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}.
2380 To switch focus between inferiors, use the @code{inferior} command:
2383 @kindex inferior @var{inferior-id}
2384 @item inferior @var{inferior-id}
2385 Make inferior number @var{inferior-id} the current inferior. The
2386 argument @var{inferior-id} is the internal inferior number assigned by
2387 @value{GDBN}, as shown in the first field of the @samp{info inferiors}
2391 To quit debugging one of the inferiors, you can either detach from it
2392 by using the @w{@code{detach inferior}} command (allowing it to run
2393 independently), or kill it using the @w{@code{kill inferior}} command:
2396 @kindex detach inferior @var{inferior-id}
2397 @item detach inferior @var{inferior-id}
2398 Detach from the inferior identified by @value{GDBN} inferior number
2399 @var{inferior-id}, and remove it from the inferior list.
2401 @kindex kill inferior @var{inferior-id}
2402 @item kill inferior @var{inferior-id}
2403 Kill the inferior identified by @value{GDBN} inferior number
2404 @var{inferior-id}, and remove it from the inferior list.
2407 To be notified when inferiors are started or exit under @value{GDBN}'s
2408 control use @w{@code{set print inferior-events}}:
2411 @kindex set print inferior-events
2412 @cindex print messages on inferior start and exit
2413 @item set print inferior-events
2414 @itemx set print inferior-events on
2415 @itemx set print inferior-events off
2416 The @code{set print inferior-events} command allows you to enable or
2417 disable printing of messages when @value{GDBN} notices that new
2418 inferiors have started or that inferiors have exited or have been
2419 detached. By default, these messages will not be printed.
2421 @kindex show print inferior-events
2422 @item show print inferior-events
2423 Show whether messages will be printed when @value{GDBN} detects that
2424 inferiors have started, exited or have been detached.
2428 @section Debugging Programs with Multiple Threads
2430 @cindex threads of execution
2431 @cindex multiple threads
2432 @cindex switching threads
2433 In some operating systems, such as HP-UX and Solaris, a single program
2434 may have more than one @dfn{thread} of execution. The precise semantics
2435 of threads differ from one operating system to another, but in general
2436 the threads of a single program are akin to multiple processes---except
2437 that they share one address space (that is, they can all examine and
2438 modify the same variables). On the other hand, each thread has its own
2439 registers and execution stack, and perhaps private memory.
2441 @value{GDBN} provides these facilities for debugging multi-thread
2445 @item automatic notification of new threads
2446 @item @samp{thread @var{threadno}}, a command to switch among threads
2447 @item @samp{info threads}, a command to inquire about existing threads
2448 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2449 a command to apply a command to a list of threads
2450 @item thread-specific breakpoints
2451 @item @samp{set print thread-events}, which controls printing of
2452 messages on thread start and exit.
2453 @item @samp{set libthread-db-search-path @var{path}}, which lets
2454 the user specify which @code{libthread_db} to use if the default choice
2455 isn't compatible with the program.
2459 @emph{Warning:} These facilities are not yet available on every
2460 @value{GDBN} configuration where the operating system supports threads.
2461 If your @value{GDBN} does not support threads, these commands have no
2462 effect. For example, a system without thread support shows no output
2463 from @samp{info threads}, and always rejects the @code{thread} command,
2467 (@value{GDBP}) info threads
2468 (@value{GDBP}) thread 1
2469 Thread ID 1 not known. Use the "info threads" command to
2470 see the IDs of currently known threads.
2472 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2473 @c doesn't support threads"?
2476 @cindex focus of debugging
2477 @cindex current thread
2478 The @value{GDBN} thread debugging facility allows you to observe all
2479 threads while your program runs---but whenever @value{GDBN} takes
2480 control, one thread in particular is always the focus of debugging.
2481 This thread is called the @dfn{current thread}. Debugging commands show
2482 program information from the perspective of the current thread.
2484 @cindex @code{New} @var{systag} message
2485 @cindex thread identifier (system)
2486 @c FIXME-implementors!! It would be more helpful if the [New...] message
2487 @c included GDB's numeric thread handle, so you could just go to that
2488 @c thread without first checking `info threads'.
2489 Whenever @value{GDBN} detects a new thread in your program, it displays
2490 the target system's identification for the thread with a message in the
2491 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2492 whose form varies depending on the particular system. For example, on
2493 @sc{gnu}/Linux, you might see
2496 [New Thread 46912507313328 (LWP 25582)]
2500 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2501 the @var{systag} is simply something like @samp{process 368}, with no
2504 @c FIXME!! (1) Does the [New...] message appear even for the very first
2505 @c thread of a program, or does it only appear for the
2506 @c second---i.e.@: when it becomes obvious we have a multithread
2508 @c (2) *Is* there necessarily a first thread always? Or do some
2509 @c multithread systems permit starting a program with multiple
2510 @c threads ab initio?
2512 @cindex thread number
2513 @cindex thread identifier (GDB)
2514 For debugging purposes, @value{GDBN} associates its own thread
2515 number---always a single integer---with each thread in your program.
2518 @kindex info threads
2520 Display a summary of all threads currently in your
2521 program. @value{GDBN} displays for each thread (in this order):
2525 the thread number assigned by @value{GDBN}
2528 the target system's thread identifier (@var{systag})
2531 the current stack frame summary for that thread
2535 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2536 indicates the current thread.
2540 @c end table here to get a little more width for example
2543 (@value{GDBP}) info threads
2544 3 process 35 thread 27 0x34e5 in sigpause ()
2545 2 process 35 thread 23 0x34e5 in sigpause ()
2546 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2552 @cindex debugging multithreaded programs (on HP-UX)
2553 @cindex thread identifier (GDB), on HP-UX
2554 For debugging purposes, @value{GDBN} associates its own thread
2555 number---a small integer assigned in thread-creation order---with each
2556 thread in your program.
2558 @cindex @code{New} @var{systag} message, on HP-UX
2559 @cindex thread identifier (system), on HP-UX
2560 @c FIXME-implementors!! It would be more helpful if the [New...] message
2561 @c included GDB's numeric thread handle, so you could just go to that
2562 @c thread without first checking `info threads'.
2563 Whenever @value{GDBN} detects a new thread in your program, it displays
2564 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2565 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2566 whose form varies depending on the particular system. For example, on
2570 [New thread 2 (system thread 26594)]
2574 when @value{GDBN} notices a new thread.
2577 @kindex info threads (HP-UX)
2579 Display a summary of all threads currently in your
2580 program. @value{GDBN} displays for each thread (in this order):
2583 @item the thread number assigned by @value{GDBN}
2585 @item the target system's thread identifier (@var{systag})
2587 @item the current stack frame summary for that thread
2591 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2592 indicates the current thread.
2596 @c end table here to get a little more width for example
2599 (@value{GDBP}) info threads
2600 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2602 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2603 from /usr/lib/libc.2
2604 1 system thread 27905 0x7b003498 in _brk () \@*
2605 from /usr/lib/libc.2
2608 On Solaris, you can display more information about user threads with a
2609 Solaris-specific command:
2612 @item maint info sol-threads
2613 @kindex maint info sol-threads
2614 @cindex thread info (Solaris)
2615 Display info on Solaris user threads.
2619 @kindex thread @var{threadno}
2620 @item thread @var{threadno}
2621 Make thread number @var{threadno} the current thread. The command
2622 argument @var{threadno} is the internal @value{GDBN} thread number, as
2623 shown in the first field of the @samp{info threads} display.
2624 @value{GDBN} responds by displaying the system identifier of the thread
2625 you selected, and its current stack frame summary:
2628 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2629 (@value{GDBP}) thread 2
2630 [Switching to process 35 thread 23]
2631 0x34e5 in sigpause ()
2635 As with the @samp{[New @dots{}]} message, the form of the text after
2636 @samp{Switching to} depends on your system's conventions for identifying
2639 @kindex thread apply
2640 @cindex apply command to several threads
2641 @item thread apply [@var{threadno}] [@var{all}] @var{command}
2642 The @code{thread apply} command allows you to apply the named
2643 @var{command} to one or more threads. Specify the numbers of the
2644 threads that you want affected with the command argument
2645 @var{threadno}. It can be a single thread number, one of the numbers
2646 shown in the first field of the @samp{info threads} display; or it
2647 could be a range of thread numbers, as in @code{2-4}. To apply a
2648 command to all threads, type @kbd{thread apply all @var{command}}.
2650 @kindex set print thread-events
2651 @cindex print messages on thread start and exit
2652 @item set print thread-events
2653 @itemx set print thread-events on
2654 @itemx set print thread-events off
2655 The @code{set print thread-events} command allows you to enable or
2656 disable printing of messages when @value{GDBN} notices that new threads have
2657 started or that threads have exited. By default, these messages will
2658 be printed if detection of these events is supported by the target.
2659 Note that these messages cannot be disabled on all targets.
2661 @kindex show print thread-events
2662 @item show print thread-events
2663 Show whether messages will be printed when @value{GDBN} detects that threads
2664 have started and exited.
2667 @xref{Thread Stops,,Stopping and Starting Multi-thread Programs}, for
2668 more information about how @value{GDBN} behaves when you stop and start
2669 programs with multiple threads.
2671 @xref{Set Watchpoints,,Setting Watchpoints}, for information about
2672 watchpoints in programs with multiple threads.
2675 @kindex set libthread-db-search-path
2676 @cindex search path for @code{libthread_db}
2677 @item set libthread-db-search-path @r{[}@var{path}@r{]}
2678 If this variable is set, @var{path} is a colon-separated list of
2679 directories @value{GDBN} will use to search for @code{libthread_db}.
2680 If you omit @var{path}, @samp{libthread-db-search-path} will be reset to
2683 On @sc{gnu}/Linux and Solaris systems, @value{GDBN} uses a ``helper''
2684 @code{libthread_db} library to obtain information about threads in the
2685 inferior process. @value{GDBN} will use @samp{libthread-db-search-path}
2686 to find @code{libthread_db}. If that fails, @value{GDBN} will continue
2687 with default system shared library directories, and finally the directory
2688 from which @code{libpthread} was loaded in the inferior process.
2690 For any @code{libthread_db} library @value{GDBN} finds in above directories,
2691 @value{GDBN} attempts to initialize it with the current inferior process.
2692 If this initialization fails (which could happen because of a version
2693 mismatch between @code{libthread_db} and @code{libpthread}), @value{GDBN}
2694 will unload @code{libthread_db}, and continue with the next directory.
2695 If none of @code{libthread_db} libraries initialize successfully,
2696 @value{GDBN} will issue a warning and thread debugging will be disabled.
2698 Setting @code{libthread-db-search-path} is currently implemented
2699 only on some platforms.
2701 @kindex show libthread-db-search-path
2702 @item show libthread-db-search-path
2703 Display current libthread_db search path.
2707 @section Debugging Programs with Multiple Processes
2709 @cindex fork, debugging programs which call
2710 @cindex multiple processes
2711 @cindex processes, multiple
2712 On most systems, @value{GDBN} has no special support for debugging
2713 programs which create additional processes using the @code{fork}
2714 function. When a program forks, @value{GDBN} will continue to debug the
2715 parent process and the child process will run unimpeded. If you have
2716 set a breakpoint in any code which the child then executes, the child
2717 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2718 will cause it to terminate.
2720 However, if you want to debug the child process there is a workaround
2721 which isn't too painful. Put a call to @code{sleep} in the code which
2722 the child process executes after the fork. It may be useful to sleep
2723 only if a certain environment variable is set, or a certain file exists,
2724 so that the delay need not occur when you don't want to run @value{GDBN}
2725 on the child. While the child is sleeping, use the @code{ps} program to
2726 get its process ID. Then tell @value{GDBN} (a new invocation of
2727 @value{GDBN} if you are also debugging the parent process) to attach to
2728 the child process (@pxref{Attach}). From that point on you can debug
2729 the child process just like any other process which you attached to.
2731 On some systems, @value{GDBN} provides support for debugging programs that
2732 create additional processes using the @code{fork} or @code{vfork} functions.
2733 Currently, the only platforms with this feature are HP-UX (11.x and later
2734 only?) and @sc{gnu}/Linux (kernel version 2.5.60 and later).
2736 By default, when a program forks, @value{GDBN} will continue to debug
2737 the parent process and the child process will run unimpeded.
2739 If you want to follow the child process instead of the parent process,
2740 use the command @w{@code{set follow-fork-mode}}.
2743 @kindex set follow-fork-mode
2744 @item set follow-fork-mode @var{mode}
2745 Set the debugger response to a program call of @code{fork} or
2746 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2747 process. The @var{mode} argument can be:
2751 The original process is debugged after a fork. The child process runs
2752 unimpeded. This is the default.
2755 The new process is debugged after a fork. The parent process runs
2760 @kindex show follow-fork-mode
2761 @item show follow-fork-mode
2762 Display the current debugger response to a @code{fork} or @code{vfork} call.
2765 @cindex debugging multiple processes
2766 On Linux, if you want to debug both the parent and child processes, use the
2767 command @w{@code{set detach-on-fork}}.
2770 @kindex set detach-on-fork
2771 @item set detach-on-fork @var{mode}
2772 Tells gdb whether to detach one of the processes after a fork, or
2773 retain debugger control over them both.
2777 The child process (or parent process, depending on the value of
2778 @code{follow-fork-mode}) will be detached and allowed to run
2779 independently. This is the default.
2782 Both processes will be held under the control of @value{GDBN}.
2783 One process (child or parent, depending on the value of
2784 @code{follow-fork-mode}) is debugged as usual, while the other
2789 @kindex show detach-on-fork
2790 @item show detach-on-fork
2791 Show whether detach-on-fork mode is on/off.
2794 If you choose to set @samp{detach-on-fork} mode off, then @value{GDBN}
2795 will retain control of all forked processes (including nested forks).
2796 You can list the forked processes under the control of @value{GDBN} by
2797 using the @w{@code{info inferiors}} command, and switch from one fork
2798 to another by using the @code{inferior} command (@pxref{Inferiors,
2799 ,Debugging Multiple Inferiors}).
2801 To quit debugging one of the forked processes, you can either detach
2802 from it by using the @w{@code{detach inferior}} command (allowing it
2803 to run independently), or kill it using the @w{@code{kill inferior}}
2804 command. @xref{Inferiors, ,Debugging Multiple Inferiors}.
2806 If you ask to debug a child process and a @code{vfork} is followed by an
2807 @code{exec}, @value{GDBN} executes the new target up to the first
2808 breakpoint in the new target. If you have a breakpoint set on
2809 @code{main} in your original program, the breakpoint will also be set on
2810 the child process's @code{main}.
2812 On some systems, when a child process is spawned by @code{vfork}, you
2813 cannot debug the child or parent until an @code{exec} call completes.
2815 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2816 call executes, the new target restarts. To restart the parent process,
2817 use the @code{file} command with the parent executable name as its
2820 You can use the @code{catch} command to make @value{GDBN} stop whenever
2821 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2822 Catchpoints, ,Setting Catchpoints}.
2824 @node Checkpoint/Restart
2825 @section Setting a @emph{Bookmark} to Return to Later
2830 @cindex snapshot of a process
2831 @cindex rewind program state
2833 On certain operating systems@footnote{Currently, only
2834 @sc{gnu}/Linux.}, @value{GDBN} is able to save a @dfn{snapshot} of a
2835 program's state, called a @dfn{checkpoint}, and come back to it
2838 Returning to a checkpoint effectively undoes everything that has
2839 happened in the program since the @code{checkpoint} was saved. This
2840 includes changes in memory, registers, and even (within some limits)
2841 system state. Effectively, it is like going back in time to the
2842 moment when the checkpoint was saved.
2844 Thus, if you're stepping thru a program and you think you're
2845 getting close to the point where things go wrong, you can save
2846 a checkpoint. Then, if you accidentally go too far and miss
2847 the critical statement, instead of having to restart your program
2848 from the beginning, you can just go back to the checkpoint and
2849 start again from there.
2851 This can be especially useful if it takes a lot of time or
2852 steps to reach the point where you think the bug occurs.
2854 To use the @code{checkpoint}/@code{restart} method of debugging:
2859 Save a snapshot of the debugged program's current execution state.
2860 The @code{checkpoint} command takes no arguments, but each checkpoint
2861 is assigned a small integer id, similar to a breakpoint id.
2863 @kindex info checkpoints
2864 @item info checkpoints
2865 List the checkpoints that have been saved in the current debugging
2866 session. For each checkpoint, the following information will be
2873 @item Source line, or label
2876 @kindex restart @var{checkpoint-id}
2877 @item restart @var{checkpoint-id}
2878 Restore the program state that was saved as checkpoint number
2879 @var{checkpoint-id}. All program variables, registers, stack frames
2880 etc.@: will be returned to the values that they had when the checkpoint
2881 was saved. In essence, gdb will ``wind back the clock'' to the point
2882 in time when the checkpoint was saved.
2884 Note that breakpoints, @value{GDBN} variables, command history etc.
2885 are not affected by restoring a checkpoint. In general, a checkpoint
2886 only restores things that reside in the program being debugged, not in
2889 @kindex delete checkpoint @var{checkpoint-id}
2890 @item delete checkpoint @var{checkpoint-id}
2891 Delete the previously-saved checkpoint identified by @var{checkpoint-id}.
2895 Returning to a previously saved checkpoint will restore the user state
2896 of the program being debugged, plus a significant subset of the system
2897 (OS) state, including file pointers. It won't ``un-write'' data from
2898 a file, but it will rewind the file pointer to the previous location,
2899 so that the previously written data can be overwritten. For files
2900 opened in read mode, the pointer will also be restored so that the
2901 previously read data can be read again.
2903 Of course, characters that have been sent to a printer (or other
2904 external device) cannot be ``snatched back'', and characters received
2905 from eg.@: a serial device can be removed from internal program buffers,
2906 but they cannot be ``pushed back'' into the serial pipeline, ready to
2907 be received again. Similarly, the actual contents of files that have
2908 been changed cannot be restored (at this time).
2910 However, within those constraints, you actually can ``rewind'' your
2911 program to a previously saved point in time, and begin debugging it
2912 again --- and you can change the course of events so as to debug a
2913 different execution path this time.
2915 @cindex checkpoints and process id
2916 Finally, there is one bit of internal program state that will be
2917 different when you return to a checkpoint --- the program's process
2918 id. Each checkpoint will have a unique process id (or @var{pid}),
2919 and each will be different from the program's original @var{pid}.
2920 If your program has saved a local copy of its process id, this could
2921 potentially pose a problem.
2923 @subsection A Non-obvious Benefit of Using Checkpoints
2925 On some systems such as @sc{gnu}/Linux, address space randomization
2926 is performed on new processes for security reasons. This makes it
2927 difficult or impossible to set a breakpoint, or watchpoint, on an
2928 absolute address if you have to restart the program, since the
2929 absolute location of a symbol will change from one execution to the
2932 A checkpoint, however, is an @emph{identical} copy of a process.
2933 Therefore if you create a checkpoint at (eg.@:) the start of main,
2934 and simply return to that checkpoint instead of restarting the
2935 process, you can avoid the effects of address randomization and
2936 your symbols will all stay in the same place.
2939 @chapter Stopping and Continuing
2941 The principal purposes of using a debugger are so that you can stop your
2942 program before it terminates; or so that, if your program runs into
2943 trouble, you can investigate and find out why.
2945 Inside @value{GDBN}, your program may stop for any of several reasons,
2946 such as a signal, a breakpoint, or reaching a new line after a
2947 @value{GDBN} command such as @code{step}. You may then examine and
2948 change variables, set new breakpoints or remove old ones, and then
2949 continue execution. Usually, the messages shown by @value{GDBN} provide
2950 ample explanation of the status of your program---but you can also
2951 explicitly request this information at any time.
2954 @kindex info program
2956 Display information about the status of your program: whether it is
2957 running or not, what process it is, and why it stopped.
2961 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2962 * Continuing and Stepping:: Resuming execution
2964 * Thread Stops:: Stopping and starting multi-thread programs
2968 @section Breakpoints, Watchpoints, and Catchpoints
2971 A @dfn{breakpoint} makes your program stop whenever a certain point in
2972 the program is reached. For each breakpoint, you can add conditions to
2973 control in finer detail whether your program stops. You can set
2974 breakpoints with the @code{break} command and its variants (@pxref{Set
2975 Breaks, ,Setting Breakpoints}), to specify the place where your program
2976 should stop by line number, function name or exact address in the
2979 On some systems, you can set breakpoints in shared libraries before
2980 the executable is run. There is a minor limitation on HP-UX systems:
2981 you must wait until the executable is run in order to set breakpoints
2982 in shared library routines that are not called directly by the program
2983 (for example, routines that are arguments in a @code{pthread_create}
2987 @cindex data breakpoints
2988 @cindex memory tracing
2989 @cindex breakpoint on memory address
2990 @cindex breakpoint on variable modification
2991 A @dfn{watchpoint} is a special breakpoint that stops your program
2992 when the value of an expression changes. The expression may be a value
2993 of a variable, or it could involve values of one or more variables
2994 combined by operators, such as @samp{a + b}. This is sometimes called
2995 @dfn{data breakpoints}. You must use a different command to set
2996 watchpoints (@pxref{Set Watchpoints, ,Setting Watchpoints}), but aside
2997 from that, you can manage a watchpoint like any other breakpoint: you
2998 enable, disable, and delete both breakpoints and watchpoints using the
3001 You can arrange to have values from your program displayed automatically
3002 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
3006 @cindex breakpoint on events
3007 A @dfn{catchpoint} is another special breakpoint that stops your program
3008 when a certain kind of event occurs, such as the throwing of a C@t{++}
3009 exception or the loading of a library. As with watchpoints, you use a
3010 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
3011 Catchpoints}), but aside from that, you can manage a catchpoint like any
3012 other breakpoint. (To stop when your program receives a signal, use the
3013 @code{handle} command; see @ref{Signals, ,Signals}.)
3015 @cindex breakpoint numbers
3016 @cindex numbers for breakpoints
3017 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
3018 catchpoint when you create it; these numbers are successive integers
3019 starting with one. In many of the commands for controlling various
3020 features of breakpoints you use the breakpoint number to say which
3021 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
3022 @dfn{disabled}; if disabled, it has no effect on your program until you
3025 @cindex breakpoint ranges
3026 @cindex ranges of breakpoints
3027 Some @value{GDBN} commands accept a range of breakpoints on which to
3028 operate. A breakpoint range is either a single breakpoint number, like
3029 @samp{5}, or two such numbers, in increasing order, separated by a
3030 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
3031 all breakpoints in that range are operated on.
3034 * Set Breaks:: Setting breakpoints
3035 * Set Watchpoints:: Setting watchpoints
3036 * Set Catchpoints:: Setting catchpoints
3037 * Delete Breaks:: Deleting breakpoints
3038 * Disabling:: Disabling breakpoints
3039 * Conditions:: Break conditions
3040 * Break Commands:: Breakpoint command lists
3041 * Error in Breakpoints:: ``Cannot insert breakpoints''
3042 * Breakpoint-related Warnings:: ``Breakpoint address adjusted...''
3046 @subsection Setting Breakpoints
3048 @c FIXME LMB what does GDB do if no code on line of breakpt?
3049 @c consider in particular declaration with/without initialization.
3051 @c FIXME 2 is there stuff on this already? break at fun start, already init?
3054 @kindex b @r{(@code{break})}
3055 @vindex $bpnum@r{, convenience variable}
3056 @cindex latest breakpoint
3057 Breakpoints are set with the @code{break} command (abbreviated
3058 @code{b}). The debugger convenience variable @samp{$bpnum} records the
3059 number of the breakpoint you've set most recently; see @ref{Convenience
3060 Vars,, Convenience Variables}, for a discussion of what you can do with
3061 convenience variables.
3064 @item break @var{location}
3065 Set a breakpoint at the given @var{location}, which can specify a
3066 function name, a line number, or an address of an instruction.
3067 (@xref{Specify Location}, for a list of all the possible ways to
3068 specify a @var{location}.) The breakpoint will stop your program just
3069 before it executes any of the code in the specified @var{location}.
3071 When using source languages that permit overloading of symbols, such as
3072 C@t{++}, a function name may refer to more than one possible place to break.
3073 @xref{Ambiguous Expressions,,Ambiguous Expressions}, for a discussion of
3076 It is also possible to insert a breakpoint that will stop the program
3077 only if a specific thread (@pxref{Thread-Specific Breakpoints})
3078 or a specific task (@pxref{Ada Tasks}) hits that breakpoint.
3081 When called without any arguments, @code{break} sets a breakpoint at
3082 the next instruction to be executed in the selected stack frame
3083 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
3084 innermost, this makes your program stop as soon as control
3085 returns to that frame. This is similar to the effect of a
3086 @code{finish} command in the frame inside the selected frame---except
3087 that @code{finish} does not leave an active breakpoint. If you use
3088 @code{break} without an argument in the innermost frame, @value{GDBN} stops
3089 the next time it reaches the current location; this may be useful
3092 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
3093 least one instruction has been executed. If it did not do this, you
3094 would be unable to proceed past a breakpoint without first disabling the
3095 breakpoint. This rule applies whether or not the breakpoint already
3096 existed when your program stopped.
3098 @item break @dots{} if @var{cond}
3099 Set a breakpoint with condition @var{cond}; evaluate the expression
3100 @var{cond} each time the breakpoint is reached, and stop only if the
3101 value is nonzero---that is, if @var{cond} evaluates as true.
3102 @samp{@dots{}} stands for one of the possible arguments described
3103 above (or no argument) specifying where to break. @xref{Conditions,
3104 ,Break Conditions}, for more information on breakpoint conditions.
3107 @item tbreak @var{args}
3108 Set a breakpoint enabled only for one stop. @var{args} are the
3109 same as for the @code{break} command, and the breakpoint is set in the same
3110 way, but the breakpoint is automatically deleted after the first time your
3111 program stops there. @xref{Disabling, ,Disabling Breakpoints}.
3114 @cindex hardware breakpoints
3115 @item hbreak @var{args}
3116 Set a hardware-assisted breakpoint. @var{args} are the same as for the
3117 @code{break} command and the breakpoint is set in the same way, but the
3118 breakpoint requires hardware support and some target hardware may not
3119 have this support. The main purpose of this is EPROM/ROM code
3120 debugging, so you can set a breakpoint at an instruction without
3121 changing the instruction. This can be used with the new trap-generation
3122 provided by SPARClite DSU and most x86-based targets. These targets
3123 will generate traps when a program accesses some data or instruction
3124 address that is assigned to the debug registers. However the hardware
3125 breakpoint registers can take a limited number of breakpoints. For
3126 example, on the DSU, only two data breakpoints can be set at a time, and
3127 @value{GDBN} will reject this command if more than two are used. Delete
3128 or disable unused hardware breakpoints before setting new ones
3129 (@pxref{Disabling, ,Disabling Breakpoints}).
3130 @xref{Conditions, ,Break Conditions}.
3131 For remote targets, you can restrict the number of hardware
3132 breakpoints @value{GDBN} will use, see @ref{set remote
3133 hardware-breakpoint-limit}.
3136 @item thbreak @var{args}
3137 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
3138 are the same as for the @code{hbreak} command and the breakpoint is set in
3139 the same way. However, like the @code{tbreak} command,
3140 the breakpoint is automatically deleted after the
3141 first time your program stops there. Also, like the @code{hbreak}
3142 command, the breakpoint requires hardware support and some target hardware
3143 may not have this support. @xref{Disabling, ,Disabling Breakpoints}.
3144 See also @ref{Conditions, ,Break Conditions}.
3147 @cindex regular expression
3148 @cindex breakpoints in functions matching a regexp
3149 @cindex set breakpoints in many functions
3150 @item rbreak @var{regex}
3151 Set breakpoints on all functions matching the regular expression
3152 @var{regex}. This command sets an unconditional breakpoint on all
3153 matches, printing a list of all breakpoints it set. Once these
3154 breakpoints are set, they are treated just like the breakpoints set with
3155 the @code{break} command. You can delete them, disable them, or make
3156 them conditional the same way as any other breakpoint.
3158 The syntax of the regular expression is the standard one used with tools
3159 like @file{grep}. Note that this is different from the syntax used by
3160 shells, so for instance @code{foo*} matches all functions that include
3161 an @code{fo} followed by zero or more @code{o}s. There is an implicit
3162 @code{.*} leading and trailing the regular expression you supply, so to
3163 match only functions that begin with @code{foo}, use @code{^foo}.
3165 @cindex non-member C@t{++} functions, set breakpoint in
3166 When debugging C@t{++} programs, @code{rbreak} is useful for setting
3167 breakpoints on overloaded functions that are not members of any special
3170 @cindex set breakpoints on all functions
3171 The @code{rbreak} command can be used to set breakpoints in
3172 @strong{all} the functions in a program, like this:
3175 (@value{GDBP}) rbreak .
3178 @kindex info breakpoints
3179 @cindex @code{$_} and @code{info breakpoints}
3180 @item info breakpoints @r{[}@var{n}@r{]}
3181 @itemx info break @r{[}@var{n}@r{]}
3182 @itemx info watchpoints @r{[}@var{n}@r{]}
3183 Print a table of all breakpoints, watchpoints, and catchpoints set and
3184 not deleted. Optional argument @var{n} means print information only
3185 about the specified breakpoint (or watchpoint or catchpoint). For
3186 each breakpoint, following columns are printed:
3189 @item Breakpoint Numbers
3191 Breakpoint, watchpoint, or catchpoint.
3193 Whether the breakpoint is marked to be disabled or deleted when hit.
3194 @item Enabled or Disabled
3195 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
3196 that are not enabled.
3198 Where the breakpoint is in your program, as a memory address. For a
3199 pending breakpoint whose address is not yet known, this field will
3200 contain @samp{<PENDING>}. Such breakpoint won't fire until a shared
3201 library that has the symbol or line referred by breakpoint is loaded.
3202 See below for details. A breakpoint with several locations will
3203 have @samp{<MULTIPLE>} in this field---see below for details.
3205 Where the breakpoint is in the source for your program, as a file and
3206 line number. For a pending breakpoint, the original string passed to
3207 the breakpoint command will be listed as it cannot be resolved until
3208 the appropriate shared library is loaded in the future.
3212 If a breakpoint is conditional, @code{info break} shows the condition on
3213 the line following the affected breakpoint; breakpoint commands, if any,
3214 are listed after that. A pending breakpoint is allowed to have a condition
3215 specified for it. The condition is not parsed for validity until a shared
3216 library is loaded that allows the pending breakpoint to resolve to a
3220 @code{info break} with a breakpoint
3221 number @var{n} as argument lists only that breakpoint. The
3222 convenience variable @code{$_} and the default examining-address for
3223 the @code{x} command are set to the address of the last breakpoint
3224 listed (@pxref{Memory, ,Examining Memory}).
3227 @code{info break} displays a count of the number of times the breakpoint
3228 has been hit. This is especially useful in conjunction with the
3229 @code{ignore} command. You can ignore a large number of breakpoint
3230 hits, look at the breakpoint info to see how many times the breakpoint
3231 was hit, and then run again, ignoring one less than that number. This
3232 will get you quickly to the last hit of that breakpoint.
3235 @value{GDBN} allows you to set any number of breakpoints at the same place in
3236 your program. There is nothing silly or meaningless about this. When
3237 the breakpoints are conditional, this is even useful
3238 (@pxref{Conditions, ,Break Conditions}).
3240 @cindex multiple locations, breakpoints
3241 @cindex breakpoints, multiple locations
3242 It is possible that a breakpoint corresponds to several locations
3243 in your program. Examples of this situation are:
3247 For a C@t{++} constructor, the @value{NGCC} compiler generates several
3248 instances of the function body, used in different cases.
3251 For a C@t{++} template function, a given line in the function can
3252 correspond to any number of instantiations.
3255 For an inlined function, a given source line can correspond to
3256 several places where that function is inlined.
3259 In all those cases, @value{GDBN} will insert a breakpoint at all
3260 the relevant locations@footnote{
3261 As of this writing, multiple-location breakpoints work only if there's
3262 line number information for all the locations. This means that they
3263 will generally not work in system libraries, unless you have debug
3264 info with line numbers for them.}.
3266 A breakpoint with multiple locations is displayed in the breakpoint
3267 table using several rows---one header row, followed by one row for
3268 each breakpoint location. The header row has @samp{<MULTIPLE>} in the
3269 address column. The rows for individual locations contain the actual
3270 addresses for locations, and show the functions to which those
3271 locations belong. The number column for a location is of the form
3272 @var{breakpoint-number}.@var{location-number}.
3277 Num Type Disp Enb Address What
3278 1 breakpoint keep y <MULTIPLE>
3280 breakpoint already hit 1 time
3281 1.1 y 0x080486a2 in void foo<int>() at t.cc:8
3282 1.2 y 0x080486ca in void foo<double>() at t.cc:8
3285 Each location can be individually enabled or disabled by passing
3286 @var{breakpoint-number}.@var{location-number} as argument to the
3287 @code{enable} and @code{disable} commands. Note that you cannot
3288 delete the individual locations from the list, you can only delete the
3289 entire list of locations that belong to their parent breakpoint (with
3290 the @kbd{delete @var{num}} command, where @var{num} is the number of
3291 the parent breakpoint, 1 in the above example). Disabling or enabling
3292 the parent breakpoint (@pxref{Disabling}) affects all of the locations
3293 that belong to that breakpoint.
3295 @cindex pending breakpoints
3296 It's quite common to have a breakpoint inside a shared library.
3297 Shared libraries can be loaded and unloaded explicitly,
3298 and possibly repeatedly, as the program is executed. To support
3299 this use case, @value{GDBN} updates breakpoint locations whenever
3300 any shared library is loaded or unloaded. Typically, you would
3301 set a breakpoint in a shared library at the beginning of your
3302 debugging session, when the library is not loaded, and when the
3303 symbols from the library are not available. When you try to set
3304 breakpoint, @value{GDBN} will ask you if you want to set
3305 a so called @dfn{pending breakpoint}---breakpoint whose address
3306 is not yet resolved.
3308 After the program is run, whenever a new shared library is loaded,
3309 @value{GDBN} reevaluates all the breakpoints. When a newly loaded
3310 shared library contains the symbol or line referred to by some
3311 pending breakpoint, that breakpoint is resolved and becomes an
3312 ordinary breakpoint. When a library is unloaded, all breakpoints
3313 that refer to its symbols or source lines become pending again.
3315 This logic works for breakpoints with multiple locations, too. For
3316 example, if you have a breakpoint in a C@t{++} template function, and
3317 a newly loaded shared library has an instantiation of that template,
3318 a new location is added to the list of locations for the breakpoint.
3320 Except for having unresolved address, pending breakpoints do not
3321 differ from regular breakpoints. You can set conditions or commands,
3322 enable and disable them and perform other breakpoint operations.
3324 @value{GDBN} provides some additional commands for controlling what
3325 happens when the @samp{break} command cannot resolve breakpoint
3326 address specification to an address:
3328 @kindex set breakpoint pending
3329 @kindex show breakpoint pending
3331 @item set breakpoint pending auto
3332 This is the default behavior. When @value{GDBN} cannot find the breakpoint
3333 location, it queries you whether a pending breakpoint should be created.
3335 @item set breakpoint pending on
3336 This indicates that an unrecognized breakpoint location should automatically
3337 result in a pending breakpoint being created.
3339 @item set breakpoint pending off
3340 This indicates that pending breakpoints are not to be created. Any
3341 unrecognized breakpoint location results in an error. This setting does
3342 not affect any pending breakpoints previously created.
3344 @item show breakpoint pending
3345 Show the current behavior setting for creating pending breakpoints.
3348 The settings above only affect the @code{break} command and its
3349 variants. Once breakpoint is set, it will be automatically updated
3350 as shared libraries are loaded and unloaded.
3352 @cindex automatic hardware breakpoints
3353 For some targets, @value{GDBN} can automatically decide if hardware or
3354 software breakpoints should be used, depending on whether the
3355 breakpoint address is read-only or read-write. This applies to
3356 breakpoints set with the @code{break} command as well as to internal
3357 breakpoints set by commands like @code{next} and @code{finish}. For
3358 breakpoints set with @code{hbreak}, @value{GDBN} will always use hardware
3361 You can control this automatic behaviour with the following commands::
3363 @kindex set breakpoint auto-hw
3364 @kindex show breakpoint auto-hw
3366 @item set breakpoint auto-hw on
3367 This is the default behavior. When @value{GDBN} sets a breakpoint, it
3368 will try to use the target memory map to decide if software or hardware
3369 breakpoint must be used.
3371 @item set breakpoint auto-hw off
3372 This indicates @value{GDBN} should not automatically select breakpoint
3373 type. If the target provides a memory map, @value{GDBN} will warn when
3374 trying to set software breakpoint at a read-only address.
3377 @value{GDBN} normally implements breakpoints by replacing the program code
3378 at the breakpoint address with a special instruction, which, when
3379 executed, given control to the debugger. By default, the program
3380 code is so modified only when the program is resumed. As soon as
3381 the program stops, @value{GDBN} restores the original instructions. This
3382 behaviour guards against leaving breakpoints inserted in the
3383 target should gdb abrubptly disconnect. However, with slow remote
3384 targets, inserting and removing breakpoint can reduce the performance.
3385 This behavior can be controlled with the following commands::
3387 @kindex set breakpoint always-inserted
3388 @kindex show breakpoint always-inserted
3390 @item set breakpoint always-inserted off
3391 All breakpoints, including newly added by the user, are inserted in
3392 the target only when the target is resumed. All breakpoints are
3393 removed from the target when it stops.
3395 @item set breakpoint always-inserted on
3396 Causes all breakpoints to be inserted in the target at all times. If
3397 the user adds a new breakpoint, or changes an existing breakpoint, the
3398 breakpoints in the target are updated immediately. A breakpoint is
3399 removed from the target only when breakpoint itself is removed.
3401 @cindex non-stop mode, and @code{breakpoint always-inserted}
3402 @item set breakpoint always-inserted auto
3403 This is the default mode. If @value{GDBN} is controlling the inferior
3404 in non-stop mode (@pxref{Non-Stop Mode}), gdb behaves as if
3405 @code{breakpoint always-inserted} mode is on. If @value{GDBN} is
3406 controlling the inferior in all-stop mode, @value{GDBN} behaves as if
3407 @code{breakpoint always-inserted} mode is off.
3410 @cindex negative breakpoint numbers
3411 @cindex internal @value{GDBN} breakpoints
3412 @value{GDBN} itself sometimes sets breakpoints in your program for
3413 special purposes, such as proper handling of @code{longjmp} (in C
3414 programs). These internal breakpoints are assigned negative numbers,
3415 starting with @code{-1}; @samp{info breakpoints} does not display them.
3416 You can see these breakpoints with the @value{GDBN} maintenance command
3417 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
3420 @node Set Watchpoints
3421 @subsection Setting Watchpoints
3423 @cindex setting watchpoints
3424 You can use a watchpoint to stop execution whenever the value of an
3425 expression changes, without having to predict a particular place where
3426 this may happen. (This is sometimes called a @dfn{data breakpoint}.)
3427 The expression may be as simple as the value of a single variable, or
3428 as complex as many variables combined by operators. Examples include:
3432 A reference to the value of a single variable.
3435 An address cast to an appropriate data type. For example,
3436 @samp{*(int *)0x12345678} will watch a 4-byte region at the specified
3437 address (assuming an @code{int} occupies 4 bytes).
3440 An arbitrarily complex expression, such as @samp{a*b + c/d}. The
3441 expression can use any operators valid in the program's native
3442 language (@pxref{Languages}).
3445 You can set a watchpoint on an expression even if the expression can
3446 not be evaluated yet. For instance, you can set a watchpoint on
3447 @samp{*global_ptr} before @samp{global_ptr} is initialized.
3448 @value{GDBN} will stop when your program sets @samp{global_ptr} and
3449 the expression produces a valid value. If the expression becomes
3450 valid in some other way than changing a variable (e.g.@: if the memory
3451 pointed to by @samp{*global_ptr} becomes readable as the result of a
3452 @code{malloc} call), @value{GDBN} may not stop until the next time
3453 the expression changes.
3455 @cindex software watchpoints
3456 @cindex hardware watchpoints
3457 Depending on your system, watchpoints may be implemented in software or
3458 hardware. @value{GDBN} does software watchpointing by single-stepping your
3459 program and testing the variable's value each time, which is hundreds of
3460 times slower than normal execution. (But this may still be worth it, to
3461 catch errors where you have no clue what part of your program is the
3464 On some systems, such as HP-UX, PowerPC, @sc{gnu}/Linux and most other
3465 x86-based targets, @value{GDBN} includes support for hardware
3466 watchpoints, which do not slow down the running of your program.
3470 @item watch @var{expr} @r{[}thread @var{threadnum}@r{]}
3471 Set a watchpoint for an expression. @value{GDBN} will break when the
3472 expression @var{expr} is written into by the program and its value
3473 changes. The simplest (and the most popular) use of this command is
3474 to watch the value of a single variable:
3477 (@value{GDBP}) watch foo
3480 If the command includes a @code{@r{[}thread @var{threadnum}@r{]}}
3481 clause, @value{GDBN} breaks only when the thread identified by
3482 @var{threadnum} changes the value of @var{expr}. If any other threads
3483 change the value of @var{expr}, @value{GDBN} will not break. Note
3484 that watchpoints restricted to a single thread in this way only work
3485 with Hardware Watchpoints.
3488 @item rwatch @var{expr} @r{[}thread @var{threadnum}@r{]}
3489 Set a watchpoint that will break when the value of @var{expr} is read
3493 @item awatch @var{expr} @r{[}thread @var{threadnum}@r{]}
3494 Set a watchpoint that will break when @var{expr} is either read from
3495 or written into by the program.
3497 @kindex info watchpoints @r{[}@var{n}@r{]}
3498 @item info watchpoints
3499 This command prints a list of watchpoints, breakpoints, and catchpoints;
3500 it is the same as @code{info break} (@pxref{Set Breaks}).
3503 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
3504 watchpoints execute very quickly, and the debugger reports a change in
3505 value at the exact instruction where the change occurs. If @value{GDBN}
3506 cannot set a hardware watchpoint, it sets a software watchpoint, which
3507 executes more slowly and reports the change in value at the next
3508 @emph{statement}, not the instruction, after the change occurs.
3510 @cindex use only software watchpoints
3511 You can force @value{GDBN} to use only software watchpoints with the
3512 @kbd{set can-use-hw-watchpoints 0} command. With this variable set to
3513 zero, @value{GDBN} will never try to use hardware watchpoints, even if
3514 the underlying system supports them. (Note that hardware-assisted
3515 watchpoints that were set @emph{before} setting
3516 @code{can-use-hw-watchpoints} to zero will still use the hardware
3517 mechanism of watching expression values.)
3520 @item set can-use-hw-watchpoints
3521 @kindex set can-use-hw-watchpoints
3522 Set whether or not to use hardware watchpoints.
3524 @item show can-use-hw-watchpoints
3525 @kindex show can-use-hw-watchpoints
3526 Show the current mode of using hardware watchpoints.
3529 For remote targets, you can restrict the number of hardware
3530 watchpoints @value{GDBN} will use, see @ref{set remote
3531 hardware-breakpoint-limit}.
3533 When you issue the @code{watch} command, @value{GDBN} reports
3536 Hardware watchpoint @var{num}: @var{expr}
3540 if it was able to set a hardware watchpoint.
3542 Currently, the @code{awatch} and @code{rwatch} commands can only set
3543 hardware watchpoints, because accesses to data that don't change the
3544 value of the watched expression cannot be detected without examining
3545 every instruction as it is being executed, and @value{GDBN} does not do
3546 that currently. If @value{GDBN} finds that it is unable to set a
3547 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
3548 will print a message like this:
3551 Expression cannot be implemented with read/access watchpoint.
3554 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
3555 data type of the watched expression is wider than what a hardware
3556 watchpoint on the target machine can handle. For example, some systems
3557 can only watch regions that are up to 4 bytes wide; on such systems you
3558 cannot set hardware watchpoints for an expression that yields a
3559 double-precision floating-point number (which is typically 8 bytes
3560 wide). As a work-around, it might be possible to break the large region
3561 into a series of smaller ones and watch them with separate watchpoints.
3563 If you set too many hardware watchpoints, @value{GDBN} might be unable
3564 to insert all of them when you resume the execution of your program.
3565 Since the precise number of active watchpoints is unknown until such
3566 time as the program is about to be resumed, @value{GDBN} might not be
3567 able to warn you about this when you set the watchpoints, and the
3568 warning will be printed only when the program is resumed:
3571 Hardware watchpoint @var{num}: Could not insert watchpoint
3575 If this happens, delete or disable some of the watchpoints.
3577 Watching complex expressions that reference many variables can also
3578 exhaust the resources available for hardware-assisted watchpoints.
3579 That's because @value{GDBN} needs to watch every variable in the
3580 expression with separately allocated resources.
3582 If you call a function interactively using @code{print} or @code{call},
3583 any watchpoints you have set will be inactive until @value{GDBN} reaches another
3584 kind of breakpoint or the call completes.
3586 @value{GDBN} automatically deletes watchpoints that watch local
3587 (automatic) variables, or expressions that involve such variables, when
3588 they go out of scope, that is, when the execution leaves the block in
3589 which these variables were defined. In particular, when the program
3590 being debugged terminates, @emph{all} local variables go out of scope,
3591 and so only watchpoints that watch global variables remain set. If you
3592 rerun the program, you will need to set all such watchpoints again. One
3593 way of doing that would be to set a code breakpoint at the entry to the
3594 @code{main} function and when it breaks, set all the watchpoints.
3596 @cindex watchpoints and threads
3597 @cindex threads and watchpoints
3598 In multi-threaded programs, watchpoints will detect changes to the
3599 watched expression from every thread.
3602 @emph{Warning:} In multi-threaded programs, software watchpoints
3603 have only limited usefulness. If @value{GDBN} creates a software
3604 watchpoint, it can only watch the value of an expression @emph{in a
3605 single thread}. If you are confident that the expression can only
3606 change due to the current thread's activity (and if you are also
3607 confident that no other thread can become current), then you can use
3608 software watchpoints as usual. However, @value{GDBN} may not notice
3609 when a non-current thread's activity changes the expression. (Hardware
3610 watchpoints, in contrast, watch an expression in all threads.)
3613 @xref{set remote hardware-watchpoint-limit}.
3615 @node Set Catchpoints
3616 @subsection Setting Catchpoints
3617 @cindex catchpoints, setting
3618 @cindex exception handlers
3619 @cindex event handling
3621 You can use @dfn{catchpoints} to cause the debugger to stop for certain
3622 kinds of program events, such as C@t{++} exceptions or the loading of a
3623 shared library. Use the @code{catch} command to set a catchpoint.
3627 @item catch @var{event}
3628 Stop when @var{event} occurs. @var{event} can be any of the following:
3631 @cindex stop on C@t{++} exceptions
3632 The throwing of a C@t{++} exception.
3635 The catching of a C@t{++} exception.
3638 @cindex Ada exception catching
3639 @cindex catch Ada exceptions
3640 An Ada exception being raised. If an exception name is specified
3641 at the end of the command (eg @code{catch exception Program_Error}),
3642 the debugger will stop only when this specific exception is raised.
3643 Otherwise, the debugger stops execution when any Ada exception is raised.
3645 When inserting an exception catchpoint on a user-defined exception whose
3646 name is identical to one of the exceptions defined by the language, the
3647 fully qualified name must be used as the exception name. Otherwise,
3648 @value{GDBN} will assume that it should stop on the pre-defined exception
3649 rather than the user-defined one. For instance, assuming an exception
3650 called @code{Constraint_Error} is defined in package @code{Pck}, then
3651 the command to use to catch such exceptions is @kbd{catch exception
3652 Pck.Constraint_Error}.
3654 @item exception unhandled
3655 An exception that was raised but is not handled by the program.
3658 A failed Ada assertion.
3661 @cindex break on fork/exec
3662 A call to @code{exec}. This is currently only available for HP-UX
3666 A call to @code{fork}. This is currently only available for HP-UX
3670 A call to @code{vfork}. This is currently only available for HP-UX
3675 @item tcatch @var{event}
3676 Set a catchpoint that is enabled only for one stop. The catchpoint is
3677 automatically deleted after the first time the event is caught.
3681 Use the @code{info break} command to list the current catchpoints.
3683 There are currently some limitations to C@t{++} exception handling
3684 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
3688 If you call a function interactively, @value{GDBN} normally returns
3689 control to you when the function has finished executing. If the call
3690 raises an exception, however, the call may bypass the mechanism that
3691 returns control to you and cause your program either to abort or to
3692 simply continue running until it hits a breakpoint, catches a signal
3693 that @value{GDBN} is listening for, or exits. This is the case even if
3694 you set a catchpoint for the exception; catchpoints on exceptions are
3695 disabled within interactive calls.
3698 You cannot raise an exception interactively.
3701 You cannot install an exception handler interactively.
3704 @cindex raise exceptions
3705 Sometimes @code{catch} is not the best way to debug exception handling:
3706 if you need to know exactly where an exception is raised, it is better to
3707 stop @emph{before} the exception handler is called, since that way you
3708 can see the stack before any unwinding takes place. If you set a
3709 breakpoint in an exception handler instead, it may not be easy to find
3710 out where the exception was raised.
3712 To stop just before an exception handler is called, you need some
3713 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
3714 raised by calling a library function named @code{__raise_exception}
3715 which has the following ANSI C interface:
3718 /* @var{addr} is where the exception identifier is stored.
3719 @var{id} is the exception identifier. */
3720 void __raise_exception (void **addr, void *id);
3724 To make the debugger catch all exceptions before any stack
3725 unwinding takes place, set a breakpoint on @code{__raise_exception}
3726 (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Exceptions}).
3728 With a conditional breakpoint (@pxref{Conditions, ,Break Conditions})
3729 that depends on the value of @var{id}, you can stop your program when
3730 a specific exception is raised. You can use multiple conditional
3731 breakpoints to stop your program when any of a number of exceptions are
3736 @subsection Deleting Breakpoints
3738 @cindex clearing breakpoints, watchpoints, catchpoints
3739 @cindex deleting breakpoints, watchpoints, catchpoints
3740 It is often necessary to eliminate a breakpoint, watchpoint, or
3741 catchpoint once it has done its job and you no longer want your program
3742 to stop there. This is called @dfn{deleting} the breakpoint. A
3743 breakpoint that has been deleted no longer exists; it is forgotten.
3745 With the @code{clear} command you can delete breakpoints according to
3746 where they are in your program. With the @code{delete} command you can
3747 delete individual breakpoints, watchpoints, or catchpoints by specifying
3748 their breakpoint numbers.
3750 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
3751 automatically ignores breakpoints on the first instruction to be executed
3752 when you continue execution without changing the execution address.
3757 Delete any breakpoints at the next instruction to be executed in the
3758 selected stack frame (@pxref{Selection, ,Selecting a Frame}). When
3759 the innermost frame is selected, this is a good way to delete a
3760 breakpoint where your program just stopped.
3762 @item clear @var{location}
3763 Delete any breakpoints set at the specified @var{location}.
3764 @xref{Specify Location}, for the various forms of @var{location}; the
3765 most useful ones are listed below:
3768 @item clear @var{function}
3769 @itemx clear @var{filename}:@var{function}
3770 Delete any breakpoints set at entry to the named @var{function}.
3772 @item clear @var{linenum}
3773 @itemx clear @var{filename}:@var{linenum}
3774 Delete any breakpoints set at or within the code of the specified
3775 @var{linenum} of the specified @var{filename}.
3778 @cindex delete breakpoints
3780 @kindex d @r{(@code{delete})}
3781 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
3782 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
3783 ranges specified as arguments. If no argument is specified, delete all
3784 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
3785 confirm off}). You can abbreviate this command as @code{d}.
3789 @subsection Disabling Breakpoints
3791 @cindex enable/disable a breakpoint
3792 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
3793 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
3794 it had been deleted, but remembers the information on the breakpoint so
3795 that you can @dfn{enable} it again later.
3797 You disable and enable breakpoints, watchpoints, and catchpoints with
3798 the @code{enable} and @code{disable} commands, optionally specifying one
3799 or more breakpoint numbers as arguments. Use @code{info break} or
3800 @code{info watch} to print a list of breakpoints, watchpoints, and
3801 catchpoints if you do not know which numbers to use.
3803 Disabling and enabling a breakpoint that has multiple locations
3804 affects all of its locations.
3806 A breakpoint, watchpoint, or catchpoint can have any of four different
3807 states of enablement:
3811 Enabled. The breakpoint stops your program. A breakpoint set
3812 with the @code{break} command starts out in this state.
3814 Disabled. The breakpoint has no effect on your program.
3816 Enabled once. The breakpoint stops your program, but then becomes
3819 Enabled for deletion. The breakpoint stops your program, but
3820 immediately after it does so it is deleted permanently. A breakpoint
3821 set with the @code{tbreak} command starts out in this state.
3824 You can use the following commands to enable or disable breakpoints,
3825 watchpoints, and catchpoints:
3829 @kindex dis @r{(@code{disable})}
3830 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
3831 Disable the specified breakpoints---or all breakpoints, if none are
3832 listed. A disabled breakpoint has no effect but is not forgotten. All
3833 options such as ignore-counts, conditions and commands are remembered in
3834 case the breakpoint is enabled again later. You may abbreviate
3835 @code{disable} as @code{dis}.
3838 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
3839 Enable the specified breakpoints (or all defined breakpoints). They
3840 become effective once again in stopping your program.
3842 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
3843 Enable the specified breakpoints temporarily. @value{GDBN} disables any
3844 of these breakpoints immediately after stopping your program.
3846 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
3847 Enable the specified breakpoints to work once, then die. @value{GDBN}
3848 deletes any of these breakpoints as soon as your program stops there.
3849 Breakpoints set by the @code{tbreak} command start out in this state.
3852 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
3853 @c confusing: tbreak is also initially enabled.
3854 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
3855 ,Setting Breakpoints}), breakpoints that you set are initially enabled;
3856 subsequently, they become disabled or enabled only when you use one of
3857 the commands above. (The command @code{until} can set and delete a
3858 breakpoint of its own, but it does not change the state of your other
3859 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
3863 @subsection Break Conditions
3864 @cindex conditional breakpoints
3865 @cindex breakpoint conditions
3867 @c FIXME what is scope of break condition expr? Context where wanted?
3868 @c in particular for a watchpoint?
3869 The simplest sort of breakpoint breaks every time your program reaches a
3870 specified place. You can also specify a @dfn{condition} for a
3871 breakpoint. A condition is just a Boolean expression in your
3872 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
3873 a condition evaluates the expression each time your program reaches it,
3874 and your program stops only if the condition is @emph{true}.
3876 This is the converse of using assertions for program validation; in that
3877 situation, you want to stop when the assertion is violated---that is,
3878 when the condition is false. In C, if you want to test an assertion expressed
3879 by the condition @var{assert}, you should set the condition
3880 @samp{! @var{assert}} on the appropriate breakpoint.
3882 Conditions are also accepted for watchpoints; you may not need them,
3883 since a watchpoint is inspecting the value of an expression anyhow---but
3884 it might be simpler, say, to just set a watchpoint on a variable name,
3885 and specify a condition that tests whether the new value is an interesting
3888 Break conditions can have side effects, and may even call functions in
3889 your program. This can be useful, for example, to activate functions
3890 that log program progress, or to use your own print functions to
3891 format special data structures. The effects are completely predictable
3892 unless there is another enabled breakpoint at the same address. (In
3893 that case, @value{GDBN} might see the other breakpoint first and stop your
3894 program without checking the condition of this one.) Note that
3895 breakpoint commands are usually more convenient and flexible than break
3897 purpose of performing side effects when a breakpoint is reached
3898 (@pxref{Break Commands, ,Breakpoint Command Lists}).
3900 Break conditions can be specified when a breakpoint is set, by using
3901 @samp{if} in the arguments to the @code{break} command. @xref{Set
3902 Breaks, ,Setting Breakpoints}. They can also be changed at any time
3903 with the @code{condition} command.
3905 You can also use the @code{if} keyword with the @code{watch} command.
3906 The @code{catch} command does not recognize the @code{if} keyword;
3907 @code{condition} is the only way to impose a further condition on a
3912 @item condition @var{bnum} @var{expression}
3913 Specify @var{expression} as the break condition for breakpoint,
3914 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3915 breakpoint @var{bnum} stops your program only if the value of
3916 @var{expression} is true (nonzero, in C). When you use
3917 @code{condition}, @value{GDBN} checks @var{expression} immediately for
3918 syntactic correctness, and to determine whether symbols in it have
3919 referents in the context of your breakpoint. If @var{expression} uses
3920 symbols not referenced in the context of the breakpoint, @value{GDBN}
3921 prints an error message:
3924 No symbol "foo" in current context.
3929 not actually evaluate @var{expression} at the time the @code{condition}
3930 command (or a command that sets a breakpoint with a condition, like
3931 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
3933 @item condition @var{bnum}
3934 Remove the condition from breakpoint number @var{bnum}. It becomes
3935 an ordinary unconditional breakpoint.
3938 @cindex ignore count (of breakpoint)
3939 A special case of a breakpoint condition is to stop only when the
3940 breakpoint has been reached a certain number of times. This is so
3941 useful that there is a special way to do it, using the @dfn{ignore
3942 count} of the breakpoint. Every breakpoint has an ignore count, which
3943 is an integer. Most of the time, the ignore count is zero, and
3944 therefore has no effect. But if your program reaches a breakpoint whose
3945 ignore count is positive, then instead of stopping, it just decrements
3946 the ignore count by one and continues. As a result, if the ignore count
3947 value is @var{n}, the breakpoint does not stop the next @var{n} times
3948 your program reaches it.
3952 @item ignore @var{bnum} @var{count}
3953 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3954 The next @var{count} times the breakpoint is reached, your program's
3955 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3958 To make the breakpoint stop the next time it is reached, specify
3961 When you use @code{continue} to resume execution of your program from a
3962 breakpoint, you can specify an ignore count directly as an argument to
3963 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3964 Stepping,,Continuing and Stepping}.
3966 If a breakpoint has a positive ignore count and a condition, the
3967 condition is not checked. Once the ignore count reaches zero,
3968 @value{GDBN} resumes checking the condition.
3970 You could achieve the effect of the ignore count with a condition such
3971 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3972 is decremented each time. @xref{Convenience Vars, ,Convenience
3976 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3979 @node Break Commands
3980 @subsection Breakpoint Command Lists
3982 @cindex breakpoint commands
3983 You can give any breakpoint (or watchpoint or catchpoint) a series of
3984 commands to execute when your program stops due to that breakpoint. For
3985 example, you might want to print the values of certain expressions, or
3986 enable other breakpoints.
3990 @kindex end@r{ (breakpoint commands)}
3991 @item commands @r{[}@var{bnum}@r{]}
3992 @itemx @dots{} @var{command-list} @dots{}
3994 Specify a list of commands for breakpoint number @var{bnum}. The commands
3995 themselves appear on the following lines. Type a line containing just
3996 @code{end} to terminate the commands.
3998 To remove all commands from a breakpoint, type @code{commands} and
3999 follow it immediately with @code{end}; that is, give no commands.
4001 With no @var{bnum} argument, @code{commands} refers to the last
4002 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
4003 recently encountered).
4006 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
4007 disabled within a @var{command-list}.
4009 You can use breakpoint commands to start your program up again. Simply
4010 use the @code{continue} command, or @code{step}, or any other command
4011 that resumes execution.
4013 Any other commands in the command list, after a command that resumes
4014 execution, are ignored. This is because any time you resume execution
4015 (even with a simple @code{next} or @code{step}), you may encounter
4016 another breakpoint---which could have its own command list, leading to
4017 ambiguities about which list to execute.
4020 If the first command you specify in a command list is @code{silent}, the
4021 usual message about stopping at a breakpoint is not printed. This may
4022 be desirable for breakpoints that are to print a specific message and
4023 then continue. If none of the remaining commands print anything, you
4024 see no sign that the breakpoint was reached. @code{silent} is
4025 meaningful only at the beginning of a breakpoint command list.
4027 The commands @code{echo}, @code{output}, and @code{printf} allow you to
4028 print precisely controlled output, and are often useful in silent
4029 breakpoints. @xref{Output, ,Commands for Controlled Output}.
4031 For example, here is how you could use breakpoint commands to print the
4032 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
4038 printf "x is %d\n",x
4043 One application for breakpoint commands is to compensate for one bug so
4044 you can test for another. Put a breakpoint just after the erroneous line
4045 of code, give it a condition to detect the case in which something
4046 erroneous has been done, and give it commands to assign correct values
4047 to any variables that need them. End with the @code{continue} command
4048 so that your program does not stop, and start with the @code{silent}
4049 command so that no output is produced. Here is an example:
4060 @c @ifclear BARETARGET
4061 @node Error in Breakpoints
4062 @subsection ``Cannot insert breakpoints''
4064 If you request too many active hardware-assisted breakpoints and
4065 watchpoints, you will see this error message:
4067 @c FIXME: the precise wording of this message may change; the relevant
4068 @c source change is not committed yet (Sep 3, 1999).
4070 Stopped; cannot insert breakpoints.
4071 You may have requested too many hardware breakpoints and watchpoints.
4075 This message is printed when you attempt to resume the program, since
4076 only then @value{GDBN} knows exactly how many hardware breakpoints and
4077 watchpoints it needs to insert.
4079 When this message is printed, you need to disable or remove some of the
4080 hardware-assisted breakpoints and watchpoints, and then continue.
4082 @node Breakpoint-related Warnings
4083 @subsection ``Breakpoint address adjusted...''
4084 @cindex breakpoint address adjusted
4086 Some processor architectures place constraints on the addresses at
4087 which breakpoints may be placed. For architectures thus constrained,
4088 @value{GDBN} will attempt to adjust the breakpoint's address to comply
4089 with the constraints dictated by the architecture.
4091 One example of such an architecture is the Fujitsu FR-V. The FR-V is
4092 a VLIW architecture in which a number of RISC-like instructions may be
4093 bundled together for parallel execution. The FR-V architecture
4094 constrains the location of a breakpoint instruction within such a
4095 bundle to the instruction with the lowest address. @value{GDBN}
4096 honors this constraint by adjusting a breakpoint's address to the
4097 first in the bundle.
