1 \input texinfo @c -*-texinfo-*-
2 @c Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,
3 @c 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
4 @c Free Software Foundation, Inc.
7 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
8 @c of @set vars. However, you can override filename with makeinfo -o.
13 @settitle Debugging with @value{GDBN}
14 @setchapternewpage odd
26 @c readline appendices use @vindex, @findex and @ftable,
27 @c annotate.texi and gdbmi use @findex.
31 @c !!set GDB manual's edition---not the same as GDB version!
32 @c This is updated by GNU Press.
35 @c !!set GDB edit command default editor
38 @c THIS MANUAL REQUIRES TEXINFO 4.0 OR LATER.
40 @c This is a dir.info fragment to support semi-automated addition of
41 @c manuals to an info tree.
42 @dircategory Software development
44 * Gdb: (gdb). The GNU debugger.
48 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996,
49 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
50 Free Software Foundation, Inc.
52 Permission is granted to copy, distribute and/or modify this document
53 under the terms of the GNU Free Documentation License, Version 1.1 or
54 any later version published by the Free Software Foundation; with the
55 Invariant Sections being ``Free Software'' and ``Free Software Needs
56 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
57 and with the Back-Cover Texts as in (a) below.
59 (a) The FSF's Back-Cover Text is: ``You are free to copy and modify
60 this GNU Manual. Buying copies from GNU Press supports the FSF in
61 developing GNU and promoting software freedom.''
65 This file documents the @sc{gnu} debugger @value{GDBN}.
67 This is the @value{EDITION} Edition, of @cite{Debugging with
68 @value{GDBN}: the @sc{gnu} Source-Level Debugger} for @value{GDBN}
69 @ifset VERSION_PACKAGE
70 @value{VERSION_PACKAGE}
72 Version @value{GDBVN}.
78 @title Debugging with @value{GDBN}
79 @subtitle The @sc{gnu} Source-Level Debugger
81 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
82 @ifset VERSION_PACKAGE
84 @subtitle @value{VERSION_PACKAGE}
86 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
90 \hfill (Send bugs and comments on @value{GDBN} to @value{BUGURL}.)\par
91 \hfill {\it Debugging with @value{GDBN}}\par
92 \hfill \TeX{}info \texinfoversion\par
96 @vskip 0pt plus 1filll
97 Published by the Free Software Foundation @*
98 51 Franklin Street, Fifth Floor,
99 Boston, MA 02110-1301, USA@*
100 ISBN 1-882114-77-9 @*
104 This edition of the GDB manual is dedicated to the memory of Fred
105 Fish. Fred was a long-standing contributor to GDB and to Free
106 software in general. We will miss him.
111 @node Top, Summary, (dir), (dir)
113 @top Debugging with @value{GDBN}
115 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
117 This is the @value{EDITION} Edition, for @value{GDBN}
118 @ifset VERSION_PACKAGE
119 @value{VERSION_PACKAGE}
121 Version @value{GDBVN}.
123 Copyright (C) 1988-2009 Free Software Foundation, Inc.
125 This edition of the GDB manual is dedicated to the memory of Fred
126 Fish. Fred was a long-standing contributor to GDB and to Free
127 software in general. We will miss him.
130 * Summary:: Summary of @value{GDBN}
131 * Sample Session:: A sample @value{GDBN} session
133 * Invocation:: Getting in and out of @value{GDBN}
134 * Commands:: @value{GDBN} commands
135 * Running:: Running programs under @value{GDBN}
136 * Stopping:: Stopping and continuing
137 * Reverse Execution:: Running programs backward
138 * Process Record and Replay:: Recording inferior's execution and replaying it
139 * Stack:: Examining the stack
140 * Source:: Examining source files
141 * Data:: Examining data
142 * Optimized Code:: Debugging optimized code
143 * Macros:: Preprocessor Macros
144 * Tracepoints:: Debugging remote targets non-intrusively
145 * Overlays:: Debugging programs that use overlays
147 * Languages:: Using @value{GDBN} with different languages
149 * Symbols:: Examining the symbol table
150 * Altering:: Altering execution
151 * GDB Files:: @value{GDBN} files
152 * Targets:: Specifying a debugging target
153 * Remote Debugging:: Debugging remote programs
154 * Configurations:: Configuration-specific information
155 * Controlling GDB:: Controlling @value{GDBN}
156 * Extending GDB:: Extending @value{GDBN}
157 * Interpreters:: Command Interpreters
158 * TUI:: @value{GDBN} Text User Interface
159 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
160 * GDB/MI:: @value{GDBN}'s Machine Interface.
161 * Annotations:: @value{GDBN}'s annotation interface.
162 * JIT Interface:: Using the JIT debugging interface.
164 * GDB Bugs:: Reporting bugs in @value{GDBN}
166 * Command Line Editing:: Command Line Editing
167 * Using History Interactively:: Using History Interactively
168 * Formatting Documentation:: How to format and print @value{GDBN} documentation
169 * Installing GDB:: Installing GDB
170 * Maintenance Commands:: Maintenance Commands
171 * Remote Protocol:: GDB Remote Serial Protocol
172 * Agent Expressions:: The GDB Agent Expression Mechanism
173 * Target Descriptions:: How targets can describe themselves to
175 * Operating System Information:: Getting additional information from
177 * Copying:: GNU General Public License says
178 how you can copy and share GDB
179 * GNU Free Documentation License:: The license for this documentation
188 @unnumbered Summary of @value{GDBN}
190 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
191 going on ``inside'' another program while it executes---or what another
192 program was doing at the moment it crashed.
194 @value{GDBN} can do four main kinds of things (plus other things in support of
195 these) to help you catch bugs in the act:
199 Start your program, specifying anything that might affect its behavior.
202 Make your program stop on specified conditions.
205 Examine what has happened, when your program has stopped.
208 Change things in your program, so you can experiment with correcting the
209 effects of one bug and go on to learn about another.
212 You can use @value{GDBN} to debug programs written in C and C@t{++}.
213 For more information, see @ref{Supported Languages,,Supported Languages}.
214 For more information, see @ref{C,,C and C++}.
217 Support for Modula-2 is partial. For information on Modula-2, see
218 @ref{Modula-2,,Modula-2}.
221 Debugging Pascal programs which use sets, subranges, file variables, or
222 nested functions does not currently work. @value{GDBN} does not support
223 entering expressions, printing values, or similar features using Pascal
227 @value{GDBN} can be used to debug programs written in Fortran, although
228 it may be necessary to refer to some variables with a trailing
231 @value{GDBN} can be used to debug programs written in Objective-C,
232 using either the Apple/NeXT or the GNU Objective-C runtime.
235 * Free Software:: Freely redistributable software
236 * Contributors:: Contributors to GDB
240 @unnumberedsec Free Software
242 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
243 General Public License
244 (GPL). The GPL gives you the freedom to copy or adapt a licensed
245 program---but every person getting a copy also gets with it the
246 freedom to modify that copy (which means that they must get access to
247 the source code), and the freedom to distribute further copies.
248 Typical software companies use copyrights to limit your freedoms; the
249 Free Software Foundation uses the GPL to preserve these freedoms.
251 Fundamentally, the General Public License is a license which says that
252 you have these freedoms and that you cannot take these freedoms away
255 @unnumberedsec Free Software Needs Free Documentation
257 The biggest deficiency in the free software community today is not in
258 the software---it is the lack of good free documentation that we can
259 include with the free software. Many of our most important
260 programs do not come with free reference manuals and free introductory
261 texts. Documentation is an essential part of any software package;
262 when an important free software package does not come with a free
263 manual and a free tutorial, that is a major gap. We have many such
266 Consider Perl, for instance. The tutorial manuals that people
267 normally use are non-free. How did this come about? Because the
268 authors of those manuals published them with restrictive terms---no
269 copying, no modification, source files not available---which exclude
270 them from the free software world.
272 That wasn't the first time this sort of thing happened, and it was far
273 from the last. Many times we have heard a GNU user eagerly describe a
274 manual that he is writing, his intended contribution to the community,
275 only to learn that he had ruined everything by signing a publication
276 contract to make it non-free.
278 Free documentation, like free software, is a matter of freedom, not
279 price. The problem with the non-free manual is not that publishers
280 charge a price for printed copies---that in itself is fine. (The Free
281 Software Foundation sells printed copies of manuals, too.) The
282 problem is the restrictions on the use of the manual. Free manuals
283 are available in source code form, and give you permission to copy and
284 modify. Non-free manuals do not allow this.
286 The criteria of freedom for a free manual are roughly the same as for
287 free software. Redistribution (including the normal kinds of
288 commercial redistribution) must be permitted, so that the manual can
289 accompany every copy of the program, both on-line and on paper.
291 Permission for modification of the technical content is crucial too.
292 When people modify the software, adding or changing features, if they
293 are conscientious they will change the manual too---so they can
294 provide accurate and clear documentation for the modified program. A
295 manual that leaves you no choice but to write a new manual to document
296 a changed version of the program is not really available to our
299 Some kinds of limits on the way modification is handled are
300 acceptable. For example, requirements to preserve the original
301 author's copyright notice, the distribution terms, or the list of
302 authors, are ok. It is also no problem to require modified versions
303 to include notice that they were modified. Even entire sections that
304 may not be deleted or changed are acceptable, as long as they deal
305 with nontechnical topics (like this one). These kinds of restrictions
306 are acceptable because they don't obstruct the community's normal use
309 However, it must be possible to modify all the @emph{technical}
310 content of the manual, and then distribute the result in all the usual
311 media, through all the usual channels. Otherwise, the restrictions
312 obstruct the use of the manual, it is not free, and we need another
313 manual to replace it.
315 Please spread the word about this issue. Our community continues to
316 lose manuals to proprietary publishing. If we spread the word that
317 free software needs free reference manuals and free tutorials, perhaps
318 the next person who wants to contribute by writing documentation will
319 realize, before it is too late, that only free manuals contribute to
320 the free software community.
322 If you are writing documentation, please insist on publishing it under
323 the GNU Free Documentation License or another free documentation
324 license. Remember that this decision requires your approval---you
325 don't have to let the publisher decide. Some commercial publishers
326 will use a free license if you insist, but they will not propose the
327 option; it is up to you to raise the issue and say firmly that this is
328 what you want. If the publisher you are dealing with refuses, please
329 try other publishers. If you're not sure whether a proposed license
330 is free, write to @email{licensing@@gnu.org}.
332 You can encourage commercial publishers to sell more free, copylefted
333 manuals and tutorials by buying them, and particularly by buying
334 copies from the publishers that paid for their writing or for major
335 improvements. Meanwhile, try to avoid buying non-free documentation
336 at all. Check the distribution terms of a manual before you buy it,
337 and insist that whoever seeks your business must respect your freedom.
338 Check the history of the book, and try to reward the publishers that
339 have paid or pay the authors to work on it.
341 The Free Software Foundation maintains a list of free documentation
342 published by other publishers, at
343 @url{http://www.fsf.org/doc/other-free-books.html}.
346 @unnumberedsec Contributors to @value{GDBN}
348 Richard Stallman was the original author of @value{GDBN}, and of many
349 other @sc{gnu} programs. Many others have contributed to its
350 development. This section attempts to credit major contributors. One
351 of the virtues of free software is that everyone is free to contribute
352 to it; with regret, we cannot actually acknowledge everyone here. The
353 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
354 blow-by-blow account.
356 Changes much prior to version 2.0 are lost in the mists of time.
359 @emph{Plea:} Additions to this section are particularly welcome. If you
360 or your friends (or enemies, to be evenhanded) have been unfairly
361 omitted from this list, we would like to add your names!
364 So that they may not regard their many labors as thankless, we
365 particularly thank those who shepherded @value{GDBN} through major
367 Andrew Cagney (releases 6.3, 6.2, 6.1, 6.0, 5.3, 5.2, 5.1 and 5.0);
368 Jim Blandy (release 4.18);
369 Jason Molenda (release 4.17);
370 Stan Shebs (release 4.14);
371 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
372 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
373 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
374 Jim Kingdon (releases 3.5, 3.4, and 3.3);
375 and Randy Smith (releases 3.2, 3.1, and 3.0).
377 Richard Stallman, assisted at various times by Peter TerMaat, Chris
378 Hanson, and Richard Mlynarik, handled releases through 2.8.
380 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
381 in @value{GDBN}, with significant additional contributions from Per
382 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
383 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
384 much general update work leading to release 3.0).
386 @value{GDBN} uses the BFD subroutine library to examine multiple
387 object-file formats; BFD was a joint project of David V.
388 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
390 David Johnson wrote the original COFF support; Pace Willison did
391 the original support for encapsulated COFF.
393 Brent Benson of Harris Computer Systems contributed DWARF 2 support.
395 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
396 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
398 Jean-Daniel Fekete contributed Sun 386i support.
399 Chris Hanson improved the HP9000 support.
400 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
401 David Johnson contributed Encore Umax support.
402 Jyrki Kuoppala contributed Altos 3068 support.
403 Jeff Law contributed HP PA and SOM support.
404 Keith Packard contributed NS32K support.
405 Doug Rabson contributed Acorn Risc Machine support.
406 Bob Rusk contributed Harris Nighthawk CX-UX support.
407 Chris Smith contributed Convex support (and Fortran debugging).
408 Jonathan Stone contributed Pyramid support.
409 Michael Tiemann contributed SPARC support.
410 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
411 Pace Willison contributed Intel 386 support.
412 Jay Vosburgh contributed Symmetry support.
413 Marko Mlinar contributed OpenRISC 1000 support.
415 Andreas Schwab contributed M68K @sc{gnu}/Linux support.
417 Rich Schaefer and Peter Schauer helped with support of SunOS shared
420 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
421 about several machine instruction sets.
423 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
424 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
425 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
426 and RDI targets, respectively.
428 Brian Fox is the author of the readline libraries providing
429 command-line editing and command history.
431 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
432 Modula-2 support, and contributed the Languages chapter of this manual.
434 Fred Fish wrote most of the support for Unix System Vr4.
435 He also enhanced the command-completion support to cover C@t{++} overloaded
438 Hitachi America (now Renesas America), Ltd. sponsored the support for
439 H8/300, H8/500, and Super-H processors.
441 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
443 Mitsubishi (now Renesas) sponsored the support for D10V, D30V, and M32R/D
446 Toshiba sponsored the support for the TX39 Mips processor.
448 Matsushita sponsored the support for the MN10200 and MN10300 processors.
450 Fujitsu sponsored the support for SPARClite and FR30 processors.
452 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
455 Michael Snyder added support for tracepoints.
457 Stu Grossman wrote gdbserver.
459 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
460 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
462 The following people at the Hewlett-Packard Company contributed
463 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
464 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
465 compiler, and the Text User Interface (nee Terminal User Interface):
466 Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann,
467 Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase
468 provided HP-specific information in this manual.
470 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
471 Robert Hoehne made significant contributions to the DJGPP port.
473 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
474 development since 1991. Cygnus engineers who have worked on @value{GDBN}
475 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
476 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
477 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
478 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
479 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
480 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
481 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
482 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
483 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
484 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
485 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
486 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
487 Zuhn have made contributions both large and small.
489 Andrew Cagney, Fernando Nasser, and Elena Zannoni, while working for
490 Cygnus Solutions, implemented the original @sc{gdb/mi} interface.
492 Jim Blandy added support for preprocessor macros, while working for Red
495 Andrew Cagney designed @value{GDBN}'s architecture vector. Many
496 people including Andrew Cagney, Stephane Carrez, Randolph Chung, Nick
497 Duffek, Richard Henderson, Mark Kettenis, Grace Sainsbury, Kei
498 Sakamoto, Yoshinori Sato, Michael Snyder, Andreas Schwab, Jason
499 Thorpe, Corinna Vinschen, Ulrich Weigand, and Elena Zannoni, helped
500 with the migration of old architectures to this new framework.
502 Andrew Cagney completely re-designed and re-implemented @value{GDBN}'s
503 unwinder framework, this consisting of a fresh new design featuring
504 frame IDs, independent frame sniffers, and the sentinel frame. Mark
505 Kettenis implemented the @sc{dwarf 2} unwinder, Jeff Johnston the
506 libunwind unwinder, and Andrew Cagney the dummy, sentinel, tramp, and
507 trad unwinders. The architecture-specific changes, each involving a
508 complete rewrite of the architecture's frame code, were carried out by
509 Jim Blandy, Joel Brobecker, Kevin Buettner, Andrew Cagney, Stephane
510 Carrez, Randolph Chung, Orjan Friberg, Richard Henderson, Daniel
511 Jacobowitz, Jeff Johnston, Mark Kettenis, Theodore A. Roth, Kei
512 Sakamoto, Yoshinori Sato, Michael Snyder, Corinna Vinschen, and Ulrich
515 Christian Zankel, Ross Morley, Bob Wilson, and Maxim Grigoriev from
516 Tensilica, Inc.@: contributed support for Xtensa processors. Others
517 who have worked on the Xtensa port of @value{GDBN} in the past include
518 Steve Tjiang, John Newlin, and Scott Foehner.
521 @chapter A Sample @value{GDBN} Session
523 You can use this manual at your leisure to read all about @value{GDBN}.
524 However, a handful of commands are enough to get started using the
525 debugger. This chapter illustrates those commands.
528 In this sample session, we emphasize user input like this: @b{input},
529 to make it easier to pick out from the surrounding output.
532 @c FIXME: this example may not be appropriate for some configs, where
533 @c FIXME...primary interest is in remote use.
535 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
536 processor) exhibits the following bug: sometimes, when we change its
537 quote strings from the default, the commands used to capture one macro
538 definition within another stop working. In the following short @code{m4}
539 session, we define a macro @code{foo} which expands to @code{0000}; we
540 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
541 same thing. However, when we change the open quote string to
542 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
543 procedure fails to define a new synonym @code{baz}:
552 @b{define(bar,defn(`foo'))}
556 @b{changequote(<QUOTE>,<UNQUOTE>)}
558 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
561 m4: End of input: 0: fatal error: EOF in string
565 Let us use @value{GDBN} to try to see what is going on.
568 $ @b{@value{GDBP} m4}
569 @c FIXME: this falsifies the exact text played out, to permit smallbook
570 @c FIXME... format to come out better.
571 @value{GDBN} is free software and you are welcome to distribute copies
572 of it under certain conditions; type "show copying" to see
574 There is absolutely no warranty for @value{GDBN}; type "show warranty"
577 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
582 @value{GDBN} reads only enough symbol data to know where to find the
583 rest when needed; as a result, the first prompt comes up very quickly.
584 We now tell @value{GDBN} to use a narrower display width than usual, so
585 that examples fit in this manual.
588 (@value{GDBP}) @b{set width 70}
592 We need to see how the @code{m4} built-in @code{changequote} works.
593 Having looked at the source, we know the relevant subroutine is
594 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
595 @code{break} command.
598 (@value{GDBP}) @b{break m4_changequote}
599 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
603 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
604 control; as long as control does not reach the @code{m4_changequote}
605 subroutine, the program runs as usual:
608 (@value{GDBP}) @b{run}
609 Starting program: /work/Editorial/gdb/gnu/m4/m4
617 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
618 suspends execution of @code{m4}, displaying information about the
619 context where it stops.
622 @b{changequote(<QUOTE>,<UNQUOTE>)}
624 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
626 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
630 Now we use the command @code{n} (@code{next}) to advance execution to
631 the next line of the current function.
635 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
640 @code{set_quotes} looks like a promising subroutine. We can go into it
641 by using the command @code{s} (@code{step}) instead of @code{next}.
642 @code{step} goes to the next line to be executed in @emph{any}
643 subroutine, so it steps into @code{set_quotes}.
647 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
649 530 if (lquote != def_lquote)
653 The display that shows the subroutine where @code{m4} is now
654 suspended (and its arguments) is called a stack frame display. It
655 shows a summary of the stack. We can use the @code{backtrace}
656 command (which can also be spelled @code{bt}), to see where we are
657 in the stack as a whole: the @code{backtrace} command displays a
658 stack frame for each active subroutine.
661 (@value{GDBP}) @b{bt}
662 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
664 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
666 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
667 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
669 #4 0x79dc in expand_input () at macro.c:40
670 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
674 We step through a few more lines to see what happens. The first two
675 times, we can use @samp{s}; the next two times we use @code{n} to avoid
676 falling into the @code{xstrdup} subroutine.
680 0x3b5c 532 if (rquote != def_rquote)
682 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
683 def_lquote : xstrdup(lq);
685 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
688 538 len_lquote = strlen(rquote);
692 The last line displayed looks a little odd; we can examine the variables
693 @code{lquote} and @code{rquote} to see if they are in fact the new left
694 and right quotes we specified. We use the command @code{p}
695 (@code{print}) to see their values.
698 (@value{GDBP}) @b{p lquote}
699 $1 = 0x35d40 "<QUOTE>"
700 (@value{GDBP}) @b{p rquote}
701 $2 = 0x35d50 "<UNQUOTE>"
705 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
706 To look at some context, we can display ten lines of source
707 surrounding the current line with the @code{l} (@code{list}) command.
713 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
715 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
718 538 len_lquote = strlen(rquote);
719 539 len_rquote = strlen(lquote);
726 Let us step past the two lines that set @code{len_lquote} and
727 @code{len_rquote}, and then examine the values of those variables.
731 539 len_rquote = strlen(lquote);
734 (@value{GDBP}) @b{p len_lquote}
736 (@value{GDBP}) @b{p len_rquote}
741 That certainly looks wrong, assuming @code{len_lquote} and
742 @code{len_rquote} are meant to be the lengths of @code{lquote} and
743 @code{rquote} respectively. We can set them to better values using
744 the @code{p} command, since it can print the value of
745 any expression---and that expression can include subroutine calls and
749 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
751 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
756 Is that enough to fix the problem of using the new quotes with the
757 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
758 executing with the @code{c} (@code{continue}) command, and then try the
759 example that caused trouble initially:
765 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
772 Success! The new quotes now work just as well as the default ones. The
773 problem seems to have been just the two typos defining the wrong
774 lengths. We allow @code{m4} exit by giving it an EOF as input:
778 Program exited normally.
782 The message @samp{Program exited normally.} is from @value{GDBN}; it
783 indicates @code{m4} has finished executing. We can end our @value{GDBN}
784 session with the @value{GDBN} @code{quit} command.
787 (@value{GDBP}) @b{quit}
791 @chapter Getting In and Out of @value{GDBN}
793 This chapter discusses how to start @value{GDBN}, and how to get out of it.
797 type @samp{@value{GDBP}} to start @value{GDBN}.
799 type @kbd{quit} or @kbd{Ctrl-d} to exit.
803 * Invoking GDB:: How to start @value{GDBN}
804 * Quitting GDB:: How to quit @value{GDBN}
805 * Shell Commands:: How to use shell commands inside @value{GDBN}
806 * Logging Output:: How to log @value{GDBN}'s output to a file
810 @section Invoking @value{GDBN}
812 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
813 @value{GDBN} reads commands from the terminal until you tell it to exit.
815 You can also run @code{@value{GDBP}} with a variety of arguments and options,
816 to specify more of your debugging environment at the outset.
818 The command-line options described here are designed
819 to cover a variety of situations; in some environments, some of these
820 options may effectively be unavailable.
822 The most usual way to start @value{GDBN} is with one argument,
823 specifying an executable program:
826 @value{GDBP} @var{program}
830 You can also start with both an executable program and a core file
834 @value{GDBP} @var{program} @var{core}
837 You can, instead, specify a process ID as a second argument, if you want
838 to debug a running process:
841 @value{GDBP} @var{program} 1234
845 would attach @value{GDBN} to process @code{1234} (unless you also have a file
846 named @file{1234}; @value{GDBN} does check for a core file first).
848 Taking advantage of the second command-line argument requires a fairly
849 complete operating system; when you use @value{GDBN} as a remote
850 debugger attached to a bare board, there may not be any notion of
851 ``process'', and there is often no way to get a core dump. @value{GDBN}
852 will warn you if it is unable to attach or to read core dumps.
854 You can optionally have @code{@value{GDBP}} pass any arguments after the
855 executable file to the inferior using @code{--args}. This option stops
858 @value{GDBP} --args gcc -O2 -c foo.c
860 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
861 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
863 You can run @code{@value{GDBP}} without printing the front material, which describes
864 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
871 You can further control how @value{GDBN} starts up by using command-line
872 options. @value{GDBN} itself can remind you of the options available.
882 to display all available options and briefly describe their use
883 (@samp{@value{GDBP} -h} is a shorter equivalent).
885 All options and command line arguments you give are processed
886 in sequential order. The order makes a difference when the
887 @samp{-x} option is used.
891 * File Options:: Choosing files
892 * Mode Options:: Choosing modes
893 * Startup:: What @value{GDBN} does during startup
897 @subsection Choosing Files
899 When @value{GDBN} starts, it reads any arguments other than options as
900 specifying an executable file and core file (or process ID). This is
901 the same as if the arguments were specified by the @samp{-se} and
902 @samp{-c} (or @samp{-p}) options respectively. (@value{GDBN} reads the
903 first argument that does not have an associated option flag as
904 equivalent to the @samp{-se} option followed by that argument; and the
905 second argument that does not have an associated option flag, if any, as
906 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
907 If the second argument begins with a decimal digit, @value{GDBN} will
908 first attempt to attach to it as a process, and if that fails, attempt
909 to open it as a corefile. If you have a corefile whose name begins with
910 a digit, you can prevent @value{GDBN} from treating it as a pid by
911 prefixing it with @file{./}, e.g.@: @file{./12345}.
913 If @value{GDBN} has not been configured to included core file support,
914 such as for most embedded targets, then it will complain about a second
915 argument and ignore it.
917 Many options have both long and short forms; both are shown in the
918 following list. @value{GDBN} also recognizes the long forms if you truncate
919 them, so long as enough of the option is present to be unambiguous.
920 (If you prefer, you can flag option arguments with @samp{--} rather
921 than @samp{-}, though we illustrate the more usual convention.)
923 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
924 @c way, both those who look for -foo and --foo in the index, will find
928 @item -symbols @var{file}
930 @cindex @code{--symbols}
932 Read symbol table from file @var{file}.
934 @item -exec @var{file}
936 @cindex @code{--exec}
938 Use file @var{file} as the executable file to execute when appropriate,
939 and for examining pure data in conjunction with a core dump.
943 Read symbol table from file @var{file} and use it as the executable
946 @item -core @var{file}
948 @cindex @code{--core}
950 Use file @var{file} as a core dump to examine.
952 @item -pid @var{number}
953 @itemx -p @var{number}
956 Connect to process ID @var{number}, as with the @code{attach} command.
958 @item -command @var{file}
960 @cindex @code{--command}
962 Execute @value{GDBN} commands from file @var{file}. @xref{Command
963 Files,, Command files}.
965 @item -eval-command @var{command}
966 @itemx -ex @var{command}
967 @cindex @code{--eval-command}
969 Execute a single @value{GDBN} command.
971 This option may be used multiple times to call multiple commands. It may
972 also be interleaved with @samp{-command} as required.
975 @value{GDBP} -ex 'target sim' -ex 'load' \
976 -x setbreakpoints -ex 'run' a.out
979 @item -directory @var{directory}
980 @itemx -d @var{directory}
981 @cindex @code{--directory}
983 Add @var{directory} to the path to search for source and script files.
987 @cindex @code{--readnow}
989 Read each symbol file's entire symbol table immediately, rather than
990 the default, which is to read it incrementally as it is needed.
991 This makes startup slower, but makes future operations faster.
996 @subsection Choosing Modes
998 You can run @value{GDBN} in various alternative modes---for example, in
999 batch mode or quiet mode.
1006 Do not execute commands found in any initialization files. Normally,
1007 @value{GDBN} executes the commands in these files after all the command
1008 options and arguments have been processed. @xref{Command Files,,Command
1014 @cindex @code{--quiet}
1015 @cindex @code{--silent}
1017 ``Quiet''. Do not print the introductory and copyright messages. These
1018 messages are also suppressed in batch mode.
1021 @cindex @code{--batch}
1022 Run in batch mode. Exit with status @code{0} after processing all the
1023 command files specified with @samp{-x} (and all commands from
1024 initialization files, if not inhibited with @samp{-n}). Exit with
1025 nonzero status if an error occurs in executing the @value{GDBN} commands
1026 in the command files.
1028 Batch mode may be useful for running @value{GDBN} as a filter, for
1029 example to download and run a program on another computer; in order to
1030 make this more useful, the message
1033 Program exited normally.
1037 (which is ordinarily issued whenever a program running under
1038 @value{GDBN} control terminates) is not issued when running in batch
1042 @cindex @code{--batch-silent}
1043 Run in batch mode exactly like @samp{-batch}, but totally silently. All
1044 @value{GDBN} output to @code{stdout} is prevented (@code{stderr} is
1045 unaffected). This is much quieter than @samp{-silent} and would be useless
1046 for an interactive session.
1048 This is particularly useful when using targets that give @samp{Loading section}
1049 messages, for example.
1051 Note that targets that give their output via @value{GDBN}, as opposed to
1052 writing directly to @code{stdout}, will also be made silent.
1054 @item -return-child-result
1055 @cindex @code{--return-child-result}
1056 The return code from @value{GDBN} will be the return code from the child
1057 process (the process being debugged), with the following exceptions:
1061 @value{GDBN} exits abnormally. E.g., due to an incorrect argument or an
1062 internal error. In this case the exit code is the same as it would have been
1063 without @samp{-return-child-result}.
1065 The user quits with an explicit value. E.g., @samp{quit 1}.
1067 The child process never runs, or is not allowed to terminate, in which case
1068 the exit code will be -1.
1071 This option is useful in conjunction with @samp{-batch} or @samp{-batch-silent},
1072 when @value{GDBN} is being used as a remote program loader or simulator
1077 @cindex @code{--nowindows}
1079 ``No windows''. If @value{GDBN} comes with a graphical user interface
1080 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1081 interface. If no GUI is available, this option has no effect.
1085 @cindex @code{--windows}
1087 If @value{GDBN} includes a GUI, then this option requires it to be
1090 @item -cd @var{directory}
1092 Run @value{GDBN} using @var{directory} as its working directory,
1093 instead of the current directory.
1097 @cindex @code{--fullname}
1099 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1100 subprocess. It tells @value{GDBN} to output the full file name and line
1101 number in a standard, recognizable fashion each time a stack frame is
1102 displayed (which includes each time your program stops). This
1103 recognizable format looks like two @samp{\032} characters, followed by
1104 the file name, line number and character position separated by colons,
1105 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1106 @samp{\032} characters as a signal to display the source code for the
1110 @cindex @code{--epoch}
1111 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1112 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1113 routines so as to allow Epoch to display values of expressions in a
1116 @item -annotate @var{level}
1117 @cindex @code{--annotate}
1118 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1119 effect is identical to using @samp{set annotate @var{level}}
1120 (@pxref{Annotations}). The annotation @var{level} controls how much
1121 information @value{GDBN} prints together with its prompt, values of
1122 expressions, source lines, and other types of output. Level 0 is the
1123 normal, level 1 is for use when @value{GDBN} is run as a subprocess of
1124 @sc{gnu} Emacs, level 3 is the maximum annotation suitable for programs
1125 that control @value{GDBN}, and level 2 has been deprecated.
1127 The annotation mechanism has largely been superseded by @sc{gdb/mi}
1131 @cindex @code{--args}
1132 Change interpretation of command line so that arguments following the
1133 executable file are passed as command line arguments to the inferior.
1134 This option stops option processing.
1136 @item -baud @var{bps}
1138 @cindex @code{--baud}
1140 Set the line speed (baud rate or bits per second) of any serial
1141 interface used by @value{GDBN} for remote debugging.
1143 @item -l @var{timeout}
1145 Set the timeout (in seconds) of any communication used by @value{GDBN}
1146 for remote debugging.
1148 @item -tty @var{device}
1149 @itemx -t @var{device}
1150 @cindex @code{--tty}
1152 Run using @var{device} for your program's standard input and output.
1153 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1155 @c resolve the situation of these eventually
1157 @cindex @code{--tui}
1158 Activate the @dfn{Text User Interface} when starting. The Text User
1159 Interface manages several text windows on the terminal, showing
1160 source, assembly, registers and @value{GDBN} command outputs
1161 (@pxref{TUI, ,@value{GDBN} Text User Interface}). Alternatively, the
1162 Text User Interface can be enabled by invoking the program
1163 @samp{@value{GDBTUI}}. Do not use this option if you run @value{GDBN} from
1164 Emacs (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1167 @c @cindex @code{--xdb}
1168 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1169 @c For information, see the file @file{xdb_trans.html}, which is usually
1170 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1173 @item -interpreter @var{interp}
1174 @cindex @code{--interpreter}
1175 Use the interpreter @var{interp} for interface with the controlling
1176 program or device. This option is meant to be set by programs which
1177 communicate with @value{GDBN} using it as a back end.
1178 @xref{Interpreters, , Command Interpreters}.
1180 @samp{--interpreter=mi} (or @samp{--interpreter=mi2}) causes
1181 @value{GDBN} to use the @dfn{@sc{gdb/mi} interface} (@pxref{GDB/MI, ,
1182 The @sc{gdb/mi} Interface}) included since @value{GDBN} version 6.0. The
1183 previous @sc{gdb/mi} interface, included in @value{GDBN} version 5.3 and
1184 selected with @samp{--interpreter=mi1}, is deprecated. Earlier
1185 @sc{gdb/mi} interfaces are no longer supported.
1188 @cindex @code{--write}
1189 Open the executable and core files for both reading and writing. This
1190 is equivalent to the @samp{set write on} command inside @value{GDBN}
1194 @cindex @code{--statistics}
1195 This option causes @value{GDBN} to print statistics about time and
1196 memory usage after it completes each command and returns to the prompt.
1199 @cindex @code{--version}
1200 This option causes @value{GDBN} to print its version number and
1201 no-warranty blurb, and exit.
1206 @subsection What @value{GDBN} Does During Startup
1207 @cindex @value{GDBN} startup
1209 Here's the description of what @value{GDBN} does during session startup:
1213 Sets up the command interpreter as specified by the command line
1214 (@pxref{Mode Options, interpreter}).
1218 Reads the system-wide @dfn{init file} (if @option{--with-system-gdbinit} was
1219 used when building @value{GDBN}; @pxref{System-wide configuration,
1220 ,System-wide configuration and settings}) and executes all the commands in
1224 Reads the init file (if any) in your home directory@footnote{On
1225 DOS/Windows systems, the home directory is the one pointed to by the
1226 @code{HOME} environment variable.} and executes all the commands in
1230 Processes command line options and operands.
1233 Reads and executes the commands from init file (if any) in the current
1234 working directory. This is only done if the current directory is
1235 different from your home directory. Thus, you can have more than one
1236 init file, one generic in your home directory, and another, specific
1237 to the program you are debugging, in the directory where you invoke
1241 Reads command files specified by the @samp{-x} option. @xref{Command
1242 Files}, for more details about @value{GDBN} command files.
1245 Reads the command history recorded in the @dfn{history file}.
1246 @xref{Command History}, for more details about the command history and the
1247 files where @value{GDBN} records it.
1250 Init files use the same syntax as @dfn{command files} (@pxref{Command
1251 Files}) and are processed by @value{GDBN} in the same way. The init
1252 file in your home directory can set options (such as @samp{set
1253 complaints}) that affect subsequent processing of command line options
1254 and operands. Init files are not executed if you use the @samp{-nx}
1255 option (@pxref{Mode Options, ,Choosing Modes}).
1257 To display the list of init files loaded by gdb at startup, you
1258 can use @kbd{gdb --help}.
1260 @cindex init file name
1261 @cindex @file{.gdbinit}
1262 @cindex @file{gdb.ini}
1263 The @value{GDBN} init files are normally called @file{.gdbinit}.
1264 The DJGPP port of @value{GDBN} uses the name @file{gdb.ini}, due to
1265 the limitations of file names imposed by DOS filesystems. The Windows
1266 ports of @value{GDBN} use the standard name, but if they find a
1267 @file{gdb.ini} file, they warn you about that and suggest to rename
1268 the file to the standard name.
1272 @section Quitting @value{GDBN}
1273 @cindex exiting @value{GDBN}
1274 @cindex leaving @value{GDBN}
1277 @kindex quit @r{[}@var{expression}@r{]}
1278 @kindex q @r{(@code{quit})}
1279 @item quit @r{[}@var{expression}@r{]}
1281 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1282 @code{q}), or type an end-of-file character (usually @kbd{Ctrl-d}). If you
1283 do not supply @var{expression}, @value{GDBN} will terminate normally;
1284 otherwise it will terminate using the result of @var{expression} as the
1289 An interrupt (often @kbd{Ctrl-c}) does not exit from @value{GDBN}, but rather
1290 terminates the action of any @value{GDBN} command that is in progress and
1291 returns to @value{GDBN} command level. It is safe to type the interrupt
1292 character at any time because @value{GDBN} does not allow it to take effect
1293 until a time when it is safe.
1295 If you have been using @value{GDBN} to control an attached process or
1296 device, you can release it with the @code{detach} command
1297 (@pxref{Attach, ,Debugging an Already-running Process}).
1299 @node Shell Commands
1300 @section Shell Commands
1302 If you need to execute occasional shell commands during your
1303 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1304 just use the @code{shell} command.
1308 @cindex shell escape
1309 @item shell @var{command string}
1310 Invoke a standard shell to execute @var{command string}.
1311 If it exists, the environment variable @code{SHELL} determines which
1312 shell to run. Otherwise @value{GDBN} uses the default shell
1313 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1316 The utility @code{make} is often needed in development environments.
1317 You do not have to use the @code{shell} command for this purpose in
1322 @cindex calling make
1323 @item make @var{make-args}
1324 Execute the @code{make} program with the specified
1325 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1328 @node Logging Output
1329 @section Logging Output
1330 @cindex logging @value{GDBN} output
1331 @cindex save @value{GDBN} output to a file
1333 You may want to save the output of @value{GDBN} commands to a file.
1334 There are several commands to control @value{GDBN}'s logging.
1338 @item set logging on
1340 @item set logging off
1342 @cindex logging file name
1343 @item set logging file @var{file}
1344 Change the name of the current logfile. The default logfile is @file{gdb.txt}.
1345 @item set logging overwrite [on|off]
1346 By default, @value{GDBN} will append to the logfile. Set @code{overwrite} if
1347 you want @code{set logging on} to overwrite the logfile instead.
1348 @item set logging redirect [on|off]
1349 By default, @value{GDBN} output will go to both the terminal and the logfile.
1350 Set @code{redirect} if you want output to go only to the log file.
1351 @kindex show logging
1353 Show the current values of the logging settings.
1357 @chapter @value{GDBN} Commands
1359 You can abbreviate a @value{GDBN} command to the first few letters of the command
1360 name, if that abbreviation is unambiguous; and you can repeat certain
1361 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1362 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1363 show you the alternatives available, if there is more than one possibility).
1366 * Command Syntax:: How to give commands to @value{GDBN}
1367 * Completion:: Command completion
1368 * Help:: How to ask @value{GDBN} for help
1371 @node Command Syntax
1372 @section Command Syntax
1374 A @value{GDBN} command is a single line of input. There is no limit on
1375 how long it can be. It starts with a command name, which is followed by
1376 arguments whose meaning depends on the command name. For example, the
1377 command @code{step} accepts an argument which is the number of times to
1378 step, as in @samp{step 5}. You can also use the @code{step} command
1379 with no arguments. Some commands do not allow any arguments.
1381 @cindex abbreviation
1382 @value{GDBN} command names may always be truncated if that abbreviation is
1383 unambiguous. Other possible command abbreviations are listed in the
1384 documentation for individual commands. In some cases, even ambiguous
1385 abbreviations are allowed; for example, @code{s} is specially defined as
1386 equivalent to @code{step} even though there are other commands whose
1387 names start with @code{s}. You can test abbreviations by using them as
1388 arguments to the @code{help} command.
1390 @cindex repeating commands
1391 @kindex RET @r{(repeat last command)}
1392 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1393 repeat the previous command. Certain commands (for example, @code{run})
1394 will not repeat this way; these are commands whose unintentional
1395 repetition might cause trouble and which you are unlikely to want to
1396 repeat. User-defined commands can disable this feature; see
1397 @ref{Define, dont-repeat}.
1399 The @code{list} and @code{x} commands, when you repeat them with
1400 @key{RET}, construct new arguments rather than repeating
1401 exactly as typed. This permits easy scanning of source or memory.
1403 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1404 output, in a way similar to the common utility @code{more}
1405 (@pxref{Screen Size,,Screen Size}). Since it is easy to press one
1406 @key{RET} too many in this situation, @value{GDBN} disables command
1407 repetition after any command that generates this sort of display.
1409 @kindex # @r{(a comment)}
1411 Any text from a @kbd{#} to the end of the line is a comment; it does
1412 nothing. This is useful mainly in command files (@pxref{Command
1413 Files,,Command Files}).
1415 @cindex repeating command sequences
1416 @kindex Ctrl-o @r{(operate-and-get-next)}
1417 The @kbd{Ctrl-o} binding is useful for repeating a complex sequence of
1418 commands. This command accepts the current line, like @key{RET}, and
1419 then fetches the next line relative to the current line from the history
1423 @section Command Completion
1426 @cindex word completion
1427 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1428 only one possibility; it can also show you what the valid possibilities
1429 are for the next word in a command, at any time. This works for @value{GDBN}
1430 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1432 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1433 of a word. If there is only one possibility, @value{GDBN} fills in the
1434 word, and waits for you to finish the command (or press @key{RET} to
1435 enter it). For example, if you type
1437 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1438 @c complete accuracy in these examples; space introduced for clarity.
1439 @c If texinfo enhancements make it unnecessary, it would be nice to
1440 @c replace " @key" by "@key" in the following...
1442 (@value{GDBP}) info bre @key{TAB}
1446 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1447 the only @code{info} subcommand beginning with @samp{bre}:
1450 (@value{GDBP}) info breakpoints
1454 You can either press @key{RET} at this point, to run the @code{info
1455 breakpoints} command, or backspace and enter something else, if
1456 @samp{breakpoints} does not look like the command you expected. (If you
1457 were sure you wanted @code{info breakpoints} in the first place, you
1458 might as well just type @key{RET} immediately after @samp{info bre},
1459 to exploit command abbreviations rather than command completion).
1461 If there is more than one possibility for the next word when you press
1462 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1463 characters and try again, or just press @key{TAB} a second time;
1464 @value{GDBN} displays all the possible completions for that word. For
1465 example, you might want to set a breakpoint on a subroutine whose name
1466 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1467 just sounds the bell. Typing @key{TAB} again displays all the
1468 function names in your program that begin with those characters, for
1472 (@value{GDBP}) b make_ @key{TAB}
1473 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1474 make_a_section_from_file make_environ
1475 make_abs_section make_function_type
1476 make_blockvector make_pointer_type
1477 make_cleanup make_reference_type
1478 make_command make_symbol_completion_list
1479 (@value{GDBP}) b make_
1483 After displaying the available possibilities, @value{GDBN} copies your
1484 partial input (@samp{b make_} in the example) so you can finish the
1487 If you just want to see the list of alternatives in the first place, you
1488 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1489 means @kbd{@key{META} ?}. You can type this either by holding down a
1490 key designated as the @key{META} shift on your keyboard (if there is
1491 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1493 @cindex quotes in commands
1494 @cindex completion of quoted strings
1495 Sometimes the string you need, while logically a ``word'', may contain
1496 parentheses or other characters that @value{GDBN} normally excludes from
1497 its notion of a word. To permit word completion to work in this
1498 situation, you may enclose words in @code{'} (single quote marks) in
1499 @value{GDBN} commands.
1501 The most likely situation where you might need this is in typing the
1502 name of a C@t{++} function. This is because C@t{++} allows function
1503 overloading (multiple definitions of the same function, distinguished
1504 by argument type). For example, when you want to set a breakpoint you
1505 may need to distinguish whether you mean the version of @code{name}
1506 that takes an @code{int} parameter, @code{name(int)}, or the version
1507 that takes a @code{float} parameter, @code{name(float)}. To use the
1508 word-completion facilities in this situation, type a single quote
1509 @code{'} at the beginning of the function name. This alerts
1510 @value{GDBN} that it may need to consider more information than usual
1511 when you press @key{TAB} or @kbd{M-?} to request word completion:
1514 (@value{GDBP}) b 'bubble( @kbd{M-?}
1515 bubble(double,double) bubble(int,int)
1516 (@value{GDBP}) b 'bubble(
1519 In some cases, @value{GDBN} can tell that completing a name requires using
1520 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1521 completing as much as it can) if you do not type the quote in the first
1525 (@value{GDBP}) b bub @key{TAB}
1526 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1527 (@value{GDBP}) b 'bubble(
1531 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1532 you have not yet started typing the argument list when you ask for
1533 completion on an overloaded symbol.
1535 For more information about overloaded functions, see @ref{C Plus Plus
1536 Expressions, ,C@t{++} Expressions}. You can use the command @code{set
1537 overload-resolution off} to disable overload resolution;
1538 see @ref{Debugging C Plus Plus, ,@value{GDBN} Features for C@t{++}}.
1540 @cindex completion of structure field names
1541 @cindex structure field name completion
1542 @cindex completion of union field names
1543 @cindex union field name completion
1544 When completing in an expression which looks up a field in a
1545 structure, @value{GDBN} also tries@footnote{The completer can be
1546 confused by certain kinds of invalid expressions. Also, it only
1547 examines the static type of the expression, not the dynamic type.} to
1548 limit completions to the field names available in the type of the
1552 (@value{GDBP}) p gdb_stdout.@kbd{M-?}
1553 magic to_delete to_fputs to_put to_rewind
1554 to_data to_flush to_isatty to_read to_write
1558 This is because the @code{gdb_stdout} is a variable of the type
1559 @code{struct ui_file} that is defined in @value{GDBN} sources as
1566 ui_file_flush_ftype *to_flush;
1567 ui_file_write_ftype *to_write;
1568 ui_file_fputs_ftype *to_fputs;
1569 ui_file_read_ftype *to_read;
1570 ui_file_delete_ftype *to_delete;
1571 ui_file_isatty_ftype *to_isatty;
1572 ui_file_rewind_ftype *to_rewind;
1573 ui_file_put_ftype *to_put;
1580 @section Getting Help
1581 @cindex online documentation
1584 You can always ask @value{GDBN} itself for information on its commands,
1585 using the command @code{help}.
1588 @kindex h @r{(@code{help})}
1591 You can use @code{help} (abbreviated @code{h}) with no arguments to
1592 display a short list of named classes of commands:
1596 List of classes of commands:
1598 aliases -- Aliases of other commands
1599 breakpoints -- Making program stop at certain points
1600 data -- Examining data
1601 files -- Specifying and examining files
1602 internals -- Maintenance commands
1603 obscure -- Obscure features
1604 running -- Running the program
1605 stack -- Examining the stack
1606 status -- Status inquiries
1607 support -- Support facilities
1608 tracepoints -- Tracing of program execution without
1609 stopping the program
1610 user-defined -- User-defined commands
1612 Type "help" followed by a class name for a list of
1613 commands in that class.
1614 Type "help" followed by command name for full
1616 Command name abbreviations are allowed if unambiguous.
1619 @c the above line break eliminates huge line overfull...
1621 @item help @var{class}
1622 Using one of the general help classes as an argument, you can get a
1623 list of the individual commands in that class. For example, here is the
1624 help display for the class @code{status}:
1627 (@value{GDBP}) help status
1632 @c Line break in "show" line falsifies real output, but needed
1633 @c to fit in smallbook page size.
1634 info -- Generic command for showing things
1635 about the program being debugged
1636 show -- Generic command for showing things
1639 Type "help" followed by command name for full
1641 Command name abbreviations are allowed if unambiguous.
1645 @item help @var{command}
1646 With a command name as @code{help} argument, @value{GDBN} displays a
1647 short paragraph on how to use that command.
1650 @item apropos @var{args}
1651 The @code{apropos} command searches through all of the @value{GDBN}
1652 commands, and their documentation, for the regular expression specified in
1653 @var{args}. It prints out all matches found. For example:
1664 set symbol-reloading -- Set dynamic symbol table reloading
1665 multiple times in one run
1666 show symbol-reloading -- Show dynamic symbol table reloading
1667 multiple times in one run
1672 @item complete @var{args}
1673 The @code{complete @var{args}} command lists all the possible completions
1674 for the beginning of a command. Use @var{args} to specify the beginning of the
1675 command you want completed. For example:
1681 @noindent results in:
1692 @noindent This is intended for use by @sc{gnu} Emacs.
1695 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1696 and @code{show} to inquire about the state of your program, or the state
1697 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1698 manual introduces each of them in the appropriate context. The listings
1699 under @code{info} and under @code{show} in the Index point to
1700 all the sub-commands. @xref{Index}.
1705 @kindex i @r{(@code{info})}
1707 This command (abbreviated @code{i}) is for describing the state of your
1708 program. For example, you can show the arguments passed to a function
1709 with @code{info args}, list the registers currently in use with @code{info
1710 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1711 You can get a complete list of the @code{info} sub-commands with
1712 @w{@code{help info}}.
1716 You can assign the result of an expression to an environment variable with
1717 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1718 @code{set prompt $}.
1722 In contrast to @code{info}, @code{show} is for describing the state of
1723 @value{GDBN} itself.
1724 You can change most of the things you can @code{show}, by using the
1725 related command @code{set}; for example, you can control what number
1726 system is used for displays with @code{set radix}, or simply inquire
1727 which is currently in use with @code{show radix}.
1730 To display all the settable parameters and their current
1731 values, you can use @code{show} with no arguments; you may also use
1732 @code{info set}. Both commands produce the same display.
1733 @c FIXME: "info set" violates the rule that "info" is for state of
1734 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1735 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1739 Here are three miscellaneous @code{show} subcommands, all of which are
1740 exceptional in lacking corresponding @code{set} commands:
1743 @kindex show version
1744 @cindex @value{GDBN} version number
1746 Show what version of @value{GDBN} is running. You should include this
1747 information in @value{GDBN} bug-reports. If multiple versions of
1748 @value{GDBN} are in use at your site, you may need to determine which
1749 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1750 commands are introduced, and old ones may wither away. Also, many
1751 system vendors ship variant versions of @value{GDBN}, and there are
1752 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1753 The version number is the same as the one announced when you start
1756 @kindex show copying
1757 @kindex info copying
1758 @cindex display @value{GDBN} copyright
1761 Display information about permission for copying @value{GDBN}.
1763 @kindex show warranty
1764 @kindex info warranty
1766 @itemx info warranty
1767 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1768 if your version of @value{GDBN} comes with one.
1773 @chapter Running Programs Under @value{GDBN}
1775 When you run a program under @value{GDBN}, you must first generate
1776 debugging information when you compile it.
1778 You may start @value{GDBN} with its arguments, if any, in an environment
1779 of your choice. If you are doing native debugging, you may redirect
1780 your program's input and output, debug an already running process, or
1781 kill a child process.
1784 * Compilation:: Compiling for debugging
1785 * Starting:: Starting your program
1786 * Arguments:: Your program's arguments
1787 * Environment:: Your program's environment
1789 * Working Directory:: Your program's working directory
1790 * Input/Output:: Your program's input and output
1791 * Attach:: Debugging an already-running process
1792 * Kill Process:: Killing the child process
1794 * Inferiors:: Debugging multiple inferiors
1795 * Threads:: Debugging programs with multiple threads
1796 * Processes:: Debugging programs with multiple processes
1797 * Checkpoint/Restart:: Setting a @emph{bookmark} to return to later
1801 @section Compiling for Debugging
1803 In order to debug a program effectively, you need to generate
1804 debugging information when you compile it. This debugging information
1805 is stored in the object file; it describes the data type of each
1806 variable or function and the correspondence between source line numbers
1807 and addresses in the executable code.
1809 To request debugging information, specify the @samp{-g} option when you run
1812 Programs that are to be shipped to your customers are compiled with
1813 optimizations, using the @samp{-O} compiler option. However, some
1814 compilers are unable to handle the @samp{-g} and @samp{-O} options
1815 together. Using those compilers, you cannot generate optimized
1816 executables containing debugging information.
1818 @value{NGCC}, the @sc{gnu} C/C@t{++} compiler, supports @samp{-g} with or
1819 without @samp{-O}, making it possible to debug optimized code. We
1820 recommend that you @emph{always} use @samp{-g} whenever you compile a
1821 program. You may think your program is correct, but there is no sense
1822 in pushing your luck. For more information, see @ref{Optimized Code}.
1824 Older versions of the @sc{gnu} C compiler permitted a variant option
1825 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1826 format; if your @sc{gnu} C compiler has this option, do not use it.
1828 @value{GDBN} knows about preprocessor macros and can show you their
1829 expansion (@pxref{Macros}). Most compilers do not include information
1830 about preprocessor macros in the debugging information if you specify
1831 the @option{-g} flag alone, because this information is rather large.
1832 Version 3.1 and later of @value{NGCC}, the @sc{gnu} C compiler,
1833 provides macro information if you specify the options
1834 @option{-gdwarf-2} and @option{-g3}; the former option requests
1835 debugging information in the Dwarf 2 format, and the latter requests
1836 ``extra information''. In the future, we hope to find more compact
1837 ways to represent macro information, so that it can be included with
1842 @section Starting your Program
1848 @kindex r @r{(@code{run})}
1851 Use the @code{run} command to start your program under @value{GDBN}.
1852 You must first specify the program name (except on VxWorks) with an
1853 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1854 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1855 (@pxref{Files, ,Commands to Specify Files}).
1859 If you are running your program in an execution environment that
1860 supports processes, @code{run} creates an inferior process and makes
1861 that process run your program. In some environments without processes,
1862 @code{run} jumps to the start of your program. Other targets,
1863 like @samp{remote}, are always running. If you get an error
1864 message like this one:
1867 The "remote" target does not support "run".
1868 Try "help target" or "continue".
1872 then use @code{continue} to run your program. You may need @code{load}
1873 first (@pxref{load}).
1875 The execution of a program is affected by certain information it
1876 receives from its superior. @value{GDBN} provides ways to specify this
1877 information, which you must do @emph{before} starting your program. (You
1878 can change it after starting your program, but such changes only affect
1879 your program the next time you start it.) This information may be
1880 divided into four categories:
1883 @item The @emph{arguments.}
1884 Specify the arguments to give your program as the arguments of the
1885 @code{run} command. If a shell is available on your target, the shell
1886 is used to pass the arguments, so that you may use normal conventions
1887 (such as wildcard expansion or variable substitution) in describing
1889 In Unix systems, you can control which shell is used with the
1890 @code{SHELL} environment variable.
1891 @xref{Arguments, ,Your Program's Arguments}.
1893 @item The @emph{environment.}
1894 Your program normally inherits its environment from @value{GDBN}, but you can
1895 use the @value{GDBN} commands @code{set environment} and @code{unset
1896 environment} to change parts of the environment that affect
1897 your program. @xref{Environment, ,Your Program's Environment}.
1899 @item The @emph{working directory.}
1900 Your program inherits its working directory from @value{GDBN}. You can set
1901 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1902 @xref{Working Directory, ,Your Program's Working Directory}.
1904 @item The @emph{standard input and output.}
1905 Your program normally uses the same device for standard input and
1906 standard output as @value{GDBN} is using. You can redirect input and output
1907 in the @code{run} command line, or you can use the @code{tty} command to
1908 set a different device for your program.
1909 @xref{Input/Output, ,Your Program's Input and Output}.
1912 @emph{Warning:} While input and output redirection work, you cannot use
1913 pipes to pass the output of the program you are debugging to another
1914 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1918 When you issue the @code{run} command, your program begins to execute
1919 immediately. @xref{Stopping, ,Stopping and Continuing}, for discussion
1920 of how to arrange for your program to stop. Once your program has
1921 stopped, you may call functions in your program, using the @code{print}
1922 or @code{call} commands. @xref{Data, ,Examining Data}.
1924 If the modification time of your symbol file has changed since the last
1925 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1926 table, and reads it again. When it does this, @value{GDBN} tries to retain
1927 your current breakpoints.
1932 @cindex run to main procedure
1933 The name of the main procedure can vary from language to language.
1934 With C or C@t{++}, the main procedure name is always @code{main}, but
1935 other languages such as Ada do not require a specific name for their
1936 main procedure. The debugger provides a convenient way to start the
1937 execution of the program and to stop at the beginning of the main
1938 procedure, depending on the language used.
1940 The @samp{start} command does the equivalent of setting a temporary
1941 breakpoint at the beginning of the main procedure and then invoking
1942 the @samp{run} command.
1944 @cindex elaboration phase
1945 Some programs contain an @dfn{elaboration} phase where some startup code is
1946 executed before the main procedure is called. This depends on the
1947 languages used to write your program. In C@t{++}, for instance,
1948 constructors for static and global objects are executed before
1949 @code{main} is called. It is therefore possible that the debugger stops
1950 before reaching the main procedure. However, the temporary breakpoint
1951 will remain to halt execution.
1953 Specify the arguments to give to your program as arguments to the
1954 @samp{start} command. These arguments will be given verbatim to the
1955 underlying @samp{run} command. Note that the same arguments will be
1956 reused if no argument is provided during subsequent calls to
1957 @samp{start} or @samp{run}.
1959 It is sometimes necessary to debug the program during elaboration. In
1960 these cases, using the @code{start} command would stop the execution of
1961 your program too late, as the program would have already completed the
1962 elaboration phase. Under these circumstances, insert breakpoints in your
1963 elaboration code before running your program.
1965 @kindex set exec-wrapper
1966 @item set exec-wrapper @var{wrapper}
1967 @itemx show exec-wrapper
1968 @itemx unset exec-wrapper
1969 When @samp{exec-wrapper} is set, the specified wrapper is used to
1970 launch programs for debugging. @value{GDBN} starts your program
1971 with a shell command of the form @kbd{exec @var{wrapper}
1972 @var{program}}. Quoting is added to @var{program} and its
1973 arguments, but not to @var{wrapper}, so you should add quotes if
1974 appropriate for your shell. The wrapper runs until it executes
1975 your program, and then @value{GDBN} takes control.
1977 You can use any program that eventually calls @code{execve} with
1978 its arguments as a wrapper. Several standard Unix utilities do
1979 this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending
1980 with @code{exec "$@@"} will also work.
1982 For example, you can use @code{env} to pass an environment variable to
1983 the debugged program, without setting the variable in your shell's
1987 (@value{GDBP}) set exec-wrapper env 'LD_PRELOAD=libtest.so'
1991 This command is available when debugging locally on most targets, excluding
1992 @sc{djgpp}, Cygwin, MS Windows, and QNX Neutrino.
1994 @kindex set disable-randomization
1995 @item set disable-randomization
1996 @itemx set disable-randomization on
1997 This option (enabled by default in @value{GDBN}) will turn off the native
1998 randomization of the virtual address space of the started program. This option
1999 is useful for multiple debugging sessions to make the execution better
2000 reproducible and memory addresses reusable across debugging sessions.
2002 This feature is implemented only on @sc{gnu}/Linux. You can get the same
2006 (@value{GDBP}) set exec-wrapper setarch `uname -m` -R
2009 @item set disable-randomization off
2010 Leave the behavior of the started executable unchanged. Some bugs rear their
2011 ugly heads only when the program is loaded at certain addresses. If your bug
2012 disappears when you run the program under @value{GDBN}, that might be because
2013 @value{GDBN} by default disables the address randomization on platforms, such
2014 as @sc{gnu}/Linux, which do that for stand-alone programs. Use @kbd{set
2015 disable-randomization off} to try to reproduce such elusive bugs.
2017 The virtual address space randomization is implemented only on @sc{gnu}/Linux.
2018 It protects the programs against some kinds of security attacks. In these
2019 cases the attacker needs to know the exact location of a concrete executable
2020 code. Randomizing its location makes it impossible to inject jumps misusing
2021 a code at its expected addresses.
2023 Prelinking shared libraries provides a startup performance advantage but it
2024 makes addresses in these libraries predictable for privileged processes by
2025 having just unprivileged access at the target system. Reading the shared
2026 library binary gives enough information for assembling the malicious code
2027 misusing it. Still even a prelinked shared library can get loaded at a new
2028 random address just requiring the regular relocation process during the
2029 startup. Shared libraries not already prelinked are always loaded at
2030 a randomly chosen address.
2032 Position independent executables (PIE) contain position independent code
2033 similar to the shared libraries and therefore such executables get loaded at
2034 a randomly chosen address upon startup. PIE executables always load even
2035 already prelinked shared libraries at a random address. You can build such
2036 executable using @command{gcc -fPIE -pie}.
2038 Heap (malloc storage), stack and custom mmap areas are always placed randomly
2039 (as long as the randomization is enabled).
2041 @item show disable-randomization
2042 Show the current setting of the explicit disable of the native randomization of
2043 the virtual address space of the started program.
2048 @section Your Program's Arguments
2050 @cindex arguments (to your program)
2051 The arguments to your program can be specified by the arguments of the
2053 They are passed to a shell, which expands wildcard characters and
2054 performs redirection of I/O, and thence to your program. Your
2055 @code{SHELL} environment variable (if it exists) specifies what shell
2056 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
2057 the default shell (@file{/bin/sh} on Unix).
2059 On non-Unix systems, the program is usually invoked directly by
2060 @value{GDBN}, which emulates I/O redirection via the appropriate system
2061 calls, and the wildcard characters are expanded by the startup code of
2062 the program, not by the shell.
2064 @code{run} with no arguments uses the same arguments used by the previous
2065 @code{run}, or those set by the @code{set args} command.
2070 Specify the arguments to be used the next time your program is run. If
2071 @code{set args} has no arguments, @code{run} executes your program
2072 with no arguments. Once you have run your program with arguments,
2073 using @code{set args} before the next @code{run} is the only way to run
2074 it again without arguments.
2078 Show the arguments to give your program when it is started.
2082 @section Your Program's Environment
2084 @cindex environment (of your program)
2085 The @dfn{environment} consists of a set of environment variables and
2086 their values. Environment variables conventionally record such things as
2087 your user name, your home directory, your terminal type, and your search
2088 path for programs to run. Usually you set up environment variables with
2089 the shell and they are inherited by all the other programs you run. When
2090 debugging, it can be useful to try running your program with a modified
2091 environment without having to start @value{GDBN} over again.
2095 @item path @var{directory}
2096 Add @var{directory} to the front of the @code{PATH} environment variable
2097 (the search path for executables) that will be passed to your program.
2098 The value of @code{PATH} used by @value{GDBN} does not change.
2099 You may specify several directory names, separated by whitespace or by a
2100 system-dependent separator character (@samp{:} on Unix, @samp{;} on
2101 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
2102 is moved to the front, so it is searched sooner.
2104 You can use the string @samp{$cwd} to refer to whatever is the current
2105 working directory at the time @value{GDBN} searches the path. If you
2106 use @samp{.} instead, it refers to the directory where you executed the
2107 @code{path} command. @value{GDBN} replaces @samp{.} in the
2108 @var{directory} argument (with the current path) before adding
2109 @var{directory} to the search path.
2110 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
2111 @c document that, since repeating it would be a no-op.
2115 Display the list of search paths for executables (the @code{PATH}
2116 environment variable).
2118 @kindex show environment
2119 @item show environment @r{[}@var{varname}@r{]}
2120 Print the value of environment variable @var{varname} to be given to
2121 your program when it starts. If you do not supply @var{varname},
2122 print the names and values of all environment variables to be given to
2123 your program. You can abbreviate @code{environment} as @code{env}.
2125 @kindex set environment
2126 @item set environment @var{varname} @r{[}=@var{value}@r{]}
2127 Set environment variable @var{varname} to @var{value}. The value
2128 changes for your program only, not for @value{GDBN} itself. @var{value} may
2129 be any string; the values of environment variables are just strings, and
2130 any interpretation is supplied by your program itself. The @var{value}
2131 parameter is optional; if it is eliminated, the variable is set to a
2133 @c "any string" here does not include leading, trailing
2134 @c blanks. Gnu asks: does anyone care?
2136 For example, this command:
2143 tells the debugged program, when subsequently run, that its user is named
2144 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
2145 are not actually required.)
2147 @kindex unset environment
2148 @item unset environment @var{varname}
2149 Remove variable @var{varname} from the environment to be passed to your
2150 program. This is different from @samp{set env @var{varname} =};
2151 @code{unset environment} removes the variable from the environment,
2152 rather than assigning it an empty value.
2155 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
2157 by your @code{SHELL} environment variable if it exists (or
2158 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
2159 that runs an initialization file---such as @file{.cshrc} for C-shell, or
2160 @file{.bashrc} for BASH---any variables you set in that file affect
2161 your program. You may wish to move setting of environment variables to
2162 files that are only run when you sign on, such as @file{.login} or
2165 @node Working Directory
2166 @section Your Program's Working Directory
2168 @cindex working directory (of your program)
2169 Each time you start your program with @code{run}, it inherits its
2170 working directory from the current working directory of @value{GDBN}.
2171 The @value{GDBN} working directory is initially whatever it inherited
2172 from its parent process (typically the shell), but you can specify a new
2173 working directory in @value{GDBN} with the @code{cd} command.
2175 The @value{GDBN} working directory also serves as a default for the commands
2176 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
2181 @cindex change working directory
2182 @item cd @var{directory}
2183 Set the @value{GDBN} working directory to @var{directory}.
2187 Print the @value{GDBN} working directory.
2190 It is generally impossible to find the current working directory of
2191 the process being debugged (since a program can change its directory
2192 during its run). If you work on a system where @value{GDBN} is
2193 configured with the @file{/proc} support, you can use the @code{info
2194 proc} command (@pxref{SVR4 Process Information}) to find out the
2195 current working directory of the debuggee.
2198 @section Your Program's Input and Output
2203 By default, the program you run under @value{GDBN} does input and output to
2204 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
2205 to its own terminal modes to interact with you, but it records the terminal
2206 modes your program was using and switches back to them when you continue
2207 running your program.
2210 @kindex info terminal
2212 Displays information recorded by @value{GDBN} about the terminal modes your
2216 You can redirect your program's input and/or output using shell
2217 redirection with the @code{run} command. For example,
2224 starts your program, diverting its output to the file @file{outfile}.
2227 @cindex controlling terminal
2228 Another way to specify where your program should do input and output is
2229 with the @code{tty} command. This command accepts a file name as
2230 argument, and causes this file to be the default for future @code{run}
2231 commands. It also resets the controlling terminal for the child
2232 process, for future @code{run} commands. For example,
2239 directs that processes started with subsequent @code{run} commands
2240 default to do input and output on the terminal @file{/dev/ttyb} and have
2241 that as their controlling terminal.
2243 An explicit redirection in @code{run} overrides the @code{tty} command's
2244 effect on the input/output device, but not its effect on the controlling
2247 When you use the @code{tty} command or redirect input in the @code{run}
2248 command, only the input @emph{for your program} is affected. The input
2249 for @value{GDBN} still comes from your terminal. @code{tty} is an alias
2250 for @code{set inferior-tty}.
2252 @cindex inferior tty
2253 @cindex set inferior controlling terminal
2254 You can use the @code{show inferior-tty} command to tell @value{GDBN} to
2255 display the name of the terminal that will be used for future runs of your
2259 @item set inferior-tty /dev/ttyb
2260 @kindex set inferior-tty
2261 Set the tty for the program being debugged to /dev/ttyb.
2263 @item show inferior-tty
2264 @kindex show inferior-tty
2265 Show the current tty for the program being debugged.
2269 @section Debugging an Already-running Process
2274 @item attach @var{process-id}
2275 This command attaches to a running process---one that was started
2276 outside @value{GDBN}. (@code{info files} shows your active
2277 targets.) The command takes as argument a process ID. The usual way to
2278 find out the @var{process-id} of a Unix process is with the @code{ps} utility,
2279 or with the @samp{jobs -l} shell command.
2281 @code{attach} does not repeat if you press @key{RET} a second time after
2282 executing the command.
2285 To use @code{attach}, your program must be running in an environment
2286 which supports processes; for example, @code{attach} does not work for
2287 programs on bare-board targets that lack an operating system. You must
2288 also have permission to send the process a signal.
2290 When you use @code{attach}, the debugger finds the program running in
2291 the process first by looking in the current working directory, then (if
2292 the program is not found) by using the source file search path
2293 (@pxref{Source Path, ,Specifying Source Directories}). You can also use
2294 the @code{file} command to load the program. @xref{Files, ,Commands to
2297 The first thing @value{GDBN} does after arranging to debug the specified
2298 process is to stop it. You can examine and modify an attached process
2299 with all the @value{GDBN} commands that are ordinarily available when
2300 you start processes with @code{run}. You can insert breakpoints; you
2301 can step and continue; you can modify storage. If you would rather the
2302 process continue running, you may use the @code{continue} command after
2303 attaching @value{GDBN} to the process.
2308 When you have finished debugging the attached process, you can use the
2309 @code{detach} command to release it from @value{GDBN} control. Detaching
2310 the process continues its execution. After the @code{detach} command,
2311 that process and @value{GDBN} become completely independent once more, and you
2312 are ready to @code{attach} another process or start one with @code{run}.
2313 @code{detach} does not repeat if you press @key{RET} again after
2314 executing the command.
2317 If you exit @value{GDBN} while you have an attached process, you detach
2318 that process. If you use the @code{run} command, you kill that process.
2319 By default, @value{GDBN} asks for confirmation if you try to do either of these
2320 things; you can control whether or not you need to confirm by using the
2321 @code{set confirm} command (@pxref{Messages/Warnings, ,Optional Warnings and
2325 @section Killing the Child Process
2330 Kill the child process in which your program is running under @value{GDBN}.
2333 This command is useful if you wish to debug a core dump instead of a
2334 running process. @value{GDBN} ignores any core dump file while your program
2337 On some operating systems, a program cannot be executed outside @value{GDBN}
2338 while you have breakpoints set on it inside @value{GDBN}. You can use the
2339 @code{kill} command in this situation to permit running your program
2340 outside the debugger.
2342 The @code{kill} command is also useful if you wish to recompile and
2343 relink your program, since on many systems it is impossible to modify an
2344 executable file while it is running in a process. In this case, when you
2345 next type @code{run}, @value{GDBN} notices that the file has changed, and
2346 reads the symbol table again (while trying to preserve your current
2347 breakpoint settings).
2350 @section Debugging Multiple Inferiors
2352 Some @value{GDBN} targets are able to run multiple processes created
2353 from a single executable. This can happen, for instance, with an
2354 embedded system reporting back several processes via the remote
2358 @value{GDBN} represents the state of each program execution with an
2359 object called an @dfn{inferior}. An inferior typically corresponds to
2360 a process, but is more general and applies also to targets that do not
2361 have processes. Inferiors may be created before a process runs, and
2362 may (in future) be retained after a process exits. Each run of an
2363 executable creates a new inferior, as does each attachment to an
2364 existing process. Inferiors have unique identifiers that are
2365 different from process ids, and may optionally be named as well.
2366 Usually each inferior will also have its own distinct address space,
2367 although some embedded targets may have several inferiors running in
2368 different parts of a single space.
2370 Each inferior may in turn have multiple threads running in it.
2372 To find out what inferiors exist at any moment, use @code{info inferiors}:
2375 @kindex info inferiors
2376 @item info inferiors
2377 Print a list of all inferiors currently being managed by @value{GDBN}.
2379 @value{GDBN} displays for each inferior (in this order):
2383 the inferior number assigned by @value{GDBN}
2386 the target system's inferior identifier
2390 An asterisk @samp{*} preceding the @value{GDBN} inferior number
2391 indicates the current inferior.
2395 @c end table here to get a little more width for example
2398 (@value{GDBP}) info inferiors
2404 To switch focus between inferiors, use the @code{inferior} command:
2407 @kindex inferior @var{infno}
2408 @item inferior @var{infno}
2409 Make inferior number @var{infno} the current inferior. The argument
2410 @var{infno} is the inferior number assigned by @value{GDBN}, as shown
2411 in the first field of the @samp{info inferiors} display.
2414 To quit debugging one of the inferiors, you can either detach from it
2415 by using the @w{@code{detach inferior}} command (allowing it to run
2416 independently), or kill it using the @w{@code{kill inferior}} command:
2419 @kindex detach inferior @var{infno}
2420 @item detach inferior @var{infno}
2421 Detach from the inferior identified by @value{GDBN} inferior number
2422 @var{infno}, and remove it from the inferior list.
2424 @kindex kill inferior @var{infno}
2425 @item kill inferior @var{infno}
2426 Kill the inferior identified by @value{GDBN} inferior number
2427 @var{infno}, and remove it from the inferior list.
2430 To be notified when inferiors are started or exit under @value{GDBN}'s
2431 control use @w{@code{set print inferior-events}}:
2434 @kindex set print inferior-events
2435 @cindex print messages on inferior start and exit
2436 @item set print inferior-events
2437 @itemx set print inferior-events on
2438 @itemx set print inferior-events off
2439 The @code{set print inferior-events} command allows you to enable or
2440 disable printing of messages when @value{GDBN} notices that new
2441 inferiors have started or that inferiors have exited or have been
2442 detached. By default, these messages will not be printed.
2444 @kindex show print inferior-events
2445 @item show print inferior-events
2446 Show whether messages will be printed when @value{GDBN} detects that
2447 inferiors have started, exited or have been detached.
2451 @section Debugging Programs with Multiple Threads
2453 @cindex threads of execution
2454 @cindex multiple threads
2455 @cindex switching threads
2456 In some operating systems, such as HP-UX and Solaris, a single program
2457 may have more than one @dfn{thread} of execution. The precise semantics
2458 of threads differ from one operating system to another, but in general
2459 the threads of a single program are akin to multiple processes---except
2460 that they share one address space (that is, they can all examine and
2461 modify the same variables). On the other hand, each thread has its own
2462 registers and execution stack, and perhaps private memory.
2464 @value{GDBN} provides these facilities for debugging multi-thread
2468 @item automatic notification of new threads
2469 @item @samp{thread @var{threadno}}, a command to switch among threads
2470 @item @samp{info threads}, a command to inquire about existing threads
2471 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2472 a command to apply a command to a list of threads
2473 @item thread-specific breakpoints
2474 @item @samp{set print thread-events}, which controls printing of
2475 messages on thread start and exit.
2476 @item @samp{set libthread-db-search-path @var{path}}, which lets
2477 the user specify which @code{libthread_db} to use if the default choice
2478 isn't compatible with the program.
2482 @emph{Warning:} These facilities are not yet available on every
2483 @value{GDBN} configuration where the operating system supports threads.
2484 If your @value{GDBN} does not support threads, these commands have no
2485 effect. For example, a system without thread support shows no output
2486 from @samp{info threads}, and always rejects the @code{thread} command,
2490 (@value{GDBP}) info threads
2491 (@value{GDBP}) thread 1
2492 Thread ID 1 not known. Use the "info threads" command to
2493 see the IDs of currently known threads.
2495 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2496 @c doesn't support threads"?
2499 @cindex focus of debugging
2500 @cindex current thread
2501 The @value{GDBN} thread debugging facility allows you to observe all
2502 threads while your program runs---but whenever @value{GDBN} takes
2503 control, one thread in particular is always the focus of debugging.
2504 This thread is called the @dfn{current thread}. Debugging commands show
2505 program information from the perspective of the current thread.
2507 @cindex @code{New} @var{systag} message
2508 @cindex thread identifier (system)
2509 @c FIXME-implementors!! It would be more helpful if the [New...] message
2510 @c included GDB's numeric thread handle, so you could just go to that
2511 @c thread without first checking `info threads'.
2512 Whenever @value{GDBN} detects a new thread in your program, it displays
2513 the target system's identification for the thread with a message in the
2514 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2515 whose form varies depending on the particular system. For example, on
2516 @sc{gnu}/Linux, you might see
2519 [New Thread 46912507313328 (LWP 25582)]
2523 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2524 the @var{systag} is simply something like @samp{process 368}, with no
2527 @c FIXME!! (1) Does the [New...] message appear even for the very first
2528 @c thread of a program, or does it only appear for the
2529 @c second---i.e.@: when it becomes obvious we have a multithread
2531 @c (2) *Is* there necessarily a first thread always? Or do some
2532 @c multithread systems permit starting a program with multiple
2533 @c threads ab initio?
2535 @cindex thread number
2536 @cindex thread identifier (GDB)
2537 For debugging purposes, @value{GDBN} associates its own thread
2538 number---always a single integer---with each thread in your program.
2541 @kindex info threads
2543 Display a summary of all threads currently in your
2544 program. @value{GDBN} displays for each thread (in this order):
2548 the thread number assigned by @value{GDBN}
2551 the target system's thread identifier (@var{systag})
2554 the current stack frame summary for that thread
2558 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2559 indicates the current thread.
2563 @c end table here to get a little more width for example
2566 (@value{GDBP}) info threads
2567 3 process 35 thread 27 0x34e5 in sigpause ()
2568 2 process 35 thread 23 0x34e5 in sigpause ()
2569 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2575 @cindex debugging multithreaded programs (on HP-UX)
2576 @cindex thread identifier (GDB), on HP-UX
2577 For debugging purposes, @value{GDBN} associates its own thread
2578 number---a small integer assigned in thread-creation order---with each
2579 thread in your program.
2581 @cindex @code{New} @var{systag} message, on HP-UX
2582 @cindex thread identifier (system), on HP-UX
2583 @c FIXME-implementors!! It would be more helpful if the [New...] message
2584 @c included GDB's numeric thread handle, so you could just go to that
2585 @c thread without first checking `info threads'.
2586 Whenever @value{GDBN} detects a new thread in your program, it displays
2587 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2588 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2589 whose form varies depending on the particular system. For example, on
2593 [New thread 2 (system thread 26594)]
2597 when @value{GDBN} notices a new thread.
2600 @kindex info threads (HP-UX)
2602 Display a summary of all threads currently in your
2603 program. @value{GDBN} displays for each thread (in this order):
2606 @item the thread number assigned by @value{GDBN}
2608 @item the target system's thread identifier (@var{systag})
2610 @item the current stack frame summary for that thread
2614 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2615 indicates the current thread.
2619 @c end table here to get a little more width for example
2622 (@value{GDBP}) info threads
2623 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2625 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2626 from /usr/lib/libc.2
2627 1 system thread 27905 0x7b003498 in _brk () \@*
2628 from /usr/lib/libc.2
2631 On Solaris, you can display more information about user threads with a
2632 Solaris-specific command:
2635 @item maint info sol-threads
2636 @kindex maint info sol-threads
2637 @cindex thread info (Solaris)
2638 Display info on Solaris user threads.
2642 @kindex thread @var{threadno}
2643 @item thread @var{threadno}
2644 Make thread number @var{threadno} the current thread. The command
2645 argument @var{threadno} is the internal @value{GDBN} thread number, as
2646 shown in the first field of the @samp{info threads} display.
2647 @value{GDBN} responds by displaying the system identifier of the thread
2648 you selected, and its current stack frame summary:
2651 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2652 (@value{GDBP}) thread 2
2653 [Switching to process 35 thread 23]
2654 0x34e5 in sigpause ()
2658 As with the @samp{[New @dots{}]} message, the form of the text after
2659 @samp{Switching to} depends on your system's conventions for identifying
2662 @kindex thread apply
2663 @cindex apply command to several threads
2664 @item thread apply [@var{threadno}] [@var{all}] @var{command}
2665 The @code{thread apply} command allows you to apply the named
2666 @var{command} to one or more threads. Specify the numbers of the
2667 threads that you want affected with the command argument
2668 @var{threadno}. It can be a single thread number, one of the numbers
2669 shown in the first field of the @samp{info threads} display; or it
2670 could be a range of thread numbers, as in @code{2-4}. To apply a
2671 command to all threads, type @kbd{thread apply all @var{command}}.
2673 @kindex set print thread-events
2674 @cindex print messages on thread start and exit
2675 @item set print thread-events
2676 @itemx set print thread-events on
2677 @itemx set print thread-events off
2678 The @code{set print thread-events} command allows you to enable or
2679 disable printing of messages when @value{GDBN} notices that new threads have
2680 started or that threads have exited. By default, these messages will
2681 be printed if detection of these events is supported by the target.
2682 Note that these messages cannot be disabled on all targets.
2684 @kindex show print thread-events
2685 @item show print thread-events
2686 Show whether messages will be printed when @value{GDBN} detects that threads
2687 have started and exited.
2690 @xref{Thread Stops,,Stopping and Starting Multi-thread Programs}, for
2691 more information about how @value{GDBN} behaves when you stop and start
2692 programs with multiple threads.
2694 @xref{Set Watchpoints,,Setting Watchpoints}, for information about
2695 watchpoints in programs with multiple threads.
2698 @kindex set libthread-db-search-path
2699 @cindex search path for @code{libthread_db}
2700 @item set libthread-db-search-path @r{[}@var{path}@r{]}
2701 If this variable is set, @var{path} is a colon-separated list of
2702 directories @value{GDBN} will use to search for @code{libthread_db}.
2703 If you omit @var{path}, @samp{libthread-db-search-path} will be reset to
2706 On @sc{gnu}/Linux and Solaris systems, @value{GDBN} uses a ``helper''
2707 @code{libthread_db} library to obtain information about threads in the
2708 inferior process. @value{GDBN} will use @samp{libthread-db-search-path}
2709 to find @code{libthread_db}. If that fails, @value{GDBN} will continue
2710 with default system shared library directories, and finally the directory
2711 from which @code{libpthread} was loaded in the inferior process.
2713 For any @code{libthread_db} library @value{GDBN} finds in above directories,
2714 @value{GDBN} attempts to initialize it with the current inferior process.
2715 If this initialization fails (which could happen because of a version
2716 mismatch between @code{libthread_db} and @code{libpthread}), @value{GDBN}
2717 will unload @code{libthread_db}, and continue with the next directory.
2718 If none of @code{libthread_db} libraries initialize successfully,
2719 @value{GDBN} will issue a warning and thread debugging will be disabled.
2721 Setting @code{libthread-db-search-path} is currently implemented
2722 only on some platforms.
2724 @kindex show libthread-db-search-path
2725 @item show libthread-db-search-path
2726 Display current libthread_db search path.
2730 @section Debugging Programs with Multiple Processes
2732 @cindex fork, debugging programs which call
2733 @cindex multiple processes
2734 @cindex processes, multiple
2735 On most systems, @value{GDBN} has no special support for debugging
2736 programs which create additional processes using the @code{fork}
2737 function. When a program forks, @value{GDBN} will continue to debug the
2738 parent process and the child process will run unimpeded. If you have
2739 set a breakpoint in any code which the child then executes, the child
2740 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2741 will cause it to terminate.
2743 However, if you want to debug the child process there is a workaround
2744 which isn't too painful. Put a call to @code{sleep} in the code which
2745 the child process executes after the fork. It may be useful to sleep
2746 only if a certain environment variable is set, or a certain file exists,
2747 so that the delay need not occur when you don't want to run @value{GDBN}
2748 on the child. While the child is sleeping, use the @code{ps} program to
2749 get its process ID. Then tell @value{GDBN} (a new invocation of
2750 @value{GDBN} if you are also debugging the parent process) to attach to
2751 the child process (@pxref{Attach}). From that point on you can debug
2752 the child process just like any other process which you attached to.
2754 On some systems, @value{GDBN} provides support for debugging programs that
2755 create additional processes using the @code{fork} or @code{vfork} functions.
2756 Currently, the only platforms with this feature are HP-UX (11.x and later
2757 only?) and @sc{gnu}/Linux (kernel version 2.5.60 and later).
2759 By default, when a program forks, @value{GDBN} will continue to debug
2760 the parent process and the child process will run unimpeded.
2762 If you want to follow the child process instead of the parent process,
2763 use the command @w{@code{set follow-fork-mode}}.
2766 @kindex set follow-fork-mode
2767 @item set follow-fork-mode @var{mode}
2768 Set the debugger response to a program call of @code{fork} or
2769 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2770 process. The @var{mode} argument can be:
2774 The original process is debugged after a fork. The child process runs
2775 unimpeded. This is the default.
2778 The new process is debugged after a fork. The parent process runs
2783 @kindex show follow-fork-mode
2784 @item show follow-fork-mode
2785 Display the current debugger response to a @code{fork} or @code{vfork} call.
2788 @cindex debugging multiple processes
2789 On Linux, if you want to debug both the parent and child processes, use the
2790 command @w{@code{set detach-on-fork}}.
2793 @kindex set detach-on-fork
2794 @item set detach-on-fork @var{mode}
2795 Tells gdb whether to detach one of the processes after a fork, or
2796 retain debugger control over them both.
2800 The child process (or parent process, depending on the value of
2801 @code{follow-fork-mode}) will be detached and allowed to run
2802 independently. This is the default.
2805 Both processes will be held under the control of @value{GDBN}.
2806 One process (child or parent, depending on the value of
2807 @code{follow-fork-mode}) is debugged as usual, while the other
2812 @kindex show detach-on-fork
2813 @item show detach-on-fork
2814 Show whether detach-on-fork mode is on/off.
2817 If you choose to set @samp{detach-on-fork} mode off, then @value{GDBN}
2818 will retain control of all forked processes (including nested forks).
2819 You can list the forked processes under the control of @value{GDBN} by
2820 using the @w{@code{info inferiors}} command, and switch from one fork
2821 to another by using the @code{inferior} command (@pxref{Inferiors,
2822 ,Debugging Multiple Inferiors}).
2824 To quit debugging one of the forked processes, you can either detach
2825 from it by using the @w{@code{detach inferior}} command (allowing it
2826 to run independently), or kill it using the @w{@code{kill inferior}}
2827 command. @xref{Inferiors, ,Debugging Multiple Inferiors}.
2829 If you ask to debug a child process and a @code{vfork} is followed by an
2830 @code{exec}, @value{GDBN} executes the new target up to the first
2831 breakpoint in the new target. If you have a breakpoint set on
2832 @code{main} in your original program, the breakpoint will also be set on
2833 the child process's @code{main}.
2835 On some systems, when a child process is spawned by @code{vfork}, you
2836 cannot debug the child or parent until an @code{exec} call completes.
2838 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2839 call executes, the new target restarts. To restart the parent process,
2840 use the @code{file} command with the parent executable name as its
2843 You can use the @code{catch} command to make @value{GDBN} stop whenever
2844 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2845 Catchpoints, ,Setting Catchpoints}.
2847 @node Checkpoint/Restart
2848 @section Setting a @emph{Bookmark} to Return to Later
2853 @cindex snapshot of a process
2854 @cindex rewind program state
2856 On certain operating systems@footnote{Currently, only
2857 @sc{gnu}/Linux.}, @value{GDBN} is able to save a @dfn{snapshot} of a
2858 program's state, called a @dfn{checkpoint}, and come back to it
2861 Returning to a checkpoint effectively undoes everything that has
2862 happened in the program since the @code{checkpoint} was saved. This
2863 includes changes in memory, registers, and even (within some limits)
2864 system state. Effectively, it is like going back in time to the
2865 moment when the checkpoint was saved.
2867 Thus, if you're stepping thru a program and you think you're
2868 getting close to the point where things go wrong, you can save
2869 a checkpoint. Then, if you accidentally go too far and miss
2870 the critical statement, instead of having to restart your program
2871 from the beginning, you can just go back to the checkpoint and
2872 start again from there.
2874 This can be especially useful if it takes a lot of time or
2875 steps to reach the point where you think the bug occurs.
2877 To use the @code{checkpoint}/@code{restart} method of debugging:
2882 Save a snapshot of the debugged program's current execution state.
2883 The @code{checkpoint} command takes no arguments, but each checkpoint
2884 is assigned a small integer id, similar to a breakpoint id.
2886 @kindex info checkpoints
2887 @item info checkpoints
2888 List the checkpoints that have been saved in the current debugging
2889 session. For each checkpoint, the following information will be
2896 @item Source line, or label
2899 @kindex restart @var{checkpoint-id}
2900 @item restart @var{checkpoint-id}
2901 Restore the program state that was saved as checkpoint number
2902 @var{checkpoint-id}. All program variables, registers, stack frames
2903 etc.@: will be returned to the values that they had when the checkpoint
2904 was saved. In essence, gdb will ``wind back the clock'' to the point
2905 in time when the checkpoint was saved.
2907 Note that breakpoints, @value{GDBN} variables, command history etc.
2908 are not affected by restoring a checkpoint. In general, a checkpoint
2909 only restores things that reside in the program being debugged, not in
2912 @kindex delete checkpoint @var{checkpoint-id}
2913 @item delete checkpoint @var{checkpoint-id}
2914 Delete the previously-saved checkpoint identified by @var{checkpoint-id}.
2918 Returning to a previously saved checkpoint will restore the user state
2919 of the program being debugged, plus a significant subset of the system
2920 (OS) state, including file pointers. It won't ``un-write'' data from
2921 a file, but it will rewind the file pointer to the previous location,
2922 so that the previously written data can be overwritten. For files
2923 opened in read mode, the pointer will also be restored so that the
2924 previously read data can be read again.
2926 Of course, characters that have been sent to a printer (or other
2927 external device) cannot be ``snatched back'', and characters received
2928 from eg.@: a serial device can be removed from internal program buffers,
2929 but they cannot be ``pushed back'' into the serial pipeline, ready to
2930 be received again. Similarly, the actual contents of files that have
2931 been changed cannot be restored (at this time).
2933 However, within those constraints, you actually can ``rewind'' your
2934 program to a previously saved point in time, and begin debugging it
2935 again --- and you can change the course of events so as to debug a
2936 different execution path this time.
2938 @cindex checkpoints and process id
2939 Finally, there is one bit of internal program state that will be
2940 different when you return to a checkpoint --- the program's process
2941 id. Each checkpoint will have a unique process id (or @var{pid}),
2942 and each will be different from the program's original @var{pid}.
2943 If your program has saved a local copy of its process id, this could
2944 potentially pose a problem.
2946 @subsection A Non-obvious Benefit of Using Checkpoints
2948 On some systems such as @sc{gnu}/Linux, address space randomization
2949 is performed on new processes for security reasons. This makes it
2950 difficult or impossible to set a breakpoint, or watchpoint, on an
2951 absolute address if you have to restart the program, since the
2952 absolute location of a symbol will change from one execution to the
2955 A checkpoint, however, is an @emph{identical} copy of a process.
2956 Therefore if you create a checkpoint at (eg.@:) the start of main,
2957 and simply return to that checkpoint instead of restarting the
2958 process, you can avoid the effects of address randomization and
2959 your symbols will all stay in the same place.
2962 @chapter Stopping and Continuing
2964 The principal purposes of using a debugger are so that you can stop your
2965 program before it terminates; or so that, if your program runs into
2966 trouble, you can investigate and find out why.
2968 Inside @value{GDBN}, your program may stop for any of several reasons,
2969 such as a signal, a breakpoint, or reaching a new line after a
2970 @value{GDBN} command such as @code{step}. You may then examine and
2971 change variables, set new breakpoints or remove old ones, and then
2972 continue execution. Usually, the messages shown by @value{GDBN} provide
2973 ample explanation of the status of your program---but you can also
2974 explicitly request this information at any time.
2977 @kindex info program
2979 Display information about the status of your program: whether it is
2980 running or not, what process it is, and why it stopped.
2984 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2985 * Continuing and Stepping:: Resuming execution
2987 * Thread Stops:: Stopping and starting multi-thread programs
2991 @section Breakpoints, Watchpoints, and Catchpoints
2994 A @dfn{breakpoint} makes your program stop whenever a certain point in
2995 the program is reached. For each breakpoint, you can add conditions to
2996 control in finer detail whether your program stops. You can set
2997 breakpoints with the @code{break} command and its variants (@pxref{Set
2998 Breaks, ,Setting Breakpoints}), to specify the place where your program
2999 should stop by line number, function name or exact address in the
3002 On some systems, you can set breakpoints in shared libraries before
3003 the executable is run. There is a minor limitation on HP-UX systems:
3004 you must wait until the executable is run in order to set breakpoints
3005 in shared library routines that are not called directly by the program
3006 (for example, routines that are arguments in a @code{pthread_create}
3010 @cindex data breakpoints
3011 @cindex memory tracing
3012 @cindex breakpoint on memory address
3013 @cindex breakpoint on variable modification
3014 A @dfn{watchpoint} is a special breakpoint that stops your program
3015 when the value of an expression changes. The expression may be a value
3016 of a variable, or it could involve values of one or more variables
3017 combined by operators, such as @samp{a + b}. This is sometimes called
3018 @dfn{data breakpoints}. You must use a different command to set
3019 watchpoints (@pxref{Set Watchpoints, ,Setting Watchpoints}), but aside
3020 from that, you can manage a watchpoint like any other breakpoint: you
3021 enable, disable, and delete both breakpoints and watchpoints using the
3024 You can arrange to have values from your program displayed automatically
3025 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
3029 @cindex breakpoint on events
3030 A @dfn{catchpoint} is another special breakpoint that stops your program
3031 when a certain kind of event occurs, such as the throwing of a C@t{++}
3032 exception or the loading of a library. As with watchpoints, you use a
3033 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
3034 Catchpoints}), but aside from that, you can manage a catchpoint like any
3035 other breakpoint. (To stop when your program receives a signal, use the
3036 @code{handle} command; see @ref{Signals, ,Signals}.)
3038 @cindex breakpoint numbers
3039 @cindex numbers for breakpoints
3040 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
3041 catchpoint when you create it; these numbers are successive integers
3042 starting with one. In many of the commands for controlling various
3043 features of breakpoints you use the breakpoint number to say which
3044 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
3045 @dfn{disabled}; if disabled, it has no effect on your program until you
3048 @cindex breakpoint ranges
3049 @cindex ranges of breakpoints
3050 Some @value{GDBN} commands accept a range of breakpoints on which to
3051 operate. A breakpoint range is either a single breakpoint number, like
3052 @samp{5}, or two such numbers, in increasing order, separated by a
3053 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
3054 all breakpoints in that range are operated on.
3057 * Set Breaks:: Setting breakpoints
3058 * Set Watchpoints:: Setting watchpoints
3059 * Set Catchpoints:: Setting catchpoints
3060 * Delete Breaks:: Deleting breakpoints
3061 * Disabling:: Disabling breakpoints
3062 * Conditions:: Break conditions
3063 * Break Commands:: Breakpoint command lists
3064 * Error in Breakpoints:: ``Cannot insert breakpoints''
3065 * Breakpoint-related Warnings:: ``Breakpoint address adjusted...''
3069 @subsection Setting Breakpoints
3071 @c FIXME LMB what does GDB do if no code on line of breakpt?
3072 @c consider in particular declaration with/without initialization.
3074 @c FIXME 2 is there stuff on this already? break at fun start, already init?
3077 @kindex b @r{(@code{break})}
3078 @vindex $bpnum@r{, convenience variable}
3079 @cindex latest breakpoint
3080 Breakpoints are set with the @code{break} command (abbreviated
3081 @code{b}). The debugger convenience variable @samp{$bpnum} records the
3082 number of the breakpoint you've set most recently; see @ref{Convenience
3083 Vars,, Convenience Variables}, for a discussion of what you can do with
3084 convenience variables.
3087 @item break @var{location}
3088 Set a breakpoint at the given @var{location}, which can specify a
3089 function name, a line number, or an address of an instruction.
3090 (@xref{Specify Location}, for a list of all the possible ways to
3091 specify a @var{location}.) The breakpoint will stop your program just
3092 before it executes any of the code in the specified @var{location}.
3094 When using source languages that permit overloading of symbols, such as
3095 C@t{++}, a function name may refer to more than one possible place to break.
3096 @xref{Ambiguous Expressions,,Ambiguous Expressions}, for a discussion of
3099 It is also possible to insert a breakpoint that will stop the program
3100 only if a specific thread (@pxref{Thread-Specific Breakpoints})
3101 or a specific task (@pxref{Ada Tasks}) hits that breakpoint.
3104 When called without any arguments, @code{break} sets a breakpoint at
3105 the next instruction to be executed in the selected stack frame
3106 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
3107 innermost, this makes your program stop as soon as control
3108 returns to that frame. This is similar to the effect of a
3109 @code{finish} command in the frame inside the selected frame---except
3110 that @code{finish} does not leave an active breakpoint. If you use
3111 @code{break} without an argument in the innermost frame, @value{GDBN} stops
3112 the next time it reaches the current location; this may be useful
3115 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
3116 least one instruction has been executed. If it did not do this, you
3117 would be unable to proceed past a breakpoint without first disabling the
3118 breakpoint. This rule applies whether or not the breakpoint already
3119 existed when your program stopped.
3121 @item break @dots{} if @var{cond}
3122 Set a breakpoint with condition @var{cond}; evaluate the expression
3123 @var{cond} each time the breakpoint is reached, and stop only if the
3124 value is nonzero---that is, if @var{cond} evaluates as true.
3125 @samp{@dots{}} stands for one of the possible arguments described
3126 above (or no argument) specifying where to break. @xref{Conditions,
3127 ,Break Conditions}, for more information on breakpoint conditions.
3130 @item tbreak @var{args}
3131 Set a breakpoint enabled only for one stop. @var{args} are the
3132 same as for the @code{break} command, and the breakpoint is set in the same
3133 way, but the breakpoint is automatically deleted after the first time your
3134 program stops there. @xref{Disabling, ,Disabling Breakpoints}.
3137 @cindex hardware breakpoints
3138 @item hbreak @var{args}
3139 Set a hardware-assisted breakpoint. @var{args} are the same as for the
3140 @code{break} command and the breakpoint is set in the same way, but the
3141 breakpoint requires hardware support and some target hardware may not
3142 have this support. The main purpose of this is EPROM/ROM code
3143 debugging, so you can set a breakpoint at an instruction without
3144 changing the instruction. This can be used with the new trap-generation
3145 provided by SPARClite DSU and most x86-based targets. These targets
3146 will generate traps when a program accesses some data or instruction
3147 address that is assigned to the debug registers. However the hardware
3148 breakpoint registers can take a limited number of breakpoints. For
3149 example, on the DSU, only two data breakpoints can be set at a time, and
3150 @value{GDBN} will reject this command if more than two are used. Delete
3151 or disable unused hardware breakpoints before setting new ones
3152 (@pxref{Disabling, ,Disabling Breakpoints}).
3153 @xref{Conditions, ,Break Conditions}.
3154 For remote targets, you can restrict the number of hardware
3155 breakpoints @value{GDBN} will use, see @ref{set remote
3156 hardware-breakpoint-limit}.
3159 @item thbreak @var{args}
3160 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
3161 are the same as for the @code{hbreak} command and the breakpoint is set in
3162 the same way. However, like the @code{tbreak} command,
3163 the breakpoint is automatically deleted after the
3164 first time your program stops there. Also, like the @code{hbreak}
3165 command, the breakpoint requires hardware support and some target hardware
3166 may not have this support. @xref{Disabling, ,Disabling Breakpoints}.
3167 See also @ref{Conditions, ,Break Conditions}.
3170 @cindex regular expression
3171 @cindex breakpoints in functions matching a regexp
3172 @cindex set breakpoints in many functions
3173 @item rbreak @var{regex}
3174 Set breakpoints on all functions matching the regular expression
3175 @var{regex}. This command sets an unconditional breakpoint on all
3176 matches, printing a list of all breakpoints it set. Once these
3177 breakpoints are set, they are treated just like the breakpoints set with
3178 the @code{break} command. You can delete them, disable them, or make
3179 them conditional the same way as any other breakpoint.
3181 The syntax of the regular expression is the standard one used with tools
3182 like @file{grep}. Note that this is different from the syntax used by
3183 shells, so for instance @code{foo*} matches all functions that include
3184 an @code{fo} followed by zero or more @code{o}s. There is an implicit
3185 @code{.*} leading and trailing the regular expression you supply, so to
3186 match only functions that begin with @code{foo}, use @code{^foo}.
3188 @cindex non-member C@t{++} functions, set breakpoint in
3189 When debugging C@t{++} programs, @code{rbreak} is useful for setting
3190 breakpoints on overloaded functions that are not members of any special
3193 @cindex set breakpoints on all functions
3194 The @code{rbreak} command can be used to set breakpoints in
3195 @strong{all} the functions in a program, like this:
3198 (@value{GDBP}) rbreak .
3201 @kindex info breakpoints
3202 @cindex @code{$_} and @code{info breakpoints}
3203 @item info breakpoints @r{[}@var{n}@r{]}
3204 @itemx info break @r{[}@var{n}@r{]}
3205 @itemx info watchpoints @r{[}@var{n}@r{]}
3206 Print a table of all breakpoints, watchpoints, and catchpoints set and
3207 not deleted. Optional argument @var{n} means print information only
3208 about the specified breakpoint (or watchpoint or catchpoint). For
3209 each breakpoint, following columns are printed:
3212 @item Breakpoint Numbers
3214 Breakpoint, watchpoint, or catchpoint.
3216 Whether the breakpoint is marked to be disabled or deleted when hit.
3217 @item Enabled or Disabled
3218 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
3219 that are not enabled.
3221 Where the breakpoint is in your program, as a memory address. For a
3222 pending breakpoint whose address is not yet known, this field will
3223 contain @samp{<PENDING>}. Such breakpoint won't fire until a shared
3224 library that has the symbol or line referred by breakpoint is loaded.
3225 See below for details. A breakpoint with several locations will
3226 have @samp{<MULTIPLE>} in this field---see below for details.
3228 Where the breakpoint is in the source for your program, as a file and
3229 line number. For a pending breakpoint, the original string passed to
3230 the breakpoint command will be listed as it cannot be resolved until
3231 the appropriate shared library is loaded in the future.
3235 If a breakpoint is conditional, @code{info break} shows the condition on
3236 the line following the affected breakpoint; breakpoint commands, if any,
3237 are listed after that. A pending breakpoint is allowed to have a condition
3238 specified for it. The condition is not parsed for validity until a shared
3239 library is loaded that allows the pending breakpoint to resolve to a
3243 @code{info break} with a breakpoint
3244 number @var{n} as argument lists only that breakpoint. The
3245 convenience variable @code{$_} and the default examining-address for
3246 the @code{x} command are set to the address of the last breakpoint
3247 listed (@pxref{Memory, ,Examining Memory}).
3250 @code{info break} displays a count of the number of times the breakpoint
3251 has been hit. This is especially useful in conjunction with the
3252 @code{ignore} command. You can ignore a large number of breakpoint
3253 hits, look at the breakpoint info to see how many times the breakpoint
3254 was hit, and then run again, ignoring one less than that number. This
3255 will get you quickly to the last hit of that breakpoint.
3258 @value{GDBN} allows you to set any number of breakpoints at the same place in
3259 your program. There is nothing silly or meaningless about this. When
3260 the breakpoints are conditional, this is even useful
3261 (@pxref{Conditions, ,Break Conditions}).
3263 @cindex multiple locations, breakpoints
3264 @cindex breakpoints, multiple locations
3265 It is possible that a breakpoint corresponds to several locations
3266 in your program. Examples of this situation are:
3270 For a C@t{++} constructor, the @value{NGCC} compiler generates several
3271 instances of the function body, used in different cases.
3274 For a C@t{++} template function, a given line in the function can
3275 correspond to any number of instantiations.
3278 For an inlined function, a given source line can correspond to
3279 several places where that function is inlined.
3282 In all those cases, @value{GDBN} will insert a breakpoint at all
3283 the relevant locations@footnote{
3284 As of this writing, multiple-location breakpoints work only if there's
3285 line number information for all the locations. This means that they
3286 will generally not work in system libraries, unless you have debug
3287 info with line numbers for them.}.
3289 A breakpoint with multiple locations is displayed in the breakpoint
3290 table using several rows---one header row, followed by one row for
3291 each breakpoint location. The header row has @samp{<MULTIPLE>} in the
3292 address column. The rows for individual locations contain the actual
3293 addresses for locations, and show the functions to which those
3294 locations belong. The number column for a location is of the form
3295 @var{breakpoint-number}.@var{location-number}.
3300 Num Type Disp Enb Address What
3301 1 breakpoint keep y <MULTIPLE>
3303 breakpoint already hit 1 time
3304 1.1 y 0x080486a2 in void foo<int>() at t.cc:8
3305 1.2 y 0x080486ca in void foo<double>() at t.cc:8
3308 Each location can be individually enabled or disabled by passing
3309 @var{breakpoint-number}.@var{location-number} as argument to the
3310 @code{enable} and @code{disable} commands. Note that you cannot
3311 delete the individual locations from the list, you can only delete the
3312 entire list of locations that belong to their parent breakpoint (with
3313 the @kbd{delete @var{num}} command, where @var{num} is the number of
3314 the parent breakpoint, 1 in the above example). Disabling or enabling
3315 the parent breakpoint (@pxref{Disabling}) affects all of the locations
3316 that belong to that breakpoint.
3318 @cindex pending breakpoints
3319 It's quite common to have a breakpoint inside a shared library.
3320 Shared libraries can be loaded and unloaded explicitly,
3321 and possibly repeatedly, as the program is executed. To support
3322 this use case, @value{GDBN} updates breakpoint locations whenever
3323 any shared library is loaded or unloaded. Typically, you would
3324 set a breakpoint in a shared library at the beginning of your
3325 debugging session, when the library is not loaded, and when the
3326 symbols from the library are not available. When you try to set
3327 breakpoint, @value{GDBN} will ask you if you want to set
3328 a so called @dfn{pending breakpoint}---breakpoint whose address
3329 is not yet resolved.
3331 After the program is run, whenever a new shared library is loaded,
3332 @value{GDBN} reevaluates all the breakpoints. When a newly loaded
3333 shared library contains the symbol or line referred to by some
3334 pending breakpoint, that breakpoint is resolved and becomes an
3335 ordinary breakpoint. When a library is unloaded, all breakpoints
3336 that refer to its symbols or source lines become pending again.
3338 This logic works for breakpoints with multiple locations, too. For
3339 example, if you have a breakpoint in a C@t{++} template function, and
3340 a newly loaded shared library has an instantiation of that template,
3341 a new location is added to the list of locations for the breakpoint.
3343 Except for having unresolved address, pending breakpoints do not
3344 differ from regular breakpoints. You can set conditions or commands,
3345 enable and disable them and perform other breakpoint operations.
3347 @value{GDBN} provides some additional commands for controlling what
3348 happens when the @samp{break} command cannot resolve breakpoint
3349 address specification to an address:
3351 @kindex set breakpoint pending
3352 @kindex show breakpoint pending
3354 @item set breakpoint pending auto
3355 This is the default behavior. When @value{GDBN} cannot find the breakpoint
3356 location, it queries you whether a pending breakpoint should be created.
3358 @item set breakpoint pending on
3359 This indicates that an unrecognized breakpoint location should automatically
3360 result in a pending breakpoint being created.
3362 @item set breakpoint pending off
3363 This indicates that pending breakpoints are not to be created. Any
3364 unrecognized breakpoint location results in an error. This setting does
3365 not affect any pending breakpoints previously created.
3367 @item show breakpoint pending
3368 Show the current behavior setting for creating pending breakpoints.
3371 The settings above only affect the @code{break} command and its
3372 variants. Once breakpoint is set, it will be automatically updated
3373 as shared libraries are loaded and unloaded.
3375 @cindex automatic hardware breakpoints
3376 For some targets, @value{GDBN} can automatically decide if hardware or
3377 software breakpoints should be used, depending on whether the
3378 breakpoint address is read-only or read-write. This applies to
3379 breakpoints set with the @code{break} command as well as to internal
3380 breakpoints set by commands like @code{next} and @code{finish}. For
3381 breakpoints set with @code{hbreak}, @value{GDBN} will always use hardware
3384 You can control this automatic behaviour with the following commands::
3386 @kindex set breakpoint auto-hw
3387 @kindex show breakpoint auto-hw
3389 @item set breakpoint auto-hw on
3390 This is the default behavior. When @value{GDBN} sets a breakpoint, it
3391 will try to use the target memory map to decide if software or hardware
3392 breakpoint must be used.
3394 @item set breakpoint auto-hw off
3395 This indicates @value{GDBN} should not automatically select breakpoint
3396 type. If the target provides a memory map, @value{GDBN} will warn when
3397 trying to set software breakpoint at a read-only address.
3400 @value{GDBN} normally implements breakpoints by replacing the program code
3401 at the breakpoint address with a special instruction, which, when
3402 executed, given control to the debugger. By default, the program
3403 code is so modified only when the program is resumed. As soon as
3404 the program stops, @value{GDBN} restores the original instructions. This
3405 behaviour guards against leaving breakpoints inserted in the
3406 target should gdb abrubptly disconnect. However, with slow remote
3407 targets, inserting and removing breakpoint can reduce the performance.
3408 This behavior can be controlled with the following commands::
3410 @kindex set breakpoint always-inserted
3411 @kindex show breakpoint always-inserted
3413 @item set breakpoint always-inserted off
3414 All breakpoints, including newly added by the user, are inserted in
3415 the target only when the target is resumed. All breakpoints are
3416 removed from the target when it stops.
3418 @item set breakpoint always-inserted on
3419 Causes all breakpoints to be inserted in the target at all times. If
3420 the user adds a new breakpoint, or changes an existing breakpoint, the
3421 breakpoints in the target are updated immediately. A breakpoint is
3422 removed from the target only when breakpoint itself is removed.
3424 @cindex non-stop mode, and @code{breakpoint always-inserted}
3425 @item set breakpoint always-inserted auto
3426 This is the default mode. If @value{GDBN} is controlling the inferior
3427 in non-stop mode (@pxref{Non-Stop Mode}), gdb behaves as if
3428 @code{breakpoint always-inserted} mode is on. If @value{GDBN} is
3429 controlling the inferior in all-stop mode, @value{GDBN} behaves as if
3430 @code{breakpoint always-inserted} mode is off.
3433 @cindex negative breakpoint numbers
3434 @cindex internal @value{GDBN} breakpoints
3435 @value{GDBN} itself sometimes sets breakpoints in your program for
3436 special purposes, such as proper handling of @code{longjmp} (in C
3437 programs). These internal breakpoints are assigned negative numbers,
3438 starting with @code{-1}; @samp{info breakpoints} does not display them.
3439 You can see these breakpoints with the @value{GDBN} maintenance command
3440 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
3443 @node Set Watchpoints
3444 @subsection Setting Watchpoints
3446 @cindex setting watchpoints
3447 You can use a watchpoint to stop execution whenever the value of an
3448 expression changes, without having to predict a particular place where
3449 this may happen. (This is sometimes called a @dfn{data breakpoint}.)
3450 The expression may be as simple as the value of a single variable, or
3451 as complex as many variables combined by operators. Examples include:
3455 A reference to the value of a single variable.
3458 An address cast to an appropriate data type. For example,
3459 @samp{*(int *)0x12345678} will watch a 4-byte region at the specified
3460 address (assuming an @code{int} occupies 4 bytes).
3463 An arbitrarily complex expression, such as @samp{a*b + c/d}. The
3464 expression can use any operators valid in the program's native
3465 language (@pxref{Languages}).
3468 You can set a watchpoint on an expression even if the expression can
3469 not be evaluated yet. For instance, you can set a watchpoint on
3470 @samp{*global_ptr} before @samp{global_ptr} is initialized.
3471 @value{GDBN} will stop when your program sets @samp{global_ptr} and
3472 the expression produces a valid value. If the expression becomes
3473 valid in some other way than changing a variable (e.g.@: if the memory
3474 pointed to by @samp{*global_ptr} becomes readable as the result of a
3475 @code{malloc} call), @value{GDBN} may not stop until the next time
3476 the expression changes.
3478 @cindex software watchpoints
3479 @cindex hardware watchpoints
3480 Depending on your system, watchpoints may be implemented in software or
3481 hardware. @value{GDBN} does software watchpointing by single-stepping your
3482 program and testing the variable's value each time, which is hundreds of
3483 times slower than normal execution. (But this may still be worth it, to
3484 catch errors where you have no clue what part of your program is the
3487 On some systems, such as HP-UX, PowerPC, @sc{gnu}/Linux and most other
3488 x86-based targets, @value{GDBN} includes support for hardware
3489 watchpoints, which do not slow down the running of your program.
3493 @item watch @var{expr} @r{[}thread @var{threadnum}@r{]}
3494 Set a watchpoint for an expression. @value{GDBN} will break when the
3495 expression @var{expr} is written into by the program and its value
3496 changes. The simplest (and the most popular) use of this command is
3497 to watch the value of a single variable:
3500 (@value{GDBP}) watch foo
3503 If the command includes a @code{@r{[}thread @var{threadnum}@r{]}}
3504 clause, @value{GDBN} breaks only when the thread identified by
3505 @var{threadnum} changes the value of @var{expr}. If any other threads
3506 change the value of @var{expr}, @value{GDBN} will not break. Note
3507 that watchpoints restricted to a single thread in this way only work
3508 with Hardware Watchpoints.
3511 @item rwatch @var{expr} @r{[}thread @var{threadnum}@r{]}
3512 Set a watchpoint that will break when the value of @var{expr} is read
3516 @item awatch @var{expr} @r{[}thread @var{threadnum}@r{]}
3517 Set a watchpoint that will break when @var{expr} is either read from
3518 or written into by the program.
3520 @kindex info watchpoints @r{[}@var{n}@r{]}
3521 @item info watchpoints
3522 This command prints a list of watchpoints, breakpoints, and catchpoints;
3523 it is the same as @code{info break} (@pxref{Set Breaks}).
3526 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
3527 watchpoints execute very quickly, and the debugger reports a change in
3528 value at the exact instruction where the change occurs. If @value{GDBN}
3529 cannot set a hardware watchpoint, it sets a software watchpoint, which
3530 executes more slowly and reports the change in value at the next
3531 @emph{statement}, not the instruction, after the change occurs.
3533 @cindex use only software watchpoints
3534 You can force @value{GDBN} to use only software watchpoints with the
3535 @kbd{set can-use-hw-watchpoints 0} command. With this variable set to
3536 zero, @value{GDBN} will never try to use hardware watchpoints, even if
3537 the underlying system supports them. (Note that hardware-assisted
3538 watchpoints that were set @emph{before} setting
3539 @code{can-use-hw-watchpoints} to zero will still use the hardware
3540 mechanism of watching expression values.)
3543 @item set can-use-hw-watchpoints
3544 @kindex set can-use-hw-watchpoints
3545 Set whether or not to use hardware watchpoints.
3547 @item show can-use-hw-watchpoints
3548 @kindex show can-use-hw-watchpoints
3549 Show the current mode of using hardware watchpoints.
3552 For remote targets, you can restrict the number of hardware
3553 watchpoints @value{GDBN} will use, see @ref{set remote
3554 hardware-breakpoint-limit}.
3556 When you issue the @code{watch} command, @value{GDBN} reports
3559 Hardware watchpoint @var{num}: @var{expr}
3563 if it was able to set a hardware watchpoint.
3565 Currently, the @code{awatch} and @code{rwatch} commands can only set
3566 hardware watchpoints, because accesses to data that don't change the
3567 value of the watched expression cannot be detected without examining
3568 every instruction as it is being executed, and @value{GDBN} does not do
3569 that currently. If @value{GDBN} finds that it is unable to set a
3570 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
3571 will print a message like this:
3574 Expression cannot be implemented with read/access watchpoint.
3577 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
3578 data type of the watched expression is wider than what a hardware
3579 watchpoint on the target machine can handle. For example, some systems
3580 can only watch regions that are up to 4 bytes wide; on such systems you
3581 cannot set hardware watchpoints for an expression that yields a
3582 double-precision floating-point number (which is typically 8 bytes
3583 wide). As a work-around, it might be possible to break the large region
3584 into a series of smaller ones and watch them with separate watchpoints.
3586 If you set too many hardware watchpoints, @value{GDBN} might be unable
3587 to insert all of them when you resume the execution of your program.
3588 Since the precise number of active watchpoints is unknown until such
3589 time as the program is about to be resumed, @value{GDBN} might not be
3590 able to warn you about this when you set the watchpoints, and the
3591 warning will be printed only when the program is resumed:
3594 Hardware watchpoint @var{num}: Could not insert watchpoint
3598 If this happens, delete or disable some of the watchpoints.
3600 Watching complex expressions that reference many variables can also
3601 exhaust the resources available for hardware-assisted watchpoints.
3602 That's because @value{GDBN} needs to watch every variable in the
3603 expression with separately allocated resources.
3605 If you call a function interactively using @code{print} or @code{call},
3606 any watchpoints you have set will be inactive until @value{GDBN} reaches another
3607 kind of breakpoint or the call completes.
3609 @value{GDBN} automatically deletes watchpoints that watch local
3610 (automatic) variables, or expressions that involve such variables, when
3611 they go out of scope, that is, when the execution leaves the block in
3612 which these variables were defined. In particular, when the program
3613 being debugged terminates, @emph{all} local variables go out of scope,
3614 and so only watchpoints that watch global variables remain set. If you
3615 rerun the program, you will need to set all such watchpoints again. One
3616 way of doing that would be to set a code breakpoint at the entry to the
3617 @code{main} function and when it breaks, set all the watchpoints.
3619 @cindex watchpoints and threads
3620 @cindex threads and watchpoints
3621 In multi-threaded programs, watchpoints will detect changes to the
3622 watched expression from every thread.
3625 @emph{Warning:} In multi-threaded programs, software watchpoints
3626 have only limited usefulness. If @value{GDBN} creates a software
3627 watchpoint, it can only watch the value of an expression @emph{in a
3628 single thread}. If you are confident that the expression can only
3629 change due to the current thread's activity (and if you are also
3630 confident that no other thread can become current), then you can use
3631 software watchpoints as usual. However, @value{GDBN} may not notice
3632 when a non-current thread's activity changes the expression. (Hardware
3633 watchpoints, in contrast, watch an expression in all threads.)
3636 @xref{set remote hardware-watchpoint-limit}.
3638 @node Set Catchpoints
3639 @subsection Setting Catchpoints
3640 @cindex catchpoints, setting
3641 @cindex exception handlers
3642 @cindex event handling
3644 You can use @dfn{catchpoints} to cause the debugger to stop for certain
3645 kinds of program events, such as C@t{++} exceptions or the loading of a
3646 shared library. Use the @code{catch} command to set a catchpoint.
3650 @item catch @var{event}
3651 Stop when @var{event} occurs. @var{event} can be any of the following:
3654 @cindex stop on C@t{++} exceptions
3655 The throwing of a C@t{++} exception.
3658 The catching of a C@t{++} exception.
3661 @cindex Ada exception catching
3662 @cindex catch Ada exceptions
3663 An Ada exception being raised. If an exception name is specified
3664 at the end of the command (eg @code{catch exception Program_Error}),
3665 the debugger will stop only when this specific exception is raised.
3666 Otherwise, the debugger stops execution when any Ada exception is raised.
3668 When inserting an exception catchpoint on a user-defined exception whose
3669 name is identical to one of the exceptions defined by the language, the
3670 fully qualified name must be used as the exception name. Otherwise,
3671 @value{GDBN} will assume that it should stop on the pre-defined exception
3672 rather than the user-defined one. For instance, assuming an exception
3673 called @code{Constraint_Error} is defined in package @code{Pck}, then
3674 the command to use to catch such exceptions is @kbd{catch exception
3675 Pck.Constraint_Error}.
3677 @item exception unhandled
3678 An exception that was raised but is not handled by the program.
3681 A failed Ada assertion.
3684 @cindex break on fork/exec
3685 A call to @code{exec}. This is currently only available for HP-UX
3689 A call to @code{fork}. This is currently only available for HP-UX
3693 A call to @code{vfork}. This is currently only available for HP-UX
3698 @item tcatch @var{event}
3699 Set a catchpoint that is enabled only for one stop. The catchpoint is
3700 automatically deleted after the first time the event is caught.
3704 Use the @code{info break} command to list the current catchpoints.
3706 There are currently some limitations to C@t{++} exception handling
3707 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
3711 If you call a function interactively, @value{GDBN} normally returns
3712 control to you when the function has finished executing. If the call
3713 raises an exception, however, the call may bypass the mechanism that
3714 returns control to you and cause your program either to abort or to
3715 simply continue running until it hits a breakpoint, catches a signal
3716 that @value{GDBN} is listening for, or exits. This is the case even if
3717 you set a catchpoint for the exception; catchpoints on exceptions are
3718 disabled within interactive calls.
3721 You cannot raise an exception interactively.
3724 You cannot install an exception handler interactively.
3727 @cindex raise exceptions
3728 Sometimes @code{catch} is not the best way to debug exception handling:
3729 if you need to know exactly where an exception is raised, it is better to
3730 stop @emph{before} the exception handler is called, since that way you
3731 can see the stack before any unwinding takes place. If you set a
3732 breakpoint in an exception handler instead, it may not be easy to find
3733 out where the exception was raised.
3735 To stop just before an exception handler is called, you need some
3736 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
3737 raised by calling a library function named @code{__raise_exception}
3738 which has the following ANSI C interface:
3741 /* @var{addr} is where the exception identifier is stored.
