directory name.
27471 If no directories are specified, the current path is displayed.
27474 @subsubheading @value{GDBN} Command
27476 The corresponding @value{GDBN} command is @samp{path}.
27478 @subsubheading Example
27483 ^done,path="/usr/bin"
27485 -environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb /bin
27486 ^done,path="/kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb:/bin:/usr/bin"
27488 -environment-path -r /usr/local/bin
27489 ^done,path="/usr/local/bin:/usr/bin"
27494 @subheading The @code{-environment-pwd} Command
27495 @findex -environment-pwd
27497 @subsubheading Synopsis
27503 Show the current working directory.
27505 @subsubheading @value{GDBN} Command
27507 The corresponding @value{GDBN} command is @samp{pwd}.
27509 @subsubheading Example
27514 ^done,cwd="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb"
27518 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27519 @node GDB/MI Thread Commands
27520 @section @sc{gdb/mi} Thread Commands
27523 @subheading The @code{-thread-info} Command
27524 @findex -thread-info
27526 @subsubheading Synopsis
27529 -thread-info [ @var{thread-id} ]
27532 Reports information about either a specific thread, if
27533 the @var{thread-id} parameter is present, or about all
27534 threads. When printing information about all threads,
27535 also reports the current thread.
27537 @subsubheading @value{GDBN} Command
27539 The @samp{info thread} command prints the same information
27542 @subsubheading Result
27544 The result is a list of threads. The following attributes are
27545 defined for a given thread:
27549 This field exists only for the current thread. It has the value @samp{*}.
27552 The identifier that @value{GDBN} uses to refer to the thread.
27555 The identifier that the target uses to refer to the thread.
27558 Extra information about the thread, in a target-specific format. This
27562 The name of the thread. If the user specified a name using the
27563 @code{thread name} command, then this name is given. Otherwise, if
27564 @value{GDBN} can extract the thread name from the target, then that
27565 name is given. If @value{GDBN} cannot find the thread name, then this
27569 The stack frame currently executing in the thread.
27572 The thread's state. The @samp{state} field may have the following
27577 The thread is stopped. Frame information is available for stopped
27581 The thread is running. There's no frame information for running
27587 If @value{GDBN} can find the CPU core on which this thread is running,
27588 then this field is the core identifier. This field is optional.
27592 @subsubheading Example
27597 @{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
27598 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",
27599 args=[]@},state="running"@},
27600 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
27601 frame=@{level="0",addr="0x0804891f",func="foo",
27602 args=[@{name="i",value="10"@}],
27603 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},
27604 state="running"@}],
27605 current-thread-id="1"
27609 @subheading The @code{-thread-list-ids} Command
27610 @findex -thread-list-ids
27612 @subsubheading Synopsis
27618 Produces a list of the currently known @value{GDBN} thread ids. At the
27619 end of the list it also prints the total number of such threads.
27621 This command is retained for historical reasons, the
27622 @code{-thread-info} command should be used instead.
27624 @subsubheading @value{GDBN} Command
27626 Part of @samp{info threads} supplies the same information.
27628 @subsubheading Example
27633 ^done,thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
27634 current-thread-id="1",number-of-threads="3"
27639 @subheading The @code{-thread-select} Command
27640 @findex -thread-select
27642 @subsubheading Synopsis
27645 -thread-select @var{threadnum}
27648 Make @var{threadnum} the current thread. It prints the number of the new
27649 current thread, and the topmost frame for that thread.
27651 This command is deprecated in favor of explicitly using the
27652 @samp{--thread} option to each command.
27654 @subsubheading @value{GDBN} Command
27656 The corresponding @value{GDBN} command is @samp{thread}.
27658 @subsubheading Example
27665 *stopped,reason="end-stepping-range",thread-id="2",line="187",
27666 file="../../../devo/gdb/testsuite/gdb.threads/linux-dp.c"
27670 thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
27671 number-of-threads="3"
27674 ^done,new-thread-id="3",
27675 frame=@{level="0",func="vprintf",
27676 args=[@{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""@},
27677 @{name="arg",value="0x2"@}],file="vprintf.c",line="31"@}
27681 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27682 @node GDB/MI Ada Tasking Commands
27683 @section @sc{gdb/mi} Ada Tasking Commands
27685 @subheading The @code{-ada-task-info} Command
27686 @findex -ada-task-info
27688 @subsubheading Synopsis
27691 -ada-task-info [ @var{task-id} ]
27694 Reports information about either a specific Ada task, if the
27695 @var{task-id} parameter is present, or about all Ada tasks.
27697 @subsubheading @value{GDBN} Command
27699 The @samp{info tasks} command prints the same information
27700 about all Ada tasks (@pxref{Ada Tasks}).
27702 @subsubheading Result
27704 The result is a table of Ada tasks. The following columns are
27705 defined for each Ada task:
27709 This field exists only for the current thread. It has the value @samp{*}.
27712 The identifier that @value{GDBN} uses to refer to the Ada task.
27715 The identifier that the target uses to refer to the Ada task.
27718 The identifier of the thread corresponding to the Ada task.
27720 This field should always exist, as Ada tasks are always implemented
27721 on top of a thread. But if @value{GDBN} cannot find this corresponding
27722 thread for any reason, the field is omitted.
27725 This field exists only when the task was created by another task.
27726 In this case, it provides the ID of the parent task.
27729 The base priority of the task.
27732 The current state of the task. For a detailed description of the
27733 possible states, see @ref{Ada Tasks}.
27736 The name of the task.
27740 @subsubheading Example
27744 ^done,tasks=@{nr_rows="3",nr_cols="8",
27745 hdr=[@{width="1",alignment="-1",col_name="current",colhdr=""@},
27746 @{width="3",alignment="1",col_name="id",colhdr="ID"@},
27747 @{width="9",alignment="1",col_name="task-id",colhdr="TID"@},
27748 @{width="4",alignment="1",col_name="thread-id",colhdr=""@},
27749 @{width="4",alignment="1",col_name="parent-id",colhdr="P-ID"@},
27750 @{width="3",alignment="1",col_name="priority",colhdr="Pri"@},
27751 @{width="22",alignment="-1",col_name="state",colhdr="State"@},
27752 @{width="1",alignment="2",col_name="name",colhdr="Name"@}],
27753 body=[@{current="*",id="1",task-id=" 644010",thread-id="1",priority="48",
27754 state="Child Termination Wait",name="main_task"@}]@}
27758 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27759 @node GDB/MI Program Execution
27760 @section @sc{gdb/mi} Program Execution
27762 These are the asynchronous commands which generate the out-of-band
27763 record @samp{*stopped}. Currently @value{GDBN} only really executes
27764 asynchronously with remote targets and this interaction is mimicked in
27767 @subheading The @code{-exec-continue} Command
27768 @findex -exec-continue
27770 @subsubheading Synopsis
27773 -exec-continue [--reverse] [--all|--thread-group N]
27776 Resumes the execution of the inferior program, which will continue
27777 to execute until it reaches a debugger stop event. If the
27778 @samp{--reverse} option is specified, execution resumes in reverse until
27779 it reaches a stop event. Stop events may include
27782 breakpoints or watchpoints
27784 signals or exceptions
27786 the end of the process (or its beginning under @samp{--reverse})
27788 the end or beginning of a replay log if one is being used.
27790 In all-stop mode (@pxref{All-Stop
27791 Mode}), may resume only one thread, or all threads, depending on the
27792 value of the @samp{scheduler-locking} variable. If @samp{--all} is
27793 specified, all threads (in all inferiors) will be resumed. The @samp{--all} option is
27794 ignored in all-stop mode. If the @samp{--thread-group} options is
27795 specified, then all threads in that thread group are resumed.
27797 @subsubheading @value{GDBN} Command
27799 The corresponding @value{GDBN} corresponding is @samp{continue}.
27801 @subsubheading Example
27808 *stopped,reason="breakpoint-hit",disp="keep",bkptno="2",frame=@{
27809 func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c",
27815 @subheading The @code{-exec-finish} Command
27816 @findex -exec-finish
27818 @subsubheading Synopsis
27821 -exec-finish [--reverse]
27824 Resumes the execution of the inferior program until the current
27825 function is exited. Displays the results returned by the function.
27826 If the @samp{--reverse} option is specified, resumes the reverse
27827 execution of the inferior program until the point where current
27828 function was called.
27830 @subsubheading @value{GDBN} Command
27832 The corresponding @value{GDBN} command is @samp{finish}.
27834 @subsubheading Example
27836 Function returning @code{void}.
27843 *stopped,reason="function-finished",frame=@{func="main",args=[],
27844 file="hello.c",fullname="/home/foo/bar/hello.c",line="7"@}
27848 Function returning other than @code{void}. The name of the internal
27849 @value{GDBN} variable storing the result is printed, together with the
27856 *stopped,reason="function-finished",frame=@{addr="0x000107b0",func="foo",
27857 args=[@{name="a",value="1"],@{name="b",value="9"@}@},
27858 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
27859 gdb-result-var="$1",return-value="0"
27864 @subheading The @code{-exec-interrupt} Command
27865 @findex -exec-interrupt
27867 @subsubheading Synopsis
27870 -exec-interrupt [--all|--thread-group N]
27873 Interrupts the background execution of the target. Note how the token
27874 associated with the stop message is the one for the execution command
27875 that has been interrupted. The token for the interrupt itself only
27876 appears in the @samp{^done} output. If the user is trying to
27877 interrupt a non-running program, an error message will be printed.
27879 Note that when asynchronous execution is enabled, this command is
27880 asynchronous just like other execution commands. That is, first the
27881 @samp{^done} response will be printed, and the target stop will be
27882 reported after that using the @samp{*stopped} notification.
27884 In non-stop mode, only the context thread is interrupted by default.
27885 All threads (in all inferiors) will be interrupted if the
27886 @samp{--all} option is specified. If the @samp{--thread-group}
27887 option is specified, all threads in that group will be interrupted.
27889 @subsubheading @value{GDBN} Command
27891 The corresponding @value{GDBN} command is @samp{interrupt}.
27893 @subsubheading Example
27904 111*stopped,signal-name="SIGINT",signal-meaning="Interrupt",
27905 frame=@{addr="0x00010140",func="foo",args=[],file="try.c",
27906 fullname="/home/foo/bar/try.c",line="13"@}
27911 ^error,msg="mi_cmd_exec_interrupt: Inferior not executing."
27915 @subheading The @code{-exec-jump} Command
27918 @subsubheading Synopsis
27921 -exec-jump @var{location}
27924 Resumes execution of the inferior program at the location specified by
27925 parameter. @xref{Specify Location}, for a description of the
27926 different forms of @var{location}.
27928 @subsubheading @value{GDBN} Command
27930 The corresponding @value{GDBN} command is @samp{jump}.
27932 @subsubheading Example
27935 -exec-jump foo.c:10
27936 *running,thread-id="all"
27941 @subheading The @code{-exec-next} Command
27944 @subsubheading Synopsis
27947 -exec-next [--reverse]
27950 Resumes execution of the inferior program, stopping when the beginning
27951 of the next source line is reached.
27953 If the @samp{--reverse} option is specified, resumes reverse execution
27954 of the inferior program, stopping at the beginning of the previous
27955 source line. If you issue this command on the first line of a
27956 function, it will take you back to the caller of that function, to the
27957 source line where the function was called.
27960 @subsubheading @value{GDBN} Command
27962 The corresponding @value{GDBN} command is @samp{next}.
27964 @subsubheading Example
27970 *stopped,reason="end-stepping-range",line="8",file="hello.c"
27975 @subheading The @code{-exec-next-instruction} Command
27976 @findex -exec-next-instruction
27978 @subsubheading Synopsis
27981 -exec-next-instruction [--reverse]
27984 Executes one machine instruction. If the instruction is a function
27985 call, continues until the function returns. If the program stops at an
27986 instruction in the middle of a source line, the address will be
27989 If the @samp{--reverse} option is specified, resumes reverse execution
27990 of the inferior program, stopping at the previous instruction. If the
27991 previously executed instruction was a return from another function,
27992 it will continue to execute in reverse until the call to that function
27993 (from the current stack frame) is reached.
27995 @subsubheading @value{GDBN} Command
27997 The corresponding @value{GDBN} command is @samp{nexti}.
27999 @subsubheading Example
28003 -exec-next-instruction
28007 *stopped,reason="end-stepping-range",
28008 addr="0x000100d4",line="5",file="hello.c"
28013 @subheading The @code{-exec-return} Command
28014 @findex -exec-return
28016 @subsubheading Synopsis
28022 Makes current function return immediately. Doesn't execute the inferior.
28023 Displays the new current frame.
28025 @subsubheading @value{GDBN} Command
28027 The corresponding @value{GDBN} command is @samp{return}.
28029 @subsubheading Example
28033 200-break-insert callee4
28034 200^done,bkpt=@{number="1",addr="0x00010734",
28035 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
28040 000*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
28041 frame=@{func="callee4",args=[],
28042 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
28043 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
28049 111^done,frame=@{level="0",func="callee3",
28050 args=[@{name="strarg",
28051 value="0x11940 \"A string argument.\""@}],
28052 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
28053 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
28058 @subheading The @code{-exec-run} Command
28061 @subsubheading Synopsis
28064 -exec-run [--all | --thread-group N]
28067 Starts execution of the inferior from the beginning. The inferior
28068 executes until either a breakpoint is encountered or the program
28069 exits. In the latter case the output will include an exit code, if
28070 the program has exited exceptionally.
28072 When no option is specified, the current inferior is started. If the
28073 @samp{--thread-group} option is specified, it should refer to a thread
28074 group of type @samp{process}, and that thread group will be started.
28075 If the @samp{--all} option is specified, then all inferiors will be started.
28077 @subsubheading @value{GDBN} Command
28079 The corresponding @value{GDBN} command is @samp{run}.
28081 @subsubheading Examples
28086 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",line="4"@}
28091 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
28092 frame=@{func="main",args=[],file="recursive2.c",
28093 fullname="/home/foo/bar/recursive2.c",line="4"@}
28098 Program exited normally:
28106 *stopped,reason="exited-normally"
28111 Program exited exceptionally:
28119 *stopped,reason="exited",exit-code="01"
28123 Another way the program can terminate is if it receives a signal such as
28124 @code{SIGINT}. In this case, @sc{gdb/mi} displays this:
28128 *stopped,reason="exited-signalled",signal-name="SIGINT",
28129 signal-meaning="Interrupt"
28133 @c @subheading -exec-signal
28136 @subheading The @code{-exec-step} Command
28139 @subsubheading Synopsis
28142 -exec-step [--reverse]
28145 Resumes execution of the inferior program, stopping when the beginning
28146 of the next source line is reached, if the next source line is not a
28147 function call. If it is, stop at the first instruction of the called
28148 function. If the @samp{--reverse} option is specified, resumes reverse
28149 execution of the inferior program, stopping at the beginning of the
28150 previously executed source line.
28152 @subsubheading @value{GDBN} Command
28154 The corresponding @value{GDBN} command is @samp{step}.
28156 @subsubheading Example
28158 Stepping into a function:
28164 *stopped,reason="end-stepping-range",
28165 frame=@{func="foo",args=[@{name="a",value="10"@},
28166 @{name="b",value="0"@}],file="recursive2.c",
28167 fullname="/home/foo/bar/recursive2.c",line="11"@}
28177 *stopped,reason="end-stepping-range",line="14",file="recursive2.c"
28182 @subheading The @code{-exec-step-instruction} Command
28183 @findex -exec-step-instruction
28185 @subsubheading Synopsis
28188 -exec-step-instruction [--reverse]
28191 Resumes the inferior which executes one machine instruction. If the
28192 @samp{--reverse} option is specified, resumes reverse execution of the
28193 inferior program, stopping at the previously executed instruction.
28194 The output, once @value{GDBN} has stopped, will vary depending on
28195 whether we have stopped in the middle of a source line or not. In the
28196 former case, the address at which the program stopped will be printed
28199 @subsubheading @value{GDBN} Command
28201 The corresponding @value{GDBN} command is @samp{stepi}.
28203 @subsubheading Example
28207 -exec-step-instruction
28211 *stopped,reason="end-stepping-range",
28212 frame=@{func="foo",args=[],file="try.c",
28213 fullname="/home/foo/bar/try.c",line="10"@}
28215 -exec-step-instruction
28219 *stopped,reason="end-stepping-range",
28220 frame=@{addr="0x000100f4",func="foo",args=[],file="try.c",
28221 fullname="/home/foo/bar/try.c",line="10"@}
28226 @subheading The @code{-exec-until} Command
28227 @findex -exec-until
28229 @subsubheading Synopsis
28232 -exec-until [ @var{location} ]
28235 Executes the inferior until the @var{location} specified in the
28236 argument is reached. If there is no argument, the inferior executes
28237 until a source line greater than the current one is reached. The
28238 reason for stopping in this case will be @samp{location-reached}.
28240 @subsubheading @value{GDBN} Command
28242 The corresponding @value{GDBN} command is @samp{until}.
28244 @subsubheading Example
28248 -exec-until recursive2.c:6
28252 *stopped,reason="location-reached",frame=@{func="main",args=[],
28253 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="6"@}
28258 @subheading -file-clear
28259 Is this going away????
28262 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
28263 @node GDB/MI Stack Manipulation
28264 @section @sc{gdb/mi} Stack Manipulation Commands
28267 @subheading The @code{-stack-info-frame} Command
28268 @findex -stack-info-frame
28270 @subsubheading Synopsis
28276 Get info on the selected frame.
28278 @subsubheading @value{GDBN} Command
28280 The corresponding @value{GDBN} command is @samp{info frame} or @samp{frame}
28281 (without arguments).
28283 @subsubheading Example
28288 ^done,frame=@{level="1",addr="0x0001076c",func="callee3",
28289 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
28290 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@}
28294 @subheading The @code{-stack-info-depth} Command
28295 @findex -stack-info-depth
28297 @subsubheading Synopsis
28300 -stack-info-depth [ @var{max-depth} ]
28303 Return the depth of the stack. If the integer argument @var{max-depth}
28304 is specified, do not count beyond @var{max-depth} frames.
28306 @subsubheading @value{GDBN} Command
28308 There's no equivalent @value{GDBN} command.
28310 @subsubheading Example
28312 For a stack with frame levels 0 through 11:
28319 -stack-info-depth 4
28322 -stack-info-depth 12
28325 -stack-info-depth 11
28328 -stack-info-depth 13
28333 @subheading The @code{-stack-list-arguments} Command
28334 @findex -stack-list-arguments
28336 @subsubheading Synopsis
28339 -stack-list-arguments @var{print-values}
28340 [ @var{low-frame} @var{high-frame} ]
28343 Display a list of the arguments for the frames between @var{low-frame}
28344 and @var{high-frame} (inclusive). If @var{low-frame} and
28345 @var{high-frame} are not provided, list the arguments for the whole
28346 call stack. If the two arguments are equal, show the single frame
28347 at the corresponding level. It is an error if @var{low-frame} is
28348 larger than the actual number of frames. On the other hand,
28349 @var{high-frame} may be larger than the actual number of frames, in
28350 which case only existing frames will be returned.
28352 If @var{print-values} is 0 or @code{--no-values}, print only the names of
28353 the variables; if it is 1 or @code{--all-values}, print also their
28354 values; and if it is 2 or @code{--simple-values}, print the name,
28355 type and value for simple data types, and the name and type for arrays,
28356 structures and unions.
28358 Use of this command to obtain arguments in a single frame is
28359 deprecated in favor of the @samp{-stack-list-variables} command.
28361 @subsubheading @value{GDBN} Command
28363 @value{GDBN} does not have an equivalent command. @code{gdbtk} has a
28364 @samp{gdb_get_args} command which partially overlaps with the
28365 functionality of @samp{-stack-list-arguments}.
28367 @subsubheading Example
28374 frame=@{level="0",addr="0x00010734",func="callee4",
28375 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
28376 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@},
28377 frame=@{level="1",addr="0x0001076c",func="callee3",
28378 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
28379 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@},
28380 frame=@{level="2",addr="0x0001078c",func="callee2",
28381 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
28382 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="22"@},
28383 frame=@{level="3",addr="0x000107b4",func="callee1",
28384 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
28385 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="27"@},
28386 frame=@{level="4",addr="0x000107e0",func="main",
28387 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
28388 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="32"@}]
28390 -stack-list-arguments 0
28393 frame=@{level="0",args=[]@},
28394 frame=@{level="1",args=[name="strarg"]@},
28395 frame=@{level="2",args=[name="intarg",name="strarg"]@},
28396 frame=@{level="3",args=[name="intarg",name="strarg",name="fltarg"]@},
28397 frame=@{level="4",args=[]@}]
28399 -stack-list-arguments 1
28402 frame=@{level="0",args=[]@},
28404 args=[@{name="strarg",value="0x11940 \"A string argument.\""@}]@},
28405 frame=@{level="2",args=[
28406 @{name="intarg",value="2"@},
28407 @{name="strarg",value="0x11940 \"A string argument.\""@}]@},
28408 @{frame=@{level="3",args=[
28409 @{name="intarg",value="2"@},
28410 @{name="strarg",value="0x11940 \"A string argument.\""@},
28411 @{name="fltarg",value="3.5"@}]@},
28412 frame=@{level="4",args=[]@}]
28414 -stack-list-arguments 0 2 2
28415 ^done,stack-args=[frame=@{level="2",args=[name="intarg",name="strarg"]@}]
28417 -stack-list-arguments 1 2 2
28418 ^done,stack-args=[frame=@{level="2",
28419 args=[@{name="intarg",value="2"@},
28420 @{name="strarg",value="0x11940 \"A string argument.\""@}]@}]
28424 @c @subheading -stack-list-exception-handlers
28427 @subheading The @code{-stack-list-frames} Command
28428 @findex -stack-list-frames
28430 @subsubheading Synopsis
28433 -stack-list-frames [ @var{low-frame} @var{high-frame} ]
28436 List the frames currently on the stack. For each frame it displays the
28441 The frame number, 0 being the topmost frame, i.e., the innermost function.
28443 The @code{$pc} value for that frame.
28447 File name of the source file where the function lives.
28448 @item @var{fullname}
28449 The full file name of the source file where the function lives.
28451 Line number corresponding to the @code{$pc}.
28453 The shared library where this function is defined. This is only given
28454 if the frame's function is not known.
28457 If invoked without arguments, this command prints a backtrace for the
28458 whole stack. If given two integer arguments, it shows the frames whose
28459 levels are between the two arguments (inclusive). If the two arguments
28460 are equal, it shows the single frame at the corresponding level. It is
28461 an error if @var{low-frame} is larger than the actual number of
28462 frames. On the other hand, @var{high-frame} may be larger than the
28463 actual number of frames, in which case only existing frames will be returned.
28465 @subsubheading @value{GDBN} Command
28467 The corresponding @value{GDBN} commands are @samp{backtrace} and @samp{where}.
28469 @subsubheading Example
28471 Full stack backtrace:
28477 [frame=@{level="0",addr="0x0001076c",func="foo",
28478 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11"@},
28479 frame=@{level="1",addr="0x000107a4",func="foo",
28480 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
28481 frame=@{level="2",addr="0x000107a4",func="foo",
28482 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
28483 frame=@{level="3",addr="0x000107a4",func="foo",
28484 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
28485 frame=@{level="4",addr="0x000107a4",func="foo",
28486 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
28487 frame=@{level="5",addr="0x000107a4",func="foo",
28488 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
28489 frame=@{level="6",addr="0x000107a4",func="foo",
28490 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
28491 frame=@{level="7",addr="0x000107a4",func="foo",
28492 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
28493 frame=@{level="8",addr="0x000107a4",func="foo",
28494 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
28495 frame=@{level="9",addr="0x000107a4",func="foo",
28496 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
28497 frame=@{level="10",addr="0x000107a4",func="foo",
28498 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
28499 frame=@{level="11",addr="0x00010738",func="main",
28500 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4"@}]
28504 Show frames between @var{low_frame} and @var{high_frame}:
28508 -stack-list-frames 3 5
28510 [frame=@{level="3",addr="0x000107a4",func="foo",
28511 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
28512 frame=@{level="4",addr="0x000107a4",func="foo",
28513 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
28514 frame=@{level="5",addr="0x000107a4",func="foo",
28515 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
28519 Show a single frame:
28523 -stack-list-frames 3 3
28525 [frame=@{level="3",addr="0x000107a4",func="foo",
28526 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
28531 @subheading The @code{-stack-list-locals} Command
28532 @findex -stack-list-locals
28534 @subsubheading Synopsis
28537 -stack-list-locals @var{print-values}
28540 Display the local variable names for the selected frame. If
28541 @var{print-values} is 0 or @code{--no-values}, print only the names of
28542 the variables; if it is 1 or @code{--all-values}, print also their
28543 values; and if it is 2 or @code{--simple-values}, print the name,
28544 type and value for simple data types, and the name and type for arrays,
28545 structures and unions. In this last case, a frontend can immediately
28546 display the value of simple data types and create variable objects for
28547 other data types when the user wishes to explore their values in
28550 This command is deprecated in favor of the
28551 @samp{-stack-list-variables} command.
28553 @subsubheading @value{GDBN} Command
28555 @samp{info locals} in @value{GDBN}, @samp{gdb_get_locals} in @code{gdbtk}.
28557 @subsubheading Example
28561 -stack-list-locals 0
28562 ^done,locals=[name="A",name="B",name="C"]
28564 -stack-list-locals --all-values
28565 ^done,locals=[@{name="A",value="1"@},@{name="B",value="2"@},
28566 @{name="C",value="@{1, 2, 3@}"@}]
28567 -stack-list-locals --simple-values
28568 ^done,locals=[@{name="A",type="int",value="1"@},
28569 @{name="B",type="int",value="2"@},@{name="C",type="int [3]"@}]
28573 @subheading The @code{-stack-list-variables} Command
28574 @findex -stack-list-variables
28576 @subsubheading Synopsis
28579 -stack-list-variables @var{print-values}
28582 Display the names of local variables and function arguments for the selected frame. If
28583 @var{print-values} is 0 or @code{--no-values}, print only the names of
28584 the variables; if it is 1 or @code{--all-values}, print also their
28585 values; and if it is 2 or @code{--simple-values}, print the name,
28586 type and value for simple data types, and the name and type for arrays,
28587 structures and unions.
28589 @subsubheading Example
28593 -stack-list-variables --thread 1 --frame 0 --all-values
28594 ^done,variables=[@{name="x",value="11"@},@{name="s",value="@{a = 1, b = 2@}"@}]
28599 @subheading The @code{-stack-select-frame} Command
28600 @findex -stack-select-frame
28602 @subsubheading Synopsis
28605 -stack-select-frame @var{framenum}
28608 Change the selected frame. Select a different frame @var{framenum} on
28611 This command in deprecated in favor of passing the @samp{--frame}
28612 option to every command.
28614 @subsubheading @value{GDBN} Command
28616 The corresponding @value{GDBN} commands are @samp{frame}, @samp{up},
28617 @samp{down}, @samp{select-frame}, @samp{up-silent}, and @samp{down-silent}.
28619 @subsubheading Example
28623 -stack-select-frame 2
28628 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
28629 @node GDB/MI Variable Objects
28630 @section @sc{gdb/mi} Variable Objects
28634 @subheading Motivation for Variable Objects in @sc{gdb/mi}
28636 For the implementation of a variable debugger window (locals, watched
28637 expressions, etc.), we are proposing the adaptation of the existing code
28638 used by @code{Insight}.
28640 The two main reasons for that are:
28644 It has been proven in practice (it is already on its second generation).
28647 It will shorten development time (needless to say how important it is
28651 The original interface was designed to be used by Tcl code, so it was
28652 slightly changed so it could be used through @sc{gdb/mi}. This section
28653 describes the @sc{gdb/mi} operations that will be available and gives some
28654 hints about their use.
28656 @emph{Note}: In addition to the set of operations described here, we
28657 expect the @sc{gui} implementation of a variable window to require, at
28658 least, the following operations:
28661 @item @code{-gdb-show} @code{output-radix}
28662 @item @code{-stack-list-arguments}
28663 @item @code{-stack-list-locals}
28664 @item @code{-stack-select-frame}
28669 @subheading Introduction to Variable Objects
28671 @cindex variable objects in @sc{gdb/mi}
28673 Variable objects are "object-oriented" MI interface for examining and
28674 changing values of expressions. Unlike some other MI interfaces that
28675 work with expressions, variable objects are specifically designed for
28676 simple and efficient presentation in the frontend. A variable object
28677 is identified by string name. When a variable object is created, the
28678 frontend specifies the expression for that variable object. The
28679 expression can be a simple variable, or it can be an arbitrary complex
28680 expression, and can even involve CPU registers. After creating a
28681 variable object, the frontend can invoke other variable object
28682 operations---for example to obtain or change the value of a variable
28683 object, or to change display format.
28685 Variable objects have hierarchical tree structure. Any variable object
28686 that corresponds to a composite type, such as structure in C, has
28687 a number of child variable objects, for example corresponding to each
28688 element of a structure. A child variable object can itself have
28689 children, recursively. Recursion ends when we reach
28690 leaf variable objects, which always have built-in types. Child variable
28691 objects are created only by explicit request, so if a frontend
28692 is not interested in the children of a particular variable object, no
28693 child will be created.
28695 For a leaf variable object it is possible to obtain its value as a
28696 string, or set the value from a string. String value can be also
28697 obtained for a non-leaf variable object, but it's generally a string
28698 that only indicates the type of the object, and does not list its
28699 contents. Assignment to a non-leaf variable object is not allowed.
28701 A frontend does not need to read the values of all variable objects each time
28702 the program stops. Instead, MI provides an update command that lists all
28703 variable objects whose values has changed since the last update
28704 operation. This considerably reduces the amount of data that must
28705 be transferred to the frontend. As noted above, children variable
28706 objects are created on demand, and only leaf variable objects have a
28707 real value. As result, gdb will read target memory only for leaf
28708 variables that frontend has created.
28710 The automatic update is not always desirable. For example, a frontend
28711 might want to keep a value of some expression for future reference,
28712 and never update it. For another example, fetching memory is
28713 relatively slow for embedded targets, so a frontend might want
28714 to disable automatic update for the variables that are either not
28715 visible on the screen, or ``closed''. This is possible using so
28716 called ``frozen variable objects''. Such variable objects are never
28717 implicitly updated.
28719 Variable objects can be either @dfn{fixed} or @dfn{floating}. For the
28720 fixed variable object, the expression is parsed when the variable
28721 object is created, including associating identifiers to specific
28722 variables. The meaning of expression never changes. For a floating
28723 variable object the values of variables whose names appear in the
28724 expressions are re-evaluated every time in the context of the current
28725 frame. Consider this example:
28730 struct work_state state;
28737 If a fixed variable object for the @code{state} variable is created in
28738 this function, and we enter the recursive call, the variable
28739 object will report the value of @code{state} in the top-level
28740 @code{do_work} invocation. On the other hand, a floating variable
28741 object will report the value of @code{state} in the current frame.
28743 If an expression specified when creating a fixed variable object
28744 refers to a local variable, the variable object becomes bound to the
28745 thread and frame in which the variable object is created. When such
28746 variable object is updated, @value{GDBN} makes sure that the
28747 thread/frame combination the variable object is bound to still exists,
28748 and re-evaluates the variable object in context of that thread/frame.
28750 The following is the complete set of @sc{gdb/mi} operations defined to
28751 access this functionality:
28753 @multitable @columnfractions .4 .6
28754 @item @strong{Operation}
28755 @tab @strong{Description}
28757 @item @code{-enable-pretty-printing}
28758 @tab enable Python-based pretty-printing
28759 @item @code{-var-create}
28760 @tab create a variable object
28761 @item @code{-var-delete}
28762 @tab delete the variable object and/or its children
28763 @item @code{-var-set-format}
28764 @tab set the display format of this variable
28765 @item @code{-var-show-format}
28766 @tab show the display format of this variable
28767 @item @code{-var-info-num-children}
28768 @tab tells how many children this object has
28769 @item @code{-var-list-children}
28770 @tab return a list of the object's children
28771 @item @code{-var-info-type}
28772 @tab show the type of this variable object
28773 @item @code{-var-info-expression}
28774 @tab print parent-relative expression that this variable object represents
28775 @item @code{-var-info-path-expression}
28776 @tab print full expression that this variable object represents
28777 @item @code{-var-show-attributes}
28778 @tab is this variable editable? does it exist here?
28779 @item @code{-var-evaluate-expression}
28780 @tab get the value of this variable
28781 @item @code{-var-assign}
28782 @tab set the value of this variable
28783 @item @code{-var-update}
28784 @tab update the variable and its children
28785 @item @code{-var-set-frozen}
28786 @tab set frozeness attribute
28787 @item @code{-var-set-update-range}
28788 @tab set range of children to display on update
28791 In the next subsection we describe each operation in detail and suggest
28792 how it can be used.
28794 @subheading Description And Use of Operations on Variable Objects
28796 @subheading The @code{-enable-pretty-printing} Command
28797 @findex -enable-pretty-printing
28800 -enable-pretty-printing
28803 @value{GDBN} allows Python-based visualizers to affect the output of the
28804 MI variable object commands. However, because there was no way to
28805 implement this in a fully backward-compatible way, a front end must
28806 request that this functionality be enabled.
28808 Once enabled, this feature cannot be disabled.
28810 Note that if Python support has not been compiled into @value{GDBN},
28811 this command will still succeed (and do nothing).
28813 This feature is currently (as of @value{GDBN} 7.0) experimental, and
28814 may work differently in future versions of @value{GDBN}.
28816 @subheading The @code{-var-create} Command
28817 @findex -var-create
28819 @subsubheading Synopsis
28822 -var-create @{@var{name} | "-"@}
28823 @{@var{frame-addr} | "*" | "@@"@} @var{expression}
28826 This operation creates a variable object, which allows the monitoring of
28827 a variable, the result of an expression, a memory cell or a CPU
28830 The @var{name} parameter is the string by which the object can be
28831 referenced. It must be unique. If @samp{-} is specified, the varobj
28832 system will generate a string ``varNNNNNN'' automatically. It will be
28833 unique provided that one does not specify @var{name} of that format.
28834 The command fails if a duplicate name is found.
28836 The frame under which the expression should be evaluated can be
28837 specified by @var{frame-addr}. A @samp{*} indicates that the current
28838 frame should be used. A @samp{@@} indicates that a floating variable
28839 object must be created.
28841 @var{expression} is any expression valid on the current language set (must not
28842 begin with a @samp{*}), or one of the following:
28846 @samp{*@var{addr}}, where @var{addr} is the address of a memory cell
28849 @samp{*@var{addr}-@var{addr}} --- a memory address range (TBD)
28852 @samp{$@var{regname}} --- a CPU register name
28855 @cindex dynamic varobj
28856 A varobj's contents may be provided by a Python-based pretty-printer. In this
28857 case the varobj is known as a @dfn{dynamic varobj}. Dynamic varobjs
28858 have slightly different semantics in some cases. If the
28859 @code{-enable-pretty-printing} command is not sent, then @value{GDBN}
28860 will never create a dynamic varobj. This ensures backward
28861 compatibility for existing clients.
28863 @subsubheading Result
28865 This operation returns attributes of the newly-created varobj. These
28870 The name of the varobj.
28873 The number of children of the varobj. This number is not necessarily
28874 reliable for a dynamic varobj. Instead, you must examine the
28875 @samp{has_more} attribute.
28878 The varobj's scalar value. For a varobj whose type is some sort of
28879 aggregate (e.g., a @code{struct}), or for a dynamic varobj, this value
28880 will not be interesting.
28883 The varobj's type. This is a string representation of the type, as
28884 would be printed by the @value{GDBN} CLI.
28887 If a variable object is bound to a specific thread, then this is the
28888 thread's identifier.
28891 For a dynamic varobj, this indicates whether there appear to be any
28892 children available. For a non-dynamic varobj, this will be 0.
28895 This attribute will be present and have the value @samp{1} if the
28896 varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
28897 then this attribute will not be present.
28900 A dynamic varobj can supply a display hint to the front end. The
28901 value comes directly from the Python pretty-printer object's
28902 @code{display_hint} method. @xref{Pretty Printing API}.
28905 Typical output will look like this:
28908 name="@var{name}",numchild="@var{N}",type="@var{type}",thread-id="@var{M}",
28909 has_more="@var{has_more}"
28913 @subheading The @code{-var-delete} Command
28914 @findex -var-delete
28916 @subsubheading Synopsis
28919 -var-delete [ -c ] @var{name}
28922 Deletes a previously created variable object and all of its children.
28923 With the @samp{-c} option, just deletes the children.
28925 Returns an error if the object @var{name} is not found.
28928 @subheading The @code{-var-set-format} Command
28929 @findex -var-set-format
28931 @subsubheading Synopsis
28934 -var-set-format @var{name} @var{format-spec}
28937 Sets the output format for the value of the object @var{name} to be
28940 @anchor{-var-set-format}
28941 The syntax for the @var{format-spec} is as follows:
28944 @var{format-spec} @expansion{}
28945 @{binary | decimal | hexadecimal | octal | natural@}
28948 The natural format is the default format choosen automatically
28949 based on the variable type (like decimal for an @code{int}, hex
28950 for pointers, etc.).
28952 For a variable with children, the format is set only on the
28953 variable itself, and the children are not affected.
28955 @subheading The @code{-var-show-format} Command
28956 @findex -var-show-format
28958 @subsubheading Synopsis
28961 -var-show-format @var{name}
28964 Returns the format used to display the value of the object @var{name}.
28967 @var{format} @expansion{}
28972 @subheading The @code{-var-info-num-children} Command
28973 @findex -var-info-num-children
28975 @subsubheading Synopsis
28978 -var-info-num-children @var{name}
28981 Returns the number of children of a variable object @var{name}:
28987 Note that this number is not completely reliable for a dynamic varobj.
28988 It will return the current number of children, but more children may
28992 @subheading The @code{-var-list-children} Command
28993 @findex -var-list-children
28995 @subsubheading Synopsis
28998 -var-list-children [@var{print-values}] @var{name} [@var{from} @var{to}]
29000 @anchor{-var-list-children}
29002 Return a list of the children of the specified variable object and
29003 create variable objects for them, if they do not already exist. With
29004 a single argument or if @var{print-values} has a value of 0 or
29005 @code{--no-values}, print only the names of the variables; if
29006 @var{print-values} is 1 or @code{--all-values}, also print their
29007 values; and if it is 2 or @code{--simple-values} print the name and
29008 value for simple data types and just the name for arrays, structures
29011 @var{from} and @var{to}, if specified, indicate the range of children
29012 to report. If @var{from} or @var{to} is less than zero, the range is
29013 reset and all children will be reported. Otherwise, children starting
29014 at @var{from} (zero-based) and up to and excluding @var{to} will be
29017 If a child range is requested, it will only affect the current call to
29018 @code{-var-list-children}, but not future calls to @code{-var-update}.
29019 For this, you must instead use @code{-var-set-update-range}. The
29020 intent of this approach is to enable a front end to implement any
29021 update approach it likes; for example, scrolling a view may cause the
29022 front end to request more children with @code{-var-list-children}, and
29023 then the front end could call @code{-var-set-update-range} with a
29024 different range to ensure that future updates are restricted to just
29027 For each child the following results are returned:
29032 Name of the variable object created for this child.
29035 The expression to be shown to the user by the front end to designate this child.
29036 For example this may be the name of a structure member.
29038 For a dynamic varobj, this value cannot be used to form an
29039 expression. There is no way to do this at all with a dynamic varobj.
29041 For C/C@t{++} structures there are several pseudo children returned to
29042 designate access qualifiers. For these pseudo children @var{exp} is
29043 @samp{public}, @samp{private}, or @samp{protected}. In this case the
29044 type and value are not present.
29046 A dynamic varobj will not report the access qualifying
29047 pseudo-children, regardless of the language. This information is not
29048 available at all with a dynamic varobj.
29051 Number of children this child has. For a dynamic varobj, this will be
29055 The type of the child.
29058 If values were requested, this is the value.
29061 If this variable object is associated with a thread, this is the thread id.
29062 Otherwise this result is not present.
29065 If the variable object is frozen, this variable will be present with a value of 1.
29068 The result may have its own attributes:
29072 A dynamic varobj can supply a display hint to the front end. The
29073 value comes directly from the Python pretty-printer object's
29074 @code{display_hint} method. @xref{Pretty Printing API}.
29077 This is an integer attribute which is nonzero if there are children
29078 remaining after the end of the selected range.
29081 @subsubheading Example
29085 -var-list-children n
29086 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
29087 numchild=@var{n},type=@var{type}@},@r{(repeats N times)}]
29089 -var-list-children --all-values n
29090 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
29091 numchild=@var{n},value=@var{value},type=@var{type}@},@r{(repeats N times)}]
29095 @subheading The @code{-var-info-type} Command
29096 @findex -var-info-type
29098 @subsubheading Synopsis
29101 -var-info-type @var{name}
29104 Returns the type of the specified variable @var{name}. The type is
29105 returned as a string in the same format as it is output by the
29109 type=@var{typename}
29113 @subheading The @code{-var-info-expression} Command
29114 @findex -var-info-expression
29116 @subsubheading Synopsis
29119 -var-info-expression @var{name}
29122 Returns a string that is suitable for presenting this
29123 variable object in user interface. The string is generally
29124 not valid expression in the current language, and cannot be evaluated.
29126 For example, if @code{a} is an array, and variable object
29127 @code{A} was created for @code{a}, then we'll get this output:
29130 (gdb) -var-info-expression A.1
29131 ^done,lang="C",exp="1"
29135 Here, the values of @code{lang} can be @code{@{"C" | "C++" | "Java"@}}.
29137 Note that the output of the @code{-var-list-children} command also
29138 includes those expressions, so the @code{-var-info-expression} command
29141 @subheading The @code{-var-info-path-expression} Command
29142 @findex -var-info-path-expression
29144 @subsubheading Synopsis
29147 -var-info-path-expression @var{name}
29150 Returns an expression that can be evaluated in the current
29151 context and will yield the same value that a variable object has.
29152 Compare this with the @code{-var-info-expression} command, which
29153 result can be used only for UI presentation. Typical use of
29154 the @code{-var-info-path-expression} command is creating a
29155 watchpoint from a variable object.
29157 This command is currently not valid for children of a dynamic varobj,
29158 and will give an error when invoked on one.
29160 For example, suppose @code{C} is a C@t{++} class, derived from class
29161 @code{Base}, and that the @code{Base} class has a member called
29162 @code{m_size}. Assume a variable @code{c} is has the type of
29163 @code{C} and a variable object @code{C} was created for variable
29164 @code{c}. Then, we'll get this output:
29166 (gdb) -var-info-path-expression C.Base.public.m_size
29167 ^done,path_expr=((Base)c).m_size)
29170 @subheading The @code{-var-show-attributes} Command
29171 @findex -var-show-attributes
29173 @subsubheading Synopsis
29176 -var-show-attributes @var{name}
29179 List attributes of the specified variable object @var{name}:
29182 status=@var{attr} [ ( ,@var{attr} )* ]
29186 where @var{attr} is @code{@{ @{ editable | noneditable @} | TBD @}}.