4099 It is not uncommon for optimized code to have bundles which contain
4100 instructions from different source statements, thus it may happen that
4101 a breakpoint's address will be adjusted from one source statement to
4102 another. Since this adjustment may significantly alter @value{GDBN}'s
4103 breakpoint related behavior from what the user expects, a warning is
4104 printed when the breakpoint is first set and also when the breakpoint
4107 A warning like the one below is printed when setting a breakpoint
4108 that's been subject to address adjustment:
4111 warning: Breakpoint address adjusted from 0x00010414 to 0x00010410.
4114 Such warnings are printed both for user settable and @value{GDBN}'s
4115 internal breakpoints. If you see one of these warnings, you should
4116 verify that a breakpoint set at the adjusted address will have the
4117 desired affect. If not, the breakpoint in question may be removed and
4118 other breakpoints may be set which will have the desired behavior.
4119 E.g., it may be sufficient to place the breakpoint at a later
4120 instruction. A conditional breakpoint may also be useful in some
4121 cases to prevent the breakpoint from triggering too often.
4123 @value{GDBN} will also issue a warning when stopping at one of these
4124 adjusted breakpoints:
4127 warning: Breakpoint 1 address previously adjusted from 0x00010414
4131 When this warning is encountered, it may be too late to take remedial
4132 action except in cases where the breakpoint is hit earlier or more
4133 frequently than expected.
4135 @node Continuing and Stepping
4136 @section Continuing and Stepping
4140 @cindex resuming execution
4141 @dfn{Continuing} means resuming program execution until your program
4142 completes normally. In contrast, @dfn{stepping} means executing just
4143 one more ``step'' of your program, where ``step'' may mean either one
4144 line of source code, or one machine instruction (depending on what
4145 particular command you use). Either when continuing or when stepping,
4146 your program may stop even sooner, due to a breakpoint or a signal. (If
4147 it stops due to a signal, you may want to use @code{handle}, or use
4148 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
4152 @kindex c @r{(@code{continue})}
4153 @kindex fg @r{(resume foreground execution)}
4154 @item continue @r{[}@var{ignore-count}@r{]}
4155 @itemx c @r{[}@var{ignore-count}@r{]}
4156 @itemx fg @r{[}@var{ignore-count}@r{]}
4157 Resume program execution, at the address where your program last stopped;
4158 any breakpoints set at that address are bypassed. The optional argument
4159 @var{ignore-count} allows you to specify a further number of times to
4160 ignore a breakpoint at this location; its effect is like that of
4161 @code{ignore} (@pxref{Conditions, ,Break Conditions}).
4163 The argument @var{ignore-count} is meaningful only when your program
4164 stopped due to a breakpoint. At other times, the argument to
4165 @code{continue} is ignored.
4167 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
4168 debugged program is deemed to be the foreground program) are provided
4169 purely for convenience, and have exactly the same behavior as
4173 To resume execution at a different place, you can use @code{return}
4174 (@pxref{Returning, ,Returning from a Function}) to go back to the
4175 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
4176 Different Address}) to go to an arbitrary location in your program.
4178 A typical technique for using stepping is to set a breakpoint
4179 (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Catchpoints}) at the
4180 beginning of the function or the section of your program where a problem
4181 is believed to lie, run your program until it stops at that breakpoint,
4182 and then step through the suspect area, examining the variables that are
4183 interesting, until you see the problem happen.
4187 @kindex s @r{(@code{step})}
4189 Continue running your program until control reaches a different source
4190 line, then stop it and return control to @value{GDBN}. This command is
4191 abbreviated @code{s}.
4194 @c "without debugging information" is imprecise; actually "without line
4195 @c numbers in the debugging information". (gcc -g1 has debugging info but
4196 @c not line numbers). But it seems complex to try to make that
4197 @c distinction here.
4198 @emph{Warning:} If you use the @code{step} command while control is
4199 within a function that was compiled without debugging information,
4200 execution proceeds until control reaches a function that does have
4201 debugging information. Likewise, it will not step into a function which
4202 is compiled without debugging information. To step through functions
4203 without debugging information, use the @code{stepi} command, described
4207 The @code{step} command only stops at the first instruction of a source
4208 line. This prevents the multiple stops that could otherwise occur in
4209 @code{switch} statements, @code{for} loops, etc. @code{step} continues
4210 to stop if a function that has debugging information is called within
4211 the line. In other words, @code{step} @emph{steps inside} any functions
4212 called within the line.
4214 Also, the @code{step} command only enters a function if there is line
4215 number information for the function. Otherwise it acts like the
4216 @code{next} command. This avoids problems when using @code{cc -gl}
4217 on MIPS machines. Previously, @code{step} entered subroutines if there
4218 was any debugging information about the routine.
4220 @item step @var{count}
4221 Continue running as in @code{step}, but do so @var{count} times. If a
4222 breakpoint is reached, or a signal not related to stepping occurs before
4223 @var{count} steps, stepping stops right away.
4226 @kindex n @r{(@code{next})}
4227 @item next @r{[}@var{count}@r{]}
4228 Continue to the next source line in the current (innermost) stack frame.
4229 This is similar to @code{step}, but function calls that appear within
4230 the line of code are executed without stopping. Execution stops when
4231 control reaches a different line of code at the original stack level
4232 that was executing when you gave the @code{next} command. This command
4233 is abbreviated @code{n}.
4235 An argument @var{count} is a repeat count, as for @code{step}.
4238 @c FIX ME!! Do we delete this, or is there a way it fits in with
4239 @c the following paragraph? --- Vctoria
4241 @c @code{next} within a function that lacks debugging information acts like
4242 @c @code{step}, but any function calls appearing within the code of the
4243 @c function are executed without stopping.
4245 The @code{next} command only stops at the first instruction of a
4246 source line. This prevents multiple stops that could otherwise occur in
4247 @code{switch} statements, @code{for} loops, etc.
4249 @kindex set step-mode
4251 @cindex functions without line info, and stepping
4252 @cindex stepping into functions with no line info
4253 @itemx set step-mode on
4254 The @code{set step-mode on} command causes the @code{step} command to
4255 stop at the first instruction of a function which contains no debug line
4256 information rather than stepping over it.
4258 This is useful in cases where you may be interested in inspecting the
4259 machine instructions of a function which has no symbolic info and do not
4260 want @value{GDBN} to automatically skip over this function.
4262 @item set step-mode off
4263 Causes the @code{step} command to step over any functions which contains no
4264 debug information. This is the default.
4266 @item show step-mode
4267 Show whether @value{GDBN} will stop in or step over functions without
4268 source line debug information.
4271 @kindex fin @r{(@code{finish})}
4273 Continue running until just after function in the selected stack frame
4274 returns. Print the returned value (if any). This command can be
4275 abbreviated as @code{fin}.
4277 Contrast this with the @code{return} command (@pxref{Returning,
4278 ,Returning from a Function}).
4281 @kindex u @r{(@code{until})}
4282 @cindex run until specified location
4285 Continue running until a source line past the current line, in the
4286 current stack frame, is reached. This command is used to avoid single
4287 stepping through a loop more than once. It is like the @code{next}
4288 command, except that when @code{until} encounters a jump, it
4289 automatically continues execution until the program counter is greater
4290 than the address of the jump.
4292 This means that when you reach the end of a loop after single stepping
4293 though it, @code{until} makes your program continue execution until it
4294 exits the loop. In contrast, a @code{next} command at the end of a loop
4295 simply steps back to the beginning of the loop, which forces you to step
4296 through the next iteration.
4298 @code{until} always stops your program if it attempts to exit the current
4301 @code{until} may produce somewhat counterintuitive results if the order
4302 of machine code does not match the order of the source lines. For
4303 example, in the following excerpt from a debugging session, the @code{f}
4304 (@code{frame}) command shows that execution is stopped at line
4305 @code{206}; yet when we use @code{until}, we get to line @code{195}:
4309 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
4311 (@value{GDBP}) until
4312 195 for ( ; argc > 0; NEXTARG) @{
4315 This happened because, for execution efficiency, the compiler had
4316 generated code for the loop closure test at the end, rather than the
4317 start, of the loop---even though the test in a C @code{for}-loop is
4318 written before the body of the loop. The @code{until} command appeared
4319 to step back to the beginning of the loop when it advanced to this
4320 expression; however, it has not really gone to an earlier
4321 statement---not in terms of the actual machine code.
4323 @code{until} with no argument works by means of single
4324 instruction stepping, and hence is slower than @code{until} with an
4327 @item until @var{location}
4328 @itemx u @var{location}
4329 Continue running your program until either the specified location is
4330 reached, or the current stack frame returns. @var{location} is any of
4331 the forms described in @ref{Specify Location}.
4332 This form of the command uses temporary breakpoints, and
4333 hence is quicker than @code{until} without an argument. The specified
4334 location is actually reached only if it is in the current frame. This
4335 implies that @code{until} can be used to skip over recursive function
4336 invocations. For instance in the code below, if the current location is
4337 line @code{96}, issuing @code{until 99} will execute the program up to
4338 line @code{99} in the same invocation of factorial, i.e., after the inner
4339 invocations have returned.
4342 94 int factorial (int value)
4344 96 if (value > 1) @{
4345 97 value *= factorial (value - 1);
4352 @kindex advance @var{location}
4353 @itemx advance @var{location}
4354 Continue running the program up to the given @var{location}. An argument is
4355 required, which should be of one of the forms described in
4356 @ref{Specify Location}.
4357 Execution will also stop upon exit from the current stack
4358 frame. This command is similar to @code{until}, but @code{advance} will
4359 not skip over recursive function calls, and the target location doesn't
4360 have to be in the same frame as the current one.
4364 @kindex si @r{(@code{stepi})}
4366 @itemx stepi @var{arg}
4368 Execute one machine instruction, then stop and return to the debugger.
4370 It is often useful to do @samp{display/i $pc} when stepping by machine
4371 instructions. This makes @value{GDBN} automatically display the next
4372 instruction to be executed, each time your program stops. @xref{Auto
4373 Display,, Automatic Display}.
4375 An argument is a repeat count, as in @code{step}.
4379 @kindex ni @r{(@code{nexti})}
4381 @itemx nexti @var{arg}
4383 Execute one machine instruction, but if it is a function call,
4384 proceed until the function returns.
4386 An argument is a repeat count, as in @code{next}.
4393 A signal is an asynchronous event that can happen in a program. The
4394 operating system defines the possible kinds of signals, and gives each
4395 kind a name and a number. For example, in Unix @code{SIGINT} is the
4396 signal a program gets when you type an interrupt character (often @kbd{Ctrl-c});
4397 @code{SIGSEGV} is the signal a program gets from referencing a place in
4398 memory far away from all the areas in use; @code{SIGALRM} occurs when
4399 the alarm clock timer goes off (which happens only if your program has
4400 requested an alarm).
4402 @cindex fatal signals
4403 Some signals, including @code{SIGALRM}, are a normal part of the
4404 functioning of your program. Others, such as @code{SIGSEGV}, indicate
4405 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
4406 program has not specified in advance some other way to handle the signal.
4407 @code{SIGINT} does not indicate an error in your program, but it is normally
4408 fatal so it can carry out the purpose of the interrupt: to kill the program.
4410 @value{GDBN} has the ability to detect any occurrence of a signal in your
4411 program. You can tell @value{GDBN} in advance what to do for each kind of
4414 @cindex handling signals
4415 Normally, @value{GDBN} is set up to let the non-erroneous signals like
4416 @code{SIGALRM} be silently passed to your program
4417 (so as not to interfere with their role in the program's functioning)
4418 but to stop your program immediately whenever an error signal happens.
4419 You can change these settings with the @code{handle} command.
4422 @kindex info signals
4426 Print a table of all the kinds of signals and how @value{GDBN} has been told to
4427 handle each one. You can use this to see the signal numbers of all
4428 the defined types of signals.
4430 @item info signals @var{sig}
4431 Similar, but print information only about the specified signal number.
4433 @code{info handle} is an alias for @code{info signals}.
4436 @item handle @var{signal} @r{[}@var{keywords}@dots{}@r{]}
4437 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
4438 can be the number of a signal or its name (with or without the
4439 @samp{SIG} at the beginning); a list of signal numbers of the form
4440 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
4441 known signals. Optional arguments @var{keywords}, described below,
4442 say what change to make.
4446 The keywords allowed by the @code{handle} command can be abbreviated.
4447 Their full names are:
4451 @value{GDBN} should not stop your program when this signal happens. It may
4452 still print a message telling you that the signal has come in.
4455 @value{GDBN} should stop your program when this signal happens. This implies
4456 the @code{print} keyword as well.
4459 @value{GDBN} should print a message when this signal happens.
4462 @value{GDBN} should not mention the occurrence of the signal at all. This
4463 implies the @code{nostop} keyword as well.
4467 @value{GDBN} should allow your program to see this signal; your program
4468 can handle the signal, or else it may terminate if the signal is fatal
4469 and not handled. @code{pass} and @code{noignore} are synonyms.
4473 @value{GDBN} should not allow your program to see this signal.
4474 @code{nopass} and @code{ignore} are synonyms.
4478 When a signal stops your program, the signal is not visible to the
4480 continue. Your program sees the signal then, if @code{pass} is in
4481 effect for the signal in question @emph{at that time}. In other words,
4482 after @value{GDBN} reports a signal, you can use the @code{handle}
4483 command with @code{pass} or @code{nopass} to control whether your
4484 program sees that signal when you continue.
4486 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
4487 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
4488 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
4491 You can also use the @code{signal} command to prevent your program from
4492 seeing a signal, or cause it to see a signal it normally would not see,
4493 or to give it any signal at any time. For example, if your program stopped
4494 due to some sort of memory reference error, you might store correct
4495 values into the erroneous variables and continue, hoping to see more
4496 execution; but your program would probably terminate immediately as
4497 a result of the fatal signal once it saw the signal. To prevent this,
4498 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
4501 @cindex extra signal information
4502 @anchor{extra signal information}
4504 On some targets, @value{GDBN} can inspect extra signal information
4505 associated with the intercepted signal, before it is actually
4506 delivered to the program being debugged. This information is exported
4507 by the convenience variable @code{$_siginfo}, and consists of data
4508 that is passed by the kernel to the signal handler at the time of the
4509 receipt of a signal. The data type of the information itself is
4510 target dependent. You can see the data type using the @code{ptype
4511 $_siginfo} command. On Unix systems, it typically corresponds to the
4512 standard @code{siginfo_t} type, as defined in the @file{signal.h}
4515 Here's an example, on a @sc{gnu}/Linux system, printing the stray
4516 referenced address that raised a segmentation fault.
4520 (@value{GDBP}) continue
4521 Program received signal SIGSEGV, Segmentation fault.
4522 0x0000000000400766 in main ()
4524 (@value{GDBP}) ptype $_siginfo
4531 struct @{...@} _kill;
4532 struct @{...@} _timer;
4534 struct @{...@} _sigchld;
4535 struct @{...@} _sigfault;
4536 struct @{...@} _sigpoll;
4539 (@value{GDBP}) ptype $_siginfo._sifields._sigfault
4543 (@value{GDBP}) p $_siginfo._sifields._sigfault.si_addr
4544 $1 = (void *) 0x7ffff7ff7000
4548 Depending on target support, @code{$_siginfo} may also be writable.
4551 @section Stopping and Starting Multi-thread Programs
4553 @cindex stopped threads
4554 @cindex threads, stopped
4556 @cindex continuing threads
4557 @cindex threads, continuing
4559 @value{GDBN} supports debugging programs with multiple threads
4560 (@pxref{Threads,, Debugging Programs with Multiple Threads}). There
4561 are two modes of controlling execution of your program within the
4562 debugger. In the default mode, referred to as @dfn{all-stop mode},
4563 when any thread in your program stops (for example, at a breakpoint
4564 or while being stepped), all other threads in the program are also stopped by
4565 @value{GDBN}. On some targets, @value{GDBN} also supports
4566 @dfn{non-stop mode}, in which other threads can continue to run freely while
4567 you examine the stopped thread in the debugger.
4570 * All-Stop Mode:: All threads stop when GDB takes control
4571 * Non-Stop Mode:: Other threads continue to execute
4572 * Background Execution:: Running your program asynchronously
4573 * Thread-Specific Breakpoints:: Controlling breakpoints
4574 * Interrupted System Calls:: GDB may interfere with system calls
4578 @subsection All-Stop Mode
4580 @cindex all-stop mode
4582 In all-stop mode, whenever your program stops under @value{GDBN} for any reason,
4583 @emph{all} threads of execution stop, not just the current thread. This
4584 allows you to examine the overall state of the program, including
4585 switching between threads, without worrying that things may change
4588 Conversely, whenever you restart the program, @emph{all} threads start
4589 executing. @emph{This is true even when single-stepping} with commands
4590 like @code{step} or @code{next}.
4592 In particular, @value{GDBN} cannot single-step all threads in lockstep.
4593 Since thread scheduling is up to your debugging target's operating
4594 system (not controlled by @value{GDBN}), other threads may
4595 execute more than one statement while the current thread completes a
4596 single step. Moreover, in general other threads stop in the middle of a
4597 statement, rather than at a clean statement boundary, when the program
4600 You might even find your program stopped in another thread after
4601 continuing or even single-stepping. This happens whenever some other
4602 thread runs into a breakpoint, a signal, or an exception before the
4603 first thread completes whatever you requested.
4605 @cindex automatic thread selection
4606 @cindex switching threads automatically
4607 @cindex threads, automatic switching
4608 Whenever @value{GDBN} stops your program, due to a breakpoint or a
4609 signal, it automatically selects the thread where that breakpoint or
4610 signal happened. @value{GDBN} alerts you to the context switch with a
4611 message such as @samp{[Switching to Thread @var{n}]} to identify the
4614 On some OSes, you can modify @value{GDBN}'s default behavior by
4615 locking the OS scheduler to allow only a single thread to run.
4618 @item set scheduler-locking @var{mode}
4619 @cindex scheduler locking mode
4620 @cindex lock scheduler
4621 Set the scheduler locking mode. If it is @code{off}, then there is no
4622 locking and any thread may run at any time. If @code{on}, then only the
4623 current thread may run when the inferior is resumed. The @code{step}
4624 mode optimizes for single-stepping; it prevents other threads
4625 from preempting the current thread while you are stepping, so that
4626 the focus of debugging does not change unexpectedly.
4627 Other threads only rarely (or never) get a chance to run
4628 when you step. They are more likely to run when you @samp{next} over a
4629 function call, and they are completely free to run when you use commands
4630 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
4631 thread hits a breakpoint during its timeslice, @value{GDBN} does not change
4632 the current thread away from the thread that you are debugging.
4634 @item show scheduler-locking
4635 Display the current scheduler locking mode.
4638 @cindex resume threads of multiple processes simultaneously
4639 By default, when you issue one of the execution commands such as
4640 @code{continue}, @code{next} or @code{step}, @value{GDBN} allows only
4641 threads of the current inferior to run. For example, if @value{GDBN}
4642 is attached to two inferiors, each with two threads, the
4643 @code{continue} command resumes only the two threads of the current
4644 inferior. This is useful, for example, when you debug a program that
4645 forks and you want to hold the parent stopped (so that, for instance,
4646 it doesn't run to exit), while you debug the child. In other
4647 situations, you may not be interested in inspecting the current state
4648 of any of the processes @value{GDBN} is attached to, and you may want
4649 to resume them all until some breakpoint is hit. In the latter case,
4650 you can instruct @value{GDBN} to allow all threads of all the
4651 inferiors to run with the @w{@code{set schedule-multiple}} command.
4654 @kindex set schedule-multiple
4655 @item set schedule-multiple
4656 Set the mode for allowing threads of multiple processes to be resumed
4657 when an execution command is issued. When @code{on}, all threads of
4658 all processes are allowed to run. When @code{off}, only the threads
4659 of the current process are resumed. The default is @code{off}. The
4660 @code{scheduler-locking} mode takes precedence when set to @code{on},
4661 or while you are stepping and set to @code{step}.
4663 @item show schedule-multiple
4664 Display the current mode for resuming the execution of threads of
4669 @subsection Non-Stop Mode
4671 @cindex non-stop mode
4673 @c This section is really only a place-holder, and needs to be expanded
4674 @c with more details.
4676 For some multi-threaded targets, @value{GDBN} supports an optional
4677 mode of operation in which you can examine stopped program threads in
4678 the debugger while other threads continue to execute freely. This
4679 minimizes intrusion when debugging live systems, such as programs
4680 where some threads have real-time constraints or must continue to
4681 respond to external events. This is referred to as @dfn{non-stop} mode.
4683 In non-stop mode, when a thread stops to report a debugging event,
4684 @emph{only} that thread is stopped; @value{GDBN} does not stop other
4685 threads as well, in contrast to the all-stop mode behavior. Additionally,
4686 execution commands such as @code{continue} and @code{step} apply by default
4687 only to the current thread in non-stop mode, rather than all threads as
4688 in all-stop mode. This allows you to control threads explicitly in
4689 ways that are not possible in all-stop mode --- for example, stepping
4690 one thread while allowing others to run freely, stepping
4691 one thread while holding all others stopped, or stepping several threads
4692 independently and simultaneously.
4694 To enter non-stop mode, use this sequence of commands before you run
4695 or attach to your program:
4698 # Enable the async interface.
4701 # If using the CLI, pagination breaks non-stop.
4704 # Finally, turn it on!
4708 You can use these commands to manipulate the non-stop mode setting:
4711 @kindex set non-stop
4712 @item set non-stop on
4713 Enable selection of non-stop mode.
4714 @item set non-stop off
4715 Disable selection of non-stop mode.
4716 @kindex show non-stop
4718 Show the current non-stop enablement setting.
4721 Note these commands only reflect whether non-stop mode is enabled,
4722 not whether the currently-executing program is being run in non-stop mode.
4723 In particular, the @code{set non-stop} preference is only consulted when
4724 @value{GDBN} starts or connects to the target program, and it is generally
4725 not possible to switch modes once debugging has started. Furthermore,
4726 since not all targets support non-stop mode, even when you have enabled
4727 non-stop mode, @value{GDBN} may still fall back to all-stop operation by
4730 In non-stop mode, all execution commands apply only to the current thread
4731 by default. That is, @code{continue} only continues one thread.
4732 To continue all threads, issue @code{continue -a} or @code{c -a}.
4734 You can use @value{GDBN}'s background execution commands
4735 (@pxref{Background Execution}) to run some threads in the background
4736 while you continue to examine or step others from @value{GDBN}.
4737 The MI execution commands (@pxref{GDB/MI Program Execution}) are
4738 always executed asynchronously in non-stop mode.
4740 Suspending execution is done with the @code{interrupt} command when
4741 running in the background, or @kbd{Ctrl-c} during foreground execution.
4742 In all-stop mode, this stops the whole process;
4743 but in non-stop mode the interrupt applies only to the current thread.
4744 To stop the whole program, use @code{interrupt -a}.
4746 Other execution commands do not currently support the @code{-a} option.
4748 In non-stop mode, when a thread stops, @value{GDBN} doesn't automatically make
4749 that thread current, as it does in all-stop mode. This is because the
4750 thread stop notifications are asynchronous with respect to @value{GDBN}'s
4751 command interpreter, and it would be confusing if @value{GDBN} unexpectedly
4752 changed to a different thread just as you entered a command to operate on the
4753 previously current thread.
4755 @node Background Execution
4756 @subsection Background Execution
4758 @cindex foreground execution
4759 @cindex background execution
4760 @cindex asynchronous execution
4761 @cindex execution, foreground, background and asynchronous
4763 @value{GDBN}'s execution commands have two variants: the normal
4764 foreground (synchronous) behavior, and a background
4765 (asynchronous) behavior. In foreground execution, @value{GDBN} waits for
4766 the program to report that some thread has stopped before prompting for
4767 another command. In background execution, @value{GDBN} immediately gives
4768 a command prompt so that you can issue other commands while your program runs.
4770 You need to explicitly enable asynchronous mode before you can use
4771 background execution commands. You can use these commands to
4772 manipulate the asynchronous mode setting:
4775 @kindex set target-async
4776 @item set target-async on
4777 Enable asynchronous mode.
4778 @item set target-async off
4779 Disable asynchronous mode.
4780 @kindex show target-async
4781 @item show target-async
4782 Show the current target-async setting.
4785 If the target doesn't support async mode, @value{GDBN} issues an error
4786 message if you attempt to use the background execution commands.
4788 To specify background execution, add a @code{&} to the command. For example,
4789 the background form of the @code{continue} command is @code{continue&}, or
4790 just @code{c&}. The execution commands that accept background execution
4796 @xref{Starting, , Starting your Program}.
4800 @xref{Attach, , Debugging an Already-running Process}.
4804 @xref{Continuing and Stepping, step}.
4808 @xref{Continuing and Stepping, stepi}.
4812 @xref{Continuing and Stepping, next}.
4816 @xref{Continuing and Stepping, nexti}.
4820 @xref{Continuing and Stepping, continue}.
4824 @xref{Continuing and Stepping, finish}.
4828 @xref{Continuing and Stepping, until}.
4832 Background execution is especially useful in conjunction with non-stop
4833 mode for debugging programs with multiple threads; see @ref{Non-Stop Mode}.
4834 However, you can also use these commands in the normal all-stop mode with
4835 the restriction that you cannot issue another execution command until the
4836 previous one finishes. Examples of commands that are valid in all-stop
4837 mode while the program is running include @code{help} and @code{info break}.
4839 You can interrupt your program while it is running in the background by
4840 using the @code{interrupt} command.
4847 Suspend execution of the running program. In all-stop mode,
4848 @code{interrupt} stops the whole process, but in non-stop mode, it stops
4849 only the current thread. To stop the whole program in non-stop mode,
4850 use @code{interrupt -a}.
4853 @node Thread-Specific Breakpoints
4854 @subsection Thread-Specific Breakpoints
4856 When your program has multiple threads (@pxref{Threads,, Debugging
4857 Programs with Multiple Threads}), you can choose whether to set
4858 breakpoints on all threads, or on a particular thread.
4861 @cindex breakpoints and threads
4862 @cindex thread breakpoints
4863 @kindex break @dots{} thread @var{threadno}
4864 @item break @var{linespec} thread @var{threadno}
4865 @itemx break @var{linespec} thread @var{threadno} if @dots{}
4866 @var{linespec} specifies source lines; there are several ways of
4867 writing them (@pxref{Specify Location}), but the effect is always to
4868 specify some source line.
4870 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
4871 to specify that you only want @value{GDBN} to stop the program when a
4872 particular thread reaches this breakpoint. @var{threadno} is one of the
4873 numeric thread identifiers assigned by @value{GDBN}, shown in the first
4874 column of the @samp{info threads} display.
4876 If you do not specify @samp{thread @var{threadno}} when you set a
4877 breakpoint, the breakpoint applies to @emph{all} threads of your
4880 You can use the @code{thread} qualifier on conditional breakpoints as
4881 well; in this case, place @samp{thread @var{threadno}} before the
4882 breakpoint condition, like this:
4885 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
4890 @node Interrupted System Calls
4891 @subsection Interrupted System Calls
4893 @cindex thread breakpoints and system calls
4894 @cindex system calls and thread breakpoints
4895 @cindex premature return from system calls
4896 There is an unfortunate side effect when using @value{GDBN} to debug
4897 multi-threaded programs. If one thread stops for a
4898 breakpoint, or for some other reason, and another thread is blocked in a
4899 system call, then the system call may return prematurely. This is a
4900 consequence of the interaction between multiple threads and the signals
4901 that @value{GDBN} uses to implement breakpoints and other events that
4904 To handle this problem, your program should check the return value of
4905 each system call and react appropriately. This is good programming
4908 For example, do not write code like this:
4914 The call to @code{sleep} will return early if a different thread stops
4915 at a breakpoint or for some other reason.
4917 Instead, write this:
4922 unslept = sleep (unslept);
4925 A system call is allowed to return early, so the system is still
4926 conforming to its specification. But @value{GDBN} does cause your
4927 multi-threaded program to behave differently than it would without
4930 Also, @value{GDBN} uses internal breakpoints in the thread library to
4931 monitor certain events such as thread creation and thread destruction.
4932 When such an event happens, a system call in another thread may return
4933 prematurely, even though your program does not appear to stop.
4936 @node Reverse Execution
4937 @chapter Running programs backward
4938 @cindex reverse execution
4939 @cindex running programs backward
4941 When you are debugging a program, it is not unusual to realize that
4942 you have gone too far, and some event of interest has already happened.
4943 If the target environment supports it, @value{GDBN} can allow you to
4944 ``rewind'' the program by running it backward.
4946 A target environment that supports reverse execution should be able
4947 to ``undo'' the changes in machine state that have taken place as the
4948 program was executing normally. Variables, registers etc.@: should
4949 revert to their previous values. Obviously this requires a great
4950 deal of sophistication on the part of the target environment; not
4951 all target environments can support reverse execution.
4953 When a program is executed in reverse, the instructions that
4954 have most recently been executed are ``un-executed'', in reverse
4955 order. The program counter runs backward, following the previous
4956 thread of execution in reverse. As each instruction is ``un-executed'',
4957 the values of memory and/or registers that were changed by that
4958 instruction are reverted to their previous states. After executing
4959 a piece of source code in reverse, all side effects of that code
4960 should be ``undone'', and all variables should be returned to their
4961 prior values@footnote{
4962 Note that some side effects are easier to undo than others. For instance,
4963 memory and registers are relatively easy, but device I/O is hard. Some
4964 targets may be able undo things like device I/O, and some may not.
4966 The contract between @value{GDBN} and the reverse executing target
4967 requires only that the target do something reasonable when
4968 @value{GDBN} tells it to execute backwards, and then report the
4969 results back to @value{GDBN}. Whatever the target reports back to
4970 @value{GDBN}, @value{GDBN} will report back to the user. @value{GDBN}
4971 assumes that the memory and registers that the target reports are in a
4972 consistant state, but @value{GDBN} accepts whatever it is given.
4975 If you are debugging in a target environment that supports
4976 reverse execution, @value{GDBN} provides the following commands.
4979 @kindex reverse-continue
4980 @kindex rc @r{(@code{reverse-continue})}
4981 @item reverse-continue @r{[}@var{ignore-count}@r{]}
4982 @itemx rc @r{[}@var{ignore-count}@r{]}
4983 Beginning at the point where your program last stopped, start executing
4984 in reverse. Reverse execution will stop for breakpoints and synchronous
4985 exceptions (signals), just like normal execution. Behavior of
4986 asynchronous signals depends on the target environment.
4988 @kindex reverse-step
4989 @kindex rs @r{(@code{step})}
4990 @item reverse-step @r{[}@var{count}@r{]}
4991 Run the program backward until control reaches the start of a
4992 different source line; then stop it, and return control to @value{GDBN}.
4994 Like the @code{step} command, @code{reverse-step} will only stop
4995 at the beginning of a source line. It ``un-executes'' the previously
4996 executed source line. If the previous source line included calls to
4997 debuggable functions, @code{reverse-step} will step (backward) into
4998 the called function, stopping at the beginning of the @emph{last}
4999 statement in the called function (typically a return statement).
5001 Also, as with the @code{step} command, if non-debuggable functions are
5002 called, @code{reverse-step} will run thru them backward without stopping.
5004 @kindex reverse-stepi
5005 @kindex rsi @r{(@code{reverse-stepi})}
5006 @item reverse-stepi @r{[}@var{count}@r{]}
5007 Reverse-execute one machine instruction. Note that the instruction
5008 to be reverse-executed is @emph{not} the one pointed to by the program
5009 counter, but the instruction executed prior to that one. For instance,
5010 if the last instruction was a jump, @code{reverse-stepi} will take you
5011 back from the destination of the jump to the jump instruction itself.
5013 @kindex reverse-next
5014 @kindex rn @r{(@code{reverse-next})}
5015 @item reverse-next @r{[}@var{count}@r{]}
5016 Run backward to the beginning of the previous line executed in
5017 the current (innermost) stack frame. If the line contains function
5018 calls, they will be ``un-executed'' without stopping. Starting from
5019 the first line of a function, @code{reverse-next} will take you back
5020 to the caller of that function, @emph{before} the function was called,
5021 just as the normal @code{next} command would take you from the last
5022 line of a function back to its return to its caller
5023 @footnote{Unles the code is too heavily optimized.}.
5025 @kindex reverse-nexti
5026 @kindex rni @r{(@code{reverse-nexti})}
5027 @item reverse-nexti @r{[}@var{count}@r{]}
5028 Like @code{nexti}, @code{reverse-nexti} executes a single instruction
5029 in reverse, except that called functions are ``un-executed'' atomically.
5030 That is, if the previously executed instruction was a return from
5031 another instruction, @code{reverse-nexti} will continue to execute
5032 in reverse until the call to that function (from the current stack
5035 @kindex reverse-finish
5036 @item reverse-finish
5037 Just as the @code{finish} command takes you to the point where the
5038 current function returns, @code{reverse-finish} takes you to the point
5039 where it was called. Instead of ending up at the end of the current
5040 function invocation, you end up at the beginning.
5042 @kindex set exec-direction
5043 @item set exec-direction
5044 Set the direction of target execution.
5045 @itemx set exec-direction reverse
5046 @cindex execute forward or backward in time
5047 @value{GDBN} will perform all execution commands in reverse, until the
5048 exec-direction mode is changed to ``forward''. Affected commands include
5049 @code{step, stepi, next, nexti, continue, and finish}. The @code{return}
5050 command cannot be used in reverse mode.
5051 @item set exec-direction forward
5052 @value{GDBN} will perform all execution commands in the normal fashion.
5053 This is the default.
5057 @node Process Record and Replay
5058 @chapter Recording Inferior's Execution and Replaying It
5059 @cindex process record and replay
5060 @cindex recording inferior's execution and replaying it
5062 On some platforms, @value{GDBN} provides a special @dfn{process record
5063 and replay} target that can record a log of the process execution, and
5064 replay it later with both forward and reverse execution commands.
5067 When this target is in use, if the execution log includes the record
5068 for the next instruction, @value{GDBN} will debug in @dfn{replay
5069 mode}. In the replay mode, the inferior does not really execute code
5070 instructions. Instead, all the events that normally happen during
5071 code execution are taken from the execution log. While code is not
5072 really executed in replay mode, the values of registers (including the
5073 program counter register) and the memory of the inferior are still
5074 changed as they normally would. Their contents are taken from the
5078 If the record for the next instruction is not in the execution log,
5079 @value{GDBN} will debug in @dfn{record mode}. In this mode, the
5080 inferior executes normally, and @value{GDBN} records the execution log
5083 The process record and replay target supports reverse execution
5084 (@pxref{Reverse Execution}), even if the platform on which the
5085 inferior runs does not. However, the reverse execution is limited in
5086 this case by the range of the instructions recorded in the execution
5087 log. In other words, reverse execution on platforms that don't
5088 support it directly can only be done in the replay mode.
5090 When debugging in the reverse direction, @value{GDBN} will work in
5091 replay mode as long as the execution log includes the record for the
5092 previous instruction; otherwise, it will work in record mode, if the
5093 platform supports reverse execution, or stop if not.
5095 For architecture environments that support process record and replay,
5096 @value{GDBN} provides the following commands:
5099 @kindex target record
5103 This command starts the process record and replay target. The process
5104 record and replay target can only debug a process that is already
5105 running. Therefore, you need first to start the process with the
5106 @kbd{run} or @kbd{start} commands, and then start the recording with
5107 the @kbd{target record} command.
5109 Both @code{record} and @code{rec} are aliases of @code{target record}.
5111 @cindex displaced stepping, and process record and replay
5112 Displaced stepping (@pxref{Maintenance Commands,, displaced stepping})
5113 will be automatically disabled when process record and replay target
5114 is started. That's because the process record and replay target
5115 doesn't support displaced stepping.
5117 @cindex non-stop mode, and process record and replay
5118 @cindex asynchronous execution, and process record and replay
5119 If the inferior is in the non-stop mode (@pxref{Non-Stop Mode}) or in
5120 the asynchronous execution mode (@pxref{Background Execution}), the
5121 process record and replay target cannot be started because it doesn't
5122 support these two modes.
5127 Stop the process record and replay target. When process record and
5128 replay target stops, the entire execution log will be deleted and the
5129 inferior will either be terminated, or will remain in its final state.
5131 When you stop the process record and replay target in record mode (at
5132 the end of the execution log), the inferior will be stopped at the
5133 next instruction that would have been recorded. In other words, if
5134 you record for a while and then stop recording, the inferior process
5135 will be left in the same state as if the recording never happened.
5137 On the other hand, if the process record and replay target is stopped
5138 while in replay mode (that is, not at the end of the execution log,
5139 but at some earlier point), the inferior process will become ``live''
5140 at that earlier state, and it will then be possible to continue the
5141 usual ``live'' debugging of the process from that state.
5143 When the inferior process exits, or @value{GDBN} detaches from it,
5144 process record and replay target will automatically stop itself.
5146 @kindex set record insn-number-max
5147 @item set record insn-number-max @var{limit}
5148 Set the limit of instructions to be recorded. Default value is 200000.
5150 If @var{limit} is a positive number, then @value{GDBN} will start
5151 deleting instructions from the log once the number of the record
5152 instructions becomes greater than @var{limit}. For every new recorded
5153 instruction, @value{GDBN} will delete the earliest recorded
5154 instruction to keep the number of recorded instructions at the limit.
5155 (Since deleting recorded instructions loses information, @value{GDBN}
5156 lets you control what happens when the limit is reached, by means of
5157 the @code{stop-at-limit} option, described below.)
5159 If @var{limit} is zero, @value{GDBN} will never delete recorded
5160 instructions from the execution log. The number of recorded
5161 instructions is unlimited in this case.
5163 @kindex show record insn-number-max
5164 @item show record insn-number-max
5165 Show the limit of instructions to be recorded.
5167 @kindex set record stop-at-limit
5168 @item set record stop-at-limit
5169 Control the behavior when the number of recorded instructions reaches
5170 the limit. If ON (the default), @value{GDBN} will stop when the limit
5171 is reached for the first time and ask you whether you want to stop the
5172 inferior or continue running it and recording the execution log. If
5173 you decide to continue recording, each new recorded instruction will
5174 cause the oldest one to be deleted.
5176 If this option is OFF, @value{GDBN} will automatically delete the
5177 oldest record to make room for each new one, without asking.
5179 @kindex show record stop-at-limit
5180 @item show record stop-at-limit
5181 Show the current setting of @code{stop-at-limit}.
5183 @kindex info record insn-number
5184 @item info record insn-number
5185 Show the current number of recorded instructions.
5187 @kindex record delete
5190 When record target runs in replay mode (``in the past''), delete the
5191 subsequent execution log and begin to record a new execution log starting
5192 from the current address. This means you will abandon the previously
5193 recorded ``future'' and begin recording a new ``future''.
5198 @chapter Examining the Stack
5200 When your program has stopped, the first thing you need to know is where it
5201 stopped and how it got there.
5204 Each time your program performs a function call, information about the call
5206 That information includes the location of the call in your program,
5207 the arguments of the call,
5208 and the local variables of the function being called.
5209 The information is saved in a block of data called a @dfn{stack frame}.
5210 The stack frames are allocated in a region of memory called the @dfn{call
5213 When your program stops, the @value{GDBN} commands for examining the
5214 stack allow you to see all of this information.
5216 @cindex selected frame
5217 One of the stack frames is @dfn{selected} by @value{GDBN} and many
5218 @value{GDBN} commands refer implicitly to the selected frame. In
5219 particular, whenever you ask @value{GDBN} for the value of a variable in
5220 your program, the value is found in the selected frame. There are
5221 special @value{GDBN} commands to select whichever frame you are
5222 interested in. @xref{Selection, ,Selecting a Frame}.
5224 When your program stops, @value{GDBN} automatically selects the
5225 currently executing frame and describes it briefly, similar to the
5226 @code{frame} command (@pxref{Frame Info, ,Information about a Frame}).
5229 * Frames:: Stack frames
5230 * Backtrace:: Backtraces
5231 * Selection:: Selecting a frame
5232 * Frame Info:: Information on a frame
5237 @section Stack Frames
5239 @cindex frame, definition
5241 The call stack is divided up into contiguous pieces called @dfn{stack
5242 frames}, or @dfn{frames} for short; each frame is the data associated
5243 with one call to one function. The frame contains the arguments given
5244 to the function, the function's local variables, and the address at
5245 which the function is executing.
5247 @cindex initial frame
5248 @cindex outermost frame
5249 @cindex innermost frame
5250 When your program is started, the stack has only one frame, that of the
5251 function @code{main}. This is called the @dfn{initial} frame or the
5252 @dfn{outermost} frame. Each time a function is called, a new frame is
5253 made. Each time a function returns, the frame for that function invocation
5254 is eliminated. If a function is recursive, there can be many frames for
5255 the same function. The frame for the function in which execution is
5256 actually occurring is called the @dfn{innermost} frame. This is the most
5257 recently created of all the stack frames that still exist.
5259 @cindex frame pointer
5260 Inside your program, stack frames are identified by their addresses. A
5261 stack frame consists of many bytes, each of which has its own address; each
5262 kind of computer has a convention for choosing one byte whose
5263 address serves as the address of the frame. Usually this address is kept
5264 in a register called the @dfn{frame pointer register}
5265 (@pxref{Registers, $fp}) while execution is going on in that frame.
5267 @cindex frame number
5268 @value{GDBN} assigns numbers to all existing stack frames, starting with
5269 zero for the innermost frame, one for the frame that called it,
5270 and so on upward. These numbers do not really exist in your program;
5271 they are assigned by @value{GDBN} to give you a way of designating stack
5272 frames in @value{GDBN} commands.
5274 @c The -fomit-frame-pointer below perennially causes hbox overflow
5275 @c underflow problems.
5276 @cindex frameless execution
5277 Some compilers provide a way to compile functions so that they operate
5278 without stack frames. (For example, the @value{NGCC} option
5280 @samp{-fomit-frame-pointer}
5282 generates functions without a frame.)
5283 This is occasionally done with heavily used library functions to save
5284 the frame setup time. @value{GDBN} has limited facilities for dealing
5285 with these function invocations. If the innermost function invocation
5286 has no stack frame, @value{GDBN} nevertheless regards it as though
5287 it had a separate frame, which is numbered zero as usual, allowing
5288 correct tracing of the function call chain. However, @value{GDBN} has
5289 no provision for frameless functions elsewhere in the stack.
5292 @kindex frame@r{, command}
5293 @cindex current stack frame
5294 @item frame @var{args}
5295 The @code{frame} command allows you to move from one stack frame to another,
5296 and to print the stack frame you select. @var{args} may be either the
5297 address of the frame or the stack frame number. Without an argument,
5298 @code{frame} prints the current stack frame.
5300 @kindex select-frame
5301 @cindex selecting frame silently
5303 The @code{select-frame} command allows you to move from one stack frame
5304 to another without printing the frame. This is the silent version of
5312 @cindex call stack traces
5313 A backtrace is a summary of how your program got where it is. It shows one
5314 line per frame, for many frames, starting with the currently executing
5315 frame (frame zero), followed by its caller (frame one), and on up the
5320 @kindex bt @r{(@code{backtrace})}
5323 Print a backtrace of the entire stack: one line per frame for all
5324 frames in the stack.
5326 You can stop the backtrace at any time by typing the system interrupt
5327 character, normally @kbd{Ctrl-c}.
5329 @item backtrace @var{n}
5331 Similar, but print only the innermost @var{n} frames.
5333 @item backtrace -@var{n}
5335 Similar, but print only the outermost @var{n} frames.
5337 @item backtrace full
5339 @itemx bt full @var{n}
5340 @itemx bt full -@var{n}
5341 Print the values of the local variables also. @var{n} specifies the
5342 number of frames to print, as described above.
5347 The names @code{where} and @code{info stack} (abbreviated @code{info s})
5348 are additional aliases for @code{backtrace}.
5350 @cindex multiple threads, backtrace
5351 In a multi-threaded program, @value{GDBN} by default shows the
5352 backtrace only for the current thread. To display the backtrace for
5353 several or all of the threads, use the command @code{thread apply}
5354 (@pxref{Threads, thread apply}). For example, if you type @kbd{thread
5355 apply all backtrace}, @value{GDBN} will display the backtrace for all
5356 the threads; this is handy when you debug a core dump of a
5357 multi-threaded program.
5359 Each line in the backtrace shows the frame number and the function name.
5360 The program counter value is also shown---unless you use @code{set
5361 print address off}. The backtrace also shows the source file name and
5362 line number, as well as the arguments to the function. The program
5363 counter value is omitted if it is at the beginning of the code for that
5366 Here is an example of a backtrace. It was made with the command
5367 @samp{bt 3}, so it shows the innermost three frames.
5371 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
5373 #1 0x6e38 in expand_macro (sym=0x2b600, data=...) at macro.c:242
5374 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
5376 (More stack frames follow...)
5381 The display for frame zero does not begin with a program counter
5382 value, indicating that your program has stopped at the beginning of the
5383 code for line @code{993} of @code{builtin.c}.
5386 The value of parameter @code{data} in frame 1 has been replaced by
5387 @code{@dots{}}. By default, @value{GDBN} prints the value of a parameter
5388 only if it is a scalar (integer, pointer, enumeration, etc). See command
5389 @kbd{set print frame-arguments} in @ref{Print Settings} for more details
5390 on how to configure the way function parameter values are printed.
5392 @cindex value optimized out, in backtrace
5393 @cindex function call arguments, optimized out
5394 If your program was compiled with optimizations, some compilers will
5395 optimize away arguments passed to functions if those arguments are
5396 never used after the call. Such optimizations generate code that
5397 passes arguments through registers, but doesn't store those arguments
5398 in the stack frame. @value{GDBN} has no way of displaying such
5399 arguments in stack frames other than the innermost one. Here's what
5400 such a backtrace might look like:
5404 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
5406 #1 0x6e38 in expand_macro (sym=<value optimized out>) at macro.c:242
5407 #2 0x6840 in expand_token (obs=0x0, t=<value optimized out>, td=0xf7fffb08)
5409 (More stack frames follow...)
5414 The values of arguments that were not saved in their stack frames are
5415 shown as @samp{<value optimized out>}.
5417 If you need to display the values of such optimized-out arguments,
5418 either deduce that from other variables whose values depend on the one
5419 you are interested in, or recompile without optimizations.
5421 @cindex backtrace beyond @code{main} function
5422 @cindex program entry point
5423 @cindex startup code, and backtrace
5424 Most programs have a standard user entry point---a place where system
5425 libraries and startup code transition into user code. For C this is
5426 @code{main}@footnote{
5427 Note that embedded programs (the so-called ``free-standing''
5428 environment) are not required to have a @code{main} function as the
5429 entry point. They could even have multiple entry points.}.
5430 When @value{GDBN} finds the entry function in a backtrace
5431 it will terminate the backtrace, to avoid tracing into highly
5432 system-specific (and generally uninteresting) code.
5434 If you need to examine the startup code, or limit the number of levels
5435 in a backtrace, you can change this behavior:
5438 @item set backtrace past-main
5439 @itemx set backtrace past-main on
5440 @kindex set backtrace
5441 Backtraces will continue past the user entry point.
5443 @item set backtrace past-main off
5444 Backtraces will stop when they encounter the user entry point. This is the
5447 @item show backtrace past-main
5448 @kindex show backtrace
5449 Display the current user entry point backtrace policy.
5451 @item set backtrace past-entry
5452 @itemx set backtrace past-entry on
5453 Backtraces will continue past the internal entry point of an application.
5454 This entry point is encoded by the linker when the application is built,
5455 and is likely before the user entry point @code{main} (or equivalent) is called.
5457 @item set backtrace past-entry off
5458 Backtraces will stop when they encounter the internal entry point of an
5459 application. This is the default.
5461 @item show backtrace past-entry
5462 Display the current internal entry point backtrace policy.
5464 @item set backtrace limit @var{n}
5465 @itemx set backtrace limit 0
5466 @cindex backtrace limit
5467 Limit the backtrace to @var{n} levels. A value of zero means
5470 @item show backtrace limit
5471 Display the current limit on backtrace levels.
5475 @section Selecting a Frame
5477 Most commands for examining the stack and other data in your program work on
5478 whichever stack frame is selected at the moment. Here are the commands for
5479 selecting a stack frame; all of them finish by printing a brief description
5480 of the stack frame just selected.
5483 @kindex frame@r{, selecting}
5484 @kindex f @r{(@code{frame})}
5487 Select frame number @var{n}. Recall that frame zero is the innermost
5488 (currently executing) frame, frame one is the frame that called the
5489 innermost one, and so on. The highest-numbered frame is the one for
5492 @item frame @var{addr}
5494 Select the frame at address @var{addr}. This is useful mainly if the
5495 chaining of stack frames has been damaged by a bug, making it
5496 impossible for @value{GDBN} to assign numbers properly to all frames. In
5497 addition, this can be useful when your program has multiple stacks and
5498 switches between them.
5500 On the SPARC architecture, @code{frame} needs two addresses to
5501 select an arbitrary frame: a frame pointer and a stack pointer.
5503 On the MIPS and Alpha architecture, it needs two addresses: a stack
5504 pointer and a program counter.
5506 On the 29k architecture, it needs three addresses: a register stack
5507 pointer, a program counter, and a memory stack pointer.
5511 Move @var{n} frames up the stack. For positive numbers @var{n}, this
5512 advances toward the outermost frame, to higher frame numbers, to frames
5513 that have existed longer. @var{n} defaults to one.
5516 @kindex do @r{(@code{down})}
5518 Move @var{n} frames down the stack. For positive numbers @var{n}, this
5519 advances toward the innermost frame, to lower frame numbers, to frames
5520 that were created more recently. @var{n} defaults to one. You may
5521 abbreviate @code{down} as @code{do}.
5524 All of these commands end by printing two lines of output describing the
5525 frame. The first line shows the frame number, the function name, the
5526 arguments, and the source file and line number of execution in that
5527 frame. The second line shows the text of that source line.
5535 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
5537 10 read_input_file (argv[i]);
5541 After such a printout, the @code{list} command with no arguments
5542 prints ten lines centered on the point of execution in the frame.
5543 You can also edit the program at the point of execution with your favorite
5544 editing program by typing @code{edit}.
5545 @xref{List, ,Printing Source Lines},
5549 @kindex down-silently
5551 @item up-silently @var{n}
5552 @itemx down-silently @var{n}
5553 These two commands are variants of @code{up} and @code{down},
5554 respectively; they differ in that they do their work silently, without
5555 causing display of the new frame. They are intended primarily for use
5556 in @value{GDBN} command scripts, where the output might be unnecessary and
5561 @section Information About a Frame
5563 There are several other commands to print information about the selected
5569 When used without any argument, this command does not change which
5570 frame is selected, but prints a brief description of the currently
5571 selected stack frame. It can be abbreviated @code{f}. With an
5572 argument, this command is used to select a stack frame.
5573 @xref{Selection, ,Selecting a Frame}.
5576 @kindex info f @r{(@code{info frame})}
5579 This command prints a verbose description of the selected stack frame,
5584 the address of the frame
5586 the address of the next frame down (called by this frame)
5588 the address of the next frame up (caller of this frame)
5590 the language in which the source code corresponding to this frame is written
5592 the address of the frame's arguments
5594 the address of the frame's local variables
5596 the program counter saved in it (the address of execution in the caller frame)
5598 which registers were saved in the frame
5601 @noindent The verbose description is useful when
5602 something has gone wrong that has made the stack format fail to fit
5603 the usual conventions.
5605 @item info frame @var{addr}
5606 @itemx info f @var{addr}
5607 Print a verbose description of the frame at address @var{addr}, without
5608 selecting that frame. The selected frame remains unchanged by this
5609 command. This requires the same kind of address (more than one for some
5610 architectures) that you specify in the @code{frame} command.
5611 @xref{Selection, ,Selecting a Frame}.
5615 Print the arguments of the selected frame, each on a separate line.
5619 Print the local variables of the selected frame, each on a separate
5620 line. These are all variables (declared either static or automatic)
5621 accessible at the point of execution of the selected frame.
5624 @cindex catch exceptions, list active handlers
5625 @cindex exception handlers, how to list
5627 Print a list of all the exception handlers that are active in the
5628 current stack frame at the current point of execution. To see other
5629 exception handlers, visit the associated frame (using the @code{up},
5630 @code{down}, or @code{frame} commands); then type @code{info catch}.
5631 @xref{Set Catchpoints, , Setting Catchpoints}.
5637 @chapter Examining Source Files
5639 @value{GDBN} can print parts of your program's source, since the debugging
5640 information recorded in the program tells @value{GDBN} what source files were
5641 used to build it. When your program stops, @value{GDBN} spontaneously prints
5642 the line where it stopped. Likewise, when you select a stack frame
5643 (@pxref{Selection, ,Selecting a Frame}), @value{GDBN} prints the line where
5644 execution in that frame has stopped. You can print other portions of
5645 source files by explicit command.
5647 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
5648 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
5649 @value{GDBN} under @sc{gnu} Emacs}.
5652 * List:: Printing source lines
5653 * Specify Location:: How to specify code locations
5654 * Edit:: Editing source files
5655 * Search:: Searching source files
5656 * Source Path:: Specifying source directories
5657 * Machine Code:: Source and machine code
5661 @section Printing Source Lines
5664 @kindex l @r{(@code{list})}
5665 To print lines from a source file, use the @code{list} command
5666 (abbreviated @code{l}). By default, ten lines are printed.
5667 There are several ways to specify what part of the file you want to
5668 print; see @ref{Specify Location}, for the full list.
5670 Here are the forms of the @code{list} command most commonly used:
5673 @item list @var{linenum}
5674 Print lines centered around line number @var{linenum} in the
5675 current source file.
5677 @item list @var{function}
5678 Print lines centered around the beginning of function
5682 Print more lines. If the last lines printed were printed with a
5683 @code{list} command, this prints lines following the last lines
5684 printed; however, if the last line printed was a solitary line printed
5685 as part of displaying a stack frame (@pxref{Stack, ,Examining the
5686 Stack}), this prints lines centered around that line.
5689 Print lines just before the lines last printed.
5692 @cindex @code{list}, how many lines to display
5693 By default, @value{GDBN} prints ten source lines with any of these forms of
5694 the @code{list} command. You can change this using @code{set listsize}:
5697 @kindex set listsize
5698 @item set listsize @var{count}
5699 Make the @code{list} command display @var{count} source lines (unless
5700 the @code{list} argument explicitly specifies some other number).
5702 @kindex show listsize
5704 Display the number of lines that @code{list} prints.
5707 Repeating a @code{list} command with @key{RET} discards the argument,
5708 so it is equivalent to typing just @code{list}. This is more useful
5709 than listing the same lines again. An exception is made for an
5710 argument of @samp{-}; that argument is preserved in repetition so that
5711 each repetition moves up in the source file.
5713 In general, the @code{list} command expects you to supply zero, one or two
5714 @dfn{linespecs}. Linespecs specify source lines; there are several ways
5715 of writing them (@pxref{Specify Location}), but the effect is always
5716 to specify some source line.
5718 Here is a complete description of the possible arguments for @code{list}:
5721 @item list @var{linespec}
5722 Print lines centered around the line specified by @var{linespec}.
5724 @item list @var{first},@var{last}
5725 Print lines from @var{first} to @var{last}. Both arguments are
5726 linespecs. When a @code{list} command has two linespecs, and the
5727 source file of the second linespec is omitted, this refers to
5728 the same source file as the first linespec.
5730 @item list ,@var{last}
5731 Print lines ending with @var{last}.
5733 @item list @var{first},
5734 Print lines starting with @var{first}.
5737 Print lines just after the lines last printed.
5740 Print lines just before the lines last printed.
5743 As described in the preceding table.
5746 @node Specify Location
5747 @section Specifying a Location
5748 @cindex specifying location
5751 Several @value{GDBN} commands accept arguments that specify a location
5752 of your program's code. Since @value{GDBN} is a source-level
5753 debugger, a location usually specifies some line in the source code;
5754 for that reason, locations are also known as @dfn{linespecs}.
5756 Here are all the different ways of specifying a code location that
5757 @value{GDBN} understands:
5761 Specifies the line number @var{linenum} of the current source file.
5764 @itemx +@var{offset}
5765 Specifies the line @var{offset} lines before or after the @dfn{current
5766 line}. For the @code{list} command, the current line is the last one
5767 printed; for the breakpoint commands, this is the line at which
5768 execution stopped in the currently selected @dfn{stack frame}
5769 (@pxref{Frames, ,Frames}, for a description of stack frames.) When
5770 used as the second of the two linespecs in a @code{list} command,
5771 this specifies the line @var{offset} lines up or down from the first
5774 @item @var{filename}:@var{linenum}
5775 Specifies the line @var{linenum} in the source file @var{filename}.
5777 @item @var{function}
5778 Specifies the line that begins the body of the function @var{function}.
5779 For example, in C, this is the line with the open brace.
5781 @item @var{filename}:@var{function}
5782 Specifies the line that begins the body of the function @var{function}
5783 in the file @var{filename}. You only need the file name with a
5784 function name to avoid ambiguity when there are identically named
5785 functions in different source files.
5787 @item *@var{address}
5788 Specifies the program address @var{address}. For line-oriented
5789 commands, such as @code{list} and @code{edit}, this specifies a source
5790 line that contains @var{address}. For @code{break} and other
5791 breakpoint oriented commands, this can be used to set breakpoints in
5792 parts of your program which do not have debugging information or
5795 Here @var{address} may be any expression valid in the current working
5796 language (@pxref{Languages, working language}) that specifies a code
5797 address. In addition, as a convenience, @value{GDBN} extends the
5798 semantics of expressions used in locations to cover the situations
5799 that frequently happen during debugging. Here are the various forms
5803 @item @var{expression}
5804 Any expression valid in the current working language.
5806 @item @var{funcaddr}
5807 An address of a function or procedure derived from its name. In C,
5808 C@t{++}, Java, Objective-C, Fortran, minimal, and assembly, this is
5809 simply the function's name @var{function} (and actually a special case
5810 of a valid expression). In Pascal and Modula-2, this is
5811 @code{&@var{function}}. In Ada, this is @code{@var{function}'Address}
5812 (although the Pascal form also works).
5814 This form specifies the address of the function's first instruction,
5815 before the stack frame and arguments have been set up.
5817 @item '@var{filename}'::@var{funcaddr}
5818 Like @var{funcaddr} above, but also specifies the name of the source
5819 file explicitly. This is useful if the name of the function does not
5820 specify the function unambiguously, e.g., if there are several
5821 functions with identical names in different source files.
5828 @section Editing Source Files
5829 @cindex editing source files
5832 @kindex e @r{(@code{edit})}
5833 To edit the lines in a source file, use the @code{edit} command.
5834 The editing program of your choice
5835 is invoked with the current line set to
5836 the active line in the program.
5837 Alternatively, there are several ways to specify what part of the file you
5838 want to print if you want to see other parts of the program:
5841 @item edit @var{location}
5842 Edit the source file specified by @code{location}. Editing starts at
5843 that @var{location}, e.g., at the specified source line of the
5844 specified file. @xref{Specify Location}, for all the possible forms
5845 of the @var{location} argument; here are the forms of the @code{edit}
5846 command most commonly used:
5849 @item edit @var{number}
5850 Edit the current source file with @var{number} as the active line number.
5852 @item edit @var{function}
5853 Edit the file containing @var{function} at the beginning of its definition.
5858 @subsection Choosing your Editor
5859 You can customize @value{GDBN} to use any editor you want
5861 The only restriction is that your editor (say @code{ex}), recognizes the
5862 following command-line syntax:
5864 ex +@var{number} file
5866 The optional numeric value +@var{number} specifies the number of the line in
5867 the file where to start editing.}.
5868 By default, it is @file{@value{EDITOR}}, but you can change this
5869 by setting the environment variable @code{EDITOR} before using
5870 @value{GDBN}. For example, to configure @value{GDBN} to use the
5871 @code{vi} editor, you could use these commands with the @code{sh} shell:
5877 or in the @code{csh} shell,
5879 setenv EDITOR /usr/bin/vi
5884 @section Searching Source Files
5885 @cindex searching source files
5887 There are two commands for searching through the current source file for a
5892 @kindex forward-search
5893 @item forward-search @var{regexp}
5894 @itemx search @var{regexp}
5895 The command @samp{forward-search @var{regexp}} checks each line,
5896 starting with the one following the last line listed, for a match for
5897 @var{regexp}. It lists the line that is found. You can use the
5898 synonym @samp{search @var{regexp}} or abbreviate the command name as
5901 @kindex reverse-search
5902 @item reverse-search @var{regexp}
5903 The command @samp{reverse-search @var{regexp}} checks each line, starting
5904 with the one before the last line listed and going backward, for a match
5905 for @var{regexp}. It lists the line that is found. You can abbreviate
5906 this command as @code{rev}.
5910 @section Specifying Source Directories
5913 @cindex directories for source files
5914 Executable programs sometimes do not record the directories of the source
5915 files from which they were compiled, just the names. Even when they do,
5916 the directories could be moved between the compilation and your debugging
5917 session. @value{GDBN} has a list of directories to search for source files;
5918 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
5919 it tries all the directories in the list, in the order they are present
5920 in the list, until it finds a file with the desired name.
5922 For example, suppose an executable references the file
5923 @file{/usr/src/foo-1.0/lib/foo.c}, and our source path is
5924 @file{/mnt/cross}. The file is first looked up literally; if this
5925 fails, @file{/mnt/cross/usr/src/foo-1.0/lib/foo.c} is tried; if this
5926 fails, @file{/mnt/cross/foo.c} is opened; if this fails, an error
5927 message is printed. @value{GDBN} does not look up the parts of the
5928 source file name, such as @file{/mnt/cross/src/foo-1.0/lib/foo.c}.
5929 Likewise, the subdirectories of the source path are not searched: if
5930 the source path is @file{/mnt/cross}, and the binary refers to
5931 @file{foo.c}, @value{GDBN} would not find it under
5932 @file{/mnt/cross/usr/src/foo-1.0/lib}.