3742 @var{id} is the exception identifier. */
3743 void __raise_exception (void **addr, void *id);
3747 To make the debugger catch all exceptions before any stack
3748 unwinding takes place, set a breakpoint on @code{__raise_exception}
3749 (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Exceptions}).
3751 With a conditional breakpoint (@pxref{Conditions, ,Break Conditions})
3752 that depends on the value of @var{id}, you can stop your program when
3753 a specific exception is raised. You can use multiple conditional
3754 breakpoints to stop your program when any of a number of exceptions are
3759 @subsection Deleting Breakpoints
3761 @cindex clearing breakpoints, watchpoints, catchpoints
3762 @cindex deleting breakpoints, watchpoints, catchpoints
3763 It is often necessary to eliminate a breakpoint, watchpoint, or
3764 catchpoint once it has done its job and you no longer want your program
3765 to stop there. This is called @dfn{deleting} the breakpoint. A
3766 breakpoint that has been deleted no longer exists; it is forgotten.
3768 With the @code{clear} command you can delete breakpoints according to
3769 where they are in your program. With the @code{delete} command you can
3770 delete individual breakpoints, watchpoints, or catchpoints by specifying
3771 their breakpoint numbers.
3773 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
3774 automatically ignores breakpoints on the first instruction to be executed
3775 when you continue execution without changing the execution address.
3780 Delete any breakpoints at the next instruction to be executed in the
3781 selected stack frame (@pxref{Selection, ,Selecting a Frame}). When
3782 the innermost frame is selected, this is a good way to delete a
3783 breakpoint where your program just stopped.
3785 @item clear @var{location}
3786 Delete any breakpoints set at the specified @var{location}.
3787 @xref{Specify Location}, for the various forms of @var{location}; the
3788 most useful ones are listed below:
3791 @item clear @var{function}
3792 @itemx clear @var{filename}:@var{function}
3793 Delete any breakpoints set at entry to the named @var{function}.
3795 @item clear @var{linenum}
3796 @itemx clear @var{filename}:@var{linenum}
3797 Delete any breakpoints set at or within the code of the specified
3798 @var{linenum} of the specified @var{filename}.
3801 @cindex delete breakpoints
3803 @kindex d @r{(@code{delete})}
3804 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
3805 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
3806 ranges specified as arguments. If no argument is specified, delete all
3807 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
3808 confirm off}). You can abbreviate this command as @code{d}.
3812 @subsection Disabling Breakpoints
3814 @cindex enable/disable a breakpoint
3815 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
3816 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
3817 it had been deleted, but remembers the information on the breakpoint so
3818 that you can @dfn{enable} it again later.
3820 You disable and enable breakpoints, watchpoints, and catchpoints with
3821 the @code{enable} and @code{disable} commands, optionally specifying one
3822 or more breakpoint numbers as arguments. Use @code{info break} or
3823 @code{info watch} to print a list of breakpoints, watchpoints, and
3824 catchpoints if you do not know which numbers to use.
3826 Disabling and enabling a breakpoint that has multiple locations
3827 affects all of its locations.
3829 A breakpoint, watchpoint, or catchpoint can have any of four different
3830 states of enablement:
3834 Enabled. The breakpoint stops your program. A breakpoint set
3835 with the @code{break} command starts out in this state.
3837 Disabled. The breakpoint has no effect on your program.
3839 Enabled once. The breakpoint stops your program, but then becomes
3842 Enabled for deletion. The breakpoint stops your program, but
3843 immediately after it does so it is deleted permanently. A breakpoint
3844 set with the @code{tbreak} command starts out in this state.
3847 You can use the following commands to enable or disable breakpoints,
3848 watchpoints, and catchpoints:
3852 @kindex dis @r{(@code{disable})}
3853 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
3854 Disable the specified breakpoints---or all breakpoints, if none are
3855 listed. A disabled breakpoint has no effect but is not forgotten. All
3856 options such as ignore-counts, conditions and commands are remembered in
3857 case the breakpoint is enabled again later. You may abbreviate
3858 @code{disable} as @code{dis}.
3861 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
3862 Enable the specified breakpoints (or all defined breakpoints). They
3863 become effective once again in stopping your program.
3865 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
3866 Enable the specified breakpoints temporarily. @value{GDBN} disables any
3867 of these breakpoints immediately after stopping your program.
3869 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
3870 Enable the specified breakpoints to work once, then die. @value{GDBN}
3871 deletes any of these breakpoints as soon as your program stops there.
3872 Breakpoints set by the @code{tbreak} command start out in this state.
3875 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
3876 @c confusing: tbreak is also initially enabled.
3877 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
3878 ,Setting Breakpoints}), breakpoints that you set are initially enabled;
3879 subsequently, they become disabled or enabled only when you use one of
3880 the commands above. (The command @code{until} can set and delete a
3881 breakpoint of its own, but it does not change the state of your other
3882 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
3886 @subsection Break Conditions
3887 @cindex conditional breakpoints
3888 @cindex breakpoint conditions
3890 @c FIXME what is scope of break condition expr? Context where wanted?
3891 @c in particular for a watchpoint?
3892 The simplest sort of breakpoint breaks every time your program reaches a
3893 specified place. You can also specify a @dfn{condition} for a
3894 breakpoint. A condition is just a Boolean expression in your
3895 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
3896 a condition evaluates the expression each time your program reaches it,
3897 and your program stops only if the condition is @emph{true}.
3899 This is the converse of using assertions for program validation; in that
3900 situation, you want to stop when the assertion is violated---that is,
3901 when the condition is false. In C, if you want to test an assertion expressed
3902 by the condition @var{assert}, you should set the condition
3903 @samp{! @var{assert}} on the appropriate breakpoint.
3905 Conditions are also accepted for watchpoints; you may not need them,
3906 since a watchpoint is inspecting the value of an expression anyhow---but
3907 it might be simpler, say, to just set a watchpoint on a variable name,
3908 and specify a condition that tests whether the new value is an interesting
3911 Break conditions can have side effects, and may even call functions in
3912 your program. This can be useful, for example, to activate functions
3913 that log program progress, or to use your own print functions to
3914 format special data structures. The effects are completely predictable
3915 unless there is another enabled breakpoint at the same address. (In
3916 that case, @value{GDBN} might see the other breakpoint first and stop your
3917 program without checking the condition of this one.) Note that
3918 breakpoint commands are usually more convenient and flexible than break
3920 purpose of performing side effects when a breakpoint is reached
3921 (@pxref{Break Commands, ,Breakpoint Command Lists}).
3923 Break conditions can be specified when a breakpoint is set, by using
3924 @samp{if} in the arguments to the @code{break} command. @xref{Set
3925 Breaks, ,Setting Breakpoints}. They can also be changed at any time
3926 with the @code{condition} command.
3928 You can also use the @code{if} keyword with the @code{watch} command.
3929 The @code{catch} command does not recognize the @code{if} keyword;
3930 @code{condition} is the only way to impose a further condition on a
3935 @item condition @var{bnum} @var{expression}
3936 Specify @var{expression} as the break condition for breakpoint,
3937 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3938 breakpoint @var{bnum} stops your program only if the value of
3939 @var{expression} is true (nonzero, in C). When you use
3940 @code{condition}, @value{GDBN} checks @var{expression} immediately for
3941 syntactic correctness, and to determine whether symbols in it have
3942 referents in the context of your breakpoint. If @var{expression} uses
3943 symbols not referenced in the context of the breakpoint, @value{GDBN}
3944 prints an error message:
3947 No symbol "foo" in current context.
3952 not actually evaluate @var{expression} at the time the @code{condition}
3953 command (or a command that sets a breakpoint with a condition, like
3954 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
3956 @item condition @var{bnum}
3957 Remove the condition from breakpoint number @var{bnum}. It becomes
3958 an ordinary unconditional breakpoint.
3961 @cindex ignore count (of breakpoint)
3962 A special case of a breakpoint condition is to stop only when the
3963 breakpoint has been reached a certain number of times. This is so
3964 useful that there is a special way to do it, using the @dfn{ignore
3965 count} of the breakpoint. Every breakpoint has an ignore count, which
3966 is an integer. Most of the time, the ignore count is zero, and
3967 therefore has no effect. But if your program reaches a breakpoint whose
3968 ignore count is positive, then instead of stopping, it just decrements
3969 the ignore count by one and continues. As a result, if the ignore count
3970 value is @var{n}, the breakpoint does not stop the next @var{n} times
3971 your program reaches it.
3975 @item ignore @var{bnum} @var{count}
3976 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3977 The next @var{count} times the breakpoint is reached, your program's
3978 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3981 To make the breakpoint stop the next time it is reached, specify
3984 When you use @code{continue} to resume execution of your program from a
3985 breakpoint, you can specify an ignore count directly as an argument to
3986 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3987 Stepping,,Continuing and Stepping}.
3989 If a breakpoint has a positive ignore count and a condition, the
3990 condition is not checked. Once the ignore count reaches zero,
3991 @value{GDBN} resumes checking the condition.
3993 You could achieve the effect of the ignore count with a condition such
3994 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3995 is decremented each time. @xref{Convenience Vars, ,Convenience
3999 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
4002 @node Break Commands
4003 @subsection Breakpoint Command Lists
4005 @cindex breakpoint commands
4006 You can give any breakpoint (or watchpoint or catchpoint) a series of
4007 commands to execute when your program stops due to that breakpoint. For
4008 example, you might want to print the values of certain expressions, or
4009 enable other breakpoints.
4013 @kindex end@r{ (breakpoint commands)}
4014 @item commands @r{[}@var{bnum}@r{]}
4015 @itemx @dots{} @var{command-list} @dots{}
4017 Specify a list of commands for breakpoint number @var{bnum}. The commands
4018 themselves appear on the following lines. Type a line containing just
4019 @code{end} to terminate the commands.
4021 To remove all commands from a breakpoint, type @code{commands} and
4022 follow it immediately with @code{end}; that is, give no commands.
4024 With no @var{bnum} argument, @code{commands} refers to the last
4025 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
4026 recently encountered).
4029 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
4030 disabled within a @var{command-list}.
4032 You can use breakpoint commands to start your program up again. Simply
4033 use the @code{continue} command, or @code{step}, or any other command
4034 that resumes execution.
4036 Any other commands in the command list, after a command that resumes
4037 execution, are ignored. This is because any time you resume execution
4038 (even with a simple @code{next} or @code{step}), you may encounter
4039 another breakpoint---which could have its own command list, leading to
4040 ambiguities about which list to execute.
4043 If the first command you specify in a command list is @code{silent}, the
4044 usual message about stopping at a breakpoint is not printed. This may
4045 be desirable for breakpoints that are to print a specific message and
4046 then continue. If none of the remaining commands print anything, you
4047 see no sign that the breakpoint was reached. @code{silent} is
4048 meaningful only at the beginning of a breakpoint command list.
4050 The commands @code{echo}, @code{output}, and @code{printf} allow you to
4051 print precisely controlled output, and are often useful in silent
4052 breakpoints. @xref{Output, ,Commands for Controlled Output}.
4054 For example, here is how you could use breakpoint commands to print the
4055 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
4061 printf "x is %d\n",x
4066 One application for breakpoint commands is to compensate for one bug so
4067 you can test for another. Put a breakpoint just after the erroneous line
4068 of code, give it a condition to detect the case in which something
4069 erroneous has been done, and give it commands to assign correct values
4070 to any variables that need them. End with the @code{continue} command
4071 so that your program does not stop, and start with the @code{silent}
4072 command so that no output is produced. Here is an example:
4083 @c @ifclear BARETARGET
4084 @node Error in Breakpoints
4085 @subsection ``Cannot insert breakpoints''
4087 If you request too many active hardware-assisted breakpoints and
4088 watchpoints, you will see this error message:
4090 @c FIXME: the precise wording of this message may change; the relevant
4091 @c source change is not committed yet (Sep 3, 1999).
4093 Stopped; cannot insert breakpoints.
4094 You may have requested too many hardware breakpoints and watchpoints.
4098 This message is printed when you attempt to resume the program, since
4099 only then @value{GDBN} knows exactly how many hardware breakpoints and
4100 watchpoints it needs to insert.
4102 When this message is printed, you need to disable or remove some of the
4103 hardware-assisted breakpoints and watchpoints, and then continue.
4105 @node Breakpoint-related Warnings
4106 @subsection ``Breakpoint address adjusted...''
4107 @cindex breakpoint address adjusted
4109 Some processor architectures place constraints on the addresses at
4110 which breakpoints may be placed. For architectures thus constrained,
4111 @value{GDBN} will attempt to adjust the breakpoint's address to comply
4112 with the constraints dictated by the architecture.
4114 One example of such an architecture is the Fujitsu FR-V. The FR-V is
4115 a VLIW architecture in which a number of RISC-like instructions may be
4116 bundled together for parallel execution. The FR-V architecture
4117 constrains the location of a breakpoint instruction within such a
4118 bundle to the instruction with the lowest address. @value{GDBN}
4119 honors this constraint by adjusting a breakpoint's address to the
4120 first in the bundle.
4122 It is not uncommon for optimized code to have bundles which contain
4123 instructions from different source statements, thus it may happen that
4124 a breakpoint's address will be adjusted from one source statement to
4125 another. Since this adjustment may significantly alter @value{GDBN}'s
4126 breakpoint related behavior from what the user expects, a warning is
4127 printed when the breakpoint is first set and also when the breakpoint
4130 A warning like the one below is printed when setting a breakpoint
4131 that's been subject to address adjustment:
4134 warning: Breakpoint address adjusted from 0x00010414 to 0x00010410.
4137 Such warnings are printed both for user settable and @value{GDBN}'s
4138 internal breakpoints. If you see one of these warnings, you should
4139 verify that a breakpoint set at the adjusted address will have the
4140 desired affect. If not, the breakpoint in question may be removed and
4141 other breakpoints may be set which will have the desired behavior.
4142 E.g., it may be sufficient to place the breakpoint at a later
4143 instruction. A conditional breakpoint may also be useful in some
4144 cases to prevent the breakpoint from triggering too often.
4146 @value{GDBN} will also issue a warning when stopping at one of these
4147 adjusted breakpoints:
4150 warning: Breakpoint 1 address previously adjusted from 0x00010414
4154 When this warning is encountered, it may be too late to take remedial
4155 action except in cases where the breakpoint is hit earlier or more
4156 frequently than expected.
4158 @node Continuing and Stepping
4159 @section Continuing and Stepping
4163 @cindex resuming execution
4164 @dfn{Continuing} means resuming program execution until your program
4165 completes normally. In contrast, @dfn{stepping} means executing just
4166 one more ``step'' of your program, where ``step'' may mean either one
4167 line of source code, or one machine instruction (depending on what
4168 particular command you use). Either when continuing or when stepping,
4169 your program may stop even sooner, due to a breakpoint or a signal. (If
4170 it stops due to a signal, you may want to use @code{handle}, or use
4171 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
4175 @kindex c @r{(@code{continue})}
4176 @kindex fg @r{(resume foreground execution)}
4177 @item continue @r{[}@var{ignore-count}@r{]}
4178 @itemx c @r{[}@var{ignore-count}@r{]}
4179 @itemx fg @r{[}@var{ignore-count}@r{]}
4180 Resume program execution, at the address where your program last stopped;
4181 any breakpoints set at that address are bypassed. The optional argument
4182 @var{ignore-count} allows you to specify a further number of times to
4183 ignore a breakpoint at this location; its effect is like that of
4184 @code{ignore} (@pxref{Conditions, ,Break Conditions}).
4186 The argument @var{ignore-count} is meaningful only when your program
4187 stopped due to a breakpoint. At other times, the argument to
4188 @code{continue} is ignored.
4190 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
4191 debugged program is deemed to be the foreground program) are provided
4192 purely for convenience, and have exactly the same behavior as
4196 To resume execution at a different place, you can use @code{return}
4197 (@pxref{Returning, ,Returning from a Function}) to go back to the
4198 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
4199 Different Address}) to go to an arbitrary location in your program.
4201 A typical technique for using stepping is to set a breakpoint
4202 (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Catchpoints}) at the
4203 beginning of the function or the section of your program where a problem
4204 is believed to lie, run your program until it stops at that breakpoint,
4205 and then step through the suspect area, examining the variables that are
4206 interesting, until you see the problem happen.
4210 @kindex s @r{(@code{step})}
4212 Continue running your program until control reaches a different source
4213 line, then stop it and return control to @value{GDBN}. This command is
4214 abbreviated @code{s}.
4217 @c "without debugging information" is imprecise; actually "without line
4218 @c numbers in the debugging information". (gcc -g1 has debugging info but
4219 @c not line numbers). But it seems complex to try to make that
4220 @c distinction here.
4221 @emph{Warning:} If you use the @code{step} command while control is
4222 within a function that was compiled without debugging information,
4223 execution proceeds until control reaches a function that does have
4224 debugging information. Likewise, it will not step into a function which
4225 is compiled without debugging information. To step through functions
4226 without debugging information, use the @code{stepi} command, described
4230 The @code{step} command only stops at the first instruction of a source
4231 line. This prevents the multiple stops that could otherwise occur in
4232 @code{switch} statements, @code{for} loops, etc. @code{step} continues
4233 to stop if a function that has debugging information is called within
4234 the line. In other words, @code{step} @emph{steps inside} any functions
4235 called within the line.
4237 Also, the @code{step} command only enters a function if there is line
4238 number information for the function. Otherwise it acts like the
4239 @code{next} command. This avoids problems when using @code{cc -gl}
4240 on MIPS machines. Previously, @code{step} entered subroutines if there
4241 was any debugging information about the routine.
4243 @item step @var{count}
4244 Continue running as in @code{step}, but do so @var{count} times. If a
4245 breakpoint is reached, or a signal not related to stepping occurs before
4246 @var{count} steps, stepping stops right away.
4249 @kindex n @r{(@code{next})}
4250 @item next @r{[}@var{count}@r{]}
4251 Continue to the next source line in the current (innermost) stack frame.
4252 This is similar to @code{step}, but function calls that appear within
4253 the line of code are executed without stopping. Execution stops when
4254 control reaches a different line of code at the original stack level
4255 that was executing when you gave the @code{next} command. This command
4256 is abbreviated @code{n}.
4258 An argument @var{count} is a repeat count, as for @code{step}.
4261 @c FIX ME!! Do we delete this, or is there a way it fits in with
4262 @c the following paragraph? --- Vctoria
4264 @c @code{next} within a function that lacks debugging information acts like
4265 @c @code{step}, but any function calls appearing within the code of the
4266 @c function are executed without stopping.
4268 The @code{next} command only stops at the first instruction of a
4269 source line. This prevents multiple stops that could otherwise occur in
4270 @code{switch} statements, @code{for} loops, etc.
4272 @kindex set step-mode
4274 @cindex functions without line info, and stepping
4275 @cindex stepping into functions with no line info
4276 @itemx set step-mode on
4277 The @code{set step-mode on} command causes the @code{step} command to
4278 stop at the first instruction of a function which contains no debug line
4279 information rather than stepping over it.
4281 This is useful in cases where you may be interested in inspecting the
4282 machine instructions of a function which has no symbolic info and do not
4283 want @value{GDBN} to automatically skip over this function.
4285 @item set step-mode off
4286 Causes the @code{step} command to step over any functions which contains no
4287 debug information. This is the default.
4289 @item show step-mode
4290 Show whether @value{GDBN} will stop in or step over functions without
4291 source line debug information.
4294 @kindex fin @r{(@code{finish})}
4296 Continue running until just after function in the selected stack frame
4297 returns. Print the returned value (if any). This command can be
4298 abbreviated as @code{fin}.
4300 Contrast this with the @code{return} command (@pxref{Returning,
4301 ,Returning from a Function}).
4304 @kindex u @r{(@code{until})}
4305 @cindex run until specified location
4308 Continue running until a source line past the current line, in the
4309 current stack frame, is reached. This command is used to avoid single
4310 stepping through a loop more than once. It is like the @code{next}
4311 command, except that when @code{until} encounters a jump, it
4312 automatically continues execution until the program counter is greater
4313 than the address of the jump.
4315 This means that when you reach the end of a loop after single stepping
4316 though it, @code{until} makes your program continue execution until it
4317 exits the loop. In contrast, a @code{next} command at the end of a loop
4318 simply steps back to the beginning of the loop, which forces you to step
4319 through the next iteration.
4321 @code{until} always stops your program if it attempts to exit the current
4324 @code{until} may produce somewhat counterintuitive results if the order
4325 of machine code does not match the order of the source lines. For
4326 example, in the following excerpt from a debugging session, the @code{f}
4327 (@code{frame}) command shows that execution is stopped at line
4328 @code{206}; yet when we use @code{until}, we get to line @code{195}:
4332 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
4334 (@value{GDBP}) until
4335 195 for ( ; argc > 0; NEXTARG) @{
4338 This happened because, for execution efficiency, the compiler had
4339 generated code for the loop closure test at the end, rather than the
4340 start, of the loop---even though the test in a C @code{for}-loop is
4341 written before the body of the loop. The @code{until} command appeared
4342 to step back to the beginning of the loop when it advanced to this
4343 expression; however, it has not really gone to an earlier
4344 statement---not in terms of the actual machine code.
4346 @code{until} with no argument works by means of single
4347 instruction stepping, and hence is slower than @code{until} with an
4350 @item until @var{location}
4351 @itemx u @var{location}
4352 Continue running your program until either the specified location is
4353 reached, or the current stack frame returns. @var{location} is any of
4354 the forms described in @ref{Specify Location}.
4355 This form of the command uses temporary breakpoints, and
4356 hence is quicker than @code{until} without an argument. The specified
4357 location is actually reached only if it is in the current frame. This
4358 implies that @code{until} can be used to skip over recursive function
4359 invocations. For instance in the code below, if the current location is
4360 line @code{96}, issuing @code{until 99} will execute the program up to
4361 line @code{99} in the same invocation of factorial, i.e., after the inner
4362 invocations have returned.
4365 94 int factorial (int value)
4367 96 if (value > 1) @{
4368 97 value *= factorial (value - 1);
4375 @kindex advance @var{location}
4376 @itemx advance @var{location}
4377 Continue running the program up to the given @var{location}. An argument is
4378 required, which should be of one of the forms described in
4379 @ref{Specify Location}.
4380 Execution will also stop upon exit from the current stack
4381 frame. This command is similar to @code{until}, but @code{advance} will
4382 not skip over recursive function calls, and the target location doesn't
4383 have to be in the same frame as the current one.
4387 @kindex si @r{(@code{stepi})}
4389 @itemx stepi @var{arg}
4391 Execute one machine instruction, then stop and return to the debugger.
4393 It is often useful to do @samp{display/i $pc} when stepping by machine
4394 instructions. This makes @value{GDBN} automatically display the next
4395 instruction to be executed, each time your program stops. @xref{Auto
4396 Display,, Automatic Display}.
4398 An argument is a repeat count, as in @code{step}.
4402 @kindex ni @r{(@code{nexti})}
4404 @itemx nexti @var{arg}
4406 Execute one machine instruction, but if it is a function call,
4407 proceed until the function returns.
4409 An argument is a repeat count, as in @code{next}.
4416 A signal is an asynchronous event that can happen in a program. The
4417 operating system defines the possible kinds of signals, and gives each
4418 kind a name and a number. For example, in Unix @code{SIGINT} is the
4419 signal a program gets when you type an interrupt character (often @kbd{Ctrl-c});
4420 @code{SIGSEGV} is the signal a program gets from referencing a place in
4421 memory far away from all the areas in use; @code{SIGALRM} occurs when
4422 the alarm clock timer goes off (which happens only if your program has
4423 requested an alarm).
4425 @cindex fatal signals
4426 Some signals, including @code{SIGALRM}, are a normal part of the
4427 functioning of your program. Others, such as @code{SIGSEGV}, indicate
4428 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
4429 program has not specified in advance some other way to handle the signal.
4430 @code{SIGINT} does not indicate an error in your program, but it is normally
4431 fatal so it can carry out the purpose of the interrupt: to kill the program.
4433 @value{GDBN} has the ability to detect any occurrence of a signal in your
4434 program. You can tell @value{GDBN} in advance what to do for each kind of
4437 @cindex handling signals
4438 Normally, @value{GDBN} is set up to let the non-erroneous signals like
4439 @code{SIGALRM} be silently passed to your program
4440 (so as not to interfere with their role in the program's functioning)
4441 but to stop your program immediately whenever an error signal happens.
4442 You can change these settings with the @code{handle} command.
4445 @kindex info signals
4449 Print a table of all the kinds of signals and how @value{GDBN} has been told to
4450 handle each one. You can use this to see the signal numbers of all
4451 the defined types of signals.
4453 @item info signals @var{sig}
4454 Similar, but print information only about the specified signal number.
4456 @code{info handle} is an alias for @code{info signals}.
4459 @item handle @var{signal} @r{[}@var{keywords}@dots{}@r{]}
4460 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
4461 can be the number of a signal or its name (with or without the
4462 @samp{SIG} at the beginning); a list of signal numbers of the form
4463 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
4464 known signals. Optional arguments @var{keywords}, described below,
4465 say what change to make.
4469 The keywords allowed by the @code{handle} command can be abbreviated.
4470 Their full names are:
4474 @value{GDBN} should not stop your program when this signal happens. It may
4475 still print a message telling you that the signal has come in.
4478 @value{GDBN} should stop your program when this signal happens. This implies
4479 the @code{print} keyword as well.
4482 @value{GDBN} should print a message when this signal happens.
4485 @value{GDBN} should not mention the occurrence of the signal at all. This
4486 implies the @code{nostop} keyword as well.
4490 @value{GDBN} should allow your program to see this signal; your program
4491 can handle the signal, or else it may terminate if the signal is fatal
4492 and not handled. @code{pass} and @code{noignore} are synonyms.
4496 @value{GDBN} should not allow your program to see this signal.
4497 @code{nopass} and @code{ignore} are synonyms.
4501 When a signal stops your program, the signal is not visible to the
4503 continue. Your program sees the signal then, if @code{pass} is in
4504 effect for the signal in question @emph{at that time}. In other words,
4505 after @value{GDBN} reports a signal, you can use the @code{handle}
4506 command with @code{pass} or @code{nopass} to control whether your
4507 program sees that signal when you continue.
4509 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
4510 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
4511 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
4514 You can also use the @code{signal} command to prevent your program from
4515 seeing a signal, or cause it to see a signal it normally would not see,
4516 or to give it any signal at any time. For example, if your program stopped
4517 due to some sort of memory reference error, you might store correct
4518 values into the erroneous variables and continue, hoping to see more
4519 execution; but your program would probably terminate immediately as
4520 a result of the fatal signal once it saw the signal. To prevent this,
4521 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
4524 @cindex extra signal information
4525 @anchor{extra signal information}
4527 On some targets, @value{GDBN} can inspect extra signal information
4528 associated with the intercepted signal, before it is actually
4529 delivered to the program being debugged. This information is exported
4530 by the convenience variable @code{$_siginfo}, and consists of data
4531 that is passed by the kernel to the signal handler at the time of the
4532 receipt of a signal. The data type of the information itself is
4533 target dependent. You can see the data type using the @code{ptype
4534 $_siginfo} command. On Unix systems, it typically corresponds to the
4535 standard @code{siginfo_t} type, as defined in the @file{signal.h}
4538 Here's an example, on a @sc{gnu}/Linux system, printing the stray
4539 referenced address that raised a segmentation fault.
4543 (@value{GDBP}) continue
4544 Program received signal SIGSEGV, Segmentation fault.
4545 0x0000000000400766 in main ()
4547 (@value{GDBP}) ptype $_siginfo
4554 struct @{...@} _kill;
4555 struct @{...@} _timer;
4557 struct @{...@} _sigchld;
4558 struct @{...@} _sigfault;
4559 struct @{...@} _sigpoll;
4562 (@value{GDBP}) ptype $_siginfo._sifields._sigfault
4566 (@value{GDBP}) p $_siginfo._sifields._sigfault.si_addr
4567 $1 = (void *) 0x7ffff7ff7000
4571 Depending on target support, @code{$_siginfo} may also be writable.
4574 @section Stopping and Starting Multi-thread Programs
4576 @cindex stopped threads
4577 @cindex threads, stopped
4579 @cindex continuing threads
4580 @cindex threads, continuing
4582 @value{GDBN} supports debugging programs with multiple threads
4583 (@pxref{Threads,, Debugging Programs with Multiple Threads}). There
4584 are two modes of controlling execution of your program within the
4585 debugger. In the default mode, referred to as @dfn{all-stop mode},
4586 when any thread in your program stops (for example, at a breakpoint
4587 or while being stepped), all other threads in the program are also stopped by
4588 @value{GDBN}. On some targets, @value{GDBN} also supports
4589 @dfn{non-stop mode}, in which other threads can continue to run freely while
4590 you examine the stopped thread in the debugger.
4593 * All-Stop Mode:: All threads stop when GDB takes control
4594 * Non-Stop Mode:: Other threads continue to execute
4595 * Background Execution:: Running your program asynchronously
4596 * Thread-Specific Breakpoints:: Controlling breakpoints
4597 * Interrupted System Calls:: GDB may interfere with system calls
4601 @subsection All-Stop Mode
4603 @cindex all-stop mode
4605 In all-stop mode, whenever your program stops under @value{GDBN} for any reason,
4606 @emph{all} threads of execution stop, not just the current thread. This
4607 allows you to examine the overall state of the program, including
4608 switching between threads, without worrying that things may change
4611 Conversely, whenever you restart the program, @emph{all} threads start
4612 executing. @emph{This is true even when single-stepping} with commands
4613 like @code{step} or @code{next}.
4615 In particular, @value{GDBN} cannot single-step all threads in lockstep.
4616 Since thread scheduling is up to your debugging target's operating
4617 system (not controlled by @value{GDBN}), other threads may
4618 execute more than one statement while the current thread completes a
4619 single step. Moreover, in general other threads stop in the middle of a
4620 statement, rather than at a clean statement boundary, when the program
4623 You might even find your program stopped in another thread after
4624 continuing or even single-stepping. This happens whenever some other
4625 thread runs into a breakpoint, a signal, or an exception before the
4626 first thread completes whatever you requested.
4628 @cindex automatic thread selection
4629 @cindex switching threads automatically
4630 @cindex threads, automatic switching
4631 Whenever @value{GDBN} stops your program, due to a breakpoint or a
4632 signal, it automatically selects the thread where that breakpoint or
4633 signal happened. @value{GDBN} alerts you to the context switch with a
4634 message such as @samp{[Switching to Thread @var{n}]} to identify the
4637 On some OSes, you can modify @value{GDBN}'s default behavior by
4638 locking the OS scheduler to allow only a single thread to run.
4641 @item set scheduler-locking @var{mode}
4642 @cindex scheduler locking mode
4643 @cindex lock scheduler
4644 Set the scheduler locking mode. If it is @code{off}, then there is no
4645 locking and any thread may run at any time. If @code{on}, then only the
4646 current thread may run when the inferior is resumed. The @code{step}
4647 mode optimizes for single-stepping; it prevents other threads
4648 from preempting the current thread while you are stepping, so that
4649 the focus of debugging does not change unexpectedly.
4650 Other threads only rarely (or never) get a chance to run
4651 when you step. They are more likely to run when you @samp{next} over a
4652 function call, and they are completely free to run when you use commands
4653 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
4654 thread hits a breakpoint during its timeslice, @value{GDBN} does not change
4655 the current thread away from the thread that you are debugging.
4657 @item show scheduler-locking
4658 Display the current scheduler locking mode.
4661 @cindex resume threads of multiple processes simultaneously
4662 By default, when you issue one of the execution commands such as
4663 @code{continue}, @code{next} or @code{step}, @value{GDBN} allows only
4664 threads of the current inferior to run. For example, if @value{GDBN}
4665 is attached to two inferiors, each with two threads, the
4666 @code{continue} command resumes only the two threads of the current
4667 inferior. This is useful, for example, when you debug a program that
4668 forks and you want to hold the parent stopped (so that, for instance,
4669 it doesn't run to exit), while you debug the child. In other
4670 situations, you may not be interested in inspecting the current state
4671 of any of the processes @value{GDBN} is attached to, and you may want
4672 to resume them all until some breakpoint is hit. In the latter case,
4673 you can instruct @value{GDBN} to allow all threads of all the
4674 inferiors to run with the @w{@code{set schedule-multiple}} command.
4677 @kindex set schedule-multiple
4678 @item set schedule-multiple
4679 Set the mode for allowing threads of multiple processes to be resumed
4680 when an execution command is issued. When @code{on}, all threads of
4681 all processes are allowed to run. When @code{off}, only the threads
4682 of the current process are resumed. The default is @code{off}. The
4683 @code{scheduler-locking} mode takes precedence when set to @code{on},
4684 or while you are stepping and set to @code{step}.
4686 @item show schedule-multiple
4687 Display the current mode for resuming the execution of threads of
4692 @subsection Non-Stop Mode
4694 @cindex non-stop mode
4696 @c This section is really only a place-holder, and needs to be expanded
4697 @c with more details.
4699 For some multi-threaded targets, @value{GDBN} supports an optional
4700 mode of operation in which you can examine stopped program threads in
4701 the debugger while other threads continue to execute freely. This
4702 minimizes intrusion when debugging live systems, such as programs
4703 where some threads have real-time constraints or must continue to
4704 respond to external events. This is referred to as @dfn{non-stop} mode.
4706 In non-stop mode, when a thread stops to report a debugging event,
4707 @emph{only} that thread is stopped; @value{GDBN} does not stop other
4708 threads as well, in contrast to the all-stop mode behavior. Additionally,
4709 execution commands such as @code{continue} and @code{step} apply by default
4710 only to the current thread in non-stop mode, rather than all threads as
4711 in all-stop mode. This allows you to control threads explicitly in
4712 ways that are not possible in all-stop mode --- for example, stepping
4713 one thread while allowing others to run freely, stepping
4714 one thread while holding all others stopped, or stepping several threads
4715 independently and simultaneously.
4717 To enter non-stop mode, use this sequence of commands before you run
4718 or attach to your program:
4721 # Enable the async interface.
4724 # If using the CLI, pagination breaks non-stop.
4727 # Finally, turn it on!
4731 You can use these commands to manipulate the non-stop mode setting:
4734 @kindex set non-stop
4735 @item set non-stop on
4736 Enable selection of non-stop mode.
4737 @item set non-stop off
4738 Disable selection of non-stop mode.
4739 @kindex show non-stop
4741 Show the current non-stop enablement setting.
4744 Note these commands only reflect whether non-stop mode is enabled,
4745 not whether the currently-executing program is being run in non-stop mode.
4746 In particular, the @code{set non-stop} preference is only consulted when
4747 @value{GDBN} starts or connects to the target program, and it is generally
4748 not possible to switch modes once debugging has started. Furthermore,
4749 since not all targets support non-stop mode, even when you have enabled
4750 non-stop mode, @value{GDBN} may still fall back to all-stop operation by
4753 In non-stop mode, all execution commands apply only to the current thread
4754 by default. That is, @code{continue} only continues one thread.
4755 To continue all threads, issue @code{continue -a} or @code{c -a}.
4757 You can use @value{GDBN}'s background execution commands
4758 (@pxref{Background Execution}) to run some threads in the background
4759 while you continue to examine or step others from @value{GDBN}.
4760 The MI execution commands (@pxref{GDB/MI Program Execution}) are
4761 always executed asynchronously in non-stop mode.
4763 Suspending execution is done with the @code{interrupt} command when
4764 running in the background, or @kbd{Ctrl-c} during foreground execution.
4765 In all-stop mode, this stops the whole process;
4766 but in non-stop mode the interrupt applies only to the current thread.
4767 To stop the whole program, use @code{interrupt -a}.
4769 Other execution commands do not currently support the @code{-a} option.
4771 In non-stop mode, when a thread stops, @value{GDBN} doesn't automatically make
4772 that thread current, as it does in all-stop mode. This is because the
4773 thread stop notifications are asynchronous with respect to @value{GDBN}'s
4774 command interpreter, and it would be confusing if @value{GDBN} unexpectedly
4775 changed to a different thread just as you entered a command to operate on the
4776 previously current thread.
4778 @node Background Execution
4779 @subsection Background Execution
4781 @cindex foreground execution
4782 @cindex background execution
4783 @cindex asynchronous execution
4784 @cindex execution, foreground, background and asynchronous
4786 @value{GDBN}'s execution commands have two variants: the normal
4787 foreground (synchronous) behavior, and a background
4788 (asynchronous) behavior. In foreground execution, @value{GDBN} waits for
4789 the program to report that some thread has stopped before prompting for
4790 another command. In background execution, @value{GDBN} immediately gives
4791 a command prompt so that you can issue other commands while your program runs.
4793 You need to explicitly enable asynchronous mode before you can use
4794 background execution commands. You can use these commands to
4795 manipulate the asynchronous mode setting:
4798 @kindex set target-async
4799 @item set target-async on
4800 Enable asynchronous mode.
4801 @item set target-async off
4802 Disable asynchronous mode.
4803 @kindex show target-async
4804 @item show target-async
4805 Show the current target-async setting.
4808 If the target doesn't support async mode, @value{GDBN} issues an error
4809 message if you attempt to use the background execution commands.
4811 To specify background execution, add a @code{&} to the command. For example,
4812 the background form of the @code{continue} command is @code{continue&}, or
4813 just @code{c&}. The execution commands that accept background execution
4819 @xref{Starting, , Starting your Program}.
4823 @xref{Attach, , Debugging an Already-running Process}.
4827 @xref{Continuing and Stepping, step}.
4831 @xref{Continuing and Stepping, stepi}.
4835 @xref{Continuing and Stepping, next}.
4839 @xref{Continuing and Stepping, nexti}.
4843 @xref{Continuing and Stepping, continue}.
4847 @xref{Continuing and Stepping, finish}.
4851 @xref{Continuing and Stepping, until}.
4855 Background execution is especially useful in conjunction with non-stop
4856 mode for debugging programs with multiple threads; see @ref{Non-Stop Mode}.
4857 However, you can also use these commands in the normal all-stop mode with
4858 the restriction that you cannot issue another execution command until the
4859 previous one finishes. Examples of commands that are valid in all-stop
4860 mode while the program is running include @code{help} and @code{info break}.
4862 You can interrupt your program while it is running in the background by
4863 using the @code{interrupt} command.
4870 Suspend execution of the running program. In all-stop mode,
4871 @code{interrupt} stops the whole process, but in non-stop mode, it stops
4872 only the current thread. To stop the whole program in non-stop mode,
4873 use @code{interrupt -a}.
4876 @node Thread-Specific Breakpoints
4877 @subsection Thread-Specific Breakpoints
4879 When your program has multiple threads (@pxref{Threads,, Debugging
4880 Programs with Multiple Threads}), you can choose whether to set
4881 breakpoints on all threads, or on a particular thread.
4884 @cindex breakpoints and threads
4885 @cindex thread breakpoints
4886 @kindex break @dots{} thread @var{threadno}
4887 @item break @var{linespec} thread @var{threadno}
4888 @itemx break @var{linespec} thread @var{threadno} if @dots{}
4889 @var{linespec} specifies source lines; there are several ways of
4890 writing them (@pxref{Specify Location}), but the effect is always to
4891 specify some source line.
4893 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
4894 to specify that you only want @value{GDBN} to stop the program when a
4895 particular thread reaches this breakpoint. @var{threadno} is one of the
4896 numeric thread identifiers assigned by @value{GDBN}, shown in the first
4897 column of the @samp{info threads} display.
4899 If you do not specify @samp{thread @var{threadno}} when you set a
4900 breakpoint, the breakpoint applies to @emph{all} threads of your
4903 You can use the @code{thread} qualifier on conditional breakpoints as
4904 well; in this case, place @samp{thread @var{threadno}} before the
4905 breakpoint condition, like this:
4908 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
4913 @node Interrupted System Calls
4914 @subsection Interrupted System Calls
4916 @cindex thread breakpoints and system calls
4917 @cindex system calls and thread breakpoints
4918 @cindex premature return from system calls
4919 There is an unfortunate side effect when using @value{GDBN} to debug
4920 multi-threaded programs. If one thread stops for a
4921 breakpoint, or for some other reason, and another thread is blocked in a
4922 system call, then the system call may return prematurely. This is a
4923 consequence of the interaction between multiple threads and the signals
4924 that @value{GDBN} uses to implement breakpoints and other events that
4927 To handle this problem, your program should check the return value of
4928 each system call and react appropriately. This is good programming
4931 For example, do not write code like this:
4937 The call to @code{sleep} will return early if a different thread stops
4938 at a breakpoint or for some other reason.
4940 Instead, write this:
4945 unslept = sleep (unslept);
4948 A system call is allowed to return early, so the system is still
4949 conforming to its specification. But @value{GDBN} does cause your
4950 multi-threaded program to behave differently than it would without
4953 Also, @value{GDBN} uses internal breakpoints in the thread library to
4954 monitor certain events such as thread creation and thread destruction.
4955 When such an event happens, a system call in another thread may return
4956 prematurely, even though your program does not appear to stop.
4959 @node Reverse Execution
4960 @chapter Running programs backward
4961 @cindex reverse execution
4962 @cindex running programs backward
4964 When you are debugging a program, it is not unusual to realize that
4965 you have gone too far, and some event of interest has already happened.
4966 If the target environment supports it, @value{GDBN} can allow you to
4967 ``rewind'' the program by running it backward.
4969 A target environment that supports reverse execution should be able
4970 to ``undo'' the changes in machine state that have taken place as the
4971 program was executing normally. Variables, registers etc.@: should
4972 revert to their previous values. Obviously this requires a great
4973 deal of sophistication on the part of the target environment; not
4974 all target environments can support reverse execution.
4976 When a program is executed in reverse, the instructions that
4977 have most recently been executed are ``un-executed'', in reverse
4978 order. The program counter runs backward, following the previous
4979 thread of execution in reverse. As each instruction is ``un-executed'',
4980 the values of memory and/or registers that were changed by that
4981 instruction are reverted to their previous states. After executing
4982 a piece of source code in reverse, all side effects of that code
4983 should be ``undone'', and all variables should be returned to their
4984 prior values@footnote{
4985 Note that some side effects are easier to undo than others. For instance,
4986 memory and registers are relatively easy, but device I/O is hard. Some
4987 targets may be able undo things like device I/O, and some may not.
4989 The contract between @value{GDBN} and the reverse executing target
4990 requires only that the target do something reasonable when
4991 @value{GDBN} tells it to execute backwards, and then report the
4992 results back to @value{GDBN}. Whatever the target reports back to
4993 @value{GDBN}, @value{GDBN} will report back to the user. @value{GDBN}
4994 assumes that the memory and registers that the target reports are in a
4995 consistant state, but @value{GDBN} accepts whatever it is given.
4998 If you are debugging in a target environment that supports
4999 reverse execution, @value{GDBN} provides the following commands.
5002 @kindex reverse-continue
5003 @kindex rc @r{(@code{reverse-continue})}
5004 @item reverse-continue @r{[}@var{ignore-count}@r{]}
5005 @itemx rc @r{[}@var{ignore-count}@r{]}
5006 Beginning at the point where your program last stopped, start executing
5007 in reverse. Reverse execution will stop for breakpoints and synchronous
5008 exceptions (signals), just like normal execution. Behavior of
5009 asynchronous signals depends on the target environment.
5011 @kindex reverse-step
5012 @kindex rs @r{(@code{step})}
5013 @item reverse-step @r{[}@var{count}@r{]}
5014 Run the program backward until control reaches the start of a
5015 different source line; then stop it, and return control to @value{GDBN}.
5017 Like the @code{step} command, @code{reverse-step} will only stop
5018 at the beginning of a source line. It ``un-executes'' the previously
5019 executed source line. If the previous source line included calls to
5020 debuggable functions, @code{reverse-step} will step (backward) into
5021 the called function, stopping at the beginning of the @emph{last}
5022 statement in the called function (typically a return statement).
5024 Also, as with the @code{step} command, if non-debuggable functions are
5025 called, @code{reverse-step} will run thru them backward without stopping.
5027 @kindex reverse-stepi
5028 @kindex rsi @r{(@code{reverse-stepi})}
5029 @item reverse-stepi @r{[}@var{count}@r{]}
5030 Reverse-execute one machine instruction. Note that the instruction
5031 to be reverse-executed is @emph{not} the one pointed to by the program
5032 counter, but the instruction executed prior to that one. For instance,
5033 if the last instruction was a jump, @code{reverse-stepi} will take you
5034 back from the destination of the jump to the jump instruction itself.
5036 @kindex reverse-next
5037 @kindex rn @r{(@code{reverse-next})}
5038 @item reverse-next @r{[}@var{count}@r{]}
5039 Run backward to the beginning of the previous line executed in
5040 the current (innermost) stack frame. If the line contains function
5041 calls, they will be ``un-executed'' without stopping. Starting from
5042 the first line of a function, @code{reverse-next} will take you back
5043 to the caller of that function, @emph{before} the function was called,
5044 just as the normal @code{next} command would take you from the last
5045 line of a function back to its return to its caller
5046 @footnote{Unles the code is too heavily optimized.}.
5048 @kindex reverse-nexti
5049 @kindex rni @r{(@code{reverse-nexti})}
5050 @item reverse-nexti @r{[}@var{count}@r{]}
5051 Like @code{nexti}, @code{reverse-nexti} executes a single instruction
5052 in reverse, except that called functions are ``un-executed'' atomically.
5053 That is, if the previously executed instruction was a return from
5054 another instruction, @code{reverse-nexti} will continue to execute
5055 in reverse until the call to that function (from the current stack
5058 @kindex reverse-finish
5059 @item reverse-finish
5060 Just as the @code{finish} command takes you to the point where the
5061 current function returns, @code{reverse-finish} takes you to the point
5062 where it was called. Instead of ending up at the end of the current
5063 function invocation, you end up at the beginning.
5065 @kindex set exec-direction
5066 @item set exec-direction
5067 Set the direction of target execution.
5068 @itemx set exec-direction reverse
5069 @cindex execute forward or backward in time
5070 @value{GDBN} will perform all execution commands in reverse, until the
5071 exec-direction mode is changed to ``forward''. Affected commands include
5072 @code{step, stepi, next, nexti, continue, and finish}. The @code{return}
5073 command cannot be used in reverse mode.
5074 @item set exec-direction forward
5075 @value{GDBN} will perform all execution commands in the normal fashion.
5076 This is the default.
5080 @node Process Record and Replay
5081 @chapter Recording Inferior's Execution and Replaying It
5082 @cindex process record and replay
5083 @cindex recording inferior's execution and replaying it
5085 On some platforms, @value{GDBN} provides a special @dfn{process record
5086 and replay} target that can record a log of the process execution, and
5087 replay it later with both forward and reverse execution commands.
5090 When this target is in use, if the execution log includes the record
5091 for the next instruction, @value{GDBN} will debug in @dfn{replay
5092 mode}. In the replay mode, the inferior does not really execute code
5093 instructions. Instead, all the events that normally happen during
5094 code execution are taken from the execution log. While code is not
5095 really executed in replay mode, the values of registers (including the
5096 program counter register) and the memory of the inferior are still
5097 changed as they normally would. Their contents are taken from the
5101 If the record for the next instruction is not in the execution log,
5102 @value{GDBN} will debug in @dfn{record mode}. In this mode, the
5103 inferior executes normally, and @value{GDBN} records the execution log
5106 The process record and replay target supports reverse execution
5107 (@pxref{Reverse Execution}), even if the platform on which the
5108 inferior runs does not. However, the reverse execution is limited in
5109 this case by the range of the instructions recorded in the execution
5110 log. In other words, reverse execution on platforms that don't
5111 support it directly can only be done in the replay mode.
5113 When debugging in the reverse direction, @value{GDBN} will work in
5114 replay mode as long as the execution log includes the record for the
5115 previous instruction; otherwise, it will work in record mode, if the
5116 platform supports reverse execution, or stop if not.
5118 For architecture environments that support process record and replay,
5119 @value{GDBN} provides the following commands:
5122 @kindex target record
5126 This command starts the process record and replay target. The process
5127 record and replay target can only debug a process that is already
5128 running. Therefore, you need first to start the process with the
5129 @kbd{run} or @kbd{start} commands, and then start the recording with
5130 the @kbd{target record} command.
5132 Both @code{record} and @code{rec} are aliases of @code{target record}.
5134 @cindex displaced stepping, and process record and replay
5135 Displaced stepping (@pxref{Maintenance Commands,, displaced stepping})
5136 will be automatically disabled when process record and replay target
5137 is started. That's because the process record and replay target
5138 doesn't support displaced stepping.
5140 @cindex non-stop mode, and process record and replay
5141 @cindex asynchronous execution, and process record and replay
5142 If the inferior is in the non-stop mode (@pxref{Non-Stop Mode}) or in
5143 the asynchronous execution mode (@pxref{Background Execution}), the
5144 process record and replay target cannot be started because it doesn't
5145 support these two modes.
5150 Stop the process record and replay target. When process record and
5151 replay target stops, the entire execution log will be deleted and the
5152 inferior will either be terminated, or will remain in its final state.
5154 When you stop the process record and replay target in record mode (at
5155 the end of the execution log), the inferior will be stopped at the
5156 next instruction that would have been recorded. In other words, if
5157 you record for a while and then stop recording, the inferior process
5158 will be left in the same state as if the recording never happened.
5160 On the other hand, if the process record and replay target is stopped
5161 while in replay mode (that is, not at the end of the execution log,
5162 but at some earlier point), the inferior process will become ``live''
5163 at that earlier state, and it will then be possible to continue the
5164 usual ``live'' debugging of the process from that state.
5166 When the inferior process exits, or @value{GDBN} detaches from it,
5167 process record and replay target will automatically stop itself.
5169 @kindex set record insn-number-max
5170 @item set record insn-number-max @var{limit}
5171 Set the limit of instructions to be recorded. Default value is 200000.
5173 If @var{limit} is a positive number, then @value{GDBN} will start
5174 deleting instructions from the log once the number of the record
5175 instructions becomes greater than @var{limit}. For every new recorded
5176 instruction, @value{GDBN} will delete the earliest recorded
5177 instruction to keep the number of recorded instructions at the limit.
5178 (Since deleting recorded instructions loses information, @value{GDBN}
5179 lets you control what happens when the limit is reached, by means of
5180 the @code{stop-at-limit} option, described below.)
5182 If @var{limit} is zero, @value{GDBN} will never delete recorded
5183 instructions from the execution log. The number of recorded
5184 instructions is unlimited in this case.
5186 @kindex show record insn-number-max
5187 @item show record insn-number-max
5188 Show the limit of instructions to be recorded.
5190 @kindex set record stop-at-limit
5191 @item set record stop-at-limit
5192 Control the behavior when the number of recorded instructions reaches
5193 the limit. If ON (the default), @value{GDBN} will stop when the limit
5194 is reached for the first time and ask you whether you want to stop the
5195 inferior or continue running it and recording the execution log. If
5196 you decide to continue recording, each new recorded instruction will
5197 cause the oldest one to be deleted.
5199 If this option is OFF, @value{GDBN} will automatically delete the
5200 oldest record to make room for each new one, without asking.
5202 @kindex show record stop-at-limit
5203 @item show record stop-at-limit
5204 Show the current setting of @code{stop-at-limit}.
5206 @kindex info record insn-number
5207 @item info record insn-number
5208 Show the current number of recorded instructions.
5210 @kindex record delete
5213 When record target runs in replay mode (``in the past''), delete the
5214 subsequent execution log and begin to record a new execution log starting
5215 from the current address. This means you will abandon the previously
5216 recorded ``future'' and begin recording a new ``future''.
5221 @chapter Examining the Stack
5223 When your program has stopped, the first thing you need to know is where it
5224 stopped and how it got there.
5227 Each time your program performs a function call, information about the call
5229 That information includes the location of the call in your program,
5230 the arguments of the call,
5231 and the local variables of the function being called.
5232 The information is saved in a block of data called a @dfn{stack frame}.
5233 The stack frames are allocated in a region of memory called the @dfn{call
5236 When your program stops, the @value{GDBN} commands for examining the
5237 stack allow you to see all of this information.
5239 @cindex selected frame
5240 One of the stack frames is @dfn{selected} by @value{GDBN} and many
5241 @value{GDBN} commands refer implicitly to the selected frame. In
5242 particular, whenever you ask @value{GDBN} for the value of a variable in
5243 your program, the value is found in the selected frame. There are
5244 special @value{GDBN} commands to select whichever frame you are
5245 interested in. @xref{Selection, ,Selecting a Frame}.
5247 When your program stops, @value{GDBN} automatically selects the
5248 currently executing frame and describes it briefly, similar to the
5249 @code{frame} command (@pxref{Frame Info, ,Information about a Frame}).
5252 * Frames:: Stack frames
5253 * Backtrace:: Backtraces
5254 * Selection:: Selecting a frame
5255 * Frame Info:: Information on a frame
5260 @section Stack Frames
5262 @cindex frame, definition
5264 The call stack is divided up into contiguous pieces called @dfn{stack
5265 frames}, or @dfn{frames} for short; each frame is the data associated
5266 with one call to one function. The frame contains the arguments given
5267 to the function, the function's local variables, and the address at
5268 which the function is executing.
5270 @cindex initial frame
5271 @cindex outermost frame
5272 @cindex innermost frame
5273 When your program is started, the stack has only one frame, that of the
5274 function @code{main}. This is called the @dfn{initial} frame or the
5275 @dfn{outermost} frame. Each time a function is called, a new frame is
5276 made. Each time a function returns, the frame for that function invocation
5277 is eliminated. If a function is recursive, there can be many frames for
5278 the same function. The frame for the function in which execution is
5279 actually occurring is called the @dfn{innermost} frame. This is the most
5280 recently created of all the stack frames that still exist.
5282 @cindex frame pointer
5283 Inside your program, stack frames are identified by their addresses. A
5284 stack frame consists of many bytes, each of which has its own address; each
5285 kind of computer has a convention for choosing one byte whose
5286 address serves as the address of the frame. Usually this address is kept
5287 in a register called the @dfn{frame pointer register}
5288 (@pxref{Registers, $fp}) while execution is going on in that frame.
5290 @cindex frame number
5291 @value{GDBN} assigns numbers to all existing stack frames, starting with
5292 zero for the innermost frame, one for the frame that called it,
5293 and so on upward. These numbers do not really exist in your program;
5294 they are assigned by @value{GDBN} to give you a way of designating stack
5295 frames in @value{GDBN} commands.
5297 @c The -fomit-frame-pointer below perennially causes hbox overflow
5298 @c underflow problems.
5299 @cindex frameless execution
5300 Some compilers provide a way to compile functions so that they operate
5301 without stack frames. (For example, the @value{NGCC} option
5303 @samp{-fomit-frame-pointer}
5305 generates functions without a frame.)
5306 This is occasionally done with heavily used library functions to save
5307 the frame setup time. @value{GDBN} has limited facilities for dealing
5308 with these function invocations. If the innermost function invocation
5309 has no stack frame, @value{GDBN} nevertheless regards it as though
5310 it had a separate frame, which is numbered zero as usual, allowing
5311 correct tracing of the function call chain. However, @value{GDBN} has
5312 no provision for frameless functions elsewhere in the stack.
5315 @kindex frame@r{, command}
5316 @cindex current stack frame
5317 @item frame @var{args}
5318 The @code{frame} command allows you to move from one stack frame to another,
5319 and to print the stack frame you select. @var{args} may be either the
5320 address of the frame or the stack frame number. Without an argument,
5321 @code{frame} prints the current stack frame.
5323 @kindex select-frame
5324 @cindex selecting frame silently
5326 The @code{select-frame} command allows you to move from one stack frame
5327 to another without printing the frame. This is the silent version of
5335 @cindex call stack traces
5336 A backtrace is a summary of how your program got where it is. It shows one
5337 line per frame, for many frames, starting with the currently executing
5338 frame (frame zero), followed by its caller (frame one), and on up the
5343 @kindex bt @r{(@code{backtrace})}
5346 Print a backtrace of the entire stack: one line per frame for all
5347 frames in the stack.
5349 You can stop the backtrace at any time by typing the system interrupt
5350 character, normally @kbd{Ctrl-c}.
5352 @item backtrace @var{n}
5354 Similar, but print only the innermost @var{n} frames.
5356 @item backtrace -@var{n}
5358 Similar, but print only the outermost @var{n} frames.
5360 @item backtrace full
5362 @itemx bt full @var{n}
5363 @itemx bt full -@var{n}
5364 Print the values of the local variables also. @var{n} specifies the
5365 number of frames to print, as described above.
5370 The names @code{where} and @code{info stack} (abbreviated @code{info s})
5371 are additional aliases for @code{backtrace}.
5373 @cindex multiple threads, backtrace
5374 In a multi-threaded program, @value{GDBN} by default shows the
5375 backtrace only for the current thread. To display the backtrace for
5376 several or all of the threads, use the command @code{thread apply}
5377 (@pxref{Threads, thread apply}). For example, if you type @kbd{thread
5378 apply all backtrace}, @value{GDBN} will display the backtrace for all
5379 the threads; this is handy when you debug a core dump of a
5380 multi-threaded program.
5382 Each line in the backtrace shows the frame number and the function name.
5383 The program counter value is also shown---unless you use @code{set
5384 print address off}. The backtrace also shows the source file name and
5385 line number, as well as the arguments to the function. The program
5386 counter value is omitted if it is at the beginning of the code for that
5389 Here is an example of a backtrace. It was made with the command
5390 @samp{bt 3}, so it shows the innermost three frames.
5394 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
5396 #1 0x6e38 in expand_macro (sym=0x2b600, data=...) at macro.c:242
5397 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
5399 (More stack frames follow...)
5404 The display for frame zero does not begin with a program counter
5405 value, indicating that your program has stopped at the beginning of the
5406 code for line @code{993} of @code{builtin.c}.
5409 The value of parameter @code{data} in frame 1 has been replaced by
5410 @code{@dots{}}. By default, @value{GDBN} prints the value of a parameter
5411 only if it is a scalar (integer, pointer, enumeration, etc). See command
5412 @kbd{set print frame-arguments} in @ref{Print Settings} for more details
5413 on how to configure the way function parameter values are printed.
5415 @cindex value optimized out, in backtrace
5416 @cindex function call arguments, optimized out
5417 If your program was compiled with optimizations, some compilers will
5418 optimize away arguments passed to functions if those arguments are
5419 never used after the call. Such optimizations generate code that
5420 passes arguments through registers, but doesn't store those arguments
5421 in the stack frame. @value{GDBN} has no way of displaying such
5422 arguments in stack frames other than the innermost one. Here's what
5423 such a backtrace might look like:
5427 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
5429 #1 0x6e38 in expand_macro (sym=<value optimized out>) at macro.c:242
5430 #2 0x6840 in expand_token (obs=0x0, t=<value optimized out>, td=0xf7fffb08)
5432 (More stack frames follow...)
5437 The values of arguments that were not saved in their stack frames are
5438 shown as @samp{<value optimized out>}.
5440 If you need to display the values of such optimized-out arguments,
5441 either deduce that from other variables whose values depend on the one
5442 you are interested in, or recompile without optimizations.
5444 @cindex backtrace beyond @code{main} function
5445 @cindex program entry point
5446 @cindex startup code, and backtrace
5447 Most programs have a standard user entry point---a place where system
5448 libraries and startup code transition into user code. For C this is
5449 @code{main}@footnote{
5450 Note that embedded programs (the so-called ``free-standing''
5451 environment) are not required to have a @code{main} function as the
5452 entry point. They could even have multiple entry points.}.
5453 When @value{GDBN} finds the entry function in a backtrace
5454 it will terminate the backtrace, to avoid tracing into highly
5455 system-specific (and generally uninteresting) code.
5457 If you need to examine the startup code, or limit the number of levels
5458 in a backtrace, you can change this behavior:
5461 @item set backtrace past-main
5462 @itemx set backtrace past-main on
5463 @kindex set backtrace
5464 Backtraces will continue past the user entry point.
5466 @item set backtrace past-main off
5467 Backtraces will stop when they encounter the user entry point. This is the
5470 @item show backtrace past-main
5471 @kindex show backtrace
5472 Display the current user entry point backtrace policy.
5474 @item set backtrace past-entry
5475 @itemx set backtrace past-entry on
5476 Backtraces will continue past the internal entry point of an application.
5477 This entry point is encoded by the linker when the application is built,
5478 and is likely before the user entry point @code{main} (or equivalent) is called.
5480 @item set backtrace past-entry off
5481 Backtraces will stop when they encounter the internal entry point of an
5482 application. This is the default.
5484 @item show backtrace past-entry
5485 Display the current internal entry point backtrace policy.
5487 @item set backtrace limit @var{n}
5488 @itemx set backtrace limit 0
5489 @cindex backtrace limit
5490 Limit the backtrace to @var{n} levels. A value of zero means
5493 @item show backtrace limit
5494 Display the current limit on backtrace levels.
5498 @section Selecting a Frame
5500 Most commands for examining the stack and other data in your program work on
5501 whichever stack frame is selected at the moment. Here are the commands for
5502 selecting a stack frame; all of them finish by printing a brief description
5503 of the stack frame just selected.
5506 @kindex frame@r{, selecting}
5507 @kindex f @r{(@code{frame})}
5510 Select frame number @var{n}. Recall that frame zero is the innermost
5511 (currently executing) frame, frame one is the frame that called the
5512 innermost one, and so on. The highest-numbered frame is the one for
5515 @item frame @var{addr}
5517 Select the frame at address @var{addr}. This is useful mainly if the
5518 chaining of stack frames has been damaged by a bug, making it
5519 impossible for @value{GDBN} to assign numbers properly to all frames. In
5520 addition, this can be useful when your program has multiple stacks and
5521 switches between them.
5523 On the SPARC architecture, @code{frame} needs two addresses to
5524 select an arbitrary frame: a frame pointer and a stack pointer.
5526 On the MIPS and Alpha architecture, it needs two addresses: a stack
5527 pointer and a program counter.
5529 On the 29k architecture, it needs three addresses: a register stack
5530 pointer, a program counter, and a memory stack pointer.
5534 Move @var{n} frames up the stack. For positive numbers @var{n}, this
5535 advances toward the outermost frame, to higher frame numbers, to frames
5536 that have existed longer. @var{n} defaults to one.
5539 @kindex do @r{(@code{down})}
5541 Move @var{n} frames down the stack. For positive numbers @var{n}, this
5542 advances toward the innermost frame, to lower frame numbers, to frames
5543 that were created more recently. @var{n} defaults to one. You may
5544 abbreviate @code{down} as @code{do}.
5547 All of these commands end by printing two lines of output describing the
5548 frame. The first line shows the frame number, the function name, the
5549 arguments, and the source file and line number of execution in that
5550 frame. The second line shows the text of that source line.
5558 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
5560 10 read_input_file (argv[i]);
5564 After such a printout, the @code{list} command with no arguments
5565 prints ten lines centered on the point of execution in the frame.
5566 You can also edit the program at the point of execution with your favorite
5567 editing program by typing @code{edit}.
5568 @xref{List, ,Printing Source Lines},
5572 @kindex down-silently
5574 @item up-silently @var{n}
5575 @itemx down-silently @var{n}
5576 These two commands are variants of @code{up} and @code{down},
5577 respectively; they differ in that they do their work silently, without
5578 causing display of the new frame. They are intended primarily for use
5579 in @value{GDBN} command scripts, where the output might be unnecessary and
5584 @section Information About a Frame
5586 There are several other commands to print information about the selected
5592 When used without any argument, this command does not change which
5593 frame is selected, but prints a brief description of the currently
5594 selected stack frame. It can be abbreviated @code{f}. With an
5595 argument, this command is used to select a stack frame.
5596 @xref{Selection, ,Selecting a Frame}.
5599 @kindex info f @r{(@code{info frame})}
5602 This command prints a verbose description of the selected stack frame,
5607 the address of the frame
5609 the address of the next frame down (called by this frame)
5611 the address of the next frame up (caller of this frame)
5613 the language in which the source code corresponding to this frame is written
5615 the address of the frame's arguments
5617 the address of the frame's local variables
5619 the program counter saved in it (the address of execution in the caller frame)
5621 which registers were saved in the frame
5624 @noindent The verbose description is useful when
5625 something has gone wrong that has made the stack format fail to fit
5626 the usual conventions.
5628 @item info frame @var{addr}
5629 @itemx info f @var{addr}
5630 Print a verbose description of the frame at address @var{addr}, without
5631 selecting that frame. The selected frame remains unchanged by this
5632 command. This requires the same kind of address (more than one for some
5633 architectures) that you specify in the @code{frame} command.
5634 @xref{Selection, ,Selecting a Frame}.
5638 Print the arguments of the selected frame, each on a separate line.
5642 Print the local variables of the selected frame, each on a separate
5643 line. These are all variables (declared either static or automatic)
5644 accessible at the point of execution of the selected frame.
5647 @cindex catch exceptions, list active handlers
5648 @cindex exception handlers, how to list
5650 Print a list of all the exception handlers that are active in the
5651 current stack frame at the current point of execution. To see other
5652 exception handlers, visit the associated frame (using the @code{up},
5653 @code{down}, or @code{frame} commands); then type @code{info catch}.
5654 @xref{Set Catchpoints, , Setting Catchpoints}.
5660 @chapter Examining Source Files
5662 @value{GDBN} can print parts of your program's source, since the debugging
5663 information recorded in the program tells @value{GDBN} what source files were
5664 used to build it. When your program stops, @value{GDBN} spontaneously prints
5665 the line where it stopped. Likewise, when you select a stack frame
5666 (@pxref{Selection, ,Selecting a Frame}), @value{GDBN} prints the line where
5667 execution in that frame has stopped. You can print other portions of
5668 source files by explicit command.
5670 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
5671 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
5672 @value{GDBN} under @sc{gnu} Emacs}.
5675 * List:: Printing source lines
5676 * Specify Location:: How to specify code locations
5677 * Edit:: Editing source files
5678 * Search:: Searching source files
5679 * Source Path:: Specifying source directories
5680 * Machine Code:: Source and machine code
5684 @section Printing Source Lines
5687 @kindex l @r{(@code{list})}
5688 To print lines from a source file, use the @code{list} command
5689 (abbreviated @code{l}). By default, ten lines are printed.
5690 There are several ways to specify what part of the file you want to
5691 print; see @ref{Specify Location}, for the full list.
5693 Here are the forms of the @code{list} command most commonly used:
5696 @item list @var{linenum}
5697 Print lines centered around line number @var{linenum} in the
5698 current source file.
5700 @item list @var{function}
5701 Print lines centered around the beginning of function
5705 Print more lines. If the last lines printed were printed with a
5706 @code{list} command, this prints lines following the last lines
5707 printed; however, if the last line printed was a solitary line printed
5708 as part of displaying a stack frame (@pxref{Stack, ,Examining the
5709 Stack}), this prints lines centered around that line.
5712 Print lines just before the lines last printed.
5715 @cindex @code{list}, how many lines to display
5716 By default, @value{GDBN} prints ten source lines with any of these forms of
5717 the @code{list} command. You can change this using @code{set listsize}:
5720 @kindex set listsize
5721 @item set listsize @var{count}
5722 Make the @code{list} command display @var{count} source lines (unless
5723 the @code{list} argument explicitly specifies some other number).
5725 @kindex show listsize
5727 Display the number of lines that @code{list} prints.
5730 Repeating a @code{list} command with @key{RET} discards the argument,
5731 so it is equivalent to typing just @code{list}. This is more useful
5732 than listing the same lines again. An exception is made for an
5733 argument of @samp{-}; that argument is preserved in repetition so that
5734 each repetition moves up in the source file.
5736 In general, the @code{list} command expects you to supply zero, one or two
5737 @dfn{linespecs}. Linespecs specify source lines; there are several ways
5738 of writing them (@pxref{Specify Location}), but the effect is always
5739 to specify some source line.
5741 Here is a complete description of the possible arguments for @code{list}:
5744 @item list @var{linespec}
5745 Print lines centered around the line specified by @var{linespec}.
5747 @item list @var{first},@var{last}
5748 Print lines from @var{first} to @var{last}. Both arguments are
5749 linespecs. When a @code{list} command has two linespecs, and the
5750 source file of the second linespec is omitted, this refers to
5751 the same source file as the first linespec.
5753 @item list ,@var{last}
5754 Print lines ending with @var{last}.
5756 @item list @var{first},
5757 Print lines starting with @var{first}.
5760 Print lines just after the lines last printed.
5763 Print lines just before the lines last printed.
5766 As described in the preceding table.
5769 @node Specify Location
5770 @section Specifying a Location
5771 @cindex specifying location
5774 Several @value{GDBN} commands accept arguments that specify a location
5775 of your program's code. Since @value{GDBN} is a source-level
5776 debugger, a location usually specifies some line in the source code;
5777 for that reason, locations are also known as @dfn{linespecs}.
5779 Here are all the different ways of specifying a code location that
5780 @value{GDBN} understands:
5784 Specifies the line number @var{linenum} of the current source file.
5787 @itemx +@var{offset}
5788 Specifies the line @var{offset} lines before or after the @dfn{current
5789 line}. For the @code{list} command, the current line is the last one
5790 printed; for the breakpoint commands, this is the line at which
5791 execution stopped in the currently selected @dfn{stack frame}
5792 (@pxref{Frames, ,Frames}, for a description of stack frames.) When
5793 used as the second of the two linespecs in a @code{list} command,
5794 this specifies the line @var{offset} lines up or down from the first
5797 @item @var{filename}:@var{linenum}
5798 Specifies the line @var{linenum} in the source file @var{filename}.
5800 @item @var{function}
5801 Specifies the line that begins the body of the function @var{function}.
5802 For example, in C, this is the line with the open brace.
5804 @item @var{filename}:@var{function}
5805 Specifies the line that begins the body of the function @var{function}
5806 in the file @var{filename}. You only need the file name with a
5807 function name to avoid ambiguity when there are identically named
5808 functions in different source files.
5810 @item *@var{address}
5811 Specifies the program address @var{address}. For line-oriented
5812 commands, such as @code{list} and @code{edit}, this specifies a source
5813 line that contains @var{address}. For @code{break} and other
5814 breakpoint oriented commands, this can be used to set breakpoints in
5815 parts of your program which do not have debugging information or
5818 Here @var{address} may be any expression valid in the current working
5819 language (@pxref{Languages, working language}) that specifies a code
5820 address. In addition, as a convenience, @value{GDBN} extends the
5821 semantics of expressions used in locations to cover the situations
5822 that frequently happen during debugging. Here are the various forms
5826 @item @var{expression}
5827 Any expression valid in the current working language.
5829 @item @var{funcaddr}
5830 An address of a function or procedure derived from its name. In C,
5831 C@t{++}, Java, Objective-C, Fortran, minimal, and assembly, this is
5832 simply the function's name @var{function} (and actually a special case
5833 of a valid expression). In Pascal and Modula-2, this is
5834 @code{&@var{function}}. In Ada, this is @code{@var{function}'Address}
5835 (although the Pascal form also works).
5837 This form specifies the address of the function's first instruction,
5838 before the stack frame and arguments have been set up.
5840 @item '@var{filename}'::@var{funcaddr}
5841 Like @var{funcaddr} above, but also specifies the name of the source
5842 file explicitly. This is useful if the name of the function does not
5843 specify the function unambiguously, e.g., if there are several
5844 functions with identical names in different source files.
5851 @section Editing Source Files
5852 @cindex editing source files
5855 @kindex e @r{(@code{edit})}
5856 To edit the lines in a source file, use the @code{edit} command.
5857 The editing program of your choice
5858 is invoked with the current line set to
5859 the active line in the program.
5860 Alternatively, there are several ways to specify what part of the file you
5861 want to print if you want to see other parts of the program:
5864 @item edit @var{location}
5865 Edit the source file specified by @code{location}. Editing starts at
5866 that @var{location}, e.g., at the specified source line of the
5867 specified file. @xref{Specify Location}, for all the possible forms
5868 of the @var{location} argument; here are the forms of the @code{edit}
5869 command most commonly used:
5872 @item edit @var{number}
5873 Edit the current source file with @var{number} as the active line number.
5875 @item edit @var{function}
5876 Edit the file containing @var{function} at the beginning of its definition.
5881 @subsection Choosing your Editor
5882 You can customize @value{GDBN} to use any editor you want
5884 The only restriction is that your editor (say @code{ex}), recognizes the
5885 following command-line syntax:
5887 ex +@var{number} file
5889 The optional numeric value +@var{number} specifies the number of the line in
5890 the file where to start editing.}.
5891 By default, it is @file{@value{EDITOR}}, but you can change this
5892 by setting the environment variable @code{EDITOR} before using
5893 @value{GDBN}. For example, to configure @value{GDBN} to use the
5894 @code{vi} editor, you could use these commands with the @code{sh} shell:
5900 or in the @code{csh} shell,
5902 setenv EDITOR /usr/bin/vi
5907 @section Searching Source Files
5908 @cindex searching source files
5910 There are two commands for searching through the current source file for a
5915 @kindex forward-search
5916 @item forward-search @var{regexp}
5917 @itemx search @var{regexp}
5918 The command @samp{forward-search @var{regexp}} checks each line,
5919 starting with the one following the last line listed, for a match for
5920 @var{regexp}. It lists the line that is found. You can use the
5921 synonym @samp{search @var{regexp}} or abbreviate the command name as
5924 @kindex reverse-search
5925 @item reverse-search @var{regexp}
5926 The command @samp{reverse-search @var{regexp}} checks each line, starting
5927 with the one before the last line listed and going backward, for a match
5928 for @var{regexp}. It lists the line that is found. You can abbreviate
5929 this command as @code{rev}.
5933 @section Specifying Source Directories
5936 @cindex directories for source files
5937 Executable programs sometimes do not record the directories of the source
5938 files from which they were compiled, just the names. Even when they do,
5939 the directories could be moved between the compilation and your debugging
5940 session. @value{GDBN} has a list of directories to search for source files;
5941 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
5942 it tries all the directories in the list, in the order they are present
5943 in the list, until it finds a file with the desired name.
5945 For example, suppose an executable references the file
5946 @file{/usr/src/foo-1.0/lib/foo.c}, and our source path is
5947 @file{/mnt/cross}. The file is first looked up literally; if this
5948 fails, @file{/mnt/cross/usr/src/foo-1.0/lib/foo.c} is tried; if this
5949 fails, @file{/mnt/cross/foo.c} is opened; if this fails, an error
5950 message is printed. @value{GDBN} does not look up the parts of the
5951 source file name, such as @file{/mnt/cross/src/foo-1.0/lib/foo.c}.
5952 Likewise, the subdirectories of the source path are not searched: if
5953 the source path is @file{/mnt/cross}, and the binary refers to
5954 @file{foo.c}, @value{GDBN} would not find it under
5955 @file{/mnt/cross/usr/src/foo-1.0/lib}.
5957 Plain file names, relative file names with leading directories, file
5958 names containing dots, etc.@: are all treated as described above; for
5959 instance, if the source path is @file{/mnt/cross}, and the source file
5960 is recorded as @file{../lib/foo.c}, @value{GDBN} would first try
5961 @file{../lib/foo.c}, then @file{/mnt/cross/../lib/foo.c}, and after
5962 that---@file{/mnt/cross/foo.c}.
5964 Note that the executable search path is @emph{not} used to locate the
5967 Whenever you reset or rearrange the source path, @value{GDBN} clears out
5968 any information it has cached about where source files are found and where
5969 each line is in the file.
5973 When you start @value{GDBN}, its source path includes only @samp{cdir}
5974 and @samp{cwd}, in that order.
5975 To add other directories, use the @code{directory} command.
5977 The search path is used to find both program source files and @value{GDBN}
5978 script files (read using the @samp{-command} option and @samp{source} command).
5980 In addition to the source path, @value{GDBN} provides a set of commands
5981 that manage a list of source path substitution rules. A @dfn{substitution
5982 rule} specifies how to rewrite source directories stored in the program's
5983 debug information in case the sources were moved to a different
5984 directory between compilation and debugging. A rule is made of
5985 two strings, the first specifying what needs to be rewritten in
5986 the path, and the second specifying how it should be rewritten.
5987 In @ref{set substitute-path}, we name these two parts @var{from} and
5988 @var{to} respectively. @value{GDBN} does a simple string replacement
5989 of @var{from} with @var{to} at the start of the directory part of the
5990 source file name, and uses that result instead of the original file
5991 name to look up the sources.
5993 Using the previous example, suppose the @file{foo-1.0} tree has been
5994 moved from @file{/usr/src} to @file{/mnt/cross}, then you can tell
5995 @value{GDBN} to replace @file{/usr/src} in all source path names with
5996 @file{/mnt/cross}. The first lookup will then be
5997 @file{/mnt/cross/foo-1.0/lib/foo.c} in place of the original location
5998 of @file{/usr/src/foo-1.0/lib/foo.c}. To define a source path
5999 substitution rule, use the @code{set substitute-path} command
6000 (@pxref{set substitute-path}).
6002 To avoid unexpected substitution results, a rule is applied only if the
6003 @var{from} part of the directory name ends at a directory separator.
6004 For instance, a rule substituting @file{/usr/source} into
6005 @file{/mnt/cross} will be applied to @file{/usr/source/foo-1.0} but
6006 not to @file{/usr/sourceware/foo-2.0}. And because the substitution
6007 is applied only at the beginning of the directory name, this rule will
6008 not be applied to @file{/root/usr/source/baz.c} either.
6010 In many cases, you can achieve the same result using the @code{directory}
6011 command. However, @code{set substitute-path} can be more efficient in
6012 the case where the sources are organized in a complex tree with multiple
6013 subdirectories. With the @code{directory} command, you need to add each
6014 subdirectory of your project. If you moved the entire tree while
6015 preserving its internal organization, then @code{set substitute-path}
6016 allows you to direct the debugger to all the sources with one single
6019 @code{set substitute-path} is also more than just a shortcut command.
6020 The source path is only used if the file at the original location no
6021 longer exists. On the other hand, @code{set substitute-path} modifies
6022 the debugger behavior to look at the rewritten location instead. So, if
6023 for any reason a source file that is not relevant to your executable is
6024 located at the original location, a substitution rule is the only
6025 method available to point @value{GDBN} at the new location.
6027 @cindex @samp{--with-relocated-sources}
6028 @cindex default source path substitution
6029 You can configure a default source path substitution rule by
6030 configuring @value{GDBN} with the
6031 @samp{--with-relocated-sources=@var{dir}} option. The @var{dir}
6032 should be the name of a directory under @value{GDBN}'s configured
6033 prefix (set with @samp{--prefix} or @samp{--exec-prefix}), and
6034 directory names in debug information under @var{dir} will be adjusted
6035 automatically if the installed @value{GDBN} is moved to a new
6036 location. This is useful if @value{GDBN}, libraries or executables
6037 with debug information and corresponding source code are being moved
6041 @item directory @var{dirname} @dots{}
6042 @item dir @var{dirname} @dots{}
6043 Add directory @var{dirname} to the front of the source path. Several
6044 directory names may be given to this command, separated by @samp{:}
6045 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
6046 part of absolute file names) or
6047 whitespace. You may specify a directory that is already in the source
6048 path; this moves it forward, so @value{GDBN} searches it sooner.
6052 @vindex $cdir@r{, convenience variable}
6053 @vindex $cwd@r{, convenience variable}
6054 @cindex compilation directory
6055 @cindex current directory
6056 @cindex working directory
6057 @cindex directory, current
6058 @cindex directory, compilation
6059 You can use the string @samp{$cdir} to refer to the compilation
6060 directory (if one is recorded), and @samp{$cwd} to refer to the current
6061 working directory. @samp{$cwd} is not the same as @samp{.}---the former
6062 tracks the current working directory as it changes during your @value{GDBN}
6063 session, while the latter is immediately expanded to the current
6064 directory at the time you add an entry to the source path.
6067 Reset the source path to its default value (@samp{$cdir:$cwd} on Unix systems). This requires confirmation.
6069 @c RET-repeat for @code{directory} is explicitly disabled, but since
6070 @c repeating it would be a no-op we do not say that. (thanks to RMS)
6072 @item show directories
6073 @kindex show directories
6074 Print the source path: show which directories it contains.
6076 @anchor{set substitute-path}
6077 @item set substitute-path @var{from} @var{to}
6078 @kindex set substitute-path
6079 Define a source path substitution rule, and add it at the end of the
6080 current list of existing substitution rules. If a rule with the same
6081 @var{from} was already defined, then the old rule is also deleted.
6083 For example, if the file @file{/foo/bar/baz.c} was moved to
6084 @file{/mnt/cross/baz.c}, then the command
6087 (@value{GDBP}) set substitute-path /usr/src /mnt/cross
6091 will tell @value{GDBN} to replace @samp{/usr/src} with
6092 @samp{/mnt/cross}, which will allow @value{GDBN} to find the file
6093 @file{baz.c} even though it was moved.
6095 In the case when more than one substitution rule have been defined,
6096 the rules are evaluated one by one in the order where they have been
6097 defined. The first one matching, if any, is selected to perform
6100 For instance, if we had entered the following commands:
6103 (@value{GDBP}) set substitute-path /usr/src/include /mnt/include
6104 (@value{GDBP}) set substitute-path /usr/src /mnt/src
6108 @value{GDBN} would then rewrite @file{/usr/src/include/defs.h} into
6109 @file{/mnt/include/defs.h} by using the first rule. However, it would
6110 use the second rule to rewrite @file{/usr/src/lib/foo.c} into
6111 @file{/mnt/src/lib/foo.c}.
6114 @item unset substitute-path [path]
6115 @kindex unset substitute-path
6116 If a path is specified, search the current list of substitution rules
6117 for a rule that would rewrite that path. Delete that rule if found.
6118 A warning is emitted by the debugger if no rule could be found.
6120 If no path is specified, then all substitution rules are deleted.
6122 @item show substitute-path [path]
6123 @kindex show substitute-path
6124 If a path is specified, then print the source path substitution rule
6125 which would rewrite that path, if any.
6127 If no path is specified, then print all existing source path substitution
6132 If your source path is cluttered with directories that are no longer of
6133 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
6134 versions of source. You can correct the situation as follows:
6138 Use @code{directory} with no argument to reset the source path to its default value.
6141 Use @code{directory} with suitable arguments to reinstall the
6142 directories you want in the source path. You can add all the
6143 directories in one command.
6147 @section Source and Machine Code
6148 @cindex source line and its code address
6150 You can use the command @code{info line} to map source lines to program
6151 addresses (and vice versa), and the command @code{disassemble} to display
6152 a range of addresses as machine instructions. You can use the command
6153 @code{set disassemble-next-line} to set whether to disassemble next
6154 source line when execution stops. When run under @sc{gnu} Emacs
6155 mode, the @code{info line} command causes the arrow to point to the
6156 line specified. Also, @code{info line} prints addresses in symbolic form as
6161 @item info line @var{linespec}
6162 Print the starting and ending addresses of the compiled code for
6163 source line @var{linespec}. You can specify source lines in any of
6164 the ways documented in @ref{Specify Location}.
6167 For example, we can use @code{info line} to discover the location of
6168 the object code for the first line of function
6169 @code{m4_changequote}:
6171 @c FIXME: I think this example should also show the addresses in
6172 @c symbolic form, as they usually would be displayed.
6174 (@value{GDBP}) info line m4_changequote
6175 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
6179 @cindex code address and its source line
6180 We can also inquire (using @code{*@var{addr}} as the form for
6181 @var{linespec}) what source line covers a particular address:
6183 (@value{GDBP}) info line *0x63ff
6184 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
6187 @cindex @code{$_} and @code{info line}
6188 @cindex @code{x} command, default address
6189 @kindex x@r{(examine), and} info line
6190 After @code{info line}, the default address for the @code{x} command
6191 is changed to the starting address of the line, so that @samp{x/i} is
6192 sufficient to begin examining the machine code (@pxref{Memory,
6193 ,Examining Memory}). Also, this address is saved as the value of the
6194 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
6199 @cindex assembly instructions
6200 @cindex instructions, assembly
6201 @cindex machine instructions
6202 @cindex listing machine instructions
6204 @itemx disassemble /m
6205 @itemx disassemble /r
6206 This specialized command dumps a range of memory as machine
6207 instructions. It can also print mixed source+disassembly by specifying
6208 the @code{/m} modifier and print the raw instructions in hex as well as
6209 in symbolic form by specifying the @code{/r}.
6210 The default memory range is the function surrounding the
6211 program counter of the selected frame. A single argument to this
6212 command is a program counter value; @value{GDBN} dumps the function
6213 surrounding this value. Two arguments specify a range of addresses
6214 (first inclusive, second exclusive) to dump.
6217 The following example shows the disassembly of a range of addresses of
6218 HP PA-RISC 2.0 code:
6221 (@value{GDBP}) disas 0x32c4 0x32e4
6222 Dump of assembler code from 0x32c4 to 0x32e4:
6223 0x32c4 <main+204>: addil 0,dp
6224 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
6225 0x32cc <main+212>: ldil 0x3000,r31
6226 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
6227 0x32d4 <main+220>: ldo 0(r31),rp
6228 0x32d8 <main+224>: addil -0x800,dp
6229 0x32dc <main+228>: ldo 0x588(r1),r26
6230 0x32e0 <main+232>: ldil 0x3000,r31
6231 End of assembler dump.
6234 Here is an example showing mixed source+assembly for Intel x86:
6237 (@value{GDBP}) disas /m main
6238 Dump of assembler code for function main:
6240 0x08048330 <main+0>: push %ebp
6241 0x08048331 <main+1>: mov %esp,%ebp
6242 0x08048333 <main+3>: sub $0x8,%esp
6243 0x08048336 <main+6>: and $0xfffffff0,%esp
6244 0x08048339 <main+9>: sub $0x10,%esp
6246 6 printf ("Hello.\n");
6247 0x0804833c <main+12>: movl $0x8048440,(%esp)
6248 0x08048343 <main+19>: call 0x8048284 <puts@@plt>
6252 0x08048348 <main+24>: mov $0x0,%eax
6253 0x0804834d <main+29>: leave
6254 0x0804834e <main+30>: ret
6256 End of assembler dump.
6259 Some architectures have more than one commonly-used set of instruction
6260 mnemonics or other syntax.
6262 For programs that were dynamically linked and use shared libraries,
6263 instructions that call functions or branch to locations in the shared
6264 libraries might show a seemingly bogus location---it's actually a
6265 location of the relocation table. On some architectures, @value{GDBN}
6266 might be able to resolve these to actual function names.
6269 @kindex set disassembly-flavor
6270 @cindex Intel disassembly flavor
6271 @cindex AT&T disassembly flavor
6272 @item set disassembly-flavor @var{instruction-set}
6273 Select the instruction set to use when disassembling the
6274 program via the @code{disassemble} or @code{x/i} commands.
6276 Currently this command is only defined for the Intel x86 family. You
6277 can set @var{instruction-set} to either @code{intel} or @code{att}.
6278 The default is @code{att}, the AT&T flavor used by default by Unix
6279 assemblers for x86-based targets.
6281 @kindex show disassembly-flavor
6282 @item show disassembly-flavor
6283 Show the current setting of the disassembly flavor.
6287 @kindex set disassemble-next-line
6288 @kindex show disassemble-next-line
6289 @item set disassemble-next-line
6290 @itemx show disassemble-next-line
6291 Control whether or not @value{GDBN} will disassemble the next source
6292 line or instruction when execution stops. If ON, @value{GDBN} will
6293 display disassembly of the next source line when execution of the
6294 program being debugged stops. This is @emph{in addition} to
6295 displaying the source line itself, which @value{GDBN} always does if
6296 possible. If the next source line cannot be displayed for some reason
6297 (e.g., if @value{GDBN} cannot find the source file, or there's no line
6298 info in the debug info), @value{GDBN} will display disassembly of the
6299 next @emph{instruction} instead of showing the next source line. If
6300 AUTO, @value{GDBN} will display disassembly of next instruction only
6301 if the source line cannot be displayed. This setting causes
6302 @value{GDBN} to display some feedback when you step through a function
6303 with no line info or whose source file is unavailable. The default is
6304 OFF, which means never display the disassembly of the next line or
6310 @chapter Examining Data
6312 @cindex printing data
6313 @cindex examining data
6316 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
6317 @c document because it is nonstandard... Under Epoch it displays in a
6318 @c different window or something like that.
6319 The usual way to examine data in your program is with the @code{print}
6320 command (abbreviated @code{p}), or its synonym @code{inspect}. It
6321 evaluates and prints the value of an expression of the language your
6322 program is written in (@pxref{Languages, ,Using @value{GDBN} with
6323 Different Languages}).
6326 @item print @var{expr}
6327 @itemx print /@var{f} @var{expr}
6328 @var{expr} is an expression (in the source language). By default the
6329 value of @var{expr} is printed in a format appropriate to its data type;
6330 you can choose a different format by specifying @samp{/@var{f}}, where
6331 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
6335 @itemx print /@var{f}
6336 @cindex reprint the last value
6337 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
6338 @dfn{value history}; @pxref{Value History, ,Value History}). This allows you to
6339 conveniently inspect the same value in an alternative format.
6342 A more low-level way of examining data is with the @code{x} command.
6343 It examines data in memory at a specified address and prints it in a
6344 specified format. @xref{Memory, ,Examining Memory}.
6346 If you are interested in information about types, or about how the
6347 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
6348 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
6352 * Expressions:: Expressions
6353 * Ambiguous Expressions:: Ambiguous Expressions
6354 * Variables:: Program variables
6355 * Arrays:: Artificial arrays
6356 * Output Formats:: Output formats
6357 * Memory:: Examining memory
6358 * Auto Display:: Automatic display
6359 * Print Settings:: Print settings
6360 * Value History:: Value history
6361 * Convenience Vars:: Convenience variables
6362 * Registers:: Registers
6363 * Floating Point Hardware:: Floating point hardware
6364 * Vector Unit:: Vector Unit
6365 * OS Information:: Auxiliary data provided by operating system
6366 * Memory Region Attributes:: Memory region attributes
6367 * Dump/Restore Files:: Copy between memory and a file
6368 * Core File Generation:: Cause a program dump its core
6369 * Character Sets:: Debugging programs that use a different
6370 character set than GDB does
6371 * Caching Remote Data:: Data caching for remote targets
6372 * Searching Memory:: Searching memory for a sequence of bytes
6376 @section Expressions
6379 @code{print} and many other @value{GDBN} commands accept an expression and
6380 compute its value. Any kind of constant, variable or operator defined
6381 by the programming language you are using is valid in an expression in
6382 @value{GDBN}. This includes conditional expressions, function calls,
6383 casts, and string constants. It also includes preprocessor macros, if
6384 you compiled your program to include this information; see
6387 @cindex arrays in expressions
6388 @value{GDBN} supports array constants in expressions input by
6389 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
6390 you can use the command @code{print @{1, 2, 3@}} to create an array
6391 of three integers. If you pass an array to a function or assign it
6392 to a program variable, @value{GDBN} copies the array to memory that
6393 is @code{malloc}ed in the target program.
6395 Because C is so widespread, most of the expressions shown in examples in
6396 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
6397 Languages}, for information on how to use expressions in other
6400 In this section, we discuss operators that you can use in @value{GDBN}
6401 expressions regardless of your programming language.
6403 @cindex casts, in expressions
6404 Casts are supported in all languages, not just in C, because it is so
6405 useful to cast a number into a pointer in order to examine a structure
6406 at that address in memory.
6407 @c FIXME: casts supported---Mod2 true?
6409 @value{GDBN} supports these operators, in addition to those common
6410 to programming languages:
6414 @samp{@@} is a binary operator for treating parts of memory as arrays.
6415 @xref{Arrays, ,Artificial Arrays}, for more information.
6418 @samp{::} allows you to specify a variable in terms of the file or
6419 function where it is defined. @xref{Variables, ,Program Variables}.
6421 @cindex @{@var{type}@}
6422 @cindex type casting memory
6423 @cindex memory, viewing as typed object
6424 @cindex casts, to view memory
6425 @item @{@var{type}@} @var{addr}
6426 Refers to an object of type @var{type} stored at address @var{addr} in
6427 memory. @var{addr} may be any expression whose value is an integer or
6428 pointer (but parentheses are required around binary operators, just as in
6429 a cast). This construct is allowed regardless of what kind of data is
6430 normally supposed to reside at @var{addr}.
6433 @node Ambiguous Expressions
6434 @section Ambiguous Expressions
6435 @cindex ambiguous expressions
6437 Expressions can sometimes contain some ambiguous elements. For instance,
6438 some programming languages (notably Ada, C@t{++} and Objective-C) permit
6439 a single function name to be defined several times, for application in
6440 different contexts. This is called @dfn{overloading}. Another example
6441 involving Ada is generics. A @dfn{generic package} is similar to C@t{++}
6442 templates and is typically instantiated several times, resulting in
6443 the same function name being defined in different contexts.
6445 In some cases and depending on the language, it is possible to adjust
6446 the expression to remove the ambiguity. For instance in C@t{++}, you
6447 can specify the signature of the function you want to break on, as in
6448 @kbd{break @var{function}(@var{types})}. In Ada, using the fully
6449 qualified name of your function often makes the expression unambiguous
6452 When an ambiguity that needs to be resolved is detected, the debugger
6453 has the capability to display a menu of numbered choices for each
6454 possibility, and then waits for the selection with the prompt @samp{>}.
6455 The first option is always @samp{[0] cancel}, and typing @kbd{0 @key{RET}}
6456 aborts the current command. If the command in which the expression was
6457 used allows more than one choice to be selected, the next option in the
6458 menu is @samp{[1] all}, and typing @kbd{1 @key{RET}} selects all possible
6461 For example, the following session excerpt shows an attempt to set a
6462 breakpoint at the overloaded symbol @code{String::after}.
6463 We choose three particular definitions of that function name:
6465 @c FIXME! This is likely to change to show arg type lists, at least
6468 (@value{GDBP}) b String::after
6471 [2] file:String.cc; line number:867
6472 [3] file:String.cc; line number:860
6473 [4] file:String.cc; line number:875
6474 [5] file:String.cc; line number:853
6475 [6] file:String.cc; line number:846
6476 [7] file:String.cc; line number:735
6478 Breakpoint 1 at 0xb26c: file String.cc, line 867.
6479 Breakpoint 2 at 0xb344: file String.cc, line 875.
6480 Breakpoint 3 at 0xafcc: file String.cc, line 846.
6481 Multiple breakpoints were set.
6482 Use the "delete" command to delete unwanted
6489 @kindex set multiple-symbols
6490 @item set multiple-symbols @var{mode}
6491 @cindex multiple-symbols menu
6493 This option allows you to adjust the debugger behavior when an expression
6496 By default, @var{mode} is set to @code{all}. If the command with which
6497 the expression is used allows more than one choice, then @value{GDBN}
6498 automatically selects all possible choices. For instance, inserting
6499 a breakpoint on a function using an ambiguous name results in a breakpoint
6500 inserted on each possible match. However, if a unique choice must be made,
6501 then @value{GDBN} uses the menu to help you disambiguate the expression.
6502 For instance, printing the address of an overloaded function will result
6503 in the use of the menu.
6505 When @var{mode} is set to @code{ask}, the debugger always uses the menu
6506 when an ambiguity is detected.
6508 Finally, when @var{mode} is set to @code{cancel}, the debugger reports
6509 an error due to the ambiguity and the command is aborted.
6511 @kindex show multiple-symbols
6512 @item show multiple-symbols
6513 Show the current value of the @code{multiple-symbols} setting.
6517 @section Program Variables
6519 The most common kind of expression to use is the name of a variable
6522 Variables in expressions are understood in the selected stack frame
6523 (@pxref{Selection, ,Selecting a Frame}); they must be either:
6527 global (or file-static)
6534 visible according to the scope rules of the
6535 programming language from the point of execution in that frame
6538 @noindent This means that in the function
6553 you can examine and use the variable @code{a} whenever your program is
6554 executing within the function @code{foo}, but you can only use or
6555 examine the variable @code{b} while your program is executing inside
6556 the block where @code{b} is declared.
6558 @cindex variable name conflict
6559 There is an exception: you can refer to a variable or function whose
6560 scope is a single source file even if the current execution point is not
6561 in this file. But it is possible to have more than one such variable or
6562 function with the same name (in different source files). If that
6563 happens, referring to that name has unpredictable effects. If you wish,
6564 you can specify a static variable in a particular function or file,
6565 using the colon-colon (@code{::}) notation:
6567 @cindex colon-colon, context for variables/functions
6569 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
6570 @cindex @code{::}, context for variables/functions
6573 @var{file}::@var{variable}
6574 @var{function}::@var{variable}
6578 Here @var{file} or @var{function} is the name of the context for the
6579 static @var{variable}. In the case of file names, you can use quotes to
6580 make sure @value{GDBN} parses the file name as a single word---for example,
6581 to print a global value of @code{x} defined in @file{f2.c}:
6584 (@value{GDBP}) p 'f2.c'::x
6587 @cindex C@t{++} scope resolution
6588 This use of @samp{::} is very rarely in conflict with the very similar
6589 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
6590 scope resolution operator in @value{GDBN} expressions.
6591 @c FIXME: Um, so what happens in one of those rare cases where it's in
6594 @cindex wrong values
6595 @cindex variable values, wrong
6596 @cindex function entry/exit, wrong values of variables
6597 @cindex optimized code, wrong values of variables
6599 @emph{Warning:} Occasionally, a local variable may appear to have the
6600 wrong value at certain points in a function---just after entry to a new
6601 scope, and just before exit.
6603 You may see this problem when you are stepping by machine instructions.
6604 This is because, on most machines, it takes more than one instruction to
6605 set up a stack frame (including local variable definitions); if you are
6606 stepping by machine instructions, variables may appear to have the wrong
6607 values until the stack frame is completely built. On exit, it usually
6608 also takes more than one machine instruction to destroy a stack frame;
6609 after you begin stepping through that group of instructions, local
6610 variable definitions may be gone.
6612 This may also happen when the compiler does significant optimizations.
6613 To be sure of always seeing accurate values, turn off all optimization
6616 @cindex ``No symbol "foo" in current context''
6617 Another possible effect of compiler optimizations is to optimize
6618 unused variables out of existence, or assign variables to registers (as
6619 opposed to memory addresses). Depending on the support for such cases
6620 offered by the debug info format used by the compiler, @value{GDBN}
6621 might not be able to display values for such local variables. If that
6622 happens, @value{GDBN} will print a message like this:
6625 No symbol "foo" in current context.
6628 To solve such problems, either recompile without optimizations, or use a
6629 different debug info format, if the compiler supports several such
6630 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler,
6631 usually supports the @option{-gstabs+} option. @option{-gstabs+}
6632 produces debug info in a format that is superior to formats such as
6633 COFF. You may be able to use DWARF 2 (@option{-gdwarf-2}), which is also
6634 an effective form for debug info. @xref{Debugging Options,,Options
6635 for Debugging Your Program or GCC, gcc.info, Using the @sc{gnu}
6636 Compiler Collection (GCC)}.
6637 @xref{C, ,C and C@t{++}}, for more information about debug info formats
6638 that are best suited to C@t{++} programs.
6640 If you ask to print an object whose contents are unknown to
6641 @value{GDBN}, e.g., because its data type is not completely specified
6642 by the debug information, @value{GDBN} will say @samp{<incomplete
6643 type>}. @xref{Symbols, incomplete type}, for more about this.
6645 Strings are identified as arrays of @code{char} values without specified
6646 signedness. Arrays of either @code{signed char} or @code{unsigned char} get
6647 printed as arrays of 1 byte sized integers. @code{-fsigned-char} or
6648 @code{-funsigned-char} @value{NGCC} options have no effect as @value{GDBN}
6649 defines literal string type @code{"char"} as @code{char} without a sign.
6654 signed char var1[] = "A";
6657 You get during debugging
6662 $2 = @{65 'A', 0 '\0'@}
6666 @section Artificial Arrays
6668 @cindex artificial array
6670 @kindex @@@r{, referencing memory as an array}
6671 It is often useful to print out several successive objects of the
6672 same type in memory; a section of an array, or an array of
6673 dynamically determined size for which only a pointer exists in the
6676 You can do this by referring to a contiguous span of memory as an
6677 @dfn{artificial array}, using the binary operator @samp{@@}. The left
6678 operand of @samp{@@} should be the first element of the desired array
6679 and be an individual object. The right operand should be the desired length
6680 of the array. The result is an array value whose elements are all of
6681 the type of the left argument. The first element is actually the left
6682 argument; the second element comes from bytes of memory immediately
6683 following those that hold the first element, and so on. Here is an
6684 example. If a program says
6687 int *array = (int *) malloc (len * sizeof (int));
6691 you can print the contents of @code{array} with
6697 The left operand of @samp{@@} must reside in memory. Array values made
6698 with @samp{@@} in this way behave just like other arrays in terms of
6699 subscripting, and are coerced to pointers when used in expressions.
6700 Artificial arrays most often appear in expressions via the value history
6701 (@pxref{Value History, ,Value History}), after printing one out.
6703 Another way to create an artificial array is to use a cast.
6704 This re-interprets a value as if it were an array.
6705 The value need not be in memory:
6707 (@value{GDBP}) p/x (short[2])0x12345678
6708 $1 = @{0x1234, 0x5678@}
6711 As a convenience, if you leave the array length out (as in
6712 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
6713 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
6715 (@value{GDBP}) p/x (short[])0x12345678
6716 $2 = @{0x1234, 0x5678@}
6719 Sometimes the artificial array mechanism is not quite enough; in
6720 moderately complex data structures, the elements of interest may not
6721 actually be adjacent---for example, if you are interested in the values
6722 of pointers in an array. One useful work-around in this situation is
6723 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
6724 Variables}) as a counter in an expression that prints the first
6725 interesting value, and then repeat that expression via @key{RET}. For
6726 instance, suppose you have an array @code{dtab} of pointers to
6727 structures, and you are interested in the values of a field @code{fv}
6728 in each structure. Here is an example of what you might type:
6738 @node Output Formats
6739 @section Output Formats
6741 @cindex formatted output
6742 @cindex output formats
6743 By default, @value{GDBN} prints a value according to its data type. Sometimes
6744 this is not what you want. For example, you might want to print a number
6745 in hex, or a pointer in decimal. Or you might want to view data in memory
6746 at a certain address as a character string or as an instruction. To do
6747 these things, specify an @dfn{output format} when you print a value.
6749 The simplest use of output formats is to say how to print a value
6750 already computed. This is done by starting the arguments of the
6751 @code{print} command with a slash and a format letter. The format
6752 letters supported are:
6756 Regard the bits of the value as an integer, and print the integer in
6760 Print as integer in signed decimal.
6763 Print as integer in unsigned decimal.
6766 Print as integer in octal.
6769 Print as integer in binary. The letter @samp{t} stands for ``two''.
6770 @footnote{@samp{b} cannot be used because these format letters are also
6771 used with the @code{x} command, where @samp{b} stands for ``byte'';
6772 see @ref{Memory,,Examining Memory}.}
6775 @cindex unknown address, locating
6776 @cindex locate address
6777 Print as an address, both absolute in hexadecimal and as an offset from
6778 the nearest preceding symbol. You can use this format used to discover
6779 where (in what function) an unknown address is located:
6782 (@value{GDBP}) p/a 0x54320
6783 $3 = 0x54320 <_initialize_vx+396>
6787 The command @code{info symbol 0x54320} yields similar results.
6788 @xref{Symbols, info symbol}.
6791 Regard as an integer and print it as a character constant. This
6792 prints both the numerical value and its character representation. The
6793 character representation is replaced with the octal escape @samp{\nnn}
6794 for characters outside the 7-bit @sc{ascii} range.
6796 Without this format, @value{GDBN} displays @code{char},
6797 @w{@code{unsigned char}}, and @w{@code{signed char}} data as character
6798 constants. Single-byte members of vectors are displayed as integer
6802 Regard the bits of the value as a floating point number and print
6803 using typical floating point syntax.
6806 @cindex printing strings
6807 @cindex printing byte arrays
6808 Regard as a string, if possible. With this format, pointers to single-byte
6809 data are displayed as null-terminated strings and arrays of single-byte data
6810 are displayed as fixed-length strings. Other values are displayed in their
6813 Without this format, @value{GDBN} displays pointers to and arrays of
6814 @code{char}, @w{@code{unsigned char}}, and @w{@code{signed char}} as
6815 strings. Single-byte members of a vector are displayed as an integer
6819 @cindex raw printing
6820 Print using the @samp{raw} formatting. By default, @value{GDBN} will
6821 use a type-specific pretty-printer. The @samp{r} format bypasses any
6822 pretty-printer which might exist for the value's type.
6825 For example, to print the program counter in hex (@pxref{Registers}), type
6832 Note that no space is required before the slash; this is because command
6833 names in @value{GDBN} cannot contain a slash.
6835 To reprint the last value in the value history with a different format,
6836 you can use the @code{print} command with just a format and no
6837 expression. For example, @samp{p/x} reprints the last value in hex.
6840 @section Examining Memory
6842 You can use the command @code{x} (for ``examine'') to examine memory in
6843 any of several formats, independently of your program's data types.
6845 @cindex examining memory
6847 @kindex x @r{(examine memory)}
6848 @item x/@var{nfu} @var{addr}
6851 Use the @code{x} command to examine memory.
6854 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
6855 much memory to display and how to format it; @var{addr} is an
6856 expression giving the address where you want to start displaying memory.
6857 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
6858 Several commands set convenient defaults for @var{addr}.
6861 @item @var{n}, the repeat count
6862 The repeat count is a decimal integer; the default is 1. It specifies
6863 how much memory (counting by units @var{u}) to display.
6864 @c This really is **decimal**; unaffected by 'set radix' as of GDB
6867 @item @var{f}, the display format
6868 The display format is one of the formats used by @code{print}
6869 (@samp{x}, @samp{d}, @samp{u}, @samp{o}, @samp{t}, @samp{a}, @samp{c},
6870 @samp{f}, @samp{s}), and in addition @samp{i} (for machine instructions).
6871 The default is @samp{x} (hexadecimal) initially. The default changes
6872 each time you use either @code{x} or @code{print}.
6874 @item @var{u}, the unit size
6875 The unit size is any of
6881 Halfwords (two bytes).
6883 Words (four bytes). This is the initial default.
6885 Giant words (eight bytes).
6888 Each time you specify a unit size with @code{x}, that size becomes the
6889 default unit the next time you use @code{x}. (For the @samp{s} and
6890 @samp{i} formats, the unit size is ignored and is normally not written.)
6892 @item @var{addr}, starting display address
6893 @var{addr} is the address where you want @value{GDBN} to begin displaying
6894 memory. The expression need not have a pointer value (though it may);
6895 it is always interpreted as an integer address of a byte of memory.
6896 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
6897 @var{addr} is usually just after the last address examined---but several
6898 other commands also set the default address: @code{info breakpoints} (to
6899 the address of the last breakpoint listed), @code{info line} (to the
6900 starting address of a line), and @code{print} (if you use it to display
6901 a value from memory).
6904 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
6905 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
6906 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
6907 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
6908 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
6910 Since the letters indicating unit sizes are all distinct from the
6911 letters specifying output formats, you do not have to remember whether
6912 unit size or format comes first; either order works. The output
6913 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
6914 (However, the count @var{n} must come first; @samp{wx4} does not work.)
6916 Even though the unit size @var{u} is ignored for the formats @samp{s}
6917 and @samp{i}, you might still want to use a count @var{n}; for example,
6918 @samp{3i} specifies that you want to see three machine instructions,
6919 including any operands. For convenience, especially when used with
6920 the @code{display} command, the @samp{i} format also prints branch delay
6921 slot instructions, if any, beyond the count specified, which immediately
6922 follow the last instruction that is within the count. The command
6923 @code{disassemble} gives an alternative way of inspecting machine
6924 instructions; see @ref{Machine Code,,Source and Machine Code}.
6926 All the defaults for the arguments to @code{x} are designed to make it
6927 easy to continue scanning memory with minimal specifications each time
6928 you use @code{x}. For example, after you have inspected three machine
6929 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
6930 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
6931 the repeat count @var{n} is used again; the other arguments default as
6932 for successive uses of @code{x}.
6934 @cindex @code{$_}, @code{$__}, and value history
6935 The addresses and contents printed by the @code{x} command are not saved
6936 in the value history because there is often too much of them and they
6937 would get in the way. Instead, @value{GDBN} makes these values available for
6938 subsequent use in expressions as values of the convenience variables
6939 @code{$_} and @code{$__}. After an @code{x} command, the last address
6940 examined is available for use in expressions in the convenience variable
6941 @code{$_}. The contents of that address, as examined, are available in
6942 the convenience variable @code{$__}.
6944 If the @code{x} command has a repeat count, the address and contents saved
6945 are from the last memory unit printed; this is not the same as the last
6946 address printed if several units were printed on the last line of output.
6948 @cindex remote memory comparison
6949 @cindex verify remote memory image
6950 When you are debugging a program running on a remote target machine
6951 (@pxref{Remote Debugging}), you may wish to verify the program's image in the
6952 remote machine's memory against the executable file you downloaded to
6953 the target. The @code{compare-sections} command is provided for such
6957 @kindex compare-sections
6958 @item compare-sections @r{[}@var{section-name}@r{]}
6959 Compare the data of a loadable section @var{section-name} in the
6960 executable file of the program being debugged with the same section in
6961 the remote machine's memory, and report any mismatches. With no
6962 arguments, compares all loadable sections. This command's
6963 availability depends on the target's support for the @code{"qCRC"}
6968 @section Automatic Display
6969 @cindex automatic display
6970 @cindex display of expressions
6972 If you find that you want to print the value of an expression frequently
6973 (to see how it changes), you might want to add it to the @dfn{automatic
6974 display list} so that @value{GDBN} prints its value each time your program stops.
6975 Each expression added to the list is given a number to identify it;
6976 to remove an expression from the list, you specify that number.
6977 The automatic display looks like this:
6981 3: bar[5] = (struct hack *) 0x3804
6985 This display shows item numbers, expressions and their current values. As with
6986 displays you request manually using @code{x} or @code{print}, you can
6987 specify the output format you prefer; in fact, @code{display} decides
6988 whether to use @code{print} or @code{x} depending your format
6989 specification---it uses @code{x} if you specify either the @samp{i}
6990 or @samp{s} format, or a unit size; otherwise it uses @code{print}.
6994 @item display @var{expr}
6995 Add the expression @var{expr} to the list of expressions to display
6996 each time your program stops. @xref{Expressions, ,Expressions}.
6998 @code{display} does not repeat if you press @key{RET} again after using it.
7000 @item display/@var{fmt} @var{expr}
7001 For @var{fmt} specifying only a display format and not a size or
7002 count, add the expression @var{expr} to the auto-display list but
7003 arrange to display it each time in the specified format @var{fmt}.
7004 @xref{Output Formats,,Output Formats}.
7006 @item display/@var{fmt} @var{addr}
7007 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
7008 number of units, add the expression @var{addr} as a memory address to
7009 be examined each time your program stops. Examining means in effect
7010 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining Memory}.
7013 For example, @samp{display/i $pc} can be helpful, to see the machine
7014 instruction about to be executed each time execution stops (@samp{$pc}
7015 is a common name for the program counter; @pxref{Registers, ,Registers}).
7018 @kindex delete display
7020 @item undisplay @var{dnums}@dots{}
7021 @itemx delete display @var{dnums}@dots{}
7022 Remove item numbers @var{dnums} from the list of expressions to display.
7024 @code{undisplay} does not repeat if you press @key{RET} after using it.
7025 (Otherwise you would just get the error @samp{No display number @dots{}}.)
7027 @kindex disable display
7028 @item disable display @var{dnums}@dots{}
7029 Disable the display of item numbers @var{dnums}. A disabled display
7030 item is not printed automatically, but is not forgotten. It may be
7031 enabled again later.
7033 @kindex enable display
7034 @item enable display @var{dnums}@dots{}
7035 Enable display of item numbers @var{dnums}. It becomes effective once
7036 again in auto display of its expression, until you specify otherwise.
7039 Display the current values of the expressions on the list, just as is
7040 done when your program stops.
7042 @kindex info display
7044 Print the list of expressions previously set up to display
7045 automatically, each one with its item number, but without showing the
7046 values. This includes disabled expressions, which are marked as such.
7047 It also includes expressions which would not be displayed right now
7048 because they refer to automatic variables not currently available.
7051 @cindex display disabled out of scope
7052 If a display expression refers to local variables, then it does not make
7053 sense outside the lexical context for which it was set up. Such an
7054 expression is disabled when execution enters a context where one of its
7055 variables is not defined. For example, if you give the command
7056 @code{display last_char} while inside a function with an argument
7057 @code{last_char}, @value{GDBN} displays this argument while your program
7058 continues to stop inside that function. When it stops elsewhere---where
7059 there is no variable @code{last_char}---the display is disabled
7060 automatically. The next time your program stops where @code{last_char}
7061 is meaningful, you can enable the display expression once again.
7063 @node Print Settings
7064 @section Print Settings
7066 @cindex format options
7067 @cindex print settings
7068 @value{GDBN} provides the following ways to control how arrays, structures,
7069 and symbols are printed.
7072 These settings are useful for debugging programs in any language:
7076 @item set print address
7077 @itemx set print address on
7078 @cindex print/don't print memory addresses
7079 @value{GDBN} prints memory addresses showing the location of stack
7080 traces, structure values, pointer values, breakpoints, and so forth,
7081 even when it also displays the contents of those addresses. The default
7082 is @code{on}. For example, this is what a stack frame display looks like with
7083 @code{set print address on}:
7088 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
7090 530 if (lquote != def_lquote)
7094 @item set print address off
7095 Do not print addresses when displaying their contents. For example,
7096 this is the same stack frame displayed with @code{set print address off}:
7100 (@value{GDBP}) set print addr off
7102 #0 set_quotes (lq="<<", rq=">>") at input.c:530
7103 530 if (lquote != def_lquote)
7107 You can use @samp{set print address off} to eliminate all machine
7108 dependent displays from the @value{GDBN} interface. For example, with
7109 @code{print address off}, you should get the same text for backtraces on
7110 all machines---whether or not they involve pointer arguments.
7113 @item show print address
7114 Show whether or not addresses are to be printed.
7117 When @value{GDBN} prints a symbolic address, it normally prints the
7118 closest earlier symbol plus an offset. If that symbol does not uniquely
7119 identify the address (for example, it is a name whose scope is a single
7120 source file), you may need to clarify. One way to do this is with
7121 @code{info line}, for example @samp{info line *0x4537}. Alternately,
7122 you can set @value{GDBN} to print the source file and line number when
7123 it prints a symbolic address:
7126 @item set print symbol-filename on
7127 @cindex source file and line of a symbol
7128 @cindex symbol, source file and line
7129 Tell @value{GDBN} to print the source file name and line number of a
7130 symbol in the symbolic form of an address.
7132 @item set print symbol-filename off
7133 Do not print source file name and line number of a symbol. This is the
7136 @item show print symbol-filename
7137 Show whether or not @value{GDBN} will print the source file name and
7138 line number of a symbol in the symbolic form of an address.
7141 Another situation where it is helpful to show symbol filenames and line
7142 numbers is when disassembling code; @value{GDBN} shows you the line
7143 number and source file that corresponds to each instruction.
7145 Also, you may wish to see the symbolic form only if the address being
7146 printed is reasonably close to the closest earlier symbol:
7149 @item set print max-symbolic-offset @var{max-offset}
7150 @cindex maximum value for offset of closest symbol
7151 Tell @value{GDBN} to only display the symbolic form of an address if the
7152 offset between the closest earlier symbol and the address is less than
7153 @var{max-offset}. The default is 0, which tells @value{GDBN}
7154 to always print the symbolic form of an address if any symbol precedes it.
7156 @item show print max-symbolic-offset
7157 Ask how large the maximum offset is that @value{GDBN} prints in a
7161 @cindex wild pointer, interpreting
7162 @cindex pointer, finding referent
7163 If you have a pointer and you are not sure where it points, try
7164 @samp{set print symbol-filename on}. Then you can determine the name
7165 and source file location of the variable where it points, using
7166 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
7167 For example, here @value{GDBN} shows that a variable @code{ptt} points
7168 at another variable @code{t}, defined in @file{hi2.c}:
7171 (@value{GDBP}) set print symbol-filename on
7172 (@value{GDBP}) p/a ptt
7173 $4 = 0xe008 <t in hi2.c>
7177 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
7178 does not show the symbol name and filename of the referent, even with
7179 the appropriate @code{set print} options turned on.
7182 Other settings control how different kinds of objects are printed:
7185 @item set print array
7186 @itemx set print array on
7187 @cindex pretty print arrays
7188 Pretty print arrays. This format is more convenient to read,
7189 but uses more space. The default is off.
7191 @item set print array off
7192 Return to compressed format for arrays.
7194 @item show print array
7195 Show whether compressed or pretty format is selected for displaying
7198 @cindex print array indexes
7199 @item set print array-indexes
7200 @itemx set print array-indexes on
7201 Print the index of each element when displaying arrays. May be more
7202 convenient to locate a given element in the array or quickly find the
7203 index of a given element in that printed array. The default is off.
7205 @item set print array-indexes off
7206 Stop printing element indexes when displaying arrays.
7208 @item show print array-indexes
7209 Show whether the index of each element is printed when displaying
7212 @item set print elements @var{number-of-elements}
7213 @cindex number of array elements to print
7214 @cindex limit on number of printed array elements
7215 Set a limit on how many elements of an array @value{GDBN} will print.
7216 If @value{GDBN} is printing a large array, it stops printing after it has
7217 printed the number of elements set by the @code{set print elements} command.
7218 This limit also applies to the display of strings.
7219 When @value{GDBN} starts, this limit is set to 200.
7220 Setting @var{number-of-elements} to zero means that the printing is unlimited.
7222 @item show print elements
7223 Display the number of elements of a large array that @value{GDBN} will print.
7224 If the number is 0, then the printing is unlimited.
7226 @item set print frame-arguments @var{value}
7227 @kindex set print frame-arguments
7228 @cindex printing frame argument values
7229 @cindex print all frame argument values
7230 @cindex print frame argument values for scalars only
7231 @cindex do not print frame argument values
7232 This command allows to control how the values of arguments are printed
7233 when the debugger prints a frame (@pxref{Frames}). The possible
7238 The values of all arguments are printed.
7241 Print the value of an argument only if it is a scalar. The value of more
7242 complex arguments such as arrays, structures, unions, etc, is replaced
7243 by @code{@dots{}}. This is the default. Here is an example where
7244 only scalar arguments are shown:
7247 #1 0x08048361 in call_me (i=3, s=@dots{}, ss=0xbf8d508c, u=@dots{}, e=green)
7252 None of the argument values are printed. Instead, the value of each argument
7253 is replaced by @code{@dots{}}. In this case, the example above now becomes:
7256 #1 0x08048361 in call_me (i=@dots{}, s=@dots{}, ss=@dots{}, u=@dots{}, e=@dots{})
7261 By default, only scalar arguments are printed. This command can be used
7262 to configure the debugger to print the value of all arguments, regardless
7263 of their type. However, it is often advantageous to not print the value
7264 of more complex parameters. For instance, it reduces the amount of
7265 information printed in each frame, making the backtrace more readable.
7266 Also, it improves performance when displaying Ada frames, because
7267 the computation of large arguments can sometimes be CPU-intensive,
7268 especially in large applications. Setting @code{print frame-arguments}
7269 to @code{scalars} (the default) or @code{none} avoids this computation,
7270 thus speeding up the display of each Ada frame.
7272 @item show print frame-arguments
7273 Show how the value of arguments should be displayed when printing a frame.
7275 @item set print repeats
7276 @cindex repeated array elements
7277 Set the threshold for suppressing display of repeated array
7278 elements. When the number of consecutive identical elements of an
7279 array exceeds the threshold, @value{GDBN} prints the string
7280 @code{"<repeats @var{n} times>"}, where @var{n} is the number of
7281 identical repetitions, instead of displaying the identical elements
7282 themselves. Setting the threshold to zero will cause all elements to
7283 be individually printed. The default threshold is 10.
7285 @item show print repeats
7286 Display the current threshold for printing repeated identical
7289 @item set print null-stop
7290 @cindex @sc{null} elements in arrays
7291 Cause @value{GDBN} to stop printing the characters of an array when the first
7292 @sc{null} is encountered. This is useful when large arrays actually
7293 contain only short strings.
7296 @item show print null-stop
7297 Show whether @value{GDBN} stops printing an array on the first
7298 @sc{null} character.