29188 @subheading The @code{-var-evaluate-expression} Command
29189 @findex -var-evaluate-expression
29191 @subsubheading Synopsis
29194 -var-evaluate-expression [-f @var{format-spec}] @var{name}
29197 Evaluates the expression that is represented by the specified variable
29198 object and returns its value as a string. The format of the string
29199 can be specified with the @samp{-f} option. The possible values of
29200 this option are the same as for @code{-var-set-format}
29201 (@pxref{-var-set-format}). If the @samp{-f} option is not specified,
29202 the current display format will be used. The current display format
29203 can be changed using the @code{-var-set-format} command.
29209 Note that one must invoke @code{-var-list-children} for a variable
29210 before the value of a child variable can be evaluated.
29212 @subheading The @code{-var-assign} Command
29213 @findex -var-assign
29215 @subsubheading Synopsis
29218 -var-assign @var{name} @var{expression}
29221 Assigns the value of @var{expression} to the variable object specified
29222 by @var{name}. The object must be @samp{editable}. If the variable's
29223 value is altered by the assign, the variable will show up in any
29224 subsequent @code{-var-update} list.
29226 @subsubheading Example
29234 ^done,changelist=[@{name="var1",in_scope="true",type_changed="false"@}]
29238 @subheading The @code{-var-update} Command
29239 @findex -var-update
29241 @subsubheading Synopsis
29244 -var-update [@var{print-values}] @{@var{name} | "*"@}
29247 Reevaluate the expressions corresponding to the variable object
29248 @var{name} and all its direct and indirect children, and return the
29249 list of variable objects whose values have changed; @var{name} must
29250 be a root variable object. Here, ``changed'' means that the result of
29251 @code{-var-evaluate-expression} before and after the
29252 @code{-var-update} is different. If @samp{*} is used as the variable
29253 object names, all existing variable objects are updated, except
29254 for frozen ones (@pxref{-var-set-frozen}). The option
29255 @var{print-values} determines whether both names and values, or just
29256 names are printed. The possible values of this option are the same
29257 as for @code{-var-list-children} (@pxref{-var-list-children}). It is
29258 recommended to use the @samp{--all-values} option, to reduce the
29259 number of MI commands needed on each program stop.
29261 With the @samp{*} parameter, if a variable object is bound to a
29262 currently running thread, it will not be updated, without any
29265 If @code{-var-set-update-range} was previously used on a varobj, then
29266 only the selected range of children will be reported.
29268 @code{-var-update} reports all the changed varobjs in a tuple named
29271 Each item in the change list is itself a tuple holding:
29275 The name of the varobj.
29278 If values were requested for this update, then this field will be
29279 present and will hold the value of the varobj.
29282 @anchor{-var-update}
29283 This field is a string which may take one of three values:
29287 The variable object's current value is valid.
29290 The variable object does not currently hold a valid value but it may
29291 hold one in the future if its associated expression comes back into
29295 The variable object no longer holds a valid value.
29296 This can occur when the executable file being debugged has changed,
29297 either through recompilation or by using the @value{GDBN} @code{file}
29298 command. The front end should normally choose to delete these variable
29302 In the future new values may be added to this list so the front should
29303 be prepared for this possibility. @xref{GDB/MI Development and Front Ends, ,@sc{GDB/MI} Development and Front Ends}.
29306 This is only present if the varobj is still valid. If the type
29307 changed, then this will be the string @samp{true}; otherwise it will
29311 If the varobj's type changed, then this field will be present and will
29314 @item new_num_children
29315 For a dynamic varobj, if the number of children changed, or if the
29316 type changed, this will be the new number of children.
29318 The @samp{numchild} field in other varobj responses is generally not
29319 valid for a dynamic varobj -- it will show the number of children that
29320 @value{GDBN} knows about, but because dynamic varobjs lazily
29321 instantiate their children, this will not reflect the number of
29322 children which may be available.
29324 The @samp{new_num_children} attribute only reports changes to the
29325 number of children known by @value{GDBN}. This is the only way to
29326 detect whether an update has removed children (which necessarily can
29327 only happen at the end of the update range).
29330 The display hint, if any.
29333 This is an integer value, which will be 1 if there are more children
29334 available outside the varobj's update range.
29337 This attribute will be present and have the value @samp{1} if the
29338 varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
29339 then this attribute will not be present.
29342 If new children were added to a dynamic varobj within the selected
29343 update range (as set by @code{-var-set-update-range}), then they will
29344 be listed in this attribute.
29347 @subsubheading Example
29354 -var-update --all-values var1
29355 ^done,changelist=[@{name="var1",value="3",in_scope="true",
29356 type_changed="false"@}]
29360 @subheading The @code{-var-set-frozen} Command
29361 @findex -var-set-frozen
29362 @anchor{-var-set-frozen}
29364 @subsubheading Synopsis
29367 -var-set-frozen @var{name} @var{flag}
29370 Set the frozenness flag on the variable object @var{name}. The
29371 @var{flag} parameter should be either @samp{1} to make the variable
29372 frozen or @samp{0} to make it unfrozen. If a variable object is
29373 frozen, then neither itself, nor any of its children, are
29374 implicitly updated by @code{-var-update} of
29375 a parent variable or by @code{-var-update *}. Only
29376 @code{-var-update} of the variable itself will update its value and
29377 values of its children. After a variable object is unfrozen, it is
29378 implicitly updated by all subsequent @code{-var-update} operations.
29379 Unfreezing a variable does not update it, only subsequent
29380 @code{-var-update} does.
29382 @subsubheading Example
29386 -var-set-frozen V 1
29391 @subheading The @code{-var-set-update-range} command
29392 @findex -var-set-update-range
29393 @anchor{-var-set-update-range}
29395 @subsubheading Synopsis
29398 -var-set-update-range @var{name} @var{from} @var{to}
29401 Set the range of children to be returned by future invocations of
29402 @code{-var-update}.
29404 @var{from} and @var{to} indicate the range of children to report. If
29405 @var{from} or @var{to} is less than zero, the range is reset and all
29406 children will be reported. Otherwise, children starting at @var{from}
29407 (zero-based) and up to and excluding @var{to} will be reported.
29409 @subsubheading Example
29413 -var-set-update-range V 1 2
29417 @subheading The @code{-var-set-visualizer} command
29418 @findex -var-set-visualizer
29419 @anchor{-var-set-visualizer}
29421 @subsubheading Synopsis
29424 -var-set-visualizer @var{name} @var{visualizer}
29427 Set a visualizer for the variable object @var{name}.
29429 @var{visualizer} is the visualizer to use. The special value
29430 @samp{None} means to disable any visualizer in use.
29432 If not @samp{None}, @var{visualizer} must be a Python expression.
29433 This expression must evaluate to a callable object which accepts a
29434 single argument. @value{GDBN} will call this object with the value of
29435 the varobj @var{name} as an argument (this is done so that the same
29436 Python pretty-printing code can be used for both the CLI and MI).
29437 When called, this object must return an object which conforms to the
29438 pretty-printing interface (@pxref{Pretty Printing API}).
29440 The pre-defined function @code{gdb.default_visualizer} may be used to
29441 select a visualizer by following the built-in process
29442 (@pxref{Selecting Pretty-Printers}). This is done automatically when
29443 a varobj is created, and so ordinarily is not needed.
29445 This feature is only available if Python support is enabled. The MI
29446 command @code{-list-features} (@pxref{GDB/MI Miscellaneous Commands})
29447 can be used to check this.
29449 @subsubheading Example
29451 Resetting the visualizer:
29455 -var-set-visualizer V None
29459 Reselecting the default (type-based) visualizer:
29463 -var-set-visualizer V gdb.default_visualizer
29467 Suppose @code{SomeClass} is a visualizer class. A lambda expression
29468 can be used to instantiate this class for a varobj:
29472 -var-set-visualizer V "lambda val: SomeClass()"
29476 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
29477 @node GDB/MI Data Manipulation
29478 @section @sc{gdb/mi} Data Manipulation
29480 @cindex data manipulation, in @sc{gdb/mi}
29481 @cindex @sc{gdb/mi}, data manipulation
29482 This section describes the @sc{gdb/mi} commands that manipulate data:
29483 examine memory and registers, evaluate expressions, etc.
29485 @c REMOVED FROM THE INTERFACE.
29486 @c @subheading -data-assign
29487 @c Change the value of a program variable. Plenty of side effects.
29488 @c @subsubheading GDB Command
29490 @c @subsubheading Example
29493 @subheading The @code{-data-disassemble} Command
29494 @findex -data-disassemble
29496 @subsubheading Synopsis
29500 [ -s @var{start-addr} -e @var{end-addr} ]
29501 | [ -f @var{filename} -l @var{linenum} [ -n @var{lines} ] ]
29509 @item @var{start-addr}
29510 is the beginning address (or @code{$pc})
29511 @item @var{end-addr}
29513 @item @var{filename}
29514 is the name of the file to disassemble
29515 @item @var{linenum}
29516 is the line number to disassemble around
29518 is the number of disassembly lines to be produced. If it is -1,
29519 the whole function will be disassembled, in case no @var{end-addr} is
29520 specified. If @var{end-addr} is specified as a non-zero value, and
29521 @var{lines} is lower than the number of disassembly lines between
29522 @var{start-addr} and @var{end-addr}, only @var{lines} lines are
29523 displayed; if @var{lines} is higher than the number of lines between
29524 @var{start-addr} and @var{end-addr}, only the lines up to @var{end-addr}
29527 is either 0 (meaning only disassembly), 1 (meaning mixed source and
29528 disassembly), 2 (meaning disassembly with raw opcodes), or 3 (meaning
29529 mixed source and disassembly with raw opcodes).
29532 @subsubheading Result
29534 The output for each instruction is composed of four fields:
29543 Note that whatever included in the instruction field, is not manipulated
29544 directly by @sc{gdb/mi}, i.e., it is not possible to adjust its format.
29546 @subsubheading @value{GDBN} Command
29548 There's no direct mapping from this command to the CLI.
29550 @subsubheading Example
29552 Disassemble from the current value of @code{$pc} to @code{$pc + 20}:
29556 -data-disassemble -s $pc -e "$pc + 20" -- 0
29559 @{address="0x000107c0",func-name="main",offset="4",
29560 inst="mov 2, %o0"@},
29561 @{address="0x000107c4",func-name="main",offset="8",
29562 inst="sethi %hi(0x11800), %o2"@},
29563 @{address="0x000107c8",func-name="main",offset="12",
29564 inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"@},
29565 @{address="0x000107cc",func-name="main",offset="16",
29566 inst="sethi %hi(0x11800), %o2"@},
29567 @{address="0x000107d0",func-name="main",offset="20",
29568 inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"@}]
29572 Disassemble the whole @code{main} function. Line 32 is part of
29576 -data-disassemble -f basics.c -l 32 -- 0
29578 @{address="0x000107bc",func-name="main",offset="0",
29579 inst="save %sp, -112, %sp"@},
29580 @{address="0x000107c0",func-name="main",offset="4",
29581 inst="mov 2, %o0"@},
29582 @{address="0x000107c4",func-name="main",offset="8",
29583 inst="sethi %hi(0x11800), %o2"@},
29585 @{address="0x0001081c",func-name="main",offset="96",inst="ret "@},
29586 @{address="0x00010820",func-name="main",offset="100",inst="restore "@}]
29590 Disassemble 3 instructions from the start of @code{main}:
29594 -data-disassemble -f basics.c -l 32 -n 3 -- 0
29596 @{address="0x000107bc",func-name="main",offset="0",
29597 inst="save %sp, -112, %sp"@},
29598 @{address="0x000107c0",func-name="main",offset="4",
29599 inst="mov 2, %o0"@},
29600 @{address="0x000107c4",func-name="main",offset="8",
29601 inst="sethi %hi(0x11800), %o2"@}]
29605 Disassemble 3 instructions from the start of @code{main} in mixed mode:
29609 -data-disassemble -f basics.c -l 32 -n 3 -- 1
29611 src_and_asm_line=@{line="31",
29612 file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
29613 testsuite/gdb.mi/basics.c",line_asm_insn=[
29614 @{address="0x000107bc",func-name="main",offset="0",
29615 inst="save %sp, -112, %sp"@}]@},
29616 src_and_asm_line=@{line="32",
29617 file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
29618 testsuite/gdb.mi/basics.c",line_asm_insn=[
29619 @{address="0x000107c0",func-name="main",offset="4",
29620 inst="mov 2, %o0"@},
29621 @{address="0x000107c4",func-name="main",offset="8",
29622 inst="sethi %hi(0x11800), %o2"@}]@}]
29627 @subheading The @code{-data-evaluate-expression} Command
29628 @findex -data-evaluate-expression
29630 @subsubheading Synopsis
29633 -data-evaluate-expression @var{expr}
29636 Evaluate @var{expr} as an expression. The expression could contain an
29637 inferior function call. The function call will execute synchronously.
29638 If the expression contains spaces, it must be enclosed in double quotes.
29640 @subsubheading @value{GDBN} Command
29642 The corresponding @value{GDBN} commands are @samp{print}, @samp{output}, and
29643 @samp{call}. In @code{gdbtk} only, there's a corresponding
29644 @samp{gdb_eval} command.
29646 @subsubheading Example
29648 In the following example, the numbers that precede the commands are the
29649 @dfn{tokens} described in @ref{GDB/MI Command Syntax, ,@sc{gdb/mi}
29650 Command Syntax}. Notice how @sc{gdb/mi} returns the same tokens in its
29654 211-data-evaluate-expression A
29657 311-data-evaluate-expression &A
29658 311^done,value="0xefffeb7c"
29660 411-data-evaluate-expression A+3
29663 511-data-evaluate-expression "A + 3"
29669 @subheading The @code{-data-list-changed-registers} Command
29670 @findex -data-list-changed-registers
29672 @subsubheading Synopsis
29675 -data-list-changed-registers
29678 Display a list of the registers that have changed.
29680 @subsubheading @value{GDBN} Command
29682 @value{GDBN} doesn't have a direct analog for this command; @code{gdbtk}
29683 has the corresponding command @samp{gdb_changed_register_list}.
29685 @subsubheading Example
29687 On a PPC MBX board:
29695 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame=@{
29696 func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c",
29699 -data-list-changed-registers
29700 ^done,changed-registers=["0","1","2","4","5","6","7","8","9",
29701 "10","11","13","14","15","16","17","18","19","20","21","22","23",
29702 "24","25","26","27","28","30","31","64","65","66","67","69"]
29707 @subheading The @code{-data-list-register-names} Command
29708 @findex -data-list-register-names
29710 @subsubheading Synopsis
29713 -data-list-register-names [ ( @var{regno} )+ ]
29716 Show a list of register names for the current target. If no arguments
29717 are given, it shows a list of the names of all the registers. If
29718 integer numbers are given as arguments, it will print a list of the
29719 names of the registers corresponding to the arguments. To ensure
29720 consistency between a register name and its number, the output list may
29721 include empty register names.
29723 @subsubheading @value{GDBN} Command
29725 @value{GDBN} does not have a command which corresponds to
29726 @samp{-data-list-register-names}. In @code{gdbtk} there is a
29727 corresponding command @samp{gdb_regnames}.
29729 @subsubheading Example
29731 For the PPC MBX board:
29734 -data-list-register-names
29735 ^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7",
29736 "r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18",
29737 "r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29",
29738 "r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9",
29739 "f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20",
29740 "f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31",
29741 "", "pc","ps","cr","lr","ctr","xer"]
29743 -data-list-register-names 1 2 3
29744 ^done,register-names=["r1","r2","r3"]
29748 @subheading The @code{-data-list-register-values} Command
29749 @findex -data-list-register-values
29751 @subsubheading Synopsis
29754 -data-list-register-values @var{fmt} [ ( @var{regno} )*]
29757 Display the registers' contents. @var{fmt} is the format according to
29758 which the registers' contents are to be returned, followed by an optional
29759 list of numbers specifying the registers to display. A missing list of
29760 numbers indicates that the contents of all the registers must be returned.
29762 Allowed formats for @var{fmt} are:
29779 @subsubheading @value{GDBN} Command
29781 The corresponding @value{GDBN} commands are @samp{info reg}, @samp{info
29782 all-reg}, and (in @code{gdbtk}) @samp{gdb_fetch_registers}.
29784 @subsubheading Example
29786 For a PPC MBX board (note: line breaks are for readability only, they
29787 don't appear in the actual output):
29791 -data-list-register-values r 64 65
29792 ^done,register-values=[@{number="64",value="0xfe00a300"@},
29793 @{number="65",value="0x00029002"@}]
29795 -data-list-register-values x
29796 ^done,register-values=[@{number="0",value="0xfe0043c8"@},
29797 @{number="1",value="0x3fff88"@},@{number="2",value="0xfffffffe"@},
29798 @{number="3",value="0x0"@},@{number="4",value="0xa"@},
29799 @{number="5",value="0x3fff68"@},@{number="6",value="0x3fff58"@},
29800 @{number="7",value="0xfe011e98"@},@{number="8",value="0x2"@},
29801 @{number="9",value="0xfa202820"@},@{number="10",value="0xfa202808"@},
29802 @{number="11",value="0x1"@},@{number="12",value="0x0"@},
29803 @{number="13",value="0x4544"@},@{number="14",value="0xffdfffff"@},
29804 @{number="15",value="0xffffffff"@},@{number="16",value="0xfffffeff"@},
29805 @{number="17",value="0xefffffed"@},@{number="18",value="0xfffffffe"@},
29806 @{number="19",value="0xffffffff"@},@{number="20",value="0xffffffff"@},
29807 @{number="21",value="0xffffffff"@},@{number="22",value="0xfffffff7"@},
29808 @{number="23",value="0xffffffff"@},@{number="24",value="0xffffffff"@},
29809 @{number="25",value="0xffffffff"@},@{number="26",value="0xfffffffb"@},
29810 @{number="27",value="0xffffffff"@},@{number="28",value="0xf7bfffff"@},
29811 @{number="29",value="0x0"@},@{number="30",value="0xfe010000"@},
29812 @{number="31",value="0x0"@},@{number="32",value="0x0"@},
29813 @{number="33",value="0x0"@},@{number="34",value="0x0"@},
29814 @{number="35",value="0x0"@},@{number="36",value="0x0"@},
29815 @{number="37",value="0x0"@},@{number="38",value="0x0"@},
29816 @{number="39",value="0x0"@},@{number="40",value="0x0"@},
29817 @{number="41",value="0x0"@},@{number="42",value="0x0"@},
29818 @{number="43",value="0x0"@},@{number="44",value="0x0"@},
29819 @{number="45",value="0x0"@},@{number="46",value="0x0"@},
29820 @{number="47",value="0x0"@},@{number="48",value="0x0"@},
29821 @{number="49",value="0x0"@},@{number="50",value="0x0"@},
29822 @{number="51",value="0x0"@},@{number="52",value="0x0"@},
29823 @{number="53",value="0x0"@},@{number="54",value="0x0"@},
29824 @{number="55",value="0x0"@},@{number="56",value="0x0"@},
29825 @{number="57",value="0x0"@},@{number="58",value="0x0"@},
29826 @{number="59",value="0x0"@},@{number="60",value="0x0"@},
29827 @{number="61",value="0x0"@},@{number="62",value="0x0"@},
29828 @{number="63",value="0x0"@},@{number="64",value="0xfe00a300"@},
29829 @{number="65",value="0x29002"@},@{number="66",value="0x202f04b5"@},
29830 @{number="67",value="0xfe0043b0"@},@{number="68",value="0xfe00b3e4"@},
29831 @{number="69",value="0x20002b03"@}]
29836 @subheading The @code{-data-read-memory} Command
29837 @findex -data-read-memory
29839 This command is deprecated, use @code{-data-read-memory-bytes} instead.
29841 @subsubheading Synopsis
29844 -data-read-memory [ -o @var{byte-offset} ]
29845 @var{address} @var{word-format} @var{word-size}
29846 @var{nr-rows} @var{nr-cols} [ @var{aschar} ]
29853 @item @var{address}
29854 An expression specifying the address of the first memory word to be
29855 read. Complex expressions containing embedded white space should be
29856 quoted using the C convention.
29858 @item @var{word-format}
29859 The format to be used to print the memory words. The notation is the
29860 same as for @value{GDBN}'s @code{print} command (@pxref{Output Formats,
29863 @item @var{word-size}
29864 The size of each memory word in bytes.
29866 @item @var{nr-rows}
29867 The number of rows in the output table.
29869 @item @var{nr-cols}
29870 The number of columns in the output table.
29873 If present, indicates that each row should include an @sc{ascii} dump. The
29874 value of @var{aschar} is used as a padding character when a byte is not a
29875 member of the printable @sc{ascii} character set (printable @sc{ascii}
29876 characters are those whose code is between 32 and 126, inclusively).
29878 @item @var{byte-offset}
29879 An offset to add to the @var{address} before fetching memory.
29882 This command displays memory contents as a table of @var{nr-rows} by
29883 @var{nr-cols} words, each word being @var{word-size} bytes. In total,
29884 @code{@var{nr-rows} * @var{nr-cols} * @var{word-size}} bytes are read
29885 (returned as @samp{total-bytes}). Should less than the requested number
29886 of bytes be returned by the target, the missing words are identified
29887 using @samp{N/A}. The number of bytes read from the target is returned
29888 in @samp{nr-bytes} and the starting address used to read memory in
29891 The address of the next/previous row or page is available in
29892 @samp{next-row} and @samp{prev-row}, @samp{next-page} and
29895 @subsubheading @value{GDBN} Command
29897 The corresponding @value{GDBN} command is @samp{x}. @code{gdbtk} has
29898 @samp{gdb_get_mem} memory read command.
29900 @subsubheading Example
29902 Read six bytes of memory starting at @code{bytes+6} but then offset by
29903 @code{-6} bytes. Format as three rows of two columns. One byte per
29904 word. Display each word in hex.
29908 9-data-read-memory -o -6 -- bytes+6 x 1 3 2
29909 9^done,addr="0x00001390",nr-bytes="6",total-bytes="6",
29910 next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396",
29911 prev-page="0x0000138a",memory=[
29912 @{addr="0x00001390",data=["0x00","0x01"]@},
29913 @{addr="0x00001392",data=["0x02","0x03"]@},
29914 @{addr="0x00001394",data=["0x04","0x05"]@}]
29918 Read two bytes of memory starting at address @code{shorts + 64} and
29919 display as a single word formatted in decimal.
29923 5-data-read-memory shorts+64 d 2 1 1
29924 5^done,addr="0x00001510",nr-bytes="2",total-bytes="2",
29925 next-row="0x00001512",prev-row="0x0000150e",
29926 next-page="0x00001512",prev-page="0x0000150e",memory=[
29927 @{addr="0x00001510",data=["128"]@}]
29931 Read thirty two bytes of memory starting at @code{bytes+16} and format
29932 as eight rows of four columns. Include a string encoding with @samp{x}
29933 used as the non-printable character.
29937 4-data-read-memory bytes+16 x 1 8 4 x
29938 4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32",
29939 next-row="0x000013c0",prev-row="0x0000139c",
29940 next-page="0x000013c0",prev-page="0x00001380",memory=[
29941 @{addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"@},
29942 @{addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"@},
29943 @{addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"@},
29944 @{addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"@},
29945 @{addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"@},
29946 @{addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"@},
29947 @{addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"@},
29948 @{addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"@}]
29952 @subheading The @code{-data-read-memory-bytes} Command
29953 @findex -data-read-memory-bytes
29955 @subsubheading Synopsis
29958 -data-read-memory-bytes [ -o @var{byte-offset} ]
29959 @var{address} @var{count}
29966 @item @var{address}
29967 An expression specifying the address of the first memory word to be
29968 read. Complex expressions containing embedded white space should be
29969 quoted using the C convention.
29972 The number of bytes to read. This should be an integer literal.
29974 @item @var{byte-offset}
29975 The offsets in bytes relative to @var{address} at which to start
29976 reading. This should be an integer literal. This option is provided
29977 so that a frontend is not required to first evaluate address and then
29978 perform address arithmetics itself.
29982 This command attempts to read all accessible memory regions in the
29983 specified range. First, all regions marked as unreadable in the memory
29984 map (if one is defined) will be skipped. @xref{Memory Region
29985 Attributes}. Second, @value{GDBN} will attempt to read the remaining
29986 regions. For each one, if reading full region results in an errors,
29987 @value{GDBN} will try to read a subset of the region.
29989 In general, every single byte in the region may be readable or not,
29990 and the only way to read every readable byte is to try a read at
29991 every address, which is not practical. Therefore, @value{GDBN} will
29992 attempt to read all accessible bytes at either beginning or the end
29993 of the region, using a binary division scheme. This heuristic works
29994 well for reading accross a memory map boundary. Note that if a region
29995 has a readable range that is neither at the beginning or the end,
29996 @value{GDBN} will not read it.
29998 The result record (@pxref{GDB/MI Result Records}) that is output of
29999 the command includes a field named @samp{memory} whose content is a
30000 list of tuples. Each tuple represent a successfully read memory block
30001 and has the following fields:
30005 The start address of the memory block, as hexadecimal literal.
30008 The end address of the memory block, as hexadecimal literal.
30011 The offset of the memory block, as hexadecimal literal, relative to
30012 the start address passed to @code{-data-read-memory-bytes}.
30015 The contents of the memory block, in hex.
30021 @subsubheading @value{GDBN} Command
30023 The corresponding @value{GDBN} command is @samp{x}.
30025 @subsubheading Example
30029 -data-read-memory-bytes &a 10
30030 ^done,memory=[@{begin="0xbffff154",offset="0x00000000",
30032 contents="01000000020000000300"@}]
30037 @subheading The @code{-data-write-memory-bytes} Command
30038 @findex -data-write-memory-bytes
30040 @subsubheading Synopsis
30043 -data-write-memory-bytes @var{address} @var{contents}
30050 @item @var{address}
30051 An expression specifying the address of the first memory word to be
30052 read. Complex expressions containing embedded white space should be
30053 quoted using the C convention.
30055 @item @var{contents}
30056 The hex-encoded bytes to write.
30060 @subsubheading @value{GDBN} Command
30062 There's no corresponding @value{GDBN} command.
30064 @subsubheading Example
30068 -data-write-memory-bytes &a "aabbccdd"
30074 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
30075 @node GDB/MI Tracepoint Commands
30076 @section @sc{gdb/mi} Tracepoint Commands
30078 The commands defined in this section implement MI support for
30079 tracepoints. For detailed introduction, see @ref{Tracepoints}.
30081 @subheading The @code{-trace-find} Command
30082 @findex -trace-find
30084 @subsubheading Synopsis
30087 -trace-find @var{mode} [@var{parameters}@dots{}]
30090 Find a trace frame using criteria defined by @var{mode} and
30091 @var{parameters}. The following table lists permissible
30092 modes and their parameters. For details of operation, see @ref{tfind}.
30097 No parameters are required. Stops examining trace frames.
30100 An integer is required as parameter. Selects tracepoint frame with
30103 @item tracepoint-number
30104 An integer is required as parameter. Finds next
30105 trace frame that corresponds to tracepoint with the specified number.
30108 An address is required as parameter. Finds
30109 next trace frame that corresponds to any tracepoint at the specified
30112 @item pc-inside-range
30113 Two addresses are required as parameters. Finds next trace
30114 frame that corresponds to a tracepoint at an address inside the
30115 specified range. Both bounds are considered to be inside the range.
30117 @item pc-outside-range
30118 Two addresses are required as parameters. Finds
30119 next trace frame that corresponds to a tracepoint at an address outside
30120 the specified range. Both bounds are considered to be inside the range.
30123 Line specification is required as parameter. @xref{Specify Location}.
30124 Finds next trace frame that corresponds to a tracepoint at
30125 the specified location.
30129 If @samp{none} was passed as @var{mode}, the response does not
30130 have fields. Otherwise, the response may have the following fields:
30134 This field has either @samp{0} or @samp{1} as the value, depending
30135 on whether a matching tracepoint was found.
30138 The index of the found traceframe. This field is present iff
30139 the @samp{found} field has value of @samp{1}.
30142 The index of the found tracepoint. This field is present iff
30143 the @samp{found} field has value of @samp{1}.
30146 The information about the frame corresponding to the found trace
30147 frame. This field is present only if a trace frame was found.
30148 @xref{GDB/MI Frame Information}, for description of this field.
30152 @subsubheading @value{GDBN} Command
30154 The corresponding @value{GDBN} command is @samp{tfind}.
30156 @subheading -trace-define-variable
30157 @findex -trace-define-variable
30159 @subsubheading Synopsis
30162 -trace-define-variable @var{name} [ @var{value} ]
30165 Create trace variable @var{name} if it does not exist. If
30166 @var{value} is specified, sets the initial value of the specified
30167 trace variable to that value. Note that the @var{name} should start
30168 with the @samp{$} character.
30170 @subsubheading @value{GDBN} Command
30172 The corresponding @value{GDBN} command is @samp{tvariable}.
30174 @subheading -trace-list-variables
30175 @findex -trace-list-variables
30177 @subsubheading Synopsis
30180 -trace-list-variables
30183 Return a table of all defined trace variables. Each element of the
30184 table has the following fields:
30188 The name of the trace variable. This field is always present.
30191 The initial value. This is a 64-bit signed integer. This
30192 field is always present.
30195 The value the trace variable has at the moment. This is a 64-bit
30196 signed integer. This field is absent iff current value is
30197 not defined, for example if the trace was never run, or is
30202 @subsubheading @value{GDBN} Command
30204 The corresponding @value{GDBN} command is @samp{tvariables}.
30206 @subsubheading Example
30210 -trace-list-variables
30211 ^done,trace-variables=@{nr_rows="1",nr_cols="3",
30212 hdr=[@{width="15",alignment="-1",col_name="name",colhdr="Name"@},
30213 @{width="11",alignment="-1",col_name="initial",colhdr="Initial"@},
30214 @{width="11",alignment="-1",col_name="current",colhdr="Current"@}],
30215 body=[variable=@{name="$trace_timestamp",initial="0"@}
30216 variable=@{name="$foo",initial="10",current="15"@}]@}
30220 @subheading -trace-save
30221 @findex -trace-save
30223 @subsubheading Synopsis
30226 -trace-save [-r ] @var{filename}
30229 Saves the collected trace data to @var{filename}. Without the
30230 @samp{-r} option, the data is downloaded from the target and saved
30231 in a local file. With the @samp{-r} option the target is asked
30232 to perform the save.
30234 @subsubheading @value{GDBN} Command
30236 The corresponding @value{GDBN} command is @samp{tsave}.
30239 @subheading -trace-start
30240 @findex -trace-start
30242 @subsubheading Synopsis
30248 Starts a tracing experiments. The result of this command does not
30251 @subsubheading @value{GDBN} Command
30253 The corresponding @value{GDBN} command is @samp{tstart}.
30255 @subheading -trace-status
30256 @findex -trace-status
30258 @subsubheading Synopsis
30264 Obtains the status of a tracing experiment. The result may include
30265 the following fields:
30270 May have a value of either @samp{0}, when no tracing operations are
30271 supported, @samp{1}, when all tracing operations are supported, or
30272 @samp{file} when examining trace file. In the latter case, examining
30273 of trace frame is possible but new tracing experiement cannot be
30274 started. This field is always present.
30277 May have a value of either @samp{0} or @samp{1} depending on whether
30278 tracing experiement is in progress on target. This field is present
30279 if @samp{supported} field is not @samp{0}.
30282 Report the reason why the tracing was stopped last time. This field
30283 may be absent iff tracing was never stopped on target yet. The
30284 value of @samp{request} means the tracing was stopped as result of
30285 the @code{-trace-stop} command. The value of @samp{overflow} means
30286 the tracing buffer is full. The value of @samp{disconnection} means
30287 tracing was automatically stopped when @value{GDBN} has disconnected.
30288 The value of @samp{passcount} means tracing was stopped when a
30289 tracepoint was passed a maximal number of times for that tracepoint.
30290 This field is present if @samp{supported} field is not @samp{0}.
30292 @item stopping-tracepoint
30293 The number of tracepoint whose passcount as exceeded. This field is
30294 present iff the @samp{stop-reason} field has the value of
30298 @itemx frames-created
30299 The @samp{frames} field is a count of the total number of trace frames
30300 in the trace buffer, while @samp{frames-created} is the total created
30301 during the run, including ones that were discarded, such as when a
30302 circular trace buffer filled up. Both fields are optional.
30306 These fields tell the current size of the tracing buffer and the
30307 remaining space. These fields are optional.
30310 The value of the circular trace buffer flag. @code{1} means that the
30311 trace buffer is circular and old trace frames will be discarded if
30312 necessary to make room, @code{0} means that the trace buffer is linear
30316 The value of the disconnected tracing flag. @code{1} means that
30317 tracing will continue after @value{GDBN} disconnects, @code{0} means
30318 that the trace run will stop.
30322 @subsubheading @value{GDBN} Command
30324 The corresponding @value{GDBN} command is @samp{tstatus}.
30326 @subheading -trace-stop
30327 @findex -trace-stop
30329 @subsubheading Synopsis
30335 Stops a tracing experiment. The result of this command has the same
30336 fields as @code{-trace-status}, except that the @samp{supported} and
30337 @samp{running} fields are not output.
30339 @subsubheading @value{GDBN} Command
30341 The corresponding @value{GDBN} command is @samp{tstop}.
30344 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
30345 @node GDB/MI Symbol Query
30346 @section @sc{gdb/mi} Symbol Query Commands
30350 @subheading The @code{-symbol-info-address} Command
30351 @findex -symbol-info-address
30353 @subsubheading Synopsis
30356 -symbol-info-address @var{symbol}
30359 Describe where @var{symbol} is stored.
30361 @subsubheading @value{GDBN} Command
30363 The corresponding @value{GDBN} command is @samp{info address}.
30365 @subsubheading Example
30369 @subheading The @code{-symbol-info-file} Command
30370 @findex -symbol-info-file
30372 @subsubheading Synopsis
30378 Show the file for the symbol.
30380 @subsubheading @value{GDBN} Command
30382 There's no equivalent @value{GDBN} command. @code{gdbtk} has
30383 @samp{gdb_find_file}.
30385 @subsubheading Example
30389 @subheading The @code{-symbol-info-function} Command
30390 @findex -symbol-info-function
30392 @subsubheading Synopsis
30395 -symbol-info-function
30398 Show which function the symbol lives in.
30400 @subsubheading @value{GDBN} Command
30402 @samp{gdb_get_function} in @code{gdbtk}.
30404 @subsubheading Example
30408 @subheading The @code{-symbol-info-line} Command
30409 @findex -symbol-info-line
30411 @subsubheading Synopsis
30417 Show the core addresses of the code for a source line.
30419 @subsubheading @value{GDBN} Command
30421 The corresponding @value{GDBN} command is @samp{info line}.
30422 @code{gdbtk} has the @samp{gdb_get_line} and @samp{gdb_get_file} commands.
30424 @subsubheading Example
30428 @subheading The @code{-symbol-info-symbol} Command
30429 @findex -symbol-info-symbol
30431 @subsubheading Synopsis
30434 -symbol-info-symbol @var{addr}
30437 Describe what symbol is at location @var{addr}.
30439 @subsubheading @value{GDBN} Command
30441 The corresponding @value{GDBN} command is @samp{info symbol}.
30443 @subsubheading Example
30447 @subheading The @code{-symbol-list-functions} Command
30448 @findex -symbol-list-functions
30450 @subsubheading Synopsis
30453 -symbol-list-functions
30456 List the functions in the executable.
30458 @subsubheading @value{GDBN} Command
30460 @samp{info functions} in @value{GDBN}, @samp{gdb_listfunc} and
30461 @samp{gdb_search} in @code{gdbtk}.
30463 @subsubheading Example
30468 @subheading The @code{-symbol-list-lines} Command
30469 @findex -symbol-list-lines
30471 @subsubheading Synopsis
30474 -symbol-list-lines @var{filename}
30477 Print the list of lines that contain code and their associated program
30478 addresses for the given source filename. The entries are sorted in
30479 ascending PC order.
30481 @subsubheading @value{GDBN} Command
30483 There is no corresponding @value{GDBN} command.
30485 @subsubheading Example
30488 -symbol-list-lines basics.c
30489 ^done,lines=[@{pc="0x08048554",line="7"@},@{pc="0x0804855a",line="8"@}]
30495 @subheading The @code{-symbol-list-types} Command
30496 @findex -symbol-list-types
30498 @subsubheading Synopsis
30504 List all the type names.
30506 @subsubheading @value{GDBN} Command
30508 The corresponding commands are @samp{info types} in @value{GDBN},
30509 @samp{gdb_search} in @code{gdbtk}.
30511 @subsubheading Example
30515 @subheading The @code{-symbol-list-variables} Command
30516 @findex -symbol-list-variables
30518 @subsubheading Synopsis
30521 -symbol-list-variables
30524 List all the global and static variable names.
30526 @subsubheading @value{GDBN} Command
30528 @samp{info variables} in @value{GDBN}, @samp{gdb_search} in @code{gdbtk}.
30530 @subsubheading Example
30534 @subheading The @code{-symbol-locate} Command
30535 @findex -symbol-locate
30537 @subsubheading Synopsis
30543 @subsubheading @value{GDBN} Command
30545 @samp{gdb_loc} in @code{gdbtk}.
30547 @subsubheading Example
30551 @subheading The @code{-symbol-type} Command
30552 @findex -symbol-type
30554 @subsubheading Synopsis
30557 -symbol-type @var{variable}
30560 Show type of @var{variable}.
30562 @subsubheading @value{GDBN} Command
30564 The corresponding @value{GDBN} command is @samp{ptype}, @code{gdbtk} has
30565 @samp{gdb_obj_variable}.
30567 @subsubheading Example
30572 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
30573 @node GDB/MI File Commands
30574 @section @sc{gdb/mi} File Commands
30576 This section describes the GDB/MI commands to specify executable file names
30577 and to read in and obtain symbol table information.
30579 @subheading The @code{-file-exec-and-symbols} Command
30580 @findex -file-exec-and-symbols
30582 @subsubheading Synopsis
30585 -file-exec-and-symbols @var{file}
30588 Specify the executable file to be debugged. This file is the one from
30589 which the symbol table is also read. If no file is specified, the
30590 command clears the executable and symbol information. If breakpoints
30591 are set when using this command with no arguments, @value{GDBN} will produce
30592 error messages. Otherwise, no output is produced, except a completion
30595 @subsubheading @value{GDBN} Command
30597 The corresponding @value{GDBN} command is @samp{file}.
30599 @subsubheading Example
30603 -file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
30609 @subheading The @code{-file-exec-file} Command
30610 @findex -file-exec-file
30612 @subsubheading Synopsis
30615 -file-exec-file @var{file}
30618 Specify the executable file to be debugged. Unlike
30619 @samp{-file-exec-and-symbols}, the symbol table is @emph{not} read
30620 from this file. If used without argument, @value{GDBN} clears the information
30621 about the executable file. No output is produced, except a completion
30624 @subsubheading @value{GDBN} Command
30626 The corresponding @value{GDBN} command is @samp{exec-file}.
30628 @subsubheading Example
30632 -file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
30639 @subheading The @code{-file-list-exec-sections} Command
30640 @findex -file-list-exec-sections
30642 @subsubheading Synopsis
30645 -file-list-exec-sections
30648 List the sections of the current executable file.
30650 @subsubheading @value{GDBN} Command
30652 The @value{GDBN} command @samp{info file} shows, among the rest, the same
30653 information as this command. @code{gdbtk} has a corresponding command
30654 @samp{gdb_load_info}.
30656 @subsubheading Example
30661 @subheading The @code{-file-list-exec-source-file} Command
30662 @findex -file-list-exec-source-file
30664 @subsubheading Synopsis
30667 -file-list-exec-source-file
30670 List the line number, the current source file, and the absolute path
30671 to the current source file for the current executable. The macro
30672 information field has a value of @samp{1} or @samp{0} depending on
30673 whether or not the file includes preprocessor macro information.
30675 @subsubheading @value{GDBN} Command
30677 The @value{GDBN} equivalent is @samp{info source}
30679 @subsubheading Example
30683 123-file-list-exec-source-file
30684 123^done,line="1",file="foo.c",fullname="/home/bar/foo.c,macro-info="1"
30689 @subheading The @code{-file-list-exec-source-files} Command
30690 @findex -file-list-exec-source-files
30692 @subsubheading Synopsis
30695 -file-list-exec-source-files
30698 List the source files for the current executable.
30700 It will always output the filename, but only when @value{GDBN} can find
30701 the absolute file name of a source file, will it output the fullname.
30703 @subsubheading @value{GDBN} Command
30705 The @value{GDBN} equivalent is @samp{info sources}.
30706 @code{gdbtk} has an analogous command @samp{gdb_listfiles}.
30708 @subsubheading Example
30711 -file-list-exec-source-files
30713 @{file=foo.c,fullname=/home/foo.c@},
30714 @{file=/home/bar.c,fullname=/home/bar.c@},
30715 @{file=gdb_could_not_find_fullpath.c@}]
30720 @subheading The @code{-file-list-shared-libraries} Command
30721 @findex -file-list-shared-libraries
30723 @subsubheading Synopsis
30726 -file-list-shared-libraries
30729 List the shared libraries in the program.
30731 @subsubheading @value{GDBN} Command
30733 The corresponding @value{GDBN} command is @samp{info shared}.
30735 @subsubheading Example
30739 @subheading The @code{-file-list-symbol-files} Command
30740 @findex -file-list-symbol-files
30742 @subsubheading Synopsis
30745 -file-list-symbol-files
30750 @subsubheading @value{GDBN} Command
30752 The corresponding @value{GDBN} command is @samp{info file} (part of it).
30754 @subsubheading Example
30759 @subheading The @code{-file-symbol-file} Command
30760 @findex -file-symbol-file
30762 @subsubheading Synopsis
30765 -file-symbol-file @var{file}
30768 Read symbol table info from the specified @var{file} argument. When
30769 used without arguments, clears @value{GDBN}'s symbol table info. No output is
30770 produced, except for a completion notification.
30772 @subsubheading @value{GDBN} Command
30774 The corresponding @value{GDBN} command is @samp{symbol-file}.
30776 @subsubheading Example
30780 -file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
30786 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
30787 @node GDB/MI Memory Overlay Commands
30788 @section @sc{gdb/mi} Memory Overlay Commands
30790 The memory overlay commands are not implemented.
30792 @c @subheading -overlay-auto
30794 @c @subheading -overlay-list-mapping-state
30796 @c @subheading -overlay-list-overlays
30798 @c @subheading -overlay-map
30800 @c @subheading -overlay-off
30802 @c @subheading -overlay-on
30804 @c @subheading -overlay-unmap
30806 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
30807 @node GDB/MI Signal Handling Commands
30808 @section @sc{gdb/mi} Signal Handling Commands
30810 Signal handling commands are not implemented.
30812 @c @subheading -signal-handle
30814 @c @subheading -signal-list-handle-actions
30816 @c @subheading -signal-list-signal-types
30820 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
30821 @node GDB/MI Target Manipulation
30822 @section @sc{gdb/mi} Target Manipulation Commands
30825 @subheading The @code{-target-attach} Command
30826 @findex -target-attach
30828 @subsubheading Synopsis
30831 -target-attach @var{pid} | @var{gid} | @var{file}
30834 Attach to a process @var{pid} or a file @var{file} outside of
30835 @value{GDBN}, or a thread group @var{gid}. If attaching to a thread
30836 group, the id previously returned by
30837 @samp{-list-thread-groups --available} must be used.