5934 Plain file names, relative file names with leading directories, file
5935 names containing dots, etc.@: are all treated as described above; for
5936 instance, if the source path is @file{/mnt/cross}, and the source file
5937 is recorded as @file{../lib/foo.c}, @value{GDBN} would first try
5938 @file{../lib/foo.c}, then @file{/mnt/cross/../lib/foo.c}, and after
5939 that---@file{/mnt/cross/foo.c}.
5941 Note that the executable search path is @emph{not} used to locate the
5944 Whenever you reset or rearrange the source path, @value{GDBN} clears out
5945 any information it has cached about where source files are found and where
5946 each line is in the file.
5950 When you start @value{GDBN}, its source path includes only @samp{cdir}
5951 and @samp{cwd}, in that order.
5952 To add other directories, use the @code{directory} command.
5954 The search path is used to find both program source files and @value{GDBN}
5955 script files (read using the @samp{-command} option and @samp{source} command).
5957 In addition to the source path, @value{GDBN} provides a set of commands
5958 that manage a list of source path substitution rules. A @dfn{substitution
5959 rule} specifies how to rewrite source directories stored in the program's
5960 debug information in case the sources were moved to a different
5961 directory between compilation and debugging. A rule is made of
5962 two strings, the first specifying what needs to be rewritten in
5963 the path, and the second specifying how it should be rewritten.
5964 In @ref{set substitute-path}, we name these two parts @var{from} and
5965 @var{to} respectively. @value{GDBN} does a simple string replacement
5966 of @var{from} with @var{to} at the start of the directory part of the
5967 source file name, and uses that result instead of the original file
5968 name to look up the sources.
5970 Using the previous example, suppose the @file{foo-1.0} tree has been
5971 moved from @file{/usr/src} to @file{/mnt/cross}, then you can tell
5972 @value{GDBN} to replace @file{/usr/src} in all source path names with
5973 @file{/mnt/cross}. The first lookup will then be
5974 @file{/mnt/cross/foo-1.0/lib/foo.c} in place of the original location
5975 of @file{/usr/src/foo-1.0/lib/foo.c}. To define a source path
5976 substitution rule, use the @code{set substitute-path} command
5977 (@pxref{set substitute-path}).
5979 To avoid unexpected substitution results, a rule is applied only if the
5980 @var{from} part of the directory name ends at a directory separator.
5981 For instance, a rule substituting @file{/usr/source} into
5982 @file{/mnt/cross} will be applied to @file{/usr/source/foo-1.0} but
5983 not to @file{/usr/sourceware/foo-2.0}. And because the substitution
5984 is applied only at the beginning of the directory name, this rule will
5985 not be applied to @file{/root/usr/source/baz.c} either.
5987 In many cases, you can achieve the same result using the @code{directory}
5988 command. However, @code{set substitute-path} can be more efficient in
5989 the case where the sources are organized in a complex tree with multiple
5990 subdirectories. With the @code{directory} command, you need to add each
5991 subdirectory of your project. If you moved the entire tree while
5992 preserving its internal organization, then @code{set substitute-path}
5993 allows you to direct the debugger to all the sources with one single
5996 @code{set substitute-path} is also more than just a shortcut command.
5997 The source path is only used if the file at the original location no
5998 longer exists. On the other hand, @code{set substitute-path} modifies
5999 the debugger behavior to look at the rewritten location instead. So, if
6000 for any reason a source file that is not relevant to your executable is
6001 located at the original location, a substitution rule is the only
6002 method available to point @value{GDBN} at the new location.
6004 @cindex @samp{--with-relocated-sources}
6005 @cindex default source path substitution
6006 You can configure a default source path substitution rule by
6007 configuring @value{GDBN} with the
6008 @samp{--with-relocated-sources=@var{dir}} option. The @var{dir}
6009 should be the name of a directory under @value{GDBN}'s configured
6010 prefix (set with @samp{--prefix} or @samp{--exec-prefix}), and
6011 directory names in debug information under @var{dir} will be adjusted
6012 automatically if the installed @value{GDBN} is moved to a new
6013 location. This is useful if @value{GDBN}, libraries or executables
6014 with debug information and corresponding source code are being moved
6018 @item directory @var{dirname} @dots{}
6019 @item dir @var{dirname} @dots{}
6020 Add directory @var{dirname} to the front of the source path. Several
6021 directory names may be given to this command, separated by @samp{:}
6022 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
6023 part of absolute file names) or
6024 whitespace. You may specify a directory that is already in the source
6025 path; this moves it forward, so @value{GDBN} searches it sooner.
6029 @vindex $cdir@r{, convenience variable}
6030 @vindex $cwd@r{, convenience variable}
6031 @cindex compilation directory
6032 @cindex current directory
6033 @cindex working directory
6034 @cindex directory, current
6035 @cindex directory, compilation
6036 You can use the string @samp{$cdir} to refer to the compilation
6037 directory (if one is recorded), and @samp{$cwd} to refer to the current
6038 working directory. @samp{$cwd} is not the same as @samp{.}---the former
6039 tracks the current working directory as it changes during your @value{GDBN}
6040 session, while the latter is immediately expanded to the current
6041 directory at the time you add an entry to the source path.
6044 Reset the source path to its default value (@samp{$cdir:$cwd} on Unix systems). This requires confirmation.
6046 @c RET-repeat for @code{directory} is explicitly disabled, but since
6047 @c repeating it would be a no-op we do not say that. (thanks to RMS)
6049 @item show directories
6050 @kindex show directories
6051 Print the source path: show which directories it contains.
6053 @anchor{set substitute-path}
6054 @item set substitute-path @var{from} @var{to}
6055 @kindex set substitute-path
6056 Define a source path substitution rule, and add it at the end of the
6057 current list of existing substitution rules. If a rule with the same
6058 @var{from} was already defined, then the old rule is also deleted.
6060 For example, if the file @file{/foo/bar/baz.c} was moved to
6061 @file{/mnt/cross/baz.c}, then the command
6064 (@value{GDBP}) set substitute-path /usr/src /mnt/cross
6068 will tell @value{GDBN} to replace @samp{/usr/src} with
6069 @samp{/mnt/cross}, which will allow @value{GDBN} to find the file
6070 @file{baz.c} even though it was moved.
6072 In the case when more than one substitution rule have been defined,
6073 the rules are evaluated one by one in the order where they have been
6074 defined. The first one matching, if any, is selected to perform
6077 For instance, if we had entered the following commands:
6080 (@value{GDBP}) set substitute-path /usr/src/include /mnt/include
6081 (@value{GDBP}) set substitute-path /usr/src /mnt/src
6085 @value{GDBN} would then rewrite @file{/usr/src/include/defs.h} into
6086 @file{/mnt/include/defs.h} by using the first rule. However, it would
6087 use the second rule to rewrite @file{/usr/src/lib/foo.c} into
6088 @file{/mnt/src/lib/foo.c}.
6091 @item unset substitute-path [path]
6092 @kindex unset substitute-path
6093 If a path is specified, search the current list of substitution rules
6094 for a rule that would rewrite that path. Delete that rule if found.
6095 A warning is emitted by the debugger if no rule could be found.
6097 If no path is specified, then all substitution rules are deleted.
6099 @item show substitute-path [path]
6100 @kindex show substitute-path
6101 If a path is specified, then print the source path substitution rule
6102 which would rewrite that path, if any.
6104 If no path is specified, then print all existing source path substitution
6109 If your source path is cluttered with directories that are no longer of
6110 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
6111 versions of source. You can correct the situation as follows:
6115 Use @code{directory} with no argument to reset the source path to its default value.
6118 Use @code{directory} with suitable arguments to reinstall the
6119 directories you want in the source path. You can add all the
6120 directories in one command.
6124 @section Source and Machine Code
6125 @cindex source line and its code address
6127 You can use the command @code{info line} to map source lines to program
6128 addresses (and vice versa), and the command @code{disassemble} to display
6129 a range of addresses as machine instructions. You can use the command
6130 @code{set disassemble-next-line} to set whether to disassemble next
6131 source line when execution stops. When run under @sc{gnu} Emacs
6132 mode, the @code{info line} command causes the arrow to point to the
6133 line specified. Also, @code{info line} prints addresses in symbolic form as
6138 @item info line @var{linespec}
6139 Print the starting and ending addresses of the compiled code for
6140 source line @var{linespec}. You can specify source lines in any of
6141 the ways documented in @ref{Specify Location}.
6144 For example, we can use @code{info line} to discover the location of
6145 the object code for the first line of function
6146 @code{m4_changequote}:
6148 @c FIXME: I think this example should also show the addresses in
6149 @c symbolic form, as they usually would be displayed.
6151 (@value{GDBP}) info line m4_changequote
6152 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
6156 @cindex code address and its source line
6157 We can also inquire (using @code{*@var{addr}} as the form for
6158 @var{linespec}) what source line covers a particular address:
6160 (@value{GDBP}) info line *0x63ff
6161 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
6164 @cindex @code{$_} and @code{info line}
6165 @cindex @code{x} command, default address
6166 @kindex x@r{(examine), and} info line
6167 After @code{info line}, the default address for the @code{x} command
6168 is changed to the starting address of the line, so that @samp{x/i} is
6169 sufficient to begin examining the machine code (@pxref{Memory,
6170 ,Examining Memory}). Also, this address is saved as the value of the
6171 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
6176 @cindex assembly instructions
6177 @cindex instructions, assembly
6178 @cindex machine instructions
6179 @cindex listing machine instructions
6181 @itemx disassemble /m
6182 @itemx disassemble /r
6183 This specialized command dumps a range of memory as machine
6184 instructions. It can also print mixed source+disassembly by specifying
6185 the @code{/m} modifier and print the raw instructions in hex as well as
6186 in symbolic form by specifying the @code{/r}.
6187 The default memory range is the function surrounding the
6188 program counter of the selected frame. A single argument to this
6189 command is a program counter value; @value{GDBN} dumps the function
6190 surrounding this value. Two arguments specify a range of addresses
6191 (first inclusive, second exclusive) to dump.
6194 The following example shows the disassembly of a range of addresses of
6195 HP PA-RISC 2.0 code:
6198 (@value{GDBP}) disas 0x32c4 0x32e4
6199 Dump of assembler code from 0x32c4 to 0x32e4:
6200 0x32c4 <main+204>: addil 0,dp
6201 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
6202 0x32cc <main+212>: ldil 0x3000,r31
6203 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
6204 0x32d4 <main+220>: ldo 0(r31),rp
6205 0x32d8 <main+224>: addil -0x800,dp
6206 0x32dc <main+228>: ldo 0x588(r1),r26
6207 0x32e0 <main+232>: ldil 0x3000,r31
6208 End of assembler dump.
6211 Here is an example showing mixed source+assembly for Intel x86:
6214 (@value{GDBP}) disas /m main
6215 Dump of assembler code for function main:
6217 0x08048330 <main+0>: push %ebp
6218 0x08048331 <main+1>: mov %esp,%ebp
6219 0x08048333 <main+3>: sub $0x8,%esp
6220 0x08048336 <main+6>: and $0xfffffff0,%esp
6221 0x08048339 <main+9>: sub $0x10,%esp
6223 6 printf ("Hello.\n");
6224 0x0804833c <main+12>: movl $0x8048440,(%esp)
6225 0x08048343 <main+19>: call 0x8048284 <puts@@plt>
6229 0x08048348 <main+24>: mov $0x0,%eax
6230 0x0804834d <main+29>: leave
6231 0x0804834e <main+30>: ret
6233 End of assembler dump.
6236 Some architectures have more than one commonly-used set of instruction
6237 mnemonics or other syntax.
6239 For programs that were dynamically linked and use shared libraries,
6240 instructions that call functions or branch to locations in the shared
6241 libraries might show a seemingly bogus location---it's actually a
6242 location of the relocation table. On some architectures, @value{GDBN}
6243 might be able to resolve these to actual function names.
6246 @kindex set disassembly-flavor
6247 @cindex Intel disassembly flavor
6248 @cindex AT&T disassembly flavor
6249 @item set disassembly-flavor @var{instruction-set}
6250 Select the instruction set to use when disassembling the
6251 program via the @code{disassemble} or @code{x/i} commands.
6253 Currently this command is only defined for the Intel x86 family. You
6254 can set @var{instruction-set} to either @code{intel} or @code{att}.
6255 The default is @code{att}, the AT&T flavor used by default by Unix
6256 assemblers for x86-based targets.
6258 @kindex show disassembly-flavor
6259 @item show disassembly-flavor
6260 Show the current setting of the disassembly flavor.
6264 @kindex set disassemble-next-line
6265 @kindex show disassemble-next-line
6266 @item set disassemble-next-line
6267 @itemx show disassemble-next-line
6268 Control whether or not @value{GDBN} will disassemble the next source
6269 line or instruction when execution stops. If ON, @value{GDBN} will
6270 display disassembly of the next source line when execution of the
6271 program being debugged stops. This is @emph{in addition} to
6272 displaying the source line itself, which @value{GDBN} always does if
6273 possible. If the next source line cannot be displayed for some reason
6274 (e.g., if @value{GDBN} cannot find the source file, or there's no line
6275 info in the debug info), @value{GDBN} will display disassembly of the
6276 next @emph{instruction} instead of showing the next source line. If
6277 AUTO, @value{GDBN} will display disassembly of next instruction only
6278 if the source line cannot be displayed. This setting causes
6279 @value{GDBN} to display some feedback when you step through a function
6280 with no line info or whose source file is unavailable. The default is
6281 OFF, which means never display the disassembly of the next line or
6287 @chapter Examining Data
6289 @cindex printing data
6290 @cindex examining data
6293 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
6294 @c document because it is nonstandard... Under Epoch it displays in a
6295 @c different window or something like that.
6296 The usual way to examine data in your program is with the @code{print}
6297 command (abbreviated @code{p}), or its synonym @code{inspect}. It
6298 evaluates and prints the value of an expression of the language your
6299 program is written in (@pxref{Languages, ,Using @value{GDBN} with
6300 Different Languages}).
6303 @item print @var{expr}
6304 @itemx print /@var{f} @var{expr}
6305 @var{expr} is an expression (in the source language). By default the
6306 value of @var{expr} is printed in a format appropriate to its data type;
6307 you can choose a different format by specifying @samp{/@var{f}}, where
6308 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
6312 @itemx print /@var{f}
6313 @cindex reprint the last value
6314 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
6315 @dfn{value history}; @pxref{Value History, ,Value History}). This allows you to
6316 conveniently inspect the same value in an alternative format.
6319 A more low-level way of examining data is with the @code{x} command.
6320 It examines data in memory at a specified address and prints it in a
6321 specified format. @xref{Memory, ,Examining Memory}.
6323 If you are interested in information about types, or about how the
6324 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
6325 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
6329 * Expressions:: Expressions
6330 * Ambiguous Expressions:: Ambiguous Expressions
6331 * Variables:: Program variables
6332 * Arrays:: Artificial arrays
6333 * Output Formats:: Output formats
6334 * Memory:: Examining memory
6335 * Auto Display:: Automatic display
6336 * Print Settings:: Print settings
6337 * Value History:: Value history
6338 * Convenience Vars:: Convenience variables
6339 * Registers:: Registers
6340 * Floating Point Hardware:: Floating point hardware
6341 * Vector Unit:: Vector Unit
6342 * OS Information:: Auxiliary data provided by operating system
6343 * Memory Region Attributes:: Memory region attributes
6344 * Dump/Restore Files:: Copy between memory and a file
6345 * Core File Generation:: Cause a program dump its core
6346 * Character Sets:: Debugging programs that use a different
6347 character set than GDB does
6348 * Caching Remote Data:: Data caching for remote targets
6349 * Searching Memory:: Searching memory for a sequence of bytes
6353 @section Expressions
6356 @code{print} and many other @value{GDBN} commands accept an expression and
6357 compute its value. Any kind of constant, variable or operator defined
6358 by the programming language you are using is valid in an expression in
6359 @value{GDBN}. This includes conditional expressions, function calls,
6360 casts, and string constants. It also includes preprocessor macros, if
6361 you compiled your program to include this information; see
6364 @cindex arrays in expressions
6365 @value{GDBN} supports array constants in expressions input by
6366 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
6367 you can use the command @code{print @{1, 2, 3@}} to create an array
6368 of three integers. If you pass an array to a function or assign it
6369 to a program variable, @value{GDBN} copies the array to memory that
6370 is @code{malloc}ed in the target program.
6372 Because C is so widespread, most of the expressions shown in examples in
6373 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
6374 Languages}, for information on how to use expressions in other
6377 In this section, we discuss operators that you can use in @value{GDBN}
6378 expressions regardless of your programming language.
6380 @cindex casts, in expressions
6381 Casts are supported in all languages, not just in C, because it is so
6382 useful to cast a number into a pointer in order to examine a structure
6383 at that address in memory.
6384 @c FIXME: casts supported---Mod2 true?
6386 @value{GDBN} supports these operators, in addition to those common
6387 to programming languages:
6391 @samp{@@} is a binary operator for treating parts of memory as arrays.
6392 @xref{Arrays, ,Artificial Arrays}, for more information.
6395 @samp{::} allows you to specify a variable in terms of the file or
6396 function where it is defined. @xref{Variables, ,Program Variables}.
6398 @cindex @{@var{type}@}
6399 @cindex type casting memory
6400 @cindex memory, viewing as typed object
6401 @cindex casts, to view memory
6402 @item @{@var{type}@} @var{addr}
6403 Refers to an object of type @var{type} stored at address @var{addr} in
6404 memory. @var{addr} may be any expression whose value is an integer or
6405 pointer (but parentheses are required around binary operators, just as in
6406 a cast). This construct is allowed regardless of what kind of data is
6407 normally supposed to reside at @var{addr}.
6410 @node Ambiguous Expressions
6411 @section Ambiguous Expressions
6412 @cindex ambiguous expressions
6414 Expressions can sometimes contain some ambiguous elements. For instance,
6415 some programming languages (notably Ada, C@t{++} and Objective-C) permit
6416 a single function name to be defined several times, for application in
6417 different contexts. This is called @dfn{overloading}. Another example
6418 involving Ada is generics. A @dfn{generic package} is similar to C@t{++}
6419 templates and is typically instantiated several times, resulting in
6420 the same function name being defined in different contexts.
6422 In some cases and depending on the language, it is possible to adjust
6423 the expression to remove the ambiguity. For instance in C@t{++}, you
6424 can specify the signature of the function you want to break on, as in
6425 @kbd{break @var{function}(@var{types})}. In Ada, using the fully
6426 qualified name of your function often makes the expression unambiguous
6429 When an ambiguity that needs to be resolved is detected, the debugger
6430 has the capability to display a menu of numbered choices for each
6431 possibility, and then waits for the selection with the prompt @samp{>}.
6432 The first option is always @samp{[0] cancel}, and typing @kbd{0 @key{RET}}
6433 aborts the current command. If the command in which the expression was
6434 used allows more than one choice to be selected, the next option in the
6435 menu is @samp{[1] all}, and typing @kbd{1 @key{RET}} selects all possible
6438 For example, the following session excerpt shows an attempt to set a
6439 breakpoint at the overloaded symbol @code{String::after}.
6440 We choose three particular definitions of that function name:
6442 @c FIXME! This is likely to change to show arg type lists, at least
6445 (@value{GDBP}) b String::after
6448 [2] file:String.cc; line number:867
6449 [3] file:String.cc; line number:860
6450 [4] file:String.cc; line number:875
6451 [5] file:String.cc; line number:853
6452 [6] file:String.cc; line number:846
6453 [7] file:String.cc; line number:735
6455 Breakpoint 1 at 0xb26c: file String.cc, line 867.
6456 Breakpoint 2 at 0xb344: file String.cc, line 875.
6457 Breakpoint 3 at 0xafcc: file String.cc, line 846.
6458 Multiple breakpoints were set.
6459 Use the "delete" command to delete unwanted
6466 @kindex set multiple-symbols
6467 @item set multiple-symbols @var{mode}
6468 @cindex multiple-symbols menu
6470 This option allows you to adjust the debugger behavior when an expression
6473 By default, @var{mode} is set to @code{all}. If the command with which
6474 the expression is used allows more than one choice, then @value{GDBN}
6475 automatically selects all possible choices. For instance, inserting
6476 a breakpoint on a function using an ambiguous name results in a breakpoint
6477 inserted on each possible match. However, if a unique choice must be made,
6478 then @value{GDBN} uses the menu to help you disambiguate the expression.
6479 For instance, printing the address of an overloaded function will result
6480 in the use of the menu.
6482 When @var{mode} is set to @code{ask}, the debugger always uses the menu
6483 when an ambiguity is detected.
6485 Finally, when @var{mode} is set to @code{cancel}, the debugger reports
6486 an error due to the ambiguity and the command is aborted.
6488 @kindex show multiple-symbols
6489 @item show multiple-symbols
6490 Show the current value of the @code{multiple-symbols} setting.
6494 @section Program Variables
6496 The most common kind of expression to use is the name of a variable
6499 Variables in expressions are understood in the selected stack frame
6500 (@pxref{Selection, ,Selecting a Frame}); they must be either:
6504 global (or file-static)
6511 visible according to the scope rules of the
6512 programming language from the point of execution in that frame
6515 @noindent This means that in the function
6530 you can examine and use the variable @code{a} whenever your program is
6531 executing within the function @code{foo}, but you can only use or
6532 examine the variable @code{b} while your program is executing inside
6533 the block where @code{b} is declared.
6535 @cindex variable name conflict
6536 There is an exception: you can refer to a variable or function whose
6537 scope is a single source file even if the current execution point is not
6538 in this file. But it is possible to have more than one such variable or
6539 function with the same name (in different source files). If that
6540 happens, referring to that name has unpredictable effects. If you wish,
6541 you can specify a static variable in a particular function or file,
6542 using the colon-colon (@code{::}) notation:
6544 @cindex colon-colon, context for variables/functions
6546 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
6547 @cindex @code{::}, context for variables/functions
6550 @var{file}::@var{variable}
6551 @var{function}::@var{variable}
6555 Here @var{file} or @var{function} is the name of the context for the
6556 static @var{variable}. In the case of file names, you can use quotes to
6557 make sure @value{GDBN} parses the file name as a single word---for example,
6558 to print a global value of @code{x} defined in @file{f2.c}:
6561 (@value{GDBP}) p 'f2.c'::x
6564 @cindex C@t{++} scope resolution
6565 This use of @samp{::} is very rarely in conflict with the very similar
6566 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
6567 scope resolution operator in @value{GDBN} expressions.
6568 @c FIXME: Um, so what happens in one of those rare cases where it's in
6571 @cindex wrong values
6572 @cindex variable values, wrong
6573 @cindex function entry/exit, wrong values of variables
6574 @cindex optimized code, wrong values of variables
6576 @emph{Warning:} Occasionally, a local variable may appear to have the
6577 wrong value at certain points in a function---just after entry to a new
6578 scope, and just before exit.
6580 You may see this problem when you are stepping by machine instructions.
6581 This is because, on most machines, it takes more than one instruction to
6582 set up a stack frame (including local variable definitions); if you are
6583 stepping by machine instructions, variables may appear to have the wrong
6584 values until the stack frame is completely built. On exit, it usually
6585 also takes more than one machine instruction to destroy a stack frame;
6586 after you begin stepping through that group of instructions, local
6587 variable definitions may be gone.
6589 This may also happen when the compiler does significant optimizations.
6590 To be sure of always seeing accurate values, turn off all optimization
6593 @cindex ``No symbol "foo" in current context''
6594 Another possible effect of compiler optimizations is to optimize
6595 unused variables out of existence, or assign variables to registers (as
6596 opposed to memory addresses). Depending on the support for such cases
6597 offered by the debug info format used by the compiler, @value{GDBN}
6598 might not be able to display values for such local variables. If that
6599 happens, @value{GDBN} will print a message like this:
6602 No symbol "foo" in current context.
6605 To solve such problems, either recompile without optimizations, or use a
6606 different debug info format, if the compiler supports several such
6607 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler,
6608 usually supports the @option{-gstabs+} option. @option{-gstabs+}
6609 produces debug info in a format that is superior to formats such as
6610 COFF. You may be able to use DWARF 2 (@option{-gdwarf-2}), which is also
6611 an effective form for debug info. @xref{Debugging Options,,Options
6612 for Debugging Your Program or GCC, gcc.info, Using the @sc{gnu}
6613 Compiler Collection (GCC)}.
6614 @xref{C, ,C and C@t{++}}, for more information about debug info formats
6615 that are best suited to C@t{++} programs.
6617 If you ask to print an object whose contents are unknown to
6618 @value{GDBN}, e.g., because its data type is not completely specified
6619 by the debug information, @value{GDBN} will say @samp{<incomplete
6620 type>}. @xref{Symbols, incomplete type}, for more about this.
6622 Strings are identified as arrays of @code{char} values without specified
6623 signedness. Arrays of either @code{signed char} or @code{unsigned char} get
6624 printed as arrays of 1 byte sized integers. @code{-fsigned-char} or
6625 @code{-funsigned-char} @value{NGCC} options have no effect as @value{GDBN}
6626 defines literal string type @code{"char"} as @code{char} without a sign.
6631 signed char var1[] = "A";
6634 You get during debugging
6639 $2 = @{65 'A', 0 '\0'@}
6643 @section Artificial Arrays
6645 @cindex artificial array
6647 @kindex @@@r{, referencing memory as an array}
6648 It is often useful to print out several successive objects of the
6649 same type in memory; a section of an array, or an array of
6650 dynamically determined size for which only a pointer exists in the
6653 You can do this by referring to a contiguous span of memory as an
6654 @dfn{artificial array}, using the binary operator @samp{@@}. The left
6655 operand of @samp{@@} should be the first element of the desired array
6656 and be an individual object. The right operand should be the desired length
6657 of the array. The result is an array value whose elements are all of
6658 the type of the left argument. The first element is actually the left
6659 argument; the second element comes from bytes of memory immediately
6660 following those that hold the first element, and so on. Here is an
6661 example. If a program says
6664 int *array = (int *) malloc (len * sizeof (int));
6668 you can print the contents of @code{array} with
6674 The left operand of @samp{@@} must reside in memory. Array values made
6675 with @samp{@@} in this way behave just like other arrays in terms of
6676 subscripting, and are coerced to pointers when used in expressions.
6677 Artificial arrays most often appear in expressions via the value history
6678 (@pxref{Value History, ,Value History}), after printing one out.
6680 Another way to create an artificial array is to use a cast.
6681 This re-interprets a value as if it were an array.
6682 The value need not be in memory:
6684 (@value{GDBP}) p/x (short[2])0x12345678
6685 $1 = @{0x1234, 0x5678@}
6688 As a convenience, if you leave the array length out (as in
6689 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
6690 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
6692 (@value{GDBP}) p/x (short[])0x12345678
6693 $2 = @{0x1234, 0x5678@}
6696 Sometimes the artificial array mechanism is not quite enough; in
6697 moderately complex data structures, the elements of interest may not
6698 actually be adjacent---for example, if you are interested in the values
6699 of pointers in an array. One useful work-around in this situation is
6700 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
6701 Variables}) as a counter in an expression that prints the first
6702 interesting value, and then repeat that expression via @key{RET}. For
6703 instance, suppose you have an array @code{dtab} of pointers to
6704 structures, and you are interested in the values of a field @code{fv}
6705 in each structure. Here is an example of what you might type:
6715 @node Output Formats
6716 @section Output Formats
6718 @cindex formatted output
6719 @cindex output formats
6720 By default, @value{GDBN} prints a value according to its data type. Sometimes
6721 this is not what you want. For example, you might want to print a number
6722 in hex, or a pointer in decimal. Or you might want to view data in memory
6723 at a certain address as a character string or as an instruction. To do
6724 these things, specify an @dfn{output format} when you print a value.
6726 The simplest use of output formats is to say how to print a value
6727 already computed. This is done by starting the arguments of the
6728 @code{print} command with a slash and a format letter. The format
6729 letters supported are:
6733 Regard the bits of the value as an integer, and print the integer in
6737 Print as integer in signed decimal.
6740 Print as integer in unsigned decimal.
6743 Print as integer in octal.
6746 Print as integer in binary. The letter @samp{t} stands for ``two''.
6747 @footnote{@samp{b} cannot be used because these format letters are also
6748 used with the @code{x} command, where @samp{b} stands for ``byte'';
6749 see @ref{Memory,,Examining Memory}.}
6752 @cindex unknown address, locating
6753 @cindex locate address
6754 Print as an address, both absolute in hexadecimal and as an offset from
6755 the nearest preceding symbol. You can use this format used to discover
6756 where (in what function) an unknown address is located:
6759 (@value{GDBP}) p/a 0x54320
6760 $3 = 0x54320 <_initialize_vx+396>
6764 The command @code{info symbol 0x54320} yields similar results.
6765 @xref{Symbols, info symbol}.
6768 Regard as an integer and print it as a character constant. This
6769 prints both the numerical value and its character representation. The
6770 character representation is replaced with the octal escape @samp{\nnn}
6771 for characters outside the 7-bit @sc{ascii} range.
6773 Without this format, @value{GDBN} displays @code{char},
6774 @w{@code{unsigned char}}, and @w{@code{signed char}} data as character
6775 constants. Single-byte members of vectors are displayed as integer
6779 Regard the bits of the value as a floating point number and print
6780 using typical floating point syntax.
6783 @cindex printing strings
6784 @cindex printing byte arrays
6785 Regard as a string, if possible. With this format, pointers to single-byte
6786 data are displayed as null-terminated strings and arrays of single-byte data
6787 are displayed as fixed-length strings. Other values are displayed in their
6790 Without this format, @value{GDBN} displays pointers to and arrays of
6791 @code{char}, @w{@code{unsigned char}}, and @w{@code{signed char}} as
6792 strings. Single-byte members of a vector are displayed as an integer
6796 @cindex raw printing
6797 Print using the @samp{raw} formatting. By default, @value{GDBN} will
6798 use a type-specific pretty-printer. The @samp{r} format bypasses any
6799 pretty-printer which might exist for the value's type.
6802 For example, to print the program counter in hex (@pxref{Registers}), type
6809 Note that no space is required before the slash; this is because command
6810 names in @value{GDBN} cannot contain a slash.
6812 To reprint the last value in the value history with a different format,
6813 you can use the @code{print} command with just a format and no
6814 expression. For example, @samp{p/x} reprints the last value in hex.
6817 @section Examining Memory
6819 You can use the command @code{x} (for ``examine'') to examine memory in
6820 any of several formats, independently of your program's data types.
6822 @cindex examining memory
6824 @kindex x @r{(examine memory)}
6825 @item x/@var{nfu} @var{addr}
6828 Use the @code{x} command to examine memory.
6831 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
6832 much memory to display and how to format it; @var{addr} is an
6833 expression giving the address where you want to start displaying memory.
6834 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
6835 Several commands set convenient defaults for @var{addr}.
6838 @item @var{n}, the repeat count
6839 The repeat count is a decimal integer; the default is 1. It specifies
6840 how much memory (counting by units @var{u}) to display.
6841 @c This really is **decimal**; unaffected by 'set radix' as of GDB
6844 @item @var{f}, the display format
6845 The display format is one of the formats used by @code{print}
6846 (@samp{x}, @samp{d}, @samp{u}, @samp{o}, @samp{t}, @samp{a}, @samp{c},
6847 @samp{f}, @samp{s}), and in addition @samp{i} (for machine instructions).
6848 The default is @samp{x} (hexadecimal) initially. The default changes
6849 each time you use either @code{x} or @code{print}.
6851 @item @var{u}, the unit size
6852 The unit size is any of
6858 Halfwords (two bytes).
6860 Words (four bytes). This is the initial default.
6862 Giant words (eight bytes).
6865 Each time you specify a unit size with @code{x}, that size becomes the
6866 default unit the next time you use @code{x}. (For the @samp{s} and
6867 @samp{i} formats, the unit size is ignored and is normally not written.)
6869 @item @var{addr}, starting display address
6870 @var{addr} is the address where you want @value{GDBN} to begin displaying
6871 memory. The expression need not have a pointer value (though it may);
6872 it is always interpreted as an integer address of a byte of memory.
6873 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
6874 @var{addr} is usually just after the last address examined---but several
6875 other commands also set the default address: @code{info breakpoints} (to
6876 the address of the last breakpoint listed), @code{info line} (to the
6877 starting address of a line), and @code{print} (if you use it to display
6878 a value from memory).
6881 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
6882 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
6883 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
6884 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
6885 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
6887 Since the letters indicating unit sizes are all distinct from the
6888 letters specifying output formats, you do not have to remember whether
6889 unit size or format comes first; either order works. The output
6890 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
6891 (However, the count @var{n} must come first; @samp{wx4} does not work.)
6893 Even though the unit size @var{u} is ignored for the formats @samp{s}
6894 and @samp{i}, you might still want to use a count @var{n}; for example,
6895 @samp{3i} specifies that you want to see three machine instructions,
6896 including any operands. For convenience, especially when used with
6897 the @code{display} command, the @samp{i} format also prints branch delay
6898 slot instructions, if any, beyond the count specified, which immediately
6899 follow the last instruction that is within the count. The command
6900 @code{disassemble} gives an alternative way of inspecting machine
6901 instructions; see @ref{Machine Code,,Source and Machine Code}.
6903 All the defaults for the arguments to @code{x} are designed to make it
6904 easy to continue scanning memory with minimal specifications each time
6905 you use @code{x}. For example, after you have inspected three machine
6906 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
6907 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
6908 the repeat count @var{n} is used again; the other arguments default as
6909 for successive uses of @code{x}.
6911 @cindex @code{$_}, @code{$__}, and value history
6912 The addresses and contents printed by the @code{x} command are not saved
6913 in the value history because there is often too much of them and they
6914 would get in the way. Instead, @value{GDBN} makes these values available for
6915 subsequent use in expressions as values of the convenience variables
6916 @code{$_} and @code{$__}. After an @code{x} command, the last address
6917 examined is available for use in expressions in the convenience variable
6918 @code{$_}. The contents of that address, as examined, are available in
6919 the convenience variable @code{$__}.
6921 If the @code{x} command has a repeat count, the address and contents saved
6922 are from the last memory unit printed; this is not the same as the last
6923 address printed if several units were printed on the last line of output.
6925 @cindex remote memory comparison
6926 @cindex verify remote memory image
6927 When you are debugging a program running on a remote target machine
6928 (@pxref{Remote Debugging}), you may wish to verify the program's image in the
6929 remote machine's memory against the executable file you downloaded to
6930 the target. The @code{compare-sections} command is provided for such
6934 @kindex compare-sections
6935 @item compare-sections @r{[}@var{section-name}@r{]}
6936 Compare the data of a loadable section @var{section-name} in the
6937 executable file of the program being debugged with the same section in
6938 the remote machine's memory, and report any mismatches. With no
6939 arguments, compares all loadable sections. This command's
6940 availability depends on the target's support for the @code{"qCRC"}
6945 @section Automatic Display
6946 @cindex automatic display
6947 @cindex display of expressions
6949 If you find that you want to print the value of an expression frequently
6950 (to see how it changes), you might want to add it to the @dfn{automatic
6951 display list} so that @value{GDBN} prints its value each time your program stops.
6952 Each expression added to the list is given a number to identify it;
6953 to remove an expression from the list, you specify that number.
6954 The automatic display looks like this:
6958 3: bar[5] = (struct hack *) 0x3804
6962 This display shows item numbers, expressions and their current values. As with
6963 displays you request manually using @code{x} or @code{print}, you can
6964 specify the output format you prefer; in fact, @code{display} decides
6965 whether to use @code{print} or @code{x} depending your format
6966 specification---it uses @code{x} if you specify either the @samp{i}
6967 or @samp{s} format, or a unit size; otherwise it uses @code{print}.
6971 @item display @var{expr}
6972 Add the expression @var{expr} to the list of expressions to display
6973 each time your program stops. @xref{Expressions, ,Expressions}.
6975 @code{display} does not repeat if you press @key{RET} again after using it.
6977 @item display/@var{fmt} @var{expr}
6978 For @var{fmt} specifying only a display format and not a size or
6979 count, add the expression @var{expr} to the auto-display list but
6980 arrange to display it each time in the specified format @var{fmt}.
6981 @xref{Output Formats,,Output Formats}.
6983 @item display/@var{fmt} @var{addr}
6984 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
6985 number of units, add the expression @var{addr} as a memory address to
6986 be examined each time your program stops. Examining means in effect
6987 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining Memory}.
6990 For example, @samp{display/i $pc} can be helpful, to see the machine
6991 instruction about to be executed each time execution stops (@samp{$pc}
6992 is a common name for the program counter; @pxref{Registers, ,Registers}).
6995 @kindex delete display
6997 @item undisplay @var{dnums}@dots{}
6998 @itemx delete display @var{dnums}@dots{}
6999 Remove item numbers @var{dnums} from the list of expressions to display.
7001 @code{undisplay} does not repeat if you press @key{RET} after using it.
7002 (Otherwise you would just get the error @samp{No display number @dots{}}.)
7004 @kindex disable display
7005 @item disable display @var{dnums}@dots{}
7006 Disable the display of item numbers @var{dnums}. A disabled display
7007 item is not printed automatically, but is not forgotten. It may be
7008 enabled again later.
7010 @kindex enable display
7011 @item enable display @var{dnums}@dots{}
7012 Enable display of item numbers @var{dnums}. It becomes effective once
7013 again in auto display of its expression, until you specify otherwise.
7016 Display the current values of the expressions on the list, just as is
7017 done when your program stops.
7019 @kindex info display
7021 Print the list of expressions previously set up to display
7022 automatically, each one with its item number, but without showing the
7023 values. This includes disabled expressions, which are marked as such.
7024 It also includes expressions which would not be displayed right now
7025 because they refer to automatic variables not currently available.
7028 @cindex display disabled out of scope
7029 If a display expression refers to local variables, then it does not make
7030 sense outside the lexical context for which it was set up. Such an
7031 expression is disabled when execution enters a context where one of its
7032 variables is not defined. For example, if you give the command
7033 @code{display last_char} while inside a function with an argument
7034 @code{last_char}, @value{GDBN} displays this argument while your program
7035 continues to stop inside that function. When it stops elsewhere---where
7036 there is no variable @code{last_char}---the display is disabled
7037 automatically. The next time your program stops where @code{last_char}
7038 is meaningful, you can enable the display expression once again.
7040 @node Print Settings
7041 @section Print Settings
7043 @cindex format options
7044 @cindex print settings
7045 @value{GDBN} provides the following ways to control how arrays, structures,
7046 and symbols are printed.
7049 These settings are useful for debugging programs in any language:
7053 @item set print address
7054 @itemx set print address on
7055 @cindex print/don't print memory addresses
7056 @value{GDBN} prints memory addresses showing the location of stack
7057 traces, structure values, pointer values, breakpoints, and so forth,
7058 even when it also displays the contents of those addresses. The default
7059 is @code{on}. For example, this is what a stack frame display looks like with
7060 @code{set print address on}:
7065 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
7067 530 if (lquote != def_lquote)
7071 @item set print address off
7072 Do not print addresses when displaying their contents. For example,
7073 this is the same stack frame displayed with @code{set print address off}:
7077 (@value{GDBP}) set print addr off
7079 #0 set_quotes (lq="<<", rq=">>") at input.c:530
7080 530 if (lquote != def_lquote)
7084 You can use @samp{set print address off} to eliminate all machine
7085 dependent displays from the @value{GDBN} interface. For example, with
7086 @code{print address off}, you should get the same text for backtraces on
7087 all machines---whether or not they involve pointer arguments.
7090 @item show print address
7091 Show whether or not addresses are to be printed.
7094 When @value{GDBN} prints a symbolic address, it normally prints the
7095 closest earlier symbol plus an offset. If that symbol does not uniquely
7096 identify the address (for example, it is a name whose scope is a single
7097 source file), you may need to clarify. One way to do this is with
7098 @code{info line}, for example @samp{info line *0x4537}. Alternately,
7099 you can set @value{GDBN} to print the source file and line number when
7100 it prints a symbolic address:
7103 @item set print symbol-filename on
7104 @cindex source file and line of a symbol
7105 @cindex symbol, source file and line
7106 Tell @value{GDBN} to print the source file name and line number of a
7107 symbol in the symbolic form of an address.
7109 @item set print symbol-filename off
7110 Do not print source file name and line number of a symbol. This is the
7113 @item show print symbol-filename
7114 Show whether or not @value{GDBN} will print the source file name and
7115 line number of a symbol in the symbolic form of an address.
7118 Another situation where it is helpful to show symbol filenames and line
7119 numbers is when disassembling code; @value{GDBN} shows you the line
7120 number and source file that corresponds to each instruction.
7122 Also, you may wish to see the symbolic form only if the address being
7123 printed is reasonably close to the closest earlier symbol:
7126 @item set print max-symbolic-offset @var{max-offset}
7127 @cindex maximum value for offset of closest symbol
7128 Tell @value{GDBN} to only display the symbolic form of an address if the
7129 offset between the closest earlier symbol and the address is less than
7130 @var{max-offset}. The default is 0, which tells @value{GDBN}
7131 to always print the symbolic form of an address if any symbol precedes it.
7133 @item show print max-symbolic-offset
7134 Ask how large the maximum offset is that @value{GDBN} prints in a
7138 @cindex wild pointer, interpreting
7139 @cindex pointer, finding referent
7140 If you have a pointer and you are not sure where it points, try
7141 @samp{set print symbol-filename on}. Then you can determine the name
7142 and source file location of the variable where it points, using
7143 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
7144 For example, here @value{GDBN} shows that a variable @code{ptt} points
7145 at another variable @code{t}, defined in @file{hi2.c}:
7148 (@value{GDBP}) set print symbol-filename on
7149 (@value{GDBP}) p/a ptt
7150 $4 = 0xe008 <t in hi2.c>
7154 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
7155 does not show the symbol name and filename of the referent, even with
7156 the appropriate @code{set print} options turned on.
7159 Other settings control how different kinds of objects are printed:
7162 @item set print array
7163 @itemx set print array on
7164 @cindex pretty print arrays
7165 Pretty print arrays. This format is more convenient to read,
7166 but uses more space. The default is off.
7168 @item set print array off
7169 Return to compressed format for arrays.
7171 @item show print array
7172 Show whether compressed or pretty format is selected for displaying
7175 @cindex print array indexes
7176 @item set print array-indexes
7177 @itemx set print array-indexes on
7178 Print the index of each element when displaying arrays. May be more
7179 convenient to locate a given element in the array or quickly find the
7180 index of a given element in that printed array. The default is off.
7182 @item set print array-indexes off
7183 Stop printing element indexes when displaying arrays.
7185 @item show print array-indexes
7186 Show whether the index of each element is printed when displaying
7189 @item set print elements @var{number-of-elements}
7190 @cindex number of array elements to print
7191 @cindex limit on number of printed array elements
7192 Set a limit on how many elements of an array @value{GDBN} will print.
7193 If @value{GDBN} is printing a large array, it stops printing after it has
7194 printed the number of elements set by the @code{set print elements} command.
7195 This limit also applies to the display of strings.
7196 When @value{GDBN} starts, this limit is set to 200.
7197 Setting @var{number-of-elements} to zero means that the printing is unlimited.
7199 @item show print elements
7200 Display the number of elements of a large array that @value{GDBN} will print.
7201 If the number is 0, then the printing is unlimited.
7203 @item set print frame-arguments @var{value}
7204 @kindex set print frame-arguments
7205 @cindex printing frame argument values
7206 @cindex print all frame argument values
7207 @cindex print frame argument values for scalars only
7208 @cindex do not print frame argument values
7209 This command allows to control how the values of arguments are printed
7210 when the debugger prints a frame (@pxref{Frames}). The possible
7215 The values of all arguments are printed.
7218 Print the value of an argument only if it is a scalar. The value of more
7219 complex arguments such as arrays, structures, unions, etc, is replaced
7220 by @code{@dots{}}. This is the default. Here is an example where
7221 only scalar arguments are shown:
7224 #1 0x08048361 in call_me (i=3, s=@dots{}, ss=0xbf8d508c, u=@dots{}, e=green)
7229 None of the argument values are printed. Instead, the value of each argument
7230 is replaced by @code{@dots{}}. In this case, the example above now becomes:
7233 #1 0x08048361 in call_me (i=@dots{}, s=@dots{}, ss=@dots{}, u=@dots{}, e=@dots{})
7238 By default, only scalar arguments are printed. This command can be used
7239 to configure the debugger to print the value of all arguments, regardless
7240 of their type. However, it is often advantageous to not print the value
7241 of more complex parameters. For instance, it reduces the amount of
7242 information printed in each frame, making the backtrace more readable.
7243 Also, it improves performance when displaying Ada frames, because
7244 the computation of large arguments can sometimes be CPU-intensive,
7245 especially in large applications. Setting @code{print frame-arguments}
7246 to @code{scalars} (the default) or @code{none} avoids this computation,
7247 thus speeding up the display of each Ada frame.
7249 @item show print frame-arguments
7250 Show how the value of arguments should be displayed when printing a frame.
7252 @item set print repeats
7253 @cindex repeated array elements
7254 Set the threshold for suppressing display of repeated array
7255 elements. When the number of consecutive identical elements of an
7256 array exceeds the threshold, @value{GDBN} prints the string
7257 @code{"<repeats @var{n} times>"}, where @var{n} is the number of
7258 identical repetitions, instead of displaying the identical elements
7259 themselves. Setting the threshold to zero will cause all elements to
7260 be individually printed. The default threshold is 10.
7262 @item show print repeats
7263 Display the current threshold for printing repeated identical
7266 @item set print null-stop
7267 @cindex @sc{null} elements in arrays
7268 Cause @value{GDBN} to stop printing the characters of an array when the first
7269 @sc{null} is encountered. This is useful when large arrays actually
7270 contain only short strings.
7273 @item show print null-stop
7274 Show whether @value{GDBN} stops printing an array on the first
7275 @sc{null} character.
7277 @item set print pretty on
7278 @cindex print structures in indented form
7279 @cindex indentation in structure display
7280 Cause @value{GDBN} to print structures in an indented format with one member
7281 per line, like this:
7296 @item set print pretty off
7297 Cause @value{GDBN} to print structures in a compact format, like this:
7301 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
7302 meat = 0x54 "Pork"@}
7307 This is the default format.
7309 @item show print pretty
7310 Show which format @value{GDBN} is using to print structures.
7312 @item set print sevenbit-strings on
7313 @cindex eight-bit characters in strings
7314 @cindex octal escapes in strings
7315 Print using only seven-bit characters; if this option is set,
7316 @value{GDBN} displays any eight-bit characters (in strings or
7317 character values) using the notation @code{\}@var{nnn}. This setting is
7318 best if you are working in English (@sc{ascii}) and you use the
7319 high-order bit of characters as a marker or ``meta'' bit.
7321 @item set print sevenbit-strings off
7322 Print full eight-bit characters. This allows the use of more
7323 international character sets, and is the default.
7325 @item show print sevenbit-strings
7326 Show whether or not @value{GDBN} is printing only seven-bit characters.
7328 @item set print union on
7329 @cindex unions in structures, printing
7330 Tell @value{GDBN} to print unions which are contained in structures
7331 and other unions. This is the default setting.
7333 @item set print union off
7334 Tell @value{GDBN} not to print unions which are contained in
7335 structures and other unions. @value{GDBN} will print @code{"@{...@}"}
7338 @item show print union
7339 Ask @value{GDBN} whether or not it will print unions which are contained in
7340 structures and other unions.
7342 For example, given the declarations
7345 typedef enum @{Tree, Bug@} Species;
7346 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
7347 typedef enum @{Caterpillar, Cocoon, Butterfly@}
7358 struct thing foo = @{Tree, @{Acorn@}@};
7362 with @code{set print union on} in effect @samp{p foo} would print
7365 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
7369 and with @code{set print union off} in effect it would print
7372 $1 = @{it = Tree, form = @{...@}@}
7376 @code{set print union} affects programs written in C-like languages
7382 These settings are of interest when debugging C@t{++} programs:
7385 @cindex demangling C@t{++} names
7386 @item set print demangle
7387 @itemx set print demangle on
7388 Print C@t{++} names in their source form rather than in the encoded
7389 (``mangled'') form passed to the assembler and linker for type-safe
7390 linkage. The default is on.
7392 @item show print demangle
7393 Show whether C@t{++} names are printed in mangled or demangled form.
7395 @item set print asm-demangle
7396 @itemx set print asm-demangle on
7397 Print C@t{++} names in their source form rather than their mangled form, even
7398 in assembler code printouts such as instruction disassemblies.
7401 @item show print asm-demangle
7402 Show whether C@t{++} names in assembly listings are printed in mangled
7405 @cindex C@t{++} symbol decoding style
7406 @cindex symbol decoding style, C@t{++}
7407 @kindex set demangle-style
7408 @item set demangle-style @var{style}
7409 Choose among several encoding schemes used by different compilers to
7410 represent C@t{++} names. The choices for @var{style} are currently:
7414 Allow @value{GDBN} to choose a decoding style by inspecting your program.
7417 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
7418 This is the default.
7421 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
7424 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
7427 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
7428 @strong{Warning:} this setting alone is not sufficient to allow
7429 debugging @code{cfront}-generated executables. @value{GDBN} would
7430 require further enhancement to permit that.
7433 If you omit @var{style}, you will see a list of possible formats.
7435 @item show demangle-style
7436 Display the encoding style currently in use for decoding C@t{++} symbols.
7438 @item set print object
7439 @itemx set print object on
7440 @cindex derived type of an object, printing
7441 @cindex display derived types
7442 When displaying a pointer to an object, identify the @emph{actual}
7443 (derived) type of the object rather than the @emph{declared} type, using
7444 the virtual function table.
7446 @item set print object off
7447 Display only the declared type of objects, without reference to the
7448 virtual function table. This is the default setting.
7450 @item show print object
7451 Show whether actual, or declared, object types are displayed.
7453 @item set print static-members
7454 @itemx set print static-members on
7455 @cindex static members of C@t{++} objects
7456 Print static members when displaying a C@t{++} object. The default is on.
7458 @item set print static-members off
7459 Do not print static members when displaying a C@t{++} object.
7461 @item show print static-members
7462 Show whether C@t{++} static members are printed or not.
7464 @item set print pascal_static-members
7465 @itemx set print pascal_static-members on
7466 @cindex static members of Pascal objects
7467 @cindex Pascal objects, static members display
7468 Print static members when displaying a Pascal object. The default is on.
7470 @item set print pascal_static-members off
7471 Do not print static members when displaying a Pascal object.
7473 @item show print pascal_static-members
7474 Show whether Pascal static members are printed or not.
7476 @c These don't work with HP ANSI C++ yet.
7477 @item set print vtbl
7478 @itemx set print vtbl on
7479 @cindex pretty print C@t{++} virtual function tables
7480 @cindex virtual functions (C@t{++}) display
7481 @cindex VTBL display
7482 Pretty print C@t{++} virtual function tables. The default is off.
7483 (The @code{vtbl} commands do not work on programs compiled with the HP
7484 ANSI C@t{++} compiler (@code{aCC}).)
7486 @item set print vtbl off
7487 Do not pretty print C@t{++} virtual function tables.
7489 @item show print vtbl
7490 Show whether C@t{++} virtual function tables are pretty printed, or not.
7494 @section Value History
7496 @cindex value history
7497 @cindex history of values printed by @value{GDBN}
7498 Values printed by the @code{print} command are saved in the @value{GDBN}
7499 @dfn{value history}. This allows you to refer to them in other expressions.
7500 Values are kept until the symbol table is re-read or discarded
7501 (for example with the @code{file} or @code{symbol-file} commands).
7502 When the symbol table changes, the value history is discarded,
7503 since the values may contain pointers back to the types defined in the
7508 @cindex history number
7509 The values printed are given @dfn{history numbers} by which you can
7510 refer to them. These are successive integers starting with one.
7511 @code{print} shows you the history number assigned to a value by
7512 printing @samp{$@var{num} = } before the value; here @var{num} is the
7515 To refer to any previous value, use @samp{$} followed by the value's
7516 history number. The way @code{print} labels its output is designed to
7517 remind you of this. Just @code{$} refers to the most recent value in
7518 the history, and @code{$$} refers to the value before that.
7519 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
7520 is the value just prior to @code{$$}, @code{$$1} is equivalent to
7521 @code{$$}, and @code{$$0} is equivalent to @code{$}.
7523 For example, suppose you have just printed a pointer to a structure and
7524 want to see the contents of the structure. It suffices to type
7530 If you have a chain of structures where the component @code{next} points
7531 to the next one, you can print the contents of the next one with this:
7538 You can print successive links in the chain by repeating this
7539 command---which you can do by just typing @key{RET}.
7541 Note that the history records values, not expressions. If the value of
7542 @code{x} is 4 and you type these commands:
7550 then the value recorded in the value history by the @code{print} command
7551 remains 4 even though the value of @code{x} has changed.
7556 Print the last ten values in the value history, with their item numbers.
7557 This is like @samp{p@ $$9} repeated ten times, except that @code{show
7558 values} does not change the history.
7560 @item show values @var{n}
7561 Print ten history values centered on history item number @var{n}.
7564 Print ten history values just after the values last printed. If no more
7565 values are available, @code{show values +} produces no display.
7568 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
7569 same effect as @samp{show values +}.
7571 @node Convenience Vars
7572 @section Convenience Variables
7574 @cindex convenience variables
7575 @cindex user-defined variables
7576 @value{GDBN} provides @dfn{convenience variables} that you can use within
7577 @value{GDBN} to hold on to a value and refer to it later. These variables
7578 exist entirely within @value{GDBN}; they are not part of your program, and
7579 setting a convenience variable has no direct effect on further execution
7580 of your program. That is why you can use them freely.
7582 Convenience variables are prefixed with @samp{$}. Any name preceded by
7583 @samp{$} can be used for a convenience variable, unless it is one of
7584 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
7585 (Value history references, in contrast, are @emph{numbers} preceded
7586 by @samp{$}. @xref{Value History, ,Value History}.)
7588 You can save a value in a convenience variable with an assignment
7589 expression, just as you would set a variable in your program.
7593 set $foo = *object_ptr
7597 would save in @code{$foo} the value contained in the object pointed to by
7600 Using a convenience variable for the first time creates it, but its
7601 value is @code{void} until you assign a new value. You can alter the
7602 value with another assignment at any time.
7604 Convenience variables have no fixed types. You can assign a convenience
7605 variable any type of value, including structures and arrays, even if
7606 that variable already has a value of a different type. The convenience
7607 variable, when used as an expression, has the type of its current value.
7610 @kindex show convenience
7611 @cindex show all user variables
7612 @item show convenience
7613 Print a list of convenience variables used so far, and their values.
7614 Abbreviated @code{show conv}.
7616 @kindex init-if-undefined
7617 @cindex convenience variables, initializing
7618 @item init-if-undefined $@var{variable} = @var{expression}
7619 Set a convenience variable if it has not already been set. This is useful
7620 for user-defined commands that keep some state. It is similar, in concept,
7621 to using local static variables with initializers in C (except that
7622 convenience variables are global). It can also be used to allow users to
7623 override default values used in a command script.
7625 If the variable is already defined then the expression is not evaluated so
7626 any side-effects do not occur.
7629 One of the ways to use a convenience variable is as a counter to be
7630 incremented or a pointer to be advanced. For example, to print
7631 a field from successive elements of an array of structures:
7635 print bar[$i++]->contents
7639 Repeat that command by typing @key{RET}.
7641 Some convenience variables are created automatically by @value{GDBN} and given
7642 values likely to be useful.
7645 @vindex $_@r{, convenience variable}
7647 The variable @code{$_} is automatically set by the @code{x} command to
7648 the last address examined (@pxref{Memory, ,Examining Memory}). Other
7649 commands which provide a default address for @code{x} to examine also
7650 set @code{$_} to that address; these commands include @code{info line}
7651 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
7652 except when set by the @code{x} command, in which case it is a pointer
7653 to the type of @code{$__}.
7655 @vindex $__@r{, convenience variable}
7657 The variable @code{$__} is automatically set by the @code{x} command
7658 to the value found in the last address examined. Its type is chosen
7659 to match the format in which the data was printed.
7662 @vindex $_exitcode@r{, convenience variable}
7663 The variable @code{$_exitcode} is automatically set to the exit code when
7664 the program being debugged terminates.
7667 @vindex $_siginfo@r{, convenience variable}
7668 The variable @code{$_siginfo} is bound to extra signal information
7669 inspection (@pxref{extra signal information}).
7672 On HP-UX systems, if you refer to a function or variable name that
7673 begins with a dollar sign, @value{GDBN} searches for a user or system
7674 name first, before it searches for a convenience variable.
7676 @cindex convenience functions
7677 @value{GDBN} also supplies some @dfn{convenience functions}. These
7678 have a syntax similar to convenience variables. A convenience
7679 function can be used in an expression just like an ordinary function;
7680 however, a convenience function is implemented internally to
7685 @kindex help function
7686 @cindex show all convenience functions
7687 Print a list of all convenience functions.
7694 You can refer to machine register contents, in expressions, as variables
7695 with names starting with @samp{$}. The names of registers are different
7696 for each machine; use @code{info registers} to see the names used on
7700 @kindex info registers
7701 @item info registers
7702 Print the names and values of all registers except floating-point
7703 and vector registers (in the selected stack frame).
7705 @kindex info all-registers
7706 @cindex floating point registers
7707 @item info all-registers
7708 Print the names and values of all registers, including floating-point
7709 and vector registers (in the selected stack frame).
7711 @item info registers @var{regname} @dots{}
7712 Print the @dfn{relativized} value of each specified register @var{regname}.
7713 As discussed in detail below, register values are normally relative to
7714 the selected stack frame. @var{regname} may be any register name valid on
7715 the machine you are using, with or without the initial @samp{$}.
7718 @cindex stack pointer register
7719 @cindex program counter register
7720 @cindex process status register
7721 @cindex frame pointer register
7722 @cindex standard registers
7723 @value{GDBN} has four ``standard'' register names that are available (in
7724 expressions) on most machines---whenever they do not conflict with an
7725 architecture's canonical mnemonics for registers. The register names
7726 @code{$pc} and @code{$sp} are used for the program counter register and
7727 the stack pointer. @code{$fp} is used for a register that contains a
7728 pointer to the current stack frame, and @code{$ps} is used for a
7729 register that contains the processor status. For example,
7730 you could print the program counter in hex with
7737 or print the instruction to be executed next with
7744 or add four to the stack pointer@footnote{This is a way of removing
7745 one word from the stack, on machines where stacks grow downward in
7746 memory (most machines, nowadays). This assumes that the innermost
7747 stack frame is selected; setting @code{$sp} is not allowed when other
7748 stack frames are selected. To pop entire frames off the stack,
7749 regardless of machine architecture, use @code{return};
7750 see @ref{Returning, ,Returning from a Function}.} with
7756 Whenever possible, these four standard register names are available on
7757 your machine even though the machine has different canonical mnemonics,
7758 so long as there is no conflict. The @code{info registers} command
7759 shows the canonical names. For example, on the SPARC, @code{info
7760 registers} displays the processor status register as @code{$psr} but you
7761 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
7762 is an alias for the @sc{eflags} register.
7764 @value{GDBN} always considers the contents of an ordinary register as an
7765 integer when the register is examined in this way. Some machines have
7766 special registers which can hold nothing but floating point; these
7767 registers are considered to have floating point values. There is no way
7768 to refer to the contents of an ordinary register as floating point value
7769 (although you can @emph{print} it as a floating point value with
7770 @samp{print/f $@var{regname}}).
7772 Some registers have distinct ``raw'' and ``virtual'' data formats. This
7773 means that the data format in which the register contents are saved by
7774 the operating system is not the same one that your program normally
7775 sees. For example, the registers of the 68881 floating point
7776 coprocessor are always saved in ``extended'' (raw) format, but all C
7777 programs expect to work with ``double'' (virtual) format. In such
7778 cases, @value{GDBN} normally works with the virtual format only (the format
7779 that makes sense for your program), but the @code{info registers} command
7780 prints the data in both formats.
7782 @cindex SSE registers (x86)
7783 @cindex MMX registers (x86)
7784 Some machines have special registers whose contents can be interpreted
7785 in several different ways. For example, modern x86-based machines
7786 have SSE and MMX registers that can hold several values packed
7787 together in several different formats. @value{GDBN} refers to such
7788 registers in @code{struct} notation:
7791 (@value{GDBP}) print $xmm1
7793 v4_float = @{0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044@},
7794 v2_double = @{9.92129282474342e-303, 2.7585945287983262e-313@},
7795 v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000",
7796 v8_int16 = @{0, 0, 14072, 315, 11, 0, 13, 0@},
7797 v4_int32 = @{0, 20657912, 11, 13@},
7798 v2_int64 = @{88725056443645952, 55834574859@},
7799 uint128 = 0x0000000d0000000b013b36f800000000
7804 To set values of such registers, you need to tell @value{GDBN} which
7805 view of the register you wish to change, as if you were assigning
7806 value to a @code{struct} member:
7809 (@value{GDBP}) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF
7812 Normally, register values are relative to the selected stack frame
7813 (@pxref{Selection, ,Selecting a Frame}). This means that you get the
7814 value that the register would contain if all stack frames farther in
7815 were exited and their saved registers restored. In order to see the
7816 true contents of hardware registers, you must select the innermost
7817 frame (with @samp{frame 0}).
7819 However, @value{GDBN} must deduce where registers are saved, from the machine
7820 code generated by your compiler. If some registers are not saved, or if
7821 @value{GDBN} is unable to locate the saved registers, the selected stack
7822 frame makes no difference.
7824 @node Floating Point Hardware
7825 @section Floating Point Hardware
7826 @cindex floating point
7828 Depending on the configuration, @value{GDBN} may be able to give
7829 you more information about the status of the floating point hardware.
7834 Display hardware-dependent information about the floating
7835 point unit. The exact contents and layout vary depending on the
7836 floating point chip. Currently, @samp{info float} is supported on
7837 the ARM and x86 machines.
7841 @section Vector Unit
7844 Depending on the configuration, @value{GDBN} may be able to give you
7845 more information about the status of the vector unit.
7850 Display information about the vector unit. The exact contents and
7851 layout vary depending on the hardware.
7854 @node OS Information
7855 @section Operating System Auxiliary Information
7856 @cindex OS information
7858 @value{GDBN} provides interfaces to useful OS facilities that can help
7859 you debug your program.