7300 @item set print pretty on
7301 @cindex print structures in indented form
7302 @cindex indentation in structure display
7303 Cause @value{GDBN} to print structures in an indented format with one member
7304 per line, like this:
7319 @item set print pretty off
7320 Cause @value{GDBN} to print structures in a compact format, like this:
7324 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
7325 meat = 0x54 "Pork"@}
7330 This is the default format.
7332 @item show print pretty
7333 Show which format @value{GDBN} is using to print structures.
7335 @item set print sevenbit-strings on
7336 @cindex eight-bit characters in strings
7337 @cindex octal escapes in strings
7338 Print using only seven-bit characters; if this option is set,
7339 @value{GDBN} displays any eight-bit characters (in strings or
7340 character values) using the notation @code{\}@var{nnn}. This setting is
7341 best if you are working in English (@sc{ascii}) and you use the
7342 high-order bit of characters as a marker or ``meta'' bit.
7344 @item set print sevenbit-strings off
7345 Print full eight-bit characters. This allows the use of more
7346 international character sets, and is the default.
7348 @item show print sevenbit-strings
7349 Show whether or not @value{GDBN} is printing only seven-bit characters.
7351 @item set print union on
7352 @cindex unions in structures, printing
7353 Tell @value{GDBN} to print unions which are contained in structures
7354 and other unions. This is the default setting.
7356 @item set print union off
7357 Tell @value{GDBN} not to print unions which are contained in
7358 structures and other unions. @value{GDBN} will print @code{"@{...@}"}
7361 @item show print union
7362 Ask @value{GDBN} whether or not it will print unions which are contained in
7363 structures and other unions.
7365 For example, given the declarations
7368 typedef enum @{Tree, Bug@} Species;
7369 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
7370 typedef enum @{Caterpillar, Cocoon, Butterfly@}
7381 struct thing foo = @{Tree, @{Acorn@}@};
7385 with @code{set print union on} in effect @samp{p foo} would print
7388 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
7392 and with @code{set print union off} in effect it would print
7395 $1 = @{it = Tree, form = @{...@}@}
7399 @code{set print union} affects programs written in C-like languages
7405 These settings are of interest when debugging C@t{++} programs:
7408 @cindex demangling C@t{++} names
7409 @item set print demangle
7410 @itemx set print demangle on
7411 Print C@t{++} names in their source form rather than in the encoded
7412 (``mangled'') form passed to the assembler and linker for type-safe
7413 linkage. The default is on.
7415 @item show print demangle
7416 Show whether C@t{++} names are printed in mangled or demangled form.
7418 @item set print asm-demangle
7419 @itemx set print asm-demangle on
7420 Print C@t{++} names in their source form rather than their mangled form, even
7421 in assembler code printouts such as instruction disassemblies.
7424 @item show print asm-demangle
7425 Show whether C@t{++} names in assembly listings are printed in mangled
7428 @cindex C@t{++} symbol decoding style
7429 @cindex symbol decoding style, C@t{++}
7430 @kindex set demangle-style
7431 @item set demangle-style @var{style}
7432 Choose among several encoding schemes used by different compilers to
7433 represent C@t{++} names. The choices for @var{style} are currently:
7437 Allow @value{GDBN} to choose a decoding style by inspecting your program.
7440 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
7441 This is the default.
7444 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
7447 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
7450 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
7451 @strong{Warning:} this setting alone is not sufficient to allow
7452 debugging @code{cfront}-generated executables. @value{GDBN} would
7453 require further enhancement to permit that.
7456 If you omit @var{style}, you will see a list of possible formats.
7458 @item show demangle-style
7459 Display the encoding style currently in use for decoding C@t{++} symbols.
7461 @item set print object
7462 @itemx set print object on
7463 @cindex derived type of an object, printing
7464 @cindex display derived types
7465 When displaying a pointer to an object, identify the @emph{actual}
7466 (derived) type of the object rather than the @emph{declared} type, using
7467 the virtual function table.
7469 @item set print object off
7470 Display only the declared type of objects, without reference to the
7471 virtual function table. This is the default setting.
7473 @item show print object
7474 Show whether actual, or declared, object types are displayed.
7476 @item set print static-members
7477 @itemx set print static-members on
7478 @cindex static members of C@t{++} objects
7479 Print static members when displaying a C@t{++} object. The default is on.
7481 @item set print static-members off
7482 Do not print static members when displaying a C@t{++} object.
7484 @item show print static-members
7485 Show whether C@t{++} static members are printed or not.
7487 @item set print pascal_static-members
7488 @itemx set print pascal_static-members on
7489 @cindex static members of Pascal objects
7490 @cindex Pascal objects, static members display
7491 Print static members when displaying a Pascal object. The default is on.
7493 @item set print pascal_static-members off
7494 Do not print static members when displaying a Pascal object.
7496 @item show print pascal_static-members
7497 Show whether Pascal static members are printed or not.
7499 @c These don't work with HP ANSI C++ yet.
7500 @item set print vtbl
7501 @itemx set print vtbl on
7502 @cindex pretty print C@t{++} virtual function tables
7503 @cindex virtual functions (C@t{++}) display
7504 @cindex VTBL display
7505 Pretty print C@t{++} virtual function tables. The default is off.
7506 (The @code{vtbl} commands do not work on programs compiled with the HP
7507 ANSI C@t{++} compiler (@code{aCC}).)
7509 @item set print vtbl off
7510 Do not pretty print C@t{++} virtual function tables.
7512 @item show print vtbl
7513 Show whether C@t{++} virtual function tables are pretty printed, or not.
7517 @section Value History
7519 @cindex value history
7520 @cindex history of values printed by @value{GDBN}
7521 Values printed by the @code{print} command are saved in the @value{GDBN}
7522 @dfn{value history}. This allows you to refer to them in other expressions.
7523 Values are kept until the symbol table is re-read or discarded
7524 (for example with the @code{file} or @code{symbol-file} commands).
7525 When the symbol table changes, the value history is discarded,
7526 since the values may contain pointers back to the types defined in the
7531 @cindex history number
7532 The values printed are given @dfn{history numbers} by which you can
7533 refer to them. These are successive integers starting with one.
7534 @code{print} shows you the history number assigned to a value by
7535 printing @samp{$@var{num} = } before the value; here @var{num} is the
7538 To refer to any previous value, use @samp{$} followed by the value's
7539 history number. The way @code{print} labels its output is designed to
7540 remind you of this. Just @code{$} refers to the most recent value in
7541 the history, and @code{$$} refers to the value before that.
7542 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
7543 is the value just prior to @code{$$}, @code{$$1} is equivalent to
7544 @code{$$}, and @code{$$0} is equivalent to @code{$}.
7546 For example, suppose you have just printed a pointer to a structure and
7547 want to see the contents of the structure. It suffices to type
7553 If you have a chain of structures where the component @code{next} points
7554 to the next one, you can print the contents of the next one with this:
7561 You can print successive links in the chain by repeating this
7562 command---which you can do by just typing @key{RET}.
7564 Note that the history records values, not expressions. If the value of
7565 @code{x} is 4 and you type these commands:
7573 then the value recorded in the value history by the @code{print} command
7574 remains 4 even though the value of @code{x} has changed.
7579 Print the last ten values in the value history, with their item numbers.
7580 This is like @samp{p@ $$9} repeated ten times, except that @code{show
7581 values} does not change the history.
7583 @item show values @var{n}
7584 Print ten history values centered on history item number @var{n}.
7587 Print ten history values just after the values last printed. If no more
7588 values are available, @code{show values +} produces no display.
7591 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
7592 same effect as @samp{show values +}.
7594 @node Convenience Vars
7595 @section Convenience Variables
7597 @cindex convenience variables
7598 @cindex user-defined variables
7599 @value{GDBN} provides @dfn{convenience variables} that you can use within
7600 @value{GDBN} to hold on to a value and refer to it later. These variables
7601 exist entirely within @value{GDBN}; they are not part of your program, and
7602 setting a convenience variable has no direct effect on further execution
7603 of your program. That is why you can use them freely.
7605 Convenience variables are prefixed with @samp{$}. Any name preceded by
7606 @samp{$} can be used for a convenience variable, unless it is one of
7607 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
7608 (Value history references, in contrast, are @emph{numbers} preceded
7609 by @samp{$}. @xref{Value History, ,Value History}.)
7611 You can save a value in a convenience variable with an assignment
7612 expression, just as you would set a variable in your program.
7616 set $foo = *object_ptr
7620 would save in @code{$foo} the value contained in the object pointed to by
7623 Using a convenience variable for the first time creates it, but its
7624 value is @code{void} until you assign a new value. You can alter the
7625 value with another assignment at any time.
7627 Convenience variables have no fixed types. You can assign a convenience
7628 variable any type of value, including structures and arrays, even if
7629 that variable already has a value of a different type. The convenience
7630 variable, when used as an expression, has the type of its current value.
7633 @kindex show convenience
7634 @cindex show all user variables
7635 @item show convenience
7636 Print a list of convenience variables used so far, and their values.
7637 Abbreviated @code{show conv}.
7639 @kindex init-if-undefined
7640 @cindex convenience variables, initializing
7641 @item init-if-undefined $@var{variable} = @var{expression}
7642 Set a convenience variable if it has not already been set. This is useful
7643 for user-defined commands that keep some state. It is similar, in concept,
7644 to using local static variables with initializers in C (except that
7645 convenience variables are global). It can also be used to allow users to
7646 override default values used in a command script.
7648 If the variable is already defined then the expression is not evaluated so
7649 any side-effects do not occur.
7652 One of the ways to use a convenience variable is as a counter to be
7653 incremented or a pointer to be advanced. For example, to print
7654 a field from successive elements of an array of structures:
7658 print bar[$i++]->contents
7662 Repeat that command by typing @key{RET}.
7664 Some convenience variables are created automatically by @value{GDBN} and given
7665 values likely to be useful.
7668 @vindex $_@r{, convenience variable}
7670 The variable @code{$_} is automatically set by the @code{x} command to
7671 the last address examined (@pxref{Memory, ,Examining Memory}). Other
7672 commands which provide a default address for @code{x} to examine also
7673 set @code{$_} to that address; these commands include @code{info line}
7674 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
7675 except when set by the @code{x} command, in which case it is a pointer
7676 to the type of @code{$__}.
7678 @vindex $__@r{, convenience variable}
7680 The variable @code{$__} is automatically set by the @code{x} command
7681 to the value found in the last address examined. Its type is chosen
7682 to match the format in which the data was printed.
7685 @vindex $_exitcode@r{, convenience variable}
7686 The variable @code{$_exitcode} is automatically set to the exit code when
7687 the program being debugged terminates.
7690 @vindex $_siginfo@r{, convenience variable}
7691 The variable @code{$_siginfo} is bound to extra signal information
7692 inspection (@pxref{extra signal information}).
7695 On HP-UX systems, if you refer to a function or variable name that
7696 begins with a dollar sign, @value{GDBN} searches for a user or system
7697 name first, before it searches for a convenience variable.
7699 @cindex convenience functions
7700 @value{GDBN} also supplies some @dfn{convenience functions}. These
7701 have a syntax similar to convenience variables. A convenience
7702 function can be used in an expression just like an ordinary function;
7703 however, a convenience function is implemented internally to
7708 @kindex help function
7709 @cindex show all convenience functions
7710 Print a list of all convenience functions.
7717 You can refer to machine register contents, in expressions, as variables
7718 with names starting with @samp{$}. The names of registers are different
7719 for each machine; use @code{info registers} to see the names used on
7723 @kindex info registers
7724 @item info registers
7725 Print the names and values of all registers except floating-point
7726 and vector registers (in the selected stack frame).
7728 @kindex info all-registers
7729 @cindex floating point registers
7730 @item info all-registers
7731 Print the names and values of all registers, including floating-point
7732 and vector registers (in the selected stack frame).
7734 @item info registers @var{regname} @dots{}
7735 Print the @dfn{relativized} value of each specified register @var{regname}.
7736 As discussed in detail below, register values are normally relative to
7737 the selected stack frame. @var{regname} may be any register name valid on
7738 the machine you are using, with or without the initial @samp{$}.
7741 @cindex stack pointer register
7742 @cindex program counter register
7743 @cindex process status register
7744 @cindex frame pointer register
7745 @cindex standard registers
7746 @value{GDBN} has four ``standard'' register names that are available (in
7747 expressions) on most machines---whenever they do not conflict with an
7748 architecture's canonical mnemonics for registers. The register names
7749 @code{$pc} and @code{$sp} are used for the program counter register and
7750 the stack pointer. @code{$fp} is used for a register that contains a
7751 pointer to the current stack frame, and @code{$ps} is used for a
7752 register that contains the processor status. For example,
7753 you could print the program counter in hex with
7760 or print the instruction to be executed next with
7767 or add four to the stack pointer@footnote{This is a way of removing
7768 one word from the stack, on machines where stacks grow downward in
7769 memory (most machines, nowadays). This assumes that the innermost
7770 stack frame is selected; setting @code{$sp} is not allowed when other
7771 stack frames are selected. To pop entire frames off the stack,
7772 regardless of machine architecture, use @code{return};
7773 see @ref{Returning, ,Returning from a Function}.} with
7779 Whenever possible, these four standard register names are available on
7780 your machine even though the machine has different canonical mnemonics,
7781 so long as there is no conflict. The @code{info registers} command
7782 shows the canonical names. For example, on the SPARC, @code{info
7783 registers} displays the processor status register as @code{$psr} but you
7784 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
7785 is an alias for the @sc{eflags} register.
7787 @value{GDBN} always considers the contents of an ordinary register as an
7788 integer when the register is examined in this way. Some machines have
7789 special registers which can hold nothing but floating point; these
7790 registers are considered to have floating point values. There is no way
7791 to refer to the contents of an ordinary register as floating point value
7792 (although you can @emph{print} it as a floating point value with
7793 @samp{print/f $@var{regname}}).
7795 Some registers have distinct ``raw'' and ``virtual'' data formats. This
7796 means that the data format in which the register contents are saved by
7797 the operating system is not the same one that your program normally
7798 sees. For example, the registers of the 68881 floating point
7799 coprocessor are always saved in ``extended'' (raw) format, but all C
7800 programs expect to work with ``double'' (virtual) format. In such
7801 cases, @value{GDBN} normally works with the virtual format only (the format
7802 that makes sense for your program), but the @code{info registers} command
7803 prints the data in both formats.
7805 @cindex SSE registers (x86)
7806 @cindex MMX registers (x86)
7807 Some machines have special registers whose contents can be interpreted
7808 in several different ways. For example, modern x86-based machines
7809 have SSE and MMX registers that can hold several values packed
7810 together in several different formats. @value{GDBN} refers to such
7811 registers in @code{struct} notation:
7814 (@value{GDBP}) print $xmm1
7816 v4_float = @{0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044@},
7817 v2_double = @{9.92129282474342e-303, 2.7585945287983262e-313@},
7818 v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000",
7819 v8_int16 = @{0, 0, 14072, 315, 11, 0, 13, 0@},
7820 v4_int32 = @{0, 20657912, 11, 13@},
7821 v2_int64 = @{88725056443645952, 55834574859@},
7822 uint128 = 0x0000000d0000000b013b36f800000000
7827 To set values of such registers, you need to tell @value{GDBN} which
7828 view of the register you wish to change, as if you were assigning
7829 value to a @code{struct} member:
7832 (@value{GDBP}) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF
7835 Normally, register values are relative to the selected stack frame
7836 (@pxref{Selection, ,Selecting a Frame}). This means that you get the
7837 value that the register would contain if all stack frames farther in
7838 were exited and their saved registers restored. In order to see the
7839 true contents of hardware registers, you must select the innermost
7840 frame (with @samp{frame 0}).
7842 However, @value{GDBN} must deduce where registers are saved, from the machine
7843 code generated by your compiler. If some registers are not saved, or if
7844 @value{GDBN} is unable to locate the saved registers, the selected stack
7845 frame makes no difference.
7847 @node Floating Point Hardware
7848 @section Floating Point Hardware
7849 @cindex floating point
7851 Depending on the configuration, @value{GDBN} may be able to give
7852 you more information about the status of the floating point hardware.
7857 Display hardware-dependent information about the floating
7858 point unit. The exact contents and layout vary depending on the
7859 floating point chip. Currently, @samp{info float} is supported on
7860 the ARM and x86 machines.
7864 @section Vector Unit
7867 Depending on the configuration, @value{GDBN} may be able to give you
7868 more information about the status of the vector unit.
7873 Display information about the vector unit. The exact contents and
7874 layout vary depending on the hardware.
7877 @node OS Information
7878 @section Operating System Auxiliary Information
7879 @cindex OS information
7881 @value{GDBN} provides interfaces to useful OS facilities that can help
7882 you debug your program.
7884 @cindex @code{ptrace} system call
7885 @cindex @code{struct user} contents
7886 When @value{GDBN} runs on a @dfn{Posix system} (such as GNU or Unix
7887 machines), it interfaces with the inferior via the @code{ptrace}
7888 system call. The operating system creates a special sata structure,
7889 called @code{struct user}, for this interface. You can use the
7890 command @code{info udot} to display the contents of this data
7896 Display the contents of the @code{struct user} maintained by the OS
7897 kernel for the program being debugged. @value{GDBN} displays the
7898 contents of @code{struct user} as a list of hex numbers, similar to
7899 the @code{examine} command.
7902 @cindex auxiliary vector
7903 @cindex vector, auxiliary
7904 Some operating systems supply an @dfn{auxiliary vector} to programs at
7905 startup. This is akin to the arguments and environment that you
7906 specify for a program, but contains a system-dependent variety of
7907 binary values that tell system libraries important details about the
7908 hardware, operating system, and process. Each value's purpose is
7909 identified by an integer tag; the meanings are well-known but system-specific.
7910 Depending on the configuration and operating system facilities,
7911 @value{GDBN} may be able to show you this information. For remote
7912 targets, this functionality may further depend on the remote stub's
7913 support of the @samp{qXfer:auxv:read} packet, see
7914 @ref{qXfer auxiliary vector read}.
7919 Display the auxiliary vector of the inferior, which can be either a
7920 live process or a core dump file. @value{GDBN} prints each tag value
7921 numerically, and also shows names and text descriptions for recognized
7922 tags. Some values in the vector are numbers, some bit masks, and some
7923 pointers to strings or other data. @value{GDBN} displays each value in the
7924 most appropriate form for a recognized tag, and in hexadecimal for
7925 an unrecognized tag.
7928 On some targets, @value{GDBN} can access operating-system-specific information
7929 and display it to user, without interpretation. For remote targets,
7930 this functionality depends on the remote stub's support of the
7931 @samp{qXfer:osdata:read} packet, see @ref{qXfer osdata read}.
7934 @kindex info os processes
7935 @item info os processes
7936 Display the list of processes on the target. For each process,
7937 @value{GDBN} prints the process identifier, the name of the user, and
7938 the command corresponding to the process.
7941 @node Memory Region Attributes
7942 @section Memory Region Attributes
7943 @cindex memory region attributes
7945 @dfn{Memory region attributes} allow you to describe special handling
7946 required by regions of your target's memory. @value{GDBN} uses
7947 attributes to determine whether to allow certain types of memory
7948 accesses; whether to use specific width accesses; and whether to cache
7949 target memory. By default the description of memory regions is
7950 fetched from the target (if the current target supports this), but the
7951 user can override the fetched regions.
7953 Defined memory regions can be individually enabled and disabled. When a
7954 memory region is disabled, @value{GDBN} uses the default attributes when
7955 accessing memory in that region. Similarly, if no memory regions have
7956 been defined, @value{GDBN} uses the default attributes when accessing
7959 When a memory region is defined, it is given a number to identify it;
7960 to enable, disable, or remove a memory region, you specify that number.
7964 @item mem @var{lower} @var{upper} @var{attributes}@dots{}
7965 Define a memory region bounded by @var{lower} and @var{upper} with
7966 attributes @var{attributes}@dots{}, and add it to the list of regions
7967 monitored by @value{GDBN}. Note that @var{upper} == 0 is a special
7968 case: it is treated as the target's maximum memory address.
7969 (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
7972 Discard any user changes to the memory regions and use target-supplied
7973 regions, if available, or no regions if the target does not support.
7976 @item delete mem @var{nums}@dots{}
7977 Remove memory regions @var{nums}@dots{} from the list of regions
7978 monitored by @value{GDBN}.
7981 @item disable mem @var{nums}@dots{}
7982 Disable monitoring of memory regions @var{nums}@dots{}.
7983 A disabled memory region is not forgotten.
7984 It may be enabled again later.
7987 @item enable mem @var{nums}@dots{}
7988 Enable monitoring of memory regions @var{nums}@dots{}.
7992 Print a table of all defined memory regions, with the following columns
7996 @item Memory Region Number
7997 @item Enabled or Disabled.
7998 Enabled memory regions are marked with @samp{y}.
7999 Disabled memory regions are marked with @samp{n}.
8002 The address defining the inclusive lower bound of the memory region.
8005 The address defining the exclusive upper bound of the memory region.
8008 The list of attributes set for this memory region.
8013 @subsection Attributes
8015 @subsubsection Memory Access Mode
8016 The access mode attributes set whether @value{GDBN} may make read or
8017 write accesses to a memory region.
8019 While these attributes prevent @value{GDBN} from performing invalid
8020 memory accesses, they do nothing to prevent the target system, I/O DMA,
8021 etc.@: from accessing memory.
8025 Memory is read only.
8027 Memory is write only.
8029 Memory is read/write. This is the default.
8032 @subsubsection Memory Access Size
8033 The access size attribute tells @value{GDBN} to use specific sized
8034 accesses in the memory region. Often memory mapped device registers
8035 require specific sized accesses. If no access size attribute is
8036 specified, @value{GDBN} may use accesses of any size.
8040 Use 8 bit memory accesses.
8042 Use 16 bit memory accesses.
8044 Use 32 bit memory accesses.
8046 Use 64 bit memory accesses.
8049 @c @subsubsection Hardware/Software Breakpoints
8050 @c The hardware/software breakpoint attributes set whether @value{GDBN}
8051 @c will use hardware or software breakpoints for the internal breakpoints
8052 @c used by the step, next, finish, until, etc. commands.
8056 @c Always use hardware breakpoints
8057 @c @item swbreak (default)
8060 @subsubsection Data Cache
8061 The data cache attributes set whether @value{GDBN} will cache target
8062 memory. While this generally improves performance by reducing debug
8063 protocol overhead, it can lead to incorrect results because @value{GDBN}
8064 does not know about volatile variables or memory mapped device
8069 Enable @value{GDBN} to cache target memory.
8071 Disable @value{GDBN} from caching target memory. This is the default.
8074 @subsection Memory Access Checking
8075 @value{GDBN} can be instructed to refuse accesses to memory that is
8076 not explicitly described. This can be useful if accessing such
8077 regions has undesired effects for a specific target, or to provide
8078 better error checking. The following commands control this behaviour.
8081 @kindex set mem inaccessible-by-default
8082 @item set mem inaccessible-by-default [on|off]
8083 If @code{on} is specified, make @value{GDBN} treat memory not
8084 explicitly described by the memory ranges as non-existent and refuse accesses
8085 to such memory. The checks are only performed if there's at least one
8086 memory range defined. If @code{off} is specified, make @value{GDBN}
8087 treat the memory not explicitly described by the memory ranges as RAM.
8088 The default value is @code{on}.
8089 @kindex show mem inaccessible-by-default
8090 @item show mem inaccessible-by-default
8091 Show the current handling of accesses to unknown memory.
8095 @c @subsubsection Memory Write Verification
8096 @c The memory write verification attributes set whether @value{GDBN}
8097 @c will re-reads data after each write to verify the write was successful.
8101 @c @item noverify (default)
8104 @node Dump/Restore Files
8105 @section Copy Between Memory and a File
8106 @cindex dump/restore files
8107 @cindex append data to a file
8108 @cindex dump data to a file
8109 @cindex restore data from a file
8111 You can use the commands @code{dump}, @code{append}, and
8112 @code{restore} to copy data between target memory and a file. The
8113 @code{dump} and @code{append} commands write data to a file, and the
8114 @code{restore} command reads data from a file back into the inferior's
8115 memory. Files may be in binary, Motorola S-record, Intel hex, or
8116 Tektronix Hex format; however, @value{GDBN} can only append to binary
8122 @item dump @r{[}@var{format}@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
8123 @itemx dump @r{[}@var{format}@r{]} value @var{filename} @var{expr}
8124 Dump the contents of memory from @var{start_addr} to @var{end_addr},
8125 or the value of @var{expr}, to @var{filename} in the given format.
8127 The @var{format} parameter may be any one of:
8134 Motorola S-record format.
8136 Tektronix Hex format.
8139 @value{GDBN} uses the same definitions of these formats as the
8140 @sc{gnu} binary utilities, like @samp{objdump} and @samp{objcopy}. If
8141 @var{format} is omitted, @value{GDBN} dumps the data in raw binary
8145 @item append @r{[}binary@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
8146 @itemx append @r{[}binary@r{]} value @var{filename} @var{expr}
8147 Append the contents of memory from @var{start_addr} to @var{end_addr},
8148 or the value of @var{expr}, to the file @var{filename}, in raw binary form.
8149 (@value{GDBN} can only append data to files in raw binary form.)
8152 @item restore @var{filename} @r{[}binary@r{]} @var{bias} @var{start} @var{end}
8153 Restore the contents of file @var{filename} into memory. The
8154 @code{restore} command can automatically recognize any known @sc{bfd}
8155 file format, except for raw binary. To restore a raw binary file you
8156 must specify the optional keyword @code{binary} after the filename.
8158 If @var{bias} is non-zero, its value will be added to the addresses
8159 contained in the file. Binary files always start at address zero, so
8160 they will be restored at address @var{bias}. Other bfd files have
8161 a built-in location; they will be restored at offset @var{bias}
8164 If @var{start} and/or @var{end} are non-zero, then only data between
8165 file offset @var{start} and file offset @var{end} will be restored.
8166 These offsets are relative to the addresses in the file, before
8167 the @var{bias} argument is applied.
8171 @node Core File Generation
8172 @section How to Produce a Core File from Your Program
8173 @cindex dump core from inferior
8175 A @dfn{core file} or @dfn{core dump} is a file that records the memory
8176 image of a running process and its process status (register values
8177 etc.). Its primary use is post-mortem debugging of a program that
8178 crashed while it ran outside a debugger. A program that crashes
8179 automatically produces a core file, unless this feature is disabled by
8180 the user. @xref{Files}, for information on invoking @value{GDBN} in
8181 the post-mortem debugging mode.
8183 Occasionally, you may wish to produce a core file of the program you
8184 are debugging in order to preserve a snapshot of its state.
8185 @value{GDBN} has a special command for that.
8189 @kindex generate-core-file
8190 @item generate-core-file [@var{file}]
8191 @itemx gcore [@var{file}]
8192 Produce a core dump of the inferior process. The optional argument
8193 @var{file} specifies the file name where to put the core dump. If not
8194 specified, the file name defaults to @file{core.@var{pid}}, where
8195 @var{pid} is the inferior process ID.
8197 Note that this command is implemented only for some systems (as of
8198 this writing, @sc{gnu}/Linux, FreeBSD, Solaris, Unixware, and S390).
8201 @node Character Sets
8202 @section Character Sets
8203 @cindex character sets
8205 @cindex translating between character sets
8206 @cindex host character set
8207 @cindex target character set
8209 If the program you are debugging uses a different character set to
8210 represent characters and strings than the one @value{GDBN} uses itself,
8211 @value{GDBN} can automatically translate between the character sets for
8212 you. The character set @value{GDBN} uses we call the @dfn{host
8213 character set}; the one the inferior program uses we call the
8214 @dfn{target character set}.
8216 For example, if you are running @value{GDBN} on a @sc{gnu}/Linux system, which
8217 uses the ISO Latin 1 character set, but you are using @value{GDBN}'s
8218 remote protocol (@pxref{Remote Debugging}) to debug a program
8219 running on an IBM mainframe, which uses the @sc{ebcdic} character set,
8220 then the host character set is Latin-1, and the target character set is
8221 @sc{ebcdic}. If you give @value{GDBN} the command @code{set
8222 target-charset EBCDIC-US}, then @value{GDBN} translates between
8223 @sc{ebcdic} and Latin 1 as you print character or string values, or use
8224 character and string literals in expressions.
8226 @value{GDBN} has no way to automatically recognize which character set
8227 the inferior program uses; you must tell it, using the @code{set
8228 target-charset} command, described below.
8230 Here are the commands for controlling @value{GDBN}'s character set
8234 @item set target-charset @var{charset}
8235 @kindex set target-charset
8236 Set the current target character set to @var{charset}. To display the
8237 list of supported target character sets, type
8238 @kbd{@w{set target-charset @key{TAB}@key{TAB}}}.
8240 @item set host-charset @var{charset}
8241 @kindex set host-charset
8242 Set the current host character set to @var{charset}.
8244 By default, @value{GDBN} uses a host character set appropriate to the
8245 system it is running on; you can override that default using the
8246 @code{set host-charset} command. On some systems, @value{GDBN} cannot
8247 automatically determine the appropriate host character set. In this
8248 case, @value{GDBN} uses @samp{UTF-8}.
8250 @value{GDBN} can only use certain character sets as its host character
8251 set. If you type @kbd{@w{set target-charset @key{TAB}@key{TAB}}},
8252 @value{GDBN} will list the host character sets it supports.
8254 @item set charset @var{charset}
8256 Set the current host and target character sets to @var{charset}. As
8257 above, if you type @kbd{@w{set charset @key{TAB}@key{TAB}}},
8258 @value{GDBN} will list the names of the character sets that can be used
8259 for both host and target.
8262 @kindex show charset
8263 Show the names of the current host and target character sets.
8265 @item show host-charset
8266 @kindex show host-charset
8267 Show the name of the current host character set.
8269 @item show target-charset
8270 @kindex show target-charset
8271 Show the name of the current target character set.
8273 @item set target-wide-charset @var{charset}
8274 @kindex set target-wide-charset
8275 Set the current target's wide character set to @var{charset}. This is
8276 the character set used by the target's @code{wchar_t} type. To
8277 display the list of supported wide character sets, type
8278 @kbd{@w{set target-wide-charset @key{TAB}@key{TAB}}}.
8280 @item show target-wide-charset
8281 @kindex show target-wide-charset
8282 Show the name of the current target's wide character set.
8285 Here is an example of @value{GDBN}'s character set support in action.
8286 Assume that the following source code has been placed in the file
8287 @file{charset-test.c}:
8293 = @{72, 101, 108, 108, 111, 44, 32, 119,
8294 111, 114, 108, 100, 33, 10, 0@};
8295 char ibm1047_hello[]
8296 = @{200, 133, 147, 147, 150, 107, 64, 166,
8297 150, 153, 147, 132, 90, 37, 0@};
8301 printf ("Hello, world!\n");
8305 In this program, @code{ascii_hello} and @code{ibm1047_hello} are arrays
8306 containing the string @samp{Hello, world!} followed by a newline,
8307 encoded in the @sc{ascii} and @sc{ibm1047} character sets.
8309 We compile the program, and invoke the debugger on it:
8312 $ gcc -g charset-test.c -o charset-test
8313 $ gdb -nw charset-test
8314 GNU gdb 2001-12-19-cvs
8315 Copyright 2001 Free Software Foundation, Inc.
8320 We can use the @code{show charset} command to see what character sets
8321 @value{GDBN} is currently using to interpret and display characters and
8325 (@value{GDBP}) show charset
8326 The current host and target character set is `ISO-8859-1'.
8330 For the sake of printing this manual, let's use @sc{ascii} as our
8331 initial character set:
8333 (@value{GDBP}) set charset ASCII
8334 (@value{GDBP}) show charset
8335 The current host and target character set is `ASCII'.
8339 Let's assume that @sc{ascii} is indeed the correct character set for our
8340 host system --- in other words, let's assume that if @value{GDBN} prints
8341 characters using the @sc{ascii} character set, our terminal will display
8342 them properly. Since our current target character set is also
8343 @sc{ascii}, the contents of @code{ascii_hello} print legibly:
8346 (@value{GDBP}) print ascii_hello
8347 $1 = 0x401698 "Hello, world!\n"
8348 (@value{GDBP}) print ascii_hello[0]
8353 @value{GDBN} uses the target character set for character and string
8354 literals you use in expressions:
8357 (@value{GDBP}) print '+'
8362 The @sc{ascii} character set uses the number 43 to encode the @samp{+}
8365 @value{GDBN} relies on the user to tell it which character set the
8366 target program uses. If we print @code{ibm1047_hello} while our target
8367 character set is still @sc{ascii}, we get jibberish:
8370 (@value{GDBP}) print ibm1047_hello
8371 $4 = 0x4016a8 "\310\205\223\223\226k@@\246\226\231\223\204Z%"
8372 (@value{GDBP}) print ibm1047_hello[0]
8377 If we invoke the @code{set target-charset} followed by @key{TAB}@key{TAB},
8378 @value{GDBN} tells us the character sets it supports:
8381 (@value{GDBP}) set target-charset
8382 ASCII EBCDIC-US IBM1047 ISO-8859-1
8383 (@value{GDBP}) set target-charset
8386 We can select @sc{ibm1047} as our target character set, and examine the
8387 program's strings again. Now the @sc{ascii} string is wrong, but
8388 @value{GDBN} translates the contents of @code{ibm1047_hello} from the
8389 target character set, @sc{ibm1047}, to the host character set,
8390 @sc{ascii}, and they display correctly:
8393 (@value{GDBP}) set target-charset IBM1047
8394 (@value{GDBP}) show charset
8395 The current host character set is `ASCII'.
8396 The current target character set is `IBM1047'.
8397 (@value{GDBP}) print ascii_hello
8398 $6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
8399 (@value{GDBP}) print ascii_hello[0]
8401 (@value{GDBP}) print ibm1047_hello
8402 $8 = 0x4016a8 "Hello, world!\n"
8403 (@value{GDBP}) print ibm1047_hello[0]
8408 As above, @value{GDBN} uses the target character set for character and
8409 string literals you use in expressions:
8412 (@value{GDBP}) print '+'
8417 The @sc{ibm1047} character set uses the number 78 to encode the @samp{+}
8420 @node Caching Remote Data
8421 @section Caching Data of Remote Targets
8422 @cindex caching data of remote targets
8424 @value{GDBN} caches data exchanged between the debugger and a
8425 remote target (@pxref{Remote Debugging}). Such caching generally improves
8426 performance, because it reduces the overhead of the remote protocol by
8427 bundling memory reads and writes into large chunks. Unfortunately, simply
8428 caching everything would lead to incorrect results, since @value{GDBN}
8429 does not necessarily know anything about volatile values, memory-mapped I/O
8430 addresses, etc. Furthermore, in non-stop mode (@pxref{Non-Stop Mode})
8431 memory can be changed @emph{while} a gdb command is executing.
8432 Therefore, by default, @value{GDBN} only caches data
8433 known to be on the stack@footnote{In non-stop mode, it is moderately
8434 rare for a running thread to modify the stack of a stopped thread
8435 in a way that would interfere with a backtrace, and caching of
8436 stack reads provides a significant speed up of remote backtraces.}.
8437 Other regions of memory can be explicitly marked as
8438 cacheable; see @pxref{Memory Region Attributes}.
8441 @kindex set remotecache
8442 @item set remotecache on
8443 @itemx set remotecache off
8444 This option no longer does anything; it exists for compatibility
8447 @kindex show remotecache
8448 @item show remotecache
8449 Show the current state of the obsolete remotecache flag.
8451 @kindex set stack-cache
8452 @item set stack-cache on
8453 @itemx set stack-cache off
8454 Enable or disable caching of stack accesses. When @code{ON}, use
8455 caching. By default, this option is @code{ON}.
8457 @kindex show stack-cache
8458 @item show stack-cache
8459 Show the current state of data caching for memory accesses.
8462 @item info dcache @r{[}line@r{]}
8463 Print the information about the data cache performance. The
8464 information displayed includes the dcache width and depth, and for
8465 each cache line, its number, address, and how many times it was
8466 referenced. This command is useful for debugging the data cache
8469 If a line number is specified, the contents of that line will be
8473 @node Searching Memory
8474 @section Search Memory
8475 @cindex searching memory
8477 Memory can be searched for a particular sequence of bytes with the
8478 @code{find} command.
8482 @item find @r{[}/@var{sn}@r{]} @var{start_addr}, +@var{len}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
8483 @itemx find @r{[}/@var{sn}@r{]} @var{start_addr}, @var{end_addr}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
8484 Search memory for the sequence of bytes specified by @var{val1}, @var{val2},
8485 etc. The search begins at address @var{start_addr} and continues for either
8486 @var{len} bytes or through to @var{end_addr} inclusive.
8489 @var{s} and @var{n} are optional parameters.
8490 They may be specified in either order, apart or together.
8493 @item @var{s}, search query size
8494 The size of each search query value.
8500 halfwords (two bytes)
8504 giant words (eight bytes)
8507 All values are interpreted in the current language.
8508 This means, for example, that if the current source language is C/C@t{++}
8509 then searching for the string ``hello'' includes the trailing '\0'.
8511 If the value size is not specified, it is taken from the
8512 value's type in the current language.
8513 This is useful when one wants to specify the search
8514 pattern as a mixture of types.
8515 Note that this means, for example, that in the case of C-like languages
8516 a search for an untyped 0x42 will search for @samp{(int) 0x42}
8517 which is typically four bytes.
8519 @item @var{n}, maximum number of finds
8520 The maximum number of matches to print. The default is to print all finds.
8523 You can use strings as search values. Quote them with double-quotes
8525 The string value is copied into the search pattern byte by byte,
8526 regardless of the endianness of the target and the size specification.
8528 The address of each match found is printed as well as a count of the
8529 number of matches found.
8531 The address of the last value found is stored in convenience variable
8533 A count of the number of matches is stored in @samp{$numfound}.
8535 For example, if stopped at the @code{printf} in this function:
8541 static char hello[] = "hello-hello";
8542 static struct @{ char c; short s; int i; @}
8543 __attribute__ ((packed)) mixed
8544 = @{ 'c', 0x1234, 0x87654321 @};
8545 printf ("%s\n", hello);
8550 you get during debugging:
8553 (gdb) find &hello[0], +sizeof(hello), "hello"
8554 0x804956d <hello.1620+6>
8556 (gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o'
8557 0x8049567 <hello.1620>
8558 0x804956d <hello.1620+6>
8560 (gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l'
8561 0x8049567 <hello.1620>
8563 (gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321
8564 0x8049560 <mixed.1625>
8566 (gdb) print $numfound
8569 $2 = (void *) 0x8049560
8572 @node Optimized Code
8573 @chapter Debugging Optimized Code
8574 @cindex optimized code, debugging
8575 @cindex debugging optimized code
8577 Almost all compilers support optimization. With optimization
8578 disabled, the compiler generates assembly code that corresponds
8579 directly to your source code, in a simplistic way. As the compiler
8580 applies more powerful optimizations, the generated assembly code
8581 diverges from your original source code. With help from debugging
8582 information generated by the compiler, @value{GDBN} can map from
8583 the running program back to constructs from your original source.
8585 @value{GDBN} is more accurate with optimization disabled. If you
8586 can recompile without optimization, it is easier to follow the
8587 progress of your program during debugging. But, there are many cases
8588 where you may need to debug an optimized version.
8590 When you debug a program compiled with @samp{-g -O}, remember that the
8591 optimizer has rearranged your code; the debugger shows you what is
8592 really there. Do not be too surprised when the execution path does not
8593 exactly match your source file! An extreme example: if you define a
8594 variable, but never use it, @value{GDBN} never sees that
8595 variable---because the compiler optimizes it out of existence.
8597 Some things do not work as well with @samp{-g -O} as with just
8598 @samp{-g}, particularly on machines with instruction scheduling. If in
8599 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
8600 please report it to us as a bug (including a test case!).
8601 @xref{Variables}, for more information about debugging optimized code.
8604 * Inline Functions:: How @value{GDBN} presents inlining
8607 @node Inline Functions
8608 @section Inline Functions
8609 @cindex inline functions, debugging
8611 @dfn{Inlining} is an optimization that inserts a copy of the function
8612 body directly at each call site, instead of jumping to a shared
8613 routine. @value{GDBN} displays inlined functions just like
8614 non-inlined functions. They appear in backtraces. You can view their
8615 arguments and local variables, step into them with @code{step}, skip
8616 them with @code{next}, and escape from them with @code{finish}.
8617 You can check whether a function was inlined by using the
8618 @code{info frame} command.
8620 For @value{GDBN} to support inlined functions, the compiler must
8621 record information about inlining in the debug information ---
8622 @value{NGCC} using the @sc{dwarf 2} format does this, and several
8623 other compilers do also. @value{GDBN} only supports inlined functions
8624 when using @sc{dwarf 2}. Versions of @value{NGCC} before 4.1
8625 do not emit two required attributes (@samp{DW_AT_call_file} and
8626 @samp{DW_AT_call_line}); @value{GDBN} does not display inlined
8627 function calls with earlier versions of @value{NGCC}. It instead
8628 displays the arguments and local variables of inlined functions as
8629 local variables in the caller.
8631 The body of an inlined function is directly included at its call site;
8632 unlike a non-inlined function, there are no instructions devoted to
8633 the call. @value{GDBN} still pretends that the call site and the
8634 start of the inlined function are different instructions. Stepping to
8635 the call site shows the call site, and then stepping again shows
8636 the first line of the inlined function, even though no additional
8637 instructions are executed.
8639 This makes source-level debugging much clearer; you can see both the
8640 context of the call and then the effect of the call. Only stepping by
8641 a single instruction using @code{stepi} or @code{nexti} does not do
8642 this; single instruction steps always show the inlined body.
8644 There are some ways that @value{GDBN} does not pretend that inlined
8645 function calls are the same as normal calls:
8649 You cannot set breakpoints on inlined functions. @value{GDBN}
8650 either reports that there is no symbol with that name, or else sets the
8651 breakpoint only on non-inlined copies of the function. This limitation
8652 will be removed in a future version of @value{GDBN}; until then,
8653 set a breakpoint by line number on the first line of the inlined
8657 Setting breakpoints at the call site of an inlined function may not
8658 work, because the call site does not contain any code. @value{GDBN}
8659 may incorrectly move the breakpoint to the next line of the enclosing
8660 function, after the call. This limitation will be removed in a future
8661 version of @value{GDBN}; until then, set a breakpoint on an earlier line
8662 or inside the inlined function instead.
8665 @value{GDBN} cannot locate the return value of inlined calls after
8666 using the @code{finish} command. This is a limitation of compiler-generated
8667 debugging information; after @code{finish}, you can step to the next line
8668 and print a variable where your program stored the return value.
8674 @chapter C Preprocessor Macros
8676 Some languages, such as C and C@t{++}, provide a way to define and invoke
8677 ``preprocessor macros'' which expand into strings of tokens.
8678 @value{GDBN} can evaluate expressions containing macro invocations, show
8679 the result of macro expansion, and show a macro's definition, including
8680 where it was defined.
8682 You may need to compile your program specially to provide @value{GDBN}
8683 with information about preprocessor macros. Most compilers do not
8684 include macros in their debugging information, even when you compile
8685 with the @option{-g} flag. @xref{Compilation}.
8687 A program may define a macro at one point, remove that definition later,
8688 and then provide a different definition after that. Thus, at different
8689 points in the program, a macro may have different definitions, or have
8690 no definition at all. If there is a current stack frame, @value{GDBN}
8691 uses the macros in scope at that frame's source code line. Otherwise,
8692 @value{GDBN} uses the macros in scope at the current listing location;
8695 Whenever @value{GDBN} evaluates an expression, it always expands any
8696 macro invocations present in the expression. @value{GDBN} also provides
8697 the following commands for working with macros explicitly.
8701 @kindex macro expand
8702 @cindex macro expansion, showing the results of preprocessor
8703 @cindex preprocessor macro expansion, showing the results of
8704 @cindex expanding preprocessor macros
8705 @item macro expand @var{expression}
8706 @itemx macro exp @var{expression}
8707 Show the results of expanding all preprocessor macro invocations in
8708 @var{expression}. Since @value{GDBN} simply expands macros, but does
8709 not parse the result, @var{expression} need not be a valid expression;
8710 it can be any string of tokens.
8713 @item macro expand-once @var{expression}
8714 @itemx macro exp1 @var{expression}
8715 @cindex expand macro once
8716 @i{(This command is not yet implemented.)} Show the results of
8717 expanding those preprocessor macro invocations that appear explicitly in
8718 @var{expression}. Macro invocations appearing in that expansion are
8719 left unchanged. This command allows you to see the effect of a
8720 particular macro more clearly, without being confused by further
8721 expansions. Since @value{GDBN} simply expands macros, but does not
8722 parse the result, @var{expression} need not be a valid expression; it
8723 can be any string of tokens.
8726 @cindex macro definition, showing
8727 @cindex definition, showing a macro's
8728 @item info macro @var{macro}
8729 Show the definition of the macro named @var{macro}, and describe the
8730 source location or compiler command-line where that definition was established.
8732 @kindex macro define
8733 @cindex user-defined macros
8734 @cindex defining macros interactively
8735 @cindex macros, user-defined
8736 @item macro define @var{macro} @var{replacement-list}
8737 @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list}
8738 Introduce a definition for a preprocessor macro named @var{macro},
8739 invocations of which are replaced by the tokens given in
8740 @var{replacement-list}. The first form of this command defines an
8741 ``object-like'' macro, which takes no arguments; the second form
8742 defines a ``function-like'' macro, which takes the arguments given in
8745 A definition introduced by this command is in scope in every
8746 expression evaluated in @value{GDBN}, until it is removed with the
8747 @code{macro undef} command, described below. The definition overrides
8748 all definitions for @var{macro} present in the program being debugged,
8749 as well as any previous user-supplied definition.
8752 @item macro undef @var{macro}
8753 Remove any user-supplied definition for the macro named @var{macro}.
8754 This command only affects definitions provided with the @code{macro
8755 define} command, described above; it cannot remove definitions present
8756 in the program being debugged.
8760 List all the macros defined using the @code{macro define} command.
8763 @cindex macros, example of debugging with
8764 Here is a transcript showing the above commands in action. First, we
8765 show our source files:
8773 #define ADD(x) (M + x)
8778 printf ("Hello, world!\n");
8780 printf ("We're so creative.\n");
8782 printf ("Goodbye, world!\n");
8789 Now, we compile the program using the @sc{gnu} C compiler, @value{NGCC}.
8790 We pass the @option{-gdwarf-2} and @option{-g3} flags to ensure the
8791 compiler includes information about preprocessor macros in the debugging
8795 $ gcc -gdwarf-2 -g3 sample.c -o sample
8799 Now, we start @value{GDBN} on our sample program:
8803 GNU gdb 2002-05-06-cvs
8804 Copyright 2002 Free Software Foundation, Inc.
8805 GDB is free software, @dots{}
8809 We can expand macros and examine their definitions, even when the
8810 program is not running. @value{GDBN} uses the current listing position
8811 to decide which macro definitions are in scope:
8814 (@value{GDBP}) list main
8817 5 #define ADD(x) (M + x)
8822 10 printf ("Hello, world!\n");
8824 12 printf ("We're so creative.\n");
8825 (@value{GDBP}) info macro ADD
8826 Defined at /home/jimb/gdb/macros/play/sample.c:5
8827 #define ADD(x) (M + x)
8828 (@value{GDBP}) info macro Q
8829 Defined at /home/jimb/gdb/macros/play/sample.h:1
8830 included at /home/jimb/gdb/macros/play/sample.c:2
8832 (@value{GDBP}) macro expand ADD(1)
8833 expands to: (42 + 1)
8834 (@value{GDBP}) macro expand-once ADD(1)
8835 expands to: once (M + 1)
8839 In the example above, note that @code{macro expand-once} expands only
8840 the macro invocation explicit in the original text --- the invocation of
8841 @code{ADD} --- but does not expand the invocation of the macro @code{M},
8842 which was introduced by @code{ADD}.
8844 Once the program is running, @value{GDBN} uses the macro definitions in
8845 force at the source line of the current stack frame:
8848 (@value{GDBP}) break main
8849 Breakpoint 1 at 0x8048370: file sample.c, line 10.
8851 Starting program: /home/jimb/gdb/macros/play/sample
8853 Breakpoint 1, main () at sample.c:10
8854 10 printf ("Hello, world!\n");
8858 At line 10, the definition of the macro @code{N} at line 9 is in force:
8861 (@value{GDBP}) info macro N
8862 Defined at /home/jimb/gdb/macros/play/sample.c:9
8864 (@value{GDBP}) macro expand N Q M
8866 (@value{GDBP}) print N Q M
8871 As we step over directives that remove @code{N}'s definition, and then
8872 give it a new definition, @value{GDBN} finds the definition (or lack
8873 thereof) in force at each point:
8878 12 printf ("We're so creative.\n");
8879 (@value{GDBP}) info macro N
8880 The symbol `N' has no definition as a C/C++ preprocessor macro
8881 at /home/jimb/gdb/macros/play/sample.c:12
8884 14 printf ("Goodbye, world!\n");
8885 (@value{GDBP}) info macro N
8886 Defined at /home/jimb/gdb/macros/play/sample.c:13
8888 (@value{GDBP}) macro expand N Q M
8889 expands to: 1729 < 42
8890 (@value{GDBP}) print N Q M
8895 In addition to source files, macros can be defined on the compilation command
8896 line using the @option{-D@var{name}=@var{value}} syntax. For macros defined in
8897 such a way, @value{GDBN} displays the location of their definition as line zero
8898 of the source file submitted to the compiler.
8901 (@value{GDBP}) info macro __STDC__
8902 Defined at /home/jimb/gdb/macros/play/sample.c:0
8909 @chapter Tracepoints
8910 @c This chapter is based on the documentation written by Michael
8911 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
8914 In some applications, it is not feasible for the debugger to interrupt
8915 the program's execution long enough for the developer to learn
8916 anything helpful about its behavior. If the program's correctness
8917 depends on its real-time behavior, delays introduced by a debugger
8918 might cause the program to change its behavior drastically, or perhaps
8919 fail, even when the code itself is correct. It is useful to be able
8920 to observe the program's behavior without interrupting it.
8922 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
8923 specify locations in the program, called @dfn{tracepoints}, and
8924 arbitrary expressions to evaluate when those tracepoints are reached.
8925 Later, using the @code{tfind} command, you can examine the values
8926 those expressions had when the program hit the tracepoints. The
8927 expressions may also denote objects in memory---structures or arrays,
8928 for example---whose values @value{GDBN} should record; while visiting
8929 a particular tracepoint, you may inspect those objects as if they were
8930 in memory at that moment. However, because @value{GDBN} records these
8931 values without interacting with you, it can do so quickly and
8932 unobtrusively, hopefully not disturbing the program's behavior.
8934 The tracepoint facility is currently available only for remote
8935 targets. @xref{Targets}. In addition, your remote target must know
8936 how to collect trace data. This functionality is implemented in the
8937 remote stub; however, none of the stubs distributed with @value{GDBN}
8938 support tracepoints as of this writing. The format of the remote
8939 packets used to implement tracepoints are described in @ref{Tracepoint
8942 This chapter describes the tracepoint commands and features.
8946 * Analyze Collected Data::
8947 * Tracepoint Variables::
8950 @node Set Tracepoints
8951 @section Commands to Set Tracepoints
8953 Before running such a @dfn{trace experiment}, an arbitrary number of
8954 tracepoints can be set. A tracepoint is actually a special type of
8955 breakpoint (@pxref{Set Breaks}), so you can manipulate it using
8956 standard breakpoint commands. For instance, as with breakpoints,
8957 tracepoint numbers are successive integers starting from one, and many
8958 of the commands associated with tracepoints take the tracepoint number
8959 as their argument, to identify which tracepoint to work on.
8961 For each tracepoint, you can specify, in advance, some arbitrary set
8962 of data that you want the target to collect in the trace buffer when
8963 it hits that tracepoint. The collected data can include registers,
8964 local variables, or global data. Later, you can use @value{GDBN}
8965 commands to examine the values these data had at the time the
8968 Tracepoints do not support every breakpoint feature. Conditional
8969 expressions and ignore counts on tracepoints have no effect, and
8970 tracepoints cannot run @value{GDBN} commands when they are
8971 hit. Tracepoints may not be thread-specific either.
8973 This section describes commands to set tracepoints and associated
8974 conditions and actions.
8977 * Create and Delete Tracepoints::
8978 * Enable and Disable Tracepoints::
8979 * Tracepoint Passcounts::
8980 * Tracepoint Conditions::
8981 * Tracepoint Actions::
8982 * Listing Tracepoints::
8983 * Starting and Stopping Trace Experiments::
8986 @node Create and Delete Tracepoints
8987 @subsection Create and Delete Tracepoints
8990 @cindex set tracepoint
8992 @item trace @var{location}
8993 The @code{trace} command is very similar to the @code{break} command.
8994 Its argument @var{location} can be a source line, a function name, or
8995 an address in the target program. @xref{Specify Location}. The
8996 @code{trace} command defines a tracepoint, which is a point in the
8997 target program where the debugger will briefly stop, collect some
8998 data, and then allow the program to continue. Setting a tracepoint or
8999 changing its actions doesn't take effect until the next @code{tstart}
9000 command, and once a trace experiment is running, further changes will
9001 not have any effect until the next trace experiment starts.
9003 Here are some examples of using the @code{trace} command:
9006 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
9008 (@value{GDBP}) @b{trace +2} // 2 lines forward
9010 (@value{GDBP}) @b{trace my_function} // first source line of function
9012 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
9014 (@value{GDBP}) @b{trace *0x2117c4} // an address
9018 You can abbreviate @code{trace} as @code{tr}.
9020 @item trace @var{location} if @var{cond}
9021 Set a tracepoint with condition @var{cond}; evaluate the expression
9022 @var{cond} each time the tracepoint is reached, and collect data only
9023 if the value is nonzero---that is, if @var{cond} evaluates as true.
9024 @xref{Tracepoint Conditions, ,Tracepoint Conditions}, for more
9025 information on tracepoint conditions.
9028 @cindex last tracepoint number
9029 @cindex recent tracepoint number
9030 @cindex tracepoint number
9031 The convenience variable @code{$tpnum} records the tracepoint number
9032 of the most recently set tracepoint.
9034 @kindex delete tracepoint
9035 @cindex tracepoint deletion
9036 @item delete tracepoint @r{[}@var{num}@r{]}
9037 Permanently delete one or more tracepoints. With no argument, the
9038 default is to delete all tracepoints. Note that the regular
9039 @code{delete} command can remove tracepoints also.
9044 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
9046 (@value{GDBP}) @b{delete trace} // remove all tracepoints
9050 You can abbreviate this command as @code{del tr}.
9053 @node Enable and Disable Tracepoints
9054 @subsection Enable and Disable Tracepoints
9056 These commands are deprecated; they are equivalent to plain @code{disable} and @code{enable}.
9059 @kindex disable tracepoint
9060 @item disable tracepoint @r{[}@var{num}@r{]}
9061 Disable tracepoint @var{num}, or all tracepoints if no argument
9062 @var{num} is given. A disabled tracepoint will have no effect during
9063 the next trace experiment, but it is not forgotten. You can re-enable
9064 a disabled tracepoint using the @code{enable tracepoint} command.
9066 @kindex enable tracepoint
9067 @item enable tracepoint @r{[}@var{num}@r{]}
9068 Enable tracepoint @var{num}, or all tracepoints. The enabled
9069 tracepoints will become effective the next time a trace experiment is
9073 @node Tracepoint Passcounts
9074 @subsection Tracepoint Passcounts
9078 @cindex tracepoint pass count
9079 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
9080 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
9081 automatically stop a trace experiment. If a tracepoint's passcount is
9082 @var{n}, then the trace experiment will be automatically stopped on
9083 the @var{n}'th time that tracepoint is hit. If the tracepoint number
9084 @var{num} is not specified, the @code{passcount} command sets the
9085 passcount of the most recently defined tracepoint. If no passcount is
9086 given, the trace experiment will run until stopped explicitly by the
9092 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
9093 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
9095 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
9096 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
9097 (@value{GDBP}) @b{trace foo}
9098 (@value{GDBP}) @b{pass 3}
9099 (@value{GDBP}) @b{trace bar}
9100 (@value{GDBP}) @b{pass 2}
9101 (@value{GDBP}) @b{trace baz}
9102 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
9103 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
9104 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
9105 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
9109 @node Tracepoint Conditions
9110 @subsection Tracepoint Conditions
9111 @cindex conditional tracepoints
9112 @cindex tracepoint conditions
9114 The simplest sort of tracepoint collects data every time your program
9115 reaches a specified place. You can also specify a @dfn{condition} for
9116 a tracepoint. A condition is just a Boolean expression in your
9117 programming language (@pxref{Expressions, ,Expressions}). A
9118 tracepoint with a condition evaluates the expression each time your
9119 program reaches it, and data collection happens only if the condition
9122 Tracepoint conditions can be specified when a tracepoint is set, by
9123 using @samp{if} in the arguments to the @code{trace} command.
9124 @xref{Create and Delete Tracepoints, ,Setting Tracepoints}. They can
9125 also be set or changed at any time with the @code{condition} command,
9126 just as with breakpoints.
9128 Unlike breakpoint conditions, @value{GDBN} does not actually evaluate
9129 the conditional expression itself. Instead, @value{GDBN} encodes the
9130 expression into an agent expression (@pxref{Agent Expressions}
9131 suitable for execution on the target, independently of @value{GDBN}.
9132 Global variables become raw memory locations, locals become stack
9133 accesses, and so forth.
9135 For instance, suppose you have a function that is usually called
9136 frequently, but should not be called after an error has occurred. You
9137 could use the following tracepoint command to collect data about calls
9138 of that function that happen while the error code is propagating
9139 through the program; an unconditional tracepoint could end up
9140 collecting thousands of useless trace frames that you would have to
9144 (@value{GDBP}) @kbd{trace normal_operation if errcode > 0}
9147 @node Tracepoint Actions
9148 @subsection Tracepoint Action Lists
9152 @cindex tracepoint actions
9153 @item actions @r{[}@var{num}@r{]}
9154 This command will prompt for a list of actions to be taken when the
9155 tracepoint is hit. If the tracepoint number @var{num} is not
9156 specified, this command sets the actions for the one that was most
9157 recently defined (so that you can define a tracepoint and then say
9158 @code{actions} without bothering about its number). You specify the
9159 actions themselves on the following lines, one action at a time, and
9160 terminate the actions list with a line containing just @code{end}. So
9161 far, the only defined actions are @code{collect} and
9162 @code{while-stepping}.
9164 @cindex remove actions from a tracepoint
9165 To remove all actions from a tracepoint, type @samp{actions @var{num}}
9166 and follow it immediately with @samp{end}.
9169 (@value{GDBP}) @b{collect @var{data}} // collect some data
9171 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
9173 (@value{GDBP}) @b{end} // signals the end of actions.
9176 In the following example, the action list begins with @code{collect}
9177 commands indicating the things to be collected when the tracepoint is
9178 hit. Then, in order to single-step and collect additional data
9179 following the tracepoint, a @code{while-stepping} command is used,
9180 followed by the list of things to be collected while stepping. The
9181 @code{while-stepping} command is terminated by its own separate
9182 @code{end} command. Lastly, the action list is terminated by an
9186 (@value{GDBP}) @b{trace foo}
9187 (@value{GDBP}) @b{actions}
9188 Enter actions for tracepoint 1, one per line:
9197 @kindex collect @r{(tracepoints)}
9198 @item collect @var{expr1}, @var{expr2}, @dots{}
9199 Collect values of the given expressions when the tracepoint is hit.
9200 This command accepts a comma-separated list of any valid expressions.
9201 In addition to global, static, or local variables, the following
9202 special arguments are supported:
9206 collect all registers
9209 collect all function arguments
9212 collect all local variables.
9215 You can give several consecutive @code{collect} commands, each one
9216 with a single argument, or one @code{collect} command with several
9217 arguments separated by commas: the effect is the same.
9219 The command @code{info scope} (@pxref{Symbols, info scope}) is
9220 particularly useful for figuring out what data to collect.
9222 @kindex while-stepping @r{(tracepoints)}
9223 @item while-stepping @var{n}
9224 Perform @var{n} single-step traces after the tracepoint, collecting
9225 new data at each step. The @code{while-stepping} command is
9226 followed by the list of what to collect while stepping (followed by
9227 its own @code{end} command):
9231 > collect $regs, myglobal
9237 You may abbreviate @code{while-stepping} as @code{ws} or
9241 @node Listing Tracepoints
9242 @subsection Listing Tracepoints
9245 @kindex info tracepoints
9247 @cindex information about tracepoints
9248 @item info tracepoints @r{[}@var{num}@r{]}
9249 Display information about the tracepoint @var{num}. If you don't
9250 specify a tracepoint number, displays information about all the
9251 tracepoints defined so far. The format is similar to that used for
9252 @code{info breakpoints}; in fact, @code{info tracepoints} is the same
9253 command, simply restricting itself to tracepoints.
9255 A tracepoint's listing may include additional information specific to
9260 its passcount as given by the @code{passcount @var{n}} command
9262 its step count as given by the @code{while-stepping @var{n}} command
9264 its action list as given by the @code{actions} command. The actions
9265 are prefixed with an @samp{A} so as to distinguish them from commands.
9269 (@value{GDBP}) @b{info trace}
9270 Num Type Disp Enb Address What
9271 1 tracepoint keep y 0x0804ab57 in foo() at main.cxx:7
9275 A collect globfoo, $regs
9283 This command can be abbreviated @code{info tp}.
9286 @node Starting and Stopping Trace Experiments
9287 @subsection Starting and Stopping Trace Experiments
9291 @cindex start a new trace experiment
9292 @cindex collected data discarded
9294 This command takes no arguments. It starts the trace experiment, and
9295 begins collecting data. This has the side effect of discarding all
9296 the data collected in the trace buffer during the previous trace
9300 @cindex stop a running trace experiment
9302 This command takes no arguments. It ends the trace experiment, and
9303 stops collecting data.
9305 @strong{Note}: a trace experiment and data collection may stop
9306 automatically if any tracepoint's passcount is reached
9307 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
9310 @cindex status of trace data collection
9311 @cindex trace experiment, status of
9313 This command displays the status of the current trace data
9317 Here is an example of the commands we described so far:
9320 (@value{GDBP}) @b{trace gdb_c_test}
9321 (@value{GDBP}) @b{actions}
9322 Enter actions for tracepoint #1, one per line.
9323 > collect $regs,$locals,$args
9328 (@value{GDBP}) @b{tstart}
9329 [time passes @dots{}]
9330 (@value{GDBP}) @b{tstop}
9334 @node Analyze Collected Data
9335 @section Using the Collected Data
9337 After the tracepoint experiment ends, you use @value{GDBN} commands
9338 for examining the trace data. The basic idea is that each tracepoint
9339 collects a trace @dfn{snapshot} every time it is hit and another
9340 snapshot every time it single-steps. All these snapshots are
9341 consecutively numbered from zero and go into a buffer, and you can
9342 examine them later. The way you examine them is to @dfn{focus} on a
9343 specific trace snapshot. When the remote stub is focused on a trace
9344 snapshot, it will respond to all @value{GDBN} requests for memory and
9345 registers by reading from the buffer which belongs to that snapshot,
9346 rather than from @emph{real} memory or registers of the program being
9347 debugged. This means that @strong{all} @value{GDBN} commands
9348 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
9349 behave as if we were currently debugging the program state as it was
9350 when the tracepoint occurred. Any requests for data that are not in
9351 the buffer will fail.
9354 * tfind:: How to select a trace snapshot
9355 * tdump:: How to display all data for a snapshot
9356 * save-tracepoints:: How to save tracepoints for a future run
9360 @subsection @code{tfind @var{n}}
9363 @cindex select trace snapshot
9364 @cindex find trace snapshot
9365 The basic command for selecting a trace snapshot from the buffer is
9366 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
9367 counting from zero. If no argument @var{n} is given, the next
9368 snapshot is selected.
9370 Here are the various forms of using the @code{tfind} command.
9374 Find the first snapshot in the buffer. This is a synonym for
9375 @code{tfind 0} (since 0 is the number of the first snapshot).
9378 Stop debugging trace snapshots, resume @emph{live} debugging.
9381 Same as @samp{tfind none}.
9384 No argument means find the next trace snapshot.
9387 Find the previous trace snapshot before the current one. This permits
9388 retracing earlier steps.
9390 @item tfind tracepoint @var{num}
9391 Find the next snapshot associated with tracepoint @var{num}. Search
9392 proceeds forward from the last examined trace snapshot. If no
9393 argument @var{num} is given, it means find the next snapshot collected
9394 for the same tracepoint as the current snapshot.
9396 @item tfind pc @var{addr}
9397 Find the next snapshot associated with the value @var{addr} of the
9398 program counter. Search proceeds forward from the last examined trace
9399 snapshot. If no argument @var{addr} is given, it means find the next
9400 snapshot with the same value of PC as the current snapshot.
9402 @item tfind outside @var{addr1}, @var{addr2}
9403 Find the next snapshot whose PC is outside the given range of
9406 @item tfind range @var{addr1}, @var{addr2}
9407 Find the next snapshot whose PC is between @var{addr1} and
9408 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
9410 @item tfind line @r{[}@var{file}:@r{]}@var{n}
9411 Find the next snapshot associated with the source line @var{n}. If
9412 the optional argument @var{file} is given, refer to line @var{n} in
9413 that source file. Search proceeds forward from the last examined
9414 trace snapshot. If no argument @var{n} is given, it means find the
9415 next line other than the one currently being examined; thus saying
9416 @code{tfind line} repeatedly can appear to have the same effect as
9417 stepping from line to line in a @emph{live} debugging session.
9420 The default arguments for the @code{tfind} commands are specifically
9421 designed to make it easy to scan through the trace buffer. For
9422 instance, @code{tfind} with no argument selects the next trace
9423 snapshot, and @code{tfind -} with no argument selects the previous
9424 trace snapshot. So, by giving one @code{tfind} command, and then
9425 simply hitting @key{RET} repeatedly you can examine all the trace
9426 snapshots in order. Or, by saying @code{tfind -} and then hitting
9427 @key{RET} repeatedly you can examine the snapshots in reverse order.
9428 The @code{tfind line} command with no argument selects the snapshot
9429 for the next source line executed. The @code{tfind pc} command with
9430 no argument selects the next snapshot with the same program counter
9431 (PC) as the current frame. The @code{tfind tracepoint} command with
9432 no argument selects the next trace snapshot collected by the same
9433 tracepoint as the current one.
9435 In addition to letting you scan through the trace buffer manually,
9436 these commands make it easy to construct @value{GDBN} scripts that
9437 scan through the trace buffer and print out whatever collected data
9438 you are interested in. Thus, if we want to examine the PC, FP, and SP
9439 registers from each trace frame in the buffer, we can say this:
9442 (@value{GDBP}) @b{tfind start}
9443 (@value{GDBP}) @b{while ($trace_frame != -1)}
9444 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
9445 $trace_frame, $pc, $sp, $fp
9449 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
9450 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
9451 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
9452 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
9453 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
9454 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
9455 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
9456 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
9457 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
9458 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
9459 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
9462 Or, if we want to examine the variable @code{X} at each source line in
9466 (@value{GDBP}) @b{tfind start}
9467 (@value{GDBP}) @b{while ($trace_frame != -1)}
9468 > printf "Frame %d, X == %d\n", $trace_frame, X
9478 @subsection @code{tdump}
9480 @cindex dump all data collected at tracepoint
9481 @cindex tracepoint data, display
9483 This command takes no arguments. It prints all the data collected at
9484 the current trace snapshot.
9487 (@value{GDBP}) @b{trace 444}
9488 (@value{GDBP}) @b{actions}
9489 Enter actions for tracepoint #2, one per line:
9490 > collect $regs, $locals, $args, gdb_long_test
9493 (@value{GDBP}) @b{tstart}
9495 (@value{GDBP}) @b{tfind line 444}
9496 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
9498 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
9500 (@value{GDBP}) @b{tdump}
9501 Data collected at tracepoint 2, trace frame 1:
9502 d0 0xc4aa0085 -995491707
9506 d4 0x71aea3d 119204413
9511 a1 0x3000668 50333288
9514 a4 0x3000698 50333336
9516 fp 0x30bf3c 0x30bf3c
9517 sp 0x30bf34 0x30bf34
9519 pc 0x20b2c8 0x20b2c8
9523 p = 0x20e5b4 "gdb-test"
9530 gdb_long_test = 17 '\021'
9535 @node save-tracepoints
9536 @subsection @code{save-tracepoints @var{filename}}
9537 @kindex save-tracepoints
9538 @cindex save tracepoints for future sessions
9540 This command saves all current tracepoint definitions together with
9541 their actions and passcounts, into a file @file{@var{filename}}
9542 suitable for use in a later debugging session. To read the saved
9543 tracepoint definitions, use the @code{source} command (@pxref{Command
9546 @node Tracepoint Variables
9547 @section Convenience Variables for Tracepoints
9548 @cindex tracepoint variables
9549 @cindex convenience variables for tracepoints
9552 @vindex $trace_frame
9553 @item (int) $trace_frame
9554 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
9555 snapshot is selected.
9558 @item (int) $tracepoint
9559 The tracepoint for the current trace snapshot.
9562 @item (int) $trace_line
9563 The line number for the current trace snapshot.
9566 @item (char []) $trace_file
9567 The source file for the current trace snapshot.
9570 @item (char []) $trace_func
9571 The name of the function containing @code{$tracepoint}.
9574 Note: @code{$trace_file} is not suitable for use in @code{printf},
9575 use @code{output} instead.
9577 Here's a simple example of using these convenience variables for
9578 stepping through all the trace snapshots and printing some of their
9582 (@value{GDBP}) @b{tfind start}
9584 (@value{GDBP}) @b{while $trace_frame != -1}
9585 > output $trace_file
9586 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
9592 @chapter Debugging Programs That Use Overlays
9595 If your program is too large to fit completely in your target system's
9596 memory, you can sometimes use @dfn{overlays} to work around this
9597 problem. @value{GDBN} provides some support for debugging programs that
9601 * How Overlays Work:: A general explanation of overlays.
9602 * Overlay Commands:: Managing overlays in @value{GDBN}.
9603 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
9604 mapped by asking the inferior.
9605 * Overlay Sample Program:: A sample program using overlays.
9608 @node How Overlays Work
9609 @section How Overlays Work
9610 @cindex mapped overlays
9611 @cindex unmapped overlays
9612 @cindex load address, overlay's
9613 @cindex mapped address
9614 @cindex overlay area
9616 Suppose you have a computer whose instruction address space is only 64
9617 kilobytes long, but which has much more memory which can be accessed by
9618 other means: special instructions, segment registers, or memory
9619 management hardware, for example. Suppose further that you want to
9620 adapt a program which is larger than 64 kilobytes to run on this system.
9622 One solution is to identify modules of your program which are relatively
9623 independent, and need not call each other directly; call these modules
9624 @dfn{overlays}. Separate the overlays from the main program, and place
9625 their machine code in the larger memory. Place your main program in
9626 instruction memory, but leave at least enough space there to hold the
9627 largest overlay as well.
9629 Now, to call a function located in an overlay, you must first copy that
9630 overlay's machine code from the large memory into the space set aside
9631 for it in the instruction memory, and then jump to its entry point
9634 @c NB: In the below the mapped area's size is greater or equal to the
9635 @c size of all overlays. This is intentional to remind the developer
9636 @c that overlays don't necessarily need to be the same size.
9640 Data Instruction Larger
9641 Address Space Address Space Address Space
9642 +-----------+ +-----------+ +-----------+
9644 +-----------+ +-----------+ +-----------+<-- overlay 1
9645 | program | | main | .----| overlay 1 | load address
9646 | variables | | program | | +-----------+
9647 | and heap | | | | | |
9648 +-----------+ | | | +-----------+<-- overlay 2
9649 | | +-----------+ | | | load address
9650 +-----------+ | | | .-| overlay 2 |
9652 mapped --->+-----------+ | | +-----------+
9654 | overlay | <-' | | |
9655 | area | <---' +-----------+<-- overlay 3
9656 | | <---. | | load address
9657 +-----------+ `--| overlay 3 |
9664 @anchor{A code overlay}A code overlay
9668 The diagram (@pxref{A code overlay}) shows a system with separate data
9669 and instruction address spaces. To map an overlay, the program copies
9670 its code from the larger address space to the instruction address space.
9671 Since the overlays shown here all use the same mapped address, only one
9672 may be mapped at a time. For a system with a single address space for
9673 data and instructions, the diagram would be similar, except that the
9674 program variables and heap would share an address space with the main
9675 program and the overlay area.
9677 An overlay loaded into instruction memory and ready for use is called a
9678 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
9679 instruction memory. An overlay not present (or only partially present)
9680 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
9681 is its address in the larger memory. The mapped address is also called
9682 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
9683 called the @dfn{load memory address}, or @dfn{LMA}.
9685 Unfortunately, overlays are not a completely transparent way to adapt a
9686 program to limited instruction memory. They introduce a new set of
9687 global constraints you must keep in mind as you design your program:
9692 Before calling or returning to a function in an overlay, your program
9693 must make sure that overlay is actually mapped. Otherwise, the call or
9694 return will transfer control to the right address, but in the wrong
9695 overlay, and your program will probably crash.
9698 If the process of mapping an overlay is expensive on your system, you
9699 will need to choose your overlays carefully to minimize their effect on
9700 your program's performance.
9703 The executable file you load onto your system must contain each
9704 overlay's instructions, appearing at the overlay's load address, not its
9705 mapped address. However, each overlay's instructions must be relocated
9706 and its symbols defined as if the overlay were at its mapped address.
9707 You can use GNU linker scripts to specify different load and relocation
9708 addresses for pieces of your program; see @ref{Overlay Description,,,
9709 ld.info, Using ld: the GNU linker}.
9712 The procedure for loading executable files onto your system must be able
9713 to load their contents into the larger address space as well as the
9714 instruction and data spaces.
9718 The overlay system described above is rather simple, and could be
9719 improved in many ways:
9724 If your system has suitable bank switch registers or memory management
9725 hardware, you could use those facilities to make an overlay's load area
9726 contents simply appear at their mapped address in instruction space.
9727 This would probably be faster than copying the overlay to its mapped
9728 area in the usual way.
9731 If your overlays are small enough, you could set aside more than one
9732 overlay area, and have more than one overlay mapped at a time.
9735 You can use overlays to manage data, as well as instructions. In
9736 general, data overlays are even less transparent to your design than
9737 code overlays: whereas code overlays only require care when you call or
9738 return to functions, data overlays require care every time you access
9739 the data. Also, if you change the contents of a data overlay, you
9740 must copy its contents back out to its load address before you can copy a
9741 different data overlay into the same mapped area.
9746 @node Overlay Commands
9747 @section Overlay Commands
9749 To use @value{GDBN}'s overlay support, each overlay in your program must
9750 correspond to a separate section of the executable file. The section's
9751 virtual memory address and load memory address must be the overlay's
9752 mapped and load addresses. Identifying overlays with sections allows
9753 @value{GDBN} to determine the appropriate address of a function or
9754 variable, depending on whether the overlay is mapped or not.
9756 @value{GDBN}'s overlay commands all start with the word @code{overlay};
9757 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
9762 Disable @value{GDBN}'s overlay support. When overlay support is
9763 disabled, @value{GDBN} assumes that all functions and variables are
9764 always present at their mapped addresses. By default, @value{GDBN}'s
9765 overlay support is disabled.
9767 @item overlay manual
9768 @cindex manual overlay debugging
9769 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
9770 relies on you to tell it which overlays are mapped, and which are not,
9771 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
9772 commands described below.
9774 @item overlay map-overlay @var{overlay}
9775 @itemx overlay map @var{overlay}
9776 @cindex map an overlay
9777 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
9778 be the name of the object file section containing the overlay. When an
9779 overlay is mapped, @value{GDBN} assumes it can find the overlay's
9780 functions and variables at their mapped addresses. @value{GDBN} assumes
9781 that any other overlays whose mapped ranges overlap that of
9782 @var{overlay} are now unmapped.
9784 @item overlay unmap-overlay @var{overlay}
9785 @itemx overlay unmap @var{overlay}
9786 @cindex unmap an overlay
9787 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
9788 must be the name of the object file section containing the overlay.
9789 When an overlay is unmapped, @value{GDBN} assumes it can find the
9790 overlay's functions and variables at their load addresses.
9793 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
9794 consults a data structure the overlay manager maintains in the inferior
9795 to see which overlays are mapped. For details, see @ref{Automatic
9798 @item overlay load-target
9800 @cindex reloading the overlay table
9801 Re-read the overlay table from the inferior. Normally, @value{GDBN}
9802 re-reads the table @value{GDBN} automatically each time the inferior
9803 stops, so this command should only be necessary if you have changed the
9804 overlay mapping yourself using @value{GDBN}. This command is only
9805 useful when using automatic overlay debugging.
9807 @item overlay list-overlays
9809 @cindex listing mapped overlays
9810 Display a list of the overlays currently mapped, along with their mapped
9811 addresses, load addresses, and sizes.
9815 Normally, when @value{GDBN} prints a code address, it includes the name
9816 of the function the address falls in:
9819 (@value{GDBP}) print main
9820 $3 = @{int ()@} 0x11a0 <main>
9823 When overlay debugging is enabled, @value{GDBN} recognizes code in
9824 unmapped overlays, and prints the names of unmapped functions with
9825 asterisks around them. For example, if @code{foo} is a function in an
9826 unmapped overlay, @value{GDBN} prints it this way:
9829 (@value{GDBP}) overlay list
9830 No sections are mapped.
9831 (@value{GDBP}) print foo
9832 $5 = @{int (int)@} 0x100000 <*foo*>
9835 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
9839 (@value{GDBP}) overlay list
9840 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
9841 mapped at 0x1016 - 0x104a
9842 (@value{GDBP}) print foo
9843 $6 = @{int (int)@} 0x1016 <foo>
9846 When overlay debugging is enabled, @value{GDBN} can find the correct
9847 address for functions and variables in an overlay, whether or not the
9848 overlay is mapped. This allows most @value{GDBN} commands, like
9849 @code{break} and @code{disassemble}, to work normally, even on unmapped
9850 code. However, @value{GDBN}'s breakpoint support has some limitations:
9854 @cindex breakpoints in overlays
9855 @cindex overlays, setting breakpoints in
9856 You can set breakpoints in functions in unmapped overlays, as long as
9857 @value{GDBN} can write to the overlay at its load address.
9859 @value{GDBN} can not set hardware or simulator-based breakpoints in
9860 unmapped overlays. However, if you set a breakpoint at the end of your
9861 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
9862 you are using manual overlay management), @value{GDBN} will re-set its
9863 breakpoints properly.
9867 @node Automatic Overlay Debugging
9868 @section Automatic Overlay Debugging
9869 @cindex automatic overlay debugging
9871 @value{GDBN} can automatically track which overlays are mapped and which
9872 are not, given some simple co-operation from the overlay manager in the
9873 inferior. If you enable automatic overlay debugging with the
9874 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
9875 looks in the inferior's memory for certain variables describing the
9876 current state of the overlays.
9878 Here are the variables your overlay manager must define to support
9879 @value{GDBN}'s automatic overlay debugging:
9883 @item @code{_ovly_table}:
9884 This variable must be an array of the following structures:
9889 /* The overlay's mapped address. */
9892 /* The size of the overlay, in bytes. */
9895 /* The overlay's load address. */
9898 /* Non-zero if the overlay is currently mapped;
9900 unsigned long mapped;
9904 @item @code{_novlys}:
9905 This variable must be a four-byte signed integer, holding the total
9906 number of elements in @code{_ovly_table}.
9910 To decide whether a particular overlay is mapped or not, @value{GDBN}
9911 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
9912 @code{lma} members equal the VMA and LMA of the overlay's section in the
9913 executable file. When @value{GDBN} finds a matching entry, it consults
9914 the entry's @code{mapped} member to determine whether the overlay is
9917 In addition, your overlay manager may define a function called
9918 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
9919 will silently set a breakpoint there. If the overlay manager then
9920 calls this function whenever it has changed the overlay table, this
9921 will enable @value{GDBN} to accurately keep track of which overlays
9922 are in program memory, and update any breakpoints that may be set
9923 in overlays. This will allow breakpoints to work even if the
9924 overlays are kept in ROM or other non-writable memory while they
9925 are not being executed.
9927 @node Overlay Sample Program
9928 @section Overlay Sample Program
9929 @cindex overlay example program
9931 When linking a program which uses overlays, you must place the overlays
9932 at their load addresses, while relocating them to run at their mapped
9933 addresses. To do this, you must write a linker script (@pxref{Overlay
9934 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
9935 since linker scripts are specific to a particular host system, target
9936 architecture, and target memory layout, this manual cannot provide
9937 portable sample code demonstrating @value{GDBN}'s overlay support.
9939 However, the @value{GDBN} source distribution does contain an overlaid
9940 program, with linker scripts for a few systems, as part of its test
9941 suite. The program consists of the following files from
9942 @file{gdb/testsuite/gdb.base}:
9946 The main program file.
9948 A simple overlay manager, used by @file{overlays.c}.
9953 Overlay modules, loaded and used by @file{overlays.c}.
9956 Linker scripts for linking the test program on the @code{d10v-elf}
9957 and @code{m32r-elf} targets.
9960 You can build the test program using the @code{d10v-elf} GCC
9961 cross-compiler like this:
9964 $ d10v-elf-gcc -g -c overlays.c
9965 $ d10v-elf-gcc -g -c ovlymgr.c
9966 $ d10v-elf-gcc -g -c foo.c
9967 $ d10v-elf-gcc -g -c bar.c
9968 $ d10v-elf-gcc -g -c baz.c
9969 $ d10v-elf-gcc -g -c grbx.c
9970 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
9971 baz.o grbx.o -Wl,-Td10v.ld -o overlays
9974 The build process is identical for any other architecture, except that
9975 you must substitute the appropriate compiler and linker script for the
9976 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
9980 @chapter Using @value{GDBN} with Different Languages
9983 Although programming languages generally have common aspects, they are
9984 rarely expressed in the same manner. For instance, in ANSI C,
9985 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
9986 Modula-2, it is accomplished by @code{p^}. Values can also be
9987 represented (and displayed) differently. Hex numbers in C appear as
9988 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
9990 @cindex working language
9991 Language-specific information is built into @value{GDBN} for some languages,
9992 allowing you to express operations like the above in your program's
9993 native language, and allowing @value{GDBN} to output values in a manner
9994 consistent with the syntax of your program's native language. The
9995 language you use to build expressions is called the @dfn{working
9999 * Setting:: Switching between source languages
10000 * Show:: Displaying the language
10001 * Checks:: Type and range checks
10002 * Supported Languages:: Supported languages
10003 * Unsupported Languages:: Unsupported languages
10007 @section Switching Between Source Languages
10009 There are two ways to control the working language---either have @value{GDBN}
10010 set it automatically, or select it manually yourself. You can use the
10011 @code{set language} command for either purpose. On startup, @value{GDBN}
10012 defaults to setting the language automatically. The working language is
10013 used to determine how expressions you type are interpreted, how values
10016 In addition to the working language, every source file that
10017 @value{GDBN} knows about has its own working language. For some object
10018 file formats, the compiler might indicate which language a particular
10019 source file is in. However, most of the time @value{GDBN} infers the
10020 language from the name of the file. The language of a source file
10021 controls whether C@t{++} names are demangled---this way @code{backtrace} can
10022 show each frame appropriately for its own language. There is no way to
10023 set the language of a source file from within @value{GDBN}, but you can
10024 set the language associated with a filename extension. @xref{Show, ,
10025 Displaying the Language}.
10027 This is most commonly a problem when you use a program, such
10028 as @code{cfront} or @code{f2c}, that generates C but is written in
10029 another language. In that case, make the
10030 program use @code{#line} directives in its C output; that way
10031 @value{GDBN} will know the correct language of the source code of the original
10032 program, and will display that source code, not the generated C code.
10035 * Filenames:: Filename extensions and languages.
10036 * Manually:: Setting the working language manually
10037 * Automatically:: Having @value{GDBN} infer the source language
10041 @subsection List of Filename Extensions and Languages
10043 If a source file name ends in one of the following extensions, then
10044 @value{GDBN} infers that its language is the one indicated.
10062 C@t{++} source file
10065 Objective-C source file
10069 Fortran source file
10072 Modula-2 source file
10076 Assembler source file. This actually behaves almost like C, but
10077 @value{GDBN} does not skip over function prologues when stepping.
10080 In addition, you may set the language associated with a filename
10081 extension. @xref{Show, , Displaying the Language}.
10084 @subsection Setting the Working Language
10086 If you allow @value{GDBN} to set the language automatically,
10087 expressions are interpreted the same way in your debugging session and
10090 @kindex set language
10091 If you wish, you may set the language manually. To do this, issue the
10092 command @samp{set language @var{lang}}, where @var{lang} is the name of
10093 a language, such as
10094 @code{c} or @code{modula-2}.
10095 For a list of the supported languages, type @samp{set language}.
10097 Setting the language manually prevents @value{GDBN} from updating the working
10098 language automatically. This can lead to confusion if you try
10099 to debug a program when the working language is not the same as the
10100 source language, when an expression is acceptable to both
10101 languages---but means different things. For instance, if the current
10102 source file were written in C, and @value{GDBN} was parsing Modula-2, a
10110 might not have the effect you intended. In C, this means to add
10111 @code{b} and @code{c} and place the result in @code{a}. The result
10112 printed would be the value of @code{a}. In Modula-2, this means to compare
10113 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
10115 @node Automatically
10116 @subsection Having @value{GDBN} Infer the Source Language
10118 To have @value{GDBN} set the working language automatically, use
10119 @samp{set language local} or @samp{set language auto}. @value{GDBN}
10120 then infers the working language. That is, when your program stops in a
10121 frame (usually by encountering a breakpoint), @value{GDBN} sets the
10122 working language to the language recorded for the function in that
10123 frame. If the language for a frame is unknown (that is, if the function
10124 or block corresponding to the frame was defined in a source file that
10125 does not have a recognized extension), the current working language is
10126 not changed, and @value{GDBN} issues a warning.
10128 This may not seem necessary for most programs, which are written
10129 entirely in one source language. However, program modules and libraries
10130 written in one source language can be used by a main program written in
10131 a different source language. Using @samp{set language auto} in this
10132 case frees you from having to set the working language manually.
10135 @section Displaying the Language
10137 The following commands help you find out which language is the
10138 working language, and also what language source files were written in.
10141 @item show language
10142 @kindex show language
10143 Display the current working language. This is the
10144 language you can use with commands such as @code{print} to
10145 build and compute expressions that may involve variables in your program.
10148 @kindex info frame@r{, show the source language}
10149 Display the source language for this frame. This language becomes the
10150 working language if you use an identifier from this frame.
10151 @xref{Frame Info, ,Information about a Frame}, to identify the other
10152 information listed here.
10155 @kindex info source@r{, show the source language}
10156 Display the source language of this source file.
10157 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
10158 information listed here.
10161 In unusual circumstances, you may have source files with extensions
10162 not in the standard list. You can then set the extension associated
10163 with a language explicitly:
10166 @item set extension-language @var{ext} @var{language}
10167 @kindex set extension-language
10168 Tell @value{GDBN} that source files with extension @var{ext} are to be
10169 assumed as written in the source language @var{language}.
10171 @item info extensions
10172 @kindex info extensions
10173 List all the filename extensions and the associated languages.
10177 @section Type and Range Checking
10180 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
10181 checking are included, but they do not yet have any effect. This
10182 section documents the intended facilities.
10184 @c FIXME remove warning when type/range code added
10186 Some languages are designed to guard you against making seemingly common
10187 errors through a series of compile- and run-time checks. These include
10188 checking the type of arguments to functions and operators, and making
10189 sure mathematical overflows are caught at run time. Checks such as
10190 these help to ensure a program's correctness once it has been compiled
10191 by eliminating type mismatches, and providing active checks for range
10192 errors when your program is running.
10194 @value{GDBN} can check for conditions like the above if you wish.
10195 Although @value{GDBN} does not check the statements in your program,
10196 it can check expressions entered directly into @value{GDBN} for
10197 evaluation via the @code{print} command, for example. As with the
10198 working language, @value{GDBN} can also decide whether or not to check
10199 automatically based on your program's source language.
10200 @xref{Supported Languages, ,Supported Languages}, for the default
10201 settings of supported languages.
10204 * Type Checking:: An overview of type checking
10205 * Range Checking:: An overview of range checking
10208 @cindex type checking
10209 @cindex checks, type
10210 @node Type Checking
10211 @subsection An Overview of Type Checking
10213 Some languages, such as Modula-2, are strongly typed, meaning that the
10214 arguments to operators and functions have to be of the correct type,
10215 otherwise an error occurs. These checks prevent type mismatch
10216 errors from ever causing any run-time problems. For example,
10224 The second example fails because the @code{CARDINAL} 1 is not
10225 type-compatible with the @code{REAL} 2.3.
10227 For the expressions you use in @value{GDBN} commands, you can tell the
10228 @value{GDBN} type checker to skip checking;
10229 to treat any mismatches as errors and abandon the expression;
10230 or to only issue warnings when type mismatches occur,
10231 but evaluate the expression anyway. When you choose the last of
10232 these, @value{GDBN} evaluates expressions like the second example above, but
10233 also issues a warning.
10235 Even if you turn type checking off, there may be other reasons
10236 related to type that prevent @value{GDBN} from evaluating an expression.
10237 For instance, @value{GDBN} does not know how to add an @code{int} and
10238 a @code{struct foo}. These particular type errors have nothing to do
10239 with the language in use, and usually arise from expressions, such as
10240 the one described above, which make little sense to evaluate anyway.
10242 Each language defines to what degree it is strict about type. For
10243 instance, both Modula-2 and C require the arguments to arithmetical
10244 operators to be numbers. In C, enumerated types and pointers can be
10245 represented as numbers, so that they are valid arguments to mathematical
10246 operators. @xref{Supported Languages, ,Supported Languages}, for further
10247 details on specific languages.
10249 @value{GDBN} provides some additional commands for controlling the type checker:
10251 @kindex set check type
10252 @kindex show check type
10254 @item set check type auto
10255 Set type checking on or off based on the current working language.
10256 @xref{Supported Languages, ,Supported Languages}, for the default settings for
10259 @item set check type on
10260 @itemx set check type off
10261 Set type checking on or off, overriding the default setting for the
10262 current working language. Issue a warning if the setting does not
10263 match the language default. If any type mismatches occur in
10264 evaluating an expression while type checking is on, @value{GDBN} prints a
10265 message and aborts evaluation of the expression.
10267 @item set check type warn
10268 Cause the type checker to issue warnings, but to always attempt to
10269 evaluate the expression. Evaluating the expression may still
10270 be impossible for other reasons. For example, @value{GDBN} cannot add
10271 numbers and structures.
10274 Show the current setting of the type checker, and whether or not @value{GDBN}
10275 is setting it automatically.
10278 @cindex range checking
10279 @cindex checks, range
10280 @node Range Checking
10281 @subsection An Overview of Range Checking
10283 In some languages (such as Modula-2), it is an error to exceed the
10284 bounds of a type; this is enforced with run-time checks. Such range
10285 checking is meant to ensure program correctness by making sure
10286 computations do not overflow, or indices on an array element access do
10287 not exceed the bounds of the array.
10289 For expressions you use in @value{GDBN} commands, you can tell
10290 @value{GDBN} to treat range errors in one of three ways: ignore them,
10291 always treat them as errors and abandon the expression, or issue
10292 warnings but evaluate the expression anyway.
10294 A range error can result from numerical overflow, from exceeding an
10295 array index bound, or when you type a constant that is not a member
10296 of any type. Some languages, however, do not treat overflows as an
10297 error. In many implementations of C, mathematical overflow causes the
10298 result to ``wrap around'' to lower values---for example, if @var{m} is
10299 the largest integer value, and @var{s} is the smallest, then
10302 @var{m} + 1 @result{} @var{s}
10305 This, too, is specific to individual languages, and in some cases
10306 specific to individual compilers or machines. @xref{Supported Languages, ,
10307 Supported Languages}, for further details on specific languages.
10309 @value{GDBN} provides some additional commands for controlling the range checker:
10311 @kindex set check range
10312 @kindex show check range
10314 @item set check range auto
10315 Set range checking on or off based on the current working language.
10316 @xref{Supported Languages, ,Supported Languages}, for the default settings for
10319 @item set check range on
10320 @itemx set check range off
10321 Set range checking on or off, overriding the default setting for the
10322 current working language. A warning is issued if the setting does not
10323 match the language default. If a range error occurs and range checking is on,
10324 then a message is printed and evaluation of the expression is aborted.
10326 @item set check range warn
10327 Output messages when the @value{GDBN} range checker detects a range error,
10328 but attempt to evaluate the expression anyway. Evaluating the
10329 expression may still be impossible for other reasons, such as accessing
10330 memory that the process does not own (a typical example from many Unix
10334 Show the current setting of the range checker, and whether or not it is
10335 being set automatically by @value{GDBN}.
10338 @node Supported Languages
10339 @section Supported Languages
10341 @value{GDBN} supports C, C@t{++}, Objective-C, Fortran, Java, Pascal,
10342 assembly, Modula-2, and Ada.
10343 @c This is false ...
10344 Some @value{GDBN} features may be used in expressions regardless of the
10345 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
10346 and the @samp{@{type@}addr} construct (@pxref{Expressions,
10347 ,Expressions}) can be used with the constructs of any supported
10350 The following sections detail to what degree each source language is
10351 supported by @value{GDBN}. These sections are not meant to be language
10352 tutorials or references, but serve only as a reference guide to what the
10353 @value{GDBN} expression parser accepts, and what input and output
10354 formats should look like for different languages. There are many good
10355 books written on each of these languages; please look to these for a
10356 language reference or tutorial.
10359 * C:: C and C@t{++}
10360 * Objective-C:: Objective-C
10361 * Fortran:: Fortran
10363 * Modula-2:: Modula-2
10368 @subsection C and C@t{++}
10370 @cindex C and C@t{++}
10371 @cindex expressions in C or C@t{++}
10373 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
10374 to both languages. Whenever this is the case, we discuss those languages
10378 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
10379 @cindex @sc{gnu} C@t{++}
10380 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
10381 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
10382 effectively, you must compile your C@t{++} programs with a supported
10383 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
10384 compiler (@code{aCC}).
10386 For best results when using @sc{gnu} C@t{++}, use the DWARF 2 debugging
10387 format; if it doesn't work on your system, try the stabs+ debugging
10388 format. You can select those formats explicitly with the @code{g++}
10389 command-line options @option{-gdwarf-2} and @option{-gstabs+}.
10390 @xref{Debugging Options,,Options for Debugging Your Program or GCC,
10391 gcc.info, Using the @sc{gnu} Compiler Collection (GCC)}.
10394 * C Operators:: C and C@t{++} operators
10395 * C Constants:: C and C@t{++} constants
10396 * C Plus Plus Expressions:: C@t{++} expressions
10397 * C Defaults:: Default settings for C and C@t{++}
10398 * C Checks:: C and C@t{++} type and range checks
10399 * Debugging C:: @value{GDBN} and C
10400 * Debugging C Plus Plus:: @value{GDBN} features for C@t{++}
10401 * Decimal Floating Point:: Numbers in Decimal Floating Point format
10405 @subsubsection C and C@t{++} Operators
10407 @cindex C and C@t{++} operators
10409 Operators must be defined on values of specific types. For instance,
10410 @code{+} is defined on numbers, but not on structures. Operators are
10411 often defined on groups of types.
10413 For the purposes of C and C@t{++}, the following definitions hold:
10418 @emph{Integral types} include @code{int} with any of its storage-class
10419 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
10422 @emph{Floating-point types} include @code{float}, @code{double}, and
10423 @code{long double} (if supported by the target platform).
10426 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
10429 @emph{Scalar types} include all of the above.
10434 The following operators are supported. They are listed here
10435 in order of increasing precedence:
10439 The comma or sequencing operator. Expressions in a comma-separated list
10440 are evaluated from left to right, with the result of the entire
10441 expression being the last expression evaluated.
10444 Assignment. The value of an assignment expression is the value
10445 assigned. Defined on scalar types.
10448 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
10449 and translated to @w{@code{@var{a} = @var{a op b}}}.
10450 @w{@code{@var{op}=}} and @code{=} have the same precedence.
10451 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
10452 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
10455 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
10456 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
10460 Logical @sc{or}. Defined on integral types.
10463 Logical @sc{and}. Defined on integral types.
10466 Bitwise @sc{or}. Defined on integral types.
10469 Bitwise exclusive-@sc{or}. Defined on integral types.
10472 Bitwise @sc{and}. Defined on integral types.
10475 Equality and inequality. Defined on scalar types. The value of these
10476 expressions is 0 for false and non-zero for true.
10478 @item <@r{, }>@r{, }<=@r{, }>=
10479 Less than, greater than, less than or equal, greater than or equal.
10480 Defined on scalar types. The value of these expressions is 0 for false
10481 and non-zero for true.
10484 left shift, and right shift. Defined on integral types.
10487 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
10490 Addition and subtraction. Defined on integral types, floating-point types and
10493 @item *@r{, }/@r{, }%
10494 Multiplication, division, and modulus. Multiplication and division are
10495 defined on integral and floating-point types. Modulus is defined on
10499 Increment and decrement. When appearing before a variable, the
10500 operation is performed before the variable is used in an expression;
10501 when appearing after it, the variable's value is used before the
10502 operation takes place.
10505 Pointer dereferencing. Defined on pointer types. Same precedence as
10509 Address operator. Defined on variables. Same precedence as @code{++}.
10511 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
10512 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
10513 to examine the address
10514 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
10518 Negative. Defined on integral and floating-point types. Same
10519 precedence as @code{++}.
10522 Logical negation. Defined on integral types. Same precedence as
10526 Bitwise complement operator. Defined on integral types. Same precedence as
10531 Structure member, and pointer-to-structure member. For convenience,
10532 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
10533 pointer based on the stored type information.
10534 Defined on @code{struct} and @code{union} data.
10537 Dereferences of pointers to members.
10540 Array indexing. @code{@var{a}[@var{i}]} is defined as
10541 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
10544 Function parameter list. Same precedence as @code{->}.
10547 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
10548 and @code{class} types.
10551 Doubled colons also represent the @value{GDBN} scope operator
10552 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
10556 If an operator is redefined in the user code, @value{GDBN} usually
10557 attempts to invoke the redefined version instead of using the operator's
10558 predefined meaning.
10561 @subsubsection C and C@t{++} Constants
10563 @cindex C and C@t{++} constants
10565 @value{GDBN} allows you to express the constants of C and C@t{++} in the
10570 Integer constants are a sequence of digits. Octal constants are
10571 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
10572 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
10573 @samp{l}, specifying that the constant should be treated as a
10577 Floating point constants are a sequence of digits, followed by a decimal
10578 point, followed by a sequence of digits, and optionally followed by an
10579 exponent. An exponent is of the form:
10580 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
10581 sequence of digits. The @samp{+} is optional for positive exponents.
10582 A floating-point constant may also end with a letter @samp{f} or
10583 @samp{F}, specifying that the constant should be treated as being of
10584 the @code{float} (as opposed to the default @code{double}) type; or with
10585 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
10589 Enumerated constants consist of enumerated identifiers, or their
10590 integral equivalents.
10593 Character constants are a single character surrounded by single quotes
10594 (@code{'}), or a number---the ordinal value of the corresponding character
10595 (usually its @sc{ascii} value). Within quotes, the single character may
10596 be represented by a letter or by @dfn{escape sequences}, which are of
10597 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
10598 of the character's ordinal value; or of the form @samp{\@var{x}}, where
10599 @samp{@var{x}} is a predefined special character---for example,
10600 @samp{\n} for newline.
10603 String constants are a sequence of character constants surrounded by
10604 double quotes (@code{"}). Any valid character constant (as described
10605 above) may appear. Double quotes within the string must be preceded by
10606 a backslash, so for instance @samp{"a\"b'c"} is a string of five
10610 Pointer constants are an integral value. You can also write pointers
10611 to constants using the C operator @samp{&}.
10614 Array constants are comma-separated lists surrounded by braces @samp{@{}
10615 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
10616 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
10617 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
10620 @node C Plus Plus Expressions
10621 @subsubsection C@t{++} Expressions
10623 @cindex expressions in C@t{++}
10624 @value{GDBN} expression handling can interpret most C@t{++} expressions.
10626 @cindex debugging C@t{++} programs
10627 @cindex C@t{++} compilers
10628 @cindex debug formats and C@t{++}
10629 @cindex @value{NGCC} and C@t{++}
10631 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
10632 proper compiler and the proper debug format. Currently, @value{GDBN}
10633 works best when debugging C@t{++} code that is compiled with
10634 @value{NGCC} 2.95.3 or with @value{NGCC} 3.1 or newer, using the options
10635 @option{-gdwarf-2} or @option{-gstabs+}. DWARF 2 is preferred over
10636 stabs+. Most configurations of @value{NGCC} emit either DWARF 2 or
10637 stabs+ as their default debug format, so you usually don't need to
10638 specify a debug format explicitly. Other compilers and/or debug formats
10639 are likely to work badly or not at all when using @value{GDBN} to debug
10645 @cindex member functions
10647 Member function calls are allowed; you can use expressions like
10650 count = aml->GetOriginal(x, y)
10653 @vindex this@r{, inside C@t{++} member functions}
10654 @cindex namespace in C@t{++}
10656 While a member function is active (in the selected stack frame), your
10657 expressions have the same namespace available as the member function;
10658 that is, @value{GDBN} allows implicit references to the class instance
10659 pointer @code{this} following the same rules as C@t{++}.
10661 @cindex call overloaded functions
10662 @cindex overloaded functions, calling
10663 @cindex type conversions in C@t{++}
10665 You can call overloaded functions; @value{GDBN} resolves the function
10666 call to the right definition, with some restrictions. @value{GDBN} does not
10667 perform overload resolution involving user-defined type conversions,
10668 calls to constructors, or instantiations of templates that do not exist
10669 in the program. It also cannot handle ellipsis argument lists or
10672 It does perform integral conversions and promotions, floating-point
10673 promotions, arithmetic conversions, pointer conversions, conversions of
10674 class objects to base classes, and standard conversions such as those of
10675 functions or arrays to pointers; it requires an exact match on the
10676 number of function arguments.
10678 Overload resolution is always performed, unless you have specified
10679 @code{set overload-resolution off}. @xref{Debugging C Plus Plus,
10680 ,@value{GDBN} Features for C@t{++}}.
10682 You must specify @code{set overload-resolution off} in order to use an
10683 explicit function signature to call an overloaded function, as in
10685 p 'foo(char,int)'('x', 13)
10688 The @value{GDBN} command-completion facility can simplify this;
10689 see @ref{Completion, ,Command Completion}.
10691 @cindex reference declarations
10693 @value{GDBN} understands variables declared as C@t{++} references; you can use
10694 them in expressions just as you do in C@t{++} source---they are automatically
10697 In the parameter list shown when @value{GDBN} displays a frame, the values of
10698 reference variables are not displayed (unlike other variables); this
10699 avoids clutter, since references are often used for large structures.
10700 The @emph{address} of a reference variable is always shown, unless
10701 you have specified @samp{set print address off}.
10704 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
10705 expressions can use it just as expressions in your program do. Since
10706 one scope may be defined in another, you can use @code{::} repeatedly if
10707 necessary, for example in an expression like
10708 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
10709 resolving name scope by reference to source files, in both C and C@t{++}
10710 debugging (@pxref{Variables, ,Program Variables}).
10713 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
10714 calling virtual functions correctly, printing out virtual bases of
10715 objects, calling functions in a base subobject, casting objects, and
10716 invoking user-defined operators.
10719 @subsubsection C and C@t{++} Defaults
10721 @cindex C and C@t{++} defaults
10723 If you allow @value{GDBN} to set type and range checking automatically, they
10724 both default to @code{off} whenever the working language changes to
10725 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
10726 selects the working language.
10728 If you allow @value{GDBN} to set the language automatically, it
10729 recognizes source files whose names end with @file{.c}, @file{.C}, or
10730 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
10731 these files, it sets the working language to C or C@t{++}.
10732 @xref{Automatically, ,Having @value{GDBN} Infer the Source Language},
10733 for further details.
10735 @c Type checking is (a) primarily motivated by Modula-2, and (b)
10736 @c unimplemented. If (b) changes, it might make sense to let this node
10737 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
10740 @subsubsection C and C@t{++} Type and Range Checks
10742 @cindex C and C@t{++} checks
10744 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
10745 is not used. However, if you turn type checking on, @value{GDBN}
10746 considers two variables type equivalent if:
10750 The two variables are structured and have the same structure, union, or
10754 The two variables have the same type name, or types that have been
10755 declared equivalent through @code{typedef}.
10758 @c leaving this out because neither J Gilmore nor R Pesch understand it.
10761 The two @code{struct}, @code{union}, or @code{enum} variables are
10762 declared in the same declaration. (Note: this may not be true for all C
10767 Range checking, if turned on, is done on mathematical operations. Array
10768 indices are not checked, since they are often used to index a pointer
10769 that is not itself an array.
10772 @subsubsection @value{GDBN} and C
10774 The @code{set print union} and @code{show print union} commands apply to
10775 the @code{union} type. When set to @samp{on}, any @code{union} that is
10776 inside a @code{struct} or @code{class} is also printed. Otherwise, it
10777 appears as @samp{@{...@}}.
10779 The @code{@@} operator aids in the debugging of dynamic arrays, formed
10780 with pointers and a memory allocation function. @xref{Expressions,
10783 @node Debugging C Plus Plus
10784 @subsubsection @value{GDBN} Features for C@t{++}
10786 @cindex commands for C@t{++}
10788 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
10789 designed specifically for use with C@t{++}. Here is a summary:
10792 @cindex break in overloaded functions
10793 @item @r{breakpoint menus}
10794 When you want a breakpoint in a function whose name is overloaded,
10795 @value{GDBN} has the capability to display a menu of possible breakpoint
10796 locations to help you specify which function definition you want.
10797 @xref{Ambiguous Expressions,,Ambiguous Expressions}.
10799 @cindex overloading in C@t{++}
10800 @item rbreak @var{regex}
10801 Setting breakpoints using regular expressions is helpful for setting
10802 breakpoints on overloaded functions that are not members of any special
10804 @xref{Set Breaks, ,Setting Breakpoints}.
10806 @cindex C@t{++} exception handling
10809 Debug C@t{++} exception handling using these commands. @xref{Set
10810 Catchpoints, , Setting Catchpoints}.
10812 @cindex inheritance
10813 @item ptype @var{typename}
10814 Print inheritance relationships as well as other information for type
10816 @xref{Symbols, ,Examining the Symbol Table}.
10818 @cindex C@t{++} symbol display
10819 @item set print demangle
10820 @itemx show print demangle
10821 @itemx set print asm-demangle
10822 @itemx show print asm-demangle
10823 Control whether C@t{++} symbols display in their source form, both when
10824 displaying code as C@t{++} source and when displaying disassemblies.
10825 @xref{Print Settings, ,Print Settings}.
10827 @item set print object
10828 @itemx show print object
10829 Choose whether to print derived (actual) or declared types of objects.
10830 @xref{Print Settings, ,Print Settings}.
10832 @item set print vtbl
10833 @itemx show print vtbl
10834 Control the format for printing virtual function tables.
10835 @xref{Print Settings, ,Print Settings}.
10836 (The @code{vtbl} commands do not work on programs compiled with the HP
10837 ANSI C@t{++} compiler (@code{aCC}).)
10839 @kindex set overload-resolution
10840 @cindex overloaded functions, overload resolution
10841 @item set overload-resolution on
10842 Enable overload resolution for C@t{++} expression evaluation. The default
10843 is on. For overloaded functions, @value{GDBN} evaluates the arguments
10844 and searches for a function whose signature matches the argument types,
10845 using the standard C@t{++} conversion rules (see @ref{C Plus Plus
10846 Expressions, ,C@t{++} Expressions}, for details).
10847 If it cannot find a match, it emits a message.
10849 @item set overload-resolution off
10850 Disable overload resolution for C@t{++} expression evaluation. For
10851 overloaded functions that are not class member functions, @value{GDBN}
10852 chooses the first function of the specified name that it finds in the
10853 symbol table, whether or not its arguments are of the correct type. For
10854 overloaded functions that are class member functions, @value{GDBN}
10855 searches for a function whose signature @emph{exactly} matches the
10858 @kindex show overload-resolution
10859 @item show overload-resolution
10860 Show the current setting of overload resolution.
10862 @item @r{Overloaded symbol names}
10863 You can specify a particular definition of an overloaded symbol, using
10864 the same notation that is used to declare such symbols in C@t{++}: type
10865 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
10866 also use the @value{GDBN} command-line word completion facilities to list the
10867 available choices, or to finish the type list for you.
10868 @xref{Completion,, Command Completion}, for details on how to do this.
10871 @node Decimal Floating Point
10872 @subsubsection Decimal Floating Point format
10873 @cindex decimal floating point format
10875 @value{GDBN} can examine, set and perform computations with numbers in
10876 decimal floating point format, which in the C language correspond to the
10877 @code{_Decimal32}, @code{_Decimal64} and @code{_Decimal128} types as
10878 specified by the extension to support decimal floating-point arithmetic.
10880 There are two encodings in use, depending on the architecture: BID (Binary
10881 Integer Decimal) for x86 and x86-64, and DPD (Densely Packed Decimal) for
10882 PowerPC. @value{GDBN} will use the appropriate encoding for the configured
10885 Because of a limitation in @file{libdecnumber}, the library used by @value{GDBN}
10886 to manipulate decimal floating point numbers, it is not possible to convert
10887 (using a cast, for example) integers wider than 32-bit to decimal float.
10889 In addition, in order to imitate @value{GDBN}'s behaviour with binary floating
10890 point computations, error checking in decimal float operations ignores
10891 underflow, overflow and divide by zero exceptions.
10893 In the PowerPC architecture, @value{GDBN} provides a set of pseudo-registers
10894 to inspect @code{_Decimal128} values stored in floating point registers.
10895 See @ref{PowerPC,,PowerPC} for more details.
10898 @subsection Objective-C
10900 @cindex Objective-C
10901 This section provides information about some commands and command
10902 options that are useful for debugging Objective-C code. See also
10903 @ref{Symbols, info classes}, and @ref{Symbols, info selectors}, for a
10904 few more commands specific to Objective-C support.
10907 * Method Names in Commands::
10908 * The Print Command with Objective-C::
10911 @node Method Names in Commands
10912 @subsubsection Method Names in Commands
10914 The following commands have been extended to accept Objective-C method
10915 names as line specifications:
10917 @kindex clear@r{, and Objective-C}
10918 @kindex break@r{, and Objective-C}
10919 @kindex info line@r{, and Objective-C}
10920 @kindex jump@r{, and Objective-C}
10921 @kindex list@r{, and Objective-C}
10925 @item @code{info line}
10930 A fully qualified Objective-C method name is specified as
10933 -[@var{Class} @var{methodName}]
10936 where the minus sign is used to indicate an instance method and a
10937 plus sign (not shown) is used to indicate a class method. The class
10938 name @var{Class} and method name @var{methodName} are enclosed in
10939 brackets, similar to the way messages are specified in Objective-C
10940 source code. For example, to set a breakpoint at the @code{create}
10941 instance method of class @code{Fruit} in the program currently being
10945 break -[Fruit create]
10948 To list ten program lines around the @code{initialize} class method,
10952 list +[NSText initialize]
10955 In the current version of @value{GDBN}, the plus or minus sign is
10956 required. In future versions of @value{GDBN}, the plus or minus
10957 sign will be optional, but you can use it to narrow the search. It
10958 is also possible to specify just a method name:
10964 You must specify the complete method name, including any colons. If
10965 your program's source files contain more than one @code{create} method,
10966 you'll be presented with a numbered list of classes that implement that
10967 method. Indicate your choice by number, or type @samp{0} to exit if
10970 As another example, to clear a breakpoint established at the
10971 @code{makeKeyAndOrderFront:} method of the @code{NSWindow} class, enter:
10974 clear -[NSWindow makeKeyAndOrderFront:]
10977 @node The Print Command with Objective-C
10978 @subsubsection The Print Command With Objective-C
10979 @cindex Objective-C, print objects
10980 @kindex print-object
10981 @kindex po @r{(@code{print-object})}
10983 The print command has also been extended to accept methods. For example:
10986 print -[@var{object} hash]
10989 @cindex print an Objective-C object description
10990 @cindex @code{_NSPrintForDebugger}, and printing Objective-C objects
10992 will tell @value{GDBN} to send the @code{hash} message to @var{object}
10993 and print the result. Also, an additional command has been added,
10994 @code{print-object} or @code{po} for short, which is meant to print
10995 the description of an object. However, this command may only work
10996 with certain Objective-C libraries that have a particular hook
10997 function, @code{_NSPrintForDebugger}, defined.
11000 @subsection Fortran
11001 @cindex Fortran-specific support in @value{GDBN}
11003 @value{GDBN} can be used to debug programs written in Fortran, but it
11004 currently supports only the features of Fortran 77 language.
11006 @cindex trailing underscore, in Fortran symbols
11007 Some Fortran compilers (@sc{gnu} Fortran 77 and Fortran 95 compilers
11008 among them) append an underscore to the names of variables and
11009 functions. When you debug programs compiled by those compilers, you
11010 will need to refer to variables and functions with a trailing
11014 * Fortran Operators:: Fortran operators and expressions
11015 * Fortran Defaults:: Default settings for Fortran
11016 * Special Fortran Commands:: Special @value{GDBN} commands for Fortran
11019 @node Fortran Operators
11020 @subsubsection Fortran Operators and Expressions
11022 @cindex Fortran operators and expressions
11024 Operators must be defined on values of specific types. For instance,
11025 @code{+} is defined on numbers, but not on characters or other non-
11026 arithmetic types. Operators are often defined on groups of types.
11030 The exponentiation operator. It raises the first operand to the power
11034 The range operator. Normally used in the form of array(low:high) to
11035 represent a section of array.
11038 The access component operator. Normally used to access elements in derived
11039 types. Also suitable for unions. As unions aren't part of regular Fortran,
11040 this can only happen when accessing a register that uses a gdbarch-defined
11044 @node Fortran Defaults
11045 @subsubsection Fortran Defaults
11047 @cindex Fortran Defaults
11049 Fortran symbols are usually case-insensitive, so @value{GDBN} by
11050 default uses case-insensitive matches for Fortran symbols. You can
11051 change that with the @samp{set case-insensitive} command, see
11052 @ref{Symbols}, for the details.
11054 @node Special Fortran Commands
11055 @subsubsection Special Fortran Commands
11057 @cindex Special Fortran commands
11059 @value{GDBN} has some commands to support Fortran-specific features,
11060 such as displaying common blocks.
11063 @cindex @code{COMMON} blocks, Fortran
11064 @kindex info common
11065 @item info common @r{[}@var{common-name}@r{]}
11066 This command prints the values contained in the Fortran @code{COMMON}
11067 block whose name is @var{common-name}. With no argument, the names of
11068 all @code{COMMON} blocks visible at the current program location are
11075 @cindex Pascal support in @value{GDBN}, limitations
11076 Debugging Pascal programs which use sets, subranges, file variables, or
11077 nested functions does not currently work. @value{GDBN} does not support
11078 entering expressions, printing values, or similar features using Pascal
11081 The Pascal-specific command @code{set print pascal_static-members}
11082 controls whether static members of Pascal objects are displayed.
11083 @xref{Print Settings, pascal_static-members}.
11086 @subsection Modula-2
11088 @cindex Modula-2, @value{GDBN} support
11090 The extensions made to @value{GDBN} to support Modula-2 only support
11091 output from the @sc{gnu} Modula-2 compiler (which is currently being
11092 developed). Other Modula-2 compilers are not currently supported, and
11093 attempting to debug executables produced by them is most likely
11094 to give an error as @value{GDBN} reads in the executable's symbol
11097 @cindex expressions in Modula-2
11099 * M2 Operators:: Built-in operators
11100 * Built-In Func/Proc:: Built-in functions and procedures
11101 * M2 Constants:: Modula-2 constants
11102 * M2 Types:: Modula-2 types
11103 * M2 Defaults:: Default settings for Modula-2
11104 * Deviations:: Deviations from standard Modula-2
11105 * M2 Checks:: Modula-2 type and range checks
11106 * M2 Scope:: The scope operators @code{::} and @code{.}
11107 * GDB/M2:: @value{GDBN} and Modula-2
11111 @subsubsection Operators
11112 @cindex Modula-2 operators
11114 Operators must be defined on values of specific types. For instance,
11115 @code{+} is defined on numbers, but not on structures. Operators are
11116 often defined on groups of types. For the purposes of Modula-2, the
11117 following definitions hold:
11122 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
11126 @emph{Character types} consist of @code{CHAR} and its subranges.
11129 @emph{Floating-point types} consist of @code{REAL}.
11132 @emph{Pointer types} consist of anything declared as @code{POINTER TO
11136 @emph{Scalar types} consist of all of the above.
11139 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
11142 @emph{Boolean types} consist of @code{BOOLEAN}.
11146 The following operators are supported, and appear in order of
11147 increasing precedence:
11151 Function argument or array index separator.
11154 Assignment. The value of @var{var} @code{:=} @var{value} is
11158 Less than, greater than on integral, floating-point, or enumerated
11162 Less than or equal to, greater than or equal to
11163 on integral, floating-point and enumerated types, or set inclusion on
11164 set types. Same precedence as @code{<}.
11166 @item =@r{, }<>@r{, }#
11167 Equality and two ways of expressing inequality, valid on scalar types.
11168 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
11169 available for inequality, since @code{#} conflicts with the script
11173 Set membership. Defined on set types and the types of their members.
11174 Same precedence as @code{<}.
11177 Boolean disjunction. Defined on boolean types.
11180 Boolean conjunction. Defined on boolean types.
11183 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
11186 Addition and subtraction on integral and floating-point types, or union
11187 and difference on set types.
11190 Multiplication on integral and floating-point types, or set intersection
11194 Division on floating-point types, or symmetric set difference on set
11195 types. Same precedence as @code{*}.
11198 Integer division and remainder. Defined on integral types. Same
11199 precedence as @code{*}.
11202 Negative. Defined on @code{INTEGER} and @code{REAL} data.
11205 Pointer dereferencing. Defined on pointer types.
11208 Boolean negation. Defined on boolean types. Same precedence as
11212 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
11213 precedence as @code{^}.
11216 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
11219 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
11223 @value{GDBN} and Modula-2 scope operators.
11227 @emph{Warning:} Set expressions and their operations are not yet supported, so @value{GDBN}
11228 treats the use of the operator @code{IN}, or the use of operators
11229 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
11230 @code{<=}, and @code{>=} on sets as an error.
11234 @node Built-In Func/Proc
11235 @subsubsection Built-in Functions and Procedures
11236 @cindex Modula-2 built-ins
11238 Modula-2 also makes available several built-in procedures and functions.
11239 In describing these, the following metavariables are used:
11244 represents an @code{ARRAY} variable.
11247 represents a @code{CHAR} constant or variable.
11250 represents a variable or constant of integral type.
11253 represents an identifier that belongs to a set. Generally used in the
11254 same function with the metavariable @var{s}. The type of @var{s} should
11255 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
11258 represents a variable or constant of integral or floating-point type.
11261 represents a variable or constant of floating-point type.
11267 represents a variable.
11270 represents a variable or constant of one of many types. See the
11271 explanation of the function for details.
11274 All Modula-2 built-in procedures also return a result, described below.
11278 Returns the absolute value of @var{n}.
11281 If @var{c} is a lower case letter, it returns its upper case
11282 equivalent, otherwise it returns its argument.
11285 Returns the character whose ordinal value is @var{i}.
11288 Decrements the value in the variable @var{v} by one. Returns the new value.
11290 @item DEC(@var{v},@var{i})
11291 Decrements the value in the variable @var{v} by @var{i}. Returns the
11294 @item EXCL(@var{m},@var{s})
11295 Removes the element @var{m} from the set @var{s}. Returns the new
11298 @item FLOAT(@var{i})
11299 Returns the floating point equivalent of the integer @var{i}.
11301 @item HIGH(@var{a})
11302 Returns the index of the last member of @var{a}.
11305 Increments the value in the variable @var{v} by one. Returns the new value.
11307 @item INC(@var{v},@var{i})
11308 Increments the value in the variable @var{v} by @var{i}. Returns the
11311 @item INCL(@var{m},@var{s})
11312 Adds the element @var{m} to the set @var{s} if it is not already
11313 there. Returns the new set.
11316 Returns the maximum value of the type @var{t}.
11319 Returns the minimum value of the type @var{t}.
11322 Returns boolean TRUE if @var{i} is an odd number.
11325 Returns the ordinal value of its argument. For example, the ordinal
11326 value of a character is its @sc{ascii} value (on machines supporting the
11327 @sc{ascii} character set). @var{x} must be of an ordered type, which include
11328 integral, character and enumerated types.