30839 @subsubheading @value{GDBN} Command
30841 The corresponding @value{GDBN} command is @samp{attach}.
30843 @subsubheading Example
30847 =thread-created,id="1"
30848 *stopped,thread-id="1",frame=@{addr="0xb7f7e410",func="bar",args=[]@}
30854 @subheading The @code{-target-compare-sections} Command
30855 @findex -target-compare-sections
30857 @subsubheading Synopsis
30860 -target-compare-sections [ @var{section} ]
30863 Compare data of section @var{section} on target to the exec file.
30864 Without the argument, all sections are compared.
30866 @subsubheading @value{GDBN} Command
30868 The @value{GDBN} equivalent is @samp{compare-sections}.
30870 @subsubheading Example
30875 @subheading The @code{-target-detach} Command
30876 @findex -target-detach
30878 @subsubheading Synopsis
30881 -target-detach [ @var{pid} | @var{gid} ]
30884 Detach from the remote target which normally resumes its execution.
30885 If either @var{pid} or @var{gid} is specified, detaches from either
30886 the specified process, or specified thread group. There's no output.
30888 @subsubheading @value{GDBN} Command
30890 The corresponding @value{GDBN} command is @samp{detach}.
30892 @subsubheading Example
30902 @subheading The @code{-target-disconnect} Command
30903 @findex -target-disconnect
30905 @subsubheading Synopsis
30911 Disconnect from the remote target. There's no output and the target is
30912 generally not resumed.
30914 @subsubheading @value{GDBN} Command
30916 The corresponding @value{GDBN} command is @samp{disconnect}.
30918 @subsubheading Example
30928 @subheading The @code{-target-download} Command
30929 @findex -target-download
30931 @subsubheading Synopsis
30937 Loads the executable onto the remote target.
30938 It prints out an update message every half second, which includes the fields:
30942 The name of the section.
30944 The size of what has been sent so far for that section.
30946 The size of the section.
30948 The total size of what was sent so far (the current and the previous sections).
30950 The size of the overall executable to download.
30954 Each message is sent as status record (@pxref{GDB/MI Output Syntax, ,
30955 @sc{gdb/mi} Output Syntax}).
30957 In addition, it prints the name and size of the sections, as they are
30958 downloaded. These messages include the following fields:
30962 The name of the section.
30964 The size of the section.
30966 The size of the overall executable to download.
30970 At the end, a summary is printed.
30972 @subsubheading @value{GDBN} Command
30974 The corresponding @value{GDBN} command is @samp{load}.
30976 @subsubheading Example
30978 Note: each status message appears on a single line. Here the messages
30979 have been broken down so that they can fit onto a page.
30984 +download,@{section=".text",section-size="6668",total-size="9880"@}
30985 +download,@{section=".text",section-sent="512",section-size="6668",
30986 total-sent="512",total-size="9880"@}
30987 +download,@{section=".text",section-sent="1024",section-size="6668",
30988 total-sent="1024",total-size="9880"@}
30989 +download,@{section=".text",section-sent="1536",section-size="6668",
30990 total-sent="1536",total-size="9880"@}
30991 +download,@{section=".text",section-sent="2048",section-size="6668",
30992 total-sent="2048",total-size="9880"@}
30993 +download,@{section=".text",section-sent="2560",section-size="6668",
30994 total-sent="2560",total-size="9880"@}
30995 +download,@{section=".text",section-sent="3072",section-size="6668",
30996 total-sent="3072",total-size="9880"@}
30997 +download,@{section=".text",section-sent="3584",section-size="6668",
30998 total-sent="3584",total-size="9880"@}
30999 +download,@{section=".text",section-sent="4096",section-size="6668",
31000 total-sent="4096",total-size="9880"@}
31001 +download,@{section=".text",section-sent="4608",section-size="6668",
31002 total-sent="4608",total-size="9880"@}
31003 +download,@{section=".text",section-sent="5120",section-size="6668",
31004 total-sent="5120",total-size="9880"@}
31005 +download,@{section=".text",section-sent="5632",section-size="6668",
31006 total-sent="5632",total-size="9880"@}
31007 +download,@{section=".text",section-sent="6144",section-size="6668",
31008 total-sent="6144",total-size="9880"@}
31009 +download,@{section=".text",section-sent="6656",section-size="6668",
31010 total-sent="6656",total-size="9880"@}
31011 +download,@{section=".init",section-size="28",total-size="9880"@}
31012 +download,@{section=".fini",section-size="28",total-size="9880"@}
31013 +download,@{section=".data",section-size="3156",total-size="9880"@}
31014 +download,@{section=".data",section-sent="512",section-size="3156",
31015 total-sent="7236",total-size="9880"@}
31016 +download,@{section=".data",section-sent="1024",section-size="3156",
31017 total-sent="7748",total-size="9880"@}
31018 +download,@{section=".data",section-sent="1536",section-size="3156",
31019 total-sent="8260",total-size="9880"@}
31020 +download,@{section=".data",section-sent="2048",section-size="3156",
31021 total-sent="8772",total-size="9880"@}
31022 +download,@{section=".data",section-sent="2560",section-size="3156",
31023 total-sent="9284",total-size="9880"@}
31024 +download,@{section=".data",section-sent="3072",section-size="3156",
31025 total-sent="9796",total-size="9880"@}
31026 ^done,address="0x10004",load-size="9880",transfer-rate="6586",
31033 @subheading The @code{-target-exec-status} Command
31034 @findex -target-exec-status
31036 @subsubheading Synopsis
31039 -target-exec-status
31042 Provide information on the state of the target (whether it is running or
31043 not, for instance).
31045 @subsubheading @value{GDBN} Command
31047 There's no equivalent @value{GDBN} command.
31049 @subsubheading Example
31053 @subheading The @code{-target-list-available-targets} Command
31054 @findex -target-list-available-targets
31056 @subsubheading Synopsis
31059 -target-list-available-targets
31062 List the possible targets to connect to.
31064 @subsubheading @value{GDBN} Command
31066 The corresponding @value{GDBN} command is @samp{help target}.
31068 @subsubheading Example
31072 @subheading The @code{-target-list-current-targets} Command
31073 @findex -target-list-current-targets
31075 @subsubheading Synopsis
31078 -target-list-current-targets
31081 Describe the current target.
31083 @subsubheading @value{GDBN} Command
31085 The corresponding information is printed by @samp{info file} (among
31088 @subsubheading Example
31092 @subheading The @code{-target-list-parameters} Command
31093 @findex -target-list-parameters
31095 @subsubheading Synopsis
31098 -target-list-parameters
31104 @subsubheading @value{GDBN} Command
31108 @subsubheading Example
31112 @subheading The @code{-target-select} Command
31113 @findex -target-select
31115 @subsubheading Synopsis
31118 -target-select @var{type} @var{parameters @dots{}}
31121 Connect @value{GDBN} to the remote target. This command takes two args:
31125 The type of target, for instance @samp{remote}, etc.
31126 @item @var{parameters}
31127 Device names, host names and the like. @xref{Target Commands, ,
31128 Commands for Managing Targets}, for more details.
31131 The output is a connection notification, followed by the address at
31132 which the target program is, in the following form:
31135 ^connected,addr="@var{address}",func="@var{function name}",
31136 args=[@var{arg list}]
31139 @subsubheading @value{GDBN} Command
31141 The corresponding @value{GDBN} command is @samp{target}.
31143 @subsubheading Example
31147 -target-select remote /dev/ttya
31148 ^connected,addr="0xfe00a300",func="??",args=[]
31152 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
31153 @node GDB/MI File Transfer Commands
31154 @section @sc{gdb/mi} File Transfer Commands
31157 @subheading The @code{-target-file-put} Command
31158 @findex -target-file-put
31160 @subsubheading Synopsis
31163 -target-file-put @var{hostfile} @var{targetfile}
31166 Copy file @var{hostfile} from the host system (the machine running
31167 @value{GDBN}) to @var{targetfile} on the target system.
31169 @subsubheading @value{GDBN} Command
31171 The corresponding @value{GDBN} command is @samp{remote put}.
31173 @subsubheading Example
31177 -target-file-put localfile remotefile
31183 @subheading The @code{-target-file-get} Command
31184 @findex -target-file-get
31186 @subsubheading Synopsis
31189 -target-file-get @var{targetfile} @var{hostfile}
31192 Copy file @var{targetfile} from the target system to @var{hostfile}
31193 on the host system.
31195 @subsubheading @value{GDBN} Command
31197 The corresponding @value{GDBN} command is @samp{remote get}.
31199 @subsubheading Example
31203 -target-file-get remotefile localfile
31209 @subheading The @code{-target-file-delete} Command
31210 @findex -target-file-delete
31212 @subsubheading Synopsis
31215 -target-file-delete @var{targetfile}
31218 Delete @var{targetfile} from the target system.
31220 @subsubheading @value{GDBN} Command
31222 The corresponding @value{GDBN} command is @samp{remote delete}.
31224 @subsubheading Example
31228 -target-file-delete remotefile
31234 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
31235 @node GDB/MI Miscellaneous Commands
31236 @section Miscellaneous @sc{gdb/mi} Commands
31238 @c @subheading -gdb-complete
31240 @subheading The @code{-gdb-exit} Command
31243 @subsubheading Synopsis
31249 Exit @value{GDBN} immediately.
31251 @subsubheading @value{GDBN} Command
31253 Approximately corresponds to @samp{quit}.
31255 @subsubheading Example
31265 @subheading The @code{-exec-abort} Command
31266 @findex -exec-abort
31268 @subsubheading Synopsis
31274 Kill the inferior running program.
31276 @subsubheading @value{GDBN} Command
31278 The corresponding @value{GDBN} command is @samp{kill}.
31280 @subsubheading Example
31285 @subheading The @code{-gdb-set} Command
31288 @subsubheading Synopsis
31294 Set an internal @value{GDBN} variable.
31295 @c IS THIS A DOLLAR VARIABLE? OR SOMETHING LIKE ANNOTATE ?????
31297 @subsubheading @value{GDBN} Command
31299 The corresponding @value{GDBN} command is @samp{set}.
31301 @subsubheading Example
31311 @subheading The @code{-gdb-show} Command
31314 @subsubheading Synopsis
31320 Show the current value of a @value{GDBN} variable.
31322 @subsubheading @value{GDBN} Command
31324 The corresponding @value{GDBN} command is @samp{show}.
31326 @subsubheading Example
31335 @c @subheading -gdb-source
31338 @subheading The @code{-gdb-version} Command
31339 @findex -gdb-version
31341 @subsubheading Synopsis
31347 Show version information for @value{GDBN}. Used mostly in testing.
31349 @subsubheading @value{GDBN} Command
31351 The @value{GDBN} equivalent is @samp{show version}. @value{GDBN} by
31352 default shows this information when you start an interactive session.
31354 @subsubheading Example
31356 @c This example modifies the actual output from GDB to avoid overfull
31362 ~Copyright 2000 Free Software Foundation, Inc.
31363 ~GDB is free software, covered by the GNU General Public License, and
31364 ~you are welcome to change it and/or distribute copies of it under
31365 ~ certain conditions.
31366 ~Type "show copying" to see the conditions.
31367 ~There is absolutely no warranty for GDB. Type "show warranty" for
31369 ~This GDB was configured as
31370 "--host=sparc-sun-solaris2.5.1 --target=ppc-eabi".
31375 @subheading The @code{-list-features} Command
31376 @findex -list-features
31378 Returns a list of particular features of the MI protocol that
31379 this version of gdb implements. A feature can be a command,
31380 or a new field in an output of some command, or even an
31381 important bugfix. While a frontend can sometimes detect presence
31382 of a feature at runtime, it is easier to perform detection at debugger
31385 The command returns a list of strings, with each string naming an
31386 available feature. Each returned string is just a name, it does not
31387 have any internal structure. The list of possible feature names
31393 (gdb) -list-features
31394 ^done,result=["feature1","feature2"]
31397 The current list of features is:
31400 @item frozen-varobjs
31401 Indicates support for the @code{-var-set-frozen} command, as well
31402 as possible presense of the @code{frozen} field in the output
31403 of @code{-varobj-create}.
31404 @item pending-breakpoints
31405 Indicates support for the @option{-f} option to the @code{-break-insert}
31408 Indicates Python scripting support, Python-based
31409 pretty-printing commands, and possible presence of the
31410 @samp{display_hint} field in the output of @code{-var-list-children}
31412 Indicates support for the @code{-thread-info} command.
31413 @item data-read-memory-bytes
31414 Indicates support for the @code{-data-read-memory-bytes} and the
31415 @code{-data-write-memory-bytes} commands.
31416 @item breakpoint-notifications
31417 Indicates that changes to breakpoints and breakpoints created via the
31418 CLI will be announced via async records.
31419 @item ada-task-info
31420 Indicates support for the @code{-ada-task-info} command.
31423 @subheading The @code{-list-target-features} Command
31424 @findex -list-target-features
31426 Returns a list of particular features that are supported by the
31427 target. Those features affect the permitted MI commands, but
31428 unlike the features reported by the @code{-list-features} command, the
31429 features depend on which target GDB is using at the moment. Whenever
31430 a target can change, due to commands such as @code{-target-select},
31431 @code{-target-attach} or @code{-exec-run}, the list of target features
31432 may change, and the frontend should obtain it again.
31436 (gdb) -list-features
31437 ^done,result=["async"]
31440 The current list of features is:
31444 Indicates that the target is capable of asynchronous command
31445 execution, which means that @value{GDBN} will accept further commands
31446 while the target is running.
31449 Indicates that the target is capable of reverse execution.
31450 @xref{Reverse Execution}, for more information.
31454 @subheading The @code{-list-thread-groups} Command
31455 @findex -list-thread-groups
31457 @subheading Synopsis
31460 -list-thread-groups [ --available ] [ --recurse 1 ] [ @var{group} ... ]
31463 Lists thread groups (@pxref{Thread groups}). When a single thread
31464 group is passed as the argument, lists the children of that group.
31465 When several thread group are passed, lists information about those
31466 thread groups. Without any parameters, lists information about all
31467 top-level thread groups.
31469 Normally, thread groups that are being debugged are reported.
31470 With the @samp{--available} option, @value{GDBN} reports thread groups
31471 available on the target.
31473 The output of this command may have either a @samp{threads} result or
31474 a @samp{groups} result. The @samp{thread} result has a list of tuples
31475 as value, with each tuple describing a thread (@pxref{GDB/MI Thread
31476 Information}). The @samp{groups} result has a list of tuples as value,
31477 each tuple describing a thread group. If top-level groups are
31478 requested (that is, no parameter is passed), or when several groups
31479 are passed, the output always has a @samp{groups} result. The format
31480 of the @samp{group} result is described below.
31482 To reduce the number of roundtrips it's possible to list thread groups
31483 together with their children, by passing the @samp{--recurse} option
31484 and the recursion depth. Presently, only recursion depth of 1 is
31485 permitted. If this option is present, then every reported thread group
31486 will also include its children, either as @samp{group} or
31487 @samp{threads} field.
31489 In general, any combination of option and parameters is permitted, with
31490 the following caveats:
31494 When a single thread group is passed, the output will typically
31495 be the @samp{threads} result. Because threads may not contain
31496 anything, the @samp{recurse} option will be ignored.
31499 When the @samp{--available} option is passed, limited information may
31500 be available. In particular, the list of threads of a process might
31501 be inaccessible. Further, specifying specific thread groups might
31502 not give any performance advantage over listing all thread groups.
31503 The frontend should assume that @samp{-list-thread-groups --available}
31504 is always an expensive operation and cache the results.
31508 The @samp{groups} result is a list of tuples, where each tuple may
31509 have the following fields:
31513 Identifier of the thread group. This field is always present.
31514 The identifier is an opaque string; frontends should not try to
31515 convert it to an integer, even though it might look like one.
31518 The type of the thread group. At present, only @samp{process} is a
31522 The target-specific process identifier. This field is only present
31523 for thread groups of type @samp{process} and only if the process exists.
31526 The number of children this thread group has. This field may be
31527 absent for an available thread group.
31530 This field has a list of tuples as value, each tuple describing a
31531 thread. It may be present if the @samp{--recurse} option is
31532 specified, and it's actually possible to obtain the threads.
31535 This field is a list of integers, each identifying a core that one
31536 thread of the group is running on. This field may be absent if
31537 such information is not available.
31540 The name of the executable file that corresponds to this thread group.
31541 The field is only present for thread groups of type @samp{process},
31542 and only if there is a corresponding executable file.
31546 @subheading Example
31550 -list-thread-groups
31551 ^done,groups=[@{id="17",type="process",pid="yyy",num_children="2"@}]
31552 -list-thread-groups 17
31553 ^done,threads=[@{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
31554 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]@},state="running"@},
31555 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
31556 frame=@{level="0",addr="0x0804891f",func="foo",args=[@{name="i",value="10"@}],
31557 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},state="running"@}]]
31558 -list-thread-groups --available
31559 ^done,groups=[@{id="17",type="process",pid="yyy",num_children="2",cores=[1,2]@}]
31560 -list-thread-groups --available --recurse 1
31561 ^done,groups=[@{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],
31562 threads=[@{id="1",target-id="Thread 0xb7e14b90",cores=[1]@},
31563 @{id="2",target-id="Thread 0xb7e14b90",cores=[2]@}]@},..]
31564 -list-thread-groups --available --recurse 1 17 18
31565 ^done,groups=[@{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],
31566 threads=[@{id="1",target-id="Thread 0xb7e14b90",cores=[1]@},
31567 @{id="2",target-id="Thread 0xb7e14b90",cores=[2]@}]@},...]
31571 @subheading The @code{-add-inferior} Command
31572 @findex -add-inferior
31574 @subheading Synopsis
31580 Creates a new inferior (@pxref{Inferiors and Programs}). The created
31581 inferior is not associated with any executable. Such association may
31582 be established with the @samp{-file-exec-and-symbols} command
31583 (@pxref{GDB/MI File Commands}). The command response has a single
31584 field, @samp{thread-group}, whose value is the identifier of the
31585 thread group corresponding to the new inferior.
31587 @subheading Example
31592 ^done,thread-group="i3"
31595 @subheading The @code{-interpreter-exec} Command
31596 @findex -interpreter-exec
31598 @subheading Synopsis
31601 -interpreter-exec @var{interpreter} @var{command}
31603 @anchor{-interpreter-exec}
31605 Execute the specified @var{command} in the given @var{interpreter}.
31607 @subheading @value{GDBN} Command
31609 The corresponding @value{GDBN} command is @samp{interpreter-exec}.
31611 @subheading Example
31615 -interpreter-exec console "break main"
31616 &"During symbol reading, couldn't parse type; debugger out of date?.\n"
31617 &"During symbol reading, bad structure-type format.\n"
31618 ~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n"
31623 @subheading The @code{-inferior-tty-set} Command
31624 @findex -inferior-tty-set
31626 @subheading Synopsis
31629 -inferior-tty-set /dev/pts/1
31632 Set terminal for future runs of the program being debugged.
31634 @subheading @value{GDBN} Command
31636 The corresponding @value{GDBN} command is @samp{set inferior-tty} /dev/pts/1.
31638 @subheading Example
31642 -inferior-tty-set /dev/pts/1
31647 @subheading The @code{-inferior-tty-show} Command
31648 @findex -inferior-tty-show
31650 @subheading Synopsis
31656 Show terminal for future runs of program being debugged.
31658 @subheading @value{GDBN} Command
31660 The corresponding @value{GDBN} command is @samp{show inferior-tty}.
31662 @subheading Example
31666 -inferior-tty-set /dev/pts/1
31670 ^done,inferior_tty_terminal="/dev/pts/1"
31674 @subheading The @code{-enable-timings} Command
31675 @findex -enable-timings
31677 @subheading Synopsis
31680 -enable-timings [yes | no]
31683 Toggle the printing of the wallclock, user and system times for an MI
31684 command as a field in its output. This command is to help frontend
31685 developers optimize the performance of their code. No argument is
31686 equivalent to @samp{yes}.
31688 @subheading @value{GDBN} Command
31692 @subheading Example
31700 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
31701 addr="0x080484ed",func="main",file="myprog.c",
31702 fullname="/home/nickrob/myprog.c",line="73",times="0"@},
31703 time=@{wallclock="0.05185",user="0.00800",system="0.00000"@}
31711 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
31712 frame=@{addr="0x080484ed",func="main",args=[@{name="argc",value="1"@},
31713 @{name="argv",value="0xbfb60364"@}],file="myprog.c",
31714 fullname="/home/nickrob/myprog.c",line="73"@}
31719 @chapter @value{GDBN} Annotations
31721 This chapter describes annotations in @value{GDBN}. Annotations were
31722 designed to interface @value{GDBN} to graphical user interfaces or other
31723 similar programs which want to interact with @value{GDBN} at a
31724 relatively high level.
31726 The annotation mechanism has largely been superseded by @sc{gdb/mi}
31730 This is Edition @value{EDITION}, @value{DATE}.
31734 * Annotations Overview:: What annotations are; the general syntax.
31735 * Server Prefix:: Issuing a command without affecting user state.
31736 * Prompting:: Annotations marking @value{GDBN}'s need for input.
31737 * Errors:: Annotations for error messages.
31738 * Invalidation:: Some annotations describe things now invalid.
31739 * Annotations for Running::
31740 Whether the program is running, how it stopped, etc.
31741 * Source Annotations:: Annotations describing source code.
31744 @node Annotations Overview
31745 @section What is an Annotation?
31746 @cindex annotations
31748 Annotations start with a newline character, two @samp{control-z}
31749 characters, and the name of the annotation. If there is no additional
31750 information associated with this annotation, the name of the annotation
31751 is followed immediately by a newline. If there is additional
31752 information, the name of the annotation is followed by a space, the
31753 additional information, and a newline. The additional information
31754 cannot contain newline characters.
31756 Any output not beginning with a newline and two @samp{control-z}
31757 characters denotes literal output from @value{GDBN}. Currently there is
31758 no need for @value{GDBN} to output a newline followed by two
31759 @samp{control-z} characters, but if there was such a need, the
31760 annotations could be extended with an @samp{escape} annotation which
31761 means those three characters as output.
31763 The annotation @var{level}, which is specified using the
31764 @option{--annotate} command line option (@pxref{Mode Options}), controls
31765 how much information @value{GDBN} prints together with its prompt,
31766 values of expressions, source lines, and other types of output. Level 0
31767 is for no annotations, level 1 is for use when @value{GDBN} is run as a
31768 subprocess of @sc{gnu} Emacs, level 3 is the maximum annotation suitable
31769 for programs that control @value{GDBN}, and level 2 annotations have
31770 been made obsolete (@pxref{Limitations, , Limitations of the Annotation
31771 Interface, annotate, GDB's Obsolete Annotations}).
31774 @kindex set annotate
31775 @item set annotate @var{level}
31776 The @value{GDBN} command @code{set annotate} sets the level of
31777 annotations to the specified @var{level}.
31779 @item show annotate
31780 @kindex show annotate
31781 Show the current annotation level.
31784 This chapter describes level 3 annotations.
31786 A simple example of starting up @value{GDBN} with annotations is:
31789 $ @kbd{gdb --annotate=3}
31791 Copyright 2003 Free Software Foundation, Inc.
31792 GDB is free software, covered by the GNU General Public License,
31793 and you are welcome to change it and/or distribute copies of it
31794 under certain conditions.
31795 Type "show copying" to see the conditions.
31796 There is absolutely no warranty for GDB. Type "show warranty"
31798 This GDB was configured as "i386-pc-linux-gnu"
31809 Here @samp{quit} is input to @value{GDBN}; the rest is output from
31810 @value{GDBN}. The three lines beginning @samp{^Z^Z} (where @samp{^Z}
31811 denotes a @samp{control-z} character) are annotations; the rest is
31812 output from @value{GDBN}.
31814 @node Server Prefix
31815 @section The Server Prefix
31816 @cindex server prefix
31818 If you prefix a command with @samp{server } then it will not affect
31819 the command history, nor will it affect @value{GDBN}'s notion of which
31820 command to repeat if @key{RET} is pressed on a line by itself. This
31821 means that commands can be run behind a user's back by a front-end in
31822 a transparent manner.
31824 The @code{server } prefix does not affect the recording of values into
31825 the value history; to print a value without recording it into the
31826 value history, use the @code{output} command instead of the
31827 @code{print} command.
31829 Using this prefix also disables confirmation requests
31830 (@pxref{confirmation requests}).
31833 @section Annotation for @value{GDBN} Input
31835 @cindex annotations for prompts
31836 When @value{GDBN} prompts for input, it annotates this fact so it is possible
31837 to know when to send output, when the output from a given command is
31840 Different kinds of input each have a different @dfn{input type}. Each
31841 input type has three annotations: a @code{pre-} annotation, which
31842 denotes the beginning of any prompt which is being output, a plain
31843 annotation, which denotes the end of the prompt, and then a @code{post-}
31844 annotation which denotes the end of any echo which may (or may not) be
31845 associated with the input. For example, the @code{prompt} input type
31846 features the following annotations:
31854 The input types are
31857 @findex pre-prompt annotation
31858 @findex prompt annotation
31859 @findex post-prompt annotation
31861 When @value{GDBN} is prompting for a command (the main @value{GDBN} prompt).
31863 @findex pre-commands annotation
31864 @findex commands annotation
31865 @findex post-commands annotation
31867 When @value{GDBN} prompts for a set of commands, like in the @code{commands}
31868 command. The annotations are repeated for each command which is input.
31870 @findex pre-overload-choice annotation
31871 @findex overload-choice annotation
31872 @findex post-overload-choice annotation
31873 @item overload-choice
31874 When @value{GDBN} wants the user to select between various overloaded functions.
31876 @findex pre-query annotation
31877 @findex query annotation
31878 @findex post-query annotation
31880 When @value{GDBN} wants the user to confirm a potentially dangerous operation.
31882 @findex pre-prompt-for-continue annotation
31883 @findex prompt-for-continue annotation
31884 @findex post-prompt-for-continue annotation
31885 @item prompt-for-continue
31886 When @value{GDBN} is asking the user to press return to continue. Note: Don't
31887 expect this to work well; instead use @code{set height 0} to disable
31888 prompting. This is because the counting of lines is buggy in the
31889 presence of annotations.
31894 @cindex annotations for errors, warnings and interrupts
31896 @findex quit annotation
31901 This annotation occurs right before @value{GDBN} responds to an interrupt.
31903 @findex error annotation
31908 This annotation occurs right before @value{GDBN} responds to an error.
31910 Quit and error annotations indicate that any annotations which @value{GDBN} was
31911 in the middle of may end abruptly. For example, if a
31912 @code{value-history-begin} annotation is followed by a @code{error}, one
31913 cannot expect to receive the matching @code{value-history-end}. One
31914 cannot expect not to receive it either, however; an error annotation
31915 does not necessarily mean that @value{GDBN} is immediately returning all the way
31918 @findex error-begin annotation
31919 A quit or error annotation may be preceded by
31925 Any output between that and the quit or error annotation is the error
31928 Warning messages are not yet annotated.
31929 @c If we want to change that, need to fix warning(), type_error(),
31930 @c range_error(), and possibly other places.
31933 @section Invalidation Notices
31935 @cindex annotations for invalidation messages
31936 The following annotations say that certain pieces of state may have
31940 @findex frames-invalid annotation
31941 @item ^Z^Zframes-invalid
31943 The frames (for example, output from the @code{backtrace} command) may
31946 @findex breakpoints-invalid annotation
31947 @item ^Z^Zbreakpoints-invalid
31949 The breakpoints may have changed. For example, the user just added or
31950 deleted a breakpoint.
31953 @node Annotations for Running
31954 @section Running the Program
31955 @cindex annotations for running programs
31957 @findex starting annotation
31958 @findex stopping annotation
31959 When the program starts executing due to a @value{GDBN} command such as
31960 @code{step} or @code{continue},
31966 is output. When the program stops,
31972 is output. Before the @code{stopped} annotation, a variety of
31973 annotations describe how the program stopped.
31976 @findex exited annotation
31977 @item ^Z^Zexited @var{exit-status}
31978 The program exited, and @var{exit-status} is the exit status (zero for
31979 successful exit, otherwise nonzero).
31981 @findex signalled annotation
31982 @findex signal-name annotation
31983 @findex signal-name-end annotation
31984 @findex signal-string annotation
31985 @findex signal-string-end annotation
31986 @item ^Z^Zsignalled
31987 The program exited with a signal. After the @code{^Z^Zsignalled}, the
31988 annotation continues:
31994 ^Z^Zsignal-name-end
31998 ^Z^Zsignal-string-end
32003 where @var{name} is the name of the signal, such as @code{SIGILL} or
32004 @code{SIGSEGV}, and @var{string} is the explanation of the signal, such
32005 as @code{Illegal Instruction} or @code{Segmentation fault}.
32006 @var{intro-text}, @var{middle-text}, and @var{end-text} are for the
32007 user's benefit and have no particular format.
32009 @findex signal annotation
32011 The syntax of this annotation is just like @code{signalled}, but @value{GDBN} is
32012 just saying that the program received the signal, not that it was
32013 terminated with it.
32015 @findex breakpoint annotation
32016 @item ^Z^Zbreakpoint @var{number}
32017 The program hit breakpoint number @var{number}.
32019 @findex watchpoint annotation
32020 @item ^Z^Zwatchpoint @var{number}
32021 The program hit watchpoint number @var{number}.
32024 @node Source Annotations
32025 @section Displaying Source
32026 @cindex annotations for source display
32028 @findex source annotation
32029 The following annotation is used instead of displaying source code:
32032 ^Z^Zsource @var{filename}:@var{line}:@var{character}:@var{middle}:@var{addr}
32035 where @var{filename} is an absolute file name indicating which source
32036 file, @var{line} is the line number within that file (where 1 is the
32037 first line in the file), @var{character} is the character position
32038 within the file (where 0 is the first character in the file) (for most
32039 debug formats this will necessarily point to the beginning of a line),
32040 @var{middle} is @samp{middle} if @var{addr} is in the middle of the
32041 line, or @samp{beg} if @var{addr} is at the beginning of the line, and
32042 @var{addr} is the address in the target program associated with the
32043 source which is being displayed. @var{addr} is in the form @samp{0x}
32044 followed by one or more lowercase hex digits (note that this does not
32045 depend on the language).
32047 @node JIT Interface
32048 @chapter JIT Compilation Interface
32049 @cindex just-in-time compilation
32050 @cindex JIT compilation interface
32052 This chapter documents @value{GDBN}'s @dfn{just-in-time} (JIT) compilation
32053 interface. A JIT compiler is a program or library that generates native
32054 executable code at runtime and executes it, usually in order to achieve good
32055 performance while maintaining platform independence.
32057 Programs that use JIT compilation are normally difficult to debug because
32058 portions of their code are generated at runtime, instead of being loaded from
32059 object files, which is where @value{GDBN} normally finds the program's symbols
32060 and debug information. In order to debug programs that use JIT compilation,
32061 @value{GDBN} has an interface that allows the program to register in-memory
32062 symbol files with @value{GDBN} at runtime.
32064 If you are using @value{GDBN} to debug a program that uses this interface, then
32065 it should work transparently so long as you have not stripped the binary. If
32066 you are developing a JIT compiler, then the interface is documented in the rest
32067 of this chapter. At this time, the only known client of this interface is the
32070 Broadly speaking, the JIT interface mirrors the dynamic loader interface. The
32071 JIT compiler communicates with @value{GDBN} by writing data into a global
32072 variable and calling a fuction at a well-known symbol. When @value{GDBN}
32073 attaches, it reads a linked list of symbol files from the global variable to
32074 find existing code, and puts a breakpoint in the function so that it can find
32075 out about additional code.
32078 * Declarations:: Relevant C struct declarations
32079 * Registering Code:: Steps to register code
32080 * Unregistering Code:: Steps to unregister code
32081 * Custom Debug Info:: Emit debug information in a custom format
32085 @section JIT Declarations
32087 These are the relevant struct declarations that a C program should include to
32088 implement the interface:
32098 struct jit_code_entry
32100 struct jit_code_entry *next_entry;
32101 struct jit_code_entry *prev_entry;
32102 const char *symfile_addr;
32103 uint64_t symfile_size;
32106 struct jit_descriptor
32109 /* This type should be jit_actions_t, but we use uint32_t
32110 to be explicit about the bitwidth. */
32111 uint32_t action_flag;
32112 struct jit_code_entry *relevant_entry;
32113 struct jit_code_entry *first_entry;
32116 /* GDB puts a breakpoint in this function. */
32117 void __attribute__((noinline)) __jit_debug_register_code() @{ @};
32119 /* Make sure to specify the version statically, because the
32120 debugger may check the version before we can set it. */
32121 struct jit_descriptor __jit_debug_descriptor = @{ 1, 0, 0, 0 @};
32124 If the JIT is multi-threaded, then it is important that the JIT synchronize any
32125 modifications to this global data properly, which can easily be done by putting
32126 a global mutex around modifications to these structures.
32128 @node Registering Code
32129 @section Registering Code
32131 To register code with @value{GDBN}, the JIT should follow this protocol:
32135 Generate an object file in memory with symbols and other desired debug
32136 information. The file must include the virtual addresses of the sections.
32139 Create a code entry for the file, which gives the start and size of the symbol
32143 Add it to the linked list in the JIT descriptor.
32146 Point the relevant_entry field of the descriptor at the entry.
32149 Set @code{action_flag} to @code{JIT_REGISTER} and call
32150 @code{__jit_debug_register_code}.
32153 When @value{GDBN} is attached and the breakpoint fires, @value{GDBN} uses the
32154 @code{relevant_entry} pointer so it doesn't have to walk the list looking for
32155 new code. However, the linked list must still be maintained in order to allow
32156 @value{GDBN} to attach to a running process and still find the symbol files.
32158 @node Unregistering Code
32159 @section Unregistering Code
32161 If code is freed, then the JIT should use the following protocol:
32165 Remove the code entry corresponding to the code from the linked list.
32168 Point the @code{relevant_entry} field of the descriptor at the code entry.
32171 Set @code{action_flag} to @code{JIT_UNREGISTER} and call
32172 @code{__jit_debug_register_code}.
32175 If the JIT frees or recompiles code without unregistering it, then @value{GDBN}
32176 and the JIT will leak the memory used for the associated symbol files.
32178 @node Custom Debug Info
32179 @section Custom Debug Info
32180 @cindex custom JIT debug info
32181 @cindex JIT debug info reader
32183 Generating debug information in platform-native file formats (like ELF
32184 or COFF) may be an overkill for JIT compilers; especially if all the
32185 debug info is used for is displaying a meaningful backtrace. The
32186 issue can be resolved by having the JIT writers decide on a debug info
32187 format and also provide a reader that parses the debug info generated
32188 by the JIT compiler. This section gives a brief overview on writing
32189 such a parser. More specific details can be found in the source file
32190 @file{gdb/jit-reader.in}, which is also installed as a header at
32191 @file{@var{includedir}/gdb/jit-reader.h} for easy inclusion.
32193 The reader is implemented as a shared object (so this functionality is
32194 not available on platforms which don't allow loading shared objects at
32195 runtime). Two @value{GDBN} commands, @code{jit-reader-load} and
32196 @code{jit-reader-unload} are provided, to be used to load and unload
32197 the readers from a preconfigured directory. Once loaded, the shared
32198 object is used the parse the debug information emitted by the JIT
32202 * Using JIT Debug Info Readers:: How to use supplied readers correctly
32203 * Writing JIT Debug Info Readers:: Creating a debug-info reader
32206 @node Using JIT Debug Info Readers
32207 @subsection Using JIT Debug Info Readers
32208 @kindex jit-reader-load
32209 @kindex jit-reader-unload
32211 Readers can be loaded and unloaded using the @code{jit-reader-load}
32212 and @code{jit-reader-unload} commands.
32215 @item jit-reader-load @var{reader-name}
32216 Load the JIT reader named @var{reader-name}. On a UNIX system, this
32217 will usually load @file{@var{libdir}/gdb/@var{reader-name}}, where
32218 @var{libdir} is the system library directory, usually
32219 @file{/usr/local/lib}. Only one reader can be active at a time;
32220 trying to load a second reader when one is already loaded will result
32221 in @value{GDBN} reporting an error. A new JIT reader can be loaded by
32222 first unloading the current one using @code{jit-reader-load} and then
32223 invoking @code{jit-reader-load}.
32225 @item jit-reader-unload
32226 Unload the currently loaded JIT reader.
32230 @node Writing JIT Debug Info Readers
32231 @subsection Writing JIT Debug Info Readers
32232 @cindex writing JIT debug info readers
32234 As mentioned, a reader is essentially a shared object conforming to a
32235 certain ABI. This ABI is described in @file{jit-reader.h}.
32237 @file{jit-reader.h} defines the structures, macros and functions
32238 required to write a reader. It is installed (along with
32239 @value{GDBN}), in @file{@var{includedir}/gdb} where @var{includedir} is
32240 the system include directory.
32242 Readers need to be released under a GPL compatible license. A reader
32243 can be declared as released under such a license by placing the macro
32244 @code{GDB_DECLARE_GPL_COMPATIBLE_READER} in a source file.
32246 The entry point for readers is the symbol @code{gdb_init_reader},
32247 which is expected to be a function with the prototype
32249 @findex gdb_init_reader
32251 extern struct gdb_reader_funcs *gdb_init_reader (void);
32254 @cindex @code{struct gdb_reader_funcs}
32256 @code{struct gdb_reader_funcs} contains a set of pointers to callback
32257 functions. These functions are executed to read the debug info
32258 generated by the JIT compiler (@code{read}), to unwind stack frames
32259 (@code{unwind}) and to create canonical frame IDs
32260 (@code{get_Frame_id}). It also has a callback that is called when the
32261 reader is being unloaded (@code{destroy}). The struct looks like this
32264 struct gdb_reader_funcs
32266 /* Must be set to GDB_READER_INTERFACE_VERSION. */
32267 int reader_version;
32269 /* For use by the reader. */
32272 gdb_read_debug_info *read;
32273 gdb_unwind_frame *unwind;
32274 gdb_get_frame_id *get_frame_id;
32275 gdb_destroy_reader *destroy;
32279 @cindex @code{struct gdb_symbol_callbacks}
32280 @cindex @code{struct gdb_unwind_callbacks}
32282 The callbacks are provided with another set of callbacks by
32283 @value{GDBN} to do their job. For @code{read}, these callbacks are
32284 passed in a @code{struct gdb_symbol_callbacks} and for @code{unwind}
32285 and @code{get_frame_id}, in a @code{struct gdb_unwind_callbacks}.
32286 @code{struct gdb_symbol_callbacks} has callbacks to create new object
32287 files and new symbol tables inside those object files. @code{struct
32288 gdb_unwind_callbacks} has callbacks to read registers off the current
32289 frame and to write out the values of the registers in the previous
32290 frame. Both have a callback (@code{target_read}) to read bytes off the
32291 target's address space.
32293 @node In-Process Agent
32294 @chapter In-Process Agent
32295 @cindex debugging agent
32296 The traditional debugging model is conceptually low-speed, but works fine,
32297 because most bugs can be reproduced in debugging-mode execution. However,
32298 as multi-core or many-core processors are becoming mainstream, and
32299 multi-threaded programs become more and more popular, there should be more
32300 and more bugs that only manifest themselves at normal-mode execution, for
32301 example, thread races, because debugger's interference with the program's
32302 timing may conceal the bugs. On the other hand, in some applications,
32303 it is not feasible for the debugger to interrupt the program's execution
32304 long enough for the developer to learn anything helpful about its behavior.
32305 If the program's correctness depends on its real-time behavior, delays
32306 introduced by a debugger might cause the program to fail, even when the
32307 code itself is correct. It is useful to be able to observe the program's
32308 behavior without interrupting it.
32310 Therefore, traditional debugging model is too intrusive to reproduce
32311 some bugs. In order to reduce the interference with the program, we can
32312 reduce the number of operations performed by debugger. The
32313 @dfn{In-Process Agent}, a shared library, is running within the same
32314 process with inferior, and is able to perform some debugging operations
32315 itself. As a result, debugger is only involved when necessary, and
32316 performance of debugging can be improved accordingly. Note that
32317 interference with program can be reduced but can't be removed completely,
32318 because the in-process agent will still stop or slow down the program.
32320 The in-process agent can interpret and execute Agent Expressions
32321 (@pxref{Agent Expressions}) during performing debugging operations. The
32322 agent expressions can be used for different purposes, such as collecting
32323 data in tracepoints, and condition evaluation in breakpoints.
32325 @anchor{Control Agent}
32326 You can control whether the in-process agent is used as an aid for
32327 debugging with the following commands:
32330 @kindex set agent on
32332 Causes the in-process agent to perform some operations on behalf of the
32333 debugger. Just which operations requested by the user will be done
32334 by the in-process agent depends on the its capabilities. For example,
32335 if you request to evaluate breakpoint conditions in the in-process agent,
32336 and the in-process agent has such capability as well, then breakpoint
32337 conditions will be evaluated in the in-process agent.
32339 @kindex set agent off
32340 @item set agent off
32341 Disables execution of debugging operations by the in-process agent. All
32342 of the operations will be performed by @value{GDBN}.
32346 Display the current setting of execution of debugging operations by
32347 the in-process agent.
32351 @chapter Reporting Bugs in @value{GDBN}
32352 @cindex bugs in @value{GDBN}
32353 @cindex reporting bugs in @value{GDBN}
32355 Your bug reports play an essential role in making @value{GDBN} reliable.
32357 Reporting a bug may help you by bringing a solution to your problem, or it
32358 may not. But in any case the principal function of a bug report is to help
32359 the entire community by making the next version of @value{GDBN} work better. Bug
32360 reports are your contribution to the maintenance of @value{GDBN}.
32362 In order for a bug report to serve its purpose, you must include the
32363 information that enables us to fix the bug.
32366 * Bug Criteria:: Have you found a bug?
32367 * Bug Reporting:: How to report bugs
32371 @section Have You Found a Bug?
32372 @cindex bug criteria
32374 If you are not sure whether you have found a bug, here are some guidelines:
32377 @cindex fatal signal
32378 @cindex debugger crash
32379 @cindex crash of debugger
32381 If the debugger gets a fatal signal, for any input whatever, that is a
32382 @value{GDBN} bug. Reliable debuggers never crash.
32384 @cindex error on valid input
32386 If @value{GDBN} produces an error message for valid input, that is a
32387 bug. (Note that if you're cross debugging, the problem may also be
32388 somewhere in the connection to the target.)
32390 @cindex invalid input
32392 If @value{GDBN} does not produce an error message for invalid input,
32393 that is a bug. However, you should note that your idea of
32394 ``invalid input'' might be our idea of ``an extension'' or ``support
32395 for traditional practice''.
32398 If you are an experienced user of debugging tools, your suggestions
32399 for improvement of @value{GDBN} are welcome in any case.