7861 @cindex @code{ptrace} system call
7862 @cindex @code{struct user} contents
7863 When @value{GDBN} runs on a @dfn{Posix system} (such as GNU or Unix
7864 machines), it interfaces with the inferior via the @code{ptrace}
7865 system call. The operating system creates a special sata structure,
7866 called @code{struct user}, for this interface. You can use the
7867 command @code{info udot} to display the contents of this data
7873 Display the contents of the @code{struct user} maintained by the OS
7874 kernel for the program being debugged. @value{GDBN} displays the
7875 contents of @code{struct user} as a list of hex numbers, similar to
7876 the @code{examine} command.
7879 @cindex auxiliary vector
7880 @cindex vector, auxiliary
7881 Some operating systems supply an @dfn{auxiliary vector} to programs at
7882 startup. This is akin to the arguments and environment that you
7883 specify for a program, but contains a system-dependent variety of
7884 binary values that tell system libraries important details about the
7885 hardware, operating system, and process. Each value's purpose is
7886 identified by an integer tag; the meanings are well-known but system-specific.
7887 Depending on the configuration and operating system facilities,
7888 @value{GDBN} may be able to show you this information. For remote
7889 targets, this functionality may further depend on the remote stub's
7890 support of the @samp{qXfer:auxv:read} packet, see
7891 @ref{qXfer auxiliary vector read}.
7896 Display the auxiliary vector of the inferior, which can be either a
7897 live process or a core dump file. @value{GDBN} prints each tag value
7898 numerically, and also shows names and text descriptions for recognized
7899 tags. Some values in the vector are numbers, some bit masks, and some
7900 pointers to strings or other data. @value{GDBN} displays each value in the
7901 most appropriate form for a recognized tag, and in hexadecimal for
7902 an unrecognized tag.
7905 On some targets, @value{GDBN} can access operating-system-specific information
7906 and display it to user, without interpretation. For remote targets,
7907 this functionality depends on the remote stub's support of the
7908 @samp{qXfer:osdata:read} packet, see @ref{qXfer osdata read}.
7911 @kindex info os processes
7912 @item info os processes
7913 Display the list of processes on the target. For each process,
7914 @value{GDBN} prints the process identifier, the name of the user, and
7915 the command corresponding to the process.
7918 @node Memory Region Attributes
7919 @section Memory Region Attributes
7920 @cindex memory region attributes
7922 @dfn{Memory region attributes} allow you to describe special handling
7923 required by regions of your target's memory. @value{GDBN} uses
7924 attributes to determine whether to allow certain types of memory
7925 accesses; whether to use specific width accesses; and whether to cache
7926 target memory. By default the description of memory regions is
7927 fetched from the target (if the current target supports this), but the
7928 user can override the fetched regions.
7930 Defined memory regions can be individually enabled and disabled. When a
7931 memory region is disabled, @value{GDBN} uses the default attributes when
7932 accessing memory in that region. Similarly, if no memory regions have
7933 been defined, @value{GDBN} uses the default attributes when accessing
7936 When a memory region is defined, it is given a number to identify it;
7937 to enable, disable, or remove a memory region, you specify that number.
7941 @item mem @var{lower} @var{upper} @var{attributes}@dots{}
7942 Define a memory region bounded by @var{lower} and @var{upper} with
7943 attributes @var{attributes}@dots{}, and add it to the list of regions
7944 monitored by @value{GDBN}. Note that @var{upper} == 0 is a special
7945 case: it is treated as the target's maximum memory address.
7946 (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
7949 Discard any user changes to the memory regions and use target-supplied
7950 regions, if available, or no regions if the target does not support.
7953 @item delete mem @var{nums}@dots{}
7954 Remove memory regions @var{nums}@dots{} from the list of regions
7955 monitored by @value{GDBN}.
7958 @item disable mem @var{nums}@dots{}
7959 Disable monitoring of memory regions @var{nums}@dots{}.
7960 A disabled memory region is not forgotten.
7961 It may be enabled again later.
7964 @item enable mem @var{nums}@dots{}
7965 Enable monitoring of memory regions @var{nums}@dots{}.
7969 Print a table of all defined memory regions, with the following columns
7973 @item Memory Region Number
7974 @item Enabled or Disabled.
7975 Enabled memory regions are marked with @samp{y}.
7976 Disabled memory regions are marked with @samp{n}.
7979 The address defining the inclusive lower bound of the memory region.
7982 The address defining the exclusive upper bound of the memory region.
7985 The list of attributes set for this memory region.
7990 @subsection Attributes
7992 @subsubsection Memory Access Mode
7993 The access mode attributes set whether @value{GDBN} may make read or
7994 write accesses to a memory region.
7996 While these attributes prevent @value{GDBN} from performing invalid
7997 memory accesses, they do nothing to prevent the target system, I/O DMA,
7998 etc.@: from accessing memory.
8002 Memory is read only.
8004 Memory is write only.
8006 Memory is read/write. This is the default.
8009 @subsubsection Memory Access Size
8010 The access size attribute tells @value{GDBN} to use specific sized
8011 accesses in the memory region. Often memory mapped device registers
8012 require specific sized accesses. If no access size attribute is
8013 specified, @value{GDBN} may use accesses of any size.
8017 Use 8 bit memory accesses.
8019 Use 16 bit memory accesses.
8021 Use 32 bit memory accesses.
8023 Use 64 bit memory accesses.
8026 @c @subsubsection Hardware/Software Breakpoints
8027 @c The hardware/software breakpoint attributes set whether @value{GDBN}
8028 @c will use hardware or software breakpoints for the internal breakpoints
8029 @c used by the step, next, finish, until, etc. commands.
8033 @c Always use hardware breakpoints
8034 @c @item swbreak (default)
8037 @subsubsection Data Cache
8038 The data cache attributes set whether @value{GDBN} will cache target
8039 memory. While this generally improves performance by reducing debug
8040 protocol overhead, it can lead to incorrect results because @value{GDBN}
8041 does not know about volatile variables or memory mapped device
8046 Enable @value{GDBN} to cache target memory.
8048 Disable @value{GDBN} from caching target memory. This is the default.
8051 @subsection Memory Access Checking
8052 @value{GDBN} can be instructed to refuse accesses to memory that is
8053 not explicitly described. This can be useful if accessing such
8054 regions has undesired effects for a specific target, or to provide
8055 better error checking. The following commands control this behaviour.
8058 @kindex set mem inaccessible-by-default
8059 @item set mem inaccessible-by-default [on|off]
8060 If @code{on} is specified, make @value{GDBN} treat memory not
8061 explicitly described by the memory ranges as non-existent and refuse accesses
8062 to such memory. The checks are only performed if there's at least one
8063 memory range defined. If @code{off} is specified, make @value{GDBN}
8064 treat the memory not explicitly described by the memory ranges as RAM.
8065 The default value is @code{on}.
8066 @kindex show mem inaccessible-by-default
8067 @item show mem inaccessible-by-default
8068 Show the current handling of accesses to unknown memory.
8072 @c @subsubsection Memory Write Verification
8073 @c The memory write verification attributes set whether @value{GDBN}
8074 @c will re-reads data after each write to verify the write was successful.
8078 @c @item noverify (default)
8081 @node Dump/Restore Files
8082 @section Copy Between Memory and a File
8083 @cindex dump/restore files
8084 @cindex append data to a file
8085 @cindex dump data to a file
8086 @cindex restore data from a file
8088 You can use the commands @code{dump}, @code{append}, and
8089 @code{restore} to copy data between target memory and a file. The
8090 @code{dump} and @code{append} commands write data to a file, and the
8091 @code{restore} command reads data from a file back into the inferior's
8092 memory. Files may be in binary, Motorola S-record, Intel hex, or
8093 Tektronix Hex format; however, @value{GDBN} can only append to binary
8099 @item dump @r{[}@var{format}@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
8100 @itemx dump @r{[}@var{format}@r{]} value @var{filename} @var{expr}
8101 Dump the contents of memory from @var{start_addr} to @var{end_addr},
8102 or the value of @var{expr}, to @var{filename} in the given format.
8104 The @var{format} parameter may be any one of:
8111 Motorola S-record format.
8113 Tektronix Hex format.
8116 @value{GDBN} uses the same definitions of these formats as the
8117 @sc{gnu} binary utilities, like @samp{objdump} and @samp{objcopy}. If
8118 @var{format} is omitted, @value{GDBN} dumps the data in raw binary
8122 @item append @r{[}binary@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
8123 @itemx append @r{[}binary@r{]} value @var{filename} @var{expr}
8124 Append the contents of memory from @var{start_addr} to @var{end_addr},
8125 or the value of @var{expr}, to the file @var{filename}, in raw binary form.
8126 (@value{GDBN} can only append data to files in raw binary form.)
8129 @item restore @var{filename} @r{[}binary@r{]} @var{bias} @var{start} @var{end}
8130 Restore the contents of file @var{filename} into memory. The
8131 @code{restore} command can automatically recognize any known @sc{bfd}
8132 file format, except for raw binary. To restore a raw binary file you
8133 must specify the optional keyword @code{binary} after the filename.
8135 If @var{bias} is non-zero, its value will be added to the addresses
8136 contained in the file. Binary files always start at address zero, so
8137 they will be restored at address @var{bias}. Other bfd files have
8138 a built-in location; they will be restored at offset @var{bias}
8141 If @var{start} and/or @var{end} are non-zero, then only data between
8142 file offset @var{start} and file offset @var{end} will be restored.
8143 These offsets are relative to the addresses in the file, before
8144 the @var{bias} argument is applied.
8148 @node Core File Generation
8149 @section How to Produce a Core File from Your Program
8150 @cindex dump core from inferior
8152 A @dfn{core file} or @dfn{core dump} is a file that records the memory
8153 image of a running process and its process status (register values
8154 etc.). Its primary use is post-mortem debugging of a program that
8155 crashed while it ran outside a debugger. A program that crashes
8156 automatically produces a core file, unless this feature is disabled by
8157 the user. @xref{Files}, for information on invoking @value{GDBN} in
8158 the post-mortem debugging mode.
8160 Occasionally, you may wish to produce a core file of the program you
8161 are debugging in order to preserve a snapshot of its state.
8162 @value{GDBN} has a special command for that.
8166 @kindex generate-core-file
8167 @item generate-core-file [@var{file}]
8168 @itemx gcore [@var{file}]
8169 Produce a core dump of the inferior process. The optional argument
8170 @var{file} specifies the file name where to put the core dump. If not
8171 specified, the file name defaults to @file{core.@var{pid}}, where
8172 @var{pid} is the inferior process ID.
8174 Note that this command is implemented only for some systems (as of
8175 this writing, @sc{gnu}/Linux, FreeBSD, Solaris, Unixware, and S390).
8178 @node Character Sets
8179 @section Character Sets
8180 @cindex character sets
8182 @cindex translating between character sets
8183 @cindex host character set
8184 @cindex target character set
8186 If the program you are debugging uses a different character set to
8187 represent characters and strings than the one @value{GDBN} uses itself,
8188 @value{GDBN} can automatically translate between the character sets for
8189 you. The character set @value{GDBN} uses we call the @dfn{host
8190 character set}; the one the inferior program uses we call the
8191 @dfn{target character set}.
8193 For example, if you are running @value{GDBN} on a @sc{gnu}/Linux system, which
8194 uses the ISO Latin 1 character set, but you are using @value{GDBN}'s
8195 remote protocol (@pxref{Remote Debugging}) to debug a program
8196 running on an IBM mainframe, which uses the @sc{ebcdic} character set,
8197 then the host character set is Latin-1, and the target character set is
8198 @sc{ebcdic}. If you give @value{GDBN} the command @code{set
8199 target-charset EBCDIC-US}, then @value{GDBN} translates between
8200 @sc{ebcdic} and Latin 1 as you print character or string values, or use
8201 character and string literals in expressions.
8203 @value{GDBN} has no way to automatically recognize which character set
8204 the inferior program uses; you must tell it, using the @code{set
8205 target-charset} command, described below.
8207 Here are the commands for controlling @value{GDBN}'s character set
8211 @item set target-charset @var{charset}
8212 @kindex set target-charset
8213 Set the current target character set to @var{charset}. To display the
8214 list of supported target character sets, type
8215 @kbd{@w{set target-charset @key{TAB}@key{TAB}}}.
8217 @item set host-charset @var{charset}
8218 @kindex set host-charset
8219 Set the current host character set to @var{charset}.
8221 By default, @value{GDBN} uses a host character set appropriate to the
8222 system it is running on; you can override that default using the
8223 @code{set host-charset} command. On some systems, @value{GDBN} cannot
8224 automatically determine the appropriate host character set. In this
8225 case, @value{GDBN} uses @samp{UTF-8}.
8227 @value{GDBN} can only use certain character sets as its host character
8228 set. If you type @kbd{@w{set target-charset @key{TAB}@key{TAB}}},
8229 @value{GDBN} will list the host character sets it supports.
8231 @item set charset @var{charset}
8233 Set the current host and target character sets to @var{charset}. As
8234 above, if you type @kbd{@w{set charset @key{TAB}@key{TAB}}},
8235 @value{GDBN} will list the names of the character sets that can be used
8236 for both host and target.
8239 @kindex show charset
8240 Show the names of the current host and target character sets.
8242 @item show host-charset
8243 @kindex show host-charset
8244 Show the name of the current host character set.
8246 @item show target-charset
8247 @kindex show target-charset
8248 Show the name of the current target character set.
8250 @item set target-wide-charset @var{charset}
8251 @kindex set target-wide-charset
8252 Set the current target's wide character set to @var{charset}. This is
8253 the character set used by the target's @code{wchar_t} type. To
8254 display the list of supported wide character sets, type
8255 @kbd{@w{set target-wide-charset @key{TAB}@key{TAB}}}.
8257 @item show target-wide-charset
8258 @kindex show target-wide-charset
8259 Show the name of the current target's wide character set.
8262 Here is an example of @value{GDBN}'s character set support in action.
8263 Assume that the following source code has been placed in the file
8264 @file{charset-test.c}:
8270 = @{72, 101, 108, 108, 111, 44, 32, 119,
8271 111, 114, 108, 100, 33, 10, 0@};
8272 char ibm1047_hello[]
8273 = @{200, 133, 147, 147, 150, 107, 64, 166,
8274 150, 153, 147, 132, 90, 37, 0@};
8278 printf ("Hello, world!\n");
8282 In this program, @code{ascii_hello} and @code{ibm1047_hello} are arrays
8283 containing the string @samp{Hello, world!} followed by a newline,
8284 encoded in the @sc{ascii} and @sc{ibm1047} character sets.
8286 We compile the program, and invoke the debugger on it:
8289 $ gcc -g charset-test.c -o charset-test
8290 $ gdb -nw charset-test
8291 GNU gdb 2001-12-19-cvs
8292 Copyright 2001 Free Software Foundation, Inc.
8297 We can use the @code{show charset} command to see what character sets
8298 @value{GDBN} is currently using to interpret and display characters and
8302 (@value{GDBP}) show charset
8303 The current host and target character set is `ISO-8859-1'.
8307 For the sake of printing this manual, let's use @sc{ascii} as our
8308 initial character set:
8310 (@value{GDBP}) set charset ASCII
8311 (@value{GDBP}) show charset
8312 The current host and target character set is `ASCII'.
8316 Let's assume that @sc{ascii} is indeed the correct character set for our
8317 host system --- in other words, let's assume that if @value{GDBN} prints
8318 characters using the @sc{ascii} character set, our terminal will display
8319 them properly. Since our current target character set is also
8320 @sc{ascii}, the contents of @code{ascii_hello} print legibly:
8323 (@value{GDBP}) print ascii_hello
8324 $1 = 0x401698 "Hello, world!\n"
8325 (@value{GDBP}) print ascii_hello[0]
8330 @value{GDBN} uses the target character set for character and string
8331 literals you use in expressions:
8334 (@value{GDBP}) print '+'
8339 The @sc{ascii} character set uses the number 43 to encode the @samp{+}
8342 @value{GDBN} relies on the user to tell it which character set the
8343 target program uses. If we print @code{ibm1047_hello} while our target
8344 character set is still @sc{ascii}, we get jibberish:
8347 (@value{GDBP}) print ibm1047_hello
8348 $4 = 0x4016a8 "\310\205\223\223\226k@@\246\226\231\223\204Z%"
8349 (@value{GDBP}) print ibm1047_hello[0]
8354 If we invoke the @code{set target-charset} followed by @key{TAB}@key{TAB},
8355 @value{GDBN} tells us the character sets it supports:
8358 (@value{GDBP}) set target-charset
8359 ASCII EBCDIC-US IBM1047 ISO-8859-1
8360 (@value{GDBP}) set target-charset
8363 We can select @sc{ibm1047} as our target character set, and examine the
8364 program's strings again. Now the @sc{ascii} string is wrong, but
8365 @value{GDBN} translates the contents of @code{ibm1047_hello} from the
8366 target character set, @sc{ibm1047}, to the host character set,
8367 @sc{ascii}, and they display correctly:
8370 (@value{GDBP}) set target-charset IBM1047
8371 (@value{GDBP}) show charset
8372 The current host character set is `ASCII'.
8373 The current target character set is `IBM1047'.
8374 (@value{GDBP}) print ascii_hello
8375 $6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
8376 (@value{GDBP}) print ascii_hello[0]
8378 (@value{GDBP}) print ibm1047_hello
8379 $8 = 0x4016a8 "Hello, world!\n"
8380 (@value{GDBP}) print ibm1047_hello[0]
8385 As above, @value{GDBN} uses the target character set for character and
8386 string literals you use in expressions:
8389 (@value{GDBP}) print '+'
8394 The @sc{ibm1047} character set uses the number 78 to encode the @samp{+}
8397 @node Caching Remote Data
8398 @section Caching Data of Remote Targets
8399 @cindex caching data of remote targets
8401 @value{GDBN} can cache data exchanged between the debugger and a
8402 remote target (@pxref{Remote Debugging}). Such caching generally improves
8403 performance, because it reduces the overhead of the remote protocol by
8404 bundling memory reads and writes into large chunks. Unfortunately,
8405 @value{GDBN} does not currently know anything about volatile
8406 registers, and thus data caching will produce incorrect results when
8407 volatile registers are in use.
8410 @kindex set remotecache
8411 @item set remotecache on
8412 @itemx set remotecache off
8413 Set caching state for remote targets. When @code{ON}, use data
8414 caching. By default, this option is @code{OFF}.
8416 @kindex show remotecache
8417 @item show remotecache
8418 Show the current state of data caching for remote targets.
8422 Print the information about the data cache performance. The
8423 information displayed includes: the dcache width and depth; and for
8424 each cache line, how many times it was referenced, and its data and
8425 state (invalid, dirty, valid). This command is useful for debugging
8426 the data cache operation.
8429 @node Searching Memory
8430 @section Search Memory
8431 @cindex searching memory
8433 Memory can be searched for a particular sequence of bytes with the
8434 @code{find} command.
8438 @item find @r{[}/@var{sn}@r{]} @var{start_addr}, +@var{len}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
8439 @itemx find @r{[}/@var{sn}@r{]} @var{start_addr}, @var{end_addr}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
8440 Search memory for the sequence of bytes specified by @var{val1}, @var{val2},
8441 etc. The search begins at address @var{start_addr} and continues for either
8442 @var{len} bytes or through to @var{end_addr} inclusive.
8445 @var{s} and @var{n} are optional parameters.
8446 They may be specified in either order, apart or together.
8449 @item @var{s}, search query size
8450 The size of each search query value.
8456 halfwords (two bytes)
8460 giant words (eight bytes)
8463 All values are interpreted in the current language.
8464 This means, for example, that if the current source language is C/C@t{++}
8465 then searching for the string ``hello'' includes the trailing '\0'.
8467 If the value size is not specified, it is taken from the
8468 value's type in the current language.
8469 This is useful when one wants to specify the search
8470 pattern as a mixture of types.
8471 Note that this means, for example, that in the case of C-like languages
8472 a search for an untyped 0x42 will search for @samp{(int) 0x42}
8473 which is typically four bytes.
8475 @item @var{n}, maximum number of finds
8476 The maximum number of matches to print. The default is to print all finds.
8479 You can use strings as search values. Quote them with double-quotes
8481 The string value is copied into the search pattern byte by byte,
8482 regardless of the endianness of the target and the size specification.
8484 The address of each match found is printed as well as a count of the
8485 number of matches found.
8487 The address of the last value found is stored in convenience variable
8489 A count of the number of matches is stored in @samp{$numfound}.
8491 For example, if stopped at the @code{printf} in this function:
8497 static char hello[] = "hello-hello";
8498 static struct @{ char c; short s; int i; @}
8499 __attribute__ ((packed)) mixed
8500 = @{ 'c', 0x1234, 0x87654321 @};
8501 printf ("%s\n", hello);
8506 you get during debugging:
8509 (gdb) find &hello[0], +sizeof(hello), "hello"
8510 0x804956d <hello.1620+6>
8512 (gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o'
8513 0x8049567 <hello.1620>
8514 0x804956d <hello.1620+6>
8516 (gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l'
8517 0x8049567 <hello.1620>
8519 (gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321
8520 0x8049560 <mixed.1625>
8522 (gdb) print $numfound
8525 $2 = (void *) 0x8049560
8528 @node Optimized Code
8529 @chapter Debugging Optimized Code
8530 @cindex optimized code, debugging
8531 @cindex debugging optimized code
8533 Almost all compilers support optimization. With optimization
8534 disabled, the compiler generates assembly code that corresponds
8535 directly to your source code, in a simplistic way. As the compiler
8536 applies more powerful optimizations, the generated assembly code
8537 diverges from your original source code. With help from debugging
8538 information generated by the compiler, @value{GDBN} can map from
8539 the running program back to constructs from your original source.
8541 @value{GDBN} is more accurate with optimization disabled. If you
8542 can recompile without optimization, it is easier to follow the
8543 progress of your program during debugging. But, there are many cases
8544 where you may need to debug an optimized version.
8546 When you debug a program compiled with @samp{-g -O}, remember that the
8547 optimizer has rearranged your code; the debugger shows you what is
8548 really there. Do not be too surprised when the execution path does not
8549 exactly match your source file! An extreme example: if you define a
8550 variable, but never use it, @value{GDBN} never sees that
8551 variable---because the compiler optimizes it out of existence.
8553 Some things do not work as well with @samp{-g -O} as with just
8554 @samp{-g}, particularly on machines with instruction scheduling. If in
8555 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
8556 please report it to us as a bug (including a test case!).
8557 @xref{Variables}, for more information about debugging optimized code.
8560 * Inline Functions:: How @value{GDBN} presents inlining
8563 @node Inline Functions
8564 @section Inline Functions
8565 @cindex inline functions, debugging
8567 @dfn{Inlining} is an optimization that inserts a copy of the function
8568 body directly at each call site, instead of jumping to a shared
8569 routine. @value{GDBN} displays inlined functions just like
8570 non-inlined functions. They appear in backtraces. You can view their
8571 arguments and local variables, step into them with @code{step}, skip
8572 them with @code{next}, and escape from them with @code{finish}.
8573 You can check whether a function was inlined by using the
8574 @code{info frame} command.
8576 For @value{GDBN} to support inlined functions, the compiler must
8577 record information about inlining in the debug information ---
8578 @value{NGCC} using the @sc{dwarf 2} format does this, and several
8579 other compilers do also. @value{GDBN} only supports inlined functions
8580 when using @sc{dwarf 2}. Versions of @value{NGCC} before 4.1
8581 do not emit two required attributes (@samp{DW_AT_call_file} and
8582 @samp{DW_AT_call_line}); @value{GDBN} does not display inlined
8583 function calls with earlier versions of @value{NGCC}. It instead
8584 displays the arguments and local variables of inlined functions as
8585 local variables in the caller.
8587 The body of an inlined function is directly included at its call site;
8588 unlike a non-inlined function, there are no instructions devoted to
8589 the call. @value{GDBN} still pretends that the call site and the
8590 start of the inlined function are different instructions. Stepping to
8591 the call site shows the call site, and then stepping again shows
8592 the first line of the inlined function, even though no additional
8593 instructions are executed.
8595 This makes source-level debugging much clearer; you can see both the
8596 context of the call and then the effect of the call. Only stepping by
8597 a single instruction using @code{stepi} or @code{nexti} does not do
8598 this; single instruction steps always show the inlined body.
8600 There are some ways that @value{GDBN} does not pretend that inlined
8601 function calls are the same as normal calls:
8605 You cannot set breakpoints on inlined functions. @value{GDBN}
8606 either reports that there is no symbol with that name, or else sets the
8607 breakpoint only on non-inlined copies of the function. This limitation
8608 will be removed in a future version of @value{GDBN}; until then,
8609 set a breakpoint by line number on the first line of the inlined
8613 Setting breakpoints at the call site of an inlined function may not
8614 work, because the call site does not contain any code. @value{GDBN}
8615 may incorrectly move the breakpoint to the next line of the enclosing
8616 function, after the call. This limitation will be removed in a future
8617 version of @value{GDBN}; until then, set a breakpoint on an earlier line
8618 or inside the inlined function instead.
8621 @value{GDBN} cannot locate the return value of inlined calls after
8622 using the @code{finish} command. This is a limitation of compiler-generated
8623 debugging information; after @code{finish}, you can step to the next line
8624 and print a variable where your program stored the return value.
8630 @chapter C Preprocessor Macros
8632 Some languages, such as C and C@t{++}, provide a way to define and invoke
8633 ``preprocessor macros'' which expand into strings of tokens.
8634 @value{GDBN} can evaluate expressions containing macro invocations, show
8635 the result of macro expansion, and show a macro's definition, including
8636 where it was defined.
8638 You may need to compile your program specially to provide @value{GDBN}
8639 with information about preprocessor macros. Most compilers do not
8640 include macros in their debugging information, even when you compile
8641 with the @option{-g} flag. @xref{Compilation}.
8643 A program may define a macro at one point, remove that definition later,
8644 and then provide a different definition after that. Thus, at different
8645 points in the program, a macro may have different definitions, or have
8646 no definition at all. If there is a current stack frame, @value{GDBN}
8647 uses the macros in scope at that frame's source code line. Otherwise,
8648 @value{GDBN} uses the macros in scope at the current listing location;
8651 Whenever @value{GDBN} evaluates an expression, it always expands any
8652 macro invocations present in the expression. @value{GDBN} also provides
8653 the following commands for working with macros explicitly.
8657 @kindex macro expand
8658 @cindex macro expansion, showing the results of preprocessor
8659 @cindex preprocessor macro expansion, showing the results of
8660 @cindex expanding preprocessor macros
8661 @item macro expand @var{expression}
8662 @itemx macro exp @var{expression}
8663 Show the results of expanding all preprocessor macro invocations in
8664 @var{expression}. Since @value{GDBN} simply expands macros, but does
8665 not parse the result, @var{expression} need not be a valid expression;
8666 it can be any string of tokens.
8669 @item macro expand-once @var{expression}
8670 @itemx macro exp1 @var{expression}
8671 @cindex expand macro once
8672 @i{(This command is not yet implemented.)} Show the results of
8673 expanding those preprocessor macro invocations that appear explicitly in
8674 @var{expression}. Macro invocations appearing in that expansion are
8675 left unchanged. This command allows you to see the effect of a
8676 particular macro more clearly, without being confused by further
8677 expansions. Since @value{GDBN} simply expands macros, but does not
8678 parse the result, @var{expression} need not be a valid expression; it
8679 can be any string of tokens.
8682 @cindex macro definition, showing
8683 @cindex definition, showing a macro's
8684 @item info macro @var{macro}
8685 Show the definition of the macro named @var{macro}, and describe the
8686 source location or compiler command-line where that definition was established.
8688 @kindex macro define
8689 @cindex user-defined macros
8690 @cindex defining macros interactively
8691 @cindex macros, user-defined
8692 @item macro define @var{macro} @var{replacement-list}
8693 @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list}
8694 Introduce a definition for a preprocessor macro named @var{macro},
8695 invocations of which are replaced by the tokens given in
8696 @var{replacement-list}. The first form of this command defines an
8697 ``object-like'' macro, which takes no arguments; the second form
8698 defines a ``function-like'' macro, which takes the arguments given in
8701 A definition introduced by this command is in scope in every
8702 expression evaluated in @value{GDBN}, until it is removed with the
8703 @code{macro undef} command, described below. The definition overrides
8704 all definitions for @var{macro} present in the program being debugged,
8705 as well as any previous user-supplied definition.
8708 @item macro undef @var{macro}
8709 Remove any user-supplied definition for the macro named @var{macro}.
8710 This command only affects definitions provided with the @code{macro
8711 define} command, described above; it cannot remove definitions present
8712 in the program being debugged.
8716 List all the macros defined using the @code{macro define} command.
8719 @cindex macros, example of debugging with
8720 Here is a transcript showing the above commands in action. First, we
8721 show our source files:
8729 #define ADD(x) (M + x)
8734 printf ("Hello, world!\n");
8736 printf ("We're so creative.\n");
8738 printf ("Goodbye, world!\n");
8745 Now, we compile the program using the @sc{gnu} C compiler, @value{NGCC}.
8746 We pass the @option{-gdwarf-2} and @option{-g3} flags to ensure the
8747 compiler includes information about preprocessor macros in the debugging
8751 $ gcc -gdwarf-2 -g3 sample.c -o sample
8755 Now, we start @value{GDBN} on our sample program:
8759 GNU gdb 2002-05-06-cvs
8760 Copyright 2002 Free Software Foundation, Inc.
8761 GDB is free software, @dots{}
8765 We can expand macros and examine their definitions, even when the
8766 program is not running. @value{GDBN} uses the current listing position
8767 to decide which macro definitions are in scope:
8770 (@value{GDBP}) list main
8773 5 #define ADD(x) (M + x)
8778 10 printf ("Hello, world!\n");
8780 12 printf ("We're so creative.\n");
8781 (@value{GDBP}) info macro ADD
8782 Defined at /home/jimb/gdb/macros/play/sample.c:5
8783 #define ADD(x) (M + x)
8784 (@value{GDBP}) info macro Q
8785 Defined at /home/jimb/gdb/macros/play/sample.h:1
8786 included at /home/jimb/gdb/macros/play/sample.c:2
8788 (@value{GDBP}) macro expand ADD(1)
8789 expands to: (42 + 1)
8790 (@value{GDBP}) macro expand-once ADD(1)
8791 expands to: once (M + 1)
8795 In the example above, note that @code{macro expand-once} expands only
8796 the macro invocation explicit in the original text --- the invocation of
8797 @code{ADD} --- but does not expand the invocation of the macro @code{M},
8798 which was introduced by @code{ADD}.
8800 Once the program is running, @value{GDBN} uses the macro definitions in
8801 force at the source line of the current stack frame:
8804 (@value{GDBP}) break main
8805 Breakpoint 1 at 0x8048370: file sample.c, line 10.
8807 Starting program: /home/jimb/gdb/macros/play/sample
8809 Breakpoint 1, main () at sample.c:10
8810 10 printf ("Hello, world!\n");
8814 At line 10, the definition of the macro @code{N} at line 9 is in force:
8817 (@value{GDBP}) info macro N
8818 Defined at /home/jimb/gdb/macros/play/sample.c:9
8820 (@value{GDBP}) macro expand N Q M
8822 (@value{GDBP}) print N Q M
8827 As we step over directives that remove @code{N}'s definition, and then
8828 give it a new definition, @value{GDBN} finds the definition (or lack
8829 thereof) in force at each point:
8834 12 printf ("We're so creative.\n");
8835 (@value{GDBP}) info macro N
8836 The symbol `N' has no definition as a C/C++ preprocessor macro
8837 at /home/jimb/gdb/macros/play/sample.c:12
8840 14 printf ("Goodbye, world!\n");
8841 (@value{GDBP}) info macro N
8842 Defined at /home/jimb/gdb/macros/play/sample.c:13
8844 (@value{GDBP}) macro expand N Q M
8845 expands to: 1729 < 42
8846 (@value{GDBP}) print N Q M
8851 In addition to source files, macros can be defined on the compilation command
8852 line using the @option{-D@var{name}=@var{value}} syntax. For macros defined in
8853 such a way, @value{GDBN} displays the location of their definition as line zero
8854 of the source file submitted to the compiler.
8857 (@value{GDBP}) info macro __STDC__
8858 Defined at /home/jimb/gdb/macros/play/sample.c:0
8865 @chapter Tracepoints
8866 @c This chapter is based on the documentation written by Michael
8867 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
8870 In some applications, it is not feasible for the debugger to interrupt
8871 the program's execution long enough for the developer to learn
8872 anything helpful about its behavior. If the program's correctness
8873 depends on its real-time behavior, delays introduced by a debugger
8874 might cause the program to change its behavior drastically, or perhaps
8875 fail, even when the code itself is correct. It is useful to be able
8876 to observe the program's behavior without interrupting it.
8878 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
8879 specify locations in the program, called @dfn{tracepoints}, and
8880 arbitrary expressions to evaluate when those tracepoints are reached.
8881 Later, using the @code{tfind} command, you can examine the values
8882 those expressions had when the program hit the tracepoints. The
8883 expressions may also denote objects in memory---structures or arrays,
8884 for example---whose values @value{GDBN} should record; while visiting
8885 a particular tracepoint, you may inspect those objects as if they were
8886 in memory at that moment. However, because @value{GDBN} records these
8887 values without interacting with you, it can do so quickly and
8888 unobtrusively, hopefully not disturbing the program's behavior.
8890 The tracepoint facility is currently available only for remote
8891 targets. @xref{Targets}. In addition, your remote target must know
8892 how to collect trace data. This functionality is implemented in the
8893 remote stub; however, none of the stubs distributed with @value{GDBN}
8894 support tracepoints as of this writing. The format of the remote
8895 packets used to implement tracepoints are described in @ref{Tracepoint
8898 This chapter describes the tracepoint commands and features.
8902 * Analyze Collected Data::
8903 * Tracepoint Variables::
8906 @node Set Tracepoints
8907 @section Commands to Set Tracepoints
8909 Before running such a @dfn{trace experiment}, an arbitrary number of
8910 tracepoints can be set. A tracepoint is actually a special type of
8911 breakpoint (@pxref{Set Breaks}), so you can manipulate it using
8912 standard breakpoint commands. For instance, as with breakpoints,
8913 tracepoint numbers are successive integers starting from one, and many
8914 of the commands associated with tracepoints take the tracepoint number
8915 as their argument, to identify which tracepoint to work on.
8917 For each tracepoint, you can specify, in advance, some arbitrary set
8918 of data that you want the target to collect in the trace buffer when
8919 it hits that tracepoint. The collected data can include registers,
8920 local variables, or global data. Later, you can use @value{GDBN}
8921 commands to examine the values these data had at the time the
8924 Tracepoints do not support every breakpoint feature. Conditional
8925 expressions and ignore counts on tracepoints have no effect, and
8926 tracepoints cannot run @value{GDBN} commands when they are
8927 hit. Tracepoints may not be thread-specific either.
8929 This section describes commands to set tracepoints and associated
8930 conditions and actions.
8933 * Create and Delete Tracepoints::
8934 * Enable and Disable Tracepoints::
8935 * Tracepoint Passcounts::
8936 * Tracepoint Conditions::
8937 * Tracepoint Actions::
8938 * Listing Tracepoints::
8939 * Starting and Stopping Trace Experiments::
8942 @node Create and Delete Tracepoints
8943 @subsection Create and Delete Tracepoints
8946 @cindex set tracepoint
8948 @item trace @var{location}
8949 The @code{trace} command is very similar to the @code{break} command.
8950 Its argument @var{location} can be a source line, a function name, or
8951 an address in the target program. @xref{Specify Location}. The
8952 @code{trace} command defines a tracepoint, which is a point in the
8953 target program where the debugger will briefly stop, collect some
8954 data, and then allow the program to continue. Setting a tracepoint or
8955 changing its actions doesn't take effect until the next @code{tstart}
8956 command, and once a trace experiment is running, further changes will
8957 not have any effect until the next trace experiment starts.
8959 Here are some examples of using the @code{trace} command:
8962 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
8964 (@value{GDBP}) @b{trace +2} // 2 lines forward
8966 (@value{GDBP}) @b{trace my_function} // first source line of function
8968 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
8970 (@value{GDBP}) @b{trace *0x2117c4} // an address
8974 You can abbreviate @code{trace} as @code{tr}.
8976 @item trace @var{location} if @var{cond}
8977 Set a tracepoint with condition @var{cond}; evaluate the expression
8978 @var{cond} each time the tracepoint is reached, and collect data only
8979 if the value is nonzero---that is, if @var{cond} evaluates as true.
8980 @xref{Tracepoint Conditions, ,Tracepoint Conditions}, for more
8981 information on tracepoint conditions.
8984 @cindex last tracepoint number
8985 @cindex recent tracepoint number
8986 @cindex tracepoint number
8987 The convenience variable @code{$tpnum} records the tracepoint number
8988 of the most recently set tracepoint.
8990 @kindex delete tracepoint
8991 @cindex tracepoint deletion
8992 @item delete tracepoint @r{[}@var{num}@r{]}
8993 Permanently delete one or more tracepoints. With no argument, the
8994 default is to delete all tracepoints. Note that the regular
8995 @code{delete} command can remove tracepoints also.
9000 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
9002 (@value{GDBP}) @b{delete trace} // remove all tracepoints
9006 You can abbreviate this command as @code{del tr}.
9009 @node Enable and Disable Tracepoints
9010 @subsection Enable and Disable Tracepoints
9012 These commands are deprecated; they are equivalent to plain @code{disable} and @code{enable}.
9015 @kindex disable tracepoint
9016 @item disable tracepoint @r{[}@var{num}@r{]}
9017 Disable tracepoint @var{num}, or all tracepoints if no argument
9018 @var{num} is given. A disabled tracepoint will have no effect during
9019 the next trace experiment, but it is not forgotten. You can re-enable
9020 a disabled tracepoint using the @code{enable tracepoint} command.
9022 @kindex enable tracepoint
9023 @item enable tracepoint @r{[}@var{num}@r{]}
9024 Enable tracepoint @var{num}, or all tracepoints. The enabled
9025 tracepoints will become effective the next time a trace experiment is
9029 @node Tracepoint Passcounts
9030 @subsection Tracepoint Passcounts
9034 @cindex tracepoint pass count
9035 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
9036 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
9037 automatically stop a trace experiment. If a tracepoint's passcount is
9038 @var{n}, then the trace experiment will be automatically stopped on
9039 the @var{n}'th time that tracepoint is hit. If the tracepoint number
9040 @var{num} is not specified, the @code{passcount} command sets the
9041 passcount of the most recently defined tracepoint. If no passcount is
9042 given, the trace experiment will run until stopped explicitly by the
9048 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
9049 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
9051 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
9052 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
9053 (@value{GDBP}) @b{trace foo}
9054 (@value{GDBP}) @b{pass 3}
9055 (@value{GDBP}) @b{trace bar}
9056 (@value{GDBP}) @b{pass 2}
9057 (@value{GDBP}) @b{trace baz}
9058 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
9059 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
9060 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
9061 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
9065 @node Tracepoint Conditions
9066 @subsection Tracepoint Conditions
9067 @cindex conditional tracepoints
9068 @cindex tracepoint conditions
9070 The simplest sort of tracepoint collects data every time your program
9071 reaches a specified place. You can also specify a @dfn{condition} for
9072 a tracepoint. A condition is just a Boolean expression in your
9073 programming language (@pxref{Expressions, ,Expressions}). A
9074 tracepoint with a condition evaluates the expression each time your
9075 program reaches it, and data collection happens only if the condition
9078 Tracepoint conditions can be specified when a tracepoint is set, by
9079 using @samp{if} in the arguments to the @code{trace} command.
9080 @xref{Create and Delete Tracepoints, ,Setting Tracepoints}. They can
9081 also be set or changed at any time with the @code{condition} command,
9082 just as with breakpoints.
9084 Unlike breakpoint conditions, @value{GDBN} does not actually evaluate
9085 the conditional expression itself. Instead, @value{GDBN} encodes the
9086 expression into an agent expression (@pxref{Agent Expressions}
9087 suitable for execution on the target, independently of @value{GDBN}.
9088 Global variables become raw memory locations, locals become stack
9089 accesses, and so forth.
9091 For instance, suppose you have a function that is usually called
9092 frequently, but should not be called after an error has occurred. You
9093 could use the following tracepoint command to collect data about calls
9094 of that function that happen while the error code is propagating
9095 through the program; an unconditional tracepoint could end up
9096 collecting thousands of useless trace frames that you would have to
9100 (@value{GDBP}) @kbd{trace normal_operation if errcode > 0}
9103 @node Tracepoint Actions
9104 @subsection Tracepoint Action Lists
9108 @cindex tracepoint actions
9109 @item actions @r{[}@var{num}@r{]}
9110 This command will prompt for a list of actions to be taken when the
9111 tracepoint is hit. If the tracepoint number @var{num} is not
9112 specified, this command sets the actions for the one that was most
9113 recently defined (so that you can define a tracepoint and then say
9114 @code{actions} without bothering about its number). You specify the
9115 actions themselves on the following lines, one action at a time, and
9116 terminate the actions list with a line containing just @code{end}. So
9117 far, the only defined actions are @code{collect} and
9118 @code{while-stepping}.
9120 @cindex remove actions from a tracepoint
9121 To remove all actions from a tracepoint, type @samp{actions @var{num}}
9122 and follow it immediately with @samp{end}.
9125 (@value{GDBP}) @b{collect @var{data}} // collect some data
9127 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
9129 (@value{GDBP}) @b{end} // signals the end of actions.
9132 In the following example, the action list begins with @code{collect}
9133 commands indicating the things to be collected when the tracepoint is
9134 hit. Then, in order to single-step and collect additional data
9135 following the tracepoint, a @code{while-stepping} command is used,
9136 followed by the list of things to be collected while stepping. The
9137 @code{while-stepping} command is terminated by its own separate
9138 @code{end} command. Lastly, the action list is terminated by an
9142 (@value{GDBP}) @b{trace foo}
9143 (@value{GDBP}) @b{actions}
9144 Enter actions for tracepoint 1, one per line:
9153 @kindex collect @r{(tracepoints)}
9154 @item collect @var{expr1}, @var{expr2}, @dots{}
9155 Collect values of the given expressions when the tracepoint is hit.
9156 This command accepts a comma-separated list of any valid expressions.
9157 In addition to global, static, or local variables, the following
9158 special arguments are supported:
9162 collect all registers
9165 collect all function arguments
9168 collect all local variables.
9171 You can give several consecutive @code{collect} commands, each one
9172 with a single argument, or one @code{collect} command with several
9173 arguments separated by commas: the effect is the same.
9175 The command @code{info scope} (@pxref{Symbols, info scope}) is
9176 particularly useful for figuring out what data to collect.
9178 @kindex while-stepping @r{(tracepoints)}
9179 @item while-stepping @var{n}
9180 Perform @var{n} single-step traces after the tracepoint, collecting
9181 new data at each step. The @code{while-stepping} command is
9182 followed by the list of what to collect while stepping (followed by
9183 its own @code{end} command):
9187 > collect $regs, myglobal
9193 You may abbreviate @code{while-stepping} as @code{ws} or
9197 @node Listing Tracepoints
9198 @subsection Listing Tracepoints
9201 @kindex info tracepoints
9203 @cindex information about tracepoints
9204 @item info tracepoints @r{[}@var{num}@r{]}
9205 Display information about the tracepoint @var{num}. If you don't
9206 specify a tracepoint number, displays information about all the
9207 tracepoints defined so far. The format is similar to that used for
9208 @code{info breakpoints}; in fact, @code{info tracepoints} is the same
9209 command, simply restricting itself to tracepoints.
9211 A tracepoint's listing may include additional information specific to
9216 its passcount as given by the @code{passcount @var{n}} command
9218 its step count as given by the @code{while-stepping @var{n}} command
9220 its action list as given by the @code{actions} command. The actions
9221 are prefixed with an @samp{A} so as to distinguish them from commands.
9225 (@value{GDBP}) @b{info trace}
9226 Num Type Disp Enb Address What
9227 1 tracepoint keep y 0x0804ab57 in foo() at main.cxx:7
9231 A collect globfoo, $regs
9239 This command can be abbreviated @code{info tp}.
9242 @node Starting and Stopping Trace Experiments
9243 @subsection Starting and Stopping Trace Experiments
9247 @cindex start a new trace experiment
9248 @cindex collected data discarded
9250 This command takes no arguments. It starts the trace experiment, and
9251 begins collecting data. This has the side effect of discarding all
9252 the data collected in the trace buffer during the previous trace
9256 @cindex stop a running trace experiment
9258 This command takes no arguments. It ends the trace experiment, and
9259 stops collecting data.
9261 @strong{Note}: a trace experiment and data collection may stop
9262 automatically if any tracepoint's passcount is reached
9263 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
9266 @cindex status of trace data collection
9267 @cindex trace experiment, status of
9269 This command displays the status of the current trace data
9273 Here is an example of the commands we described so far:
9276 (@value{GDBP}) @b{trace gdb_c_test}
9277 (@value{GDBP}) @b{actions}
9278 Enter actions for tracepoint #1, one per line.
9279 > collect $regs,$locals,$args
9284 (@value{GDBP}) @b{tstart}
9285 [time passes @dots{}]
9286 (@value{GDBP}) @b{tstop}
9290 @node Analyze Collected Data
9291 @section Using the Collected Data
9293 After the tracepoint experiment ends, you use @value{GDBN} commands
9294 for examining the trace data. The basic idea is that each tracepoint
9295 collects a trace @dfn{snapshot} every time it is hit and another
9296 snapshot every time it single-steps. All these snapshots are
9297 consecutively numbered from zero and go into a buffer, and you can
9298 examine them later. The way you examine them is to @dfn{focus} on a
9299 specific trace snapshot. When the remote stub is focused on a trace
9300 snapshot, it will respond to all @value{GDBN} requests for memory and
9301 registers by reading from the buffer which belongs to that snapshot,
9302 rather than from @emph{real} memory or registers of the program being
9303 debugged. This means that @strong{all} @value{GDBN} commands
9304 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
9305 behave as if we were currently debugging the program state as it was
9306 when the tracepoint occurred. Any requests for data that are not in
9307 the buffer will fail.
9310 * tfind:: How to select a trace snapshot
9311 * tdump:: How to display all data for a snapshot
9312 * save-tracepoints:: How to save tracepoints for a future run
9316 @subsection @code{tfind @var{n}}
9319 @cindex select trace snapshot
9320 @cindex find trace snapshot
9321 The basic command for selecting a trace snapshot from the buffer is
9322 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
9323 counting from zero. If no argument @var{n} is given, the next
9324 snapshot is selected.
9326 Here are the various forms of using the @code{tfind} command.
9330 Find the first snapshot in the buffer. This is a synonym for
9331 @code{tfind 0} (since 0 is the number of the first snapshot).
9334 Stop debugging trace snapshots, resume @emph{live} debugging.
9337 Same as @samp{tfind none}.
9340 No argument means find the next trace snapshot.
9343 Find the previous trace snapshot before the current one. This permits
9344 retracing earlier steps.
9346 @item tfind tracepoint @var{num}
9347 Find the next snapshot associated with tracepoint @var{num}. Search
9348 proceeds forward from the last examined trace snapshot. If no
9349 argument @var{num} is given, it means find the next snapshot collected
9350 for the same tracepoint as the current snapshot.
9352 @item tfind pc @var{addr}
9353 Find the next snapshot associated with the value @var{addr} of the
9354 program counter. Search proceeds forward from the last examined trace
9355 snapshot. If no argument @var{addr} is given, it means find the next
9356 snapshot with the same value of PC as the current snapshot.
9358 @item tfind outside @var{addr1}, @var{addr2}
9359 Find the next snapshot whose PC is outside the given range of
9362 @item tfind range @var{addr1}, @var{addr2}
9363 Find the next snapshot whose PC is between @var{addr1} and
9364 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
9366 @item tfind line @r{[}@var{file}:@r{]}@var{n}
9367 Find the next snapshot associated with the source line @var{n}. If
9368 the optional argument @var{file} is given, refer to line @var{n} in
9369 that source file. Search proceeds forward from the last examined
9370 trace snapshot. If no argument @var{n} is given, it means find the
9371 next line other than the one currently being examined; thus saying
9372 @code{tfind line} repeatedly can appear to have the same effect as
9373 stepping from line to line in a @emph{live} debugging session.
9376 The default arguments for the @code{tfind} commands are specifically
9377 designed to make it easy to scan through the trace buffer. For
9378 instance, @code{tfind} with no argument selects the next trace
9379 snapshot, and @code{tfind -} with no argument selects the previous
9380 trace snapshot. So, by giving one @code{tfind} command, and then
9381 simply hitting @key{RET} repeatedly you can examine all the trace
9382 snapshots in order. Or, by saying @code{tfind -} and then hitting
9383 @key{RET} repeatedly you can examine the snapshots in reverse order.
9384 The @code{tfind line} command with no argument selects the snapshot
9385 for the next source line executed. The @code{tfind pc} command with
9386 no argument selects the next snapshot with the same program counter
9387 (PC) as the current frame. The @code{tfind tracepoint} command with
9388 no argument selects the next trace snapshot collected by the same
9389 tracepoint as the current one.
9391 In addition to letting you scan through the trace buffer manually,
9392 these commands make it easy to construct @value{GDBN} scripts that
9393 scan through the trace buffer and print out whatever collected data
9394 you are interested in. Thus, if we want to examine the PC, FP, and SP
9395 registers from each trace frame in the buffer, we can say this:
9398 (@value{GDBP}) @b{tfind start}
9399 (@value{GDBP}) @b{while ($trace_frame != -1)}
9400 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
9401 $trace_frame, $pc, $sp, $fp
9405 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
9406 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
9407 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
9408 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
9409 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
9410 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
9411 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
9412 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
9413 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
9414 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
9415 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
9418 Or, if we want to examine the variable @code{X} at each source line in
9422 (@value{GDBP}) @b{tfind start}
9423 (@value{GDBP}) @b{while ($trace_frame != -1)}
9424 > printf "Frame %d, X == %d\n", $trace_frame, X
9434 @subsection @code{tdump}
9436 @cindex dump all data collected at tracepoint
9437 @cindex tracepoint data, display
9439 This command takes no arguments. It prints all the data collected at
9440 the current trace snapshot.
9443 (@value{GDBP}) @b{trace 444}
9444 (@value{GDBP}) @b{actions}
9445 Enter actions for tracepoint #2, one per line:
9446 > collect $regs, $locals, $args, gdb_long_test
9449 (@value{GDBP}) @b{tstart}
9451 (@value{GDBP}) @b{tfind line 444}
9452 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
9454 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
9456 (@value{GDBP}) @b{tdump}
9457 Data collected at tracepoint 2, trace frame 1:
9458 d0 0xc4aa0085 -995491707
9462 d4 0x71aea3d 119204413
9467 a1 0x3000668 50333288
9470 a4 0x3000698 50333336
9472 fp 0x30bf3c 0x30bf3c
9473 sp 0x30bf34 0x30bf34
9475 pc 0x20b2c8 0x20b2c8
9479 p = 0x20e5b4 "gdb-test"
9486 gdb_long_test = 17 '\021'
9491 @node save-tracepoints
9492 @subsection @code{save-tracepoints @var{filename}}
9493 @kindex save-tracepoints
9494 @cindex save tracepoints for future sessions
9496 This command saves all current tracepoint definitions together with
9497 their actions and passcounts, into a file @file{@var{filename}}
9498 suitable for use in a later debugging session. To read the saved
9499 tracepoint definitions, use the @code{source} command (@pxref{Command
9502 @node Tracepoint Variables
9503 @section Convenience Variables for Tracepoints
9504 @cindex tracepoint variables
9505 @cindex convenience variables for tracepoints
9508 @vindex $trace_frame
9509 @item (int) $trace_frame
9510 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
9511 snapshot is selected.
9514 @item (int) $tracepoint
9515 The tracepoint for the current trace snapshot.
9518 @item (int) $trace_line
9519 The line number for the current trace snapshot.
9522 @item (char []) $trace_file
9523 The source file for the current trace snapshot.
9526 @item (char []) $trace_func
9527 The name of the function containing @code{$tracepoint}.
9530 Note: @code{$trace_file} is not suitable for use in @code{printf},
9531 use @code{output} instead.
9533 Here's a simple example of using these convenience variables for
9534 stepping through all the trace snapshots and printing some of their
9538 (@value{GDBP}) @b{tfind start}
9540 (@value{GDBP}) @b{while $trace_frame != -1}
9541 > output $trace_file
9542 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
9548 @chapter Debugging Programs That Use Overlays
9551 If your program is too large to fit completely in your target system's
9552 memory, you can sometimes use @dfn{overlays} to work around this
9553 problem. @value{GDBN} provides some support for debugging programs that
9557 * How Overlays Work:: A general explanation of overlays.
9558 * Overlay Commands:: Managing overlays in @value{GDBN}.
9559 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
9560 mapped by asking the inferior.
9561 * Overlay Sample Program:: A sample program using overlays.
9564 @node How Overlays Work
9565 @section How Overlays Work
9566 @cindex mapped overlays
9567 @cindex unmapped overlays
9568 @cindex load address, overlay's
9569 @cindex mapped address
9570 @cindex overlay area
9572 Suppose you have a computer whose instruction address space is only 64
9573 kilobytes long, but which has much more memory which can be accessed by
9574 other means: special instructions, segment registers, or memory
9575 management hardware, for example. Suppose further that you want to
9576 adapt a program which is larger than 64 kilobytes to run on this system.
9578 One solution is to identify modules of your program which are relatively
9579 independent, and need not call each other directly; call these modules
9580 @dfn{overlays}. Separate the overlays from the main program, and place
9581 their machine code in the larger memory. Place your main program in
9582 instruction memory, but leave at least enough space there to hold the
9583 largest overlay as well.
9585 Now, to call a function located in an overlay, you must first copy that
9586 overlay's machine code from the large memory into the space set aside
9587 for it in the instruction memory, and then jump to its entry point
9590 @c NB: In the below the mapped area's size is greater or equal to the
9591 @c size of all overlays. This is intentional to remind the developer
9592 @c that overlays don't necessarily need to be the same size.
9596 Data Instruction Larger
9597 Address Space Address Space Address Space
9598 +-----------+ +-----------+ +-----------+
9600 +-----------+ +-----------+ +-----------+<-- overlay 1
9601 | program | | main | .----| overlay 1 | load address
9602 | variables | | program | | +-----------+
9603 | and heap | | | | | |
9604 +-----------+ | | | +-----------+<-- overlay 2
9605 | | +-----------+ | | | load address
9606 +-----------+ | | | .-| overlay 2 |
9608 mapped --->+-----------+ | | +-----------+
9610 | overlay | <-' | | |
9611 | area | <---' +-----------+<-- overlay 3
9612 | | <---. | | load address
9613 +-----------+ `--| overlay 3 |
9620 @anchor{A code overlay}A code overlay
9624 The diagram (@pxref{A code overlay}) shows a system with separate data
9625 and instruction address spaces. To map an overlay, the program copies
9626 its code from the larger address space to the instruction address space.
9627 Since the overlays shown here all use the same mapped address, only one
9628 may be mapped at a time. For a system with a single address space for
9629 data and instructions, the diagram would be similar, except that the
9630 program variables and heap would share an address space with the main
9631 program and the overlay area.
9633 An overlay loaded into instruction memory and ready for use is called a
9634 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
9635 instruction memory. An overlay not present (or only partially present)
9636 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
9637 is its address in the larger memory. The mapped address is also called
9638 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
9639 called the @dfn{load memory address}, or @dfn{LMA}.
9641 Unfortunately, overlays are not a completely transparent way to adapt a
9642 program to limited instruction memory. They introduce a new set of
9643 global constraints you must keep in mind as you design your program:
9648 Before calling or returning to a function in an overlay, your program
9649 must make sure that overlay is actually mapped. Otherwise, the call or
9650 return will transfer control to the right address, but in the wrong
9651 overlay, and your program will probably crash.
9654 If the process of mapping an overlay is expensive on your system, you
9655 will need to choose your overlays carefully to minimize their effect on
9656 your program's performance.
9659 The executable file you load onto your system must contain each
9660 overlay's instructions, appearing at the overlay's load address, not its
9661 mapped address. However, each overlay's instructions must be relocated
9662 and its symbols defined as if the overlay were at its mapped address.
9663 You can use GNU linker scripts to specify different load and relocation
9664 addresses for pieces of your program; see @ref{Overlay Description,,,
9665 ld.info, Using ld: the GNU linker}.
9668 The procedure for loading executable files onto your system must be able
9669 to load their contents into the larger address space as well as the
9670 instruction and data spaces.
9674 The overlay system described above is rather simple, and could be
9675 improved in many ways:
9680 If your system has suitable bank switch registers or memory management
9681 hardware, you could use those facilities to make an overlay's load area
9682 contents simply appear at their mapped address in instruction space.
9683 This would probably be faster than copying the overlay to its mapped
9684 area in the usual way.
9687 If your overlays are small enough, you could set aside more than one
9688 overlay area, and have more than one overlay mapped at a time.
9691 You can use overlays to manage data, as well as instructions. In
9692 general, data overlays are even less transparent to your design than
9693 code overlays: whereas code overlays only require care when you call or
9694 return to functions, data overlays require care every time you access
9695 the data. Also, if you change the contents of a data overlay, you
9696 must copy its contents back out to its load address before you can copy a
9697 different data overlay into the same mapped area.
9702 @node Overlay Commands
9703 @section Overlay Commands
9705 To use @value{GDBN}'s overlay support, each overlay in your program must
9706 correspond to a separate section of the executable file. The section's
9707 virtual memory address and load memory address must be the overlay's
9708 mapped and load addresses. Identifying overlays with sections allows
9709 @value{GDBN} to determine the appropriate address of a function or
9710 variable, depending on whether the overlay is mapped or not.
9712 @value{GDBN}'s overlay commands all start with the word @code{overlay};
9713 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
9718 Disable @value{GDBN}'s overlay support. When overlay support is
9719 disabled, @value{GDBN} assumes that all functions and variables are
9720 always present at their mapped addresses. By default, @value{GDBN}'s
9721 overlay support is disabled.
9723 @item overlay manual
9724 @cindex manual overlay debugging
9725 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
9726 relies on you to tell it which overlays are mapped, and which are not,
9727 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
9728 commands described below.
9730 @item overlay map-overlay @var{overlay}
9731 @itemx overlay map @var{overlay}
9732 @cindex map an overlay
9733 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
9734 be the name of the object file section containing the overlay. When an
9735 overlay is mapped, @value{GDBN} assumes it can find the overlay's
9736 functions and variables at their mapped addresses. @value{GDBN} assumes
9737 that any other overlays whose mapped ranges overlap that of
9738 @var{overlay} are now unmapped.
9740 @item overlay unmap-overlay @var{overlay}
9741 @itemx overlay unmap @var{overlay}
9742 @cindex unmap an overlay
9743 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
9744 must be the name of the object file section containing the overlay.
9745 When an overlay is unmapped, @value{GDBN} assumes it can find the
9746 overlay's functions and variables at their load addresses.
9749 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
9750 consults a data structure the overlay manager maintains in the inferior
9751 to see which overlays are mapped. For details, see @ref{Automatic
9754 @item overlay load-target
9756 @cindex reloading the overlay table
9757 Re-read the overlay table from the inferior. Normally, @value{GDBN}
9758 re-reads the table @value{GDBN} automatically each time the inferior
9759 stops, so this command should only be necessary if you have changed the
9760 overlay mapping yourself using @value{GDBN}. This command is only
9761 useful when using automatic overlay debugging.
9763 @item overlay list-overlays
9765 @cindex listing mapped overlays
9766 Display a list of the overlays currently mapped, along with their mapped
9767 addresses, load addresses, and sizes.
9771 Normally, when @value{GDBN} prints a code address, it includes the name
9772 of the function the address falls in:
9775 (@value{GDBP}) print main
9776 $3 = @{int ()@} 0x11a0 <main>
9779 When overlay debugging is enabled, @value{GDBN} recognizes code in
9780 unmapped overlays, and prints the names of unmapped functions with
9781 asterisks around them. For example, if @code{foo} is a function in an
9782 unmapped overlay, @value{GDBN} prints it this way:
9785 (@value{GDBP}) overlay list
9786 No sections are mapped.
9787 (@value{GDBP}) print foo
9788 $5 = @{int (int)@} 0x100000 <*foo*>
9791 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
9795 (@value{GDBP}) overlay list
9796 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
9797 mapped at 0x1016 - 0x104a
9798 (@value{GDBP}) print foo
9799 $6 = @{int (int)@} 0x1016 <foo>
9802 When overlay debugging is enabled, @value{GDBN} can find the correct
9803 address for functions and variables in an overlay, whether or not the
9804 overlay is mapped. This allows most @value{GDBN} commands, like
9805 @code{break} and @code{disassemble}, to work normally, even on unmapped
9806 code. However, @value{GDBN}'s breakpoint support has some limitations:
9810 @cindex breakpoints in overlays
9811 @cindex overlays, setting breakpoints in
9812 You can set breakpoints in functions in unmapped overlays, as long as
9813 @value{GDBN} can write to the overlay at its load address.
9815 @value{GDBN} can not set hardware or simulator-based breakpoints in
9816 unmapped overlays. However, if you set a breakpoint at the end of your
9817 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
9818 you are using manual overlay management), @value{GDBN} will re-set its
9819 breakpoints properly.
9823 @node Automatic Overlay Debugging
9824 @section Automatic Overlay Debugging
9825 @cindex automatic overlay debugging
9827 @value{GDBN} can automatically track which overlays are mapped and which
9828 are not, given some simple co-operation from the overlay manager in the
9829 inferior. If you enable automatic overlay debugging with the
9830 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
9831 looks in the inferior's memory for certain variables describing the
9832 current state of the overlays.
9834 Here are the variables your overlay manager must define to support
9835 @value{GDBN}'s automatic overlay debugging:
9839 @item @code{_ovly_table}:
9840 This variable must be an array of the following structures:
9845 /* The overlay's mapped address. */
9848 /* The size of the overlay, in bytes. */
9851 /* The overlay's load address. */
9854 /* Non-zero if the overlay is currently mapped;
9856 unsigned long mapped;
9860 @item @code{_novlys}:
9861 This variable must be a four-byte signed integer, holding the total
9862 number of elements in @code{_ovly_table}.