11330 @item SIZE(@var{x})
11331 Returns the size of its argument. @var{x} can be a variable or a type.
11333 @item TRUNC(@var{r})
11334 Returns the integral part of @var{r}.
11336 @item TSIZE(@var{x})
11337 Returns the size of its argument. @var{x} can be a variable or a type.
11339 @item VAL(@var{t},@var{i})
11340 Returns the member of the type @var{t} whose ordinal value is @var{i}.
11344 @emph{Warning:} Sets and their operations are not yet supported, so
11345 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
11349 @cindex Modula-2 constants
11351 @subsubsection Constants
11353 @value{GDBN} allows you to express the constants of Modula-2 in the following
11359 Integer constants are simply a sequence of digits. When used in an
11360 expression, a constant is interpreted to be type-compatible with the
11361 rest of the expression. Hexadecimal integers are specified by a
11362 trailing @samp{H}, and octal integers by a trailing @samp{B}.
11365 Floating point constants appear as a sequence of digits, followed by a
11366 decimal point and another sequence of digits. An optional exponent can
11367 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
11368 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
11369 digits of the floating point constant must be valid decimal (base 10)
11373 Character constants consist of a single character enclosed by a pair of
11374 like quotes, either single (@code{'}) or double (@code{"}). They may
11375 also be expressed by their ordinal value (their @sc{ascii} value, usually)
11376 followed by a @samp{C}.
11379 String constants consist of a sequence of characters enclosed by a
11380 pair of like quotes, either single (@code{'}) or double (@code{"}).
11381 Escape sequences in the style of C are also allowed. @xref{C
11382 Constants, ,C and C@t{++} Constants}, for a brief explanation of escape
11386 Enumerated constants consist of an enumerated identifier.
11389 Boolean constants consist of the identifiers @code{TRUE} and
11393 Pointer constants consist of integral values only.
11396 Set constants are not yet supported.
11400 @subsubsection Modula-2 Types
11401 @cindex Modula-2 types
11403 Currently @value{GDBN} can print the following data types in Modula-2
11404 syntax: array types, record types, set types, pointer types, procedure
11405 types, enumerated types, subrange types and base types. You can also
11406 print the contents of variables declared using these type.
11407 This section gives a number of simple source code examples together with
11408 sample @value{GDBN} sessions.
11410 The first example contains the following section of code:
11419 and you can request @value{GDBN} to interrogate the type and value of
11420 @code{r} and @code{s}.
11423 (@value{GDBP}) print s
11425 (@value{GDBP}) ptype s
11427 (@value{GDBP}) print r
11429 (@value{GDBP}) ptype r
11434 Likewise if your source code declares @code{s} as:
11438 s: SET ['A'..'Z'] ;
11442 then you may query the type of @code{s} by:
11445 (@value{GDBP}) ptype s
11446 type = SET ['A'..'Z']
11450 Note that at present you cannot interactively manipulate set
11451 expressions using the debugger.
11453 The following example shows how you might declare an array in Modula-2
11454 and how you can interact with @value{GDBN} to print its type and contents:
11458 s: ARRAY [-10..10] OF CHAR ;
11462 (@value{GDBP}) ptype s
11463 ARRAY [-10..10] OF CHAR
11466 Note that the array handling is not yet complete and although the type
11467 is printed correctly, expression handling still assumes that all
11468 arrays have a lower bound of zero and not @code{-10} as in the example
11471 Here are some more type related Modula-2 examples:
11475 colour = (blue, red, yellow, green) ;
11476 t = [blue..yellow] ;
11484 The @value{GDBN} interaction shows how you can query the data type
11485 and value of a variable.
11488 (@value{GDBP}) print s
11490 (@value{GDBP}) ptype t
11491 type = [blue..yellow]
11495 In this example a Modula-2 array is declared and its contents
11496 displayed. Observe that the contents are written in the same way as
11497 their @code{C} counterparts.
11501 s: ARRAY [1..5] OF CARDINAL ;
11507 (@value{GDBP}) print s
11508 $1 = @{1, 0, 0, 0, 0@}
11509 (@value{GDBP}) ptype s
11510 type = ARRAY [1..5] OF CARDINAL
11513 The Modula-2 language interface to @value{GDBN} also understands
11514 pointer types as shown in this example:
11518 s: POINTER TO ARRAY [1..5] OF CARDINAL ;
11525 and you can request that @value{GDBN} describes the type of @code{s}.
11528 (@value{GDBP}) ptype s
11529 type = POINTER TO ARRAY [1..5] OF CARDINAL
11532 @value{GDBN} handles compound types as we can see in this example.
11533 Here we combine array types, record types, pointer types and subrange
11544 myarray = ARRAY myrange OF CARDINAL ;
11545 myrange = [-2..2] ;
11547 s: POINTER TO ARRAY myrange OF foo ;
11551 and you can ask @value{GDBN} to describe the type of @code{s} as shown
11555 (@value{GDBP}) ptype s
11556 type = POINTER TO ARRAY [-2..2] OF foo = RECORD
11559 f3 : ARRAY [-2..2] OF CARDINAL;
11564 @subsubsection Modula-2 Defaults
11565 @cindex Modula-2 defaults
11567 If type and range checking are set automatically by @value{GDBN}, they
11568 both default to @code{on} whenever the working language changes to
11569 Modula-2. This happens regardless of whether you or @value{GDBN}
11570 selected the working language.
11572 If you allow @value{GDBN} to set the language automatically, then entering
11573 code compiled from a file whose name ends with @file{.mod} sets the
11574 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN}
11575 Infer the Source Language}, for further details.
11578 @subsubsection Deviations from Standard Modula-2
11579 @cindex Modula-2, deviations from
11581 A few changes have been made to make Modula-2 programs easier to debug.
11582 This is done primarily via loosening its type strictness:
11586 Unlike in standard Modula-2, pointer constants can be formed by
11587 integers. This allows you to modify pointer variables during
11588 debugging. (In standard Modula-2, the actual address contained in a
11589 pointer variable is hidden from you; it can only be modified
11590 through direct assignment to another pointer variable or expression that
11591 returned a pointer.)
11594 C escape sequences can be used in strings and characters to represent
11595 non-printable characters. @value{GDBN} prints out strings with these
11596 escape sequences embedded. Single non-printable characters are
11597 printed using the @samp{CHR(@var{nnn})} format.
11600 The assignment operator (@code{:=}) returns the value of its right-hand
11604 All built-in procedures both modify @emph{and} return their argument.
11608 @subsubsection Modula-2 Type and Range Checks
11609 @cindex Modula-2 checks
11612 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
11615 @c FIXME remove warning when type/range checks added
11617 @value{GDBN} considers two Modula-2 variables type equivalent if:
11621 They are of types that have been declared equivalent via a @code{TYPE
11622 @var{t1} = @var{t2}} statement
11625 They have been declared on the same line. (Note: This is true of the
11626 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
11629 As long as type checking is enabled, any attempt to combine variables
11630 whose types are not equivalent is an error.
11632 Range checking is done on all mathematical operations, assignment, array
11633 index bounds, and all built-in functions and procedures.
11636 @subsubsection The Scope Operators @code{::} and @code{.}
11638 @cindex @code{.}, Modula-2 scope operator
11639 @cindex colon, doubled as scope operator
11641 @vindex colon-colon@r{, in Modula-2}
11642 @c Info cannot handle :: but TeX can.
11645 @vindex ::@r{, in Modula-2}
11648 There are a few subtle differences between the Modula-2 scope operator
11649 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
11654 @var{module} . @var{id}
11655 @var{scope} :: @var{id}
11659 where @var{scope} is the name of a module or a procedure,
11660 @var{module} the name of a module, and @var{id} is any declared
11661 identifier within your program, except another module.
11663 Using the @code{::} operator makes @value{GDBN} search the scope
11664 specified by @var{scope} for the identifier @var{id}. If it is not
11665 found in the specified scope, then @value{GDBN} searches all scopes
11666 enclosing the one specified by @var{scope}.
11668 Using the @code{.} operator makes @value{GDBN} search the current scope for
11669 the identifier specified by @var{id} that was imported from the
11670 definition module specified by @var{module}. With this operator, it is
11671 an error if the identifier @var{id} was not imported from definition
11672 module @var{module}, or if @var{id} is not an identifier in
11676 @subsubsection @value{GDBN} and Modula-2
11678 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
11679 Five subcommands of @code{set print} and @code{show print} apply
11680 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
11681 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
11682 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
11683 analogue in Modula-2.
11685 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
11686 with any language, is not useful with Modula-2. Its
11687 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
11688 created in Modula-2 as they can in C or C@t{++}. However, because an
11689 address can be specified by an integral constant, the construct
11690 @samp{@{@var{type}@}@var{adrexp}} is still useful.
11692 @cindex @code{#} in Modula-2
11693 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
11694 interpreted as the beginning of a comment. Use @code{<>} instead.
11700 The extensions made to @value{GDBN} for Ada only support
11701 output from the @sc{gnu} Ada (GNAT) compiler.
11702 Other Ada compilers are not currently supported, and
11703 attempting to debug executables produced by them is most likely
11707 @cindex expressions in Ada
11709 * Ada Mode Intro:: General remarks on the Ada syntax
11710 and semantics supported by Ada mode
11712 * Omissions from Ada:: Restrictions on the Ada expression syntax.
11713 * Additions to Ada:: Extensions of the Ada expression syntax.
11714 * Stopping Before Main Program:: Debugging the program during elaboration.
11715 * Ada Tasks:: Listing and setting breakpoints in tasks.
11716 * Ada Tasks and Core Files:: Tasking Support when Debugging Core Files
11717 * Ada Glitches:: Known peculiarities of Ada mode.
11720 @node Ada Mode Intro
11721 @subsubsection Introduction
11722 @cindex Ada mode, general
11724 The Ada mode of @value{GDBN} supports a fairly large subset of Ada expression
11725 syntax, with some extensions.
11726 The philosophy behind the design of this subset is
11730 That @value{GDBN} should provide basic literals and access to operations for
11731 arithmetic, dereferencing, field selection, indexing, and subprogram calls,
11732 leaving more sophisticated computations to subprograms written into the
11733 program (which therefore may be called from @value{GDBN}).
11736 That type safety and strict adherence to Ada language restrictions
11737 are not particularly important to the @value{GDBN} user.
11740 That brevity is important to the @value{GDBN} user.
11743 Thus, for brevity, the debugger acts as if all names declared in
11744 user-written packages are directly visible, even if they are not visible
11745 according to Ada rules, thus making it unnecessary to fully qualify most
11746 names with their packages, regardless of context. Where this causes
11747 ambiguity, @value{GDBN} asks the user's intent.
11749 The debugger will start in Ada mode if it detects an Ada main program.
11750 As for other languages, it will enter Ada mode when stopped in a program that
11751 was translated from an Ada source file.
11753 While in Ada mode, you may use `@t{--}' for comments. This is useful
11754 mostly for documenting command files. The standard @value{GDBN} comment
11755 (@samp{#}) still works at the beginning of a line in Ada mode, but not in the
11756 middle (to allow based literals).
11758 The debugger supports limited overloading. Given a subprogram call in which
11759 the function symbol has multiple definitions, it will use the number of
11760 actual parameters and some information about their types to attempt to narrow
11761 the set of definitions. It also makes very limited use of context, preferring
11762 procedures to functions in the context of the @code{call} command, and
11763 functions to procedures elsewhere.
11765 @node Omissions from Ada
11766 @subsubsection Omissions from Ada
11767 @cindex Ada, omissions from
11769 Here are the notable omissions from the subset:
11773 Only a subset of the attributes are supported:
11777 @t{'First}, @t{'Last}, and @t{'Length}
11778 on array objects (not on types and subtypes).
11781 @t{'Min} and @t{'Max}.
11784 @t{'Pos} and @t{'Val}.
11790 @t{'Range} on array objects (not subtypes), but only as the right
11791 operand of the membership (@code{in}) operator.
11794 @t{'Access}, @t{'Unchecked_Access}, and
11795 @t{'Unrestricted_Access} (a GNAT extension).
11803 @code{Characters.Latin_1} are not available and
11804 concatenation is not implemented. Thus, escape characters in strings are
11805 not currently available.
11808 Equality tests (@samp{=} and @samp{/=}) on arrays test for bitwise
11809 equality of representations. They will generally work correctly
11810 for strings and arrays whose elements have integer or enumeration types.
11811 They may not work correctly for arrays whose element
11812 types have user-defined equality, for arrays of real values
11813 (in particular, IEEE-conformant floating point, because of negative
11814 zeroes and NaNs), and for arrays whose elements contain unused bits with
11815 indeterminate values.
11818 The other component-by-component array operations (@code{and}, @code{or},
11819 @code{xor}, @code{not}, and relational tests other than equality)
11820 are not implemented.
11823 @cindex array aggregates (Ada)
11824 @cindex record aggregates (Ada)
11825 @cindex aggregates (Ada)
11826 There is limited support for array and record aggregates. They are
11827 permitted only on the right sides of assignments, as in these examples:
11830 (@value{GDBP}) set An_Array := (1, 2, 3, 4, 5, 6)
11831 (@value{GDBP}) set An_Array := (1, others => 0)
11832 (@value{GDBP}) set An_Array := (0|4 => 1, 1..3 => 2, 5 => 6)
11833 (@value{GDBP}) set A_2D_Array := ((1, 2, 3), (4, 5, 6), (7, 8, 9))
11834 (@value{GDBP}) set A_Record := (1, "Peter", True);
11835 (@value{GDBP}) set A_Record := (Name => "Peter", Id => 1, Alive => True)
11839 discriminant's value by assigning an aggregate has an
11840 undefined effect if that discriminant is used within the record.
11841 However, you can first modify discriminants by directly assigning to
11842 them (which normally would not be allowed in Ada), and then performing an
11843 aggregate assignment. For example, given a variable @code{A_Rec}
11844 declared to have a type such as:
11847 type Rec (Len : Small_Integer := 0) is record
11849 Vals : IntArray (1 .. Len);
11853 you can assign a value with a different size of @code{Vals} with two
11857 (@value{GDBP}) set A_Rec.Len := 4
11858 (@value{GDBP}) set A_Rec := (Id => 42, Vals => (1, 2, 3, 4))
11861 As this example also illustrates, @value{GDBN} is very loose about the usual
11862 rules concerning aggregates. You may leave out some of the
11863 components of an array or record aggregate (such as the @code{Len}
11864 component in the assignment to @code{A_Rec} above); they will retain their
11865 original values upon assignment. You may freely use dynamic values as
11866 indices in component associations. You may even use overlapping or
11867 redundant component associations, although which component values are
11868 assigned in such cases is not defined.
11871 Calls to dispatching subprograms are not implemented.
11874 The overloading algorithm is much more limited (i.e., less selective)
11875 than that of real Ada. It makes only limited use of the context in
11876 which a subexpression appears to resolve its meaning, and it is much
11877 looser in its rules for allowing type matches. As a result, some
11878 function calls will be ambiguous, and the user will be asked to choose
11879 the proper resolution.
11882 The @code{new} operator is not implemented.
11885 Entry calls are not implemented.
11888 Aside from printing, arithmetic operations on the native VAX floating-point
11889 formats are not supported.
11892 It is not possible to slice a packed array.
11895 The names @code{True} and @code{False}, when not part of a qualified name,
11896 are interpreted as if implicitly prefixed by @code{Standard}, regardless of
11898 Should your program
11899 redefine these names in a package or procedure (at best a dubious practice),
11900 you will have to use fully qualified names to access their new definitions.
11903 @node Additions to Ada
11904 @subsubsection Additions to Ada
11905 @cindex Ada, deviations from
11907 As it does for other languages, @value{GDBN} makes certain generic
11908 extensions to Ada (@pxref{Expressions}):
11912 If the expression @var{E} is a variable residing in memory (typically
11913 a local variable or array element) and @var{N} is a positive integer,
11914 then @code{@var{E}@@@var{N}} displays the values of @var{E} and the
11915 @var{N}-1 adjacent variables following it in memory as an array. In
11916 Ada, this operator is generally not necessary, since its prime use is
11917 in displaying parts of an array, and slicing will usually do this in
11918 Ada. However, there are occasional uses when debugging programs in
11919 which certain debugging information has been optimized away.
11922 @code{@var{B}::@var{var}} means ``the variable named @var{var} that
11923 appears in function or file @var{B}.'' When @var{B} is a file name,
11924 you must typically surround it in single quotes.
11927 The expression @code{@{@var{type}@} @var{addr}} means ``the variable of type
11928 @var{type} that appears at address @var{addr}.''
11931 A name starting with @samp{$} is a convenience variable
11932 (@pxref{Convenience Vars}) or a machine register (@pxref{Registers}).
11935 In addition, @value{GDBN} provides a few other shortcuts and outright
11936 additions specific to Ada:
11940 The assignment statement is allowed as an expression, returning
11941 its right-hand operand as its value. Thus, you may enter
11944 (@value{GDBP}) set x := y + 3
11945 (@value{GDBP}) print A(tmp := y + 1)
11949 The semicolon is allowed as an ``operator,'' returning as its value
11950 the value of its right-hand operand.
11951 This allows, for example,
11952 complex conditional breaks:
11955 (@value{GDBP}) break f
11956 (@value{GDBP}) condition 1 (report(i); k += 1; A(k) > 100)
11960 Rather than use catenation and symbolic character names to introduce special
11961 characters into strings, one may instead use a special bracket notation,
11962 which is also used to print strings. A sequence of characters of the form
11963 @samp{["@var{XX}"]} within a string or character literal denotes the
11964 (single) character whose numeric encoding is @var{XX} in hexadecimal. The
11965 sequence of characters @samp{["""]} also denotes a single quotation mark
11966 in strings. For example,
11968 "One line.["0a"]Next line.["0a"]"
11971 contains an ASCII newline character (@code{Ada.Characters.Latin_1.LF})
11975 The subtype used as a prefix for the attributes @t{'Pos}, @t{'Min}, and
11976 @t{'Max} is optional (and is ignored in any case). For example, it is valid
11980 (@value{GDBP}) print 'max(x, y)
11984 When printing arrays, @value{GDBN} uses positional notation when the
11985 array has a lower bound of 1, and uses a modified named notation otherwise.
11986 For example, a one-dimensional array of three integers with a lower bound
11987 of 3 might print as
11994 That is, in contrast to valid Ada, only the first component has a @code{=>}
11998 You may abbreviate attributes in expressions with any unique,
11999 multi-character subsequence of
12000 their names (an exact match gets preference).
12001 For example, you may use @t{a'len}, @t{a'gth}, or @t{a'lh}
12002 in place of @t{a'length}.
12005 @cindex quoting Ada internal identifiers
12006 Since Ada is case-insensitive, the debugger normally maps identifiers you type
12007 to lower case. The GNAT compiler uses upper-case characters for
12008 some of its internal identifiers, which are normally of no interest to users.
12009 For the rare occasions when you actually have to look at them,
12010 enclose them in angle brackets to avoid the lower-case mapping.
12013 (@value{GDBP}) print <JMPBUF_SAVE>[0]
12017 Printing an object of class-wide type or dereferencing an
12018 access-to-class-wide value will display all the components of the object's
12019 specific type (as indicated by its run-time tag). Likewise, component
12020 selection on such a value will operate on the specific type of the
12025 @node Stopping Before Main Program
12026 @subsubsection Stopping at the Very Beginning
12028 @cindex breakpointing Ada elaboration code
12029 It is sometimes necessary to debug the program during elaboration, and
12030 before reaching the main procedure.
12031 As defined in the Ada Reference
12032 Manual, the elaboration code is invoked from a procedure called
12033 @code{adainit}. To run your program up to the beginning of
12034 elaboration, simply use the following two commands:
12035 @code{tbreak adainit} and @code{run}.
12038 @subsubsection Extensions for Ada Tasks
12039 @cindex Ada, tasking
12041 Support for Ada tasks is analogous to that for threads (@pxref{Threads}).
12042 @value{GDBN} provides the following task-related commands:
12047 This command shows a list of current Ada tasks, as in the following example:
12054 (@value{GDBP}) info tasks
12055 ID TID P-ID Pri State Name
12056 1 8088000 0 15 Child Activation Wait main_task
12057 2 80a4000 1 15 Accept Statement b
12058 3 809a800 1 15 Child Activation Wait a
12059 * 4 80ae800 3 15 Runnable c
12064 In this listing, the asterisk before the last task indicates it to be the
12065 task currently being inspected.
12069 Represents @value{GDBN}'s internal task number.
12075 The parent's task ID (@value{GDBN}'s internal task number).
12078 The base priority of the task.
12081 Current state of the task.
12085 The task has been created but has not been activated. It cannot be
12089 The task is not blocked for any reason known to Ada. (It may be waiting
12090 for a mutex, though.) It is conceptually "executing" in normal mode.
12093 The task is terminated, in the sense of ARM 9.3 (5). Any dependents
12094 that were waiting on terminate alternatives have been awakened and have
12095 terminated themselves.
12097 @item Child Activation Wait
12098 The task is waiting for created tasks to complete activation.
12100 @item Accept Statement
12101 The task is waiting on an accept or selective wait statement.
12103 @item Waiting on entry call
12104 The task is waiting on an entry call.
12106 @item Async Select Wait
12107 The task is waiting to start the abortable part of an asynchronous
12111 The task is waiting on a select statement with only a delay
12114 @item Child Termination Wait
12115 The task is sleeping having completed a master within itself, and is
12116 waiting for the tasks dependent on that master to become terminated or
12117 waiting on a terminate Phase.
12119 @item Wait Child in Term Alt
12120 The task is sleeping waiting for tasks on terminate alternatives to
12121 finish terminating.
12123 @item Accepting RV with @var{taskno}
12124 The task is accepting a rendez-vous with the task @var{taskno}.
12128 Name of the task in the program.
12132 @kindex info task @var{taskno}
12133 @item info task @var{taskno}
12134 This command shows detailled informations on the specified task, as in
12135 the following example:
12140 (@value{GDBP}) info tasks
12141 ID TID P-ID Pri State Name
12142 1 8077880 0 15 Child Activation Wait main_task
12143 * 2 807c468 1 15 Runnable task_1
12144 (@value{GDBP}) info task 2
12145 Ada Task: 0x807c468
12148 Parent: 1 (main_task)
12154 @kindex task@r{ (Ada)}
12155 @cindex current Ada task ID
12156 This command prints the ID of the current task.
12162 (@value{GDBP}) info tasks
12163 ID TID P-ID Pri State Name
12164 1 8077870 0 15 Child Activation Wait main_task
12165 * 2 807c458 1 15 Runnable t
12166 (@value{GDBP}) task
12167 [Current task is 2]
12170 @item task @var{taskno}
12171 @cindex Ada task switching
12172 This command is like the @code{thread @var{threadno}}
12173 command (@pxref{Threads}). It switches the context of debugging
12174 from the current task to the given task.
12180 (@value{GDBP}) info tasks
12181 ID TID P-ID Pri State Name
12182 1 8077870 0 15 Child Activation Wait main_task
12183 * 2 807c458 1 15 Runnable t
12184 (@value{GDBP}) task 1
12185 [Switching to task 1]
12186 #0 0x8067726 in pthread_cond_wait ()
12188 #0 0x8067726 in pthread_cond_wait ()
12189 #1 0x8056714 in system.os_interface.pthread_cond_wait ()
12190 #2 0x805cb63 in system.task_primitives.operations.sleep ()
12191 #3 0x806153e in system.tasking.stages.activate_tasks ()
12192 #4 0x804aacc in un () at un.adb:5
12195 @item break @var{linespec} task @var{taskno}
12196 @itemx break @var{linespec} task @var{taskno} if @dots{}
12197 @cindex breakpoints and tasks, in Ada
12198 @cindex task breakpoints, in Ada
12199 @kindex break @dots{} task @var{taskno}@r{ (Ada)}
12200 These commands are like the @code{break @dots{} thread @dots{}}
12201 command (@pxref{Thread Stops}).
12202 @var{linespec} specifies source lines, as described
12203 in @ref{Specify Location}.
12205 Use the qualifier @samp{task @var{taskno}} with a breakpoint command
12206 to specify that you only want @value{GDBN} to stop the program when a
12207 particular Ada task reaches this breakpoint. @var{taskno} is one of the
12208 numeric task identifiers assigned by @value{GDBN}, shown in the first
12209 column of the @samp{info tasks} display.
12211 If you do not specify @samp{task @var{taskno}} when you set a
12212 breakpoint, the breakpoint applies to @emph{all} tasks of your
12215 You can use the @code{task} qualifier on conditional breakpoints as
12216 well; in this case, place @samp{task @var{taskno}} before the
12217 breakpoint condition (before the @code{if}).
12225 (@value{GDBP}) info tasks
12226 ID TID P-ID Pri State Name
12227 1 140022020 0 15 Child Activation Wait main_task
12228 2 140045060 1 15 Accept/Select Wait t2
12229 3 140044840 1 15 Runnable t1
12230 * 4 140056040 1 15 Runnable t3
12231 (@value{GDBP}) b 15 task 2
12232 Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15.
12233 (@value{GDBP}) cont
12238 Breakpoint 5, test_task_debug () at test_task_debug.adb:15
12240 (@value{GDBP}) info tasks
12241 ID TID P-ID Pri State Name
12242 1 140022020 0 15 Child Activation Wait main_task
12243 * 2 140045060 1 15 Runnable t2
12244 3 140044840 1 15 Runnable t1
12245 4 140056040 1 15 Delay Sleep t3
12249 @node Ada Tasks and Core Files
12250 @subsubsection Tasking Support when Debugging Core Files
12251 @cindex Ada tasking and core file debugging
12253 When inspecting a core file, as opposed to debugging a live program,
12254 tasking support may be limited or even unavailable, depending on
12255 the platform being used.
12256 For instance, on x86-linux, the list of tasks is available, but task
12257 switching is not supported. On Tru64, however, task switching will work
12260 On certain platforms, including Tru64, the debugger needs to perform some
12261 memory writes in order to provide Ada tasking support. When inspecting
12262 a core file, this means that the core file must be opened with read-write
12263 privileges, using the command @samp{"set write on"} (@pxref{Patching}).
12264 Under these circumstances, you should make a backup copy of the core
12265 file before inspecting it with @value{GDBN}.
12268 @subsubsection Known Peculiarities of Ada Mode
12269 @cindex Ada, problems
12271 Besides the omissions listed previously (@pxref{Omissions from Ada}),
12272 we know of several problems with and limitations of Ada mode in
12274 some of which will be fixed with planned future releases of the debugger
12275 and the GNU Ada compiler.
12279 Currently, the debugger
12280 has insufficient information to determine whether certain pointers represent
12281 pointers to objects or the objects themselves.
12282 Thus, the user may have to tack an extra @code{.all} after an expression
12283 to get it printed properly.
12286 Static constants that the compiler chooses not to materialize as objects in
12287 storage are invisible to the debugger.
12290 Named parameter associations in function argument lists are ignored (the
12291 argument lists are treated as positional).
12294 Many useful library packages are currently invisible to the debugger.
12297 Fixed-point arithmetic, conversions, input, and output is carried out using
12298 floating-point arithmetic, and may give results that only approximate those on
12302 The GNAT compiler never generates the prefix @code{Standard} for any of
12303 the standard symbols defined by the Ada language. @value{GDBN} knows about
12304 this: it will strip the prefix from names when you use it, and will never
12305 look for a name you have so qualified among local symbols, nor match against
12306 symbols in other packages or subprograms. If you have
12307 defined entities anywhere in your program other than parameters and
12308 local variables whose simple names match names in @code{Standard},
12309 GNAT's lack of qualification here can cause confusion. When this happens,
12310 you can usually resolve the confusion
12311 by qualifying the problematic names with package
12312 @code{Standard} explicitly.
12315 @node Unsupported Languages
12316 @section Unsupported Languages
12318 @cindex unsupported languages
12319 @cindex minimal language
12320 In addition to the other fully-supported programming languages,
12321 @value{GDBN} also provides a pseudo-language, called @code{minimal}.
12322 It does not represent a real programming language, but provides a set
12323 of capabilities close to what the C or assembly languages provide.
12324 This should allow most simple operations to be performed while debugging
12325 an application that uses a language currently not supported by @value{GDBN}.
12327 If the language is set to @code{auto}, @value{GDBN} will automatically
12328 select this language if the current frame corresponds to an unsupported
12332 @chapter Examining the Symbol Table
12334 The commands described in this chapter allow you to inquire about the
12335 symbols (names of variables, functions and types) defined in your
12336 program. This information is inherent in the text of your program and
12337 does not change as your program executes. @value{GDBN} finds it in your
12338 program's symbol table, in the file indicated when you started @value{GDBN}
12339 (@pxref{File Options, ,Choosing Files}), or by one of the
12340 file-management commands (@pxref{Files, ,Commands to Specify Files}).
12342 @cindex symbol names
12343 @cindex names of symbols
12344 @cindex quoting names
12345 Occasionally, you may need to refer to symbols that contain unusual
12346 characters, which @value{GDBN} ordinarily treats as word delimiters. The
12347 most frequent case is in referring to static variables in other
12348 source files (@pxref{Variables,,Program Variables}). File names
12349 are recorded in object files as debugging symbols, but @value{GDBN} would
12350 ordinarily parse a typical file name, like @file{foo.c}, as the three words
12351 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
12352 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
12359 looks up the value of @code{x} in the scope of the file @file{foo.c}.
12362 @cindex case-insensitive symbol names
12363 @cindex case sensitivity in symbol names
12364 @kindex set case-sensitive
12365 @item set case-sensitive on
12366 @itemx set case-sensitive off
12367 @itemx set case-sensitive auto
12368 Normally, when @value{GDBN} looks up symbols, it matches their names
12369 with case sensitivity determined by the current source language.
12370 Occasionally, you may wish to control that. The command @code{set
12371 case-sensitive} lets you do that by specifying @code{on} for
12372 case-sensitive matches or @code{off} for case-insensitive ones. If
12373 you specify @code{auto}, case sensitivity is reset to the default
12374 suitable for the source language. The default is case-sensitive
12375 matches for all languages except for Fortran, for which the default is
12376 case-insensitive matches.
12378 @kindex show case-sensitive
12379 @item show case-sensitive
12380 This command shows the current setting of case sensitivity for symbols
12383 @kindex info address
12384 @cindex address of a symbol
12385 @item info address @var{symbol}
12386 Describe where the data for @var{symbol} is stored. For a register
12387 variable, this says which register it is kept in. For a non-register
12388 local variable, this prints the stack-frame offset at which the variable
12391 Note the contrast with @samp{print &@var{symbol}}, which does not work
12392 at all for a register variable, and for a stack local variable prints
12393 the exact address of the current instantiation of the variable.
12395 @kindex info symbol
12396 @cindex symbol from address
12397 @cindex closest symbol and offset for an address
12398 @item info symbol @var{addr}
12399 Print the name of a symbol which is stored at the address @var{addr}.
12400 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
12401 nearest symbol and an offset from it:
12404 (@value{GDBP}) info symbol 0x54320
12405 _initialize_vx + 396 in section .text
12409 This is the opposite of the @code{info address} command. You can use
12410 it to find out the name of a variable or a function given its address.
12412 For dynamically linked executables, the name of executable or shared
12413 library containing the symbol is also printed:
12416 (@value{GDBP}) info symbol 0x400225
12417 _start + 5 in section .text of /tmp/a.out
12418 (@value{GDBP}) info symbol 0x2aaaac2811cf
12419 __read_nocancel + 6 in section .text of /usr/lib64/libc.so.6
12423 @item whatis [@var{arg}]
12424 Print the data type of @var{arg}, which can be either an expression or
12425 a data type. With no argument, print the data type of @code{$}, the
12426 last value in the value history. If @var{arg} is an expression, it is
12427 not actually evaluated, and any side-effecting operations (such as
12428 assignments or function calls) inside it do not take place. If
12429 @var{arg} is a type name, it may be the name of a type or typedef, or
12430 for C code it may have the form @samp{class @var{class-name}},
12431 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
12432 @samp{enum @var{enum-tag}}.
12433 @xref{Expressions, ,Expressions}.
12436 @item ptype [@var{arg}]
12437 @code{ptype} accepts the same arguments as @code{whatis}, but prints a
12438 detailed description of the type, instead of just the name of the type.
12439 @xref{Expressions, ,Expressions}.
12441 For example, for this variable declaration:
12444 struct complex @{double real; double imag;@} v;
12448 the two commands give this output:
12452 (@value{GDBP}) whatis v
12453 type = struct complex
12454 (@value{GDBP}) ptype v
12455 type = struct complex @{
12463 As with @code{whatis}, using @code{ptype} without an argument refers to
12464 the type of @code{$}, the last value in the value history.
12466 @cindex incomplete type
12467 Sometimes, programs use opaque data types or incomplete specifications
12468 of complex data structure. If the debug information included in the
12469 program does not allow @value{GDBN} to display a full declaration of
12470 the data type, it will say @samp{<incomplete type>}. For example,
12471 given these declarations:
12475 struct foo *fooptr;
12479 but no definition for @code{struct foo} itself, @value{GDBN} will say:
12482 (@value{GDBP}) ptype foo
12483 $1 = <incomplete type>
12487 ``Incomplete type'' is C terminology for data types that are not
12488 completely specified.
12491 @item info types @var{regexp}
12493 Print a brief description of all types whose names match the regular
12494 expression @var{regexp} (or all types in your program, if you supply
12495 no argument). Each complete typename is matched as though it were a
12496 complete line; thus, @samp{i type value} gives information on all
12497 types in your program whose names include the string @code{value}, but
12498 @samp{i type ^value$} gives information only on types whose complete
12499 name is @code{value}.
12501 This command differs from @code{ptype} in two ways: first, like
12502 @code{whatis}, it does not print a detailed description; second, it
12503 lists all source files where a type is defined.
12506 @cindex local variables
12507 @item info scope @var{location}
12508 List all the variables local to a particular scope. This command
12509 accepts a @var{location} argument---a function name, a source line, or
12510 an address preceded by a @samp{*}, and prints all the variables local
12511 to the scope defined by that location. (@xref{Specify Location}, for
12512 details about supported forms of @var{location}.) For example:
12515 (@value{GDBP}) @b{info scope command_line_handler}
12516 Scope for command_line_handler:
12517 Symbol rl is an argument at stack/frame offset 8, length 4.
12518 Symbol linebuffer is in static storage at address 0x150a18, length 4.
12519 Symbol linelength is in static storage at address 0x150a1c, length 4.
12520 Symbol p is a local variable in register $esi, length 4.
12521 Symbol p1 is a local variable in register $ebx, length 4.
12522 Symbol nline is a local variable in register $edx, length 4.
12523 Symbol repeat is a local variable at frame offset -8, length 4.
12527 This command is especially useful for determining what data to collect
12528 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
12531 @kindex info source
12533 Show information about the current source file---that is, the source file for
12534 the function containing the current point of execution:
12537 the name of the source file, and the directory containing it,
12539 the directory it was compiled in,
12541 its length, in lines,
12543 which programming language it is written in,
12545 whether the executable includes debugging information for that file, and
12546 if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and
12548 whether the debugging information includes information about
12549 preprocessor macros.
12553 @kindex info sources
12555 Print the names of all source files in your program for which there is
12556 debugging information, organized into two lists: files whose symbols
12557 have already been read, and files whose symbols will be read when needed.
12559 @kindex info functions
12560 @item info functions
12561 Print the names and data types of all defined functions.
12563 @item info functions @var{regexp}
12564 Print the names and data types of all defined functions
12565 whose names contain a match for regular expression @var{regexp}.
12566 Thus, @samp{info fun step} finds all functions whose names
12567 include @code{step}; @samp{info fun ^step} finds those whose names
12568 start with @code{step}. If a function name contains characters
12569 that conflict with the regular expression language (e.g.@:
12570 @samp{operator*()}), they may be quoted with a backslash.
12572 @kindex info variables
12573 @item info variables
12574 Print the names and data types of all variables that are declared
12575 outside of functions (i.e.@: excluding local variables).
12577 @item info variables @var{regexp}
12578 Print the names and data types of all variables (except for local
12579 variables) whose names contain a match for regular expression
12582 @kindex info classes
12583 @cindex Objective-C, classes and selectors
12585 @itemx info classes @var{regexp}
12586 Display all Objective-C classes in your program, or
12587 (with the @var{regexp} argument) all those matching a particular regular
12590 @kindex info selectors
12591 @item info selectors
12592 @itemx info selectors @var{regexp}
12593 Display all Objective-C selectors in your program, or
12594 (with the @var{regexp} argument) all those matching a particular regular
12598 This was never implemented.
12599 @kindex info methods
12601 @itemx info methods @var{regexp}
12602 The @code{info methods} command permits the user to examine all defined
12603 methods within C@t{++} program, or (with the @var{regexp} argument) a
12604 specific set of methods found in the various C@t{++} classes. Many
12605 C@t{++} classes provide a large number of methods. Thus, the output
12606 from the @code{ptype} command can be overwhelming and hard to use. The
12607 @code{info-methods} command filters the methods, printing only those
12608 which match the regular-expression @var{regexp}.
12611 @cindex reloading symbols
12612 Some systems allow individual object files that make up your program to
12613 be replaced without stopping and restarting your program. For example,
12614 in VxWorks you can simply recompile a defective object file and keep on
12615 running. If you are running on one of these systems, you can allow
12616 @value{GDBN} to reload the symbols for automatically relinked modules:
12619 @kindex set symbol-reloading
12620 @item set symbol-reloading on
12621 Replace symbol definitions for the corresponding source file when an
12622 object file with a particular name is seen again.
12624 @item set symbol-reloading off
12625 Do not replace symbol definitions when encountering object files of the
12626 same name more than once. This is the default state; if you are not
12627 running on a system that permits automatic relinking of modules, you
12628 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
12629 may discard symbols when linking large programs, that may contain
12630 several modules (from different directories or libraries) with the same
12633 @kindex show symbol-reloading
12634 @item show symbol-reloading
12635 Show the current @code{on} or @code{off} setting.
12638 @cindex opaque data types
12639 @kindex set opaque-type-resolution
12640 @item set opaque-type-resolution on
12641 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
12642 declared as a pointer to a @code{struct}, @code{class}, or
12643 @code{union}---for example, @code{struct MyType *}---that is used in one
12644 source file although the full declaration of @code{struct MyType} is in
12645 another source file. The default is on.
12647 A change in the setting of this subcommand will not take effect until
12648 the next time symbols for a file are loaded.
12650 @item set opaque-type-resolution off
12651 Tell @value{GDBN} not to resolve opaque types. In this case, the type
12652 is printed as follows:
12654 @{<no data fields>@}
12657 @kindex show opaque-type-resolution
12658 @item show opaque-type-resolution
12659 Show whether opaque types are resolved or not.
12661 @kindex maint print symbols
12662 @cindex symbol dump
12663 @kindex maint print psymbols
12664 @cindex partial symbol dump
12665 @item maint print symbols @var{filename}
12666 @itemx maint print psymbols @var{filename}
12667 @itemx maint print msymbols @var{filename}
12668 Write a dump of debugging symbol data into the file @var{filename}.
12669 These commands are used to debug the @value{GDBN} symbol-reading code. Only
12670 symbols with debugging data are included. If you use @samp{maint print
12671 symbols}, @value{GDBN} includes all the symbols for which it has already
12672 collected full details: that is, @var{filename} reflects symbols for
12673 only those files whose symbols @value{GDBN} has read. You can use the
12674 command @code{info sources} to find out which files these are. If you
12675 use @samp{maint print psymbols} instead, the dump shows information about
12676 symbols that @value{GDBN} only knows partially---that is, symbols defined in
12677 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
12678 @samp{maint print msymbols} dumps just the minimal symbol information
12679 required for each object file from which @value{GDBN} has read some symbols.
12680 @xref{Files, ,Commands to Specify Files}, for a discussion of how
12681 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
12683 @kindex maint info symtabs
12684 @kindex maint info psymtabs
12685 @cindex listing @value{GDBN}'s internal symbol tables
12686 @cindex symbol tables, listing @value{GDBN}'s internal
12687 @cindex full symbol tables, listing @value{GDBN}'s internal
12688 @cindex partial symbol tables, listing @value{GDBN}'s internal
12689 @item maint info symtabs @r{[} @var{regexp} @r{]}
12690 @itemx maint info psymtabs @r{[} @var{regexp} @r{]}
12692 List the @code{struct symtab} or @code{struct partial_symtab}
12693 structures whose names match @var{regexp}. If @var{regexp} is not
12694 given, list them all. The output includes expressions which you can
12695 copy into a @value{GDBN} debugging this one to examine a particular
12696 structure in more detail. For example:
12699 (@value{GDBP}) maint info psymtabs dwarf2read
12700 @{ objfile /home/gnu/build/gdb/gdb
12701 ((struct objfile *) 0x82e69d0)
12702 @{ psymtab /home/gnu/src/gdb/dwarf2read.c
12703 ((struct partial_symtab *) 0x8474b10)
12706 text addresses 0x814d3c8 -- 0x8158074
12707 globals (* (struct partial_symbol **) 0x8507a08 @@ 9)
12708 statics (* (struct partial_symbol **) 0x40e95b78 @@ 2882)
12709 dependencies (none)
12712 (@value{GDBP}) maint info symtabs
12716 We see that there is one partial symbol table whose filename contains
12717 the string @samp{dwarf2read}, belonging to the @samp{gdb} executable;
12718 and we see that @value{GDBN} has not read in any symtabs yet at all.
12719 If we set a breakpoint on a function, that will cause @value{GDBN} to
12720 read the symtab for the compilation unit containing that function:
12723 (@value{GDBP}) break dwarf2_psymtab_to_symtab
12724 Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c,
12726 (@value{GDBP}) maint info symtabs
12727 @{ objfile /home/gnu/build/gdb/gdb
12728 ((struct objfile *) 0x82e69d0)
12729 @{ symtab /home/gnu/src/gdb/dwarf2read.c
12730 ((struct symtab *) 0x86c1f38)
12733 blockvector ((struct blockvector *) 0x86c1bd0) (primary)
12734 linetable ((struct linetable *) 0x8370fa0)
12735 debugformat DWARF 2
12744 @chapter Altering Execution
12746 Once you think you have found an error in your program, you might want to
12747 find out for certain whether correcting the apparent error would lead to
12748 correct results in the rest of the run. You can find the answer by
12749 experiment, using the @value{GDBN} features for altering execution of the
12752 For example, you can store new values into variables or memory
12753 locations, give your program a signal, restart it at a different
12754 address, or even return prematurely from a function.
12757 * Assignment:: Assignment to variables
12758 * Jumping:: Continuing at a different address
12759 * Signaling:: Giving your program a signal
12760 * Returning:: Returning from a function
12761 * Calling:: Calling your program's functions
12762 * Patching:: Patching your program
12766 @section Assignment to Variables
12769 @cindex setting variables
12770 To alter the value of a variable, evaluate an assignment expression.
12771 @xref{Expressions, ,Expressions}. For example,
12778 stores the value 4 into the variable @code{x}, and then prints the
12779 value of the assignment expression (which is 4).
12780 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
12781 information on operators in supported languages.
12783 @kindex set variable
12784 @cindex variables, setting
12785 If you are not interested in seeing the value of the assignment, use the
12786 @code{set} command instead of the @code{print} command. @code{set} is
12787 really the same as @code{print} except that the expression's value is
12788 not printed and is not put in the value history (@pxref{Value History,
12789 ,Value History}). The expression is evaluated only for its effects.
12791 If the beginning of the argument string of the @code{set} command
12792 appears identical to a @code{set} subcommand, use the @code{set
12793 variable} command instead of just @code{set}. This command is identical
12794 to @code{set} except for its lack of subcommands. For example, if your
12795 program has a variable @code{width}, you get an error if you try to set
12796 a new value with just @samp{set width=13}, because @value{GDBN} has the
12797 command @code{set width}:
12800 (@value{GDBP}) whatis width
12802 (@value{GDBP}) p width
12804 (@value{GDBP}) set width=47
12805 Invalid syntax in expression.
12809 The invalid expression, of course, is @samp{=47}. In
12810 order to actually set the program's variable @code{width}, use
12813 (@value{GDBP}) set var width=47
12816 Because the @code{set} command has many subcommands that can conflict
12817 with the names of program variables, it is a good idea to use the
12818 @code{set variable} command instead of just @code{set}. For example, if
12819 your program has a variable @code{g}, you run into problems if you try
12820 to set a new value with just @samp{set g=4}, because @value{GDBN} has
12821 the command @code{set gnutarget}, abbreviated @code{set g}:
12825 (@value{GDBP}) whatis g
12829 (@value{GDBP}) set g=4
12833 The program being debugged has been started already.
12834 Start it from the beginning? (y or n) y
12835 Starting program: /home/smith/cc_progs/a.out
12836 "/home/smith/cc_progs/a.out": can't open to read symbols:
12837 Invalid bfd target.
12838 (@value{GDBP}) show g
12839 The current BFD target is "=4".
12844 The program variable @code{g} did not change, and you silently set the
12845 @code{gnutarget} to an invalid value. In order to set the variable
12849 (@value{GDBP}) set var g=4
12852 @value{GDBN} allows more implicit conversions in assignments than C; you can
12853 freely store an integer value into a pointer variable or vice versa,
12854 and you can convert any structure to any other structure that is the
12855 same length or shorter.
12856 @comment FIXME: how do structs align/pad in these conversions?
12857 @comment /doc@cygnus.com 18dec1990
12859 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
12860 construct to generate a value of specified type at a specified address
12861 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
12862 to memory location @code{0x83040} as an integer (which implies a certain size
12863 and representation in memory), and
12866 set @{int@}0x83040 = 4
12870 stores the value 4 into that memory location.
12873 @section Continuing at a Different Address
12875 Ordinarily, when you continue your program, you do so at the place where
12876 it stopped, with the @code{continue} command. You can instead continue at
12877 an address of your own choosing, with the following commands:
12881 @item jump @var{linespec}
12882 @itemx jump @var{location}
12883 Resume execution at line @var{linespec} or at address given by
12884 @var{location}. Execution stops again immediately if there is a
12885 breakpoint there. @xref{Specify Location}, for a description of the
12886 different forms of @var{linespec} and @var{location}. It is common
12887 practice to use the @code{tbreak} command in conjunction with
12888 @code{jump}. @xref{Set Breaks, ,Setting Breakpoints}.
12890 The @code{jump} command does not change the current stack frame, or
12891 the stack pointer, or the contents of any memory location or any
12892 register other than the program counter. If line @var{linespec} is in
12893 a different function from the one currently executing, the results may
12894 be bizarre if the two functions expect different patterns of arguments or
12895 of local variables. For this reason, the @code{jump} command requests
12896 confirmation if the specified line is not in the function currently
12897 executing. However, even bizarre results are predictable if you are
12898 well acquainted with the machine-language code of your program.
12901 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
12902 On many systems, you can get much the same effect as the @code{jump}
12903 command by storing a new value into the register @code{$pc}. The
12904 difference is that this does not start your program running; it only
12905 changes the address of where it @emph{will} run when you continue. For
12913 makes the next @code{continue} command or stepping command execute at
12914 address @code{0x485}, rather than at the address where your program stopped.
12915 @xref{Continuing and Stepping, ,Continuing and Stepping}.
12917 The most common occasion to use the @code{jump} command is to back
12918 up---perhaps with more breakpoints set---over a portion of a program
12919 that has already executed, in order to examine its execution in more
12924 @section Giving your Program a Signal
12925 @cindex deliver a signal to a program
12929 @item signal @var{signal}
12930 Resume execution where your program stopped, but immediately give it the
12931 signal @var{signal}. @var{signal} can be the name or the number of a
12932 signal. For example, on many systems @code{signal 2} and @code{signal
12933 SIGINT} are both ways of sending an interrupt signal.
12935 Alternatively, if @var{signal} is zero, continue execution without
12936 giving a signal. This is useful when your program stopped on account of
12937 a signal and would ordinary see the signal when resumed with the
12938 @code{continue} command; @samp{signal 0} causes it to resume without a
12941 @code{signal} does not repeat when you press @key{RET} a second time
12942 after executing the command.
12946 Invoking the @code{signal} command is not the same as invoking the
12947 @code{kill} utility from the shell. Sending a signal with @code{kill}
12948 causes @value{GDBN} to decide what to do with the signal depending on
12949 the signal handling tables (@pxref{Signals}). The @code{signal} command
12950 passes the signal directly to your program.
12954 @section Returning from a Function
12957 @cindex returning from a function
12960 @itemx return @var{expression}
12961 You can cancel execution of a function call with the @code{return}
12962 command. If you give an
12963 @var{expression} argument, its value is used as the function's return
12967 When you use @code{return}, @value{GDBN} discards the selected stack frame
12968 (and all frames within it). You can think of this as making the
12969 discarded frame return prematurely. If you wish to specify a value to
12970 be returned, give that value as the argument to @code{return}.
12972 This pops the selected stack frame (@pxref{Selection, ,Selecting a
12973 Frame}), and any other frames inside of it, leaving its caller as the
12974 innermost remaining frame. That frame becomes selected. The
12975 specified value is stored in the registers used for returning values
12978 The @code{return} command does not resume execution; it leaves the
12979 program stopped in the state that would exist if the function had just
12980 returned. In contrast, the @code{finish} command (@pxref{Continuing
12981 and Stepping, ,Continuing and Stepping}) resumes execution until the
12982 selected stack frame returns naturally.
12984 @value{GDBN} needs to know how the @var{expression} argument should be set for
12985 the inferior. The concrete registers assignment depends on the OS ABI and the
12986 type being returned by the selected stack frame. For example it is common for
12987 OS ABI to return floating point values in FPU registers while integer values in
12988 CPU registers. Still some ABIs return even floating point values in CPU
12989 registers. Larger integer widths (such as @code{long long int}) also have
12990 specific placement rules. @value{GDBN} already knows the OS ABI from its
12991 current target so it needs to find out also the type being returned to make the
12992 assignment into the right register(s).
12994 Normally, the selected stack frame has debug info. @value{GDBN} will always
12995 use the debug info instead of the implicit type of @var{expression} when the
12996 debug info is available. For example, if you type @kbd{return -1}, and the
12997 function in the current stack frame is declared to return a @code{long long
12998 int}, @value{GDBN} transparently converts the implicit @code{int} value of -1
12999 into a @code{long long int}:
13002 Breakpoint 1, func () at gdb.base/return-nodebug.c:29
13004 (@value{GDBP}) return -1
13005 Make func return now? (y or n) y
13006 #0 0x004004f6 in main () at gdb.base/return-nodebug.c:43
13007 43 printf ("result=%lld\n", func ());
13011 However, if the selected stack frame does not have a debug info, e.g., if the
13012 function was compiled without debug info, @value{GDBN} has to find out the type
13013 to return from user. Specifying a different type by mistake may set the value
13014 in different inferior registers than the caller code expects. For example,
13015 typing @kbd{return -1} with its implicit type @code{int} would set only a part
13016 of a @code{long long int} result for a debug info less function (on 32-bit
13017 architectures). Therefore the user is required to specify the return type by
13018 an appropriate cast explicitly:
13021 Breakpoint 2, 0x0040050b in func ()
13022 (@value{GDBP}) return -1
13023 Return value type not available for selected stack frame.
13024 Please use an explicit cast of the value to return.
13025 (@value{GDBP}) return (long long int) -1
13026 Make selected stack frame return now? (y or n) y
13027 #0 0x00400526 in main ()
13032 @section Calling Program Functions
13035 @cindex calling functions
13036 @cindex inferior functions, calling
13037 @item print @var{expr}
13038 Evaluate the expression @var{expr} and display the resulting value.
13039 @var{expr} may include calls to functions in the program being
13043 @item call @var{expr}
13044 Evaluate the expression @var{expr} without displaying @code{void}
13047 You can use this variant of the @code{print} command if you want to
13048 execute a function from your program that does not return anything
13049 (a.k.a.@: @dfn{a void function}), but without cluttering the output
13050 with @code{void} returned values that @value{GDBN} will otherwise
13051 print. If the result is not void, it is printed and saved in the
13055 It is possible for the function you call via the @code{print} or
13056 @code{call} command to generate a signal (e.g., if there's a bug in
13057 the function, or if you passed it incorrect arguments). What happens
13058 in that case is controlled by the @code{set unwindonsignal} command.
13060 Similarly, with a C@t{++} program it is possible for the function you
13061 call via the @code{print} or @code{call} command to generate an
13062 exception that is not handled due to the constraints of the dummy
13063 frame. In this case, any exception that is raised in the frame, but has
13064 an out-of-frame exception handler will not be found. GDB builds a
13065 dummy-frame for the inferior function call, and the unwinder cannot
13066 seek for exception handlers outside of this dummy-frame. What happens
13067 in that case is controlled by the
13068 @code{set unwind-on-terminating-exception} command.
13071 @item set unwindonsignal
13072 @kindex set unwindonsignal
13073 @cindex unwind stack in called functions
13074 @cindex call dummy stack unwinding
13075 Set unwinding of the stack if a signal is received while in a function
13076 that @value{GDBN} called in the program being debugged. If set to on,
13077 @value{GDBN} unwinds the stack it created for the call and restores
13078 the context to what it was before the call. If set to off (the
13079 default), @value{GDBN} stops in the frame where the signal was
13082 @item show unwindonsignal
13083 @kindex show unwindonsignal
13084 Show the current setting of stack unwinding in the functions called by
13087 @item set unwind-on-terminating-exception
13088 @kindex set unwind-on-terminating-exception
13089 @cindex unwind stack in called functions with unhandled exceptions
13090 @cindex call dummy stack unwinding on unhandled exception.
13091 Set unwinding of the stack if a C@t{++} exception is raised, but left
13092 unhandled while in a function that @value{GDBN} called in the program being
13093 debugged. If set to on (the default), @value{GDBN} unwinds the stack
13094 it created for the call and restores the context to what it was before
13095 the call. If set to off, @value{GDBN} the exception is delivered to
13096 the default C@t{++} exception handler and the inferior terminated.
13098 @item show unwind-on-terminating-exception
13099 @kindex show unwind-on-terminating-exception
13100 Show the current setting of stack unwinding in the functions called by
13105 @cindex weak alias functions
13106 Sometimes, a function you wish to call is actually a @dfn{weak alias}
13107 for another function. In such case, @value{GDBN} might not pick up
13108 the type information, including the types of the function arguments,
13109 which causes @value{GDBN} to call the inferior function incorrectly.
13110 As a result, the called function will function erroneously and may
13111 even crash. A solution to that is to use the name of the aliased
13115 @section Patching Programs
13117 @cindex patching binaries
13118 @cindex writing into executables
13119 @cindex writing into corefiles
13121 By default, @value{GDBN} opens the file containing your program's
13122 executable code (or the corefile) read-only. This prevents accidental
13123 alterations to machine code; but it also prevents you from intentionally
13124 patching your program's binary.
13126 If you'd like to be able to patch the binary, you can specify that
13127 explicitly with the @code{set write} command. For example, you might
13128 want to turn on internal debugging flags, or even to make emergency
13134 @itemx set write off
13135 If you specify @samp{set write on}, @value{GDBN} opens executable and
13136 core files for both reading and writing; if you specify @kbd{set write
13137 off} (the default), @value{GDBN} opens them read-only.
13139 If you have already loaded a file, you must load it again (using the
13140 @code{exec-file} or @code{core-file} command) after changing @code{set
13141 write}, for your new setting to take effect.
13145 Display whether executable files and core files are opened for writing
13146 as well as reading.
13150 @chapter @value{GDBN} Files
13152 @value{GDBN} needs to know the file name of the program to be debugged,
13153 both in order to read its symbol table and in order to start your
13154 program. To debug a core dump of a previous run, you must also tell
13155 @value{GDBN} the name of the core dump file.
13158 * Files:: Commands to specify files
13159 * Separate Debug Files:: Debugging information in separate files
13160 * Symbol Errors:: Errors reading symbol files
13161 * Data Files:: GDB data files
13165 @section Commands to Specify Files
13167 @cindex symbol table
13168 @cindex core dump file
13170 You may want to specify executable and core dump file names. The usual
13171 way to do this is at start-up time, using the arguments to
13172 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
13173 Out of @value{GDBN}}).
13175 Occasionally it is necessary to change to a different file during a
13176 @value{GDBN} session. Or you may run @value{GDBN} and forget to
13177 specify a file you want to use. Or you are debugging a remote target
13178 via @code{gdbserver} (@pxref{Server, file, Using the @code{gdbserver}
13179 Program}). In these situations the @value{GDBN} commands to specify
13180 new files are useful.
13183 @cindex executable file
13185 @item file @var{filename}
13186 Use @var{filename} as the program to be debugged. It is read for its
13187 symbols and for the contents of pure memory. It is also the program
13188 executed when you use the @code{run} command. If you do not specify a
13189 directory and the file is not found in the @value{GDBN} working directory,
13190 @value{GDBN} uses the environment variable @code{PATH} as a list of
13191 directories to search, just as the shell does when looking for a program
13192 to run. You can change the value of this variable, for both @value{GDBN}
13193 and your program, using the @code{path} command.
13195 @cindex unlinked object files
13196 @cindex patching object files
13197 You can load unlinked object @file{.o} files into @value{GDBN} using
13198 the @code{file} command. You will not be able to ``run'' an object
13199 file, but you can disassemble functions and inspect variables. Also,
13200 if the underlying BFD functionality supports it, you could use
13201 @kbd{gdb -write} to patch object files using this technique. Note
13202 that @value{GDBN} can neither interpret nor modify relocations in this
13203 case, so branches and some initialized variables will appear to go to
13204 the wrong place. But this feature is still handy from time to time.
13207 @code{file} with no argument makes @value{GDBN} discard any information it
13208 has on both executable file and the symbol table.
13211 @item exec-file @r{[} @var{filename} @r{]}
13212 Specify that the program to be run (but not the symbol table) is found
13213 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
13214 if necessary to locate your program. Omitting @var{filename} means to
13215 discard information on the executable file.
13217 @kindex symbol-file
13218 @item symbol-file @r{[} @var{filename} @r{]}
13219 Read symbol table information from file @var{filename}. @code{PATH} is
13220 searched when necessary. Use the @code{file} command to get both symbol
13221 table and program to run from the same file.
13223 @code{symbol-file} with no argument clears out @value{GDBN} information on your
13224 program's symbol table.
13226 The @code{symbol-file} command causes @value{GDBN} to forget the contents of
13227 some breakpoints and auto-display expressions. This is because they may
13228 contain pointers to the internal data recording symbols and data types,
13229 which are part of the old symbol table data being discarded inside
13232 @code{symbol-file} does not repeat if you press @key{RET} again after
13235 When @value{GDBN} is configured for a particular environment, it
13236 understands debugging information in whatever format is the standard
13237 generated for that environment; you may use either a @sc{gnu} compiler, or
13238 other compilers that adhere to the local conventions.
13239 Best results are usually obtained from @sc{gnu} compilers; for example,
13240 using @code{@value{NGCC}} you can generate debugging information for
13243 For most kinds of object files, with the exception of old SVR3 systems
13244 using COFF, the @code{symbol-file} command does not normally read the
13245 symbol table in full right away. Instead, it scans the symbol table
13246 quickly to find which source files and which symbols are present. The
13247 details are read later, one source file at a time, as they are needed.
13249 The purpose of this two-stage reading strategy is to make @value{GDBN}
13250 start up faster. For the most part, it is invisible except for
13251 occasional pauses while the symbol table details for a particular source
13252 file are being read. (The @code{set verbose} command can turn these
13253 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
13254 Warnings and Messages}.)
13256 We have not implemented the two-stage strategy for COFF yet. When the
13257 symbol table is stored in COFF format, @code{symbol-file} reads the
13258 symbol table data in full right away. Note that ``stabs-in-COFF''
13259 still does the two-stage strategy, since the debug info is actually
13263 @cindex reading symbols immediately
13264 @cindex symbols, reading immediately
13265 @item symbol-file @var{filename} @r{[} -readnow @r{]}
13266 @itemx file @var{filename} @r{[} -readnow @r{]}
13267 You can override the @value{GDBN} two-stage strategy for reading symbol
13268 tables by using the @samp{-readnow} option with any of the commands that
13269 load symbol table information, if you want to be sure @value{GDBN} has the
13270 entire symbol table available.
13272 @c FIXME: for now no mention of directories, since this seems to be in
13273 @c flux. 13mar1992 status is that in theory GDB would look either in
13274 @c current dir or in same dir as myprog; but issues like competing
13275 @c GDB's, or clutter in system dirs, mean that in practice right now
13276 @c only current dir is used. FFish says maybe a special GDB hierarchy
13277 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
13281 @item core-file @r{[}@var{filename}@r{]}
13283 Specify the whereabouts of a core dump file to be used as the ``contents
13284 of memory''. Traditionally, core files contain only some parts of the
13285 address space of the process that generated them; @value{GDBN} can access the
13286 executable file itself for other parts.
13288 @code{core-file} with no argument specifies that no core file is
13291 Note that the core file is ignored when your program is actually running
13292 under @value{GDBN}. So, if you have been running your program and you
13293 wish to debug a core file instead, you must kill the subprocess in which
13294 the program is running. To do this, use the @code{kill} command
13295 (@pxref{Kill Process, ,Killing the Child Process}).
13297 @kindex add-symbol-file
13298 @cindex dynamic linking
13299 @item add-symbol-file @var{filename} @var{address}
13300 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]}
13301 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
13302 The @code{add-symbol-file} command reads additional symbol table
13303 information from the file @var{filename}. You would use this command
13304 when @var{filename} has been dynamically loaded (by some other means)
13305 into the program that is running. @var{address} should be the memory
13306 address at which the file has been loaded; @value{GDBN} cannot figure
13307 this out for itself. You can additionally specify an arbitrary number
13308 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
13309 section name and base address for that section. You can specify any
13310 @var{address} as an expression.
13312 The symbol table of the file @var{filename} is added to the symbol table
13313 originally read with the @code{symbol-file} command. You can use the
13314 @code{add-symbol-file} command any number of times; the new symbol data
13315 thus read keeps adding to the old. To discard all old symbol data
13316 instead, use the @code{symbol-file} command without any arguments.
13318 @cindex relocatable object files, reading symbols from
13319 @cindex object files, relocatable, reading symbols from
13320 @cindex reading symbols from relocatable object files
13321 @cindex symbols, reading from relocatable object files
13322 @cindex @file{.o} files, reading symbols from
13323 Although @var{filename} is typically a shared library file, an
13324 executable file, or some other object file which has been fully
13325 relocated for loading into a process, you can also load symbolic
13326 information from relocatable @file{.o} files, as long as:
13330 the file's symbolic information refers only to linker symbols defined in
13331 that file, not to symbols defined by other object files,
13333 every section the file's symbolic information refers to has actually
13334 been loaded into the inferior, as it appears in the file, and
13336 you can determine the address at which every section was loaded, and
13337 provide these to the @code{add-symbol-file} command.
13341 Some embedded operating systems, like Sun Chorus and VxWorks, can load
13342 relocatable files into an already running program; such systems
13343 typically make the requirements above easy to meet. However, it's
13344 important to recognize that many native systems use complex link
13345 procedures (@code{.linkonce} section factoring and C@t{++} constructor table
13346 assembly, for example) that make the requirements difficult to meet. In
13347 general, one cannot assume that using @code{add-symbol-file} to read a
13348 relocatable object file's symbolic information will have the same effect
13349 as linking the relocatable object file into the program in the normal
13352 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
13354 @kindex add-symbol-file-from-memory
13355 @cindex @code{syscall DSO}
13356 @cindex load symbols from memory
13357 @item add-symbol-file-from-memory @var{address}
13358 Load symbols from the given @var{address} in a dynamically loaded
13359 object file whose image is mapped directly into the inferior's memory.
13360 For example, the Linux kernel maps a @code{syscall DSO} into each
13361 process's address space; this DSO provides kernel-specific code for
13362 some system calls. The argument can be any expression whose
13363 evaluation yields the address of the file's shared object file header.
13364 For this command to work, you must have used @code{symbol-file} or
13365 @code{exec-file} commands in advance.
13367 @kindex add-shared-symbol-files
13369 @item add-shared-symbol-files @var{library-file}
13370 @itemx assf @var{library-file}
13371 The @code{add-shared-symbol-files} command can currently be used only
13372 in the Cygwin build of @value{GDBN} on MS-Windows OS, where it is an
13373 alias for the @code{dll-symbols} command (@pxref{Cygwin Native}).
13374 @value{GDBN} automatically looks for shared libraries, however if
13375 @value{GDBN} does not find yours, you can invoke
13376 @code{add-shared-symbol-files}. It takes one argument: the shared
13377 library's file name. @code{assf} is a shorthand alias for
13378 @code{add-shared-symbol-files}.
13381 @item section @var{section} @var{addr}
13382 The @code{section} command changes the base address of the named
13383 @var{section} of the exec file to @var{addr}. This can be used if the
13384 exec file does not contain section addresses, (such as in the
13385 @code{a.out} format), or when the addresses specified in the file
13386 itself are wrong. Each section must be changed separately. The
13387 @code{info files} command, described below, lists all the sections and
13391 @kindex info target
13394 @code{info files} and @code{info target} are synonymous; both print the
13395 current target (@pxref{Targets, ,Specifying a Debugging Target}),
13396 including the names of the executable and core dump files currently in
13397 use by @value{GDBN}, and the files from which symbols were loaded. The
13398 command @code{help target} lists all possible targets rather than
13401 @kindex maint info sections
13402 @item maint info sections
13403 Another command that can give you extra information about program sections
13404 is @code{maint info sections}. In addition to the section information
13405 displayed by @code{info files}, this command displays the flags and file
13406 offset of each section in the executable and core dump files. In addition,
13407 @code{maint info sections} provides the following command options (which
13408 may be arbitrarily combined):
13412 Display sections for all loaded object files, including shared libraries.
13413 @item @var{sections}
13414 Display info only for named @var{sections}.
13415 @item @var{section-flags}
13416 Display info only for sections for which @var{section-flags} are true.
13417 The section flags that @value{GDBN} currently knows about are:
13420 Section will have space allocated in the process when loaded.
13421 Set for all sections except those containing debug information.
13423 Section will be loaded from the file into the child process memory.
13424 Set for pre-initialized code and data, clear for @code{.bss} sections.
13426 Section needs to be relocated before loading.
13428 Section cannot be modified by the child process.
13430 Section contains executable code only.
13432 Section contains data only (no executable code).
13434 Section will reside in ROM.
13436 Section contains data for constructor/destructor lists.
13438 Section is not empty.
13440 An instruction to the linker to not output the section.
13441 @item COFF_SHARED_LIBRARY
13442 A notification to the linker that the section contains
13443 COFF shared library information.
13445 Section contains common symbols.
13448 @kindex set trust-readonly-sections
13449 @cindex read-only sections
13450 @item set trust-readonly-sections on
13451 Tell @value{GDBN} that readonly sections in your object file
13452 really are read-only (i.e.@: that their contents will not change).
13453 In that case, @value{GDBN} can fetch values from these sections
13454 out of the object file, rather than from the target program.
13455 For some targets (notably embedded ones), this can be a significant
13456 enhancement to debugging performance.
13458 The default is off.
13460 @item set trust-readonly-sections off
13461 Tell @value{GDBN} not to trust readonly sections. This means that
13462 the contents of the section might change while the program is running,
13463 and must therefore be fetched from the target when needed.
13465 @item show trust-readonly-sections
13466 Show the current setting of trusting readonly sections.
13469 All file-specifying commands allow both absolute and relative file names
13470 as arguments. @value{GDBN} always converts the file name to an absolute file
13471 name and remembers it that way.
13473 @cindex shared libraries
13474 @anchor{Shared Libraries}
13475 @value{GDBN} supports @sc{gnu}/Linux, MS-Windows, HP-UX, SunOS, SVr4, Irix,
13476 and IBM RS/6000 AIX shared libraries.
13478 On MS-Windows @value{GDBN} must be linked with the Expat library to support
13479 shared libraries. @xref{Expat}.
13481 @value{GDBN} automatically loads symbol definitions from shared libraries
13482 when you use the @code{run} command, or when you examine a core file.
13483 (Before you issue the @code{run} command, @value{GDBN} does not understand
13484 references to a function in a shared library, however---unless you are
13485 debugging a core file).
13487 On HP-UX, if the program loads a library explicitly, @value{GDBN}
13488 automatically loads the symbols at the time of the @code{shl_load} call.
13490 @c FIXME: some @value{GDBN} release may permit some refs to undef
13491 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
13492 @c FIXME...lib; check this from time to time when updating manual
13494 There are times, however, when you may wish to not automatically load
13495 symbol definitions from shared libraries, such as when they are
13496 particularly large or there are many of them.
13498 To control the automatic loading of shared library symbols, use the
13502 @kindex set auto-solib-add
13503 @item set auto-solib-add @var{mode}
13504 If @var{mode} is @code{on}, symbols from all shared object libraries
13505 will be loaded automatically when the inferior begins execution, you
13506 attach to an independently started inferior, or when the dynamic linker
13507 informs @value{GDBN} that a new library has been loaded. If @var{mode}
13508 is @code{off}, symbols must be loaded manually, using the
13509 @code{sharedlibrary} command. The default value is @code{on}.
13511 @cindex memory used for symbol tables
13512 If your program uses lots of shared libraries with debug info that
13513 takes large amounts of memory, you can decrease the @value{GDBN}
13514 memory footprint by preventing it from automatically loading the
13515 symbols from shared libraries. To that end, type @kbd{set
13516 auto-solib-add off} before running the inferior, then load each
13517 library whose debug symbols you do need with @kbd{sharedlibrary
13518 @var{regexp}}, where @var{regexp} is a regular expression that matches
13519 the libraries whose symbols you want to be loaded.
13521 @kindex show auto-solib-add
13522 @item show auto-solib-add
13523 Display the current autoloading mode.
13526 @cindex load shared library
13527 To explicitly load shared library symbols, use the @code{sharedlibrary}
13531 @kindex info sharedlibrary
13533 @item info share @var{regex}
13534 @itemx info sharedlibrary @var{regex}
13535 Print the names of the shared libraries which are currently loaded
13536 that match @var{regex}. If @var{regex} is omitted then print
13537 all shared libraries that are loaded.
13539 @kindex sharedlibrary
13541 @item sharedlibrary @var{regex}
13542 @itemx share @var{regex}
13543 Load shared object library symbols for files matching a
13544 Unix regular expression.
13545 As with files loaded automatically, it only loads shared libraries
13546 required by your program for a core file or after typing @code{run}. If
13547 @var{regex} is omitted all shared libraries required by your program are
13550 @item nosharedlibrary
13551 @kindex nosharedlibrary
13552 @cindex unload symbols from shared libraries
13553 Unload all shared object library symbols. This discards all symbols
13554 that have been loaded from all shared libraries. Symbols from shared
13555 libraries that were loaded by explicit user requests are not
13559 Sometimes you may wish that @value{GDBN} stops and gives you control
13560 when any of shared library events happen. Use the @code{set
13561 stop-on-solib-events} command for this:
13564 @item set stop-on-solib-events
13565 @kindex set stop-on-solib-events
13566 This command controls whether @value{GDBN} should give you control
13567 when the dynamic linker notifies it about some shared library event.
13568 The most common event of interest is loading or unloading of a new
13571 @item show stop-on-solib-events
13572 @kindex show stop-on-solib-events
13573 Show whether @value{GDBN} stops and gives you control when shared
13574 library events happen.
13577 Shared libraries are also supported in many cross or remote debugging
13578 configurations. @value{GDBN} needs to have access to the target's libraries;
13579 this can be accomplished either by providing copies of the libraries
13580 on the host system, or by asking @value{GDBN} to automatically retrieve the
13581 libraries from the target. If copies of the target libraries are
13582 provided, they need to be the same as the target libraries, although the
13583 copies on the target can be stripped as long as the copies on the host are
13586 @cindex where to look for shared libraries
13587 For remote debugging, you need to tell @value{GDBN} where the target
13588 libraries are, so that it can load the correct copies---otherwise, it
13589 may try to load the host's libraries. @value{GDBN} has two variables
13590 to specify the search directories for target libraries.
13593 @cindex prefix for shared library file names
13594 @cindex system root, alternate
13595 @kindex set solib-absolute-prefix
13596 @kindex set sysroot
13597 @item set sysroot @var{path}
13598 Use @var{path} as the system root for the program being debugged. Any
13599 absolute shared library paths will be prefixed with @var{path}; many
13600 runtime loaders store the absolute paths to the shared library in the
13601 target program's memory. If you use @code{set sysroot} to find shared
13602 libraries, they need to be laid out in the same way that they are on
13603 the target, with e.g.@: a @file{/lib} and @file{/usr/lib} hierarchy
13606 If @var{path} starts with the sequence @file{remote:}, @value{GDBN} will
13607 retrieve the target libraries from the remote system. This is only
13608 supported when using a remote target that supports the @code{remote get}
13609 command (@pxref{File Transfer,,Sending files to a remote system}).
13610 The part of @var{path} following the initial @file{remote:}
13611 (if present) is used as system root prefix on the remote file system.
13612 @footnote{If you want to specify a local system root using a directory
13613 that happens to be named @file{remote:}, you need to use some equivalent
13614 variant of the name like @file{./remote:}.}
13616 The @code{set solib-absolute-prefix} command is an alias for @code{set
13619 @cindex default system root
13620 @cindex @samp{--with-sysroot}
13621 You can set the default system root by using the configure-time
13622 @samp{--with-sysroot} option. If the system root is inside
13623 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
13624 @samp{--exec-prefix}), then the default system root will be updated
13625 automatically if the installed @value{GDBN} is moved to a new
13628 @kindex show sysroot
13630 Display the current shared library prefix.
13632 @kindex set solib-search-path
13633 @item set solib-search-path @var{path}
13634 If this variable is set, @var{path} is a colon-separated list of
13635 directories to search for shared libraries. @samp{solib-search-path}
13636 is used after @samp{sysroot} fails to locate the library, or if the
13637 path to the library is relative instead of absolute. If you want to
13638 use @samp{solib-search-path} instead of @samp{sysroot}, be sure to set
13639 @samp{sysroot} to a nonexistent directory to prevent @value{GDBN} from
13640 finding your host's libraries. @samp{sysroot} is preferred; setting
13641 it to a nonexistent directory may interfere with automatic loading
13642 of shared library symbols.
13644 @kindex show solib-search-path
13645 @item show solib-search-path
13646 Display the current shared library search path.
13650 @node Separate Debug Files
13651 @section Debugging Information in Separate Files
13652 @cindex separate debugging information files
13653 @cindex debugging information in separate files
13654 @cindex @file{.debug} subdirectories
13655 @cindex debugging information directory, global
13656 @cindex global debugging information directory
13657 @cindex build ID, and separate debugging files
13658 @cindex @file{.build-id} directory
13660 @value{GDBN} allows you to put a program's debugging information in a
13661 file separate from the executable itself, in a way that allows
13662 @value{GDBN} to find and load the debugging information automatically.
13663 Since debugging information can be very large---sometimes larger
13664 than the executable code itself---some systems distribute debugging
13665 information for their executables in separate files, which users can
13666 install only when they need to debug a problem.
13668 @value{GDBN} supports two ways of specifying the separate debug info
13673 The executable contains a @dfn{debug link} that specifies the name of
13674 the separate debug info file. The separate debug file's name is
13675 usually @file{@var{executable}.debug}, where @var{executable} is the
13676 name of the corresponding executable file without leading directories
13677 (e.g., @file{ls.debug} for @file{/usr/bin/ls}). In addition, the
13678 debug link specifies a 32-bit @dfn{Cyclic Redundancy Check} (CRC)
13679 checksum for the debug file, which @value{GDBN} uses to validate that
13680 the executable and the debug file came from the same build.
13683 The executable contains a @dfn{build ID}, a unique bit string that is
13684 also present in the corresponding debug info file. (This is supported
13685 only on some operating systems, notably those which use the ELF format
13686 for binary files and the @sc{gnu} Binutils.) For more details about
13687 this feature, see the description of the @option{--build-id}
13688 command-line option in @ref{Options, , Command Line Options, ld.info,
13689 The GNU Linker}. The debug info file's name is not specified
13690 explicitly by the build ID, but can be computed from the build ID, see
13694 Depending on the way the debug info file is specified, @value{GDBN}
13695 uses two different methods of looking for the debug file:
13699 For the ``debug link'' method, @value{GDBN} looks up the named file in
13700 the directory of the executable file, then in a subdirectory of that
13701 directory named @file{.debug}, and finally under the global debug
13702 directory, in a subdirectory whose name is identical to the leading
13703 directories of the executable's absolute file name.
13706 For the ``build ID'' method, @value{GDBN} looks in the
13707 @file{.build-id} subdirectory of the global debug directory for a file
13708 named @file{@var{nn}/@var{nnnnnnnn}.debug}, where @var{nn} are the
13709 first 2 hex characters of the build ID bit string, and @var{nnnnnnnn}
13710 are the rest of the bit string. (Real build ID strings are 32 or more
13711 hex characters, not 10.)
13714 So, for example, suppose you ask @value{GDBN} to debug
13715 @file{/usr/bin/ls}, which has a debug link that specifies the
13716 file @file{ls.debug}, and a build ID whose value in hex is
13717 @code{abcdef1234}. If the global debug directory is
13718 @file{/usr/lib/debug}, then @value{GDBN} will look for the following
13719 debug information files, in the indicated order:
13723 @file{/usr/lib/debug/.build-id/ab/cdef1234.debug}
13725 @file{/usr/bin/ls.debug}
13727 @file{/usr/bin/.debug/ls.debug}
13729 @file{/usr/lib/debug/usr/bin/ls.debug}.
13732 You can set the global debugging info directory's name, and view the
13733 name @value{GDBN} is currently using.
13737 @kindex set debug-file-directory
13738 @item set debug-file-directory @var{directory}
13739 Set the directory which @value{GDBN} searches for separate debugging
13740 information files to @var{directory}.
13742 @kindex show debug-file-directory
13743 @item show debug-file-directory
13744 Show the directory @value{GDBN} searches for separate debugging
13749 @cindex @code{.gnu_debuglink} sections
13750 @cindex debug link sections
13751 A debug link is a special section of the executable file named
13752 @code{.gnu_debuglink}. The section must contain:
13756 A filename, with any leading directory components removed, followed by
13759 zero to three bytes of padding, as needed to reach the next four-byte
13760 boundary within the section, and
13762 a four-byte CRC checksum, stored in the same endianness used for the
13763 executable file itself. The checksum is computed on the debugging
13764 information file's full contents by the function given below, passing
13765 zero as the @var{crc} argument.
13768 Any executable file format can carry a debug link, as long as it can
13769 contain a section named @code{.gnu_debuglink} with the contents
13772 @cindex @code{.note.gnu.build-id} sections
13773 @cindex build ID sections
13774 The build ID is a special section in the executable file (and in other
13775 ELF binary files that @value{GDBN} may consider). This section is
13776 often named @code{.note.gnu.build-id}, but that name is not mandatory.
13777 It contains unique identification for the built files---the ID remains
13778 the same across multiple builds of the same build tree. The default
13779 algorithm SHA1 produces 160 bits (40 hexadecimal characters) of the
13780 content for the build ID string. The same section with an identical
13781 value is present in the original built binary with symbols, in its
13782 stripped variant, and in the separate debugging information file.
13784 The debugging information file itself should be an ordinary
13785 executable, containing a full set of linker symbols, sections, and
13786 debugging information. The sections of the debugging information file
13787 should have the same names, addresses, and sizes as the original file,
13788 but they need not contain any data---much like a @code{.bss} section
13789 in an ordinary executable.
13791 The @sc{gnu} binary utilities (Binutils) package includes the
13792 @samp{objcopy} utility that can produce
13793 the separated executable / debugging information file pairs using the
13794 following commands:
13797 @kbd{objcopy --only-keep-debug foo foo.debug}
13802 These commands remove the debugging
13803 information from the executable file @file{foo} and place it in the file
13804 @file{foo.debug}. You can use the first, second or both methods to link the
13809 The debug link method needs the following additional command to also leave
13810 behind a debug link in @file{foo}:
13813 @kbd{objcopy --add-gnu-debuglink=foo.debug foo}
13816 Ulrich Drepper's @file{elfutils} package, starting with version 0.53, contains
13817 a version of the @code{strip} command such that the command @kbd{strip foo -f
13818 foo.debug} has the same functionality as the two @code{objcopy} commands and
13819 the @code{ln -s} command above, together.
13822 Build ID gets embedded into the main executable using @code{ld --build-id} or
13823 the @value{NGCC} counterpart @code{gcc -Wl,--build-id}. Build ID support plus
13824 compatibility fixes for debug files separation are present in @sc{gnu} binary
13825 utilities (Binutils) package since version 2.18.
13830 @cindex CRC algorithm definition
13831 The CRC used in @code{.gnu_debuglink} is the CRC-32 defined in
13832 IEEE 802.3 using the polynomial:
13834 @c TexInfo requires naked braces for multi-digit exponents for Tex
13835 @c output, but this causes HTML output to barf. HTML has to be set using
13836 @c raw commands. So we end up having to specify this equation in 2
13841 <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>
13842 + <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
13848 @math{x^{32} + x^{26} + x^{23} + x^{22} + x^{16} + x^{12} + x^{11}}
13849 @math{+ x^{10} + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1}
13853 The function is computed byte at a time, taking the least
13854 significant bit of each byte first. The initial pattern
13855 @code{0xffffffff} is used, to ensure leading zeros affect the CRC and
13856 the final result is inverted to ensure trailing zeros also affect the
13859 @emph{Note:} This is the same CRC polynomial as used in handling the
13860 @dfn{Remote Serial Protocol} @code{qCRC} packet (@pxref{Remote Protocol,
13861 , @value{GDBN} Remote Serial Protocol}). However in the
13862 case of the Remote Serial Protocol, the CRC is computed @emph{most}
13863 significant bit first, and the result is not inverted, so trailing
13864 zeros have no effect on the CRC value.
13866 To complete the description, we show below the code of the function
13867 which produces the CRC used in @code{.gnu_debuglink}. Inverting the
13868 initially supplied @code{crc} argument means that an initial call to
13869 this function passing in zero will start computing the CRC using
13872 @kindex gnu_debuglink_crc32
13875 gnu_debuglink_crc32 (unsigned long crc,
13876 unsigned char *buf, size_t len)
13878 static const unsigned long crc32_table[256] =
13880 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
13881 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
13882 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
13883 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
13884 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
13885 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
13886 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
13887 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
13888 0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
13889 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
13890 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
13891 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
13892 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
13893 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
13894 0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
13895 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
13896 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
13897 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
13898 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
13899 0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
13900 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
13901 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
13902 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
13903 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
13904 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
13905 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
13906 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
13907 0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
13908 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
13909 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
13910 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
13911 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
13912 0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
13913 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
13914 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
13915 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
13916 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
13917 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
13918 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
13919 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
13920 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
13921 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
13922 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
13923 0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
13924 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
13925 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
13926 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
13927 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
13928 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
13929 0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
13930 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
13933 unsigned char *end;
13935 crc = ~crc & 0xffffffff;
13936 for (end = buf + len; buf < end; ++buf)
13937 crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
13938 return ~crc & 0xffffffff;
13943 This computation does not apply to the ``build ID'' method.
13946 @node Symbol Errors
13947 @section Errors Reading Symbol Files
13949 While reading a symbol file, @value{GDBN} occasionally encounters problems,
13950 such as symbol types it does not recognize, or known bugs in compiler
13951 output. By default, @value{GDBN} does not notify you of such problems, since
13952 they are relatively common and primarily of interest to people
13953 debugging compilers. If you are interested in seeing information
13954 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
13955 only one message about each such type of problem, no matter how many
13956 times the problem occurs; or you can ask @value{GDBN} to print more messages,
13957 to see how many times the problems occur, with the @code{set
13958 complaints} command (@pxref{Messages/Warnings, ,Optional Warnings and
13961 The messages currently printed, and their meanings, include:
13964 @item inner block not inside outer block in @var{symbol}
13966 The symbol information shows where symbol scopes begin and end
13967 (such as at the start of a function or a block of statements). This
13968 error indicates that an inner scope block is not fully contained
13969 in its outer scope blocks.
13971 @value{GDBN} circumvents the problem by treating the inner block as if it had
13972 the same scope as the outer block. In the error message, @var{symbol}
13973 may be shown as ``@code{(don't know)}'' if the outer block is not a
13976 @item block at @var{address} out of order
13978 The symbol information for symbol scope blocks should occur in
13979 order of increasing addresses. This error indicates that it does not
13982 @value{GDBN} does not circumvent this problem, and has trouble
13983 locating symbols in the source file whose symbols it is reading. (You
13984 can often determine what source file is affected by specifying
13985 @code{set verbose on}. @xref{Messages/Warnings, ,Optional Warnings and
13988 @item bad block start address patched
13990 The symbol information for a symbol scope block has a start address
13991 smaller than the address of the preceding source line. This is known
13992 to occur in the SunOS 4.1.1 (and earlier) C compiler.
13994 @value{GDBN} circumvents the problem by treating the symbol scope block as
13995 starting on the previous source line.
13997 @item bad string table offset in symbol @var{n}
14000 Symbol number @var{n} contains a pointer into the string table which is
14001 larger than the size of the string table.
14003 @value{GDBN} circumvents the problem by considering the symbol to have the
14004 name @code{foo}, which may cause other problems if many symbols end up
14007 @item unknown symbol type @code{0x@var{nn}}
14009 The symbol information contains new data types that @value{GDBN} does
14010 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
14011 uncomprehended information, in hexadecimal.
14013 @value{GDBN} circumvents the error by ignoring this symbol information.
14014 This usually allows you to debug your program, though certain symbols
14015 are not accessible. If you encounter such a problem and feel like
14016 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
14017 on @code{complain}, then go up to the function @code{read_dbx_symtab}
14018 and examine @code{*bufp} to see the symbol.
14020 @item stub type has NULL name
14022 @value{GDBN} could not find the full definition for a struct or class.
14024 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
14025 The symbol information for a C@t{++} member function is missing some
14026 information that recent versions of the compiler should have output for
14029 @item info mismatch between compiler and debugger
14031 @value{GDBN} could not parse a type specification output by the compiler.
14036 @section GDB Data Files
14038 @cindex prefix for data files
14039 @value{GDBN} will sometimes read an auxiliary data file. These files
14040 are kept in a directory known as the @dfn{data directory}.
14042 You can set the data directory's name, and view the name @value{GDBN}
14043 is currently using.
14046 @kindex set data-directory
14047 @item set data-directory @var{directory}
14048 Set the directory which @value{GDBN} searches for auxiliary data files
14049 to @var{directory}.
14051 @kindex show data-directory
14052 @item show data-directory
14053 Show the directory @value{GDBN} searches for auxiliary data files.
14056 @cindex default data directory
14057 @cindex @samp{--with-gdb-datadir}
14058 You can set the default data directory by using the configure-time
14059 @samp{--with-gdb-datadir} option. If the data directory is inside
14060 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
14061 @samp{--exec-prefix}), then the default data directory will be updated
14062 automatically if the installed @value{GDBN} is moved to a new
14066 @chapter Specifying a Debugging Target
14068 @cindex debugging target
14069 A @dfn{target} is the execution environment occupied by your program.
14071 Often, @value{GDBN} runs in the same host environment as your program;
14072 in that case, the debugging target is specified as a side effect when
14073 you use the @code{file} or @code{core} commands. When you need more
14074 flexibility---for example, running @value{GDBN} on a physically separate
14075 host, or controlling a standalone system over a serial port or a
14076 realtime system over a TCP/IP connection---you can use the @code{target}
14077 command to specify one of the target types configured for @value{GDBN}
14078 (@pxref{Target Commands, ,Commands for Managing Targets}).
14080 @cindex target architecture
14081 It is possible to build @value{GDBN} for several different @dfn{target
14082 architectures}. When @value{GDBN} is built like that, you can choose
14083 one of the available architectures with the @kbd{set architecture}
14087 @kindex set architecture
14088 @kindex show architecture
14089 @item set architecture @var{arch}
14090 This command sets the current target architecture to @var{arch}. The
14091 value of @var{arch} can be @code{"auto"}, in addition to one of the
14092 supported architectures.
14094 @item show architecture
14095 Show the current target architecture.
14097 @item set processor
14099 @kindex set processor
14100 @kindex show processor
14101 These are alias commands for, respectively, @code{set architecture}
14102 and @code{show architecture}.
14106 * Active Targets:: Active targets
14107 * Target Commands:: Commands for managing targets
14108 * Byte Order:: Choosing target byte order
14111 @node Active Targets
14112 @section Active Targets
14114 @cindex stacking targets
14115 @cindex active targets
14116 @cindex multiple targets
14118 There are three classes of targets: processes, core files, and
14119 executable files. @value{GDBN} can work concurrently on up to three
14120 active targets, one in each class. This allows you to (for example)
14121 start a process and inspect its activity without abandoning your work on
14124 For example, if you execute @samp{gdb a.out}, then the executable file
14125 @code{a.out} is the only active target. If you designate a core file as
14126 well---presumably from a prior run that crashed and coredumped---then
14127 @value{GDBN} has two active targets and uses them in tandem, looking
14128 first in the corefile target, then in the executable file, to satisfy
14129 requests for memory addresses. (Typically, these two classes of target
14130 are complementary, since core files contain only a program's
14131 read-write memory---variables and so on---plus machine status, while
14132 executable files contain only the program text and initialized data.)
14134 When you type @code{run}, your executable file becomes an active process
14135 target as well. When a process target is active, all @value{GDBN}
14136 commands requesting memory addresses refer to that target; addresses in
14137 an active core file or executable file target are obscured while the
14138 process target is active.
14140 Use the @code{core-file} and @code{exec-file} commands to select a new
14141 core file or executable target (@pxref{Files, ,Commands to Specify
14142 Files}). To specify as a target a process that is already running, use
14143 the @code{attach} command (@pxref{Attach, ,Debugging an Already-running
14146 @node Target Commands
14147 @section Commands for Managing Targets
14150 @item target @var{type} @var{parameters}
14151 Connects the @value{GDBN} host environment to a target machine or
14152 process. A target is typically a protocol for talking to debugging
14153 facilities. You use the argument @var{type} to specify the type or
14154 protocol of the target machine.
14156 Further @var{parameters} are interpreted by the target protocol, but
14157 typically include things like device names or host names to connect
14158 with, process numbers, and baud rates.
14160 The @code{target} command does not repeat if you press @key{RET} again
14161 after executing the command.
14163 @kindex help target
14165 Displays the names of all targets available. To display targets
14166 currently selected, use either @code{info target} or @code{info files}
14167 (@pxref{Files, ,Commands to Specify Files}).
14169 @item help target @var{name}
14170 Describe a particular target, including any parameters necessary to
14173 @kindex set gnutarget
14174 @item set gnutarget @var{args}
14175 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
14176 knows whether it is reading an @dfn{executable},
14177 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
14178 with the @code{set gnutarget} command. Unlike most @code{target} commands,
14179 with @code{gnutarget} the @code{target} refers to a program, not a machine.
14182 @emph{Warning:} To specify a file format with @code{set gnutarget},
14183 you must know the actual BFD name.
14187 @xref{Files, , Commands to Specify Files}.
14189 @kindex show gnutarget
14190 @item show gnutarget
14191 Use the @code{show gnutarget} command to display what file format
14192 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
14193 @value{GDBN} will determine the file format for each file automatically,
14194 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
14197 @cindex common targets
14198 Here are some common targets (available, or not, depending on the GDB
14203 @item target exec @var{program}
14204 @cindex executable file target
14205 An executable file. @samp{target exec @var{program}} is the same as
14206 @samp{exec-file @var{program}}.
14208 @item target core @var{filename}
14209 @cindex core dump file target
14210 A core dump file. @samp{target core @var{filename}} is the same as
14211 @samp{core-file @var{filename}}.
14213 @item target remote @var{medium}
14214 @cindex remote target
14215 A remote system connected to @value{GDBN} via a serial line or network
14216 connection. This command tells @value{GDBN} to use its own remote
14217 protocol over @var{medium} for debugging. @xref{Remote Debugging}.
14219 For example, if you have a board connected to @file{/dev/ttya} on the
14220 machine running @value{GDBN}, you could say:
14223 target remote /dev/ttya
14226 @code{target remote} supports the @code{load} command. This is only
14227 useful if you have some other way of getting the stub to the target
14228 system, and you can put it somewhere in memory where it won't get
14229 clobbered by the download.
14232 @cindex built-in simulator target
14233 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
14241 works; however, you cannot assume that a specific memory map, device
14242 drivers, or even basic I/O is available, although some simulators do
14243 provide these. For info about any processor-specific simulator details,
14244 see the appropriate section in @ref{Embedded Processors, ,Embedded
14249 Some configurations may include these targets as well:
14253 @item target nrom @var{dev}
14254 @cindex NetROM ROM emulator target
14255 NetROM ROM emulator. This target only supports downloading.
14259 Different targets are available on different configurations of @value{GDBN};
14260 your configuration may have more or fewer targets.
14262 Many remote targets require you to download the executable's code once
14263 you've successfully established a connection. You may wish to control
14264 various aspects of this process.
14269 @kindex set hash@r{, for remote monitors}
14270 @cindex hash mark while downloading
14271 This command controls whether a hash mark @samp{#} is displayed while
14272 downloading a file to the remote monitor. If on, a hash mark is
14273 displayed after each S-record is successfully downloaded to the
14277 @kindex show hash@r{, for remote monitors}
14278 Show the current status of displaying the hash mark.
14280 @item set debug monitor
14281 @kindex set debug monitor
14282 @cindex display remote monitor communications
14283 Enable or disable display of communications messages between
14284 @value{GDBN} and the remote monitor.
14286 @item show debug monitor
14287 @kindex show debug monitor
14288 Show the current status of displaying communications between
14289 @value{GDBN} and the remote monitor.
14294 @kindex load @var{filename}
14295 @item load @var{filename}
14297 Depending on what remote debugging facilities are configured into
14298 @value{GDBN}, the @code{load} command may be available. Where it exists, it
14299 is meant to make @var{filename} (an executable) available for debugging
14300 on the remote system---by downloading, or dynamic linking, for example.
14301 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
14302 the @code{add-symbol-file} command.
14304 If your @value{GDBN} does not have a @code{load} command, attempting to
14305 execute it gets the error message ``@code{You can't do that when your
14306 target is @dots{}}''
14308 The file is loaded at whatever address is specified in the executable.
14309 For some object file formats, you can specify the load address when you
14310 link the program; for other formats, like a.out, the object file format
14311 specifies a fixed address.
14312 @c FIXME! This would be a good place for an xref to the GNU linker doc.
14314 Depending on the remote side capabilities, @value{GDBN} may be able to
14315 load programs into flash memory.
14317 @code{load} does not repeat if you press @key{RET} again after using it.
14321 @section Choosing Target Byte Order
14323 @cindex choosing target byte order
14324 @cindex target byte order
14326 Some types of processors, such as the MIPS, PowerPC, and Renesas SH,
14327 offer the ability to run either big-endian or little-endian byte
14328 orders. Usually the executable or symbol will include a bit to
14329 designate the endian-ness, and you will not need to worry about
14330 which to use. However, you may still find it useful to adjust
14331 @value{GDBN}'s idea of processor endian-ness manually.
14335 @item set endian big
14336 Instruct @value{GDBN} to assume the target is big-endian.
14338 @item set endian little
14339 Instruct @value{GDBN} to assume the target is little-endian.
14341 @item set endian auto
14342 Instruct @value{GDBN} to use the byte order associated with the
14346 Display @value{GDBN}'s current idea of the target byte order.
14350 Note that these commands merely adjust interpretation of symbolic
14351 data on the host, and that they have absolutely no effect on the
14355 @node Remote Debugging
14356 @chapter Debugging Remote Programs
14357 @cindex remote debugging
14359 If you are trying to debug a program running on a machine that cannot run
14360 @value{GDBN} in the usual way, it is often useful to use remote debugging.
14361 For example, you might use remote debugging on an operating system kernel,
14362 or on a small system which does not have a general purpose operating system
14363 powerful enough to run a full-featured debugger.
14365 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
14366 to make this work with particular debugging targets. In addition,
14367 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
14368 but not specific to any particular target system) which you can use if you
14369 write the remote stubs---the code that runs on the remote system to
14370 communicate with @value{GDBN}.
14372 Other remote targets may be available in your
14373 configuration of @value{GDBN}; use @code{help target} to list them.
14376 * Connecting:: Connecting to a remote target
14377 * File Transfer:: Sending files to a remote system
14378 * Server:: Using the gdbserver program
14379 * Remote Configuration:: Remote configuration
14380 * Remote Stub:: Implementing a remote stub
14384 @section Connecting to a Remote Target
14386 On the @value{GDBN} host machine, you will need an unstripped copy of
14387 your program, since @value{GDBN} needs symbol and debugging information.
14388 Start up @value{GDBN} as usual, using the name of the local copy of your
14389 program as the first argument.
14391 @cindex @code{target remote}
14392 @value{GDBN} can communicate with the target over a serial line, or
14393 over an @acronym{IP} network using @acronym{TCP} or @acronym{UDP}. In
14394 each case, @value{GDBN} uses the same protocol for debugging your
14395 program; only the medium carrying the debugging packets varies. The
14396 @code{target remote} command establishes a connection to the target.
14397 Its arguments indicate which medium to use:
14401 @item target remote @var{serial-device}
14402 @cindex serial line, @code{target remote}
14403 Use @var{serial-device} to communicate with the target. For example,
14404 to use a serial line connected to the device named @file{/dev/ttyb}:
14407 target remote /dev/ttyb
14410 If you're using a serial line, you may want to give @value{GDBN} the
14411 @w{@samp{--baud}} option, or use the @code{set remotebaud} command
14412 (@pxref{Remote Configuration, set remotebaud}) before the
14413 @code{target} command.
14415 @item target remote @code{@var{host}:@var{port}}
14416 @itemx target remote @code{tcp:@var{host}:@var{port}}
14417 @cindex @acronym{TCP} port, @code{target remote}
14418 Debug using a @acronym{TCP} connection to @var{port} on @var{host}.
14419 The @var{host} may be either a host name or a numeric @acronym{IP}
14420 address; @var{port} must be a decimal number. The @var{host} could be
14421 the target machine itself, if it is directly connected to the net, or
14422 it might be a terminal server which in turn has a serial line to the
14425 For example, to connect to port 2828 on a terminal server named
14429 target remote manyfarms:2828
14432 If your remote target is actually running on the same machine as your
14433 debugger session (e.g.@: a simulator for your target running on the
14434 same host), you can omit the hostname. For example, to connect to
14435 port 1234 on your local machine:
14438 target remote :1234
14442 Note that the colon is still required here.
14444 @item target remote @code{udp:@var{host}:@var{port}}
14445 @cindex @acronym{UDP} port, @code{target remote}
14446 Debug using @acronym{UDP} packets to @var{port} on @var{host}. For example, to
14447 connect to @acronym{UDP} port 2828 on a terminal server named @code{manyfarms}:
14450 target remote udp:manyfarms:2828
14453 When using a @acronym{UDP} connection for remote debugging, you should
14454 keep in mind that the `U' stands for ``Unreliable''. @acronym{UDP}
14455 can silently drop packets on busy or unreliable networks, which will
14456 cause havoc with your debugging session.
14458 @item target remote | @var{command}
14459 @cindex pipe, @code{target remote} to
14460 Run @var{command} in the background and communicate with it using a
14461 pipe. The @var{command} is a shell command, to be parsed and expanded
14462 by the system's command shell, @code{/bin/sh}; it should expect remote
14463 protocol packets on its standard input, and send replies on its
14464 standard output. You could use this to run a stand-alone simulator
14465 that speaks the remote debugging protocol, to make net connections
14466 using programs like @code{ssh}, or for other similar tricks.
14468 If @var{command} closes its standard output (perhaps by exiting),
14469 @value{GDBN} will try to send it a @code{SIGTERM} signal. (If the
14470 program has already exited, this will have no effect.)
14474 Once the connection has been established, you can use all the usual
14475 commands to examine and change data. The remote program is already
14476 running; you can use @kbd{step} and @kbd{continue}, and you do not
14477 need to use @kbd{run}.
14479 @cindex interrupting remote programs
14480 @cindex remote programs, interrupting
14481 Whenever @value{GDBN} is waiting for the remote program, if you type the
14482 interrupt character (often @kbd{Ctrl-c}), @value{GDBN} attempts to stop the
14483 program. This may or may not succeed, depending in part on the hardware
14484 and the serial drivers the remote system uses. If you type the
14485 interrupt character once again, @value{GDBN} displays this prompt:
14488 Interrupted while waiting for the program.
14489 Give up (and stop debugging it)? (y or n)
14492 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
14493 (If you decide you want to try again later, you can use @samp{target
14494 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
14495 goes back to waiting.
14498 @kindex detach (remote)
14500 When you have finished debugging the remote program, you can use the
14501 @code{detach} command to release it from @value{GDBN} control.
14502 Detaching from the target normally resumes its execution, but the results
14503 will depend on your particular remote stub. After the @code{detach}
14504 command, @value{GDBN} is free to connect to another target.
14508 The @code{disconnect} command behaves like @code{detach}, except that
14509 the target is generally not resumed. It will wait for @value{GDBN}
14510 (this instance or another one) to connect and continue debugging. After
14511 the @code{disconnect} command, @value{GDBN} is again free to connect to
14514 @cindex send command to remote monitor
14515 @cindex extend @value{GDBN} for remote targets
14516 @cindex add new commands for external monitor
14518 @item monitor @var{cmd}
14519 This command allows you to send arbitrary commands directly to the
14520 remote monitor. Since @value{GDBN} doesn't care about the commands it
14521 sends like this, this command is the way to extend @value{GDBN}---you
14522 can add new commands that only the external monitor will understand
14526 @node File Transfer
14527 @section Sending files to a remote system
14528 @cindex remote target, file transfer
14529 @cindex file transfer
14530 @cindex sending files to remote systems
14532 Some remote targets offer the ability to transfer files over the same
14533 connection used to communicate with @value{GDBN}. This is convenient
14534 for targets accessible through other means, e.g.@: @sc{gnu}/Linux systems
14535 running @code{gdbserver} over a network interface. For other targets,
14536 e.g.@: embedded devices with only a single serial port, this may be
14537 the only way to upload or download files.
14539 Not all remote targets support these commands.
14543 @item remote put @var{hostfile} @var{targetfile}
14544 Copy file @var{hostfile} from the host system (the machine running
14545 @value{GDBN}) to @var{targetfile} on the target system.
14548 @item remote get @var{targetfile} @var{hostfile}
14549 Copy file @var{targetfile} from the target system to @var{hostfile}
14550 on the host system.
14552 @kindex remote delete
14553 @item remote delete @var{targetfile}
14554 Delete @var{targetfile} from the target system.
14559 @section Using the @code{gdbserver} Program
14562 @cindex remote connection without stubs
14563 @code{gdbserver} is a control program for Unix-like systems, which
14564 allows you to connect your program with a remote @value{GDBN} via
14565 @code{target remote}---but without linking in the usual debugging stub.
14567 @code{gdbserver} is not a complete replacement for the debugging stubs,
14568 because it requires essentially the same operating-system facilities
14569 that @value{GDBN} itself does. In fact, a system that can run
14570 @code{gdbserver} to connect to a remote @value{GDBN} could also run
14571 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
14572 because it is a much smaller program than @value{GDBN} itself. It is
14573 also easier to port than all of @value{GDBN}, so you may be able to get
14574 started more quickly on a new system by using @code{gdbserver}.
14575 Finally, if you develop code for real-time systems, you may find that
14576 the tradeoffs involved in real-time operation make it more convenient to
14577 do as much development work as possible on another system, for example
14578 by cross-compiling. You can use @code{gdbserver} to make a similar
14579 choice for debugging.
14581 @value{GDBN} and @code{gdbserver} communicate via either a serial line
14582 or a TCP connection, using the standard @value{GDBN} remote serial
14586 @emph{Warning:} @code{gdbserver} does not have any built-in security.
14587 Do not run @code{gdbserver} connected to any public network; a
14588 @value{GDBN} connection to @code{gdbserver} provides access to the
14589 target system with the same privileges as the user running
14593 @subsection Running @code{gdbserver}
14594 @cindex arguments, to @code{gdbserver}
14596 Run @code{gdbserver} on the target system. You need a copy of the
14597 program you want to debug, including any libraries it requires.
14598 @code{gdbserver} does not need your program's symbol table, so you can
14599 strip the program if necessary to save space. @value{GDBN} on the host
14600 system does all the symbol handling.
14602 To use the server, you must tell it how to communicate with @value{GDBN};
14603 the name of your program; and the arguments for your program. The usual
14607 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
14610 @var{comm} is either a device name (to use a serial line) or a TCP
14611 hostname and portnumber. For example, to debug Emacs with the argument
14612 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
14616 target> gdbserver /dev/com1 emacs foo.txt
14619 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
14622 To use a TCP connection instead of a serial line:
14625 target> gdbserver host:2345 emacs foo.txt
14628 The only difference from the previous example is the first argument,
14629 specifying that you are communicating with the host @value{GDBN} via
14630 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
14631 expect a TCP connection from machine @samp{host} to local TCP port 2345.
14632 (Currently, the @samp{host} part is ignored.) You can choose any number
14633 you want for the port number as long as it does not conflict with any
14634 TCP ports already in use on the target system (for example, @code{23} is
14635 reserved for @code{telnet}).@footnote{If you choose a port number that
14636 conflicts with another service, @code{gdbserver} prints an error message
14637 and exits.} You must use the same port number with the host @value{GDBN}
14638 @code{target remote} command.
14640 @subsubsection Attaching to a Running Program
14642 On some targets, @code{gdbserver} can also attach to running programs.
14643 This is accomplished via the @code{--attach} argument. The syntax is:
14646 target> gdbserver --attach @var{comm} @var{pid}
14649 @var{pid} is the process ID of a currently running process. It isn't necessary
14650 to point @code{gdbserver} at a binary for the running process.
14653 @cindex attach to a program by name
14654 You can debug processes by name instead of process ID if your target has the
14655 @code{pidof} utility:
14658 target> gdbserver --attach @var{comm} `pidof @var{program}`
14661 In case more than one copy of @var{program} is running, or @var{program}
14662 has multiple threads, most versions of @code{pidof} support the
14663 @code{-s} option to only return the first process ID.
14665 @subsubsection Multi-Process Mode for @code{gdbserver}
14666 @cindex gdbserver, multiple processes
14667 @cindex multiple processes with gdbserver
14669 When you connect to @code{gdbserver} using @code{target remote},
14670 @code{gdbserver} debugs the specified program only once. When the
14671 program exits, or you detach from it, @value{GDBN} closes the connection
14672 and @code{gdbserver} exits.
14674 If you connect using @kbd{target extended-remote}, @code{gdbserver}
14675 enters multi-process mode. When the debugged program exits, or you
14676 detach from it, @value{GDBN} stays connected to @code{gdbserver} even
14677 though no program is running. The @code{run} and @code{attach}
14678 commands instruct @code{gdbserver} to run or attach to a new program.
14679 The @code{run} command uses @code{set remote exec-file} (@pxref{set
14680 remote exec-file}) to select the program to run. Command line
14681 arguments are supported, except for wildcard expansion and I/O
14682 redirection (@pxref{Arguments}).
14684 To start @code{gdbserver} without supplying an initial command to run
14685 or process ID to attach, use the @option{--multi} command line option.
14686 Then you can connect using @kbd{target extended-remote} and start
14687 the program you want to debug.
14689 @code{gdbserver} does not automatically exit in multi-process mode.
14690 You can terminate it by using @code{monitor exit}
14691 (@pxref{Monitor Commands for gdbserver}).
14693 @subsubsection Other Command-Line Arguments for @code{gdbserver}
14695 The @option{--debug} option tells @code{gdbserver} to display extra
14696 status information about the debugging process. The
14697 @option{--remote-debug} option tells @code{gdbserver} to display
14698 remote protocol debug output. These options are intended for
14699 @code{gdbserver} development and for bug reports to the developers.
14701 The @option{--wrapper} option specifies a wrapper to launch programs
14702 for debugging. The option should be followed by the name of the
14703 wrapper, then any command-line arguments to pass to the wrapper, then
14704 @kbd{--} indicating the end of the wrapper arguments.
14706 @code{gdbserver} runs the specified wrapper program with a combined
14707 command line including the wrapper arguments, then the name of the
14708 program to debug, then any arguments to the program. The wrapper
14709 runs until it executes your program, and then @value{GDBN} gains control.
14711 You can use any program that eventually calls @code{execve} with
14712 its arguments as a wrapper. Several standard Unix utilities do
14713 this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending
14714 with @code{exec "$@@"} will also work.
14716 For example, you can use @code{env} to pass an environment variable to
14717 the debugged program, without setting the variable in @code{gdbserver}'s
14721 $ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog
14724 @subsection Connecting to @code{gdbserver}
14726 Run @value{GDBN} on the host system.
14728 First make sure you have the necessary symbol files. Load symbols for
14729 your application using the @code{file} command before you connect. Use
14730 @code{set sysroot} to locate target libraries (unless your @value{GDBN}
14731 was compiled with the correct sysroot using @code{--with-sysroot}).
14733 The symbol file and target libraries must exactly match the executable
14734 and libraries on the target, with one exception: the files on the host
14735 system should not be stripped, even if the files on the target system
14736 are. Mismatched or missing files will lead to confusing results
14737 during debugging. On @sc{gnu}/Linux targets, mismatched or missing
14738 files may also prevent @code{gdbserver} from debugging multi-threaded
14741 Connect to your target (@pxref{Connecting,,Connecting to a Remote Target}).
14742 For TCP connections, you must start up @code{gdbserver} prior to using
14743 the @code{target remote} command. Otherwise you may get an error whose
14744 text depends on the host system, but which usually looks something like
14745 @samp{Connection refused}. Don't use the @code{load}
14746 command in @value{GDBN} when using @code{gdbserver}, since the program is
14747 already on the target.
14749 @subsection Monitor Commands for @code{gdbserver}
14750 @cindex monitor commands, for @code{gdbserver}
14751 @anchor{Monitor Commands for gdbserver}
14753 During a @value{GDBN} session using @code{gdbserver}, you can use the
14754 @code{monitor} command to send special requests to @code{gdbserver}.
14755 Here are the available commands.
14759 List the available monitor commands.
14761 @item monitor set debug 0
14762 @itemx monitor set debug 1
14763 Disable or enable general debugging messages.
14765 @item monitor set remote-debug 0
14766 @itemx monitor set remote-debug 1
14767 Disable or enable specific debugging messages associated with the remote
14768 protocol (@pxref{Remote Protocol}).
14771 Tell gdbserver to exit immediately. This command should be followed by
14772 @code{disconnect} to close the debugging session. @code{gdbserver} will
14773 detach from any attached processes and kill any processes it created.
14774 Use @code{monitor exit} to terminate @code{gdbserver} at the end
14775 of a multi-process mode debug session.
14779 @node Remote Configuration
14780 @section Remote Configuration
14783 @kindex show remote
14784 This section documents the configuration options available when
14785 debugging remote programs. For the options related to the File I/O
14786 extensions of the remote protocol, see @ref{system,
14787 system-call-allowed}.
14790 @item set remoteaddresssize @var{bits}
14791 @cindex address size for remote targets
14792 @cindex bits in remote address
14793 Set the maximum size of address in a memory packet to the specified
14794 number of bits. @value{GDBN} will mask off the address bits above
14795 that number, when it passes addresses to the remote target. The
14796 default value is the number of bits in the target's address.
14798 @item show remoteaddresssize
14799 Show the current value of remote address size in bits.
14801 @item set remotebaud @var{n}
14802 @cindex baud rate for remote targets
14803 Set the baud rate for the remote serial I/O to @var{n} baud. The
14804 value is used to set the speed of the serial port used for debugging
14807 @item show remotebaud
14808 Show the current speed of the remote connection.
14810 @item set remotebreak
14811 @cindex interrupt remote programs
14812 @cindex BREAK signal instead of Ctrl-C
14813 @anchor{set remotebreak}
14814 If set to on, @value{GDBN} sends a @code{BREAK} signal to the remote
14815 when you type @kbd{Ctrl-c} to interrupt the program running
14816 on the remote. If set to off, @value{GDBN} sends the @samp{Ctrl-C}
14817 character instead. The default is off, since most remote systems
14818 expect to see @samp{Ctrl-C} as the interrupt signal.
14820 @item show remotebreak
14821 Show whether @value{GDBN} sends @code{BREAK} or @samp{Ctrl-C} to
14822 interrupt the remote program.
14824 @item set remoteflow on
14825 @itemx set remoteflow off
14826 @kindex set remoteflow
14827 Enable or disable hardware flow control (@code{RTS}/@code{CTS})
14828 on the serial port used to communicate to the remote target.
14830 @item show remoteflow
14831 @kindex show remoteflow
14832 Show the current setting of hardware flow control.
14834 @item set remotelogbase @var{base}
14835 Set the base (a.k.a.@: radix) of logging serial protocol
14836 communications to @var{base}. Supported values of @var{base} are:
14837 @code{ascii}, @code{octal}, and @code{hex}. The default is
14840 @item show remotelogbase
14841 Show the current setting of the radix for logging remote serial
14844 @item set remotelogfile @var{file}
14845 @cindex record serial communications on file
14846 Record remote serial communications on the named @var{file}. The
14847 default is not to record at all.
14849 @item show remotelogfile.
14850 Show the current setting of the file name on which to record the
14851 serial communications.
14853 @item set remotetimeout @var{num}
14854 @cindex timeout for serial communications
14855 @cindex remote timeout
14856 Set the timeout limit to wait for the remote target to respond to
14857 @var{num} seconds. The default is 2 seconds.
14859 @item show remotetimeout
14860 Show the current number of seconds to wait for the remote target
14863 @cindex limit hardware breakpoints and watchpoints
14864 @cindex remote target, limit break- and watchpoints
14865 @anchor{set remote hardware-watchpoint-limit}
14866 @anchor{set remote hardware-breakpoint-limit}
14867 @item set remote hardware-watchpoint-limit @var{limit}
14868 @itemx set remote hardware-breakpoint-limit @var{limit}
14869 Restrict @value{GDBN} to using @var{limit} remote hardware breakpoint or
14870 watchpoints. A limit of -1, the default, is treated as unlimited.
14872 @item set remote exec-file @var{filename}
14873 @itemx show remote exec-file
14874 @anchor{set remote exec-file}
14875 @cindex executable file, for remote target
14876 Select the file used for @code{run} with @code{target
14877 extended-remote}. This should be set to a filename valid on the
14878 target system. If it is not set, the target will use a default
14879 filename (e.g.@: the last program run).
14883 @item set tcp auto-retry on
14884 @cindex auto-retry, for remote TCP target
14885 Enable auto-retry for remote TCP connections. This is useful if the remote
14886 debugging agent is launched in parallel with @value{GDBN}; there is a race
14887 condition because the agent may not become ready to accept the connection
14888 before @value{GDBN} attempts to connect. When auto-retry is
14889 enabled, if the initial attempt to connect fails, @value{GDBN} reattempts
14890 to establish the connection using the timeout specified by
14891 @code{set tcp connect-timeout}.
14893 @item set tcp auto-retry off
14894 Do not auto-retry failed TCP connections.
14896 @item show tcp auto-retry
14897 Show the current auto-retry setting.
14899 @item set tcp connect-timeout @var{seconds}
14900 @cindex connection timeout, for remote TCP target
14901 @cindex timeout, for remote target connection
14902 Set the timeout for establishing a TCP connection to the remote target to
14903 @var{seconds}. The timeout affects both polling to retry failed connections
14904 (enabled by @code{set tcp auto-retry on}) and waiting for connections
14905 that are merely slow to complete, and represents an approximate cumulative
14908 @item show tcp connect-timeout
14909 Show the current connection timeout setting.
14912 @cindex remote packets, enabling and disabling
14913 The @value{GDBN} remote protocol autodetects the packets supported by
14914 your debugging stub. If you need to override the autodetection, you
14915 can use these commands to enable or disable individual packets. Each
14916 packet can be set to @samp{on} (the remote target supports this
14917 packet), @samp{off} (the remote target does not support this packet),
14918 or @samp{auto} (detect remote target support for this packet). They
14919 all default to @samp{auto}. For more information about each packet,
14920 see @ref{Remote Protocol}.
14922 During normal use, you should not have to use any of these commands.
14923 If you do, that may be a bug in your remote debugging stub, or a bug
14924 in @value{GDBN}. You may want to report the problem to the
14925 @value{GDBN} developers.
14927 For each packet @var{name}, the command to enable or disable the
14928 packet is @code{set remote @var{name}-packet}. The available settings
14931 @multitable @columnfractions 0.28 0.32 0.25
14934 @tab Related Features
14936 @item @code{fetch-register}
14938 @tab @code{info registers}
14940 @item @code{set-register}
14944 @item @code{binary-download}
14946 @tab @code{load}, @code{set}
14948 @item @code{read-aux-vector}
14949 @tab @code{qXfer:auxv:read}
14950 @tab @code{info auxv}
14952 @item @code{symbol-lookup}
14953 @tab @code{qSymbol}
14954 @tab Detecting multiple threads
14956 @item @code{attach}
14957 @tab @code{vAttach}
14960 @item @code{verbose-resume}
14962 @tab Stepping or resuming multiple threads
14968 @item @code{software-breakpoint}
14972 @item @code{hardware-breakpoint}
14976 @item @code{write-watchpoint}
14980 @item @code{read-watchpoint}
14984 @item @code{access-watchpoint}
14988 @item @code{target-features}
14989 @tab @code{qXfer:features:read}
14990 @tab @code{set architecture}
14992 @item @code{library-info}
14993 @tab @code{qXfer:libraries:read}
14994 @tab @code{info sharedlibrary}
14996 @item @code{memory-map}
14997 @tab @code{qXfer:memory-map:read}
14998 @tab @code{info mem}
15000 @item @code{read-spu-object}
15001 @tab @code{qXfer:spu:read}
15002 @tab @code{info spu}
15004 @item @code{write-spu-object}
15005 @tab @code{qXfer:spu:write}
15006 @tab @code{info spu}
15008 @item @code{read-siginfo-object}
15009 @tab @code{qXfer:siginfo:read}
15010 @tab @code{print $_siginfo}
15012 @item @code{write-siginfo-object}
15013 @tab @code{qXfer:siginfo:write}
15014 @tab @code{set $_siginfo}
15016 @item @code{get-thread-local-@*storage-address}
15017 @tab @code{qGetTLSAddr}
15018 @tab Displaying @code{__thread} variables
15020 @item @code{search-memory}
15021 @tab @code{qSearch:memory}
15024 @item @code{supported-packets}
15025 @tab @code{qSupported}
15026 @tab Remote communications parameters
15028 @item @code{pass-signals}
15029 @tab @code{QPassSignals}
15030 @tab @code{handle @var{signal}}
15032 @item @code{hostio-close-packet}
15033 @tab @code{vFile:close}
15034 @tab @code{remote get}, @code{remote put}
15036 @item @code{hostio-open-packet}
15037 @tab @code{vFile:open}
15038 @tab @code{remote get}, @code{remote put}
15040 @item @code{hostio-pread-packet}
15041 @tab @code{vFile:pread}
15042 @tab @code{remote get}, @code{remote put}
15044 @item @code{hostio-pwrite-packet}
15045 @tab @code{vFile:pwrite}
15046 @tab @code{remote get}, @code{remote put}
15048 @item @code{hostio-unlink-packet}
15049 @tab @code{vFile:unlink}
15050 @tab @code{remote delete}
15052 @item @code{noack-packet}
15053 @tab @code{QStartNoAckMode}
15054 @tab Packet acknowledgment
15056 @item @code{osdata}
15057 @tab @code{qXfer:osdata:read}
15058 @tab @code{info os}
15060 @item @code{query-attached}
15061 @tab @code{qAttached}
15062 @tab Querying remote process attach state.
15066 @section Implementing a Remote Stub
15068 @cindex debugging stub, example
15069 @cindex remote stub, example
15070 @cindex stub example, remote debugging
15071 The stub files provided with @value{GDBN} implement the target side of the
15072 communication protocol, and the @value{GDBN} side is implemented in the
15073 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
15074 these subroutines to communicate, and ignore the details. (If you're
15075 implementing your own stub file, you can still ignore the details: start
15076 with one of the existing stub files. @file{sparc-stub.c} is the best
15077 organized, and therefore the easiest to read.)
15079 @cindex remote serial debugging, overview
15080 To debug a program running on another machine (the debugging
15081 @dfn{target} machine), you must first arrange for all the usual
15082 prerequisites for the program to run by itself. For example, for a C
15087 A startup routine to set up the C runtime environment; these usually
15088 have a name like @file{crt0}. The startup routine may be supplied by
15089 your hardware supplier, or you may have to write your own.