32402 @node Bug Reporting
32403 @section How to Report Bugs
32404 @cindex bug reports
32405 @cindex @value{GDBN} bugs, reporting
32407 A number of companies and individuals offer support for @sc{gnu} products.
32408 If you obtained @value{GDBN} from a support organization, we recommend you
32409 contact that organization first.
32411 You can find contact information for many support companies and
32412 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
32414 @c should add a web page ref...
32417 @ifset BUGURL_DEFAULT
32418 In any event, we also recommend that you submit bug reports for
32419 @value{GDBN}. The preferred method is to submit them directly using
32420 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
32421 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
32424 @strong{Do not send bug reports to @samp{info-gdb}, or to
32425 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
32426 not want to receive bug reports. Those that do have arranged to receive
32429 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
32430 serves as a repeater. The mailing list and the newsgroup carry exactly
32431 the same messages. Often people think of posting bug reports to the
32432 newsgroup instead of mailing them. This appears to work, but it has one
32433 problem which can be crucial: a newsgroup posting often lacks a mail
32434 path back to the sender. Thus, if we need to ask for more information,
32435 we may be unable to reach you. For this reason, it is better to send
32436 bug reports to the mailing list.
32438 @ifclear BUGURL_DEFAULT
32439 In any event, we also recommend that you submit bug reports for
32440 @value{GDBN} to @value{BUGURL}.
32444 The fundamental principle of reporting bugs usefully is this:
32445 @strong{report all the facts}. If you are not sure whether to state a
32446 fact or leave it out, state it!
32448 Often people omit facts because they think they know what causes the
32449 problem and assume that some details do not matter. Thus, you might
32450 assume that the name of the variable you use in an example does not matter.
32451 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
32452 stray memory reference which happens to fetch from the location where that
32453 name is stored in memory; perhaps, if the name were different, the contents
32454 of that location would fool the debugger into doing the right thing despite
32455 the bug. Play it safe and give a specific, complete example. That is the
32456 easiest thing for you to do, and the most helpful.
32458 Keep in mind that the purpose of a bug report is to enable us to fix the
32459 bug. It may be that the bug has been reported previously, but neither
32460 you nor we can know that unless your bug report is complete and
32463 Sometimes people give a few sketchy facts and ask, ``Does this ring a
32464 bell?'' Those bug reports are useless, and we urge everyone to
32465 @emph{refuse to respond to them} except to chide the sender to report
32468 To enable us to fix the bug, you should include all these things:
32472 The version of @value{GDBN}. @value{GDBN} announces it if you start
32473 with no arguments; you can also print it at any time using @code{show
32476 Without this, we will not know whether there is any point in looking for
32477 the bug in the current version of @value{GDBN}.
32480 The type of machine you are using, and the operating system name and
32484 What compiler (and its version) was used to compile @value{GDBN}---e.g.@:
32485 ``@value{GCC}--2.8.1''.
32488 What compiler (and its version) was used to compile the program you are
32489 debugging---e.g.@: ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
32490 C Compiler''. For @value{NGCC}, you can say @kbd{@value{GCC} --version}
32491 to get this information; for other compilers, see the documentation for
32495 The command arguments you gave the compiler to compile your example and
32496 observe the bug. For example, did you use @samp{-O}? To guarantee
32497 you will not omit something important, list them all. A copy of the
32498 Makefile (or the output from make) is sufficient.
32500 If we were to try to guess the arguments, we would probably guess wrong
32501 and then we might not encounter the bug.
32504 A complete input script, and all necessary source files, that will
32508 A description of what behavior you observe that you believe is
32509 incorrect. For example, ``It gets a fatal signal.''
32511 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
32512 will certainly notice it. But if the bug is incorrect output, we might
32513 not notice unless it is glaringly wrong. You might as well not give us
32514 a chance to make a mistake.
32516 Even if the problem you experience is a fatal signal, you should still
32517 say so explicitly. Suppose something strange is going on, such as, your
32518 copy of @value{GDBN} is out of synch, or you have encountered a bug in
32519 the C library on your system. (This has happened!) Your copy might
32520 crash and ours would not. If you told us to expect a crash, then when
32521 ours fails to crash, we would know that the bug was not happening for
32522 us. If you had not told us to expect a crash, then we would not be able
32523 to draw any conclusion from our observations.
32526 @cindex recording a session script
32527 To collect all this information, you can use a session recording program
32528 such as @command{script}, which is available on many Unix systems.
32529 Just run your @value{GDBN} session inside @command{script} and then
32530 include the @file{typescript} file with your bug report.
32532 Another way to record a @value{GDBN} session is to run @value{GDBN}
32533 inside Emacs and then save the entire buffer to a file.
32536 If you wish to suggest changes to the @value{GDBN} source, send us context
32537 diffs. If you even discuss something in the @value{GDBN} source, refer to
32538 it by context, not by line number.
32540 The line numbers in our development sources will not match those in your
32541 sources. Your line numbers would convey no useful information to us.
32545 Here are some things that are not necessary:
32549 A description of the envelope of the bug.
32551 Often people who encounter a bug spend a lot of time investigating
32552 which changes to the input file will make the bug go away and which
32553 changes will not affect it.
32555 This is often time consuming and not very useful, because the way we
32556 will find the bug is by running a single example under the debugger
32557 with breakpoints, not by pure deduction from a series of examples.
32558 We recommend that you save your time for something else.
32560 Of course, if you can find a simpler example to report @emph{instead}
32561 of the original one, that is a convenience for us. Errors in the
32562 output will be easier to spot, running under the debugger will take
32563 less time, and so on.
32565 However, simplification is not vital; if you do not want to do this,
32566 report the bug anyway and send us the entire test case you used.
32569 A patch for the bug.
32571 A patch for the bug does help us if it is a good one. But do not omit
32572 the necessary information, such as the test case, on the assumption that
32573 a patch is all we need. We might see problems with your patch and decide
32574 to fix the problem another way, or we might not understand it at all.
32576 Sometimes with a program as complicated as @value{GDBN} it is very hard to
32577 construct an example that will make the program follow a certain path
32578 through the code. If you do not send us the example, we will not be able
32579 to construct one, so we will not be able to verify that the bug is fixed.
32581 And if we cannot understand what bug you are trying to fix, or why your
32582 patch should be an improvement, we will not install it. A test case will
32583 help us to understand.
32586 A guess about what the bug is or what it depends on.
32588 Such guesses are usually wrong. Even we cannot guess right about such
32589 things without first using the debugger to find the facts.
32592 @c The readline documentation is distributed with the readline code
32593 @c and consists of the two following files:
32596 @c Use -I with makeinfo to point to the appropriate directory,
32597 @c environment var TEXINPUTS with TeX.
32598 @ifclear SYSTEM_READLINE
32599 @include rluser.texi
32600 @include hsuser.texi
32604 @appendix In Memoriam
32606 The @value{GDBN} project mourns the loss of the following long-time
32611 Fred was a long-standing contributor to @value{GDBN} (1991-2006), and
32612 to Free Software in general. Outside of @value{GDBN}, he was known in
32613 the Amiga world for his series of Fish Disks, and the GeekGadget project.
32615 @item Michael Snyder
32616 Michael was one of the Global Maintainers of the @value{GDBN} project,
32617 with contributions recorded as early as 1996, until 2011. In addition
32618 to his day to day participation, he was a large driving force behind
32619 adding Reverse Debugging to @value{GDBN}.
32622 Beyond their technical contributions to the project, they were also
32623 enjoyable members of the Free Software Community. We will miss them.
32625 @node Formatting Documentation
32626 @appendix Formatting Documentation
32628 @cindex @value{GDBN} reference card
32629 @cindex reference card
32630 The @value{GDBN} 4 release includes an already-formatted reference card, ready
32631 for printing with PostScript or Ghostscript, in the @file{gdb}
32632 subdirectory of the main source directory@footnote{In
32633 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
32634 release.}. If you can use PostScript or Ghostscript with your printer,
32635 you can print the reference card immediately with @file{refcard.ps}.
32637 The release also includes the source for the reference card. You
32638 can format it, using @TeX{}, by typing:
32644 The @value{GDBN} reference card is designed to print in @dfn{landscape}
32645 mode on US ``letter'' size paper;
32646 that is, on a sheet 11 inches wide by 8.5 inches
32647 high. You will need to specify this form of printing as an option to
32648 your @sc{dvi} output program.
32650 @cindex documentation
32652 All the documentation for @value{GDBN} comes as part of the machine-readable
32653 distribution. The documentation is written in Texinfo format, which is
32654 a documentation system that uses a single source file to produce both
32655 on-line information and a printed manual. You can use one of the Info
32656 formatting commands to create the on-line version of the documentation
32657 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
32659 @value{GDBN} includes an already formatted copy of the on-line Info
32660 version of this manual in the @file{gdb} subdirectory. The main Info
32661 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
32662 subordinate files matching @samp{gdb.info*} in the same directory. If
32663 necessary, you can print out these files, or read them with any editor;
32664 but they are easier to read using the @code{info} subsystem in @sc{gnu}
32665 Emacs or the standalone @code{info} program, available as part of the
32666 @sc{gnu} Texinfo distribution.
32668 If you want to format these Info files yourself, you need one of the
32669 Info formatting programs, such as @code{texinfo-format-buffer} or
32672 If you have @code{makeinfo} installed, and are in the top level
32673 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
32674 version @value{GDBVN}), you can make the Info file by typing:
32681 If you want to typeset and print copies of this manual, you need @TeX{},
32682 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
32683 Texinfo definitions file.
32685 @TeX{} is a typesetting program; it does not print files directly, but
32686 produces output files called @sc{dvi} files. To print a typeset
32687 document, you need a program to print @sc{dvi} files. If your system
32688 has @TeX{} installed, chances are it has such a program. The precise
32689 command to use depends on your system; @kbd{lpr -d} is common; another
32690 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
32691 require a file name without any extension or a @samp{.dvi} extension.
32693 @TeX{} also requires a macro definitions file called
32694 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
32695 written in Texinfo format. On its own, @TeX{} cannot either read or
32696 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
32697 and is located in the @file{gdb-@var{version-number}/texinfo}
32700 If you have @TeX{} and a @sc{dvi} printer program installed, you can
32701 typeset and print this manual. First switch to the @file{gdb}
32702 subdirectory of the main source directory (for example, to
32703 @file{gdb-@value{GDBVN}/gdb}) and type:
32709 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
32711 @node Installing GDB
32712 @appendix Installing @value{GDBN}
32713 @cindex installation
32716 * Requirements:: Requirements for building @value{GDBN}
32717 * Running Configure:: Invoking the @value{GDBN} @file{configure} script
32718 * Separate Objdir:: Compiling @value{GDBN} in another directory
32719 * Config Names:: Specifying names for hosts and targets
32720 * Configure Options:: Summary of options for configure
32721 * System-wide configuration:: Having a system-wide init file
32725 @section Requirements for Building @value{GDBN}
32726 @cindex building @value{GDBN}, requirements for
32728 Building @value{GDBN} requires various tools and packages to be available.
32729 Other packages will be used only if they are found.
32731 @heading Tools/Packages Necessary for Building @value{GDBN}
32733 @item ISO C90 compiler
32734 @value{GDBN} is written in ISO C90. It should be buildable with any
32735 working C90 compiler, e.g.@: GCC.
32739 @heading Tools/Packages Optional for Building @value{GDBN}
32743 @value{GDBN} can use the Expat XML parsing library. This library may be
32744 included with your operating system distribution; if it is not, you
32745 can get the latest version from @url{http://expat.sourceforge.net}.
32746 The @file{configure} script will search for this library in several
32747 standard locations; if it is installed in an unusual path, you can
32748 use the @option{--with-libexpat-prefix} option to specify its location.
32754 Remote protocol memory maps (@pxref{Memory Map Format})
32756 Target descriptions (@pxref{Target Descriptions})
32758 Remote shared library lists (@xref{Library List Format},
32759 or alternatively @pxref{Library List Format for SVR4 Targets})
32761 MS-Windows shared libraries (@pxref{Shared Libraries})
32763 Traceframe info (@pxref{Traceframe Info Format})
32767 @cindex compressed debug sections
32768 @value{GDBN} will use the @samp{zlib} library, if available, to read
32769 compressed debug sections. Some linkers, such as GNU gold, are capable
32770 of producing binaries with compressed debug sections. If @value{GDBN}
32771 is compiled with @samp{zlib}, it will be able to read the debug
32772 information in such binaries.
32774 The @samp{zlib} library is likely included with your operating system
32775 distribution; if it is not, you can get the latest version from
32776 @url{http://zlib.net}.
32779 @value{GDBN}'s features related to character sets (@pxref{Character
32780 Sets}) require a functioning @code{iconv} implementation. If you are
32781 on a GNU system, then this is provided by the GNU C Library. Some
32782 other systems also provide a working @code{iconv}.
32784 If @value{GDBN} is using the @code{iconv} program which is installed
32785 in a non-standard place, you will need to tell @value{GDBN} where to find it.
32786 This is done with @option{--with-iconv-bin} which specifies the
32787 directory that contains the @code{iconv} program.
32789 On systems without @code{iconv}, you can install GNU Libiconv. If you
32790 have previously installed Libiconv, you can use the
32791 @option{--with-libiconv-prefix} option to configure.
32793 @value{GDBN}'s top-level @file{configure} and @file{Makefile} will
32794 arrange to build Libiconv if a directory named @file{libiconv} appears
32795 in the top-most source directory. If Libiconv is built this way, and
32796 if the operating system does not provide a suitable @code{iconv}
32797 implementation, then the just-built library will automatically be used
32798 by @value{GDBN}. One easy way to set this up is to download GNU
32799 Libiconv, unpack it, and then rename the directory holding the
32800 Libiconv source code to @samp{libiconv}.
32803 @node Running Configure
32804 @section Invoking the @value{GDBN} @file{configure} Script
32805 @cindex configuring @value{GDBN}
32806 @value{GDBN} comes with a @file{configure} script that automates the process
32807 of preparing @value{GDBN} for installation; you can then use @code{make} to
32808 build the @code{gdb} program.
32810 @c irrelevant in info file; it's as current as the code it lives with.
32811 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
32812 look at the @file{README} file in the sources; we may have improved the
32813 installation procedures since publishing this manual.}
32816 The @value{GDBN} distribution includes all the source code you need for
32817 @value{GDBN} in a single directory, whose name is usually composed by
32818 appending the version number to @samp{gdb}.
32820 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
32821 @file{gdb-@value{GDBVN}} directory. That directory contains:
32824 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
32825 script for configuring @value{GDBN} and all its supporting libraries
32827 @item gdb-@value{GDBVN}/gdb
32828 the source specific to @value{GDBN} itself
32830 @item gdb-@value{GDBVN}/bfd
32831 source for the Binary File Descriptor library
32833 @item gdb-@value{GDBVN}/include
32834 @sc{gnu} include files
32836 @item gdb-@value{GDBVN}/libiberty
32837 source for the @samp{-liberty} free software library
32839 @item gdb-@value{GDBVN}/opcodes
32840 source for the library of opcode tables and disassemblers
32842 @item gdb-@value{GDBVN}/readline
32843 source for the @sc{gnu} command-line interface
32845 @item gdb-@value{GDBVN}/glob
32846 source for the @sc{gnu} filename pattern-matching subroutine
32848 @item gdb-@value{GDBVN}/mmalloc
32849 source for the @sc{gnu} memory-mapped malloc package
32852 The simplest way to configure and build @value{GDBN} is to run @file{configure}
32853 from the @file{gdb-@var{version-number}} source directory, which in
32854 this example is the @file{gdb-@value{GDBVN}} directory.
32856 First switch to the @file{gdb-@var{version-number}} source directory
32857 if you are not already in it; then run @file{configure}. Pass the
32858 identifier for the platform on which @value{GDBN} will run as an
32864 cd gdb-@value{GDBVN}
32865 ./configure @var{host}
32870 where @var{host} is an identifier such as @samp{sun4} or
32871 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
32872 (You can often leave off @var{host}; @file{configure} tries to guess the
32873 correct value by examining your system.)
32875 Running @samp{configure @var{host}} and then running @code{make} builds the
32876 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
32877 libraries, then @code{gdb} itself. The configured source files, and the
32878 binaries, are left in the corresponding source directories.
32881 @file{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
32882 system does not recognize this automatically when you run a different
32883 shell, you may need to run @code{sh} on it explicitly:
32886 sh configure @var{host}
32889 If you run @file{configure} from a directory that contains source
32890 directories for multiple libraries or programs, such as the
32891 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN},
32893 creates configuration files for every directory level underneath (unless
32894 you tell it not to, with the @samp{--norecursion} option).
32896 You should run the @file{configure} script from the top directory in the
32897 source tree, the @file{gdb-@var{version-number}} directory. If you run
32898 @file{configure} from one of the subdirectories, you will configure only
32899 that subdirectory. That is usually not what you want. In particular,
32900 if you run the first @file{configure} from the @file{gdb} subdirectory
32901 of the @file{gdb-@var{version-number}} directory, you will omit the
32902 configuration of @file{bfd}, @file{readline}, and other sibling
32903 directories of the @file{gdb} subdirectory. This leads to build errors
32904 about missing include files such as @file{bfd/bfd.h}.
32906 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
32907 However, you should make sure that the shell on your path (named by
32908 the @samp{SHELL} environment variable) is publicly readable. Remember
32909 that @value{GDBN} uses the shell to start your program---some systems refuse to
32910 let @value{GDBN} debug child processes whose programs are not readable.
32912 @node Separate Objdir
32913 @section Compiling @value{GDBN} in Another Directory
32915 If you want to run @value{GDBN} versions for several host or target machines,
32916 you need a different @code{gdb} compiled for each combination of
32917 host and target. @file{configure} is designed to make this easy by
32918 allowing you to generate each configuration in a separate subdirectory,
32919 rather than in the source directory. If your @code{make} program
32920 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
32921 @code{make} in each of these directories builds the @code{gdb}
32922 program specified there.
32924 To build @code{gdb} in a separate directory, run @file{configure}
32925 with the @samp{--srcdir} option to specify where to find the source.
32926 (You also need to specify a path to find @file{configure}
32927 itself from your working directory. If the path to @file{configure}
32928 would be the same as the argument to @samp{--srcdir}, you can leave out
32929 the @samp{--srcdir} option; it is assumed.)
32931 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
32932 separate directory for a Sun 4 like this:
32936 cd gdb-@value{GDBVN}
32939 ../gdb-@value{GDBVN}/configure sun4
32944 When @file{configure} builds a configuration using a remote source
32945 directory, it creates a tree for the binaries with the same structure
32946 (and using the same names) as the tree under the source directory. In
32947 the example, you'd find the Sun 4 library @file{libiberty.a} in the
32948 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
32949 @file{gdb-sun4/gdb}.
32951 Make sure that your path to the @file{configure} script has just one
32952 instance of @file{gdb} in it. If your path to @file{configure} looks
32953 like @file{../gdb-@value{GDBVN}/gdb/configure}, you are configuring only
32954 one subdirectory of @value{GDBN}, not the whole package. This leads to
32955 build errors about missing include files such as @file{bfd/bfd.h}.
32957 One popular reason to build several @value{GDBN} configurations in separate
32958 directories is to configure @value{GDBN} for cross-compiling (where
32959 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
32960 programs that run on another machine---the @dfn{target}).
32961 You specify a cross-debugging target by
32962 giving the @samp{--target=@var{target}} option to @file{configure}.
32964 When you run @code{make} to build a program or library, you must run
32965 it in a configured directory---whatever directory you were in when you
32966 called @file{configure} (or one of its subdirectories).
32968 The @code{Makefile} that @file{configure} generates in each source
32969 directory also runs recursively. If you type @code{make} in a source
32970 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
32971 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
32972 will build all the required libraries, and then build GDB.
32974 When you have multiple hosts or targets configured in separate
32975 directories, you can run @code{make} on them in parallel (for example,
32976 if they are NFS-mounted on each of the hosts); they will not interfere
32980 @section Specifying Names for Hosts and Targets
32982 The specifications used for hosts and targets in the @file{configure}
32983 script are based on a three-part naming scheme, but some short predefined
32984 aliases are also supported. The full naming scheme encodes three pieces
32985 of information in the following pattern:
32988 @var{architecture}-@var{vendor}-@var{os}
32991 For example, you can use the alias @code{sun4} as a @var{host} argument,
32992 or as the value for @var{target} in a @code{--target=@var{target}}
32993 option. The equivalent full name is @samp{sparc-sun-sunos4}.
32995 The @file{configure} script accompanying @value{GDBN} does not provide
32996 any query facility to list all supported host and target names or
32997 aliases. @file{configure} calls the Bourne shell script
32998 @code{config.sub} to map abbreviations to full names; you can read the
32999 script, if you wish, or you can use it to test your guesses on
33000 abbreviations---for example:
33003 % sh config.sub i386-linux
33005 % sh config.sub alpha-linux
33006 alpha-unknown-linux-gnu
33007 % sh config.sub hp9k700
33009 % sh config.sub sun4
33010 sparc-sun-sunos4.1.1
33011 % sh config.sub sun3
33012 m68k-sun-sunos4.1.1
33013 % sh config.sub i986v
33014 Invalid configuration `i986v': machine `i986v' not recognized
33018 @code{config.sub} is also distributed in the @value{GDBN} source
33019 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
33021 @node Configure Options
33022 @section @file{configure} Options
33024 Here is a summary of the @file{configure} options and arguments that
33025 are most often useful for building @value{GDBN}. @file{configure} also has
33026 several other options not listed here. @inforef{What Configure
33027 Does,,configure.info}, for a full explanation of @file{configure}.
33030 configure @r{[}--help@r{]}
33031 @r{[}--prefix=@var{dir}@r{]}
33032 @r{[}--exec-prefix=@var{dir}@r{]}
33033 @r{[}--srcdir=@var{dirname}@r{]}
33034 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
33035 @r{[}--target=@var{target}@r{]}
33040 You may introduce options with a single @samp{-} rather than
33041 @samp{--} if you prefer; but you may abbreviate option names if you use
33046 Display a quick summary of how to invoke @file{configure}.
33048 @item --prefix=@var{dir}
33049 Configure the source to install programs and files under directory
33052 @item --exec-prefix=@var{dir}
33053 Configure the source to install programs under directory
33056 @c avoid splitting the warning from the explanation:
33058 @item --srcdir=@var{dirname}
33059 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
33060 @code{make} that implements the @code{VPATH} feature.}@*
33061 Use this option to make configurations in directories separate from the
33062 @value{GDBN} source directories. Among other things, you can use this to
33063 build (or maintain) several configurations simultaneously, in separate
33064 directories. @file{configure} writes configuration-specific files in
33065 the current directory, but arranges for them to use the source in the
33066 directory @var{dirname}. @file{configure} creates directories under
33067 the working directory in parallel to the source directories below
33070 @item --norecursion
33071 Configure only the directory level where @file{configure} is executed; do not
33072 propagate configuration to subdirectories.
33074 @item --target=@var{target}
33075 Configure @value{GDBN} for cross-debugging programs running on the specified
33076 @var{target}. Without this option, @value{GDBN} is configured to debug
33077 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
33079 There is no convenient way to generate a list of all available targets.
33081 @item @var{host} @dots{}
33082 Configure @value{GDBN} to run on the specified @var{host}.
33084 There is no convenient way to generate a list of all available hosts.
33087 There are many other options available as well, but they are generally
33088 needed for special purposes only.
33090 @node System-wide configuration
33091 @section System-wide configuration and settings
33092 @cindex system-wide init file
33094 @value{GDBN} can be configured to have a system-wide init file;
33095 this file will be read and executed at startup (@pxref{Startup, , What
33096 @value{GDBN} does during startup}).
33098 Here is the corresponding configure option:
33101 @item --with-system-gdbinit=@var{file}
33102 Specify that the default location of the system-wide init file is
33106 If @value{GDBN} has been configured with the option @option{--prefix=$prefix},
33107 it may be subject to relocation. Two possible cases:
33111 If the default location of this init file contains @file{$prefix},
33112 it will be subject to relocation. Suppose that the configure options
33113 are @option{--prefix=$prefix --with-system-gdbinit=$prefix/etc/gdbinit};
33114 if @value{GDBN} is moved from @file{$prefix} to @file{$install}, the system
33115 init file is looked for as @file{$install/etc/gdbinit} instead of
33116 @file{$prefix/etc/gdbinit}.
33119 By contrast, if the default location does not contain the prefix,
33120 it will not be relocated. E.g.@: if @value{GDBN} has been configured with
33121 @option{--prefix=/usr/local --with-system-gdbinit=/usr/share/gdb/gdbinit},
33122 then @value{GDBN} will always look for @file{/usr/share/gdb/gdbinit},
33123 wherever @value{GDBN} is installed.
33126 @node Maintenance Commands
33127 @appendix Maintenance Commands
33128 @cindex maintenance commands
33129 @cindex internal commands
33131 In addition to commands intended for @value{GDBN} users, @value{GDBN}
33132 includes a number of commands intended for @value{GDBN} developers,
33133 that are not documented elsewhere in this manual. These commands are
33134 provided here for reference. (For commands that turn on debugging
33135 messages, see @ref{Debugging Output}.)
33138 @kindex maint agent
33139 @kindex maint agent-eval
33140 @item maint agent @var{expression}
33141 @itemx maint agent-eval @var{expression}
33142 Translate the given @var{expression} into remote agent bytecodes.
33143 This command is useful for debugging the Agent Expression mechanism
33144 (@pxref{Agent Expressions}). The @samp{agent} version produces an
33145 expression useful for data collection, such as by tracepoints, while
33146 @samp{maint agent-eval} produces an expression that evaluates directly
33147 to a result. For instance, a collection expression for @code{globa +
33148 globb} will include bytecodes to record four bytes of memory at each
33149 of the addresses of @code{globa} and @code{globb}, while discarding
33150 the result of the addition, while an evaluation expression will do the
33151 addition and return the sum.
33153 @kindex maint info breakpoints
33154 @item @anchor{maint info breakpoints}maint info breakpoints
33155 Using the same format as @samp{info breakpoints}, display both the
33156 breakpoints you've set explicitly, and those @value{GDBN} is using for
33157 internal purposes. Internal breakpoints are shown with negative
33158 breakpoint numbers. The type column identifies what kind of breakpoint
33163 Normal, explicitly set breakpoint.
33166 Normal, explicitly set watchpoint.
33169 Internal breakpoint, used to handle correctly stepping through
33170 @code{longjmp} calls.
33172 @item longjmp resume
33173 Internal breakpoint at the target of a @code{longjmp}.
33176 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
33179 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
33182 Shared library events.
33186 @kindex set displaced-stepping
33187 @kindex show displaced-stepping
33188 @cindex displaced stepping support
33189 @cindex out-of-line single-stepping
33190 @item set displaced-stepping
33191 @itemx show displaced-stepping
33192 Control whether or not @value{GDBN} will do @dfn{displaced stepping}
33193 if the target supports it. Displaced stepping is a way to single-step
33194 over breakpoints without removing them from the inferior, by executing
33195 an out-of-line copy of the instruction that was originally at the
33196 breakpoint location. It is also known as out-of-line single-stepping.
33199 @item set displaced-stepping on
33200 If the target architecture supports it, @value{GDBN} will use
33201 displaced stepping to step over breakpoints.
33203 @item set displaced-stepping off
33204 @value{GDBN} will not use displaced stepping to step over breakpoints,
33205 even if such is supported by the target architecture.
33207 @cindex non-stop mode, and @samp{set displaced-stepping}
33208 @item set displaced-stepping auto
33209 This is the default mode. @value{GDBN} will use displaced stepping
33210 only if non-stop mode is active (@pxref{Non-Stop Mode}) and the target
33211 architecture supports displaced stepping.
33214 @kindex maint check-symtabs
33215 @item maint check-symtabs
33216 Check the consistency of psymtabs and symtabs.
33218 @kindex maint cplus first_component
33219 @item maint cplus first_component @var{name}
33220 Print the first C@t{++} class/namespace component of @var{name}.
33222 @kindex maint cplus namespace
33223 @item maint cplus namespace
33224 Print the list of possible C@t{++} namespaces.
33226 @kindex maint demangle
33227 @item maint demangle @var{name}
33228 Demangle a C@t{++} or Objective-C mangled @var{name}.
33230 @kindex maint deprecate
33231 @kindex maint undeprecate
33232 @cindex deprecated commands
33233 @item maint deprecate @var{command} @r{[}@var{replacement}@r{]}
33234 @itemx maint undeprecate @var{command}
33235 Deprecate or undeprecate the named @var{command}. Deprecated commands
33236 cause @value{GDBN} to issue a warning when you use them. The optional
33237 argument @var{replacement} says which newer command should be used in
33238 favor of the deprecated one; if it is given, @value{GDBN} will mention
33239 the replacement as part of the warning.
33241 @kindex maint dump-me
33242 @item maint dump-me
33243 @cindex @code{SIGQUIT} signal, dump core of @value{GDBN}
33244 Cause a fatal signal in the debugger and force it to dump its core.
33245 This is supported only on systems which support aborting a program
33246 with the @code{SIGQUIT} signal.
33248 @kindex maint internal-error
33249 @kindex maint internal-warning
33250 @item maint internal-error @r{[}@var{message-text}@r{]}
33251 @itemx maint internal-warning @r{[}@var{message-text}@r{]}
33252 Cause @value{GDBN} to call the internal function @code{internal_error}
33253 or @code{internal_warning} and hence behave as though an internal error
33254 or internal warning has been detected. In addition to reporting the
33255 internal problem, these functions give the user the opportunity to
33256 either quit @value{GDBN} or create a core file of the current
33257 @value{GDBN} session.
33259 These commands take an optional parameter @var{message-text} that is
33260 used as the text of the error or warning message.
33262 Here's an example of using @code{internal-error}:
33265 (@value{GDBP}) @kbd{maint internal-error testing, 1, 2}
33266 @dots{}/maint.c:121: internal-error: testing, 1, 2
33267 A problem internal to GDB has been detected. Further
33268 debugging may prove unreliable.
33269 Quit this debugging session? (y or n) @kbd{n}
33270 Create a core file? (y or n) @kbd{n}
33274 @cindex @value{GDBN} internal error
33275 @cindex internal errors, control of @value{GDBN} behavior
33277 @kindex maint set internal-error
33278 @kindex maint show internal-error
33279 @kindex maint set internal-warning
33280 @kindex maint show internal-warning
33281 @item maint set internal-error @var{action} [ask|yes|no]
33282 @itemx maint show internal-error @var{action}
33283 @itemx maint set internal-warning @var{action} [ask|yes|no]
33284 @itemx maint show internal-warning @var{action}
33285 When @value{GDBN} reports an internal problem (error or warning) it
33286 gives the user the opportunity to both quit @value{GDBN} and create a
33287 core file of the current @value{GDBN} session. These commands let you
33288 override the default behaviour for each particular @var{action},
33289 described in the table below.
33293 You can specify that @value{GDBN} should always (yes) or never (no)
33294 quit. The default is to ask the user what to do.
33297 You can specify that @value{GDBN} should always (yes) or never (no)
33298 create a core file. The default is to ask the user what to do.
33301 @kindex maint packet
33302 @item maint packet @var{text}
33303 If @value{GDBN} is talking to an inferior via the serial protocol,
33304 then this command sends the string @var{text} to the inferior, and
33305 displays the response packet. @value{GDBN} supplies the initial
33306 @samp{$} character, the terminating @samp{#} character, and the
33309 @kindex maint print architecture
33310 @item maint print architecture @r{[}@var{file}@r{]}
33311 Print the entire architecture configuration. The optional argument
33312 @var{file} names the file where the output goes.
33314 @kindex maint print c-tdesc
33315 @item maint print c-tdesc
33316 Print the current target description (@pxref{Target Descriptions}) as
33317 a C source file. The created source file can be used in @value{GDBN}
33318 when an XML parser is not available to parse the description.
33320 @kindex maint print dummy-frames
33321 @item maint print dummy-frames
33322 Prints the contents of @value{GDBN}'s internal dummy-frame stack.
33325 (@value{GDBP}) @kbd{b add}
33327 (@value{GDBP}) @kbd{print add(2,3)}
33328 Breakpoint 2, add (a=2, b=3) at @dots{}
33330 The program being debugged stopped while in a function called from GDB.
33332 (@value{GDBP}) @kbd{maint print dummy-frames}
33333 0x1a57c80: pc=0x01014068 fp=0x0200bddc sp=0x0200bdd6
33334 top=0x0200bdd4 id=@{stack=0x200bddc,code=0x101405c@}
33335 call_lo=0x01014000 call_hi=0x01014001
33339 Takes an optional file parameter.
33341 @kindex maint print registers
33342 @kindex maint print raw-registers
33343 @kindex maint print cooked-registers
33344 @kindex maint print register-groups
33345 @kindex maint print remote-registers
33346 @item maint print registers @r{[}@var{file}@r{]}
33347 @itemx maint print raw-registers @r{[}@var{file}@r{]}
33348 @itemx maint print cooked-registers @r{[}@var{file}@r{]}
33349 @itemx maint print register-groups @r{[}@var{file}@r{]}
33350 @itemx maint print remote-registers @r{[}@var{file}@r{]}
33351 Print @value{GDBN}'s internal register data structures.
33353 The command @code{maint print raw-registers} includes the contents of
33354 the raw register cache; the command @code{maint print
33355 cooked-registers} includes the (cooked) value of all registers,
33356 including registers which aren't available on the target nor visible
33357 to user; the command @code{maint print register-groups} includes the
33358 groups that each register is a member of; and the command @code{maint
33359 print remote-registers} includes the remote target's register numbers
33360 and offsets in the `G' packets. @xref{Registers,, Registers, gdbint,
33361 @value{GDBN} Internals}.
33363 These commands take an optional parameter, a file name to which to
33364 write the information.
33366 @kindex maint print reggroups
33367 @item maint print reggroups @r{[}@var{file}@r{]}
33368 Print @value{GDBN}'s internal register group data structures. The
33369 optional argument @var{file} tells to what file to write the
33372 The register groups info looks like this:
33375 (@value{GDBP}) @kbd{maint print reggroups}
33388 This command forces @value{GDBN} to flush its internal register cache.
33390 @kindex maint print objfiles
33391 @cindex info for known object files
33392 @item maint print objfiles
33393 Print a dump of all known object files. For each object file, this
33394 command prints its name, address in memory, and all of its psymtabs
33397 @kindex maint print section-scripts
33398 @cindex info for known .debug_gdb_scripts-loaded scripts
33399 @item maint print section-scripts [@var{regexp}]
33400 Print a dump of scripts specified in the @code{.debug_gdb_section} section.
33401 If @var{regexp} is specified, only print scripts loaded by object files
33402 matching @var{regexp}.
33403 For each script, this command prints its name as specified in the objfile,
33404 and the full path if known.
33405 @xref{.debug_gdb_scripts section}.
33407 @kindex maint print statistics
33408 @cindex bcache statistics
33409 @item maint print statistics
33410 This command prints, for each object file in the program, various data
33411 about that object file followed by the byte cache (@dfn{bcache})
33412 statistics for the object file. The objfile data includes the number
33413 of minimal, partial, full, and stabs symbols, the number of types
33414 defined by the objfile, the number of as yet unexpanded psym tables,
33415 the number of line tables and string tables, and the amount of memory
33416 used by the various tables. The bcache statistics include the counts,
33417 sizes, and counts of duplicates of all and unique objects, max,
33418 average, and median entry size, total memory used and its overhead and
33419 savings, and various measures of the hash table size and chain
33422 @kindex maint print target-stack
33423 @cindex target stack description
33424 @item maint print target-stack
33425 A @dfn{target} is an interface between the debugger and a particular
33426 kind of file or process. Targets can be stacked in @dfn{strata},
33427 so that more than one target can potentially respond to a request.
33428 In particular, memory accesses will walk down the stack of targets
33429 until they find a target that is interested in handling that particular
33432 This command prints a short description of each layer that was pushed on
33433 the @dfn{target stack}, starting from the top layer down to the bottom one.
33435 @kindex maint print type
33436 @cindex type chain of a data type
33437 @item maint print type @var{expr}
33438 Print the type chain for a type specified by @var{expr}. The argument
33439 can be either a type name or a symbol. If it is a symbol, the type of
33440 that symbol is described. The type chain produced by this command is
33441 a recursive definition of the data type as stored in @value{GDBN}'s
33442 data structures, including its flags and contained types.
33444 @kindex maint set dwarf2 always-disassemble
33445 @kindex maint show dwarf2 always-disassemble
33446 @item maint set dwarf2 always-disassemble
33447 @item maint show dwarf2 always-disassemble
33448 Control the behavior of @code{info address} when using DWARF debugging
33451 The default is @code{off}, which means that @value{GDBN} should try to
33452 describe a variable's location in an easily readable format. When
33453 @code{on}, @value{GDBN} will instead display the DWARF location
33454 expression in an assembly-like format. Note that some locations are
33455 too complex for @value{GDBN} to describe simply; in this case you will
33456 always see the disassembly form.
33458 Here is an example of the resulting disassembly:
33461 (gdb) info addr argc
33462 Symbol "argc" is a complex DWARF expression:
33466 For more information on these expressions, see
33467 @uref{http://www.dwarfstd.org/, the DWARF standard}.
33469 @kindex maint set dwarf2 max-cache-age
33470 @kindex maint show dwarf2 max-cache-age
33471 @item maint set dwarf2 max-cache-age
33472 @itemx maint show dwarf2 max-cache-age
33473 Control the DWARF 2 compilation unit cache.
33475 @cindex DWARF 2 compilation units cache
33476 In object files with inter-compilation-unit references, such as those
33477 produced by the GCC option @samp{-feliminate-dwarf2-dups}, the DWARF 2
33478 reader needs to frequently refer to previously read compilation units.
33479 This setting controls how long a compilation unit will remain in the
33480 cache if it is not referenced. A higher limit means that cached
33481 compilation units will be stored in memory longer, and more total
33482 memory will be used. Setting it to zero disables caching, which will
33483 slow down @value{GDBN} startup, but reduce memory consumption.
33485 @kindex maint set profile
33486 @kindex maint show profile
33487 @cindex profiling GDB
33488 @item maint set profile
33489 @itemx maint show profile
33490 Control profiling of @value{GDBN}.
33492 Profiling will be disabled until you use the @samp{maint set profile}
33493 command to enable it. When you enable profiling, the system will begin
33494 collecting timing and execution count data; when you disable profiling or
33495 exit @value{GDBN}, the results will be written to a log file. Remember that
33496 if you use profiling, @value{GDBN} will overwrite the profiling log file
33497 (often called @file{gmon.out}). If you have a record of important profiling
33498 data in a @file{gmon.out} file, be sure to move it to a safe location.
33500 Configuring with @samp{--enable-profiling} arranges for @value{GDBN} to be
33501 compiled with the @samp{-pg} compiler option.
33503 @kindex maint set show-debug-regs
33504 @kindex maint show show-debug-regs
33505 @cindex hardware debug registers
33506 @item maint set show-debug-regs
33507 @itemx maint show show-debug-regs
33508 Control whether to show variables that mirror the hardware debug
33509 registers. Use @code{ON} to enable, @code{OFF} to disable. If
33510 enabled, the debug registers values are shown when @value{GDBN} inserts or
33511 removes a hardware breakpoint or watchpoint, and when the inferior
33512 triggers a hardware-assisted breakpoint or watchpoint.
33514 @kindex maint set show-all-tib
33515 @kindex maint show show-all-tib
33516 @item maint set show-all-tib
33517 @itemx maint show show-all-tib
33518 Control whether to show all non zero areas within a 1k block starting
33519 at thread local base, when using the @samp{info w32 thread-information-block}
33522 @kindex maint space
33523 @cindex memory used by commands
33525 Control whether to display memory usage for each command. If set to a
33526 nonzero value, @value{GDBN} will display how much memory each command
33527 took, following the command's own output. This can also be requested
33528 by invoking @value{GDBN} with the @option{--statistics} command-line
33529 switch (@pxref{Mode Options}).
33532 @cindex time of command execution
33534 Control whether to display the execution time of @value{GDBN} for each command.
33535 If set to a nonzero value, @value{GDBN} will display how much time it
33536 took to execute each command, following the command's own output.
33537 Both CPU time and wallclock time are printed.
33538 Printing both is useful when trying to determine whether the cost is
33539 CPU or, e.g., disk/network, latency.
33540 Note that the CPU time printed is for @value{GDBN} only, it does not include
33541 the execution time of the inferior because there's no mechanism currently
33542 to compute how much time was spent by @value{GDBN} and how much time was
33543 spent by the program been debugged.
33544 This can also be requested by invoking @value{GDBN} with the
33545 @option{--statistics} command-line switch (@pxref{Mode Options}).
33547 @kindex maint translate-address
33548 @item maint translate-address @r{[}@var{section}@r{]} @var{addr}
33549 Find the symbol stored at the location specified by the address
33550 @var{addr} and an optional section name @var{section}. If found,
33551 @value{GDBN} prints the name of the closest symbol and an offset from
33552 the symbol's location to the specified address. This is similar to
33553 the @code{info address} command (@pxref{Symbols}), except that this
33554 command also allows to find symbols in other sections.
33556 If section was not specified, the section in which the symbol was found
33557 is also printed. For dynamically linked executables, the name of
33558 executable or shared library containing the symbol is printed as well.
33562 The following command is useful for non-interactive invocations of
33563 @value{GDBN}, such as in the test suite.
33566 @item set watchdog @var{nsec}
33567 @kindex set watchdog
33568 @cindex watchdog timer
33569 @cindex timeout for commands
33570 Set the maximum number of seconds @value{GDBN} will wait for the
33571 target operation to finish. If this time expires, @value{GDBN}
33572 reports and error and the command is aborted.
33574 @item show watchdog
33575 Show the current setting of the target wait timeout.
33578 @node Remote Protocol
33579 @appendix @value{GDBN} Remote Serial Protocol
33584 * Stop Reply Packets::
33585 * General Query Packets::
33586 * Architecture-Specific Protocol Details::
33587 * Tracepoint Packets::
33588 * Host I/O Packets::
33590 * Notification Packets::
33591 * Remote Non-Stop::
33592 * Packet Acknowledgment::
33594 * File-I/O Remote Protocol Extension::
33595 * Library List Format::
33596 * Library List Format for SVR4 Targets::
33597 * Memory Map Format::
33598 * Thread List Format::
33599 * Traceframe Info Format::
33605 There may be occasions when you need to know something about the
33606 protocol---for example, if there is only one serial port to your target
33607 machine, you might want your program to do something special if it
33608 recognizes a packet meant for @value{GDBN}.
33610 In the examples below, @samp{->} and @samp{<-} are used to indicate
33611 transmitted and received data, respectively.
33613 @cindex protocol, @value{GDBN} remote serial
33614 @cindex serial protocol, @value{GDBN} remote
33615 @cindex remote serial protocol
33616 All @value{GDBN} commands and responses (other than acknowledgments
33617 and notifications, see @ref{Notification Packets}) are sent as a
33618 @var{packet}. A @var{packet} is introduced with the character
33619 @samp{$}, the actual @var{packet-data}, and the terminating character
33620 @samp{#} followed by a two-digit @var{checksum}:
33623 @code{$}@var{packet-data}@code{#}@var{checksum}
33627 @cindex checksum, for @value{GDBN} remote
33629 The two-digit @var{checksum} is computed as the modulo 256 sum of all
33630 characters between the leading @samp{$} and the trailing @samp{#} (an
33631 eight bit unsigned checksum).