9866 To decide whether a particular overlay is mapped or not, @value{GDBN}
9867 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
9868 @code{lma} members equal the VMA and LMA of the overlay's section in the
9869 executable file. When @value{GDBN} finds a matching entry, it consults
9870 the entry's @code{mapped} member to determine whether the overlay is
9873 In addition, your overlay manager may define a function called
9874 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
9875 will silently set a breakpoint there. If the overlay manager then
9876 calls this function whenever it has changed the overlay table, this
9877 will enable @value{GDBN} to accurately keep track of which overlays
9878 are in program memory, and update any breakpoints that may be set
9879 in overlays. This will allow breakpoints to work even if the
9880 overlays are kept in ROM or other non-writable memory while they
9881 are not being executed.
9883 @node Overlay Sample Program
9884 @section Overlay Sample Program
9885 @cindex overlay example program
9887 When linking a program which uses overlays, you must place the overlays
9888 at their load addresses, while relocating them to run at their mapped
9889 addresses. To do this, you must write a linker script (@pxref{Overlay
9890 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
9891 since linker scripts are specific to a particular host system, target
9892 architecture, and target memory layout, this manual cannot provide
9893 portable sample code demonstrating @value{GDBN}'s overlay support.
9895 However, the @value{GDBN} source distribution does contain an overlaid
9896 program, with linker scripts for a few systems, as part of its test
9897 suite. The program consists of the following files from
9898 @file{gdb/testsuite/gdb.base}:
9902 The main program file.
9904 A simple overlay manager, used by @file{overlays.c}.
9909 Overlay modules, loaded and used by @file{overlays.c}.
9912 Linker scripts for linking the test program on the @code{d10v-elf}
9913 and @code{m32r-elf} targets.
9916 You can build the test program using the @code{d10v-elf} GCC
9917 cross-compiler like this:
9920 $ d10v-elf-gcc -g -c overlays.c
9921 $ d10v-elf-gcc -g -c ovlymgr.c
9922 $ d10v-elf-gcc -g -c foo.c
9923 $ d10v-elf-gcc -g -c bar.c
9924 $ d10v-elf-gcc -g -c baz.c
9925 $ d10v-elf-gcc -g -c grbx.c
9926 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
9927 baz.o grbx.o -Wl,-Td10v.ld -o overlays
9930 The build process is identical for any other architecture, except that
9931 you must substitute the appropriate compiler and linker script for the
9932 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
9936 @chapter Using @value{GDBN} with Different Languages
9939 Although programming languages generally have common aspects, they are
9940 rarely expressed in the same manner. For instance, in ANSI C,
9941 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
9942 Modula-2, it is accomplished by @code{p^}. Values can also be
9943 represented (and displayed) differently. Hex numbers in C appear as
9944 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
9946 @cindex working language
9947 Language-specific information is built into @value{GDBN} for some languages,
9948 allowing you to express operations like the above in your program's
9949 native language, and allowing @value{GDBN} to output values in a manner
9950 consistent with the syntax of your program's native language. The
9951 language you use to build expressions is called the @dfn{working
9955 * Setting:: Switching between source languages
9956 * Show:: Displaying the language
9957 * Checks:: Type and range checks
9958 * Supported Languages:: Supported languages
9959 * Unsupported Languages:: Unsupported languages
9963 @section Switching Between Source Languages
9965 There are two ways to control the working language---either have @value{GDBN}
9966 set it automatically, or select it manually yourself. You can use the
9967 @code{set language} command for either purpose. On startup, @value{GDBN}
9968 defaults to setting the language automatically. The working language is
9969 used to determine how expressions you type are interpreted, how values
9972 In addition to the working language, every source file that
9973 @value{GDBN} knows about has its own working language. For some object
9974 file formats, the compiler might indicate which language a particular
9975 source file is in. However, most of the time @value{GDBN} infers the
9976 language from the name of the file. The language of a source file
9977 controls whether C@t{++} names are demangled---this way @code{backtrace} can
9978 show each frame appropriately for its own language. There is no way to
9979 set the language of a source file from within @value{GDBN}, but you can
9980 set the language associated with a filename extension. @xref{Show, ,
9981 Displaying the Language}.
9983 This is most commonly a problem when you use a program, such
9984 as @code{cfront} or @code{f2c}, that generates C but is written in
9985 another language. In that case, make the
9986 program use @code{#line} directives in its C output; that way
9987 @value{GDBN} will know the correct language of the source code of the original
9988 program, and will display that source code, not the generated C code.
9991 * Filenames:: Filename extensions and languages.
9992 * Manually:: Setting the working language manually
9993 * Automatically:: Having @value{GDBN} infer the source language
9997 @subsection List of Filename Extensions and Languages
9999 If a source file name ends in one of the following extensions, then
10000 @value{GDBN} infers that its language is the one indicated.
10018 C@t{++} source file
10021 Objective-C source file
10025 Fortran source file
10028 Modula-2 source file
10032 Assembler source file. This actually behaves almost like C, but
10033 @value{GDBN} does not skip over function prologues when stepping.
10036 In addition, you may set the language associated with a filename
10037 extension. @xref{Show, , Displaying the Language}.
10040 @subsection Setting the Working Language
10042 If you allow @value{GDBN} to set the language automatically,
10043 expressions are interpreted the same way in your debugging session and
10046 @kindex set language
10047 If you wish, you may set the language manually. To do this, issue the
10048 command @samp{set language @var{lang}}, where @var{lang} is the name of
10049 a language, such as
10050 @code{c} or @code{modula-2}.
10051 For a list of the supported languages, type @samp{set language}.
10053 Setting the language manually prevents @value{GDBN} from updating the working
10054 language automatically. This can lead to confusion if you try
10055 to debug a program when the working language is not the same as the
10056 source language, when an expression is acceptable to both
10057 languages---but means different things. For instance, if the current
10058 source file were written in C, and @value{GDBN} was parsing Modula-2, a
10066 might not have the effect you intended. In C, this means to add
10067 @code{b} and @code{c} and place the result in @code{a}. The result
10068 printed would be the value of @code{a}. In Modula-2, this means to compare
10069 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
10071 @node Automatically
10072 @subsection Having @value{GDBN} Infer the Source Language
10074 To have @value{GDBN} set the working language automatically, use
10075 @samp{set language local} or @samp{set language auto}. @value{GDBN}
10076 then infers the working language. That is, when your program stops in a
10077 frame (usually by encountering a breakpoint), @value{GDBN} sets the
10078 working language to the language recorded for the function in that
10079 frame. If the language for a frame is unknown (that is, if the function
10080 or block corresponding to the frame was defined in a source file that
10081 does not have a recognized extension), the current working language is
10082 not changed, and @value{GDBN} issues a warning.
10084 This may not seem necessary for most programs, which are written
10085 entirely in one source language. However, program modules and libraries
10086 written in one source language can be used by a main program written in
10087 a different source language. Using @samp{set language auto} in this
10088 case frees you from having to set the working language manually.
10091 @section Displaying the Language
10093 The following commands help you find out which language is the
10094 working language, and also what language source files were written in.
10097 @item show language
10098 @kindex show language
10099 Display the current working language. This is the
10100 language you can use with commands such as @code{print} to
10101 build and compute expressions that may involve variables in your program.
10104 @kindex info frame@r{, show the source language}
10105 Display the source language for this frame. This language becomes the
10106 working language if you use an identifier from this frame.
10107 @xref{Frame Info, ,Information about a Frame}, to identify the other
10108 information listed here.
10111 @kindex info source@r{, show the source language}
10112 Display the source language of this source file.
10113 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
10114 information listed here.
10117 In unusual circumstances, you may have source files with extensions
10118 not in the standard list. You can then set the extension associated
10119 with a language explicitly:
10122 @item set extension-language @var{ext} @var{language}
10123 @kindex set extension-language
10124 Tell @value{GDBN} that source files with extension @var{ext} are to be
10125 assumed as written in the source language @var{language}.
10127 @item info extensions
10128 @kindex info extensions
10129 List all the filename extensions and the associated languages.
10133 @section Type and Range Checking
10136 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
10137 checking are included, but they do not yet have any effect. This
10138 section documents the intended facilities.
10140 @c FIXME remove warning when type/range code added
10142 Some languages are designed to guard you against making seemingly common
10143 errors through a series of compile- and run-time checks. These include
10144 checking the type of arguments to functions and operators, and making
10145 sure mathematical overflows are caught at run time. Checks such as
10146 these help to ensure a program's correctness once it has been compiled
10147 by eliminating type mismatches, and providing active checks for range
10148 errors when your program is running.
10150 @value{GDBN} can check for conditions like the above if you wish.
10151 Although @value{GDBN} does not check the statements in your program,
10152 it can check expressions entered directly into @value{GDBN} for
10153 evaluation via the @code{print} command, for example. As with the
10154 working language, @value{GDBN} can also decide whether or not to check
10155 automatically based on your program's source language.
10156 @xref{Supported Languages, ,Supported Languages}, for the default
10157 settings of supported languages.
10160 * Type Checking:: An overview of type checking
10161 * Range Checking:: An overview of range checking
10164 @cindex type checking
10165 @cindex checks, type
10166 @node Type Checking
10167 @subsection An Overview of Type Checking
10169 Some languages, such as Modula-2, are strongly typed, meaning that the
10170 arguments to operators and functions have to be of the correct type,
10171 otherwise an error occurs. These checks prevent type mismatch
10172 errors from ever causing any run-time problems. For example,
10180 The second example fails because the @code{CARDINAL} 1 is not
10181 type-compatible with the @code{REAL} 2.3.
10183 For the expressions you use in @value{GDBN} commands, you can tell the
10184 @value{GDBN} type checker to skip checking;
10185 to treat any mismatches as errors and abandon the expression;
10186 or to only issue warnings when type mismatches occur,
10187 but evaluate the expression anyway. When you choose the last of
10188 these, @value{GDBN} evaluates expressions like the second example above, but
10189 also issues a warning.
10191 Even if you turn type checking off, there may be other reasons
10192 related to type that prevent @value{GDBN} from evaluating an expression.
10193 For instance, @value{GDBN} does not know how to add an @code{int} and
10194 a @code{struct foo}. These particular type errors have nothing to do
10195 with the language in use, and usually arise from expressions, such as
10196 the one described above, which make little sense to evaluate anyway.
10198 Each language defines to what degree it is strict about type. For
10199 instance, both Modula-2 and C require the arguments to arithmetical
10200 operators to be numbers. In C, enumerated types and pointers can be
10201 represented as numbers, so that they are valid arguments to mathematical
10202 operators. @xref{Supported Languages, ,Supported Languages}, for further
10203 details on specific languages.
10205 @value{GDBN} provides some additional commands for controlling the type checker:
10207 @kindex set check type
10208 @kindex show check type
10210 @item set check type auto
10211 Set type checking on or off based on the current working language.
10212 @xref{Supported Languages, ,Supported Languages}, for the default settings for
10215 @item set check type on
10216 @itemx set check type off
10217 Set type checking on or off, overriding the default setting for the
10218 current working language. Issue a warning if the setting does not
10219 match the language default. If any type mismatches occur in
10220 evaluating an expression while type checking is on, @value{GDBN} prints a
10221 message and aborts evaluation of the expression.
10223 @item set check type warn
10224 Cause the type checker to issue warnings, but to always attempt to
10225 evaluate the expression. Evaluating the expression may still
10226 be impossible for other reasons. For example, @value{GDBN} cannot add
10227 numbers and structures.
10230 Show the current setting of the type checker, and whether or not @value{GDBN}
10231 is setting it automatically.
10234 @cindex range checking
10235 @cindex checks, range
10236 @node Range Checking
10237 @subsection An Overview of Range Checking
10239 In some languages (such as Modula-2), it is an error to exceed the
10240 bounds of a type; this is enforced with run-time checks. Such range
10241 checking is meant to ensure program correctness by making sure
10242 computations do not overflow, or indices on an array element access do
10243 not exceed the bounds of the array.
10245 For expressions you use in @value{GDBN} commands, you can tell
10246 @value{GDBN} to treat range errors in one of three ways: ignore them,
10247 always treat them as errors and abandon the expression, or issue
10248 warnings but evaluate the expression anyway.
10250 A range error can result from numerical overflow, from exceeding an
10251 array index bound, or when you type a constant that is not a member
10252 of any type. Some languages, however, do not treat overflows as an
10253 error. In many implementations of C, mathematical overflow causes the
10254 result to ``wrap around'' to lower values---for example, if @var{m} is
10255 the largest integer value, and @var{s} is the smallest, then
10258 @var{m} + 1 @result{} @var{s}
10261 This, too, is specific to individual languages, and in some cases
10262 specific to individual compilers or machines. @xref{Supported Languages, ,
10263 Supported Languages}, for further details on specific languages.
10265 @value{GDBN} provides some additional commands for controlling the range checker:
10267 @kindex set check range
10268 @kindex show check range
10270 @item set check range auto
10271 Set range checking on or off based on the current working language.
10272 @xref{Supported Languages, ,Supported Languages}, for the default settings for
10275 @item set check range on
10276 @itemx set check range off
10277 Set range checking on or off, overriding the default setting for the
10278 current working language. A warning is issued if the setting does not
10279 match the language default. If a range error occurs and range checking is on,
10280 then a message is printed and evaluation of the expression is aborted.
10282 @item set check range warn
10283 Output messages when the @value{GDBN} range checker detects a range error,
10284 but attempt to evaluate the expression anyway. Evaluating the
10285 expression may still be impossible for other reasons, such as accessing
10286 memory that the process does not own (a typical example from many Unix
10290 Show the current setting of the range checker, and whether or not it is
10291 being set automatically by @value{GDBN}.
10294 @node Supported Languages
10295 @section Supported Languages
10297 @value{GDBN} supports C, C@t{++}, Objective-C, Fortran, Java, Pascal,
10298 assembly, Modula-2, and Ada.
10299 @c This is false ...
10300 Some @value{GDBN} features may be used in expressions regardless of the
10301 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
10302 and the @samp{@{type@}addr} construct (@pxref{Expressions,
10303 ,Expressions}) can be used with the constructs of any supported
10306 The following sections detail to what degree each source language is
10307 supported by @value{GDBN}. These sections are not meant to be language
10308 tutorials or references, but serve only as a reference guide to what the
10309 @value{GDBN} expression parser accepts, and what input and output
10310 formats should look like for different languages. There are many good
10311 books written on each of these languages; please look to these for a
10312 language reference or tutorial.
10315 * C:: C and C@t{++}
10316 * Objective-C:: Objective-C
10317 * Fortran:: Fortran
10319 * Modula-2:: Modula-2
10324 @subsection C and C@t{++}
10326 @cindex C and C@t{++}
10327 @cindex expressions in C or C@t{++}
10329 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
10330 to both languages. Whenever this is the case, we discuss those languages
10334 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
10335 @cindex @sc{gnu} C@t{++}
10336 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
10337 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
10338 effectively, you must compile your C@t{++} programs with a supported
10339 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
10340 compiler (@code{aCC}).
10342 For best results when using @sc{gnu} C@t{++}, use the DWARF 2 debugging
10343 format; if it doesn't work on your system, try the stabs+ debugging
10344 format. You can select those formats explicitly with the @code{g++}
10345 command-line options @option{-gdwarf-2} and @option{-gstabs+}.
10346 @xref{Debugging Options,,Options for Debugging Your Program or GCC,
10347 gcc.info, Using the @sc{gnu} Compiler Collection (GCC)}.
10350 * C Operators:: C and C@t{++} operators
10351 * C Constants:: C and C@t{++} constants
10352 * C Plus Plus Expressions:: C@t{++} expressions
10353 * C Defaults:: Default settings for C and C@t{++}
10354 * C Checks:: C and C@t{++} type and range checks
10355 * Debugging C:: @value{GDBN} and C
10356 * Debugging C Plus Plus:: @value{GDBN} features for C@t{++}
10357 * Decimal Floating Point:: Numbers in Decimal Floating Point format
10361 @subsubsection C and C@t{++} Operators
10363 @cindex C and C@t{++} operators
10365 Operators must be defined on values of specific types. For instance,
10366 @code{+} is defined on numbers, but not on structures. Operators are
10367 often defined on groups of types.
10369 For the purposes of C and C@t{++}, the following definitions hold:
10374 @emph{Integral types} include @code{int} with any of its storage-class
10375 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
10378 @emph{Floating-point types} include @code{float}, @code{double}, and
10379 @code{long double} (if supported by the target platform).
10382 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
10385 @emph{Scalar types} include all of the above.
10390 The following operators are supported. They are listed here
10391 in order of increasing precedence:
10395 The comma or sequencing operator. Expressions in a comma-separated list
10396 are evaluated from left to right, with the result of the entire
10397 expression being the last expression evaluated.
10400 Assignment. The value of an assignment expression is the value
10401 assigned. Defined on scalar types.
10404 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
10405 and translated to @w{@code{@var{a} = @var{a op b}}}.
10406 @w{@code{@var{op}=}} and @code{=} have the same precedence.
10407 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
10408 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
10411 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
10412 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
10416 Logical @sc{or}. Defined on integral types.
10419 Logical @sc{and}. Defined on integral types.
10422 Bitwise @sc{or}. Defined on integral types.
10425 Bitwise exclusive-@sc{or}. Defined on integral types.
10428 Bitwise @sc{and}. Defined on integral types.
10431 Equality and inequality. Defined on scalar types. The value of these
10432 expressions is 0 for false and non-zero for true.
10434 @item <@r{, }>@r{, }<=@r{, }>=
10435 Less than, greater than, less than or equal, greater than or equal.
10436 Defined on scalar types. The value of these expressions is 0 for false
10437 and non-zero for true.
10440 left shift, and right shift. Defined on integral types.
10443 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
10446 Addition and subtraction. Defined on integral types, floating-point types and
10449 @item *@r{, }/@r{, }%
10450 Multiplication, division, and modulus. Multiplication and division are
10451 defined on integral and floating-point types. Modulus is defined on
10455 Increment and decrement. When appearing before a variable, the
10456 operation is performed before the variable is used in an expression;
10457 when appearing after it, the variable's value is used before the
10458 operation takes place.
10461 Pointer dereferencing. Defined on pointer types. Same precedence as
10465 Address operator. Defined on variables. Same precedence as @code{++}.
10467 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
10468 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
10469 to examine the address
10470 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
10474 Negative. Defined on integral and floating-point types. Same
10475 precedence as @code{++}.
10478 Logical negation. Defined on integral types. Same precedence as
10482 Bitwise complement operator. Defined on integral types. Same precedence as
10487 Structure member, and pointer-to-structure member. For convenience,
10488 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
10489 pointer based on the stored type information.
10490 Defined on @code{struct} and @code{union} data.
10493 Dereferences of pointers to members.
10496 Array indexing. @code{@var{a}[@var{i}]} is defined as
10497 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
10500 Function parameter list. Same precedence as @code{->}.
10503 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
10504 and @code{class} types.
10507 Doubled colons also represent the @value{GDBN} scope operator
10508 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
10512 If an operator is redefined in the user code, @value{GDBN} usually
10513 attempts to invoke the redefined version instead of using the operator's
10514 predefined meaning.
10517 @subsubsection C and C@t{++} Constants
10519 @cindex C and C@t{++} constants
10521 @value{GDBN} allows you to express the constants of C and C@t{++} in the
10526 Integer constants are a sequence of digits. Octal constants are
10527 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
10528 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
10529 @samp{l}, specifying that the constant should be treated as a
10533 Floating point constants are a sequence of digits, followed by a decimal
10534 point, followed by a sequence of digits, and optionally followed by an
10535 exponent. An exponent is of the form:
10536 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
10537 sequence of digits. The @samp{+} is optional for positive exponents.
10538 A floating-point constant may also end with a letter @samp{f} or
10539 @samp{F}, specifying that the constant should be treated as being of
10540 the @code{float} (as opposed to the default @code{double}) type; or with
10541 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
10545 Enumerated constants consist of enumerated identifiers, or their
10546 integral equivalents.
10549 Character constants are a single character surrounded by single quotes
10550 (@code{'}), or a number---the ordinal value of the corresponding character
10551 (usually its @sc{ascii} value). Within quotes, the single character may
10552 be represented by a letter or by @dfn{escape sequences}, which are of
10553 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
10554 of the character's ordinal value; or of the form @samp{\@var{x}}, where
10555 @samp{@var{x}} is a predefined special character---for example,
10556 @samp{\n} for newline.
10559 String constants are a sequence of character constants surrounded by
10560 double quotes (@code{"}). Any valid character constant (as described
10561 above) may appear. Double quotes within the string must be preceded by
10562 a backslash, so for instance @samp{"a\"b'c"} is a string of five
10566 Pointer constants are an integral value. You can also write pointers
10567 to constants using the C operator @samp{&}.
10570 Array constants are comma-separated lists surrounded by braces @samp{@{}
10571 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
10572 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
10573 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
10576 @node C Plus Plus Expressions
10577 @subsubsection C@t{++} Expressions
10579 @cindex expressions in C@t{++}
10580 @value{GDBN} expression handling can interpret most C@t{++} expressions.
10582 @cindex debugging C@t{++} programs
10583 @cindex C@t{++} compilers
10584 @cindex debug formats and C@t{++}
10585 @cindex @value{NGCC} and C@t{++}
10587 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
10588 proper compiler and the proper debug format. Currently, @value{GDBN}
10589 works best when debugging C@t{++} code that is compiled with
10590 @value{NGCC} 2.95.3 or with @value{NGCC} 3.1 or newer, using the options
10591 @option{-gdwarf-2} or @option{-gstabs+}. DWARF 2 is preferred over
10592 stabs+. Most configurations of @value{NGCC} emit either DWARF 2 or
10593 stabs+ as their default debug format, so you usually don't need to
10594 specify a debug format explicitly. Other compilers and/or debug formats
10595 are likely to work badly or not at all when using @value{GDBN} to debug
10601 @cindex member functions
10603 Member function calls are allowed; you can use expressions like
10606 count = aml->GetOriginal(x, y)
10609 @vindex this@r{, inside C@t{++} member functions}
10610 @cindex namespace in C@t{++}
10612 While a member function is active (in the selected stack frame), your
10613 expressions have the same namespace available as the member function;
10614 that is, @value{GDBN} allows implicit references to the class instance
10615 pointer @code{this} following the same rules as C@t{++}.
10617 @cindex call overloaded functions
10618 @cindex overloaded functions, calling
10619 @cindex type conversions in C@t{++}
10621 You can call overloaded functions; @value{GDBN} resolves the function
10622 call to the right definition, with some restrictions. @value{GDBN} does not
10623 perform overload resolution involving user-defined type conversions,
10624 calls to constructors, or instantiations of templates that do not exist
10625 in the program. It also cannot handle ellipsis argument lists or
10628 It does perform integral conversions and promotions, floating-point
10629 promotions, arithmetic conversions, pointer conversions, conversions of
10630 class objects to base classes, and standard conversions such as those of
10631 functions or arrays to pointers; it requires an exact match on the
10632 number of function arguments.
10634 Overload resolution is always performed, unless you have specified
10635 @code{set overload-resolution off}. @xref{Debugging C Plus Plus,
10636 ,@value{GDBN} Features for C@t{++}}.
10638 You must specify @code{set overload-resolution off} in order to use an
10639 explicit function signature to call an overloaded function, as in
10641 p 'foo(char,int)'('x', 13)
10644 The @value{GDBN} command-completion facility can simplify this;
10645 see @ref{Completion, ,Command Completion}.
10647 @cindex reference declarations
10649 @value{GDBN} understands variables declared as C@t{++} references; you can use
10650 them in expressions just as you do in C@t{++} source---they are automatically
10653 In the parameter list shown when @value{GDBN} displays a frame, the values of
10654 reference variables are not displayed (unlike other variables); this
10655 avoids clutter, since references are often used for large structures.
10656 The @emph{address} of a reference variable is always shown, unless
10657 you have specified @samp{set print address off}.
10660 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
10661 expressions can use it just as expressions in your program do. Since
10662 one scope may be defined in another, you can use @code{::} repeatedly if
10663 necessary, for example in an expression like
10664 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
10665 resolving name scope by reference to source files, in both C and C@t{++}
10666 debugging (@pxref{Variables, ,Program Variables}).
10669 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
10670 calling virtual functions correctly, printing out virtual bases of
10671 objects, calling functions in a base subobject, casting objects, and
10672 invoking user-defined operators.
10675 @subsubsection C and C@t{++} Defaults
10677 @cindex C and C@t{++} defaults
10679 If you allow @value{GDBN} to set type and range checking automatically, they
10680 both default to @code{off} whenever the working language changes to
10681 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
10682 selects the working language.
10684 If you allow @value{GDBN} to set the language automatically, it
10685 recognizes source files whose names end with @file{.c}, @file{.C}, or
10686 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
10687 these files, it sets the working language to C or C@t{++}.
10688 @xref{Automatically, ,Having @value{GDBN} Infer the Source Language},
10689 for further details.
10691 @c Type checking is (a) primarily motivated by Modula-2, and (b)
10692 @c unimplemented. If (b) changes, it might make sense to let this node
10693 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
10696 @subsubsection C and C@t{++} Type and Range Checks
10698 @cindex C and C@t{++} checks
10700 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
10701 is not used. However, if you turn type checking on, @value{GDBN}
10702 considers two variables type equivalent if:
10706 The two variables are structured and have the same structure, union, or
10710 The two variables have the same type name, or types that have been
10711 declared equivalent through @code{typedef}.
10714 @c leaving this out because neither J Gilmore nor R Pesch understand it.
10717 The two @code{struct}, @code{union}, or @code{enum} variables are
10718 declared in the same declaration. (Note: this may not be true for all C
10723 Range checking, if turned on, is done on mathematical operations. Array
10724 indices are not checked, since they are often used to index a pointer
10725 that is not itself an array.
10728 @subsubsection @value{GDBN} and C
10730 The @code{set print union} and @code{show print union} commands apply to
10731 the @code{union} type. When set to @samp{on}, any @code{union} that is
10732 inside a @code{struct} or @code{class} is also printed. Otherwise, it
10733 appears as @samp{@{...@}}.
10735 The @code{@@} operator aids in the debugging of dynamic arrays, formed
10736 with pointers and a memory allocation function. @xref{Expressions,
10739 @node Debugging C Plus Plus
10740 @subsubsection @value{GDBN} Features for C@t{++}
10742 @cindex commands for C@t{++}
10744 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
10745 designed specifically for use with C@t{++}. Here is a summary:
10748 @cindex break in overloaded functions
10749 @item @r{breakpoint menus}
10750 When you want a breakpoint in a function whose name is overloaded,
10751 @value{GDBN} has the capability to display a menu of possible breakpoint
10752 locations to help you specify which function definition you want.
10753 @xref{Ambiguous Expressions,,Ambiguous Expressions}.
10755 @cindex overloading in C@t{++}
10756 @item rbreak @var{regex}
10757 Setting breakpoints using regular expressions is helpful for setting
10758 breakpoints on overloaded functions that are not members of any special
10760 @xref{Set Breaks, ,Setting Breakpoints}.
10762 @cindex C@t{++} exception handling
10765 Debug C@t{++} exception handling using these commands. @xref{Set
10766 Catchpoints, , Setting Catchpoints}.
10768 @cindex inheritance
10769 @item ptype @var{typename}
10770 Print inheritance relationships as well as other information for type
10772 @xref{Symbols, ,Examining the Symbol Table}.
10774 @cindex C@t{++} symbol display
10775 @item set print demangle
10776 @itemx show print demangle
10777 @itemx set print asm-demangle
10778 @itemx show print asm-demangle
10779 Control whether C@t{++} symbols display in their source form, both when
10780 displaying code as C@t{++} source and when displaying disassemblies.
10781 @xref{Print Settings, ,Print Settings}.
10783 @item set print object
10784 @itemx show print object
10785 Choose whether to print derived (actual) or declared types of objects.
10786 @xref{Print Settings, ,Print Settings}.
10788 @item set print vtbl
10789 @itemx show print vtbl
10790 Control the format for printing virtual function tables.
10791 @xref{Print Settings, ,Print Settings}.
10792 (The @code{vtbl} commands do not work on programs compiled with the HP
10793 ANSI C@t{++} compiler (@code{aCC}).)
10795 @kindex set overload-resolution
10796 @cindex overloaded functions, overload resolution
10797 @item set overload-resolution on
10798 Enable overload resolution for C@t{++} expression evaluation. The default
10799 is on. For overloaded functions, @value{GDBN} evaluates the arguments
10800 and searches for a function whose signature matches the argument types,
10801 using the standard C@t{++} conversion rules (see @ref{C Plus Plus
10802 Expressions, ,C@t{++} Expressions}, for details).
10803 If it cannot find a match, it emits a message.
10805 @item set overload-resolution off
10806 Disable overload resolution for C@t{++} expression evaluation. For
10807 overloaded functions that are not class member functions, @value{GDBN}
10808 chooses the first function of the specified name that it finds in the
10809 symbol table, whether or not its arguments are of the correct type. For
10810 overloaded functions that are class member functions, @value{GDBN}
10811 searches for a function whose signature @emph{exactly} matches the
10814 @kindex show overload-resolution
10815 @item show overload-resolution
10816 Show the current setting of overload resolution.
10818 @item @r{Overloaded symbol names}
10819 You can specify a particular definition of an overloaded symbol, using
10820 the same notation that is used to declare such symbols in C@t{++}: type
10821 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
10822 also use the @value{GDBN} command-line word completion facilities to list the
10823 available choices, or to finish the type list for you.
10824 @xref{Completion,, Command Completion}, for details on how to do this.
10827 @node Decimal Floating Point
10828 @subsubsection Decimal Floating Point format
10829 @cindex decimal floating point format
10831 @value{GDBN} can examine, set and perform computations with numbers in
10832 decimal floating point format, which in the C language correspond to the
10833 @code{_Decimal32}, @code{_Decimal64} and @code{_Decimal128} types as
10834 specified by the extension to support decimal floating-point arithmetic.
10836 There are two encodings in use, depending on the architecture: BID (Binary
10837 Integer Decimal) for x86 and x86-64, and DPD (Densely Packed Decimal) for
10838 PowerPC. @value{GDBN} will use the appropriate encoding for the configured
10841 Because of a limitation in @file{libdecnumber}, the library used by @value{GDBN}
10842 to manipulate decimal floating point numbers, it is not possible to convert
10843 (using a cast, for example) integers wider than 32-bit to decimal float.
10845 In addition, in order to imitate @value{GDBN}'s behaviour with binary floating
10846 point computations, error checking in decimal float operations ignores
10847 underflow, overflow and divide by zero exceptions.
10849 In the PowerPC architecture, @value{GDBN} provides a set of pseudo-registers
10850 to inspect @code{_Decimal128} values stored in floating point registers.
10851 See @ref{PowerPC,,PowerPC} for more details.
10854 @subsection Objective-C
10856 @cindex Objective-C
10857 This section provides information about some commands and command
10858 options that are useful for debugging Objective-C code. See also
10859 @ref{Symbols, info classes}, and @ref{Symbols, info selectors}, for a
10860 few more commands specific to Objective-C support.
10863 * Method Names in Commands::
10864 * The Print Command with Objective-C::
10867 @node Method Names in Commands
10868 @subsubsection Method Names in Commands
10870 The following commands have been extended to accept Objective-C method
10871 names as line specifications:
10873 @kindex clear@r{, and Objective-C}
10874 @kindex break@r{, and Objective-C}
10875 @kindex info line@r{, and Objective-C}
10876 @kindex jump@r{, and Objective-C}
10877 @kindex list@r{, and Objective-C}
10881 @item @code{info line}
10886 A fully qualified Objective-C method name is specified as
10889 -[@var{Class} @var{methodName}]
10892 where the minus sign is used to indicate an instance method and a
10893 plus sign (not shown) is used to indicate a class method. The class
10894 name @var{Class} and method name @var{methodName} are enclosed in
10895 brackets, similar to the way messages are specified in Objective-C
10896 source code. For example, to set a breakpoint at the @code{create}
10897 instance method of class @code{Fruit} in the program currently being
10901 break -[Fruit create]
10904 To list ten program lines around the @code{initialize} class method,
10908 list +[NSText initialize]
10911 In the current version of @value{GDBN}, the plus or minus sign is
10912 required. In future versions of @value{GDBN}, the plus or minus
10913 sign will be optional, but you can use it to narrow the search. It
10914 is also possible to specify just a method name:
10920 You must specify the complete method name, including any colons. If
10921 your program's source files contain more than one @code{create} method,
10922 you'll be presented with a numbered list of classes that implement that
10923 method. Indicate your choice by number, or type @samp{0} to exit if
10926 As another example, to clear a breakpoint established at the
10927 @code{makeKeyAndOrderFront:} method of the @code{NSWindow} class, enter:
10930 clear -[NSWindow makeKeyAndOrderFront:]
10933 @node The Print Command with Objective-C
10934 @subsubsection The Print Command With Objective-C
10935 @cindex Objective-C, print objects
10936 @kindex print-object
10937 @kindex po @r{(@code{print-object})}
10939 The print command has also been extended to accept methods. For example:
10942 print -[@var{object} hash]
10945 @cindex print an Objective-C object description
10946 @cindex @code{_NSPrintForDebugger}, and printing Objective-C objects
10948 will tell @value{GDBN} to send the @code{hash} message to @var{object}
10949 and print the result. Also, an additional command has been added,
10950 @code{print-object} or @code{po} for short, which is meant to print
10951 the description of an object. However, this command may only work
10952 with certain Objective-C libraries that have a particular hook
10953 function, @code{_NSPrintForDebugger}, defined.
10956 @subsection Fortran
10957 @cindex Fortran-specific support in @value{GDBN}
10959 @value{GDBN} can be used to debug programs written in Fortran, but it
10960 currently supports only the features of Fortran 77 language.
10962 @cindex trailing underscore, in Fortran symbols
10963 Some Fortran compilers (@sc{gnu} Fortran 77 and Fortran 95 compilers
10964 among them) append an underscore to the names of variables and
10965 functions. When you debug programs compiled by those compilers, you
10966 will need to refer to variables and functions with a trailing
10970 * Fortran Operators:: Fortran operators and expressions
10971 * Fortran Defaults:: Default settings for Fortran
10972 * Special Fortran Commands:: Special @value{GDBN} commands for Fortran
10975 @node Fortran Operators
10976 @subsubsection Fortran Operators and Expressions
10978 @cindex Fortran operators and expressions
10980 Operators must be defined on values of specific types. For instance,
10981 @code{+} is defined on numbers, but not on characters or other non-
10982 arithmetic types. Operators are often defined on groups of types.
10986 The exponentiation operator. It raises the first operand to the power
10990 The range operator. Normally used in the form of array(low:high) to
10991 represent a section of array.
10994 The access component operator. Normally used to access elements in derived
10995 types. Also suitable for unions. As unions aren't part of regular Fortran,
10996 this can only happen when accessing a register that uses a gdbarch-defined
11000 @node Fortran Defaults
11001 @subsubsection Fortran Defaults
11003 @cindex Fortran Defaults
11005 Fortran symbols are usually case-insensitive, so @value{GDBN} by
11006 default uses case-insensitive matches for Fortran symbols. You can
11007 change that with the @samp{set case-insensitive} command, see
11008 @ref{Symbols}, for the details.
11010 @node Special Fortran Commands
11011 @subsubsection Special Fortran Commands
11013 @cindex Special Fortran commands
11015 @value{GDBN} has some commands to support Fortran-specific features,
11016 such as displaying common blocks.
11019 @cindex @code{COMMON} blocks, Fortran
11020 @kindex info common
11021 @item info common @r{[}@var{common-name}@r{]}
11022 This command prints the values contained in the Fortran @code{COMMON}
11023 block whose name is @var{common-name}. With no argument, the names of
11024 all @code{COMMON} blocks visible at the current program location are
11031 @cindex Pascal support in @value{GDBN}, limitations
11032 Debugging Pascal programs which use sets, subranges, file variables, or
11033 nested functions does not currently work. @value{GDBN} does not support
11034 entering expressions, printing values, or similar features using Pascal
11037 The Pascal-specific command @code{set print pascal_static-members}
11038 controls whether static members of Pascal objects are displayed.
11039 @xref{Print Settings, pascal_static-members}.
11042 @subsection Modula-2
11044 @cindex Modula-2, @value{GDBN} support
11046 The extensions made to @value{GDBN} to support Modula-2 only support
11047 output from the @sc{gnu} Modula-2 compiler (which is currently being
11048 developed). Other Modula-2 compilers are not currently supported, and
11049 attempting to debug executables produced by them is most likely
11050 to give an error as @value{GDBN} reads in the executable's symbol
11053 @cindex expressions in Modula-2
11055 * M2 Operators:: Built-in operators
11056 * Built-In Func/Proc:: Built-in functions and procedures
11057 * M2 Constants:: Modula-2 constants
11058 * M2 Types:: Modula-2 types
11059 * M2 Defaults:: Default settings for Modula-2
11060 * Deviations:: Deviations from standard Modula-2
11061 * M2 Checks:: Modula-2 type and range checks
11062 * M2 Scope:: The scope operators @code{::} and @code{.}
11063 * GDB/M2:: @value{GDBN} and Modula-2
11067 @subsubsection Operators
11068 @cindex Modula-2 operators
11070 Operators must be defined on values of specific types. For instance,
11071 @code{+} is defined on numbers, but not on structures. Operators are
11072 often defined on groups of types. For the purposes of Modula-2, the
11073 following definitions hold:
11078 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
11082 @emph{Character types} consist of @code{CHAR} and its subranges.
11085 @emph{Floating-point types} consist of @code{REAL}.
11088 @emph{Pointer types} consist of anything declared as @code{POINTER TO
11092 @emph{Scalar types} consist of all of the above.
11095 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
11098 @emph{Boolean types} consist of @code{BOOLEAN}.
11102 The following operators are supported, and appear in order of
11103 increasing precedence:
11107 Function argument or array index separator.
11110 Assignment. The value of @var{var} @code{:=} @var{value} is
11114 Less than, greater than on integral, floating-point, or enumerated
11118 Less than or equal to, greater than or equal to
11119 on integral, floating-point and enumerated types, or set inclusion on
11120 set types. Same precedence as @code{<}.
11122 @item =@r{, }<>@r{, }#
11123 Equality and two ways of expressing inequality, valid on scalar types.
11124 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
11125 available for inequality, since @code{#} conflicts with the script
11129 Set membership. Defined on set types and the types of their members.
11130 Same precedence as @code{<}.
11133 Boolean disjunction. Defined on boolean types.
11136 Boolean conjunction. Defined on boolean types.
11139 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
11142 Addition and subtraction on integral and floating-point types, or union
11143 and difference on set types.
11146 Multiplication on integral and floating-point types, or set intersection
11150 Division on floating-point types, or symmetric set difference on set
11151 types. Same precedence as @code{*}.
11154 Integer division and remainder. Defined on integral types. Same
11155 precedence as @code{*}.
11158 Negative. Defined on @code{INTEGER} and @code{REAL} data.
11161 Pointer dereferencing. Defined on pointer types.
11164 Boolean negation. Defined on boolean types. Same precedence as
11168 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
11169 precedence as @code{^}.
11172 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
11175 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
11179 @value{GDBN} and Modula-2 scope operators.
11183 @emph{Warning:} Set expressions and their operations are not yet supported, so @value{GDBN}
11184 treats the use of the operator @code{IN}, or the use of operators
11185 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
11186 @code{<=}, and @code{>=} on sets as an error.
11190 @node Built-In Func/Proc
11191 @subsubsection Built-in Functions and Procedures
11192 @cindex Modula-2 built-ins
11194 Modula-2 also makes available several built-in procedures and functions.
11195 In describing these, the following metavariables are used:
11200 represents an @code{ARRAY} variable.
11203 represents a @code{CHAR} constant or variable.
11206 represents a variable or constant of integral type.
11209 represents an identifier that belongs to a set. Generally used in the
11210 same function with the metavariable @var{s}. The type of @var{s} should
11211 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
11214 represents a variable or constant of integral or floating-point type.
11217 represents a variable or constant of floating-point type.
11223 represents a variable.
11226 represents a variable or constant of one of many types. See the
11227 explanation of the function for details.
11230 All Modula-2 built-in procedures also return a result, described below.
11234 Returns the absolute value of @var{n}.
11237 If @var{c} is a lower case letter, it returns its upper case
11238 equivalent, otherwise it returns its argument.
11241 Returns the character whose ordinal value is @var{i}.
11244 Decrements the value in the variable @var{v} by one. Returns the new value.
11246 @item DEC(@var{v},@var{i})
11247 Decrements the value in the variable @var{v} by @var{i}. Returns the
11250 @item EXCL(@var{m},@var{s})
11251 Removes the element @var{m} from the set @var{s}. Returns the new
11254 @item FLOAT(@var{i})
11255 Returns the floating point equivalent of the integer @var{i}.
11257 @item HIGH(@var{a})
11258 Returns the index of the last member of @var{a}.
11261 Increments the value in the variable @var{v} by one. Returns the new value.
11263 @item INC(@var{v},@var{i})
11264 Increments the value in the variable @var{v} by @var{i}. Returns the
11267 @item INCL(@var{m},@var{s})
11268 Adds the element @var{m} to the set @var{s} if it is not already
11269 there. Returns the new set.
11272 Returns the maximum value of the type @var{t}.
11275 Returns the minimum value of the type @var{t}.
11278 Returns boolean TRUE if @var{i} is an odd number.
11281 Returns the ordinal value of its argument. For example, the ordinal
11282 value of a character is its @sc{ascii} value (on machines supporting the
11283 @sc{ascii} character set). @var{x} must be of an ordered type, which include
11284 integral, character and enumerated types.
11286 @item SIZE(@var{x})
11287 Returns the size of its argument. @var{x} can be a variable or a type.
11289 @item TRUNC(@var{r})
11290 Returns the integral part of @var{r}.
11292 @item TSIZE(@var{x})
11293 Returns the size of its argument. @var{x} can be a variable or a type.
11295 @item VAL(@var{t},@var{i})
11296 Returns the member of the type @var{t} whose ordinal value is @var{i}.
11300 @emph{Warning:} Sets and their operations are not yet supported, so
11301 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
11305 @cindex Modula-2 constants
11307 @subsubsection Constants
11309 @value{GDBN} allows you to express the constants of Modula-2 in the following
11315 Integer constants are simply a sequence of digits. When used in an
11316 expression, a constant is interpreted to be type-compatible with the
11317 rest of the expression. Hexadecimal integers are specified by a
11318 trailing @samp{H}, and octal integers by a trailing @samp{B}.
11321 Floating point constants appear as a sequence of digits, followed by a
11322 decimal point and another sequence of digits. An optional exponent can
11323 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
11324 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
11325 digits of the floating point constant must be valid decimal (base 10)
11329 Character constants consist of a single character enclosed by a pair of
11330 like quotes, either single (@code{'}) or double (@code{"}). They may
11331 also be expressed by their ordinal value (their @sc{ascii} value, usually)
11332 followed by a @samp{C}.
11335 String constants consist of a sequence of characters enclosed by a
11336 pair of like quotes, either single (@code{'}) or double (@code{"}).
11337 Escape sequences in the style of C are also allowed. @xref{C
11338 Constants, ,C and C@t{++} Constants}, for a brief explanation of escape
11342 Enumerated constants consist of an enumerated identifier.
11345 Boolean constants consist of the identifiers @code{TRUE} and
11349 Pointer constants consist of integral values only.
11352 Set constants are not yet supported.
11356 @subsubsection Modula-2 Types
11357 @cindex Modula-2 types
11359 Currently @value{GDBN} can print the following data types in Modula-2
11360 syntax: array types, record types, set types, pointer types, procedure
11361 types, enumerated types, subrange types and base types. You can also
11362 print the contents of variables declared using these type.
11363 This section gives a number of simple source code examples together with
11364 sample @value{GDBN} sessions.
11366 The first example contains the following section of code:
11375 and you can request @value{GDBN} to interrogate the type and value of
11376 @code{r} and @code{s}.
11379 (@value{GDBP}) print s
11381 (@value{GDBP}) ptype s
11383 (@value{GDBP}) print r
11385 (@value{GDBP}) ptype r
11390 Likewise if your source code declares @code{s} as:
11394 s: SET ['A'..'Z'] ;
11398 then you may query the type of @code{s} by:
11401 (@value{GDBP}) ptype s
11402 type = SET ['A'..'Z']
11406 Note that at present you cannot interactively manipulate set
11407 expressions using the debugger.
11409 The following example shows how you might declare an array in Modula-2
11410 and how you can interact with @value{GDBN} to print its type and contents:
11414 s: ARRAY [-10..10] OF CHAR ;
11418 (@value{GDBP}) ptype s
11419 ARRAY [-10..10] OF CHAR
11422 Note that the array handling is not yet complete and although the type
11423 is printed correctly, expression handling still assumes that all
11424 arrays have a lower bound of zero and not @code{-10} as in the example
11427 Here are some more type related Modula-2 examples:
11431 colour = (blue, red, yellow, green) ;
11432 t = [blue..yellow] ;
11440 The @value{GDBN} interaction shows how you can query the data type
11441 and value of a variable.
11444 (@value{GDBP}) print s
11446 (@value{GDBP}) ptype t
11447 type = [blue..yellow]
11451 In this example a Modula-2 array is declared and its contents
11452 displayed. Observe that the contents are written in the same way as
11453 their @code{C} counterparts.
11457 s: ARRAY [1..5] OF CARDINAL ;
11463 (@value{GDBP}) print s
11464 $1 = @{1, 0, 0, 0, 0@}
11465 (@value{GDBP}) ptype s
11466 type = ARRAY [1..5] OF CARDINAL
11469 The Modula-2 language interface to @value{GDBN} also understands
11470 pointer types as shown in this example:
11474 s: POINTER TO ARRAY [1..5] OF CARDINAL ;
11481 and you can request that @value{GDBN} describes the type of @code{s}.
11484 (@value{GDBP}) ptype s
11485 type = POINTER TO ARRAY [1..5] OF CARDINAL
11488 @value{GDBN} handles compound types as we can see in this example.
11489 Here we combine array types, record types, pointer types and subrange
11500 myarray = ARRAY myrange OF CARDINAL ;
11501 myrange = [-2..2] ;
11503 s: POINTER TO ARRAY myrange OF foo ;
11507 and you can ask @value{GDBN} to describe the type of @code{s} as shown
11511 (@value{GDBP}) ptype s
11512 type = POINTER TO ARRAY [-2..2] OF foo = RECORD
11515 f3 : ARRAY [-2..2] OF CARDINAL;
11520 @subsubsection Modula-2 Defaults
11521 @cindex Modula-2 defaults
11523 If type and range checking are set automatically by @value{GDBN}, they
11524 both default to @code{on} whenever the working language changes to
11525 Modula-2. This happens regardless of whether you or @value{GDBN}
11526 selected the working language.
11528 If you allow @value{GDBN} to set the language automatically, then entering
11529 code compiled from a file whose name ends with @file{.mod} sets the
11530 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN}
11531 Infer the Source Language}, for further details.
11534 @subsubsection Deviations from Standard Modula-2
11535 @cindex Modula-2, deviations from
11537 A few changes have been made to make Modula-2 programs easier to debug.
11538 This is done primarily via loosening its type strictness:
11542 Unlike in standard Modula-2, pointer constants can be formed by
11543 integers. This allows you to modify pointer variables during
11544 debugging. (In standard Modula-2, the actual address contained in a
11545 pointer variable is hidden from you; it can only be modified
11546 through direct assignment to another pointer variable or expression that
11547 returned a pointer.)
11550 C escape sequences can be used in strings and characters to represent
11551 non-printable characters. @value{GDBN} prints out strings with these
11552 escape sequences embedded. Single non-printable characters are
11553 printed using the @samp{CHR(@var{nnn})} format.
11556 The assignment operator (@code{:=}) returns the value of its right-hand
11560 All built-in procedures both modify @emph{and} return their argument.
11564 @subsubsection Modula-2 Type and Range Checks
11565 @cindex Modula-2 checks
11568 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
11571 @c FIXME remove warning when type/range checks added
11573 @value{GDBN} considers two Modula-2 variables type equivalent if:
11577 They are of types that have been declared equivalent via a @code{TYPE
11578 @var{t1} = @var{t2}} statement
11581 They have been declared on the same line. (Note: This is true of the
11582 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
11585 As long as type checking is enabled, any attempt to combine variables
11586 whose types are not equivalent is an error.
11588 Range checking is done on all mathematical operations, assignment, array
11589 index bounds, and all built-in functions and procedures.
11592 @subsubsection The Scope Operators @code{::} and @code{.}
11594 @cindex @code{.}, Modula-2 scope operator
11595 @cindex colon, doubled as scope operator
11597 @vindex colon-colon@r{, in Modula-2}
11598 @c Info cannot handle :: but TeX can.
11601 @vindex ::@r{, in Modula-2}
11604 There are a few subtle differences between the Modula-2 scope operator
11605 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
11610 @var{module} . @var{id}
11611 @var{scope} :: @var{id}
11615 where @var{scope} is the name of a module or a procedure,
11616 @var{module} the name of a module, and @var{id} is any declared
11617 identifier within your program, except another module.
11619 Using the @code{::} operator makes @value{GDBN} search the scope
11620 specified by @var{scope} for the identifier @var{id}. If it is not
11621 found in the specified scope, then @value{GDBN} searches all scopes
11622 enclosing the one specified by @var{scope}.
11624 Using the @code{.} operator makes @value{GDBN} search the current scope for
11625 the identifier specified by @var{id} that was imported from the
11626 definition module specified by @var{module}. With this operator, it is
11627 an error if the identifier @var{id} was not imported from definition
11628 module @var{module}, or if @var{id} is not an identifier in
11632 @subsubsection @value{GDBN} and Modula-2
11634 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
11635 Five subcommands of @code{set print} and @code{show print} apply
11636 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
11637 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
11638 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
11639 analogue in Modula-2.
11641 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
11642 with any language, is not useful with Modula-2. Its
11643 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
11644 created in Modula-2 as they can in C or C@t{++}. However, because an
11645 address can be specified by an integral constant, the construct
11646 @samp{@{@var{type}@}@var{adrexp}} is still useful.
11648 @cindex @code{#} in Modula-2
11649 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
11650 interpreted as the beginning of a comment. Use @code{<>} instead.
11656 The extensions made to @value{GDBN} for Ada only support
11657 output from the @sc{gnu} Ada (GNAT) compiler.
11658 Other Ada compilers are not currently supported, and
11659 attempting to debug executables produced by them is most likely
11663 @cindex expressions in Ada
11665 * Ada Mode Intro:: General remarks on the Ada syntax
11666 and semantics supported by Ada mode
11668 * Omissions from Ada:: Restrictions on the Ada expression syntax.
11669 * Additions to Ada:: Extensions of the Ada expression syntax.
11670 * Stopping Before Main Program:: Debugging the program during elaboration.
11671 * Ada Tasks:: Listing and setting breakpoints in tasks.
11672 * Ada Tasks and Core Files:: Tasking Support when Debugging Core Files
11673 * Ada Glitches:: Known peculiarities of Ada mode.
11676 @node Ada Mode Intro
11677 @subsubsection Introduction
11678 @cindex Ada mode, general
11680 The Ada mode of @value{GDBN} supports a fairly large subset of Ada expression
11681 syntax, with some extensions.
11682 The philosophy behind the design of this subset is
11686 That @value{GDBN} should provide basic literals and access to operations for
11687 arithmetic, dereferencing, field selection, indexing, and subprogram calls,
11688 leaving more sophisticated computations to subprograms written into the
11689 program (which therefore may be called from @value{GDBN}).
11692 That type safety and strict adherence to Ada language restrictions
11693 are not particularly important to the @value{GDBN} user.
11696 That brevity is important to the @value{GDBN} user.
11699 Thus, for brevity, the debugger acts as if all names declared in
11700 user-written packages are directly visible, even if they are not visible
11701 according to Ada rules, thus making it unnecessary to fully qualify most
11702 names with their packages, regardless of context. Where this causes
11703 ambiguity, @value{GDBN} asks the user's intent.
11705 The debugger will start in Ada mode if it detects an Ada main program.
11706 As for other languages, it will enter Ada mode when stopped in a program that
11707 was translated from an Ada source file.
11709 While in Ada mode, you may use `@t{--}' for comments. This is useful
11710 mostly for documenting command files. The standard @value{GDBN} comment
11711 (@samp{#}) still works at the beginning of a line in Ada mode, but not in the
11712 middle (to allow based literals).
11714 The debugger supports limited overloading. Given a subprogram call in which
11715 the function symbol has multiple definitions, it will use the number of
11716 actual parameters and some information about their types to attempt to narrow
11717 the set of definitions. It also makes very limited use of context, preferring
11718 procedures to functions in the context of the @code{call} command, and
11719 functions to procedures elsewhere.
11721 @node Omissions from Ada
11722 @subsubsection Omissions from Ada
11723 @cindex Ada, omissions from
11725 Here are the notable omissions from the subset:
11729 Only a subset of the attributes are supported:
11733 @t{'First}, @t{'Last}, and @t{'Length}
11734 on array objects (not on types and subtypes).
11737 @t{'Min} and @t{'Max}.
11740 @t{'Pos} and @t{'Val}.
11746 @t{'Range} on array objects (not subtypes), but only as the right
11747 operand of the membership (@code{in}) operator.
11750 @t{'Access}, @t{'Unchecked_Access}, and
11751 @t{'Unrestricted_Access} (a GNAT extension).
11759 @code{Characters.Latin_1} are not available and
11760 concatenation is not implemented. Thus, escape characters in strings are
11761 not currently available.
11764 Equality tests (@samp{=} and @samp{/=}) on arrays test for bitwise
11765 equality of representations. They will generally work correctly
11766 for strings and arrays whose elements have integer or enumeration types.
11767 They may not work correctly for arrays whose element
11768 types have user-defined equality, for arrays of real values
11769 (in particular, IEEE-conformant floating point, because of negative
11770 zeroes and NaNs), and for arrays whose elements contain unused bits with
11771 indeterminate values.
11774 The other component-by-component array operations (@code{and}, @code{or},
11775 @code{xor}, @code{not}, and relational tests other than equality)
11776 are not implemented.
11779 @cindex array aggregates (Ada)
11780 @cindex record aggregates (Ada)
11781 @cindex aggregates (Ada)
11782 There is limited support for array and record aggregates. They are
11783 permitted only on the right sides of assignments, as in these examples:
11786 (@value{GDBP}) set An_Array := (1, 2, 3, 4, 5, 6)
11787 (@value{GDBP}) set An_Array := (1, others => 0)
11788 (@value{GDBP}) set An_Array := (0|4 => 1, 1..3 => 2, 5 => 6)
11789 (@value{GDBP}) set A_2D_Array := ((1, 2, 3), (4, 5, 6), (7, 8, 9))
11790 (@value{GDBP}) set A_Record := (1, "Peter", True);
11791 (@value{GDBP}) set A_Record := (Name => "Peter", Id => 1, Alive => True)
11795 discriminant's value by assigning an aggregate has an
11796 undefined effect if that discriminant is used within the record.
11797 However, you can first modify discriminants by directly assigning to
11798 them (which normally would not be allowed in Ada), and then performing an
11799 aggregate assignment. For example, given a variable @code{A_Rec}
11800 declared to have a type such as:
11803 type Rec (Len : Small_Integer := 0) is record
11805 Vals : IntArray (1 .. Len);
11809 you can assign a value with a different size of @code{Vals} with two
11813 (@value{GDBP}) set A_Rec.Len := 4
11814 (@value{GDBP}) set A_Rec := (Id => 42, Vals => (1, 2, 3, 4))
11817 As this example also illustrates, @value{GDBN} is very loose about the usual
11818 rules concerning aggregates. You may leave out some of the
11819 components of an array or record aggregate (such as the @code{Len}
11820 component in the assignment to @code{A_Rec} above); they will retain their
11821 original values upon assignment. You may freely use dynamic values as
11822 indices in component associations. You may even use overlapping or
11823 redundant component associations, although which component values are
11824 assigned in such cases is not defined.
11827 Calls to dispatching subprograms are not implemented.
11830 The overloading algorithm is much more limited (i.e., less selective)
11831 than that of real Ada. It makes only limited use of the context in
11832 which a subexpression appears to resolve its meaning, and it is much
11833 looser in its rules for allowing type matches. As a result, some
11834 function calls will be ambiguous, and the user will be asked to choose
11835 the proper resolution.
11838 The @code{new} operator is not implemented.
11841 Entry calls are not implemented.
11844 Aside from printing, arithmetic operations on the native VAX floating-point
11845 formats are not supported.
11848 It is not possible to slice a packed array.
11851 The names @code{True} and @code{False}, when not part of a qualified name,
11852 are interpreted as if implicitly prefixed by @code{Standard}, regardless of
11854 Should your program
11855 redefine these names in a package or procedure (at best a dubious practice),
11856 you will have to use fully qualified names to access their new definitions.
11859 @node Additions to Ada
11860 @subsubsection Additions to Ada
11861 @cindex Ada, deviations from
11863 As it does for other languages, @value{GDBN} makes certain generic
11864 extensions to Ada (@pxref{Expressions}):
11868 If the expression @var{E} is a variable residing in memory (typically
11869 a local variable or array element) and @var{N} is a positive integer,
11870 then @code{@var{E}@@@var{N}} displays the values of @var{E} and the
11871 @var{N}-1 adjacent variables following it in memory as an array. In
11872 Ada, this operator is generally not necessary, since its prime use is
11873 in displaying parts of an array, and slicing will usually do this in
11874 Ada. However, there are occasional uses when debugging programs in
11875 which certain debugging information has been optimized away.
11878 @code{@var{B}::@var{var}} means ``the variable named @var{var} that
11879 appears in function or file @var{B}.'' When @var{B} is a file name,
11880 you must typically surround it in single quotes.
11883 The expression @code{@{@var{type}@} @var{addr}} means ``the variable of type
11884 @var{type} that appears at address @var{addr}.''
11887 A name starting with @samp{$} is a convenience variable
11888 (@pxref{Convenience Vars}) or a machine register (@pxref{Registers}).
11891 In addition, @value{GDBN} provides a few other shortcuts and outright
11892 additions specific to Ada:
11896 The assignment statement is allowed as an expression, returning
11897 its right-hand operand as its value. Thus, you may enter
11900 (@value{GDBP}) set x := y + 3
11901 (@value{GDBP}) print A(tmp := y + 1)
11905 The semicolon is allowed as an ``operator,'' returning as its value
11906 the value of its right-hand operand.
11907 This allows, for example,
11908 complex conditional breaks:
11911 (@value{GDBP}) break f
11912 (@value{GDBP}) condition 1 (report(i); k += 1; A(k) > 100)
11916 Rather than use catenation and symbolic character names to introduce special
11917 characters into strings, one may instead use a special bracket notation,
11918 which is also used to print strings. A sequence of characters of the form
11919 @samp{["@var{XX}"]} within a string or character literal denotes the
11920 (single) character whose numeric encoding is @var{XX} in hexadecimal. The
11921 sequence of characters @samp{["""]} also denotes a single quotation mark
11922 in strings. For example,
11924 "One line.["0a"]Next line.["0a"]"
11927 contains an ASCII newline character (@code{Ada.Characters.Latin_1.LF})
11931 The subtype used as a prefix for the attributes @t{'Pos}, @t{'Min}, and
11932 @t{'Max} is optional (and is ignored in any case). For example, it is valid
11936 (@value{GDBP}) print 'max(x, y)
11940 When printing arrays, @value{GDBN} uses positional notation when the
11941 array has a lower bound of 1, and uses a modified named notation otherwise.
11942 For example, a one-dimensional array of three integers with a lower bound
11943 of 3 might print as
11950 That is, in contrast to valid Ada, only the first component has a @code{=>}
11954 You may abbreviate attributes in expressions with any unique,
11955 multi-character subsequence of
11956 their names (an exact match gets preference).
11957 For example, you may use @t{a'len}, @t{a'gth}, or @t{a'lh}
11958 in place of @t{a'length}.
11961 @cindex quoting Ada internal identifiers
11962 Since Ada is case-insensitive, the debugger normally maps identifiers you type
11963 to lower case. The GNAT compiler uses upper-case characters for
11964 some of its internal identifiers, which are normally of no interest to users.
11965 For the rare occasions when you actually have to look at them,
11966 enclose them in angle brackets to avoid the lower-case mapping.
11969 (@value{GDBP}) print <JMPBUF_SAVE>[0]
11973 Printing an object of class-wide type or dereferencing an
11974 access-to-class-wide value will display all the components of the object's
11975 specific type (as indicated by its run-time tag). Likewise, component
11976 selection on such a value will operate on the specific type of the
11981 @node Stopping Before Main Program
11982 @subsubsection Stopping at the Very Beginning
11984 @cindex breakpointing Ada elaboration code
11985 It is sometimes necessary to debug the program during elaboration, and
11986 before reaching the main procedure.
11987 As defined in the Ada Reference
11988 Manual, the elaboration code is invoked from a procedure called
11989 @code{adainit}. To run your program up to the beginning of
11990 elaboration, simply use the following two commands:
11991 @code{tbreak adainit} and @code{run}.
11994 @subsubsection Extensions for Ada Tasks
11995 @cindex Ada, tasking
11997 Support for Ada tasks is analogous to that for threads (@pxref{Threads}).
11998 @value{GDBN} provides the following task-related commands:
12003 This command shows a list of current Ada tasks, as in the following example:
12010 (@value{GDBP}) info tasks
12011 ID TID P-ID Pri State Name
12012 1 8088000 0 15 Child Activation Wait main_task
12013 2 80a4000 1 15 Accept Statement b
12014 3 809a800 1 15 Child Activation Wait a
12015 * 4 80ae800 3 15 Runnable c
12020 In this listing, the asterisk before the last task indicates it to be the
12021 task currently being inspected.
12025 Represents @value{GDBN}'s internal task number.
12031 The parent's task ID (@value{GDBN}'s internal task number).
12034 The base priority of the task.
12037 Current state of the task.
12041 The task has been created but has not been activated. It cannot be
12045 The task is not blocked for any reason known to Ada. (It may be waiting
12046 for a mutex, though.) It is conceptually "executing" in normal mode.