15092 A C subroutine library to support your program's
15093 subroutine calls, notably managing input and output.
15096 A way of getting your program to the other machine---for example, a
15097 download program. These are often supplied by the hardware
15098 manufacturer, but you may have to write your own from hardware
15102 The next step is to arrange for your program to use a serial port to
15103 communicate with the machine where @value{GDBN} is running (the @dfn{host}
15104 machine). In general terms, the scheme looks like this:
15108 @value{GDBN} already understands how to use this protocol; when everything
15109 else is set up, you can simply use the @samp{target remote} command
15110 (@pxref{Targets,,Specifying a Debugging Target}).
15112 @item On the target,
15113 you must link with your program a few special-purpose subroutines that
15114 implement the @value{GDBN} remote serial protocol. The file containing these
15115 subroutines is called a @dfn{debugging stub}.
15117 On certain remote targets, you can use an auxiliary program
15118 @code{gdbserver} instead of linking a stub into your program.
15119 @xref{Server,,Using the @code{gdbserver} Program}, for details.
15122 The debugging stub is specific to the architecture of the remote
15123 machine; for example, use @file{sparc-stub.c} to debug programs on
15126 @cindex remote serial stub list
15127 These working remote stubs are distributed with @value{GDBN}:
15132 @cindex @file{i386-stub.c}
15135 For Intel 386 and compatible architectures.
15138 @cindex @file{m68k-stub.c}
15139 @cindex Motorola 680x0
15141 For Motorola 680x0 architectures.
15144 @cindex @file{sh-stub.c}
15147 For Renesas SH architectures.
15150 @cindex @file{sparc-stub.c}
15152 For @sc{sparc} architectures.
15154 @item sparcl-stub.c
15155 @cindex @file{sparcl-stub.c}
15158 For Fujitsu @sc{sparclite} architectures.
15162 The @file{README} file in the @value{GDBN} distribution may list other
15163 recently added stubs.
15166 * Stub Contents:: What the stub can do for you
15167 * Bootstrapping:: What you must do for the stub
15168 * Debug Session:: Putting it all together
15171 @node Stub Contents
15172 @subsection What the Stub Can Do for You
15174 @cindex remote serial stub
15175 The debugging stub for your architecture supplies these three
15179 @item set_debug_traps
15180 @findex set_debug_traps
15181 @cindex remote serial stub, initialization
15182 This routine arranges for @code{handle_exception} to run when your
15183 program stops. You must call this subroutine explicitly near the
15184 beginning of your program.
15186 @item handle_exception
15187 @findex handle_exception
15188 @cindex remote serial stub, main routine
15189 This is the central workhorse, but your program never calls it
15190 explicitly---the setup code arranges for @code{handle_exception} to
15191 run when a trap is triggered.
15193 @code{handle_exception} takes control when your program stops during
15194 execution (for example, on a breakpoint), and mediates communications
15195 with @value{GDBN} on the host machine. This is where the communications
15196 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
15197 representative on the target machine. It begins by sending summary
15198 information on the state of your program, then continues to execute,
15199 retrieving and transmitting any information @value{GDBN} needs, until you
15200 execute a @value{GDBN} command that makes your program resume; at that point,
15201 @code{handle_exception} returns control to your own code on the target
15205 @cindex @code{breakpoint} subroutine, remote
15206 Use this auxiliary subroutine to make your program contain a
15207 breakpoint. Depending on the particular situation, this may be the only
15208 way for @value{GDBN} to get control. For instance, if your target
15209 machine has some sort of interrupt button, you won't need to call this;
15210 pressing the interrupt button transfers control to
15211 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
15212 simply receiving characters on the serial port may also trigger a trap;
15213 again, in that situation, you don't need to call @code{breakpoint} from
15214 your own program---simply running @samp{target remote} from the host
15215 @value{GDBN} session gets control.
15217 Call @code{breakpoint} if none of these is true, or if you simply want
15218 to make certain your program stops at a predetermined point for the
15219 start of your debugging session.
15222 @node Bootstrapping
15223 @subsection What You Must Do for the Stub
15225 @cindex remote stub, support routines
15226 The debugging stubs that come with @value{GDBN} are set up for a particular
15227 chip architecture, but they have no information about the rest of your
15228 debugging target machine.
15230 First of all you need to tell the stub how to communicate with the
15234 @item int getDebugChar()
15235 @findex getDebugChar
15236 Write this subroutine to read a single character from the serial port.
15237 It may be identical to @code{getchar} for your target system; a
15238 different name is used to allow you to distinguish the two if you wish.
15240 @item void putDebugChar(int)
15241 @findex putDebugChar
15242 Write this subroutine to write a single character to the serial port.
15243 It may be identical to @code{putchar} for your target system; a
15244 different name is used to allow you to distinguish the two if you wish.
15247 @cindex control C, and remote debugging
15248 @cindex interrupting remote targets
15249 If you want @value{GDBN} to be able to stop your program while it is
15250 running, you need to use an interrupt-driven serial driver, and arrange
15251 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
15252 character). That is the character which @value{GDBN} uses to tell the
15253 remote system to stop.
15255 Getting the debugging target to return the proper status to @value{GDBN}
15256 probably requires changes to the standard stub; one quick and dirty way
15257 is to just execute a breakpoint instruction (the ``dirty'' part is that
15258 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
15260 Other routines you need to supply are:
15263 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
15264 @findex exceptionHandler
15265 Write this function to install @var{exception_address} in the exception
15266 handling tables. You need to do this because the stub does not have any
15267 way of knowing what the exception handling tables on your target system
15268 are like (for example, the processor's table might be in @sc{rom},
15269 containing entries which point to a table in @sc{ram}).
15270 @var{exception_number} is the exception number which should be changed;
15271 its meaning is architecture-dependent (for example, different numbers
15272 might represent divide by zero, misaligned access, etc). When this
15273 exception occurs, control should be transferred directly to
15274 @var{exception_address}, and the processor state (stack, registers,
15275 and so on) should be just as it is when a processor exception occurs. So if
15276 you want to use a jump instruction to reach @var{exception_address}, it
15277 should be a simple jump, not a jump to subroutine.
15279 For the 386, @var{exception_address} should be installed as an interrupt
15280 gate so that interrupts are masked while the handler runs. The gate
15281 should be at privilege level 0 (the most privileged level). The
15282 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
15283 help from @code{exceptionHandler}.
15285 @item void flush_i_cache()
15286 @findex flush_i_cache
15287 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
15288 instruction cache, if any, on your target machine. If there is no
15289 instruction cache, this subroutine may be a no-op.
15291 On target machines that have instruction caches, @value{GDBN} requires this
15292 function to make certain that the state of your program is stable.
15296 You must also make sure this library routine is available:
15299 @item void *memset(void *, int, int)
15301 This is the standard library function @code{memset} that sets an area of
15302 memory to a known value. If you have one of the free versions of
15303 @code{libc.a}, @code{memset} can be found there; otherwise, you must
15304 either obtain it from your hardware manufacturer, or write your own.
15307 If you do not use the GNU C compiler, you may need other standard
15308 library subroutines as well; this varies from one stub to another,
15309 but in general the stubs are likely to use any of the common library
15310 subroutines which @code{@value{NGCC}} generates as inline code.
15313 @node Debug Session
15314 @subsection Putting it All Together
15316 @cindex remote serial debugging summary
15317 In summary, when your program is ready to debug, you must follow these
15322 Make sure you have defined the supporting low-level routines
15323 (@pxref{Bootstrapping,,What You Must Do for the Stub}):
15325 @code{getDebugChar}, @code{putDebugChar},
15326 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
15330 Insert these lines near the top of your program:
15338 For the 680x0 stub only, you need to provide a variable called
15339 @code{exceptionHook}. Normally you just use:
15342 void (*exceptionHook)() = 0;
15346 but if before calling @code{set_debug_traps}, you set it to point to a
15347 function in your program, that function is called when
15348 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
15349 error). The function indicated by @code{exceptionHook} is called with
15350 one parameter: an @code{int} which is the exception number.
15353 Compile and link together: your program, the @value{GDBN} debugging stub for
15354 your target architecture, and the supporting subroutines.
15357 Make sure you have a serial connection between your target machine and
15358 the @value{GDBN} host, and identify the serial port on the host.
15361 @c The "remote" target now provides a `load' command, so we should
15362 @c document that. FIXME.
15363 Download your program to your target machine (or get it there by
15364 whatever means the manufacturer provides), and start it.
15367 Start @value{GDBN} on the host, and connect to the target
15368 (@pxref{Connecting,,Connecting to a Remote Target}).
15372 @node Configurations
15373 @chapter Configuration-Specific Information
15375 While nearly all @value{GDBN} commands are available for all native and
15376 cross versions of the debugger, there are some exceptions. This chapter
15377 describes things that are only available in certain configurations.
15379 There are three major categories of configurations: native
15380 configurations, where the host and target are the same, embedded
15381 operating system configurations, which are usually the same for several
15382 different processor architectures, and bare embedded processors, which
15383 are quite different from each other.
15388 * Embedded Processors::
15395 This section describes details specific to particular native
15400 * BSD libkvm Interface:: Debugging BSD kernel memory images
15401 * SVR4 Process Information:: SVR4 process information
15402 * DJGPP Native:: Features specific to the DJGPP port
15403 * Cygwin Native:: Features specific to the Cygwin port
15404 * Hurd Native:: Features specific to @sc{gnu} Hurd
15405 * Neutrino:: Features specific to QNX Neutrino
15406 * Darwin:: Features specific to Darwin
15412 On HP-UX systems, if you refer to a function or variable name that
15413 begins with a dollar sign, @value{GDBN} searches for a user or system
15414 name first, before it searches for a convenience variable.
15417 @node BSD libkvm Interface
15418 @subsection BSD libkvm Interface
15421 @cindex kernel memory image
15422 @cindex kernel crash dump
15424 BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory
15425 interface that provides a uniform interface for accessing kernel virtual
15426 memory images, including live systems and crash dumps. @value{GDBN}
15427 uses this interface to allow you to debug live kernels and kernel crash
15428 dumps on many native BSD configurations. This is implemented as a
15429 special @code{kvm} debugging target. For debugging a live system, load
15430 the currently running kernel into @value{GDBN} and connect to the
15434 (@value{GDBP}) @b{target kvm}
15437 For debugging crash dumps, provide the file name of the crash dump as an
15441 (@value{GDBP}) @b{target kvm /var/crash/bsd.0}
15444 Once connected to the @code{kvm} target, the following commands are
15450 Set current context from the @dfn{Process Control Block} (PCB) address.
15453 Set current context from proc address. This command isn't available on
15454 modern FreeBSD systems.
15457 @node SVR4 Process Information
15458 @subsection SVR4 Process Information
15460 @cindex examine process image
15461 @cindex process info via @file{/proc}
15463 Many versions of SVR4 and compatible systems provide a facility called
15464 @samp{/proc} that can be used to examine the image of a running
15465 process using file-system subroutines. If @value{GDBN} is configured
15466 for an operating system with this facility, the command @code{info
15467 proc} is available to report information about the process running
15468 your program, or about any process running on your system. @code{info
15469 proc} works only on SVR4 systems that include the @code{procfs} code.
15470 This includes, as of this writing, @sc{gnu}/Linux, OSF/1 (Digital
15471 Unix), Solaris, Irix, and Unixware, but not HP-UX, for example.
15477 @itemx info proc @var{process-id}
15478 Summarize available information about any running process. If a
15479 process ID is specified by @var{process-id}, display information about
15480 that process; otherwise display information about the program being
15481 debugged. The summary includes the debugged process ID, the command
15482 line used to invoke it, its current working directory, and its
15483 executable file's absolute file name.
15485 On some systems, @var{process-id} can be of the form
15486 @samp{[@var{pid}]/@var{tid}} which specifies a certain thread ID
15487 within a process. If the optional @var{pid} part is missing, it means
15488 a thread from the process being debugged (the leading @samp{/} still
15489 needs to be present, or else @value{GDBN} will interpret the number as
15490 a process ID rather than a thread ID).
15492 @item info proc mappings
15493 @cindex memory address space mappings
15494 Report the memory address space ranges accessible in the program, with
15495 information on whether the process has read, write, or execute access
15496 rights to each range. On @sc{gnu}/Linux systems, each memory range
15497 includes the object file which is mapped to that range, instead of the
15498 memory access rights to that range.
15500 @item info proc stat
15501 @itemx info proc status
15502 @cindex process detailed status information
15503 These subcommands are specific to @sc{gnu}/Linux systems. They show
15504 the process-related information, including the user ID and group ID;
15505 how many threads are there in the process; its virtual memory usage;
15506 the signals that are pending, blocked, and ignored; its TTY; its
15507 consumption of system and user time; its stack size; its @samp{nice}
15508 value; etc. For more information, see the @samp{proc} man page
15509 (type @kbd{man 5 proc} from your shell prompt).
15511 @item info proc all
15512 Show all the information about the process described under all of the
15513 above @code{info proc} subcommands.
15516 @comment These sub-options of 'info proc' were not included when
15517 @comment procfs.c was re-written. Keep their descriptions around
15518 @comment against the day when someone finds the time to put them back in.
15519 @kindex info proc times
15520 @item info proc times
15521 Starting time, user CPU time, and system CPU time for your program and
15524 @kindex info proc id
15526 Report on the process IDs related to your program: its own process ID,
15527 the ID of its parent, the process group ID, and the session ID.
15530 @item set procfs-trace
15531 @kindex set procfs-trace
15532 @cindex @code{procfs} API calls
15533 This command enables and disables tracing of @code{procfs} API calls.
15535 @item show procfs-trace
15536 @kindex show procfs-trace
15537 Show the current state of @code{procfs} API call tracing.
15539 @item set procfs-file @var{file}
15540 @kindex set procfs-file
15541 Tell @value{GDBN} to write @code{procfs} API trace to the named
15542 @var{file}. @value{GDBN} appends the trace info to the previous
15543 contents of the file. The default is to display the trace on the
15546 @item show procfs-file
15547 @kindex show procfs-file
15548 Show the file to which @code{procfs} API trace is written.
15550 @item proc-trace-entry
15551 @itemx proc-trace-exit
15552 @itemx proc-untrace-entry
15553 @itemx proc-untrace-exit
15554 @kindex proc-trace-entry
15555 @kindex proc-trace-exit
15556 @kindex proc-untrace-entry
15557 @kindex proc-untrace-exit
15558 These commands enable and disable tracing of entries into and exits
15559 from the @code{syscall} interface.
15562 @kindex info pidlist
15563 @cindex process list, QNX Neutrino
15564 For QNX Neutrino only, this command displays the list of all the
15565 processes and all the threads within each process.
15568 @kindex info meminfo
15569 @cindex mapinfo list, QNX Neutrino
15570 For QNX Neutrino only, this command displays the list of all mapinfos.
15574 @subsection Features for Debugging @sc{djgpp} Programs
15575 @cindex @sc{djgpp} debugging
15576 @cindex native @sc{djgpp} debugging
15577 @cindex MS-DOS-specific commands
15580 @sc{djgpp} is a port of the @sc{gnu} development tools to MS-DOS and
15581 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
15582 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
15583 top of real-mode DOS systems and their emulations.
15585 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
15586 defines a few commands specific to the @sc{djgpp} port. This
15587 subsection describes those commands.
15592 This is a prefix of @sc{djgpp}-specific commands which print
15593 information about the target system and important OS structures.
15596 @cindex MS-DOS system info
15597 @cindex free memory information (MS-DOS)
15598 @item info dos sysinfo
15599 This command displays assorted information about the underlying
15600 platform: the CPU type and features, the OS version and flavor, the
15601 DPMI version, and the available conventional and DPMI memory.
15606 @cindex segment descriptor tables
15607 @cindex descriptor tables display
15609 @itemx info dos ldt
15610 @itemx info dos idt
15611 These 3 commands display entries from, respectively, Global, Local,
15612 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
15613 tables are data structures which store a descriptor for each segment
15614 that is currently in use. The segment's selector is an index into a
15615 descriptor table; the table entry for that index holds the
15616 descriptor's base address and limit, and its attributes and access
15619 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
15620 segment (used for both data and the stack), and a DOS segment (which
15621 allows access to DOS/BIOS data structures and absolute addresses in
15622 conventional memory). However, the DPMI host will usually define
15623 additional segments in order to support the DPMI environment.
15625 @cindex garbled pointers
15626 These commands allow to display entries from the descriptor tables.
15627 Without an argument, all entries from the specified table are
15628 displayed. An argument, which should be an integer expression, means
15629 display a single entry whose index is given by the argument. For
15630 example, here's a convenient way to display information about the
15631 debugged program's data segment:
15634 @exdent @code{(@value{GDBP}) info dos ldt $ds}
15635 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
15639 This comes in handy when you want to see whether a pointer is outside
15640 the data segment's limit (i.e.@: @dfn{garbled}).
15642 @cindex page tables display (MS-DOS)
15644 @itemx info dos pte
15645 These two commands display entries from, respectively, the Page
15646 Directory and the Page Tables. Page Directories and Page Tables are
15647 data structures which control how virtual memory addresses are mapped
15648 into physical addresses. A Page Table includes an entry for every
15649 page of memory that is mapped into the program's address space; there
15650 may be several Page Tables, each one holding up to 4096 entries. A
15651 Page Directory has up to 4096 entries, one each for every Page Table
15652 that is currently in use.
15654 Without an argument, @kbd{info dos pde} displays the entire Page
15655 Directory, and @kbd{info dos pte} displays all the entries in all of
15656 the Page Tables. An argument, an integer expression, given to the
15657 @kbd{info dos pde} command means display only that entry from the Page
15658 Directory table. An argument given to the @kbd{info dos pte} command
15659 means display entries from a single Page Table, the one pointed to by
15660 the specified entry in the Page Directory.
15662 @cindex direct memory access (DMA) on MS-DOS
15663 These commands are useful when your program uses @dfn{DMA} (Direct
15664 Memory Access), which needs physical addresses to program the DMA
15667 These commands are supported only with some DPMI servers.
15669 @cindex physical address from linear address
15670 @item info dos address-pte @var{addr}
15671 This command displays the Page Table entry for a specified linear
15672 address. The argument @var{addr} is a linear address which should
15673 already have the appropriate segment's base address added to it,
15674 because this command accepts addresses which may belong to @emph{any}
15675 segment. For example, here's how to display the Page Table entry for
15676 the page where a variable @code{i} is stored:
15679 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
15680 @exdent @code{Page Table entry for address 0x11a00d30:}
15681 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
15685 This says that @code{i} is stored at offset @code{0xd30} from the page
15686 whose physical base address is @code{0x02698000}, and shows all the
15687 attributes of that page.
15689 Note that you must cast the addresses of variables to a @code{char *},
15690 since otherwise the value of @code{__djgpp_base_address}, the base
15691 address of all variables and functions in a @sc{djgpp} program, will
15692 be added using the rules of C pointer arithmetics: if @code{i} is
15693 declared an @code{int}, @value{GDBN} will add 4 times the value of
15694 @code{__djgpp_base_address} to the address of @code{i}.
15696 Here's another example, it displays the Page Table entry for the
15700 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
15701 @exdent @code{Page Table entry for address 0x29110:}
15702 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
15706 (The @code{+ 3} offset is because the transfer buffer's address is the
15707 3rd member of the @code{_go32_info_block} structure.) The output
15708 clearly shows that this DPMI server maps the addresses in conventional
15709 memory 1:1, i.e.@: the physical (@code{0x00029000} + @code{0x110}) and
15710 linear (@code{0x29110}) addresses are identical.
15712 This command is supported only with some DPMI servers.
15715 @cindex DOS serial data link, remote debugging
15716 In addition to native debugging, the DJGPP port supports remote
15717 debugging via a serial data link. The following commands are specific
15718 to remote serial debugging in the DJGPP port of @value{GDBN}.
15721 @kindex set com1base
15722 @kindex set com1irq
15723 @kindex set com2base
15724 @kindex set com2irq
15725 @kindex set com3base
15726 @kindex set com3irq
15727 @kindex set com4base
15728 @kindex set com4irq
15729 @item set com1base @var{addr}
15730 This command sets the base I/O port address of the @file{COM1} serial
15733 @item set com1irq @var{irq}
15734 This command sets the @dfn{Interrupt Request} (@code{IRQ}) line to use
15735 for the @file{COM1} serial port.
15737 There are similar commands @samp{set com2base}, @samp{set com3irq},
15738 etc.@: for setting the port address and the @code{IRQ} lines for the
15741 @kindex show com1base
15742 @kindex show com1irq
15743 @kindex show com2base
15744 @kindex show com2irq
15745 @kindex show com3base
15746 @kindex show com3irq
15747 @kindex show com4base
15748 @kindex show com4irq
15749 The related commands @samp{show com1base}, @samp{show com1irq} etc.@:
15750 display the current settings of the base address and the @code{IRQ}
15751 lines used by the COM ports.
15754 @kindex info serial
15755 @cindex DOS serial port status
15756 This command prints the status of the 4 DOS serial ports. For each
15757 port, it prints whether it's active or not, its I/O base address and
15758 IRQ number, whether it uses a 16550-style FIFO, its baudrate, and the
15759 counts of various errors encountered so far.
15763 @node Cygwin Native
15764 @subsection Features for Debugging MS Windows PE Executables
15765 @cindex MS Windows debugging
15766 @cindex native Cygwin debugging
15767 @cindex Cygwin-specific commands
15769 @value{GDBN} supports native debugging of MS Windows programs, including
15770 DLLs with and without symbolic debugging information. There are various
15771 additional Cygwin-specific commands, described in this section.
15772 Working with DLLs that have no debugging symbols is described in
15773 @ref{Non-debug DLL Symbols}.
15778 This is a prefix of MS Windows-specific commands which print
15779 information about the target system and important OS structures.
15781 @item info w32 selector
15782 This command displays information returned by
15783 the Win32 API @code{GetThreadSelectorEntry} function.
15784 It takes an optional argument that is evaluated to
15785 a long value to give the information about this given selector.
15786 Without argument, this command displays information
15787 about the six segment registers.
15791 This is a Cygwin-specific alias of @code{info shared}.
15793 @kindex dll-symbols
15795 This command loads symbols from a dll similarly to
15796 add-sym command but without the need to specify a base address.
15798 @kindex set cygwin-exceptions
15799 @cindex debugging the Cygwin DLL
15800 @cindex Cygwin DLL, debugging
15801 @item set cygwin-exceptions @var{mode}
15802 If @var{mode} is @code{on}, @value{GDBN} will break on exceptions that
15803 happen inside the Cygwin DLL. If @var{mode} is @code{off},
15804 @value{GDBN} will delay recognition of exceptions, and may ignore some
15805 exceptions which seem to be caused by internal Cygwin DLL
15806 ``bookkeeping''. This option is meant primarily for debugging the
15807 Cygwin DLL itself; the default value is @code{off} to avoid annoying
15808 @value{GDBN} users with false @code{SIGSEGV} signals.
15810 @kindex show cygwin-exceptions
15811 @item show cygwin-exceptions
15812 Displays whether @value{GDBN} will break on exceptions that happen
15813 inside the Cygwin DLL itself.
15815 @kindex set new-console
15816 @item set new-console @var{mode}
15817 If @var{mode} is @code{on} the debuggee will
15818 be started in a new console on next start.
15819 If @var{mode} is @code{off}i, the debuggee will
15820 be started in the same console as the debugger.
15822 @kindex show new-console
15823 @item show new-console
15824 Displays whether a new console is used
15825 when the debuggee is started.
15827 @kindex set new-group
15828 @item set new-group @var{mode}
15829 This boolean value controls whether the debuggee should
15830 start a new group or stay in the same group as the debugger.
15831 This affects the way the Windows OS handles
15834 @kindex show new-group
15835 @item show new-group
15836 Displays current value of new-group boolean.
15838 @kindex set debugevents
15839 @item set debugevents
15840 This boolean value adds debug output concerning kernel events related
15841 to the debuggee seen by the debugger. This includes events that
15842 signal thread and process creation and exit, DLL loading and
15843 unloading, console interrupts, and debugging messages produced by the
15844 Windows @code{OutputDebugString} API call.
15846 @kindex set debugexec
15847 @item set debugexec
15848 This boolean value adds debug output concerning execute events
15849 (such as resume thread) seen by the debugger.
15851 @kindex set debugexceptions
15852 @item set debugexceptions
15853 This boolean value adds debug output concerning exceptions in the
15854 debuggee seen by the debugger.
15856 @kindex set debugmemory
15857 @item set debugmemory
15858 This boolean value adds debug output concerning debuggee memory reads
15859 and writes by the debugger.
15863 This boolean values specifies whether the debuggee is called
15864 via a shell or directly (default value is on).
15868 Displays if the debuggee will be started with a shell.
15873 * Non-debug DLL Symbols:: Support for DLLs without debugging symbols
15876 @node Non-debug DLL Symbols
15877 @subsubsection Support for DLLs without Debugging Symbols
15878 @cindex DLLs with no debugging symbols
15879 @cindex Minimal symbols and DLLs
15881 Very often on windows, some of the DLLs that your program relies on do
15882 not include symbolic debugging information (for example,
15883 @file{kernel32.dll}). When @value{GDBN} doesn't recognize any debugging
15884 symbols in a DLL, it relies on the minimal amount of symbolic
15885 information contained in the DLL's export table. This section
15886 describes working with such symbols, known internally to @value{GDBN} as
15887 ``minimal symbols''.
15889 Note that before the debugged program has started execution, no DLLs
15890 will have been loaded. The easiest way around this problem is simply to
15891 start the program --- either by setting a breakpoint or letting the
15892 program run once to completion. It is also possible to force
15893 @value{GDBN} to load a particular DLL before starting the executable ---
15894 see the shared library information in @ref{Files}, or the
15895 @code{dll-symbols} command in @ref{Cygwin Native}. Currently,
15896 explicitly loading symbols from a DLL with no debugging information will
15897 cause the symbol names to be duplicated in @value{GDBN}'s lookup table,
15898 which may adversely affect symbol lookup performance.
15900 @subsubsection DLL Name Prefixes
15902 In keeping with the naming conventions used by the Microsoft debugging
15903 tools, DLL export symbols are made available with a prefix based on the
15904 DLL name, for instance @code{KERNEL32!CreateFileA}. The plain name is
15905 also entered into the symbol table, so @code{CreateFileA} is often
15906 sufficient. In some cases there will be name clashes within a program
15907 (particularly if the executable itself includes full debugging symbols)
15908 necessitating the use of the fully qualified name when referring to the
15909 contents of the DLL. Use single-quotes around the name to avoid the
15910 exclamation mark (``!'') being interpreted as a language operator.
15912 Note that the internal name of the DLL may be all upper-case, even
15913 though the file name of the DLL is lower-case, or vice-versa. Since
15914 symbols within @value{GDBN} are @emph{case-sensitive} this may cause
15915 some confusion. If in doubt, try the @code{info functions} and
15916 @code{info variables} commands or even @code{maint print msymbols}
15917 (@pxref{Symbols}). Here's an example:
15920 (@value{GDBP}) info function CreateFileA
15921 All functions matching regular expression "CreateFileA":
15923 Non-debugging symbols:
15924 0x77e885f4 CreateFileA
15925 0x77e885f4 KERNEL32!CreateFileA
15929 (@value{GDBP}) info function !
15930 All functions matching regular expression "!":
15932 Non-debugging symbols:
15933 0x6100114c cygwin1!__assert
15934 0x61004034 cygwin1!_dll_crt0@@0
15935 0x61004240 cygwin1!dll_crt0(per_process *)
15939 @subsubsection Working with Minimal Symbols
15941 Symbols extracted from a DLL's export table do not contain very much
15942 type information. All that @value{GDBN} can do is guess whether a symbol
15943 refers to a function or variable depending on the linker section that
15944 contains the symbol. Also note that the actual contents of the memory
15945 contained in a DLL are not available unless the program is running. This
15946 means that you cannot examine the contents of a variable or disassemble
15947 a function within a DLL without a running program.
15949 Variables are generally treated as pointers and dereferenced
15950 automatically. For this reason, it is often necessary to prefix a
15951 variable name with the address-of operator (``&'') and provide explicit
15952 type information in the command. Here's an example of the type of
15956 (@value{GDBP}) print 'cygwin1!__argv'
15961 (@value{GDBP}) x 'cygwin1!__argv'
15962 0x10021610: "\230y\""
15965 And two possible solutions:
15968 (@value{GDBP}) print ((char **)'cygwin1!__argv')[0]
15969 $2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"
15973 (@value{GDBP}) x/2x &'cygwin1!__argv'
15974 0x610c0aa8 <cygwin1!__argv>: 0x10021608 0x00000000
15975 (@value{GDBP}) x/x 0x10021608
15976 0x10021608: 0x0022fd98
15977 (@value{GDBP}) x/s 0x0022fd98
15978 0x22fd98: "/cygdrive/c/mydirectory/myprogram"
15981 Setting a break point within a DLL is possible even before the program
15982 starts execution. However, under these circumstances, @value{GDBN} can't
15983 examine the initial instructions of the function in order to skip the
15984 function's frame set-up code. You can work around this by using ``*&''
15985 to set the breakpoint at a raw memory address:
15988 (@value{GDBP}) break *&'python22!PyOS_Readline'
15989 Breakpoint 1 at 0x1e04eff0
15992 The author of these extensions is not entirely convinced that setting a
15993 break point within a shared DLL like @file{kernel32.dll} is completely
15997 @subsection Commands Specific to @sc{gnu} Hurd Systems
15998 @cindex @sc{gnu} Hurd debugging
16000 This subsection describes @value{GDBN} commands specific to the
16001 @sc{gnu} Hurd native debugging.
16006 @kindex set signals@r{, Hurd command}
16007 @kindex set sigs@r{, Hurd command}
16008 This command toggles the state of inferior signal interception by
16009 @value{GDBN}. Mach exceptions, such as breakpoint traps, are not
16010 affected by this command. @code{sigs} is a shorthand alias for
16015 @kindex show signals@r{, Hurd command}
16016 @kindex show sigs@r{, Hurd command}
16017 Show the current state of intercepting inferior's signals.
16019 @item set signal-thread
16020 @itemx set sigthread
16021 @kindex set signal-thread
16022 @kindex set sigthread
16023 This command tells @value{GDBN} which thread is the @code{libc} signal
16024 thread. That thread is run when a signal is delivered to a running
16025 process. @code{set sigthread} is the shorthand alias of @code{set
16028 @item show signal-thread
16029 @itemx show sigthread
16030 @kindex show signal-thread
16031 @kindex show sigthread
16032 These two commands show which thread will run when the inferior is
16033 delivered a signal.
16036 @kindex set stopped@r{, Hurd command}
16037 This commands tells @value{GDBN} that the inferior process is stopped,
16038 as with the @code{SIGSTOP} signal. The stopped process can be
16039 continued by delivering a signal to it.
16042 @kindex show stopped@r{, Hurd command}
16043 This command shows whether @value{GDBN} thinks the debuggee is
16046 @item set exceptions
16047 @kindex set exceptions@r{, Hurd command}
16048 Use this command to turn off trapping of exceptions in the inferior.
16049 When exception trapping is off, neither breakpoints nor
16050 single-stepping will work. To restore the default, set exception
16053 @item show exceptions
16054 @kindex show exceptions@r{, Hurd command}
16055 Show the current state of trapping exceptions in the inferior.
16057 @item set task pause
16058 @kindex set task@r{, Hurd commands}
16059 @cindex task attributes (@sc{gnu} Hurd)
16060 @cindex pause current task (@sc{gnu} Hurd)
16061 This command toggles task suspension when @value{GDBN} has control.
16062 Setting it to on takes effect immediately, and the task is suspended
16063 whenever @value{GDBN} gets control. Setting it to off will take
16064 effect the next time the inferior is continued. If this option is set
16065 to off, you can use @code{set thread default pause on} or @code{set
16066 thread pause on} (see below) to pause individual threads.
16068 @item show task pause
16069 @kindex show task@r{, Hurd commands}
16070 Show the current state of task suspension.
16072 @item set task detach-suspend-count
16073 @cindex task suspend count
16074 @cindex detach from task, @sc{gnu} Hurd
16075 This command sets the suspend count the task will be left with when
16076 @value{GDBN} detaches from it.
16078 @item show task detach-suspend-count
16079 Show the suspend count the task will be left with when detaching.
16081 @item set task exception-port
16082 @itemx set task excp
16083 @cindex task exception port, @sc{gnu} Hurd
16084 This command sets the task exception port to which @value{GDBN} will
16085 forward exceptions. The argument should be the value of the @dfn{send
16086 rights} of the task. @code{set task excp} is a shorthand alias.
16088 @item set noninvasive
16089 @cindex noninvasive task options
16090 This command switches @value{GDBN} to a mode that is the least
16091 invasive as far as interfering with the inferior is concerned. This
16092 is the same as using @code{set task pause}, @code{set exceptions}, and
16093 @code{set signals} to values opposite to the defaults.
16095 @item info send-rights
16096 @itemx info receive-rights
16097 @itemx info port-rights
16098 @itemx info port-sets
16099 @itemx info dead-names
16102 @cindex send rights, @sc{gnu} Hurd
16103 @cindex receive rights, @sc{gnu} Hurd
16104 @cindex port rights, @sc{gnu} Hurd
16105 @cindex port sets, @sc{gnu} Hurd
16106 @cindex dead names, @sc{gnu} Hurd
16107 These commands display information about, respectively, send rights,
16108 receive rights, port rights, port sets, and dead names of a task.
16109 There are also shorthand aliases: @code{info ports} for @code{info
16110 port-rights} and @code{info psets} for @code{info port-sets}.
16112 @item set thread pause
16113 @kindex set thread@r{, Hurd command}
16114 @cindex thread properties, @sc{gnu} Hurd
16115 @cindex pause current thread (@sc{gnu} Hurd)
16116 This command toggles current thread suspension when @value{GDBN} has
16117 control. Setting it to on takes effect immediately, and the current
16118 thread is suspended whenever @value{GDBN} gets control. Setting it to
16119 off will take effect the next time the inferior is continued.
16120 Normally, this command has no effect, since when @value{GDBN} has
16121 control, the whole task is suspended. However, if you used @code{set
16122 task pause off} (see above), this command comes in handy to suspend
16123 only the current thread.
16125 @item show thread pause
16126 @kindex show thread@r{, Hurd command}
16127 This command shows the state of current thread suspension.
16129 @item set thread run
16130 This command sets whether the current thread is allowed to run.
16132 @item show thread run
16133 Show whether the current thread is allowed to run.
16135 @item set thread detach-suspend-count
16136 @cindex thread suspend count, @sc{gnu} Hurd
16137 @cindex detach from thread, @sc{gnu} Hurd
16138 This command sets the suspend count @value{GDBN} will leave on a
16139 thread when detaching. This number is relative to the suspend count
16140 found by @value{GDBN} when it notices the thread; use @code{set thread
16141 takeover-suspend-count} to force it to an absolute value.
16143 @item show thread detach-suspend-count
16144 Show the suspend count @value{GDBN} will leave on the thread when
16147 @item set thread exception-port
16148 @itemx set thread excp
16149 Set the thread exception port to which to forward exceptions. This
16150 overrides the port set by @code{set task exception-port} (see above).
16151 @code{set thread excp} is the shorthand alias.
16153 @item set thread takeover-suspend-count
16154 Normally, @value{GDBN}'s thread suspend counts are relative to the
16155 value @value{GDBN} finds when it notices each thread. This command
16156 changes the suspend counts to be absolute instead.
16158 @item set thread default
16159 @itemx show thread default
16160 @cindex thread default settings, @sc{gnu} Hurd
16161 Each of the above @code{set thread} commands has a @code{set thread
16162 default} counterpart (e.g., @code{set thread default pause}, @code{set
16163 thread default exception-port}, etc.). The @code{thread default}
16164 variety of commands sets the default thread properties for all
16165 threads; you can then change the properties of individual threads with
16166 the non-default commands.
16171 @subsection QNX Neutrino
16172 @cindex QNX Neutrino
16174 @value{GDBN} provides the following commands specific to the QNX
16178 @item set debug nto-debug
16179 @kindex set debug nto-debug
16180 When set to on, enables debugging messages specific to the QNX
16183 @item show debug nto-debug
16184 @kindex show debug nto-debug
16185 Show the current state of QNX Neutrino messages.
16192 @value{GDBN} provides the following commands specific to the Darwin target:
16195 @item set debug darwin @var{num}
16196 @kindex set debug darwin
16197 When set to a non zero value, enables debugging messages specific to
16198 the Darwin support. Higher values produce more verbose output.
16200 @item show debug darwin
16201 @kindex show debug darwin
16202 Show the current state of Darwin messages.
16204 @item set debug mach-o @var{num}
16205 @kindex set debug mach-o
16206 When set to a non zero value, enables debugging messages while
16207 @value{GDBN} is reading Darwin object files. (@dfn{Mach-O} is the
16208 file format used on Darwin for object and executable files.) Higher
16209 values produce more verbose output. This is a command to diagnose
16210 problems internal to @value{GDBN} and should not be needed in normal
16213 @item show debug mach-o
16214 @kindex show debug mach-o
16215 Show the current state of Mach-O file messages.
16217 @item set mach-exceptions on
16218 @itemx set mach-exceptions off
16219 @kindex set mach-exceptions
16220 On Darwin, faults are first reported as a Mach exception and are then
16221 mapped to a Posix signal. Use this command to turn on trapping of
16222 Mach exceptions in the inferior. This might be sometimes useful to
16223 better understand the cause of a fault. The default is off.
16225 @item show mach-exceptions
16226 @kindex show mach-exceptions
16227 Show the current state of exceptions trapping.
16232 @section Embedded Operating Systems
16234 This section describes configurations involving the debugging of
16235 embedded operating systems that are available for several different
16239 * VxWorks:: Using @value{GDBN} with VxWorks
16242 @value{GDBN} includes the ability to debug programs running on
16243 various real-time operating systems.
16246 @subsection Using @value{GDBN} with VxWorks
16252 @kindex target vxworks
16253 @item target vxworks @var{machinename}
16254 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
16255 is the target system's machine name or IP address.
16259 On VxWorks, @code{load} links @var{filename} dynamically on the
16260 current target system as well as adding its symbols in @value{GDBN}.
16262 @value{GDBN} enables developers to spawn and debug tasks running on networked
16263 VxWorks targets from a Unix host. Already-running tasks spawned from
16264 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
16265 both the Unix host and on the VxWorks target. The program
16266 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
16267 installed with the name @code{vxgdb}, to distinguish it from a
16268 @value{GDBN} for debugging programs on the host itself.)
16271 @item VxWorks-timeout @var{args}
16272 @kindex vxworks-timeout
16273 All VxWorks-based targets now support the option @code{vxworks-timeout}.
16274 This option is set by the user, and @var{args} represents the number of
16275 seconds @value{GDBN} waits for responses to rpc's. You might use this if
16276 your VxWorks target is a slow software simulator or is on the far side
16277 of a thin network line.
16280 The following information on connecting to VxWorks was current when
16281 this manual was produced; newer releases of VxWorks may use revised
16284 @findex INCLUDE_RDB
16285 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
16286 to include the remote debugging interface routines in the VxWorks
16287 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
16288 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
16289 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
16290 source debugging task @code{tRdbTask} when VxWorks is booted. For more
16291 information on configuring and remaking VxWorks, see the manufacturer's
16293 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
16295 Once you have included @file{rdb.a} in your VxWorks system image and set
16296 your Unix execution search path to find @value{GDBN}, you are ready to
16297 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
16298 @code{vxgdb}, depending on your installation).
16300 @value{GDBN} comes up showing the prompt:
16307 * VxWorks Connection:: Connecting to VxWorks
16308 * VxWorks Download:: VxWorks download
16309 * VxWorks Attach:: Running tasks
16312 @node VxWorks Connection
16313 @subsubsection Connecting to VxWorks
16315 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
16316 network. To connect to a target whose host name is ``@code{tt}'', type:
16319 (vxgdb) target vxworks tt
16323 @value{GDBN} displays messages like these:
16326 Attaching remote machine across net...
16331 @value{GDBN} then attempts to read the symbol tables of any object modules
16332 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
16333 these files by searching the directories listed in the command search
16334 path (@pxref{Environment, ,Your Program's Environment}); if it fails
16335 to find an object file, it displays a message such as:
16338 prog.o: No such file or directory.
16341 When this happens, add the appropriate directory to the search path with
16342 the @value{GDBN} command @code{path}, and execute the @code{target}
16345 @node VxWorks Download
16346 @subsubsection VxWorks Download
16348 @cindex download to VxWorks
16349 If you have connected to the VxWorks target and you want to debug an
16350 object that has not yet been loaded, you can use the @value{GDBN}
16351 @code{load} command to download a file from Unix to VxWorks
16352 incrementally. The object file given as an argument to the @code{load}
16353 command is actually opened twice: first by the VxWorks target in order
16354 to download the code, then by @value{GDBN} in order to read the symbol
16355 table. This can lead to problems if the current working directories on
16356 the two systems differ. If both systems have NFS mounted the same
16357 filesystems, you can avoid these problems by using absolute paths.
16358 Otherwise, it is simplest to set the working directory on both systems
16359 to the directory in which the object file resides, and then to reference
16360 the file by its name, without any path. For instance, a program
16361 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
16362 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
16363 program, type this on VxWorks:
16366 -> cd "@var{vxpath}/vw/demo/rdb"
16370 Then, in @value{GDBN}, type:
16373 (vxgdb) cd @var{hostpath}/vw/demo/rdb
16374 (vxgdb) load prog.o
16377 @value{GDBN} displays a response similar to this:
16380 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
16383 You can also use the @code{load} command to reload an object module
16384 after editing and recompiling the corresponding source file. Note that
16385 this makes @value{GDBN} delete all currently-defined breakpoints,
16386 auto-displays, and convenience variables, and to clear the value
16387 history. (This is necessary in order to preserve the integrity of
16388 debugger's data structures that reference the target system's symbol
16391 @node VxWorks Attach
16392 @subsubsection Running Tasks
16394 @cindex running VxWorks tasks
16395 You can also attach to an existing task using the @code{attach} command as
16399 (vxgdb) attach @var{task}
16403 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
16404 or suspended when you attach to it. Running tasks are suspended at
16405 the time of attachment.
16407 @node Embedded Processors
16408 @section Embedded Processors
16410 This section goes into details specific to particular embedded
16413 @cindex send command to simulator
16414 Whenever a specific embedded processor has a simulator, @value{GDBN}
16415 allows to send an arbitrary command to the simulator.
16418 @item sim @var{command}
16419 @kindex sim@r{, a command}
16420 Send an arbitrary @var{command} string to the simulator. Consult the
16421 documentation for the specific simulator in use for information about
16422 acceptable commands.
16428 * M32R/D:: Renesas M32R/D
16429 * M68K:: Motorola M68K
16430 * MIPS Embedded:: MIPS Embedded
16431 * OpenRISC 1000:: OpenRisc 1000
16432 * PA:: HP PA Embedded
16433 * PowerPC Embedded:: PowerPC Embedded
16434 * Sparclet:: Tsqware Sparclet
16435 * Sparclite:: Fujitsu Sparclite
16436 * Z8000:: Zilog Z8000
16439 * Super-H:: Renesas Super-H
16448 @item target rdi @var{dev}
16449 ARM Angel monitor, via RDI library interface to ADP protocol. You may
16450 use this target to communicate with both boards running the Angel
16451 monitor, or with the EmbeddedICE JTAG debug device.
16454 @item target rdp @var{dev}
16459 @value{GDBN} provides the following ARM-specific commands:
16462 @item set arm disassembler
16464 This commands selects from a list of disassembly styles. The
16465 @code{"std"} style is the standard style.
16467 @item show arm disassembler
16469 Show the current disassembly style.
16471 @item set arm apcs32
16472 @cindex ARM 32-bit mode
16473 This command toggles ARM operation mode between 32-bit and 26-bit.
16475 @item show arm apcs32
16476 Display the current usage of the ARM 32-bit mode.
16478 @item set arm fpu @var{fputype}
16479 This command sets the ARM floating-point unit (FPU) type. The
16480 argument @var{fputype} can be one of these:
16484 Determine the FPU type by querying the OS ABI.
16486 Software FPU, with mixed-endian doubles on little-endian ARM
16489 GCC-compiled FPA co-processor.
16491 Software FPU with pure-endian doubles.
16497 Show the current type of the FPU.
16500 This command forces @value{GDBN} to use the specified ABI.
16503 Show the currently used ABI.
16505 @item set arm fallback-mode (arm|thumb|auto)
16506 @value{GDBN} uses the symbol table, when available, to determine
16507 whether instructions are ARM or Thumb. This command controls
16508 @value{GDBN}'s default behavior when the symbol table is not
16509 available. The default is @samp{auto}, which causes @value{GDBN} to
16510 use the current execution mode (from the @code{T} bit in the @code{CPSR}
16513 @item show arm fallback-mode
16514 Show the current fallback instruction mode.
16516 @item set arm force-mode (arm|thumb|auto)
16517 This command overrides use of the symbol table to determine whether
16518 instructions are ARM or Thumb. The default is @samp{auto}, which
16519 causes @value{GDBN} to use the symbol table and then the setting
16520 of @samp{set arm fallback-mode}.
16522 @item show arm force-mode
16523 Show the current forced instruction mode.
16525 @item set debug arm
16526 Toggle whether to display ARM-specific debugging messages from the ARM
16527 target support subsystem.
16529 @item show debug arm
16530 Show whether ARM-specific debugging messages are enabled.
16533 The following commands are available when an ARM target is debugged
16534 using the RDI interface:
16537 @item rdilogfile @r{[}@var{file}@r{]}
16539 @cindex ADP (Angel Debugger Protocol) logging
16540 Set the filename for the ADP (Angel Debugger Protocol) packet log.
16541 With an argument, sets the log file to the specified @var{file}. With
16542 no argument, show the current log file name. The default log file is
16545 @item rdilogenable @r{[}@var{arg}@r{]}
16546 @kindex rdilogenable
16547 Control logging of ADP packets. With an argument of 1 or @code{"yes"}
16548 enables logging, with an argument 0 or @code{"no"} disables it. With
16549 no arguments displays the current setting. When logging is enabled,
16550 ADP packets exchanged between @value{GDBN} and the RDI target device
16551 are logged to a file.
16553 @item set rdiromatzero
16554 @kindex set rdiromatzero
16555 @cindex ROM at zero address, RDI
16556 Tell @value{GDBN} whether the target has ROM at address 0. If on,
16557 vector catching is disabled, so that zero address can be used. If off
16558 (the default), vector catching is enabled. For this command to take
16559 effect, it needs to be invoked prior to the @code{target rdi} command.
16561 @item show rdiromatzero
16562 @kindex show rdiromatzero
16563 Show the current setting of ROM at zero address.
16565 @item set rdiheartbeat
16566 @kindex set rdiheartbeat
16567 @cindex RDI heartbeat
16568 Enable or disable RDI heartbeat packets. It is not recommended to
16569 turn on this option, since it confuses ARM and EPI JTAG interface, as
16570 well as the Angel monitor.
16572 @item show rdiheartbeat
16573 @kindex show rdiheartbeat
16574 Show the setting of RDI heartbeat packets.
16579 @subsection Renesas M32R/D and M32R/SDI
16582 @kindex target m32r
16583 @item target m32r @var{dev}
16584 Renesas M32R/D ROM monitor.
16586 @kindex target m32rsdi
16587 @item target m32rsdi @var{dev}
16588 Renesas M32R SDI server, connected via parallel port to the board.
16591 The following @value{GDBN} commands are specific to the M32R monitor:
16594 @item set download-path @var{path}
16595 @kindex set download-path
16596 @cindex find downloadable @sc{srec} files (M32R)
16597 Set the default path for finding downloadable @sc{srec} files.
16599 @item show download-path
16600 @kindex show download-path
16601 Show the default path for downloadable @sc{srec} files.
16603 @item set board-address @var{addr}
16604 @kindex set board-address
16605 @cindex M32-EVA target board address
16606 Set the IP address for the M32R-EVA target board.
16608 @item show board-address
16609 @kindex show board-address
16610 Show the current IP address of the target board.
16612 @item set server-address @var{addr}
16613 @kindex set server-address
16614 @cindex download server address (M32R)
16615 Set the IP address for the download server, which is the @value{GDBN}'s
16618 @item show server-address
16619 @kindex show server-address
16620 Display the IP address of the download server.
16622 @item upload @r{[}@var{file}@r{]}
16623 @kindex upload@r{, M32R}
16624 Upload the specified @sc{srec} @var{file} via the monitor's Ethernet
16625 upload capability. If no @var{file} argument is given, the current
16626 executable file is uploaded.
16628 @item tload @r{[}@var{file}@r{]}
16629 @kindex tload@r{, M32R}
16630 Test the @code{upload} command.
16633 The following commands are available for M32R/SDI:
16638 @cindex reset SDI connection, M32R
16639 This command resets the SDI connection.
16643 This command shows the SDI connection status.
16646 @kindex debug_chaos
16647 @cindex M32R/Chaos debugging
16648 Instructs the remote that M32R/Chaos debugging is to be used.
16650 @item use_debug_dma
16651 @kindex use_debug_dma
16652 Instructs the remote to use the DEBUG_DMA method of accessing memory.
16655 @kindex use_mon_code
16656 Instructs the remote to use the MON_CODE method of accessing memory.
16659 @kindex use_ib_break
16660 Instructs the remote to set breakpoints by IB break.
16662 @item use_dbt_break
16663 @kindex use_dbt_break
16664 Instructs the remote to set breakpoints by DBT.
16670 The Motorola m68k configuration includes ColdFire support, and a
16671 target command for the following ROM monitor.
16675 @kindex target dbug
16676 @item target dbug @var{dev}
16677 dBUG ROM monitor for Motorola ColdFire.
16681 @node MIPS Embedded
16682 @subsection MIPS Embedded
16684 @cindex MIPS boards
16685 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
16686 MIPS board attached to a serial line. This is available when
16687 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
16690 Use these @value{GDBN} commands to specify the connection to your target board:
16693 @item target mips @var{port}
16694 @kindex target mips @var{port}
16695 To run a program on the board, start up @code{@value{GDBP}} with the
16696 name of your program as the argument. To connect to the board, use the
16697 command @samp{target mips @var{port}}, where @var{port} is the name of
16698 the serial port connected to the board. If the program has not already
16699 been downloaded to the board, you may use the @code{load} command to
16700 download it. You can then use all the usual @value{GDBN} commands.
16702 For example, this sequence connects to the target board through a serial
16703 port, and loads and runs a program called @var{prog} through the
16707 host$ @value{GDBP} @var{prog}
16708 @value{GDBN} is free software and @dots{}
16709 (@value{GDBP}) target mips /dev/ttyb
16710 (@value{GDBP}) load @var{prog}
16714 @item target mips @var{hostname}:@var{portnumber}
16715 On some @value{GDBN} host configurations, you can specify a TCP
16716 connection (for instance, to a serial line managed by a terminal
16717 concentrator) instead of a serial port, using the syntax
16718 @samp{@var{hostname}:@var{portnumber}}.
16720 @item target pmon @var{port}
16721 @kindex target pmon @var{port}
16724 @item target ddb @var{port}
16725 @kindex target ddb @var{port}
16726 NEC's DDB variant of PMON for Vr4300.
16728 @item target lsi @var{port}
16729 @kindex target lsi @var{port}
16730 LSI variant of PMON.
16732 @kindex target r3900
16733 @item target r3900 @var{dev}
16734 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
16736 @kindex target array
16737 @item target array @var{dev}
16738 Array Tech LSI33K RAID controller board.
16744 @value{GDBN} also supports these special commands for MIPS targets:
16747 @item set mipsfpu double
16748 @itemx set mipsfpu single
16749 @itemx set mipsfpu none
16750 @itemx set mipsfpu auto
16751 @itemx show mipsfpu
16752 @kindex set mipsfpu
16753 @kindex show mipsfpu
16754 @cindex MIPS remote floating point
16755 @cindex floating point, MIPS remote
16756 If your target board does not support the MIPS floating point
16757 coprocessor, you should use the command @samp{set mipsfpu none} (if you
16758 need this, you may wish to put the command in your @value{GDBN} init
16759 file). This tells @value{GDBN} how to find the return value of
16760 functions which return floating point values. It also allows
16761 @value{GDBN} to avoid saving the floating point registers when calling
16762 functions on the board. If you are using a floating point coprocessor
16763 with only single precision floating point support, as on the @sc{r4650}
16764 processor, use the command @samp{set mipsfpu single}. The default
16765 double precision floating point coprocessor may be selected using
16766 @samp{set mipsfpu double}.
16768 In previous versions the only choices were double precision or no
16769 floating point, so @samp{set mipsfpu on} will select double precision
16770 and @samp{set mipsfpu off} will select no floating point.
16772 As usual, you can inquire about the @code{mipsfpu} variable with
16773 @samp{show mipsfpu}.
16775 @item set timeout @var{seconds}
16776 @itemx set retransmit-timeout @var{seconds}
16777 @itemx show timeout
16778 @itemx show retransmit-timeout
16779 @cindex @code{timeout}, MIPS protocol
16780 @cindex @code{retransmit-timeout}, MIPS protocol
16781 @kindex set timeout
16782 @kindex show timeout
16783 @kindex set retransmit-timeout
16784 @kindex show retransmit-timeout
16785 You can control the timeout used while waiting for a packet, in the MIPS
16786 remote protocol, with the @code{set timeout @var{seconds}} command. The
16787 default is 5 seconds. Similarly, you can control the timeout used while
16788 waiting for an acknowledgment of a packet with the @code{set
16789 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
16790 You can inspect both values with @code{show timeout} and @code{show
16791 retransmit-timeout}. (These commands are @emph{only} available when
16792 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
16794 The timeout set by @code{set timeout} does not apply when @value{GDBN}
16795 is waiting for your program to stop. In that case, @value{GDBN} waits
16796 forever because it has no way of knowing how long the program is going
16797 to run before stopping.
16799 @item set syn-garbage-limit @var{num}
16800 @kindex set syn-garbage-limit@r{, MIPS remote}
16801 @cindex synchronize with remote MIPS target
16802 Limit the maximum number of characters @value{GDBN} should ignore when
16803 it tries to synchronize with the remote target. The default is 10
16804 characters. Setting the limit to -1 means there's no limit.
16806 @item show syn-garbage-limit
16807 @kindex show syn-garbage-limit@r{, MIPS remote}
16808 Show the current limit on the number of characters to ignore when
16809 trying to synchronize with the remote system.
16811 @item set monitor-prompt @var{prompt}
16812 @kindex set monitor-prompt@r{, MIPS remote}
16813 @cindex remote monitor prompt
16814 Tell @value{GDBN} to expect the specified @var{prompt} string from the
16815 remote monitor. The default depends on the target:
16825 @item show monitor-prompt
16826 @kindex show monitor-prompt@r{, MIPS remote}
16827 Show the current strings @value{GDBN} expects as the prompt from the
16830 @item set monitor-warnings
16831 @kindex set monitor-warnings@r{, MIPS remote}
16832 Enable or disable monitor warnings about hardware breakpoints. This
16833 has effect only for the @code{lsi} target. When on, @value{GDBN} will
16834 display warning messages whose codes are returned by the @code{lsi}
16835 PMON monitor for breakpoint commands.
16837 @item show monitor-warnings
16838 @kindex show monitor-warnings@r{, MIPS remote}
16839 Show the current setting of printing monitor warnings.
16841 @item pmon @var{command}
16842 @kindex pmon@r{, MIPS remote}
16843 @cindex send PMON command
16844 This command allows sending an arbitrary @var{command} string to the
16845 monitor. The monitor must be in debug mode for this to work.
16848 @node OpenRISC 1000
16849 @subsection OpenRISC 1000
16850 @cindex OpenRISC 1000
16852 @cindex or1k boards
16853 See OR1k Architecture document (@uref{www.opencores.org}) for more information
16854 about platform and commands.
16858 @kindex target jtag
16859 @item target jtag jtag://@var{host}:@var{port}
16861 Connects to remote JTAG server.
16862 JTAG remote server can be either an or1ksim or JTAG server,
16863 connected via parallel port to the board.
16865 Example: @code{target jtag jtag://localhost:9999}
16868 @item or1ksim @var{command}
16869 If connected to @code{or1ksim} OpenRISC 1000 Architectural
16870 Simulator, proprietary commands can be executed.
16872 @kindex info or1k spr
16873 @item info or1k spr
16874 Displays spr groups.
16876 @item info or1k spr @var{group}
16877 @itemx info or1k spr @var{groupno}
16878 Displays register names in selected group.
16880 @item info or1k spr @var{group} @var{register}
16881 @itemx info or1k spr @var{register}
16882 @itemx info or1k spr @var{groupno} @var{registerno}
16883 @itemx info or1k spr @var{registerno}
16884 Shows information about specified spr register.
16887 @item spr @var{group} @var{register} @var{value}
16888 @itemx spr @var{register @var{value}}
16889 @itemx spr @var{groupno} @var{registerno @var{value}}
16890 @itemx spr @var{registerno @var{value}}
16891 Writes @var{value} to specified spr register.
16894 Some implementations of OpenRISC 1000 Architecture also have hardware trace.
16895 It is very similar to @value{GDBN} trace, except it does not interfere with normal
16896 program execution and is thus much faster. Hardware breakpoints/watchpoint
16897 triggers can be set using:
16900 Load effective address/data
16902 Store effective address/data
16904 Access effective address ($SEA or $LEA) or data ($SDATA/$LDATA)
16909 When triggered, it can capture low level data, like: @code{PC}, @code{LSEA},
16910 @code{LDATA}, @code{SDATA}, @code{READSPR}, @code{WRITESPR}, @code{INSTR}.
16912 @code{htrace} commands:
16913 @cindex OpenRISC 1000 htrace
16916 @item hwatch @var{conditional}
16917 Set hardware watchpoint on combination of Load/Store Effective Address(es)
16918 or Data. For example:
16920 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
16922 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
16926 Display information about current HW trace configuration.
16928 @item htrace trigger @var{conditional}
16929 Set starting criteria for HW trace.
16931 @item htrace qualifier @var{conditional}
16932 Set acquisition qualifier for HW trace.
16934 @item htrace stop @var{conditional}
16935 Set HW trace stopping criteria.
16937 @item htrace record [@var{data}]*
16938 Selects the data to be recorded, when qualifier is met and HW trace was
16941 @item htrace enable
16942 @itemx htrace disable
16943 Enables/disables the HW trace.
16945 @item htrace rewind [@var{filename}]
16946 Clears currently recorded trace data.
16948 If filename is specified, new trace file is made and any newly collected data
16949 will be written there.
16951 @item htrace print [@var{start} [@var{len}]]
16952 Prints trace buffer, using current record configuration.
16954 @item htrace mode continuous
16955 Set continuous trace mode.
16957 @item htrace mode suspend
16958 Set suspend trace mode.
16962 @node PowerPC Embedded
16963 @subsection PowerPC Embedded
16965 @value{GDBN} provides the following PowerPC-specific commands:
16968 @kindex set powerpc
16969 @item set powerpc soft-float
16970 @itemx show powerpc soft-float
16971 Force @value{GDBN} to use (or not use) a software floating point calling
16972 convention. By default, @value{GDBN} selects the calling convention based
16973 on the selected architecture and the provided executable file.
16975 @item set powerpc vector-abi
16976 @itemx show powerpc vector-abi
16977 Force @value{GDBN} to use the specified calling convention for vector
16978 arguments and return values. The valid options are @samp{auto};
16979 @samp{generic}, to avoid vector registers even if they are present;
16980 @samp{altivec}, to use AltiVec registers; and @samp{spe} to use SPE
16981 registers. By default, @value{GDBN} selects the calling convention
16982 based on the selected architecture and the provided executable file.
16984 @kindex target dink32
16985 @item target dink32 @var{dev}
16986 DINK32 ROM monitor.
16988 @kindex target ppcbug
16989 @item target ppcbug @var{dev}
16990 @kindex target ppcbug1
16991 @item target ppcbug1 @var{dev}
16992 PPCBUG ROM monitor for PowerPC.
16995 @item target sds @var{dev}
16996 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
16999 @cindex SDS protocol
17000 The following commands specific to the SDS protocol are supported
17004 @item set sdstimeout @var{nsec}
17005 @kindex set sdstimeout
17006 Set the timeout for SDS protocol reads to be @var{nsec} seconds. The
17007 default is 2 seconds.
17009 @item show sdstimeout
17010 @kindex show sdstimeout
17011 Show the current value of the SDS timeout.
17013 @item sds @var{command}
17014 @kindex sds@r{, a command}
17015 Send the specified @var{command} string to the SDS monitor.
17020 @subsection HP PA Embedded
17024 @kindex target op50n
17025 @item target op50n @var{dev}
17026 OP50N monitor, running on an OKI HPPA board.
17028 @kindex target w89k
17029 @item target w89k @var{dev}
17030 W89K monitor, running on a Winbond HPPA board.
17035 @subsection Tsqware Sparclet
17039 @value{GDBN} enables developers to debug tasks running on
17040 Sparclet targets from a Unix host.
17041 @value{GDBN} uses code that runs on
17042 both the Unix host and on the Sparclet target. The program
17043 @code{@value{GDBP}} is installed and executed on the Unix host.
17046 @item remotetimeout @var{args}
17047 @kindex remotetimeout
17048 @value{GDBN} supports the option @code{remotetimeout}.
17049 This option is set by the user, and @var{args} represents the number of
17050 seconds @value{GDBN} waits for responses.
17053 @cindex compiling, on Sparclet
17054 When compiling for debugging, include the options @samp{-g} to get debug
17055 information and @samp{-Ttext} to relocate the program to where you wish to
17056 load it on the target. You may also want to add the options @samp{-n} or
17057 @samp{-N} in order to reduce the size of the sections. Example:
17060 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
17063 You can use @code{objdump} to verify that the addresses are what you intended:
17066 sparclet-aout-objdump --headers --syms prog
17069 @cindex running, on Sparclet
17071 your Unix execution search path to find @value{GDBN}, you are ready to
17072 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
17073 (or @code{sparclet-aout-gdb}, depending on your installation).
17075 @value{GDBN} comes up showing the prompt:
17082 * Sparclet File:: Setting the file to debug
17083 * Sparclet Connection:: Connecting to Sparclet
17084 * Sparclet Download:: Sparclet download
17085 * Sparclet Execution:: Running and debugging
17088 @node Sparclet File
17089 @subsubsection Setting File to Debug
17091 The @value{GDBN} command @code{file} lets you choose with program to debug.
17094 (gdbslet) file prog
17098 @value{GDBN} then attempts to read the symbol table of @file{prog}.
17099 @value{GDBN} locates
17100 the file by searching the directories listed in the command search
17102 If the file was compiled with debug information (option @samp{-g}), source
17103 files will be searched as well.
17104 @value{GDBN} locates
17105 the source files by searching the directories listed in the directory search
17106 path (@pxref{Environment, ,Your Program's Environment}).
17108 to find a file, it displays a message such as:
17111 prog: No such file or directory.
17114 When this happens, add the appropriate directories to the search paths with
17115 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
17116 @code{target} command again.
17118 @node Sparclet Connection
17119 @subsubsection Connecting to Sparclet
17121 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
17122 To connect to a target on serial port ``@code{ttya}'', type:
17125 (gdbslet) target sparclet /dev/ttya
17126 Remote target sparclet connected to /dev/ttya
17127 main () at ../prog.c:3
17131 @value{GDBN} displays messages like these:
17137 @node Sparclet Download
17138 @subsubsection Sparclet Download
17140 @cindex download to Sparclet
17141 Once connected to the Sparclet target,
17142 you can use the @value{GDBN}
17143 @code{load} command to download the file from the host to the target.
17144 The file name and load offset should be given as arguments to the @code{load}
17146 Since the file format is aout, the program must be loaded to the starting
17147 address. You can use @code{objdump} to find out what this value is. The load
17148 offset is an offset which is added to the VMA (virtual memory address)
17149 of each of the file's sections.
17150 For instance, if the program
17151 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
17152 and bss at 0x12010170, in @value{GDBN}, type:
17155 (gdbslet) load prog 0x12010000
17156 Loading section .text, size 0xdb0 vma 0x12010000
17159 If the code is loaded at a different address then what the program was linked
17160 to, you may need to use the @code{section} and @code{add-symbol-file} commands
17161 to tell @value{GDBN} where to map the symbol table.
17163 @node Sparclet Execution
17164 @subsubsection Running and Debugging
17166 @cindex running and debugging Sparclet programs
17167 You can now begin debugging the task using @value{GDBN}'s execution control
17168 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
17169 manual for the list of commands.
17173 Breakpoint 1 at 0x12010000: file prog.c, line 3.
17175 Starting program: prog
17176 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
17177 3 char *symarg = 0;
17179 4 char *execarg = "hello!";
17184 @subsection Fujitsu Sparclite
17188 @kindex target sparclite
17189 @item target sparclite @var{dev}
17190 Fujitsu sparclite boards, used only for the purpose of loading.
17191 You must use an additional command to debug the program.
17192 For example: target remote @var{dev} using @value{GDBN} standard
17198 @subsection Zilog Z8000
17201 @cindex simulator, Z8000
17202 @cindex Zilog Z8000 simulator
17204 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
17207 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
17208 unsegmented variant of the Z8000 architecture) or the Z8001 (the
17209 segmented variant). The simulator recognizes which architecture is
17210 appropriate by inspecting the object code.
17213 @item target sim @var{args}
17215 @kindex target sim@r{, with Z8000}
17216 Debug programs on a simulated CPU. If the simulator supports setup
17217 options, specify them via @var{args}.
17221 After specifying this target, you can debug programs for the simulated
17222 CPU in the same style as programs for your host computer; use the
17223 @code{file} command to load a new program image, the @code{run} command
17224 to run your program, and so on.
17226 As well as making available all the usual machine registers
17227 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
17228 additional items of information as specially named registers:
17233 Counts clock-ticks in the simulator.
17236 Counts instructions run in the simulator.
17239 Execution time in 60ths of a second.
17243 You can refer to these values in @value{GDBN} expressions with the usual
17244 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
17245 conditional breakpoint that suspends only after at least 5000
17246 simulated clock ticks.
17249 @subsection Atmel AVR
17252 When configured for debugging the Atmel AVR, @value{GDBN} supports the
17253 following AVR-specific commands:
17256 @item info io_registers
17257 @kindex info io_registers@r{, AVR}
17258 @cindex I/O registers (Atmel AVR)
17259 This command displays information about the AVR I/O registers. For
17260 each register, @value{GDBN} prints its number and value.
17267 When configured for debugging CRIS, @value{GDBN} provides the
17268 following CRIS-specific commands:
17271 @item set cris-version @var{ver}
17272 @cindex CRIS version
17273 Set the current CRIS version to @var{ver}, either @samp{10} or @samp{32}.
17274 The CRIS version affects register names and sizes. This command is useful in
17275 case autodetection of the CRIS version fails.
17277 @item show cris-version
17278 Show the current CRIS version.
17280 @item set cris-dwarf2-cfi
17281 @cindex DWARF-2 CFI and CRIS
17282 Set the usage of DWARF-2 CFI for CRIS debugging. The default is @samp{on}.
17283 Change to @samp{off} when using @code{gcc-cris} whose version is below
17286 @item show cris-dwarf2-cfi
17287 Show the current state of using DWARF-2 CFI.
17289 @item set cris-mode @var{mode}
17291 Set the current CRIS mode to @var{mode}. It should only be changed when
17292 debugging in guru mode, in which case it should be set to
17293 @samp{guru} (the default is @samp{normal}).
17295 @item show cris-mode
17296 Show the current CRIS mode.
17300 @subsection Renesas Super-H
17303 For the Renesas Super-H processor, @value{GDBN} provides these
17308 @kindex regs@r{, Super-H}
17309 Show the values of all Super-H registers.
17311 @item set sh calling-convention @var{convention}
17312 @kindex set sh calling-convention
17313 Set the calling-convention used when calling functions from @value{GDBN}.
17314 Allowed values are @samp{gcc}, which is the default setting, and @samp{renesas}.
17315 With the @samp{gcc} setting, functions are called using the @value{NGCC} calling
17316 convention. If the DWARF-2 information of the called function specifies
17317 that the function follows the Renesas calling convention, the function
17318 is called using the Renesas calling convention. If the calling convention
17319 is set to @samp{renesas}, the Renesas calling convention is always used,
17320 regardless of the DWARF-2 information. This can be used to override the
17321 default of @samp{gcc} if debug information is missing, or the compiler
17322 does not emit the DWARF-2 calling convention entry for a function.
17324 @item show sh calling-convention
17325 @kindex show sh calling-convention
17326 Show the current calling convention setting.
17331 @node Architectures
17332 @section Architectures
17334 This section describes characteristics of architectures that affect
17335 all uses of @value{GDBN} with the architecture, both native and cross.
17342 * HPPA:: HP PA architecture
17343 * SPU:: Cell Broadband Engine SPU architecture
17348 @subsection x86 Architecture-specific Issues
17351 @item set struct-convention @var{mode}
17352 @kindex set struct-convention
17353 @cindex struct return convention
17354 @cindex struct/union returned in registers
17355 Set the convention used by the inferior to return @code{struct}s and
17356 @code{union}s from functions to @var{mode}. Possible values of
17357 @var{mode} are @code{"pcc"}, @code{"reg"}, and @code{"default"} (the
17358 default). @code{"default"} or @code{"pcc"} means that @code{struct}s
17359 are returned on the stack, while @code{"reg"} means that a
17360 @code{struct} or a @code{union} whose size is 1, 2, 4, or 8 bytes will
17361 be returned in a register.
17363 @item show struct-convention
17364 @kindex show struct-convention
17365 Show the current setting of the convention to return @code{struct}s
17374 @kindex set rstack_high_address
17375 @cindex AMD 29K register stack
17376 @cindex register stack, AMD29K
17377 @item set rstack_high_address @var{address}
17378 On AMD 29000 family processors, registers are saved in a separate
17379 @dfn{register stack}. There is no way for @value{GDBN} to determine the
17380 extent of this stack. Normally, @value{GDBN} just assumes that the
17381 stack is ``large enough''. This may result in @value{GDBN} referencing
17382 memory locations that do not exist. If necessary, you can get around
17383 this problem by specifying the ending address of the register stack with
17384 the @code{set rstack_high_address} command. The argument should be an
17385 address, which you probably want to precede with @samp{0x} to specify in
17388 @kindex show rstack_high_address
17389 @item show rstack_high_address
17390 Display the current limit of the register stack, on AMD 29000 family
17398 See the following section.
17403 @cindex stack on Alpha
17404 @cindex stack on MIPS
17405 @cindex Alpha stack
17407 Alpha- and MIPS-based computers use an unusual stack frame, which
17408 sometimes requires @value{GDBN} to search backward in the object code to
17409 find the beginning of a function.
17411 @cindex response time, MIPS debugging
17412 To improve response time (especially for embedded applications, where
17413 @value{GDBN} may be restricted to a slow serial line for this search)
17414 you may want to limit the size of this search, using one of these
17418 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
17419 @item set heuristic-fence-post @var{limit}
17420 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
17421 search for the beginning of a function. A value of @var{0} (the
17422 default) means there is no limit. However, except for @var{0}, the
17423 larger the limit the more bytes @code{heuristic-fence-post} must search
17424 and therefore the longer it takes to run. You should only need to use
17425 this command when debugging a stripped executable.
17427 @item show heuristic-fence-post
17428 Display the current limit.
17432 These commands are available @emph{only} when @value{GDBN} is configured
17433 for debugging programs on Alpha or MIPS processors.
17435 Several MIPS-specific commands are available when debugging MIPS
17439 @item set mips abi @var{arg}
17440 @kindex set mips abi
17441 @cindex set ABI for MIPS
17442 Tell @value{GDBN} which MIPS ABI is used by the inferior. Possible
17443 values of @var{arg} are:
17447 The default ABI associated with the current binary (this is the
17458 @item show mips abi
17459 @kindex show mips abi
17460 Show the MIPS ABI used by @value{GDBN} to debug the inferior.
17463 @itemx show mipsfpu
17464 @xref{MIPS Embedded, set mipsfpu}.
17466 @item set mips mask-address @var{arg}
17467 @kindex set mips mask-address
17468 @cindex MIPS addresses, masking
17469 This command determines whether the most-significant 32 bits of 64-bit
17470 MIPS addresses are masked off. The argument @var{arg} can be
17471 @samp{on}, @samp{off}, or @samp{auto}. The latter is the default
17472 setting, which lets @value{GDBN} determine the correct value.
17474 @item show mips mask-address
17475 @kindex show mips mask-address
17476 Show whether the upper 32 bits of MIPS addresses are masked off or
17479 @item set remote-mips64-transfers-32bit-regs
17480 @kindex set remote-mips64-transfers-32bit-regs
17481 This command controls compatibility with 64-bit MIPS targets that
17482 transfer data in 32-bit quantities. If you have an old MIPS 64 target
17483 that transfers 32 bits for some registers, like @sc{sr} and @sc{fsr},
17484 and 64 bits for other registers, set this option to @samp{on}.
17486 @item show remote-mips64-transfers-32bit-regs
17487 @kindex show remote-mips64-transfers-32bit-regs
17488 Show the current setting of compatibility with older MIPS 64 targets.
17490 @item set debug mips
17491 @kindex set debug mips
17492 This command turns on and off debugging messages for the MIPS-specific
17493 target code in @value{GDBN}.
17495 @item show debug mips
17496 @kindex show debug mips
17497 Show the current setting of MIPS debugging messages.
17503 @cindex HPPA support
17505 When @value{GDBN} is debugging the HP PA architecture, it provides the
17506 following special commands:
17509 @item set debug hppa
17510 @kindex set debug hppa
17511 This command determines whether HPPA architecture-specific debugging
17512 messages are to be displayed.
17514 @item show debug hppa
17515 Show whether HPPA debugging messages are displayed.
17517 @item maint print unwind @var{address}
17518 @kindex maint print unwind@r{, HPPA}
17519 This command displays the contents of the unwind table entry at the
17520 given @var{address}.
17526 @subsection Cell Broadband Engine SPU architecture
17527 @cindex Cell Broadband Engine
17530 When @value{GDBN} is debugging the Cell Broadband Engine SPU architecture,
17531 it provides the following special commands:
17534 @item info spu event
17536 Display SPU event facility status. Shows current event mask
17537 and pending event status.
17539 @item info spu signal
17540 Display SPU signal notification facility status. Shows pending
17541 signal-control word and signal notification mode of both signal
17542 notification channels.
17544 @item info spu mailbox
17545 Display SPU mailbox facility status. Shows all pending entries,
17546 in order of processing, in each of the SPU Write Outbound,
17547 SPU Write Outbound Interrupt, and SPU Read Inbound mailboxes.
17550 Display MFC DMA status. Shows all pending commands in the MFC
17551 DMA queue. For each entry, opcode, tag, class IDs, effective
17552 and local store addresses and transfer size are shown.
17554 @item info spu proxydma
17555 Display MFC Proxy-DMA status. Shows all pending commands in the MFC
17556 Proxy-DMA queue. For each entry, opcode, tag, class IDs, effective
17557 and local store addresses and transfer size are shown.
17561 When @value{GDBN} is debugging a combined PowerPC/SPU application
17562 on the Cell Broadband Engine, it provides in addition the following
17566 @item set spu stop-on-load @var{arg}
17568 Set whether to stop for new SPE threads. When set to @code{on}, @value{GDBN}
17569 will give control to the user when a new SPE thread enters its @code{main}
17570 function. The default is @code{off}.
17572 @item show spu stop-on-load
17574 Show whether to stop for new SPE threads.
17576 @item set spu auto-flush-cache @var{arg}
17577 Set whether to automatically flush the software-managed cache. When set to
17578 @code{on}, @value{GDBN} will automatically cause the SPE software-managed
17579 cache to be flushed whenever SPE execution stops. This provides a consistent
17580 view of PowerPC memory that is accessed via the cache. If an application
17581 does not use the software-managed cache, this option has no effect.
17583 @item show spu auto-flush-cache
17584 Show whether to automatically flush the software-managed cache.
17589 @subsection PowerPC
17590 @cindex PowerPC architecture
17592 When @value{GDBN} is debugging the PowerPC architecture, it provides a set of
17593 pseudo-registers to enable inspection of 128-bit wide Decimal Floating Point
17594 numbers stored in the floating point registers. These values must be stored
17595 in two consecutive registers, always starting at an even register like
17596 @code{f0} or @code{f2}.
17598 The pseudo-registers go from @code{$dl0} through @code{$dl15}, and are formed
17599 by joining the even/odd register pairs @code{f0} and @code{f1} for @code{$dl0},
17600 @code{f2} and @code{f3} for @code{$dl1} and so on.
17602 For POWER7 processors, @value{GDBN} provides a set of pseudo-registers, the 64-bit
17603 wide Extended Floating Point Registers (@samp{f32} through @samp{f63}).
17606 @node Controlling GDB
17607 @chapter Controlling @value{GDBN}
17609 You can alter the way @value{GDBN} interacts with you by using the
17610 @code{set} command. For commands controlling how @value{GDBN} displays
17611 data, see @ref{Print Settings, ,Print Settings}. Other settings are
17616 * Editing:: Command editing
17617 * Command History:: Command history
17618 * Screen Size:: Screen size
17619 * Numbers:: Numbers
17620 * ABI:: Configuring the current ABI
17621 * Messages/Warnings:: Optional warnings and messages
17622 * Debugging Output:: Optional messages about internal happenings
17630 @value{GDBN} indicates its readiness to read a command by printing a string
17631 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
17632 can change the prompt string with the @code{set prompt} command. For
17633 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
17634 the prompt in one of the @value{GDBN} sessions so that you can always tell
17635 which one you are talking to.
17637 @emph{Note:} @code{set prompt} does not add a space for you after the
17638 prompt you set. This allows you to set a prompt which ends in a space
17639 or a prompt that does not.
17643 @item set prompt @var{newprompt}
17644 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
17646 @kindex show prompt
17648 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
17652 @section Command Editing
17654 @cindex command line editing
17656 @value{GDBN} reads its input commands via the @dfn{Readline} interface. This
17657 @sc{gnu} library provides consistent behavior for programs which provide a
17658 command line interface to the user. Advantages are @sc{gnu} Emacs-style
17659 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
17660 substitution, and a storage and recall of command history across
17661 debugging sessions.
17663 You may control the behavior of command line editing in @value{GDBN} with the
17664 command @code{set}.
17667 @kindex set editing
17670 @itemx set editing on
17671 Enable command line editing (enabled by default).
17673 @item set editing off
17674 Disable command line editing.
17676 @kindex show editing
17678 Show whether command line editing is enabled.
17681 @xref{Command Line Editing}, for more details about the Readline
17682 interface. Users unfamiliar with @sc{gnu} Emacs or @code{vi} are
17683 encouraged to read that chapter.
17685 @node Command History
17686 @section Command History
17687 @cindex command history
17689 @value{GDBN} can keep track of the commands you type during your
17690 debugging sessions, so that you can be certain of precisely what
17691 happened. Use these commands to manage the @value{GDBN} command
17694 @value{GDBN} uses the @sc{gnu} History library, a part of the Readline
17695 package, to provide the history facility. @xref{Using History
17696 Interactively}, for the detailed description of the History library.
17698 To issue a command to @value{GDBN} without affecting certain aspects of
17699 the state which is seen by users, prefix it with @samp{server }
17700 (@pxref{Server Prefix}). This
17701 means that this command will not affect the command history, nor will it
17702 affect @value{GDBN}'s notion of which command to repeat if @key{RET} is
17703 pressed on a line by itself.
17705 @cindex @code{server}, command prefix
17706 The server prefix does not affect the recording of values into the value
17707 history; to print a value without recording it into the value history,
17708 use the @code{output} command instead of the @code{print} command.
17710 Here is the description of @value{GDBN} commands related to command
17714 @cindex history substitution
17715 @cindex history file
17716 @kindex set history filename
17717 @cindex @env{GDBHISTFILE}, environment variable
17718 @item set history filename @var{fname}
17719 Set the name of the @value{GDBN} command history file to @var{fname}.
17720 This is the file where @value{GDBN} reads an initial command history
17721 list, and where it writes the command history from this session when it
17722 exits. You can access this list through history expansion or through
17723 the history command editing characters listed below. This file defaults
17724 to the value of the environment variable @code{GDBHISTFILE}, or to
17725 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
17728 @cindex save command history
17729 @kindex set history save
17730 @item set history save
17731 @itemx set history save on
17732 Record command history in a file, whose name may be specified with the
17733 @code{set history filename} command. By default, this option is disabled.
17735 @item set history save off
17736 Stop recording command history in a file.
17738 @cindex history size
17739 @kindex set history size
17740 @cindex @env{HISTSIZE}, environment variable
17741 @item set history size @var{size}
17742 Set the number of commands which @value{GDBN} keeps in its history list.
17743 This defaults to the value of the environment variable
17744 @code{HISTSIZE}, or to 256 if this variable is not set.
17747 History expansion assigns special meaning to the character @kbd{!}.
17748 @xref{Event Designators}, for more details.
17750 @cindex history expansion, turn on/off
17751 Since @kbd{!} is also the logical not operator in C, history expansion
17752 is off by default. If you decide to enable history expansion with the
17753 @code{set history expansion on} command, you may sometimes need to
17754 follow @kbd{!} (when it is used as logical not, in an expression) with
17755 a space or a tab to prevent it from being expanded. The readline
17756 history facilities do not attempt substitution on the strings
17757 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
17759 The commands to control history expansion are:
17762 @item set history expansion on
17763 @itemx set history expansion
17764 @kindex set history expansion
17765 Enable history expansion. History expansion is off by default.
17767 @item set history expansion off
17768 Disable history expansion.
17771 @kindex show history
17773 @itemx show history filename
17774 @itemx show history save
17775 @itemx show history size
17776 @itemx show history expansion
17777 These commands display the state of the @value{GDBN} history parameters.
17778 @code{show history} by itself displays all four states.
17783 @kindex show commands
17784 @cindex show last commands
17785 @cindex display command history
17786 @item show commands
17787 Display the last ten commands in the command history.
17789 @item show commands @var{n}
17790 Print ten commands centered on command number @var{n}.
17792 @item show commands +
17793 Print ten commands just after the commands last printed.
17797 @section Screen Size
17798 @cindex size of screen
17799 @cindex pauses in output
17801 Certain commands to @value{GDBN} may produce large amounts of
17802 information output to the screen. To help you read all of it,
17803 @value{GDBN} pauses and asks you for input at the end of each page of
17804 output. Type @key{RET} when you want to continue the output, or @kbd{q}
17805 to discard the remaining output. Also, the screen width setting
17806 determines when to wrap lines of output. Depending on what is being
17807 printed, @value{GDBN} tries to break the line at a readable place,
17808 rather than simply letting it overflow onto the following line.
17810 Normally @value{GDBN} knows the size of the screen from the terminal
17811 driver software. For example, on Unix @value{GDBN} uses the termcap data base
17812 together with the value of the @code{TERM} environment variable and the
17813 @code{stty rows} and @code{stty cols} settings. If this is not correct,
17814 you can override it with the @code{set height} and @code{set
17821 @kindex show height
17822 @item set height @var{lpp}
17824 @itemx set width @var{cpl}
17826 These @code{set} commands specify a screen height of @var{lpp} lines and
17827 a screen width of @var{cpl} characters. The associated @code{show}
17828 commands display the current settings.
17830 If you specify a height of zero lines, @value{GDBN} does not pause during
17831 output no matter how long the output is. This is useful if output is to a
17832 file or to an editor buffer.
17834 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
17835 from wrapping its output.
17837 @item set pagination on
17838 @itemx set pagination off
17839 @kindex set pagination
17840 Turn the output pagination on or off; the default is on. Turning
17841 pagination off is the alternative to @code{set height 0}.
17843 @item show pagination
17844 @kindex show pagination
17845 Show the current pagination mode.
17850 @cindex number representation
17851 @cindex entering numbers
17853 You can always enter numbers in octal, decimal, or hexadecimal in
17854 @value{GDBN} by the usual conventions: octal numbers begin with
17855 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
17856 begin with @samp{0x}. Numbers that neither begin with @samp{0} or
17857 @samp{0x}, nor end with a @samp{.} are, by default, entered in base
17858 10; likewise, the default display for numbers---when no particular
17859 format is specified---is base 10. You can change the default base for
17860 both input and output with the commands described below.
17863 @kindex set input-radix
17864 @item set input-radix @var{base}
17865 Set the default base for numeric input. Supported choices
17866 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
17867 specified either unambiguously or using the current input radix; for
17871 set input-radix 012
17872 set input-radix 10.
17873 set input-radix 0xa
17877 sets the input base to decimal. On the other hand, @samp{set input-radix 10}
17878 leaves the input radix unchanged, no matter what it was, since
17879 @samp{10}, being without any leading or trailing signs of its base, is
17880 interpreted in the current radix. Thus, if the current radix is 16,
17881 @samp{10} is interpreted in hex, i.e.@: as 16 decimal, which doesn't
17884 @kindex set output-radix
17885 @item set output-radix @var{base}
17886 Set the default base for numeric display. Supported choices
17887 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
17888 specified either unambiguously or using the current input radix.
17890 @kindex show input-radix
17891 @item show input-radix
17892 Display the current default base for numeric input.
17894 @kindex show output-radix
17895 @item show output-radix
17896 Display the current default base for numeric display.
17898 @item set radix @r{[}@var{base}@r{]}
17902 These commands set and show the default base for both input and output
17903 of numbers. @code{set radix} sets the radix of input and output to
17904 the same base; without an argument, it resets the radix back to its
17905 default value of 10.
17910 @section Configuring the Current ABI
17912 @value{GDBN} can determine the @dfn{ABI} (Application Binary Interface) of your
17913 application automatically. However, sometimes you need to override its
17914 conclusions. Use these commands to manage @value{GDBN}'s view of the
17921 One @value{GDBN} configuration can debug binaries for multiple operating
17922 system targets, either via remote debugging or native emulation.
17923 @value{GDBN} will autodetect the @dfn{OS ABI} (Operating System ABI) in use,
17924 but you can override its conclusion using the @code{set osabi} command.
17925 One example where this is useful is in debugging of binaries which use
17926 an alternate C library (e.g.@: @sc{uClibc} for @sc{gnu}/Linux) which does
17927 not have the same identifying marks that the standard C library for your
17932 Show the OS ABI currently in use.
17935 With no argument, show the list of registered available OS ABI's.
17937 @item set osabi @var{abi}
17938 Set the current OS ABI to @var{abi}.
17941 @cindex float promotion
17943 Generally, the way that an argument of type @code{float} is passed to a
17944 function depends on whether the function is prototyped. For a prototyped
17945 (i.e.@: ANSI/ISO style) function, @code{float} arguments are passed unchanged,
17946 according to the architecture's convention for @code{float}. For unprototyped
17947 (i.e.@: K&R style) functions, @code{float} arguments are first promoted to type
17948 @code{double} and then passed.
17950 Unfortunately, some forms of debug information do not reliably indicate whether
17951 a function is prototyped. If @value{GDBN} calls a function that is not marked
17952 as prototyped, it consults @kbd{set coerce-float-to-double}.
17955 @kindex set coerce-float-to-double
17956 @item set coerce-float-to-double
17957 @itemx set coerce-float-to-double on
17958 Arguments of type @code{float} will be promoted to @code{double} when passed
17959 to an unprototyped function. This is the default setting.
17961 @item set coerce-float-to-double off
17962 Arguments of type @code{float} will be passed directly to unprototyped
17965 @kindex show coerce-float-to-double
17966 @item show coerce-float-to-double
17967 Show the current setting of promoting @code{float} to @code{double}.
17971 @kindex show cp-abi
17972 @value{GDBN} needs to know the ABI used for your program's C@t{++}
17973 objects. The correct C@t{++} ABI depends on which C@t{++} compiler was
17974 used to build your application. @value{GDBN} only fully supports
17975 programs with a single C@t{++} ABI; if your program contains code using
17976 multiple C@t{++} ABI's or if @value{GDBN} can not identify your
17977 program's ABI correctly, you can tell @value{GDBN} which ABI to use.
17978 Currently supported ABI's include ``gnu-v2'', for @code{g++} versions
17979 before 3.0, ``gnu-v3'', for @code{g++} versions 3.0 and later, and
17980 ``hpaCC'' for the HP ANSI C@t{++} compiler. Other C@t{++} compilers may
17981 use the ``gnu-v2'' or ``gnu-v3'' ABI's as well. The default setting is
17986 Show the C@t{++} ABI currently in use.
17989 With no argument, show the list of supported C@t{++} ABI's.
17991 @item set cp-abi @var{abi}
17992 @itemx set cp-abi auto
17993 Set the current C@t{++} ABI to @var{abi}, or return to automatic detection.
17996 @node Messages/Warnings
17997 @section Optional Warnings and Messages
17999 @cindex verbose operation
18000 @cindex optional warnings
18001 By default, @value{GDBN} is silent about its inner workings. If you are
18002 running on a slow machine, you may want to use the @code{set verbose}
18003 command. This makes @value{GDBN} tell you when it does a lengthy
18004 internal operation, so you will not think it has crashed.
18006 Currently, the messages controlled by @code{set verbose} are those
18007 which announce that the symbol table for a source file is being read;
18008 see @code{symbol-file} in @ref{Files, ,Commands to Specify Files}.
18011 @kindex set verbose
18012 @item set verbose on
18013 Enables @value{GDBN} output of certain informational messages.
18015 @item set verbose off
18016 Disables @value{GDBN} output of certain informational messages.
18018 @kindex show verbose
18020 Displays whether @code{set verbose} is on or off.
18023 By default, if @value{GDBN} encounters bugs in the symbol table of an
18024 object file, it is silent; but if you are debugging a compiler, you may
18025 find this information useful (@pxref{Symbol Errors, ,Errors Reading
18030 @kindex set complaints
18031 @item set complaints @var{limit}
18032 Permits @value{GDBN} to output @var{limit} complaints about each type of
18033 unusual symbols before becoming silent about the problem. Set
18034 @var{limit} to zero to suppress all complaints; set it to a large number
18035 to prevent complaints from being suppressed.
18037 @kindex show complaints
18038 @item show complaints
18039 Displays how many symbol complaints @value{GDBN} is permitted to produce.
18043 @anchor{confirmation requests}
18044 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
18045 lot of stupid questions to confirm certain commands. For example, if
18046 you try to run a program which is already running:
18050 The program being debugged has been started already.
18051 Start it from the beginning? (y or n)
18054 If you are willing to unflinchingly face the consequences of your own
18055 commands, you can disable this ``feature'':
18059 @kindex set confirm
18061 @cindex confirmation
18062 @cindex stupid questions
18063 @item set confirm off
18064 Disables confirmation requests.
18066 @item set confirm on
18067 Enables confirmation requests (the default).
18069 @kindex show confirm
18071 Displays state of confirmation requests.
18075 @cindex command tracing
18076 If you need to debug user-defined commands or sourced files you may find it
18077 useful to enable @dfn{command tracing}. In this mode each command will be
18078 printed as it is executed, prefixed with one or more @samp{+} symbols, the
18079 quantity denoting the call depth of each command.
18082 @kindex set trace-commands
18083 @cindex command scripts, debugging
18084 @item set trace-commands on
18085 Enable command tracing.
18086 @item set trace-commands off
18087 Disable command tracing.
18088 @item show trace-commands
18089 Display the current state of command tracing.
18092 @node Debugging Output
18093 @section Optional Messages about Internal Happenings
18094 @cindex optional debugging messages
18096 @value{GDBN} has commands that enable optional debugging messages from
18097 various @value{GDBN} subsystems; normally these commands are of
18098 interest to @value{GDBN} maintainers, or when reporting a bug. This
18099 section documents those commands.
18102 @kindex set exec-done-display
18103 @item set exec-done-display
18104 Turns on or off the notification of asynchronous commands'
18105 completion. When on, @value{GDBN} will print a message when an
18106 asynchronous command finishes its execution. The default is off.
18107 @kindex show exec-done-display
18108 @item show exec-done-display
18109 Displays the current setting of asynchronous command completion
18112 @cindex gdbarch debugging info
18113 @cindex architecture debugging info
18114 @item set debug arch
18115 Turns on or off display of gdbarch debugging info. The default is off
18117 @item show debug arch
18118 Displays the current state of displaying gdbarch debugging info.
18119 @item set debug aix-thread
18120 @cindex AIX threads
18121 Display debugging messages about inner workings of the AIX thread
18123 @item show debug aix-thread
18124 Show the current state of AIX thread debugging info display.
18125 @item set debug dwarf2-die
18126 @cindex DWARF2 DIEs
18127 Dump DWARF2 DIEs after they are read in.
18128 The value is the number of nesting levels to print.
18129 A value of zero turns off the display.
18130 @item show debug dwarf2-die
18131 Show the current state of DWARF2 DIE debugging.
18132 @item set debug displaced
18133 @cindex displaced stepping debugging info
18134 Turns on or off display of @value{GDBN} debugging info for the
18135 displaced stepping support. The default is off.
18136 @item show debug displaced
18137 Displays the current state of displaying @value{GDBN} debugging info
18138 related to displaced stepping.
18139 @item set debug event
18140 @cindex event debugging info
18141 Turns on or off display of @value{GDBN} event debugging info. The
18143 @item show debug event
18144 Displays the current state of displaying @value{GDBN} event debugging
18146 @item set debug expression
18147 @cindex expression debugging info
18148 Turns on or off display of debugging info about @value{GDBN}
18149 expression parsing. The default is off.
18150 @item show debug expression
18151 Displays the current state of displaying debugging info about
18152 @value{GDBN} expression parsing.
18153 @item set debug frame
18154 @cindex frame debugging info
18155 Turns on or off display of @value{GDBN} frame debugging info. The
18157 @item show debug frame
18158 Displays the current state of displaying @value{GDBN} frame debugging
18160 @item set debug gnu-nat
18161 @cindex @sc{gnu}/Hurd debug messages
18162 Turns on or off debugging messages from the @sc{gnu}/Hurd debug support.
18163 @item show debug gnu-nat
18164 Show the current state of @sc{gnu}/Hurd debugging messages.
18165 @item set debug infrun
18166 @cindex inferior debugging info
18167 Turns on or off display of @value{GDBN} debugging info for running the inferior.
18168 The default is off. @file{infrun.c} contains GDB's runtime state machine used
18169 for implementing operations such as single-stepping the inferior.
18170 @item show debug infrun
18171 Displays the current state of @value{GDBN} inferior debugging.
18172 @item set debug lin-lwp
18173 @cindex @sc{gnu}/Linux LWP debug messages
18174 @cindex Linux lightweight processes
18175 Turns on or off debugging messages from the Linux LWP debug support.
18176 @item show debug lin-lwp
18177 Show the current state of Linux LWP debugging messages.
18178 @item set debug lin-lwp-async
18179 @cindex @sc{gnu}/Linux LWP async debug messages
18180 @cindex Linux lightweight processes
18181 Turns on or off debugging messages from the Linux LWP async debug support.
18182 @item show debug lin-lwp-async
18183 Show the current state of Linux LWP async debugging messages.
18184 @item set debug observer
18185 @cindex observer debugging info
18186 Turns on or off display of @value{GDBN} observer debugging. This
18187 includes info such as the notification of observable events.
18188 @item show debug observer
18189 Displays the current state of observer debugging.
18190 @item set debug overload
18191 @cindex C@t{++} overload debugging info
18192 Turns on or off display of @value{GDBN} C@t{++} overload debugging
18193 info. This includes info such as ranking of functions, etc. The default
18195 @item show debug overload
18196 Displays the current state of displaying @value{GDBN} C@t{++} overload
18198 @cindex packets, reporting on stdout
18199 @cindex serial connections, debugging
18200 @cindex debug remote protocol
18201 @cindex remote protocol debugging
18202 @cindex display remote packets
18203 @item set debug remote
18204 Turns on or off display of reports on all packets sent back and forth across
18205 the serial line to the remote machine. The info is printed on the
18206 @value{GDBN} standard output stream. The default is off.
18207 @item show debug remote
18208 Displays the state of display of remote packets.
18209 @item set debug serial
18210 Turns on or off display of @value{GDBN} serial debugging info. The
18212 @item show debug serial
18213 Displays the current state of displaying @value{GDBN} serial debugging
18215 @item set debug solib-frv
18216 @cindex FR-V shared-library debugging
18217 Turns on or off debugging messages for FR-V shared-library code.
18218 @item show debug solib-frv
18219 Display the current state of FR-V shared-library code debugging
18221 @item set debug target
18222 @cindex target debugging info
18223 Turns on or off display of @value{GDBN} target debugging info. This info
18224 includes what is going on at the target level of GDB, as it happens. The
18225 default is 0. Set it to 1 to track events, and to 2 to also track the
18226 value of large memory transfers. Changes to this flag do not take effect
18227 until the next time you connect to a target or use the @code{run} command.
18228 @item show debug target
18229 Displays the current state of displaying @value{GDBN} target debugging
18231 @item set debug timestamp
18232 @cindex timestampping debugging info
18233 Turns on or off display of timestamps with @value{GDBN} debugging info.
18234 When enabled, seconds and microseconds are displayed before each debugging
18236 @item show debug timestamp
18237 Displays the current state of displaying timestamps with @value{GDBN}
18239 @item set debugvarobj
18240 @cindex variable object debugging info
18241 Turns on or off display of @value{GDBN} variable object debugging
18242 info. The default is off.
18243 @item show debugvarobj
18244 Displays the current state of displaying @value{GDBN} variable object
18246 @item set debug xml
18247 @cindex XML parser debugging
18248 Turns on or off debugging messages for built-in XML parsers.
18249 @item show debug xml
18250 Displays the current state of XML debugging messages.
18253 @node Extending GDB
18254 @chapter Extending @value{GDBN}
18255 @cindex extending GDB
18257 @value{GDBN} provides two mechanisms for extension. The first is based
18258 on composition of @value{GDBN} commands, and the second is based on the
18259 Python scripting language.
18262 * Sequences:: Canned Sequences of Commands
18263 * Python:: Scripting @value{GDBN} using Python
18267 @section Canned Sequences of Commands
18269 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
18270 Command Lists}), @value{GDBN} provides two ways to store sequences of
18271 commands for execution as a unit: user-defined commands and command
18275 * Define:: How to define your own commands
18276 * Hooks:: Hooks for user-defined commands
18277 * Command Files:: How to write scripts of commands to be stored in a file
18278 * Output:: Commands for controlled output
18282 @subsection User-defined Commands
18284 @cindex user-defined command
18285 @cindex arguments, to user-defined commands
18286 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
18287 which you assign a new name as a command. This is done with the
18288 @code{define} command. User commands may accept up to 10 arguments
18289 separated by whitespace. Arguments are accessed within the user command
18290 via @code{$arg0@dots{}$arg9}. A trivial example:
18294 print $arg0 + $arg1 + $arg2
18299 To execute the command use:
18306 This defines the command @code{adder}, which prints the sum of
18307 its three arguments. Note the arguments are text substitutions, so they may
18308 reference variables, use complex expressions, or even perform inferior
18311 @cindex argument count in user-defined commands
18312 @cindex how many arguments (user-defined commands)
18313 In addition, @code{$argc} may be used to find out how many arguments have
18314 been passed. This expands to a number in the range 0@dots{}10.
18319 print $arg0 + $arg1
18322 print $arg0 + $arg1 + $arg2
18330 @item define @var{commandname}
18331 Define a command named @var{commandname}. If there is already a command
18332 by that name, you are asked to confirm that you want to redefine it.
18333 @var{commandname} may be a bare command name consisting of letters,
18334 numbers, dashes, and underscores. It may also start with any predefined
18335 prefix command. For example, @samp{define target my-target} creates
18336 a user-defined @samp{target my-target} command.
18338 The definition of the command is made up of other @value{GDBN} command lines,
18339 which are given following the @code{define} command. The end of these
18340 commands is marked by a line containing @code{end}.
18343 @kindex end@r{ (user-defined commands)}
18344 @item document @var{commandname}
18345 Document the user-defined command @var{commandname}, so that it can be
18346 accessed by @code{help}. The command @var{commandname} must already be
18347 defined. This command reads lines of documentation just as @code{define}
18348 reads the lines of the command definition, ending with @code{end}.
18349 After the @code{document} command is finished, @code{help} on command
18350 @var{commandname} displays the documentation you have written.
18352 You may use the @code{document} command again to change the
18353 documentation of a command. Redefining the command with @code{define}
18354 does not change the documentation.
18356 @kindex dont-repeat
18357 @cindex don't repeat command
18359 Used inside a user-defined command, this tells @value{GDBN} that this
18360 command should not be repeated when the user hits @key{RET}
18361 (@pxref{Command Syntax, repeat last command}).
18363 @kindex help user-defined
18364 @item help user-defined
18365 List all user-defined commands, with the first line of the documentation
18370 @itemx show user @var{commandname}
18371 Display the @value{GDBN} commands used to define @var{commandname} (but
18372 not its documentation). If no @var{commandname} is given, display the
18373 definitions for all user-defined commands.
18375 @cindex infinite recursion in user-defined commands
18376 @kindex show max-user-call-depth
18377 @kindex set max-user-call-depth
18378 @item show max-user-call-depth
18379 @itemx set max-user-call-depth
18380 The value of @code{max-user-call-depth} controls how many recursion
18381 levels are allowed in user-defined commands before @value{GDBN} suspects an
18382 infinite recursion and aborts the command.
18385 In addition to the above commands, user-defined commands frequently
18386 use control flow commands, described in @ref{Command Files}.
18388 When user-defined commands are executed, the
18389 commands of the definition are not printed. An error in any command
18390 stops execution of the user-defined command.
18392 If used interactively, commands that would ask for confirmation proceed
18393 without asking when used inside a user-defined command. Many @value{GDBN}
18394 commands that normally print messages to say what they are doing omit the
18395 messages when used in a user-defined command.
18398 @subsection User-defined Command Hooks
18399 @cindex command hooks
18400 @cindex hooks, for commands
18401 @cindex hooks, pre-command
18404 You may define @dfn{hooks}, which are a special kind of user-defined
18405 command. Whenever you run the command @samp{foo}, if the user-defined
18406 command @samp{hook-foo} exists, it is executed (with no arguments)
18407 before that command.
18409 @cindex hooks, post-command
18411 A hook may also be defined which is run after the command you executed.
18412 Whenever you run the command @samp{foo}, if the user-defined command
18413 @samp{hookpost-foo} exists, it is executed (with no arguments) after
18414 that command. Post-execution hooks may exist simultaneously with
18415 pre-execution hooks, for the same command.
18417 It is valid for a hook to call the command which it hooks. If this
18418 occurs, the hook is not re-executed, thereby avoiding infinite recursion.
18420 @c It would be nice if hookpost could be passed a parameter indicating
18421 @c if the command it hooks executed properly or not. FIXME!
18423 @kindex stop@r{, a pseudo-command}
18424 In addition, a pseudo-command, @samp{stop} exists. Defining
18425 (@samp{hook-stop}) makes the associated commands execute every time
18426 execution stops in your program: before breakpoint commands are run,
18427 displays are printed, or the stack frame is printed.
18429 For example, to ignore @code{SIGALRM} signals while
18430 single-stepping, but treat them normally during normal execution,
18435 handle SIGALRM nopass
18439 handle SIGALRM pass
18442 define hook-continue
18443 handle SIGALRM pass
18447 As a further example, to hook at the beginning and end of the @code{echo}
18448 command, and to add extra text to the beginning and end of the message,
18456 define hookpost-echo
18460 (@value{GDBP}) echo Hello World
18461 <<<---Hello World--->>>
18466 You can define a hook for any single-word command in @value{GDBN}, but
18467 not for command aliases; you should define a hook for the basic command
18468 name, e.g.@: @code{backtrace} rather than @code{bt}.
18469 @c FIXME! So how does Joe User discover whether a command is an alias
18471 You can hook a multi-word command by adding @code{hook-} or
18472 @code{hookpost-} to the last word of the command, e.g.@:
18473 @samp{define target hook-remote} to add a hook to @samp{target remote}.
18475 If an error occurs during the execution of your hook, execution of
18476 @value{GDBN} commands stops and @value{GDBN} issues a prompt
18477 (before the command that you actually typed had a chance to run).
18479 If you try to define a hook which does not match any known command, you
18480 get a warning from the @code{define} command.
18482 @node Command Files
18483 @subsection Command Files
18485 @cindex command files
18486 @cindex scripting commands
18487 A command file for @value{GDBN} is a text file made of lines that are
18488 @value{GDBN} commands. Comments (lines starting with @kbd{#}) may
18489 also be included. An empty line in a command file does nothing; it
18490 does not mean to repeat the last command, as it would from the
18493 You can request the execution of a command file with the @code{source}
18498 @cindex execute commands from a file
18499 @item source [@code{-v}] @var{filename}
18500 Execute the command file @var{filename}.
18503 The lines in a command file are generally executed sequentially,
18504 unless the order of execution is changed by one of the
18505 @emph{flow-control commands} described below. The commands are not
18506 printed as they are executed. An error in any command terminates
18507 execution of the command file and control is returned to the console.
18509 @value{GDBN} searches for @var{filename} in the current directory and then
18510 on the search path (specified with the @samp{directory} command).
18512 If @code{-v}, for verbose mode, is given then @value{GDBN} displays
18513 each command as it is executed. The option must be given before
18514 @var{filename}, and is interpreted as part of the filename anywhere else.
18516 Commands that would ask for confirmation if used interactively proceed
18517 without asking when used in a command file. Many @value{GDBN} commands that
18518 normally print messages to say what they are doing omit the messages
18519 when called from command files.
18521 @value{GDBN} also accepts command input from standard input. In this
18522 mode, normal output goes to standard output and error output goes to
18523 standard error. Errors in a command file supplied on standard input do
18524 not terminate execution of the command file---execution continues with
18528 gdb < cmds > log 2>&1
18531 (The syntax above will vary depending on the shell used.) This example
18532 will execute commands from the file @file{cmds}. All output and errors
18533 would be directed to @file{log}.
18535 Since commands stored on command files tend to be more general than
18536 commands typed interactively, they frequently need to deal with
18537 complicated situations, such as different or unexpected values of
18538 variables and symbols, changes in how the program being debugged is
18539 built, etc. @value{GDBN} provides a set of flow-control commands to
18540 deal with these complexities. Using these commands, you can write
18541 complex scripts that loop over data structures, execute commands
18542 conditionally, etc.
18549 This command allows to include in your script conditionally executed
18550 commands. The @code{if} command takes a single argument, which is an
18551 expression to evaluate. It is followed by a series of commands that
18552 are executed only if the expression is true (its value is nonzero).
18553 There can then optionally be an @code{else} line, followed by a series
18554 of commands that are only executed if the expression was false. The
18555 end of the list is marked by a line containing @code{end}.
18559 This command allows to write loops. Its syntax is similar to
18560 @code{if}: the command takes a single argument, which is an expression
18561 to evaluate, and must be followed by the commands to execute, one per
18562 line, terminated by an @code{end}. These commands are called the
18563 @dfn{body} of the loop. The commands in the body of @code{while} are
18564 executed repeatedly as long as the expression evaluates to true.
18568 This command exits the @code{while} loop in whose body it is included.
18569 Execution of the script continues after that @code{while}s @code{end}
18572 @kindex loop_continue
18573 @item loop_continue
18574 This command skips the execution of the rest of the body of commands
18575 in the @code{while} loop in whose body it is included. Execution
18576 branches to the beginning of the @code{while} loop, where it evaluates
18577 the controlling expression.
18579 @kindex end@r{ (if/else/while commands)}
18581 Terminate the block of commands that are the body of @code{if},
18582 @code{else}, or @code{while} flow-control commands.
18587 @subsection Commands for Controlled Output
18589 During the execution of a command file or a user-defined command, normal
18590 @value{GDBN} output is suppressed; the only output that appears is what is
18591 explicitly printed by the commands in the definition. This section
18592 describes three commands useful for generating exactly the output you
18597 @item echo @var{text}
18598 @c I do not consider backslash-space a standard C escape sequence
18599 @c because it is not in ANSI.
18600 Print @var{text}. Nonprinting characters can be included in
18601 @var{text} using C escape sequences, such as @samp{\n} to print a
18602 newline. @strong{No newline is printed unless you specify one.}
18603 In addition to the standard C escape sequences, a backslash followed
18604 by a space stands for a space. This is useful for displaying a
18605 string with spaces at the beginning or the end, since leading and
18606 trailing spaces are otherwise trimmed from all arguments.
18607 To print @samp{@w{ }and foo =@w{ }}, use the command
18608 @samp{echo \@w{ }and foo = \@w{ }}.
18610 A backslash at the end of @var{text} can be used, as in C, to continue
18611 the command onto subsequent lines. For example,
18614 echo This is some text\n\
18615 which is continued\n\
18616 onto several lines.\n
18619 produces the same output as
18622 echo This is some text\n
18623 echo which is continued\n
18624 echo onto several lines.\n
18628 @item output @var{expression}
18629 Print the value of @var{expression} and nothing but that value: no
18630 newlines, no @samp{$@var{nn} = }. The value is not entered in the
18631 value history either. @xref{Expressions, ,Expressions}, for more information
18634 @item output/@var{fmt} @var{expression}
18635 Print the value of @var{expression} in format @var{fmt}. You can use
18636 the same formats as for @code{print}. @xref{Output Formats,,Output
18637 Formats}, for more information.
18640 @item printf @var{template}, @var{expressions}@dots{}
18641 Print the values of one or more @var{expressions} under the control of
18642 the string @var{template}. To print several values, make
18643 @var{expressions} be a comma-separated list of individual expressions,
18644 which may be either numbers or pointers. Their values are printed as
18645 specified by @var{template}, exactly as a C program would do by
18646 executing the code below:
18649 printf (@var{template}, @var{expressions}@dots{});
18652 As in @code{C} @code{printf}, ordinary characters in @var{template}
18653 are printed verbatim, while @dfn{conversion specification} introduced
18654 by the @samp{%} character cause subsequent @var{expressions} to be
18655 evaluated, their values converted and formatted according to type and
18656 style information encoded in the conversion specifications, and then
18659 For example, you can print two values in hex like this:
18662 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
18665 @code{printf} supports all the standard @code{C} conversion
18666 specifications, including the flags and modifiers between the @samp{%}
18667 character and the conversion letter, with the following exceptions:
18671 The argument-ordering modifiers, such as @samp{2$}, are not supported.
18674 The modifier @samp{*} is not supported for specifying precision or
18678 The @samp{'} flag (for separation of digits into groups according to
18679 @code{LC_NUMERIC'}) is not supported.
18682 The type modifiers @samp{hh}, @samp{j}, @samp{t}, and @samp{z} are not
18686 The conversion letter @samp{n} (as in @samp{%n}) is not supported.
18689 The conversion letters @samp{a} and @samp{A} are not supported.
18693 Note that the @samp{ll} type modifier is supported only if the
18694 underlying @code{C} implementation used to build @value{GDBN} supports
18695 the @code{long long int} type, and the @samp{L} type modifier is
18696 supported only if @code{long double} type is available.
18698 As in @code{C}, @code{printf} supports simple backslash-escape
18699 sequences, such as @code{\n}, @samp{\t}, @samp{\\}, @samp{\"},
18700 @samp{\a}, and @samp{\f}, that consist of backslash followed by a
18701 single character. Octal and hexadecimal escape sequences are not
18704 Additionally, @code{printf} supports conversion specifications for DFP
18705 (@dfn{Decimal Floating Point}) types using the following length modifiers
18706 together with a floating point specifier.
18711 @samp{H} for printing @code{Decimal32} types.
18714 @samp{D} for printing @code{Decimal64} types.
18717 @samp{DD} for printing @code{Decimal128} types.
18720 If the underlying @code{C} implementation used to build @value{GDBN} has
18721 support for the three length modifiers for DFP types, other modifiers
18722 such as width and precision will also be available for @value{GDBN} to use.
18724 In case there is no such @code{C} support, no additional modifiers will be
18725 available and the value will be printed in the standard way.
18727 Here's an example of printing DFP types using the above conversion letters:
18729 printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl
18735 @section Scripting @value{GDBN} using Python
18736 @cindex python scripting
18737 @cindex scripting with python
18739 You can script @value{GDBN} using the @uref{http://www.python.org/,
18740 Python programming language}. This feature is available only if
18741 @value{GDBN} was configured using @option{--with-python}.
18744 * Python Commands:: Accessing Python from @value{GDBN}.
18745 * Python API:: Accessing @value{GDBN} from Python.
18748 @node Python Commands
18749 @subsection Python Commands
18750 @cindex python commands
18751 @cindex commands to access python
18753 @value{GDBN} provides one command for accessing the Python interpreter,
18754 and one related setting:
18758 @item python @r{[}@var{code}@r{]}
18759 The @code{python} command can be used to evaluate Python code.
18761 If given an argument, the @code{python} command will evaluate the
18762 argument as a Python command. For example:
18765 (@value{GDBP}) python print 23
18769 If you do not provide an argument to @code{python}, it will act as a
18770 multi-line command, like @code{define}. In this case, the Python
18771 script is made up of subsequent command lines, given after the
18772 @code{python} command. This command list is terminated using a line
18773 containing @code{end}. For example:
18776 (@value{GDBP}) python
18778 End with a line saying just "end".
18784 @kindex maint set python print-stack
18785 @item maint set python print-stack
18786 By default, @value{GDBN} will print a stack trace when an error occurs
18787 in a Python script. This can be controlled using @code{maint set
18788 python print-stack}: if @code{on}, the default, then Python stack
18789 printing is enabled; if @code{off}, then Python stack printing is
18794 @subsection Python API
18796 @cindex programming in python
18798 @cindex python stdout
18799 @cindex python pagination
18800 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
18801 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
18802 A Python program which outputs to one of these streams may have its
18803 output interrupted by the user (@pxref{Screen Size}). In this
18804 situation, a Python @code{KeyboardInterrupt} exception is thrown.
18807 * Basic Python:: Basic Python Functions.
18808 * Exception Handling::
18809 * Auto-loading:: Automatically loading Python code.
18810 * Values From Inferior::
18811 * Types In Python:: Python representation of types.
18812 * Pretty Printing:: Pretty-printing values.
18813 * Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
18814 * Commands In Python:: Implementing new commands in Python.
18815 * Functions In Python:: Writing new convenience functions.
18816 * Objfiles In Python:: Object files.
18817 * Frames In Python:: Acessing inferior stack frames from Python.
18821 @subsubsection Basic Python
18823 @cindex python functions
18824 @cindex python module
18826 @value{GDBN} introduces a new Python module, named @code{gdb}. All
18827 methods and classes added by @value{GDBN} are placed in this module.
18828 @value{GDBN} automatically @code{import}s the @code{gdb} module for
18829 use in all scripts evaluated by the @code{python} command.
18831 @findex gdb.execute
18832 @defun execute command [from_tty]
18833 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
18834 If a GDB exception happens while @var{command} runs, it is
18835 translated as described in @ref{Exception Handling,,Exception Handling}.
18836 If no exceptions occur, this function returns @code{None}.
18838 @var{from_tty} specifies whether @value{GDBN} ought to consider this
18839 command as having originated from the user invoking it interactively.
18840 It must be a boolean value. If omitted, it defaults to @code{False}.
18843 @findex gdb.parameter
18844 @defun parameter parameter
18845 Return the value of a @value{GDBN} parameter. @var{parameter} is a
18846 string naming the parameter to look up; @var{parameter} may contain
18847 spaces if the parameter has a multi-part name. For example,
18848 @samp{print object} is a valid parameter name.
18850 If the named parameter does not exist, this function throws a
18851 @code{RuntimeError}. Otherwise, the parameter's value is converted to
18852 a Python value of the appropriate type, and returned.
18855 @findex gdb.history
18856 @defun history number
18857 Return a value from @value{GDBN}'s value history (@pxref{Value
18858 History}). @var{number} indicates which history element to return.
18859 If @var{number} is negative, then @value{GDBN} will take its absolute value
18860 and count backward from the last element (i.e., the most recent element) to
18861 find the value to return. If @var{number} is zero, then @value{GDBN} will
18862 return the most recent element. If the element specified by @var{number}
18863 doesn't exist in the value history, a @code{RuntimeError} exception will be
18866 If no exception is raised, the return value is always an instance of
18867 @code{gdb.Value} (@pxref{Values From Inferior}).
18871 @defun write string
18872 Print a string to @value{GDBN}'s paginated standard output stream.
18873 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
18874 call this function.
18879 Flush @value{GDBN}'s paginated standard output stream. Flushing
18880 @code{sys.stdout} or @code{sys.stderr} will automatically call this
18884 @node Exception Handling
18885 @subsubsection Exception Handling
18886 @cindex python exceptions
18887 @cindex exceptions, python
18889 When executing the @code{python} command, Python exceptions
18890 uncaught within the Python code are translated to calls to
18891 @value{GDBN} error-reporting mechanism. If the command that called
18892 @code{python} does not handle the error, @value{GDBN} will
18893 terminate it and print an error message containing the Python
18894 exception name, the associated value, and the Python call stack
18895 backtrace at the point where the exception was raised. Example:
18898 (@value{GDBP}) python print foo
18899 Traceback (most recent call last):
18900 File "<string>", line 1, in <module>
18901 NameError: name 'foo' is not defined
18904 @value{GDBN} errors that happen in @value{GDBN} commands invoked by Python
18905 code are converted to Python @code{RuntimeError} exceptions. User
18906 interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
18907 prompt) is translated to a Python @code{KeyboardInterrupt}
18908 exception. If you catch these exceptions in your Python code, your
18909 exception handler will see @code{RuntimeError} or
18910 @code{KeyboardInterrupt} as the exception type, the @value{GDBN} error
18911 message as its value, and the Python call stack backtrace at the
18912 Python statement closest to where the @value{GDBN} error occured as the
18916 @subsubsection Auto-loading
18917 @cindex auto-loading, Python
18919 When a new object file is read (for example, due to the @code{file}
18920 command, or because the inferior has loaded a shared library),
18921 @value{GDBN} will look for a file named @file{@var{objfile}-gdb.py},
18922 where @var{objfile} is the object file's real name, formed by ensuring
18923 that the file name is absolute, following all symlinks, and resolving
18924 @code{.} and @code{..} components. If this file exists and is
18925 readable, @value{GDBN} will evaluate it as a Python script.
18927 If this file does not exist, and if the parameter
18928 @code{debug-file-directory} is set (@pxref{Separate Debug Files}),
18929 then @value{GDBN} will use the file named
18930 @file{@var{debug-file-directory}/@var{real-name}}, where
18931 @var{real-name} is the object file's real name, as described above.
18933 Finally, if this file does not exist, then @value{GDBN} will look for
18934 a file named @file{@var{data-directory}/python/auto-load/@var{real-name}}, where
18935 @var{data-directory} is @value{GDBN}'s data directory (available via
18936 @code{show data-directory}, @pxref{Data Files}), and @var{real-name}
18937 is the object file's real name, as described above.
18939 When reading an auto-loaded file, @value{GDBN} sets the ``current
18940 objfile''. This is available via the @code{gdb.current_objfile}
18941 function (@pxref{Objfiles In Python}). This can be useful for
18942 registering objfile-specific pretty-printers.
18944 The auto-loading feature is useful for supplying application-specific
18945 debugging commands and scripts. You can enable or disable this
18946 feature, and view its current state.
18949 @kindex maint set python auto-load
18950 @item maint set python auto-load [yes|no]
18951 Enable or disable the Python auto-loading feature.
18953 @kindex show python auto-load
18954 @item show python auto-load
18955 Show whether Python auto-loading is enabled or disabled.
18958 @value{GDBN} does not track which files it has already auto-loaded.
18959 So, your @samp{-gdb.py} file should take care to ensure that it may be
18960 evaluated multiple times without error.
18962 @node Values From Inferior
18963 @subsubsection Values From Inferior
18964 @cindex values from inferior, with Python
18965 @cindex python, working with values from inferior
18967 @cindex @code{gdb.Value}
18968 @value{GDBN} provides values it obtains from the inferior program in
18969 an object of type @code{gdb.Value}. @value{GDBN} uses this object
18970 for its internal bookkeeping of the inferior's values, and for
18971 fetching values when necessary.
18973 Inferior values that are simple scalars can be used directly in
18974 Python expressions that are valid for the value's data type. Here's
18975 an example for an integer or floating-point value @code{some_val}:
18982 As result of this, @code{bar} will also be a @code{gdb.Value} object
18983 whose values are of the same type as those of @code{some_val}.