33633 Implementors should note that prior to @value{GDBN} 5.0 the protocol
33634 specification also included an optional two-digit @var{sequence-id}:
33637 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
33640 @cindex sequence-id, for @value{GDBN} remote
33642 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
33643 has never output @var{sequence-id}s. Stubs that handle packets added
33644 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
33646 When either the host or the target machine receives a packet, the first
33647 response expected is an acknowledgment: either @samp{+} (to indicate
33648 the package was received correctly) or @samp{-} (to request
33652 -> @code{$}@var{packet-data}@code{#}@var{checksum}
33657 The @samp{+}/@samp{-} acknowledgments can be disabled
33658 once a connection is established.
33659 @xref{Packet Acknowledgment}, for details.
33661 The host (@value{GDBN}) sends @var{command}s, and the target (the
33662 debugging stub incorporated in your program) sends a @var{response}. In
33663 the case of step and continue @var{command}s, the response is only sent
33664 when the operation has completed, and the target has again stopped all
33665 threads in all attached processes. This is the default all-stop mode
33666 behavior, but the remote protocol also supports @value{GDBN}'s non-stop
33667 execution mode; see @ref{Remote Non-Stop}, for details.
33669 @var{packet-data} consists of a sequence of characters with the
33670 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
33673 @cindex remote protocol, field separator
33674 Fields within the packet should be separated using @samp{,} @samp{;} or
33675 @samp{:}. Except where otherwise noted all numbers are represented in
33676 @sc{hex} with leading zeros suppressed.
33678 Implementors should note that prior to @value{GDBN} 5.0, the character
33679 @samp{:} could not appear as the third character in a packet (as it
33680 would potentially conflict with the @var{sequence-id}).
33682 @cindex remote protocol, binary data
33683 @anchor{Binary Data}
33684 Binary data in most packets is encoded either as two hexadecimal
33685 digits per byte of binary data. This allowed the traditional remote
33686 protocol to work over connections which were only seven-bit clean.
33687 Some packets designed more recently assume an eight-bit clean
33688 connection, and use a more efficient encoding to send and receive
33691 The binary data representation uses @code{7d} (@sc{ascii} @samp{@}})
33692 as an escape character. Any escaped byte is transmitted as the escape
33693 character followed by the original character XORed with @code{0x20}.
33694 For example, the byte @code{0x7d} would be transmitted as the two
33695 bytes @code{0x7d 0x5d}. The bytes @code{0x23} (@sc{ascii} @samp{#}),
33696 @code{0x24} (@sc{ascii} @samp{$}), and @code{0x7d} (@sc{ascii}
33697 @samp{@}}) must always be escaped. Responses sent by the stub
33698 must also escape @code{0x2a} (@sc{ascii} @samp{*}), so that it
33699 is not interpreted as the start of a run-length encoded sequence
33702 Response @var{data} can be run-length encoded to save space.
33703 Run-length encoding replaces runs of identical characters with one
33704 instance of the repeated character, followed by a @samp{*} and a
33705 repeat count. The repeat count is itself sent encoded, to avoid
33706 binary characters in @var{data}: a value of @var{n} is sent as
33707 @code{@var{n}+29}. For a repeat count greater or equal to 3, this
33708 produces a printable @sc{ascii} character, e.g.@: a space (@sc{ascii}
33709 code 32) for a repeat count of 3. (This is because run-length
33710 encoding starts to win for counts 3 or more.) Thus, for example,
33711 @samp{0* } is a run-length encoding of ``0000'': the space character
33712 after @samp{*} means repeat the leading @code{0} @w{@code{32 - 29 =
33715 The printable characters @samp{#} and @samp{$} or with a numeric value
33716 greater than 126 must not be used. Runs of six repeats (@samp{#}) or
33717 seven repeats (@samp{$}) can be expanded using a repeat count of only
33718 five (@samp{"}). For example, @samp{00000000} can be encoded as
33721 The error response returned for some packets includes a two character
33722 error number. That number is not well defined.
33724 @cindex empty response, for unsupported packets
33725 For any @var{command} not supported by the stub, an empty response
33726 (@samp{$#00}) should be returned. That way it is possible to extend the
33727 protocol. A newer @value{GDBN} can tell if a packet is supported based
33730 At a minimum, a stub is required to support the @samp{g} and @samp{G}
33731 commands for register access, and the @samp{m} and @samp{M} commands
33732 for memory access. Stubs that only control single-threaded targets
33733 can implement run control with the @samp{c} (continue), and @samp{s}
33734 (step) commands. Stubs that support multi-threading targets should
33735 support the @samp{vCont} command. All other commands are optional.
33740 The following table provides a complete list of all currently defined
33741 @var{command}s and their corresponding response @var{data}.
33742 @xref{File-I/O Remote Protocol Extension}, for details about the File
33743 I/O extension of the remote protocol.
33745 Each packet's description has a template showing the packet's overall
33746 syntax, followed by an explanation of the packet's meaning. We
33747 include spaces in some of the templates for clarity; these are not
33748 part of the packet's syntax. No @value{GDBN} packet uses spaces to
33749 separate its components. For example, a template like @samp{foo
33750 @var{bar} @var{baz}} describes a packet beginning with the three ASCII
33751 bytes @samp{foo}, followed by a @var{bar}, followed directly by a
33752 @var{baz}. @value{GDBN} does not transmit a space character between the
33753 @samp{foo} and the @var{bar}, or between the @var{bar} and the
33756 @cindex @var{thread-id}, in remote protocol
33757 @anchor{thread-id syntax}
33758 Several packets and replies include a @var{thread-id} field to identify
33759 a thread. Normally these are positive numbers with a target-specific
33760 interpretation, formatted as big-endian hex strings. A @var{thread-id}
33761 can also be a literal @samp{-1} to indicate all threads, or @samp{0} to
33764 In addition, the remote protocol supports a multiprocess feature in
33765 which the @var{thread-id} syntax is extended to optionally include both
33766 process and thread ID fields, as @samp{p@var{pid}.@var{tid}}.
33767 The @var{pid} (process) and @var{tid} (thread) components each have the
33768 format described above: a positive number with target-specific
33769 interpretation formatted as a big-endian hex string, literal @samp{-1}
33770 to indicate all processes or threads (respectively), or @samp{0} to
33771 indicate an arbitrary process or thread. Specifying just a process, as
33772 @samp{p@var{pid}}, is equivalent to @samp{p@var{pid}.-1}. It is an
33773 error to specify all processes but a specific thread, such as
33774 @samp{p-1.@var{tid}}. Note that the @samp{p} prefix is @emph{not} used
33775 for those packets and replies explicitly documented to include a process
33776 ID, rather than a @var{thread-id}.
33778 The multiprocess @var{thread-id} syntax extensions are only used if both
33779 @value{GDBN} and the stub report support for the @samp{multiprocess}
33780 feature using @samp{qSupported}. @xref{multiprocess extensions}, for
33783 Note that all packet forms beginning with an upper- or lower-case
33784 letter, other than those described here, are reserved for future use.
33786 Here are the packet descriptions.
33791 @cindex @samp{!} packet
33792 @anchor{extended mode}
33793 Enable extended mode. In extended mode, the remote server is made
33794 persistent. The @samp{R} packet is used to restart the program being
33800 The remote target both supports and has enabled extended mode.
33804 @cindex @samp{?} packet
33805 Indicate the reason the target halted. The reply is the same as for
33806 step and continue. This packet has a special interpretation when the
33807 target is in non-stop mode; see @ref{Remote Non-Stop}.
33810 @xref{Stop Reply Packets}, for the reply specifications.
33812 @item A @var{arglen},@var{argnum},@var{arg},@dots{}
33813 @cindex @samp{A} packet
33814 Initialized @code{argv[]} array passed into program. @var{arglen}
33815 specifies the number of bytes in the hex encoded byte stream
33816 @var{arg}. See @code{gdbserver} for more details.
33821 The arguments were set.
33827 @cindex @samp{b} packet
33828 (Don't use this packet; its behavior is not well-defined.)
33829 Change the serial line speed to @var{baud}.
33831 JTC: @emph{When does the transport layer state change? When it's
33832 received, or after the ACK is transmitted. In either case, there are
33833 problems if the command or the acknowledgment packet is dropped.}
33835 Stan: @emph{If people really wanted to add something like this, and get
33836 it working for the first time, they ought to modify ser-unix.c to send
33837 some kind of out-of-band message to a specially-setup stub and have the
33838 switch happen "in between" packets, so that from remote protocol's point
33839 of view, nothing actually happened.}
33841 @item B @var{addr},@var{mode}
33842 @cindex @samp{B} packet
33843 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
33844 breakpoint at @var{addr}.
33846 Don't use this packet. Use the @samp{Z} and @samp{z} packets instead
33847 (@pxref{insert breakpoint or watchpoint packet}).
33849 @cindex @samp{bc} packet
33852 Backward continue. Execute the target system in reverse. No parameter.
33853 @xref{Reverse Execution}, for more information.
33856 @xref{Stop Reply Packets}, for the reply specifications.
33858 @cindex @samp{bs} packet
33861 Backward single step. Execute one instruction in reverse. No parameter.
33862 @xref{Reverse Execution}, for more information.
33865 @xref{Stop Reply Packets}, for the reply specifications.
33867 @item c @r{[}@var{addr}@r{]}
33868 @cindex @samp{c} packet
33869 Continue. @var{addr} is address to resume. If @var{addr} is omitted,
33870 resume at current address.
33872 This packet is deprecated for multi-threading support. @xref{vCont
33876 @xref{Stop Reply Packets}, for the reply specifications.
33878 @item C @var{sig}@r{[};@var{addr}@r{]}
33879 @cindex @samp{C} packet
33880 Continue with signal @var{sig} (hex signal number). If
33881 @samp{;@var{addr}} is omitted, resume at same address.
33883 This packet is deprecated for multi-threading support. @xref{vCont
33887 @xref{Stop Reply Packets}, for the reply specifications.
33890 @cindex @samp{d} packet
33893 Don't use this packet; instead, define a general set packet
33894 (@pxref{General Query Packets}).
33898 @cindex @samp{D} packet
33899 The first form of the packet is used to detach @value{GDBN} from the
33900 remote system. It is sent to the remote target
33901 before @value{GDBN} disconnects via the @code{detach} command.
33903 The second form, including a process ID, is used when multiprocess
33904 protocol extensions are enabled (@pxref{multiprocess extensions}), to
33905 detach only a specific process. The @var{pid} is specified as a
33906 big-endian hex string.
33916 @item F @var{RC},@var{EE},@var{CF};@var{XX}
33917 @cindex @samp{F} packet
33918 A reply from @value{GDBN} to an @samp{F} packet sent by the target.
33919 This is part of the File-I/O protocol extension. @xref{File-I/O
33920 Remote Protocol Extension}, for the specification.
33923 @anchor{read registers packet}
33924 @cindex @samp{g} packet
33925 Read general registers.
33929 @item @var{XX@dots{}}
33930 Each byte of register data is described by two hex digits. The bytes
33931 with the register are transmitted in target byte order. The size of
33932 each register and their position within the @samp{g} packet are
33933 determined by the @value{GDBN} internal gdbarch functions
33934 @code{DEPRECATED_REGISTER_RAW_SIZE} and @code{gdbarch_register_name}. The
33935 specification of several standard @samp{g} packets is specified below.
33937 When reading registers from a trace frame (@pxref{Analyze Collected
33938 Data,,Using the Collected Data}), the stub may also return a string of
33939 literal @samp{x}'s in place of the register data digits, to indicate
33940 that the corresponding register has not been collected, thus its value
33941 is unavailable. For example, for an architecture with 4 registers of
33942 4 bytes each, the following reply indicates to @value{GDBN} that
33943 registers 0 and 2 have not been collected, while registers 1 and 3
33944 have been collected, and both have zero value:
33948 <- @code{xxxxxxxx00000000xxxxxxxx00000000}
33955 @item G @var{XX@dots{}}
33956 @cindex @samp{G} packet
33957 Write general registers. @xref{read registers packet}, for a
33958 description of the @var{XX@dots{}} data.
33968 @item H @var{op} @var{thread-id}
33969 @cindex @samp{H} packet
33970 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
33971 @samp{G}, et.al.). @var{op} depends on the operation to be performed:
33972 it should be @samp{c} for step and continue operations (note that this
33973 is deprecated, supporting the @samp{vCont} command is a better
33974 option), @samp{g} for other operations. The thread designator
33975 @var{thread-id} has the format and interpretation described in
33976 @ref{thread-id syntax}.
33987 @c 'H': How restrictive (or permissive) is the thread model. If a
33988 @c thread is selected and stopped, are other threads allowed
33989 @c to continue to execute? As I mentioned above, I think the
33990 @c semantics of each command when a thread is selected must be
33991 @c described. For example:
33993 @c 'g': If the stub supports threads and a specific thread is
33994 @c selected, returns the register block from that thread;
33995 @c otherwise returns current registers.
33997 @c 'G' If the stub supports threads and a specific thread is
33998 @c selected, sets the registers of the register block of
33999 @c that thread; otherwise sets current registers.
34001 @item i @r{[}@var{addr}@r{[},@var{nnn}@r{]]}
34002 @anchor{cycle step packet}
34003 @cindex @samp{i} packet
34004 Step the remote target by a single clock cycle. If @samp{,@var{nnn}} is
34005 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
34006 step starting at that address.
34009 @cindex @samp{I} packet
34010 Signal, then cycle step. @xref{step with signal packet}. @xref{cycle
34014 @cindex @samp{k} packet
34017 FIXME: @emph{There is no description of how to operate when a specific
34018 thread context has been selected (i.e.@: does 'k' kill only that
34021 @item m @var{addr},@var{length}
34022 @cindex @samp{m} packet
34023 Read @var{length} bytes of memory starting at address @var{addr}.
34024 Note that @var{addr} may not be aligned to any particular boundary.
34026 The stub need not use any particular size or alignment when gathering
34027 data from memory for the response; even if @var{addr} is word-aligned
34028 and @var{length} is a multiple of the word size, the stub is free to
34029 use byte accesses, or not. For this reason, this packet may not be
34030 suitable for accessing memory-mapped I/O devices.
34031 @cindex alignment of remote memory accesses
34032 @cindex size of remote memory accesses
34033 @cindex memory, alignment and size of remote accesses
34037 @item @var{XX@dots{}}
34038 Memory contents; each byte is transmitted as a two-digit hexadecimal
34039 number. The reply may contain fewer bytes than requested if the
34040 server was able to read only part of the region of memory.
34045 @item M @var{addr},@var{length}:@var{XX@dots{}}
34046 @cindex @samp{M} packet
34047 Write @var{length} bytes of memory starting at address @var{addr}.
34048 @var{XX@dots{}} is the data; each byte is transmitted as a two-digit
34049 hexadecimal number.
34056 for an error (this includes the case where only part of the data was
34061 @cindex @samp{p} packet
34062 Read the value of register @var{n}; @var{n} is in hex.
34063 @xref{read registers packet}, for a description of how the returned
34064 register value is encoded.
34068 @item @var{XX@dots{}}
34069 the register's value
34073 Indicating an unrecognized @var{query}.
34076 @item P @var{n@dots{}}=@var{r@dots{}}
34077 @anchor{write register packet}
34078 @cindex @samp{P} packet
34079 Write register @var{n@dots{}} with value @var{r@dots{}}. The register
34080 number @var{n} is in hexadecimal, and @var{r@dots{}} contains two hex
34081 digits for each byte in the register (target byte order).
34091 @item q @var{name} @var{params}@dots{}
34092 @itemx Q @var{name} @var{params}@dots{}
34093 @cindex @samp{q} packet
34094 @cindex @samp{Q} packet
34095 General query (@samp{q}) and set (@samp{Q}). These packets are
34096 described fully in @ref{General Query Packets}.
34099 @cindex @samp{r} packet
34100 Reset the entire system.
34102 Don't use this packet; use the @samp{R} packet instead.
34105 @cindex @samp{R} packet
34106 Restart the program being debugged. @var{XX}, while needed, is ignored.
34107 This packet is only available in extended mode (@pxref{extended mode}).
34109 The @samp{R} packet has no reply.
34111 @item s @r{[}@var{addr}@r{]}
34112 @cindex @samp{s} packet
34113 Single step. @var{addr} is the address at which to resume. If
34114 @var{addr} is omitted, resume at same address.
34116 This packet is deprecated for multi-threading support. @xref{vCont
34120 @xref{Stop Reply Packets}, for the reply specifications.
34122 @item S @var{sig}@r{[};@var{addr}@r{]}
34123 @anchor{step with signal packet}
34124 @cindex @samp{S} packet
34125 Step with signal. This is analogous to the @samp{C} packet, but
34126 requests a single-step, rather than a normal resumption of execution.
34128 This packet is deprecated for multi-threading support. @xref{vCont
34132 @xref{Stop Reply Packets}, for the reply specifications.
34134 @item t @var{addr}:@var{PP},@var{MM}
34135 @cindex @samp{t} packet
34136 Search backwards starting at address @var{addr} for a match with pattern
34137 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4 bytes.
34138 @var{addr} must be at least 3 digits.
34140 @item T @var{thread-id}
34141 @cindex @samp{T} packet
34142 Find out if the thread @var{thread-id} is alive. @xref{thread-id syntax}.
34147 thread is still alive
34153 Packets starting with @samp{v} are identified by a multi-letter name,
34154 up to the first @samp{;} or @samp{?} (or the end of the packet).
34156 @item vAttach;@var{pid}
34157 @cindex @samp{vAttach} packet
34158 Attach to a new process with the specified process ID @var{pid}.
34159 The process ID is a
34160 hexadecimal integer identifying the process. In all-stop mode, all
34161 threads in the attached process are stopped; in non-stop mode, it may be
34162 attached without being stopped if that is supported by the target.
34164 @c In non-stop mode, on a successful vAttach, the stub should set the
34165 @c current thread to a thread of the newly-attached process. After
34166 @c attaching, GDB queries for the attached process's thread ID with qC.
34167 @c Also note that, from a user perspective, whether or not the
34168 @c target is stopped on attach in non-stop mode depends on whether you
34169 @c use the foreground or background version of the attach command, not
34170 @c on what vAttach does; GDB does the right thing with respect to either
34171 @c stopping or restarting threads.
34173 This packet is only available in extended mode (@pxref{extended mode}).
34179 @item @r{Any stop packet}
34180 for success in all-stop mode (@pxref{Stop Reply Packets})
34182 for success in non-stop mode (@pxref{Remote Non-Stop})
34185 @item vCont@r{[};@var{action}@r{[}:@var{thread-id}@r{]]}@dots{}
34186 @cindex @samp{vCont} packet
34187 @anchor{vCont packet}
34188 Resume the inferior, specifying different actions for each thread.
34189 If an action is specified with no @var{thread-id}, then it is applied to any
34190 threads that don't have a specific action specified; if no default action is
34191 specified then other threads should remain stopped in all-stop mode and
34192 in their current state in non-stop mode.
34193 Specifying multiple
34194 default actions is an error; specifying no actions is also an error.
34195 Thread IDs are specified using the syntax described in @ref{thread-id syntax}.
34197 Currently supported actions are:
34203 Continue with signal @var{sig}. The signal @var{sig} should be two hex digits.
34207 Step with signal @var{sig}. The signal @var{sig} should be two hex digits.
34212 The optional argument @var{addr} normally associated with the
34213 @samp{c}, @samp{C}, @samp{s}, and @samp{S} packets is
34214 not supported in @samp{vCont}.
34216 The @samp{t} action is only relevant in non-stop mode
34217 (@pxref{Remote Non-Stop}) and may be ignored by the stub otherwise.
34218 A stop reply should be generated for any affected thread not already stopped.
34219 When a thread is stopped by means of a @samp{t} action,
34220 the corresponding stop reply should indicate that the thread has stopped with
34221 signal @samp{0}, regardless of whether the target uses some other signal
34222 as an implementation detail.
34224 The stub must support @samp{vCont} if it reports support for
34225 multiprocess extensions (@pxref{multiprocess extensions}). Note that in
34226 this case @samp{vCont} actions can be specified to apply to all threads
34227 in a process by using the @samp{p@var{pid}.-1} form of the
34231 @xref{Stop Reply Packets}, for the reply specifications.
34234 @cindex @samp{vCont?} packet
34235 Request a list of actions supported by the @samp{vCont} packet.
34239 @item vCont@r{[};@var{action}@dots{}@r{]}
34240 The @samp{vCont} packet is supported. Each @var{action} is a supported
34241 command in the @samp{vCont} packet.
34243 The @samp{vCont} packet is not supported.
34246 @item vFile:@var{operation}:@var{parameter}@dots{}
34247 @cindex @samp{vFile} packet
34248 Perform a file operation on the target system. For details,
34249 see @ref{Host I/O Packets}.
34251 @item vFlashErase:@var{addr},@var{length}
34252 @cindex @samp{vFlashErase} packet
34253 Direct the stub to erase @var{length} bytes of flash starting at
34254 @var{addr}. The region may enclose any number of flash blocks, but
34255 its start and end must fall on block boundaries, as indicated by the
34256 flash block size appearing in the memory map (@pxref{Memory Map
34257 Format}). @value{GDBN} groups flash memory programming operations
34258 together, and sends a @samp{vFlashDone} request after each group; the
34259 stub is allowed to delay erase operation until the @samp{vFlashDone}
34260 packet is received.
34270 @item vFlashWrite:@var{addr}:@var{XX@dots{}}
34271 @cindex @samp{vFlashWrite} packet
34272 Direct the stub to write data to flash address @var{addr}. The data
34273 is passed in binary form using the same encoding as for the @samp{X}
34274 packet (@pxref{Binary Data}). The memory ranges specified by
34275 @samp{vFlashWrite} packets preceding a @samp{vFlashDone} packet must
34276 not overlap, and must appear in order of increasing addresses
34277 (although @samp{vFlashErase} packets for higher addresses may already
34278 have been received; the ordering is guaranteed only between
34279 @samp{vFlashWrite} packets). If a packet writes to an address that was
34280 neither erased by a preceding @samp{vFlashErase} packet nor by some other
34281 target-specific method, the results are unpredictable.
34289 for vFlashWrite addressing non-flash memory
34295 @cindex @samp{vFlashDone} packet
34296 Indicate to the stub that flash programming operation is finished.
34297 The stub is permitted to delay or batch the effects of a group of
34298 @samp{vFlashErase} and @samp{vFlashWrite} packets until a
34299 @samp{vFlashDone} packet is received. The contents of the affected
34300 regions of flash memory are unpredictable until the @samp{vFlashDone}
34301 request is completed.
34303 @item vKill;@var{pid}
34304 @cindex @samp{vKill} packet
34305 Kill the process with the specified process ID. @var{pid} is a
34306 hexadecimal integer identifying the process. This packet is used in
34307 preference to @samp{k} when multiprocess protocol extensions are
34308 supported; see @ref{multiprocess extensions}.
34318 @item vRun;@var{filename}@r{[};@var{argument}@r{]}@dots{}
34319 @cindex @samp{vRun} packet
34320 Run the program @var{filename}, passing it each @var{argument} on its
34321 command line. The file and arguments are hex-encoded strings. If
34322 @var{filename} is an empty string, the stub may use a default program
34323 (e.g.@: the last program run). The program is created in the stopped
34326 @c FIXME: What about non-stop mode?
34328 This packet is only available in extended mode (@pxref{extended mode}).
34334 @item @r{Any stop packet}
34335 for success (@pxref{Stop Reply Packets})
34339 @anchor{vStopped packet}
34340 @cindex @samp{vStopped} packet
34342 In non-stop mode (@pxref{Remote Non-Stop}), acknowledge a previous stop
34343 reply and prompt for the stub to report another one.
34347 @item @r{Any stop packet}
34348 if there is another unreported stop event (@pxref{Stop Reply Packets})
34350 if there are no unreported stop events
34353 @item X @var{addr},@var{length}:@var{XX@dots{}}
34355 @cindex @samp{X} packet
34356 Write data to memory, where the data is transmitted in binary.
34357 @var{addr} is address, @var{length} is number of bytes,
34358 @samp{@var{XX}@dots{}} is binary data (@pxref{Binary Data}).
34368 @item z @var{type},@var{addr},@var{kind}
34369 @itemx Z @var{type},@var{addr},@var{kind}
34370 @anchor{insert breakpoint or watchpoint packet}
34371 @cindex @samp{z} packet
34372 @cindex @samp{Z} packets
34373 Insert (@samp{Z}) or remove (@samp{z}) a @var{type} breakpoint or
34374 watchpoint starting at address @var{address} of kind @var{kind}.
34376 Each breakpoint and watchpoint packet @var{type} is documented
34379 @emph{Implementation notes: A remote target shall return an empty string
34380 for an unrecognized breakpoint or watchpoint packet @var{type}. A
34381 remote target shall support either both or neither of a given
34382 @samp{Z@var{type}@dots{}} and @samp{z@var{type}@dots{}} packet pair. To
34383 avoid potential problems with duplicate packets, the operations should
34384 be implemented in an idempotent way.}
34386 @item z0,@var{addr},@var{kind}
34387 @itemx Z0,@var{addr},@var{kind}@r{[};@var{cond_list}@dots{}@r{]}
34388 @cindex @samp{z0} packet
34389 @cindex @samp{Z0} packet
34390 Insert (@samp{Z0}) or remove (@samp{z0}) a memory breakpoint at address
34391 @var{addr} of type @var{kind}.
34393 A memory breakpoint is implemented by replacing the instruction at
34394 @var{addr} with a software breakpoint or trap instruction. The
34395 @var{kind} is target-specific and typically indicates the size of
34396 the breakpoint in bytes that should be inserted. E.g., the @sc{arm}
34397 and @sc{mips} can insert either a 2 or 4 byte breakpoint. Some
34398 architectures have additional meanings for @var{kind};
34399 @var{cond_list} is an optional list of conditional expressions in bytecode
34400 form that should be evaluated on the target's side. These are the
34401 conditions that should be taken into consideration when deciding if
34402 the breakpoint trigger should be reported back to @var{GDBN}.
34404 The @var{cond_list} parameter is comprised of a series of expressions,
34405 concatenated without separators. Each expression has the following form:
34409 @item X @var{len},@var{expr}
34410 @var{len} is the length of the bytecode expression and @var{expr} is the
34411 actual conditional expression in bytecode form.
34415 see @ref{Architecture-Specific Protocol Details}.
34417 @emph{Implementation note: It is possible for a target to copy or move
34418 code that contains memory breakpoints (e.g., when implementing
34419 overlays). The behavior of this packet, in the presence of such a
34420 target, is not defined.}
34432 @item z1,@var{addr},@var{kind}
34433 @itemx Z1,@var{addr},@var{kind}@r{[};@var{cond_list}@dots{}@r{]}
34434 @cindex @samp{z1} packet
34435 @cindex @samp{Z1} packet
34436 Insert (@samp{Z1}) or remove (@samp{z1}) a hardware breakpoint at
34437 address @var{addr}.
34439 A hardware breakpoint is implemented using a mechanism that is not
34440 dependant on being able to modify the target's memory. @var{kind}
34441 and @var{cond_list} have the same meaning as in @samp{Z0} packets.
34443 @emph{Implementation note: A hardware breakpoint is not affected by code
34456 @item z2,@var{addr},@var{kind}
34457 @itemx Z2,@var{addr},@var{kind}
34458 @cindex @samp{z2} packet
34459 @cindex @samp{Z2} packet
34460 Insert (@samp{Z2}) or remove (@samp{z2}) a write watchpoint at @var{addr}.
34461 @var{kind} is interpreted as the number of bytes to watch.
34473 @item z3,@var{addr},@var{kind}
34474 @itemx Z3,@var{addr},@var{kind}
34475 @cindex @samp{z3} packet
34476 @cindex @samp{Z3} packet
34477 Insert (@samp{Z3}) or remove (@samp{z3}) a read watchpoint at @var{addr}.
34478 @var{kind} is interpreted as the number of bytes to watch.
34490 @item z4,@var{addr},@var{kind}
34491 @itemx Z4,@var{addr},@var{kind}
34492 @cindex @samp{z4} packet
34493 @cindex @samp{Z4} packet
34494 Insert (@samp{Z4}) or remove (@samp{z4}) an access watchpoint at @var{addr}.
34495 @var{kind} is interpreted as the number of bytes to watch.
34509 @node Stop Reply Packets
34510 @section Stop Reply Packets
34511 @cindex stop reply packets
34513 The @samp{C}, @samp{c}, @samp{S}, @samp{s}, @samp{vCont},
34514 @samp{vAttach}, @samp{vRun}, @samp{vStopped}, and @samp{?} packets can
34515 receive any of the below as a reply. Except for @samp{?}
34516 and @samp{vStopped}, that reply is only returned
34517 when the target halts. In the below the exact meaning of @dfn{signal
34518 number} is defined by the header @file{include/gdb/signals.h} in the
34519 @value{GDBN} source code.
34521 As in the description of request packets, we include spaces in the
34522 reply templates for clarity; these are not part of the reply packet's
34523 syntax. No @value{GDBN} stop reply packet uses spaces to separate its
34529 The program received signal number @var{AA} (a two-digit hexadecimal
34530 number). This is equivalent to a @samp{T} response with no
34531 @var{n}:@var{r} pairs.
34533 @item T @var{AA} @var{n1}:@var{r1};@var{n2}:@var{r2};@dots{}
34534 @cindex @samp{T} packet reply
34535 The program received signal number @var{AA} (a two-digit hexadecimal
34536 number). This is equivalent to an @samp{S} response, except that the
34537 @samp{@var{n}:@var{r}} pairs can carry values of important registers
34538 and other information directly in the stop reply packet, reducing
34539 round-trip latency. Single-step and breakpoint traps are reported
34540 this way. Each @samp{@var{n}:@var{r}} pair is interpreted as follows:
34544 If @var{n} is a hexadecimal number, it is a register number, and the
34545 corresponding @var{r} gives that register's value. @var{r} is a
34546 series of bytes in target byte order, with each byte given by a
34547 two-digit hex number.
34550 If @var{n} is @samp{thread}, then @var{r} is the @var{thread-id} of
34551 the stopped thread, as specified in @ref{thread-id syntax}.
34554 If @var{n} is @samp{core}, then @var{r} is the hexadecimal number of
34555 the core on which the stop event was detected.
34558 If @var{n} is a recognized @dfn{stop reason}, it describes a more
34559 specific event that stopped the target. The currently defined stop
34560 reasons are listed below. @var{aa} should be @samp{05}, the trap
34561 signal. At most one stop reason should be present.
34564 Otherwise, @value{GDBN} should ignore this @samp{@var{n}:@var{r}} pair
34565 and go on to the next; this allows us to extend the protocol in the
34569 The currently defined stop reasons are:
34575 The packet indicates a watchpoint hit, and @var{r} is the data address, in
34578 @cindex shared library events, remote reply
34580 The packet indicates that the loaded libraries have changed.
34581 @value{GDBN} should use @samp{qXfer:libraries:read} to fetch a new
34582 list of loaded libraries. @var{r} is ignored.
34584 @cindex replay log events, remote reply
34586 The packet indicates that the target cannot continue replaying
34587 logged execution events, because it has reached the end (or the
34588 beginning when executing backward) of the log. The value of @var{r}
34589 will be either @samp{begin} or @samp{end}. @xref{Reverse Execution},
34590 for more information.
34594 @itemx W @var{AA} ; process:@var{pid}
34595 The process exited, and @var{AA} is the exit status. This is only
34596 applicable to certain targets.
34598 The second form of the response, including the process ID of the exited
34599 process, can be used only when @value{GDBN} has reported support for
34600 multiprocess protocol extensions; see @ref{multiprocess extensions}.
34601 The @var{pid} is formatted as a big-endian hex string.
34604 @itemx X @var{AA} ; process:@var{pid}
34605 The process terminated with signal @var{AA}.
34607 The second form of the response, including the process ID of the
34608 terminated process, can be used only when @value{GDBN} has reported
34609 support for multiprocess protocol extensions; see @ref{multiprocess
34610 extensions}. The @var{pid} is formatted as a big-endian hex string.
34612 @item O @var{XX}@dots{}
34613 @samp{@var{XX}@dots{}} is hex encoding of @sc{ascii} data, to be
34614 written as the program's console output. This can happen at any time
34615 while the program is running and the debugger should continue to wait
34616 for @samp{W}, @samp{T}, etc. This reply is not permitted in non-stop mode.
34618 @item F @var{call-id},@var{parameter}@dots{}
34619 @var{call-id} is the identifier which says which host system call should
34620 be called. This is just the name of the function. Translation into the
34621 correct system call is only applicable as it's defined in @value{GDBN}.
34622 @xref{File-I/O Remote Protocol Extension}, for a list of implemented
34625 @samp{@var{parameter}@dots{}} is a list of parameters as defined for
34626 this very system call.
34628 The target replies with this packet when it expects @value{GDBN} to
34629 call a host system call on behalf of the target. @value{GDBN} replies
34630 with an appropriate @samp{F} packet and keeps up waiting for the next
34631 reply packet from the target. The latest @samp{C}, @samp{c}, @samp{S}
34632 or @samp{s} action is expected to be continued. @xref{File-I/O Remote
34633 Protocol Extension}, for more details.
34637 @node General Query Packets
34638 @section General Query Packets
34639 @cindex remote query requests
34641 Packets starting with @samp{q} are @dfn{general query packets};
34642 packets starting with @samp{Q} are @dfn{general set packets}. General
34643 query and set packets are a semi-unified form for retrieving and
34644 sending information to and from the stub.
34646 The initial letter of a query or set packet is followed by a name
34647 indicating what sort of thing the packet applies to. For example,
34648 @value{GDBN} may use a @samp{qSymbol} packet to exchange symbol
34649 definitions with the stub. These packet names follow some
34654 The name must not contain commas, colons or semicolons.
34656 Most @value{GDBN} query and set packets have a leading upper case
34659 The names of custom vendor packets should use a company prefix, in
34660 lower case, followed by a period. For example, packets designed at
34661 the Acme Corporation might begin with @samp{qacme.foo} (for querying
34662 foos) or @samp{Qacme.bar} (for setting bars).
34665 The name of a query or set packet should be separated from any
34666 parameters by a @samp{:}; the parameters themselves should be
34667 separated by @samp{,} or @samp{;}. Stubs must be careful to match the
34668 full packet name, and check for a separator or the end of the packet,
34669 in case two packet names share a common prefix. New packets should not begin
34670 with @samp{qC}, @samp{qP}, or @samp{qL}@footnote{The @samp{qP} and @samp{qL}
34671 packets predate these conventions, and have arguments without any terminator
34672 for the packet name; we suspect they are in widespread use in places that
34673 are difficult to upgrade. The @samp{qC} packet has no arguments, but some
34674 existing stubs (e.g.@: RedBoot) are known to not check for the end of the
34677 Like the descriptions of the other packets, each description here
34678 has a template showing the packet's overall syntax, followed by an
34679 explanation of the packet's meaning. We include spaces in some of the
34680 templates for clarity; these are not part of the packet's syntax. No
34681 @value{GDBN} packet uses spaces to separate its components.
34683 Here are the currently defined query and set packets:
34689 Turn on or off the agent as a helper to perform some debugging operations
34690 delegated from @value{GDBN} (@pxref{Control Agent}).
34692 @item QAllow:@var{op}:@var{val}@dots{}
34693 @cindex @samp{QAllow} packet
34694 Specify which operations @value{GDBN} expects to request of the
34695 target, as a semicolon-separated list of operation name and value
34696 pairs. Possible values for @var{op} include @samp{WriteReg},
34697 @samp{WriteMem}, @samp{InsertBreak}, @samp{InsertTrace},
34698 @samp{InsertFastTrace}, and @samp{Stop}. @var{val} is either 0,
34699 indicating that @value{GDBN} will not request the operation, or 1,
34700 indicating that it may. (The target can then use this to set up its
34701 own internals optimally, for instance if the debugger never expects to
34702 insert breakpoints, it may not need to install its own trap handler.)
34705 @cindex current thread, remote request
34706 @cindex @samp{qC} packet
34707 Return the current thread ID.
34711 @item QC @var{thread-id}
34712 Where @var{thread-id} is a thread ID as documented in
34713 @ref{thread-id syntax}.
34714 @item @r{(anything else)}
34715 Any other reply implies the old thread ID.
34718 @item qCRC:@var{addr},@var{length}
34719 @cindex CRC of memory block, remote request
34720 @cindex @samp{qCRC} packet
34721 Compute the CRC checksum of a block of memory using CRC-32 defined in
34722 IEEE 802.3. The CRC is computed byte at a time, taking the most
34723 significant bit of each byte first. The initial pattern code
34724 @code{0xffffffff} is used to ensure leading zeros affect the CRC.
34726 @emph{Note:} This is the same CRC used in validating separate debug
34727 files (@pxref{Separate Debug Files, , Debugging Information in Separate
34728 Files}). However the algorithm is slightly different. When validating
34729 separate debug files, the CRC is computed taking the @emph{least}
34730 significant bit of each byte first, and the final result is inverted to
34731 detect trailing zeros.
34736 An error (such as memory fault)
34737 @item C @var{crc32}
34738 The specified memory region's checksum is @var{crc32}.
34741 @item QDisableRandomization:@var{value}
34742 @cindex disable address space randomization, remote request
34743 @cindex @samp{QDisableRandomization} packet
34744 Some target operating systems will randomize the virtual address space
34745 of the inferior process as a security feature, but provide a feature
34746 to disable such randomization, e.g.@: to allow for a more deterministic
34747 debugging experience. On such systems, this packet with a @var{value}
34748 of 1 directs the target to disable address space randomization for
34749 processes subsequently started via @samp{vRun} packets, while a packet
34750 with a @var{value} of 0 tells the target to enable address space
34753 This packet is only available in extended mode (@pxref{extended mode}).
34758 The request succeeded.
34761 An error occurred. @var{nn} are hex digits.
34764 An empty reply indicates that @samp{QDisableRandomization} is not supported
34768 This packet is not probed by default; the remote stub must request it,
34769 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
34770 This should only be done on targets that actually support disabling
34771 address space randomization.
34774 @itemx qsThreadInfo
34775 @cindex list active threads, remote request
34776 @cindex @samp{qfThreadInfo} packet
34777 @cindex @samp{qsThreadInfo} packet
34778 Obtain a list of all active thread IDs from the target (OS). Since there
34779 may be too many active threads to fit into one reply packet, this query
34780 works iteratively: it may require more than one query/reply sequence to
34781 obtain the entire list of threads. The first query of the sequence will
34782 be the @samp{qfThreadInfo} query; subsequent queries in the
34783 sequence will be the @samp{qsThreadInfo} query.
34785 NOTE: This packet replaces the @samp{qL} query (see below).
34789 @item m @var{thread-id}
34791 @item m @var{thread-id},@var{thread-id}@dots{}
34792 a comma-separated list of thread IDs
34794 (lower case letter @samp{L}) denotes end of list.
34797 In response to each query, the target will reply with a list of one or
34798 more thread IDs, separated by commas.
34799 @value{GDBN} will respond to each reply with a request for more thread
34800 ids (using the @samp{qs} form of the query), until the target responds
34801 with @samp{l} (lower-case ell, for @dfn{last}).
34802 Refer to @ref{thread-id syntax}, for the format of the @var{thread-id}
34805 @item qGetTLSAddr:@var{thread-id},@var{offset},@var{lm}
34806 @cindex get thread-local storage address, remote request
34807 @cindex @samp{qGetTLSAddr} packet
34808 Fetch the address associated with thread local storage specified
34809 by @var{thread-id}, @var{offset}, and @var{lm}.
34811 @var{thread-id} is the thread ID associated with the
34812 thread for which to fetch the TLS address. @xref{thread-id syntax}.
34814 @var{offset} is the (big endian, hex encoded) offset associated with the
34815 thread local variable. (This offset is obtained from the debug
34816 information associated with the variable.)
34818 @var{lm} is the (big endian, hex encoded) OS/ABI-specific encoding of the
34819 load module associated with the thread local storage. For example,
34820 a @sc{gnu}/Linux system will pass the link map address of the shared
34821 object associated with the thread local storage under consideration.
34822 Other operating environments may choose to represent the load module
34823 differently, so the precise meaning of this parameter will vary.
34827 @item @var{XX}@dots{}
34828 Hex encoded (big endian) bytes representing the address of the thread
34829 local storage requested.
34832 An error occurred. @var{nn} are hex digits.
34835 An empty reply indicates that @samp{qGetTLSAddr} is not supported by the stub.
34838 @item qGetTIBAddr:@var{thread-id}
34839 @cindex get thread information block address
34840 @cindex @samp{qGetTIBAddr} packet
34841 Fetch address of the Windows OS specific Thread Information Block.
34843 @var{thread-id} is the thread ID associated with the thread.
34847 @item @var{XX}@dots{}
34848 Hex encoded (big endian) bytes representing the linear address of the
34849 thread information block.
34852 An error occured. This means that either the thread was not found, or the
34853 address could not be retrieved.
34856 An empty reply indicates that @samp{qGetTIBAddr} is not supported by the stub.
34859 @item qL @var{startflag} @var{threadcount} @var{nextthread}
34860 Obtain thread information from RTOS. Where: @var{startflag} (one hex
34861 digit) is one to indicate the first query and zero to indicate a
34862 subsequent query; @var{threadcount} (two hex digits) is the maximum
34863 number of threads the response packet can contain; and @var{nextthread}
34864 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
34865 returned in the response as @var{argthread}.
34867 Don't use this packet; use the @samp{qfThreadInfo} query instead (see above).
34871 @item qM @var{count} @var{done} @var{argthread} @var{thread}@dots{}
34872 Where: @var{count} (two hex digits) is the number of threads being
34873 returned; @var{done} (one hex digit) is zero to indicate more threads
34874 and one indicates no further threads; @var{argthreadid} (eight hex
34875 digits) is @var{nextthread} from the request packet; @var{thread}@dots{}
34876 is a sequence of thread IDs from the target. @var{threadid} (eight hex
34877 digits). See @code{remote.c:parse_threadlist_response()}.
34881 @cindex section offsets, remote request
34882 @cindex @samp{qOffsets} packet
34883 Get section offsets that the target used when relocating the downloaded
34888 @item Text=@var{xxx};Data=@var{yyy}@r{[};Bss=@var{zzz}@r{]}
34889 Relocate the @code{Text} section by @var{xxx} from its original address.
34890 Relocate the @code{Data} section by @var{yyy} from its original address.
34891 If the object file format provides segment information (e.g.@: @sc{elf}
34892 @samp{PT_LOAD} program headers), @value{GDBN} will relocate entire
34893 segments by the supplied offsets.