12049 The task is terminated, in the sense of ARM 9.3 (5). Any dependents
12050 that were waiting on terminate alternatives have been awakened and have
12051 terminated themselves.
12053 @item Child Activation Wait
12054 The task is waiting for created tasks to complete activation.
12056 @item Accept Statement
12057 The task is waiting on an accept or selective wait statement.
12059 @item Waiting on entry call
12060 The task is waiting on an entry call.
12062 @item Async Select Wait
12063 The task is waiting to start the abortable part of an asynchronous
12067 The task is waiting on a select statement with only a delay
12070 @item Child Termination Wait
12071 The task is sleeping having completed a master within itself, and is
12072 waiting for the tasks dependent on that master to become terminated or
12073 waiting on a terminate Phase.
12075 @item Wait Child in Term Alt
12076 The task is sleeping waiting for tasks on terminate alternatives to
12077 finish terminating.
12079 @item Accepting RV with @var{taskno}
12080 The task is accepting a rendez-vous with the task @var{taskno}.
12084 Name of the task in the program.
12088 @kindex info task @var{taskno}
12089 @item info task @var{taskno}
12090 This command shows detailled informations on the specified task, as in
12091 the following example:
12096 (@value{GDBP}) info tasks
12097 ID TID P-ID Pri State Name
12098 1 8077880 0 15 Child Activation Wait main_task
12099 * 2 807c468 1 15 Runnable task_1
12100 (@value{GDBP}) info task 2
12101 Ada Task: 0x807c468
12104 Parent: 1 (main_task)
12110 @kindex task@r{ (Ada)}
12111 @cindex current Ada task ID
12112 This command prints the ID of the current task.
12118 (@value{GDBP}) info tasks
12119 ID TID P-ID Pri State Name
12120 1 8077870 0 15 Child Activation Wait main_task
12121 * 2 807c458 1 15 Runnable t
12122 (@value{GDBP}) task
12123 [Current task is 2]
12126 @item task @var{taskno}
12127 @cindex Ada task switching
12128 This command is like the @code{thread @var{threadno}}
12129 command (@pxref{Threads}). It switches the context of debugging
12130 from the current task to the given task.
12136 (@value{GDBP}) info tasks
12137 ID TID P-ID Pri State Name
12138 1 8077870 0 15 Child Activation Wait main_task
12139 * 2 807c458 1 15 Runnable t
12140 (@value{GDBP}) task 1
12141 [Switching to task 1]
12142 #0 0x8067726 in pthread_cond_wait ()
12144 #0 0x8067726 in pthread_cond_wait ()
12145 #1 0x8056714 in system.os_interface.pthread_cond_wait ()
12146 #2 0x805cb63 in system.task_primitives.operations.sleep ()
12147 #3 0x806153e in system.tasking.stages.activate_tasks ()
12148 #4 0x804aacc in un () at un.adb:5
12151 @item break @var{linespec} task @var{taskno}
12152 @itemx break @var{linespec} task @var{taskno} if @dots{}
12153 @cindex breakpoints and tasks, in Ada
12154 @cindex task breakpoints, in Ada
12155 @kindex break @dots{} task @var{taskno}@r{ (Ada)}
12156 These commands are like the @code{break @dots{} thread @dots{}}
12157 command (@pxref{Thread Stops}).
12158 @var{linespec} specifies source lines, as described
12159 in @ref{Specify Location}.
12161 Use the qualifier @samp{task @var{taskno}} with a breakpoint command
12162 to specify that you only want @value{GDBN} to stop the program when a
12163 particular Ada task reaches this breakpoint. @var{taskno} is one of the
12164 numeric task identifiers assigned by @value{GDBN}, shown in the first
12165 column of the @samp{info tasks} display.
12167 If you do not specify @samp{task @var{taskno}} when you set a
12168 breakpoint, the breakpoint applies to @emph{all} tasks of your
12171 You can use the @code{task} qualifier on conditional breakpoints as
12172 well; in this case, place @samp{task @var{taskno}} before the
12173 breakpoint condition (before the @code{if}).
12181 (@value{GDBP}) info tasks
12182 ID TID P-ID Pri State Name
12183 1 140022020 0 15 Child Activation Wait main_task
12184 2 140045060 1 15 Accept/Select Wait t2
12185 3 140044840 1 15 Runnable t1
12186 * 4 140056040 1 15 Runnable t3
12187 (@value{GDBP}) b 15 task 2
12188 Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15.
12189 (@value{GDBP}) cont
12194 Breakpoint 5, test_task_debug () at test_task_debug.adb:15
12196 (@value{GDBP}) info tasks
12197 ID TID P-ID Pri State Name
12198 1 140022020 0 15 Child Activation Wait main_task
12199 * 2 140045060 1 15 Runnable t2
12200 3 140044840 1 15 Runnable t1
12201 4 140056040 1 15 Delay Sleep t3
12205 @node Ada Tasks and Core Files
12206 @subsubsection Tasking Support when Debugging Core Files
12207 @cindex Ada tasking and core file debugging
12209 When inspecting a core file, as opposed to debugging a live program,
12210 tasking support may be limited or even unavailable, depending on
12211 the platform being used.
12212 For instance, on x86-linux, the list of tasks is available, but task
12213 switching is not supported. On Tru64, however, task switching will work
12216 On certain platforms, including Tru64, the debugger needs to perform some
12217 memory writes in order to provide Ada tasking support. When inspecting
12218 a core file, this means that the core file must be opened with read-write
12219 privileges, using the command @samp{"set write on"} (@pxref{Patching}).
12220 Under these circumstances, you should make a backup copy of the core
12221 file before inspecting it with @value{GDBN}.
12224 @subsubsection Known Peculiarities of Ada Mode
12225 @cindex Ada, problems
12227 Besides the omissions listed previously (@pxref{Omissions from Ada}),
12228 we know of several problems with and limitations of Ada mode in
12230 some of which will be fixed with planned future releases of the debugger
12231 and the GNU Ada compiler.
12235 Currently, the debugger
12236 has insufficient information to determine whether certain pointers represent
12237 pointers to objects or the objects themselves.
12238 Thus, the user may have to tack an extra @code{.all} after an expression
12239 to get it printed properly.
12242 Static constants that the compiler chooses not to materialize as objects in
12243 storage are invisible to the debugger.
12246 Named parameter associations in function argument lists are ignored (the
12247 argument lists are treated as positional).
12250 Many useful library packages are currently invisible to the debugger.
12253 Fixed-point arithmetic, conversions, input, and output is carried out using
12254 floating-point arithmetic, and may give results that only approximate those on
12258 The GNAT compiler never generates the prefix @code{Standard} for any of
12259 the standard symbols defined by the Ada language. @value{GDBN} knows about
12260 this: it will strip the prefix from names when you use it, and will never
12261 look for a name you have so qualified among local symbols, nor match against
12262 symbols in other packages or subprograms. If you have
12263 defined entities anywhere in your program other than parameters and
12264 local variables whose simple names match names in @code{Standard},
12265 GNAT's lack of qualification here can cause confusion. When this happens,
12266 you can usually resolve the confusion
12267 by qualifying the problematic names with package
12268 @code{Standard} explicitly.
12271 @node Unsupported Languages
12272 @section Unsupported Languages
12274 @cindex unsupported languages
12275 @cindex minimal language
12276 In addition to the other fully-supported programming languages,
12277 @value{GDBN} also provides a pseudo-language, called @code{minimal}.
12278 It does not represent a real programming language, but provides a set
12279 of capabilities close to what the C or assembly languages provide.
12280 This should allow most simple operations to be performed while debugging
12281 an application that uses a language currently not supported by @value{GDBN}.
12283 If the language is set to @code{auto}, @value{GDBN} will automatically
12284 select this language if the current frame corresponds to an unsupported
12288 @chapter Examining the Symbol Table
12290 The commands described in this chapter allow you to inquire about the
12291 symbols (names of variables, functions and types) defined in your
12292 program. This information is inherent in the text of your program and
12293 does not change as your program executes. @value{GDBN} finds it in your
12294 program's symbol table, in the file indicated when you started @value{GDBN}
12295 (@pxref{File Options, ,Choosing Files}), or by one of the
12296 file-management commands (@pxref{Files, ,Commands to Specify Files}).
12298 @cindex symbol names
12299 @cindex names of symbols
12300 @cindex quoting names
12301 Occasionally, you may need to refer to symbols that contain unusual
12302 characters, which @value{GDBN} ordinarily treats as word delimiters. The
12303 most frequent case is in referring to static variables in other
12304 source files (@pxref{Variables,,Program Variables}). File names
12305 are recorded in object files as debugging symbols, but @value{GDBN} would
12306 ordinarily parse a typical file name, like @file{foo.c}, as the three words
12307 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
12308 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
12315 looks up the value of @code{x} in the scope of the file @file{foo.c}.
12318 @cindex case-insensitive symbol names
12319 @cindex case sensitivity in symbol names
12320 @kindex set case-sensitive
12321 @item set case-sensitive on
12322 @itemx set case-sensitive off
12323 @itemx set case-sensitive auto
12324 Normally, when @value{GDBN} looks up symbols, it matches their names
12325 with case sensitivity determined by the current source language.
12326 Occasionally, you may wish to control that. The command @code{set
12327 case-sensitive} lets you do that by specifying @code{on} for
12328 case-sensitive matches or @code{off} for case-insensitive ones. If
12329 you specify @code{auto}, case sensitivity is reset to the default
12330 suitable for the source language. The default is case-sensitive
12331 matches for all languages except for Fortran, for which the default is
12332 case-insensitive matches.
12334 @kindex show case-sensitive
12335 @item show case-sensitive
12336 This command shows the current setting of case sensitivity for symbols
12339 @kindex info address
12340 @cindex address of a symbol
12341 @item info address @var{symbol}
12342 Describe where the data for @var{symbol} is stored. For a register
12343 variable, this says which register it is kept in. For a non-register
12344 local variable, this prints the stack-frame offset at which the variable
12347 Note the contrast with @samp{print &@var{symbol}}, which does not work
12348 at all for a register variable, and for a stack local variable prints
12349 the exact address of the current instantiation of the variable.
12351 @kindex info symbol
12352 @cindex symbol from address
12353 @cindex closest symbol and offset for an address
12354 @item info symbol @var{addr}
12355 Print the name of a symbol which is stored at the address @var{addr}.
12356 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
12357 nearest symbol and an offset from it:
12360 (@value{GDBP}) info symbol 0x54320
12361 _initialize_vx + 396 in section .text
12365 This is the opposite of the @code{info address} command. You can use
12366 it to find out the name of a variable or a function given its address.
12368 For dynamically linked executables, the name of executable or shared
12369 library containing the symbol is also printed:
12372 (@value{GDBP}) info symbol 0x400225
12373 _start + 5 in section .text of /tmp/a.out
12374 (@value{GDBP}) info symbol 0x2aaaac2811cf
12375 __read_nocancel + 6 in section .text of /usr/lib64/libc.so.6
12379 @item whatis [@var{arg}]
12380 Print the data type of @var{arg}, which can be either an expression or
12381 a data type. With no argument, print the data type of @code{$}, the
12382 last value in the value history. If @var{arg} is an expression, it is
12383 not actually evaluated, and any side-effecting operations (such as
12384 assignments or function calls) inside it do not take place. If
12385 @var{arg} is a type name, it may be the name of a type or typedef, or
12386 for C code it may have the form @samp{class @var{class-name}},
12387 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
12388 @samp{enum @var{enum-tag}}.
12389 @xref{Expressions, ,Expressions}.
12392 @item ptype [@var{arg}]
12393 @code{ptype} accepts the same arguments as @code{whatis}, but prints a
12394 detailed description of the type, instead of just the name of the type.
12395 @xref{Expressions, ,Expressions}.
12397 For example, for this variable declaration:
12400 struct complex @{double real; double imag;@} v;
12404 the two commands give this output:
12408 (@value{GDBP}) whatis v
12409 type = struct complex
12410 (@value{GDBP}) ptype v
12411 type = struct complex @{
12419 As with @code{whatis}, using @code{ptype} without an argument refers to
12420 the type of @code{$}, the last value in the value history.
12422 @cindex incomplete type
12423 Sometimes, programs use opaque data types or incomplete specifications
12424 of complex data structure. If the debug information included in the
12425 program does not allow @value{GDBN} to display a full declaration of
12426 the data type, it will say @samp{<incomplete type>}. For example,
12427 given these declarations:
12431 struct foo *fooptr;
12435 but no definition for @code{struct foo} itself, @value{GDBN} will say:
12438 (@value{GDBP}) ptype foo
12439 $1 = <incomplete type>
12443 ``Incomplete type'' is C terminology for data types that are not
12444 completely specified.
12447 @item info types @var{regexp}
12449 Print a brief description of all types whose names match the regular
12450 expression @var{regexp} (or all types in your program, if you supply
12451 no argument). Each complete typename is matched as though it were a
12452 complete line; thus, @samp{i type value} gives information on all
12453 types in your program whose names include the string @code{value}, but
12454 @samp{i type ^value$} gives information only on types whose complete
12455 name is @code{value}.
12457 This command differs from @code{ptype} in two ways: first, like
12458 @code{whatis}, it does not print a detailed description; second, it
12459 lists all source files where a type is defined.
12462 @cindex local variables
12463 @item info scope @var{location}
12464 List all the variables local to a particular scope. This command
12465 accepts a @var{location} argument---a function name, a source line, or
12466 an address preceded by a @samp{*}, and prints all the variables local
12467 to the scope defined by that location. (@xref{Specify Location}, for
12468 details about supported forms of @var{location}.) For example:
12471 (@value{GDBP}) @b{info scope command_line_handler}
12472 Scope for command_line_handler:
12473 Symbol rl is an argument at stack/frame offset 8, length 4.
12474 Symbol linebuffer is in static storage at address 0x150a18, length 4.
12475 Symbol linelength is in static storage at address 0x150a1c, length 4.
12476 Symbol p is a local variable in register $esi, length 4.
12477 Symbol p1 is a local variable in register $ebx, length 4.
12478 Symbol nline is a local variable in register $edx, length 4.
12479 Symbol repeat is a local variable at frame offset -8, length 4.
12483 This command is especially useful for determining what data to collect
12484 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
12487 @kindex info source
12489 Show information about the current source file---that is, the source file for
12490 the function containing the current point of execution:
12493 the name of the source file, and the directory containing it,
12495 the directory it was compiled in,
12497 its length, in lines,
12499 which programming language it is written in,
12501 whether the executable includes debugging information for that file, and
12502 if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and
12504 whether the debugging information includes information about
12505 preprocessor macros.
12509 @kindex info sources
12511 Print the names of all source files in your program for which there is
12512 debugging information, organized into two lists: files whose symbols
12513 have already been read, and files whose symbols will be read when needed.
12515 @kindex info functions
12516 @item info functions
12517 Print the names and data types of all defined functions.
12519 @item info functions @var{regexp}
12520 Print the names and data types of all defined functions
12521 whose names contain a match for regular expression @var{regexp}.
12522 Thus, @samp{info fun step} finds all functions whose names
12523 include @code{step}; @samp{info fun ^step} finds those whose names
12524 start with @code{step}. If a function name contains characters
12525 that conflict with the regular expression language (e.g.@:
12526 @samp{operator*()}), they may be quoted with a backslash.
12528 @kindex info variables
12529 @item info variables
12530 Print the names and data types of all variables that are declared
12531 outside of functions (i.e.@: excluding local variables).
12533 @item info variables @var{regexp}
12534 Print the names and data types of all variables (except for local
12535 variables) whose names contain a match for regular expression
12538 @kindex info classes
12539 @cindex Objective-C, classes and selectors
12541 @itemx info classes @var{regexp}
12542 Display all Objective-C classes in your program, or
12543 (with the @var{regexp} argument) all those matching a particular regular
12546 @kindex info selectors
12547 @item info selectors
12548 @itemx info selectors @var{regexp}
12549 Display all Objective-C selectors in your program, or
12550 (with the @var{regexp} argument) all those matching a particular regular
12554 This was never implemented.
12555 @kindex info methods
12557 @itemx info methods @var{regexp}
12558 The @code{info methods} command permits the user to examine all defined
12559 methods within C@t{++} program, or (with the @var{regexp} argument) a
12560 specific set of methods found in the various C@t{++} classes. Many
12561 C@t{++} classes provide a large number of methods. Thus, the output
12562 from the @code{ptype} command can be overwhelming and hard to use. The
12563 @code{info-methods} command filters the methods, printing only those
12564 which match the regular-expression @var{regexp}.
12567 @cindex reloading symbols
12568 Some systems allow individual object files that make up your program to
12569 be replaced without stopping and restarting your program. For example,
12570 in VxWorks you can simply recompile a defective object file and keep on
12571 running. If you are running on one of these systems, you can allow
12572 @value{GDBN} to reload the symbols for automatically relinked modules:
12575 @kindex set symbol-reloading
12576 @item set symbol-reloading on
12577 Replace symbol definitions for the corresponding source file when an
12578 object file with a particular name is seen again.
12580 @item set symbol-reloading off
12581 Do not replace symbol definitions when encountering object files of the
12582 same name more than once. This is the default state; if you are not
12583 running on a system that permits automatic relinking of modules, you
12584 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
12585 may discard symbols when linking large programs, that may contain
12586 several modules (from different directories or libraries) with the same
12589 @kindex show symbol-reloading
12590 @item show symbol-reloading
12591 Show the current @code{on} or @code{off} setting.
12594 @cindex opaque data types
12595 @kindex set opaque-type-resolution
12596 @item set opaque-type-resolution on
12597 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
12598 declared as a pointer to a @code{struct}, @code{class}, or
12599 @code{union}---for example, @code{struct MyType *}---that is used in one
12600 source file although the full declaration of @code{struct MyType} is in
12601 another source file. The default is on.
12603 A change in the setting of this subcommand will not take effect until
12604 the next time symbols for a file are loaded.
12606 @item set opaque-type-resolution off
12607 Tell @value{GDBN} not to resolve opaque types. In this case, the type
12608 is printed as follows:
12610 @{<no data fields>@}
12613 @kindex show opaque-type-resolution
12614 @item show opaque-type-resolution
12615 Show whether opaque types are resolved or not.
12617 @kindex set print symbol-loading
12618 @cindex print messages when symbols are loaded
12619 @item set print symbol-loading
12620 @itemx set print symbol-loading on
12621 @itemx set print symbol-loading off
12622 The @code{set print symbol-loading} command allows you to enable or
12623 disable printing of messages when @value{GDBN} loads symbols.
12624 By default, these messages will be printed, and normally this is what
12625 you want. Disabling these messages is useful when debugging applications
12626 with lots of shared libraries where the quantity of output can be more
12627 annoying than useful.
12629 @kindex show print symbol-loading
12630 @item show print symbol-loading
12631 Show whether messages will be printed when @value{GDBN} loads symbols.
12633 @kindex maint print symbols
12634 @cindex symbol dump
12635 @kindex maint print psymbols
12636 @cindex partial symbol dump
12637 @item maint print symbols @var{filename}
12638 @itemx maint print psymbols @var{filename}
12639 @itemx maint print msymbols @var{filename}
12640 Write a dump of debugging symbol data into the file @var{filename}.
12641 These commands are used to debug the @value{GDBN} symbol-reading code. Only
12642 symbols with debugging data are included. If you use @samp{maint print
12643 symbols}, @value{GDBN} includes all the symbols for which it has already
12644 collected full details: that is, @var{filename} reflects symbols for
12645 only those files whose symbols @value{GDBN} has read. You can use the
12646 command @code{info sources} to find out which files these are. If you
12647 use @samp{maint print psymbols} instead, the dump shows information about
12648 symbols that @value{GDBN} only knows partially---that is, symbols defined in
12649 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
12650 @samp{maint print msymbols} dumps just the minimal symbol information
12651 required for each object file from which @value{GDBN} has read some symbols.
12652 @xref{Files, ,Commands to Specify Files}, for a discussion of how
12653 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
12655 @kindex maint info symtabs
12656 @kindex maint info psymtabs
12657 @cindex listing @value{GDBN}'s internal symbol tables
12658 @cindex symbol tables, listing @value{GDBN}'s internal
12659 @cindex full symbol tables, listing @value{GDBN}'s internal
12660 @cindex partial symbol tables, listing @value{GDBN}'s internal
12661 @item maint info symtabs @r{[} @var{regexp} @r{]}
12662 @itemx maint info psymtabs @r{[} @var{regexp} @r{]}
12664 List the @code{struct symtab} or @code{struct partial_symtab}
12665 structures whose names match @var{regexp}. If @var{regexp} is not
12666 given, list them all. The output includes expressions which you can
12667 copy into a @value{GDBN} debugging this one to examine a particular
12668 structure in more detail. For example:
12671 (@value{GDBP}) maint info psymtabs dwarf2read
12672 @{ objfile /home/gnu/build/gdb/gdb
12673 ((struct objfile *) 0x82e69d0)
12674 @{ psymtab /home/gnu/src/gdb/dwarf2read.c
12675 ((struct partial_symtab *) 0x8474b10)
12678 text addresses 0x814d3c8 -- 0x8158074
12679 globals (* (struct partial_symbol **) 0x8507a08 @@ 9)
12680 statics (* (struct partial_symbol **) 0x40e95b78 @@ 2882)
12681 dependencies (none)
12684 (@value{GDBP}) maint info symtabs
12688 We see that there is one partial symbol table whose filename contains
12689 the string @samp{dwarf2read}, belonging to the @samp{gdb} executable;
12690 and we see that @value{GDBN} has not read in any symtabs yet at all.
12691 If we set a breakpoint on a function, that will cause @value{GDBN} to
12692 read the symtab for the compilation unit containing that function:
12695 (@value{GDBP}) break dwarf2_psymtab_to_symtab
12696 Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c,
12698 (@value{GDBP}) maint info symtabs
12699 @{ objfile /home/gnu/build/gdb/gdb
12700 ((struct objfile *) 0x82e69d0)
12701 @{ symtab /home/gnu/src/gdb/dwarf2read.c
12702 ((struct symtab *) 0x86c1f38)
12705 blockvector ((struct blockvector *) 0x86c1bd0) (primary)
12706 linetable ((struct linetable *) 0x8370fa0)
12707 debugformat DWARF 2
12716 @chapter Altering Execution
12718 Once you think you have found an error in your program, you might want to
12719 find out for certain whether correcting the apparent error would lead to
12720 correct results in the rest of the run. You can find the answer by
12721 experiment, using the @value{GDBN} features for altering execution of the
12724 For example, you can store new values into variables or memory
12725 locations, give your program a signal, restart it at a different
12726 address, or even return prematurely from a function.
12729 * Assignment:: Assignment to variables
12730 * Jumping:: Continuing at a different address
12731 * Signaling:: Giving your program a signal
12732 * Returning:: Returning from a function
12733 * Calling:: Calling your program's functions
12734 * Patching:: Patching your program
12738 @section Assignment to Variables
12741 @cindex setting variables
12742 To alter the value of a variable, evaluate an assignment expression.
12743 @xref{Expressions, ,Expressions}. For example,
12750 stores the value 4 into the variable @code{x}, and then prints the
12751 value of the assignment expression (which is 4).
12752 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
12753 information on operators in supported languages.
12755 @kindex set variable
12756 @cindex variables, setting
12757 If you are not interested in seeing the value of the assignment, use the
12758 @code{set} command instead of the @code{print} command. @code{set} is
12759 really the same as @code{print} except that the expression's value is
12760 not printed and is not put in the value history (@pxref{Value History,
12761 ,Value History}). The expression is evaluated only for its effects.
12763 If the beginning of the argument string of the @code{set} command
12764 appears identical to a @code{set} subcommand, use the @code{set
12765 variable} command instead of just @code{set}. This command is identical
12766 to @code{set} except for its lack of subcommands. For example, if your
12767 program has a variable @code{width}, you get an error if you try to set
12768 a new value with just @samp{set width=13}, because @value{GDBN} has the
12769 command @code{set width}:
12772 (@value{GDBP}) whatis width
12774 (@value{GDBP}) p width
12776 (@value{GDBP}) set width=47
12777 Invalid syntax in expression.
12781 The invalid expression, of course, is @samp{=47}. In
12782 order to actually set the program's variable @code{width}, use
12785 (@value{GDBP}) set var width=47
12788 Because the @code{set} command has many subcommands that can conflict
12789 with the names of program variables, it is a good idea to use the
12790 @code{set variable} command instead of just @code{set}. For example, if
12791 your program has a variable @code{g}, you run into problems if you try
12792 to set a new value with just @samp{set g=4}, because @value{GDBN} has
12793 the command @code{set gnutarget}, abbreviated @code{set g}:
12797 (@value{GDBP}) whatis g
12801 (@value{GDBP}) set g=4
12805 The program being debugged has been started already.
12806 Start it from the beginning? (y or n) y
12807 Starting program: /home/smith/cc_progs/a.out
12808 "/home/smith/cc_progs/a.out": can't open to read symbols:
12809 Invalid bfd target.
12810 (@value{GDBP}) show g
12811 The current BFD target is "=4".
12816 The program variable @code{g} did not change, and you silently set the
12817 @code{gnutarget} to an invalid value. In order to set the variable
12821 (@value{GDBP}) set var g=4
12824 @value{GDBN} allows more implicit conversions in assignments than C; you can
12825 freely store an integer value into a pointer variable or vice versa,
12826 and you can convert any structure to any other structure that is the
12827 same length or shorter.
12828 @comment FIXME: how do structs align/pad in these conversions?
12829 @comment /doc@cygnus.com 18dec1990
12831 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
12832 construct to generate a value of specified type at a specified address
12833 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
12834 to memory location @code{0x83040} as an integer (which implies a certain size
12835 and representation in memory), and
12838 set @{int@}0x83040 = 4
12842 stores the value 4 into that memory location.
12845 @section Continuing at a Different Address
12847 Ordinarily, when you continue your program, you do so at the place where
12848 it stopped, with the @code{continue} command. You can instead continue at
12849 an address of your own choosing, with the following commands:
12853 @item jump @var{linespec}
12854 @itemx jump @var{location}
12855 Resume execution at line @var{linespec} or at address given by
12856 @var{location}. Execution stops again immediately if there is a
12857 breakpoint there. @xref{Specify Location}, for a description of the
12858 different forms of @var{linespec} and @var{location}. It is common
12859 practice to use the @code{tbreak} command in conjunction with
12860 @code{jump}. @xref{Set Breaks, ,Setting Breakpoints}.
12862 The @code{jump} command does not change the current stack frame, or
12863 the stack pointer, or the contents of any memory location or any
12864 register other than the program counter. If line @var{linespec} is in
12865 a different function from the one currently executing, the results may
12866 be bizarre if the two functions expect different patterns of arguments or
12867 of local variables. For this reason, the @code{jump} command requests
12868 confirmation if the specified line is not in the function currently
12869 executing. However, even bizarre results are predictable if you are
12870 well acquainted with the machine-language code of your program.
12873 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
12874 On many systems, you can get much the same effect as the @code{jump}
12875 command by storing a new value into the register @code{$pc}. The
12876 difference is that this does not start your program running; it only
12877 changes the address of where it @emph{will} run when you continue. For
12885 makes the next @code{continue} command or stepping command execute at
12886 address @code{0x485}, rather than at the address where your program stopped.
12887 @xref{Continuing and Stepping, ,Continuing and Stepping}.
12889 The most common occasion to use the @code{jump} command is to back
12890 up---perhaps with more breakpoints set---over a portion of a program
12891 that has already executed, in order to examine its execution in more
12896 @section Giving your Program a Signal
12897 @cindex deliver a signal to a program
12901 @item signal @var{signal}
12902 Resume execution where your program stopped, but immediately give it the
12903 signal @var{signal}. @var{signal} can be the name or the number of a
12904 signal. For example, on many systems @code{signal 2} and @code{signal
12905 SIGINT} are both ways of sending an interrupt signal.
12907 Alternatively, if @var{signal} is zero, continue execution without
12908 giving a signal. This is useful when your program stopped on account of
12909 a signal and would ordinary see the signal when resumed with the
12910 @code{continue} command; @samp{signal 0} causes it to resume without a
12913 @code{signal} does not repeat when you press @key{RET} a second time
12914 after executing the command.
12918 Invoking the @code{signal} command is not the same as invoking the
12919 @code{kill} utility from the shell. Sending a signal with @code{kill}
12920 causes @value{GDBN} to decide what to do with the signal depending on
12921 the signal handling tables (@pxref{Signals}). The @code{signal} command
12922 passes the signal directly to your program.
12926 @section Returning from a Function
12929 @cindex returning from a function
12932 @itemx return @var{expression}
12933 You can cancel execution of a function call with the @code{return}
12934 command. If you give an
12935 @var{expression} argument, its value is used as the function's return
12939 When you use @code{return}, @value{GDBN} discards the selected stack frame
12940 (and all frames within it). You can think of this as making the
12941 discarded frame return prematurely. If you wish to specify a value to
12942 be returned, give that value as the argument to @code{return}.
12944 This pops the selected stack frame (@pxref{Selection, ,Selecting a
12945 Frame}), and any other frames inside of it, leaving its caller as the
12946 innermost remaining frame. That frame becomes selected. The
12947 specified value is stored in the registers used for returning values
12950 The @code{return} command does not resume execution; it leaves the
12951 program stopped in the state that would exist if the function had just
12952 returned. In contrast, the @code{finish} command (@pxref{Continuing
12953 and Stepping, ,Continuing and Stepping}) resumes execution until the
12954 selected stack frame returns naturally.
12956 @value{GDBN} needs to know how the @var{expression} argument should be set for
12957 the inferior. The concrete registers assignment depends on the OS ABI and the
12958 type being returned by the selected stack frame. For example it is common for
12959 OS ABI to return floating point values in FPU registers while integer values in
12960 CPU registers. Still some ABIs return even floating point values in CPU
12961 registers. Larger integer widths (such as @code{long long int}) also have
12962 specific placement rules. @value{GDBN} already knows the OS ABI from its
12963 current target so it needs to find out also the type being returned to make the
12964 assignment into the right register(s).
12966 Normally, the selected stack frame has debug info. @value{GDBN} will always
12967 use the debug info instead of the implicit type of @var{expression} when the
12968 debug info is available. For example, if you type @kbd{return -1}, and the
12969 function in the current stack frame is declared to return a @code{long long
12970 int}, @value{GDBN} transparently converts the implicit @code{int} value of -1
12971 into a @code{long long int}:
12974 Breakpoint 1, func () at gdb.base/return-nodebug.c:29
12976 (@value{GDBP}) return -1
12977 Make func return now? (y or n) y
12978 #0 0x004004f6 in main () at gdb.base/return-nodebug.c:43
12979 43 printf ("result=%lld\n", func ());
12983 However, if the selected stack frame does not have a debug info, e.g., if the
12984 function was compiled without debug info, @value{GDBN} has to find out the type
12985 to return from user. Specifying a different type by mistake may set the value
12986 in different inferior registers than the caller code expects. For example,
12987 typing @kbd{return -1} with its implicit type @code{int} would set only a part
12988 of a @code{long long int} result for a debug info less function (on 32-bit
12989 architectures). Therefore the user is required to specify the return type by
12990 an appropriate cast explicitly:
12993 Breakpoint 2, 0x0040050b in func ()
12994 (@value{GDBP}) return -1
12995 Return value type not available for selected stack frame.
12996 Please use an explicit cast of the value to return.
12997 (@value{GDBP}) return (long long int) -1
12998 Make selected stack frame return now? (y or n) y
12999 #0 0x00400526 in main ()
13004 @section Calling Program Functions
13007 @cindex calling functions
13008 @cindex inferior functions, calling
13009 @item print @var{expr}
13010 Evaluate the expression @var{expr} and display the resulting value.
13011 @var{expr} may include calls to functions in the program being
13015 @item call @var{expr}
13016 Evaluate the expression @var{expr} without displaying @code{void}
13019 You can use this variant of the @code{print} command if you want to
13020 execute a function from your program that does not return anything
13021 (a.k.a.@: @dfn{a void function}), but without cluttering the output
13022 with @code{void} returned values that @value{GDBN} will otherwise
13023 print. If the result is not void, it is printed and saved in the
13027 It is possible for the function you call via the @code{print} or
13028 @code{call} command to generate a signal (e.g., if there's a bug in
13029 the function, or if you passed it incorrect arguments). What happens
13030 in that case is controlled by the @code{set unwindonsignal} command.
13032 Similarly, with a C@t{++} program it is possible for the function you
13033 call via the @code{print} or @code{call} command to generate an
13034 exception that is not handled due to the constraints of the dummy
13035 frame. In this case, any exception that is raised in the frame, but has
13036 an out-of-frame exception handler will not be found. GDB builds a
13037 dummy-frame for the inferior function call, and the unwinder cannot
13038 seek for exception handlers outside of this dummy-frame. What happens
13039 in that case is controlled by the
13040 @code{set unwind-on-terminating-exception} command.
13043 @item set unwindonsignal
13044 @kindex set unwindonsignal
13045 @cindex unwind stack in called functions
13046 @cindex call dummy stack unwinding
13047 Set unwinding of the stack if a signal is received while in a function
13048 that @value{GDBN} called in the program being debugged. If set to on,
13049 @value{GDBN} unwinds the stack it created for the call and restores
13050 the context to what it was before the call. If set to off (the
13051 default), @value{GDBN} stops in the frame where the signal was
13054 @item show unwindonsignal
13055 @kindex show unwindonsignal
13056 Show the current setting of stack unwinding in the functions called by
13059 @item set unwind-on-terminating-exception
13060 @kindex set unwind-on-terminating-exception
13061 @cindex unwind stack in called functions with unhandled exceptions
13062 @cindex call dummy stack unwinding on unhandled exception.
13063 Set unwinding of the stack if a C@t{++} exception is raised, but left
13064 unhandled while in a function that @value{GDBN} called in the program being
13065 debugged. If set to on (the default), @value{GDBN} unwinds the stack
13066 it created for the call and restores the context to what it was before
13067 the call. If set to off, @value{GDBN} the exception is delivered to
13068 the default C@t{++} exception handler and the inferior terminated.
13070 @item show unwind-on-terminating-exception
13071 @kindex show unwind-on-terminating-exception
13072 Show the current setting of stack unwinding in the functions called by
13077 @cindex weak alias functions
13078 Sometimes, a function you wish to call is actually a @dfn{weak alias}
13079 for another function. In such case, @value{GDBN} might not pick up
13080 the type information, including the types of the function arguments,
13081 which causes @value{GDBN} to call the inferior function incorrectly.
13082 As a result, the called function will function erroneously and may
13083 even crash. A solution to that is to use the name of the aliased
13087 @section Patching Programs
13089 @cindex patching binaries
13090 @cindex writing into executables
13091 @cindex writing into corefiles
13093 By default, @value{GDBN} opens the file containing your program's
13094 executable code (or the corefile) read-only. This prevents accidental
13095 alterations to machine code; but it also prevents you from intentionally
13096 patching your program's binary.
13098 If you'd like to be able to patch the binary, you can specify that
13099 explicitly with the @code{set write} command. For example, you might
13100 want to turn on internal debugging flags, or even to make emergency
13106 @itemx set write off
13107 If you specify @samp{set write on}, @value{GDBN} opens executable and
13108 core files for both reading and writing; if you specify @kbd{set write
13109 off} (the default), @value{GDBN} opens them read-only.
13111 If you have already loaded a file, you must load it again (using the
13112 @code{exec-file} or @code{core-file} command) after changing @code{set
13113 write}, for your new setting to take effect.
13117 Display whether executable files and core files are opened for writing
13118 as well as reading.
13122 @chapter @value{GDBN} Files
13124 @value{GDBN} needs to know the file name of the program to be debugged,
13125 both in order to read its symbol table and in order to start your
13126 program. To debug a core dump of a previous run, you must also tell
13127 @value{GDBN} the name of the core dump file.
13130 * Files:: Commands to specify files
13131 * Separate Debug Files:: Debugging information in separate files
13132 * Symbol Errors:: Errors reading symbol files
13133 * Data Files:: GDB data files
13137 @section Commands to Specify Files
13139 @cindex symbol table
13140 @cindex core dump file
13142 You may want to specify executable and core dump file names. The usual
13143 way to do this is at start-up time, using the arguments to
13144 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
13145 Out of @value{GDBN}}).
13147 Occasionally it is necessary to change to a different file during a
13148 @value{GDBN} session. Or you may run @value{GDBN} and forget to
13149 specify a file you want to use. Or you are debugging a remote target
13150 via @code{gdbserver} (@pxref{Server, file, Using the @code{gdbserver}
13151 Program}). In these situations the @value{GDBN} commands to specify
13152 new files are useful.
13155 @cindex executable file
13157 @item file @var{filename}
13158 Use @var{filename} as the program to be debugged. It is read for its
13159 symbols and for the contents of pure memory. It is also the program
13160 executed when you use the @code{run} command. If you do not specify a
13161 directory and the file is not found in the @value{GDBN} working directory,
13162 @value{GDBN} uses the environment variable @code{PATH} as a list of
13163 directories to search, just as the shell does when looking for a program
13164 to run. You can change the value of this variable, for both @value{GDBN}
13165 and your program, using the @code{path} command.
13167 @cindex unlinked object files
13168 @cindex patching object files
13169 You can load unlinked object @file{.o} files into @value{GDBN} using
13170 the @code{file} command. You will not be able to ``run'' an object
13171 file, but you can disassemble functions and inspect variables. Also,
13172 if the underlying BFD functionality supports it, you could use
13173 @kbd{gdb -write} to patch object files using this technique. Note
13174 that @value{GDBN} can neither interpret nor modify relocations in this
13175 case, so branches and some initialized variables will appear to go to
13176 the wrong place. But this feature is still handy from time to time.
13179 @code{file} with no argument makes @value{GDBN} discard any information it
13180 has on both executable file and the symbol table.
13183 @item exec-file @r{[} @var{filename} @r{]}
13184 Specify that the program to be run (but not the symbol table) is found
13185 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
13186 if necessary to locate your program. Omitting @var{filename} means to
13187 discard information on the executable file.
13189 @kindex symbol-file
13190 @item symbol-file @r{[} @var{filename} @r{]}
13191 Read symbol table information from file @var{filename}. @code{PATH} is
13192 searched when necessary. Use the @code{file} command to get both symbol
13193 table and program to run from the same file.
13195 @code{symbol-file} with no argument clears out @value{GDBN} information on your
13196 program's symbol table.
13198 The @code{symbol-file} command causes @value{GDBN} to forget the contents of
13199 some breakpoints and auto-display expressions. This is because they may
13200 contain pointers to the internal data recording symbols and data types,
13201 which are part of the old symbol table data being discarded inside
13204 @code{symbol-file} does not repeat if you press @key{RET} again after
13207 When @value{GDBN} is configured for a particular environment, it
13208 understands debugging information in whatever format is the standard
13209 generated for that environment; you may use either a @sc{gnu} compiler, or
13210 other compilers that adhere to the local conventions.
13211 Best results are usually obtained from @sc{gnu} compilers; for example,
13212 using @code{@value{NGCC}} you can generate debugging information for
13215 For most kinds of object files, with the exception of old SVR3 systems
13216 using COFF, the @code{symbol-file} command does not normally read the
13217 symbol table in full right away. Instead, it scans the symbol table
13218 quickly to find which source files and which symbols are present. The
13219 details are read later, one source file at a time, as they are needed.
13221 The purpose of this two-stage reading strategy is to make @value{GDBN}
13222 start up faster. For the most part, it is invisible except for
13223 occasional pauses while the symbol table details for a particular source
13224 file are being read. (The @code{set verbose} command can turn these
13225 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
13226 Warnings and Messages}.)
13228 We have not implemented the two-stage strategy for COFF yet. When the
13229 symbol table is stored in COFF format, @code{symbol-file} reads the
13230 symbol table data in full right away. Note that ``stabs-in-COFF''
13231 still does the two-stage strategy, since the debug info is actually
13235 @cindex reading symbols immediately
13236 @cindex symbols, reading immediately
13237 @item symbol-file @var{filename} @r{[} -readnow @r{]}
13238 @itemx file @var{filename} @r{[} -readnow @r{]}
13239 You can override the @value{GDBN} two-stage strategy for reading symbol
13240 tables by using the @samp{-readnow} option with any of the commands that
13241 load symbol table information, if you want to be sure @value{GDBN} has the
13242 entire symbol table available.
13244 @c FIXME: for now no mention of directories, since this seems to be in
13245 @c flux. 13mar1992 status is that in theory GDB would look either in
13246 @c current dir or in same dir as myprog; but issues like competing
13247 @c GDB's, or clutter in system dirs, mean that in practice right now
13248 @c only current dir is used. FFish says maybe a special GDB hierarchy
13249 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
13253 @item core-file @r{[}@var{filename}@r{]}
13255 Specify the whereabouts of a core dump file to be used as the ``contents
13256 of memory''. Traditionally, core files contain only some parts of the
13257 address space of the process that generated them; @value{GDBN} can access the
13258 executable file itself for other parts.
13260 @code{core-file} with no argument specifies that no core file is
13263 Note that the core file is ignored when your program is actually running
13264 under @value{GDBN}. So, if you have been running your program and you
13265 wish to debug a core file instead, you must kill the subprocess in which
13266 the program is running. To do this, use the @code{kill} command
13267 (@pxref{Kill Process, ,Killing the Child Process}).
13269 @kindex add-symbol-file
13270 @cindex dynamic linking
13271 @item add-symbol-file @var{filename} @var{address}
13272 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]}
13273 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
13274 The @code{add-symbol-file} command reads additional symbol table
13275 information from the file @var{filename}. You would use this command
13276 when @var{filename} has been dynamically loaded (by some other means)
13277 into the program that is running. @var{address} should be the memory
13278 address at which the file has been loaded; @value{GDBN} cannot figure
13279 this out for itself. You can additionally specify an arbitrary number
13280 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
13281 section name and base address for that section. You can specify any
13282 @var{address} as an expression.
13284 The symbol table of the file @var{filename} is added to the symbol table
13285 originally read with the @code{symbol-file} command. You can use the
13286 @code{add-symbol-file} command any number of times; the new symbol data
13287 thus read keeps adding to the old. To discard all old symbol data
13288 instead, use the @code{symbol-file} command without any arguments.
13290 @cindex relocatable object files, reading symbols from
13291 @cindex object files, relocatable, reading symbols from
13292 @cindex reading symbols from relocatable object files
13293 @cindex symbols, reading from relocatable object files
13294 @cindex @file{.o} files, reading symbols from
13295 Although @var{filename} is typically a shared library file, an
13296 executable file, or some other object file which has been fully
13297 relocated for loading into a process, you can also load symbolic
13298 information from relocatable @file{.o} files, as long as:
13302 the file's symbolic information refers only to linker symbols defined in
13303 that file, not to symbols defined by other object files,
13305 every section the file's symbolic information refers to has actually
13306 been loaded into the inferior, as it appears in the file, and
13308 you can determine the address at which every section was loaded, and
13309 provide these to the @code{add-symbol-file} command.
13313 Some embedded operating systems, like Sun Chorus and VxWorks, can load
13314 relocatable files into an already running program; such systems
13315 typically make the requirements above easy to meet. However, it's
13316 important to recognize that many native systems use complex link
13317 procedures (@code{.linkonce} section factoring and C@t{++} constructor table
13318 assembly, for example) that make the requirements difficult to meet. In
13319 general, one cannot assume that using @code{add-symbol-file} to read a
13320 relocatable object file's symbolic information will have the same effect
13321 as linking the relocatable object file into the program in the normal
13324 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
13326 @kindex add-symbol-file-from-memory
13327 @cindex @code{syscall DSO}
13328 @cindex load symbols from memory
13329 @item add-symbol-file-from-memory @var{address}
13330 Load symbols from the given @var{address} in a dynamically loaded
13331 object file whose image is mapped directly into the inferior's memory.
13332 For example, the Linux kernel maps a @code{syscall DSO} into each
13333 process's address space; this DSO provides kernel-specific code for
13334 some system calls. The argument can be any expression whose
13335 evaluation yields the address of the file's shared object file header.
13336 For this command to work, you must have used @code{symbol-file} or
13337 @code{exec-file} commands in advance.
13339 @kindex add-shared-symbol-files
13341 @item add-shared-symbol-files @var{library-file}
13342 @itemx assf @var{library-file}
13343 The @code{add-shared-symbol-files} command can currently be used only
13344 in the Cygwin build of @value{GDBN} on MS-Windows OS, where it is an
13345 alias for the @code{dll-symbols} command (@pxref{Cygwin Native}).
13346 @value{GDBN} automatically looks for shared libraries, however if
13347 @value{GDBN} does not find yours, you can invoke
13348 @code{add-shared-symbol-files}. It takes one argument: the shared
13349 library's file name. @code{assf} is a shorthand alias for
13350 @code{add-shared-symbol-files}.
13353 @item section @var{section} @var{addr}
13354 The @code{section} command changes the base address of the named
13355 @var{section} of the exec file to @var{addr}. This can be used if the
13356 exec file does not contain section addresses, (such as in the
13357 @code{a.out} format), or when the addresses specified in the file
13358 itself are wrong. Each section must be changed separately. The
13359 @code{info files} command, described below, lists all the sections and
13363 @kindex info target
13366 @code{info files} and @code{info target} are synonymous; both print the
13367 current target (@pxref{Targets, ,Specifying a Debugging Target}),
13368 including the names of the executable and core dump files currently in
13369 use by @value{GDBN}, and the files from which symbols were loaded. The
13370 command @code{help target} lists all possible targets rather than
13373 @kindex maint info sections
13374 @item maint info sections
13375 Another command that can give you extra information about program sections
13376 is @code{maint info sections}. In addition to the section information
13377 displayed by @code{info files}, this command displays the flags and file
13378 offset of each section in the executable and core dump files. In addition,
13379 @code{maint info sections} provides the following command options (which
13380 may be arbitrarily combined):
13384 Display sections for all loaded object files, including shared libraries.
13385 @item @var{sections}
13386 Display info only for named @var{sections}.
13387 @item @var{section-flags}
13388 Display info only for sections for which @var{section-flags} are true.
13389 The section flags that @value{GDBN} currently knows about are:
13392 Section will have space allocated in the process when loaded.
13393 Set for all sections except those containing debug information.
13395 Section will be loaded from the file into the child process memory.
13396 Set for pre-initialized code and data, clear for @code{.bss} sections.
13398 Section needs to be relocated before loading.
13400 Section cannot be modified by the child process.
13402 Section contains executable code only.
13404 Section contains data only (no executable code).
13406 Section will reside in ROM.
13408 Section contains data for constructor/destructor lists.
13410 Section is not empty.
13412 An instruction to the linker to not output the section.
13413 @item COFF_SHARED_LIBRARY
13414 A notification to the linker that the section contains
13415 COFF shared library information.
13417 Section contains common symbols.
13420 @kindex set trust-readonly-sections
13421 @cindex read-only sections
13422 @item set trust-readonly-sections on
13423 Tell @value{GDBN} that readonly sections in your object file
13424 really are read-only (i.e.@: that their contents will not change).
13425 In that case, @value{GDBN} can fetch values from these sections
13426 out of the object file, rather than from the target program.
13427 For some targets (notably embedded ones), this can be a significant
13428 enhancement to debugging performance.
13430 The default is off.
13432 @item set trust-readonly-sections off
13433 Tell @value{GDBN} not to trust readonly sections. This means that
13434 the contents of the section might change while the program is running,
13435 and must therefore be fetched from the target when needed.
13437 @item show trust-readonly-sections
13438 Show the current setting of trusting readonly sections.
13441 All file-specifying commands allow both absolute and relative file names
13442 as arguments. @value{GDBN} always converts the file name to an absolute file
13443 name and remembers it that way.
13445 @cindex shared libraries
13446 @anchor{Shared Libraries}
13447 @value{GDBN} supports @sc{gnu}/Linux, MS-Windows, HP-UX, SunOS, SVr4, Irix,
13448 and IBM RS/6000 AIX shared libraries.
13450 On MS-Windows @value{GDBN} must be linked with the Expat library to support
13451 shared libraries. @xref{Expat}.
13453 @value{GDBN} automatically loads symbol definitions from shared libraries
13454 when you use the @code{run} command, or when you examine a core file.
13455 (Before you issue the @code{run} command, @value{GDBN} does not understand
13456 references to a function in a shared library, however---unless you are
13457 debugging a core file).
13459 On HP-UX, if the program loads a library explicitly, @value{GDBN}
13460 automatically loads the symbols at the time of the @code{shl_load} call.
13462 @c FIXME: some @value{GDBN} release may permit some refs to undef
13463 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
13464 @c FIXME...lib; check this from time to time when updating manual
13466 There are times, however, when you may wish to not automatically load
13467 symbol definitions from shared libraries, such as when they are
13468 particularly large or there are many of them.
13470 To control the automatic loading of shared library symbols, use the
13474 @kindex set auto-solib-add
13475 @item set auto-solib-add @var{mode}
13476 If @var{mode} is @code{on}, symbols from all shared object libraries
13477 will be loaded automatically when the inferior begins execution, you
13478 attach to an independently started inferior, or when the dynamic linker
13479 informs @value{GDBN} that a new library has been loaded. If @var{mode}
13480 is @code{off}, symbols must be loaded manually, using the
13481 @code{sharedlibrary} command. The default value is @code{on}.
13483 @cindex memory used for symbol tables
13484 If your program uses lots of shared libraries with debug info that
13485 takes large amounts of memory, you can decrease the @value{GDBN}
13486 memory footprint by preventing it from automatically loading the
13487 symbols from shared libraries. To that end, type @kbd{set
13488 auto-solib-add off} before running the inferior, then load each
13489 library whose debug symbols you do need with @kbd{sharedlibrary
13490 @var{regexp}}, where @var{regexp} is a regular expression that matches
13491 the libraries whose symbols you want to be loaded.
13493 @kindex show auto-solib-add
13494 @item show auto-solib-add
13495 Display the current autoloading mode.
13498 @cindex load shared library
13499 To explicitly load shared library symbols, use the @code{sharedlibrary}
13503 @kindex info sharedlibrary
13506 @itemx info sharedlibrary
13507 Print the names of the shared libraries which are currently loaded.
13509 @kindex sharedlibrary
13511 @item sharedlibrary @var{regex}
13512 @itemx share @var{regex}
13513 Load shared object library symbols for files matching a
13514 Unix regular expression.
13515 As with files loaded automatically, it only loads shared libraries
13516 required by your program for a core file or after typing @code{run}. If
13517 @var{regex} is omitted all shared libraries required by your program are
13520 @item nosharedlibrary
13521 @kindex nosharedlibrary
13522 @cindex unload symbols from shared libraries
13523 Unload all shared object library symbols. This discards all symbols
13524 that have been loaded from all shared libraries. Symbols from shared
13525 libraries that were loaded by explicit user requests are not
13529 Sometimes you may wish that @value{GDBN} stops and gives you control
13530 when any of shared library events happen. Use the @code{set
13531 stop-on-solib-events} command for this:
13534 @item set stop-on-solib-events
13535 @kindex set stop-on-solib-events
13536 This command controls whether @value{GDBN} should give you control
13537 when the dynamic linker notifies it about some shared library event.
13538 The most common event of interest is loading or unloading of a new
13541 @item show stop-on-solib-events
13542 @kindex show stop-on-solib-events
13543 Show whether @value{GDBN} stops and gives you control when shared
13544 library events happen.
13547 Shared libraries are also supported in many cross or remote debugging
13548 configurations. @value{GDBN} needs to have access to the target's libraries;
13549 this can be accomplished either by providing copies of the libraries
13550 on the host system, or by asking @value{GDBN} to automatically retrieve the
13551 libraries from the target. If copies of the target libraries are
13552 provided, they need to be the same as the target libraries, although the
13553 copies on the target can be stripped as long as the copies on the host are
13556 @cindex where to look for shared libraries
13557 For remote debugging, you need to tell @value{GDBN} where the target
13558 libraries are, so that it can load the correct copies---otherwise, it
13559 may try to load the host's libraries. @value{GDBN} has two variables
13560 to specify the search directories for target libraries.
13563 @cindex prefix for shared library file names
13564 @cindex system root, alternate
13565 @kindex set solib-absolute-prefix
13566 @kindex set sysroot
13567 @item set sysroot @var{path}
13568 Use @var{path} as the system root for the program being debugged. Any
13569 absolute shared library paths will be prefixed with @var{path}; many
13570 runtime loaders store the absolute paths to the shared library in the
13571 target program's memory. If you use @code{set sysroot} to find shared
13572 libraries, they need to be laid out in the same way that they are on
13573 the target, with e.g.@: a @file{/lib} and @file{/usr/lib} hierarchy
13576 If @var{path} starts with the sequence @file{remote:}, @value{GDBN} will
13577 retrieve the target libraries from the remote system. This is only
13578 supported when using a remote target that supports the @code{remote get}
13579 command (@pxref{File Transfer,,Sending files to a remote system}).
13580 The part of @var{path} following the initial @file{remote:}
13581 (if present) is used as system root prefix on the remote file system.
13582 @footnote{If you want to specify a local system root using a directory
13583 that happens to be named @file{remote:}, you need to use some equivalent
13584 variant of the name like @file{./remote:}.}
13586 The @code{set solib-absolute-prefix} command is an alias for @code{set
13589 @cindex default system root
13590 @cindex @samp{--with-sysroot}
13591 You can set the default system root by using the configure-time
13592 @samp{--with-sysroot} option. If the system root is inside
13593 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
13594 @samp{--exec-prefix}), then the default system root will be updated
13595 automatically if the installed @value{GDBN} is moved to a new
13598 @kindex show sysroot
13600 Display the current shared library prefix.
13602 @kindex set solib-search-path
13603 @item set solib-search-path @var{path}
13604 If this variable is set, @var{path} is a colon-separated list of
13605 directories to search for shared libraries. @samp{solib-search-path}
13606 is used after @samp{sysroot} fails to locate the library, or if the
13607 path to the library is relative instead of absolute. If you want to
13608 use @samp{solib-search-path} instead of @samp{sysroot}, be sure to set
13609 @samp{sysroot} to a nonexistent directory to prevent @value{GDBN} from
13610 finding your host's libraries. @samp{sysroot} is preferred; setting
13611 it to a nonexistent directory may interfere with automatic loading
13612 of shared library symbols.
13614 @kindex show solib-search-path
13615 @item show solib-search-path
13616 Display the current shared library search path.
13620 @node Separate Debug Files
13621 @section Debugging Information in Separate Files
13622 @cindex separate debugging information files
13623 @cindex debugging information in separate files
13624 @cindex @file{.debug} subdirectories
13625 @cindex debugging information directory, global
13626 @cindex global debugging information directory
13627 @cindex build ID, and separate debugging files
13628 @cindex @file{.build-id} directory
13630 @value{GDBN} allows you to put a program's debugging information in a
13631 file separate from the executable itself, in a way that allows
13632 @value{GDBN} to find and load the debugging information automatically.
13633 Since debugging information can be very large---sometimes larger
13634 than the executable code itself---some systems distribute debugging
13635 information for their executables in separate files, which users can
13636 install only when they need to debug a problem.
13638 @value{GDBN} supports two ways of specifying the separate debug info
13643 The executable contains a @dfn{debug link} that specifies the name of
13644 the separate debug info file. The separate debug file's name is
13645 usually @file{@var{executable}.debug}, where @var{executable} is the
13646 name of the corresponding executable file without leading directories
13647 (e.g., @file{ls.debug} for @file{/usr/bin/ls}). In addition, the
13648 debug link specifies a 32-bit @dfn{Cyclic Redundancy Check} (CRC)
13649 checksum for the debug file, which @value{GDBN} uses to validate that
13650 the executable and the debug file came from the same build.
13653 The executable contains a @dfn{build ID}, a unique bit string that is
13654 also present in the corresponding debug info file. (This is supported
13655 only on some operating systems, notably those which use the ELF format
13656 for binary files and the @sc{gnu} Binutils.) For more details about
13657 this feature, see the description of the @option{--build-id}
13658 command-line option in @ref{Options, , Command Line Options, ld.info,
13659 The GNU Linker}. The debug info file's name is not specified
13660 explicitly by the build ID, but can be computed from the build ID, see
13664 Depending on the way the debug info file is specified, @value{GDBN}
13665 uses two different methods of looking for the debug file:
13669 For the ``debug link'' method, @value{GDBN} looks up the named file in
13670 the directory of the executable file, then in a subdirectory of that
13671 directory named @file{.debug}, and finally under the global debug
13672 directory, in a subdirectory whose name is identical to the leading
13673 directories of the executable's absolute file name.
13676 For the ``build ID'' method, @value{GDBN} looks in the
13677 @file{.build-id} subdirectory of the global debug directory for a file
13678 named @file{@var{nn}/@var{nnnnnnnn}.debug}, where @var{nn} are the
13679 first 2 hex characters of the build ID bit string, and @var{nnnnnnnn}
13680 are the rest of the bit string. (Real build ID strings are 32 or more
13681 hex characters, not 10.)
13684 So, for example, suppose you ask @value{GDBN} to debug
13685 @file{/usr/bin/ls}, which has a debug link that specifies the
13686 file @file{ls.debug}, and a build ID whose value in hex is
13687 @code{abcdef1234}. If the global debug directory is
13688 @file{/usr/lib/debug}, then @value{GDBN} will look for the following
13689 debug information files, in the indicated order:
13693 @file{/usr/lib/debug/.build-id/ab/cdef1234.debug}
13695 @file{/usr/bin/ls.debug}
13697 @file{/usr/bin/.debug/ls.debug}
13699 @file{/usr/lib/debug/usr/bin/ls.debug}.
13702 You can set the global debugging info directory's name, and view the
13703 name @value{GDBN} is currently using.
13707 @kindex set debug-file-directory
13708 @item set debug-file-directory @var{directory}
13709 Set the directory which @value{GDBN} searches for separate debugging
13710 information files to @var{directory}.
13712 @kindex show debug-file-directory
13713 @item show debug-file-directory
13714 Show the directory @value{GDBN} searches for separate debugging
13719 @cindex @code{.gnu_debuglink} sections
13720 @cindex debug link sections
13721 A debug link is a special section of the executable file named
13722 @code{.gnu_debuglink}. The section must contain:
13726 A filename, with any leading directory components removed, followed by
13729 zero to three bytes of padding, as needed to reach the next four-byte
13730 boundary within the section, and
13732 a four-byte CRC checksum, stored in the same endianness used for the
13733 executable file itself. The checksum is computed on the debugging
13734 information file's full contents by the function given below, passing
13735 zero as the @var{crc} argument.
13738 Any executable file format can carry a debug link, as long as it can
13739 contain a section named @code{.gnu_debuglink} with the contents
13742 @cindex @code{.note.gnu.build-id} sections
13743 @cindex build ID sections
13744 The build ID is a special section in the executable file (and in other
13745 ELF binary files that @value{GDBN} may consider). This section is
13746 often named @code{.note.gnu.build-id}, but that name is not mandatory.
13747 It contains unique identification for the built files---the ID remains
13748 the same across multiple builds of the same build tree. The default
13749 algorithm SHA1 produces 160 bits (40 hexadecimal characters) of the
13750 content for the build ID string. The same section with an identical
13751 value is present in the original built binary with symbols, in its
13752 stripped variant, and in the separate debugging information file.
13754 The debugging information file itself should be an ordinary
13755 executable, containing a full set of linker symbols, sections, and
13756 debugging information. The sections of the debugging information file
13757 should have the same names, addresses, and sizes as the original file,
13758 but they need not contain any data---much like a @code{.bss} section
13759 in an ordinary executable.
13761 The @sc{gnu} binary utilities (Binutils) package includes the
13762 @samp{objcopy} utility that can produce
13763 the separated executable / debugging information file pairs using the
13764 following commands:
13767 @kbd{objcopy --only-keep-debug foo foo.debug}
13772 These commands remove the debugging
13773 information from the executable file @file{foo} and place it in the file
13774 @file{foo.debug}. You can use the first, second or both methods to link the
13779 The debug link method needs the following additional command to also leave
13780 behind a debug link in @file{foo}:
13783 @kbd{objcopy --add-gnu-debuglink=foo.debug foo}
13786 Ulrich Drepper's @file{elfutils} package, starting with version 0.53, contains
13787 a version of the @code{strip} command such that the command @kbd{strip foo -f
13788 foo.debug} has the same functionality as the two @code{objcopy} commands and
13789 the @code{ln -s} command above, together.
13792 Build ID gets embedded into the main executable using @code{ld --build-id} or
13793 the @value{NGCC} counterpart @code{gcc -Wl,--build-id}. Build ID support plus
13794 compatibility fixes for debug files separation are present in @sc{gnu} binary
13795 utilities (Binutils) package since version 2.18.
13800 @cindex CRC algorithm definition
13801 The CRC used in @code{.gnu_debuglink} is the CRC-32 defined in
13802 IEEE 802.3 using the polynomial:
13804 @c TexInfo requires naked braces for multi-digit exponents for Tex
13805 @c output, but this causes HTML output to barf. HTML has to be set using
13806 @c raw commands. So we end up having to specify this equation in 2
13811 <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>
13812 + <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
13818 @math{x^{32} + x^{26} + x^{23} + x^{22} + x^{16} + x^{12} + x^{11}}
13819 @math{+ x^{10} + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1}
13823 The function is computed byte at a time, taking the least
13824 significant bit of each byte first. The initial pattern
13825 @code{0xffffffff} is used, to ensure leading zeros affect the CRC and
13826 the final result is inverted to ensure trailing zeros also affect the
13829 @emph{Note:} This is the same CRC polynomial as used in handling the
13830 @dfn{Remote Serial Protocol} @code{qCRC} packet (@pxref{Remote Protocol,
13831 , @value{GDBN} Remote Serial Protocol}). However in the
13832 case of the Remote Serial Protocol, the CRC is computed @emph{most}
13833 significant bit first, and the result is not inverted, so trailing
13834 zeros have no effect on the CRC value.