18985 Inferior values that are structures or instances of some class can
18986 be accessed using the Python @dfn{dictionary syntax}. For example, if
18987 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
18988 can access its @code{foo} element with:
18991 bar = some_val['foo']
18994 Again, @code{bar} will also be a @code{gdb.Value} object.
18996 The following attributes are provided:
18999 @defivar Value address
19000 If this object is addressable, this read-only attribute holds a
19001 @code{gdb.Value} object representing the address. Otherwise,
19002 this attribute holds @code{None}.
19005 @cindex optimized out value in Python
19006 @defivar Value is_optimized_out
19007 This read-only boolean attribute is true if the compiler optimized out
19008 this value, thus it is not available for fetching from the inferior.
19011 @defivar Value type
19012 The type of this @code{gdb.Value}. The value of this attribute is a
19013 @code{gdb.Type} object.
19017 The following methods are provided:
19020 @defmethod Value dereference
19021 For pointer data types, this method returns a new @code{gdb.Value} object
19022 whose contents is the object pointed to by the pointer. For example, if
19023 @code{foo} is a C pointer to an @code{int}, declared in your C program as
19030 then you can use the corresponding @code{gdb.Value} to access what
19031 @code{foo} points to like this:
19034 bar = foo.dereference ()
19037 The result @code{bar} will be a @code{gdb.Value} object holding the
19038 value pointed to by @code{foo}.
19041 @defmethod Value string @r{[}encoding@r{]} @r{[}errors@r{]} @r{[}length@r{]}
19042 If this @code{gdb.Value} represents a string, then this method
19043 converts the contents to a Python string. Otherwise, this method will
19044 throw an exception.
19046 Strings are recognized in a language-specific way; whether a given
19047 @code{gdb.Value} represents a string is determined by the current
19050 For C-like languages, a value is a string if it is a pointer to or an
19051 array of characters or ints. The string is assumed to be terminated
19052 by a zero of the appropriate width. However if the optional length
19053 argument is given, the string will be converted to that given length,
19054 ignoring any embedded zeros that the string may contain.
19056 If the optional @var{encoding} argument is given, it must be a string
19057 naming the encoding of the string in the @code{gdb.Value}, such as
19058 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
19059 the same encodings as the corresponding argument to Python's
19060 @code{string.decode} method, and the Python codec machinery will be used
19061 to convert the string. If @var{encoding} is not given, or if
19062 @var{encoding} is the empty string, then either the @code{target-charset}
19063 (@pxref{Character Sets}) will be used, or a language-specific encoding
19064 will be used, if the current language is able to supply one.
19066 The optional @var{errors} argument is the same as the corresponding
19067 argument to Python's @code{string.decode} method.
19069 If the optional @var{length} argument is given, the string will be
19070 fetched and converted to the given length.
19074 @node Types In Python
19075 @subsubsection Types In Python
19076 @cindex types in Python
19077 @cindex Python, working with types
19080 @value{GDBN} represents types from the inferior using the class
19083 The following type-related functions are available in the @code{gdb}
19086 @findex gdb.lookup_type
19087 @defun lookup_type name [block]
19088 This function looks up a type by name. @var{name} is the name of the
19089 type to look up. It must be a string.
19091 Ordinarily, this function will return an instance of @code{gdb.Type}.
19092 If the named type cannot be found, it will throw an exception.
19095 An instance of @code{Type} has the following attributes:
19099 The type code for this type. The type code will be one of the
19100 @code{TYPE_CODE_} constants defined below.
19103 @defivar Type sizeof
19104 The size of this type, in target @code{char} units. Usually, a
19105 target's @code{char} type will be an 8-bit byte. However, on some
19106 unusual platforms, this type may have a different size.
19110 The tag name for this type. The tag name is the name after
19111 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
19112 languages have this concept. If this type has no tag name, then
19113 @code{None} is returned.
19117 The following methods are provided:
19120 @defmethod Type fields
19121 For structure and union types, this method returns the fields. Range
19122 types have two fields, the minimum and maximum values. Enum types
19123 have one field per enum constant. Function and method types have one
19124 field per parameter. The base types of C@t{++} classes are also
19125 represented as fields. If the type has no fields, or does not fit
19126 into one of these categories, an empty sequence will be returned.
19128 Each field is an object, with some pre-defined attributes:
19131 This attribute is not available for @code{static} fields (as in
19132 C@t{++} or Java). For non-@code{static} fields, the value is the bit
19133 position of the field.
19136 The name of the field, or @code{None} for anonymous fields.
19139 This is @code{True} if the field is artificial, usually meaning that
19140 it was provided by the compiler and not the user. This attribute is
19141 always provided, and is @code{False} if the field is not artificial.
19144 If the field is packed, or is a bitfield, then this will have a
19145 non-zero value, which is the size of the field in bits. Otherwise,
19146 this will be zero; in this case the field's size is given by its type.
19149 The type of the field. This is usually an instance of @code{Type},
19150 but it can be @code{None} in some situations.
19154 @defmethod Type const
19155 Return a new @code{gdb.Type} object which represents a
19156 @code{const}-qualified variant of this type.
19159 @defmethod Type volatile
19160 Return a new @code{gdb.Type} object which represents a
19161 @code{volatile}-qualified variant of this type.
19164 @defmethod Type unqualified
19165 Return a new @code{gdb.Type} object which represents an unqualified
19166 variant of this type. That is, the result is neither @code{const} nor
19170 @defmethod Type reference
19171 Return a new @code{gdb.Type} object which represents a reference to this
19175 @defmethod Type strip_typedefs
19176 Return a new @code{gdb.Type} that represents the real type,
19177 after removing all layers of typedefs.
19180 @defmethod Type target
19181 Return a new @code{gdb.Type} object which represents the target type
19184 For a pointer type, the target type is the type of the pointed-to
19185 object. For an array type (meaning C-like arrays), the target type is
19186 the type of the elements of the array. For a function or method type,
19187 the target type is the type of the return value. For a complex type,
19188 the target type is the type of the elements. For a typedef, the
19189 target type is the aliased type.
19191 If the type does not have a target, this method will throw an
19195 @defmethod Type template_argument n
19196 If this @code{gdb.Type} is an instantiation of a template, this will
19197 return a new @code{gdb.Type} which represents the type of the
19198 @var{n}th template argument.
19200 If this @code{gdb.Type} is not a template type, this will throw an
19201 exception. Ordinarily, only C@t{++} code will have template types.
19203 @var{name} is searched for globally.
19208 Each type has a code, which indicates what category this type falls
19209 into. The available type categories are represented by constants
19210 defined in the @code{gdb} module:
19213 @findex TYPE_CODE_PTR
19214 @findex gdb.TYPE_CODE_PTR
19215 @item TYPE_CODE_PTR
19216 The type is a pointer.
19218 @findex TYPE_CODE_ARRAY
19219 @findex gdb.TYPE_CODE_ARRAY
19220 @item TYPE_CODE_ARRAY
19221 The type is an array.
19223 @findex TYPE_CODE_STRUCT
19224 @findex gdb.TYPE_CODE_STRUCT
19225 @item TYPE_CODE_STRUCT
19226 The type is a structure.
19228 @findex TYPE_CODE_UNION
19229 @findex gdb.TYPE_CODE_UNION
19230 @item TYPE_CODE_UNION
19231 The type is a union.
19233 @findex TYPE_CODE_ENUM
19234 @findex gdb.TYPE_CODE_ENUM
19235 @item TYPE_CODE_ENUM
19236 The type is an enum.
19238 @findex TYPE_CODE_FLAGS
19239 @findex gdb.TYPE_CODE_FLAGS
19240 @item TYPE_CODE_FLAGS
19241 A bit flags type, used for things such as status registers.
19243 @findex TYPE_CODE_FUNC
19244 @findex gdb.TYPE_CODE_FUNC
19245 @item TYPE_CODE_FUNC
19246 The type is a function.
19248 @findex TYPE_CODE_INT
19249 @findex gdb.TYPE_CODE_INT
19250 @item TYPE_CODE_INT
19251 The type is an integer type.
19253 @findex TYPE_CODE_FLT
19254 @findex gdb.TYPE_CODE_FLT
19255 @item TYPE_CODE_FLT
19256 A floating point type.
19258 @findex TYPE_CODE_VOID
19259 @findex gdb.TYPE_CODE_VOID
19260 @item TYPE_CODE_VOID
19261 The special type @code{void}.
19263 @findex TYPE_CODE_SET
19264 @findex gdb.TYPE_CODE_SET
19265 @item TYPE_CODE_SET
19268 @findex TYPE_CODE_RANGE
19269 @findex gdb.TYPE_CODE_RANGE
19270 @item TYPE_CODE_RANGE
19271 A range type, that is, an integer type with bounds.
19273 @findex TYPE_CODE_STRING
19274 @findex gdb.TYPE_CODE_STRING
19275 @item TYPE_CODE_STRING
19276 A string type. Note that this is only used for certain languages with
19277 language-defined string types; C strings are not represented this way.
19279 @findex TYPE_CODE_BITSTRING
19280 @findex gdb.TYPE_CODE_BITSTRING
19281 @item TYPE_CODE_BITSTRING
19284 @findex TYPE_CODE_ERROR
19285 @findex gdb.TYPE_CODE_ERROR
19286 @item TYPE_CODE_ERROR
19287 An unknown or erroneous type.
19289 @findex TYPE_CODE_METHOD
19290 @findex gdb.TYPE_CODE_METHOD
19291 @item TYPE_CODE_METHOD
19292 A method type, as found in C@t{++} or Java.
19294 @findex TYPE_CODE_METHODPTR
19295 @findex gdb.TYPE_CODE_METHODPTR
19296 @item TYPE_CODE_METHODPTR
19297 A pointer-to-member-function.
19299 @findex TYPE_CODE_MEMBERPTR
19300 @findex gdb.TYPE_CODE_MEMBERPTR
19301 @item TYPE_CODE_MEMBERPTR
19302 A pointer-to-member.
19304 @findex TYPE_CODE_REF
19305 @findex gdb.TYPE_CODE_REF
19306 @item TYPE_CODE_REF
19309 @findex TYPE_CODE_CHAR
19310 @findex gdb.TYPE_CODE_CHAR
19311 @item TYPE_CODE_CHAR
19314 @findex TYPE_CODE_BOOL
19315 @findex gdb.TYPE_CODE_BOOL
19316 @item TYPE_CODE_BOOL
19319 @findex TYPE_CODE_COMPLEX
19320 @findex gdb.TYPE_CODE_COMPLEX
19321 @item TYPE_CODE_COMPLEX
19322 A complex float type.
19324 @findex TYPE_CODE_TYPEDEF
19325 @findex gdb.TYPE_CODE_TYPEDEF
19326 @item TYPE_CODE_TYPEDEF
19327 A typedef to some other type.
19329 @findex TYPE_CODE_NAMESPACE
19330 @findex gdb.TYPE_CODE_NAMESPACE
19331 @item TYPE_CODE_NAMESPACE
19332 A C@t{++} namespace.
19334 @findex TYPE_CODE_DECFLOAT
19335 @findex gdb.TYPE_CODE_DECFLOAT
19336 @item TYPE_CODE_DECFLOAT
19337 A decimal floating point type.
19339 @findex TYPE_CODE_INTERNAL_FUNCTION
19340 @findex gdb.TYPE_CODE_INTERNAL_FUNCTION
19341 @item TYPE_CODE_INTERNAL_FUNCTION
19342 A function internal to @value{GDBN}. This is the type used to represent
19343 convenience functions.
19346 @node Pretty Printing
19347 @subsubsection Pretty Printing
19349 @value{GDBN} provides a mechanism to allow pretty-printing of values
19350 using Python code. The pretty-printer API allows application-specific
19351 code to greatly simplify the display of complex objects. This
19352 mechanism works for both MI and the CLI.
19354 For example, here is how a C@t{++} @code{std::string} looks without a
19358 (@value{GDBP}) print s
19360 static npos = 4294967295,
19362 <std::allocator<char>> = @{
19363 <__gnu_cxx::new_allocator<char>> = @{<No data fields>@}, <No data fields>@},
19364 members of std::basic_string<char, std::char_traits<char>, std::allocator<char> >::_Alloc_hider:
19365 _M_p = 0x804a014 "abcd"
19370 After a pretty-printer for @code{std::string} has been installed, only
19371 the contents are printed:
19374 (@value{GDBP}) print s
19378 A pretty-printer is just an object that holds a value and implements a
19379 specific interface, defined here.
19381 @defop Operation {pretty printer} children (self)
19382 @value{GDBN} will call this method on a pretty-printer to compute the
19383 children of the pretty-printer's value.
19385 This method must return an object conforming to the Python iterator
19386 protocol. Each item returned by the iterator must be a tuple holding
19387 two elements. The first element is the ``name'' of the child; the
19388 second element is the child's value. The value can be any Python
19389 object which is convertible to a @value{GDBN} value.
19391 This method is optional. If it does not exist, @value{GDBN} will act
19392 as though the value has no children.
19395 @defop Operation {pretty printer} display_hint (self)
19396 The CLI may call this method and use its result to change the
19397 formatting of a value. The result will also be supplied to an MI
19398 consumer as a @samp{displayhint} attribute of the variable being
19401 This method is optional. If it does exist, this method must return a
19404 Some display hints are predefined by @value{GDBN}:
19408 Indicate that the object being printed is ``array-like''. The CLI
19409 uses this to respect parameters such as @code{set print elements} and
19410 @code{set print array}.
19413 Indicate that the object being printed is ``map-like'', and that the
19414 children of this value can be assumed to alternate between keys and
19418 Indicate that the object being printed is ``string-like''. If the
19419 printer's @code{to_string} method returns a Python string of some
19420 kind, then @value{GDBN} will call its internal language-specific
19421 string-printing function to format the string. For the CLI this means
19422 adding quotation marks, possibly escaping some characters, respecting
19423 @code{set print elements}, and the like.
19427 @defop Operation {pretty printer} to_string (self)
19428 @value{GDBN} will call this method to display the string
19429 representation of the value passed to the object's constructor.
19431 When printing from the CLI, if the @code{to_string} method exists,
19432 then @value{GDBN} will prepend its result to the values returned by
19433 @code{children}. Exactly how this formatting is done is dependent on
19434 the display hint, and may change as more hints are added. Also,
19435 depending on the print settings (@pxref{Print Settings}), the CLI may
19436 print just the result of @code{to_string} in a stack trace, omitting
19437 the result of @code{children}.
19439 If this method returns a string, it is printed verbatim.
19441 Otherwise, if this method returns an instance of @code{gdb.Value},
19442 then @value{GDBN} prints this value. This may result in a call to
19443 another pretty-printer.
19445 If instead the method returns a Python value which is convertible to a
19446 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
19447 the resulting value. Again, this may result in a call to another
19448 pretty-printer. Python scalars (integers, floats, and booleans) and
19449 strings are convertible to @code{gdb.Value}; other types are not.
19451 If the result is not one of these types, an exception is raised.
19454 @node Selecting Pretty-Printers
19455 @subsubsection Selecting Pretty-Printers
19457 The Python list @code{gdb.pretty_printers} contains an array of
19458 functions that have been registered via addition as a pretty-printer.
19459 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
19462 A function on one of these lists is passed a single @code{gdb.Value}
19463 argument and should return a pretty-printer object conforming to the
19464 interface definition above (@pxref{Pretty Printing}). If a function
19465 cannot create a pretty-printer for the value, it should return
19468 @value{GDBN} first checks the @code{pretty_printers} attribute of each
19469 @code{gdb.Objfile} and iteratively calls each function in the list for
19470 that @code{gdb.Objfile} until it receives a pretty-printer object.
19471 After these lists have been exhausted, it tries the global
19472 @code{gdb.pretty-printers} list, again calling each function until an
19473 object is returned.
19475 The order in which the objfiles are searched is not specified. For a
19476 given list, functions are always invoked from the head of the list,
19477 and iterated over sequentially until the end of the list, or a printer
19478 object is returned.
19480 Here is an example showing how a @code{std::string} printer might be
19484 class StdStringPrinter:
19485 "Print a std::string"
19487 def __init__ (self, val):
19490 def to_string (self):
19491 return self.val['_M_dataplus']['_M_p']
19493 def display_hint (self):
19497 And here is an example showing how a lookup function for the printer
19498 example above might be written.
19501 def str_lookup_function (val):
19503 lookup_tag = val.type.tag
19504 regex = re.compile ("^std::basic_string<char,.*>$")
19505 if lookup_tag == None:
19507 if regex.match (lookup_tag):
19508 return StdStringPrinter (val)
19513 The example lookup function extracts the value's type, and attempts to
19514 match it to a type that it can pretty-print. If it is a type the
19515 printer can pretty-print, it will return a printer object. If not, it
19516 returns @code{None}.
19518 We recommend that you put your core pretty-printers into a Python
19519 package. If your pretty-printers are for use with a library, we
19520 further recommend embedding a version number into the package name.
19521 This practice will enable @value{GDBN} to load multiple versions of
19522 your pretty-printers at the same time, because they will have
19525 You should write auto-loaded code (@pxref{Auto-loading}) such that it
19526 can be evaluated multiple times without changing its meaning. An
19527 ideal auto-load file will consist solely of @code{import}s of your
19528 printer modules, followed by a call to a register pretty-printers with
19529 the current objfile.
19531 Taken as a whole, this approach will scale nicely to multiple
19532 inferiors, each potentially using a different library version.
19533 Embedding a version number in the Python package name will ensure that
19534 @value{GDBN} is able to load both sets of printers simultaneously.
19535 Then, because the search for pretty-printers is done by objfile, and
19536 because your auto-loaded code took care to register your library's
19537 printers with a specific objfile, @value{GDBN} will find the correct
19538 printers for the specific version of the library used by each
19541 To continue the @code{std::string} example (@pxref{Pretty Printing}),
19542 this code might appear in @code{gdb.libstdcxx.v6}:
19545 def register_printers (objfile):
19546 objfile.pretty_printers.add (str_lookup_function)
19550 And then the corresponding contents of the auto-load file would be:
19553 import gdb.libstdcxx.v6
19554 gdb.libstdcxx.v6.register_printers (gdb.current_objfile ())
19557 @node Commands In Python
19558 @subsubsection Commands In Python
19560 @cindex commands in python
19561 @cindex python commands
19562 You can implement new @value{GDBN} CLI commands in Python. A CLI
19563 command is implemented using an instance of the @code{gdb.Command}
19564 class, most commonly using a subclass.
19566 @defmethod Command __init__ name @var{command_class} @r{[}@var{completer_class}@r{]} @r{[}@var{prefix}@r{]}
19567 The object initializer for @code{Command} registers the new command
19568 with @value{GDBN}. This initializer is normally invoked from the
19569 subclass' own @code{__init__} method.
19571 @var{name} is the name of the command. If @var{name} consists of
19572 multiple words, then the initial words are looked for as prefix
19573 commands. In this case, if one of the prefix commands does not exist,
19574 an exception is raised.
19576 There is no support for multi-line commands.
19578 @var{command_class} should be one of the @samp{COMMAND_} constants
19579 defined below. This argument tells @value{GDBN} how to categorize the
19580 new command in the help system.
19582 @var{completer_class} is an optional argument. If given, it should be
19583 one of the @samp{COMPLETE_} constants defined below. This argument
19584 tells @value{GDBN} how to perform completion for this command. If not
19585 given, @value{GDBN} will attempt to complete using the object's
19586 @code{complete} method (see below); if no such method is found, an
19587 error will occur when completion is attempted.
19589 @var{prefix} is an optional argument. If @code{True}, then the new
19590 command is a prefix command; sub-commands of this command may be
19593 The help text for the new command is taken from the Python
19594 documentation string for the command's class, if there is one. If no
19595 documentation string is provided, the default value ``This command is
19596 not documented.'' is used.
19599 @cindex don't repeat Python command
19600 @defmethod Command dont_repeat
19601 By default, a @value{GDBN} command is repeated when the user enters a
19602 blank line at the command prompt. A command can suppress this
19603 behavior by invoking the @code{dont_repeat} method. This is similar
19604 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
19607 @defmethod Command invoke argument from_tty
19608 This method is called by @value{GDBN} when this command is invoked.
19610 @var{argument} is a string. It is the argument to the command, after
19611 leading and trailing whitespace has been stripped.
19613 @var{from_tty} is a boolean argument. When true, this means that the
19614 command was entered by the user at the terminal; when false it means
19615 that the command came from elsewhere.
19617 If this method throws an exception, it is turned into a @value{GDBN}
19618 @code{error} call. Otherwise, the return value is ignored.
19621 @cindex completion of Python commands
19622 @defmethod Command complete text word
19623 This method is called by @value{GDBN} when the user attempts
19624 completion on this command. All forms of completion are handled by
19625 this method, that is, the @key{TAB} and @key{M-?} key bindings
19626 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
19629 The arguments @var{text} and @var{word} are both strings. @var{text}
19630 holds the complete command line up to the cursor's location.
19631 @var{word} holds the last word of the command line; this is computed
19632 using a word-breaking heuristic.
19634 The @code{complete} method can return several values:
19637 If the return value is a sequence, the contents of the sequence are
19638 used as the completions. It is up to @code{complete} to ensure that the
19639 contents actually do complete the word. A zero-length sequence is
19640 allowed, it means that there were no completions available. Only
19641 string elements of the sequence are used; other elements in the
19642 sequence are ignored.
19645 If the return value is one of the @samp{COMPLETE_} constants defined
19646 below, then the corresponding @value{GDBN}-internal completion
19647 function is invoked, and its result is used.
19650 All other results are treated as though there were no available
19655 When a new command is registered, it must be declared as a member of
19656 some general class of commands. This is used to classify top-level
19657 commands in the on-line help system; note that prefix commands are not
19658 listed under their own category but rather that of their top-level
19659 command. The available classifications are represented by constants
19660 defined in the @code{gdb} module:
19663 @findex COMMAND_NONE
19664 @findex gdb.COMMAND_NONE
19666 The command does not belong to any particular class. A command in
19667 this category will not be displayed in any of the help categories.
19669 @findex COMMAND_RUNNING
19670 @findex gdb.COMMAND_RUNNING
19671 @item COMMAND_RUNNING
19672 The command is related to running the inferior. For example,
19673 @code{start}, @code{step}, and @code{continue} are in this category.
19674 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
19675 commands in this category.
19677 @findex COMMAND_DATA
19678 @findex gdb.COMMAND_DATA
19680 The command is related to data or variables. For example,
19681 @code{call}, @code{find}, and @code{print} are in this category. Type
19682 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
19685 @findex COMMAND_STACK
19686 @findex gdb.COMMAND_STACK
19687 @item COMMAND_STACK
19688 The command has to do with manipulation of the stack. For example,
19689 @code{backtrace}, @code{frame}, and @code{return} are in this
19690 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
19691 list of commands in this category.
19693 @findex COMMAND_FILES
19694 @findex gdb.COMMAND_FILES
19695 @item COMMAND_FILES
19696 This class is used for file-related commands. For example,
19697 @code{file}, @code{list} and @code{section} are in this category.
19698 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
19699 commands in this category.
19701 @findex COMMAND_SUPPORT
19702 @findex gdb.COMMAND_SUPPORT
19703 @item COMMAND_SUPPORT
19704 This should be used for ``support facilities'', generally meaning
19705 things that are useful to the user when interacting with @value{GDBN},
19706 but not related to the state of the inferior. For example,
19707 @code{help}, @code{make}, and @code{shell} are in this category. Type
19708 @kbd{help support} at the @value{GDBN} prompt to see a list of
19709 commands in this category.
19711 @findex COMMAND_STATUS
19712 @findex gdb.COMMAND_STATUS
19713 @item COMMAND_STATUS
19714 The command is an @samp{info}-related command, that is, related to the
19715 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
19716 and @code{show} are in this category. Type @kbd{help status} at the
19717 @value{GDBN} prompt to see a list of commands in this category.
19719 @findex COMMAND_BREAKPOINTS
19720 @findex gdb.COMMAND_BREAKPOINTS
19721 @item COMMAND_BREAKPOINTS
19722 The command has to do with breakpoints. For example, @code{break},
19723 @code{clear}, and @code{delete} are in this category. Type @kbd{help
19724 breakpoints} at the @value{GDBN} prompt to see a list of commands in
19727 @findex COMMAND_TRACEPOINTS
19728 @findex gdb.COMMAND_TRACEPOINTS
19729 @item COMMAND_TRACEPOINTS
19730 The command has to do with tracepoints. For example, @code{trace},
19731 @code{actions}, and @code{tfind} are in this category. Type
19732 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
19733 commands in this category.
19735 @findex COMMAND_OBSCURE
19736 @findex gdb.COMMAND_OBSCURE
19737 @item COMMAND_OBSCURE
19738 The command is only used in unusual circumstances, or is not of
19739 general interest to users. For example, @code{checkpoint},
19740 @code{fork}, and @code{stop} are in this category. Type @kbd{help
19741 obscure} at the @value{GDBN} prompt to see a list of commands in this
19744 @findex COMMAND_MAINTENANCE
19745 @findex gdb.COMMAND_MAINTENANCE
19746 @item COMMAND_MAINTENANCE
19747 The command is only useful to @value{GDBN} maintainers. The
19748 @code{maintenance} and @code{flushregs} commands are in this category.
19749 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
19750 commands in this category.
19753 A new command can use a predefined completion function, either by
19754 specifying it via an argument at initialization, or by returning it
19755 from the @code{complete} method. These predefined completion
19756 constants are all defined in the @code{gdb} module:
19759 @findex COMPLETE_NONE
19760 @findex gdb.COMPLETE_NONE
19761 @item COMPLETE_NONE
19762 This constant means that no completion should be done.
19764 @findex COMPLETE_FILENAME
19765 @findex gdb.COMPLETE_FILENAME
19766 @item COMPLETE_FILENAME
19767 This constant means that filename completion should be performed.
19769 @findex COMPLETE_LOCATION
19770 @findex gdb.COMPLETE_LOCATION
19771 @item COMPLETE_LOCATION
19772 This constant means that location completion should be done.
19773 @xref{Specify Location}.
19775 @findex COMPLETE_COMMAND
19776 @findex gdb.COMPLETE_COMMAND
19777 @item COMPLETE_COMMAND
19778 This constant means that completion should examine @value{GDBN}
19781 @findex COMPLETE_SYMBOL
19782 @findex gdb.COMPLETE_SYMBOL
19783 @item COMPLETE_SYMBOL
19784 This constant means that completion should be done using symbol names
19788 The following code snippet shows how a trivial CLI command can be
19789 implemented in Python:
19792 class HelloWorld (gdb.Command):
19793 """Greet the whole world."""
19795 def __init__ (self):
19796 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_OBSCURE)
19798 def invoke (self, arg, from_tty):
19799 print "Hello, World!"
19804 The last line instantiates the class, and is necessary to trigger the
19805 registration of the command with @value{GDBN}. Depending on how the
19806 Python code is read into @value{GDBN}, you may need to import the
19807 @code{gdb} module explicitly.
19809 @node Functions In Python
19810 @subsubsection Writing new convenience functions
19812 @cindex writing convenience functions
19813 @cindex convenience functions in python
19814 @cindex python convenience functions
19815 @tindex gdb.Function
19817 You can implement new convenience functions (@pxref{Convenience Vars})
19818 in Python. A convenience function is an instance of a subclass of the
19819 class @code{gdb.Function}.
19821 @defmethod Function __init__ name
19822 The initializer for @code{Function} registers the new function with
19823 @value{GDBN}. The argument @var{name} is the name of the function,
19824 a string. The function will be visible to the user as a convenience
19825 variable of type @code{internal function}, whose name is the same as
19826 the given @var{name}.
19828 The documentation for the new function is taken from the documentation
19829 string for the new class.
19832 @defmethod Function invoke @var{*args}
19833 When a convenience function is evaluated, its arguments are converted
19834 to instances of @code{gdb.Value}, and then the function's
19835 @code{invoke} method is called. Note that @value{GDBN} does not
19836 predetermine the arity of convenience functions. Instead, all
19837 available arguments are passed to @code{invoke}, following the
19838 standard Python calling convention. In particular, a convenience
19839 function can have default values for parameters without ill effect.
19841 The return value of this method is used as its value in the enclosing
19842 expression. If an ordinary Python value is returned, it is converted
19843 to a @code{gdb.Value} following the usual rules.
19846 The following code snippet shows how a trivial convenience function can
19847 be implemented in Python:
19850 class Greet (gdb.Function):
19851 """Return string to greet someone.
19852 Takes a name as argument."""
19854 def __init__ (self):
19855 super (Greet, self).__init__ ("greet")
19857 def invoke (self, name):
19858 return "Hello, %s!" % name.string ()
19863 The last line instantiates the class, and is necessary to trigger the
19864 registration of the function with @value{GDBN}. Depending on how the
19865 Python code is read into @value{GDBN}, you may need to import the
19866 @code{gdb} module explicitly.
19868 @node Objfiles In Python
19869 @subsubsection Objfiles In Python
19871 @cindex objfiles in python
19872 @tindex gdb.Objfile
19874 @value{GDBN} loads symbols for an inferior from various
19875 symbol-containing files (@pxref{Files}). These include the primary
19876 executable file, any shared libraries used by the inferior, and any
19877 separate debug info files (@pxref{Separate Debug Files}).
19878 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
19880 The following objfile-related functions are available in the
19883 @findex gdb.current_objfile
19884 @defun current_objfile
19885 When auto-loading a Python script (@pxref{Auto-loading}), @value{GDBN}
19886 sets the ``current objfile'' to the corresponding objfile. This
19887 function returns the current objfile. If there is no current objfile,
19888 this function returns @code{None}.
19891 @findex gdb.objfiles
19893 Return a sequence of all the objfiles current known to @value{GDBN}.
19894 @xref{Objfiles In Python}.
19897 Each objfile is represented by an instance of the @code{gdb.Objfile}
19900 @defivar Objfile filename
19901 The file name of the objfile as a string.
19904 @defivar Objfile pretty_printers
19905 The @code{pretty_printers} attribute is a list of functions. It is
19906 used to look up pretty-printers. A @code{Value} is passed to each
19907 function in order; if the function returns @code{None}, then the
19908 search continues. Otherwise, the return value should be an object
19909 which is used to format the value. @xref{Pretty Printing}, for more
19913 @node Frames In Python
19914 @subsubsection Acessing inferior stack frames from Python.
19916 @cindex frames in python
19917 When the debugged program stops, @value{GDBN} is able to analyze its call
19918 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
19919 represents a frame in the stack. A @code{gdb.Frame} object is only valid
19920 while its corresponding frame exists in the inferior's stack. If you try
19921 to use an invalid frame object, @value{GDBN} will throw a @code{RuntimeError}
19924 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
19928 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
19932 The following frame-related functions are available in the @code{gdb} module:
19934 @findex gdb.selected_frame
19935 @defun selected_frame
19936 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
19939 @defun frame_stop_reason_string reason
19940 Return a string explaining the reason why @value{GDBN} stopped unwinding
19941 frames, as expressed by the given @var{reason} code (an integer, see the
19942 @code{unwind_stop_reason} method further down in this section).
19945 A @code{gdb.Frame} object has the following methods:
19948 @defmethod Frame is_valid
19949 Returns true if the @code{gdb.Frame} object is valid, false if not.
19950 A frame object can become invalid if the frame it refers to doesn't
19951 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
19952 an exception if it is invalid at the time the method is called.
19955 @defmethod Frame name
19956 Returns the function name of the frame, or @code{None} if it can't be
19960 @defmethod Frame type
19961 Returns the type of the frame. The value can be one of
19962 @code{gdb.NORMAL_FRAME}, @code{gdb.DUMMY_FRAME}, @code{gdb.SIGTRAMP_FRAME}
19963 or @code{gdb.SENTINEL_FRAME}.
19966 @defmethod Frame unwind_stop_reason
19967 Return an integer representing the reason why it's not possible to find
19968 more frames toward the outermost frame. Use
19969 @code{gdb.frame_stop_reason_string} to convert the value returned by this
19970 function to a string.
19973 @defmethod Frame pc
19974 Returns the frame's resume address.
19977 @defmethod Frame older
19978 Return the frame that called this frame.
19981 @defmethod Frame newer
19982 Return the frame called by this frame.
19985 @defmethod Frame read_var variable
19986 Return the value of the given variable in this frame. @var{variable} must
19992 @chapter Command Interpreters
19993 @cindex command interpreters
19995 @value{GDBN} supports multiple command interpreters, and some command
19996 infrastructure to allow users or user interface writers to switch
19997 between interpreters or run commands in other interpreters.
19999 @value{GDBN} currently supports two command interpreters, the console
20000 interpreter (sometimes called the command-line interpreter or @sc{cli})
20001 and the machine interface interpreter (or @sc{gdb/mi}). This manual
20002 describes both of these interfaces in great detail.
20004 By default, @value{GDBN} will start with the console interpreter.
20005 However, the user may choose to start @value{GDBN} with another
20006 interpreter by specifying the @option{-i} or @option{--interpreter}
20007 startup options. Defined interpreters include:
20011 @cindex console interpreter
20012 The traditional console or command-line interpreter. This is the most often
20013 used interpreter with @value{GDBN}. With no interpreter specified at runtime,
20014 @value{GDBN} will use this interpreter.
20017 @cindex mi interpreter
20018 The newest @sc{gdb/mi} interface (currently @code{mi2}). Used primarily
20019 by programs wishing to use @value{GDBN} as a backend for a debugger GUI
20020 or an IDE. For more information, see @ref{GDB/MI, ,The @sc{gdb/mi}
20024 @cindex mi2 interpreter
20025 The current @sc{gdb/mi} interface.
20028 @cindex mi1 interpreter
20029 The @sc{gdb/mi} interface included in @value{GDBN} 5.1, 5.2, and 5.3.
20033 @cindex invoke another interpreter
20034 The interpreter being used by @value{GDBN} may not be dynamically
20035 switched at runtime. Although possible, this could lead to a very
20036 precarious situation. Consider an IDE using @sc{gdb/mi}. If a user
20037 enters the command "interpreter-set console" in a console view,
20038 @value{GDBN} would switch to using the console interpreter, rendering
20039 the IDE inoperable!
20041 @kindex interpreter-exec
20042 Although you may only choose a single interpreter at startup, you may execute
20043 commands in any interpreter from the current interpreter using the appropriate
20044 command. If you are running the console interpreter, simply use the
20045 @code{interpreter-exec} command:
20048 interpreter-exec mi "-data-list-register-names"
20051 @sc{gdb/mi} has a similar command, although it is only available in versions of
20052 @value{GDBN} which support @sc{gdb/mi} version 2 (or greater).
20055 @chapter @value{GDBN} Text User Interface
20057 @cindex Text User Interface
20060 * TUI Overview:: TUI overview
20061 * TUI Keys:: TUI key bindings
20062 * TUI Single Key Mode:: TUI single key mode
20063 * TUI Commands:: TUI-specific commands
20064 * TUI Configuration:: TUI configuration variables
20067 The @value{GDBN} Text User Interface (TUI) is a terminal
20068 interface which uses the @code{curses} library to show the source
20069 file, the assembly output, the program registers and @value{GDBN}
20070 commands in separate text windows. The TUI mode is supported only
20071 on platforms where a suitable version of the @code{curses} library
20074 @pindex @value{GDBTUI}
20075 The TUI mode is enabled by default when you invoke @value{GDBN} as
20076 either @samp{@value{GDBTUI}} or @samp{@value{GDBP} -tui}.
20077 You can also switch in and out of TUI mode while @value{GDBN} runs by
20078 using various TUI commands and key bindings, such as @kbd{C-x C-a}.
20079 @xref{TUI Keys, ,TUI Key Bindings}.
20082 @section TUI Overview
20084 In TUI mode, @value{GDBN} can display several text windows:
20088 This window is the @value{GDBN} command window with the @value{GDBN}
20089 prompt and the @value{GDBN} output. The @value{GDBN} input is still
20090 managed using readline.
20093 The source window shows the source file of the program. The current
20094 line and active breakpoints are displayed in this window.
20097 The assembly window shows the disassembly output of the program.
20100 This window shows the processor registers. Registers are highlighted
20101 when their values change.
20104 The source and assembly windows show the current program position
20105 by highlighting the current line and marking it with a @samp{>} marker.
20106 Breakpoints are indicated with two markers. The first marker
20107 indicates the breakpoint type:
20111 Breakpoint which was hit at least once.
20114 Breakpoint which was never hit.
20117 Hardware breakpoint which was hit at least once.
20120 Hardware breakpoint which was never hit.
20123 The second marker indicates whether the breakpoint is enabled or not:
20127 Breakpoint is enabled.
20130 Breakpoint is disabled.
20133 The source, assembly and register windows are updated when the current
20134 thread changes, when the frame changes, or when the program counter
20137 These windows are not all visible at the same time. The command
20138 window is always visible. The others can be arranged in several
20149 source and assembly,
20152 source and registers, or
20155 assembly and registers.
20158 A status line above the command window shows the following information:
20162 Indicates the current @value{GDBN} target.
20163 (@pxref{Targets, ,Specifying a Debugging Target}).
20166 Gives the current process or thread number.
20167 When no process is being debugged, this field is set to @code{No process}.
20170 Gives the current function name for the selected frame.
20171 The name is demangled if demangling is turned on (@pxref{Print Settings}).
20172 When there is no symbol corresponding to the current program counter,
20173 the string @code{??} is displayed.
20176 Indicates the current line number for the selected frame.
20177 When the current line number is not known, the string @code{??} is displayed.
20180 Indicates the current program counter address.
20184 @section TUI Key Bindings
20185 @cindex TUI key bindings
20187 The TUI installs several key bindings in the readline keymaps
20188 (@pxref{Command Line Editing}). The following key bindings
20189 are installed for both TUI mode and the @value{GDBN} standard mode.
20198 Enter or leave the TUI mode. When leaving the TUI mode,
20199 the curses window management stops and @value{GDBN} operates using
20200 its standard mode, writing on the terminal directly. When reentering
20201 the TUI mode, control is given back to the curses windows.
20202 The screen is then refreshed.
20206 Use a TUI layout with only one window. The layout will
20207 either be @samp{source} or @samp{assembly}. When the TUI mode
20208 is not active, it will switch to the TUI mode.
20210 Think of this key binding as the Emacs @kbd{C-x 1} binding.
20214 Use a TUI layout with at least two windows. When the current
20215 layout already has two windows, the next layout with two windows is used.
20216 When a new layout is chosen, one window will always be common to the
20217 previous layout and the new one.
20219 Think of it as the Emacs @kbd{C-x 2} binding.
20223 Change the active window. The TUI associates several key bindings
20224 (like scrolling and arrow keys) with the active window. This command
20225 gives the focus to the next TUI window.
20227 Think of it as the Emacs @kbd{C-x o} binding.
20231 Switch in and out of the TUI SingleKey mode that binds single
20232 keys to @value{GDBN} commands (@pxref{TUI Single Key Mode}).
20235 The following key bindings only work in the TUI mode:
20240 Scroll the active window one page up.
20244 Scroll the active window one page down.
20248 Scroll the active window one line up.
20252 Scroll the active window one line down.
20256 Scroll the active window one column left.
20260 Scroll the active window one column right.
20264 Refresh the screen.
20267 Because the arrow keys scroll the active window in the TUI mode, they
20268 are not available for their normal use by readline unless the command
20269 window has the focus. When another window is active, you must use
20270 other readline key bindings such as @kbd{C-p}, @kbd{C-n}, @kbd{C-b}
20271 and @kbd{C-f} to control the command window.
20273 @node TUI Single Key Mode
20274 @section TUI Single Key Mode
20275 @cindex TUI single key mode
20277 The TUI also provides a @dfn{SingleKey} mode, which binds several
20278 frequently used @value{GDBN} commands to single keys. Type @kbd{C-x s} to
20279 switch into this mode, where the following key bindings are used:
20282 @kindex c @r{(SingleKey TUI key)}
20286 @kindex d @r{(SingleKey TUI key)}
20290 @kindex f @r{(SingleKey TUI key)}
20294 @kindex n @r{(SingleKey TUI key)}
20298 @kindex q @r{(SingleKey TUI key)}
20300 exit the SingleKey mode.
20302 @kindex r @r{(SingleKey TUI key)}
20306 @kindex s @r{(SingleKey TUI key)}
20310 @kindex u @r{(SingleKey TUI key)}
20314 @kindex v @r{(SingleKey TUI key)}
20318 @kindex w @r{(SingleKey TUI key)}
20323 Other keys temporarily switch to the @value{GDBN} command prompt.
20324 The key that was pressed is inserted in the editing buffer so that
20325 it is possible to type most @value{GDBN} commands without interaction
20326 with the TUI SingleKey mode. Once the command is entered the TUI
20327 SingleKey mode is restored. The only way to permanently leave
20328 this mode is by typing @kbd{q} or @kbd{C-x s}.
20332 @section TUI-specific Commands
20333 @cindex TUI commands
20335 The TUI has specific commands to control the text windows.
20336 These commands are always available, even when @value{GDBN} is not in
20337 the TUI mode. When @value{GDBN} is in the standard mode, most
20338 of these commands will automatically switch to the TUI mode.
20343 List and give the size of all displayed windows.
20347 Display the next layout.
20350 Display the previous layout.
20353 Display the source window only.
20356 Display the assembly window only.
20359 Display the source and assembly window.
20362 Display the register window together with the source or assembly window.
20366 Make the next window active for scrolling.
20369 Make the previous window active for scrolling.
20372 Make the source window active for scrolling.
20375 Make the assembly window active for scrolling.
20378 Make the register window active for scrolling.
20381 Make the command window active for scrolling.
20385 Refresh the screen. This is similar to typing @kbd{C-L}.
20387 @item tui reg float
20389 Show the floating point registers in the register window.
20391 @item tui reg general
20392 Show the general registers in the register window.
20395 Show the next register group. The list of register groups as well as
20396 their order is target specific. The predefined register groups are the
20397 following: @code{general}, @code{float}, @code{system}, @code{vector},
20398 @code{all}, @code{save}, @code{restore}.
20400 @item tui reg system
20401 Show the system registers in the register window.
20405 Update the source window and the current execution point.
20407 @item winheight @var{name} +@var{count}
20408 @itemx winheight @var{name} -@var{count}
20410 Change the height of the window @var{name} by @var{count}
20411 lines. Positive counts increase the height, while negative counts
20414 @item tabset @var{nchars}
20416 Set the width of tab stops to be @var{nchars} characters.
20419 @node TUI Configuration
20420 @section TUI Configuration Variables
20421 @cindex TUI configuration variables
20423 Several configuration variables control the appearance of TUI windows.
20426 @item set tui border-kind @var{kind}
20427 @kindex set tui border-kind
20428 Select the border appearance for the source, assembly and register windows.
20429 The possible values are the following:
20432 Use a space character to draw the border.
20435 Use @sc{ascii} characters @samp{+}, @samp{-} and @samp{|} to draw the border.
20438 Use the Alternate Character Set to draw the border. The border is
20439 drawn using character line graphics if the terminal supports them.
20442 @item set tui border-mode @var{mode}
20443 @kindex set tui border-mode
20444 @itemx set tui active-border-mode @var{mode}
20445 @kindex set tui active-border-mode
20446 Select the display attributes for the borders of the inactive windows
20447 or the active window. The @var{mode} can be one of the following:
20450 Use normal attributes to display the border.
20456 Use reverse video mode.
20459 Use half bright mode.
20461 @item half-standout
20462 Use half bright and standout mode.
20465 Use extra bright or bold mode.
20467 @item bold-standout
20468 Use extra bright or bold and standout mode.
20473 @chapter Using @value{GDBN} under @sc{gnu} Emacs
20476 @cindex @sc{gnu} Emacs
20477 A special interface allows you to use @sc{gnu} Emacs to view (and
20478 edit) the source files for the program you are debugging with
20481 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
20482 executable file you want to debug as an argument. This command starts
20483 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
20484 created Emacs buffer.
20485 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
20487 Running @value{GDBN} under Emacs can be just like running @value{GDBN} normally except for two
20492 All ``terminal'' input and output goes through an Emacs buffer, called
20495 This applies both to @value{GDBN} commands and their output, and to the input
20496 and output done by the program you are debugging.
20498 This is useful because it means that you can copy the text of previous
20499 commands and input them again; you can even use parts of the output
20502 All the facilities of Emacs' Shell mode are available for interacting
20503 with your program. In particular, you can send signals the usual
20504 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
20508 @value{GDBN} displays source code through Emacs.
20510 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
20511 source file for that frame and puts an arrow (@samp{=>}) at the
20512 left margin of the current line. Emacs uses a separate buffer for
20513 source display, and splits the screen to show both your @value{GDBN} session
20516 Explicit @value{GDBN} @code{list} or search commands still produce output as
20517 usual, but you probably have no reason to use them from Emacs.
20520 We call this @dfn{text command mode}. Emacs 22.1, and later, also uses
20521 a graphical mode, enabled by default, which provides further buffers
20522 that can control the execution and describe the state of your program.
20523 @xref{GDB Graphical Interface,,, Emacs, The @sc{gnu} Emacs Manual}.
20525 If you specify an absolute file name when prompted for the @kbd{M-x
20526 gdb} argument, then Emacs sets your current working directory to where
20527 your program resides. If you only specify the file name, then Emacs
20528 sets your current working directory to to the directory associated
20529 with the previous buffer. In this case, @value{GDBN} may find your
20530 program by searching your environment's @code{PATH} variable, but on
20531 some operating systems it might not find the source. So, although the
20532 @value{GDBN} input and output session proceeds normally, the auxiliary
20533 buffer does not display the current source and line of execution.
20535 The initial working directory of @value{GDBN} is printed on the top
20536 line of the GUD buffer and this serves as a default for the commands
20537 that specify files for @value{GDBN} to operate on. @xref{Files,
20538 ,Commands to Specify Files}.
20540 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If you
20541 need to call @value{GDBN} by a different name (for example, if you
20542 keep several configurations around, with different names) you can
20543 customize the Emacs variable @code{gud-gdb-command-name} to run the
20546 In the GUD buffer, you can use these special Emacs commands in
20547 addition to the standard Shell mode commands:
20551 Describe the features of Emacs' GUD Mode.
20554 Execute to another source line, like the @value{GDBN} @code{step} command; also
20555 update the display window to show the current file and location.
20558 Execute to next source line in this function, skipping all function
20559 calls, like the @value{GDBN} @code{next} command. Then update the display window
20560 to show the current file and location.
20563 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
20564 display window accordingly.
20567 Execute until exit from the selected stack frame, like the @value{GDBN}
20568 @code{finish} command.
20571 Continue execution of your program, like the @value{GDBN} @code{continue}
20575 Go up the number of frames indicated by the numeric argument
20576 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
20577 like the @value{GDBN} @code{up} command.
20580 Go down the number of frames indicated by the numeric argument, like the
20581 @value{GDBN} @code{down} command.
20584 In any source file, the Emacs command @kbd{C-x @key{SPC}} (@code{gud-break})
20585 tells @value{GDBN} to set a breakpoint on the source line point is on.
20587 In text command mode, if you type @kbd{M-x speedbar}, Emacs displays a
20588 separate frame which shows a backtrace when the GUD buffer is current.
20589 Move point to any frame in the stack and type @key{RET} to make it
20590 become the current frame and display the associated source in the
20591 source buffer. Alternatively, click @kbd{Mouse-2} to make the
20592 selected frame become the current one. In graphical mode, the
20593 speedbar displays watch expressions.
20595 If you accidentally delete the source-display buffer, an easy way to get
20596 it back is to type the command @code{f} in the @value{GDBN} buffer, to
20597 request a frame display; when you run under Emacs, this recreates
20598 the source buffer if necessary to show you the context of the current
20601 The source files displayed in Emacs are in ordinary Emacs buffers
20602 which are visiting the source files in the usual way. You can edit
20603 the files with these buffers if you wish; but keep in mind that @value{GDBN}
20604 communicates with Emacs in terms of line numbers. If you add or
20605 delete lines from the text, the line numbers that @value{GDBN} knows cease
20606 to correspond properly with the code.
20608 A more detailed description of Emacs' interaction with @value{GDBN} is
20609 given in the Emacs manual (@pxref{Debuggers,,, Emacs, The @sc{gnu}
20612 @c The following dropped because Epoch is nonstandard. Reactivate
20613 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
20615 @kindex Emacs Epoch environment
20619 Version 18 of @sc{gnu} Emacs has a built-in window system
20620 called the @code{epoch}
20621 environment. Users of this environment can use a new command,
20622 @code{inspect} which performs identically to @code{print} except that
20623 each value is printed in its own window.
20628 @chapter The @sc{gdb/mi} Interface
20630 @unnumberedsec Function and Purpose
20632 @cindex @sc{gdb/mi}, its purpose
20633 @sc{gdb/mi} is a line based machine oriented text interface to
20634 @value{GDBN} and is activated by specifying using the
20635 @option{--interpreter} command line option (@pxref{Mode Options}). It
20636 is specifically intended to support the development of systems which
20637 use the debugger as just one small component of a larger system.
20639 This chapter is a specification of the @sc{gdb/mi} interface. It is written
20640 in the form of a reference manual.
20642 Note that @sc{gdb/mi} is still under construction, so some of the
20643 features described below are incomplete and subject to change
20644 (@pxref{GDB/MI Development and Front Ends, , @sc{gdb/mi} Development and Front Ends}).
20646 @unnumberedsec Notation and Terminology
20648 @cindex notational conventions, for @sc{gdb/mi}
20649 This chapter uses the following notation:
20653 @code{|} separates two alternatives.
20656 @code{[ @var{something} ]} indicates that @var{something} is optional:
20657 it may or may not be given.
20660 @code{( @var{group} )*} means that @var{group} inside the parentheses
20661 may repeat zero or more times.
20664 @code{( @var{group} )+} means that @var{group} inside the parentheses
20665 may repeat one or more times.
20668 @code{"@var{string}"} means a literal @var{string}.
20672 @heading Dependencies
20676 * GDB/MI General Design::
20677 * GDB/MI Command Syntax::
20678 * GDB/MI Compatibility with CLI::
20679 * GDB/MI Development and Front Ends::
20680 * GDB/MI Output Records::
20681 * GDB/MI Simple Examples::
20682 * GDB/MI Command Description Format::
20683 * GDB/MI Breakpoint Commands::
20684 * GDB/MI Program Context::
20685 * GDB/MI Thread Commands::
20686 * GDB/MI Program Execution::
20687 * GDB/MI Stack Manipulation::
20688 * GDB/MI Variable Objects::
20689 * GDB/MI Data Manipulation::
20690 * GDB/MI Tracepoint Commands::
20691 * GDB/MI Symbol Query::
20692 * GDB/MI File Commands::
20694 * GDB/MI Kod Commands::
20695 * GDB/MI Memory Overlay Commands::
20696 * GDB/MI Signal Handling Commands::
20698 * GDB/MI Target Manipulation::
20699 * GDB/MI File Transfer Commands::
20700 * GDB/MI Miscellaneous Commands::
20703 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
20704 @node GDB/MI General Design
20705 @section @sc{gdb/mi} General Design
20706 @cindex GDB/MI General Design
20708 Interaction of a @sc{GDB/MI} frontend with @value{GDBN} involves three
20709 parts---commands sent to @value{GDBN}, responses to those commands
20710 and notifications. Each command results in exactly one response,
20711 indicating either successful completion of the command, or an error.
20712 For the commands that do not resume the target, the response contains the
20713 requested information. For the commands that resume the target, the
20714 response only indicates whether the target was successfully resumed.
20715 Notifications is the mechanism for reporting changes in the state of the
20716 target, or in @value{GDBN} state, that cannot conveniently be associated with
20717 a command and reported as part of that command response.
20719 The important examples of notifications are:
20723 Exec notifications. These are used to report changes in
20724 target state---when a target is resumed, or stopped. It would not
20725 be feasible to include this information in response of resuming
20726 commands, because one resume commands can result in multiple events in
20727 different threads. Also, quite some time may pass before any event
20728 happens in the target, while a frontend needs to know whether the resuming
20729 command itself was successfully executed.
20732 Console output, and status notifications. Console output
20733 notifications are used to report output of CLI commands, as well as
20734 diagnostics for other commands. Status notifications are used to
20735 report the progress of a long-running operation. Naturally, including
20736 this information in command response would mean no output is produced
20737 until the command is finished, which is undesirable.
20740 General notifications. Commands may have various side effects on
20741 the @value{GDBN} or target state beyond their official purpose. For example,
20742 a command may change the selected thread. Although such changes can
20743 be included in command response, using notification allows for more
20744 orthogonal frontend design.
20748 There's no guarantee that whenever an MI command reports an error,
20749 @value{GDBN} or the target are in any specific state, and especially,
20750 the state is not reverted to the state before the MI command was
20751 processed. Therefore, whenever an MI command results in an error,
20752 we recommend that the frontend refreshes all the information shown in
20753 the user interface.
20757 * Context management::
20758 * Asynchronous and non-stop modes::
20762 @node Context management
20763 @subsection Context management
20765 In most cases when @value{GDBN} accesses the target, this access is
20766 done in context of a specific thread and frame (@pxref{Frames}).
20767 Often, even when accessing global data, the target requires that a thread
20768 be specified. The CLI interface maintains the selected thread and frame,
20769 and supplies them to target on each command. This is convenient,
20770 because a command line user would not want to specify that information
20771 explicitly on each command, and because user interacts with
20772 @value{GDBN} via a single terminal, so no confusion is possible as
20773 to what thread and frame are the current ones.
20775 In the case of MI, the concept of selected thread and frame is less
20776 useful. First, a frontend can easily remember this information
20777 itself. Second, a graphical frontend can have more than one window,
20778 each one used for debugging a different thread, and the frontend might
20779 want to access additional threads for internal purposes. This
20780 increases the risk that by relying on implicitly selected thread, the
20781 frontend may be operating on a wrong one. Therefore, each MI command
20782 should explicitly specify which thread and frame to operate on. To
20783 make it possible, each MI command accepts the @samp{--thread} and
20784 @samp{--frame} options, the value to each is @value{GDBN} identifier
20785 for thread and frame to operate on.
20787 Usually, each top-level window in a frontend allows the user to select
20788 a thread and a frame, and remembers the user selection for further
20789 operations. However, in some cases @value{GDBN} may suggest that the
20790 current thread be changed. For example, when stopping on a breakpoint
20791 it is reasonable to switch to the thread where breakpoint is hit. For
20792 another example, if the user issues the CLI @samp{thread} command via
20793 the frontend, it is desirable to change the frontend's selected thread to the
20794 one specified by user. @value{GDBN} communicates the suggestion to
20795 change current thread using the @samp{=thread-selected} notification.
20796 No such notification is available for the selected frame at the moment.
20798 Note that historically, MI shares the selected thread with CLI, so
20799 frontends used the @code{-thread-select} to execute commands in the
20800 right context. However, getting this to work right is cumbersome. The
20801 simplest way is for frontend to emit @code{-thread-select} command
20802 before every command. This doubles the number of commands that need
20803 to be sent. The alternative approach is to suppress @code{-thread-select}
20804 if the selected thread in @value{GDBN} is supposed to be identical to the
20805 thread the frontend wants to operate on. However, getting this
20806 optimization right can be tricky. In particular, if the frontend
20807 sends several commands to @value{GDBN}, and one of the commands changes the
20808 selected thread, then the behaviour of subsequent commands will
20809 change. So, a frontend should either wait for response from such
20810 problematic commands, or explicitly add @code{-thread-select} for
20811 all subsequent commands. No frontend is known to do this exactly
20812 right, so it is suggested to just always pass the @samp{--thread} and
20813 @samp{--frame} options.
20815 @node Asynchronous and non-stop modes
20816 @subsection Asynchronous command execution and non-stop mode
20818 On some targets, @value{GDBN} is capable of processing MI commands
20819 even while the target is running. This is called @dfn{asynchronous
20820 command execution} (@pxref{Background Execution}). The frontend may
20821 specify a preferrence for asynchronous execution using the
20822 @code{-gdb-set target-async 1} command, which should be emitted before
20823 either running the executable or attaching to the target. After the
20824 frontend has started the executable or attached to the target, it can
20825 find if asynchronous execution is enabled using the
20826 @code{-list-target-features} command.
20828 Even if @value{GDBN} can accept a command while target is running,
20829 many commands that access the target do not work when the target is
20830 running. Therefore, asynchronous command execution is most useful
20831 when combined with non-stop mode (@pxref{Non-Stop Mode}). Then,
20832 it is possible to examine the state of one thread, while other threads
20835 When a given thread is running, MI commands that try to access the
20836 target in the context of that thread may not work, or may work only on
20837 some targets. In particular, commands that try to operate on thread's
20838 stack will not work, on any target. Commands that read memory, or
20839 modify breakpoints, may work or not work, depending on the target. Note
20840 that even commands that operate on global state, such as @code{print},
20841 @code{set}, and breakpoint commands, still access the target in the
20842 context of a specific thread, so frontend should try to find a
20843 stopped thread and perform the operation on that thread (using the
20844 @samp{--thread} option).
20846 Which commands will work in the context of a running thread is
20847 highly target dependent. However, the two commands
20848 @code{-exec-interrupt}, to stop a thread, and @code{-thread-info},
20849 to find the state of a thread, will always work.
20851 @node Thread groups
20852 @subsection Thread groups
20853 @value{GDBN} may be used to debug several processes at the same time.
20854 On some platfroms, @value{GDBN} may support debugging of several
20855 hardware systems, each one having several cores with several different
20856 processes running on each core. This section describes the MI
20857 mechanism to support such debugging scenarios.
20859 The key observation is that regardless of the structure of the
20860 target, MI can have a global list of threads, because most commands that
20861 accept the @samp{--thread} option do not need to know what process that
20862 thread belongs to. Therefore, it is not necessary to introduce
20863 neither additional @samp{--process} option, nor an notion of the
20864 current process in the MI interface. The only strictly new feature
20865 that is required is the ability to find how the threads are grouped
20868 To allow the user to discover such grouping, and to support arbitrary
20869 hierarchy of machines/cores/processes, MI introduces the concept of a
20870 @dfn{thread group}. Thread group is a collection of threads and other
20871 thread groups. A thread group always has a string identifier, a type,
20872 and may have additional attributes specific to the type. A new
20873 command, @code{-list-thread-groups}, returns the list of top-level
20874 thread groups, which correspond to processes that @value{GDBN} is
20875 debugging at the moment. By passing an identifier of a thread group
20876 to the @code{-list-thread-groups} command, it is possible to obtain
20877 the members of specific thread group.
20879 To allow the user to easily discover processes, and other objects, he
20880 wishes to debug, a concept of @dfn{available thread group} is
20881 introduced. Available thread group is an thread group that
20882 @value{GDBN} is not debugging, but that can be attached to, using the
20883 @code{-target-attach} command. The list of available top-level thread
20884 groups can be obtained using @samp{-list-thread-groups --available}.
20885 In general, the content of a thread group may be only retrieved only
20886 after attaching to that thread group.
20888 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
20889 @node GDB/MI Command Syntax
20890 @section @sc{gdb/mi} Command Syntax
20893 * GDB/MI Input Syntax::
20894 * GDB/MI Output Syntax::
20897 @node GDB/MI Input Syntax
20898 @subsection @sc{gdb/mi} Input Syntax
20900 @cindex input syntax for @sc{gdb/mi}
20901 @cindex @sc{gdb/mi}, input syntax
20903 @item @var{command} @expansion{}
20904 @code{@var{cli-command} | @var{mi-command}}
20906 @item @var{cli-command} @expansion{}
20907 @code{[ @var{token} ] @var{cli-command} @var{nl}}, where
20908 @var{cli-command} is any existing @value{GDBN} CLI command.
20910 @item @var{mi-command} @expansion{}
20911 @code{[ @var{token} ] "-" @var{operation} ( " " @var{option} )*
20912 @code{[} " --" @code{]} ( " " @var{parameter} )* @var{nl}}
20914 @item @var{token} @expansion{}
20915 "any sequence of digits"
20917 @item @var{option} @expansion{}
20918 @code{"-" @var{parameter} [ " " @var{parameter} ]}
20920 @item @var{parameter} @expansion{}
20921 @code{@var{non-blank-sequence} | @var{c-string}}
20923 @item @var{operation} @expansion{}
20924 @emph{any of the operations described in this chapter}
20926 @item @var{non-blank-sequence} @expansion{}
20927 @emph{anything, provided it doesn't contain special characters such as
20928 "-", @var{nl}, """ and of course " "}
20930 @item @var{c-string} @expansion{}
20931 @code{""" @var{seven-bit-iso-c-string-content} """}
20933 @item @var{nl} @expansion{}
20942 The CLI commands are still handled by the @sc{mi} interpreter; their
20943 output is described below.
20946 The @code{@var{token}}, when present, is passed back when the command
20950 Some @sc{mi} commands accept optional arguments as part of the parameter
20951 list. Each option is identified by a leading @samp{-} (dash) and may be
20952 followed by an optional argument parameter. Options occur first in the
20953 parameter list and can be delimited from normal parameters using
20954 @samp{--} (this is useful when some parameters begin with a dash).
20961 We want easy access to the existing CLI syntax (for debugging).
20964 We want it to be easy to spot a @sc{mi} operation.
20967 @node GDB/MI Output Syntax
20968 @subsection @sc{gdb/mi} Output Syntax
20970 @cindex output syntax of @sc{gdb/mi}
20971 @cindex @sc{gdb/mi}, output syntax
20972 The output from @sc{gdb/mi} consists of zero or more out-of-band records
20973 followed, optionally, by a single result record. This result record
20974 is for the most recent command. The sequence of output records is
20975 terminated by @samp{(gdb)}.
20977 If an input command was prefixed with a @code{@var{token}} then the
20978 corresponding output for that command will also be prefixed by that same
20982 @item @var{output} @expansion{}
20983 @code{( @var{out-of-band-record} )* [ @var{result-record} ] "(gdb)" @var{nl}}
20985 @item @var{result-record} @expansion{}
20986 @code{ [ @var{token} ] "^" @var{result-class} ( "," @var{result} )* @var{nl}}
20988 @item @var{out-of-band-record} @expansion{}
20989 @code{@var{async-record} | @var{stream-record}}
20991 @item @var{async-record} @expansion{}
20992 @code{@var{exec-async-output} | @var{status-async-output} | @var{notify-async-output}}
20994 @item @var{exec-async-output} @expansion{}
20995 @code{[ @var{token} ] "*" @var{async-output}}
20997 @item @var{status-async-output} @expansion{}
20998 @code{[ @var{token} ] "+" @var{async-output}}
21000 @item @var{notify-async-output} @expansion{}
21001 @code{[ @var{token} ] "=" @var{async-output}}
21003 @item @var{async-output} @expansion{}
21004 @code{@var{async-class} ( "," @var{result} )* @var{nl}}
21006 @item @var{result-class} @expansion{}
21007 @code{"done" | "running" | "connected" | "error" | "exit"}
21009 @item @var{async-class} @expansion{}
21010 @code{"stopped" | @var{others}} (where @var{others} will be added
21011 depending on the needs---this is still in development).
21013 @item @var{result} @expansion{}
21014 @code{ @var{variable} "=" @var{value}}
21016 @item @var{variable} @expansion{}
21017 @code{ @var{string} }
21019 @item @var{value} @expansion{}
21020 @code{ @var{const} | @var{tuple} | @var{list} }
21022 @item @var{const} @expansion{}
21023 @code{@var{c-string}}
21025 @item @var{tuple} @expansion{}
21026 @code{ "@{@}" | "@{" @var{result} ( "," @var{result} )* "@}" }
21028 @item @var{list} @expansion{}
21029 @code{ "[]" | "[" @var{value} ( "," @var{value} )* "]" | "["
21030 @var{result} ( "," @var{result} )* "]" }
21032 @item @var{stream-record} @expansion{}
21033 @code{@var{console-stream-output} | @var{target-stream-output} | @var{log-stream-output}}
21035 @item @var{console-stream-output} @expansion{}
21036 @code{"~" @var{c-string}}
21038 @item @var{target-stream-output} @expansion{}
21039 @code{"@@" @var{c-string}}
21041 @item @var{log-stream-output} @expansion{}
21042 @code{"&" @var{c-string}}
21044 @item @var{nl} @expansion{}
21047 @item @var{token} @expansion{}
21048 @emph{any sequence of digits}.
21056 All output sequences end in a single line containing a period.
21059 The @code{@var{token}} is from the corresponding request. Note that
21060 for all async output, while the token is allowed by the grammar and
21061 may be output by future versions of @value{GDBN} for select async
21062 output messages, it is generally omitted. Frontends should treat
21063 all async output as reporting general changes in the state of the
21064 target and there should be no need to associate async output to any
21068 @cindex status output in @sc{gdb/mi}
21069 @var{status-async-output} contains on-going status information about the
21070 progress of a slow operation. It can be discarded. All status output is
21071 prefixed by @samp{+}.
21074 @cindex async output in @sc{gdb/mi}
21075 @var{exec-async-output} contains asynchronous state change on the target
21076 (stopped, started, disappeared). All async output is prefixed by
21080 @cindex notify output in @sc{gdb/mi}
21081 @var{notify-async-output} contains supplementary information that the
21082 client should handle (e.g., a new breakpoint information). All notify
21083 output is prefixed by @samp{=}.
21086 @cindex console output in @sc{gdb/mi}
21087 @var{console-stream-output} is output that should be displayed as is in the
21088 console. It is the textual response to a CLI command. All the console
21089 output is prefixed by @samp{~}.
21092 @cindex target output in @sc{gdb/mi}
21093 @var{target-stream-output} is the output produced by the target program.
21094 All the target output is prefixed by @samp{@@}.
21097 @cindex log output in @sc{gdb/mi}
21098 @var{log-stream-output} is output text coming from @value{GDBN}'s internals, for
21099 instance messages that should be displayed as part of an error log. All
21100 the log output is prefixed by @samp{&}.
21103 @cindex list output in @sc{gdb/mi}
21104 New @sc{gdb/mi} commands should only output @var{lists} containing
21110 @xref{GDB/MI Stream Records, , @sc{gdb/mi} Stream Records}, for more
21111 details about the various output records.
21113 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21114 @node GDB/MI Compatibility with CLI
21115 @section @sc{gdb/mi} Compatibility with CLI
21117 @cindex compatibility, @sc{gdb/mi} and CLI
21118 @cindex @sc{gdb/mi}, compatibility with CLI
21120 For the developers convenience CLI commands can be entered directly,
21121 but there may be some unexpected behaviour. For example, commands
21122 that query the user will behave as if the user replied yes, breakpoint
21123 command lists are not executed and some CLI commands, such as
21124 @code{if}, @code{when} and @code{define}, prompt for further input with
21125 @samp{>}, which is not valid MI output.
21127 This feature may be removed at some stage in the future and it is
21128 recommended that front ends use the @code{-interpreter-exec} command
21129 (@pxref{-interpreter-exec}).
21131 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21132 @node GDB/MI Development and Front Ends
21133 @section @sc{gdb/mi} Development and Front Ends
21134 @cindex @sc{gdb/mi} development
21136 The application which takes the MI output and presents the state of the
21137 program being debugged to the user is called a @dfn{front end}.
21139 Although @sc{gdb/mi} is still incomplete, it is currently being used
21140 by a variety of front ends to @value{GDBN}. This makes it difficult
21141 to introduce new functionality without breaking existing usage. This
21142 section tries to minimize the problems by describing how the protocol
21145 Some changes in MI need not break a carefully designed front end, and
21146 for these the MI version will remain unchanged. The following is a
21147 list of changes that may occur within one level, so front ends should
21148 parse MI output in a way that can handle them:
21152 New MI commands may be added.
21155 New fields may be added to the output of any MI command.
21158 The range of values for fields with specified values, e.g.,
21159 @code{in_scope} (@pxref{-var-update}) may be extended.
21161 @c The format of field's content e.g type prefix, may change so parse it
21162 @c at your own risk. Yes, in general?
21164 @c The order of fields may change? Shouldn't really matter but it might
21165 @c resolve inconsistencies.
21168 If the changes are likely to break front ends, the MI version level
21169 will be increased by one. This will allow the front end to parse the
21170 output according to the MI version. Apart from mi0, new versions of
21171 @value{GDBN} will not support old versions of MI and it will be the
21172 responsibility of the front end to work with the new one.
21174 @c Starting with mi3, add a new command -mi-version that prints the MI
21177 The best way to avoid unexpected changes in MI that might break your front
21178 end is to make your project known to @value{GDBN} developers and
21179 follow development on @email{gdb@@sourceware.org} and
21180 @email{gdb-patches@@sourceware.org}.
21181 @cindex mailing lists
21183 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21184 @node GDB/MI Output Records
21185 @section @sc{gdb/mi} Output Records
21188 * GDB/MI Result Records::
21189 * GDB/MI Stream Records::
21190 * GDB/MI Async Records::
21191 * GDB/MI Frame Information::
21194 @node GDB/MI Result Records
21195 @subsection @sc{gdb/mi} Result Records
21197 @cindex result records in @sc{gdb/mi}
21198 @cindex @sc{gdb/mi}, result records
21199 In addition to a number of out-of-band notifications, the response to a
21200 @sc{gdb/mi} command includes one of the following result indications:
21204 @item "^done" [ "," @var{results} ]
21205 The synchronous operation was successful, @code{@var{results}} are the return
21210 @c Is this one correct? Should it be an out-of-band notification?
21211 The asynchronous operation was successfully started. The target is
21216 @value{GDBN} has connected to a remote target.
21218 @item "^error" "," @var{c-string}
21220 The operation failed. The @code{@var{c-string}} contains the corresponding
21225 @value{GDBN} has terminated.
21229 @node GDB/MI Stream Records
21230 @subsection @sc{gdb/mi} Stream Records
21232 @cindex @sc{gdb/mi}, stream records
21233 @cindex stream records in @sc{gdb/mi}
21234 @value{GDBN} internally maintains a number of output streams: the console, the
21235 target, and the log. The output intended for each of these streams is
21236 funneled through the @sc{gdb/mi} interface using @dfn{stream records}.
21238 Each stream record begins with a unique @dfn{prefix character} which
21239 identifies its stream (@pxref{GDB/MI Output Syntax, , @sc{gdb/mi} Output
21240 Syntax}). In addition to the prefix, each stream record contains a
21241 @code{@var{string-output}}. This is either raw text (with an implicit new
21242 line) or a quoted C string (which does not contain an implicit newline).
21245 @item "~" @var{string-output}
21246 The console output stream contains text that should be displayed in the
21247 CLI console window. It contains the textual responses to CLI commands.
21249 @item "@@" @var{string-output}
21250 The target output stream contains any textual output from the running
21251 target. This is only present when GDB's event loop is truly
21252 asynchronous, which is currently only the case for remote targets.
21254 @item "&" @var{string-output}
21255 The log stream contains debugging messages being produced by @value{GDBN}'s
21259 @node GDB/MI Async Records
21260 @subsection @sc{gdb/mi} Async Records
21262 @cindex async records in @sc{gdb/mi}
21263 @cindex @sc{gdb/mi}, async records
21264 @dfn{Async} records are used to notify the @sc{gdb/mi} client of
21265 additional changes that have occurred. Those changes can either be a
21266 consequence of @sc{gdb/mi} commands (e.g., a breakpoint modified) or a result of
21267 target activity (e.g., target stopped).
21269 The following is the list of possible async records:
21273 @item *running,thread-id="@var{thread}"
21274 The target is now running. The @var{thread} field tells which
21275 specific thread is now running, and can be @samp{all} if all threads
21276 are running. The frontend should assume that no interaction with a
21277 running thread is possible after this notification is produced.
21278 The frontend should not assume that this notification is output
21279 only once for any command. @value{GDBN} may emit this notification
21280 several times, either for different threads, because it cannot resume
21281 all threads together, or even for a single thread, if the thread must
21282 be stepped though some code before letting it run freely.
21284 @item *stopped,reason="@var{reason}",thread-id="@var{id}",stopped-threads="@var{stopped}"
21285 The target has stopped. The @var{reason} field can have one of the
21289 @item breakpoint-hit
21290 A breakpoint was reached.
21291 @item watchpoint-trigger
21292 A watchpoint was triggered.
21293 @item read-watchpoint-trigger
21294 A read watchpoint was triggered.
21295 @item access-watchpoint-trigger
21296 An access watchpoint was triggered.
21297 @item function-finished
21298 An -exec-finish or similar CLI command was accomplished.
21299 @item location-reached
21300 An -exec-until or similar CLI command was accomplished.
21301 @item watchpoint-scope
21302 A watchpoint has gone out of scope.
21303 @item end-stepping-range
21304 An -exec-next, -exec-next-instruction, -exec-step, -exec-step-instruction or
21305 similar CLI command was accomplished.
21306 @item exited-signalled
21307 The inferior exited because of a signal.
21309 The inferior exited.
21310 @item exited-normally
21311 The inferior exited normally.
21312 @item signal-received
21313 A signal was received by the inferior.
21316 The @var{id} field identifies the thread that directly caused the stop
21317 -- for example by hitting a breakpoint. Depending on whether all-stop
21318 mode is in effect (@pxref{All-Stop Mode}), @value{GDBN} may either
21319 stop all threads, or only the thread that directly triggered the stop.
21320 If all threads are stopped, the @var{stopped} field will have the
21321 value of @code{"all"}. Otherwise, the value of the @var{stopped}
21322 field will be a list of thread identifiers. Presently, this list will
21323 always include a single thread, but frontend should be prepared to see
21324 several threads in the list.
21326 @item =thread-group-created,id="@var{id}"
21327 @itemx =thread-group-exited,id="@var{id}"
21328 A thread thread group either was attached to, or has exited/detached
21329 from. The @var{id} field contains the @value{GDBN} identifier of the
21332 @item =thread-created,id="@var{id}",group-id="@var{gid}"
21333 @itemx =thread-exited,id="@var{id}",group-id="@var{gid}"
21334 A thread either was created, or has exited. The @var{id} field
21335 contains the @value{GDBN} identifier of the thread. The @var{gid}
21336 field identifies the thread group this thread belongs to.
21338 @item =thread-selected,id="@var{id}"
21339 Informs that the selected thread was changed as result of the last
21340 command. This notification is not emitted as result of @code{-thread-select}
21341 command but is emitted whenever an MI command that is not documented
21342 to change the selected thread actually changes it. In particular,
21343 invoking, directly or indirectly (via user-defined command), the CLI
21344 @code{thread} command, will generate this notification.
21346 We suggest that in response to this notification, front ends
21347 highlight the selected thread and cause subsequent commands to apply to
21350 @item =library-loaded,...
21351 Reports that a new library file was loaded by the program. This
21352 notification has 4 fields---@var{id}, @var{target-name},
21353 @var{host-name}, and @var{symbols-loaded}. The @var{id} field is an
21354 opaque identifier of the library. For remote debugging case,
21355 @var{target-name} and @var{host-name} fields give the name of the
21356 library file on the target, and on the host respectively. For native
21357 debugging, both those fields have the same value. The
21358 @var{symbols-loaded} field reports if the debug symbols for this
21359 library are loaded.
21361 @item =library-unloaded,...
21362 Reports that a library was unloaded by the program. This notification
21363 has 3 fields---@var{id}, @var{target-name} and @var{host-name} with
21364 the same meaning as for the @code{=library-loaded} notification
21368 @node GDB/MI Frame Information
21369 @subsection @sc{gdb/mi} Frame Information
21371 Response from many MI commands includes an information about stack
21372 frame. This information is a tuple that may have the following
21377 The level of the stack frame. The innermost frame has the level of
21378 zero. This field is always present.
21381 The name of the function corresponding to the frame. This field may
21382 be absent if @value{GDBN} is unable to determine the function name.
21385 The code address for the frame. This field is always present.
21388 The name of the source files that correspond to the frame's code
21389 address. This field may be absent.
21392 The source line corresponding to the frames' code address. This field
21396 The name of the binary file (either executable or shared library) the
21397 corresponds to the frame's code address. This field may be absent.
21402 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21403 @node GDB/MI Simple Examples
21404 @section Simple Examples of @sc{gdb/mi} Interaction
21405 @cindex @sc{gdb/mi}, simple examples
21407 This subsection presents several simple examples of interaction using
21408 the @sc{gdb/mi} interface. In these examples, @samp{->} means that the
21409 following line is passed to @sc{gdb/mi} as input, while @samp{<-} means
21410 the output received from @sc{gdb/mi}.
21412 Note the line breaks shown in the examples are here only for
21413 readability, they don't appear in the real output.
21415 @subheading Setting a Breakpoint
21417 Setting a breakpoint generates synchronous output which contains detailed
21418 information of the breakpoint.
21421 -> -break-insert main
21422 <- ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
21423 enabled="y",addr="0x08048564",func="main",file="myprog.c",
21424 fullname="/home/nickrob/myprog.c",line="68",times="0"@}
21428 @subheading Program Execution
21430 Program execution generates asynchronous records and MI gives the
21431 reason that execution stopped.
21437 <- *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
21438 frame=@{addr="0x08048564",func="main",
21439 args=[@{name="argc",value="1"@},@{name="argv",value="0xbfc4d4d4"@}],
21440 file="myprog.c",fullname="/home/nickrob/myprog.c",line="68"@}
21445 <- *stopped,reason="exited-normally"
21449 @subheading Quitting @value{GDBN}
21451 Quitting @value{GDBN} just prints the result class @samp{^exit}.
21459 @subheading A Bad Command
21461 Here's what happens if you pass a non-existent command:
21465 <- ^error,msg="Undefined MI command: rubbish"
21470 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21471 @node GDB/MI Command Description Format
21472 @section @sc{gdb/mi} Command Description Format
21474 The remaining sections describe blocks of commands. Each block of
21475 commands is laid out in a fashion similar to this section.
21477 @subheading Motivation
21479 The motivation for this collection of commands.
21481 @subheading Introduction
21483 A brief introduction to this collection of commands as a whole.
21485 @subheading Commands
21487 For each command in the block, the following is described:
21489 @subsubheading Synopsis
21492 -command @var{args}@dots{}
21495 @subsubheading Result
21497 @subsubheading @value{GDBN} Command
21499 The corresponding @value{GDBN} CLI command(s), if any.
21501 @subsubheading Example
21503 Example(s) formatted for readability. Some of the described commands have
21504 not been implemented yet and these are labeled N.A.@: (not available).
21507 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21508 @node GDB/MI Breakpoint Commands
21509 @section @sc{gdb/mi} Breakpoint Commands
21511 @cindex breakpoint commands for @sc{gdb/mi}
21512 @cindex @sc{gdb/mi}, breakpoint commands
21513 This section documents @sc{gdb/mi} commands for manipulating
21516 @subheading The @code{-break-after} Command
21517 @findex -break-after
21519 @subsubheading Synopsis
21522 -break-after @var{number} @var{count}
21525 The breakpoint number @var{number} is not in effect until it has been
21526 hit @var{count} times. To see how this is reflected in the output of
21527 the @samp{-break-list} command, see the description of the
21528 @samp{-break-list} command below.
21530 @subsubheading @value{GDBN} Command
21532 The corresponding @value{GDBN} command is @samp{ignore}.
21534 @subsubheading Example
21539 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
21540 enabled="y",addr="0x000100d0",func="main",file="hello.c",
21541 fullname="/home/foo/hello.c",line="5",times="0"@}
21548 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
21549 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21550 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21551 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21552 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21553 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21554 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21555 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
21556 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
21557 line="5",times="0",ignore="3"@}]@}
21562 @subheading The @code{-break-catch} Command
21563 @findex -break-catch
21566 @subheading The @code{-break-commands} Command
21567 @findex -break-commands
21569 @subsubheading Synopsis
21572 -break-commands @var{number} [ @var{command1} ... @var{commandN} ]
21575 Specifies the CLI commands that should be executed when breakpoint
21576 @var{number} is hit. The parameters @var{command1} to @var{commandN}
21577 are the commands. If no command is specified, any previously-set
21578 commands are cleared. @xref{Break Commands}. Typical use of this
21579 functionality is tracing a program, that is, printing of values of
21580 some variables whenever breakpoint is hit and then continuing.
21582 @subsubheading @value{GDBN} Command
21584 The corresponding @value{GDBN} command is @samp{commands}.
21586 @subsubheading Example
21591 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
21592 enabled="y",addr="0x000100d0",func="main",file="hello.c",
21593 fullname="/home/foo/hello.c",line="5",times="0"@}
21595 -break-commands 1 "print v" "continue"
21600 @subheading The @code{-break-condition} Command
21601 @findex -break-condition
21603 @subsubheading Synopsis
21606 -break-condition @var{number} @var{expr}
21609 Breakpoint @var{number} will stop the program only if the condition in
21610 @var{expr} is true. The condition becomes part of the
21611 @samp{-break-list} output (see the description of the @samp{-break-list}
21614 @subsubheading @value{GDBN} Command
21616 The corresponding @value{GDBN} command is @samp{condition}.
21618 @subsubheading Example
21622 -break-condition 1 1
21626 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
21627 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21628 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21629 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21630 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21631 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21632 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21633 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
21634 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
21635 line="5",cond="1",times="0",ignore="3"@}]@}
21639 @subheading The @code{-break-delete} Command
21640 @findex -break-delete
21642 @subsubheading Synopsis
21645 -break-delete ( @var{breakpoint} )+
21648 Delete the breakpoint(s) whose number(s) are specified in the argument
21649 list. This is obviously reflected in the breakpoint list.
21651 @subsubheading @value{GDBN} Command
21653 The corresponding @value{GDBN} command is @samp{delete}.
21655 @subsubheading Example
21663 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
21664 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21665 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21666 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21667 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21668 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21669 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21674 @subheading The @code{-break-disable} Command
21675 @findex -break-disable
21677 @subsubheading Synopsis
21680 -break-disable ( @var{breakpoint} )+
21683 Disable the named @var{breakpoint}(s). The field @samp{enabled} in the
21684 break list is now set to @samp{n} for the named @var{breakpoint}(s).
21686 @subsubheading @value{GDBN} Command
21688 The corresponding @value{GDBN} command is @samp{disable}.
21690 @subsubheading Example
21698 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
21699 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21700 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21701 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21702 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21703 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21704 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21705 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="n",
21706 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
21707 line="5",times="0"@}]@}
21711 @subheading The @code{-break-enable} Command
21712 @findex -break-enable
21714 @subsubheading Synopsis
21717 -break-enable ( @var{breakpoint} )+
21720 Enable (previously disabled) @var{breakpoint}(s).
21722 @subsubheading @value{GDBN} Command
21724 The corresponding @value{GDBN} command is @samp{enable}.
21726 @subsubheading Example
21734 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
21735 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21736 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21737 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21738 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21739 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21740 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21741 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
21742 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
21743 line="5",times="0"@}]@}
21747 @subheading The @code{-break-info} Command
21748 @findex -break-info
21750 @subsubheading Synopsis
21753 -break-info @var{breakpoint}
21757 Get information about a single breakpoint.
21759 @subsubheading @value{GDBN} Command
21761 The corresponding @value{GDBN} command is @samp{info break @var{breakpoint}}.
21763 @subsubheading Example
21766 @subheading The @code{-break-insert} Command
21767 @findex -break-insert
21769 @subsubheading Synopsis
21772 -break-insert [ -t ] [ -h ] [ -f ] [ -d ]
21773 [ -c @var{condition} ] [ -i @var{ignore-count} ]
21774 [ -p @var{thread} ] [ @var{location} ]
21778 If specified, @var{location}, can be one of:
21785 @item filename:linenum
21786 @item filename:function
21790 The possible optional parameters of this command are:
21794 Insert a temporary breakpoint.
21796 Insert a hardware breakpoint.
21797 @item -c @var{condition}
21798 Make the breakpoint conditional on @var{condition}.
21799 @item -i @var{ignore-count}
21800 Initialize the @var{ignore-count}.
21802 If @var{location} cannot be parsed (for example if it
21803 refers to unknown files or functions), create a pending
21804 breakpoint. Without this flag, @value{GDBN} will report
21805 an error, and won't create a breakpoint, if @var{location}
21808 Create a disabled breakpoint.
21811 @subsubheading Result
21813 The result is in the form:
21816 ^done,bkpt=@{number="@var{number}",type="@var{type}",disp="del"|"keep",
21817 enabled="y"|"n",addr="@var{hex}",func="@var{funcname}",file="@var{filename}",
21818 fullname="@var{full_filename}",line="@var{lineno}",[thread="@var{threadno},]
21819 times="@var{times}"@}
21823 where @var{number} is the @value{GDBN} number for this breakpoint,
21824 @var{funcname} is the name of the function where the breakpoint was
21825 inserted, @var{filename} is the name of the source file which contains
21826 this function, @var{lineno} is the source line number within that file
21827 and @var{times} the number of times that the breakpoint has been hit
21828 (always 0 for -break-insert but may be greater for -break-info or -break-list
21829 which use the same output).
21831 Note: this format is open to change.
21832 @c An out-of-band breakpoint instead of part of the result?
21834 @subsubheading @value{GDBN} Command
21836 The corresponding @value{GDBN} commands are @samp{break}, @samp{tbreak},
21837 @samp{hbreak}, @samp{thbreak}, and @samp{rbreak}.
21839 @subsubheading Example
21844 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",
21845 fullname="/home/foo/recursive2.c,line="4",times="0"@}
21847 -break-insert -t foo
21848 ^done,bkpt=@{number="2",addr="0x00010774",file="recursive2.c",
21849 fullname="/home/foo/recursive2.c,line="11",times="0"@}
21852 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
21853 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21854 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21855 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21856 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21857 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21858 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21859 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
21860 addr="0x0001072c", func="main",file="recursive2.c",
21861 fullname="/home/foo/recursive2.c,"line="4",times="0"@},
21862 bkpt=@{number="2",type="breakpoint",disp="del",enabled="y",
21863 addr="0x00010774",func="foo",file="recursive2.c",
21864 fullname="/home/foo/recursive2.c",line="11",times="0"@}]@}
21866 -break-insert -r foo.*
21867 ~int foo(int, int);
21868 ^done,bkpt=@{number="3",addr="0x00010774",file="recursive2.c,
21869 "fullname="/home/foo/recursive2.c",line="11",times="0"@}
21873 @subheading The @code{-break-list} Command
21874 @findex -break-list
21876 @subsubheading Synopsis
21882 Displays the list of inserted breakpoints, showing the following fields:
21886 number of the breakpoint
21888 type of the breakpoint: @samp{breakpoint} or @samp{watchpoint}
21890 should the breakpoint be deleted or disabled when it is hit: @samp{keep}
21893 is the breakpoint enabled or no: @samp{y} or @samp{n}
21895 memory location at which the breakpoint is set
21897 logical location of the breakpoint, expressed by function name, file
21900 number of times the breakpoint has been hit
21903 If there are no breakpoints or watchpoints, the @code{BreakpointTable}
21904 @code{body} field is an empty list.
21906 @subsubheading @value{GDBN} Command
21908 The corresponding @value{GDBN} command is @samp{info break}.
21910 @subsubheading Example
21915 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
21916 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21917 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21918 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21919 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21920 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21921 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21922 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
21923 addr="0x000100d0",func="main",file="hello.c",line="5",times="0"@},
21924 bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
21925 addr="0x00010114",func="foo",file="hello.c",fullname="/home/foo/hello.c",
21926 line="13",times="0"@}]@}
21930 Here's an example of the result when there are no breakpoints:
21935 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
21936 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21937 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21938 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21939 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21940 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21941 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21946 @subheading The @code{-break-watch} Command
21947 @findex -break-watch
21949 @subsubheading Synopsis
21952 -break-watch [ -a | -r ]
21955 Create a watchpoint. With the @samp{-a} option it will create an
21956 @dfn{access} watchpoint, i.e., a watchpoint that triggers either on a
21957 read from or on a write to the memory location. With the @samp{-r}
21958 option, the watchpoint created is a @dfn{read} watchpoint, i.e., it will
21959 trigger only when the memory location is accessed for reading. Without
21960 either of the options, the watchpoint created is a regular watchpoint,
21961 i.e., it will trigger when the memory location is accessed for writing.
21962 @xref{Set Watchpoints, , Setting Watchpoints}.
21964 Note that @samp{-break-list} will report a single list of watchpoints and
21965 breakpoints inserted.
21967 @subsubheading @value{GDBN} Command
21969 The corresponding @value{GDBN} commands are @samp{watch}, @samp{awatch}, and
21972 @subsubheading Example
21974 Setting a watchpoint on a variable in the @code{main} function:
21979 ^done,wpt=@{number="2",exp="x"@}
21984 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="x"@},
21985 value=@{old="-268439212",new="55"@},
21986 frame=@{func="main",args=[],file="recursive2.c",
21987 fullname="/home/foo/bar/recursive2.c",line="5"@}
21991 Setting a watchpoint on a variable local to a function. @value{GDBN} will stop
21992 the program execution twice: first for the variable changing value, then
21993 for the watchpoint going out of scope.
21998 ^done,wpt=@{number="5",exp="C"@}
22003 *stopped,reason="watchpoint-trigger",
22004 wpt=@{number="5",exp="C"@},value=@{old="-276895068",new="3"@},
22005 frame=@{func="callee4",args=[],
22006 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22007 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
22012 *stopped,reason="watchpoint-scope",wpnum="5",
22013 frame=@{func="callee3",args=[@{name="strarg",
22014 value="0x11940 \"A string argument.\""@}],
22015 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22016 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
22020 Listing breakpoints and watchpoints, at different points in the program
22021 execution. Note that once the watchpoint goes out of scope, it is
22027 ^done,wpt=@{number="2",exp="C"@}
22030 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
22031 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
22032 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
22033 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
22034 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
22035 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
22036 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
22037 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
22038 addr="0x00010734",func="callee4",
22039 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22040 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c"line="8",times="1"@},
22041 bkpt=@{number="2",type="watchpoint",disp="keep",
22042 enabled="y",addr="",what="C",times="0"@}]@}
22047 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="C"@},
22048 value=@{old="-276895068",new="3"@},
22049 frame=@{func="callee4",args=[],
22050 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22051 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
22054 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
22055 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
22056 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
22057 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
22058 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
22059 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
22060 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
22061 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
22062 addr="0x00010734",func="callee4",
22063 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22064 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",times="1"@},
22065 bkpt=@{number="2",type="watchpoint",disp="keep",
22066 enabled="y",addr="",what="C",times="-5"@}]@}
22070 ^done,reason="watchpoint-scope",wpnum="2",
22071 frame=@{func="callee3",args=[@{name="strarg",
22072 value="0x11940 \"A string argument.\""@}],
22073 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22074 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
22077 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
22078 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
22079 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
22080 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
22081 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
22082 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
22083 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
22084 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
22085 addr="0x00010734",func="callee4",
22086 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22087 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",
22092 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22093 @node GDB/MI Program Context
22094 @section @sc{gdb/mi} Program Context
22096 @subheading The @code{-exec-arguments} Command
22097 @findex -exec-arguments
22100 @subsubheading Synopsis
22103 -exec-arguments @var{args}
22106 Set the inferior program arguments, to be used in the next
22109 @subsubheading @value{GDBN} Command
22111 The corresponding @value{GDBN} command is @samp{set args}.
22113 @subsubheading Example
22117 -exec-arguments -v word
22124 @subheading The @code{-exec-show-arguments} Command
22125 @findex -exec-show-arguments
22127 @subsubheading Synopsis
22130 -exec-show-arguments
22133 Print the arguments of the program.
22135 @subsubheading @value{GDBN} Command
22137 The corresponding @value{GDBN} command is @samp{show args}.
22139 @subsubheading Example
22144 @subheading The @code{-environment-cd} Command
22145 @findex -environment-cd
22147 @subsubheading Synopsis
22150 -environment-cd @var{pathdir}
22153 Set @value{GDBN}'s working directory.
22155 @subsubheading @value{GDBN} Command
22157 The corresponding @value{GDBN} command is @samp{cd}.
22159 @subsubheading Example
22163 -environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
22169 @subheading The @code{-environment-directory} Command
22170 @findex -environment-directory
22172 @subsubheading Synopsis
22175 -environment-directory [ -r ] [ @var{pathdir} ]+
22178 Add directories @var{pathdir} to beginning of search path for source files.
22179 If the @samp{-r} option is used, the search path is reset to the default
22180 search path. If directories @var{pathdir} are supplied in addition to the
22181 @samp{-r} option, the search path is first reset and then addition
22183 Multiple directories may be specified, separated by blanks. Specifying
22184 multiple directories in a single command
22185 results in the directories added to the beginning of the
22186 search path in the same order they were presented in the command.
22187 If blanks are needed as
22188 part of a directory name, double-quotes should be used around
22189 the name. In the command output, the path will show up separated
22190 by the system directory-separator character. The directory-separator
22191 character must not be used
22192 in any directory name.
22193 If no directories are specified, the current search path is displayed.
22195 @subsubheading @value{GDBN} Command
22197 The corresponding @value{GDBN} command is @samp{dir}.
22199 @subsubheading Example
22203 -environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
22204 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
22206 -environment-directory ""
22207 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
22209 -environment-directory -r /home/jjohnstn/src/gdb /usr/src
22210 ^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd"
22212 -environment-directory -r
22213 ^done,source-path="$cdir:$cwd"
22218 @subheading The @code{-environment-path} Command
22219 @findex -environment-path
22221 @subsubheading Synopsis
22224 -environment-path [ -r ] [ @var{pathdir} ]+
22227 Add directories @var{pathdir} to beginning of search path for object files.
22228 If the @samp{-r} option is used, the search path is reset to the original
22229 search path that existed at gdb start-up. If directories @var{pathdir} are
22230 supplied in addition to the
22231 @samp{-r} option, the search path is first reset and then addition
22233 Multiple directories may be specified, separated by blanks. Specifying
22234 multiple directories in a single command
22235 results in the directories added to the beginning of the
22236 search path in the same order they were presented in the command.
22237 If blanks are needed as
22238 part of a directory name, double-quotes should be used around
22239 the name. In the command output, the path will show up separated
22240 by the system directory-separator character. The directory-separator
22241 character must not be used
22242 in any directory name.
22243 If no directories are specified, the current path is displayed.
22246 @subsubheading @value{GDBN} Command
22248 The corresponding @value{GDBN} command is @samp{path}.
22250 @subsubheading Example
22255 ^done,path="/usr/bin"
22257 -environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb /bin
22258 ^done,path="/kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb:/bin:/usr/bin"
22260 -environment-path -r /usr/local/bin
22261 ^done,path="/usr/local/bin:/usr/bin"
22266 @subheading The @code{-environment-pwd} Command
22267 @findex -environment-pwd
22269 @subsubheading Synopsis
22275 Show the current working directory.
22277 @subsubheading @value{GDBN} Command
22279 The corresponding @value{GDBN} command is @samp{pwd}.
22281 @subsubheading Example
22286 ^done,cwd="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb"
22290 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22291 @node GDB/MI Thread Commands
22292 @section @sc{gdb/mi} Thread Commands
22295 @subheading The @code{-thread-info} Command
22296 @findex -thread-info
22298 @subsubheading Synopsis
22301 -thread-info [ @var{thread-id} ]
22304 Reports information about either a specific thread, if
22305 the @var{thread-id} parameter is present, or about all
22306 threads. When printing information about all threads,
22307 also reports the current thread.
22309 @subsubheading @value{GDBN} Command
22311 The @samp{info thread} command prints the same information
22314 @subsubheading Example
22319 @{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
22320 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]@},state="running"@},
22321 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
22322 frame=@{level="0",addr="0x0804891f",func="foo",args=[@{name="i",value="10"@}],
22323 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},state="running"@}],
22324 current-thread-id="1"
22328 The @samp{state} field may have the following values:
22332 The thread is stopped. Frame information is available for stopped
22336 The thread is running. There's no frame information for running
22341 @subheading The @code{-thread-list-ids} Command
22342 @findex -thread-list-ids
22344 @subsubheading Synopsis
22350 Produces a list of the currently known @value{GDBN} thread ids. At the
22351 end of the list it also prints the total number of such threads.
22353 This command is retained for historical reasons, the
22354 @code{-thread-info} command should be used instead.
22356 @subsubheading @value{GDBN} Command
22358 Part of @samp{info threads} supplies the same information.
22360 @subsubheading Example
22365 ^done,thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
22366 current-thread-id="1",number-of-threads="3"
22371 @subheading The @code{-thread-select} Command
22372 @findex -thread-select
22374 @subsubheading Synopsis
22377 -thread-select @var{threadnum}
22380 Make @var{threadnum} the current thread. It prints the number of the new
22381 current thread, and the topmost frame for that thread.
22383 This command is deprecated in favor of explicitly using the
22384 @samp{--thread} option to each command.
22386 @subsubheading @value{GDBN} Command
22388 The corresponding @value{GDBN} command is @samp{thread}.
22390 @subsubheading Example
22397 *stopped,reason="end-stepping-range",thread-id="2",line="187",
22398 file="../../../devo/gdb/testsuite/gdb.threads/linux-dp.c"
22402 thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
22403 number-of-threads="3"
22406 ^done,new-thread-id="3",
22407 frame=@{level="0",func="vprintf",
22408 args=[@{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""@},
22409 @{name="arg",value="0x2"@}],file="vprintf.c",line="31"@}
22413 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22414 @node GDB/MI Program Execution
22415 @section @sc{gdb/mi} Program Execution
22417 These are the asynchronous commands which generate the out-of-band
22418 record @samp{*stopped}. Currently @value{GDBN} only really executes
22419 asynchronously with remote targets and this interaction is mimicked in
22422 @subheading The @code{-exec-continue} Command
22423 @findex -exec-continue
22425 @subsubheading Synopsis
22428 -exec-continue [--all|--thread-group N]
22431 Resumes the execution of the inferior program until a breakpoint is
22432 encountered, or until the inferior exits. In all-stop mode
22433 (@pxref{All-Stop Mode}), may resume only one thread, or all threads,
22434 depending on the value of the @samp{scheduler-locking} variable. In
22435 non-stop mode (@pxref{Non-Stop Mode}), if the @samp{--all} is not
22436 specified, only the thread specified with the @samp{--thread} option
22437 (or current thread, if no @samp{--thread} is provided) is resumed. If
22438 @samp{--all} is specified, all threads will be resumed. The
22439 @samp{--all} option is ignored in all-stop mode. If the
22440 @samp{--thread-group} options is specified, then all threads in that
22441 thread group are resumed.
22443 @subsubheading @value{GDBN} Command
22445 The corresponding @value{GDBN} corresponding is @samp{continue}.
22447 @subsubheading Example
22454 *stopped,reason="breakpoint-hit",disp="keep",bkptno="2",frame=@{
22455 func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c",
22461 @subheading The @code{-exec-finish} Command
22462 @findex -exec-finish
22464 @subsubheading Synopsis
22470 Resumes the execution of the inferior program until the current
22471 function is exited. Displays the results returned by the function.
22473 @subsubheading @value{GDBN} Command
22475 The corresponding @value{GDBN} command is @samp{finish}.
22477 @subsubheading Example
22479 Function returning @code{void}.
22486 *stopped,reason="function-finished",frame=@{func="main",args=[],
22487 file="hello.c",fullname="/home/foo/bar/hello.c",line="7"@}
22491 Function returning other than @code{void}. The name of the internal
22492 @value{GDBN} variable storing the result is printed, together with the
22499 *stopped,reason="function-finished",frame=@{addr="0x000107b0",func="foo",
22500 args=[@{name="a",value="1"],@{name="b",value="9"@}@},
22501 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
22502 gdb-result-var="$1",return-value="0"
22507 @subheading The @code{-exec-interrupt} Command
22508 @findex -exec-interrupt
22510 @subsubheading Synopsis
22513 -exec-interrupt [--all|--thread-group N]
22516 Interrupts the background execution of the target. Note how the token
22517 associated with the stop message is the one for the execution command
22518 that has been interrupted. The token for the interrupt itself only
22519 appears in the @samp{^done} output. If the user is trying to
22520 interrupt a non-running program, an error message will be printed.
22522 Note that when asynchronous execution is enabled, this command is
22523 asynchronous just like other execution commands. That is, first the
22524 @samp{^done} response will be printed, and the target stop will be
22525 reported after that using the @samp{*stopped} notification.
22527 In non-stop mode, only the context thread is interrupted by default.
22528 All threads will be interrupted if the @samp{--all} option is
22529 specified. If the @samp{--thread-group} option is specified, all
22530 threads in that group will be interrupted.
22532 @subsubheading @value{GDBN} Command
22534 The corresponding @value{GDBN} command is @samp{interrupt}.
22536 @subsubheading Example
22547 111*stopped,signal-name="SIGINT",signal-meaning="Interrupt",
22548 frame=@{addr="0x00010140",func="foo",args=[],file="try.c",
22549 fullname="/home/foo/bar/try.c",line="13"@}
22554 ^error,msg="mi_cmd_exec_interrupt: Inferior not executing."
22558 @subheading The @code{-exec-jump} Command
22561 @subsubheading Synopsis
22564 -exec-jump @var{location}
22567 Resumes execution of the inferior program at the location specified by
22568 parameter. @xref{Specify Location}, for a description of the
22569 different forms of @var{location}.
22571 @subsubheading @value{GDBN} Command
22573 The corresponding @value{GDBN} command is @samp{jump}.
22575 @subsubheading Example
22578 -exec-jump foo.c:10
22579 *running,thread-id="all"
22584 @subheading The @code{-exec-next} Command
22587 @subsubheading Synopsis
22593 Resumes execution of the inferior program, stopping when the beginning
22594 of the next source line is reached.
22596 @subsubheading @value{GDBN} Command
22598 The corresponding @value{GDBN} command is @samp{next}.
22600 @subsubheading Example
22606 *stopped,reason="end-stepping-range",line="8",file="hello.c"
22611 @subheading The @code{-exec-next-instruction} Command
22612 @findex -exec-next-instruction
22614 @subsubheading Synopsis
22617 -exec-next-instruction
22620 Executes one machine instruction. If the instruction is a function
22621 call, continues until the function returns. If the program stops at an
22622 instruction in the middle of a source line, the address will be
22625 @subsubheading @value{GDBN} Command
22627 The corresponding @value{GDBN} command is @samp{nexti}.
22629 @subsubheading Example
22633 -exec-next-instruction
22637 *stopped,reason="end-stepping-range",
22638 addr="0x000100d4",line="5",file="hello.c"
22643 @subheading The @code{-exec-return} Command
22644 @findex -exec-return
22646 @subsubheading Synopsis
22652 Makes current function return immediately. Doesn't execute the inferior.
22653 Displays the new current frame.
22655 @subsubheading @value{GDBN} Command
22657 The corresponding @value{GDBN} command is @samp{return}.
22659 @subsubheading Example
22663 200-break-insert callee4
22664 200^done,bkpt=@{number="1",addr="0x00010734",
22665 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
22670 000*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
22671 frame=@{func="callee4",args=[],
22672 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22673 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
22679 111^done,frame=@{level="0",func="callee3",
22680 args=[@{name="strarg",
22681 value="0x11940 \"A string argument.\""@}],
22682 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22683 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
22688 @subheading The @code{-exec-run} Command
22691 @subsubheading Synopsis
22697 Starts execution of the inferior from the beginning. The inferior
22698 executes until either a breakpoint is encountered or the program
22699 exits. In the latter case the output will include an exit code, if
22700 the program has exited exceptionally.
22702 @subsubheading @value{GDBN} Command
22704 The corresponding @value{GDBN} command is @samp{run}.
22706 @subsubheading Examples
22711 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",line="4"@}
22716 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
22717 frame=@{func="main",args=[],file="recursive2.c",
22718 fullname="/home/foo/bar/recursive2.c",line="4"@}
22723 Program exited normally:
22731 *stopped,reason="exited-normally"
22736 Program exited exceptionally:
22744 *stopped,reason="exited",exit-code="01"
22748 Another way the program can terminate is if it receives a signal such as
22749 @code{SIGINT}. In this case, @sc{gdb/mi} displays this:
22753 *stopped,reason="exited-signalled",signal-name="SIGINT",
22754 signal-meaning="Interrupt"
22758 @c @subheading -exec-signal
22761 @subheading The @code{-exec-step} Command
22764 @subsubheading Synopsis
22770 Resumes execution of the inferior program, stopping when the beginning
22771 of the next source line is reached, if the next source line is not a
22772 function call. If it is, stop at the first instruction of the called
22775 @subsubheading @value{GDBN} Command
22777 The corresponding @value{GDBN} command is @samp{step}.
22779 @subsubheading Example
22781 Stepping into a function:
22787 *stopped,reason="end-stepping-range",
22788 frame=@{func="foo",args=[@{name="a",value="10"@},
22789 @{name="b",value="0"@}],file="recursive2.c",
22790 fullname="/home/foo/bar/recursive2.c",line="11"@}
22800 *stopped,reason="end-stepping-range",line="14",file="recursive2.c"
22805 @subheading The @code{-exec-step-instruction} Command
22806 @findex -exec-step-instruction
22808 @subsubheading Synopsis
22811 -exec-step-instruction
22814 Resumes the inferior which executes one machine instruction. The
22815 output, once @value{GDBN} has stopped, will vary depending on whether
22816 we have stopped in the middle of a source line or not. In the former
22817 case, the address at which the program stopped will be printed as
22820 @subsubheading @value{GDBN} Command
22822 The corresponding @value{GDBN} command is @samp{stepi}.
22824 @subsubheading Example
22828 -exec-step-instruction
22832 *stopped,reason="end-stepping-range",
22833 frame=@{func="foo",args=[],file="try.c",
22834 fullname="/home/foo/bar/try.c",line="10"@}
22836 -exec-step-instruction
22840 *stopped,reason="end-stepping-range",
22841 frame=@{addr="0x000100f4",func="foo",args=[],file="try.c",
22842 fullname="/home/foo/bar/try.c",line="10"@}
22847 @subheading The @code{-exec-until} Command
22848 @findex -exec-until
22850 @subsubheading Synopsis
22853 -exec-until [ @var{location} ]
22856 Executes the inferior until the @var{location} specified in the
22857 argument is reached. If there is no argument, the inferior executes
22858 until a source line greater than the current one is reached. The
22859 reason for stopping in this case will be @samp{location-reached}.
22861 @subsubheading @value{GDBN} Command
22863 The corresponding @value{GDBN} command is @samp{until}.
22865 @subsubheading Example
22869 -exec-until recursive2.c:6
22873 *stopped,reason="location-reached",frame=@{func="main",args=[],
22874 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="6"@}
22879 @subheading -file-clear
22880 Is this going away????
22883 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22884 @node GDB/MI Stack Manipulation
22885 @section @sc{gdb/mi} Stack Manipulation Commands
22888 @subheading The @code{-stack-info-frame} Command
22889 @findex -stack-info-frame
22891 @subsubheading Synopsis
22897 Get info on the selected frame.
22899 @subsubheading @value{GDBN} Command
22901 The corresponding @value{GDBN} command is @samp{info frame} or @samp{frame}
22902 (without arguments).
22904 @subsubheading Example
22909 ^done,frame=@{level="1",addr="0x0001076c",func="callee3",
22910 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22911 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@}
22915 @subheading The @code{-stack-info-depth} Command
22916 @findex -stack-info-depth
22918 @subsubheading Synopsis
22921 -stack-info-depth [ @var{max-depth} ]
22924 Return the depth of the stack. If the integer argument @var{max-depth}
22925 is specified, do not count beyond @var{max-depth} frames.
22927 @subsubheading @value{GDBN} Command
22929 There's no equivalent @value{GDBN} command.
22931 @subsubheading Example
22933 For a stack with frame levels 0 through 11:
22940 -stack-info-depth 4
22943 -stack-info-depth 12
22946 -stack-info-depth 11
22949 -stack-info-depth 13
22954 @subheading The @code{-stack-list-arguments} Command
22955 @findex -stack-list-arguments
22957 @subsubheading Synopsis
22960 -stack-list-arguments @var{show-values}
22961 [ @var{low-frame} @var{high-frame} ]
22964 Display a list of the arguments for the frames between @var{low-frame}
22965 and @var{high-frame} (inclusive). If @var{low-frame} and
22966 @var{high-frame} are not provided, list the arguments for the whole
22967 call stack. If the two arguments are equal, show the single frame
22968 at the corresponding level. It is an error if @var{low-frame} is
22969 larger than the actual number of frames. On the other hand,
22970 @var{high-frame} may be larger than the actual number of frames, in
22971 which case only existing frames will be returned.
22973 The @var{show-values} argument must have a value of 0 or 1. A value of
22974 0 means that only the names of the arguments are listed, a value of 1
22975 means that both names and values of the arguments are printed.
22977 @subsubheading @value{GDBN} Command
22979 @value{GDBN} does not have an equivalent command. @code{gdbtk} has a
22980 @samp{gdb_get_args} command which partially overlaps with the
22981 functionality of @samp{-stack-list-arguments}.
22983 @subsubheading Example
22990 frame=@{level="0",addr="0x00010734",func="callee4",
22991 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22992 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@},
22993 frame=@{level="1",addr="0x0001076c",func="callee3",
22994 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22995 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@},
22996 frame=@{level="2",addr="0x0001078c",func="callee2",
22997 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22998 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="22"@},
22999 frame=@{level="3",addr="0x000107b4",func="callee1",
23000 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23001 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="27"@},
23002 frame=@{level="4",addr="0x000107e0",func="main",
23003 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23004 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="32"@}]
23006 -stack-list-arguments 0
23009 frame=@{level="0",args=[]@},
23010 frame=@{level="1",args=[name="strarg"]@},
23011 frame=@{level="2",args=[name="intarg",name="strarg"]@},
23012 frame=@{level="3",args=[name="intarg",name="strarg",name="fltarg"]@},
23013 frame=@{level="4",args=[]@}]
23015 -stack-list-arguments 1
23018 frame=@{level="0",args=[]@},
23020 args=[@{name="strarg",value="0x11940 \"A string argument.\""@}]@},
23021 frame=@{level="2",args=[
23022 @{name="intarg",value="2"@},
23023 @{name="strarg",value="0x11940 \"A string argument.\""@}]@},
23024 @{frame=@{level="3",args=[
23025 @{name="intarg",value="2"@},
23026 @{name="strarg",value="0x11940 \"A string argument.\""@},
23027 @{name="fltarg",value="3.5"@}]@},
23028 frame=@{level="4",args=[]@}]
23030 -stack-list-arguments 0 2 2
23031 ^done,stack-args=[frame=@{level="2",args=[name="intarg",name="strarg"]@}]
23033 -stack-list-arguments 1 2 2
23034 ^done,stack-args=[frame=@{level="2",
23035 args=[@{name="intarg",value="2"@},
23036 @{name="strarg",value="0x11940 \"A string argument.\""@}]@}]
23040 @c @subheading -stack-list-exception-handlers
23043 @subheading The @code{-stack-list-frames} Command
23044 @findex -stack-list-frames
23046 @subsubheading Synopsis
23049 -stack-list-frames [ @var{low-frame} @var{high-frame} ]
23052 List the frames currently on the stack. For each frame it displays the
23057 The frame number, 0 being the topmost frame, i.e., the innermost function.
23059 The @code{$pc} value for that frame.
23063 File name of the source file where the function lives.
23065 Line number corresponding to the @code{$pc}.
23068 If invoked without arguments, this command prints a backtrace for the
23069 whole stack. If given two integer arguments, it shows the frames whose
23070 levels are between the two arguments (inclusive). If the two arguments
23071 are equal, it shows the single frame at the corresponding level. It is
23072 an error if @var{low-frame} is larger than the actual number of
23073 frames. On the other hand, @var{high-frame} may be larger than the
23074 actual number of frames, in which case only existing frames will be returned.
23076 @subsubheading @value{GDBN} Command
23078 The corresponding @value{GDBN} commands are @samp{backtrace} and @samp{where}.
23080 @subsubheading Example
23082 Full stack backtrace:
23088 [frame=@{level="0",addr="0x0001076c",func="foo",
23089 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11"@},
23090 frame=@{level="1",addr="0x000107a4",func="foo",
23091 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23092 frame=@{level="2",addr="0x000107a4",func="foo",
23093 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23094 frame=@{level="3",addr="0x000107a4",func="foo",
23095 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23096 frame=@{level="4",addr="0x000107a4",func="foo",
23097 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23098 frame=@{level="5",addr="0x000107a4",func="foo",
23099 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23100 frame=@{level="6",addr="0x000107a4",func="foo",
23101 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23102 frame=@{level="7",addr="0x000107a4",func="foo",
23103 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23104 frame=@{level="8",addr="0x000107a4",func="foo",
23105 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23106 frame=@{level="9",addr="0x000107a4",func="foo",
23107 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23108 frame=@{level="10",addr="0x000107a4",func="foo",
23109 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23110 frame=@{level="11",addr="0x00010738",func="main",
23111 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4"@}]
23115 Show frames between @var{low_frame} and @var{high_frame}:
23119 -stack-list-frames 3 5
23121 [frame=@{level="3",addr="0x000107a4",func="foo",
23122 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23123 frame=@{level="4",addr="0x000107a4",func="foo",
23124 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23125 frame=@{level="5",addr="0x000107a4",func="foo",
23126 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
23130 Show a single frame:
23134 -stack-list-frames 3 3
23136 [frame=@{level="3",addr="0x000107a4",func="foo",
23137 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
23142 @subheading The @code{-stack-list-locals} Command
23143 @findex -stack-list-locals
23145 @subsubheading Synopsis
23148 -stack-list-locals @var{print-values}
23151 Display the local variable names for the selected frame. If
23152 @var{print-values} is 0 or @code{--no-values}, print only the names of
23153 the variables; if it is 1 or @code{--all-values}, print also their
23154 values; and if it is 2 or @code{--simple-values}, print the name,
23155 type and value for simple data types and the name and type for arrays,
23156 structures and unions. In this last case, a frontend can immediately
23157 display the value of simple data types and create variable objects for
23158 other data types when the user wishes to explore their values in
23161 @subsubheading @value{GDBN} Command
23163 @samp{info locals} in @value{GDBN}, @samp{gdb_get_locals} in @code{gdbtk}.
23165 @subsubheading Example
23169 -stack-list-locals 0
23170 ^done,locals=[name="A",name="B",name="C"]
23172 -stack-list-locals --all-values
23173 ^done,locals=[@{name="A",value="1"@},@{name="B",value="2"@},
23174 @{name="C",value="@{1, 2, 3@}"@}]
23175 -stack-list-locals --simple-values
23176 ^done,locals=[@{name="A",type="int",value="1"@},
23177 @{name="B",type="int",value="2"@},@{name="C",type="int [3]"@}]
23182 @subheading The @code{-stack-select-frame} Command
23183 @findex -stack-select-frame
23185 @subsubheading Synopsis
23188 -stack-select-frame @var{framenum}
23191 Change the selected frame. Select a different frame @var{framenum} on
23194 This command in deprecated in favor of passing the @samp{--frame}
23195 option to every command.
23197 @subsubheading @value{GDBN} Command
23199 The corresponding @value{GDBN} commands are @samp{frame}, @samp{up},
23200 @samp{down}, @samp{select-frame}, @samp{up-silent}, and @samp{down-silent}.
23202 @subsubheading Example
23206 -stack-select-frame 2
23211 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
23212 @node GDB/MI Variable Objects
23213 @section @sc{gdb/mi} Variable Objects
23217 @subheading Motivation for Variable Objects in @sc{gdb/mi}
23219 For the implementation of a variable debugger window (locals, watched
23220 expressions, etc.), we are proposing the adaptation of the existing code
23221 used by @code{Insight}.
23223 The two main reasons for that are:
23227 It has been proven in practice (it is already on its second generation).
23230 It will shorten development time (needless to say how important it is
23234 The original interface was designed to be used by Tcl code, so it was
23235 slightly changed so it could be used through @sc{gdb/mi}. This section
23236 describes the @sc{gdb/mi} operations that will be available and gives some
23237 hints about their use.
23239 @emph{Note}: In addition to the set of operations described here, we
23240 expect the @sc{gui} implementation of a variable window to require, at
23241 least, the following operations:
23244 @item @code{-gdb-show} @code{output-radix}
23245 @item @code{-stack-list-arguments}
23246 @item @code{-stack-list-locals}
23247 @item @code{-stack-select-frame}
23252 @subheading Introduction to Variable Objects
23254 @cindex variable objects in @sc{gdb/mi}
23256 Variable objects are "object-oriented" MI interface for examining and
23257 changing values of expressions. Unlike some other MI interfaces that
23258 work with expressions, variable objects are specifically designed for
23259 simple and efficient presentation in the frontend. A variable object
23260 is identified by string name. When a variable object is created, the
23261 frontend specifies the expression for that variable object. The
23262 expression can be a simple variable, or it can be an arbitrary complex
23263 expression, and can even involve CPU registers. After creating a
23264 variable object, the frontend can invoke other variable object
23265 operations---for example to obtain or change the value of a variable
23266 object, or to change display format.
23268 Variable objects have hierarchical tree structure. Any variable object
23269 that corresponds to a composite type, such as structure in C, has
23270 a number of child variable objects, for example corresponding to each
23271 element of a structure. A child variable object can itself have
23272 children, recursively. Recursion ends when we reach
23273 leaf variable objects, which always have built-in types. Child variable
23274 objects are created only by explicit request, so if a frontend
23275 is not interested in the children of a particular variable object, no
23276 child will be created.
23278 For a leaf variable object it is possible to obtain its value as a
23279 string, or set the value from a string. String value can be also
23280 obtained for a non-leaf variable object, but it's generally a string
23281 that only indicates the type of the object, and does not list its
23282 contents. Assignment to a non-leaf variable object is not allowed.
23284 A frontend does not need to read the values of all variable objects each time
23285 the program stops. Instead, MI provides an update command that lists all
23286 variable objects whose values has changed since the last update
23287 operation. This considerably reduces the amount of data that must
23288 be transferred to the frontend. As noted above, children variable
23289 objects are created on demand, and only leaf variable objects have a
23290 real value. As result, gdb will read target memory only for leaf
23291 variables that frontend has created.
23293 The automatic update is not always desirable. For example, a frontend
23294 might want to keep a value of some expression for future reference,
23295 and never update it. For another example, fetching memory is
23296 relatively slow for embedded targets, so a frontend might want
23297 to disable automatic update for the variables that are either not
23298 visible on the screen, or ``closed''. This is possible using so
23299 called ``frozen variable objects''. Such variable objects are never
23300 implicitly updated.
23302 Variable objects can be either @dfn{fixed} or @dfn{floating}. For the
23303 fixed variable object, the expression is parsed when the variable
23304 object is created, including associating identifiers to specific
23305 variables. The meaning of expression never changes. For a floating
23306 variable object the values of variables whose names appear in the
23307 expressions are re-evaluated every time in the context of the current
23308 frame. Consider this example:
23313 struct work_state state;
23320 If a fixed variable object for the @code{state} variable is created in
23321 this function, and we enter the recursive call, the the variable
23322 object will report the value of @code{state} in the top-level
23323 @code{do_work} invocation. On the other hand, a floating variable
23324 object will report the value of @code{state} in the current frame.
23326 If an expression specified when creating a fixed variable object
23327 refers to a local variable, the variable object becomes bound to the
23328 thread and frame in which the variable object is created. When such
23329 variable object is updated, @value{GDBN} makes sure that the
23330 thread/frame combination the variable object is bound to still exists,
23331 and re-evaluates the variable object in context of that thread/frame.
23333 The following is the complete set of @sc{gdb/mi} operations defined to
23334 access this functionality:
23336 @multitable @columnfractions .4 .6
23337 @item @strong{Operation}
23338 @tab @strong{Description}
23340 @item @code{-var-create}
23341 @tab create a variable object
23342 @item @code{-var-delete}
23343 @tab delete the variable object and/or its children
23344 @item @code{-var-set-format}
23345 @tab set the display format of this variable
23346 @item @code{-var-show-format}
23347 @tab show the display format of this variable
23348 @item @code{-var-info-num-children}
23349 @tab tells how many children this object has
23350 @item @code{-var-list-children}
23351 @tab return a list of the object's children
23352 @item @code{-var-info-type}
23353 @tab show the type of this variable object
23354 @item @code{-var-info-expression}
23355 @tab print parent-relative expression that this variable object represents
23356 @item @code{-var-info-path-expression}
23357 @tab print full expression that this variable object represents
23358 @item @code{-var-show-attributes}
23359 @tab is this variable editable? does it exist here?
23360 @item @code{-var-evaluate-expression}
23361 @tab get the value of this variable
23362 @item @code{-var-assign}
23363 @tab set the value of this variable
23364 @item @code{-var-update}
23365 @tab update the variable and its children
23366 @item @code{-var-set-frozen}
23367 @tab set frozeness attribute
23370 In the next subsection we describe each operation in detail and suggest
23371 how it can be used.