34895 @emph{Note: while a @code{Bss} offset may be included in the response,
34896 @value{GDBN} ignores this and instead applies the @code{Data} offset
34897 to the @code{Bss} section.}
34899 @item TextSeg=@var{xxx}@r{[};DataSeg=@var{yyy}@r{]}
34900 Relocate the first segment of the object file, which conventionally
34901 contains program code, to a starting address of @var{xxx}. If
34902 @samp{DataSeg} is specified, relocate the second segment, which
34903 conventionally contains modifiable data, to a starting address of
34904 @var{yyy}. @value{GDBN} will report an error if the object file
34905 does not contain segment information, or does not contain at least
34906 as many segments as mentioned in the reply. Extra segments are
34907 kept at fixed offsets relative to the last relocated segment.
34910 @item qP @var{mode} @var{thread-id}
34911 @cindex thread information, remote request
34912 @cindex @samp{qP} packet
34913 Returns information on @var{thread-id}. Where: @var{mode} is a hex
34914 encoded 32 bit mode; @var{thread-id} is a thread ID
34915 (@pxref{thread-id syntax}).
34917 Don't use this packet; use the @samp{qThreadExtraInfo} query instead
34920 Reply: see @code{remote.c:remote_unpack_thread_info_response()}.
34924 @cindex non-stop mode, remote request
34925 @cindex @samp{QNonStop} packet
34927 Enter non-stop (@samp{QNonStop:1}) or all-stop (@samp{QNonStop:0}) mode.
34928 @xref{Remote Non-Stop}, for more information.
34933 The request succeeded.
34936 An error occurred. @var{nn} are hex digits.
34939 An empty reply indicates that @samp{QNonStop} is not supported by
34943 This packet is not probed by default; the remote stub must request it,
34944 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
34945 Use of this packet is controlled by the @code{set non-stop} command;
34946 @pxref{Non-Stop Mode}.
34948 @item QPassSignals: @var{signal} @r{[};@var{signal}@r{]}@dots{}
34949 @cindex pass signals to inferior, remote request
34950 @cindex @samp{QPassSignals} packet
34951 @anchor{QPassSignals}
34952 Each listed @var{signal} should be passed directly to the inferior process.
34953 Signals are numbered identically to continue packets and stop replies
34954 (@pxref{Stop Reply Packets}). Each @var{signal} list item should be
34955 strictly greater than the previous item. These signals do not need to stop
34956 the inferior, or be reported to @value{GDBN}. All other signals should be
34957 reported to @value{GDBN}. Multiple @samp{QPassSignals} packets do not
34958 combine; any earlier @samp{QPassSignals} list is completely replaced by the
34959 new list. This packet improves performance when using @samp{handle
34960 @var{signal} nostop noprint pass}.
34965 The request succeeded.
34968 An error occurred. @var{nn} are hex digits.
34971 An empty reply indicates that @samp{QPassSignals} is not supported by
34975 Use of this packet is controlled by the @code{set remote pass-signals}
34976 command (@pxref{Remote Configuration, set remote pass-signals}).
34977 This packet is not probed by default; the remote stub must request it,
34978 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
34980 @item QProgramSignals: @var{signal} @r{[};@var{signal}@r{]}@dots{}
34981 @cindex signals the inferior may see, remote request
34982 @cindex @samp{QProgramSignals} packet
34983 @anchor{QProgramSignals}
34984 Each listed @var{signal} may be delivered to the inferior process.
34985 Others should be silently discarded.
34987 In some cases, the remote stub may need to decide whether to deliver a
34988 signal to the program or not without @value{GDBN} involvement. One
34989 example of that is while detaching --- the program's threads may have
34990 stopped for signals that haven't yet had a chance of being reported to
34991 @value{GDBN}, and so the remote stub can use the signal list specified
34992 by this packet to know whether to deliver or ignore those pending
34995 This does not influence whether to deliver a signal as requested by a
34996 resumption packet (@pxref{vCont packet}).
34998 Signals are numbered identically to continue packets and stop replies
34999 (@pxref{Stop Reply Packets}). Each @var{signal} list item should be
35000 strictly greater than the previous item. Multiple
35001 @samp{QProgramSignals} packets do not combine; any earlier
35002 @samp{QProgramSignals} list is completely replaced by the new list.
35007 The request succeeded.
35010 An error occurred. @var{nn} are hex digits.
35013 An empty reply indicates that @samp{QProgramSignals} is not supported
35017 Use of this packet is controlled by the @code{set remote program-signals}
35018 command (@pxref{Remote Configuration, set remote program-signals}).
35019 This packet is not probed by default; the remote stub must request it,
35020 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
35022 @item qRcmd,@var{command}
35023 @cindex execute remote command, remote request
35024 @cindex @samp{qRcmd} packet
35025 @var{command} (hex encoded) is passed to the local interpreter for
35026 execution. Invalid commands should be reported using the output
35027 string. Before the final result packet, the target may also respond
35028 with a number of intermediate @samp{O@var{output}} console output
35029 packets. @emph{Implementors should note that providing access to a
35030 stubs's interpreter may have security implications}.
35035 A command response with no output.
35037 A command response with the hex encoded output string @var{OUTPUT}.
35039 Indicate a badly formed request.
35041 An empty reply indicates that @samp{qRcmd} is not recognized.
35044 (Note that the @code{qRcmd} packet's name is separated from the
35045 command by a @samp{,}, not a @samp{:}, contrary to the naming
35046 conventions above. Please don't use this packet as a model for new
35049 @item qSearch:memory:@var{address};@var{length};@var{search-pattern}
35050 @cindex searching memory, in remote debugging
35051 @cindex @samp{qSearch:memory} packet
35052 @anchor{qSearch memory}
35053 Search @var{length} bytes at @var{address} for @var{search-pattern}.
35054 @var{address} and @var{length} are encoded in hex.
35055 @var{search-pattern} is a sequence of bytes, hex encoded.
35060 The pattern was not found.
35062 The pattern was found at @var{address}.
35064 A badly formed request or an error was encountered while searching memory.
35066 An empty reply indicates that @samp{qSearch:memory} is not recognized.
35069 @item QStartNoAckMode
35070 @cindex @samp{QStartNoAckMode} packet
35071 @anchor{QStartNoAckMode}
35072 Request that the remote stub disable the normal @samp{+}/@samp{-}
35073 protocol acknowledgments (@pxref{Packet Acknowledgment}).
35078 The stub has switched to no-acknowledgment mode.
35079 @value{GDBN} acknowledges this reponse,
35080 but neither the stub nor @value{GDBN} shall send or expect further
35081 @samp{+}/@samp{-} acknowledgments in the current connection.
35083 An empty reply indicates that the stub does not support no-acknowledgment mode.
35086 @item qSupported @r{[}:@var{gdbfeature} @r{[};@var{gdbfeature}@r{]}@dots{} @r{]}
35087 @cindex supported packets, remote query
35088 @cindex features of the remote protocol
35089 @cindex @samp{qSupported} packet
35090 @anchor{qSupported}
35091 Tell the remote stub about features supported by @value{GDBN}, and
35092 query the stub for features it supports. This packet allows
35093 @value{GDBN} and the remote stub to take advantage of each others'
35094 features. @samp{qSupported} also consolidates multiple feature probes
35095 at startup, to improve @value{GDBN} performance---a single larger
35096 packet performs better than multiple smaller probe packets on
35097 high-latency links. Some features may enable behavior which must not
35098 be on by default, e.g.@: because it would confuse older clients or
35099 stubs. Other features may describe packets which could be
35100 automatically probed for, but are not. These features must be
35101 reported before @value{GDBN} will use them. This ``default
35102 unsupported'' behavior is not appropriate for all packets, but it
35103 helps to keep the initial connection time under control with new
35104 versions of @value{GDBN} which support increasing numbers of packets.
35108 @item @var{stubfeature} @r{[};@var{stubfeature}@r{]}@dots{}
35109 The stub supports or does not support each returned @var{stubfeature},
35110 depending on the form of each @var{stubfeature} (see below for the
35113 An empty reply indicates that @samp{qSupported} is not recognized,
35114 or that no features needed to be reported to @value{GDBN}.
35117 The allowed forms for each feature (either a @var{gdbfeature} in the
35118 @samp{qSupported} packet, or a @var{stubfeature} in the response)
35122 @item @var{name}=@var{value}
35123 The remote protocol feature @var{name} is supported, and associated
35124 with the specified @var{value}. The format of @var{value} depends
35125 on the feature, but it must not include a semicolon.
35127 The remote protocol feature @var{name} is supported, and does not
35128 need an associated value.
35130 The remote protocol feature @var{name} is not supported.
35132 The remote protocol feature @var{name} may be supported, and
35133 @value{GDBN} should auto-detect support in some other way when it is
35134 needed. This form will not be used for @var{gdbfeature} notifications,
35135 but may be used for @var{stubfeature} responses.
35138 Whenever the stub receives a @samp{qSupported} request, the
35139 supplied set of @value{GDBN} features should override any previous
35140 request. This allows @value{GDBN} to put the stub in a known
35141 state, even if the stub had previously been communicating with
35142 a different version of @value{GDBN}.
35144 The following values of @var{gdbfeature} (for the packet sent by @value{GDBN})
35149 This feature indicates whether @value{GDBN} supports multiprocess
35150 extensions to the remote protocol. @value{GDBN} does not use such
35151 extensions unless the stub also reports that it supports them by
35152 including @samp{multiprocess+} in its @samp{qSupported} reply.
35153 @xref{multiprocess extensions}, for details.
35156 This feature indicates that @value{GDBN} supports the XML target
35157 description. If the stub sees @samp{xmlRegisters=} with target
35158 specific strings separated by a comma, it will report register
35162 This feature indicates whether @value{GDBN} supports the
35163 @samp{qRelocInsn} packet (@pxref{Tracepoint Packets,,Relocate
35164 instruction reply packet}).
35167 Stubs should ignore any unknown values for
35168 @var{gdbfeature}. Any @value{GDBN} which sends a @samp{qSupported}
35169 packet supports receiving packets of unlimited length (earlier
35170 versions of @value{GDBN} may reject overly long responses). Additional values
35171 for @var{gdbfeature} may be defined in the future to let the stub take
35172 advantage of new features in @value{GDBN}, e.g.@: incompatible
35173 improvements in the remote protocol---the @samp{multiprocess} feature is
35174 an example of such a feature. The stub's reply should be independent
35175 of the @var{gdbfeature} entries sent by @value{GDBN}; first @value{GDBN}
35176 describes all the features it supports, and then the stub replies with
35177 all the features it supports.
35179 Similarly, @value{GDBN} will silently ignore unrecognized stub feature
35180 responses, as long as each response uses one of the standard forms.
35182 Some features are flags. A stub which supports a flag feature
35183 should respond with a @samp{+} form response. Other features
35184 require values, and the stub should respond with an @samp{=}
35187 Each feature has a default value, which @value{GDBN} will use if
35188 @samp{qSupported} is not available or if the feature is not mentioned
35189 in the @samp{qSupported} response. The default values are fixed; a
35190 stub is free to omit any feature responses that match the defaults.
35192 Not all features can be probed, but for those which can, the probing
35193 mechanism is useful: in some cases, a stub's internal
35194 architecture may not allow the protocol layer to know some information
35195 about the underlying target in advance. This is especially common in
35196 stubs which may be configured for multiple targets.
35198 These are the currently defined stub features and their properties:
35200 @multitable @columnfractions 0.35 0.2 0.12 0.2
35201 @c NOTE: The first row should be @headitem, but we do not yet require
35202 @c a new enough version of Texinfo (4.7) to use @headitem.
35204 @tab Value Required
35208 @item @samp{PacketSize}
35213 @item @samp{qXfer:auxv:read}
35218 @item @samp{qXfer:features:read}
35223 @item @samp{qXfer:libraries:read}
35228 @item @samp{qXfer:memory-map:read}
35233 @item @samp{qXfer:sdata:read}
35238 @item @samp{qXfer:spu:read}
35243 @item @samp{qXfer:spu:write}
35248 @item @samp{qXfer:siginfo:read}
35253 @item @samp{qXfer:siginfo:write}
35258 @item @samp{qXfer:threads:read}
35263 @item @samp{qXfer:traceframe-info:read}
35268 @item @samp{qXfer:uib:read}
35273 @item @samp{qXfer:fdpic:read}
35278 @item @samp{QNonStop}
35283 @item @samp{QPassSignals}
35288 @item @samp{QStartNoAckMode}
35293 @item @samp{multiprocess}
35298 @item @samp{ConditionalBreakpoints}
35303 @item @samp{ConditionalTracepoints}
35308 @item @samp{ReverseContinue}
35313 @item @samp{ReverseStep}
35318 @item @samp{TracepointSource}
35323 @item @samp{QAgent}
35328 @item @samp{QAllow}
35333 @item @samp{QDisableRandomization}
35338 @item @samp{EnableDisableTracepoints}
35343 @item @samp{tracenz}
35350 These are the currently defined stub features, in more detail:
35353 @cindex packet size, remote protocol
35354 @item PacketSize=@var{bytes}
35355 The remote stub can accept packets up to at least @var{bytes} in
35356 length. @value{GDBN} will send packets up to this size for bulk
35357 transfers, and will never send larger packets. This is a limit on the
35358 data characters in the packet, including the frame and checksum.
35359 There is no trailing NUL byte in a remote protocol packet; if the stub
35360 stores packets in a NUL-terminated format, it should allow an extra
35361 byte in its buffer for the NUL. If this stub feature is not supported,
35362 @value{GDBN} guesses based on the size of the @samp{g} packet response.
35364 @item qXfer:auxv:read
35365 The remote stub understands the @samp{qXfer:auxv:read} packet
35366 (@pxref{qXfer auxiliary vector read}).
35368 @item qXfer:features:read
35369 The remote stub understands the @samp{qXfer:features:read} packet
35370 (@pxref{qXfer target description read}).
35372 @item qXfer:libraries:read
35373 The remote stub understands the @samp{qXfer:libraries:read} packet
35374 (@pxref{qXfer library list read}).
35376 @item qXfer:libraries-svr4:read
35377 The remote stub understands the @samp{qXfer:libraries-svr4:read} packet
35378 (@pxref{qXfer svr4 library list read}).
35380 @item qXfer:memory-map:read
35381 The remote stub understands the @samp{qXfer:memory-map:read} packet
35382 (@pxref{qXfer memory map read}).
35384 @item qXfer:sdata:read
35385 The remote stub understands the @samp{qXfer:sdata:read} packet
35386 (@pxref{qXfer sdata read}).
35388 @item qXfer:spu:read
35389 The remote stub understands the @samp{qXfer:spu:read} packet
35390 (@pxref{qXfer spu read}).
35392 @item qXfer:spu:write
35393 The remote stub understands the @samp{qXfer:spu:write} packet
35394 (@pxref{qXfer spu write}).
35396 @item qXfer:siginfo:read
35397 The remote stub understands the @samp{qXfer:siginfo:read} packet
35398 (@pxref{qXfer siginfo read}).
35400 @item qXfer:siginfo:write
35401 The remote stub understands the @samp{qXfer:siginfo:write} packet
35402 (@pxref{qXfer siginfo write}).
35404 @item qXfer:threads:read
35405 The remote stub understands the @samp{qXfer:threads:read} packet
35406 (@pxref{qXfer threads read}).
35408 @item qXfer:traceframe-info:read
35409 The remote stub understands the @samp{qXfer:traceframe-info:read}
35410 packet (@pxref{qXfer traceframe info read}).
35412 @item qXfer:uib:read
35413 The remote stub understands the @samp{qXfer:uib:read}
35414 packet (@pxref{qXfer unwind info block}).
35416 @item qXfer:fdpic:read
35417 The remote stub understands the @samp{qXfer:fdpic:read}
35418 packet (@pxref{qXfer fdpic loadmap read}).
35421 The remote stub understands the @samp{QNonStop} packet
35422 (@pxref{QNonStop}).
35425 The remote stub understands the @samp{QPassSignals} packet
35426 (@pxref{QPassSignals}).
35428 @item QStartNoAckMode
35429 The remote stub understands the @samp{QStartNoAckMode} packet and
35430 prefers to operate in no-acknowledgment mode. @xref{Packet Acknowledgment}.
35433 @anchor{multiprocess extensions}
35434 @cindex multiprocess extensions, in remote protocol
35435 The remote stub understands the multiprocess extensions to the remote
35436 protocol syntax. The multiprocess extensions affect the syntax of
35437 thread IDs in both packets and replies (@pxref{thread-id syntax}), and
35438 add process IDs to the @samp{D} packet and @samp{W} and @samp{X}
35439 replies. Note that reporting this feature indicates support for the
35440 syntactic extensions only, not that the stub necessarily supports
35441 debugging of more than one process at a time. The stub must not use
35442 multiprocess extensions in packet replies unless @value{GDBN} has also
35443 indicated it supports them in its @samp{qSupported} request.
35445 @item qXfer:osdata:read
35446 The remote stub understands the @samp{qXfer:osdata:read} packet
35447 ((@pxref{qXfer osdata read}).
35449 @item ConditionalBreakpoints
35450 The target accepts and implements evaluation of conditional expressions
35451 defined for breakpoints. The target will only report breakpoint triggers
35452 when such conditions are true (@pxref{Conditions, ,Break Conditions}).
35454 @item ConditionalTracepoints
35455 The remote stub accepts and implements conditional expressions defined
35456 for tracepoints (@pxref{Tracepoint Conditions}).
35458 @item ReverseContinue
35459 The remote stub accepts and implements the reverse continue packet
35463 The remote stub accepts and implements the reverse step packet
35466 @item TracepointSource
35467 The remote stub understands the @samp{QTDPsrc} packet that supplies
35468 the source form of tracepoint definitions.
35471 The remote stub understands the @samp{QAgent} packet.
35474 The remote stub understands the @samp{QAllow} packet.
35476 @item QDisableRandomization
35477 The remote stub understands the @samp{QDisableRandomization} packet.
35479 @item StaticTracepoint
35480 @cindex static tracepoints, in remote protocol
35481 The remote stub supports static tracepoints.
35483 @item InstallInTrace
35484 @anchor{install tracepoint in tracing}
35485 The remote stub supports installing tracepoint in tracing.
35487 @item EnableDisableTracepoints
35488 The remote stub supports the @samp{QTEnable} (@pxref{QTEnable}) and
35489 @samp{QTDisable} (@pxref{QTDisable}) packets that allow tracepoints
35490 to be enabled and disabled while a trace experiment is running.
35493 @cindex string tracing, in remote protocol
35494 The remote stub supports the @samp{tracenz} bytecode for collecting strings.
35495 See @ref{Bytecode Descriptions} for details about the bytecode.
35500 @cindex symbol lookup, remote request
35501 @cindex @samp{qSymbol} packet
35502 Notify the target that @value{GDBN} is prepared to serve symbol lookup
35503 requests. Accept requests from the target for the values of symbols.
35508 The target does not need to look up any (more) symbols.
35509 @item qSymbol:@var{sym_name}
35510 The target requests the value of symbol @var{sym_name} (hex encoded).
35511 @value{GDBN} may provide the value by using the
35512 @samp{qSymbol:@var{sym_value}:@var{sym_name}} message, described
35516 @item qSymbol:@var{sym_value}:@var{sym_name}
35517 Set the value of @var{sym_name} to @var{sym_value}.
35519 @var{sym_name} (hex encoded) is the name of a symbol whose value the
35520 target has previously requested.
35522 @var{sym_value} (hex) is the value for symbol @var{sym_name}. If
35523 @value{GDBN} cannot supply a value for @var{sym_name}, then this field
35529 The target does not need to look up any (more) symbols.
35530 @item qSymbol:@var{sym_name}
35531 The target requests the value of a new symbol @var{sym_name} (hex
35532 encoded). @value{GDBN} will continue to supply the values of symbols
35533 (if available), until the target ceases to request them.
35538 @item QTDisconnected
35545 @itemx qTMinFTPILen
35547 @xref{Tracepoint Packets}.
35549 @item qThreadExtraInfo,@var{thread-id}
35550 @cindex thread attributes info, remote request
35551 @cindex @samp{qThreadExtraInfo} packet
35552 Obtain a printable string description of a thread's attributes from
35553 the target OS. @var{thread-id} is a thread ID;
35554 see @ref{thread-id syntax}. This
35555 string may contain anything that the target OS thinks is interesting
35556 for @value{GDBN} to tell the user about the thread. The string is
35557 displayed in @value{GDBN}'s @code{info threads} display. Some
35558 examples of possible thread extra info strings are @samp{Runnable}, or
35559 @samp{Blocked on Mutex}.
35563 @item @var{XX}@dots{}
35564 Where @samp{@var{XX}@dots{}} is a hex encoding of @sc{ascii} data,
35565 comprising the printable string containing the extra information about
35566 the thread's attributes.
35569 (Note that the @code{qThreadExtraInfo} packet's name is separated from
35570 the command by a @samp{,}, not a @samp{:}, contrary to the naming
35571 conventions above. Please don't use this packet as a model for new
35590 @xref{Tracepoint Packets}.
35592 @item qXfer:@var{object}:read:@var{annex}:@var{offset},@var{length}
35593 @cindex read special object, remote request
35594 @cindex @samp{qXfer} packet
35595 @anchor{qXfer read}
35596 Read uninterpreted bytes from the target's special data area
35597 identified by the keyword @var{object}. Request @var{length} bytes
35598 starting at @var{offset} bytes into the data. The content and
35599 encoding of @var{annex} is specific to @var{object}; it can supply
35600 additional details about what data to access.
35602 Here are the specific requests of this form defined so far. All
35603 @samp{qXfer:@var{object}:read:@dots{}} requests use the same reply
35604 formats, listed below.
35607 @item qXfer:auxv:read::@var{offset},@var{length}
35608 @anchor{qXfer auxiliary vector read}
35609 Access the target's @dfn{auxiliary vector}. @xref{OS Information,
35610 auxiliary vector}. Note @var{annex} must be empty.
35612 This packet is not probed by default; the remote stub must request it,
35613 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
35615 @item qXfer:features:read:@var{annex}:@var{offset},@var{length}
35616 @anchor{qXfer target description read}
35617 Access the @dfn{target description}. @xref{Target Descriptions}. The
35618 annex specifies which XML document to access. The main description is
35619 always loaded from the @samp{target.xml} annex.
35621 This packet is not probed by default; the remote stub must request it,
35622 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
35624 @item qXfer:libraries:read:@var{annex}:@var{offset},@var{length}
35625 @anchor{qXfer library list read}
35626 Access the target's list of loaded libraries. @xref{Library List Format}.
35627 The annex part of the generic @samp{qXfer} packet must be empty
35628 (@pxref{qXfer read}).
35630 Targets which maintain a list of libraries in the program's memory do
35631 not need to implement this packet; it is designed for platforms where
35632 the operating system manages the list of loaded libraries.
35634 This packet is not probed by default; the remote stub must request it,
35635 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
35637 @item qXfer:libraries-svr4:read:@var{annex}:@var{offset},@var{length}
35638 @anchor{qXfer svr4 library list read}
35639 Access the target's list of loaded libraries when the target is an SVR4
35640 platform. @xref{Library List Format for SVR4 Targets}. The annex part
35641 of the generic @samp{qXfer} packet must be empty (@pxref{qXfer read}).
35643 This packet is optional for better performance on SVR4 targets.
35644 @value{GDBN} uses memory read packets to read the SVR4 library list otherwise.
35646 This packet is not probed by default; the remote stub must request it,
35647 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
35649 @item qXfer:memory-map:read::@var{offset},@var{length}
35650 @anchor{qXfer memory map read}
35651 Access the target's @dfn{memory-map}. @xref{Memory Map Format}. The
35652 annex part of the generic @samp{qXfer} packet must be empty
35653 (@pxref{qXfer read}).
35655 This packet is not probed by default; the remote stub must request it,
35656 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
35658 @item qXfer:sdata:read::@var{offset},@var{length}
35659 @anchor{qXfer sdata read}
35661 Read contents of the extra collected static tracepoint marker
35662 information. The annex part of the generic @samp{qXfer} packet must
35663 be empty (@pxref{qXfer read}). @xref{Tracepoint Actions,,Tracepoint
35666 This packet is not probed by default; the remote stub must request it,
35667 by supplying an appropriate @samp{qSupported} response
35668 (@pxref{qSupported}).
35670 @item qXfer:siginfo:read::@var{offset},@var{length}
35671 @anchor{qXfer siginfo read}
35672 Read contents of the extra signal information on the target
35673 system. The annex part of the generic @samp{qXfer} packet must be
35674 empty (@pxref{qXfer read}).
35676 This packet is not probed by default; the remote stub must request it,
35677 by supplying an appropriate @samp{qSupported} response
35678 (@pxref{qSupported}).
35680 @item qXfer:spu:read:@var{annex}:@var{offset},@var{length}
35681 @anchor{qXfer spu read}
35682 Read contents of an @code{spufs} file on the target system. The
35683 annex specifies which file to read; it must be of the form
35684 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
35685 in the target process, and @var{name} identifes the @code{spufs} file
35686 in that context to be accessed.
35688 This packet is not probed by default; the remote stub must request it,
35689 by supplying an appropriate @samp{qSupported} response
35690 (@pxref{qSupported}).
35692 @item qXfer:threads:read::@var{offset},@var{length}
35693 @anchor{qXfer threads read}
35694 Access the list of threads on target. @xref{Thread List Format}. The
35695 annex part of the generic @samp{qXfer} packet must be empty
35696 (@pxref{qXfer read}).
35698 This packet is not probed by default; the remote stub must request it,
35699 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
35701 @item qXfer:traceframe-info:read::@var{offset},@var{length}
35702 @anchor{qXfer traceframe info read}
35704 Return a description of the current traceframe's contents.
35705 @xref{Traceframe Info Format}. The annex part of the generic
35706 @samp{qXfer} packet must be empty (@pxref{qXfer read}).
35708 This packet is not probed by default; the remote stub must request it,
35709 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
35711 @item qXfer:uib:read:@var{pc}:@var{offset},@var{length}
35712 @anchor{qXfer unwind info block}
35714 Return the unwind information block for @var{pc}. This packet is used
35715 on OpenVMS/ia64 to ask the kernel unwind information.
35717 This packet is not probed by default.
35719 @item qXfer:fdpic:read:@var{annex}:@var{offset},@var{length}
35720 @anchor{qXfer fdpic loadmap read}
35721 Read contents of @code{loadmap}s on the target system. The
35722 annex, either @samp{exec} or @samp{interp}, specifies which @code{loadmap},
35723 executable @code{loadmap} or interpreter @code{loadmap} to read.
35725 This packet is not probed by default; the remote stub must request it,
35726 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
35728 @item qXfer:osdata:read::@var{offset},@var{length}
35729 @anchor{qXfer osdata read}
35730 Access the target's @dfn{operating system information}.
35731 @xref{Operating System Information}.
35738 Data @var{data} (@pxref{Binary Data}) has been read from the
35739 target. There may be more data at a higher address (although
35740 it is permitted to return @samp{m} even for the last valid
35741 block of data, as long as at least one byte of data was read).
35742 @var{data} may have fewer bytes than the @var{length} in the
35746 Data @var{data} (@pxref{Binary Data}) has been read from the target.
35747 There is no more data to be read. @var{data} may have fewer bytes
35748 than the @var{length} in the request.
35751 The @var{offset} in the request is at the end of the data.
35752 There is no more data to be read.
35755 The request was malformed, or @var{annex} was invalid.
35758 The offset was invalid, or there was an error encountered reading the data.
35759 @var{nn} is a hex-encoded @code{errno} value.
35762 An empty reply indicates the @var{object} string was not recognized by
35763 the stub, or that the object does not support reading.
35766 @item qXfer:@var{object}:write:@var{annex}:@var{offset}:@var{data}@dots{}
35767 @cindex write data into object, remote request
35768 @anchor{qXfer write}
35769 Write uninterpreted bytes into the target's special data area
35770 identified by the keyword @var{object}, starting at @var{offset} bytes
35771 into the data. @var{data}@dots{} is the binary-encoded data
35772 (@pxref{Binary Data}) to be written. The content and encoding of @var{annex}
35773 is specific to @var{object}; it can supply additional details about what data
35776 Here are the specific requests of this form defined so far. All
35777 @samp{qXfer:@var{object}:write:@dots{}} requests use the same reply
35778 formats, listed below.
35781 @item qXfer:siginfo:write::@var{offset}:@var{data}@dots{}
35782 @anchor{qXfer siginfo write}
35783 Write @var{data} to the extra signal information on the target system.
35784 The annex part of the generic @samp{qXfer} packet must be
35785 empty (@pxref{qXfer write}).
35787 This packet is not probed by default; the remote stub must request it,
35788 by supplying an appropriate @samp{qSupported} response
35789 (@pxref{qSupported}).
35791 @item qXfer:spu:write:@var{annex}:@var{offset}:@var{data}@dots{}
35792 @anchor{qXfer spu write}
35793 Write @var{data} to an @code{spufs} file on the target system. The
35794 annex specifies which file to write; it must be of the form
35795 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
35796 in the target process, and @var{name} identifes the @code{spufs} file
35797 in that context to be accessed.
35799 This packet is not probed by default; the remote stub must request it,
35800 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
35806 @var{nn} (hex encoded) is the number of bytes written.
35807 This may be fewer bytes than supplied in the request.
35810 The request was malformed, or @var{annex} was invalid.
35813 The offset was invalid, or there was an error encountered writing the data.
35814 @var{nn} is a hex-encoded @code{errno} value.
35817 An empty reply indicates the @var{object} string was not
35818 recognized by the stub, or that the object does not support writing.
35821 @item qXfer:@var{object}:@var{operation}:@dots{}
35822 Requests of this form may be added in the future. When a stub does
35823 not recognize the @var{object} keyword, or its support for
35824 @var{object} does not recognize the @var{operation} keyword, the stub
35825 must respond with an empty packet.
35827 @item qAttached:@var{pid}
35828 @cindex query attached, remote request
35829 @cindex @samp{qAttached} packet
35830 Return an indication of whether the remote server attached to an
35831 existing process or created a new process. When the multiprocess
35832 protocol extensions are supported (@pxref{multiprocess extensions}),
35833 @var{pid} is an integer in hexadecimal format identifying the target
35834 process. Otherwise, @value{GDBN} will omit the @var{pid} field and
35835 the query packet will be simplified as @samp{qAttached}.
35837 This query is used, for example, to know whether the remote process
35838 should be detached or killed when a @value{GDBN} session is ended with
35839 the @code{quit} command.
35844 The remote server attached to an existing process.
35846 The remote server created a new process.
35848 A badly formed request or an error was encountered.
35853 @node Architecture-Specific Protocol Details
35854 @section Architecture-Specific Protocol Details
35856 This section describes how the remote protocol is applied to specific
35857 target architectures. Also see @ref{Standard Target Features}, for
35858 details of XML target descriptions for each architecture.
35862 @subsubsection Breakpoint Kinds
35864 These breakpoint kinds are defined for the @samp{Z0} and @samp{Z1} packets.
35869 16-bit Thumb mode breakpoint.
35872 32-bit Thumb mode (Thumb-2) breakpoint.
35875 32-bit ARM mode breakpoint.
35881 @subsubsection Register Packet Format
35883 The following @code{g}/@code{G} packets have previously been defined.
35884 In the below, some thirty-two bit registers are transferred as
35885 sixty-four bits. Those registers should be zero/sign extended (which?)
35886 to fill the space allocated. Register bytes are transferred in target
35887 byte order. The two nibbles within a register byte are transferred
35888 most-significant - least-significant.
35894 All registers are transferred as thirty-two bit quantities in the order:
35895 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
35896 registers; fsr; fir; fp.
35900 All registers are transferred as sixty-four bit quantities (including
35901 thirty-two bit registers such as @code{sr}). The ordering is the same
35906 @node Tracepoint Packets
35907 @section Tracepoint Packets
35908 @cindex tracepoint packets
35909 @cindex packets, tracepoint
35911 Here we describe the packets @value{GDBN} uses to implement
35912 tracepoints (@pxref{Tracepoints}).
35916 @item QTDP:@var{n}:@var{addr}:@var{ena}:@var{step}:@var{pass}[:F@var{flen}][:X@var{len},@var{bytes}]@r{[}-@r{]}
35917 Create a new tracepoint, number @var{n}, at @var{addr}. If @var{ena}
35918 is @samp{E}, then the tracepoint is enabled; if it is @samp{D}, then
35919 the tracepoint is disabled. @var{step} is the tracepoint's step
35920 count, and @var{pass} is its pass count. If an @samp{F} is present,
35921 then the tracepoint is to be a fast tracepoint, and the @var{flen} is
35922 the number of bytes that the target should copy elsewhere to make room
35923 for the tracepoint. If an @samp{X} is present, it introduces a
35924 tracepoint condition, which consists of a hexadecimal length, followed
35925 by a comma and hex-encoded bytes, in a manner similar to action
35926 encodings as described below. If the trailing @samp{-} is present,
35927 further @samp{QTDP} packets will follow to specify this tracepoint's
35933 The packet was understood and carried out.
35935 @xref{Tracepoint Packets,,Relocate instruction reply packet}.
35937 The packet was not recognized.
35940 @item QTDP:-@var{n}:@var{addr}:@r{[}S@r{]}@var{action}@dots{}@r{[}-@r{]}
35941 Define actions to be taken when a tracepoint is hit. @var{n} and
35942 @var{addr} must be the same as in the initial @samp{QTDP} packet for
35943 this tracepoint. This packet may only be sent immediately after
35944 another @samp{QTDP} packet that ended with a @samp{-}. If the
35945 trailing @samp{-} is present, further @samp{QTDP} packets will follow,
35946 specifying more actions for this tracepoint.
35948 In the series of action packets for a given tracepoint, at most one
35949 can have an @samp{S} before its first @var{action}. If such a packet
35950 is sent, it and the following packets define ``while-stepping''
35951 actions. Any prior packets define ordinary actions --- that is, those
35952 taken when the tracepoint is first hit. If no action packet has an
35953 @samp{S}, then all the packets in the series specify ordinary
35954 tracepoint actions.
35956 The @samp{@var{action}@dots{}} portion of the packet is a series of
35957 actions, concatenated without separators. Each action has one of the
35963 Collect the registers whose bits are set in @var{mask}. @var{mask} is
35964 a hexadecimal number whose @var{i}'th bit is set if register number
35965 @var{i} should be collected. (The least significant bit is numbered
35966 zero.) Note that @var{mask} may be any number of digits long; it may
35967 not fit in a 32-bit word.
35969 @item M @var{basereg},@var{offset},@var{len}
35970 Collect @var{len} bytes of memory starting at the address in register
35971 number @var{basereg}, plus @var{offset}. If @var{basereg} is
35972 @samp{-1}, then the range has a fixed address: @var{offset} is the
35973 address of the lowest byte to collect. The @var{basereg},
35974 @var{offset}, and @var{len} parameters are all unsigned hexadecimal
35975 values (the @samp{-1} value for @var{basereg} is a special case).
35977 @item X @var{len},@var{expr}
35978 Evaluate @var{expr}, whose length is @var{len}, and collect memory as
35979 it directs. @var{expr} is an agent expression, as described in
35980 @ref{Agent Expressions}. Each byte of the expression is encoded as a
35981 two-digit hex number in the packet; @var{len} is the number of bytes
35982 in the expression (and thus one-half the number of hex digits in the
35987 Any number of actions may be packed together in a single @samp{QTDP}
35988 packet, as long as the packet does not exceed the maximum packet
35989 length (400 bytes, for many stubs). There may be only one @samp{R}
35990 action per tracepoint, and it must precede any @samp{M} or @samp{X}
35991 actions. Any registers referred to by @samp{M} and @samp{X} actions
35992 must be collected by a preceding @samp{R} action. (The
35993 ``while-stepping'' actions are treated as if they were attached to a
35994 separate tracepoint, as far as these restrictions are concerned.)
35999 The packet was understood and carried out.
36001 @xref{Tracepoint Packets,,Relocate instruction reply packet}.
36003 The packet was not recognized.
36006 @item QTDPsrc:@var{n}:@var{addr}:@var{type}:@var{start}:@var{slen}:@var{bytes}
36007 @cindex @samp{QTDPsrc} packet
36008 Specify a source string of tracepoint @var{n} at address @var{addr}.
36009 This is useful to get accurate reproduction of the tracepoints
36010 originally downloaded at the beginning of the trace run. @var{type}
36011 is the name of the tracepoint part, such as @samp{cond} for the
36012 tracepoint's conditional expression (see below for a list of types), while
36013 @var{bytes} is the string, encoded in hexadecimal.
36015 @var{start} is the offset of the @var{bytes} within the overall source
36016 string, while @var{slen} is the total length of the source string.
36017 This is intended for handling source strings that are longer than will
36018 fit in a single packet.
36019 @c Add detailed example when this info is moved into a dedicated
36020 @c tracepoint descriptions section.
36022 The available string types are @samp{at} for the location,
36023 @samp{cond} for the conditional, and @samp{cmd} for an action command.
36024 @value{GDBN} sends a separate packet for each command in the action
36025 list, in the same order in which the commands are stored in the list.
36027 The target does not need to do anything with source strings except
36028 report them back as part of the replies to the @samp{qTfP}/@samp{qTsP}
36031 Although this packet is optional, and @value{GDBN} will only send it
36032 if the target replies with @samp{TracepointSource} @xref{General
36033 Query Packets}, it makes both disconnected tracing and trace files
36034 much easier to use. Otherwise the user must be careful that the
36035 tracepoints in effect while looking at trace frames are identical to
36036 the ones in effect during the trace run; even a small discrepancy
36037 could cause @samp{tdump} not to work, or a particular trace frame not
36040 @item QTDV:@var{n}:@var{value}
36041 @cindex define trace state variable, remote request
36042 @cindex @samp{QTDV} packet
36043 Create a new trace state variable, number @var{n}, with an initial
36044 value of @var{value}, which is a 64-bit signed integer. Both @var{n}
36045 and @var{value} are encoded as hexadecimal values. @value{GDBN} has
36046 the option of not using this packet for initial values of zero; the
36047 target should simply create the trace state variables as they are
36048 mentioned in expressions.
36050 @item QTFrame:@var{n}
36051 Select the @var{n}'th tracepoint frame from the buffer, and use the
36052 register and memory contents recorded there to answer subsequent
36053 request packets from @value{GDBN}.
36055 A successful reply from the stub indicates that the stub has found the
36056 requested frame. The response is a series of parts, concatenated
36057 without separators, describing the frame we selected. Each part has
36058 one of the following forms:
36062 The selected frame is number @var{n} in the trace frame buffer;
36063 @var{f} is a hexadecimal number. If @var{f} is @samp{-1}, then there
36064 was no frame matching the criteria in the request packet.
36067 The selected trace frame records a hit of tracepoint number @var{t};
36068 @var{t} is a hexadecimal number.
36072 @item QTFrame:pc:@var{addr}
36073 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
36074 currently selected frame whose PC is @var{addr};
36075 @var{addr} is a hexadecimal number.
36077 @item QTFrame:tdp:@var{t}
36078 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
36079 currently selected frame that is a hit of tracepoint @var{t}; @var{t}
36080 is a hexadecimal number.
36082 @item QTFrame:range:@var{start}:@var{end}
36083 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
36084 currently selected frame whose PC is between @var{start} (inclusive)
36085 and @var{end} (inclusive); @var{start} and @var{end} are hexadecimal
36088 @item QTFrame:outside:@var{start}:@var{end}
36089 Like @samp{QTFrame:range:@var{start}:@var{end}}, but select the first
36090 frame @emph{outside} the given range of addresses (exclusive).
36093 This packet requests the minimum length of instruction at which a fast
36094 tracepoint (@pxref{Set Tracepoints}) may be placed. For instance, on
36095 the 32-bit x86 architecture, it is possible to use a 4-byte jump, but
36096 it depends on the target system being able to create trampolines in
36097 the first 64K of memory, which might or might not be possible for that
36098 system. So the reply to this packet will be 4 if it is able to
36105 The minimum instruction length is currently unknown.
36107 The minimum instruction length is @var{length}, where @var{length} is greater
36108 or equal to 1. @var{length} is a hexadecimal number. A reply of 1 means
36109 that a fast tracepoint may be placed on any instruction regardless of size.
36111 An error has occurred.
36113 An empty reply indicates that the request is not supported by the stub.
36117 Begin the tracepoint experiment. Begin collecting data from
36118 tracepoint hits in the trace frame buffer. This packet supports the
36119 @samp{qRelocInsn} reply (@pxref{Tracepoint Packets,,Relocate
36120 instruction reply packet}).
36123 End the tracepoint experiment. Stop collecting trace frames.
36125 @item QTEnable:@var{n}:@var{addr}
36127 Enable tracepoint @var{n} at address @var{addr} in a started tracepoint
36128 experiment. If the tracepoint was previously disabled, then collection
36129 of data from it will resume.
36131 @item QTDisable:@var{n}:@var{addr}
36133 Disable tracepoint @var{n} at address @var{addr} in a started tracepoint
36134 experiment. No more data will be collected from the tracepoint unless
36135 @samp{QTEnable:@var{n}:@var{addr}} is subsequently issued.
36138 Clear the table of tracepoints, and empty the trace frame buffer.
36140 @item QTro:@var{start1},@var{end1}:@var{start2},@var{end2}:@dots{}
36141 Establish the given ranges of memory as ``transparent''. The stub
36142 will answer requests for these ranges from memory's current contents,
36143 if they were not collected as part of the tracepoint hit.
36145 @value{GDBN} uses this to mark read-only regions of memory, like those
36146 containing program code. Since these areas never change, they should
36147 still have the same contents they did when the tracepoint was hit, so
36148 there's no reason for the stub to refuse to provide their contents.
36150 @item QTDisconnected:@var{value}
36151 Set the choice to what to do with the tracing run when @value{GDBN}
36152 disconnects from the target. A @var{value} of 1 directs the target to
36153 continue the tracing run, while 0 tells the target to stop tracing if
36154 @value{GDBN} is no longer in the picture.
36157 Ask the stub if there is a trace experiment running right now.
36159 The reply has the form:
36163 @item T@var{running}@r{[};@var{field}@r{]}@dots{}
36164 @var{running} is a single digit @code{1} if the trace is presently
36165 running, or @code{0} if not. It is followed by semicolon-separated
36166 optional fields that an agent may use to report additional status.
36170 If the trace is not running, the agent may report any of several
36171 explanations as one of the optional fields:
36176 No trace has been run yet.
36178 @item tstop[:@var{text}]:0
36179 The trace was stopped by a user-originated stop command. The optional
36180 @var{text} field is a user-supplied string supplied as part of the
36181 stop command (for instance, an explanation of why the trace was
36182 stopped manually). It is hex-encoded.
36185 The trace stopped because the trace buffer filled up.
36187 @item tdisconnected:0
36188 The trace stopped because @value{GDBN} disconnected from the target.
36190 @item tpasscount:@var{tpnum}
36191 The trace stopped because tracepoint @var{tpnum} exceeded its pass count.
36193 @item terror:@var{text}:@var{tpnum}
36194 The trace stopped because tracepoint @var{tpnum} had an error. The
36195 string @var{text} is available to describe the nature of the error
36196 (for instance, a divide by zero in the condition expression).
36197 @var{text} is hex encoded.