13836 To complete the description, we show below the code of the function
13837 which produces the CRC used in @code{.gnu_debuglink}. Inverting the
13838 initially supplied @code{crc} argument means that an initial call to
13839 this function passing in zero will start computing the CRC using
13842 @kindex gnu_debuglink_crc32
13845 gnu_debuglink_crc32 (unsigned long crc,
13846 unsigned char *buf, size_t len)
13848 static const unsigned long crc32_table[256] =
13850 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
13851 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
13852 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
13853 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
13854 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
13855 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
13856 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
13857 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
13858 0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
13859 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
13860 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
13861 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
13862 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
13863 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
13864 0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
13865 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
13866 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
13867 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
13868 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
13869 0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
13870 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
13871 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
13872 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
13873 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
13874 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
13875 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
13876 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
13877 0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
13878 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
13879 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
13880 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
13881 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
13882 0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
13883 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
13884 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
13885 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
13886 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
13887 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
13888 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
13889 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
13890 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
13891 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
13892 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
13893 0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
13894 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
13895 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
13896 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
13897 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
13898 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
13899 0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
13900 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
13903 unsigned char *end;
13905 crc = ~crc & 0xffffffff;
13906 for (end = buf + len; buf < end; ++buf)
13907 crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
13908 return ~crc & 0xffffffff;
13913 This computation does not apply to the ``build ID'' method.
13916 @node Symbol Errors
13917 @section Errors Reading Symbol Files
13919 While reading a symbol file, @value{GDBN} occasionally encounters problems,
13920 such as symbol types it does not recognize, or known bugs in compiler
13921 output. By default, @value{GDBN} does not notify you of such problems, since
13922 they are relatively common and primarily of interest to people
13923 debugging compilers. If you are interested in seeing information
13924 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
13925 only one message about each such type of problem, no matter how many
13926 times the problem occurs; or you can ask @value{GDBN} to print more messages,
13927 to see how many times the problems occur, with the @code{set
13928 complaints} command (@pxref{Messages/Warnings, ,Optional Warnings and
13931 The messages currently printed, and their meanings, include:
13934 @item inner block not inside outer block in @var{symbol}
13936 The symbol information shows where symbol scopes begin and end
13937 (such as at the start of a function or a block of statements). This
13938 error indicates that an inner scope block is not fully contained
13939 in its outer scope blocks.
13941 @value{GDBN} circumvents the problem by treating the inner block as if it had
13942 the same scope as the outer block. In the error message, @var{symbol}
13943 may be shown as ``@code{(don't know)}'' if the outer block is not a
13946 @item block at @var{address} out of order
13948 The symbol information for symbol scope blocks should occur in
13949 order of increasing addresses. This error indicates that it does not
13952 @value{GDBN} does not circumvent this problem, and has trouble
13953 locating symbols in the source file whose symbols it is reading. (You
13954 can often determine what source file is affected by specifying
13955 @code{set verbose on}. @xref{Messages/Warnings, ,Optional Warnings and
13958 @item bad block start address patched
13960 The symbol information for a symbol scope block has a start address
13961 smaller than the address of the preceding source line. This is known
13962 to occur in the SunOS 4.1.1 (and earlier) C compiler.
13964 @value{GDBN} circumvents the problem by treating the symbol scope block as
13965 starting on the previous source line.
13967 @item bad string table offset in symbol @var{n}
13970 Symbol number @var{n} contains a pointer into the string table which is
13971 larger than the size of the string table.
13973 @value{GDBN} circumvents the problem by considering the symbol to have the
13974 name @code{foo}, which may cause other problems if many symbols end up
13977 @item unknown symbol type @code{0x@var{nn}}
13979 The symbol information contains new data types that @value{GDBN} does
13980 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
13981 uncomprehended information, in hexadecimal.
13983 @value{GDBN} circumvents the error by ignoring this symbol information.
13984 This usually allows you to debug your program, though certain symbols
13985 are not accessible. If you encounter such a problem and feel like
13986 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
13987 on @code{complain}, then go up to the function @code{read_dbx_symtab}
13988 and examine @code{*bufp} to see the symbol.
13990 @item stub type has NULL name
13992 @value{GDBN} could not find the full definition for a struct or class.
13994 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
13995 The symbol information for a C@t{++} member function is missing some
13996 information that recent versions of the compiler should have output for
13999 @item info mismatch between compiler and debugger
14001 @value{GDBN} could not parse a type specification output by the compiler.
14006 @section GDB Data Files
14008 @cindex prefix for data files
14009 @value{GDBN} will sometimes read an auxiliary data file. These files
14010 are kept in a directory known as the @dfn{data directory}.
14012 You can set the data directory's name, and view the name @value{GDBN}
14013 is currently using.
14016 @kindex set data-directory
14017 @item set data-directory @var{directory}
14018 Set the directory which @value{GDBN} searches for auxiliary data files
14019 to @var{directory}.
14021 @kindex show data-directory
14022 @item show data-directory
14023 Show the directory @value{GDBN} searches for auxiliary data files.
14026 @cindex default data directory
14027 @cindex @samp{--with-gdb-datadir}
14028 You can set the default data directory by using the configure-time
14029 @samp{--with-gdb-datadir} option. If the data directory is inside
14030 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
14031 @samp{--exec-prefix}), then the default data directory will be updated
14032 automatically if the installed @value{GDBN} is moved to a new
14036 @chapter Specifying a Debugging Target
14038 @cindex debugging target
14039 A @dfn{target} is the execution environment occupied by your program.
14041 Often, @value{GDBN} runs in the same host environment as your program;
14042 in that case, the debugging target is specified as a side effect when
14043 you use the @code{file} or @code{core} commands. When you need more
14044 flexibility---for example, running @value{GDBN} on a physically separate
14045 host, or controlling a standalone system over a serial port or a
14046 realtime system over a TCP/IP connection---you can use the @code{target}
14047 command to specify one of the target types configured for @value{GDBN}
14048 (@pxref{Target Commands, ,Commands for Managing Targets}).
14050 @cindex target architecture
14051 It is possible to build @value{GDBN} for several different @dfn{target
14052 architectures}. When @value{GDBN} is built like that, you can choose
14053 one of the available architectures with the @kbd{set architecture}
14057 @kindex set architecture
14058 @kindex show architecture
14059 @item set architecture @var{arch}
14060 This command sets the current target architecture to @var{arch}. The
14061 value of @var{arch} can be @code{"auto"}, in addition to one of the
14062 supported architectures.
14064 @item show architecture
14065 Show the current target architecture.
14067 @item set processor
14069 @kindex set processor
14070 @kindex show processor
14071 These are alias commands for, respectively, @code{set architecture}
14072 and @code{show architecture}.
14076 * Active Targets:: Active targets
14077 * Target Commands:: Commands for managing targets
14078 * Byte Order:: Choosing target byte order
14081 @node Active Targets
14082 @section Active Targets
14084 @cindex stacking targets
14085 @cindex active targets
14086 @cindex multiple targets
14088 There are three classes of targets: processes, core files, and
14089 executable files. @value{GDBN} can work concurrently on up to three
14090 active targets, one in each class. This allows you to (for example)
14091 start a process and inspect its activity without abandoning your work on
14094 For example, if you execute @samp{gdb a.out}, then the executable file
14095 @code{a.out} is the only active target. If you designate a core file as
14096 well---presumably from a prior run that crashed and coredumped---then
14097 @value{GDBN} has two active targets and uses them in tandem, looking
14098 first in the corefile target, then in the executable file, to satisfy
14099 requests for memory addresses. (Typically, these two classes of target
14100 are complementary, since core files contain only a program's
14101 read-write memory---variables and so on---plus machine status, while
14102 executable files contain only the program text and initialized data.)
14104 When you type @code{run}, your executable file becomes an active process
14105 target as well. When a process target is active, all @value{GDBN}
14106 commands requesting memory addresses refer to that target; addresses in
14107 an active core file or executable file target are obscured while the
14108 process target is active.
14110 Use the @code{core-file} and @code{exec-file} commands to select a new
14111 core file or executable target (@pxref{Files, ,Commands to Specify
14112 Files}). To specify as a target a process that is already running, use
14113 the @code{attach} command (@pxref{Attach, ,Debugging an Already-running
14116 @node Target Commands
14117 @section Commands for Managing Targets
14120 @item target @var{type} @var{parameters}
14121 Connects the @value{GDBN} host environment to a target machine or
14122 process. A target is typically a protocol for talking to debugging
14123 facilities. You use the argument @var{type} to specify the type or
14124 protocol of the target machine.
14126 Further @var{parameters} are interpreted by the target protocol, but
14127 typically include things like device names or host names to connect
14128 with, process numbers, and baud rates.
14130 The @code{target} command does not repeat if you press @key{RET} again
14131 after executing the command.
14133 @kindex help target
14135 Displays the names of all targets available. To display targets
14136 currently selected, use either @code{info target} or @code{info files}
14137 (@pxref{Files, ,Commands to Specify Files}).
14139 @item help target @var{name}
14140 Describe a particular target, including any parameters necessary to
14143 @kindex set gnutarget
14144 @item set gnutarget @var{args}
14145 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
14146 knows whether it is reading an @dfn{executable},
14147 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
14148 with the @code{set gnutarget} command. Unlike most @code{target} commands,
14149 with @code{gnutarget} the @code{target} refers to a program, not a machine.
14152 @emph{Warning:} To specify a file format with @code{set gnutarget},
14153 you must know the actual BFD name.
14157 @xref{Files, , Commands to Specify Files}.
14159 @kindex show gnutarget
14160 @item show gnutarget
14161 Use the @code{show gnutarget} command to display what file format
14162 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
14163 @value{GDBN} will determine the file format for each file automatically,
14164 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
14167 @cindex common targets
14168 Here are some common targets (available, or not, depending on the GDB
14173 @item target exec @var{program}
14174 @cindex executable file target
14175 An executable file. @samp{target exec @var{program}} is the same as
14176 @samp{exec-file @var{program}}.
14178 @item target core @var{filename}
14179 @cindex core dump file target
14180 A core dump file. @samp{target core @var{filename}} is the same as
14181 @samp{core-file @var{filename}}.
14183 @item target remote @var{medium}
14184 @cindex remote target
14185 A remote system connected to @value{GDBN} via a serial line or network
14186 connection. This command tells @value{GDBN} to use its own remote
14187 protocol over @var{medium} for debugging. @xref{Remote Debugging}.
14189 For example, if you have a board connected to @file{/dev/ttya} on the
14190 machine running @value{GDBN}, you could say:
14193 target remote /dev/ttya
14196 @code{target remote} supports the @code{load} command. This is only
14197 useful if you have some other way of getting the stub to the target
14198 system, and you can put it somewhere in memory where it won't get
14199 clobbered by the download.
14202 @cindex built-in simulator target
14203 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
14211 works; however, you cannot assume that a specific memory map, device
14212 drivers, or even basic I/O is available, although some simulators do
14213 provide these. For info about any processor-specific simulator details,
14214 see the appropriate section in @ref{Embedded Processors, ,Embedded
14219 Some configurations may include these targets as well:
14223 @item target nrom @var{dev}
14224 @cindex NetROM ROM emulator target
14225 NetROM ROM emulator. This target only supports downloading.
14229 Different targets are available on different configurations of @value{GDBN};
14230 your configuration may have more or fewer targets.
14232 Many remote targets require you to download the executable's code once
14233 you've successfully established a connection. You may wish to control
14234 various aspects of this process.
14239 @kindex set hash@r{, for remote monitors}
14240 @cindex hash mark while downloading
14241 This command controls whether a hash mark @samp{#} is displayed while
14242 downloading a file to the remote monitor. If on, a hash mark is
14243 displayed after each S-record is successfully downloaded to the
14247 @kindex show hash@r{, for remote monitors}
14248 Show the current status of displaying the hash mark.
14250 @item set debug monitor
14251 @kindex set debug monitor
14252 @cindex display remote monitor communications
14253 Enable or disable display of communications messages between
14254 @value{GDBN} and the remote monitor.
14256 @item show debug monitor
14257 @kindex show debug monitor
14258 Show the current status of displaying communications between
14259 @value{GDBN} and the remote monitor.
14264 @kindex load @var{filename}
14265 @item load @var{filename}
14267 Depending on what remote debugging facilities are configured into
14268 @value{GDBN}, the @code{load} command may be available. Where it exists, it
14269 is meant to make @var{filename} (an executable) available for debugging
14270 on the remote system---by downloading, or dynamic linking, for example.
14271 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
14272 the @code{add-symbol-file} command.
14274 If your @value{GDBN} does not have a @code{load} command, attempting to
14275 execute it gets the error message ``@code{You can't do that when your
14276 target is @dots{}}''
14278 The file is loaded at whatever address is specified in the executable.
14279 For some object file formats, you can specify the load address when you
14280 link the program; for other formats, like a.out, the object file format
14281 specifies a fixed address.
14282 @c FIXME! This would be a good place for an xref to the GNU linker doc.
14284 Depending on the remote side capabilities, @value{GDBN} may be able to
14285 load programs into flash memory.
14287 @code{load} does not repeat if you press @key{RET} again after using it.
14291 @section Choosing Target Byte Order
14293 @cindex choosing target byte order
14294 @cindex target byte order
14296 Some types of processors, such as the MIPS, PowerPC, and Renesas SH,
14297 offer the ability to run either big-endian or little-endian byte
14298 orders. Usually the executable or symbol will include a bit to
14299 designate the endian-ness, and you will not need to worry about
14300 which to use. However, you may still find it useful to adjust
14301 @value{GDBN}'s idea of processor endian-ness manually.
14305 @item set endian big
14306 Instruct @value{GDBN} to assume the target is big-endian.
14308 @item set endian little
14309 Instruct @value{GDBN} to assume the target is little-endian.
14311 @item set endian auto
14312 Instruct @value{GDBN} to use the byte order associated with the
14316 Display @value{GDBN}'s current idea of the target byte order.
14320 Note that these commands merely adjust interpretation of symbolic
14321 data on the host, and that they have absolutely no effect on the
14325 @node Remote Debugging
14326 @chapter Debugging Remote Programs
14327 @cindex remote debugging
14329 If you are trying to debug a program running on a machine that cannot run
14330 @value{GDBN} in the usual way, it is often useful to use remote debugging.
14331 For example, you might use remote debugging on an operating system kernel,
14332 or on a small system which does not have a general purpose operating system
14333 powerful enough to run a full-featured debugger.
14335 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
14336 to make this work with particular debugging targets. In addition,
14337 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
14338 but not specific to any particular target system) which you can use if you
14339 write the remote stubs---the code that runs on the remote system to
14340 communicate with @value{GDBN}.
14342 Other remote targets may be available in your
14343 configuration of @value{GDBN}; use @code{help target} to list them.
14346 * Connecting:: Connecting to a remote target
14347 * File Transfer:: Sending files to a remote system
14348 * Server:: Using the gdbserver program
14349 * Remote Configuration:: Remote configuration
14350 * Remote Stub:: Implementing a remote stub
14354 @section Connecting to a Remote Target
14356 On the @value{GDBN} host machine, you will need an unstripped copy of
14357 your program, since @value{GDBN} needs symbol and debugging information.
14358 Start up @value{GDBN} as usual, using the name of the local copy of your
14359 program as the first argument.
14361 @cindex @code{target remote}
14362 @value{GDBN} can communicate with the target over a serial line, or
14363 over an @acronym{IP} network using @acronym{TCP} or @acronym{UDP}. In
14364 each case, @value{GDBN} uses the same protocol for debugging your
14365 program; only the medium carrying the debugging packets varies. The
14366 @code{target remote} command establishes a connection to the target.
14367 Its arguments indicate which medium to use:
14371 @item target remote @var{serial-device}
14372 @cindex serial line, @code{target remote}
14373 Use @var{serial-device} to communicate with the target. For example,
14374 to use a serial line connected to the device named @file{/dev/ttyb}:
14377 target remote /dev/ttyb
14380 If you're using a serial line, you may want to give @value{GDBN} the
14381 @w{@samp{--baud}} option, or use the @code{set remotebaud} command
14382 (@pxref{Remote Configuration, set remotebaud}) before the
14383 @code{target} command.
14385 @item target remote @code{@var{host}:@var{port}}
14386 @itemx target remote @code{tcp:@var{host}:@var{port}}
14387 @cindex @acronym{TCP} port, @code{target remote}
14388 Debug using a @acronym{TCP} connection to @var{port} on @var{host}.
14389 The @var{host} may be either a host name or a numeric @acronym{IP}
14390 address; @var{port} must be a decimal number. The @var{host} could be
14391 the target machine itself, if it is directly connected to the net, or
14392 it might be a terminal server which in turn has a serial line to the
14395 For example, to connect to port 2828 on a terminal server named
14399 target remote manyfarms:2828
14402 If your remote target is actually running on the same machine as your
14403 debugger session (e.g.@: a simulator for your target running on the
14404 same host), you can omit the hostname. For example, to connect to
14405 port 1234 on your local machine:
14408 target remote :1234
14412 Note that the colon is still required here.
14414 @item target remote @code{udp:@var{host}:@var{port}}
14415 @cindex @acronym{UDP} port, @code{target remote}
14416 Debug using @acronym{UDP} packets to @var{port} on @var{host}. For example, to
14417 connect to @acronym{UDP} port 2828 on a terminal server named @code{manyfarms}:
14420 target remote udp:manyfarms:2828
14423 When using a @acronym{UDP} connection for remote debugging, you should
14424 keep in mind that the `U' stands for ``Unreliable''. @acronym{UDP}
14425 can silently drop packets on busy or unreliable networks, which will
14426 cause havoc with your debugging session.
14428 @item target remote | @var{command}
14429 @cindex pipe, @code{target remote} to
14430 Run @var{command} in the background and communicate with it using a
14431 pipe. The @var{command} is a shell command, to be parsed and expanded
14432 by the system's command shell, @code{/bin/sh}; it should expect remote
14433 protocol packets on its standard input, and send replies on its
14434 standard output. You could use this to run a stand-alone simulator
14435 that speaks the remote debugging protocol, to make net connections
14436 using programs like @code{ssh}, or for other similar tricks.
14438 If @var{command} closes its standard output (perhaps by exiting),
14439 @value{GDBN} will try to send it a @code{SIGTERM} signal. (If the
14440 program has already exited, this will have no effect.)
14444 Once the connection has been established, you can use all the usual
14445 commands to examine and change data. The remote program is already
14446 running; you can use @kbd{step} and @kbd{continue}, and you do not
14447 need to use @kbd{run}.
14449 @cindex interrupting remote programs
14450 @cindex remote programs, interrupting
14451 Whenever @value{GDBN} is waiting for the remote program, if you type the
14452 interrupt character (often @kbd{Ctrl-c}), @value{GDBN} attempts to stop the
14453 program. This may or may not succeed, depending in part on the hardware
14454 and the serial drivers the remote system uses. If you type the
14455 interrupt character once again, @value{GDBN} displays this prompt:
14458 Interrupted while waiting for the program.
14459 Give up (and stop debugging it)? (y or n)
14462 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
14463 (If you decide you want to try again later, you can use @samp{target
14464 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
14465 goes back to waiting.
14468 @kindex detach (remote)
14470 When you have finished debugging the remote program, you can use the
14471 @code{detach} command to release it from @value{GDBN} control.
14472 Detaching from the target normally resumes its execution, but the results
14473 will depend on your particular remote stub. After the @code{detach}
14474 command, @value{GDBN} is free to connect to another target.
14478 The @code{disconnect} command behaves like @code{detach}, except that
14479 the target is generally not resumed. It will wait for @value{GDBN}
14480 (this instance or another one) to connect and continue debugging. After
14481 the @code{disconnect} command, @value{GDBN} is again free to connect to
14484 @cindex send command to remote monitor
14485 @cindex extend @value{GDBN} for remote targets
14486 @cindex add new commands for external monitor
14488 @item monitor @var{cmd}
14489 This command allows you to send arbitrary commands directly to the
14490 remote monitor. Since @value{GDBN} doesn't care about the commands it
14491 sends like this, this command is the way to extend @value{GDBN}---you
14492 can add new commands that only the external monitor will understand
14496 @node File Transfer
14497 @section Sending files to a remote system
14498 @cindex remote target, file transfer
14499 @cindex file transfer
14500 @cindex sending files to remote systems
14502 Some remote targets offer the ability to transfer files over the same
14503 connection used to communicate with @value{GDBN}. This is convenient
14504 for targets accessible through other means, e.g.@: @sc{gnu}/Linux systems
14505 running @code{gdbserver} over a network interface. For other targets,
14506 e.g.@: embedded devices with only a single serial port, this may be
14507 the only way to upload or download files.
14509 Not all remote targets support these commands.
14513 @item remote put @var{hostfile} @var{targetfile}
14514 Copy file @var{hostfile} from the host system (the machine running
14515 @value{GDBN}) to @var{targetfile} on the target system.
14518 @item remote get @var{targetfile} @var{hostfile}
14519 Copy file @var{targetfile} from the target system to @var{hostfile}
14520 on the host system.
14522 @kindex remote delete
14523 @item remote delete @var{targetfile}
14524 Delete @var{targetfile} from the target system.
14529 @section Using the @code{gdbserver} Program
14532 @cindex remote connection without stubs
14533 @code{gdbserver} is a control program for Unix-like systems, which
14534 allows you to connect your program with a remote @value{GDBN} via
14535 @code{target remote}---but without linking in the usual debugging stub.
14537 @code{gdbserver} is not a complete replacement for the debugging stubs,
14538 because it requires essentially the same operating-system facilities
14539 that @value{GDBN} itself does. In fact, a system that can run
14540 @code{gdbserver} to connect to a remote @value{GDBN} could also run
14541 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
14542 because it is a much smaller program than @value{GDBN} itself. It is
14543 also easier to port than all of @value{GDBN}, so you may be able to get
14544 started more quickly on a new system by using @code{gdbserver}.
14545 Finally, if you develop code for real-time systems, you may find that
14546 the tradeoffs involved in real-time operation make it more convenient to
14547 do as much development work as possible on another system, for example
14548 by cross-compiling. You can use @code{gdbserver} to make a similar
14549 choice for debugging.
14551 @value{GDBN} and @code{gdbserver} communicate via either a serial line
14552 or a TCP connection, using the standard @value{GDBN} remote serial
14556 @emph{Warning:} @code{gdbserver} does not have any built-in security.
14557 Do not run @code{gdbserver} connected to any public network; a
14558 @value{GDBN} connection to @code{gdbserver} provides access to the
14559 target system with the same privileges as the user running
14563 @subsection Running @code{gdbserver}
14564 @cindex arguments, to @code{gdbserver}
14566 Run @code{gdbserver} on the target system. You need a copy of the
14567 program you want to debug, including any libraries it requires.
14568 @code{gdbserver} does not need your program's symbol table, so you can
14569 strip the program if necessary to save space. @value{GDBN} on the host
14570 system does all the symbol handling.
14572 To use the server, you must tell it how to communicate with @value{GDBN};
14573 the name of your program; and the arguments for your program. The usual
14577 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
14580 @var{comm} is either a device name (to use a serial line) or a TCP
14581 hostname and portnumber. For example, to debug Emacs with the argument
14582 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
14586 target> gdbserver /dev/com1 emacs foo.txt
14589 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
14592 To use a TCP connection instead of a serial line:
14595 target> gdbserver host:2345 emacs foo.txt
14598 The only difference from the previous example is the first argument,
14599 specifying that you are communicating with the host @value{GDBN} via
14600 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
14601 expect a TCP connection from machine @samp{host} to local TCP port 2345.
14602 (Currently, the @samp{host} part is ignored.) You can choose any number
14603 you want for the port number as long as it does not conflict with any
14604 TCP ports already in use on the target system (for example, @code{23} is
14605 reserved for @code{telnet}).@footnote{If you choose a port number that
14606 conflicts with another service, @code{gdbserver} prints an error message
14607 and exits.} You must use the same port number with the host @value{GDBN}
14608 @code{target remote} command.
14610 @subsubsection Attaching to a Running Program
14612 On some targets, @code{gdbserver} can also attach to running programs.
14613 This is accomplished via the @code{--attach} argument. The syntax is:
14616 target> gdbserver --attach @var{comm} @var{pid}
14619 @var{pid} is the process ID of a currently running process. It isn't necessary
14620 to point @code{gdbserver} at a binary for the running process.
14623 @cindex attach to a program by name
14624 You can debug processes by name instead of process ID if your target has the
14625 @code{pidof} utility:
14628 target> gdbserver --attach @var{comm} `pidof @var{program}`
14631 In case more than one copy of @var{program} is running, or @var{program}
14632 has multiple threads, most versions of @code{pidof} support the
14633 @code{-s} option to only return the first process ID.
14635 @subsubsection Multi-Process Mode for @code{gdbserver}
14636 @cindex gdbserver, multiple processes
14637 @cindex multiple processes with gdbserver
14639 When you connect to @code{gdbserver} using @code{target remote},
14640 @code{gdbserver} debugs the specified program only once. When the
14641 program exits, or you detach from it, @value{GDBN} closes the connection
14642 and @code{gdbserver} exits.
14644 If you connect using @kbd{target extended-remote}, @code{gdbserver}
14645 enters multi-process mode. When the debugged program exits, or you
14646 detach from it, @value{GDBN} stays connected to @code{gdbserver} even
14647 though no program is running. The @code{run} and @code{attach}
14648 commands instruct @code{gdbserver} to run or attach to a new program.
14649 The @code{run} command uses @code{set remote exec-file} (@pxref{set
14650 remote exec-file}) to select the program to run. Command line
14651 arguments are supported, except for wildcard expansion and I/O
14652 redirection (@pxref{Arguments}).
14654 To start @code{gdbserver} without supplying an initial command to run
14655 or process ID to attach, use the @option{--multi} command line option.
14656 Then you can connect using @kbd{target extended-remote} and start
14657 the program you want to debug.
14659 @code{gdbserver} does not automatically exit in multi-process mode.
14660 You can terminate it by using @code{monitor exit}
14661 (@pxref{Monitor Commands for gdbserver}).
14663 @subsubsection Other Command-Line Arguments for @code{gdbserver}
14665 The @option{--debug} option tells @code{gdbserver} to display extra
14666 status information about the debugging process. The
14667 @option{--remote-debug} option tells @code{gdbserver} to display
14668 remote protocol debug output. These options are intended for
14669 @code{gdbserver} development and for bug reports to the developers.
14671 The @option{--wrapper} option specifies a wrapper to launch programs
14672 for debugging. The option should be followed by the name of the
14673 wrapper, then any command-line arguments to pass to the wrapper, then
14674 @kbd{--} indicating the end of the wrapper arguments.
14676 @code{gdbserver} runs the specified wrapper program with a combined
14677 command line including the wrapper arguments, then the name of the
14678 program to debug, then any arguments to the program. The wrapper
14679 runs until it executes your program, and then @value{GDBN} gains control.
14681 You can use any program that eventually calls @code{execve} with
14682 its arguments as a wrapper. Several standard Unix utilities do
14683 this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending
14684 with @code{exec "$@@"} will also work.
14686 For example, you can use @code{env} to pass an environment variable to
14687 the debugged program, without setting the variable in @code{gdbserver}'s
14691 $ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog
14694 @subsection Connecting to @code{gdbserver}
14696 Run @value{GDBN} on the host system.
14698 First make sure you have the necessary symbol files. Load symbols for
14699 your application using the @code{file} command before you connect. Use
14700 @code{set sysroot} to locate target libraries (unless your @value{GDBN}
14701 was compiled with the correct sysroot using @code{--with-sysroot}).
14703 The symbol file and target libraries must exactly match the executable
14704 and libraries on the target, with one exception: the files on the host
14705 system should not be stripped, even if the files on the target system
14706 are. Mismatched or missing files will lead to confusing results
14707 during debugging. On @sc{gnu}/Linux targets, mismatched or missing
14708 files may also prevent @code{gdbserver} from debugging multi-threaded
14711 Connect to your target (@pxref{Connecting,,Connecting to a Remote Target}).
14712 For TCP connections, you must start up @code{gdbserver} prior to using
14713 the @code{target remote} command. Otherwise you may get an error whose
14714 text depends on the host system, but which usually looks something like
14715 @samp{Connection refused}. Don't use the @code{load}
14716 command in @value{GDBN} when using @code{gdbserver}, since the program is
14717 already on the target.
14719 @subsection Monitor Commands for @code{gdbserver}
14720 @cindex monitor commands, for @code{gdbserver}
14721 @anchor{Monitor Commands for gdbserver}
14723 During a @value{GDBN} session using @code{gdbserver}, you can use the
14724 @code{monitor} command to send special requests to @code{gdbserver}.
14725 Here are the available commands.
14729 List the available monitor commands.
14731 @item monitor set debug 0
14732 @itemx monitor set debug 1
14733 Disable or enable general debugging messages.
14735 @item monitor set remote-debug 0
14736 @itemx monitor set remote-debug 1
14737 Disable or enable specific debugging messages associated with the remote
14738 protocol (@pxref{Remote Protocol}).
14741 Tell gdbserver to exit immediately. This command should be followed by
14742 @code{disconnect} to close the debugging session. @code{gdbserver} will
14743 detach from any attached processes and kill any processes it created.
14744 Use @code{monitor exit} to terminate @code{gdbserver} at the end
14745 of a multi-process mode debug session.
14749 @node Remote Configuration
14750 @section Remote Configuration
14753 @kindex show remote
14754 This section documents the configuration options available when
14755 debugging remote programs. For the options related to the File I/O
14756 extensions of the remote protocol, see @ref{system,
14757 system-call-allowed}.
14760 @item set remoteaddresssize @var{bits}
14761 @cindex address size for remote targets
14762 @cindex bits in remote address
14763 Set the maximum size of address in a memory packet to the specified
14764 number of bits. @value{GDBN} will mask off the address bits above
14765 that number, when it passes addresses to the remote target. The
14766 default value is the number of bits in the target's address.
14768 @item show remoteaddresssize
14769 Show the current value of remote address size in bits.
14771 @item set remotebaud @var{n}
14772 @cindex baud rate for remote targets
14773 Set the baud rate for the remote serial I/O to @var{n} baud. The
14774 value is used to set the speed of the serial port used for debugging
14777 @item show remotebaud
14778 Show the current speed of the remote connection.
14780 @item set remotebreak
14781 @cindex interrupt remote programs
14782 @cindex BREAK signal instead of Ctrl-C
14783 @anchor{set remotebreak}
14784 If set to on, @value{GDBN} sends a @code{BREAK} signal to the remote
14785 when you type @kbd{Ctrl-c} to interrupt the program running
14786 on the remote. If set to off, @value{GDBN} sends the @samp{Ctrl-C}
14787 character instead. The default is off, since most remote systems
14788 expect to see @samp{Ctrl-C} as the interrupt signal.
14790 @item show remotebreak
14791 Show whether @value{GDBN} sends @code{BREAK} or @samp{Ctrl-C} to
14792 interrupt the remote program.
14794 @item set remoteflow on
14795 @itemx set remoteflow off
14796 @kindex set remoteflow
14797 Enable or disable hardware flow control (@code{RTS}/@code{CTS})
14798 on the serial port used to communicate to the remote target.
14800 @item show remoteflow
14801 @kindex show remoteflow
14802 Show the current setting of hardware flow control.
14804 @item set remotelogbase @var{base}
14805 Set the base (a.k.a.@: radix) of logging serial protocol
14806 communications to @var{base}. Supported values of @var{base} are:
14807 @code{ascii}, @code{octal}, and @code{hex}. The default is
14810 @item show remotelogbase
14811 Show the current setting of the radix for logging remote serial
14814 @item set remotelogfile @var{file}
14815 @cindex record serial communications on file
14816 Record remote serial communications on the named @var{file}. The
14817 default is not to record at all.
14819 @item show remotelogfile.
14820 Show the current setting of the file name on which to record the
14821 serial communications.
14823 @item set remotetimeout @var{num}
14824 @cindex timeout for serial communications
14825 @cindex remote timeout
14826 Set the timeout limit to wait for the remote target to respond to
14827 @var{num} seconds. The default is 2 seconds.
14829 @item show remotetimeout
14830 Show the current number of seconds to wait for the remote target
14833 @cindex limit hardware breakpoints and watchpoints
14834 @cindex remote target, limit break- and watchpoints
14835 @anchor{set remote hardware-watchpoint-limit}
14836 @anchor{set remote hardware-breakpoint-limit}
14837 @item set remote hardware-watchpoint-limit @var{limit}
14838 @itemx set remote hardware-breakpoint-limit @var{limit}
14839 Restrict @value{GDBN} to using @var{limit} remote hardware breakpoint or
14840 watchpoints. A limit of -1, the default, is treated as unlimited.
14842 @item set remote exec-file @var{filename}
14843 @itemx show remote exec-file
14844 @anchor{set remote exec-file}
14845 @cindex executable file, for remote target
14846 Select the file used for @code{run} with @code{target
14847 extended-remote}. This should be set to a filename valid on the
14848 target system. If it is not set, the target will use a default
14849 filename (e.g.@: the last program run).
14853 @item set tcp auto-retry on
14854 @cindex auto-retry, for remote TCP target
14855 Enable auto-retry for remote TCP connections. This is useful if the remote
14856 debugging agent is launched in parallel with @value{GDBN}; there is a race
14857 condition because the agent may not become ready to accept the connection
14858 before @value{GDBN} attempts to connect. When auto-retry is
14859 enabled, if the initial attempt to connect fails, @value{GDBN} reattempts
14860 to establish the connection using the timeout specified by
14861 @code{set tcp connect-timeout}.
14863 @item set tcp auto-retry off
14864 Do not auto-retry failed TCP connections.
14866 @item show tcp auto-retry
14867 Show the current auto-retry setting.
14869 @item set tcp connect-timeout @var{seconds}
14870 @cindex connection timeout, for remote TCP target
14871 @cindex timeout, for remote target connection
14872 Set the timeout for establishing a TCP connection to the remote target to
14873 @var{seconds}. The timeout affects both polling to retry failed connections
14874 (enabled by @code{set tcp auto-retry on}) and waiting for connections
14875 that are merely slow to complete, and represents an approximate cumulative
14878 @item show tcp connect-timeout
14879 Show the current connection timeout setting.
14882 @cindex remote packets, enabling and disabling
14883 The @value{GDBN} remote protocol autodetects the packets supported by
14884 your debugging stub. If you need to override the autodetection, you
14885 can use these commands to enable or disable individual packets. Each
14886 packet can be set to @samp{on} (the remote target supports this
14887 packet), @samp{off} (the remote target does not support this packet),
14888 or @samp{auto} (detect remote target support for this packet). They
14889 all default to @samp{auto}. For more information about each packet,
14890 see @ref{Remote Protocol}.
14892 During normal use, you should not have to use any of these commands.
14893 If you do, that may be a bug in your remote debugging stub, or a bug
14894 in @value{GDBN}. You may want to report the problem to the
14895 @value{GDBN} developers.
14897 For each packet @var{name}, the command to enable or disable the
14898 packet is @code{set remote @var{name}-packet}. The available settings
14901 @multitable @columnfractions 0.28 0.32 0.25
14904 @tab Related Features
14906 @item @code{fetch-register}
14908 @tab @code{info registers}
14910 @item @code{set-register}
14914 @item @code{binary-download}
14916 @tab @code{load}, @code{set}
14918 @item @code{read-aux-vector}
14919 @tab @code{qXfer:auxv:read}
14920 @tab @code{info auxv}
14922 @item @code{symbol-lookup}
14923 @tab @code{qSymbol}
14924 @tab Detecting multiple threads
14926 @item @code{attach}
14927 @tab @code{vAttach}
14930 @item @code{verbose-resume}
14932 @tab Stepping or resuming multiple threads
14938 @item @code{software-breakpoint}
14942 @item @code{hardware-breakpoint}
14946 @item @code{write-watchpoint}
14950 @item @code{read-watchpoint}
14954 @item @code{access-watchpoint}
14958 @item @code{target-features}
14959 @tab @code{qXfer:features:read}
14960 @tab @code{set architecture}
14962 @item @code{library-info}
14963 @tab @code{qXfer:libraries:read}
14964 @tab @code{info sharedlibrary}
14966 @item @code{memory-map}
14967 @tab @code{qXfer:memory-map:read}
14968 @tab @code{info mem}
14970 @item @code{read-spu-object}
14971 @tab @code{qXfer:spu:read}
14972 @tab @code{info spu}
14974 @item @code{write-spu-object}
14975 @tab @code{qXfer:spu:write}
14976 @tab @code{info spu}
14978 @item @code{read-siginfo-object}
14979 @tab @code{qXfer:siginfo:read}
14980 @tab @code{print $_siginfo}
14982 @item @code{write-siginfo-object}
14983 @tab @code{qXfer:siginfo:write}
14984 @tab @code{set $_siginfo}
14986 @item @code{get-thread-local-@*storage-address}
14987 @tab @code{qGetTLSAddr}
14988 @tab Displaying @code{__thread} variables
14990 @item @code{search-memory}
14991 @tab @code{qSearch:memory}
14994 @item @code{supported-packets}
14995 @tab @code{qSupported}
14996 @tab Remote communications parameters
14998 @item @code{pass-signals}
14999 @tab @code{QPassSignals}
15000 @tab @code{handle @var{signal}}
15002 @item @code{hostio-close-packet}
15003 @tab @code{vFile:close}
15004 @tab @code{remote get}, @code{remote put}
15006 @item @code{hostio-open-packet}
15007 @tab @code{vFile:open}
15008 @tab @code{remote get}, @code{remote put}
15010 @item @code{hostio-pread-packet}
15011 @tab @code{vFile:pread}
15012 @tab @code{remote get}, @code{remote put}
15014 @item @code{hostio-pwrite-packet}
15015 @tab @code{vFile:pwrite}
15016 @tab @code{remote get}, @code{remote put}
15018 @item @code{hostio-unlink-packet}
15019 @tab @code{vFile:unlink}
15020 @tab @code{remote delete}
15022 @item @code{noack-packet}
15023 @tab @code{QStartNoAckMode}
15024 @tab Packet acknowledgment
15026 @item @code{osdata}
15027 @tab @code{qXfer:osdata:read}
15028 @tab @code{info os}
15030 @item @code{query-attached}
15031 @tab @code{qAttached}
15032 @tab Querying remote process attach state.
15036 @section Implementing a Remote Stub
15038 @cindex debugging stub, example
15039 @cindex remote stub, example
15040 @cindex stub example, remote debugging
15041 The stub files provided with @value{GDBN} implement the target side of the
15042 communication protocol, and the @value{GDBN} side is implemented in the
15043 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
15044 these subroutines to communicate, and ignore the details. (If you're
15045 implementing your own stub file, you can still ignore the details: start
15046 with one of the existing stub files. @file{sparc-stub.c} is the best
15047 organized, and therefore the easiest to read.)
15049 @cindex remote serial debugging, overview
15050 To debug a program running on another machine (the debugging
15051 @dfn{target} machine), you must first arrange for all the usual
15052 prerequisites for the program to run by itself. For example, for a C
15057 A startup routine to set up the C runtime environment; these usually
15058 have a name like @file{crt0}. The startup routine may be supplied by
15059 your hardware supplier, or you may have to write your own.
15062 A C subroutine library to support your program's
15063 subroutine calls, notably managing input and output.
15066 A way of getting your program to the other machine---for example, a
15067 download program. These are often supplied by the hardware
15068 manufacturer, but you may have to write your own from hardware
15072 The next step is to arrange for your program to use a serial port to
15073 communicate with the machine where @value{GDBN} is running (the @dfn{host}
15074 machine). In general terms, the scheme looks like this:
15078 @value{GDBN} already understands how to use this protocol; when everything
15079 else is set up, you can simply use the @samp{target remote} command
15080 (@pxref{Targets,,Specifying a Debugging Target}).
15082 @item On the target,
15083 you must link with your program a few special-purpose subroutines that
15084 implement the @value{GDBN} remote serial protocol. The file containing these
15085 subroutines is called a @dfn{debugging stub}.
15087 On certain remote targets, you can use an auxiliary program
15088 @code{gdbserver} instead of linking a stub into your program.
15089 @xref{Server,,Using the @code{gdbserver} Program}, for details.
15092 The debugging stub is specific to the architecture of the remote
15093 machine; for example, use @file{sparc-stub.c} to debug programs on
15096 @cindex remote serial stub list
15097 These working remote stubs are distributed with @value{GDBN}:
15102 @cindex @file{i386-stub.c}
15105 For Intel 386 and compatible architectures.
15108 @cindex @file{m68k-stub.c}
15109 @cindex Motorola 680x0
15111 For Motorola 680x0 architectures.
15114 @cindex @file{sh-stub.c}
15117 For Renesas SH architectures.
15120 @cindex @file{sparc-stub.c}
15122 For @sc{sparc} architectures.
15124 @item sparcl-stub.c
15125 @cindex @file{sparcl-stub.c}
15128 For Fujitsu @sc{sparclite} architectures.
15132 The @file{README} file in the @value{GDBN} distribution may list other
15133 recently added stubs.
15136 * Stub Contents:: What the stub can do for you
15137 * Bootstrapping:: What you must do for the stub
15138 * Debug Session:: Putting it all together
15141 @node Stub Contents
15142 @subsection What the Stub Can Do for You
15144 @cindex remote serial stub
15145 The debugging stub for your architecture supplies these three
15149 @item set_debug_traps
15150 @findex set_debug_traps
15151 @cindex remote serial stub, initialization
15152 This routine arranges for @code{handle_exception} to run when your
15153 program stops. You must call this subroutine explicitly near the
15154 beginning of your program.
15156 @item handle_exception
15157 @findex handle_exception
15158 @cindex remote serial stub, main routine
15159 This is the central workhorse, but your program never calls it
15160 explicitly---the setup code arranges for @code{handle_exception} to
15161 run when a trap is triggered.
15163 @code{handle_exception} takes control when your program stops during
15164 execution (for example, on a breakpoint), and mediates communications
15165 with @value{GDBN} on the host machine. This is where the communications
15166 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
15167 representative on the target machine. It begins by sending summary
15168 information on the state of your program, then continues to execute,
15169 retrieving and transmitting any information @value{GDBN} needs, until you
15170 execute a @value{GDBN} command that makes your program resume; at that point,
15171 @code{handle_exception} returns control to your own code on the target
15175 @cindex @code{breakpoint} subroutine, remote
15176 Use this auxiliary subroutine to make your program contain a
15177 breakpoint. Depending on the particular situation, this may be the only
15178 way for @value{GDBN} to get control. For instance, if your target
15179 machine has some sort of interrupt button, you won't need to call this;
15180 pressing the interrupt button transfers control to
15181 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
15182 simply receiving characters on the serial port may also trigger a trap;
15183 again, in that situation, you don't need to call @code{breakpoint} from
15184 your own program---simply running @samp{target remote} from the host
15185 @value{GDBN} session gets control.
15187 Call @code{breakpoint} if none of these is true, or if you simply want
15188 to make certain your program stops at a predetermined point for the
15189 start of your debugging session.
15192 @node Bootstrapping
15193 @subsection What You Must Do for the Stub
15195 @cindex remote stub, support routines
15196 The debugging stubs that come with @value{GDBN} are set up for a particular
15197 chip architecture, but they have no information about the rest of your
15198 debugging target machine.
15200 First of all you need to tell the stub how to communicate with the
15204 @item int getDebugChar()
15205 @findex getDebugChar
15206 Write this subroutine to read a single character from the serial port.
15207 It may be identical to @code{getchar} for your target system; a
15208 different name is used to allow you to distinguish the two if you wish.
15210 @item void putDebugChar(int)
15211 @findex putDebugChar
15212 Write this subroutine to write a single character to the serial port.
15213 It may be identical to @code{putchar} for your target system; a
15214 different name is used to allow you to distinguish the two if you wish.
15217 @cindex control C, and remote debugging
15218 @cindex interrupting remote targets
15219 If you want @value{GDBN} to be able to stop your program while it is
15220 running, you need to use an interrupt-driven serial driver, and arrange
15221 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
15222 character). That is the character which @value{GDBN} uses to tell the
15223 remote system to stop.
15225 Getting the debugging target to return the proper status to @value{GDBN}
15226 probably requires changes to the standard stub; one quick and dirty way
15227 is to just execute a breakpoint instruction (the ``dirty'' part is that
15228 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
15230 Other routines you need to supply are:
15233 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
15234 @findex exceptionHandler
15235 Write this function to install @var{exception_address} in the exception
15236 handling tables. You need to do this because the stub does not have any
15237 way of knowing what the exception handling tables on your target system
15238 are like (for example, the processor's table might be in @sc{rom},
15239 containing entries which point to a table in @sc{ram}).
15240 @var{exception_number} is the exception number which should be changed;
15241 its meaning is architecture-dependent (for example, different numbers
15242 might represent divide by zero, misaligned access, etc). When this
15243 exception occurs, control should be transferred directly to
15244 @var{exception_address}, and the processor state (stack, registers,
15245 and so on) should be just as it is when a processor exception occurs. So if
15246 you want to use a jump instruction to reach @var{exception_address}, it
15247 should be a simple jump, not a jump to subroutine.
15249 For the 386, @var{exception_address} should be installed as an interrupt
15250 gate so that interrupts are masked while the handler runs. The gate
15251 should be at privilege level 0 (the most privileged level). The
15252 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
15253 help from @code{exceptionHandler}.
15255 @item void flush_i_cache()
15256 @findex flush_i_cache
15257 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
15258 instruction cache, if any, on your target machine. If there is no
15259 instruction cache, this subroutine may be a no-op.
15261 On target machines that have instruction caches, @value{GDBN} requires this
15262 function to make certain that the state of your program is stable.
15266 You must also make sure this library routine is available:
15269 @item void *memset(void *, int, int)
15271 This is the standard library function @code{memset} that sets an area of
15272 memory to a known value. If you have one of the free versions of
15273 @code{libc.a}, @code{memset} can be found there; otherwise, you must
15274 either obtain it from your hardware manufacturer, or write your own.
15277 If you do not use the GNU C compiler, you may need other standard
15278 library subroutines as well; this varies from one stub to another,
15279 but in general the stubs are likely to use any of the common library
15280 subroutines which @code{@value{NGCC}} generates as inline code.
15283 @node Debug Session
15284 @subsection Putting it All Together
15286 @cindex remote serial debugging summary
15287 In summary, when your program is ready to debug, you must follow these
15292 Make sure you have defined the supporting low-level routines
15293 (@pxref{Bootstrapping,,What You Must Do for the Stub}):
15295 @code{getDebugChar}, @code{putDebugChar},
15296 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
15300 Insert these lines near the top of your program:
15308 For the 680x0 stub only, you need to provide a variable called
15309 @code{exceptionHook}. Normally you just use:
15312 void (*exceptionHook)() = 0;
15316 but if before calling @code{set_debug_traps}, you set it to point to a
15317 function in your program, that function is called when
15318 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
15319 error). The function indicated by @code{exceptionHook} is called with
15320 one parameter: an @code{int} which is the exception number.
15323 Compile and link together: your program, the @value{GDBN} debugging stub for
15324 your target architecture, and the supporting subroutines.
15327 Make sure you have a serial connection between your target machine and
15328 the @value{GDBN} host, and identify the serial port on the host.
15331 @c The "remote" target now provides a `load' command, so we should
15332 @c document that. FIXME.
15333 Download your program to your target machine (or get it there by
15334 whatever means the manufacturer provides), and start it.
15337 Start @value{GDBN} on the host, and connect to the target
15338 (@pxref{Connecting,,Connecting to a Remote Target}).
15342 @node Configurations
15343 @chapter Configuration-Specific Information
15345 While nearly all @value{GDBN} commands are available for all native and
15346 cross versions of the debugger, there are some exceptions. This chapter
15347 describes things that are only available in certain configurations.
15349 There are three major categories of configurations: native
15350 configurations, where the host and target are the same, embedded
15351 operating system configurations, which are usually the same for several
15352 different processor architectures, and bare embedded processors, which
15353 are quite different from each other.
15358 * Embedded Processors::
15365 This section describes details specific to particular native
15370 * BSD libkvm Interface:: Debugging BSD kernel memory images
15371 * SVR4 Process Information:: SVR4 process information
15372 * DJGPP Native:: Features specific to the DJGPP port
15373 * Cygwin Native:: Features specific to the Cygwin port
15374 * Hurd Native:: Features specific to @sc{gnu} Hurd
15375 * Neutrino:: Features specific to QNX Neutrino
15376 * Darwin:: Features specific to Darwin
15382 On HP-UX systems, if you refer to a function or variable name that
15383 begins with a dollar sign, @value{GDBN} searches for a user or system
15384 name first, before it searches for a convenience variable.
15387 @node BSD libkvm Interface
15388 @subsection BSD libkvm Interface
15391 @cindex kernel memory image
15392 @cindex kernel crash dump
15394 BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory
15395 interface that provides a uniform interface for accessing kernel virtual
15396 memory images, including live systems and crash dumps. @value{GDBN}
15397 uses this interface to allow you to debug live kernels and kernel crash
15398 dumps on many native BSD configurations. This is implemented as a
15399 special @code{kvm} debugging target. For debugging a live system, load
15400 the currently running kernel into @value{GDBN} and connect to the
15404 (@value{GDBP}) @b{target kvm}
15407 For debugging crash dumps, provide the file name of the crash dump as an
15411 (@value{GDBP}) @b{target kvm /var/crash/bsd.0}
15414 Once connected to the @code{kvm} target, the following commands are
15420 Set current context from the @dfn{Process Control Block} (PCB) address.
15423 Set current context from proc address. This command isn't available on
15424 modern FreeBSD systems.
15427 @node SVR4 Process Information
15428 @subsection SVR4 Process Information
15430 @cindex examine process image
15431 @cindex process info via @file{/proc}
15433 Many versions of SVR4 and compatible systems provide a facility called
15434 @samp{/proc} that can be used to examine the image of a running
15435 process using file-system subroutines. If @value{GDBN} is configured
15436 for an operating system with this facility, the command @code{info
15437 proc} is available to report information about the process running
15438 your program, or about any process running on your system. @code{info
15439 proc} works only on SVR4 systems that include the @code{procfs} code.
15440 This includes, as of this writing, @sc{gnu}/Linux, OSF/1 (Digital
15441 Unix), Solaris, Irix, and Unixware, but not HP-UX, for example.
15447 @itemx info proc @var{process-id}
15448 Summarize available information about any running process. If a
15449 process ID is specified by @var{process-id}, display information about
15450 that process; otherwise display information about the program being
15451 debugged. The summary includes the debugged process ID, the command
15452 line used to invoke it, its current working directory, and its
15453 executable file's absolute file name.
15455 On some systems, @var{process-id} can be of the form
15456 @samp{[@var{pid}]/@var{tid}} which specifies a certain thread ID
15457 within a process. If the optional @var{pid} part is missing, it means
15458 a thread from the process being debugged (the leading @samp{/} still
15459 needs to be present, or else @value{GDBN} will interpret the number as
15460 a process ID rather than a thread ID).
15462 @item info proc mappings
15463 @cindex memory address space mappings
15464 Report the memory address space ranges accessible in the program, with
15465 information on whether the process has read, write, or execute access
15466 rights to each range. On @sc{gnu}/Linux systems, each memory range
15467 includes the object file which is mapped to that range, instead of the
15468 memory access rights to that range.
15470 @item info proc stat
15471 @itemx info proc status
15472 @cindex process detailed status information
15473 These subcommands are specific to @sc{gnu}/Linux systems. They show
15474 the process-related information, including the user ID and group ID;
15475 how many threads are there in the process; its virtual memory usage;
15476 the signals that are pending, blocked, and ignored; its TTY; its
15477 consumption of system and user time; its stack size; its @samp{nice}
15478 value; etc. For more information, see the @samp{proc} man page
15479 (type @kbd{man 5 proc} from your shell prompt).
15481 @item info proc all
15482 Show all the information about the process described under all of the
15483 above @code{info proc} subcommands.
15486 @comment These sub-options of 'info proc' were not included when
15487 @comment procfs.c was re-written. Keep their descriptions around
15488 @comment against the day when someone finds the time to put them back in.
15489 @kindex info proc times
15490 @item info proc times
15491 Starting time, user CPU time, and system CPU time for your program and
15494 @kindex info proc id
15496 Report on the process IDs related to your program: its own process ID,
15497 the ID of its parent, the process group ID, and the session ID.
15500 @item set procfs-trace
15501 @kindex set procfs-trace
15502 @cindex @code{procfs} API calls
15503 This command enables and disables tracing of @code{procfs} API calls.
15505 @item show procfs-trace
15506 @kindex show procfs-trace
15507 Show the current state of @code{procfs} API call tracing.
15509 @item set procfs-file @var{file}
15510 @kindex set procfs-file
15511 Tell @value{GDBN} to write @code{procfs} API trace to the named
15512 @var{file}. @value{GDBN} appends the trace info to the previous
15513 contents of the file. The default is to display the trace on the
15516 @item show procfs-file
15517 @kindex show procfs-file
15518 Show the file to which @code{procfs} API trace is written.
15520 @item proc-trace-entry
15521 @itemx proc-trace-exit
15522 @itemx proc-untrace-entry
15523 @itemx proc-untrace-exit
15524 @kindex proc-trace-entry
15525 @kindex proc-trace-exit
15526 @kindex proc-untrace-entry
15527 @kindex proc-untrace-exit
15528 These commands enable and disable tracing of entries into and exits
15529 from the @code{syscall} interface.
15532 @kindex info pidlist
15533 @cindex process list, QNX Neutrino
15534 For QNX Neutrino only, this command displays the list of all the
15535 processes and all the threads within each process.
15538 @kindex info meminfo
15539 @cindex mapinfo list, QNX Neutrino
15540 For QNX Neutrino only, this command displays the list of all mapinfos.
15544 @subsection Features for Debugging @sc{djgpp} Programs
15545 @cindex @sc{djgpp} debugging
15546 @cindex native @sc{djgpp} debugging
15547 @cindex MS-DOS-specific commands
15550 @sc{djgpp} is a port of the @sc{gnu} development tools to MS-DOS and
15551 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
15552 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
15553 top of real-mode DOS systems and their emulations.
15555 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
15556 defines a few commands specific to the @sc{djgpp} port. This
15557 subsection describes those commands.
15562 This is a prefix of @sc{djgpp}-specific commands which print
15563 information about the target system and important OS structures.
15566 @cindex MS-DOS system info
15567 @cindex free memory information (MS-DOS)
15568 @item info dos sysinfo
15569 This command displays assorted information about the underlying
15570 platform: the CPU type and features, the OS version and flavor, the
15571 DPMI version, and the available conventional and DPMI memory.
15576 @cindex segment descriptor tables
15577 @cindex descriptor tables display
15579 @itemx info dos ldt
15580 @itemx info dos idt
15581 These 3 commands display entries from, respectively, Global, Local,
15582 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
15583 tables are data structures which store a descriptor for each segment
15584 that is currently in use. The segment's selector is an index into a
15585 descriptor table; the table entry for that index holds the
15586 descriptor's base address and limit, and its attributes and access
15589 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
15590 segment (used for both data and the stack), and a DOS segment (which
15591 allows access to DOS/BIOS data structures and absolute addresses in
15592 conventional memory). However, the DPMI host will usually define
15593 additional segments in order to support the DPMI environment.
15595 @cindex garbled pointers
15596 These commands allow to display entries from the descriptor tables.
15597 Without an argument, all entries from the specified table are
15598 displayed. An argument, which should be an integer expression, means
15599 display a single entry whose index is given by the argument. For
15600 example, here's a convenient way to display information about the
15601 debugged program's data segment:
15604 @exdent @code{(@value{GDBP}) info dos ldt $ds}
15605 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
15609 This comes in handy when you want to see whether a pointer is outside
15610 the data segment's limit (i.e.@: @dfn{garbled}).
15612 @cindex page tables display (MS-DOS)
15614 @itemx info dos pte
15615 These two commands display entries from, respectively, the Page
15616 Directory and the Page Tables. Page Directories and Page Tables are
15617 data structures which control how virtual memory addresses are mapped
15618 into physical addresses. A Page Table includes an entry for every
15619 page of memory that is mapped into the program's address space; there
15620 may be several Page Tables, each one holding up to 4096 entries. A
15621 Page Directory has up to 4096 entries, one each for every Page Table
15622 that is currently in use.
15624 Without an argument, @kbd{info dos pde} displays the entire Page
15625 Directory, and @kbd{info dos pte} displays all the entries in all of
15626 the Page Tables. An argument, an integer expression, given to the
15627 @kbd{info dos pde} command means display only that entry from the Page
15628 Directory table. An argument given to the @kbd{info dos pte} command
15629 means display entries from a single Page Table, the one pointed to by
15630 the specified entry in the Page Directory.
15632 @cindex direct memory access (DMA) on MS-DOS
15633 These commands are useful when your program uses @dfn{DMA} (Direct
15634 Memory Access), which needs physical addresses to program the DMA
15637 These commands are supported only with some DPMI servers.
15639 @cindex physical address from linear address
15640 @item info dos address-pte @var{addr}
15641 This command displays the Page Table entry for a specified linear
15642 address. The argument @var{addr} is a linear address which should
15643 already have the appropriate segment's base address added to it,
15644 because this command accepts addresses which may belong to @emph{any}
15645 segment. For example, here's how to display the Page Table entry for
15646 the page where a variable @code{i} is stored:
15649 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
15650 @exdent @code{Page Table entry for address 0x11a00d30:}
15651 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
15655 This says that @code{i} is stored at offset @code{0xd30} from the page
15656 whose physical base address is @code{0x02698000}, and shows all the
15657 attributes of that page.
15659 Note that you must cast the addresses of variables to a @code{char *},
15660 since otherwise the value of @code{__djgpp_base_address}, the base
15661 address of all variables and functions in a @sc{djgpp} program, will
15662 be added using the rules of C pointer arithmetics: if @code{i} is
15663 declared an @code{int}, @value{GDBN} will add 4 times the value of
15664 @code{__djgpp_base_address} to the address of @code{i}.
15666 Here's another example, it displays the Page Table entry for the
15670 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
15671 @exdent @code{Page Table entry for address 0x29110:}
15672 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
15676 (The @code{+ 3} offset is because the transfer buffer's address is the
15677 3rd member of the @code{_go32_info_block} structure.) The output
15678 clearly shows that this DPMI server maps the addresses in conventional
15679 memory 1:1, i.e.@: the physical (@code{0x00029000} + @code{0x110}) and
15680 linear (@code{0x29110}) addresses are identical.
15682 This command is supported only with some DPMI servers.
15685 @cindex DOS serial data link, remote debugging
15686 In addition to native debugging, the DJGPP port supports remote
15687 debugging via a serial data link. The following commands are specific
15688 to remote serial debugging in the DJGPP port of @value{GDBN}.
15691 @kindex set com1base
15692 @kindex set com1irq
15693 @kindex set com2base
15694 @kindex set com2irq
15695 @kindex set com3base
15696 @kindex set com3irq
15697 @kindex set com4base
15698 @kindex set com4irq
15699 @item set com1base @var{addr}
15700 This command sets the base I/O port address of the @file{COM1} serial
15703 @item set com1irq @var{irq}
15704 This command sets the @dfn{Interrupt Request} (@code{IRQ}) line to use
15705 for the @file{COM1} serial port.
15707 There are similar commands @samp{set com2base}, @samp{set com3irq},
15708 etc.@: for setting the port address and the @code{IRQ} lines for the
15711 @kindex show com1base
15712 @kindex show com1irq
15713 @kindex show com2base
15714 @kindex show com2irq
15715 @kindex show com3base
15716 @kindex show com3irq
15717 @kindex show com4base
15718 @kindex show com4irq
15719 The related commands @samp{show com1base}, @samp{show com1irq} etc.@:
15720 display the current settings of the base address and the @code{IRQ}
15721 lines used by the COM ports.
15724 @kindex info serial
15725 @cindex DOS serial port status
15726 This command prints the status of the 4 DOS serial ports. For each
15727 port, it prints whether it's active or not, its I/O base address and
15728 IRQ number, whether it uses a 16550-style FIFO, its baudrate, and the
15729 counts of various errors encountered so far.
15733 @node Cygwin Native
15734 @subsection Features for Debugging MS Windows PE Executables
15735 @cindex MS Windows debugging
15736 @cindex native Cygwin debugging
15737 @cindex Cygwin-specific commands
15739 @value{GDBN} supports native debugging of MS Windows programs, including
15740 DLLs with and without symbolic debugging information. There are various
15741 additional Cygwin-specific commands, described in this section.
15742 Working with DLLs that have no debugging symbols is described in
15743 @ref{Non-debug DLL Symbols}.
15748 This is a prefix of MS Windows-specific commands which print
15749 information about the target system and important OS structures.
15751 @item info w32 selector
15752 This command displays information returned by
15753 the Win32 API @code{GetThreadSelectorEntry} function.
15754 It takes an optional argument that is evaluated to
15755 a long value to give the information about this given selector.
15756 Without argument, this command displays information
15757 about the six segment registers.
15761 This is a Cygwin-specific alias of @code{info shared}.
15763 @kindex dll-symbols
15765 This command loads symbols from a dll similarly to
15766 add-sym command but without the need to specify a base address.
15768 @kindex set cygwin-exceptions
15769 @cindex debugging the Cygwin DLL
15770 @cindex Cygwin DLL, debugging
15771 @item set cygwin-exceptions @var{mode}
15772 If @var{mode} is @code{on}, @value{GDBN} will break on exceptions that
15773 happen inside the Cygwin DLL. If @var{mode} is @code{off},
15774 @value{GDBN} will delay recognition of exceptions, and may ignore some
15775 exceptions which seem to be caused by internal Cygwin DLL
15776 ``bookkeeping''. This option is meant primarily for debugging the
15777 Cygwin DLL itself; the default value is @code{off} to avoid annoying
15778 @value{GDBN} users with false @code{SIGSEGV} signals.
15780 @kindex show cygwin-exceptions
15781 @item show cygwin-exceptions
15782 Displays whether @value{GDBN} will break on exceptions that happen
15783 inside the Cygwin DLL itself.
15785 @kindex set new-console
15786 @item set new-console @var{mode}
15787 If @var{mode} is @code{on} the debuggee will
15788 be started in a new console on next start.
15789 If @var{mode} is @code{off}i, the debuggee will
15790 be started in the same console as the debugger.