23373 @subheading Description And Use of Operations on Variable Objects
23375 @subheading The @code{-var-create} Command
23376 @findex -var-create
23378 @subsubheading Synopsis
23381 -var-create @{@var{name} | "-"@}
23382 @{@var{frame-addr} | "*" | "@@"@} @var{expression}
23385 This operation creates a variable object, which allows the monitoring of
23386 a variable, the result of an expression, a memory cell or a CPU
23389 The @var{name} parameter is the string by which the object can be
23390 referenced. It must be unique. If @samp{-} is specified, the varobj
23391 system will generate a string ``varNNNNNN'' automatically. It will be
23392 unique provided that one does not specify @var{name} of that format.
23393 The command fails if a duplicate name is found.
23395 The frame under which the expression should be evaluated can be
23396 specified by @var{frame-addr}. A @samp{*} indicates that the current
23397 frame should be used. A @samp{@@} indicates that a floating variable
23398 object must be created.
23400 @var{expression} is any expression valid on the current language set (must not
23401 begin with a @samp{*}), or one of the following:
23405 @samp{*@var{addr}}, where @var{addr} is the address of a memory cell
23408 @samp{*@var{addr}-@var{addr}} --- a memory address range (TBD)
23411 @samp{$@var{regname}} --- a CPU register name
23414 @subsubheading Result
23416 This operation returns the name, number of children and the type of the
23417 object created. Type is returned as a string as the ones generated by
23418 the @value{GDBN} CLI. If a fixed variable object is bound to a
23419 specific thread, the thread is is also printed:
23422 name="@var{name}",numchild="@var{N}",type="@var{type}",thread-id="@var{M}"
23426 @subheading The @code{-var-delete} Command
23427 @findex -var-delete
23429 @subsubheading Synopsis
23432 -var-delete [ -c ] @var{name}
23435 Deletes a previously created variable object and all of its children.
23436 With the @samp{-c} option, just deletes the children.
23438 Returns an error if the object @var{name} is not found.
23441 @subheading The @code{-var-set-format} Command
23442 @findex -var-set-format
23444 @subsubheading Synopsis
23447 -var-set-format @var{name} @var{format-spec}
23450 Sets the output format for the value of the object @var{name} to be
23453 @anchor{-var-set-format}
23454 The syntax for the @var{format-spec} is as follows:
23457 @var{format-spec} @expansion{}
23458 @{binary | decimal | hexadecimal | octal | natural@}
23461 The natural format is the default format choosen automatically
23462 based on the variable type (like decimal for an @code{int}, hex
23463 for pointers, etc.).
23465 For a variable with children, the format is set only on the
23466 variable itself, and the children are not affected.
23468 @subheading The @code{-var-show-format} Command
23469 @findex -var-show-format
23471 @subsubheading Synopsis
23474 -var-show-format @var{name}
23477 Returns the format used to display the value of the object @var{name}.
23480 @var{format} @expansion{}
23485 @subheading The @code{-var-info-num-children} Command
23486 @findex -var-info-num-children
23488 @subsubheading Synopsis
23491 -var-info-num-children @var{name}
23494 Returns the number of children of a variable object @var{name}:
23501 @subheading The @code{-var-list-children} Command
23502 @findex -var-list-children
23504 @subsubheading Synopsis
23507 -var-list-children [@var{print-values}] @var{name}
23509 @anchor{-var-list-children}
23511 Return a list of the children of the specified variable object and
23512 create variable objects for them, if they do not already exist. With
23513 a single argument or if @var{print-values} has a value for of 0 or
23514 @code{--no-values}, print only the names of the variables; if
23515 @var{print-values} is 1 or @code{--all-values}, also print their
23516 values; and if it is 2 or @code{--simple-values} print the name and
23517 value for simple data types and just the name for arrays, structures
23520 For each child the following results are returned:
23525 Name of the variable object created for this child.
23528 The expression to be shown to the user by the front end to designate this child.
23529 For example this may be the name of a structure member.
23531 For C/C@t{++} structures there are several pseudo children returned to
23532 designate access qualifiers. For these pseudo children @var{exp} is
23533 @samp{public}, @samp{private}, or @samp{protected}. In this case the
23534 type and value are not present.
23537 Number of children this child has.
23540 The type of the child.
23543 If values were requested, this is the value.
23546 If this variable object is associated with a thread, this is the thread id.
23547 Otherwise this result is not present.
23550 If the variable object is frozen, this variable will be present with a value of 1.
23553 @subsubheading Example
23557 -var-list-children n
23558 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
23559 numchild=@var{n},type=@var{type}@},@r{(repeats N times)}]
23561 -var-list-children --all-values n
23562 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
23563 numchild=@var{n},value=@var{value},type=@var{type}@},@r{(repeats N times)}]
23567 @subheading The @code{-var-info-type} Command
23568 @findex -var-info-type
23570 @subsubheading Synopsis
23573 -var-info-type @var{name}
23576 Returns the type of the specified variable @var{name}. The type is
23577 returned as a string in the same format as it is output by the
23581 type=@var{typename}
23585 @subheading The @code{-var-info-expression} Command
23586 @findex -var-info-expression
23588 @subsubheading Synopsis
23591 -var-info-expression @var{name}
23594 Returns a string that is suitable for presenting this
23595 variable object in user interface. The string is generally
23596 not valid expression in the current language, and cannot be evaluated.
23598 For example, if @code{a} is an array, and variable object
23599 @code{A} was created for @code{a}, then we'll get this output:
23602 (gdb) -var-info-expression A.1
23603 ^done,lang="C",exp="1"
23607 Here, the values of @code{lang} can be @code{@{"C" | "C++" | "Java"@}}.
23609 Note that the output of the @code{-var-list-children} command also
23610 includes those expressions, so the @code{-var-info-expression} command
23613 @subheading The @code{-var-info-path-expression} Command
23614 @findex -var-info-path-expression
23616 @subsubheading Synopsis
23619 -var-info-path-expression @var{name}
23622 Returns an expression that can be evaluated in the current
23623 context and will yield the same value that a variable object has.
23624 Compare this with the @code{-var-info-expression} command, which
23625 result can be used only for UI presentation. Typical use of
23626 the @code{-var-info-path-expression} command is creating a
23627 watchpoint from a variable object.
23629 For example, suppose @code{C} is a C@t{++} class, derived from class
23630 @code{Base}, and that the @code{Base} class has a member called
23631 @code{m_size}. Assume a variable @code{c} is has the type of
23632 @code{C} and a variable object @code{C} was created for variable
23633 @code{c}. Then, we'll get this output:
23635 (gdb) -var-info-path-expression C.Base.public.m_size
23636 ^done,path_expr=((Base)c).m_size)
23639 @subheading The @code{-var-show-attributes} Command
23640 @findex -var-show-attributes
23642 @subsubheading Synopsis
23645 -var-show-attributes @var{name}
23648 List attributes of the specified variable object @var{name}:
23651 status=@var{attr} [ ( ,@var{attr} )* ]
23655 where @var{attr} is @code{@{ @{ editable | noneditable @} | TBD @}}.
23657 @subheading The @code{-var-evaluate-expression} Command
23658 @findex -var-evaluate-expression
23660 @subsubheading Synopsis
23663 -var-evaluate-expression [-f @var{format-spec}] @var{name}
23666 Evaluates the expression that is represented by the specified variable
23667 object and returns its value as a string. The format of the string
23668 can be specified with the @samp{-f} option. The possible values of
23669 this option are the same as for @code{-var-set-format}
23670 (@pxref{-var-set-format}). If the @samp{-f} option is not specified,
23671 the current display format will be used. The current display format
23672 can be changed using the @code{-var-set-format} command.
23678 Note that one must invoke @code{-var-list-children} for a variable
23679 before the value of a child variable can be evaluated.
23681 @subheading The @code{-var-assign} Command
23682 @findex -var-assign
23684 @subsubheading Synopsis
23687 -var-assign @var{name} @var{expression}
23690 Assigns the value of @var{expression} to the variable object specified
23691 by @var{name}. The object must be @samp{editable}. If the variable's
23692 value is altered by the assign, the variable will show up in any
23693 subsequent @code{-var-update} list.
23695 @subsubheading Example
23703 ^done,changelist=[@{name="var1",in_scope="true",type_changed="false"@}]
23707 @subheading The @code{-var-update} Command
23708 @findex -var-update
23710 @subsubheading Synopsis
23713 -var-update [@var{print-values}] @{@var{name} | "*"@}
23716 Reevaluate the expressions corresponding to the variable object
23717 @var{name} and all its direct and indirect children, and return the
23718 list of variable objects whose values have changed; @var{name} must
23719 be a root variable object. Here, ``changed'' means that the result of
23720 @code{-var-evaluate-expression} before and after the
23721 @code{-var-update} is different. If @samp{*} is used as the variable
23722 object names, all existing variable objects are updated, except
23723 for frozen ones (@pxref{-var-set-frozen}). The option
23724 @var{print-values} determines whether both names and values, or just
23725 names are printed. The possible values of this option are the same
23726 as for @code{-var-list-children} (@pxref{-var-list-children}). It is
23727 recommended to use the @samp{--all-values} option, to reduce the
23728 number of MI commands needed on each program stop.
23730 With the @samp{*} parameter, if a variable object is bound to a
23731 currently running thread, it will not be updated, without any
23734 @subsubheading Example
23741 -var-update --all-values var1
23742 ^done,changelist=[@{name="var1",value="3",in_scope="true",
23743 type_changed="false"@}]
23747 @anchor{-var-update}
23748 The field in_scope may take three values:
23752 The variable object's current value is valid.
23755 The variable object does not currently hold a valid value but it may
23756 hold one in the future if its associated expression comes back into
23760 The variable object no longer holds a valid value.
23761 This can occur when the executable file being debugged has changed,
23762 either through recompilation or by using the @value{GDBN} @code{file}
23763 command. The front end should normally choose to delete these variable
23767 In the future new values may be added to this list so the front should
23768 be prepared for this possibility. @xref{GDB/MI Development and Front Ends, ,@sc{GDB/MI} Development and Front Ends}.
23770 @subheading The @code{-var-set-frozen} Command
23771 @findex -var-set-frozen
23772 @anchor{-var-set-frozen}
23774 @subsubheading Synopsis
23777 -var-set-frozen @var{name} @var{flag}
23780 Set the frozenness flag on the variable object @var{name}. The
23781 @var{flag} parameter should be either @samp{1} to make the variable
23782 frozen or @samp{0} to make it unfrozen. If a variable object is
23783 frozen, then neither itself, nor any of its children, are
23784 implicitly updated by @code{-var-update} of
23785 a parent variable or by @code{-var-update *}. Only
23786 @code{-var-update} of the variable itself will update its value and
23787 values of its children. After a variable object is unfrozen, it is
23788 implicitly updated by all subsequent @code{-var-update} operations.
23789 Unfreezing a variable does not update it, only subsequent
23790 @code{-var-update} does.
23792 @subsubheading Example
23796 -var-set-frozen V 1
23801 @subheading The @code{-var-set-visualizer} command
23802 @findex -var-set-visualizer
23803 @anchor{-var-set-visualizer}
23805 @subsubheading Synopsis
23808 -var-set-visualizer @var{name} @var{visualizer}
23811 Set a visualizer for the variable object @var{name}.
23813 @var{visualizer} is the visualizer to use. The special value
23814 @samp{None} means to disable any visualizer in use.
23816 If not @samp{None}, @var{visualizer} must be a Python expression.
23817 This expression must evaluate to a callable object which accepts a
23818 single argument. @value{GDBN} will call this object with the value of
23819 the varobj @var{name} as an argument (this is done so that the same
23820 Python pretty-printing code can be used for both the CLI and MI).
23821 When called, this object must return an object which conforms to the
23822 pretty-printing interface (@pxref{Pretty Printing}).
23824 The pre-defined function @code{gdb.default_visualizer} may be used to
23825 select a visualizer by following the built-in process
23826 (@pxref{Selecting Pretty-Printers}). This is done automatically when
23827 a varobj is created, and so ordinarily is not needed.
23829 This feature is only available if Python support is enabled. The MI
23830 command @code{-list-features} (@pxref{GDB/MI Miscellaneous Commands})
23831 can be used to check this.
23833 @subsubheading Example
23835 Resetting the visualizer:
23839 -var-set-visualizer V None
23843 Reselecting the default (type-based) visualizer:
23847 -var-set-visualizer V gdb.default_visualizer
23851 Suppose @code{SomeClass} is a visualizer class. A lambda expression
23852 can be used to instantiate this class for a varobj:
23856 -var-set-visualizer V "lambda val: SomeClass()"
23860 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
23861 @node GDB/MI Data Manipulation
23862 @section @sc{gdb/mi} Data Manipulation
23864 @cindex data manipulation, in @sc{gdb/mi}
23865 @cindex @sc{gdb/mi}, data manipulation
23866 This section describes the @sc{gdb/mi} commands that manipulate data:
23867 examine memory and registers, evaluate expressions, etc.
23869 @c REMOVED FROM THE INTERFACE.
23870 @c @subheading -data-assign
23871 @c Change the value of a program variable. Plenty of side effects.
23872 @c @subsubheading GDB Command
23874 @c @subsubheading Example
23877 @subheading The @code{-data-disassemble} Command
23878 @findex -data-disassemble
23880 @subsubheading Synopsis
23884 [ -s @var{start-addr} -e @var{end-addr} ]
23885 | [ -f @var{filename} -l @var{linenum} [ -n @var{lines} ] ]
23893 @item @var{start-addr}
23894 is the beginning address (or @code{$pc})
23895 @item @var{end-addr}
23897 @item @var{filename}
23898 is the name of the file to disassemble
23899 @item @var{linenum}
23900 is the line number to disassemble around
23902 is the number of disassembly lines to be produced. If it is -1,
23903 the whole function will be disassembled, in case no @var{end-addr} is
23904 specified. If @var{end-addr} is specified as a non-zero value, and
23905 @var{lines} is lower than the number of disassembly lines between
23906 @var{start-addr} and @var{end-addr}, only @var{lines} lines are
23907 displayed; if @var{lines} is higher than the number of lines between
23908 @var{start-addr} and @var{end-addr}, only the lines up to @var{end-addr}
23911 is either 0 (meaning only disassembly) or 1 (meaning mixed source and
23915 @subsubheading Result
23917 The output for each instruction is composed of four fields:
23926 Note that whatever included in the instruction field, is not manipulated
23927 directly by @sc{gdb/mi}, i.e., it is not possible to adjust its format.
23929 @subsubheading @value{GDBN} Command
23931 There's no direct mapping from this command to the CLI.
23933 @subsubheading Example
23935 Disassemble from the current value of @code{$pc} to @code{$pc + 20}:
23939 -data-disassemble -s $pc -e "$pc + 20" -- 0
23942 @{address="0x000107c0",func-name="main",offset="4",
23943 inst="mov 2, %o0"@},
23944 @{address="0x000107c4",func-name="main",offset="8",
23945 inst="sethi %hi(0x11800), %o2"@},
23946 @{address="0x000107c8",func-name="main",offset="12",
23947 inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"@},
23948 @{address="0x000107cc",func-name="main",offset="16",
23949 inst="sethi %hi(0x11800), %o2"@},
23950 @{address="0x000107d0",func-name="main",offset="20",
23951 inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"@}]
23955 Disassemble the whole @code{main} function. Line 32 is part of
23959 -data-disassemble -f basics.c -l 32 -- 0
23961 @{address="0x000107bc",func-name="main",offset="0",
23962 inst="save %sp, -112, %sp"@},
23963 @{address="0x000107c0",func-name="main",offset="4",
23964 inst="mov 2, %o0"@},
23965 @{address="0x000107c4",func-name="main",offset="8",
23966 inst="sethi %hi(0x11800), %o2"@},
23968 @{address="0x0001081c",func-name="main",offset="96",inst="ret "@},
23969 @{address="0x00010820",func-name="main",offset="100",inst="restore "@}]
23973 Disassemble 3 instructions from the start of @code{main}:
23977 -data-disassemble -f basics.c -l 32 -n 3 -- 0
23979 @{address="0x000107bc",func-name="main",offset="0",
23980 inst="save %sp, -112, %sp"@},
23981 @{address="0x000107c0",func-name="main",offset="4",
23982 inst="mov 2, %o0"@},
23983 @{address="0x000107c4",func-name="main",offset="8",
23984 inst="sethi %hi(0x11800), %o2"@}]
23988 Disassemble 3 instructions from the start of @code{main} in mixed mode:
23992 -data-disassemble -f basics.c -l 32 -n 3 -- 1
23994 src_and_asm_line=@{line="31",
23995 file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
23996 testsuite/gdb.mi/basics.c",line_asm_insn=[
23997 @{address="0x000107bc",func-name="main",offset="0",
23998 inst="save %sp, -112, %sp"@}]@},
23999 src_and_asm_line=@{line="32",
24000 file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
24001 testsuite/gdb.mi/basics.c",line_asm_insn=[
24002 @{address="0x000107c0",func-name="main",offset="4",
24003 inst="mov 2, %o0"@},
24004 @{address="0x000107c4",func-name="main",offset="8",
24005 inst="sethi %hi(0x11800), %o2"@}]@}]
24010 @subheading The @code{-data-evaluate-expression} Command
24011 @findex -data-evaluate-expression
24013 @subsubheading Synopsis
24016 -data-evaluate-expression @var{expr}
24019 Evaluate @var{expr} as an expression. The expression could contain an
24020 inferior function call. The function call will execute synchronously.
24021 If the expression contains spaces, it must be enclosed in double quotes.
24023 @subsubheading @value{GDBN} Command
24025 The corresponding @value{GDBN} commands are @samp{print}, @samp{output}, and
24026 @samp{call}. In @code{gdbtk} only, there's a corresponding
24027 @samp{gdb_eval} command.
24029 @subsubheading Example
24031 In the following example, the numbers that precede the commands are the
24032 @dfn{tokens} described in @ref{GDB/MI Command Syntax, ,@sc{gdb/mi}
24033 Command Syntax}. Notice how @sc{gdb/mi} returns the same tokens in its
24037 211-data-evaluate-expression A
24040 311-data-evaluate-expression &A
24041 311^done,value="0xefffeb7c"
24043 411-data-evaluate-expression A+3
24046 511-data-evaluate-expression "A + 3"
24052 @subheading The @code{-data-list-changed-registers} Command
24053 @findex -data-list-changed-registers
24055 @subsubheading Synopsis
24058 -data-list-changed-registers
24061 Display a list of the registers that have changed.
24063 @subsubheading @value{GDBN} Command
24065 @value{GDBN} doesn't have a direct analog for this command; @code{gdbtk}
24066 has the corresponding command @samp{gdb_changed_register_list}.
24068 @subsubheading Example
24070 On a PPC MBX board:
24078 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame=@{
24079 func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c",
24082 -data-list-changed-registers
24083 ^done,changed-registers=["0","1","2","4","5","6","7","8","9",
24084 "10","11","13","14","15","16","17","18","19","20","21","22","23",
24085 "24","25","26","27","28","30","31","64","65","66","67","69"]
24090 @subheading The @code{-data-list-register-names} Command
24091 @findex -data-list-register-names
24093 @subsubheading Synopsis
24096 -data-list-register-names [ ( @var{regno} )+ ]
24099 Show a list of register names for the current target. If no arguments
24100 are given, it shows a list of the names of all the registers. If
24101 integer numbers are given as arguments, it will print a list of the
24102 names of the registers corresponding to the arguments. To ensure
24103 consistency between a register name and its number, the output list may
24104 include empty register names.
24106 @subsubheading @value{GDBN} Command
24108 @value{GDBN} does not have a command which corresponds to
24109 @samp{-data-list-register-names}. In @code{gdbtk} there is a
24110 corresponding command @samp{gdb_regnames}.
24112 @subsubheading Example
24114 For the PPC MBX board:
24117 -data-list-register-names
24118 ^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7",
24119 "r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18",
24120 "r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29",
24121 "r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9",
24122 "f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20",
24123 "f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31",
24124 "", "pc","ps","cr","lr","ctr","xer"]
24126 -data-list-register-names 1 2 3
24127 ^done,register-names=["r1","r2","r3"]
24131 @subheading The @code{-data-list-register-values} Command
24132 @findex -data-list-register-values
24134 @subsubheading Synopsis
24137 -data-list-register-values @var{fmt} [ ( @var{regno} )*]
24140 Display the registers' contents. @var{fmt} is the format according to
24141 which the registers' contents are to be returned, followed by an optional
24142 list of numbers specifying the registers to display. A missing list of
24143 numbers indicates that the contents of all the registers must be returned.
24145 Allowed formats for @var{fmt} are:
24162 @subsubheading @value{GDBN} Command
24164 The corresponding @value{GDBN} commands are @samp{info reg}, @samp{info
24165 all-reg}, and (in @code{gdbtk}) @samp{gdb_fetch_registers}.
24167 @subsubheading Example
24169 For a PPC MBX board (note: line breaks are for readability only, they
24170 don't appear in the actual output):
24174 -data-list-register-values r 64 65
24175 ^done,register-values=[@{number="64",value="0xfe00a300"@},
24176 @{number="65",value="0x00029002"@}]
24178 -data-list-register-values x
24179 ^done,register-values=[@{number="0",value="0xfe0043c8"@},
24180 @{number="1",value="0x3fff88"@},@{number="2",value="0xfffffffe"@},
24181 @{number="3",value="0x0"@},@{number="4",value="0xa"@},
24182 @{number="5",value="0x3fff68"@},@{number="6",value="0x3fff58"@},
24183 @{number="7",value="0xfe011e98"@},@{number="8",value="0x2"@},
24184 @{number="9",value="0xfa202820"@},@{number="10",value="0xfa202808"@},
24185 @{number="11",value="0x1"@},@{number="12",value="0x0"@},
24186 @{number="13",value="0x4544"@},@{number="14",value="0xffdfffff"@},
24187 @{number="15",value="0xffffffff"@},@{number="16",value="0xfffffeff"@},
24188 @{number="17",value="0xefffffed"@},@{number="18",value="0xfffffffe"@},
24189 @{number="19",value="0xffffffff"@},@{number="20",value="0xffffffff"@},
24190 @{number="21",value="0xffffffff"@},@{number="22",value="0xfffffff7"@},
24191 @{number="23",value="0xffffffff"@},@{number="24",value="0xffffffff"@},
24192 @{number="25",value="0xffffffff"@},@{number="26",value="0xfffffffb"@},
24193 @{number="27",value="0xffffffff"@},@{number="28",value="0xf7bfffff"@},
24194 @{number="29",value="0x0"@},@{number="30",value="0xfe010000"@},
24195 @{number="31",value="0x0"@},@{number="32",value="0x0"@},
24196 @{number="33",value="0x0"@},@{number="34",value="0x0"@},
24197 @{number="35",value="0x0"@},@{number="36",value="0x0"@},
24198 @{number="37",value="0x0"@},@{number="38",value="0x0"@},
24199 @{number="39",value="0x0"@},@{number="40",value="0x0"@},
24200 @{number="41",value="0x0"@},@{number="42",value="0x0"@},
24201 @{number="43",value="0x0"@},@{number="44",value="0x0"@},
24202 @{number="45",value="0x0"@},@{number="46",value="0x0"@},
24203 @{number="47",value="0x0"@},@{number="48",value="0x0"@},
24204 @{number="49",value="0x0"@},@{number="50",value="0x0"@},
24205 @{number="51",value="0x0"@},@{number="52",value="0x0"@},
24206 @{number="53",value="0x0"@},@{number="54",value="0x0"@},
24207 @{number="55",value="0x0"@},@{number="56",value="0x0"@},
24208 @{number="57",value="0x0"@},@{number="58",value="0x0"@},
24209 @{number="59",value="0x0"@},@{number="60",value="0x0"@},
24210 @{number="61",value="0x0"@},@{number="62",value="0x0"@},
24211 @{number="63",value="0x0"@},@{number="64",value="0xfe00a300"@},
24212 @{number="65",value="0x29002"@},@{number="66",value="0x202f04b5"@},
24213 @{number="67",value="0xfe0043b0"@},@{number="68",value="0xfe00b3e4"@},
24214 @{number="69",value="0x20002b03"@}]
24219 @subheading The @code{-data-read-memory} Command
24220 @findex -data-read-memory
24222 @subsubheading Synopsis
24225 -data-read-memory [ -o @var{byte-offset} ]
24226 @var{address} @var{word-format} @var{word-size}
24227 @var{nr-rows} @var{nr-cols} [ @var{aschar} ]
24234 @item @var{address}
24235 An expression specifying the address of the first memory word to be
24236 read. Complex expressions containing embedded white space should be
24237 quoted using the C convention.
24239 @item @var{word-format}
24240 The format to be used to print the memory words. The notation is the
24241 same as for @value{GDBN}'s @code{print} command (@pxref{Output Formats,
24244 @item @var{word-size}
24245 The size of each memory word in bytes.
24247 @item @var{nr-rows}
24248 The number of rows in the output table.
24250 @item @var{nr-cols}
24251 The number of columns in the output table.
24254 If present, indicates that each row should include an @sc{ascii} dump. The
24255 value of @var{aschar} is used as a padding character when a byte is not a
24256 member of the printable @sc{ascii} character set (printable @sc{ascii}
24257 characters are those whose code is between 32 and 126, inclusively).
24259 @item @var{byte-offset}
24260 An offset to add to the @var{address} before fetching memory.
24263 This command displays memory contents as a table of @var{nr-rows} by
24264 @var{nr-cols} words, each word being @var{word-size} bytes. In total,
24265 @code{@var{nr-rows} * @var{nr-cols} * @var{word-size}} bytes are read
24266 (returned as @samp{total-bytes}). Should less than the requested number
24267 of bytes be returned by the target, the missing words are identified
24268 using @samp{N/A}. The number of bytes read from the target is returned
24269 in @samp{nr-bytes} and the starting address used to read memory in
24272 The address of the next/previous row or page is available in
24273 @samp{next-row} and @samp{prev-row}, @samp{next-page} and
24276 @subsubheading @value{GDBN} Command
24278 The corresponding @value{GDBN} command is @samp{x}. @code{gdbtk} has
24279 @samp{gdb_get_mem} memory read command.
24281 @subsubheading Example
24283 Read six bytes of memory starting at @code{bytes+6} but then offset by
24284 @code{-6} bytes. Format as three rows of two columns. One byte per
24285 word. Display each word in hex.
24289 9-data-read-memory -o -6 -- bytes+6 x 1 3 2
24290 9^done,addr="0x00001390",nr-bytes="6",total-bytes="6",
24291 next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396",
24292 prev-page="0x0000138a",memory=[
24293 @{addr="0x00001390",data=["0x00","0x01"]@},
24294 @{addr="0x00001392",data=["0x02","0x03"]@},
24295 @{addr="0x00001394",data=["0x04","0x05"]@}]
24299 Read two bytes of memory starting at address @code{shorts + 64} and
24300 display as a single word formatted in decimal.
24304 5-data-read-memory shorts+64 d 2 1 1
24305 5^done,addr="0x00001510",nr-bytes="2",total-bytes="2",
24306 next-row="0x00001512",prev-row="0x0000150e",
24307 next-page="0x00001512",prev-page="0x0000150e",memory=[
24308 @{addr="0x00001510",data=["128"]@}]
24312 Read thirty two bytes of memory starting at @code{bytes+16} and format
24313 as eight rows of four columns. Include a string encoding with @samp{x}
24314 used as the non-printable character.
24318 4-data-read-memory bytes+16 x 1 8 4 x
24319 4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32",
24320 next-row="0x000013c0",prev-row="0x0000139c",
24321 next-page="0x000013c0",prev-page="0x00001380",memory=[
24322 @{addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"@},
24323 @{addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"@},
24324 @{addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"@},
24325 @{addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"@},
24326 @{addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"@},
24327 @{addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"@},
24328 @{addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"@},
24329 @{addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"@}]
24333 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24334 @node GDB/MI Tracepoint Commands
24335 @section @sc{gdb/mi} Tracepoint Commands
24337 The tracepoint commands are not yet implemented.
24339 @c @subheading -trace-actions
24341 @c @subheading -trace-delete
24343 @c @subheading -trace-disable
24345 @c @subheading -trace-dump
24347 @c @subheading -trace-enable
24349 @c @subheading -trace-exists
24351 @c @subheading -trace-find
24353 @c @subheading -trace-frame-number
24355 @c @subheading -trace-info
24357 @c @subheading -trace-insert
24359 @c @subheading -trace-list
24361 @c @subheading -trace-pass-count
24363 @c @subheading -trace-save
24365 @c @subheading -trace-start
24367 @c @subheading -trace-stop
24370 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24371 @node GDB/MI Symbol Query
24372 @section @sc{gdb/mi} Symbol Query Commands
24376 @subheading The @code{-symbol-info-address} Command
24377 @findex -symbol-info-address
24379 @subsubheading Synopsis
24382 -symbol-info-address @var{symbol}
24385 Describe where @var{symbol} is stored.
24387 @subsubheading @value{GDBN} Command
24389 The corresponding @value{GDBN} command is @samp{info address}.
24391 @subsubheading Example
24395 @subheading The @code{-symbol-info-file} Command
24396 @findex -symbol-info-file
24398 @subsubheading Synopsis
24404 Show the file for the symbol.
24406 @subsubheading @value{GDBN} Command
24408 There's no equivalent @value{GDBN} command. @code{gdbtk} has
24409 @samp{gdb_find_file}.
24411 @subsubheading Example
24415 @subheading The @code{-symbol-info-function} Command
24416 @findex -symbol-info-function
24418 @subsubheading Synopsis
24421 -symbol-info-function
24424 Show which function the symbol lives in.
24426 @subsubheading @value{GDBN} Command
24428 @samp{gdb_get_function} in @code{gdbtk}.
24430 @subsubheading Example
24434 @subheading The @code{-symbol-info-line} Command
24435 @findex -symbol-info-line
24437 @subsubheading Synopsis
24443 Show the core addresses of the code for a source line.
24445 @subsubheading @value{GDBN} Command
24447 The corresponding @value{GDBN} command is @samp{info line}.
24448 @code{gdbtk} has the @samp{gdb_get_line} and @samp{gdb_get_file} commands.
24450 @subsubheading Example
24454 @subheading The @code{-symbol-info-symbol} Command
24455 @findex -symbol-info-symbol
24457 @subsubheading Synopsis
24460 -symbol-info-symbol @var{addr}
24463 Describe what symbol is at location @var{addr}.
24465 @subsubheading @value{GDBN} Command
24467 The corresponding @value{GDBN} command is @samp{info symbol}.
24469 @subsubheading Example
24473 @subheading The @code{-symbol-list-functions} Command
24474 @findex -symbol-list-functions
24476 @subsubheading Synopsis
24479 -symbol-list-functions
24482 List the functions in the executable.
24484 @subsubheading @value{GDBN} Command
24486 @samp{info functions} in @value{GDBN}, @samp{gdb_listfunc} and
24487 @samp{gdb_search} in @code{gdbtk}.
24489 @subsubheading Example
24494 @subheading The @code{-symbol-list-lines} Command
24495 @findex -symbol-list-lines
24497 @subsubheading Synopsis
24500 -symbol-list-lines @var{filename}
24503 Print the list of lines that contain code and their associated program
24504 addresses for the given source filename. The entries are sorted in
24505 ascending PC order.
24507 @subsubheading @value{GDBN} Command
24509 There is no corresponding @value{GDBN} command.
24511 @subsubheading Example
24514 -symbol-list-lines basics.c
24515 ^done,lines=[@{pc="0x08048554",line="7"@},@{pc="0x0804855a",line="8"@}]
24521 @subheading The @code{-symbol-list-types} Command
24522 @findex -symbol-list-types
24524 @subsubheading Synopsis
24530 List all the type names.
24532 @subsubheading @value{GDBN} Command
24534 The corresponding commands are @samp{info types} in @value{GDBN},
24535 @samp{gdb_search} in @code{gdbtk}.
24537 @subsubheading Example
24541 @subheading The @code{-symbol-list-variables} Command
24542 @findex -symbol-list-variables
24544 @subsubheading Synopsis
24547 -symbol-list-variables
24550 List all the global and static variable names.
24552 @subsubheading @value{GDBN} Command
24554 @samp{info variables} in @value{GDBN}, @samp{gdb_search} in @code{gdbtk}.
24556 @subsubheading Example
24560 @subheading The @code{-symbol-locate} Command
24561 @findex -symbol-locate
24563 @subsubheading Synopsis
24569 @subsubheading @value{GDBN} Command
24571 @samp{gdb_loc} in @code{gdbtk}.
24573 @subsubheading Example
24577 @subheading The @code{-symbol-type} Command
24578 @findex -symbol-type
24580 @subsubheading Synopsis
24583 -symbol-type @var{variable}
24586 Show type of @var{variable}.
24588 @subsubheading @value{GDBN} Command
24590 The corresponding @value{GDBN} command is @samp{ptype}, @code{gdbtk} has
24591 @samp{gdb_obj_variable}.
24593 @subsubheading Example
24598 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24599 @node GDB/MI File Commands
24600 @section @sc{gdb/mi} File Commands
24602 This section describes the GDB/MI commands to specify executable file names
24603 and to read in and obtain symbol table information.
24605 @subheading The @code{-file-exec-and-symbols} Command
24606 @findex -file-exec-and-symbols
24608 @subsubheading Synopsis
24611 -file-exec-and-symbols @var{file}
24614 Specify the executable file to be debugged. This file is the one from
24615 which the symbol table is also read. If no file is specified, the
24616 command clears the executable and symbol information. If breakpoints
24617 are set when using this command with no arguments, @value{GDBN} will produce
24618 error messages. Otherwise, no output is produced, except a completion
24621 @subsubheading @value{GDBN} Command
24623 The corresponding @value{GDBN} command is @samp{file}.
24625 @subsubheading Example
24629 -file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
24635 @subheading The @code{-file-exec-file} Command
24636 @findex -file-exec-file
24638 @subsubheading Synopsis
24641 -file-exec-file @var{file}
24644 Specify the executable file to be debugged. Unlike
24645 @samp{-file-exec-and-symbols}, the symbol table is @emph{not} read
24646 from this file. If used without argument, @value{GDBN} clears the information
24647 about the executable file. No output is produced, except a completion
24650 @subsubheading @value{GDBN} Command
24652 The corresponding @value{GDBN} command is @samp{exec-file}.
24654 @subsubheading Example
24658 -file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
24665 @subheading The @code{-file-list-exec-sections} Command
24666 @findex -file-list-exec-sections
24668 @subsubheading Synopsis
24671 -file-list-exec-sections
24674 List the sections of the current executable file.
24676 @subsubheading @value{GDBN} Command
24678 The @value{GDBN} command @samp{info file} shows, among the rest, the same
24679 information as this command. @code{gdbtk} has a corresponding command
24680 @samp{gdb_load_info}.
24682 @subsubheading Example
24687 @subheading The @code{-file-list-exec-source-file} Command
24688 @findex -file-list-exec-source-file
24690 @subsubheading Synopsis
24693 -file-list-exec-source-file
24696 List the line number, the current source file, and the absolute path
24697 to the current source file for the current executable. The macro
24698 information field has a value of @samp{1} or @samp{0} depending on
24699 whether or not the file includes preprocessor macro information.
24701 @subsubheading @value{GDBN} Command
24703 The @value{GDBN} equivalent is @samp{info source}
24705 @subsubheading Example
24709 123-file-list-exec-source-file
24710 123^done,line="1",file="foo.c",fullname="/home/bar/foo.c,macro-info="1"
24715 @subheading The @code{-file-list-exec-source-files} Command
24716 @findex -file-list-exec-source-files
24718 @subsubheading Synopsis
24721 -file-list-exec-source-files
24724 List the source files for the current executable.
24726 It will always output the filename, but only when @value{GDBN} can find
24727 the absolute file name of a source file, will it output the fullname.
24729 @subsubheading @value{GDBN} Command
24731 The @value{GDBN} equivalent is @samp{info sources}.
24732 @code{gdbtk} has an analogous command @samp{gdb_listfiles}.
24734 @subsubheading Example
24737 -file-list-exec-source-files
24739 @{file=foo.c,fullname=/home/foo.c@},
24740 @{file=/home/bar.c,fullname=/home/bar.c@},
24741 @{file=gdb_could_not_find_fullpath.c@}]
24746 @subheading The @code{-file-list-shared-libraries} Command
24747 @findex -file-list-shared-libraries
24749 @subsubheading Synopsis
24752 -file-list-shared-libraries
24755 List the shared libraries in the program.
24757 @subsubheading @value{GDBN} Command
24759 The corresponding @value{GDBN} command is @samp{info shared}.
24761 @subsubheading Example
24765 @subheading The @code{-file-list-symbol-files} Command
24766 @findex -file-list-symbol-files
24768 @subsubheading Synopsis
24771 -file-list-symbol-files
24776 @subsubheading @value{GDBN} Command
24778 The corresponding @value{GDBN} command is @samp{info file} (part of it).
24780 @subsubheading Example
24785 @subheading The @code{-file-symbol-file} Command
24786 @findex -file-symbol-file
24788 @subsubheading Synopsis
24791 -file-symbol-file @var{file}
24794 Read symbol table info from the specified @var{file} argument. When
24795 used without arguments, clears @value{GDBN}'s symbol table info. No output is
24796 produced, except for a completion notification.
24798 @subsubheading @value{GDBN} Command
24800 The corresponding @value{GDBN} command is @samp{symbol-file}.
24802 @subsubheading Example
24806 -file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
24812 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24813 @node GDB/MI Memory Overlay Commands
24814 @section @sc{gdb/mi} Memory Overlay Commands
24816 The memory overlay commands are not implemented.
24818 @c @subheading -overlay-auto
24820 @c @subheading -overlay-list-mapping-state
24822 @c @subheading -overlay-list-overlays
24824 @c @subheading -overlay-map
24826 @c @subheading -overlay-off
24828 @c @subheading -overlay-on
24830 @c @subheading -overlay-unmap
24832 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24833 @node GDB/MI Signal Handling Commands
24834 @section @sc{gdb/mi} Signal Handling Commands
24836 Signal handling commands are not implemented.
24838 @c @subheading -signal-handle
24840 @c @subheading -signal-list-handle-actions
24842 @c @subheading -signal-list-signal-types
24846 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24847 @node GDB/MI Target Manipulation
24848 @section @sc{gdb/mi} Target Manipulation Commands
24851 @subheading The @code{-target-attach} Command
24852 @findex -target-attach
24854 @subsubheading Synopsis
24857 -target-attach @var{pid} | @var{gid} | @var{file}
24860 Attach to a process @var{pid} or a file @var{file} outside of
24861 @value{GDBN}, or a thread group @var{gid}. If attaching to a thread
24862 group, the id previously returned by
24863 @samp{-list-thread-groups --available} must be used.
24865 @subsubheading @value{GDBN} Command
24867 The corresponding @value{GDBN} command is @samp{attach}.
24869 @subsubheading Example
24873 =thread-created,id="1"
24874 *stopped,thread-id="1",frame=@{addr="0xb7f7e410",func="bar",args=[]@}
24880 @subheading The @code{-target-compare-sections} Command
24881 @findex -target-compare-sections
24883 @subsubheading Synopsis
24886 -target-compare-sections [ @var{section} ]
24889 Compare data of section @var{section} on target to the exec file.
24890 Without the argument, all sections are compared.
24892 @subsubheading @value{GDBN} Command
24894 The @value{GDBN} equivalent is @samp{compare-sections}.
24896 @subsubheading Example
24901 @subheading The @code{-target-detach} Command
24902 @findex -target-detach
24904 @subsubheading Synopsis
24907 -target-detach [ @var{pid} | @var{gid} ]
24910 Detach from the remote target which normally resumes its execution.
24911 If either @var{pid} or @var{gid} is specified, detaches from either
24912 the specified process, or specified thread group. There's no output.
24914 @subsubheading @value{GDBN} Command
24916 The corresponding @value{GDBN} command is @samp{detach}.
24918 @subsubheading Example
24928 @subheading The @code{-target-disconnect} Command
24929 @findex -target-disconnect
24931 @subsubheading Synopsis
24937 Disconnect from the remote target. There's no output and the target is
24938 generally not resumed.
24940 @subsubheading @value{GDBN} Command
24942 The corresponding @value{GDBN} command is @samp{disconnect}.
24944 @subsubheading Example
24954 @subheading The @code{-target-download} Command
24955 @findex -target-download
24957 @subsubheading Synopsis
24963 Loads the executable onto the remote target.
24964 It prints out an update message every half second, which includes the fields:
24968 The name of the section.
24970 The size of what has been sent so far for that section.
24972 The size of the section.
24974 The total size of what was sent so far (the current and the previous sections).
24976 The size of the overall executable to download.
24980 Each message is sent as status record (@pxref{GDB/MI Output Syntax, ,
24981 @sc{gdb/mi} Output Syntax}).
24983 In addition, it prints the name and size of the sections, as they are
24984 downloaded. These messages include the following fields:
24988 The name of the section.
24990 The size of the section.
24992 The size of the overall executable to download.
24996 At the end, a summary is printed.
24998 @subsubheading @value{GDBN} Command
25000 The corresponding @value{GDBN} command is @samp{load}.
25002 @subsubheading Example
25004 Note: each status message appears on a single line. Here the messages
25005 have been broken down so that they can fit onto a page.
25010 +download,@{section=".text",section-size="6668",total-size="9880"@}
25011 +download,@{section=".text",section-sent="512",section-size="6668",
25012 total-sent="512",total-size="9880"@}
25013 +download,@{section=".text",section-sent="1024",section-size="6668",
25014 total-sent="1024",total-size="9880"@}
25015 +download,@{section=".text",section-sent="1536",section-size="6668",
25016 total-sent="1536",total-size="9880"@}
25017 +download,@{section=".text",section-sent="2048",section-size="6668",
25018 total-sent="2048",total-size="9880"@}
25019 +download,@{section=".text",section-sent="2560",section-size="6668",
25020 total-sent="2560",total-size="9880"@}
25021 +download,@{section=".text",section-sent="3072",section-size="6668",
25022 total-sent="3072",total-size="9880"@}
25023 +download,@{section=".text",section-sent="3584",section-size="6668",
25024 total-sent="3584",total-size="9880"@}
25025 +download,@{section=".text",section-sent="4096",section-size="6668",
25026 total-sent="4096",total-size="9880"@}
25027 +download,@{section=".text",section-sent="4608",section-size="6668",
25028 total-sent="4608",total-size="9880"@}
25029 +download,@{section=".text",section-sent="5120",section-size="6668",
25030 total-sent="5120",total-size="9880"@}
25031 +download,@{section=".text",section-sent="5632",section-size="6668",
25032 total-sent="5632",total-size="9880"@}
25033 +download,@{section=".text",section-sent="6144",section-size="6668",
25034 total-sent="6144",total-size="9880"@}
25035 +download,@{section=".text",section-sent="6656",section-size="6668",
25036 total-sent="6656",total-size="9880"@}
25037 +download,@{section=".init",section-size="28",total-size="9880"@}
25038 +download,@{section=".fini",section-size="28",total-size="9880"@}
25039 +download,@{section=".data",section-size="3156",total-size="9880"@}
25040 +download,@{section=".data",section-sent="512",section-size="3156",
25041 total-sent="7236",total-size="9880"@}
25042 +download,@{section=".data",section-sent="1024",section-size="3156",
25043 total-sent="7748",total-size="9880"@}
25044 +download,@{section=".data",section-sent="1536",section-size="3156",
25045 total-sent="8260",total-size="9880"@}
25046 +download,@{section=".data",section-sent="2048",section-size="3156",
25047 total-sent="8772",total-size="9880"@}
25048 +download,@{section=".data",section-sent="2560",section-size="3156",
25049 total-sent="9284",total-size="9880"@}
25050 +download,@{section=".data",section-sent="3072",section-size="3156",
25051 total-sent="9796",total-size="9880"@}
25052 ^done,address="0x10004",load-size="9880",transfer-rate="6586",
25059 @subheading The @code{-target-exec-status} Command
25060 @findex -target-exec-status
25062 @subsubheading Synopsis
25065 -target-exec-status
25068 Provide information on the state of the target (whether it is running or
25069 not, for instance).
25071 @subsubheading @value{GDBN} Command
25073 There's no equivalent @value{GDBN} command.
25075 @subsubheading Example
25079 @subheading The @code{-target-list-available-targets} Command
25080 @findex -target-list-available-targets
25082 @subsubheading Synopsis
25085 -target-list-available-targets
25088 List the possible targets to connect to.
25090 @subsubheading @value{GDBN} Command
25092 The corresponding @value{GDBN} command is @samp{help target}.
25094 @subsubheading Example
25098 @subheading The @code{-target-list-current-targets} Command
25099 @findex -target-list-current-targets
25101 @subsubheading Synopsis
25104 -target-list-current-targets
25107 Describe the current target.
25109 @subsubheading @value{GDBN} Command
25111 The corresponding information is printed by @samp{info file} (among
25114 @subsubheading Example
25118 @subheading The @code{-target-list-parameters} Command
25119 @findex -target-list-parameters
25121 @subsubheading Synopsis
25124 -target-list-parameters
25130 @subsubheading @value{GDBN} Command
25134 @subsubheading Example
25138 @subheading The @code{-target-select} Command
25139 @findex -target-select
25141 @subsubheading Synopsis
25144 -target-select @var{type} @var{parameters @dots{}}
25147 Connect @value{GDBN} to the remote target. This command takes two args:
25151 The type of target, for instance @samp{remote}, etc.
25152 @item @var{parameters}
25153 Device names, host names and the like. @xref{Target Commands, ,
25154 Commands for Managing Targets}, for more details.
25157 The output is a connection notification, followed by the address at
25158 which the target program is, in the following form:
25161 ^connected,addr="@var{address}",func="@var{function name}",
25162 args=[@var{arg list}]
25165 @subsubheading @value{GDBN} Command
25167 The corresponding @value{GDBN} command is @samp{target}.
25169 @subsubheading Example
25173 -target-select remote /dev/ttya
25174 ^connected,addr="0xfe00a300",func="??",args=[]
25178 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25179 @node GDB/MI File Transfer Commands
25180 @section @sc{gdb/mi} File Transfer Commands
25183 @subheading The @code{-target-file-put} Command
25184 @findex -target-file-put
25186 @subsubheading Synopsis
25189 -target-file-put @var{hostfile} @var{targetfile}
25192 Copy file @var{hostfile} from the host system (the machine running
25193 @value{GDBN}) to @var{targetfile} on the target system.
25195 @subsubheading @value{GDBN} Command
25197 The corresponding @value{GDBN} command is @samp{remote put}.
25199 @subsubheading Example
25203 -target-file-put localfile remotefile
25209 @subheading The @code{-target-file-get} Command
25210 @findex -target-file-get
25212 @subsubheading Synopsis
25215 -target-file-get @var{targetfile} @var{hostfile}
25218 Copy file @var{targetfile} from the target system to @var{hostfile}
25219 on the host system.
25221 @subsubheading @value{GDBN} Command
25223 The corresponding @value{GDBN} command is @samp{remote get}.
25225 @subsubheading Example
25229 -target-file-get remotefile localfile
25235 @subheading The @code{-target-file-delete} Command
25236 @findex -target-file-delete
25238 @subsubheading Synopsis
25241 -target-file-delete @var{targetfile}
25244 Delete @var{targetfile} from the target system.
25246 @subsubheading @value{GDBN} Command
25248 The corresponding @value{GDBN} command is @samp{remote delete}.
25250 @subsubheading Example
25254 -target-file-delete remotefile
25260 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25261 @node GDB/MI Miscellaneous Commands
25262 @section Miscellaneous @sc{gdb/mi} Commands
25264 @c @subheading -gdb-complete
25266 @subheading The @code{-gdb-exit} Command
25269 @subsubheading Synopsis
25275 Exit @value{GDBN} immediately.
25277 @subsubheading @value{GDBN} Command
25279 Approximately corresponds to @samp{quit}.
25281 @subsubheading Example
25291 @subheading The @code{-exec-abort} Command
25292 @findex -exec-abort
25294 @subsubheading Synopsis
25300 Kill the inferior running program.
25302 @subsubheading @value{GDBN} Command
25304 The corresponding @value{GDBN} command is @samp{kill}.
25306 @subsubheading Example
25311 @subheading The @code{-gdb-set} Command
25314 @subsubheading Synopsis
25320 Set an internal @value{GDBN} variable.
25321 @c IS THIS A DOLLAR VARIABLE? OR SOMETHING LIKE ANNOTATE ?????
25323 @subsubheading @value{GDBN} Command
25325 The corresponding @value{GDBN} command is @samp{set}.
25327 @subsubheading Example
25337 @subheading The @code{-gdb-show} Command
25340 @subsubheading Synopsis
25346 Show the current value of a @value{GDBN} variable.
25348 @subsubheading @value{GDBN} Command
25350 The corresponding @value{GDBN} command is @samp{show}.
25352 @subsubheading Example
25361 @c @subheading -gdb-source
25364 @subheading The @code{-gdb-version} Command
25365 @findex -gdb-version
25367 @subsubheading Synopsis
25373 Show version information for @value{GDBN}. Used mostly in testing.
25375 @subsubheading @value{GDBN} Command
25377 The @value{GDBN} equivalent is @samp{show version}. @value{GDBN} by
25378 default shows this information when you start an interactive session.
25380 @subsubheading Example
25382 @c This example modifies the actual output from GDB to avoid overfull
25388 ~Copyright 2000 Free Software Foundation, Inc.
25389 ~GDB is free software, covered by the GNU General Public License, and
25390 ~you are welcome to change it and/or distribute copies of it under
25391 ~ certain conditions.
25392 ~Type "show copying" to see the conditions.
25393 ~There is absolutely no warranty for GDB. Type "show warranty" for
25395 ~This GDB was configured as
25396 "--host=sparc-sun-solaris2.5.1 --target=ppc-eabi".
25401 @subheading The @code{-list-features} Command
25402 @findex -list-features
25404 Returns a list of particular features of the MI protocol that
25405 this version of gdb implements. A feature can be a command,
25406 or a new field in an output of some command, or even an
25407 important bugfix. While a frontend can sometimes detect presence
25408 of a feature at runtime, it is easier to perform detection at debugger
25411 The command returns a list of strings, with each string naming an
25412 available feature. Each returned string is just a name, it does not
25413 have any internal structure. The list of possible feature names
25419 (gdb) -list-features
25420 ^done,result=["feature1","feature2"]
25423 The current list of features is:
25426 @item frozen-varobjs
25427 Indicates presence of the @code{-var-set-frozen} command, as well
25428 as possible presense of the @code{frozen} field in the output
25429 of @code{-varobj-create}.
25430 @item pending-breakpoints
25431 Indicates presence of the @option{-f} option to the @code{-break-insert} command.
25433 Indicates presence of Python scripting support, Python-based
25434 pretty-printing commands, and possible presence of the
25435 @samp{display_hint} field in the output of @code{-var-list-children}
25437 Indicates presence of the @code{-thread-info} command.
25441 @subheading The @code{-list-target-features} Command
25442 @findex -list-target-features
25444 Returns a list of particular features that are supported by the
25445 target. Those features affect the permitted MI commands, but
25446 unlike the features reported by the @code{-list-features} command, the
25447 features depend on which target GDB is using at the moment. Whenever
25448 a target can change, due to commands such as @code{-target-select},
25449 @code{-target-attach} or @code{-exec-run}, the list of target features
25450 may change, and the frontend should obtain it again.
25454 (gdb) -list-features
25455 ^done,result=["async"]
25458 The current list of features is:
25462 Indicates that the target is capable of asynchronous command
25463 execution, which means that @value{GDBN} will accept further commands
25464 while the target is running.
25468 @subheading The @code{-list-thread-groups} Command
25469 @findex -list-thread-groups
25471 @subheading Synopsis
25474 -list-thread-groups [ --available ] [ @var{group} ]
25477 When used without the @var{group} parameter, lists top-level thread
25478 groups that are being debugged. When used with the @var{group}
25479 parameter, the children of the specified group are listed. The
25480 children can be either threads, or other groups. At present,
25481 @value{GDBN} will not report both threads and groups as children at
25482 the same time, but it may change in future.
25484 With the @samp{--available} option, instead of reporting groups that
25485 are been debugged, GDB will report all thread groups available on the
25486 target. Using the @samp{--available} option together with @var{group}
25489 @subheading Example
25493 -list-thread-groups
25494 ^done,groups=[@{id="17",type="process",pid="yyy",num_children="2"@}]
25495 -list-thread-groups 17
25496 ^done,threads=[@{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
25497 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]@},state="running"@},
25498 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
25499 frame=@{level="0",addr="0x0804891f",func="foo",args=[@{name="i",value="10"@}],
25500 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},state="running"@}]]
25503 @subheading The @code{-interpreter-exec} Command
25504 @findex -interpreter-exec
25506 @subheading Synopsis
25509 -interpreter-exec @var{interpreter} @var{command}
25511 @anchor{-interpreter-exec}
25513 Execute the specified @var{command} in the given @var{interpreter}.
25515 @subheading @value{GDBN} Command
25517 The corresponding @value{GDBN} command is @samp{interpreter-exec}.
25519 @subheading Example
25523 -interpreter-exec console "break main"
25524 &"During symbol reading, couldn't parse type; debugger out of date?.\n"
25525 &"During symbol reading, bad structure-type format.\n"
25526 ~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n"
25531 @subheading The @code{-inferior-tty-set} Command
25532 @findex -inferior-tty-set
25534 @subheading Synopsis
25537 -inferior-tty-set /dev/pts/1
25540 Set terminal for future runs of the program being debugged.
25542 @subheading @value{GDBN} Command
25544 The corresponding @value{GDBN} command is @samp{set inferior-tty} /dev/pts/1.
25546 @subheading Example
25550 -inferior-tty-set /dev/pts/1
25555 @subheading The @code{-inferior-tty-show} Command
25556 @findex -inferior-tty-show
25558 @subheading Synopsis
25564 Show terminal for future runs of program being debugged.
25566 @subheading @value{GDBN} Command
25568 The corresponding @value{GDBN} command is @samp{show inferior-tty}.
25570 @subheading Example
25574 -inferior-tty-set /dev/pts/1
25578 ^done,inferior_tty_terminal="/dev/pts/1"
25582 @subheading The @code{-enable-timings} Command
25583 @findex -enable-timings
25585 @subheading Synopsis
25588 -enable-timings [yes | no]
25591 Toggle the printing of the wallclock, user and system times for an MI
25592 command as a field in its output. This command is to help frontend
25593 developers optimize the performance of their code. No argument is
25594 equivalent to @samp{yes}.
25596 @subheading @value{GDBN} Command
25600 @subheading Example
25608 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
25609 addr="0x080484ed",func="main",file="myprog.c",
25610 fullname="/home/nickrob/myprog.c",line="73",times="0"@},
25611 time=@{wallclock="0.05185",user="0.00800",system="0.00000"@}
25619 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
25620 frame=@{addr="0x080484ed",func="main",args=[@{name="argc",value="1"@},
25621 @{name="argv",value="0xbfb60364"@}],file="myprog.c",
25622 fullname="/home/nickrob/myprog.c",line="73"@}
25627 @chapter @value{GDBN} Annotations
25629 This chapter describes annotations in @value{GDBN}. Annotations were
25630 designed to interface @value{GDBN} to graphical user interfaces or other
25631 similar programs which want to interact with @value{GDBN} at a
25632 relatively high level.
25634 The annotation mechanism has largely been superseded by @sc{gdb/mi}
25638 This is Edition @value{EDITION}, @value{DATE}.
25642 * Annotations Overview:: What annotations are; the general syntax.
25643 * Server Prefix:: Issuing a command without affecting user state.
25644 * Prompting:: Annotations marking @value{GDBN}'s need for input.
25645 * Errors:: Annotations for error messages.
25646 * Invalidation:: Some annotations describe things now invalid.
25647 * Annotations for Running::
25648 Whether the program is running, how it stopped, etc.
25649 * Source Annotations:: Annotations describing source code.
25652 @node Annotations Overview
25653 @section What is an Annotation?
25654 @cindex annotations
25656 Annotations start with a newline character, two @samp{control-z}
25657 characters, and the name of the annotation. If there is no additional
25658 information associated with this annotation, the name of the annotation
25659 is followed immediately by a newline. If there is additional
25660 information, the name of the annotation is followed by a space, the
25661 additional information, and a newline. The additional information
25662 cannot contain newline characters.
25664 Any output not beginning with a newline and two @samp{control-z}
25665 characters denotes literal output from @value{GDBN}. Currently there is
25666 no need for @value{GDBN} to output a newline followed by two
25667 @samp{control-z} characters, but if there was such a need, the
25668 annotations could be extended with an @samp{escape} annotation which
25669 means those three characters as output.
25671 The annotation @var{level}, which is specified using the
25672 @option{--annotate} command line option (@pxref{Mode Options}), controls
25673 how much information @value{GDBN} prints together with its prompt,
25674 values of expressions, source lines, and other types of output. Level 0
25675 is for no annotations, level 1 is for use when @value{GDBN} is run as a
25676 subprocess of @sc{gnu} Emacs, level 3 is the maximum annotation suitable
25677 for programs that control @value{GDBN}, and level 2 annotations have
25678 been made obsolete (@pxref{Limitations, , Limitations of the Annotation
25679 Interface, annotate, GDB's Obsolete Annotations}).
25682 @kindex set annotate
25683 @item set annotate @var{level}
25684 The @value{GDBN} command @code{set annotate} sets the level of
25685 annotations to the specified @var{level}.
25687 @item show annotate
25688 @kindex show annotate
25689 Show the current annotation level.
25692 This chapter describes level 3 annotations.
25694 A simple example of starting up @value{GDBN} with annotations is:
25697 $ @kbd{gdb --annotate=3}
25699 Copyright 2003 Free Software Foundation, Inc.
25700 GDB is free software, covered by the GNU General Public License,
25701 and you are welcome to change it and/or distribute copies of it
25702 under certain conditions.
25703 Type "show copying" to see the conditions.
25704 There is absolutely no warranty for GDB. Type "show warranty"
25706 This GDB was configured as "i386-pc-linux-gnu"
25717 Here @samp{quit} is input to @value{GDBN}; the rest is output from
25718 @value{GDBN}. The three lines beginning @samp{^Z^Z} (where @samp{^Z}
25719 denotes a @samp{control-z} character) are annotations; the rest is
25720 output from @value{GDBN}.
25722 @node Server Prefix
25723 @section The Server Prefix
25724 @cindex server prefix
25726 If you prefix a command with @samp{server } then it will not affect
25727 the command history, nor will it affect @value{GDBN}'s notion of which
25728 command to repeat if @key{RET} is pressed on a line by itself. This
25729 means that commands can be run behind a user's back by a front-end in
25730 a transparent manner.
25732 The @code{server } prefix does not affect the recording of values into
25733 the value history; to print a value without recording it into the
25734 value history, use the @code{output} command instead of the
25735 @code{print} command.
25737 Using this prefix also disables confirmation requests
25738 (@pxref{confirmation requests}).
25741 @section Annotation for @value{GDBN} Input
25743 @cindex annotations for prompts
25744 When @value{GDBN} prompts for input, it annotates this fact so it is possible
25745 to know when to send output, when the output from a given command is
25748 Different kinds of input each have a different @dfn{input type}. Each
25749 input type has three annotations: a @code{pre-} annotation, which
25750 denotes the beginning of any prompt which is being output, a plain
25751 annotation, which denotes the end of the prompt, and then a @code{post-}
25752 annotation which denotes the end of any echo which may (or may not) be
25753 associated with the input. For example, the @code{prompt} input type
25754 features the following annotations:
25762 The input types are
25765 @findex pre-prompt annotation
25766 @findex prompt annotation
25767 @findex post-prompt annotation
25769 When @value{GDBN} is prompting for a command (the main @value{GDBN} prompt).
25771 @findex pre-commands annotation
25772 @findex commands annotation
25773 @findex post-commands annotation
25775 When @value{GDBN} prompts for a set of commands, like in the @code{commands}
25776 command. The annotations are repeated for each command which is input.
25778 @findex pre-overload-choice annotation
25779 @findex overload-choice annotation
25780 @findex post-overload-choice annotation
25781 @item overload-choice
25782 When @value{GDBN} wants the user to select between various overloaded functions.
25784 @findex pre-query annotation
25785 @findex query annotation
25786 @findex post-query annotation
25788 When @value{GDBN} wants the user to confirm a potentially dangerous operation.
25790 @findex pre-prompt-for-continue annotation
25791 @findex prompt-for-continue annotation
25792 @findex post-prompt-for-continue annotation
25793 @item prompt-for-continue
25794 When @value{GDBN} is asking the user to press return to continue. Note: Don't
25795 expect this to work well; instead use @code{set height 0} to disable
25796 prompting. This is because the counting of lines is buggy in the
25797 presence of annotations.
25802 @cindex annotations for errors, warnings and interrupts
25804 @findex quit annotation
25809 This annotation occurs right before @value{GDBN} responds to an interrupt.
25811 @findex error annotation
25816 This annotation occurs right before @value{GDBN} responds to an error.
25818 Quit and error annotations indicate that any annotations which @value{GDBN} was
25819 in the middle of may end abruptly. For example, if a
25820 @code{value-history-begin} annotation is followed by a @code{error}, one
25821 cannot expect to receive the matching @code{value-history-end}. One
25822 cannot expect not to receive it either, however; an error annotation
25823 does not necessarily mean that @value{GDBN} is immediately returning all the way
25826 @findex error-begin annotation
25827 A quit or error annotation may be preceded by
25833 Any output between that and the quit or error annotation is the error
25836 Warning messages are not yet annotated.
25837 @c If we want to change that, need to fix warning(), type_error(),
25838 @c range_error(), and possibly other places.
25841 @section Invalidation Notices
25843 @cindex annotations for invalidation messages
25844 The following annotations say that certain pieces of state may have
25848 @findex frames-invalid annotation
25849 @item ^Z^Zframes-invalid
25851 The frames (for example, output from the @code{backtrace} command) may
25854 @findex breakpoints-invalid annotation
25855 @item ^Z^Zbreakpoints-invalid
25857 The breakpoints may have changed. For example, the user just added or
25858 deleted a breakpoint.
25861 @node Annotations for Running
25862 @section Running the Program
25863 @cindex annotations for running programs
25865 @findex starting annotation
25866 @findex stopping annotation
25867 When the program starts executing due to a @value{GDBN} command such as
25868 @code{step} or @code{continue},
25874 is output. When the program stops,
25880 is output. Before the @code{stopped} annotation, a variety of
25881 annotations describe how the program stopped.
25884 @findex exited annotation
25885 @item ^Z^Zexited @var{exit-status}
25886 The program exited, and @var{exit-status} is the exit status (zero for
25887 successful exit, otherwise nonzero).
25889 @findex signalled annotation
25890 @findex signal-name annotation
25891 @findex signal-name-end annotation
25892 @findex signal-string annotation
25893 @findex signal-string-end annotation
25894 @item ^Z^Zsignalled
25895 The program exited with a signal. After the @code{^Z^Zsignalled}, the
25896 annotation continues:
25902 ^Z^Zsignal-name-end
25906 ^Z^Zsignal-string-end
25911 where @var{name} is the name of the signal, such as @code{SIGILL} or
25912 @code{SIGSEGV}, and @var{string} is the explanation of the signal, such
25913 as @code{Illegal Instruction} or @code{Segmentation fault}.
25914 @var{intro-text}, @var{middle-text}, and @var{end-text} are for the
25915 user's benefit and have no particular format.
25917 @findex signal annotation
25919 The syntax of this annotation is just like @code{signalled}, but @value{GDBN} is
25920 just saying that the program received the signal, not that it was
25921 terminated with it.
25923 @findex breakpoint annotation
25924 @item ^Z^Zbreakpoint @var{number}
25925 The program hit breakpoint number @var{number}.
25927 @findex watchpoint annotation
25928 @item ^Z^Zwatchpoint @var{number}
25929 The program hit watchpoint number @var{number}.
25932 @node Source Annotations
25933 @section Displaying Source
25934 @cindex annotations for source display
25936 @findex source annotation
25937 The following annotation is used instead of displaying source code:
25940 ^Z^Zsource @var{filename}:@var{line}:@var{character}:@var{middle}:@var{addr}
25943 where @var{filename} is an absolute file name indicating which source
25944 file, @var{line} is the line number within that file (where 1 is the
25945 first line in the file), @var{character} is the character position
25946 within the file (where 0 is the first character in the file) (for most
25947 debug formats this will necessarily point to the beginning of a line),
25948 @var{middle} is @samp{middle} if @var{addr} is in the middle of the
25949 line, or @samp{beg} if @var{addr} is at the beginning of the line, and
25950 @var{addr} is the address in the target program associated with the
25951 source which is being displayed. @var{addr} is in the form @samp{0x}
25952 followed by one or more lowercase hex digits (note that this does not
25953 depend on the language).
25955 @node JIT Interface
25956 @chapter JIT Compilation Interface
25957 @cindex just-in-time compilation
25958 @cindex JIT compilation interface
25960 This chapter documents @value{GDBN}'s @dfn{just-in-time} (JIT) compilation
25961 interface. A JIT compiler is a program or library that generates native
25962 executable code at runtime and executes it, usually in order to achieve good
25963 performance while maintaining platform independence.
25965 Programs that use JIT compilation are normally difficult to debug because
25966 portions of their code are generated at runtime, instead of being loaded from
25967 object files, which is where @value{GDBN} normally finds the program's symbols
25968 and debug information. In order to debug programs that use JIT compilation,
25969 @value{GDBN} has an interface that allows the program to register in-memory
25970 symbol files with @value{GDBN} at runtime.
25972 If you are using @value{GDBN} to debug a program that uses this interface, then
25973 it should work transparently so long as you have not stripped the binary. If
25974 you are developing a JIT compiler, then the interface is documented in the rest
25975 of this chapter. At this time, the only known client of this interface is the
25978 Broadly speaking, the JIT interface mirrors the dynamic loader interface. The
25979 JIT compiler communicates with @value{GDBN} by writing data into a global
25980 variable and calling a fuction at a well-known symbol. When @value{GDBN}
25981 attaches, it reads a linked list of symbol files from the global variable to
25982 find existing code, and puts a breakpoint in the function so that it can find
25983 out about additional code.
25986 * Declarations:: Relevant C struct declarations
25987 * Registering Code:: Steps to register code
25988 * Unregistering Code:: Steps to unregister code
25992 @section JIT Declarations
25994 These are the relevant struct declarations that a C program should include to
25995 implement the interface:
26005 struct jit_code_entry
26007 struct jit_code_entry *next_entry;
26008 struct jit_code_entry *prev_entry;
26009 const char *symfile_addr;
26010 uint64_t symfile_size;
26013 struct jit_descriptor
26016 /* This type should be jit_actions_t, but we use uint32_t
26017 to be explicit about the bitwidth. */
26018 uint32_t action_flag;
26019 struct jit_code_entry *relevant_entry;
26020 struct jit_code_entry *first_entry;
26023 /* GDB puts a breakpoint in this function. */
26024 void __attribute__((noinline)) __jit_debug_register_code() @{ @};
26026 /* Make sure to specify the version statically, because the
26027 debugger may check the version before we can set it. */
26028 struct jit_descriptor __jit_debug_descriptor = @{ 1, 0, 0, 0 @};
26031 If the JIT is multi-threaded, then it is important that the JIT synchronize any
26032 modifications to this global data properly, which can easily be done by putting
26033 a global mutex around modifications to these structures.
26035 @node Registering Code
26036 @section Registering Code
26038 To register code with @value{GDBN}, the JIT should follow this protocol:
26042 Generate an object file in memory with symbols and other desired debug
26043 information. The file must include the virtual addresses of the sections.
26046 Create a code entry for the file, which gives the start and size of the symbol
26050 Add it to the linked list in the JIT descriptor.
26053 Point the relevant_entry field of the descriptor at the entry.
26056 Set @code{action_flag} to @code{JIT_REGISTER} and call
26057 @code{__jit_debug_register_code}.
26060 When @value{GDBN} is attached and the breakpoint fires, @value{GDBN} uses the
26061 @code{relevant_entry} pointer so it doesn't have to walk the list looking for
26062 new code. However, the linked list must still be maintained in order to allow
26063 @value{GDBN} to attach to a running process and still find the symbol files.
26065 @node Unregistering Code
26066 @section Unregistering Code
26068 If code is freed, then the JIT should use the following protocol:
26072 Remove the code entry corresponding to the code from the linked list.
26075 Point the @code{relevant_entry} field of the descriptor at the code entry.
26078 Set @code{action_flag} to @code{JIT_UNREGISTER} and call
26079 @code{__jit_debug_register_code}.
26082 If the JIT frees or recompiles code without unregistering it, then @value{GDBN}
26083 and the JIT will leak the memory used for the associated symbol files.
26086 @chapter Reporting Bugs in @value{GDBN}
26087 @cindex bugs in @value{GDBN}
26088 @cindex reporting bugs in @value{GDBN}
26090 Your bug reports play an essential role in making @value{GDBN} reliable.
26092 Reporting a bug may help you by bringing a solution to your problem, or it
26093 may not. But in any case the principal function of a bug report is to help
26094 the entire community by making the next version of @value{GDBN} work better. Bug
26095 reports are your contribution to the maintenance of @value{GDBN}.
26097 In order for a bug report to serve its purpose, you must include the
26098 information that enables us to fix the bug.
26101 * Bug Criteria:: Have you found a bug?
26102 * Bug Reporting:: How to report bugs
26106 @section Have You Found a Bug?
26107 @cindex bug criteria
26109 If you are not sure whether you have found a bug, here are some guidelines:
26112 @cindex fatal signal
26113 @cindex debugger crash
26114 @cindex crash of debugger
26116 If the debugger gets a fatal signal, for any input whatever, that is a
26117 @value{GDBN} bug. Reliable debuggers never crash.
26119 @cindex error on valid input
26121 If @value{GDBN} produces an error message for valid input, that is a
26122 bug. (Note that if you're cross debugging, the problem may also be
26123 somewhere in the connection to the target.)
26125 @cindex invalid input
26127 If @value{GDBN} does not produce an error message for invalid input,
26128 that is a bug. However, you should note that your idea of
26129 ``invalid input'' might be our idea of ``an extension'' or ``support
26130 for traditional practice''.
26133 If you are an experienced user of debugging tools, your suggestions
26134 for improvement of @value{GDBN} are welcome in any case.
26137 @node Bug Reporting
26138 @section How to Report Bugs
26139 @cindex bug reports
26140 @cindex @value{GDBN} bugs, reporting
26142 A number of companies and individuals offer support for @sc{gnu} products.
26143 If you obtained @value{GDBN} from a support organization, we recommend you
26144 contact that organization first.
26146 You can find contact information for many support companies and
26147 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
26149 @c should add a web page ref...
26152 @ifset BUGURL_DEFAULT
26153 In any event, we also recommend that you submit bug reports for
26154 @value{GDBN}. The preferred method is to submit them directly using
26155 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
26156 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
26159 @strong{Do not send bug reports to @samp{info-gdb}, or to
26160 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
26161 not want to receive bug reports. Those that do have arranged to receive
26164 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
26165 serves as a repeater. The mailing list and the newsgroup carry exactly
26166 the same messages. Often people think of posting bug reports to the
26167 newsgroup instead of mailing them. This appears to work, but it has one
26168 problem which can be crucial: a newsgroup posting often lacks a mail
26169 path back to the sender. Thus, if we need to ask for more information,
26170 we may be unable to reach you. For this reason, it is better to send
26171 bug reports to the mailing list.
26173 @ifclear BUGURL_DEFAULT
26174 In any event, we also recommend that you submit bug reports for
26175 @value{GDBN} to @value{BUGURL}.
26179 The fundamental principle of reporting bugs usefully is this:
26180 @strong{report all the facts}. If you are not sure whether to state a
26181 fact or leave it out, state it!
26183 Often people omit facts because they think they know what causes the
26184 problem and assume that some details do not matter. Thus, you might
26185 assume that the name of the variable you use in an example does not matter.
26186 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
26187 stray memory reference which happens to fetch from the location where that
26188 name is stored in memory; perhaps, if the name were different, the contents
26189 of that location would fool the debugger into doing the right thing despite
26190 the bug. Play it safe and give a specific, complete example. That is the
26191 easiest thing for you to do, and the most helpful.
26193 Keep in mind that the purpose of a bug report is to enable us to fix the
26194 bug. It may be that the bug has been reported previously, but neither
26195 you nor we can know that unless your bug report is complete and
26198 Sometimes people give a few sketchy facts and ask, ``Does this ring a
26199 bell?'' Those bug reports are useless, and we urge everyone to
26200 @emph{refuse to respond to them} except to chide the sender to report
26203 To enable us to fix the bug, you should include all these things:
26207 The version of @value{GDBN}. @value{GDBN} announces it if you start
26208 with no arguments; you can also print it at any time using @code{show
26211 Without this, we will not know whether there is any point in looking for
26212 the bug in the current version of @value{GDBN}.
26215 The type of machine you are using, and the operating system name and
26219 What compiler (and its version) was used to compile @value{GDBN}---e.g.@:
26220 ``@value{GCC}--2.8.1''.
26223 What compiler (and its version) was used to compile the program you are
26224 debugging---e.g.@: ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
26225 C Compiler''. For @value{NGCC}, you can say @kbd{@value{GCC} --version}
26226 to get this information; for other compilers, see the documentation for
26230 The command arguments you gave the compiler to compile your example and
26231 observe the bug. For example, did you use @samp{-O}? To guarantee
26232 you will not omit something important, list them all. A copy of the
26233 Makefile (or the output from make) is sufficient.
26235 If we were to try to guess the arguments, we would probably guess wrong
26236 and then we might not encounter the bug.
26239 A complete input script, and all necessary source files, that will
26243 A description of what behavior you observe that you believe is
26244 incorrect. For example, ``It gets a fatal signal.''
26246 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
26247 will certainly notice it. But if the bug is incorrect output, we might
26248 not notice unless it is glaringly wrong. You might as well not give us
26249 a chance to make a mistake.
26251 Even if the problem you experience is a fatal signal, you should still
26252 say so explicitly. Suppose something strange is going on, such as, your
26253 copy of @value{GDBN} is out of synch, or you have encountered a bug in
26254 the C library on your system. (This has happened!) Your copy might
26255 crash and ours would not. If you told us to expect a crash, then when
26256 ours fails to crash, we would know that the bug was not happening for
26257 us. If you had not told us to expect a crash, then we would not be able
26258 to draw any conclusion from our observations.
26261 @cindex recording a session script
26262 To collect all this information, you can use a session recording program
26263 such as @command{script}, which is available on many Unix systems.
26264 Just run your @value{GDBN} session inside @command{script} and then
26265 include the @file{typescript} file with your bug report.
26267 Another way to record a @value{GDBN} session is to run @value{GDBN}
26268 inside Emacs and then save the entire buffer to a file.
26271 If you wish to suggest changes to the @value{GDBN} source, send us context
26272 diffs. If you even discuss something in the @value{GDBN} source, refer to
26273 it by context, not by line number.
26275 The line numbers in our development sources will not match those in your
26276 sources. Your line numbers would convey no useful information to us.
26280 Here are some things that are not necessary:
26284 A description of the envelope of the bug.
26286 Often people who encounter a bug spend a lot of time investigating
26287 which changes to the input file will make the bug go away and which
26288 changes will not affect it.
26290 This is often time consuming and not very useful, because the way we
26291 will find the bug is by running a single example under the debugger
26292 with breakpoints, not by pure deduction from a series of examples.
26293 We recommend that you save your time for something else.
26295 Of course, if you can find a simpler example to report @emph{instead}
26296 of the original one, that is a convenience for us. Errors in the
26297 output will be easier to spot, running under the debugger will take
26298 less time, and so on.
26300 However, simplification is not vital; if you do not want to do this,
26301 report the bug anyway and send us the entire test case you used.
26304 A patch for the bug.
26306 A patch for the bug does help us if it is a good one. But do not omit
26307 the necessary information, such as the test case, on the assumption that
26308 a patch is all we need. We might see problems with your patch and decide
26309 to fix the problem another way, or we might not understand it at all.
26311 Sometimes with a program as complicated as @value{GDBN} it is very hard to
26312 construct an example that will make the program follow a certain path
26313 through the code. If you do not send us the example, we will not be able
26314 to construct one, so we will not be able to verify that the bug is fixed.
26316 And if we cannot understand what bug you are trying to fix, or why your
26317 patch should be an improvement, we will not install it. A test case will
26318 help us to understand.
26321 A guess about what the bug is or what it depends on.
26323 Such guesses are usually wrong. Even we cannot guess right about such
26324 things without first using the debugger to find the facts.
26327 @c The readline documentation is distributed with the readline code
26328 @c and consists of the two following files:
26330 @c inc-hist.texinfo
26331 @c Use -I with makeinfo to point to the appropriate directory,
26332 @c environment var TEXINPUTS with TeX.
26333 @include rluser.texi
26334 @include inc-hist.texinfo
26337 @node Formatting Documentation
26338 @appendix Formatting Documentation
26340 @cindex @value{GDBN} reference card
26341 @cindex reference card
26342 The @value{GDBN} 4 release includes an already-formatted reference card, ready
26343 for printing with PostScript or Ghostscript, in the @file{gdb}
26344 subdirectory of the main source directory@footnote{In
26345 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
26346 release.}. If you can use PostScript or Ghostscript with your printer,
26347 you can print the reference card immediately with @file{refcard.ps}.
26349 The release also includes the source for the reference card. You
26350 can format it, using @TeX{}, by typing:
26356 The @value{GDBN} reference card is designed to print in @dfn{landscape}
26357 mode on US ``letter'' size paper;
26358 that is, on a sheet 11 inches wide by 8.5 inches
26359 high. You will need to specify this form of printing as an option to
26360 your @sc{dvi} output program.
26362 @cindex documentation
26364 All the documentation for @value{GDBN} comes as part of the machine-readable
26365 distribution. The documentation is written in Texinfo format, which is
26366 a documentation system that uses a single source file to produce both
26367 on-line information and a printed manual. You can use one of the Info
26368 formatting commands to create the on-line version of the documentation
26369 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
26371 @value{GDBN} includes an already formatted copy of the on-line Info
26372 version of this manual in the @file{gdb} subdirectory. The main Info
26373 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
26374 subordinate files matching @samp{gdb.info*} in the same directory. If
26375 necessary, you can print out these files, or read them with any editor;
26376 but they are easier to read using the @code{info} subsystem in @sc{gnu}
26377 Emacs or the standalone @code{info} program, available as part of the
26378 @sc{gnu} Texinfo distribution.
26380 If you want to format these Info files yourself, you need one of the
26381 Info formatting programs, such as @code{texinfo-format-buffer} or
26384 If you have @code{makeinfo} installed, and are in the top level
26385 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
26386 version @value{GDBVN}), you can make the Info file by typing:
26393 If you want to typeset and print copies of this manual, you need @TeX{},
26394 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
26395 Texinfo definitions file.
26397 @TeX{} is a typesetting program; it does not print files directly, but
26398 produces output files called @sc{dvi} files. To print a typeset
26399 document, you need a program to print @sc{dvi} files. If your system
26400 has @TeX{} installed, chances are it has such a program. The precise
26401 command to use depends on your system; @kbd{lpr -d} is common; another
26402 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
26403 require a file name without any extension or a @samp{.dvi} extension.
26405 @TeX{} also requires a macro definitions file called
26406 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
26407 written in Texinfo format. On its own, @TeX{} cannot either read or
26408 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
26409 and is located in the @file{gdb-@var{version-number}/texinfo}
26412 If you have @TeX{} and a @sc{dvi} printer program installed, you can
26413 typeset and print this manual. First switch to the @file{gdb}
26414 subdirectory of the main source directory (for example, to
26415 @file{gdb-@value{GDBVN}/gdb}) and type:
26421 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
26423 @node Installing GDB
26424 @appendix Installing @value{GDBN}
26425 @cindex installation
26428 * Requirements:: Requirements for building @value{GDBN}
26429 * Running Configure:: Invoking the @value{GDBN} @file{configure} script
26430 * Separate Objdir:: Compiling @value{GDBN} in another directory
26431 * Config Names:: Specifying names for hosts and targets
26432 * Configure Options:: Summary of options for configure
26433 * System-wide configuration:: Having a system-wide init file
26437 @section Requirements for Building @value{GDBN}
26438 @cindex building @value{GDBN}, requirements for
26440 Building @value{GDBN} requires various tools and packages to be available.
26441 Other packages will be used only if they are found.
26443 @heading Tools/Packages Necessary for Building @value{GDBN}
26445 @item ISO C90 compiler
26446 @value{GDBN} is written in ISO C90. It should be buildable with any
26447 working C90 compiler, e.g.@: GCC.
26451 @heading Tools/Packages Optional for Building @value{GDBN}
26455 @value{GDBN} can use the Expat XML parsing library. This library may be
26456 included with your operating system distribution; if it is not, you
26457 can get the latest version from @url{http://expat.sourceforge.net}.
26458 The @file{configure} script will search for this library in several
26459 standard locations; if it is installed in an unusual path, you can
26460 use the @option{--with-libexpat-prefix} option to specify its location.
26466 Remote protocol memory maps (@pxref{Memory Map Format})
26468 Target descriptions (@pxref{Target Descriptions})
26470 Remote shared library lists (@pxref{Library List Format})
26472 MS-Windows shared libraries (@pxref{Shared Libraries})
26476 @cindex compressed debug sections
26477 @value{GDBN} will use the @samp{zlib} library, if available, to read
26478 compressed debug sections. Some linkers, such as GNU gold, are capable
26479 of producing binaries with compressed debug sections. If @value{GDBN}
26480 is compiled with @samp{zlib}, it will be able to read the debug
26481 information in such binaries.
26483 The @samp{zlib} library is likely included with your operating system
26484 distribution; if it is not, you can get the latest version from
26485 @url{http://zlib.net}.
26488 @value{GDBN}'s features related to character sets (@pxref{Character
26489 Sets}) require a functioning @code{iconv} implementation. If you are
26490 on a GNU system, then this is provided by the GNU C Library. Some
26491 other systems also provide a working @code{iconv}.
26493 On systems with @code{iconv}, you can install GNU Libiconv. If you
26494 have previously installed Libiconv, you can use the
26495 @option{--with-libiconv-prefix} option to configure.
26497 @value{GDBN}'s top-level @file{configure} and @file{Makefile} will
26498 arrange to build Libiconv if a directory named @file{libiconv} appears
26499 in the top-most source directory. If Libiconv is built this way, and
26500 if the operating system does not provide a suitable @code{iconv}
26501 implementation, then the just-built library will automatically be used
26502 by @value{GDBN}. One easy way to set this up is to download GNU
26503 Libiconv, unpack it, and then rename the directory holding the
26504 Libiconv source code to @samp{libiconv}.
26507 @node Running Configure
26508 @section Invoking the @value{GDBN} @file{configure} Script
26509 @cindex configuring @value{GDBN}
26510 @value{GDBN} comes with a @file{configure} script that automates the process
26511 of preparing @value{GDBN} for installation; you can then use @code{make} to
26512 build the @code{gdb} program.
26514 @c irrelevant in info file; it's as current as the code it lives with.
26515 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
26516 look at the @file{README} file in the sources; we may have improved the
26517 installation procedures since publishing this manual.}
26520 The @value{GDBN} distribution includes all the source code you need for
26521 @value{GDBN} in a single directory, whose name is usually composed by
26522 appending the version number to @samp{gdb}.
26524 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
26525 @file{gdb-@value{GDBVN}} directory. That directory contains:
26528 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
26529 script for configuring @value{GDBN} and all its supporting libraries
26531 @item gdb-@value{GDBVN}/gdb
26532 the source specific to @value{GDBN} itself
26534 @item gdb-@value{GDBVN}/bfd
26535 source for the Binary File Descriptor library
26537 @item gdb-@value{GDBVN}/include
26538 @sc{gnu} include files
26540 @item gdb-@value{GDBVN}/libiberty
26541 source for the @samp{-liberty} free software library
26543 @item gdb-@value{GDBVN}/opcodes
26544 source for the library of opcode tables and disassemblers
26546 @item gdb-@value{GDBVN}/readline
26547 source for the @sc{gnu} command-line interface
26549 @item gdb-@value{GDBVN}/glob
26550 source for the @sc{gnu} filename pattern-matching subroutine
26552 @item gdb-@value{GDBVN}/mmalloc
26553 source for the @sc{gnu} memory-mapped malloc package
26556 The simplest way to configure and build @value{GDBN} is to run @file{configure}
26557 from the @file{gdb-@var{version-number}} source directory, which in
26558 this example is the @file{gdb-@value{GDBVN}} directory.
26560 First switch to the @file{gdb-@var{version-number}} source directory
26561 if you are not already in it; then run @file{configure}. Pass the
26562 identifier for the platform on which @value{GDBN} will run as an
26568 cd gdb-@value{GDBVN}
26569 ./configure @var{host}
26574 where @var{host} is an identifier such as @samp{sun4} or
26575 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
26576 (You can often leave off @var{host}; @file{configure} tries to guess the
26577 correct value by examining your system.)
26579 Running @samp{configure @var{host}} and then running @code{make} builds the
26580 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
26581 libraries, then @code{gdb} itself. The configured source files, and the
26582 binaries, are left in the corresponding source directories.
26585 @file{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
26586 system does not recognize this automatically when you run a different
26587 shell, you may need to run @code{sh} on it explicitly:
26590 sh configure @var{host}
26593 If you run @file{configure} from a directory that contains source
26594 directories for multiple libraries or programs, such as the
26595 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN},
26597 creates configuration files for every directory level underneath (unless
26598 you tell it not to, with the @samp{--norecursion} option).
26600 You should run the @file{configure} script from the top directory in the
26601 source tree, the @file{gdb-@var{version-number}} directory. If you run
26602 @file{configure} from one of the subdirectories, you will configure only
26603 that subdirectory. That is usually not what you want. In particular,
26604 if you run the first @file{configure} from the @file{gdb} subdirectory
26605 of the @file{gdb-@var{version-number}} directory, you will omit the
26606 configuration of @file{bfd}, @file{readline}, and other sibling
26607 directories of the @file{gdb} subdirectory. This leads to build errors
26608 about missing include files such as @file{bfd/bfd.h}.
26610 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
26611 However, you should make sure that the shell on your path (named by
26612 the @samp{SHELL} environment variable) is publicly readable. Remember
26613 that @value{GDBN} uses the shell to start your program---some systems refuse to
26614 let @value{GDBN} debug child processes whose programs are not readable.
26616 @node Separate Objdir
26617 @section Compiling @value{GDBN} in Another Directory
26619 If you want to run @value{GDBN} versions for several host or target machines,
26620 you need a different @code{gdb} compiled for each combination of
26621 host and target. @file{configure} is designed to make this easy by
26622 allowing you to generate each configuration in a separate subdirectory,
26623 rather than in the source directory. If your @code{make} program
26624 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
26625 @code{make} in each of these directories builds the @code{gdb}
26626 program specified there.
26628 To build @code{gdb} in a separate directory, run @file{configure}
26629 with the @samp{--srcdir} option to specify where to find the source.
26630 (You also need to specify a path to find @file{configure}
26631 itself from your working directory. If the path to @file{configure}
26632 would be the same as the argument to @samp{--srcdir}, you can leave out
26633 the @samp{--srcdir} option; it is assumed.)
26635 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
26636 separate directory for a Sun 4 like this:
26640 cd gdb-@value{GDBVN}
26643 ../gdb-@value{GDBVN}/configure sun4
26648 When @file{configure} builds a configuration using a remote source
26649 directory, it creates a tree for the binaries with the same structure
26650 (and using the same names) as the tree under the source directory. In
26651 the example, you'd find the Sun 4 library @file{libiberty.a} in the
26652 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
26653 @file{gdb-sun4/gdb}.
26655 Make sure that your path to the @file{configure} script has just one
26656 instance of @file{gdb} in it. If your path to @file{configure} looks
26657 like @file{../gdb-@value{GDBVN}/gdb/configure}, you are configuring only
26658 one subdirectory of @value{GDBN}, not the whole package. This leads to
26659 build errors about missing include files such as @file{bfd/bfd.h}.
26661 One popular reason to build several @value{GDBN} configurations in separate
26662 directories is to configure @value{GDBN} for cross-compiling (where
26663 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
26664 programs that run on another machine---the @dfn{target}).
26665 You specify a cross-debugging target by
26666 giving the @samp{--target=@var{target}} option to @file{configure}.
26668 When you run @code{make} to build a program or library, you must run
26669 it in a configured directory---whatever directory you were in when you
26670 called @file{configure} (or one of its subdirectories).
26672 The @code{Makefile} that @file{configure} generates in each source
26673 directory also runs recursively. If you type @code{make} in a source
26674 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
26675 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
26676 will build all the required libraries, and then build GDB.
26678 When you have multiple hosts or targets configured in separate
26679 directories, you can run @code{make} on them in parallel (for example,
26680 if they are NFS-mounted on each of the hosts); they will not interfere
26684 @section Specifying Names for Hosts and Targets
26686 The specifications used for hosts and targets in the @file{configure}
26687 script are based on a three-part naming scheme, but some short predefined
26688 aliases are also supported. The full naming scheme encodes three pieces
26689 of information in the following pattern:
26692 @var{architecture}-@var{vendor}-@var{os}
26695 For example, you can use the alias @code{sun4} as a @var{host} argument,
26696 or as the value for @var{target} in a @code{--target=@var{target}}
26697 option. The equivalent full name is @samp{sparc-sun-sunos4}.
26699 The @file{configure} script accompanying @value{GDBN} does not provide
26700 any query facility to list all supported host and target names or
26701 aliases. @file{configure} calls the Bourne shell script
26702 @code{config.sub} to map abbreviations to full names; you can read the
26703 script, if you wish, or you can use it to test your guesses on
26704 abbreviations---for example:
26707 % sh config.sub i386-linux
26709 % sh config.sub alpha-linux
26710 alpha-unknown-linux-gnu
26711 % sh config.sub hp9k700
26713 % sh config.sub sun4
26714 sparc-sun-sunos4.1.1
26715 % sh config.sub sun3
26716 m68k-sun-sunos4.1.1
26717 % sh config.sub i986v
26718 Invalid configuration `i986v': machine `i986v' not recognized
26722 @code{config.sub} is also distributed in the @value{GDBN} source
26723 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
26725 @node Configure Options
26726 @section @file{configure} Options
26728 Here is a summary of the @file{configure} options and arguments that
26729 are most often useful for building @value{GDBN}. @file{configure} also has
26730 several other options not listed here. @inforef{What Configure
26731 Does,,configure.info}, for a full explanation of @file{configure}.
26734 configure @r{[}--help@r{]}
26735 @r{[}--prefix=@var{dir}@r{]}
26736 @r{[}--exec-prefix=@var{dir}@r{]}
26737 @r{[}--srcdir=@var{dirname}@r{]}
26738 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
26739 @r{[}--target=@var{target}@r{]}
26744 You may introduce options with a single @samp{-} rather than
26745 @samp{--} if you prefer; but you may abbreviate option names if you use
26750 Display a quick summary of how to invoke @file{configure}.
26752 @item --prefix=@var{dir}
26753 Configure the source to install programs and files under directory
26756 @item --exec-prefix=@var{dir}
26757 Configure the source to install programs under directory
26760 @c avoid splitting the warning from the explanation:
26762 @item --srcdir=@var{dirname}
26763 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
26764 @code{make} that implements the @code{VPATH} feature.}@*
26765 Use this option to make configurations in directories separate from the
26766 @value{GDBN} source directories. Among other things, you can use this to
26767 build (or maintain) several configurations simultaneously, in separate
26768 directories. @file{configure} writes configuration-specific files in
26769 the current directory, but arranges for them to use the source in the
26770 directory @var{dirname}. @file{configure} creates directories under
26771 the working directory in parallel to the source directories below
26774 @item --norecursion
26775 Configure only the directory level where @file{configure} is executed; do not
26776 propagate configuration to subdirectories.
26778 @item --target=@var{target}
26779 Configure @value{GDBN} for cross-debugging programs running on the specified
26780 @var{target}. Without this option, @value{GDBN} is configured to debug
26781 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
26783 There is no convenient way to generate a list of all available targets.
26785 @item @var{host} @dots{}
26786 Configure @value{GDBN} to run on the specified @var{host}.
26788 There is no convenient way to generate a list of all available hosts.
26791 There are many other options available as well, but they are generally
26792 needed for special purposes only.
26794 @node System-wide configuration
26795 @section System-wide configuration and settings
26796 @cindex system-wide init file
26798 @value{GDBN} can be configured to have a system-wide init file;
26799 this file will be read and executed at startup (@pxref{Startup, , What
26800 @value{GDBN} does during startup}).
26802 Here is the corresponding configure option:
26805 @item --with-system-gdbinit=@var{file}
26806 Specify that the default location of the system-wide init file is
26810 If @value{GDBN} has been configured with the option @option{--prefix=$prefix},
26811 it may be subject to relocation. Two possible cases:
26815 If the default location of this init file contains @file{$prefix},
26816 it will be subject to relocation. Suppose that the configure options
26817 are @option{--prefix=$prefix --with-system-gdbinit=$prefix/etc/gdbinit};
26818 if @value{GDBN} is moved from @file{$prefix} to @file{$install}, the system
26819 init file is looked for as @file{$install/etc/gdbinit} instead of
26820 @file{$prefix/etc/gdbinit}.
26823 By contrast, if the default location does not contain the prefix,
26824 it will not be relocated. E.g.@: if @value{GDBN} has been configured with
26825 @option{--prefix=/usr/local --with-system-gdbinit=/usr/share/gdb/gdbinit},
26826 then @value{GDBN} will always look for @file{/usr/share/gdb/gdbinit},
26827 wherever @value{GDBN} is installed.
26830 @node Maintenance Commands
26831 @appendix Maintenance Commands
26832 @cindex maintenance commands
26833 @cindex internal commands
26835 In addition to commands intended for @value{GDBN} users, @value{GDBN}
26836 includes a number of commands intended for @value{GDBN} developers,
26837 that are not documented elsewhere in this manual. These commands are
26838 provided here for reference. (For commands that turn on debugging
26839 messages, see @ref{Debugging Output}.)
26842 @kindex maint agent
26843 @kindex maint agent-eval
26844 @item maint agent @var{expression}
26845 @itemx maint agent-eval @var{expression}
26846 Translate the given @var{expression} into remote agent bytecodes.
26847 This command is useful for debugging the Agent Expression mechanism
26848 (@pxref{Agent Expressions}). The @samp{agent} version produces an
26849 expression useful for data collection, such as by tracepoints, while
26850 @samp{maint agent-eval} produces an expression that evaluates directly
26851 to a result. For instance, a collection expression for @code{globa +
26852 globb} will include bytecodes to record four bytes of memory at each
26853 of the addresses of @code{globa} and @code{globb}, while discarding
26854 the result of the addition, while an evaluation expression will do the
26855 addition and return the sum.
26857 @kindex maint info breakpoints
26858 @item @anchor{maint info breakpoints}maint info breakpoints
26859 Using the same format as @samp{info breakpoints}, display both the
26860 breakpoints you've set explicitly, and those @value{GDBN} is using for
26861 internal purposes. Internal breakpoints are shown with negative
26862 breakpoint numbers. The type column identifies what kind of breakpoint
26867 Normal, explicitly set breakpoint.
26870 Normal, explicitly set watchpoint.
26873 Internal breakpoint, used to handle correctly stepping through
26874 @code{longjmp} calls.
26876 @item longjmp resume
26877 Internal breakpoint at the target of a @code{longjmp}.
26880 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
26883 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
26886 Shared library events.
26890 @kindex set displaced-stepping
26891 @kindex show displaced-stepping
26892 @cindex displaced stepping support
26893 @cindex out-of-line single-stepping
26894 @item set displaced-stepping
26895 @itemx show displaced-stepping
26896 Control whether or not @value{GDBN} will do @dfn{displaced stepping}
26897 if the target supports it. Displaced stepping is a way to single-step
26898 over breakpoints without removing them from the inferior, by executing
26899 an out-of-line copy of the instruction that was originally at the
26900 breakpoint location. It is also known as out-of-line single-stepping.
26903 @item set displaced-stepping on
26904 If the target architecture supports it, @value{GDBN} will use
26905 displaced stepping to step over breakpoints.
26907 @item set displaced-stepping off
26908 @value{GDBN} will not use displaced stepping to step over breakpoints,
26909 even if such is supported by the target architecture.
26911 @cindex non-stop mode, and @samp{set displaced-stepping}
26912 @item set displaced-stepping auto
26913 This is the default mode. @value{GDBN} will use displaced stepping
26914 only if non-stop mode is active (@pxref{Non-Stop Mode}) and the target
26915 architecture supports displaced stepping.
26918 @kindex maint check-symtabs
26919 @item maint check-symtabs
26920 Check the consistency of psymtabs and symtabs.
26922 @kindex maint cplus first_component
26923 @item maint cplus first_component @var{name}
26924 Print the first C@t{++} class/namespace component of @var{name}.
26926 @kindex maint cplus namespace
26927 @item maint cplus namespace
26928 Print the list of possible C@t{++} namespaces.
26930 @kindex maint demangle
26931 @item maint demangle @var{name}
26932 Demangle a C@t{++} or Objective-C mangled @var{name}.
26934 @kindex maint deprecate
26935 @kindex maint undeprecate
26936 @cindex deprecated commands
26937 @item maint deprecate @var{command} @r{[}@var{replacement}@r{]}
26938 @itemx maint undeprecate @var{command}
26939 Deprecate or undeprecate the named @var{command}. Deprecated commands
26940 cause @value{GDBN} to issue a warning when you use them. The optional
26941 argument @var{replacement} says which newer command should be used in
26942 favor of the deprecated one; if it is given, @value{GDBN} will mention
26943 the replacement as part of the warning.
26945 @kindex maint dump-me
26946 @item maint dump-me
26947 @cindex @code{SIGQUIT} signal, dump core of @value{GDBN}
26948 Cause a fatal signal in the debugger and force it to dump its core.
26949 This is supported only on systems which support aborting a program
26950 with the @code{SIGQUIT} signal.
26952 @kindex maint internal-error
26953 @kindex maint internal-warning
26954 @item maint internal-error @r{[}@var{message-text}@r{]}
26955 @itemx maint internal-warning @r{[}@var{message-text}@r{]}
26956 Cause @value{GDBN} to call the internal function @code{internal_error}
26957 or @code{internal_warning} and hence behave as though an internal error
26958 or internal warning has been detected. In addition to reporting the
26959 internal problem, these functions give the user the opportunity to
26960 either quit @value{GDBN} or create a core file of the current
26961 @value{GDBN} session.
26963 These commands take an optional parameter @var{message-text} that is
26964 used as the text of the error or warning message.
26966 Here's an example of using @code{internal-error}:
26969 (@value{GDBP}) @kbd{maint internal-error testing, 1, 2}
26970 @dots{}/maint.c:121: internal-error: testing, 1, 2
26971 A problem internal to GDB has been detected. Further
26972 debugging may prove unreliable.
26973 Quit this debugging session? (y or n) @kbd{n}
26974 Create a core file? (y or n) @kbd{n}
26978 @cindex @value{GDBN} internal error
26979 @cindex internal errors, control of @value{GDBN} behavior
26981 @kindex maint set internal-error
26982 @kindex maint show internal-error
26983 @kindex maint set internal-warning
26984 @kindex maint show internal-warning
26985 @item maint set internal-error @var{action} [ask|yes|no]
26986 @itemx maint show internal-error @var{action}
26987 @itemx maint set internal-warning @var{action} [ask|yes|no]
26988 @itemx maint show internal-warning @var{action}
26989 When @value{GDBN} reports an internal problem (error or warning) it
26990 gives the user the opportunity to both quit @value{GDBN} and create a
26991 core file of the current @value{GDBN} session. These commands let you
26992 override the default behaviour for each particular @var{action},
26993 described in the table below.
26997 You can specify that @value{GDBN} should always (yes) or never (no)
26998 quit. The default is to ask the user what to do.
27001 You can specify that @value{GDBN} should always (yes) or never (no)
27002 create a core file. The default is to ask the user what to do.
27005 @kindex maint packet
27006 @item maint packet @var{text}
27007 If @value{GDBN} is talking to an inferior via the serial protocol,
27008 then this command sends the string @var{text} to the inferior, and
27009 displays the response packet. @value{GDBN} supplies the initial
27010 @samp{$} character, the terminating @samp{#} character, and the
27013 @kindex maint print architecture
27014 @item maint print architecture @r{[}@var{file}@r{]}
27015 Print the entire architecture configuration. The optional argument
27016 @var{file} names the file where the output goes.
27018 @kindex maint print c-tdesc
27019 @item maint print c-tdesc
27020 Print the current target description (@pxref{Target Descriptions}) as
27021 a C source file. The created source file can be used in @value{GDBN}
27022 when an XML parser is not available to parse the description.
27024 @kindex maint print dummy-frames
27025 @item maint print dummy-frames
27026 Prints the contents of @value{GDBN}'s internal dummy-frame stack.
27029 (@value{GDBP}) @kbd{b add}
27031 (@value{GDBP}) @kbd{print add(2,3)}
27032 Breakpoint 2, add (a=2, b=3) at @dots{}
27034 The program being debugged stopped while in a function called from GDB.
27036 (@value{GDBP}) @kbd{maint print dummy-frames}
27037 0x1a57c80: pc=0x01014068 fp=0x0200bddc sp=0x0200bdd6
27038 top=0x0200bdd4 id=@{stack=0x200bddc,code=0x101405c@}
27039 call_lo=0x01014000 call_hi=0x01014001
27043 Takes an optional file parameter.
27045 @kindex maint print registers
27046 @kindex maint print raw-registers
27047 @kindex maint print cooked-registers
27048 @kindex maint print register-groups
27049 @item maint print registers @r{[}@var{file}@r{]}
27050 @itemx maint print raw-registers @r{[}@var{file}@r{]}
27051 @itemx maint print cooked-registers @r{[}@var{file}@r{]}
27052 @itemx maint print register-groups @r{[}@var{file}@r{]}
27053 Print @value{GDBN}'s internal register data structures.
27055 The command @code{maint print raw-registers} includes the contents of
27056 the raw register cache; the command @code{maint print cooked-registers}
27057 includes the (cooked) value of all registers; and the command
27058 @code{maint print register-groups} includes the groups that each
27059 register is a member of. @xref{Registers,, Registers, gdbint,
27060 @value{GDBN} Internals}.
27062 These commands take an optional parameter, a file name to which to
27063 write the information.
27065 @kindex maint print reggroups
27066 @item maint print reggroups @r{[}@var{file}@r{]}
27067 Print @value{GDBN}'s internal register group data structures. The
27068 optional argument @var{file} tells to what file to write the
27071 The register groups info looks like this:
27074 (@value{GDBP}) @kbd{maint print reggroups}
27087 This command forces @value{GDBN} to flush its internal register cache.
27089 @kindex maint print objfiles
27090 @cindex info for known object files
27091 @item maint print objfiles
27092 Print a dump of all known object files. For each object file, this
27093 command prints its name, address in memory, and all of its psymtabs
27096 @kindex maint print statistics
27097 @cindex bcache statistics
27098 @item maint print statistics
27099 This command prints, for each object file in the program, various data
27100 about that object file followed by the byte cache (@dfn{bcache})
27101 statistics for the object file. The objfile data includes the number
27102 of minimal, partial, full, and stabs symbols, the number of types
27103 defined by the objfile, the number of as yet unexpanded psym tables,
27104 the number of line tables and string tables, and the amount of memory
27105 used by the various tables. The bcache statistics include the counts,
27106 sizes, and counts of duplicates of all and unique objects, max,
27107 average, and median entry size, total memory used and its overhead and
27108 savings, and various measures of the hash table size and chain
27111 @kindex maint print target-stack
27112 @cindex target stack description
27113 @item maint print target-stack
27114 A @dfn{target} is an interface between the debugger and a particular
27115 kind of file or process. Targets can be stacked in @dfn{strata},
27116 so that more than one target can potentially respond to a request.
27117 In particular, memory accesses will walk down the stack of targets
27118 until they find a target that is interested in handling that particular
27121 This command prints a short description of each layer that was pushed on
27122 the @dfn{target stack}, starting from the top layer down to the bottom one.
27124 @kindex maint print type
27125 @cindex type chain of a data type
27126 @item maint print type @var{expr}
27127 Print the type chain for a type specified by @var{expr}. The argument
27128 can be either a type name or a symbol. If it is a symbol, the type of
27129 that symbol is described. The type chain produced by this command is
27130 a recursive definition of the data type as stored in @value{GDBN}'s
27131 data structures, including its flags and contained types.
27133 @kindex maint set dwarf2 max-cache-age
27134 @kindex maint show dwarf2 max-cache-age
27135 @item maint set dwarf2 max-cache-age
27136 @itemx maint show dwarf2 max-cache-age
27137 Control the DWARF 2 compilation unit cache.
27139 @cindex DWARF 2 compilation units cache
27140 In object files with inter-compilation-unit references, such as those
27141 produced by the GCC option @samp{-feliminate-dwarf2-dups}, the DWARF 2
27142 reader needs to frequently refer to previously read compilation units.
27143 This setting controls how long a compilation unit will remain in the
27144 cache if it is not referenced. A higher limit means that cached
27145 compilation units will be stored in memory longer, and more total
27146 memory will be used. Setting it to zero disables caching, which will
27147 slow down @value{GDBN} startup, but reduce memory consumption.
27149 @kindex maint set profile
27150 @kindex maint show profile
27151 @cindex profiling GDB
27152 @item maint set profile
27153 @itemx maint show profile
27154 Control profiling of @value{GDBN}.
27156 Profiling will be disabled until you use the @samp{maint set profile}
27157 command to enable it. When you enable profiling, the system will begin
27158 collecting timing and execution count data; when you disable profiling or
27159 exit @value{GDBN}, the results will be written to a log file. Remember that
27160 if you use profiling, @value{GDBN} will overwrite the profiling log file
27161 (often called @file{gmon.out}). If you have a record of important profiling
27162 data in a @file{gmon.out} file, be sure to move it to a safe location.
27164 Configuring with @samp{--enable-profiling} arranges for @value{GDBN} to be
27165 compiled with the @samp{-pg} compiler option.
27167 @kindex maint set show-debug-regs
27168 @kindex maint show show-debug-regs
27169 @cindex hardware debug registers
27170 @item maint set show-debug-regs
27171 @itemx maint show show-debug-regs
27172 Control whether to show variables that mirror the hardware debug
27173 registers. Use @code{ON} to enable, @code{OFF} to disable. If
27174 enabled, the debug registers values are shown when @value{GDBN} inserts or
27175 removes a hardware breakpoint or watchpoint, and when the inferior
27176 triggers a hardware-assisted breakpoint or watchpoint.
27178 @kindex maint space
27179 @cindex memory used by commands
27181 Control whether to display memory usage for each command. If set to a
27182 nonzero value, @value{GDBN} will display how much memory each command
27183 took, following the command's own output. This can also be requested
27184 by invoking @value{GDBN} with the @option{--statistics} command-line
27185 switch (@pxref{Mode Options}).
27188 @cindex time of command execution
27190 Control whether to display the execution time for each command. If
27191 set to a nonzero value, @value{GDBN} will display how much time it
27192 took to execute each command, following the command's own output.
27193 The time is not printed for the commands that run the target, since
27194 there's no mechanism currently to compute how much time was spend
27195 by @value{GDBN} and how much time was spend by the program been debugged.
27196 it's not possibly currently
27197 This can also be requested by invoking @value{GDBN} with the
27198 @option{--statistics} command-line switch (@pxref{Mode Options}).
27200 @kindex maint translate-address
27201 @item maint translate-address @r{[}@var{section}@r{]} @var{addr}
27202 Find the symbol stored at the location specified by the address
27203 @var{addr} and an optional section name @var{section}. If found,
27204 @value{GDBN} prints the name of the closest symbol and an offset from
27205 the symbol's location to the specified address. This is similar to
27206 the @code{info address} command (@pxref{Symbols}), except that this
27207 command also allows to find symbols in other sections.
27209 If section was not specified, the section in which the symbol was found
27210 is also printed. For dynamically linked executables, the name of
27211 executable or shared library containing the symbol is printed as well.
27215 The following command is useful for non-interactive invocations of
27216 @value{GDBN}, such as in the test suite.
27219 @item set watchdog @var{nsec}
27220 @kindex set watchdog
27221 @cindex watchdog timer
27222 @cindex timeout for commands
27223 Set the maximum number of seconds @value{GDBN} will wait for the
27224 target operation to finish. If this time expires, @value{GDBN}
27225 reports and error and the command is aborted.
27227 @item show watchdog
27228 Show the current setting of the target wait timeout.
27231 @node Remote Protocol
27232 @appendix @value{GDBN} Remote Serial Protocol
27237 * Stop Reply Packets::
27238 * General Query Packets::
27239 * Register Packet Format::
27240 * Tracepoint Packets::
27241 * Host I/O Packets::
27243 * Notification Packets::
27244 * Remote Non-Stop::
27245 * Packet Acknowledgment::
27247 * File-I/O Remote Protocol Extension::
27248 * Library List Format::
27249 * Memory Map Format::
27255 There may be occasions when you need to know something about the
27256 protocol---for example, if there is only one serial port to your target
27257 machine, you might want your program to do something special if it
27258 recognizes a packet meant for @value{GDBN}.
27260 In the examples below, @samp{->} and @samp{<-} are used to indicate
27261 transmitted and received data, respectively.
27263 @cindex protocol, @value{GDBN} remote serial
27264 @cindex serial protocol, @value{GDBN} remote
27265 @cindex remote serial protocol
27266 All @value{GDBN} commands and responses (other than acknowledgments
27267 and notifications, see @ref{Notification Packets}) are sent as a
27268 @var{packet}. A @var{packet} is introduced with the character
27269 @samp{$}, the actual @var{packet-data}, and the terminating character
27270 @samp{#} followed by a two-digit @var{checksum}:
27273 @code{$}@var{packet-data}@code{#}@var{checksum}
27277 @cindex checksum, for @value{GDBN} remote
27279 The two-digit @var{checksum} is computed as the modulo 256 sum of all
27280 characters between the leading @samp{$} and the trailing @samp{#} (an
27281 eight bit unsigned checksum).
27283 Implementors should note that prior to @value{GDBN} 5.0 the protocol
27284 specification also included an optional two-digit @var{sequence-id}:
27287 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
27290 @cindex sequence-id, for @value{GDBN} remote
27292 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
27293 has never output @var{sequence-id}s. Stubs that handle packets added
27294 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
27296 When either the host or the target machine receives a packet, the first
27297 response expected is an acknowledgment: either @samp{+} (to indicate
27298 the package was received correctly) or @samp{-} (to request
27302 -> @code{$}@var{packet-data}@code{#}@var{checksum}
27307 The @samp{+}/@samp{-} acknowledgments can be disabled
27308 once a connection is established.
27309 @xref{Packet Acknowledgment}, for details.
27311 The host (@value{GDBN}) sends @var{command}s, and the target (the
27312 debugging stub incorporated in your program) sends a @var{response}. In
27313 the case of step and continue @var{command}s, the response is only sent
27314 when the operation has completed, and the target has again stopped all
27315 threads in all attached processes. This is the default all-stop mode
27316 behavior, but the remote protocol also supports @value{GDBN}'s non-stop
27317 execution mode; see @ref{Remote Non-Stop}, for details.
27319 @var{packet-data} consists of a sequence of characters with the
27320 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
27323 @cindex remote protocol, field separator
27324 Fields within the packet should be separated using @samp{,} @samp{;} or
27325 @samp{:}. Except where otherwise noted all numbers are represented in
27326 @sc{hex} with leading zeros suppressed.
27328 Implementors should note that prior to @value{GDBN} 5.0, the character
27329 @samp{:} could not appear as the third character in a packet (as it
27330 would potentially conflict with the @var{sequence-id}).
27332 @cindex remote protocol, binary data
27333 @anchor{Binary Data}
27334 Binary data in most packets is encoded either as two hexadecimal
27335 digits per byte of binary data. This allowed the traditional remote
27336 protocol to work over connections which were only seven-bit clean.
27337 Some packets designed more recently assume an eight-bit clean
27338 connection, and use a more efficient encoding to send and receive
27341 The binary data representation uses @code{7d} (@sc{ascii} @samp{@}})
27342 as an escape character. Any escaped byte is transmitted as the escape
27343 character followed by the original character XORed with @code{0x20}.
27344 For example, the byte @code{0x7d} would be transmitted as the two
27345 bytes @code{0x7d 0x5d}. The bytes @code{0x23} (@sc{ascii} @samp{#}),
27346 @code{0x24} (@sc{ascii} @samp{$}), and @code{0x7d} (@sc{ascii}
27347 @samp{@}}) must always be escaped. Responses sent by the stub
27348 must also escape @code{0x2a} (@sc{ascii} @samp{*}), so that it
27349 is not interpreted as the start of a run-length encoded sequence
27352 Response @var{data} can be run-length encoded to save space.
27353 Run-length encoding replaces runs of identical characters with one
27354 instance of the repeated character, followed by a @samp{*} and a
27355 repeat count. The repeat count is itself sent encoded, to avoid
27356 binary characters in @var{data}: a value of @var{n} is sent as
27357 @code{@var{n}+29}. For a repeat count greater or equal to 3, this
27358 produces a printable @sc{ascii} character, e.g.@: a space (@sc{ascii}
27359 code 32) for a repeat count of 3. (This is because run-length
27360 encoding starts to win for counts 3 or more.) Thus, for example,
27361 @samp{0* } is a run-length encoding of ``0000'': the space character
27362 after @samp{*} means repeat the leading @code{0} @w{@code{32 - 29 =
27365 The printable characters @samp{#} and @samp{$} or with a numeric value
27366 greater than 126 must not be used. Runs of six repeats (@samp{#}) or
27367 seven repeats (@samp{$}) can be expanded using a repeat count of only
27368 five (@samp{"}). For example, @samp{00000000} can be encoded as
27371 The error response returned for some packets includes a two character
27372 error number. That number is not well defined.
27374 @cindex empty response, for unsupported packets
27375 For any @var{command} not supported by the stub, an empty response
27376 (@samp{$#00}) should be returned. That way it is possible to extend the
27377 protocol. A newer @value{GDBN} can tell if a packet is supported based
27380 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
27381 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
27387 The following table provides a complete list of all currently defined
27388 @var{command}s and their corresponding response @var{data}.
27389 @xref{File-I/O Remote Protocol Extension}, for details about the File
27390 I/O extension of the remote protocol.
27392 Each packet's description has a template showing the packet's overall
27393 syntax, followed by an explanation of the packet's meaning. We
27394 include spaces in some of the templates for clarity; these are not
27395 part of the packet's syntax. No @value{GDBN} packet uses spaces to
27396 separate its components. For example, a template like @samp{foo
27397 @var{bar} @var{baz}} describes a packet beginning with the three ASCII
27398 bytes @samp{foo}, followed by a @var{bar}, followed directly by a
27399 @var{baz}. @value{GDBN} does not transmit a space character between the
27400 @samp{foo} and the @var{bar}, or between the @var{bar} and the
27403 @cindex @var{thread-id}, in remote protocol
27404 @anchor{thread-id syntax}
27405 Several packets and replies include a @var{thread-id} field to identify
27406 a thread. Normally these are positive numbers with a target-specific
27407 interpretation, formatted as big-endian hex strings. A @var{thread-id}
27408 can also be a literal @samp{-1} to indicate all threads, or @samp{0} to
27411 In addition, the remote protocol supports a multiprocess feature in
27412 which the @var{thread-id} syntax is extended to optionally include both
27413 process and thread ID fields, as @samp{p@var{pid}.@var{tid}}.
27414 The @var{pid} (process) and @var{tid} (thread) components each have the
27415 format described above: a positive number with target-specific
27416 interpretation formatted as a big-endian hex string, literal @samp{-1}
27417 to indicate all processes or threads (respectively), or @samp{0} to
27418 indicate an arbitrary process or thread. Specifying just a process, as
27419 @samp{p@var{pid}}, is equivalent to @samp{p@var{pid}.-1}. It is an
27420 error to specify all processes but a specific thread, such as
27421 @samp{p-1.@var{tid}}. Note that the @samp{p} prefix is @emph{not} used
27422 for those packets and replies explicitly documented to include a process
27423 ID, rather than a @var{thread-id}.
27425 The multiprocess @var{thread-id} syntax extensions are only used if both
27426 @value{GDBN} and the stub report support for the @samp{multiprocess}
27427 feature using @samp{qSupported}. @xref{multiprocess extensions}, for
27430 Note that all packet forms beginning with an upper- or lower-case
27431 letter, other than those described here, are reserved for future use.
27433 Here are the packet descriptions.
27438 @cindex @samp{!} packet
27439 @anchor{extended mode}
27440 Enable extended mode. In extended mode, the remote server is made
27441 persistent. The @samp{R} packet is used to restart the program being
27447 The remote target both supports and has enabled extended mode.
27451 @cindex @samp{?} packet
27452 Indicate the reason the target halted. The reply is the same as for
27453 step and continue. This packet has a special interpretation when the
27454 target is in non-stop mode; see @ref{Remote Non-Stop}.
27457 @xref{Stop Reply Packets}, for the reply specifications.
27459 @item A @var{arglen},@var{argnum},@var{arg},@dots{}
27460 @cindex @samp{A} packet
27461 Initialized @code{argv[]} array passed into program. @var{arglen}
27462 specifies the number of bytes in the hex encoded byte stream
27463 @var{arg}. See @code{gdbserver} for more details.
27468 The arguments were set.
27474 @cindex @samp{b} packet
27475 (Don't use this packet; its behavior is not well-defined.)
27476 Change the serial line speed to @var{baud}.
27478 JTC: @emph{When does the transport layer state change? When it's
27479 received, or after the ACK is transmitted. In either case, there are
27480 problems if the command or the acknowledgment packet is dropped.}
27482 Stan: @emph{If people really wanted to add something like this, and get
27483 it working for the first time, they ought to modify ser-unix.c to send
27484 some kind of out-of-band message to a specially-setup stub and have the
27485 switch happen "in between" packets, so that from remote protocol's point
27486 of view, nothing actually happened.}
27488 @item B @var{addr},@var{mode}
27489 @cindex @samp{B} packet
27490 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
27491 breakpoint at @var{addr}.
27493 Don't use this packet. Use the @samp{Z} and @samp{z} packets instead
27494 (@pxref{insert breakpoint or watchpoint packet}).
27497 @cindex @samp{bc} packet
27498 Backward continue. Execute the target system in reverse. No parameter.
27499 @xref{Reverse Execution}, for more information.
27502 @xref{Stop Reply Packets}, for the reply specifications.
27505 @cindex @samp{bs} packet
27506 Backward single step. Execute one instruction in reverse. No parameter.
27507 @xref{Reverse Execution}, for more information.
27510 @xref{Stop Reply Packets}, for the reply specifications.
27512 @item c @r{[}@var{addr}@r{]}
27513 @cindex @samp{c} packet
27514 Continue. @var{addr} is address to resume. If @var{addr} is omitted,
27515 resume at current address.
27518 @xref{Stop Reply Packets}, for the reply specifications.
27520 @item C @var{sig}@r{[};@var{addr}@r{]}
27521 @cindex @samp{C} packet
27522 Continue with signal @var{sig} (hex signal number). If
27523 @samp{;@var{addr}} is omitted, resume at same address.
27526 @xref{Stop Reply Packets}, for the reply specifications.
27529 @cindex @samp{d} packet
27532 Don't use this packet; instead, define a general set packet
27533 (@pxref{General Query Packets}).
27537 @cindex @samp{D} packet
27538 The first form of the packet is used to detach @value{GDBN} from the
27539 remote system. It is sent to the remote target
27540 before @value{GDBN} disconnects via the @code{detach} command.
27542 The second form, including a process ID, is used when multiprocess
27543 protocol extensions are enabled (@pxref{multiprocess extensions}), to
27544 detach only a specific process. The @var{pid} is specified as a
27545 big-endian hex string.
27555 @item F @var{RC},@var{EE},@var{CF};@var{XX}
27556 @cindex @samp{F} packet
27557 A reply from @value{GDBN} to an @samp{F} packet sent by the target.
27558 This is part of the File-I/O protocol extension. @xref{File-I/O
27559 Remote Protocol Extension}, for the specification.
27562 @anchor{read registers packet}
27563 @cindex @samp{g} packet
27564 Read general registers.
27568 @item @var{XX@dots{}}
27569 Each byte of register data is described by two hex digits. The bytes
27570 with the register are transmitted in target byte order. The size of
27571 each register and their position within the @samp{g} packet are
27572 determined by the @value{GDBN} internal gdbarch functions
27573 @code{DEPRECATED_REGISTER_RAW_SIZE} and @code{gdbarch_register_name}. The
27574 specification of several standard @samp{g} packets is specified below.