36200 The trace stopped for some other reason.
36204 Additional optional fields supply statistical and other information.
36205 Although not required, they are extremely useful for users monitoring
36206 the progress of a trace run. If a trace has stopped, and these
36207 numbers are reported, they must reflect the state of the just-stopped
36212 @item tframes:@var{n}
36213 The number of trace frames in the buffer.
36215 @item tcreated:@var{n}
36216 The total number of trace frames created during the run. This may
36217 be larger than the trace frame count, if the buffer is circular.
36219 @item tsize:@var{n}
36220 The total size of the trace buffer, in bytes.
36222 @item tfree:@var{n}
36223 The number of bytes still unused in the buffer.
36225 @item circular:@var{n}
36226 The value of the circular trace buffer flag. @code{1} means that the
36227 trace buffer is circular and old trace frames will be discarded if
36228 necessary to make room, @code{0} means that the trace buffer is linear
36231 @item disconn:@var{n}
36232 The value of the disconnected tracing flag. @code{1} means that
36233 tracing will continue after @value{GDBN} disconnects, @code{0} means
36234 that the trace run will stop.
36238 @item qTP:@var{tp}:@var{addr}
36239 @cindex tracepoint status, remote request
36240 @cindex @samp{qTP} packet
36241 Ask the stub for the current state of tracepoint number @var{tp} at
36242 address @var{addr}.
36246 @item V@var{hits}:@var{usage}
36247 The tracepoint has been hit @var{hits} times so far during the trace
36248 run, and accounts for @var{usage} in the trace buffer. Note that
36249 @code{while-stepping} steps are not counted as separate hits, but the
36250 steps' space consumption is added into the usage number.
36254 @item qTV:@var{var}
36255 @cindex trace state variable value, remote request
36256 @cindex @samp{qTV} packet
36257 Ask the stub for the value of the trace state variable number @var{var}.
36262 The value of the variable is @var{value}. This will be the current
36263 value of the variable if the user is examining a running target, or a
36264 saved value if the variable was collected in the trace frame that the
36265 user is looking at. Note that multiple requests may result in
36266 different reply values, such as when requesting values while the
36267 program is running.
36270 The value of the variable is unknown. This would occur, for example,
36271 if the user is examining a trace frame in which the requested variable
36277 These packets request data about tracepoints that are being used by
36278 the target. @value{GDBN} sends @code{qTfP} to get the first piece
36279 of data, and multiple @code{qTsP} to get additional pieces. Replies
36280 to these packets generally take the form of the @code{QTDP} packets
36281 that define tracepoints. (FIXME add detailed syntax)
36285 These packets request data about trace state variables that are on the
36286 target. @value{GDBN} sends @code{qTfV} to get the first vari of data,
36287 and multiple @code{qTsV} to get additional variables. Replies to
36288 these packets follow the syntax of the @code{QTDV} packets that define
36289 trace state variables.
36293 These packets request data about static tracepoint markers that exist
36294 in the target program. @value{GDBN} sends @code{qTfSTM} to get the
36295 first piece of data, and multiple @code{qTsSTM} to get additional
36296 pieces. Replies to these packets take the following form:
36300 @item m @var{address}:@var{id}:@var{extra}
36302 @item m @var{address}:@var{id}:@var{extra},@var{address}:@var{id}:@var{extra}@dots{}
36303 a comma-separated list of markers
36305 (lower case letter @samp{L}) denotes end of list.
36307 An error occurred. @var{nn} are hex digits.
36309 An empty reply indicates that the request is not supported by the
36313 @var{address} is encoded in hex.
36314 @var{id} and @var{extra} are strings encoded in hex.
36316 In response to each query, the target will reply with a list of one or
36317 more markers, separated by commas. @value{GDBN} will respond to each
36318 reply with a request for more markers (using the @samp{qs} form of the
36319 query), until the target responds with @samp{l} (lower-case ell, for
36322 @item qTSTMat:@var{address}
36323 This packets requests data about static tracepoint markers in the
36324 target program at @var{address}. Replies to this packet follow the
36325 syntax of the @samp{qTfSTM} and @code{qTsSTM} packets that list static
36326 tracepoint markers.
36328 @item QTSave:@var{filename}
36329 This packet directs the target to save trace data to the file name
36330 @var{filename} in the target's filesystem. @var{filename} is encoded
36331 as a hex string; the interpretation of the file name (relative vs
36332 absolute, wild cards, etc) is up to the target.
36334 @item qTBuffer:@var{offset},@var{len}
36335 Return up to @var{len} bytes of the current contents of trace buffer,
36336 starting at @var{offset}. The trace buffer is treated as if it were
36337 a contiguous collection of traceframes, as per the trace file format.
36338 The reply consists as many hex-encoded bytes as the target can deliver
36339 in a packet; it is not an error to return fewer than were asked for.
36340 A reply consisting of just @code{l} indicates that no bytes are
36343 @item QTBuffer:circular:@var{value}
36344 This packet directs the target to use a circular trace buffer if
36345 @var{value} is 1, or a linear buffer if the value is 0.
36347 @item QTNotes:@r{[}@var{type}:@var{text}@r{]}@r{[};@var{type}:@var{text}@r{]}@dots{}
36348 This packet adds optional textual notes to the trace run. Allowable
36349 types include @code{user}, @code{notes}, and @code{tstop}, the
36350 @var{text} fields are arbitrary strings, hex-encoded.
36354 @subsection Relocate instruction reply packet
36355 When installing fast tracepoints in memory, the target may need to
36356 relocate the instruction currently at the tracepoint address to a
36357 different address in memory. For most instructions, a simple copy is
36358 enough, but, for example, call instructions that implicitly push the
36359 return address on the stack, and relative branches or other
36360 PC-relative instructions require offset adjustment, so that the effect
36361 of executing the instruction at a different address is the same as if
36362 it had executed in the original location.
36364 In response to several of the tracepoint packets, the target may also
36365 respond with a number of intermediate @samp{qRelocInsn} request
36366 packets before the final result packet, to have @value{GDBN} handle
36367 this relocation operation. If a packet supports this mechanism, its
36368 documentation will explicitly say so. See for example the above
36369 descriptions for the @samp{QTStart} and @samp{QTDP} packets. The
36370 format of the request is:
36373 @item qRelocInsn:@var{from};@var{to}
36375 This requests @value{GDBN} to copy instruction at address @var{from}
36376 to address @var{to}, possibly adjusted so that executing the
36377 instruction at @var{to} has the same effect as executing it at
36378 @var{from}. @value{GDBN} writes the adjusted instruction to target
36379 memory starting at @var{to}.
36384 @item qRelocInsn:@var{adjusted_size}
36385 Informs the stub the relocation is complete. @var{adjusted_size} is
36386 the length in bytes of resulting relocated instruction sequence.
36388 A badly formed request was detected, or an error was encountered while
36389 relocating the instruction.
36392 @node Host I/O Packets
36393 @section Host I/O Packets
36394 @cindex Host I/O, remote protocol
36395 @cindex file transfer, remote protocol
36397 The @dfn{Host I/O} packets allow @value{GDBN} to perform I/O
36398 operations on the far side of a remote link. For example, Host I/O is
36399 used to upload and download files to a remote target with its own
36400 filesystem. Host I/O uses the same constant values and data structure
36401 layout as the target-initiated File-I/O protocol. However, the
36402 Host I/O packets are structured differently. The target-initiated
36403 protocol relies on target memory to store parameters and buffers.
36404 Host I/O requests are initiated by @value{GDBN}, and the
36405 target's memory is not involved. @xref{File-I/O Remote Protocol
36406 Extension}, for more details on the target-initiated protocol.
36408 The Host I/O request packets all encode a single operation along with
36409 its arguments. They have this format:
36413 @item vFile:@var{operation}: @var{parameter}@dots{}
36414 @var{operation} is the name of the particular request; the target
36415 should compare the entire packet name up to the second colon when checking
36416 for a supported operation. The format of @var{parameter} depends on
36417 the operation. Numbers are always passed in hexadecimal. Negative
36418 numbers have an explicit minus sign (i.e.@: two's complement is not
36419 used). Strings (e.g.@: filenames) are encoded as a series of
36420 hexadecimal bytes. The last argument to a system call may be a
36421 buffer of escaped binary data (@pxref{Binary Data}).
36425 The valid responses to Host I/O packets are:
36429 @item F @var{result} [, @var{errno}] [; @var{attachment}]
36430 @var{result} is the integer value returned by this operation, usually
36431 non-negative for success and -1 for errors. If an error has occured,
36432 @var{errno} will be included in the result. @var{errno} will have a
36433 value defined by the File-I/O protocol (@pxref{Errno Values}). For
36434 operations which return data, @var{attachment} supplies the data as a
36435 binary buffer. Binary buffers in response packets are escaped in the
36436 normal way (@pxref{Binary Data}). See the individual packet
36437 documentation for the interpretation of @var{result} and
36441 An empty response indicates that this operation is not recognized.
36445 These are the supported Host I/O operations:
36448 @item vFile:open: @var{pathname}, @var{flags}, @var{mode}
36449 Open a file at @var{pathname} and return a file descriptor for it, or
36450 return -1 if an error occurs. @var{pathname} is a string,
36451 @var{flags} is an integer indicating a mask of open flags
36452 (@pxref{Open Flags}), and @var{mode} is an integer indicating a mask
36453 of mode bits to use if the file is created (@pxref{mode_t Values}).
36454 @xref{open}, for details of the open flags and mode values.
36456 @item vFile:close: @var{fd}
36457 Close the open file corresponding to @var{fd} and return 0, or
36458 -1 if an error occurs.
36460 @item vFile:pread: @var{fd}, @var{count}, @var{offset}
36461 Read data from the open file corresponding to @var{fd}. Up to
36462 @var{count} bytes will be read from the file, starting at @var{offset}
36463 relative to the start of the file. The target may read fewer bytes;
36464 common reasons include packet size limits and an end-of-file
36465 condition. The number of bytes read is returned. Zero should only be
36466 returned for a successful read at the end of the file, or if
36467 @var{count} was zero.
36469 The data read should be returned as a binary attachment on success.
36470 If zero bytes were read, the response should include an empty binary
36471 attachment (i.e.@: a trailing semicolon). The return value is the
36472 number of target bytes read; the binary attachment may be longer if
36473 some characters were escaped.
36475 @item vFile:pwrite: @var{fd}, @var{offset}, @var{data}
36476 Write @var{data} (a binary buffer) to the open file corresponding
36477 to @var{fd}. Start the write at @var{offset} from the start of the
36478 file. Unlike many @code{write} system calls, there is no
36479 separate @var{count} argument; the length of @var{data} in the
36480 packet is used. @samp{vFile:write} returns the number of bytes written,
36481 which may be shorter than the length of @var{data}, or -1 if an
36484 @item vFile:unlink: @var{pathname}
36485 Delete the file at @var{pathname} on the target. Return 0,
36486 or -1 if an error occurs. @var{pathname} is a string.
36488 @item vFile:readlink: @var{filename}
36489 Read value of symbolic link @var{filename} on the target. Return
36490 the number of bytes read, or -1 if an error occurs.
36492 The data read should be returned as a binary attachment on success.
36493 If zero bytes were read, the response should include an empty binary
36494 attachment (i.e.@: a trailing semicolon). The return value is the
36495 number of target bytes read; the binary attachment may be longer if
36496 some characters were escaped.
36501 @section Interrupts
36502 @cindex interrupts (remote protocol)
36504 When a program on the remote target is running, @value{GDBN} may
36505 attempt to interrupt it by sending a @samp{Ctrl-C}, @code{BREAK} or
36506 a @code{BREAK} followed by @code{g},
36507 control of which is specified via @value{GDBN}'s @samp{interrupt-sequence}.
36509 The precise meaning of @code{BREAK} is defined by the transport
36510 mechanism and may, in fact, be undefined. @value{GDBN} does not
36511 currently define a @code{BREAK} mechanism for any of the network
36512 interfaces except for TCP, in which case @value{GDBN} sends the
36513 @code{telnet} BREAK sequence.
36515 @samp{Ctrl-C}, on the other hand, is defined and implemented for all
36516 transport mechanisms. It is represented by sending the single byte
36517 @code{0x03} without any of the usual packet overhead described in
36518 the Overview section (@pxref{Overview}). When a @code{0x03} byte is
36519 transmitted as part of a packet, it is considered to be packet data
36520 and does @emph{not} represent an interrupt. E.g., an @samp{X} packet
36521 (@pxref{X packet}), used for binary downloads, may include an unescaped
36522 @code{0x03} as part of its packet.
36524 @code{BREAK} followed by @code{g} is also known as Magic SysRq g.
36525 When Linux kernel receives this sequence from serial port,
36526 it stops execution and connects to gdb.
36528 Stubs are not required to recognize these interrupt mechanisms and the
36529 precise meaning associated with receipt of the interrupt is
36530 implementation defined. If the target supports debugging of multiple
36531 threads and/or processes, it should attempt to interrupt all
36532 currently-executing threads and processes.
36533 If the stub is successful at interrupting the
36534 running program, it should send one of the stop
36535 reply packets (@pxref{Stop Reply Packets}) to @value{GDBN} as a result
36536 of successfully stopping the program in all-stop mode, and a stop reply
36537 for each stopped thread in non-stop mode.
36538 Interrupts received while the
36539 program is stopped are discarded.
36541 @node Notification Packets
36542 @section Notification Packets
36543 @cindex notification packets
36544 @cindex packets, notification
36546 The @value{GDBN} remote serial protocol includes @dfn{notifications},
36547 packets that require no acknowledgment. Both the GDB and the stub
36548 may send notifications (although the only notifications defined at
36549 present are sent by the stub). Notifications carry information
36550 without incurring the round-trip latency of an acknowledgment, and so
36551 are useful for low-impact communications where occasional packet loss
36554 A notification packet has the form @samp{% @var{data} #
36555 @var{checksum}}, where @var{data} is the content of the notification,
36556 and @var{checksum} is a checksum of @var{data}, computed and formatted
36557 as for ordinary @value{GDBN} packets. A notification's @var{data}
36558 never contains @samp{$}, @samp{%} or @samp{#} characters. Upon
36559 receiving a notification, the recipient sends no @samp{+} or @samp{-}
36560 to acknowledge the notification's receipt or to report its corruption.
36562 Every notification's @var{data} begins with a name, which contains no
36563 colon characters, followed by a colon character.
36565 Recipients should silently ignore corrupted notifications and
36566 notifications they do not understand. Recipients should restart
36567 timeout periods on receipt of a well-formed notification, whether or
36568 not they understand it.
36570 Senders should only send the notifications described here when this
36571 protocol description specifies that they are permitted. In the
36572 future, we may extend the protocol to permit existing notifications in
36573 new contexts; this rule helps older senders avoid confusing newer
36576 (Older versions of @value{GDBN} ignore bytes received until they see
36577 the @samp{$} byte that begins an ordinary packet, so new stubs may
36578 transmit notifications without fear of confusing older clients. There
36579 are no notifications defined for @value{GDBN} to send at the moment, but we
36580 assume that most older stubs would ignore them, as well.)
36582 The following notification packets from the stub to @value{GDBN} are
36586 @item Stop: @var{reply}
36587 Report an asynchronous stop event in non-stop mode.
36588 The @var{reply} has the form of a stop reply, as
36589 described in @ref{Stop Reply Packets}. Refer to @ref{Remote Non-Stop},
36590 for information on how these notifications are acknowledged by
36594 @node Remote Non-Stop
36595 @section Remote Protocol Support for Non-Stop Mode
36597 @value{GDBN}'s remote protocol supports non-stop debugging of
36598 multi-threaded programs, as described in @ref{Non-Stop Mode}. If the stub
36599 supports non-stop mode, it should report that to @value{GDBN} by including
36600 @samp{QNonStop+} in its @samp{qSupported} response (@pxref{qSupported}).
36602 @value{GDBN} typically sends a @samp{QNonStop} packet only when
36603 establishing a new connection with the stub. Entering non-stop mode
36604 does not alter the state of any currently-running threads, but targets
36605 must stop all threads in any already-attached processes when entering
36606 all-stop mode. @value{GDBN} uses the @samp{?} packet as necessary to
36607 probe the target state after a mode change.
36609 In non-stop mode, when an attached process encounters an event that
36610 would otherwise be reported with a stop reply, it uses the
36611 asynchronous notification mechanism (@pxref{Notification Packets}) to
36612 inform @value{GDBN}. In contrast to all-stop mode, where all threads
36613 in all processes are stopped when a stop reply is sent, in non-stop
36614 mode only the thread reporting the stop event is stopped. That is,
36615 when reporting a @samp{S} or @samp{T} response to indicate completion
36616 of a step operation, hitting a breakpoint, or a fault, only the
36617 affected thread is stopped; any other still-running threads continue
36618 to run. When reporting a @samp{W} or @samp{X} response, all running
36619 threads belonging to other attached processes continue to run.
36621 Only one stop reply notification at a time may be pending; if
36622 additional stop events occur before @value{GDBN} has acknowledged the
36623 previous notification, they must be queued by the stub for later
36624 synchronous transmission in response to @samp{vStopped} packets from
36625 @value{GDBN}. Because the notification mechanism is unreliable,
36626 the stub is permitted to resend a stop reply notification
36627 if it believes @value{GDBN} may not have received it. @value{GDBN}
36628 ignores additional stop reply notifications received before it has
36629 finished processing a previous notification and the stub has completed
36630 sending any queued stop events.
36632 Otherwise, @value{GDBN} must be prepared to receive a stop reply
36633 notification at any time. Specifically, they may appear when
36634 @value{GDBN} is not otherwise reading input from the stub, or when
36635 @value{GDBN} is expecting to read a normal synchronous response or a
36636 @samp{+}/@samp{-} acknowledgment to a packet it has sent.
36637 Notification packets are distinct from any other communication from
36638 the stub so there is no ambiguity.
36640 After receiving a stop reply notification, @value{GDBN} shall
36641 acknowledge it by sending a @samp{vStopped} packet (@pxref{vStopped packet})
36642 as a regular, synchronous request to the stub. Such acknowledgment
36643 is not required to happen immediately, as @value{GDBN} is permitted to
36644 send other, unrelated packets to the stub first, which the stub should
36647 Upon receiving a @samp{vStopped} packet, if the stub has other queued
36648 stop events to report to @value{GDBN}, it shall respond by sending a
36649 normal stop reply response. @value{GDBN} shall then send another
36650 @samp{vStopped} packet to solicit further responses; again, it is
36651 permitted to send other, unrelated packets as well which the stub
36652 should process normally.
36654 If the stub receives a @samp{vStopped} packet and there are no
36655 additional stop events to report, the stub shall return an @samp{OK}
36656 response. At this point, if further stop events occur, the stub shall
36657 send a new stop reply notification, @value{GDBN} shall accept the
36658 notification, and the process shall be repeated.
36660 In non-stop mode, the target shall respond to the @samp{?} packet as
36661 follows. First, any incomplete stop reply notification/@samp{vStopped}
36662 sequence in progress is abandoned. The target must begin a new
36663 sequence reporting stop events for all stopped threads, whether or not
36664 it has previously reported those events to @value{GDBN}. The first
36665 stop reply is sent as a synchronous reply to the @samp{?} packet, and
36666 subsequent stop replies are sent as responses to @samp{vStopped} packets
36667 using the mechanism described above. The target must not send
36668 asynchronous stop reply notifications until the sequence is complete.
36669 If all threads are running when the target receives the @samp{?} packet,
36670 or if the target is not attached to any process, it shall respond
36673 @node Packet Acknowledgment
36674 @section Packet Acknowledgment
36676 @cindex acknowledgment, for @value{GDBN} remote
36677 @cindex packet acknowledgment, for @value{GDBN} remote
36678 By default, when either the host or the target machine receives a packet,
36679 the first response expected is an acknowledgment: either @samp{+} (to indicate
36680 the package was received correctly) or @samp{-} (to request retransmission).
36681 This mechanism allows the @value{GDBN} remote protocol to operate over
36682 unreliable transport mechanisms, such as a serial line.
36684 In cases where the transport mechanism is itself reliable (such as a pipe or
36685 TCP connection), the @samp{+}/@samp{-} acknowledgments are redundant.
36686 It may be desirable to disable them in that case to reduce communication
36687 overhead, or for other reasons. This can be accomplished by means of the
36688 @samp{QStartNoAckMode} packet; @pxref{QStartNoAckMode}.
36690 When in no-acknowledgment mode, neither the stub nor @value{GDBN} shall send or
36691 expect @samp{+}/@samp{-} protocol acknowledgments. The packet
36692 and response format still includes the normal checksum, as described in
36693 @ref{Overview}, but the checksum may be ignored by the receiver.
36695 If the stub supports @samp{QStartNoAckMode} and prefers to operate in
36696 no-acknowledgment mode, it should report that to @value{GDBN}
36697 by including @samp{QStartNoAckMode+} in its response to @samp{qSupported};
36698 @pxref{qSupported}.
36699 If @value{GDBN} also supports @samp{QStartNoAckMode} and it has not been
36700 disabled via the @code{set remote noack-packet off} command
36701 (@pxref{Remote Configuration}),
36702 @value{GDBN} may then send a @samp{QStartNoAckMode} packet to the stub.
36703 Only then may the stub actually turn off packet acknowledgments.
36704 @value{GDBN} sends a final @samp{+} acknowledgment of the stub's @samp{OK}
36705 response, which can be safely ignored by the stub.
36707 Note that @code{set remote noack-packet} command only affects negotiation
36708 between @value{GDBN} and the stub when subsequent connections are made;
36709 it does not affect the protocol acknowledgment state for any current
36711 Since @samp{+}/@samp{-} acknowledgments are enabled by default when a
36712 new connection is established,
36713 there is also no protocol request to re-enable the acknowledgments
36714 for the current connection, once disabled.
36719 Example sequence of a target being re-started. Notice how the restart
36720 does not get any direct output:
36725 @emph{target restarts}
36728 <- @code{T001:1234123412341234}
36732 Example sequence of a target being stepped by a single instruction:
36735 -> @code{G1445@dots{}}
36740 <- @code{T001:1234123412341234}
36744 <- @code{1455@dots{}}
36748 @node File-I/O Remote Protocol Extension
36749 @section File-I/O Remote Protocol Extension
36750 @cindex File-I/O remote protocol extension
36753 * File-I/O Overview::
36754 * Protocol Basics::
36755 * The F Request Packet::
36756 * The F Reply Packet::
36757 * The Ctrl-C Message::
36759 * List of Supported Calls::
36760 * Protocol-specific Representation of Datatypes::
36762 * File-I/O Examples::
36765 @node File-I/O Overview
36766 @subsection File-I/O Overview
36767 @cindex file-i/o overview
36769 The @dfn{File I/O remote protocol extension} (short: File-I/O) allows the
36770 target to use the host's file system and console I/O to perform various
36771 system calls. System calls on the target system are translated into a
36772 remote protocol packet to the host system, which then performs the needed
36773 actions and returns a response packet to the target system.
36774 This simulates file system operations even on targets that lack file systems.
36776 The protocol is defined to be independent of both the host and target systems.
36777 It uses its own internal representation of datatypes and values. Both
36778 @value{GDBN} and the target's @value{GDBN} stub are responsible for
36779 translating the system-dependent value representations into the internal
36780 protocol representations when data is transmitted.
36782 The communication is synchronous. A system call is possible only when
36783 @value{GDBN} is waiting for a response from the @samp{C}, @samp{c}, @samp{S}
36784 or @samp{s} packets. While @value{GDBN} handles the request for a system call,
36785 the target is stopped to allow deterministic access to the target's
36786 memory. Therefore File-I/O is not interruptible by target signals. On
36787 the other hand, it is possible to interrupt File-I/O by a user interrupt
36788 (@samp{Ctrl-C}) within @value{GDBN}.
36790 The target's request to perform a host system call does not finish
36791 the latest @samp{C}, @samp{c}, @samp{S} or @samp{s} action. That means,
36792 after finishing the system call, the target returns to continuing the
36793 previous activity (continue, step). No additional continue or step
36794 request from @value{GDBN} is required.
36797 (@value{GDBP}) continue
36798 <- target requests 'system call X'
36799 target is stopped, @value{GDBN} executes system call
36800 -> @value{GDBN} returns result
36801 ... target continues, @value{GDBN} returns to wait for the target
36802 <- target hits breakpoint and sends a Txx packet
36805 The protocol only supports I/O on the console and to regular files on
36806 the host file system. Character or block special devices, pipes,
36807 named pipes, sockets or any other communication method on the host
36808 system are not supported by this protocol.
36810 File I/O is not supported in non-stop mode.
36812 @node Protocol Basics
36813 @subsection Protocol Basics
36814 @cindex protocol basics, file-i/o
36816 The File-I/O protocol uses the @code{F} packet as the request as well
36817 as reply packet. Since a File-I/O system call can only occur when
36818 @value{GDBN} is waiting for a response from the continuing or stepping target,
36819 the File-I/O request is a reply that @value{GDBN} has to expect as a result
36820 of a previous @samp{C}, @samp{c}, @samp{S} or @samp{s} packet.
36821 This @code{F} packet contains all information needed to allow @value{GDBN}
36822 to call the appropriate host system call:
36826 A unique identifier for the requested system call.
36829 All parameters to the system call. Pointers are given as addresses
36830 in the target memory address space. Pointers to strings are given as
36831 pointer/length pair. Numerical values are given as they are.
36832 Numerical control flags are given in a protocol-specific representation.
36836 At this point, @value{GDBN} has to perform the following actions.
36840 If the parameters include pointer values to data needed as input to a
36841 system call, @value{GDBN} requests this data from the target with a
36842 standard @code{m} packet request. This additional communication has to be
36843 expected by the target implementation and is handled as any other @code{m}
36847 @value{GDBN} translates all value from protocol representation to host
36848 representation as needed. Datatypes are coerced into the host types.
36851 @value{GDBN} calls the system call.
36854 It then coerces datatypes back to protocol representation.
36857 If the system call is expected to return data in buffer space specified
36858 by pointer parameters to the call, the data is transmitted to the
36859 target using a @code{M} or @code{X} packet. This packet has to be expected
36860 by the target implementation and is handled as any other @code{M} or @code{X}
36865 Eventually @value{GDBN} replies with another @code{F} packet which contains all
36866 necessary information for the target to continue. This at least contains
36873 @code{errno}, if has been changed by the system call.
36880 After having done the needed type and value coercion, the target continues
36881 the latest continue or step action.
36883 @node The F Request Packet
36884 @subsection The @code{F} Request Packet
36885 @cindex file-i/o request packet
36886 @cindex @code{F} request packet
36888 The @code{F} request packet has the following format:
36891 @item F@var{call-id},@var{parameter@dots{}}
36893 @var{call-id} is the identifier to indicate the host system call to be called.
36894 This is just the name of the function.
36896 @var{parameter@dots{}} are the parameters to the system call.
36897 Parameters are hexadecimal integer values, either the actual values in case
36898 of scalar datatypes, pointers to target buffer space in case of compound
36899 datatypes and unspecified memory areas, or pointer/length pairs in case
36900 of string parameters. These are appended to the @var{call-id} as a
36901 comma-delimited list. All values are transmitted in ASCII
36902 string representation, pointer/length pairs separated by a slash.
36908 @node The F Reply Packet
36909 @subsection The @code{F} Reply Packet
36910 @cindex file-i/o reply packet
36911 @cindex @code{F} reply packet
36913 The @code{F} reply packet has the following format:
36917 @item F@var{retcode},@var{errno},@var{Ctrl-C flag};@var{call-specific attachment}
36919 @var{retcode} is the return code of the system call as hexadecimal value.
36921 @var{errno} is the @code{errno} set by the call, in protocol-specific
36923 This parameter can be omitted if the call was successful.
36925 @var{Ctrl-C flag} is only sent if the user requested a break. In this
36926 case, @var{errno} must be sent as well, even if the call was successful.
36927 The @var{Ctrl-C flag} itself consists of the character @samp{C}:
36934 or, if the call was interrupted before the host call has been performed:
36941 assuming 4 is the protocol-specific representation of @code{EINTR}.
36946 @node The Ctrl-C Message
36947 @subsection The @samp{Ctrl-C} Message
36948 @cindex ctrl-c message, in file-i/o protocol
36950 If the @samp{Ctrl-C} flag is set in the @value{GDBN}
36951 reply packet (@pxref{The F Reply Packet}),
36952 the target should behave as if it had
36953 gotten a break message. The meaning for the target is ``system call
36954 interrupted by @code{SIGINT}''. Consequentially, the target should actually stop
36955 (as with a break message) and return to @value{GDBN} with a @code{T02}
36958 It's important for the target to know in which
36959 state the system call was interrupted. There are two possible cases:
36963 The system call hasn't been performed on the host yet.
36966 The system call on the host has been finished.
36970 These two states can be distinguished by the target by the value of the
36971 returned @code{errno}. If it's the protocol representation of @code{EINTR}, the system
36972 call hasn't been performed. This is equivalent to the @code{EINTR} handling
36973 on POSIX systems. In any other case, the target may presume that the
36974 system call has been finished --- successfully or not --- and should behave
36975 as if the break message arrived right after the system call.
36977 @value{GDBN} must behave reliably. If the system call has not been called
36978 yet, @value{GDBN} may send the @code{F} reply immediately, setting @code{EINTR} as
36979 @code{errno} in the packet. If the system call on the host has been finished
36980 before the user requests a break, the full action must be finished by
36981 @value{GDBN}. This requires sending @code{M} or @code{X} packets as necessary.
36982 The @code{F} packet may only be sent when either nothing has happened
36983 or the full action has been completed.
36986 @subsection Console I/O
36987 @cindex console i/o as part of file-i/o
36989 By default and if not explicitly closed by the target system, the file
36990 descriptors 0, 1 and 2 are connected to the @value{GDBN} console. Output
36991 on the @value{GDBN} console is handled as any other file output operation
36992 (@code{write(1, @dots{})} or @code{write(2, @dots{})}). Console input is handled
36993 by @value{GDBN} so that after the target read request from file descriptor
36994 0 all following typing is buffered until either one of the following
36999 The user types @kbd{Ctrl-c}. The behaviour is as explained above, and the
37001 system call is treated as finished.
37004 The user presses @key{RET}. This is treated as end of input with a trailing
37008 The user types @kbd{Ctrl-d}. This is treated as end of input. No trailing
37009 character (neither newline nor @samp{Ctrl-D}) is appended to the input.
37013 If the user has typed more characters than fit in the buffer given to
37014 the @code{read} call, the trailing characters are buffered in @value{GDBN} until
37015 either another @code{read(0, @dots{})} is requested by the target, or debugging
37016 is stopped at the user's request.
37019 @node List of Supported Calls
37020 @subsection List of Supported Calls
37021 @cindex list of supported file-i/o calls
37038 @unnumberedsubsubsec open
37039 @cindex open, file-i/o system call
37044 int open(const char *pathname, int flags);
37045 int open(const char *pathname, int flags, mode_t mode);
37049 @samp{Fopen,@var{pathptr}/@var{len},@var{flags},@var{mode}}
37052 @var{flags} is the bitwise @code{OR} of the following values:
37056 If the file does not exist it will be created. The host
37057 rules apply as far as file ownership and time stamps
37061 When used with @code{O_CREAT}, if the file already exists it is
37062 an error and open() fails.
37065 If the file already exists and the open mode allows
37066 writing (@code{O_RDWR} or @code{O_WRONLY} is given) it will be
37067 truncated to zero length.
37070 The file is opened in append mode.
37073 The file is opened for reading only.
37076 The file is opened for writing only.
37079 The file is opened for reading and writing.
37083 Other bits are silently ignored.
37087 @var{mode} is the bitwise @code{OR} of the following values:
37091 User has read permission.
37094 User has write permission.
37097 Group has read permission.
37100 Group has write permission.
37103 Others have read permission.
37106 Others have write permission.
37110 Other bits are silently ignored.
37113 @item Return value:
37114 @code{open} returns the new file descriptor or -1 if an error
37121 @var{pathname} already exists and @code{O_CREAT} and @code{O_EXCL} were used.
37124 @var{pathname} refers to a directory.
37127 The requested access is not allowed.
37130 @var{pathname} was too long.
37133 A directory component in @var{pathname} does not exist.
37136 @var{pathname} refers to a device, pipe, named pipe or socket.
37139 @var{pathname} refers to a file on a read-only filesystem and
37140 write access was requested.
37143 @var{pathname} is an invalid pointer value.
37146 No space on device to create the file.
37149 The process already has the maximum number of files open.
37152 The limit on the total number of files open on the system
37156 The call was interrupted by the user.
37162 @unnumberedsubsubsec close
37163 @cindex close, file-i/o system call
37172 @samp{Fclose,@var{fd}}
37174 @item Return value:
37175 @code{close} returns zero on success, or -1 if an error occurred.
37181 @var{fd} isn't a valid open file descriptor.
37184 The call was interrupted by the user.
37190 @unnumberedsubsubsec read
37191 @cindex read, file-i/o system call
37196 int read(int fd, void *buf, unsigned int count);
37200 @samp{Fread,@var{fd},@var{bufptr},@var{count}}
37202 @item Return value:
37203 On success, the number of bytes read is returned.
37204 Zero indicates end of file. If count is zero, read
37205 returns zero as well. On error, -1 is returned.
37211 @var{fd} is not a valid file descriptor or is not open for
37215 @var{bufptr} is an invalid pointer value.
37218 The call was interrupted by the user.
37224 @unnumberedsubsubsec write
37225 @cindex write, file-i/o system call
37230 int write(int fd, const void *buf, unsigned int count);
37234 @samp{Fwrite,@var{fd},@var{bufptr},@var{count}}
37236 @item Return value:
37237 On success, the number of bytes written are returned.
37238 Zero indicates nothing was written. On error, -1
37245 @var{fd} is not a valid file descriptor or is not open for
37249 @var{bufptr} is an invalid pointer value.
37252 An attempt was made to write a file that exceeds the
37253 host-specific maximum file size allowed.
37256 No space on device to write the data.
37259 The call was interrupted by the user.
37265 @unnumberedsubsubsec lseek
37266 @cindex lseek, file-i/o system call
37271 long lseek (int fd, long offset, int flag);
37275 @samp{Flseek,@var{fd},@var{offset},@var{flag}}
37277 @var{flag} is one of:
37281 The offset is set to @var{offset} bytes.
37284 The offset is set to its current location plus @var{offset}
37288 The offset is set to the size of the file plus @var{offset}
37292 @item Return value:
37293 On success, the resulting unsigned offset in bytes from
37294 the beginning of the file is returned. Otherwise, a
37295 value of -1 is returned.
37301 @var{fd} is not a valid open file descriptor.
37304 @var{fd} is associated with the @value{GDBN} console.
37307 @var{flag} is not a proper value.
37310 The call was interrupted by the user.
37316 @unnumberedsubsubsec rename
37317 @cindex rename, file-i/o system call
37322 int rename(const char *oldpath, const char *newpath);
37326 @samp{Frename,@var{oldpathptr}/@var{len},@var{newpathptr}/@var{len}}
37328 @item Return value:
37329 On success, zero is returned. On error, -1 is returned.
37335 @var{newpath} is an existing directory, but @var{oldpath} is not a
37339 @var{newpath} is a non-empty directory.
37342 @var{oldpath} or @var{newpath} is a directory that is in use by some
37346 An attempt was made to make a directory a subdirectory
37350 A component used as a directory in @var{oldpath} or new
37351 path is not a directory. Or @var{oldpath} is a directory
37352 and @var{newpath} exists but is not a directory.
37355 @var{oldpathptr} or @var{newpathptr} are invalid pointer values.
37358 No access to the file or the path of the file.
37362 @var{oldpath} or @var{newpath} was too long.
37365 A directory component in @var{oldpath} or @var{newpath} does not exist.
37368 The file is on a read-only filesystem.
37371 The device containing the file has no room for the new
37375 The call was interrupted by the user.
37381 @unnumberedsubsubsec unlink
37382 @cindex unlink, file-i/o system call
37387 int unlink(const char *pathname);
37391 @samp{Funlink,@var{pathnameptr}/@var{len}}
37393 @item Return value:
37394 On success, zero is returned. On error, -1 is returned.
37400 No access to the file or the path of the file.
37403 The system does not allow unlinking of directories.
37406 The file @var{pathname} cannot be unlinked because it's
37407 being used by another process.
37410 @var{pathnameptr} is an invalid pointer value.
37413 @var{pathname} was too long.
37416 A directory component in @var{pathname} does not exist.
37419 A component of the path is not a directory.
37422 The file is on a read-only filesystem.
37425 The call was interrupted by the user.
37431 @unnumberedsubsubsec stat/fstat
37432 @cindex fstat, file-i/o system call
37433 @cindex stat, file-i/o system call
37438 int stat(const char *pathname, struct stat *buf);
37439 int fstat(int fd, struct stat *buf);
37443 @samp{Fstat,@var{pathnameptr}/@var{len},@var{bufptr}}@*
37444 @samp{Ffstat,@var{fd},@var{bufptr}}
37446 @item Return value:
37447 On success, zero is returned. On error, -1 is returned.
37453 @var{fd} is not a valid open file.
37456 A directory component in @var{pathname} does not exist or the
37457 path is an empty string.
37460 A component of the path is not a directory.
37463 @var{pathnameptr} is an invalid pointer value.
37466 No access to the file or the path of the file.
37469 @var{pathname} was too long.
37472 The call was interrupted by the user.
37478 @unnumberedsubsubsec gettimeofday
37479 @cindex gettimeofday, file-i/o system call
37484 int gettimeofday(struct timeval *tv, void *tz);
37488 @samp{Fgettimeofday,@var{tvptr},@var{tzptr}}
37490 @item Return value:
37491 On success, 0 is returned, -1 otherwise.
37497 @var{tz} is a non-NULL pointer.
37500 @var{tvptr} and/or @var{tzptr} is an invalid pointer value.
37506 @unnumberedsubsubsec isatty
37507 @cindex isatty, file-i/o system call
37512 int isatty(int fd);
37516 @samp{Fisatty,@var{fd}}
37518 @item Return value:
37519 Returns 1 if @var{fd} refers to the @value{GDBN} console, 0 otherwise.
37525 The call was interrupted by the user.
37530 Note that the @code{isatty} call is treated as a special case: it returns
37531 1 to the target if the file descriptor is attached
37532 to the @value{GDBN} console, 0 otherwise. Implementing through system calls
37533 would require implementing @code{ioctl} and would be more complex than
37538 @unnumberedsubsubsec system
37539 @cindex system, file-i/o system call
37544 int system(const char *command);
37548 @samp{Fsystem,@var{commandptr}/@var{len}}
37550 @item Return value:
37551 If @var{len} is zero, the return value indicates whether a shell is
37552 available. A zero return value indicates a shell is not available.
37553 For non-zero @var{len}, the value returned is -1 on error and the
37554 return status of the command otherwise. Only the exit status of the
37555 command is returned, which is extracted from the host's @code{system}
37556 return value by calling @code{WEXITSTATUS(retval)}. In case
37557 @file{/bin/sh} could not be executed, 127 is returned.
37563 The call was interrupted by the user.
37568 @value{GDBN} takes over the full task of calling the necessary host calls
37569 to perform the @code{system} call. The return value of @code{system} on
37570 the host is simplified before it's returned
37571 to the target. Any termination signal information from the child process
37572 is discarded, and the return value consists
37573 entirely of the exit status of the called command.
37575 Due to security concerns, the @code{system} call is by default refused
37576 by @value{GDBN}. The user has to allow this call explicitly with the
37577 @code{set remote system-call-allowed 1} command.
37580 @item set remote system-call-allowed
37581 @kindex set remote system-call-allowed
37582 Control whether to allow the @code{system} calls in the File I/O
37583 protocol for the remote target. The default is zero (disabled).
37585 @item show remote system-call-allowed
37586 @kindex show remote system-call-allowed
37587 Show whether the @code{system} calls are allowed in the File I/O
37591 @node Protocol-specific Representation of Datatypes
37592 @subsection Protocol-specific Representation of Datatypes
37593 @cindex protocol-specific representation of datatypes, in file-i/o protocol
37596 * Integral Datatypes::
37598 * Memory Transfer::
37603 @node Integral Datatypes
37604 @unnumberedsubsubsec Integral Datatypes
37605 @cindex integral datatypes, in file-i/o protocol
37607 The integral datatypes used in the system calls are @code{int},
37608 @code{unsigned int}, @code{long}, @code{unsigned long},
37609 @code{mode_t}, and @code{time_t}.
37611 @code{int}, @code{unsigned int}, @code{mode_t} and @code{time_t} are
37612 implemented as 32 bit values in this protocol.
37614 @code{long} and @code{unsigned long} are implemented as 64 bit types.
37616 @xref{Limits}, for corresponding MIN and MAX values (similar to those
37617 in @file{limits.h}) to allow range checking on host and target.
37619 @code{time_t} datatypes are defined as seconds since the Epoch.
37621 All integral datatypes transferred as part of a memory read or write of a
37622 structured datatype e.g.@: a @code{struct stat} have to be given in big endian
37625 @node Pointer Values
37626 @unnumberedsubsubsec Pointer Values
37627 @cindex pointer values, in file-i/o protocol
37629 Pointers to target data are transmitted as they are. An exception
37630 is made for pointers to buffers for which the length isn't
37631 transmitted as part of the function call, namely strings. Strings
37632 are transmitted as a pointer/length pair, both as hex values, e.g.@:
37639 which is a pointer to data of length 18 bytes at position 0x1aaf.
37640 The length is defined as the full string length in bytes, including
37641 the trailing null byte. For example, the string @code{"hello world"}
37642 at address 0x123456 is transmitted as
37648 @node Memory Transfer
37649 @unnumberedsubsubsec Memory Transfer
37650 @cindex memory transfer, in file-i/o protocol
37652 Structured data which is transferred using a memory read or write (for
37653 example, a @code{struct stat}) is expected to be in a protocol-specific format
37654 with all scalar multibyte datatypes being big endian. Translation to
37655 this representation needs to be done both by the target before the @code{F}
37656 packet is sent, and by @value{GDBN} before
37657 it transfers memory to the target. Transferred pointers to structured
37658 data should point to the already-coerced data at any time.
37662 @unnumberedsubsubsec struct stat
37663 @cindex struct stat, in file-i/o protocol
37665 The buffer of type @code{struct stat} used by the target and @value{GDBN}
37666 is defined as follows:
37670 unsigned int st_dev; /* device */
37671 unsigned int st_ino; /* inode */
37672 mode_t st_mode; /* protection */
37673 unsigned int st_nlink; /* number of hard links */
37674 unsigned int st_uid; /* user ID of owner */
37675 unsigned int st_gid; /* group ID of owner */
37676 unsigned int st_rdev; /* device type (if inode device) */
37677 unsigned long st_size; /* total size, in bytes */
37678 unsigned long st_blksize; /* blocksize for filesystem I/O */
37679 unsigned long st_blocks; /* number of blocks allocated */
37680 time_t st_atime; /* time of last access */
37681 time_t st_mtime; /* time of last modification */
37682 time_t st_ctime; /* time of last change */
37686 The integral datatypes conform to the definitions given in the
37687 appropriate section (see @ref{Integral Datatypes}, for details) so this
37688 structure is of size 64 bytes.