27579 @item G @var{XX@dots{}}
27580 @cindex @samp{G} packet
27581 Write general registers. @xref{read registers packet}, for a
27582 description of the @var{XX@dots{}} data.
27592 @item H @var{c} @var{thread-id}
27593 @cindex @samp{H} packet
27594 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
27595 @samp{G}, et.al.). @var{c} depends on the operation to be performed: it
27596 should be @samp{c} for step and continue operations, @samp{g} for other
27597 operations. The thread designator @var{thread-id} has the format and
27598 interpretation described in @ref{thread-id syntax}.
27609 @c 'H': How restrictive (or permissive) is the thread model. If a
27610 @c thread is selected and stopped, are other threads allowed
27611 @c to continue to execute? As I mentioned above, I think the
27612 @c semantics of each command when a thread is selected must be
27613 @c described. For example:
27615 @c 'g': If the stub supports threads and a specific thread is
27616 @c selected, returns the register block from that thread;
27617 @c otherwise returns current registers.
27619 @c 'G' If the stub supports threads and a specific thread is
27620 @c selected, sets the registers of the register block of
27621 @c that thread; otherwise sets current registers.
27623 @item i @r{[}@var{addr}@r{[},@var{nnn}@r{]]}
27624 @anchor{cycle step packet}
27625 @cindex @samp{i} packet
27626 Step the remote target by a single clock cycle. If @samp{,@var{nnn}} is
27627 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
27628 step starting at that address.
27631 @cindex @samp{I} packet
27632 Signal, then cycle step. @xref{step with signal packet}. @xref{cycle
27636 @cindex @samp{k} packet
27639 FIXME: @emph{There is no description of how to operate when a specific
27640 thread context has been selected (i.e.@: does 'k' kill only that
27643 @item m @var{addr},@var{length}
27644 @cindex @samp{m} packet
27645 Read @var{length} bytes of memory starting at address @var{addr}.
27646 Note that @var{addr} may not be aligned to any particular boundary.
27648 The stub need not use any particular size or alignment when gathering
27649 data from memory for the response; even if @var{addr} is word-aligned
27650 and @var{length} is a multiple of the word size, the stub is free to
27651 use byte accesses, or not. For this reason, this packet may not be
27652 suitable for accessing memory-mapped I/O devices.
27653 @cindex alignment of remote memory accesses
27654 @cindex size of remote memory accesses
27655 @cindex memory, alignment and size of remote accesses
27659 @item @var{XX@dots{}}
27660 Memory contents; each byte is transmitted as a two-digit hexadecimal
27661 number. The reply may contain fewer bytes than requested if the
27662 server was able to read only part of the region of memory.
27667 @item M @var{addr},@var{length}:@var{XX@dots{}}
27668 @cindex @samp{M} packet
27669 Write @var{length} bytes of memory starting at address @var{addr}.
27670 @var{XX@dots{}} is the data; each byte is transmitted as a two-digit
27671 hexadecimal number.
27678 for an error (this includes the case where only part of the data was
27683 @cindex @samp{p} packet
27684 Read the value of register @var{n}; @var{n} is in hex.
27685 @xref{read registers packet}, for a description of how the returned
27686 register value is encoded.
27690 @item @var{XX@dots{}}
27691 the register's value
27695 Indicating an unrecognized @var{query}.
27698 @item P @var{n@dots{}}=@var{r@dots{}}
27699 @anchor{write register packet}
27700 @cindex @samp{P} packet
27701 Write register @var{n@dots{}} with value @var{r@dots{}}. The register
27702 number @var{n} is in hexadecimal, and @var{r@dots{}} contains two hex
27703 digits for each byte in the register (target byte order).
27713 @item q @var{name} @var{params}@dots{}
27714 @itemx Q @var{name} @var{params}@dots{}
27715 @cindex @samp{q} packet
27716 @cindex @samp{Q} packet
27717 General query (@samp{q}) and set (@samp{Q}). These packets are
27718 described fully in @ref{General Query Packets}.
27721 @cindex @samp{r} packet
27722 Reset the entire system.
27724 Don't use this packet; use the @samp{R} packet instead.
27727 @cindex @samp{R} packet
27728 Restart the program being debugged. @var{XX}, while needed, is ignored.
27729 This packet is only available in extended mode (@pxref{extended mode}).
27731 The @samp{R} packet has no reply.
27733 @item s @r{[}@var{addr}@r{]}
27734 @cindex @samp{s} packet
27735 Single step. @var{addr} is the address at which to resume. If
27736 @var{addr} is omitted, resume at same address.
27739 @xref{Stop Reply Packets}, for the reply specifications.
27741 @item S @var{sig}@r{[};@var{addr}@r{]}
27742 @anchor{step with signal packet}
27743 @cindex @samp{S} packet
27744 Step with signal. This is analogous to the @samp{C} packet, but
27745 requests a single-step, rather than a normal resumption of execution.
27748 @xref{Stop Reply Packets}, for the reply specifications.
27750 @item t @var{addr}:@var{PP},@var{MM}
27751 @cindex @samp{t} packet
27752 Search backwards starting at address @var{addr} for a match with pattern
27753 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4 bytes.
27754 @var{addr} must be at least 3 digits.
27756 @item T @var{thread-id}
27757 @cindex @samp{T} packet
27758 Find out if the thread @var{thread-id} is alive. @xref{thread-id syntax}.
27763 thread is still alive
27769 Packets starting with @samp{v} are identified by a multi-letter name,
27770 up to the first @samp{;} or @samp{?} (or the end of the packet).
27772 @item vAttach;@var{pid}
27773 @cindex @samp{vAttach} packet
27774 Attach to a new process with the specified process ID @var{pid}.
27775 The process ID is a
27776 hexadecimal integer identifying the process. In all-stop mode, all
27777 threads in the attached process are stopped; in non-stop mode, it may be
27778 attached without being stopped if that is supported by the target.
27780 @c In non-stop mode, on a successful vAttach, the stub should set the
27781 @c current thread to a thread of the newly-attached process. After
27782 @c attaching, GDB queries for the attached process's thread ID with qC.
27783 @c Also note that, from a user perspective, whether or not the
27784 @c target is stopped on attach in non-stop mode depends on whether you
27785 @c use the foreground or background version of the attach command, not
27786 @c on what vAttach does; GDB does the right thing with respect to either
27787 @c stopping or restarting threads.
27789 This packet is only available in extended mode (@pxref{extended mode}).
27795 @item @r{Any stop packet}
27796 for success in all-stop mode (@pxref{Stop Reply Packets})
27798 for success in non-stop mode (@pxref{Remote Non-Stop})
27801 @item vCont@r{[};@var{action}@r{[}:@var{thread-id}@r{]]}@dots{}
27802 @cindex @samp{vCont} packet
27803 Resume the inferior, specifying different actions for each thread.
27804 If an action is specified with no @var{thread-id}, then it is applied to any
27805 threads that don't have a specific action specified; if no default action is
27806 specified then other threads should remain stopped in all-stop mode and
27807 in their current state in non-stop mode.
27808 Specifying multiple
27809 default actions is an error; specifying no actions is also an error.
27810 Thread IDs are specified using the syntax described in @ref{thread-id syntax}.
27812 Currently supported actions are:
27818 Continue with signal @var{sig}. The signal @var{sig} should be two hex digits.
27822 Step with signal @var{sig}. The signal @var{sig} should be two hex digits.
27826 Stop with signal @var{sig}. The signal @var{sig} should be two hex digits.
27829 The optional argument @var{addr} normally associated with the
27830 @samp{c}, @samp{C}, @samp{s}, and @samp{S} packets is
27831 not supported in @samp{vCont}.
27833 The @samp{t} and @samp{T} actions are only relevant in non-stop mode
27834 (@pxref{Remote Non-Stop}) and may be ignored by the stub otherwise.
27835 A stop reply should be generated for any affected thread not already stopped.
27836 When a thread is stopped by means of a @samp{t} action,
27837 the corresponding stop reply should indicate that the thread has stopped with
27838 signal @samp{0}, regardless of whether the target uses some other signal
27839 as an implementation detail.
27842 @xref{Stop Reply Packets}, for the reply specifications.
27845 @cindex @samp{vCont?} packet
27846 Request a list of actions supported by the @samp{vCont} packet.
27850 @item vCont@r{[};@var{action}@dots{}@r{]}
27851 The @samp{vCont} packet is supported. Each @var{action} is a supported
27852 command in the @samp{vCont} packet.
27854 The @samp{vCont} packet is not supported.
27857 @item vFile:@var{operation}:@var{parameter}@dots{}
27858 @cindex @samp{vFile} packet
27859 Perform a file operation on the target system. For details,
27860 see @ref{Host I/O Packets}.
27862 @item vFlashErase:@var{addr},@var{length}
27863 @cindex @samp{vFlashErase} packet
27864 Direct the stub to erase @var{length} bytes of flash starting at
27865 @var{addr}. The region may enclose any number of flash blocks, but
27866 its start and end must fall on block boundaries, as indicated by the
27867 flash block size appearing in the memory map (@pxref{Memory Map
27868 Format}). @value{GDBN} groups flash memory programming operations
27869 together, and sends a @samp{vFlashDone} request after each group; the
27870 stub is allowed to delay erase operation until the @samp{vFlashDone}
27871 packet is received.
27873 The stub must support @samp{vCont} if it reports support for
27874 multiprocess extensions (@pxref{multiprocess extensions}). Note that in
27875 this case @samp{vCont} actions can be specified to apply to all threads
27876 in a process by using the @samp{p@var{pid}.-1} form of the
27887 @item vFlashWrite:@var{addr}:@var{XX@dots{}}
27888 @cindex @samp{vFlashWrite} packet
27889 Direct the stub to write data to flash address @var{addr}. The data
27890 is passed in binary form using the same encoding as for the @samp{X}
27891 packet (@pxref{Binary Data}). The memory ranges specified by
27892 @samp{vFlashWrite} packets preceding a @samp{vFlashDone} packet must
27893 not overlap, and must appear in order of increasing addresses
27894 (although @samp{vFlashErase} packets for higher addresses may already
27895 have been received; the ordering is guaranteed only between
27896 @samp{vFlashWrite} packets). If a packet writes to an address that was
27897 neither erased by a preceding @samp{vFlashErase} packet nor by some other
27898 target-specific method, the results are unpredictable.
27906 for vFlashWrite addressing non-flash memory
27912 @cindex @samp{vFlashDone} packet
27913 Indicate to the stub that flash programming operation is finished.
27914 The stub is permitted to delay or batch the effects of a group of
27915 @samp{vFlashErase} and @samp{vFlashWrite} packets until a
27916 @samp{vFlashDone} packet is received. The contents of the affected
27917 regions of flash memory are unpredictable until the @samp{vFlashDone}
27918 request is completed.
27920 @item vKill;@var{pid}
27921 @cindex @samp{vKill} packet
27922 Kill the process with the specified process ID. @var{pid} is a
27923 hexadecimal integer identifying the process. This packet is used in
27924 preference to @samp{k} when multiprocess protocol extensions are
27925 supported; see @ref{multiprocess extensions}.
27935 @item vRun;@var{filename}@r{[};@var{argument}@r{]}@dots{}
27936 @cindex @samp{vRun} packet
27937 Run the program @var{filename}, passing it each @var{argument} on its
27938 command line. The file and arguments are hex-encoded strings. If
27939 @var{filename} is an empty string, the stub may use a default program
27940 (e.g.@: the last program run). The program is created in the stopped
27943 @c FIXME: What about non-stop mode?
27945 This packet is only available in extended mode (@pxref{extended mode}).
27951 @item @r{Any stop packet}
27952 for success (@pxref{Stop Reply Packets})
27956 @anchor{vStopped packet}
27957 @cindex @samp{vStopped} packet
27959 In non-stop mode (@pxref{Remote Non-Stop}), acknowledge a previous stop
27960 reply and prompt for the stub to report another one.
27964 @item @r{Any stop packet}
27965 if there is another unreported stop event (@pxref{Stop Reply Packets})
27967 if there are no unreported stop events
27970 @item X @var{addr},@var{length}:@var{XX@dots{}}
27972 @cindex @samp{X} packet
27973 Write data to memory, where the data is transmitted in binary.
27974 @var{addr} is address, @var{length} is number of bytes,
27975 @samp{@var{XX}@dots{}} is binary data (@pxref{Binary Data}).
27985 @item z @var{type},@var{addr},@var{length}
27986 @itemx Z @var{type},@var{addr},@var{length}
27987 @anchor{insert breakpoint or watchpoint packet}
27988 @cindex @samp{z} packet
27989 @cindex @samp{Z} packets
27990 Insert (@samp{Z}) or remove (@samp{z}) a @var{type} breakpoint or
27991 watchpoint starting at address @var{address} and covering the next
27992 @var{length} bytes.
27994 Each breakpoint and watchpoint packet @var{type} is documented
27997 @emph{Implementation notes: A remote target shall return an empty string
27998 for an unrecognized breakpoint or watchpoint packet @var{type}. A
27999 remote target shall support either both or neither of a given
28000 @samp{Z@var{type}@dots{}} and @samp{z@var{type}@dots{}} packet pair. To
28001 avoid potential problems with duplicate packets, the operations should
28002 be implemented in an idempotent way.}
28004 @item z0,@var{addr},@var{length}
28005 @itemx Z0,@var{addr},@var{length}
28006 @cindex @samp{z0} packet
28007 @cindex @samp{Z0} packet
28008 Insert (@samp{Z0}) or remove (@samp{z0}) a memory breakpoint at address
28009 @var{addr} of size @var{length}.
28011 A memory breakpoint is implemented by replacing the instruction at
28012 @var{addr} with a software breakpoint or trap instruction. The
28013 @var{length} is used by targets that indicates the size of the
28014 breakpoint (in bytes) that should be inserted (e.g., the @sc{arm} and
28015 @sc{mips} can insert either a 2 or 4 byte breakpoint).
28017 @emph{Implementation note: It is possible for a target to copy or move
28018 code that contains memory breakpoints (e.g., when implementing
28019 overlays). The behavior of this packet, in the presence of such a
28020 target, is not defined.}
28032 @item z1,@var{addr},@var{length}
28033 @itemx Z1,@var{addr},@var{length}
28034 @cindex @samp{z1} packet
28035 @cindex @samp{Z1} packet
28036 Insert (@samp{Z1}) or remove (@samp{z1}) a hardware breakpoint at
28037 address @var{addr} of size @var{length}.
28039 A hardware breakpoint is implemented using a mechanism that is not
28040 dependant on being able to modify the target's memory.
28042 @emph{Implementation note: A hardware breakpoint is not affected by code
28055 @item z2,@var{addr},@var{length}
28056 @itemx Z2,@var{addr},@var{length}
28057 @cindex @samp{z2} packet
28058 @cindex @samp{Z2} packet
28059 Insert (@samp{Z2}) or remove (@samp{z2}) a write watchpoint.
28071 @item z3,@var{addr},@var{length}
28072 @itemx Z3,@var{addr},@var{length}
28073 @cindex @samp{z3} packet
28074 @cindex @samp{Z3} packet
28075 Insert (@samp{Z3}) or remove (@samp{z3}) a read watchpoint.
28087 @item z4,@var{addr},@var{length}
28088 @itemx Z4,@var{addr},@var{length}
28089 @cindex @samp{z4} packet
28090 @cindex @samp{Z4} packet
28091 Insert (@samp{Z4}) or remove (@samp{z4}) an access watchpoint.
28105 @node Stop Reply Packets
28106 @section Stop Reply Packets
28107 @cindex stop reply packets
28109 The @samp{C}, @samp{c}, @samp{S}, @samp{s}, @samp{vCont},
28110 @samp{vAttach}, @samp{vRun}, @samp{vStopped}, and @samp{?} packets can
28111 receive any of the below as a reply. Except for @samp{?}
28112 and @samp{vStopped}, that reply is only returned
28113 when the target halts. In the below the exact meaning of @dfn{signal
28114 number} is defined by the header @file{include/gdb/signals.h} in the
28115 @value{GDBN} source code.
28117 As in the description of request packets, we include spaces in the
28118 reply templates for clarity; these are not part of the reply packet's
28119 syntax. No @value{GDBN} stop reply packet uses spaces to separate its
28125 The program received signal number @var{AA} (a two-digit hexadecimal
28126 number). This is equivalent to a @samp{T} response with no
28127 @var{n}:@var{r} pairs.
28129 @item T @var{AA} @var{n1}:@var{r1};@var{n2}:@var{r2};@dots{}
28130 @cindex @samp{T} packet reply
28131 The program received signal number @var{AA} (a two-digit hexadecimal
28132 number). This is equivalent to an @samp{S} response, except that the
28133 @samp{@var{n}:@var{r}} pairs can carry values of important registers
28134 and other information directly in the stop reply packet, reducing
28135 round-trip latency. Single-step and breakpoint traps are reported
28136 this way. Each @samp{@var{n}:@var{r}} pair is interpreted as follows:
28140 If @var{n} is a hexadecimal number, it is a register number, and the
28141 corresponding @var{r} gives that register's value. @var{r} is a
28142 series of bytes in target byte order, with each byte given by a
28143 two-digit hex number.
28146 If @var{n} is @samp{thread}, then @var{r} is the @var{thread-id} of
28147 the stopped thread, as specified in @ref{thread-id syntax}.
28150 If @var{n} is a recognized @dfn{stop reason}, it describes a more
28151 specific event that stopped the target. The currently defined stop
28152 reasons are listed below. @var{aa} should be @samp{05}, the trap
28153 signal. At most one stop reason should be present.
28156 Otherwise, @value{GDBN} should ignore this @samp{@var{n}:@var{r}} pair
28157 and go on to the next; this allows us to extend the protocol in the
28161 The currently defined stop reasons are:
28167 The packet indicates a watchpoint hit, and @var{r} is the data address, in
28170 @cindex shared library events, remote reply
28172 The packet indicates that the loaded libraries have changed.
28173 @value{GDBN} should use @samp{qXfer:libraries:read} to fetch a new
28174 list of loaded libraries. @var{r} is ignored.
28176 @cindex replay log events, remote reply
28178 The packet indicates that the target cannot continue replaying
28179 logged execution events, because it has reached the end (or the
28180 beginning when executing backward) of the log. The value of @var{r}
28181 will be either @samp{begin} or @samp{end}. @xref{Reverse Execution},
28182 for more information.
28188 @itemx W @var{AA} ; process:@var{pid}
28189 The process exited, and @var{AA} is the exit status. This is only
28190 applicable to certain targets.
28192 The second form of the response, including the process ID of the exited
28193 process, can be used only when @value{GDBN} has reported support for
28194 multiprocess protocol extensions; see @ref{multiprocess extensions}.
28195 The @var{pid} is formatted as a big-endian hex string.
28198 @itemx X @var{AA} ; process:@var{pid}
28199 The process terminated with signal @var{AA}.
28201 The second form of the response, including the process ID of the
28202 terminated process, can be used only when @value{GDBN} has reported
28203 support for multiprocess protocol extensions; see @ref{multiprocess
28204 extensions}. The @var{pid} is formatted as a big-endian hex string.
28206 @item O @var{XX}@dots{}
28207 @samp{@var{XX}@dots{}} is hex encoding of @sc{ascii} data, to be
28208 written as the program's console output. This can happen at any time
28209 while the program is running and the debugger should continue to wait
28210 for @samp{W}, @samp{T}, etc. This reply is not permitted in non-stop mode.
28212 @item F @var{call-id},@var{parameter}@dots{}
28213 @var{call-id} is the identifier which says which host system call should
28214 be called. This is just the name of the function. Translation into the
28215 correct system call is only applicable as it's defined in @value{GDBN}.
28216 @xref{File-I/O Remote Protocol Extension}, for a list of implemented
28219 @samp{@var{parameter}@dots{}} is a list of parameters as defined for
28220 this very system call.
28222 The target replies with this packet when it expects @value{GDBN} to
28223 call a host system call on behalf of the target. @value{GDBN} replies
28224 with an appropriate @samp{F} packet and keeps up waiting for the next
28225 reply packet from the target. The latest @samp{C}, @samp{c}, @samp{S}
28226 or @samp{s} action is expected to be continued. @xref{File-I/O Remote
28227 Protocol Extension}, for more details.
28231 @node General Query Packets
28232 @section General Query Packets
28233 @cindex remote query requests
28235 Packets starting with @samp{q} are @dfn{general query packets};
28236 packets starting with @samp{Q} are @dfn{general set packets}. General
28237 query and set packets are a semi-unified form for retrieving and
28238 sending information to and from the stub.
28240 The initial letter of a query or set packet is followed by a name
28241 indicating what sort of thing the packet applies to. For example,
28242 @value{GDBN} may use a @samp{qSymbol} packet to exchange symbol
28243 definitions with the stub. These packet names follow some
28248 The name must not contain commas, colons or semicolons.
28250 Most @value{GDBN} query and set packets have a leading upper case
28253 The names of custom vendor packets should use a company prefix, in
28254 lower case, followed by a period. For example, packets designed at
28255 the Acme Corporation might begin with @samp{qacme.foo} (for querying
28256 foos) or @samp{Qacme.bar} (for setting bars).
28259 The name of a query or set packet should be separated from any
28260 parameters by a @samp{:}; the parameters themselves should be
28261 separated by @samp{,} or @samp{;}. Stubs must be careful to match the
28262 full packet name, and check for a separator or the end of the packet,
28263 in case two packet names share a common prefix. New packets should not begin
28264 with @samp{qC}, @samp{qP}, or @samp{qL}@footnote{The @samp{qP} and @samp{qL}
28265 packets predate these conventions, and have arguments without any terminator
28266 for the packet name; we suspect they are in widespread use in places that
28267 are difficult to upgrade. The @samp{qC} packet has no arguments, but some
28268 existing stubs (e.g.@: RedBoot) are known to not check for the end of the
28271 Like the descriptions of the other packets, each description here
28272 has a template showing the packet's overall syntax, followed by an
28273 explanation of the packet's meaning. We include spaces in some of the
28274 templates for clarity; these are not part of the packet's syntax. No
28275 @value{GDBN} packet uses spaces to separate its components.
28277 Here are the currently defined query and set packets:
28282 @cindex current thread, remote request
28283 @cindex @samp{qC} packet
28284 Return the current thread ID.
28288 @item QC @var{thread-id}
28289 Where @var{thread-id} is a thread ID as documented in
28290 @ref{thread-id syntax}.
28291 @item @r{(anything else)}
28292 Any other reply implies the old thread ID.
28295 @item qCRC:@var{addr},@var{length}
28296 @cindex CRC of memory block, remote request
28297 @cindex @samp{qCRC} packet
28298 Compute the CRC checksum of a block of memory using CRC-32 defined in
28299 IEEE 802.3. The CRC is computed byte at a time, taking the most
28300 significant bit of each byte first. The initial pattern code
28301 @code{0xffffffff} is used to ensure leading zeros affect the CRC.
28303 @emph{Note:} This is the same CRC used in validating separate debug
28304 files (@pxref{Separate Debug Files, , Debugging Information in Separate
28305 Files}). However the algorithm is slightly different. When validating
28306 separate debug files, the CRC is computed taking the @emph{least}
28307 significant bit of each byte first, and the final result is inverted to
28308 detect trailing zeros.
28313 An error (such as memory fault)
28314 @item C @var{crc32}
28315 The specified memory region's checksum is @var{crc32}.
28319 @itemx qsThreadInfo
28320 @cindex list active threads, remote request
28321 @cindex @samp{qfThreadInfo} packet
28322 @cindex @samp{qsThreadInfo} packet
28323 Obtain a list of all active thread IDs from the target (OS). Since there
28324 may be too many active threads to fit into one reply packet, this query
28325 works iteratively: it may require more than one query/reply sequence to
28326 obtain the entire list of threads. The first query of the sequence will
28327 be the @samp{qfThreadInfo} query; subsequent queries in the
28328 sequence will be the @samp{qsThreadInfo} query.
28330 NOTE: This packet replaces the @samp{qL} query (see below).
28334 @item m @var{thread-id}
28336 @item m @var{thread-id},@var{thread-id}@dots{}
28337 a comma-separated list of thread IDs
28339 (lower case letter @samp{L}) denotes end of list.
28342 In response to each query, the target will reply with a list of one or
28343 more thread IDs, separated by commas.
28344 @value{GDBN} will respond to each reply with a request for more thread
28345 ids (using the @samp{qs} form of the query), until the target responds
28346 with @samp{l} (lower-case el, for @dfn{last}).
28347 Refer to @ref{thread-id syntax}, for the format of the @var{thread-id}
28350 @item qGetTLSAddr:@var{thread-id},@var{offset},@var{lm}
28351 @cindex get thread-local storage address, remote request
28352 @cindex @samp{qGetTLSAddr} packet
28353 Fetch the address associated with thread local storage specified
28354 by @var{thread-id}, @var{offset}, and @var{lm}.
28356 @var{thread-id} is the thread ID associated with the
28357 thread for which to fetch the TLS address. @xref{thread-id syntax}.
28359 @var{offset} is the (big endian, hex encoded) offset associated with the
28360 thread local variable. (This offset is obtained from the debug
28361 information associated with the variable.)
28363 @var{lm} is the (big endian, hex encoded) OS/ABI-specific encoding of the
28364 the load module associated with the thread local storage. For example,
28365 a @sc{gnu}/Linux system will pass the link map address of the shared
28366 object associated with the thread local storage under consideration.
28367 Other operating environments may choose to represent the load module
28368 differently, so the precise meaning of this parameter will vary.
28372 @item @var{XX}@dots{}
28373 Hex encoded (big endian) bytes representing the address of the thread
28374 local storage requested.
28377 An error occurred. @var{nn} are hex digits.
28380 An empty reply indicates that @samp{qGetTLSAddr} is not supported by the stub.
28383 @item qL @var{startflag} @var{threadcount} @var{nextthread}
28384 Obtain thread information from RTOS. Where: @var{startflag} (one hex
28385 digit) is one to indicate the first query and zero to indicate a
28386 subsequent query; @var{threadcount} (two hex digits) is the maximum
28387 number of threads the response packet can contain; and @var{nextthread}
28388 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
28389 returned in the response as @var{argthread}.
28391 Don't use this packet; use the @samp{qfThreadInfo} query instead (see above).
28395 @item qM @var{count} @var{done} @var{argthread} @var{thread}@dots{}
28396 Where: @var{count} (two hex digits) is the number of threads being
28397 returned; @var{done} (one hex digit) is zero to indicate more threads
28398 and one indicates no further threads; @var{argthreadid} (eight hex
28399 digits) is @var{nextthread} from the request packet; @var{thread}@dots{}
28400 is a sequence of thread IDs from the target. @var{threadid} (eight hex
28401 digits). See @code{remote.c:parse_threadlist_response()}.
28405 @cindex section offsets, remote request
28406 @cindex @samp{qOffsets} packet
28407 Get section offsets that the target used when relocating the downloaded
28412 @item Text=@var{xxx};Data=@var{yyy}@r{[};Bss=@var{zzz}@r{]}
28413 Relocate the @code{Text} section by @var{xxx} from its original address.
28414 Relocate the @code{Data} section by @var{yyy} from its original address.
28415 If the object file format provides segment information (e.g.@: @sc{elf}
28416 @samp{PT_LOAD} program headers), @value{GDBN} will relocate entire
28417 segments by the supplied offsets.
28419 @emph{Note: while a @code{Bss} offset may be included in the response,
28420 @value{GDBN} ignores this and instead applies the @code{Data} offset
28421 to the @code{Bss} section.}
28423 @item TextSeg=@var{xxx}@r{[};DataSeg=@var{yyy}@r{]}
28424 Relocate the first segment of the object file, which conventionally
28425 contains program code, to a starting address of @var{xxx}. If
28426 @samp{DataSeg} is specified, relocate the second segment, which
28427 conventionally contains modifiable data, to a starting address of
28428 @var{yyy}. @value{GDBN} will report an error if the object file
28429 does not contain segment information, or does not contain at least
28430 as many segments as mentioned in the reply. Extra segments are
28431 kept at fixed offsets relative to the last relocated segment.
28434 @item qP @var{mode} @var{thread-id}
28435 @cindex thread information, remote request
28436 @cindex @samp{qP} packet
28437 Returns information on @var{thread-id}. Where: @var{mode} is a hex
28438 encoded 32 bit mode; @var{thread-id} is a thread ID
28439 (@pxref{thread-id syntax}).
28441 Don't use this packet; use the @samp{qThreadExtraInfo} query instead
28444 Reply: see @code{remote.c:remote_unpack_thread_info_response()}.
28448 @cindex non-stop mode, remote request
28449 @cindex @samp{QNonStop} packet
28451 Enter non-stop (@samp{QNonStop:1}) or all-stop (@samp{QNonStop:0}) mode.
28452 @xref{Remote Non-Stop}, for more information.
28457 The request succeeded.
28460 An error occurred. @var{nn} are hex digits.
28463 An empty reply indicates that @samp{QNonStop} is not supported by
28467 This packet is not probed by default; the remote stub must request it,
28468 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28469 Use of this packet is controlled by the @code{set non-stop} command;
28470 @pxref{Non-Stop Mode}.
28472 @item QPassSignals: @var{signal} @r{[};@var{signal}@r{]}@dots{}
28473 @cindex pass signals to inferior, remote request
28474 @cindex @samp{QPassSignals} packet
28475 @anchor{QPassSignals}
28476 Each listed @var{signal} should be passed directly to the inferior process.
28477 Signals are numbered identically to continue packets and stop replies
28478 (@pxref{Stop Reply Packets}). Each @var{signal} list item should be
28479 strictly greater than the previous item. These signals do not need to stop
28480 the inferior, or be reported to @value{GDBN}. All other signals should be
28481 reported to @value{GDBN}. Multiple @samp{QPassSignals} packets do not
28482 combine; any earlier @samp{QPassSignals} list is completely replaced by the
28483 new list. This packet improves performance when using @samp{handle
28484 @var{signal} nostop noprint pass}.
28489 The request succeeded.
28492 An error occurred. @var{nn} are hex digits.
28495 An empty reply indicates that @samp{QPassSignals} is not supported by
28499 Use of this packet is controlled by the @code{set remote pass-signals}
28500 command (@pxref{Remote Configuration, set remote pass-signals}).
28501 This packet is not probed by default; the remote stub must request it,
28502 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28504 @item qRcmd,@var{command}
28505 @cindex execute remote command, remote request
28506 @cindex @samp{qRcmd} packet
28507 @var{command} (hex encoded) is passed to the local interpreter for
28508 execution. Invalid commands should be reported using the output
28509 string. Before the final result packet, the target may also respond
28510 with a number of intermediate @samp{O@var{output}} console output
28511 packets. @emph{Implementors should note that providing access to a
28512 stubs's interpreter may have security implications}.
28517 A command response with no output.
28519 A command response with the hex encoded output string @var{OUTPUT}.
28521 Indicate a badly formed request.
28523 An empty reply indicates that @samp{qRcmd} is not recognized.
28526 (Note that the @code{qRcmd} packet's name is separated from the
28527 command by a @samp{,}, not a @samp{:}, contrary to the naming
28528 conventions above. Please don't use this packet as a model for new
28531 @item qSearch:memory:@var{address};@var{length};@var{search-pattern}
28532 @cindex searching memory, in remote debugging
28533 @cindex @samp{qSearch:memory} packet
28534 @anchor{qSearch memory}
28535 Search @var{length} bytes at @var{address} for @var{search-pattern}.
28536 @var{address} and @var{length} are encoded in hex.
28537 @var{search-pattern} is a sequence of bytes, hex encoded.
28542 The pattern was not found.
28544 The pattern was found at @var{address}.
28546 A badly formed request or an error was encountered while searching memory.
28548 An empty reply indicates that @samp{qSearch:memory} is not recognized.
28551 @item QStartNoAckMode
28552 @cindex @samp{QStartNoAckMode} packet
28553 @anchor{QStartNoAckMode}
28554 Request that the remote stub disable the normal @samp{+}/@samp{-}
28555 protocol acknowledgments (@pxref{Packet Acknowledgment}).
28560 The stub has switched to no-acknowledgment mode.
28561 @value{GDBN} acknowledges this reponse,
28562 but neither the stub nor @value{GDBN} shall send or expect further
28563 @samp{+}/@samp{-} acknowledgments in the current connection.
28565 An empty reply indicates that the stub does not support no-acknowledgment mode.
28568 @item qSupported @r{[}:@var{gdbfeature} @r{[};@var{gdbfeature}@r{]}@dots{} @r{]}
28569 @cindex supported packets, remote query
28570 @cindex features of the remote protocol
28571 @cindex @samp{qSupported} packet
28572 @anchor{qSupported}
28573 Tell the remote stub about features supported by @value{GDBN}, and
28574 query the stub for features it supports. This packet allows
28575 @value{GDBN} and the remote stub to take advantage of each others'
28576 features. @samp{qSupported} also consolidates multiple feature probes
28577 at startup, to improve @value{GDBN} performance---a single larger
28578 packet performs better than multiple smaller probe packets on
28579 high-latency links. Some features may enable behavior which must not
28580 be on by default, e.g.@: because it would confuse older clients or
28581 stubs. Other features may describe packets which could be
28582 automatically probed for, but are not. These features must be
28583 reported before @value{GDBN} will use them. This ``default
28584 unsupported'' behavior is not appropriate for all packets, but it
28585 helps to keep the initial connection time under control with new
28586 versions of @value{GDBN} which support increasing numbers of packets.
28590 @item @var{stubfeature} @r{[};@var{stubfeature}@r{]}@dots{}
28591 The stub supports or does not support each returned @var{stubfeature},
28592 depending on the form of each @var{stubfeature} (see below for the
28595 An empty reply indicates that @samp{qSupported} is not recognized,
28596 or that no features needed to be reported to @value{GDBN}.
28599 The allowed forms for each feature (either a @var{gdbfeature} in the
28600 @samp{qSupported} packet, or a @var{stubfeature} in the response)
28604 @item @var{name}=@var{value}
28605 The remote protocol feature @var{name} is supported, and associated
28606 with the specified @var{value}. The format of @var{value} depends
28607 on the feature, but it must not include a semicolon.
28609 The remote protocol feature @var{name} is supported, and does not
28610 need an associated value.
28612 The remote protocol feature @var{name} is not supported.
28614 The remote protocol feature @var{name} may be supported, and
28615 @value{GDBN} should auto-detect support in some other way when it is
28616 needed. This form will not be used for @var{gdbfeature} notifications,
28617 but may be used for @var{stubfeature} responses.
28620 Whenever the stub receives a @samp{qSupported} request, the
28621 supplied set of @value{GDBN} features should override any previous
28622 request. This allows @value{GDBN} to put the stub in a known
28623 state, even if the stub had previously been communicating with
28624 a different version of @value{GDBN}.
28626 The following values of @var{gdbfeature} (for the packet sent by @value{GDBN})
28631 This feature indicates whether @value{GDBN} supports multiprocess
28632 extensions to the remote protocol. @value{GDBN} does not use such
28633 extensions unless the stub also reports that it supports them by
28634 including @samp{multiprocess+} in its @samp{qSupported} reply.
28635 @xref{multiprocess extensions}, for details.
28638 Stubs should ignore any unknown values for
28639 @var{gdbfeature}. Any @value{GDBN} which sends a @samp{qSupported}
28640 packet supports receiving packets of unlimited length (earlier
28641 versions of @value{GDBN} may reject overly long responses). Additional values
28642 for @var{gdbfeature} may be defined in the future to let the stub take
28643 advantage of new features in @value{GDBN}, e.g.@: incompatible
28644 improvements in the remote protocol---the @samp{multiprocess} feature is
28645 an example of such a feature. The stub's reply should be independent
28646 of the @var{gdbfeature} entries sent by @value{GDBN}; first @value{GDBN}
28647 describes all the features it supports, and then the stub replies with
28648 all the features it supports.
28650 Similarly, @value{GDBN} will silently ignore unrecognized stub feature
28651 responses, as long as each response uses one of the standard forms.
28653 Some features are flags. A stub which supports a flag feature
28654 should respond with a @samp{+} form response. Other features
28655 require values, and the stub should respond with an @samp{=}
28658 Each feature has a default value, which @value{GDBN} will use if
28659 @samp{qSupported} is not available or if the feature is not mentioned
28660 in the @samp{qSupported} response. The default values are fixed; a
28661 stub is free to omit any feature responses that match the defaults.
28663 Not all features can be probed, but for those which can, the probing
28664 mechanism is useful: in some cases, a stub's internal
28665 architecture may not allow the protocol layer to know some information
28666 about the underlying target in advance. This is especially common in
28667 stubs which may be configured for multiple targets.
28669 These are the currently defined stub features and their properties:
28671 @multitable @columnfractions 0.35 0.2 0.12 0.2
28672 @c NOTE: The first row should be @headitem, but we do not yet require
28673 @c a new enough version of Texinfo (4.7) to use @headitem.
28675 @tab Value Required
28679 @item @samp{PacketSize}
28684 @item @samp{qXfer:auxv:read}
28689 @item @samp{qXfer:features:read}
28694 @item @samp{qXfer:libraries:read}
28699 @item @samp{qXfer:memory-map:read}
28704 @item @samp{qXfer:spu:read}
28709 @item @samp{qXfer:spu:write}
28714 @item @samp{qXfer:siginfo:read}
28719 @item @samp{qXfer:siginfo:write}
28724 @item @samp{QNonStop}
28729 @item @samp{QPassSignals}
28734 @item @samp{QStartNoAckMode}
28739 @item @samp{multiprocess}
28744 @item @samp{ConditionalTracepoints}
28751 These are the currently defined stub features, in more detail:
28754 @cindex packet size, remote protocol
28755 @item PacketSize=@var{bytes}
28756 The remote stub can accept packets up to at least @var{bytes} in
28757 length. @value{GDBN} will send packets up to this size for bulk
28758 transfers, and will never send larger packets. This is a limit on the
28759 data characters in the packet, including the frame and checksum.
28760 There is no trailing NUL byte in a remote protocol packet; if the stub
28761 stores packets in a NUL-terminated format, it should allow an extra
28762 byte in its buffer for the NUL. If this stub feature is not supported,
28763 @value{GDBN} guesses based on the size of the @samp{g} packet response.
28765 @item qXfer:auxv:read
28766 The remote stub understands the @samp{qXfer:auxv:read} packet
28767 (@pxref{qXfer auxiliary vector read}).
28769 @item qXfer:features:read
28770 The remote stub understands the @samp{qXfer:features:read} packet
28771 (@pxref{qXfer target description read}).
28773 @item qXfer:libraries:read
28774 The remote stub understands the @samp{qXfer:libraries:read} packet
28775 (@pxref{qXfer library list read}).
28777 @item qXfer:memory-map:read
28778 The remote stub understands the @samp{qXfer:memory-map:read} packet
28779 (@pxref{qXfer memory map read}).
28781 @item qXfer:spu:read
28782 The remote stub understands the @samp{qXfer:spu:read} packet
28783 (@pxref{qXfer spu read}).
28785 @item qXfer:spu:write
28786 The remote stub understands the @samp{qXfer:spu:write} packet
28787 (@pxref{qXfer spu write}).
28789 @item qXfer:siginfo:read
28790 The remote stub understands the @samp{qXfer:siginfo:read} packet
28791 (@pxref{qXfer siginfo read}).
28793 @item qXfer:siginfo:write
28794 The remote stub understands the @samp{qXfer:siginfo:write} packet
28795 (@pxref{qXfer siginfo write}).
28798 The remote stub understands the @samp{QNonStop} packet
28799 (@pxref{QNonStop}).
28802 The remote stub understands the @samp{QPassSignals} packet
28803 (@pxref{QPassSignals}).
28805 @item QStartNoAckMode
28806 The remote stub understands the @samp{QStartNoAckMode} packet and
28807 prefers to operate in no-acknowledgment mode. @xref{Packet Acknowledgment}.
28810 @anchor{multiprocess extensions}
28811 @cindex multiprocess extensions, in remote protocol
28812 The remote stub understands the multiprocess extensions to the remote
28813 protocol syntax. The multiprocess extensions affect the syntax of
28814 thread IDs in both packets and replies (@pxref{thread-id syntax}), and
28815 add process IDs to the @samp{D} packet and @samp{W} and @samp{X}
28816 replies. Note that reporting this feature indicates support for the
28817 syntactic extensions only, not that the stub necessarily supports
28818 debugging of more than one process at a time. The stub must not use
28819 multiprocess extensions in packet replies unless @value{GDBN} has also
28820 indicated it supports them in its @samp{qSupported} request.
28822 @item qXfer:osdata:read
28823 The remote stub understands the @samp{qXfer:osdata:read} packet
28824 ((@pxref{qXfer osdata read}).
28826 @item ConditionalTracepoints
28827 The remote stub accepts and implements conditional expressions defined
28828 for tracepoints (@pxref{Tracepoint Conditions}).
28833 @cindex symbol lookup, remote request
28834 @cindex @samp{qSymbol} packet
28835 Notify the target that @value{GDBN} is prepared to serve symbol lookup
28836 requests. Accept requests from the target for the values of symbols.
28841 The target does not need to look up any (more) symbols.
28842 @item qSymbol:@var{sym_name}
28843 The target requests the value of symbol @var{sym_name} (hex encoded).
28844 @value{GDBN} may provide the value by using the
28845 @samp{qSymbol:@var{sym_value}:@var{sym_name}} message, described
28849 @item qSymbol:@var{sym_value}:@var{sym_name}
28850 Set the value of @var{sym_name} to @var{sym_value}.
28852 @var{sym_name} (hex encoded) is the name of a symbol whose value the
28853 target has previously requested.
28855 @var{sym_value} (hex) is the value for symbol @var{sym_name}. If
28856 @value{GDBN} cannot supply a value for @var{sym_name}, then this field
28862 The target does not need to look up any (more) symbols.
28863 @item qSymbol:@var{sym_name}
28864 The target requests the value of a new symbol @var{sym_name} (hex
28865 encoded). @value{GDBN} will continue to supply the values of symbols
28866 (if available), until the target ceases to request them.
28871 @xref{Tracepoint Packets}.
28873 @item qThreadExtraInfo,@var{thread-id}
28874 @cindex thread attributes info, remote request
28875 @cindex @samp{qThreadExtraInfo} packet
28876 Obtain a printable string description of a thread's attributes from
28877 the target OS. @var{thread-id} is a thread ID;
28878 see @ref{thread-id syntax}. This
28879 string may contain anything that the target OS thinks is interesting
28880 for @value{GDBN} to tell the user about the thread. The string is
28881 displayed in @value{GDBN}'s @code{info threads} display. Some
28882 examples of possible thread extra info strings are @samp{Runnable}, or
28883 @samp{Blocked on Mutex}.
28887 @item @var{XX}@dots{}
28888 Where @samp{@var{XX}@dots{}} is a hex encoding of @sc{ascii} data,
28889 comprising the printable string containing the extra information about
28890 the thread's attributes.
28893 (Note that the @code{qThreadExtraInfo} packet's name is separated from
28894 the command by a @samp{,}, not a @samp{:}, contrary to the naming
28895 conventions above. Please don't use this packet as a model for new
28903 @xref{Tracepoint Packets}.
28905 @item qXfer:@var{object}:read:@var{annex}:@var{offset},@var{length}
28906 @cindex read special object, remote request
28907 @cindex @samp{qXfer} packet
28908 @anchor{qXfer read}
28909 Read uninterpreted bytes from the target's special data area
28910 identified by the keyword @var{object}. Request @var{length} bytes
28911 starting at @var{offset} bytes into the data. The content and
28912 encoding of @var{annex} is specific to @var{object}; it can supply
28913 additional details about what data to access.
28915 Here are the specific requests of this form defined so far. All
28916 @samp{qXfer:@var{object}:read:@dots{}} requests use the same reply
28917 formats, listed below.
28920 @item qXfer:auxv:read::@var{offset},@var{length}
28921 @anchor{qXfer auxiliary vector read}
28922 Access the target's @dfn{auxiliary vector}. @xref{OS Information,
28923 auxiliary vector}. Note @var{annex} must be empty.
28925 This packet is not probed by default; the remote stub must request it,
28926 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28928 @item qXfer:features:read:@var{annex}:@var{offset},@var{length}
28929 @anchor{qXfer target description read}
28930 Access the @dfn{target description}. @xref{Target Descriptions}. The
28931 annex specifies which XML document to access. The main description is
28932 always loaded from the @samp{target.xml} annex.
28934 This packet is not probed by default; the remote stub must request it,
28935 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28937 @item qXfer:libraries:read:@var{annex}:@var{offset},@var{length}
28938 @anchor{qXfer library list read}
28939 Access the target's list of loaded libraries. @xref{Library List Format}.
28940 The annex part of the generic @samp{qXfer} packet must be empty
28941 (@pxref{qXfer read}).
28943 Targets which maintain a list of libraries in the program's memory do
28944 not need to implement this packet; it is designed for platforms where
28945 the operating system manages the list of loaded libraries.
28947 This packet is not probed by default; the remote stub must request it,
28948 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28950 @item qXfer:memory-map:read::@var{offset},@var{length}
28951 @anchor{qXfer memory map read}
28952 Access the target's @dfn{memory-map}. @xref{Memory Map Format}. The
28953 annex part of the generic @samp{qXfer} packet must be empty
28954 (@pxref{qXfer read}).
28956 This packet is not probed by default; the remote stub must request it,
28957 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28959 @item qXfer:siginfo:read::@var{offset},@var{length}
28960 @anchor{qXfer siginfo read}
28961 Read contents of the extra signal information on the target
28962 system. The annex part of the generic @samp{qXfer} packet must be
28963 empty (@pxref{qXfer read}).
28965 This packet is not probed by default; the remote stub must request it,
28966 by supplying an appropriate @samp{qSupported} response
28967 (@pxref{qSupported}).
28969 @item qXfer:spu:read:@var{annex}:@var{offset},@var{length}
28970 @anchor{qXfer spu read}
28971 Read contents of an @code{spufs} file on the target system. The
28972 annex specifies which file to read; it must be of the form
28973 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
28974 in the target process, and @var{name} identifes the @code{spufs} file
28975 in that context to be accessed.
28977 This packet is not probed by default; the remote stub must request it,
28978 by supplying an appropriate @samp{qSupported} response
28979 (@pxref{qSupported}).
28981 @item qXfer:osdata:read::@var{offset},@var{length}
28982 @anchor{qXfer osdata read}
28983 Access the target's @dfn{operating system information}.
28984 @xref{Operating System Information}.
28991 Data @var{data} (@pxref{Binary Data}) has been read from the
28992 target. There may be more data at a higher address (although
28993 it is permitted to return @samp{m} even for the last valid
28994 block of data, as long as at least one byte of data was read).
28995 @var{data} may have fewer bytes than the @var{length} in the
28999 Data @var{data} (@pxref{Binary Data}) has been read from the target.
29000 There is no more data to be read. @var{data} may have fewer bytes
29001 than the @var{length} in the request.
29004 The @var{offset} in the request is at the end of the data.
29005 There is no more data to be read.
29008 The request was malformed, or @var{annex} was invalid.
29011 The offset was invalid, or there was an error encountered reading the data.
29012 @var{nn} is a hex-encoded @code{errno} value.
29015 An empty reply indicates the @var{object} string was not recognized by
29016 the stub, or that the object does not support reading.
29019 @item qXfer:@var{object}:write:@var{annex}:@var{offset}:@var{data}@dots{}
29020 @cindex write data into object, remote request
29021 @anchor{qXfer write}
29022 Write uninterpreted bytes into the target's special data area
29023 identified by the keyword @var{object}, starting at @var{offset} bytes
29024 into the data. @var{data}@dots{} is the binary-encoded data
29025 (@pxref{Binary Data}) to be written. The content and encoding of @var{annex}
29026 is specific to @var{object}; it can supply additional details about what data
29029 Here are the specific requests of this form defined so far. All
29030 @samp{qXfer:@var{object}:write:@dots{}} requests use the same reply
29031 formats, listed below.
29034 @item qXfer:siginfo:write::@var{offset}:@var{data}@dots{}
29035 @anchor{qXfer siginfo write}
29036 Write @var{data} to the extra signal information on the target system.
29037 The annex part of the generic @samp{qXfer} packet must be
29038 empty (@pxref{qXfer write}).
29040 This packet is not probed by default; the remote stub must request it,
29041 by supplying an appropriate @samp{qSupported} response
29042 (@pxref{qSupported}).
29044 @item qXfer:spu:write:@var{annex}:@var{offset}:@var{data}@dots{}
29045 @anchor{qXfer spu write}
29046 Write @var{data} to an @code{spufs} file on the target system. The
29047 annex specifies which file to write; it must be of the form
29048 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
29049 in the target process, and @var{name} identifes the @code{spufs} file
29050 in that context to be accessed.
29052 This packet is not probed by default; the remote stub must request it,
29053 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
29059 @var{nn} (hex encoded) is the number of bytes written.
29060 This may be fewer bytes than supplied in the request.
29063 The request was malformed, or @var{annex} was invalid.
29066 The offset was invalid, or there was an error encountered writing the data.
29067 @var{nn} is a hex-encoded @code{errno} value.
29070 An empty reply indicates the @var{object} string was not
29071 recognized by the stub, or that the object does not support writing.
29074 @item qXfer:@var{object}:@var{operation}:@dots{}
29075 Requests of this form may be added in the future. When a stub does
29076 not recognize the @var{object} keyword, or its support for
29077 @var{object} does not recognize the @var{operation} keyword, the stub
29078 must respond with an empty packet.
29080 @item qAttached:@var{pid}
29081 @cindex query attached, remote request
29082 @cindex @samp{qAttached} packet
29083 Return an indication of whether the remote server attached to an
29084 existing process or created a new process. When the multiprocess
29085 protocol extensions are supported (@pxref{multiprocess extensions}),
29086 @var{pid} is an integer in hexadecimal format identifying the target
29087 process. Otherwise, @value{GDBN} will omit the @var{pid} field and
29088 the query packet will be simplified as @samp{qAttached}.
29090 This query is used, for example, to know whether the remote process
29091 should be detached or killed when a @value{GDBN} session is ended with
29092 the @code{quit} command.
29097 The remote server attached to an existing process.
29099 The remote server created a new process.
29101 A badly formed request or an error was encountered.
29106 @node Register Packet Format
29107 @section Register Packet Format
29109 The following @code{g}/@code{G} packets have previously been defined.
29110 In the below, some thirty-two bit registers are transferred as
29111 sixty-four bits. Those registers should be zero/sign extended (which?)
29112 to fill the space allocated. Register bytes are transferred in target
29113 byte order. The two nibbles within a register byte are transferred
29114 most-significant - least-significant.
29120 All registers are transferred as thirty-two bit quantities in the order:
29121 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
29122 registers; fsr; fir; fp.
29126 All registers are transferred as sixty-four bit quantities (including
29127 thirty-two bit registers such as @code{sr}). The ordering is the same
29132 @node Tracepoint Packets
29133 @section Tracepoint Packets
29134 @cindex tracepoint packets
29135 @cindex packets, tracepoint
29137 Here we describe the packets @value{GDBN} uses to implement
29138 tracepoints (@pxref{Tracepoints}).
29142 @item QTDP:@var{n}:@var{addr}:@var{ena}:@var{step}:@var{pass}[:X@var{len},@var{bytes}]@r{[}-@r{]}
29143 Create a new tracepoint, number @var{n}, at @var{addr}. If @var{ena}
29144 is @samp{E}, then the tracepoint is enabled; if it is @samp{D}, then
29145 the tracepoint is disabled. @var{step} is the tracepoint's step
29146 count, and @var{pass} is its pass count. If an @samp{X} is present,
29147 it introduces a tracepoint condition, which consists of a hexadecimal
29148 length, followed by a comma and hex-encoded bytes, in a manner similar
29149 to action encodings as described below. If the trailing @samp{-} is
29150 present, further @samp{QTDP} packets will follow to specify this
29151 tracepoint's actions.
29156 The packet was understood and carried out.
29158 The packet was not recognized.
29161 @item QTDP:-@var{n}:@var{addr}:@r{[}S@r{]}@var{action}@dots{}@r{[}-@r{]}
29162 Define actions to be taken when a tracepoint is hit. @var{n} and
29163 @var{addr} must be the same as in the initial @samp{QTDP} packet for
29164 this tracepoint. This packet may only be sent immediately after
29165 another @samp{QTDP} packet that ended with a @samp{-}. If the
29166 trailing @samp{-} is present, further @samp{QTDP} packets will follow,
29167 specifying more actions for this tracepoint.
29169 In the series of action packets for a given tracepoint, at most one
29170 can have an @samp{S} before its first @var{action}. If such a packet
29171 is sent, it and the following packets define ``while-stepping''
29172 actions. Any prior packets define ordinary actions --- that is, those
29173 taken when the tracepoint is first hit. If no action packet has an
29174 @samp{S}, then all the packets in the series specify ordinary
29175 tracepoint actions.
29177 The @samp{@var{action}@dots{}} portion of the packet is a series of
29178 actions, concatenated without separators. Each action has one of the
29184 Collect the registers whose bits are set in @var{mask}. @var{mask} is
29185 a hexadecimal number whose @var{i}'th bit is set if register number
29186 @var{i} should be collected. (The least significant bit is numbered
29187 zero.) Note that @var{mask} may be any number of digits long; it may
29188 not fit in a 32-bit word.
29190 @item M @var{basereg},@var{offset},@var{len}
29191 Collect @var{len} bytes of memory starting at the address in register
29192 number @var{basereg}, plus @var{offset}. If @var{basereg} is
29193 @samp{-1}, then the range has a fixed address: @var{offset} is the
29194 address of the lowest byte to collect. The @var{basereg},
29195 @var{offset}, and @var{len} parameters are all unsigned hexadecimal
29196 values (the @samp{-1} value for @var{basereg} is a special case).
29198 @item X @var{len},@var{expr}
29199 Evaluate @var{expr}, whose length is @var{len}, and collect memory as
29200 it directs. @var{expr} is an agent expression, as described in
29201 @ref{Agent Expressions}. Each byte of the expression is encoded as a
29202 two-digit hex number in the packet; @var{len} is the number of bytes
29203 in the expression (and thus one-half the number of hex digits in the
29208 Any number of actions may be packed together in a single @samp{QTDP}
29209 packet, as long as the packet does not exceed the maximum packet
29210 length (400 bytes, for many stubs). There may be only one @samp{R}
29211 action per tracepoint, and it must precede any @samp{M} or @samp{X}
29212 actions. Any registers referred to by @samp{M} and @samp{X} actions
29213 must be collected by a preceding @samp{R} action. (The
29214 ``while-stepping'' actions are treated as if they were attached to a
29215 separate tracepoint, as far as these restrictions are concerned.)
29220 The packet was understood and carried out.
29222 The packet was not recognized.
29225 @item QTFrame:@var{n}
29226 Select the @var{n}'th tracepoint frame from the buffer, and use the
29227 register and memory contents recorded there to answer subsequent
29228 request packets from @value{GDBN}.
29230 A successful reply from the stub indicates that the stub has found the
29231 requested frame. The response is a series of parts, concatenated
29232 without separators, describing the frame we selected. Each part has
29233 one of the following forms:
29237 The selected frame is number @var{n} in the trace frame buffer;
29238 @var{f} is a hexadecimal number. If @var{f} is @samp{-1}, then there
29239 was no frame matching the criteria in the request packet.
29242 The selected trace frame records a hit of tracepoint number @var{t};
29243 @var{t} is a hexadecimal number.
29247 @item QTFrame:pc:@var{addr}
29248 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
29249 currently selected frame whose PC is @var{addr};
29250 @var{addr} is a hexadecimal number.
29252 @item QTFrame:tdp:@var{t}
29253 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
29254 currently selected frame that is a hit of tracepoint @var{t}; @var{t}
29255 is a hexadecimal number.
29257 @item QTFrame:range:@var{start}:@var{end}
29258 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
29259 currently selected frame whose PC is between @var{start} (inclusive)
29260 and @var{end} (exclusive); @var{start} and @var{end} are hexadecimal
29263 @item QTFrame:outside:@var{start}:@var{end}
29264 Like @samp{QTFrame:range:@var{start}:@var{end}}, but select the first
29265 frame @emph{outside} the given range of addresses.
29268 Begin the tracepoint experiment. Begin collecting data from tracepoint
29269 hits in the trace frame buffer.
29272 End the tracepoint experiment. Stop collecting trace frames.
29275 Clear the table of tracepoints, and empty the trace frame buffer.
29277 @item QTro:@var{start1},@var{end1}:@var{start2},@var{end2}:@dots{}
29278 Establish the given ranges of memory as ``transparent''. The stub
29279 will answer requests for these ranges from memory's current contents,
29280 if they were not collected as part of the tracepoint hit.
29282 @value{GDBN} uses this to mark read-only regions of memory, like those
29283 containing program code. Since these areas never change, they should
29284 still have the same contents they did when the tracepoint was hit, so
29285 there's no reason for the stub to refuse to provide their contents.
29288 Ask the stub if there is a trace experiment running right now.
29293 There is no trace experiment running.
29295 There is a trace experiment running.
29301 @node Host I/O Packets
29302 @section Host I/O Packets
29303 @cindex Host I/O, remote protocol
29304 @cindex file transfer, remote protocol
29306 The @dfn{Host I/O} packets allow @value{GDBN} to perform I/O
29307 operations on the far side of a remote link. For example, Host I/O is
29308 used to upload and download files to a remote target with its own
29309 filesystem. Host I/O uses the same constant values and data structure
29310 layout as the target-initiated File-I/O protocol. However, the
29311 Host I/O packets are structured differently. The target-initiated
29312 protocol relies on target memory to store parameters and buffers.
29313 Host I/O requests are initiated by @value{GDBN}, and the
29314 target's memory is not involved. @xref{File-I/O Remote Protocol
29315 Extension}, for more details on the target-initiated protocol.
29317 The Host I/O request packets all encode a single operation along with
29318 its arguments. They have this format:
29322 @item vFile:@var{operation}: @var{parameter}@dots{}
29323 @var{operation} is the name of the particular request; the target
29324 should compare the entire packet name up to the second colon when checking
29325 for a supported operation. The format of @var{parameter} depends on
29326 the operation. Numbers are always passed in hexadecimal. Negative
29327 numbers have an explicit minus sign (i.e.@: two's complement is not
29328 used). Strings (e.g.@: filenames) are encoded as a series of
29329 hexadecimal bytes. The last argument to a system call may be a
29330 buffer of escaped binary data (@pxref{Binary Data}).
29334 The valid responses to Host I/O packets are:
29338 @item F @var{result} [, @var{errno}] [; @var{attachment}]
29339 @var{result} is the integer value returned by this operation, usually
29340 non-negative for success and -1 for errors. If an error has occured,
29341 @var{errno} will be included in the result. @var{errno} will have a
29342 value defined by the File-I/O protocol (@pxref{Errno Values}). For
29343 operations which return data, @var{attachment} supplies the data as a
29344 binary buffer. Binary buffers in response packets are escaped in the
29345 normal way (@pxref{Binary Data}). See the individual packet
29346 documentation for the interpretation of @var{result} and
29350 An empty response indicates that this operation is not recognized.
29354 These are the supported Host I/O operations:
29357 @item vFile:open: @var{pathname}, @var{flags}, @var{mode}
29358 Open a file at @var{pathname} and return a file descriptor for it, or
29359 return -1 if an error occurs. @var{pathname} is a string,
29360 @var{flags} is an integer indicating a mask of open flags
29361 (@pxref{Open Flags}), and @var{mode} is an integer indicating a mask
29362 of mode bits to use if the file is created (@pxref{mode_t Values}).
29363 @xref{open}, for details of the open flags and mode values.
29365 @item vFile:close: @var{fd}
29366 Close the open file corresponding to @var{fd} and return 0, or
29367 -1 if an error occurs.
29369 @item vFile:pread: @var{fd}, @var{count}, @var{offset}
29370 Read data from the open file corresponding to @var{fd}. Up to
29371 @var{count} bytes will be read from the file, starting at @var{offset}
29372 relative to the start of the file. The target may read fewer bytes;
29373 common reasons include packet size limits and an end-of-file
29374 condition. The number of bytes read is returned. Zero should only be
29375 returned for a successful read at the end of the file, or if
29376 @var{count} was zero.
29378 The data read should be returned as a binary attachment on success.
29379 If zero bytes were read, the response should include an empty binary
29380 attachment (i.e.@: a trailing semicolon). The return value is the
29381 number of target bytes read; the binary attachment may be longer if
29382 some characters were escaped.
29384 @item vFile:pwrite: @var{fd}, @var{offset}, @var{data}
29385 Write @var{data} (a binary buffer) to the open file corresponding
29386 to @var{fd}. Start the write at @var{offset} from the start of the
29387 file. Unlike many @code{write} system calls, there is no
29388 separate @var{count} argument; the length of @var{data} in the
29389 packet is used. @samp{vFile:write} returns the number of bytes written,
29390 which may be shorter than the length of @var{data}, or -1 if an
29393 @item vFile:unlink: @var{pathname}
29394 Delete the file at @var{pathname} on the target. Return 0,
29395 or -1 if an error occurs. @var{pathname} is a string.
29400 @section Interrupts
29401 @cindex interrupts (remote protocol)
29403 When a program on the remote target is running, @value{GDBN} may
29404 attempt to interrupt it by sending a @samp{Ctrl-C} or a @code{BREAK},
29405 control of which is specified via @value{GDBN}'s @samp{remotebreak}
29406 setting (@pxref{set remotebreak}).
29408 The precise meaning of @code{BREAK} is defined by the transport
29409 mechanism and may, in fact, be undefined. @value{GDBN} does not
29410 currently define a @code{BREAK} mechanism for any of the network
29411 interfaces except for TCP, in which case @value{GDBN} sends the
29412 @code{telnet} BREAK sequence.
29414 @samp{Ctrl-C}, on the other hand, is defined and implemented for all
29415 transport mechanisms. It is represented by sending the single byte
29416 @code{0x03} without any of the usual packet overhead described in
29417 the Overview section (@pxref{Overview}). When a @code{0x03} byte is
29418 transmitted as part of a packet, it is considered to be packet data
29419 and does @emph{not} represent an interrupt. E.g., an @samp{X} packet
29420 (@pxref{X packet}), used for binary downloads, may include an unescaped
29421 @code{0x03} as part of its packet.
29423 Stubs are not required to recognize these interrupt mechanisms and the
29424 precise meaning associated with receipt of the interrupt is
29425 implementation defined. If the target supports debugging of multiple
29426 threads and/or processes, it should attempt to interrupt all
29427 currently-executing threads and processes.
29428 If the stub is successful at interrupting the
29429 running program, it should send one of the stop
29430 reply packets (@pxref{Stop Reply Packets}) to @value{GDBN} as a result
29431 of successfully stopping the program in all-stop mode, and a stop reply
29432 for each stopped thread in non-stop mode.
29433 Interrupts received while the
29434 program is stopped are discarded.
29436 @node Notification Packets
29437 @section Notification Packets
29438 @cindex notification packets
29439 @cindex packets, notification
29441 The @value{GDBN} remote serial protocol includes @dfn{notifications},
29442 packets that require no acknowledgment. Both the GDB and the stub
29443 may send notifications (although the only notifications defined at
29444 present are sent by the stub). Notifications carry information
29445 without incurring the round-trip latency of an acknowledgment, and so
29446 are useful for low-impact communications where occasional packet loss
29449 A notification packet has the form @samp{% @var{data} #
29450 @var{checksum}}, where @var{data} is the content of the notification,
29451 and @var{checksum} is a checksum of @var{data}, computed and formatted
29452 as for ordinary @value{GDBN} packets. A notification's @var{data}
29453 never contains @samp{$}, @samp{%} or @samp{#} characters. Upon
29454 receiving a notification, the recipient sends no @samp{+} or @samp{-}
29455 to acknowledge the notification's receipt or to report its corruption.
29457 Every notification's @var{data} begins with a name, which contains no
29458 colon characters, followed by a colon character.
29460 Recipients should silently ignore corrupted notifications and
29461 notifications they do not understand. Recipients should restart
29462 timeout periods on receipt of a well-formed notification, whether or
29463 not they understand it.
29465 Senders should only send the notifications described here when this
29466 protocol description specifies that they are permitted. In the
29467 future, we may extend the protocol to permit existing notifications in
29468 new contexts; this rule helps older senders avoid confusing newer
29471 (Older versions of @value{GDBN} ignore bytes received until they see
29472 the @samp{$} byte that begins an ordinary packet, so new stubs may
29473 transmit notifications without fear of confusing older clients. There
29474 are no notifications defined for @value{GDBN} to send at the moment, but we
29475 assume that most older stubs would ignore them, as well.)
29477 The following notification packets from the stub to @value{GDBN} are
29481 @item Stop: @var{reply}
29482 Report an asynchronous stop event in non-stop mode.
29483 The @var{reply} has the form of a stop reply, as
29484 described in @ref{Stop Reply Packets}. Refer to @ref{Remote Non-Stop},
29485 for information on how these notifications are acknowledged by
29489 @node Remote Non-Stop
29490 @section Remote Protocol Support for Non-Stop Mode
29492 @value{GDBN}'s remote protocol supports non-stop debugging of
29493 multi-threaded programs, as described in @ref{Non-Stop Mode}. If the stub
29494 supports non-stop mode, it should report that to @value{GDBN} by including
29495 @samp{QNonStop+} in its @samp{qSupported} response (@pxref{qSupported}).
29497 @value{GDBN} typically sends a @samp{QNonStop} packet only when
29498 establishing a new connection with the stub. Entering non-stop mode
29499 does not alter the state of any currently-running threads, but targets
29500 must stop all threads in any already-attached processes when entering
29501 all-stop mode. @value{GDBN} uses the @samp{?} packet as necessary to
29502 probe the target state after a mode change.
29504 In non-stop mode, when an attached process encounters an event that
29505 would otherwise be reported with a stop reply, it uses the
29506 asynchronous notification mechanism (@pxref{Notification Packets}) to
29507 inform @value{GDBN}. In contrast to all-stop mode, where all threads
29508 in all processes are stopped when a stop reply is sent, in non-stop
29509 mode only the thread reporting the stop event is stopped. That is,
29510 when reporting a @samp{S} or @samp{T} response to indicate completion
29511 of a step operation, hitting a breakpoint, or a fault, only the
29512 affected thread is stopped; any other still-running threads continue
29513 to run. When reporting a @samp{W} or @samp{X} response, all running
29514 threads belonging to other attached processes continue to run.
29516 Only one stop reply notification at a time may be pending; if
29517 additional stop events occur before @value{GDBN} has acknowledged the
29518 previous notification, they must be queued by the stub for later
29519 synchronous transmission in response to @samp{vStopped} packets from
29520 @value{GDBN}. Because the notification mechanism is unreliable,
29521 the stub is permitted to resend a stop reply notification
29522 if it believes @value{GDBN} may not have received it. @value{GDBN}
29523 ignores additional stop reply notifications received before it has
29524 finished processing a previous notification and the stub has completed
29525 sending any queued stop events.
29527 Otherwise, @value{GDBN} must be prepared to receive a stop reply
29528 notification at any time. Specifically, they may appear when
29529 @value{GDBN} is not otherwise reading input from the stub, or when
29530 @value{GDBN} is expecting to read a normal synchronous response or a
29531 @samp{+}/@samp{-} acknowledgment to a packet it has sent.
29532 Notification packets are distinct from any other communication from
29533 the stub so there is no ambiguity.
29535 After receiving a stop reply notification, @value{GDBN} shall
29536 acknowledge it by sending a @samp{vStopped} packet (@pxref{vStopped packet})
29537 as a regular, synchronous request to the stub. Such acknowledgment
29538 is not required to happen immediately, as @value{GDBN} is permitted to
29539 send other, unrelated packets to the stub first, which the stub should
29542 Upon receiving a @samp{vStopped} packet, if the stub has other queued
29543 stop events to report to @value{GDBN}, it shall respond by sending a
29544 normal stop reply response. @value{GDBN} shall then send another
29545 @samp{vStopped} packet to solicit further responses; again, it is
29546 permitted to send other, unrelated packets as well which the stub
29547 should process normally.
29549 If the stub receives a @samp{vStopped} packet and there are no
29550 additional stop events to report, the stub shall return an @samp{OK}
29551 response. At this point, if further stop events occur, the stub shall
29552 send a new stop reply notification, @value{GDBN} shall accept the
29553 notification, and the process shall be repeated.
29555 In non-stop mode, the target shall respond to the @samp{?} packet as
29556 follows. First, any incomplete stop reply notification/@samp{vStopped}
29557 sequence in progress is abandoned. The target must begin a new
29558 sequence reporting stop events for all stopped threads, whether or not
29559 it has previously reported those events to @value{GDBN}. The first
29560 stop reply is sent as a synchronous reply to the @samp{?} packet, and
29561 subsequent stop replies are sent as responses to @samp{vStopped} packets
29562 using the mechanism described above. The target must not send
29563 asynchronous stop reply notifications until the sequence is complete.
29564 If all threads are running when the target receives the @samp{?} packet,
29565 or if the target is not attached to any process, it shall respond
29568 @node Packet Acknowledgment
29569 @section Packet Acknowledgment
29571 @cindex acknowledgment, for @value{GDBN} remote
29572 @cindex packet acknowledgment, for @value{GDBN} remote
29573 By default, when either the host or the target machine receives a packet,
29574 the first response expected is an acknowledgment: either @samp{+} (to indicate
29575 the package was received correctly) or @samp{-} (to request retransmission).
29576 This mechanism allows the @value{GDBN} remote protocol to operate over
29577 unreliable transport mechanisms, such as a serial line.
29579 In cases where the transport mechanism is itself reliable (such as a pipe or
29580 TCP connection), the @samp{+}/@samp{-} acknowledgments are redundant.
29581 It may be desirable to disable them in that case to reduce communication
29582 overhead, or for other reasons. This can be accomplished by means of the
29583 @samp{QStartNoAckMode} packet; @pxref{QStartNoAckMode}.
29585 When in no-acknowledgment mode, neither the stub nor @value{GDBN} shall send or
29586 expect @samp{+}/@samp{-} protocol acknowledgments. The packet
29587 and response format still includes the normal checksum, as described in
29588 @ref{Overview}, but the checksum may be ignored by the receiver.
29590 If the stub supports @samp{QStartNoAckMode} and prefers to operate in
29591 no-acknowledgment mode, it should report that to @value{GDBN}
29592 by including @samp{QStartNoAckMode+} in its response to @samp{qSupported};
29593 @pxref{qSupported}.
29594 If @value{GDBN} also supports @samp{QStartNoAckMode} and it has not been
29595 disabled via the @code{set remote noack-packet off} command
29596 (@pxref{Remote Configuration}),
29597 @value{GDBN} may then send a @samp{QStartNoAckMode} packet to the stub.
29598 Only then may the stub actually turn off packet acknowledgments.
29599 @value{GDBN} sends a final @samp{+} acknowledgment of the stub's @samp{OK}
29600 response, which can be safely ignored by the stub.
29602 Note that @code{set remote noack-packet} command only affects negotiation
29603 between @value{GDBN} and the stub when subsequent connections are made;
29604 it does not affect the protocol acknowledgment state for any current
29606 Since @samp{+}/@samp{-} acknowledgments are enabled by default when a
29607 new connection is established,
29608 there is also no protocol request to re-enable the acknowledgments
29609 for the current connection, once disabled.
29614 Example sequence of a target being re-started. Notice how the restart
29615 does not get any direct output:
29620 @emph{target restarts}
29623 <- @code{T001:1234123412341234}
29627 Example sequence of a target being stepped by a single instruction:
29630 -> @code{G1445@dots{}}
29635 <- @code{T001:1234123412341234}
29639 <- @code{1455@dots{}}
29643 @node File-I/O Remote Protocol Extension
29644 @section File-I/O Remote Protocol Extension
29645 @cindex File-I/O remote protocol extension
29648 * File-I/O Overview::
29649 * Protocol Basics::
29650 * The F Request Packet::
29651 * The F Reply Packet::
29652 * The Ctrl-C Message::
29654 * List of Supported Calls::
29655 * Protocol-specific Representation of Datatypes::
29657 * File-I/O Examples::
29660 @node File-I/O Overview
29661 @subsection File-I/O Overview
29662 @cindex file-i/o overview
29664 The @dfn{File I/O remote protocol extension} (short: File-I/O) allows the
29665 target to use the host's file system and console I/O to perform various
29666 system calls. System calls on the target system are translated into a
29667 remote protocol packet to the host system, which then performs the needed
29668 actions and returns a response packet to the target system.
29669 This simulates file system operations even on targets that lack file systems.
29671 The protocol is defined to be independent of both the host and target systems.
29672 It uses its own internal representation of datatypes and values. Both
29673 @value{GDBN} and the target's @value{GDBN} stub are responsible for
29674 translating the system-dependent value representations into the internal
29675 protocol representations when data is transmitted.
29677 The communication is synchronous. A system call is possible only when
29678 @value{GDBN} is waiting for a response from the @samp{C}, @samp{c}, @samp{S}
29679 or @samp{s} packets. While @value{GDBN} handles the request for a system call,
29680 the target is stopped to allow deterministic access to the target's
29681 memory. Therefore File-I/O is not interruptible by target signals. On
29682 the other hand, it is possible to interrupt File-I/O by a user interrupt
29683 (@samp{Ctrl-C}) within @value{GDBN}.
29685 The target's request to perform a host system call does not finish
29686 the latest @samp{C}, @samp{c}, @samp{S} or @samp{s} action. That means,
29687 after finishing the system call, the target returns to continuing the
29688 previous activity (continue, step). No additional continue or step
29689 request from @value{GDBN} is required.
29692 (@value{GDBP}) continue
29693 <- target requests 'system call X'
29694 target is stopped, @value{GDBN} executes system call
29695 -> @value{GDBN} returns result
29696 ... target continues, @value{GDBN} returns to wait for the target
29697 <- target hits breakpoint and sends a Txx packet
29700 The protocol only supports I/O on the console and to regular files on
29701 the host file system. Character or block special devices, pipes,
29702 named pipes, sockets or any other communication method on the host
29703 system are not supported by this protocol.
29705 File I/O is not supported in non-stop mode.
29707 @node Protocol Basics
29708 @subsection Protocol Basics
29709 @cindex protocol basics, file-i/o
29711 The File-I/O protocol uses the @code{F} packet as the request as well
29712 as reply packet. Since a File-I/O system call can only occur when
29713 @value{GDBN} is waiting for a response from the continuing or stepping target,
29714 the File-I/O request is a reply that @value{GDBN} has to expect as a result
29715 of a previous @samp{C}, @samp{c}, @samp{S} or @samp{s} packet.
29716 This @code{F} packet contains all information needed to allow @value{GDBN}
29717 to call the appropriate host system call:
29721 A unique identifier for the requested system call.
29724 All parameters to the system call. Pointers are given as addresses
29725 in the target memory address space. Pointers to strings are given as
29726 pointer/length pair. Numerical values are given as they are.
29727 Numerical control flags are given in a protocol-specific representation.
29731 At this point, @value{GDBN} has to perform the following actions.
29735 If the parameters include pointer values to data needed as input to a
29736 system call, @value{GDBN} requests this data from the target with a
29737 standard @code{m} packet request. This additional communication has to be
29738 expected by the target implementation and is handled as any other @code{m}
29742 @value{GDBN} translates all value from protocol representation to host
29743 representation as needed. Datatypes are coerced into the host types.
29746 @value{GDBN} calls the system call.
29749 It then coerces datatypes back to protocol representation.
29752 If the system call is expected to return data in buffer space specified
29753 by pointer parameters to the call, the data is transmitted to the
29754 target using a @code{M} or @code{X} packet. This packet has to be expected
29755 by the target implementation and is handled as any other @code{M} or @code{X}
29760 Eventually @value{GDBN} replies with another @code{F} packet which contains all
29761 necessary information for the target to continue. This at least contains
29768 @code{errno}, if has been changed by the system call.
29775 After having done the needed type and value coercion, the target continues
29776 the latest continue or step action.
29778 @node The F Request Packet
29779 @subsection The @code{F} Request Packet
29780 @cindex file-i/o request packet
29781 @cindex @code{F} request packet
29783 The @code{F} request packet has the following format:
29786 @item F@var{call-id},@var{parameter@dots{}}
29788 @var{call-id} is the identifier to indicate the host system call to be called.
29789 This is just the name of the function.
29791 @var{parameter@dots{}} are the parameters to the system call.
29792 Parameters are hexadecimal integer values, either the actual values in case
29793 of scalar datatypes, pointers to target buffer space in case of compound
29794 datatypes and unspecified memory areas, or pointer/length pairs in case
29795 of string parameters. These are appended to the @var{call-id} as a
29796 comma-delimited list. All values are transmitted in ASCII
29797 string representation, pointer/length pairs separated by a slash.
29803 @node The F Reply Packet
29804 @subsection The @code{F} Reply Packet
29805 @cindex file-i/o reply packet
29806 @cindex @code{F} reply packet
29808 The @code{F} reply packet has the following format:
29812 @item F@var{retcode},@var{errno},@var{Ctrl-C flag};@var{call-specific attachment}
29814 @var{retcode} is the return code of the system call as hexadecimal value.
29816 @var{errno} is the @code{errno} set by the call, in protocol-specific
29818 This parameter can be omitted if the call was successful.
29820 @var{Ctrl-C flag} is only sent if the user requested a break. In this
29821 case, @var{errno} must be sent as well, even if the call was successful.
29822 The @var{Ctrl-C flag} itself consists of the character @samp{C}:
29829 or, if the call was interrupted before the host call has been performed:
29836 assuming 4 is the protocol-specific representation of @code{EINTR}.
29841 @node The Ctrl-C Message
29842 @subsection The @samp{Ctrl-C} Message
29843 @cindex ctrl-c message, in file-i/o protocol
29845 If the @samp{Ctrl-C} flag is set in the @value{GDBN}
29846 reply packet (@pxref{The F Reply Packet}),
29847 the target should behave as if it had
29848 gotten a break message. The meaning for the target is ``system call
29849 interrupted by @code{SIGINT}''. Consequentially, the target should actually stop
29850 (as with a break message) and return to @value{GDBN} with a @code{T02}
29853 It's important for the target to know in which
29854 state the system call was interrupted. There are two possible cases:
29858 The system call hasn't been performed on the host yet.
29861 The system call on the host has been finished.
29865 These two states can be distinguished by the target by the value of the
29866 returned @code{errno}. If it's the protocol representation of @code{EINTR}, the system
29867 call hasn't been performed. This is equivalent to the @code{EINTR} handling
29868 on POSIX systems. In any other case, the target may presume that the
29869 system call has been finished --- successfully or not --- and should behave
29870 as if the break message arrived right after the system call.
29872 @value{GDBN} must behave reliably. If the system call has not been called
29873 yet, @value{GDBN} may send the @code{F} reply immediately, setting @code{EINTR} as
29874 @code{errno} in the packet. If the system call on the host has been finished
29875 before the user requests a break, the full action must be finished by
29876 @value{GDBN}. This requires sending @code{M} or @code{X} packets as necessary.
29877 The @code{F} packet may only be sent when either nothing has happened
29878 or the full action has been completed.
29881 @subsection Console I/O
29882 @cindex console i/o as part of file-i/o
29884 By default and if not explicitly closed by the target system, the file
29885 descriptors 0, 1 and 2 are connected to the @value{GDBN} console. Output
29886 on the @value{GDBN} console is handled as any other file output operation
29887 (@code{write(1, @dots{})} or @code{write(2, @dots{})}). Console input is handled
29888 by @value{GDBN} so that after the target read request from file descriptor
29889 0 all following typing is buffered until either one of the following
29894 The user types @kbd{Ctrl-c}. The behaviour is as explained above, and the
29896 system call is treated as finished.
29899 The user presses @key{RET}. This is treated as end of input with a trailing
29903 The user types @kbd{Ctrl-d}. This is treated as end of input. No trailing
29904 character (neither newline nor @samp{Ctrl-D}) is appended to the input.
29908 If the user has typed more characters than fit in the buffer given to
29909 the @code{read} call, the trailing characters are buffered in @value{GDBN} until
29910 either another @code{read(0, @dots{})} is requested by the target, or debugging
29911 is stopped at the user's request.
29914 @node List of Supported Calls
29915 @subsection List of Supported Calls
29916 @cindex list of supported file-i/o calls
29933 @unnumberedsubsubsec open
29934 @cindex open, file-i/o system call
29939 int open(const char *pathname, int flags);
29940 int open(const char *pathname, int flags, mode_t mode);
29944 @samp{Fopen,@var{pathptr}/@var{len},@var{flags},@var{mode}}
29947 @var{flags} is the bitwise @code{OR} of the following values:
29951 If the file does not exist it will be created. The host
29952 rules apply as far as file ownership and time stamps
29956 When used with @code{O_CREAT}, if the file already exists it is
29957 an error and open() fails.
29960 If the file already exists and the open mode allows
29961 writing (@code{O_RDWR} or @code{O_WRONLY} is given) it will be
29962 truncated to zero length.
29965 The file is opened in append mode.
29968 The file is opened for reading only.
29971 The file is opened for writing only.
29974 The file is opened for reading and writing.
29978 Other bits are silently ignored.
29982 @var{mode} is the bitwise @code{OR} of the following values:
29986 User has read permission.
29989 User has write permission.
29992 Group has read permission.
29995 Group has write permission.
29998 Others have read permission.
30001 Others have write permission.
30005 Other bits are silently ignored.
30008 @item Return value:
30009 @code{open} returns the new file descriptor or -1 if an error
30016 @var{pathname} already exists and @code{O_CREAT} and @code{O_EXCL} were used.
30019 @var{pathname} refers to a directory.
30022 The requested access is not allowed.
30025 @var{pathname} was too long.
30028 A directory component in @var{pathname} does not exist.
30031 @var{pathname} refers to a device, pipe, named pipe or socket.
30034 @var{pathname} refers to a file on a read-only filesystem and
30035 write access was requested.
30038 @var{pathname} is an invalid pointer value.
30041 No space on device to create the file.
30044 The process already has the maximum number of files open.
30047 The limit on the total number of files open on the system
30051 The call was interrupted by the user.
30057 @unnumberedsubsubsec close
30058 @cindex close, file-i/o system call
30067 @samp{Fclose,@var{fd}}
30069 @item Return value:
30070 @code{close} returns zero on success, or -1 if an error occurred.
30076 @var{fd} isn't a valid open file descriptor.
30079 The call was interrupted by the user.
30085 @unnumberedsubsubsec read
30086 @cindex read, file-i/o system call
30091 int read(int fd, void *buf, unsigned int count);
30095 @samp{Fread,@var{fd},@var{bufptr},@var{count}}
30097 @item Return value:
30098 On success, the number of bytes read is returned.
30099 Zero indicates end of file. If count is zero, read
30100 returns zero as well. On error, -1 is returned.
30106 @var{fd} is not a valid file descriptor or is not open for
30110 @var{bufptr} is an invalid pointer value.
30113 The call was interrupted by the user.
30119 @unnumberedsubsubsec write
30120 @cindex write, file-i/o system call
30125 int write(int fd, const void *buf, unsigned int count);
30129 @samp{Fwrite,@var{fd},@var{bufptr},@var{count}}
30131 @item Return value:
30132 On success, the number of bytes written are returned.
30133 Zero indicates nothing was written. On error, -1
30140 @var{fd} is not a valid file descriptor or is not open for
30144 @var{bufptr} is an invalid pointer value.
30147 An attempt was made to write a file that exceeds the
30148 host-specific maximum file size allowed.
30151 No space on device to write the data.
30154 The call was interrupted by the user.
30160 @unnumberedsubsubsec lseek
30161 @cindex lseek, file-i/o system call
30166 long lseek (int fd, long offset, int flag);
30170 @samp{Flseek,@var{fd},@var{offset},@var{flag}}
30172 @var{flag} is one of:
30176 The offset is set to @var{offset} bytes.
30179 The offset is set to its current location plus @var{offset}
30183 The offset is set to the size of the file plus @var{offset}
30187 @item Return value:
30188 On success, the resulting unsigned offset in bytes from
30189 the beginning of the file is returned. Otherwise, a
30190 value of -1 is returned.
30196 @var{fd} is not a valid open file descriptor.
30199 @var{fd} is associated with the @value{GDBN} console.
30202 @var{flag} is not a proper value.
30205 The call was interrupted by the user.
30211 @unnumberedsubsubsec rename
30212 @cindex rename, file-i/o system call
30217 int rename(const char *oldpath, const char *newpath);
30221 @samp{Frename,@var{oldpathptr}/@var{len},@var{newpathptr}/@var{len}}
30223 @item Return value:
30224 On success, zero is returned. On error, -1 is returned.
30230 @var{newpath} is an existing directory, but @var{oldpath} is not a
30234 @var{newpath} is a non-empty directory.
30237 @var{oldpath} or @var{newpath} is a directory that is in use by some
30241 An attempt was made to make a directory a subdirectory
30245 A component used as a directory in @var{oldpath} or new
30246 path is not a directory. Or @var{oldpath} is a directory
30247 and @var{newpath} exists but is not a directory.
30250 @var{oldpathptr} or @var{newpathptr} are invalid pointer values.
30253 No access to the file or the path of the file.
30257 @var{oldpath} or @var{newpath} was too long.
30260 A directory component in @var{oldpath} or @var{newpath} does not exist.
30263 The file is on a read-only filesystem.
30266 The device containing the file has no room for the new
30270 The call was interrupted by the user.
30276 @unnumberedsubsubsec unlink
30277 @cindex unlink, file-i/o system call
30282 int unlink(const char *pathname);
30286 @samp{Funlink,@var{pathnameptr}/@var{len}}
30288 @item Return value:
30289 On success, zero is returned. On error, -1 is returned.
30295 No access to the file or the path of the file.
30298 The system does not allow unlinking of directories.
30301 The file @var{pathname} cannot be unlinked because it's
30302 being used by another process.
30305 @var{pathnameptr} is an invalid pointer value.
30308 @var{pathname} was too long.
30311 A directory component in @var{pathname} does not exist.
30314 A component of the path is not a directory.
30317 The file is on a read-only filesystem.
30320 The call was interrupted by the user.
30326 @unnumberedsubsubsec stat/fstat
30327 @cindex fstat, file-i/o system call
30328 @cindex stat, file-i/o system call
30333 int stat(const char *pathname, struct stat *buf);
30334 int fstat(int fd, struct stat *buf);
30338 @samp{Fstat,@var{pathnameptr}/@var{len},@var{bufptr}}@*
30339 @samp{Ffstat,@var{fd},@var{bufptr}}
30341 @item Return value:
30342 On success, zero is returned. On error, -1 is returned.
30348 @var{fd} is not a valid open file.
30351 A directory component in @var{pathname} does not exist or the
30352 path is an empty string.
30355 A component of the path is not a directory.
30358 @var{pathnameptr} is an invalid pointer value.
30361 No access to the file or the path of the file.
30364 @var{pathname} was too long.
30367 The call was interrupted by the user.
30373 @unnumberedsubsubsec gettimeofday
30374 @cindex gettimeofday, file-i/o system call
30379 int gettimeofday(struct timeval *tv, void *tz);
30383 @samp{Fgettimeofday,@var{tvptr},@var{tzptr}}
30385 @item Return value:
30386 On success, 0 is returned, -1 otherwise.
30392 @var{tz} is a non-NULL pointer.
30395 @var{tvptr} and/or @var{tzptr} is an invalid pointer value.
30401 @unnumberedsubsubsec isatty
30402 @cindex isatty, file-i/o system call
30407 int isatty(int fd);
30411 @samp{Fisatty,@var{fd}}
30413 @item Return value:
30414 Returns 1 if @var{fd} refers to the @value{GDBN} console, 0 otherwise.
30420 The call was interrupted by the user.
30425 Note that the @code{isatty} call is treated as a special case: it returns
30426 1 to the target if the file descriptor is attached
30427 to the @value{GDBN} console, 0 otherwise. Implementing through system calls
30428 would require implementing @code{ioctl} and would be more complex than
30433 @unnumberedsubsubsec system
30434 @cindex system, file-i/o system call
30439 int system(const char *command);
30443 @samp{Fsystem,@var{commandptr}/@var{len}}
30445 @item Return value:
30446 If @var{len} is zero, the return value indicates whether a shell is
30447 available. A zero return value indicates a shell is not available.
30448 For non-zero @var{len}, the value returned is -1 on error and the
30449 return status of the command otherwise. Only the exit status of the
30450 command is returned, which is extracted from the host's @code{system}
30451 return value by calling @code{WEXITSTATUS(retval)}. In case
30452 @file{/bin/sh} could not be executed, 127 is returned.
30458 The call was interrupted by the user.
30463 @value{GDBN} takes over the full task of calling the necessary host calls
30464 to perform the @code{system} call. The return value of @code{system} on
30465 the host is simplified before it's returned
30466 to the target. Any termination signal information from the child process
30467 is discarded, and the return value consists
30468 entirely of the exit status of the called command.
30470 Due to security concerns, the @code{system} call is by default refused
30471 by @value{GDBN}. The user has to allow this call explicitly with the
30472 @code{set remote system-call-allowed 1} command.
30475 @item set remote system-call-allowed
30476 @kindex set remote system-call-allowed
30477 Control whether to allow the @code{system} calls in the File I/O
30478 protocol for the remote target. The default is zero (disabled).
30480 @item show remote system-call-allowed
30481 @kindex show remote system-call-allowed
30482 Show whether the @code{system} calls are allowed in the File I/O
30486 @node Protocol-specific Representation of Datatypes
30487 @subsection Protocol-specific Representation of Datatypes
30488 @cindex protocol-specific representation of datatypes, in file-i/o protocol
30491 * Integral Datatypes::
30493 * Memory Transfer::
30498 @node Integral Datatypes
30499 @unnumberedsubsubsec Integral Datatypes
30500 @cindex integral datatypes, in file-i/o protocol
30502 The integral datatypes used in the system calls are @code{int},
30503 @code{unsigned int}, @code{long}, @code{unsigned long},
30504 @code{mode_t}, and @code{time_t}.
30506 @code{int}, @code{unsigned int}, @code{mode_t} and @code{time_t} are
30507 implemented as 32 bit values in this protocol.
30509 @code{long} and @code{unsigned long} are implemented as 64 bit types.
30511 @xref{Limits}, for corresponding MIN and MAX values (similar to those
30512 in @file{limits.h}) to allow range checking on host and target.
30514 @code{time_t} datatypes are defined as seconds since the Epoch.
30516 All integral datatypes transferred as part of a memory read or write of a
30517 structured datatype e.g.@: a @code{struct stat} have to be given in big endian
30520 @node Pointer Values
30521 @unnumberedsubsubsec Pointer Values
30522 @cindex pointer values, in file-i/o protocol
30524 Pointers to target data are transmitted as they are. An exception
30525 is made for pointers to buffers for which the length isn't
30526 transmitted as part of the function call, namely strings. Strings
30527 are transmitted as a pointer/length pair, both as hex values, e.g.@:
30534 which is a pointer to data of length 18 bytes at position 0x1aaf.
30535 The length is defined as the full string length in bytes, including
30536 the trailing null byte. For example, the string @code{"hello world"}
30537 at address 0x123456 is transmitted as
30543 @node Memory Transfer
30544 @unnumberedsubsubsec Memory Transfer
30545 @cindex memory transfer, in file-i/o protocol
30547 Structured data which is transferred using a memory read or write (for
30548 example, a @code{struct stat}) is expected to be in a protocol-specific format
30549 with all scalar multibyte datatypes being big endian. Translation to
30550 this representation needs to be done both by the target before the @code{F}
30551 packet is sent, and by @value{GDBN} before
30552 it transfers memory to the target. Transferred pointers to structured
30553 data should point to the already-coerced data at any time.
30557 @unnumberedsubsubsec struct stat
30558 @cindex struct stat, in file-i/o protocol
30560 The buffer of type @code{struct stat} used by the target and @value{GDBN}
30561 is defined as follows:
30565 unsigned int st_dev; /* device */
30566 unsigned int st_ino; /* inode */
30567 mode_t st_mode; /* protection */
30568 unsigned int st_nlink; /* number of hard links */
30569 unsigned int st_uid; /* user ID of owner */
30570 unsigned int st_gid; /* group ID of owner */
30571 unsigned int st_rdev; /* device type (if inode device) */
30572 unsigned long st_size; /* total size, in bytes */
30573 unsigned long st_blksize; /* blocksize for filesystem I/O */
30574 unsigned long st_blocks; /* number of blocks allocated */
30575 time_t st_atime; /* time of last access */
30576 time_t st_mtime; /* time of last modification */
30577 time_t st_ctime; /* time of last change */
30581 The integral datatypes conform to the definitions given in the
30582 appropriate section (see @ref{Integral Datatypes}, for details) so this
30583 structure is of size 64 bytes.
30585 The values of several fields have a restricted meaning and/or
30591 A value of 0 represents a file, 1 the console.
30594 No valid meaning for the target. Transmitted unchanged.
30597 Valid mode bits are described in @ref{Constants}. Any other
30598 bits have currently no meaning for the target.
30603 No valid meaning for the target. Transmitted unchanged.
30608 These values have a host and file system dependent
30609 accuracy. Especially on Windows hosts, the file system may not
30610 support exact timing values.
30613 The target gets a @code{struct stat} of the above representation and is
30614 responsible for coercing it to the target representation before
30617 Note that due to size differences between the host, target, and protocol
30618 representations of @code{struct stat} members, these members could eventually
30619 get truncated on the target.
30621 @node struct timeval
30622 @unnumberedsubsubsec struct timeval
30623 @cindex struct timeval, in file-i/o protocol
30625 The buffer of type @code{struct timeval} used by the File-I/O protocol
30626 is defined as follows:
30630 time_t tv_sec; /* second */
30631 long tv_usec; /* microsecond */
30635 The integral datatypes conform to the definitions given in the
30636 appropriate section (see @ref{Integral Datatypes}, for details) so this
30637 structure is of size 8 bytes.
30640 @subsection Constants
30641 @cindex constants, in file-i/o protocol
30643 The following values are used for the constants inside of the
30644 protocol. @value{GDBN} and target are responsible for translating these
30645 values before and after the call as needed.
30656 @unnumberedsubsubsec Open Flags
30657 @cindex open flags, in file-i/o protocol
30659 All values are given in hexadecimal representation.
30671 @node mode_t Values
30672 @unnumberedsubsubsec mode_t Values
30673 @cindex mode_t values, in file-i/o protocol
30675 All values are given in octal representation.
30692 @unnumberedsubsubsec Errno Values
30693 @cindex errno values, in file-i/o protocol
30695 All values are given in decimal representation.
30720 @code{EUNKNOWN} is used as a fallback error value if a host system returns
30721 any error value not in the list of supported error numbers.
30724 @unnumberedsubsubsec Lseek Flags
30725 @cindex lseek flags, in file-i/o protocol
30734 @unnumberedsubsubsec Limits
30735 @cindex limits, in file-i/o protocol
30737 All values are given in decimal representation.
30740 INT_MIN -2147483648
30742 UINT_MAX 4294967295
30743 LONG_MIN -9223372036854775808
30744 LONG_MAX 9223372036854775807
30745 ULONG_MAX 18446744073709551615
30748 @node File-I/O Examples
30749 @subsection File-I/O Examples
30750 @cindex file-i/o examples
30752 Example sequence of a write call, file descriptor 3, buffer is at target
30753 address 0x1234, 6 bytes should be written:
30756 <- @code{Fwrite,3,1234,6}
30757 @emph{request memory read from target}
30760 @emph{return "6 bytes written"}
30764 Example sequence of a read call, file descriptor 3, buffer is at target
30765 address 0x1234, 6 bytes should be read:
30768 <- @code{Fread,3,1234,6}
30769 @emph{request memory write to target}
30770 -> @code{X1234,6:XXXXXX}
30771 @emph{return "6 bytes read"}
30775 Example sequence of a read call, call fails on the host due to invalid
30776 file descriptor (@code{EBADF}):
30779 <- @code{Fread,3,1234,6}
30783 Example sequence of a read call, user presses @kbd{Ctrl-c} before syscall on
30787 <- @code{Fread,3,1234,6}
30792 Example sequence of a read call, user presses @kbd{Ctrl-c} after syscall on
30796 <- @code{Fread,3,1234,6}
30797 -> @code{X1234,6:XXXXXX}
30801 @node Library List Format
30802 @section Library List Format
30803 @cindex library list format, remote protocol
30805 On some platforms, a dynamic loader (e.g.@: @file{ld.so}) runs in the
30806 same process as your application to manage libraries. In this case,
30807 @value{GDBN} can use the loader's symbol table and normal memory
30808 operations to maintain a list of shared libraries. On other
30809 platforms, the operating system manages loaded libraries.
30810 @value{GDBN} can not retrieve the list of currently loaded libraries
30811 through memory operations, so it uses the @samp{qXfer:libraries:read}
30812 packet (@pxref{qXfer library list read}) instead. The remote stub
30813 queries the target's operating system and reports which libraries
30816 The @samp{qXfer:libraries:read} packet returns an XML document which
30817 lists loaded libraries and their offsets. Each library has an
30818 associated name and one or more segment or section base addresses,
30819 which report where the library was loaded in memory.
30821 For the common case of libraries that are fully linked binaries, the
30822 library should have a list of segments. If the target supports
30823 dynamic linking of a relocatable object file, its library XML element
30824 should instead include a list of allocated sections. The segment or
30825 section bases are start addresses, not relocation offsets; they do not
30826 depend on the library's link-time base addresses.
30828 @value{GDBN} must be linked with the Expat library to support XML
30829 library lists. @xref{Expat}.
30831 A simple memory map, with one loaded library relocated by a single
30832 offset, looks like this:
30836 <library name="/lib/libc.so.6">
30837 <segment address="0x10000000"/>
30842 Another simple memory map, with one loaded library with three
30843 allocated sections (.text, .data, .bss), looks like this:
30847 <library name="sharedlib.o">
30848 <section address="0x10000000"/>
30849 <section address="0x20000000"/>
30850 <section address="0x30000000"/>
30855 The format of a library list is described by this DTD:
30858 <!-- library-list: Root element with versioning -->
30859 <!ELEMENT library-list (library)*>
30860 <!ATTLIST library-list version CDATA #FIXED "1.0">
30861 <!ELEMENT library (segment*, section*)>
30862 <!ATTLIST library name CDATA #REQUIRED>
30863 <!ELEMENT segment EMPTY>
30864 <!ATTLIST segment address CDATA #REQUIRED>
30865 <!ELEMENT section EMPTY>
30866 <!ATTLIST section address CDATA #REQUIRED>
30869 In addition, segments and section descriptors cannot be mixed within a
30870 single library element, and you must supply at least one segment or
30871 section for each library.
30873 @node Memory Map Format
30874 @section Memory Map Format
30875 @cindex memory map format
30877 To be able to write into flash memory, @value{GDBN} needs to obtain a
30878 memory map from the target. This section describes the format of the
30881 The memory map is obtained using the @samp{qXfer:memory-map:read}
30882 (@pxref{qXfer memory map read}) packet and is an XML document that
30883 lists memory regions.
30885 @value{GDBN} must be linked with the Expat library to support XML
30886 memory maps. @xref{Expat}.
30888 The top-level structure of the document is shown below:
30891 <?xml version="1.0"?>
30892 <!DOCTYPE memory-map
30893 PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
30894 "http://sourceware.org/gdb/gdb-memory-map.dtd">
30900 Each region can be either:
30905 A region of RAM starting at @var{addr} and extending for @var{length}
30909 <memory type="ram" start="@var{addr}" length="@var{length}"/>
30914 A region of read-only memory:
30917 <memory type="rom" start="@var{addr}" length="@var{length}"/>
30922 A region of flash memory, with erasure blocks @var{blocksize}
30926 <memory type="flash" start="@var{addr}" length="@var{length}">
30927 <property name="blocksize">@var{blocksize}</property>
30933 Regions must not overlap. @value{GDBN} assumes that areas of memory not covered
30934 by the memory map are RAM, and uses the ordinary @samp{M} and @samp{X}
30935 packets to write to addresses in such ranges.
30937 The formal DTD for memory map format is given below:
30940 <!-- ................................................... -->
30941 <!-- Memory Map XML DTD ................................ -->
30942 <!-- File: memory-map.dtd .............................. -->
30943 <!-- .................................... .............. -->
30944 <!-- memory-map.dtd -->
30945 <!-- memory-map: Root element with versioning -->
30946 <!ELEMENT memory-map (memory | property)>
30947 <!ATTLIST memory-map version CDATA #FIXED "1.0.0">
30948 <!ELEMENT memory (property)>
30949 <!-- memory: Specifies a memory region,
30950 and its type, or device. -->
30951 <!ATTLIST memory type CDATA #REQUIRED
30952 start CDATA #REQUIRED
30953 length CDATA #REQUIRED
30954 device CDATA #IMPLIED>
30955 <!-- property: Generic attribute tag -->
30956 <!ELEMENT property (#PCDATA | property)*>
30957 <!ATTLIST property name CDATA #REQUIRED>
30960 @include agentexpr.texi
30962 @node Target Descriptions
30963 @appendix Target Descriptions
30964 @cindex target descriptions
30966 @strong{Warning:} target descriptions are still under active development,
30967 and the contents and format may change between @value{GDBN} releases.
30968 The format is expected to stabilize in the future.
30970 One of the challenges of using @value{GDBN} to debug embedded systems
30971 is that there are so many minor variants of each processor
30972 architecture in use. It is common practice for vendors to start with
30973 a standard processor core --- ARM, PowerPC, or MIPS, for example ---
30974 and then make changes to adapt it to a particular market niche. Some
30975 architectures have hundreds of variants, available from dozens of
30976 vendors. This leads to a number of problems:
30980 With so many different customized processors, it is difficult for
30981 the @value{GDBN} maintainers to keep up with the changes.
30983 Since individual variants may have short lifetimes or limited
30984 audiences, it may not be worthwhile to carry information about every
30985 variant in the @value{GDBN} source tree.
30987 When @value{GDBN} does support the architecture of the embedded system
30988 at hand, the task of finding the correct architecture name to give the
30989 @command{set architecture} command can be error-prone.
30992 To address these problems, the @value{GDBN} remote protocol allows a
30993 target system to not only identify itself to @value{GDBN}, but to
30994 actually describe its own features. This lets @value{GDBN} support
30995 processor variants it has never seen before --- to the extent that the
30996 descriptions are accurate, and that @value{GDBN} understands them.
30998 @value{GDBN} must be linked with the Expat library to support XML
30999 target descriptions. @xref{Expat}.
31002 * Retrieving Descriptions:: How descriptions are fetched from a target.
31003 * Target Description Format:: The contents of a target description.
31004 * Predefined Target Types:: Standard types available for target
31006 * Standard Target Features:: Features @value{GDBN} knows about.
31009 @node Retrieving Descriptions
31010 @section Retrieving Descriptions
31012 Target descriptions can be read from the target automatically, or
31013 specified by the user manually. The default behavior is to read the
31014 description from the target. @value{GDBN} retrieves it via the remote
31015 protocol using @samp{qXfer} requests (@pxref{General Query Packets,
31016 qXfer}). The @var{annex} in the @samp{qXfer} packet will be
31017 @samp{target.xml}. The contents of the @samp{target.xml} annex are an
31018 XML document, of the form described in @ref{Target Description
31021 Alternatively, you can specify a file to read for the target description.
31022 If a file is set, the target will not be queried. The commands to
31023 specify a file are:
31026 @cindex set tdesc filename
31027 @item set tdesc filename @var{path}
31028 Read the target description from @var{path}.
31030 @cindex unset tdesc filename
31031 @item unset tdesc filename
31032 Do not read the XML target description from a file. @value{GDBN}
31033 will use the description supplied by the current target.
31035 @cindex show tdesc filename
31036 @item show tdesc filename
31037 Show the filename to read for a target description, if any.
31041 @node Target Description Format
31042 @section Target Description Format
31043 @cindex target descriptions, XML format
31045 A target description annex is an @uref{http://www.w3.org/XML/, XML}
31046 document which complies with the Document Type Definition provided in
31047 the @value{GDBN} sources in @file{gdb/features/gdb-target.dtd}. This
31048 means you can use generally available tools like @command{xmllint} to
31049 check that your feature descriptions are well-formed and valid.
31050 However, to help people unfamiliar with XML write descriptions for
31051 their targets, we also describe the grammar here.
31053 Target descriptions can identify the architecture of the remote target
31054 and (for some architectures) provide information about custom register
31055 sets. They can also identify the OS ABI of the remote target.
31056 @value{GDBN} can use this information to autoconfigure for your
31057 target, or to warn you if you connect to an unsupported target.
31059 Here is a simple target description:
31062 <target version="1.0">
31063 <architecture>i386:x86-64</architecture>
31068 This minimal description only says that the target uses
31069 the x86-64 architecture.
31071 A target description has the following overall form, with [ ] marking
31072 optional elements and @dots{} marking repeatable elements. The elements
31073 are explained further below.
31076 <?xml version="1.0"?>
31077 <!DOCTYPE target SYSTEM "gdb-target.dtd">
31078 <target version="1.0">
31079 @r{[}@var{architecture}@r{]}
31080 @r{[}@var{osabi}@r{]}
31081 @r{[}@var{compatible}@r{]}
31082 @r{[}@var{feature}@dots{}@r{]}
31087 The description is generally insensitive to whitespace and line
31088 breaks, under the usual common-sense rules. The XML version
31089 declaration and document type declaration can generally be omitted
31090 (@value{GDBN} does not require them), but specifying them may be
31091 useful for XML validation tools. The @samp{version} attribute for
31092 @samp{<target>} may also be omitted, but we recommend
31093 including it; if future versions of @value{GDBN} use an incompatible
31094 revision of @file{gdb-target.dtd}, they will detect and report
31095 the version mismatch.
31097 @subsection Inclusion
31098 @cindex target descriptions, inclusion
31101 @cindex <xi:include>
31104 It can sometimes be valuable to split a target description up into
31105 several different annexes, either for organizational purposes, or to
31106 share files between different possible target descriptions. You can
31107 divide a description into multiple files by replacing any element of
31108 the target description with an inclusion directive of the form:
31111 <xi:include href="@var{document}"/>
31115 When @value{GDBN} encounters an element of this form, it will retrieve
31116 the named XML @var{document}, and replace the inclusion directive with
31117 the contents of that document. If the current description was read
31118 using @samp{qXfer}, then so will be the included document;
31119 @var{document} will be interpreted as the name of an annex. If the
31120 current description was read from a file, @value{GDBN} will look for
31121 @var{document} as a file in the same directory where it found the
31122 original description.
31124 @subsection Architecture
31125 @cindex <architecture>
31127 An @samp{<architecture>} element has this form:
31130 <architecture>@var{arch}</architecture>
31133 @var{arch} is one of the architectures from the set accepted by
31134 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
31137 @cindex @code{<osabi>}
31139 This optional field was introduced in @value{GDBN} version 7.0.
31140 Previous versions of @value{GDBN} ignore it.
31142 An @samp{<osabi>} element has this form:
31145 <osabi>@var{abi-name}</osabi>
31148 @var{abi-name} is an OS ABI name from the same selection accepted by
31149 @w{@code{set osabi}} (@pxref{ABI, ,Configuring the Current ABI}).
31151 @subsection Compatible Architecture
31152 @cindex @code{<compatible>}
31154 This optional field was introduced in @value{GDBN} version 7.0.
31155 Previous versions of @value{GDBN} ignore it.
31157 A @samp{<compatible>} element has this form:
31160 <compatible>@var{arch}</compatible>
31163 @var{arch} is one of the architectures from the set accepted by
31164 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
31166 A @samp{<compatible>} element is used to specify that the target
31167 is able to run binaries in some other than the main target architecture
31168 given by the @samp{<architecture>} element. For example, on the
31169 Cell Broadband Engine, the main architecture is @code{powerpc:common}
31170 or @code{powerpc:common64}, but the system is able to run binaries
31171 in the @code{spu} architecture as well. The way to describe this
31172 capability with @samp{<compatible>} is as follows:
31175 <architecture>powerpc:common</architecture>
31176 <compatible>spu</compatible>
31179 @subsection Features
31182 Each @samp{<feature>} describes some logical portion of the target
31183 system. Features are currently used to describe available CPU
31184 registers and the types of their contents. A @samp{<feature>} element
31188 <feature name="@var{name}">
31189 @r{[}@var{type}@dots{}@r{]}
31195 Each feature's name should be unique within the description. The name
31196 of a feature does not matter unless @value{GDBN} has some special
31197 knowledge of the contents of that feature; if it does, the feature
31198 should have its standard name. @xref{Standard Target Features}.
31202 Any register's value is a collection of bits which @value{GDBN} must
31203 interpret. The default interpretation is a two's complement integer,
31204 but other types can be requested by name in the register description.
31205 Some predefined types are provided by @value{GDBN} (@pxref{Predefined
31206 Target Types}), and the description can define additional composite types.
31208 Each type element must have an @samp{id} attribute, which gives
31209 a unique (within the containing @samp{<feature>}) name to the type.
31210 Types must be defined before they are used.
31213 Some targets offer vector registers, which can be treated as arrays
31214 of scalar elements. These types are written as @samp{<vector>} elements,
31215 specifying the array element type, @var{type}, and the number of elements,
31219 <vector id="@var{id}" type="@var{type}" count="@var{count}"/>
31223 If a register's value is usefully viewed in multiple ways, define it
31224 with a union type containing the useful representations. The
31225 @samp{<union>} element contains one or more @samp{<field>} elements,
31226 each of which has a @var{name} and a @var{type}:
31229 <union id="@var{id}">
31230 <field name="@var{name}" type="@var{type}"/>
31235 @subsection Registers
31238 Each register is represented as an element with this form:
31241 <reg name="@var{name}"
31242 bitsize="@var{size}"
31243 @r{[}regnum="@var{num}"@r{]}
31244 @r{[}save-restore="@var{save-restore}"@r{]}
31245 @r{[}type="@var{type}"@r{]}
31246 @r{[}group="@var{group}"@r{]}/>
31250 The components are as follows:
31255 The register's name; it must be unique within the target description.
31258 The register's size, in bits.
31261 The register's number. If omitted, a register's number is one greater
31262 than that of the previous register (either in the current feature or in
31263 a preceeding feature); the first register in the target description
31264 defaults to zero. This register number is used to read or write
31265 the register; e.g.@: it is used in the remote @code{p} and @code{P}
31266 packets, and registers appear in the @code{g} and @code{G} packets
31267 in order of increasing register number.
31270 Whether the register should be preserved across inferior function
31271 calls; this must be either @code{yes} or @code{no}. The default is
31272 @code{yes}, which is appropriate for most registers except for
31273 some system control registers; this is not related to the target's
31277 The type of the register. @var{type} may be a predefined type, a type
31278 defined in the current feature, or one of the special types @code{int}
31279 and @code{float}. @code{int} is an integer type of the correct size
31280 for @var{bitsize}, and @code{float} is a floating point type (in the
31281 architecture's normal floating point format) of the correct size for
31282 @var{bitsize}. The default is @code{int}.
31285 The register group to which this register belongs. @var{group} must
31286 be either @code{general}, @code{float}, or @code{vector}. If no
31287 @var{group} is specified, @value{GDBN} will not display the register
31288 in @code{info registers}.
31292 @node Predefined Target Types
31293 @section Predefined Target Types
31294 @cindex target descriptions, predefined types
31296 Type definitions in the self-description can build up composite types
31297 from basic building blocks, but can not define fundamental types. Instead,
31298 standard identifiers are provided by @value{GDBN} for the fundamental
31299 types. The currently supported types are:
31308 Signed integer types holding the specified number of bits.
31315 Unsigned integer types holding the specified number of bits.
31319 Pointers to unspecified code and data. The program counter and
31320 any dedicated return address register may be marked as code
31321 pointers; printing a code pointer converts it into a symbolic
31322 address. The stack pointer and any dedicated address registers
31323 may be marked as data pointers.
31326 Single precision IEEE floating point.
31329 Double precision IEEE floating point.
31332 The 12-byte extended precision format used by ARM FPA registers.
31336 @node Standard Target Features
31337 @section Standard Target Features
31338 @cindex target descriptions, standard features
31340 A target description must contain either no registers or all the
31341 target's registers. If the description contains no registers, then
31342 @value{GDBN} will assume a default register layout, selected based on
31343 the architecture. If the description contains any registers, the
31344 default layout will not be used; the standard registers must be
31345 described in the target description, in such a way that @value{GDBN}
31346 can recognize them.
31348 This is accomplished by giving specific names to feature elements
31349 which contain standard registers. @value{GDBN} will look for features
31350 with those names and verify that they contain the expected registers;
31351 if any known feature is missing required registers, or if any required
31352 feature is missing, @value{GDBN} will reject the target
31353 description. You can add additional registers to any of the
31354 standard features --- @value{GDBN} will display them just as if
31355 they were added to an unrecognized feature.
31357 This section lists the known features and their expected contents.
31358 Sample XML documents for these features are included in the
31359 @value{GDBN} source tree, in the directory @file{gdb/features}.
31361 Names recognized by @value{GDBN} should include the name of the
31362 company or organization which selected the name, and the overall
31363 architecture to which the feature applies; so e.g.@: the feature
31364 containing ARM core registers is named @samp{org.gnu.gdb.arm.core}.
31366 The names of registers are not case sensitive for the purpose
31367 of recognizing standard features, but @value{GDBN} will only display
31368 registers using the capitalization used in the description.
31374 * PowerPC Features::
31379 @subsection ARM Features
31380 @cindex target descriptions, ARM features
31382 The @samp{org.gnu.gdb.arm.core} feature is required for ARM targets.
31383 It should contain registers @samp{r0} through @samp{r13}, @samp{sp},
31384 @samp{lr}, @samp{pc}, and @samp{cpsr}.
31386 The @samp{org.gnu.gdb.arm.fpa} feature is optional. If present, it
31387 should contain registers @samp{f0} through @samp{f7} and @samp{fps}.
31389 The @samp{org.gnu.gdb.xscale.iwmmxt} feature is optional. If present,
31390 it should contain at least registers @samp{wR0} through @samp{wR15} and
31391 @samp{wCGR0} through @samp{wCGR3}. The @samp{wCID}, @samp{wCon},
31392 @samp{wCSSF}, and @samp{wCASF} registers are optional.
31394 The @samp{org.gnu.gdb.arm.vfp} feature is optional. If present, it
31395 should contain at least registers @samp{d0} through @samp{d15}. If
31396 they are present, @samp{d16} through @samp{d31} should also be included.
31397 @value{GDBN} will synthesize the single-precision registers from
31398 halves of the double-precision registers.
31400 The @samp{org.gnu.gdb.arm.neon} feature is optional. It does not
31401 need to contain registers; it instructs @value{GDBN} to display the
31402 VFP double-precision registers as vectors and to synthesize the
31403 quad-precision registers from pairs of double-precision registers.
31404 If this feature is present, @samp{org.gnu.gdb.arm.vfp} must also
31405 be present and include 32 double-precision registers.
31407 @node MIPS Features
31408 @subsection MIPS Features
31409 @cindex target descriptions, MIPS features
31411 The @samp{org.gnu.gdb.mips.cpu} feature is required for MIPS targets.
31412 It should contain registers @samp{r0} through @samp{r31}, @samp{lo},
31413 @samp{hi}, and @samp{pc}. They may be 32-bit or 64-bit depending
31416 The @samp{org.gnu.gdb.mips.cp0} feature is also required. It should
31417 contain at least the @samp{status}, @samp{badvaddr}, and @samp{cause}
31418 registers. They may be 32-bit or 64-bit depending on the target.
31420 The @samp{org.gnu.gdb.mips.fpu} feature is currently required, though
31421 it may be optional in a future version of @value{GDBN}. It should
31422 contain registers @samp{f0} through @samp{f31}, @samp{fcsr}, and
31423 @samp{fir}. They may be 32-bit or 64-bit depending on the target.
31425 The @samp{org.gnu.gdb.mips.linux} feature is optional. It should
31426 contain a single register, @samp{restart}, which is used by the
31427 Linux kernel to control restartable syscalls.
31429 @node M68K Features
31430 @subsection M68K Features
31431 @cindex target descriptions, M68K features
31434 @item @samp{org.gnu.gdb.m68k.core}
31435 @itemx @samp{org.gnu.gdb.coldfire.core}
31436 @itemx @samp{org.gnu.gdb.fido.core}
31437 One of those features must be always present.
31438 The feature that is present determines which flavor of m68k is
31439 used. The feature that is present should contain registers
31440 @samp{d0} through @samp{d7}, @samp{a0} through @samp{a5}, @samp{fp},
31441 @samp{sp}, @samp{ps} and @samp{pc}.
31443 @item @samp{org.gnu.gdb.coldfire.fp}
31444 This feature is optional. If present, it should contain registers
31445 @samp{fp0} through @samp{fp7}, @samp{fpcontrol}, @samp{fpstatus} and
31449 @node PowerPC Features
31450 @subsection PowerPC Features
31451 @cindex target descriptions, PowerPC features
31453 The @samp{org.gnu.gdb.power.core} feature is required for PowerPC
31454 targets. It should contain registers @samp{r0} through @samp{r31},
31455 @samp{pc}, @samp{msr}, @samp{cr}, @samp{lr}, @samp{ctr}, and
31456 @samp{xer}. They may be 32-bit or 64-bit depending on the target.
31458 The @samp{org.gnu.gdb.power.fpu} feature is optional. It should
31459 contain registers @samp{f0} through @samp{f31} and @samp{fpscr}.
31461 The @samp{org.gnu.gdb.power.altivec} feature is optional. It should
31462 contain registers @samp{vr0} through @samp{vr31}, @samp{vscr},
31465 The @samp{org.gnu.gdb.power.vsx} feature is optional. It should
31466 contain registers @samp{vs0h} through @samp{vs31h}. @value{GDBN}
31467 will combine these registers with the floating point registers
31468 (@samp{f0} through @samp{f31}) and the altivec registers (@samp{vr0}
31469 through @samp{vr31}) to present the 128-bit wide registers @samp{vs0}
31470 through @samp{vs63}, the set of vector registers for POWER7.
31472 The @samp{org.gnu.gdb.power.spe} feature is optional. It should
31473 contain registers @samp{ev0h} through @samp{ev31h}, @samp{acc}, and
31474 @samp{spefscr}. SPE targets should provide 32-bit registers in
31475 @samp{org.gnu.gdb.power.core} and provide the upper halves in
31476 @samp{ev0h} through @samp{ev31h}. @value{GDBN} will combine
31477 these to present registers @samp{ev0} through @samp{ev31} to the
31480 @node Operating System Information
31481 @appendix Operating System Information
31482 @cindex operating system information
31488 Users of @value{GDBN} often wish to obtain information about the state of
31489 the operating system running on the target---for example the list of
31490 processes, or the list of open files. This section describes the
31491 mechanism that makes it possible. This mechanism is similar to the
31492 target features mechanism (@pxref{Target Descriptions}), but focuses
31493 on a different aspect of target.
31495 Operating system information is retrived from the target via the
31496 remote protocol, using @samp{qXfer} requests (@pxref{qXfer osdata
31497 read}). The object name in the request should be @samp{osdata}, and
31498 the @var{annex} identifies the data to be fetched.
31501 @appendixsection Process list
31502 @cindex operating system information, process list
31504 When requesting the process list, the @var{annex} field in the
31505 @samp{qXfer} request should be @samp{processes}. The returned data is
31506 an XML document. The formal syntax of this document is defined in
31507 @file{gdb/features/osdata.dtd}.
31509 An example document is:
31512 <?xml version="1.0"?>
31513 <!DOCTYPE target SYSTEM "osdata.dtd">
31514 <osdata type="processes">
31516 <column name="pid">1</column>
31517 <column name="user">root</column>
31518 <column name="command">/sbin/init</column>
31523 Each item should include a column whose name is @samp{pid}. The value
31524 of that column should identify the process on the target. The
31525 @samp{user} and @samp{command} columns are optional, and will be
31526 displayed by @value{GDBN}. Target may provide additional columns,
31527 which @value{GDBN} currently ignores.
31541 % I think something like @colophon should be in texinfo. In the
31543 \long\def\colophon{\hbox to0pt{}\vfill
31544 \centerline{The body of this manual is set in}
31545 \centerline{\fontname\tenrm,}
31546 \centerline{with headings in {\bf\fontname\tenbf}}
31547 \centerline{and examples in {\tt\fontname\tentt}.}
31548 \centerline{{\it\fontname\tenit\/},}
31549 \centerline{{\bf\fontname\tenbf}, and}
31550 \centerline{{\sl\fontname\tensl\/}}
31551 \centerline{are used for emphasis.}\vfill}
31553 % Blame: doc@cygnus.com, 1991.