37690 The values of several fields have a restricted meaning and/or
37696 A value of 0 represents a file, 1 the console.
37699 No valid meaning for the target. Transmitted unchanged.
37702 Valid mode bits are described in @ref{Constants}. Any other
37703 bits have currently no meaning for the target.
37708 No valid meaning for the target. Transmitted unchanged.
37713 These values have a host and file system dependent
37714 accuracy. Especially on Windows hosts, the file system may not
37715 support exact timing values.
37718 The target gets a @code{struct stat} of the above representation and is
37719 responsible for coercing it to the target representation before
37722 Note that due to size differences between the host, target, and protocol
37723 representations of @code{struct stat} members, these members could eventually
37724 get truncated on the target.
37726 @node struct timeval
37727 @unnumberedsubsubsec struct timeval
37728 @cindex struct timeval, in file-i/o protocol
37730 The buffer of type @code{struct timeval} used by the File-I/O protocol
37731 is defined as follows:
37735 time_t tv_sec; /* second */
37736 long tv_usec; /* microsecond */
37740 The integral datatypes conform to the definitions given in the
37741 appropriate section (see @ref{Integral Datatypes}, for details) so this
37742 structure is of size 8 bytes.
37745 @subsection Constants
37746 @cindex constants, in file-i/o protocol
37748 The following values are used for the constants inside of the
37749 protocol. @value{GDBN} and target are responsible for translating these
37750 values before and after the call as needed.
37761 @unnumberedsubsubsec Open Flags
37762 @cindex open flags, in file-i/o protocol
37764 All values are given in hexadecimal representation.
37776 @node mode_t Values
37777 @unnumberedsubsubsec mode_t Values
37778 @cindex mode_t values, in file-i/o protocol
37780 All values are given in octal representation.
37797 @unnumberedsubsubsec Errno Values
37798 @cindex errno values, in file-i/o protocol
37800 All values are given in decimal representation.
37825 @code{EUNKNOWN} is used as a fallback error value if a host system returns
37826 any error value not in the list of supported error numbers.
37829 @unnumberedsubsubsec Lseek Flags
37830 @cindex lseek flags, in file-i/o protocol
37839 @unnumberedsubsubsec Limits
37840 @cindex limits, in file-i/o protocol
37842 All values are given in decimal representation.
37845 INT_MIN -2147483648
37847 UINT_MAX 4294967295
37848 LONG_MIN -9223372036854775808
37849 LONG_MAX 9223372036854775807
37850 ULONG_MAX 18446744073709551615
37853 @node File-I/O Examples
37854 @subsection File-I/O Examples
37855 @cindex file-i/o examples
37857 Example sequence of a write call, file descriptor 3, buffer is at target
37858 address 0x1234, 6 bytes should be written:
37861 <- @code{Fwrite,3,1234,6}
37862 @emph{request memory read from target}
37865 @emph{return "6 bytes written"}
37869 Example sequence of a read call, file descriptor 3, buffer is at target
37870 address 0x1234, 6 bytes should be read:
37873 <- @code{Fread,3,1234,6}
37874 @emph{request memory write to target}
37875 -> @code{X1234,6:XXXXXX}
37876 @emph{return "6 bytes read"}
37880 Example sequence of a read call, call fails on the host due to invalid
37881 file descriptor (@code{EBADF}):
37884 <- @code{Fread,3,1234,6}
37888 Example sequence of a read call, user presses @kbd{Ctrl-c} before syscall on
37892 <- @code{Fread,3,1234,6}
37897 Example sequence of a read call, user presses @kbd{Ctrl-c} after syscall on
37901 <- @code{Fread,3,1234,6}
37902 -> @code{X1234,6:XXXXXX}
37906 @node Library List Format
37907 @section Library List Format
37908 @cindex library list format, remote protocol
37910 On some platforms, a dynamic loader (e.g.@: @file{ld.so}) runs in the
37911 same process as your application to manage libraries. In this case,
37912 @value{GDBN} can use the loader's symbol table and normal memory
37913 operations to maintain a list of shared libraries. On other
37914 platforms, the operating system manages loaded libraries.
37915 @value{GDBN} can not retrieve the list of currently loaded libraries
37916 through memory operations, so it uses the @samp{qXfer:libraries:read}
37917 packet (@pxref{qXfer library list read}) instead. The remote stub
37918 queries the target's operating system and reports which libraries
37921 The @samp{qXfer:libraries:read} packet returns an XML document which
37922 lists loaded libraries and their offsets. Each library has an
37923 associated name and one or more segment or section base addresses,
37924 which report where the library was loaded in memory.
37926 For the common case of libraries that are fully linked binaries, the
37927 library should have a list of segments. If the target supports
37928 dynamic linking of a relocatable object file, its library XML element
37929 should instead include a list of allocated sections. The segment or
37930 section bases are start addresses, not relocation offsets; they do not
37931 depend on the library's link-time base addresses.
37933 @value{GDBN} must be linked with the Expat library to support XML
37934 library lists. @xref{Expat}.
37936 A simple memory map, with one loaded library relocated by a single
37937 offset, looks like this:
37941 <library name="/lib/libc.so.6">
37942 <segment address="0x10000000"/>
37947 Another simple memory map, with one loaded library with three
37948 allocated sections (.text, .data, .bss), looks like this:
37952 <library name="sharedlib.o">
37953 <section address="0x10000000"/>
37954 <section address="0x20000000"/>
37955 <section address="0x30000000"/>
37960 The format of a library list is described by this DTD:
37963 <!-- library-list: Root element with versioning -->
37964 <!ELEMENT library-list (library)*>
37965 <!ATTLIST library-list version CDATA #FIXED "1.0">
37966 <!ELEMENT library (segment*, section*)>
37967 <!ATTLIST library name CDATA #REQUIRED>
37968 <!ELEMENT segment EMPTY>
37969 <!ATTLIST segment address CDATA #REQUIRED>
37970 <!ELEMENT section EMPTY>
37971 <!ATTLIST section address CDATA #REQUIRED>
37974 In addition, segments and section descriptors cannot be mixed within a
37975 single library element, and you must supply at least one segment or
37976 section for each library.
37978 @node Library List Format for SVR4 Targets
37979 @section Library List Format for SVR4 Targets
37980 @cindex library list format, remote protocol
37982 On SVR4 platforms @value{GDBN} can use the symbol table of a dynamic loader
37983 (e.g.@: @file{ld.so}) and normal memory operations to maintain a list of
37984 shared libraries. Still a special library list provided by this packet is
37985 more efficient for the @value{GDBN} remote protocol.
37987 The @samp{qXfer:libraries-svr4:read} packet returns an XML document which lists
37988 loaded libraries and their SVR4 linker parameters. For each library on SVR4
37989 target, the following parameters are reported:
37993 @code{name}, the absolute file name from the @code{l_name} field of
37994 @code{struct link_map}.
37996 @code{lm} with address of @code{struct link_map} used for TLS
37997 (Thread Local Storage) access.
37999 @code{l_addr}, the displacement as read from the field @code{l_addr} of
38000 @code{struct link_map}. For prelinked libraries this is not an absolute
38001 memory address. It is a displacement of absolute memory address against
38002 address the file was prelinked to during the library load.
38004 @code{l_ld}, which is memory address of the @code{PT_DYNAMIC} segment
38007 Additionally the single @code{main-lm} attribute specifies address of
38008 @code{struct link_map} used for the main executable. This parameter is used
38009 for TLS access and its presence is optional.
38011 @value{GDBN} must be linked with the Expat library to support XML
38012 SVR4 library lists. @xref{Expat}.
38014 A simple memory map, with two loaded libraries (which do not use prelink),
38018 <library-list-svr4 version="1.0" main-lm="0xe4f8f8">
38019 <library name="/lib/ld-linux.so.2" lm="0xe4f51c" l_addr="0xe2d000"
38021 <library name="/lib/libc.so.6" lm="0xe4fbe8" l_addr="0x154000"
38023 </library-list-svr>
38026 The format of an SVR4 library list is described by this DTD:
38029 <!-- library-list-svr4: Root element with versioning -->
38030 <!ELEMENT library-list-svr4 (library)*>
38031 <!ATTLIST library-list-svr4 version CDATA #FIXED "1.0">
38032 <!ATTLIST library-list-svr4 main-lm CDATA #IMPLIED>
38033 <!ELEMENT library EMPTY>
38034 <!ATTLIST library name CDATA #REQUIRED>
38035 <!ATTLIST library lm CDATA #REQUIRED>
38036 <!ATTLIST library l_addr CDATA #REQUIRED>
38037 <!ATTLIST library l_ld CDATA #REQUIRED>
38040 @node Memory Map Format
38041 @section Memory Map Format
38042 @cindex memory map format
38044 To be able to write into flash memory, @value{GDBN} needs to obtain a
38045 memory map from the target. This section describes the format of the
38048 The memory map is obtained using the @samp{qXfer:memory-map:read}
38049 (@pxref{qXfer memory map read}) packet and is an XML document that
38050 lists memory regions.
38052 @value{GDBN} must be linked with the Expat library to support XML
38053 memory maps. @xref{Expat}.
38055 The top-level structure of the document is shown below:
38058 <?xml version="1.0"?>
38059 <!DOCTYPE memory-map
38060 PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
38061 "http://sourceware.org/gdb/gdb-memory-map.dtd">
38067 Each region can be either:
38072 A region of RAM starting at @var{addr} and extending for @var{length}
38076 <memory type="ram" start="@var{addr}" length="@var{length}"/>
38081 A region of read-only memory:
38084 <memory type="rom" start="@var{addr}" length="@var{length}"/>
38089 A region of flash memory, with erasure blocks @var{blocksize}
38093 <memory type="flash" start="@var{addr}" length="@var{length}">
38094 <property name="blocksize">@var{blocksize}</property>
38100 Regions must not overlap. @value{GDBN} assumes that areas of memory not covered
38101 by the memory map are RAM, and uses the ordinary @samp{M} and @samp{X}
38102 packets to write to addresses in such ranges.
38104 The formal DTD for memory map format is given below:
38107 <!-- ................................................... -->
38108 <!-- Memory Map XML DTD ................................ -->
38109 <!-- File: memory-map.dtd .............................. -->
38110 <!-- .................................... .............. -->
38111 <!-- memory-map.dtd -->
38112 <!-- memory-map: Root element with versioning -->
38113 <!ELEMENT memory-map (memory | property)>
38114 <!ATTLIST memory-map version CDATA #FIXED "1.0.0">
38115 <!ELEMENT memory (property)>
38116 <!-- memory: Specifies a memory region,
38117 and its type, or device. -->
38118 <!ATTLIST memory type CDATA #REQUIRED
38119 start CDATA #REQUIRED
38120 length CDATA #REQUIRED
38121 device CDATA #IMPLIED>
38122 <!-- property: Generic attribute tag -->
38123 <!ELEMENT property (#PCDATA | property)*>
38124 <!ATTLIST property name CDATA #REQUIRED>
38127 @node Thread List Format
38128 @section Thread List Format
38129 @cindex thread list format
38131 To efficiently update the list of threads and their attributes,
38132 @value{GDBN} issues the @samp{qXfer:threads:read} packet
38133 (@pxref{qXfer threads read}) and obtains the XML document with
38134 the following structure:
38137 <?xml version="1.0"?>
38139 <thread id="id" core="0">
38140 ... description ...
38145 Each @samp{thread} element must have the @samp{id} attribute that
38146 identifies the thread (@pxref{thread-id syntax}). The
38147 @samp{core} attribute, if present, specifies which processor core
38148 the thread was last executing on. The content of the of @samp{thread}
38149 element is interpreted as human-readable auxilliary information.
38151 @node Traceframe Info Format
38152 @section Traceframe Info Format
38153 @cindex traceframe info format
38155 To be able to know which objects in the inferior can be examined when
38156 inspecting a tracepoint hit, @value{GDBN} needs to obtain the list of
38157 memory ranges, registers and trace state variables that have been
38158 collected in a traceframe.
38160 This list is obtained using the @samp{qXfer:traceframe-info:read}
38161 (@pxref{qXfer traceframe info read}) packet and is an XML document.
38163 @value{GDBN} must be linked with the Expat library to support XML
38164 traceframe info discovery. @xref{Expat}.
38166 The top-level structure of the document is shown below:
38169 <?xml version="1.0"?>
38170 <!DOCTYPE traceframe-info
38171 PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
38172 "http://sourceware.org/gdb/gdb-traceframe-info.dtd">
38178 Each traceframe block can be either:
38183 A region of collected memory starting at @var{addr} and extending for
38184 @var{length} bytes from there:
38187 <memory start="@var{addr}" length="@var{length}"/>
38192 The formal DTD for the traceframe info format is given below:
38195 <!ELEMENT traceframe-info (memory)* >
38196 <!ATTLIST traceframe-info version CDATA #FIXED "1.0">
38198 <!ELEMENT memory EMPTY>
38199 <!ATTLIST memory start CDATA #REQUIRED
38200 length CDATA #REQUIRED>
38203 @include agentexpr.texi
38205 @node Target Descriptions
38206 @appendix Target Descriptions
38207 @cindex target descriptions
38209 One of the challenges of using @value{GDBN} to debug embedded systems
38210 is that there are so many minor variants of each processor
38211 architecture in use. It is common practice for vendors to start with
38212 a standard processor core --- ARM, PowerPC, or MIPS, for example ---
38213 and then make changes to adapt it to a particular market niche. Some
38214 architectures have hundreds of variants, available from dozens of
38215 vendors. This leads to a number of problems:
38219 With so many different customized processors, it is difficult for
38220 the @value{GDBN} maintainers to keep up with the changes.
38222 Since individual variants may have short lifetimes or limited
38223 audiences, it may not be worthwhile to carry information about every
38224 variant in the @value{GDBN} source tree.
38226 When @value{GDBN} does support the architecture of the embedded system
38227 at hand, the task of finding the correct architecture name to give the
38228 @command{set architecture} command can be error-prone.
38231 To address these problems, the @value{GDBN} remote protocol allows a
38232 target system to not only identify itself to @value{GDBN}, but to
38233 actually describe its own features. This lets @value{GDBN} support
38234 processor variants it has never seen before --- to the extent that the
38235 descriptions are accurate, and that @value{GDBN} understands them.
38237 @value{GDBN} must be linked with the Expat library to support XML
38238 target descriptions. @xref{Expat}.
38241 * Retrieving Descriptions:: How descriptions are fetched from a target.
38242 * Target Description Format:: The contents of a target description.
38243 * Predefined Target Types:: Standard types available for target
38245 * Standard Target Features:: Features @value{GDBN} knows about.
38248 @node Retrieving Descriptions
38249 @section Retrieving Descriptions
38251 Target descriptions can be read from the target automatically, or
38252 specified by the user manually. The default behavior is to read the
38253 description from the target. @value{GDBN} retrieves it via the remote
38254 protocol using @samp{qXfer} requests (@pxref{General Query Packets,
38255 qXfer}). The @var{annex} in the @samp{qXfer} packet will be
38256 @samp{target.xml}. The contents of the @samp{target.xml} annex are an
38257 XML document, of the form described in @ref{Target Description
38260 Alternatively, you can specify a file to read for the target description.
38261 If a file is set, the target will not be queried. The commands to
38262 specify a file are:
38265 @cindex set tdesc filename
38266 @item set tdesc filename @var{path}
38267 Read the target description from @var{path}.
38269 @cindex unset tdesc filename
38270 @item unset tdesc filename
38271 Do not read the XML target description from a file. @value{GDBN}
38272 will use the description supplied by the current target.
38274 @cindex show tdesc filename
38275 @item show tdesc filename
38276 Show the filename to read for a target description, if any.
38280 @node Target Description Format
38281 @section Target Description Format
38282 @cindex target descriptions, XML format
38284 A target description annex is an @uref{http://www.w3.org/XML/, XML}
38285 document which complies with the Document Type Definition provided in
38286 the @value{GDBN} sources in @file{gdb/features/gdb-target.dtd}. This
38287 means you can use generally available tools like @command{xmllint} to
38288 check that your feature descriptions are well-formed and valid.
38289 However, to help people unfamiliar with XML write descriptions for
38290 their targets, we also describe the grammar here.
38292 Target descriptions can identify the architecture of the remote target
38293 and (for some architectures) provide information about custom register
38294 sets. They can also identify the OS ABI of the remote target.
38295 @value{GDBN} can use this information to autoconfigure for your
38296 target, or to warn you if you connect to an unsupported target.
38298 Here is a simple target description:
38301 <target version="1.0">
38302 <architecture>i386:x86-64</architecture>
38307 This minimal description only says that the target uses
38308 the x86-64 architecture.
38310 A target description has the following overall form, with [ ] marking
38311 optional elements and @dots{} marking repeatable elements. The elements
38312 are explained further below.
38315 <?xml version="1.0"?>
38316 <!DOCTYPE target SYSTEM "gdb-target.dtd">
38317 <target version="1.0">
38318 @r{[}@var{architecture}@r{]}
38319 @r{[}@var{osabi}@r{]}
38320 @r{[}@var{compatible}@r{]}
38321 @r{[}@var{feature}@dots{}@r{]}
38326 The description is generally insensitive to whitespace and line
38327 breaks, under the usual common-sense rules. The XML version
38328 declaration and document type declaration can generally be omitted
38329 (@value{GDBN} does not require them), but specifying them may be
38330 useful for XML validation tools. The @samp{version} attribute for
38331 @samp{<target>} may also be omitted, but we recommend
38332 including it; if future versions of @value{GDBN} use an incompatible
38333 revision of @file{gdb-target.dtd}, they will detect and report
38334 the version mismatch.
38336 @subsection Inclusion
38337 @cindex target descriptions, inclusion
38340 @cindex <xi:include>
38343 It can sometimes be valuable to split a target description up into
38344 several different annexes, either for organizational purposes, or to
38345 share files between different possible target descriptions. You can
38346 divide a description into multiple files by replacing any element of
38347 the target description with an inclusion directive of the form:
38350 <xi:include href="@var{document}"/>
38354 When @value{GDBN} encounters an element of this form, it will retrieve
38355 the named XML @var{document}, and replace the inclusion directive with
38356 the contents of that document. If the current description was read
38357 using @samp{qXfer}, then so will be the included document;
38358 @var{document} will be interpreted as the name of an annex. If the
38359 current description was read from a file, @value{GDBN} will look for
38360 @var{document} as a file in the same directory where it found the
38361 original description.
38363 @subsection Architecture
38364 @cindex <architecture>
38366 An @samp{<architecture>} element has this form:
38369 <architecture>@var{arch}</architecture>
38372 @var{arch} is one of the architectures from the set accepted by
38373 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
38376 @cindex @code{<osabi>}
38378 This optional field was introduced in @value{GDBN} version 7.0.
38379 Previous versions of @value{GDBN} ignore it.
38381 An @samp{<osabi>} element has this form:
38384 <osabi>@var{abi-name}</osabi>
38387 @var{abi-name} is an OS ABI name from the same selection accepted by
38388 @w{@code{set osabi}} (@pxref{ABI, ,Configuring the Current ABI}).
38390 @subsection Compatible Architecture
38391 @cindex @code{<compatible>}
38393 This optional field was introduced in @value{GDBN} version 7.0.
38394 Previous versions of @value{GDBN} ignore it.
38396 A @samp{<compatible>} element has this form:
38399 <compatible>@var{arch}</compatible>
38402 @var{arch} is one of the architectures from the set accepted by
38403 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
38405 A @samp{<compatible>} element is used to specify that the target
38406 is able to run binaries in some other than the main target architecture
38407 given by the @samp{<architecture>} element. For example, on the
38408 Cell Broadband Engine, the main architecture is @code{powerpc:common}
38409 or @code{powerpc:common64}, but the system is able to run binaries
38410 in the @code{spu} architecture as well. The way to describe this
38411 capability with @samp{<compatible>} is as follows:
38414 <architecture>powerpc:common</architecture>
38415 <compatible>spu</compatible>
38418 @subsection Features
38421 Each @samp{<feature>} describes some logical portion of the target
38422 system. Features are currently used to describe available CPU
38423 registers and the types of their contents. A @samp{<feature>} element
38427 <feature name="@var{name}">
38428 @r{[}@var{type}@dots{}@r{]}
38434 Each feature's name should be unique within the description. The name
38435 of a feature does not matter unless @value{GDBN} has some special
38436 knowledge of the contents of that feature; if it does, the feature
38437 should have its standard name. @xref{Standard Target Features}.
38441 Any register's value is a collection of bits which @value{GDBN} must
38442 interpret. The default interpretation is a two's complement integer,
38443 but other types can be requested by name in the register description.
38444 Some predefined types are provided by @value{GDBN} (@pxref{Predefined
38445 Target Types}), and the description can define additional composite types.
38447 Each type element must have an @samp{id} attribute, which gives
38448 a unique (within the containing @samp{<feature>}) name to the type.
38449 Types must be defined before they are used.
38452 Some targets offer vector registers, which can be treated as arrays
38453 of scalar elements. These types are written as @samp{<vector>} elements,
38454 specifying the array element type, @var{type}, and the number of elements,
38458 <vector id="@var{id}" type="@var{type}" count="@var{count}"/>
38462 If a register's value is usefully viewed in multiple ways, define it
38463 with a union type containing the useful representations. The
38464 @samp{<union>} element contains one or more @samp{<field>} elements,
38465 each of which has a @var{name} and a @var{type}:
38468 <union id="@var{id}">
38469 <field name="@var{name}" type="@var{type}"/>
38475 If a register's value is composed from several separate values, define
38476 it with a structure type. There are two forms of the @samp{<struct>}
38477 element; a @samp{<struct>} element must either contain only bitfields
38478 or contain no bitfields. If the structure contains only bitfields,
38479 its total size in bytes must be specified, each bitfield must have an
38480 explicit start and end, and bitfields are automatically assigned an
38481 integer type. The field's @var{start} should be less than or
38482 equal to its @var{end}, and zero represents the least significant bit.
38485 <struct id="@var{id}" size="@var{size}">
38486 <field name="@var{name}" start="@var{start}" end="@var{end}"/>
38491 If the structure contains no bitfields, then each field has an
38492 explicit type, and no implicit padding is added.
38495 <struct id="@var{id}">
38496 <field name="@var{name}" type="@var{type}"/>
38502 If a register's value is a series of single-bit flags, define it with
38503 a flags type. The @samp{<flags>} element has an explicit @var{size}
38504 and contains one or more @samp{<field>} elements. Each field has a
38505 @var{name}, a @var{start}, and an @var{end}. Only single-bit flags
38509 <flags id="@var{id}" size="@var{size}">
38510 <field name="@var{name}" start="@var{start}" end="@var{end}"/>
38515 @subsection Registers
38518 Each register is represented as an element with this form:
38521 <reg name="@var{name}"
38522 bitsize="@var{size}"
38523 @r{[}regnum="@var{num}"@r{]}
38524 @r{[}save-restore="@var{save-restore}"@r{]}
38525 @r{[}type="@var{type}"@r{]}
38526 @r{[}group="@var{group}"@r{]}/>
38530 The components are as follows:
38535 The register's name; it must be unique within the target description.
38538 The register's size, in bits.
38541 The register's number. If omitted, a register's number is one greater
38542 than that of the previous register (either in the current feature or in
38543 a preceding feature); the first register in the target description
38544 defaults to zero. This register number is used to read or write
38545 the register; e.g.@: it is used in the remote @code{p} and @code{P}
38546 packets, and registers appear in the @code{g} and @code{G} packets
38547 in order of increasing register number.
38550 Whether the register should be preserved across inferior function
38551 calls; this must be either @code{yes} or @code{no}. The default is
38552 @code{yes}, which is appropriate for most registers except for
38553 some system control registers; this is not related to the target's
38557 The type of the register. @var{type} may be a predefined type, a type
38558 defined in the current feature, or one of the special types @code{int}
38559 and @code{float}. @code{int} is an integer type of the correct size
38560 for @var{bitsize}, and @code{float} is a floating point type (in the
38561 architecture's normal floating point format) of the correct size for
38562 @var{bitsize}. The default is @code{int}.
38565 The register group to which this register belongs. @var{group} must
38566 be either @code{general}, @code{float}, or @code{vector}. If no
38567 @var{group} is specified, @value{GDBN} will not display the register
38568 in @code{info registers}.
38572 @node Predefined Target Types
38573 @section Predefined Target Types
38574 @cindex target descriptions, predefined types
38576 Type definitions in the self-description can build up composite types
38577 from basic building blocks, but can not define fundamental types. Instead,
38578 standard identifiers are provided by @value{GDBN} for the fundamental
38579 types. The currently supported types are:
38588 Signed integer types holding the specified number of bits.
38595 Unsigned integer types holding the specified number of bits.
38599 Pointers to unspecified code and data. The program counter and
38600 any dedicated return address register may be marked as code
38601 pointers; printing a code pointer converts it into a symbolic
38602 address. The stack pointer and any dedicated address registers
38603 may be marked as data pointers.
38606 Single precision IEEE floating point.
38609 Double precision IEEE floating point.
38612 The 12-byte extended precision format used by ARM FPA registers.
38615 The 10-byte extended precision format used by x87 registers.
38618 32bit @sc{eflags} register used by x86.
38621 32bit @sc{mxcsr} register used by x86.
38625 @node Standard Target Features
38626 @section Standard Target Features
38627 @cindex target descriptions, standard features
38629 A target description must contain either no registers or all the
38630 target's registers. If the description contains no registers, then
38631 @value{GDBN} will assume a default register layout, selected based on
38632 the architecture. If the description contains any registers, the
38633 default layout will not be used; the standard registers must be
38634 described in the target description, in such a way that @value{GDBN}
38635 can recognize them.
38637 This is accomplished by giving specific names to feature elements
38638 which contain standard registers. @value{GDBN} will look for features
38639 with those names and verify that they contain the expected registers;
38640 if any known feature is missing required registers, or if any required
38641 feature is missing, @value{GDBN} will reject the target
38642 description. You can add additional registers to any of the
38643 standard features --- @value{GDBN} will display them just as if
38644 they were added to an unrecognized feature.
38646 This section lists the known features and their expected contents.
38647 Sample XML documents for these features are included in the
38648 @value{GDBN} source tree, in the directory @file{gdb/features}.
38650 Names recognized by @value{GDBN} should include the name of the
38651 company or organization which selected the name, and the overall
38652 architecture to which the feature applies; so e.g.@: the feature
38653 containing ARM core registers is named @samp{org.gnu.gdb.arm.core}.
38655 The names of registers are not case sensitive for the purpose
38656 of recognizing standard features, but @value{GDBN} will only display
38657 registers using the capitalization used in the description.
38664 * PowerPC Features::
38670 @subsection ARM Features
38671 @cindex target descriptions, ARM features
38673 The @samp{org.gnu.gdb.arm.core} feature is required for non-M-profile
38675 It should contain registers @samp{r0} through @samp{r13}, @samp{sp},
38676 @samp{lr}, @samp{pc}, and @samp{cpsr}.
38678 For M-profile targets (e.g. Cortex-M3), the @samp{org.gnu.gdb.arm.core}
38679 feature is replaced by @samp{org.gnu.gdb.arm.m-profile}. It should contain
38680 registers @samp{r0} through @samp{r13}, @samp{sp}, @samp{lr}, @samp{pc},
38683 The @samp{org.gnu.gdb.arm.fpa} feature is optional. If present, it
38684 should contain registers @samp{f0} through @samp{f7} and @samp{fps}.
38686 The @samp{org.gnu.gdb.xscale.iwmmxt} feature is optional. If present,
38687 it should contain at least registers @samp{wR0} through @samp{wR15} and
38688 @samp{wCGR0} through @samp{wCGR3}. The @samp{wCID}, @samp{wCon},
38689 @samp{wCSSF}, and @samp{wCASF} registers are optional.
38691 The @samp{org.gnu.gdb.arm.vfp} feature is optional. If present, it
38692 should contain at least registers @samp{d0} through @samp{d15}. If
38693 they are present, @samp{d16} through @samp{d31} should also be included.
38694 @value{GDBN} will synthesize the single-precision registers from
38695 halves of the double-precision registers.
38697 The @samp{org.gnu.gdb.arm.neon} feature is optional. It does not
38698 need to contain registers; it instructs @value{GDBN} to display the
38699 VFP double-precision registers as vectors and to synthesize the
38700 quad-precision registers from pairs of double-precision registers.
38701 If this feature is present, @samp{org.gnu.gdb.arm.vfp} must also
38702 be present and include 32 double-precision registers.
38704 @node i386 Features
38705 @subsection i386 Features
38706 @cindex target descriptions, i386 features
38708 The @samp{org.gnu.gdb.i386.core} feature is required for i386/amd64
38709 targets. It should describe the following registers:
38713 @samp{eax} through @samp{edi} plus @samp{eip} for i386
38715 @samp{rax} through @samp{r15} plus @samp{rip} for amd64
38717 @samp{eflags}, @samp{cs}, @samp{ss}, @samp{ds}, @samp{es},
38718 @samp{fs}, @samp{gs}
38720 @samp{st0} through @samp{st7}
38722 @samp{fctrl}, @samp{fstat}, @samp{ftag}, @samp{fiseg}, @samp{fioff},
38723 @samp{foseg}, @samp{fooff} and @samp{fop}
38726 The register sets may be different, depending on the target.
38728 The @samp{org.gnu.gdb.i386.sse} feature is optional. It should
38729 describe registers:
38733 @samp{xmm0} through @samp{xmm7} for i386
38735 @samp{xmm0} through @samp{xmm15} for amd64
38740 The @samp{org.gnu.gdb.i386.avx} feature is optional and requires the
38741 @samp{org.gnu.gdb.i386.sse} feature. It should
38742 describe the upper 128 bits of @sc{ymm} registers:
38746 @samp{ymm0h} through @samp{ymm7h} for i386
38748 @samp{ymm0h} through @samp{ymm15h} for amd64
38751 The @samp{org.gnu.gdb.i386.linux} feature is optional. It should
38752 describe a single register, @samp{orig_eax}.
38754 @node MIPS Features
38755 @subsection MIPS Features
38756 @cindex target descriptions, MIPS features
38758 The @samp{org.gnu.gdb.mips.cpu} feature is required for MIPS targets.
38759 It should contain registers @samp{r0} through @samp{r31}, @samp{lo},
38760 @samp{hi}, and @samp{pc}. They may be 32-bit or 64-bit depending
38763 The @samp{org.gnu.gdb.mips.cp0} feature is also required. It should
38764 contain at least the @samp{status}, @samp{badvaddr}, and @samp{cause}
38765 registers. They may be 32-bit or 64-bit depending on the target.
38767 The @samp{org.gnu.gdb.mips.fpu} feature is currently required, though
38768 it may be optional in a future version of @value{GDBN}. It should
38769 contain registers @samp{f0} through @samp{f31}, @samp{fcsr}, and
38770 @samp{fir}. They may be 32-bit or 64-bit depending on the target.
38772 The @samp{org.gnu.gdb.mips.dsp} feature is optional. It should
38773 contain registers @samp{hi1} through @samp{hi3}, @samp{lo1} through
38774 @samp{lo3}, and @samp{dspctl}. The @samp{dspctl} register should
38775 be 32-bit and the rest may be 32-bit or 64-bit depending on the target.
38777 The @samp{org.gnu.gdb.mips.linux} feature is optional. It should
38778 contain a single register, @samp{restart}, which is used by the
38779 Linux kernel to control restartable syscalls.
38781 @node M68K Features
38782 @subsection M68K Features
38783 @cindex target descriptions, M68K features
38786 @item @samp{org.gnu.gdb.m68k.core}
38787 @itemx @samp{org.gnu.gdb.coldfire.core}
38788 @itemx @samp{org.gnu.gdb.fido.core}
38789 One of those features must be always present.
38790 The feature that is present determines which flavor of m68k is
38791 used. The feature that is present should contain registers
38792 @samp{d0} through @samp{d7}, @samp{a0} through @samp{a5}, @samp{fp},
38793 @samp{sp}, @samp{ps} and @samp{pc}.
38795 @item @samp{org.gnu.gdb.coldfire.fp}
38796 This feature is optional. If present, it should contain registers
38797 @samp{fp0} through @samp{fp7}, @samp{fpcontrol}, @samp{fpstatus} and
38801 @node PowerPC Features
38802 @subsection PowerPC Features
38803 @cindex target descriptions, PowerPC features
38805 The @samp{org.gnu.gdb.power.core} feature is required for PowerPC
38806 targets. It should contain registers @samp{r0} through @samp{r31},
38807 @samp{pc}, @samp{msr}, @samp{cr}, @samp{lr}, @samp{ctr}, and
38808 @samp{xer}. They may be 32-bit or 64-bit depending on the target.
38810 The @samp{org.gnu.gdb.power.fpu} feature is optional. It should
38811 contain registers @samp{f0} through @samp{f31} and @samp{fpscr}.
38813 The @samp{org.gnu.gdb.power.altivec} feature is optional. It should
38814 contain registers @samp{vr0} through @samp{vr31}, @samp{vscr},
38817 The @samp{org.gnu.gdb.power.vsx} feature is optional. It should
38818 contain registers @samp{vs0h} through @samp{vs31h}. @value{GDBN}
38819 will combine these registers with the floating point registers
38820 (@samp{f0} through @samp{f31}) and the altivec registers (@samp{vr0}
38821 through @samp{vr31}) to present the 128-bit wide registers @samp{vs0}
38822 through @samp{vs63}, the set of vector registers for POWER7.
38824 The @samp{org.gnu.gdb.power.spe} feature is optional. It should
38825 contain registers @samp{ev0h} through @samp{ev31h}, @samp{acc}, and
38826 @samp{spefscr}. SPE targets should provide 32-bit registers in
38827 @samp{org.gnu.gdb.power.core} and provide the upper halves in
38828 @samp{ev0h} through @samp{ev31h}. @value{GDBN} will combine
38829 these to present registers @samp{ev0} through @samp{ev31} to the
38832 @node TIC6x Features
38833 @subsection TMS320C6x Features
38834 @cindex target descriptions, TIC6x features
38835 @cindex target descriptions, TMS320C6x features
38836 The @samp{org.gnu.gdb.tic6x.core} feature is required for TMS320C6x
38837 targets. It should contain registers @samp{A0} through @samp{A15},
38838 registers @samp{B0} through @samp{B15}, @samp{CSR} and @samp{PC}.
38840 The @samp{org.gnu.gdb.tic6x.gp} feature is optional. It should
38841 contain registers @samp{A16} through @samp{A31} and @samp{B16}
38842 through @samp{B31}.
38844 The @samp{org.gnu.gdb.tic6x.c6xp} feature is optional. It should
38845 contain registers @samp{TSR}, @samp{ILC} and @samp{RILC}.
38847 @node Operating System Information
38848 @appendix Operating System Information
38849 @cindex operating system information
38855 Users of @value{GDBN} often wish to obtain information about the state of
38856 the operating system running on the target---for example the list of
38857 processes, or the list of open files. This section describes the
38858 mechanism that makes it possible. This mechanism is similar to the
38859 target features mechanism (@pxref{Target Descriptions}), but focuses
38860 on a different aspect of target.
38862 Operating system information is retrived from the target via the
38863 remote protocol, using @samp{qXfer} requests (@pxref{qXfer osdata
38864 read}). The object name in the request should be @samp{osdata}, and
38865 the @var{annex} identifies the data to be fetched.
38868 @appendixsection Process list
38869 @cindex operating system information, process list
38871 When requesting the process list, the @var{annex} field in the
38872 @samp{qXfer} request should be @samp{processes}. The returned data is
38873 an XML document. The formal syntax of this document is defined in
38874 @file{gdb/features/osdata.dtd}.
38876 An example document is:
38879 <?xml version="1.0"?>
38880 <!DOCTYPE target SYSTEM "osdata.dtd">
38881 <osdata type="processes">
38883 <column name="pid">1</column>
38884 <column name="user">root</column>
38885 <column name="command">/sbin/init</column>
38886 <column name="cores">1,2,3</column>
38891 Each item should include a column whose name is @samp{pid}. The value
38892 of that column should identify the process on the target. The
38893 @samp{user} and @samp{command} columns are optional, and will be
38894 displayed by @value{GDBN}. The @samp{cores} column, if present,
38895 should contain a comma-separated list of cores that this process
38896 is running on. Target may provide additional columns,
38897 which @value{GDBN} currently ignores.
38899 @node Trace File Format
38900 @appendix Trace File Format
38901 @cindex trace file format
38903 The trace file comes in three parts: a header, a textual description
38904 section, and a trace frame section with binary data.
38906 The header has the form @code{\x7fTRACE0\n}. The first byte is
38907 @code{0x7f} so as to indicate that the file contains binary data,
38908 while the @code{0} is a version number that may have different values
38911 The description section consists of multiple lines of @sc{ascii} text
38912 separated by newline characters (@code{0xa}). The lines may include a
38913 variety of optional descriptive or context-setting information, such
38914 as tracepoint definitions or register set size. @value{GDBN} will
38915 ignore any line that it does not recognize. An empty line marks the end
38918 @c FIXME add some specific types of data
38920 The trace frame section consists of a number of consecutive frames.
38921 Each frame begins with a two-byte tracepoint number, followed by a
38922 four-byte size giving the amount of data in the frame. The data in
38923 the frame consists of a number of blocks, each introduced by a
38924 character indicating its type (at least register, memory, and trace
38925 state variable). The data in this section is raw binary, not a
38926 hexadecimal or other encoding; its endianness matches the target's
38929 @c FIXME bi-arch may require endianness/arch info in description section
38932 @item R @var{bytes}
38933 Register block. The number and ordering of bytes matches that of a
38934 @code{g} packet in the remote protocol. Note that these are the
38935 actual bytes, in target order and @value{GDBN} register order, not a
38936 hexadecimal encoding.
38938 @item M @var{address} @var{length} @var{bytes}...
38939 Memory block. This is a contiguous block of memory, at the 8-byte
38940 address @var{address}, with a 2-byte length @var{length}, followed by
38941 @var{length} bytes.
38943 @item V @var{number} @var{value}
38944 Trace state variable block. This records the 8-byte signed value
38945 @var{value} of trace state variable numbered @var{number}.
38949 Future enhancements of the trace file format may include additional types
38952 @node Index Section Format
38953 @appendix @code{.gdb_index} section format
38954 @cindex .gdb_index section format
38955 @cindex index section format
38957 This section documents the index section that is created by @code{save
38958 gdb-index} (@pxref{Index Files}). The index section is
38959 DWARF-specific; some knowledge of DWARF is assumed in this
38962 The mapped index file format is designed to be directly
38963 @code{mmap}able on any architecture. In most cases, a datum is
38964 represented using a little-endian 32-bit integer value, called an
38965 @code{offset_type}. Big endian machines must byte-swap the values
38966 before using them. Exceptions to this rule are noted. The data is
38967 laid out such that alignment is always respected.
38969 A mapped index consists of several areas, laid out in order.
38973 The file header. This is a sequence of values, of @code{offset_type}
38974 unless otherwise noted:
38978 The version number, currently 6. Versions 1, 2 and 3 are obsolete.
38979 Version 4 uses a different hashing function from versions 5 and 6.
38980 Version 6 includes symbols for inlined functions, whereas versions
38981 4 and 5 do not. @value{GDBN} will only read version 4 and 5 indices
38982 if the @code{--use-deprecated-index-sections} option is used.
38985 The offset, from the start of the file, of the CU list.
38988 The offset, from the start of the file, of the types CU list. Note
38989 that this area can be empty, in which case this offset will be equal
38990 to the next offset.
38993 The offset, from the start of the file, of the address area.
38996 The offset, from the start of the file, of the symbol table.
38999 The offset, from the start of the file, of the constant pool.
39003 The CU list. This is a sequence of pairs of 64-bit little-endian
39004 values, sorted by the CU offset. The first element in each pair is
39005 the offset of a CU in the @code{.debug_info} section. The second
39006 element in each pair is the length of that CU. References to a CU
39007 elsewhere in the map are done using a CU index, which is just the
39008 0-based index into this table. Note that if there are type CUs, then
39009 conceptually CUs and type CUs form a single list for the purposes of
39013 The types CU list. This is a sequence of triplets of 64-bit
39014 little-endian values. In a triplet, the first value is the CU offset,
39015 the second value is the type offset in the CU, and the third value is
39016 the type signature. The types CU list is not sorted.
39019 The address area. The address area consists of a sequence of address
39020 entries. Each address entry has three elements:
39024 The low address. This is a 64-bit little-endian value.
39027 The high address. This is a 64-bit little-endian value. Like
39028 @code{DW_AT_high_pc}, the value is one byte beyond the end.
39031 The CU index. This is an @code{offset_type} value.
39035 The symbol table. This is an open-addressed hash table. The size of
39036 the hash table is always a power of 2.
39038 Each slot in the hash table consists of a pair of @code{offset_type}
39039 values. The first value is the offset of the symbol's name in the
39040 constant pool. The second value is the offset of the CU vector in the
39043 If both values are 0, then this slot in the hash table is empty. This
39044 is ok because while 0 is a valid constant pool index, it cannot be a
39045 valid index for both a string and a CU vector.
39047 The hash value for a table entry is computed by applying an
39048 iterative hash function to the symbol's name. Starting with an
39049 initial value of @code{r = 0}, each (unsigned) character @samp{c} in
39050 the string is incorporated into the hash using the formula depending on the
39055 The formula is @code{r = r * 67 + c - 113}.
39057 @item Versions 5 and 6
39058 The formula is @code{r = r * 67 + tolower (c) - 113}.
39061 The terminating @samp{\0} is not incorporated into the hash.
39063 The step size used in the hash table is computed via
39064 @code{((hash * 17) & (size - 1)) | 1}, where @samp{hash} is the hash
39065 value, and @samp{size} is the size of the hash table. The step size
39066 is used to find the next candidate slot when handling a hash
39069 The names of C@t{++} symbols in the hash table are canonicalized. We
39070 don't currently have a simple description of the canonicalization
39071 algorithm; if you intend to create new index sections, you must read
39075 The constant pool. This is simply a bunch of bytes. It is organized
39076 so that alignment is correct: CU vectors are stored first, followed by
39079 A CU vector in the constant pool is a sequence of @code{offset_type}
39080 values. The first value is the number of CU indices in the vector.
39081 Each subsequent value is the index of a CU in the CU list. This
39082 element in the hash table is used to indicate which CUs define the
39085 A string in the constant pool is zero-terminated.
39090 @node GNU Free Documentation License
39091 @appendix GNU Free Documentation License
39100 % I think something like @colophon should be in texinfo. In the
39102 \long\def\colophon{\hbox to0pt{}\vfill
39103 \centerline{The body of this manual is set in}
39104 \centerline{\fontname\tenrm,}
39105 \centerline{with headings in {\bf\fontname\tenbf}}
39106 \centerline{and examples in {\tt\fontname\tentt}.}
39107 \centerline{{\it\fontname\tenit\/},}
39108 \centerline{{\bf\fontname\tenbf}, and}
39109 \centerline{{\sl\fontname\tensl\/}}
39110 \centerline{are used for emphasis.}\vfill}
39112 % Blame: doc@cygnus.com, 1991.