15792 @kindex show new-console
15793 @item show new-console
15794 Displays whether a new console is used
15795 when the debuggee is started.
15797 @kindex set new-group
15798 @item set new-group @var{mode}
15799 This boolean value controls whether the debuggee should
15800 start a new group or stay in the same group as the debugger.
15801 This affects the way the Windows OS handles
15804 @kindex show new-group
15805 @item show new-group
15806 Displays current value of new-group boolean.
15808 @kindex set debugevents
15809 @item set debugevents
15810 This boolean value adds debug output concerning kernel events related
15811 to the debuggee seen by the debugger. This includes events that
15812 signal thread and process creation and exit, DLL loading and
15813 unloading, console interrupts, and debugging messages produced by the
15814 Windows @code{OutputDebugString} API call.
15816 @kindex set debugexec
15817 @item set debugexec
15818 This boolean value adds debug output concerning execute events
15819 (such as resume thread) seen by the debugger.
15821 @kindex set debugexceptions
15822 @item set debugexceptions
15823 This boolean value adds debug output concerning exceptions in the
15824 debuggee seen by the debugger.
15826 @kindex set debugmemory
15827 @item set debugmemory
15828 This boolean value adds debug output concerning debuggee memory reads
15829 and writes by the debugger.
15833 This boolean values specifies whether the debuggee is called
15834 via a shell or directly (default value is on).
15838 Displays if the debuggee will be started with a shell.
15843 * Non-debug DLL Symbols:: Support for DLLs without debugging symbols
15846 @node Non-debug DLL Symbols
15847 @subsubsection Support for DLLs without Debugging Symbols
15848 @cindex DLLs with no debugging symbols
15849 @cindex Minimal symbols and DLLs
15851 Very often on windows, some of the DLLs that your program relies on do
15852 not include symbolic debugging information (for example,
15853 @file{kernel32.dll}). When @value{GDBN} doesn't recognize any debugging
15854 symbols in a DLL, it relies on the minimal amount of symbolic
15855 information contained in the DLL's export table. This section
15856 describes working with such symbols, known internally to @value{GDBN} as
15857 ``minimal symbols''.
15859 Note that before the debugged program has started execution, no DLLs
15860 will have been loaded. The easiest way around this problem is simply to
15861 start the program --- either by setting a breakpoint or letting the
15862 program run once to completion. It is also possible to force
15863 @value{GDBN} to load a particular DLL before starting the executable ---
15864 see the shared library information in @ref{Files}, or the
15865 @code{dll-symbols} command in @ref{Cygwin Native}. Currently,
15866 explicitly loading symbols from a DLL with no debugging information will
15867 cause the symbol names to be duplicated in @value{GDBN}'s lookup table,
15868 which may adversely affect symbol lookup performance.
15870 @subsubsection DLL Name Prefixes
15872 In keeping with the naming conventions used by the Microsoft debugging
15873 tools, DLL export symbols are made available with a prefix based on the
15874 DLL name, for instance @code{KERNEL32!CreateFileA}. The plain name is
15875 also entered into the symbol table, so @code{CreateFileA} is often
15876 sufficient. In some cases there will be name clashes within a program
15877 (particularly if the executable itself includes full debugging symbols)
15878 necessitating the use of the fully qualified name when referring to the
15879 contents of the DLL. Use single-quotes around the name to avoid the
15880 exclamation mark (``!'') being interpreted as a language operator.
15882 Note that the internal name of the DLL may be all upper-case, even
15883 though the file name of the DLL is lower-case, or vice-versa. Since
15884 symbols within @value{GDBN} are @emph{case-sensitive} this may cause
15885 some confusion. If in doubt, try the @code{info functions} and
15886 @code{info variables} commands or even @code{maint print msymbols}
15887 (@pxref{Symbols}). Here's an example:
15890 (@value{GDBP}) info function CreateFileA
15891 All functions matching regular expression "CreateFileA":
15893 Non-debugging symbols:
15894 0x77e885f4 CreateFileA
15895 0x77e885f4 KERNEL32!CreateFileA
15899 (@value{GDBP}) info function !
15900 All functions matching regular expression "!":
15902 Non-debugging symbols:
15903 0x6100114c cygwin1!__assert
15904 0x61004034 cygwin1!_dll_crt0@@0
15905 0x61004240 cygwin1!dll_crt0(per_process *)
15909 @subsubsection Working with Minimal Symbols
15911 Symbols extracted from a DLL's export table do not contain very much
15912 type information. All that @value{GDBN} can do is guess whether a symbol
15913 refers to a function or variable depending on the linker section that
15914 contains the symbol. Also note that the actual contents of the memory
15915 contained in a DLL are not available unless the program is running. This
15916 means that you cannot examine the contents of a variable or disassemble
15917 a function within a DLL without a running program.
15919 Variables are generally treated as pointers and dereferenced
15920 automatically. For this reason, it is often necessary to prefix a
15921 variable name with the address-of operator (``&'') and provide explicit
15922 type information in the command. Here's an example of the type of
15926 (@value{GDBP}) print 'cygwin1!__argv'
15931 (@value{GDBP}) x 'cygwin1!__argv'
15932 0x10021610: "\230y\""
15935 And two possible solutions:
15938 (@value{GDBP}) print ((char **)'cygwin1!__argv')[0]
15939 $2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"
15943 (@value{GDBP}) x/2x &'cygwin1!__argv'
15944 0x610c0aa8 <cygwin1!__argv>: 0x10021608 0x00000000
15945 (@value{GDBP}) x/x 0x10021608
15946 0x10021608: 0x0022fd98
15947 (@value{GDBP}) x/s 0x0022fd98
15948 0x22fd98: "/cygdrive/c/mydirectory/myprogram"
15951 Setting a break point within a DLL is possible even before the program
15952 starts execution. However, under these circumstances, @value{GDBN} can't
15953 examine the initial instructions of the function in order to skip the
15954 function's frame set-up code. You can work around this by using ``*&''
15955 to set the breakpoint at a raw memory address:
15958 (@value{GDBP}) break *&'python22!PyOS_Readline'
15959 Breakpoint 1 at 0x1e04eff0
15962 The author of these extensions is not entirely convinced that setting a
15963 break point within a shared DLL like @file{kernel32.dll} is completely
15967 @subsection Commands Specific to @sc{gnu} Hurd Systems
15968 @cindex @sc{gnu} Hurd debugging
15970 This subsection describes @value{GDBN} commands specific to the
15971 @sc{gnu} Hurd native debugging.
15976 @kindex set signals@r{, Hurd command}
15977 @kindex set sigs@r{, Hurd command}
15978 This command toggles the state of inferior signal interception by
15979 @value{GDBN}. Mach exceptions, such as breakpoint traps, are not
15980 affected by this command. @code{sigs} is a shorthand alias for
15985 @kindex show signals@r{, Hurd command}
15986 @kindex show sigs@r{, Hurd command}
15987 Show the current state of intercepting inferior's signals.
15989 @item set signal-thread
15990 @itemx set sigthread
15991 @kindex set signal-thread
15992 @kindex set sigthread
15993 This command tells @value{GDBN} which thread is the @code{libc} signal
15994 thread. That thread is run when a signal is delivered to a running
15995 process. @code{set sigthread} is the shorthand alias of @code{set
15998 @item show signal-thread
15999 @itemx show sigthread
16000 @kindex show signal-thread
16001 @kindex show sigthread
16002 These two commands show which thread will run when the inferior is
16003 delivered a signal.
16006 @kindex set stopped@r{, Hurd command}
16007 This commands tells @value{GDBN} that the inferior process is stopped,
16008 as with the @code{SIGSTOP} signal. The stopped process can be
16009 continued by delivering a signal to it.
16012 @kindex show stopped@r{, Hurd command}
16013 This command shows whether @value{GDBN} thinks the debuggee is
16016 @item set exceptions
16017 @kindex set exceptions@r{, Hurd command}
16018 Use this command to turn off trapping of exceptions in the inferior.
16019 When exception trapping is off, neither breakpoints nor
16020 single-stepping will work. To restore the default, set exception
16023 @item show exceptions
16024 @kindex show exceptions@r{, Hurd command}
16025 Show the current state of trapping exceptions in the inferior.
16027 @item set task pause
16028 @kindex set task@r{, Hurd commands}
16029 @cindex task attributes (@sc{gnu} Hurd)
16030 @cindex pause current task (@sc{gnu} Hurd)
16031 This command toggles task suspension when @value{GDBN} has control.
16032 Setting it to on takes effect immediately, and the task is suspended
16033 whenever @value{GDBN} gets control. Setting it to off will take
16034 effect the next time the inferior is continued. If this option is set
16035 to off, you can use @code{set thread default pause on} or @code{set
16036 thread pause on} (see below) to pause individual threads.
16038 @item show task pause
16039 @kindex show task@r{, Hurd commands}
16040 Show the current state of task suspension.
16042 @item set task detach-suspend-count
16043 @cindex task suspend count
16044 @cindex detach from task, @sc{gnu} Hurd
16045 This command sets the suspend count the task will be left with when
16046 @value{GDBN} detaches from it.
16048 @item show task detach-suspend-count
16049 Show the suspend count the task will be left with when detaching.
16051 @item set task exception-port
16052 @itemx set task excp
16053 @cindex task exception port, @sc{gnu} Hurd
16054 This command sets the task exception port to which @value{GDBN} will
16055 forward exceptions. The argument should be the value of the @dfn{send
16056 rights} of the task. @code{set task excp} is a shorthand alias.
16058 @item set noninvasive
16059 @cindex noninvasive task options
16060 This command switches @value{GDBN} to a mode that is the least
16061 invasive as far as interfering with the inferior is concerned. This
16062 is the same as using @code{set task pause}, @code{set exceptions}, and
16063 @code{set signals} to values opposite to the defaults.
16065 @item info send-rights
16066 @itemx info receive-rights
16067 @itemx info port-rights
16068 @itemx info port-sets
16069 @itemx info dead-names
16072 @cindex send rights, @sc{gnu} Hurd
16073 @cindex receive rights, @sc{gnu} Hurd
16074 @cindex port rights, @sc{gnu} Hurd
16075 @cindex port sets, @sc{gnu} Hurd
16076 @cindex dead names, @sc{gnu} Hurd
16077 These commands display information about, respectively, send rights,
16078 receive rights, port rights, port sets, and dead names of a task.
16079 There are also shorthand aliases: @code{info ports} for @code{info
16080 port-rights} and @code{info psets} for @code{info port-sets}.
16082 @item set thread pause
16083 @kindex set thread@r{, Hurd command}
16084 @cindex thread properties, @sc{gnu} Hurd
16085 @cindex pause current thread (@sc{gnu} Hurd)
16086 This command toggles current thread suspension when @value{GDBN} has
16087 control. Setting it to on takes effect immediately, and the current
16088 thread is suspended whenever @value{GDBN} gets control. Setting it to
16089 off will take effect the next time the inferior is continued.
16090 Normally, this command has no effect, since when @value{GDBN} has
16091 control, the whole task is suspended. However, if you used @code{set
16092 task pause off} (see above), this command comes in handy to suspend
16093 only the current thread.
16095 @item show thread pause
16096 @kindex show thread@r{, Hurd command}
16097 This command shows the state of current thread suspension.
16099 @item set thread run
16100 This command sets whether the current thread is allowed to run.
16102 @item show thread run
16103 Show whether the current thread is allowed to run.
16105 @item set thread detach-suspend-count
16106 @cindex thread suspend count, @sc{gnu} Hurd
16107 @cindex detach from thread, @sc{gnu} Hurd
16108 This command sets the suspend count @value{GDBN} will leave on a
16109 thread when detaching. This number is relative to the suspend count
16110 found by @value{GDBN} when it notices the thread; use @code{set thread
16111 takeover-suspend-count} to force it to an absolute value.
16113 @item show thread detach-suspend-count
16114 Show the suspend count @value{GDBN} will leave on the thread when
16117 @item set thread exception-port
16118 @itemx set thread excp
16119 Set the thread exception port to which to forward exceptions. This
16120 overrides the port set by @code{set task exception-port} (see above).
16121 @code{set thread excp} is the shorthand alias.
16123 @item set thread takeover-suspend-count
16124 Normally, @value{GDBN}'s thread suspend counts are relative to the
16125 value @value{GDBN} finds when it notices each thread. This command
16126 changes the suspend counts to be absolute instead.
16128 @item set thread default
16129 @itemx show thread default
16130 @cindex thread default settings, @sc{gnu} Hurd
16131 Each of the above @code{set thread} commands has a @code{set thread
16132 default} counterpart (e.g., @code{set thread default pause}, @code{set
16133 thread default exception-port}, etc.). The @code{thread default}
16134 variety of commands sets the default thread properties for all
16135 threads; you can then change the properties of individual threads with
16136 the non-default commands.
16141 @subsection QNX Neutrino
16142 @cindex QNX Neutrino
16144 @value{GDBN} provides the following commands specific to the QNX
16148 @item set debug nto-debug
16149 @kindex set debug nto-debug
16150 When set to on, enables debugging messages specific to the QNX
16153 @item show debug nto-debug
16154 @kindex show debug nto-debug
16155 Show the current state of QNX Neutrino messages.
16162 @value{GDBN} provides the following commands specific to the Darwin target:
16165 @item set debug darwin @var{num}
16166 @kindex set debug darwin
16167 When set to a non zero value, enables debugging messages specific to
16168 the Darwin support. Higher values produce more verbose output.
16170 @item show debug darwin
16171 @kindex show debug darwin
16172 Show the current state of Darwin messages.
16174 @item set debug mach-o @var{num}
16175 @kindex set debug mach-o
16176 When set to a non zero value, enables debugging messages while
16177 @value{GDBN} is reading Darwin object files. (@dfn{Mach-O} is the
16178 file format used on Darwin for object and executable files.) Higher
16179 values produce more verbose output. This is a command to diagnose
16180 problems internal to @value{GDBN} and should not be needed in normal
16183 @item show debug mach-o
16184 @kindex show debug mach-o
16185 Show the current state of Mach-O file messages.
16187 @item set mach-exceptions on
16188 @itemx set mach-exceptions off
16189 @kindex set mach-exceptions
16190 On Darwin, faults are first reported as a Mach exception and are then
16191 mapped to a Posix signal. Use this command to turn on trapping of
16192 Mach exceptions in the inferior. This might be sometimes useful to
16193 better understand the cause of a fault. The default is off.
16195 @item show mach-exceptions
16196 @kindex show mach-exceptions
16197 Show the current state of exceptions trapping.
16202 @section Embedded Operating Systems
16204 This section describes configurations involving the debugging of
16205 embedded operating systems that are available for several different
16209 * VxWorks:: Using @value{GDBN} with VxWorks
16212 @value{GDBN} includes the ability to debug programs running on
16213 various real-time operating systems.
16216 @subsection Using @value{GDBN} with VxWorks
16222 @kindex target vxworks
16223 @item target vxworks @var{machinename}
16224 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
16225 is the target system's machine name or IP address.
16229 On VxWorks, @code{load} links @var{filename} dynamically on the
16230 current target system as well as adding its symbols in @value{GDBN}.
16232 @value{GDBN} enables developers to spawn and debug tasks running on networked
16233 VxWorks targets from a Unix host. Already-running tasks spawned from
16234 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
16235 both the Unix host and on the VxWorks target. The program
16236 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
16237 installed with the name @code{vxgdb}, to distinguish it from a
16238 @value{GDBN} for debugging programs on the host itself.)
16241 @item VxWorks-timeout @var{args}
16242 @kindex vxworks-timeout
16243 All VxWorks-based targets now support the option @code{vxworks-timeout}.
16244 This option is set by the user, and @var{args} represents the number of
16245 seconds @value{GDBN} waits for responses to rpc's. You might use this if
16246 your VxWorks target is a slow software simulator or is on the far side
16247 of a thin network line.
16250 The following information on connecting to VxWorks was current when
16251 this manual was produced; newer releases of VxWorks may use revised
16254 @findex INCLUDE_RDB
16255 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
16256 to include the remote debugging interface routines in the VxWorks
16257 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
16258 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
16259 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
16260 source debugging task @code{tRdbTask} when VxWorks is booted. For more
16261 information on configuring and remaking VxWorks, see the manufacturer's
16263 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
16265 Once you have included @file{rdb.a} in your VxWorks system image and set
16266 your Unix execution search path to find @value{GDBN}, you are ready to
16267 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
16268 @code{vxgdb}, depending on your installation).
16270 @value{GDBN} comes up showing the prompt:
16277 * VxWorks Connection:: Connecting to VxWorks
16278 * VxWorks Download:: VxWorks download
16279 * VxWorks Attach:: Running tasks
16282 @node VxWorks Connection
16283 @subsubsection Connecting to VxWorks
16285 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
16286 network. To connect to a target whose host name is ``@code{tt}'', type:
16289 (vxgdb) target vxworks tt
16293 @value{GDBN} displays messages like these:
16296 Attaching remote machine across net...
16301 @value{GDBN} then attempts to read the symbol tables of any object modules
16302 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
16303 these files by searching the directories listed in the command search
16304 path (@pxref{Environment, ,Your Program's Environment}); if it fails
16305 to find an object file, it displays a message such as:
16308 prog.o: No such file or directory.
16311 When this happens, add the appropriate directory to the search path with
16312 the @value{GDBN} command @code{path}, and execute the @code{target}
16315 @node VxWorks Download
16316 @subsubsection VxWorks Download
16318 @cindex download to VxWorks
16319 If you have connected to the VxWorks target and you want to debug an
16320 object that has not yet been loaded, you can use the @value{GDBN}
16321 @code{load} command to download a file from Unix to VxWorks
16322 incrementally. The object file given as an argument to the @code{load}
16323 command is actually opened twice: first by the VxWorks target in order
16324 to download the code, then by @value{GDBN} in order to read the symbol
16325 table. This can lead to problems if the current working directories on
16326 the two systems differ. If both systems have NFS mounted the same
16327 filesystems, you can avoid these problems by using absolute paths.
16328 Otherwise, it is simplest to set the working directory on both systems
16329 to the directory in which the object file resides, and then to reference
16330 the file by its name, without any path. For instance, a program
16331 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
16332 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
16333 program, type this on VxWorks:
16336 -> cd "@var{vxpath}/vw/demo/rdb"
16340 Then, in @value{GDBN}, type:
16343 (vxgdb) cd @var{hostpath}/vw/demo/rdb
16344 (vxgdb) load prog.o
16347 @value{GDBN} displays a response similar to this:
16350 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
16353 You can also use the @code{load} command to reload an object module
16354 after editing and recompiling the corresponding source file. Note that
16355 this makes @value{GDBN} delete all currently-defined breakpoints,
16356 auto-displays, and convenience variables, and to clear the value
16357 history. (This is necessary in order to preserve the integrity of
16358 debugger's data structures that reference the target system's symbol
16361 @node VxWorks Attach
16362 @subsubsection Running Tasks
16364 @cindex running VxWorks tasks
16365 You can also attach to an existing task using the @code{attach} command as
16369 (vxgdb) attach @var{task}
16373 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
16374 or suspended when you attach to it. Running tasks are suspended at
16375 the time of attachment.
16377 @node Embedded Processors
16378 @section Embedded Processors
16380 This section goes into details specific to particular embedded
16383 @cindex send command to simulator
16384 Whenever a specific embedded processor has a simulator, @value{GDBN}
16385 allows to send an arbitrary command to the simulator.
16388 @item sim @var{command}
16389 @kindex sim@r{, a command}
16390 Send an arbitrary @var{command} string to the simulator. Consult the
16391 documentation for the specific simulator in use for information about
16392 acceptable commands.
16398 * M32R/D:: Renesas M32R/D
16399 * M68K:: Motorola M68K
16400 * MIPS Embedded:: MIPS Embedded
16401 * OpenRISC 1000:: OpenRisc 1000
16402 * PA:: HP PA Embedded
16403 * PowerPC Embedded:: PowerPC Embedded
16404 * Sparclet:: Tsqware Sparclet
16405 * Sparclite:: Fujitsu Sparclite
16406 * Z8000:: Zilog Z8000
16409 * Super-H:: Renesas Super-H
16418 @item target rdi @var{dev}
16419 ARM Angel monitor, via RDI library interface to ADP protocol. You may
16420 use this target to communicate with both boards running the Angel
16421 monitor, or with the EmbeddedICE JTAG debug device.
16424 @item target rdp @var{dev}
16429 @value{GDBN} provides the following ARM-specific commands:
16432 @item set arm disassembler
16434 This commands selects from a list of disassembly styles. The
16435 @code{"std"} style is the standard style.
16437 @item show arm disassembler
16439 Show the current disassembly style.
16441 @item set arm apcs32
16442 @cindex ARM 32-bit mode
16443 This command toggles ARM operation mode between 32-bit and 26-bit.
16445 @item show arm apcs32
16446 Display the current usage of the ARM 32-bit mode.
16448 @item set arm fpu @var{fputype}
16449 This command sets the ARM floating-point unit (FPU) type. The
16450 argument @var{fputype} can be one of these:
16454 Determine the FPU type by querying the OS ABI.
16456 Software FPU, with mixed-endian doubles on little-endian ARM
16459 GCC-compiled FPA co-processor.
16461 Software FPU with pure-endian doubles.
16467 Show the current type of the FPU.
16470 This command forces @value{GDBN} to use the specified ABI.
16473 Show the currently used ABI.
16475 @item set arm fallback-mode (arm|thumb|auto)
16476 @value{GDBN} uses the symbol table, when available, to determine
16477 whether instructions are ARM or Thumb. This command controls
16478 @value{GDBN}'s default behavior when the symbol table is not
16479 available. The default is @samp{auto}, which causes @value{GDBN} to
16480 use the current execution mode (from the @code{T} bit in the @code{CPSR}
16483 @item show arm fallback-mode
16484 Show the current fallback instruction mode.
16486 @item set arm force-mode (arm|thumb|auto)
16487 This command overrides use of the symbol table to determine whether
16488 instructions are ARM or Thumb. The default is @samp{auto}, which
16489 causes @value{GDBN} to use the symbol table and then the setting
16490 of @samp{set arm fallback-mode}.
16492 @item show arm force-mode
16493 Show the current forced instruction mode.
16495 @item set debug arm
16496 Toggle whether to display ARM-specific debugging messages from the ARM
16497 target support subsystem.
16499 @item show debug arm
16500 Show whether ARM-specific debugging messages are enabled.
16503 The following commands are available when an ARM target is debugged
16504 using the RDI interface:
16507 @item rdilogfile @r{[}@var{file}@r{]}
16509 @cindex ADP (Angel Debugger Protocol) logging
16510 Set the filename for the ADP (Angel Debugger Protocol) packet log.
16511 With an argument, sets the log file to the specified @var{file}. With
16512 no argument, show the current log file name. The default log file is
16515 @item rdilogenable @r{[}@var{arg}@r{]}
16516 @kindex rdilogenable
16517 Control logging of ADP packets. With an argument of 1 or @code{"yes"}
16518 enables logging, with an argument 0 or @code{"no"} disables it. With
16519 no arguments displays the current setting. When logging is enabled,
16520 ADP packets exchanged between @value{GDBN} and the RDI target device
16521 are logged to a file.
16523 @item set rdiromatzero
16524 @kindex set rdiromatzero
16525 @cindex ROM at zero address, RDI
16526 Tell @value{GDBN} whether the target has ROM at address 0. If on,
16527 vector catching is disabled, so that zero address can be used. If off
16528 (the default), vector catching is enabled. For this command to take
16529 effect, it needs to be invoked prior to the @code{target rdi} command.
16531 @item show rdiromatzero
16532 @kindex show rdiromatzero
16533 Show the current setting of ROM at zero address.
16535 @item set rdiheartbeat
16536 @kindex set rdiheartbeat
16537 @cindex RDI heartbeat
16538 Enable or disable RDI heartbeat packets. It is not recommended to
16539 turn on this option, since it confuses ARM and EPI JTAG interface, as
16540 well as the Angel monitor.
16542 @item show rdiheartbeat
16543 @kindex show rdiheartbeat
16544 Show the setting of RDI heartbeat packets.
16549 @subsection Renesas M32R/D and M32R/SDI
16552 @kindex target m32r
16553 @item target m32r @var{dev}
16554 Renesas M32R/D ROM monitor.
16556 @kindex target m32rsdi
16557 @item target m32rsdi @var{dev}
16558 Renesas M32R SDI server, connected via parallel port to the board.
16561 The following @value{GDBN} commands are specific to the M32R monitor:
16564 @item set download-path @var{path}
16565 @kindex set download-path
16566 @cindex find downloadable @sc{srec} files (M32R)
16567 Set the default path for finding downloadable @sc{srec} files.
16569 @item show download-path
16570 @kindex show download-path
16571 Show the default path for downloadable @sc{srec} files.
16573 @item set board-address @var{addr}
16574 @kindex set board-address
16575 @cindex M32-EVA target board address
16576 Set the IP address for the M32R-EVA target board.
16578 @item show board-address
16579 @kindex show board-address
16580 Show the current IP address of the target board.
16582 @item set server-address @var{addr}
16583 @kindex set server-address
16584 @cindex download server address (M32R)
16585 Set the IP address for the download server, which is the @value{GDBN}'s
16588 @item show server-address
16589 @kindex show server-address
16590 Display the IP address of the download server.
16592 @item upload @r{[}@var{file}@r{]}
16593 @kindex upload@r{, M32R}
16594 Upload the specified @sc{srec} @var{file} via the monitor's Ethernet
16595 upload capability. If no @var{file} argument is given, the current
16596 executable file is uploaded.
16598 @item tload @r{[}@var{file}@r{]}
16599 @kindex tload@r{, M32R}
16600 Test the @code{upload} command.
16603 The following commands are available for M32R/SDI:
16608 @cindex reset SDI connection, M32R
16609 This command resets the SDI connection.
16613 This command shows the SDI connection status.
16616 @kindex debug_chaos
16617 @cindex M32R/Chaos debugging
16618 Instructs the remote that M32R/Chaos debugging is to be used.
16620 @item use_debug_dma
16621 @kindex use_debug_dma
16622 Instructs the remote to use the DEBUG_DMA method of accessing memory.
16625 @kindex use_mon_code
16626 Instructs the remote to use the MON_CODE method of accessing memory.
16629 @kindex use_ib_break
16630 Instructs the remote to set breakpoints by IB break.
16632 @item use_dbt_break
16633 @kindex use_dbt_break
16634 Instructs the remote to set breakpoints by DBT.
16640 The Motorola m68k configuration includes ColdFire support, and a
16641 target command for the following ROM monitor.
16645 @kindex target dbug
16646 @item target dbug @var{dev}
16647 dBUG ROM monitor for Motorola ColdFire.
16651 @node MIPS Embedded
16652 @subsection MIPS Embedded
16654 @cindex MIPS boards
16655 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
16656 MIPS board attached to a serial line. This is available when
16657 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
16660 Use these @value{GDBN} commands to specify the connection to your target board:
16663 @item target mips @var{port}
16664 @kindex target mips @var{port}
16665 To run a program on the board, start up @code{@value{GDBP}} with the
16666 name of your program as the argument. To connect to the board, use the
16667 command @samp{target mips @var{port}}, where @var{port} is the name of
16668 the serial port connected to the board. If the program has not already
16669 been downloaded to the board, you may use the @code{load} command to
16670 download it. You can then use all the usual @value{GDBN} commands.
16672 For example, this sequence connects to the target board through a serial
16673 port, and loads and runs a program called @var{prog} through the
16677 host$ @value{GDBP} @var{prog}
16678 @value{GDBN} is free software and @dots{}
16679 (@value{GDBP}) target mips /dev/ttyb
16680 (@value{GDBP}) load @var{prog}
16684 @item target mips @var{hostname}:@var{portnumber}
16685 On some @value{GDBN} host configurations, you can specify a TCP
16686 connection (for instance, to a serial line managed by a terminal
16687 concentrator) instead of a serial port, using the syntax
16688 @samp{@var{hostname}:@var{portnumber}}.
16690 @item target pmon @var{port}
16691 @kindex target pmon @var{port}
16694 @item target ddb @var{port}
16695 @kindex target ddb @var{port}
16696 NEC's DDB variant of PMON for Vr4300.
16698 @item target lsi @var{port}
16699 @kindex target lsi @var{port}
16700 LSI variant of PMON.
16702 @kindex target r3900
16703 @item target r3900 @var{dev}
16704 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
16706 @kindex target array
16707 @item target array @var{dev}
16708 Array Tech LSI33K RAID controller board.
16714 @value{GDBN} also supports these special commands for MIPS targets:
16717 @item set mipsfpu double
16718 @itemx set mipsfpu single
16719 @itemx set mipsfpu none
16720 @itemx set mipsfpu auto
16721 @itemx show mipsfpu
16722 @kindex set mipsfpu
16723 @kindex show mipsfpu
16724 @cindex MIPS remote floating point
16725 @cindex floating point, MIPS remote
16726 If your target board does not support the MIPS floating point
16727 coprocessor, you should use the command @samp{set mipsfpu none} (if you
16728 need this, you may wish to put the command in your @value{GDBN} init
16729 file). This tells @value{GDBN} how to find the return value of
16730 functions which return floating point values. It also allows
16731 @value{GDBN} to avoid saving the floating point registers when calling
16732 functions on the board. If you are using a floating point coprocessor
16733 with only single precision floating point support, as on the @sc{r4650}
16734 processor, use the command @samp{set mipsfpu single}. The default
16735 double precision floating point coprocessor may be selected using
16736 @samp{set mipsfpu double}.
16738 In previous versions the only choices were double precision or no
16739 floating point, so @samp{set mipsfpu on} will select double precision
16740 and @samp{set mipsfpu off} will select no floating point.
16742 As usual, you can inquire about the @code{mipsfpu} variable with
16743 @samp{show mipsfpu}.
16745 @item set timeout @var{seconds}
16746 @itemx set retransmit-timeout @var{seconds}
16747 @itemx show timeout
16748 @itemx show retransmit-timeout
16749 @cindex @code{timeout}, MIPS protocol
16750 @cindex @code{retransmit-timeout}, MIPS protocol
16751 @kindex set timeout
16752 @kindex show timeout
16753 @kindex set retransmit-timeout
16754 @kindex show retransmit-timeout
16755 You can control the timeout used while waiting for a packet, in the MIPS
16756 remote protocol, with the @code{set timeout @var{seconds}} command. The
16757 default is 5 seconds. Similarly, you can control the timeout used while
16758 waiting for an acknowledgment of a packet with the @code{set
16759 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
16760 You can inspect both values with @code{show timeout} and @code{show
16761 retransmit-timeout}. (These commands are @emph{only} available when
16762 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
16764 The timeout set by @code{set timeout} does not apply when @value{GDBN}
16765 is waiting for your program to stop. In that case, @value{GDBN} waits
16766 forever because it has no way of knowing how long the program is going
16767 to run before stopping.
16769 @item set syn-garbage-limit @var{num}
16770 @kindex set syn-garbage-limit@r{, MIPS remote}
16771 @cindex synchronize with remote MIPS target
16772 Limit the maximum number of characters @value{GDBN} should ignore when
16773 it tries to synchronize with the remote target. The default is 10
16774 characters. Setting the limit to -1 means there's no limit.
16776 @item show syn-garbage-limit
16777 @kindex show syn-garbage-limit@r{, MIPS remote}
16778 Show the current limit on the number of characters to ignore when
16779 trying to synchronize with the remote system.
16781 @item set monitor-prompt @var{prompt}
16782 @kindex set monitor-prompt@r{, MIPS remote}
16783 @cindex remote monitor prompt
16784 Tell @value{GDBN} to expect the specified @var{prompt} string from the
16785 remote monitor. The default depends on the target:
16795 @item show monitor-prompt
16796 @kindex show monitor-prompt@r{, MIPS remote}
16797 Show the current strings @value{GDBN} expects as the prompt from the
16800 @item set monitor-warnings
16801 @kindex set monitor-warnings@r{, MIPS remote}
16802 Enable or disable monitor warnings about hardware breakpoints. This
16803 has effect only for the @code{lsi} target. When on, @value{GDBN} will
16804 display warning messages whose codes are returned by the @code{lsi}
16805 PMON monitor for breakpoint commands.
16807 @item show monitor-warnings
16808 @kindex show monitor-warnings@r{, MIPS remote}
16809 Show the current setting of printing monitor warnings.
16811 @item pmon @var{command}
16812 @kindex pmon@r{, MIPS remote}
16813 @cindex send PMON command
16814 This command allows sending an arbitrary @var{command} string to the
16815 monitor. The monitor must be in debug mode for this to work.
16818 @node OpenRISC 1000
16819 @subsection OpenRISC 1000
16820 @cindex OpenRISC 1000
16822 @cindex or1k boards
16823 See OR1k Architecture document (@uref{www.opencores.org}) for more information
16824 about platform and commands.
16828 @kindex target jtag
16829 @item target jtag jtag://@var{host}:@var{port}
16831 Connects to remote JTAG server.
16832 JTAG remote server can be either an or1ksim or JTAG server,
16833 connected via parallel port to the board.
16835 Example: @code{target jtag jtag://localhost:9999}
16838 @item or1ksim @var{command}
16839 If connected to @code{or1ksim} OpenRISC 1000 Architectural
16840 Simulator, proprietary commands can be executed.
16842 @kindex info or1k spr
16843 @item info or1k spr
16844 Displays spr groups.
16846 @item info or1k spr @var{group}
16847 @itemx info or1k spr @var{groupno}
16848 Displays register names in selected group.
16850 @item info or1k spr @var{group} @var{register}
16851 @itemx info or1k spr @var{register}
16852 @itemx info or1k spr @var{groupno} @var{registerno}
16853 @itemx info or1k spr @var{registerno}
16854 Shows information about specified spr register.
16857 @item spr @var{group} @var{register} @var{value}
16858 @itemx spr @var{register @var{value}}
16859 @itemx spr @var{groupno} @var{registerno @var{value}}
16860 @itemx spr @var{registerno @var{value}}
16861 Writes @var{value} to specified spr register.
16864 Some implementations of OpenRISC 1000 Architecture also have hardware trace.
16865 It is very similar to @value{GDBN} trace, except it does not interfere with normal
16866 program execution and is thus much faster. Hardware breakpoints/watchpoint
16867 triggers can be set using:
16870 Load effective address/data
16872 Store effective address/data
16874 Access effective address ($SEA or $LEA) or data ($SDATA/$LDATA)
16879 When triggered, it can capture low level data, like: @code{PC}, @code{LSEA},
16880 @code{LDATA}, @code{SDATA}, @code{READSPR}, @code{WRITESPR}, @code{INSTR}.
16882 @code{htrace} commands:
16883 @cindex OpenRISC 1000 htrace
16886 @item hwatch @var{conditional}
16887 Set hardware watchpoint on combination of Load/Store Effective Address(es)
16888 or Data. For example:
16890 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
16892 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
16896 Display information about current HW trace configuration.
16898 @item htrace trigger @var{conditional}
16899 Set starting criteria for HW trace.
16901 @item htrace qualifier @var{conditional}
16902 Set acquisition qualifier for HW trace.
16904 @item htrace stop @var{conditional}
16905 Set HW trace stopping criteria.
16907 @item htrace record [@var{data}]*
16908 Selects the data to be recorded, when qualifier is met and HW trace was
16911 @item htrace enable
16912 @itemx htrace disable
16913 Enables/disables the HW trace.
16915 @item htrace rewind [@var{filename}]
16916 Clears currently recorded trace data.
16918 If filename is specified, new trace file is made and any newly collected data
16919 will be written there.
16921 @item htrace print [@var{start} [@var{len}]]
16922 Prints trace buffer, using current record configuration.
16924 @item htrace mode continuous
16925 Set continuous trace mode.
16927 @item htrace mode suspend
16928 Set suspend trace mode.
16932 @node PowerPC Embedded
16933 @subsection PowerPC Embedded
16935 @value{GDBN} provides the following PowerPC-specific commands:
16938 @kindex set powerpc
16939 @item set powerpc soft-float
16940 @itemx show powerpc soft-float
16941 Force @value{GDBN} to use (or not use) a software floating point calling
16942 convention. By default, @value{GDBN} selects the calling convention based
16943 on the selected architecture and the provided executable file.
16945 @item set powerpc vector-abi
16946 @itemx show powerpc vector-abi
16947 Force @value{GDBN} to use the specified calling convention for vector
16948 arguments and return values. The valid options are @samp{auto};
16949 @samp{generic}, to avoid vector registers even if they are present;
16950 @samp{altivec}, to use AltiVec registers; and @samp{spe} to use SPE
16951 registers. By default, @value{GDBN} selects the calling convention
16952 based on the selected architecture and the provided executable file.
16954 @kindex target dink32
16955 @item target dink32 @var{dev}
16956 DINK32 ROM monitor.
16958 @kindex target ppcbug
16959 @item target ppcbug @var{dev}
16960 @kindex target ppcbug1
16961 @item target ppcbug1 @var{dev}
16962 PPCBUG ROM monitor for PowerPC.
16965 @item target sds @var{dev}
16966 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
16969 @cindex SDS protocol
16970 The following commands specific to the SDS protocol are supported
16974 @item set sdstimeout @var{nsec}
16975 @kindex set sdstimeout
16976 Set the timeout for SDS protocol reads to be @var{nsec} seconds. The
16977 default is 2 seconds.
16979 @item show sdstimeout
16980 @kindex show sdstimeout
16981 Show the current value of the SDS timeout.
16983 @item sds @var{command}
16984 @kindex sds@r{, a command}
16985 Send the specified @var{command} string to the SDS monitor.
16990 @subsection HP PA Embedded
16994 @kindex target op50n
16995 @item target op50n @var{dev}
16996 OP50N monitor, running on an OKI HPPA board.
16998 @kindex target w89k
16999 @item target w89k @var{dev}
17000 W89K monitor, running on a Winbond HPPA board.
17005 @subsection Tsqware Sparclet
17009 @value{GDBN} enables developers to debug tasks running on
17010 Sparclet targets from a Unix host.
17011 @value{GDBN} uses code that runs on
17012 both the Unix host and on the Sparclet target. The program
17013 @code{@value{GDBP}} is installed and executed on the Unix host.
17016 @item remotetimeout @var{args}
17017 @kindex remotetimeout
17018 @value{GDBN} supports the option @code{remotetimeout}.
17019 This option is set by the user, and @var{args} represents the number of
17020 seconds @value{GDBN} waits for responses.
17023 @cindex compiling, on Sparclet
17024 When compiling for debugging, include the options @samp{-g} to get debug
17025 information and @samp{-Ttext} to relocate the program to where you wish to
17026 load it on the target. You may also want to add the options @samp{-n} or
17027 @samp{-N} in order to reduce the size of the sections. Example:
17030 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
17033 You can use @code{objdump} to verify that the addresses are what you intended:
17036 sparclet-aout-objdump --headers --syms prog
17039 @cindex running, on Sparclet
17041 your Unix execution search path to find @value{GDBN}, you are ready to
17042 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
17043 (or @code{sparclet-aout-gdb}, depending on your installation).
17045 @value{GDBN} comes up showing the prompt:
17052 * Sparclet File:: Setting the file to debug
17053 * Sparclet Connection:: Connecting to Sparclet
17054 * Sparclet Download:: Sparclet download
17055 * Sparclet Execution:: Running and debugging
17058 @node Sparclet File
17059 @subsubsection Setting File to Debug
17061 The @value{GDBN} command @code{file} lets you choose with program to debug.
17064 (gdbslet) file prog
17068 @value{GDBN} then attempts to read the symbol table of @file{prog}.
17069 @value{GDBN} locates
17070 the file by searching the directories listed in the command search
17072 If the file was compiled with debug information (option @samp{-g}), source
17073 files will be searched as well.
17074 @value{GDBN} locates
17075 the source files by searching the directories listed in the directory search
17076 path (@pxref{Environment, ,Your Program's Environment}).
17078 to find a file, it displays a message such as:
17081 prog: No such file or directory.
17084 When this happens, add the appropriate directories to the search paths with
17085 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
17086 @code{target} command again.
17088 @node Sparclet Connection
17089 @subsubsection Connecting to Sparclet
17091 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
17092 To connect to a target on serial port ``@code{ttya}'', type:
17095 (gdbslet) target sparclet /dev/ttya
17096 Remote target sparclet connected to /dev/ttya
17097 main () at ../prog.c:3
17101 @value{GDBN} displays messages like these:
17107 @node Sparclet Download
17108 @subsubsection Sparclet Download
17110 @cindex download to Sparclet
17111 Once connected to the Sparclet target,
17112 you can use the @value{GDBN}
17113 @code{load} command to download the file from the host to the target.
17114 The file name and load offset should be given as arguments to the @code{load}
17116 Since the file format is aout, the program must be loaded to the starting
17117 address. You can use @code{objdump} to find out what this value is. The load
17118 offset is an offset which is added to the VMA (virtual memory address)
17119 of each of the file's sections.
17120 For instance, if the program
17121 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
17122 and bss at 0x12010170, in @value{GDBN}, type:
17125 (gdbslet) load prog 0x12010000
17126 Loading section .text, size 0xdb0 vma 0x12010000
17129 If the code is loaded at a different address then what the program was linked
17130 to, you may need to use the @code{section} and @code{add-symbol-file} commands
17131 to tell @value{GDBN} where to map the symbol table.
17133 @node Sparclet Execution
17134 @subsubsection Running and Debugging
17136 @cindex running and debugging Sparclet programs
17137 You can now begin debugging the task using @value{GDBN}'s execution control
17138 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
17139 manual for the list of commands.
17143 Breakpoint 1 at 0x12010000: file prog.c, line 3.
17145 Starting program: prog
17146 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
17147 3 char *symarg = 0;
17149 4 char *execarg = "hello!";
17154 @subsection Fujitsu Sparclite
17158 @kindex target sparclite
17159 @item target sparclite @var{dev}
17160 Fujitsu sparclite boards, used only for the purpose of loading.
17161 You must use an additional command to debug the program.
17162 For example: target remote @var{dev} using @value{GDBN} standard
17168 @subsection Zilog Z8000
17171 @cindex simulator, Z8000
17172 @cindex Zilog Z8000 simulator
17174 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
17177 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
17178 unsegmented variant of the Z8000 architecture) or the Z8001 (the
17179 segmented variant). The simulator recognizes which architecture is
17180 appropriate by inspecting the object code.
17183 @item target sim @var{args}
17185 @kindex target sim@r{, with Z8000}
17186 Debug programs on a simulated CPU. If the simulator supports setup
17187 options, specify them via @var{args}.
17191 After specifying this target, you can debug programs for the simulated
17192 CPU in the same style as programs for your host computer; use the
17193 @code{file} command to load a new program image, the @code{run} command
17194 to run your program, and so on.
17196 As well as making available all the usual machine registers
17197 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
17198 additional items of information as specially named registers:
17203 Counts clock-ticks in the simulator.
17206 Counts instructions run in the simulator.
17209 Execution time in 60ths of a second.
17213 You can refer to these values in @value{GDBN} expressions with the usual
17214 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
17215 conditional breakpoint that suspends only after at least 5000
17216 simulated clock ticks.
17219 @subsection Atmel AVR
17222 When configured for debugging the Atmel AVR, @value{GDBN} supports the
17223 following AVR-specific commands:
17226 @item info io_registers
17227 @kindex info io_registers@r{, AVR}
17228 @cindex I/O registers (Atmel AVR)
17229 This command displays information about the AVR I/O registers. For
17230 each register, @value{GDBN} prints its number and value.
17237 When configured for debugging CRIS, @value{GDBN} provides the
17238 following CRIS-specific commands:
17241 @item set cris-version @var{ver}
17242 @cindex CRIS version
17243 Set the current CRIS version to @var{ver}, either @samp{10} or @samp{32}.
17244 The CRIS version affects register names and sizes. This command is useful in
17245 case autodetection of the CRIS version fails.
17247 @item show cris-version
17248 Show the current CRIS version.
17250 @item set cris-dwarf2-cfi
17251 @cindex DWARF-2 CFI and CRIS
17252 Set the usage of DWARF-2 CFI for CRIS debugging. The default is @samp{on}.
17253 Change to @samp{off} when using @code{gcc-cris} whose version is below
17256 @item show cris-dwarf2-cfi
17257 Show the current state of using DWARF-2 CFI.
17259 @item set cris-mode @var{mode}
17261 Set the current CRIS mode to @var{mode}. It should only be changed when
17262 debugging in guru mode, in which case it should be set to
17263 @samp{guru} (the default is @samp{normal}).
17265 @item show cris-mode
17266 Show the current CRIS mode.
17270 @subsection Renesas Super-H
17273 For the Renesas Super-H processor, @value{GDBN} provides these
17278 @kindex regs@r{, Super-H}
17279 Show the values of all Super-H registers.
17281 @item set sh calling-convention @var{convention}
17282 @kindex set sh calling-convention
17283 Set the calling-convention used when calling functions from @value{GDBN}.
17284 Allowed values are @samp{gcc}, which is the default setting, and @samp{renesas}.
17285 With the @samp{gcc} setting, functions are called using the @value{NGCC} calling
17286 convention. If the DWARF-2 information of the called function specifies
17287 that the function follows the Renesas calling convention, the function
17288 is called using the Renesas calling convention. If the calling convention
17289 is set to @samp{renesas}, the Renesas calling convention is always used,
17290 regardless of the DWARF-2 information. This can be used to override the
17291 default of @samp{gcc} if debug information is missing, or the compiler
17292 does not emit the DWARF-2 calling convention entry for a function.
17294 @item show sh calling-convention
17295 @kindex show sh calling-convention
17296 Show the current calling convention setting.
17301 @node Architectures
17302 @section Architectures
17304 This section describes characteristics of architectures that affect
17305 all uses of @value{GDBN} with the architecture, both native and cross.
17312 * HPPA:: HP PA architecture
17313 * SPU:: Cell Broadband Engine SPU architecture
17318 @subsection x86 Architecture-specific Issues
17321 @item set struct-convention @var{mode}
17322 @kindex set struct-convention
17323 @cindex struct return convention
17324 @cindex struct/union returned in registers
17325 Set the convention used by the inferior to return @code{struct}s and
17326 @code{union}s from functions to @var{mode}. Possible values of
17327 @var{mode} are @code{"pcc"}, @code{"reg"}, and @code{"default"} (the
17328 default). @code{"default"} or @code{"pcc"} means that @code{struct}s
17329 are returned on the stack, while @code{"reg"} means that a
17330 @code{struct} or a @code{union} whose size is 1, 2, 4, or 8 bytes will
17331 be returned in a register.
17333 @item show struct-convention
17334 @kindex show struct-convention
17335 Show the current setting of the convention to return @code{struct}s
17344 @kindex set rstack_high_address
17345 @cindex AMD 29K register stack
17346 @cindex register stack, AMD29K
17347 @item set rstack_high_address @var{address}
17348 On AMD 29000 family processors, registers are saved in a separate
17349 @dfn{register stack}. There is no way for @value{GDBN} to determine the
17350 extent of this stack. Normally, @value{GDBN} just assumes that the
17351 stack is ``large enough''. This may result in @value{GDBN} referencing
17352 memory locations that do not exist. If necessary, you can get around
17353 this problem by specifying the ending address of the register stack with
17354 the @code{set rstack_high_address} command. The argument should be an
17355 address, which you probably want to precede with @samp{0x} to specify in
17358 @kindex show rstack_high_address
17359 @item show rstack_high_address
17360 Display the current limit of the register stack, on AMD 29000 family
17368 See the following section.
17373 @cindex stack on Alpha
17374 @cindex stack on MIPS
17375 @cindex Alpha stack
17377 Alpha- and MIPS-based computers use an unusual stack frame, which
17378 sometimes requires @value{GDBN} to search backward in the object code to
17379 find the beginning of a function.
17381 @cindex response time, MIPS debugging
17382 To improve response time (especially for embedded applications, where
17383 @value{GDBN} may be restricted to a slow serial line for this search)
17384 you may want to limit the size of this search, using one of these
17388 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
17389 @item set heuristic-fence-post @var{limit}
17390 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
17391 search for the beginning of a function. A value of @var{0} (the
17392 default) means there is no limit. However, except for @var{0}, the
17393 larger the limit the more bytes @code{heuristic-fence-post} must search
17394 and therefore the longer it takes to run. You should only need to use
17395 this command when debugging a stripped executable.
17397 @item show heuristic-fence-post
17398 Display the current limit.
17402 These commands are available @emph{only} when @value{GDBN} is configured
17403 for debugging programs on Alpha or MIPS processors.
17405 Several MIPS-specific commands are available when debugging MIPS
17409 @item set mips abi @var{arg}
17410 @kindex set mips abi
17411 @cindex set ABI for MIPS
17412 Tell @value{GDBN} which MIPS ABI is used by the inferior. Possible
17413 values of @var{arg} are:
17417 The default ABI associated with the current binary (this is the
17428 @item show mips abi
17429 @kindex show mips abi
17430 Show the MIPS ABI used by @value{GDBN} to debug the inferior.
17433 @itemx show mipsfpu
17434 @xref{MIPS Embedded, set mipsfpu}.
17436 @item set mips mask-address @var{arg}
17437 @kindex set mips mask-address
17438 @cindex MIPS addresses, masking
17439 This command determines whether the most-significant 32 bits of 64-bit
17440 MIPS addresses are masked off. The argument @var{arg} can be
17441 @samp{on}, @samp{off}, or @samp{auto}. The latter is the default
17442 setting, which lets @value{GDBN} determine the correct value.
17444 @item show mips mask-address
17445 @kindex show mips mask-address
17446 Show whether the upper 32 bits of MIPS addresses are masked off or
17449 @item set remote-mips64-transfers-32bit-regs
17450 @kindex set remote-mips64-transfers-32bit-regs
17451 This command controls compatibility with 64-bit MIPS targets that
17452 transfer data in 32-bit quantities. If you have an old MIPS 64 target
17453 that transfers 32 bits for some registers, like @sc{sr} and @sc{fsr},
17454 and 64 bits for other registers, set this option to @samp{on}.
17456 @item show remote-mips64-transfers-32bit-regs
17457 @kindex show remote-mips64-transfers-32bit-regs
17458 Show the current setting of compatibility with older MIPS 64 targets.
17460 @item set debug mips
17461 @kindex set debug mips
17462 This command turns on and off debugging messages for the MIPS-specific
17463 target code in @value{GDBN}.
17465 @item show debug mips
17466 @kindex show debug mips
17467 Show the current setting of MIPS debugging messages.
17473 @cindex HPPA support
17475 When @value{GDBN} is debugging the HP PA architecture, it provides the
17476 following special commands:
17479 @item set debug hppa
17480 @kindex set debug hppa
17481 This command determines whether HPPA architecture-specific debugging
17482 messages are to be displayed.
17484 @item show debug hppa
17485 Show whether HPPA debugging messages are displayed.
17487 @item maint print unwind @var{address}
17488 @kindex maint print unwind@r{, HPPA}
17489 This command displays the contents of the unwind table entry at the
17490 given @var{address}.
17496 @subsection Cell Broadband Engine SPU architecture
17497 @cindex Cell Broadband Engine
17500 When @value{GDBN} is debugging the Cell Broadband Engine SPU architecture,
17501 it provides the following special commands:
17504 @item info spu event
17506 Display SPU event facility status. Shows current event mask
17507 and pending event status.
17509 @item info spu signal
17510 Display SPU signal notification facility status. Shows pending
17511 signal-control word and signal notification mode of both signal
17512 notification channels.
17514 @item info spu mailbox
17515 Display SPU mailbox facility status. Shows all pending entries,
17516 in order of processing, in each of the SPU Write Outbound,
17517 SPU Write Outbound Interrupt, and SPU Read Inbound mailboxes.
17520 Display MFC DMA status. Shows all pending commands in the MFC
17521 DMA queue. For each entry, opcode, tag, class IDs, effective
17522 and local store addresses and transfer size are shown.
17524 @item info spu proxydma
17525 Display MFC Proxy-DMA status. Shows all pending commands in the MFC
17526 Proxy-DMA queue. For each entry, opcode, tag, class IDs, effective
17527 and local store addresses and transfer size are shown.
17531 When @value{GDBN} is debugging a combined PowerPC/SPU application
17532 on the Cell Broadband Engine, it provides in addition the following
17536 @item set spu stop-on-load @var{arg}
17538 Set whether to stop for new SPE threads. When set to @code{on}, @value{GDBN}
17539 will give control to the user when a new SPE thread enters its @code{main}
17540 function. The default is @code{off}.
17542 @item show spu stop-on-load
17544 Show whether to stop for new SPE threads.
17546 @item set spu auto-flush-cache @var{arg}
17547 Set whether to automatically flush the software-managed cache. When set to
17548 @code{on}, @value{GDBN} will automatically cause the SPE software-managed
17549 cache to be flushed whenever SPE execution stops. This provides a consistent
17550 view of PowerPC memory that is accessed via the cache. If an application
17551 does not use the software-managed cache, this option has no effect.
17553 @item show spu auto-flush-cache
17554 Show whether to automatically flush the software-managed cache.
17559 @subsection PowerPC
17560 @cindex PowerPC architecture
17562 When @value{GDBN} is debugging the PowerPC architecture, it provides a set of
17563 pseudo-registers to enable inspection of 128-bit wide Decimal Floating Point
17564 numbers stored in the floating point registers. These values must be stored
17565 in two consecutive registers, always starting at an even register like
17566 @code{f0} or @code{f2}.
17568 The pseudo-registers go from @code{$dl0} through @code{$dl15}, and are formed
17569 by joining the even/odd register pairs @code{f0} and @code{f1} for @code{$dl0},
17570 @code{f2} and @code{f3} for @code{$dl1} and so on.
17572 For POWER7 processors, @value{GDBN} provides a set of pseudo-registers, the 64-bit
17573 wide Extended Floating Point Registers (@samp{f32} through @samp{f63}).
17576 @node Controlling GDB
17577 @chapter Controlling @value{GDBN}
17579 You can alter the way @value{GDBN} interacts with you by using the
17580 @code{set} command. For commands controlling how @value{GDBN} displays
17581 data, see @ref{Print Settings, ,Print Settings}. Other settings are
17586 * Editing:: Command editing
17587 * Command History:: Command history
17588 * Screen Size:: Screen size
17589 * Numbers:: Numbers
17590 * ABI:: Configuring the current ABI
17591 * Messages/Warnings:: Optional warnings and messages
17592 * Debugging Output:: Optional messages about internal happenings
17600 @value{GDBN} indicates its readiness to read a command by printing a string
17601 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
17602 can change the prompt string with the @code{set prompt} command. For
17603 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
17604 the prompt in one of the @value{GDBN} sessions so that you can always tell
17605 which one you are talking to.
17607 @emph{Note:} @code{set prompt} does not add a space for you after the
17608 prompt you set. This allows you to set a prompt which ends in a space
17609 or a prompt that does not.
17613 @item set prompt @var{newprompt}
17614 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
17616 @kindex show prompt
17618 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
17622 @section Command Editing
17624 @cindex command line editing
17626 @value{GDBN} reads its input commands via the @dfn{Readline} interface. This
17627 @sc{gnu} library provides consistent behavior for programs which provide a
17628 command line interface to the user. Advantages are @sc{gnu} Emacs-style
17629 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
17630 substitution, and a storage and recall of command history across
17631 debugging sessions.
17633 You may control the behavior of command line editing in @value{GDBN} with the
17634 command @code{set}.
17637 @kindex set editing
17640 @itemx set editing on
17641 Enable command line editing (enabled by default).
17643 @item set editing off
17644 Disable command line editing.
17646 @kindex show editing
17648 Show whether command line editing is enabled.
17651 @xref{Command Line Editing}, for more details about the Readline
17652 interface. Users unfamiliar with @sc{gnu} Emacs or @code{vi} are
17653 encouraged to read that chapter.
17655 @node Command History
17656 @section Command History
17657 @cindex command history
17659 @value{GDBN} can keep track of the commands you type during your
17660 debugging sessions, so that you can be certain of precisely what
17661 happened. Use these commands to manage the @value{GDBN} command
17664 @value{GDBN} uses the @sc{gnu} History library, a part of the Readline
17665 package, to provide the history facility. @xref{Using History
17666 Interactively}, for the detailed description of the History library.
17668 To issue a command to @value{GDBN} without affecting certain aspects of
17669 the state which is seen by users, prefix it with @samp{server }
17670 (@pxref{Server Prefix}). This
17671 means that this command will not affect the command history, nor will it
17672 affect @value{GDBN}'s notion of which command to repeat if @key{RET} is
17673 pressed on a line by itself.
17675 @cindex @code{server}, command prefix
17676 The server prefix does not affect the recording of values into the value
17677 history; to print a value without recording it into the value history,
17678 use the @code{output} command instead of the @code{print} command.
17680 Here is the description of @value{GDBN} commands related to command
17684 @cindex history substitution
17685 @cindex history file
17686 @kindex set history filename
17687 @cindex @env{GDBHISTFILE}, environment variable
17688 @item set history filename @var{fname}
17689 Set the name of the @value{GDBN} command history file to @var{fname}.
17690 This is the file where @value{GDBN} reads an initial command history
17691 list, and where it writes the command history from this session when it
17692 exits. You can access this list through history expansion or through
17693 the history command editing characters listed below. This file defaults
17694 to the value of the environment variable @code{GDBHISTFILE}, or to
17695 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
17698 @cindex save command history
17699 @kindex set history save
17700 @item set history save
17701 @itemx set history save on
17702 Record command history in a file, whose name may be specified with the
17703 @code{set history filename} command. By default, this option is disabled.
17705 @item set history save off
17706 Stop recording command history in a file.
17708 @cindex history size
17709 @kindex set history size
17710 @cindex @env{HISTSIZE}, environment variable
17711 @item set history size @var{size}
17712 Set the number of commands which @value{GDBN} keeps in its history list.
17713 This defaults to the value of the environment variable
17714 @code{HISTSIZE}, or to 256 if this variable is not set.
17717 History expansion assigns special meaning to the character @kbd{!}.
17718 @xref{Event Designators}, for more details.
17720 @cindex history expansion, turn on/off
17721 Since @kbd{!} is also the logical not operator in C, history expansion
17722 is off by default. If you decide to enable history expansion with the
17723 @code{set history expansion on} command, you may sometimes need to
17724 follow @kbd{!} (when it is used as logical not, in an expression) with
17725 a space or a tab to prevent it from being expanded. The readline
17726 history facilities do not attempt substitution on the strings
17727 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
17729 The commands to control history expansion are:
17732 @item set history expansion on
17733 @itemx set history expansion
17734 @kindex set history expansion
17735 Enable history expansion. History expansion is off by default.
17737 @item set history expansion off
17738 Disable history expansion.
17741 @kindex show history
17743 @itemx show history filename
17744 @itemx show history save
17745 @itemx show history size
17746 @itemx show history expansion
17747 These commands display the state of the @value{GDBN} history parameters.
17748 @code{show history} by itself displays all four states.
17753 @kindex show commands
17754 @cindex show last commands
17755 @cindex display command history
17756 @item show commands
17757 Display the last ten commands in the command history.
17759 @item show commands @var{n}
17760 Print ten commands centered on command number @var{n}.
17762 @item show commands +
17763 Print ten commands just after the commands last printed.
17767 @section Screen Size
17768 @cindex size of screen
17769 @cindex pauses in output
17771 Certain commands to @value{GDBN} may produce large amounts of
17772 information output to the screen. To help you read all of it,
17773 @value{GDBN} pauses and asks you for input at the end of each page of
17774 output. Type @key{RET} when you want to continue the output, or @kbd{q}
17775 to discard the remaining output. Also, the screen width setting
17776 determines when to wrap lines of output. Depending on what is being
17777 printed, @value{GDBN} tries to break the line at a readable place,
17778 rather than simply letting it overflow onto the following line.
17780 Normally @value{GDBN} knows the size of the screen from the terminal
17781 driver software. For example, on Unix @value{GDBN} uses the termcap data base
17782 together with the value of the @code{TERM} environment variable and the
17783 @code{stty rows} and @code{stty cols} settings. If this is not correct,
17784 you can override it with the @code{set height} and @code{set
17791 @kindex show height
17792 @item set height @var{lpp}
17794 @itemx set width @var{cpl}
17796 These @code{set} commands specify a screen height of @var{lpp} lines and
17797 a screen width of @var{cpl} characters. The associated @code{show}
17798 commands display the current settings.
17800 If you specify a height of zero lines, @value{GDBN} does not pause during
17801 output no matter how long the output is. This is useful if output is to a
17802 file or to an editor buffer.
17804 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
17805 from wrapping its output.
17807 @item set pagination on
17808 @itemx set pagination off
17809 @kindex set pagination
17810 Turn the output pagination on or off; the default is on. Turning
17811 pagination off is the alternative to @code{set height 0}.
17813 @item show pagination
17814 @kindex show pagination
17815 Show the current pagination mode.
17820 @cindex number representation
17821 @cindex entering numbers
17823 You can always enter numbers in octal, decimal, or hexadecimal in
17824 @value{GDBN} by the usual conventions: octal numbers begin with
17825 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
17826 begin with @samp{0x}. Numbers that neither begin with @samp{0} or
17827 @samp{0x}, nor end with a @samp{.} are, by default, entered in base
17828 10; likewise, the default display for numbers---when no particular
17829 format is specified---is base 10. You can change the default base for
17830 both input and output with the commands described below.
17833 @kindex set input-radix
17834 @item set input-radix @var{base}
17835 Set the default base for numeric input. Supported choices
17836 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
17837 specified either unambiguously or using the current input radix; for
17841 set input-radix 012
17842 set input-radix 10.
17843 set input-radix 0xa
17847 sets the input base to decimal. On the other hand, @samp{set input-radix 10}
17848 leaves the input radix unchanged, no matter what it was, since
17849 @samp{10}, being without any leading or trailing signs of its base, is
17850 interpreted in the current radix. Thus, if the current radix is 16,
17851 @samp{10} is interpreted in hex, i.e.@: as 16 decimal, which doesn't
17854 @kindex set output-radix
17855 @item set output-radix @var{base}
17856 Set the default base for numeric display. Supported choices
17857 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
17858 specified either unambiguously or using the current input radix.
17860 @kindex show input-radix
17861 @item show input-radix
17862 Display the current default base for numeric input.
17864 @kindex show output-radix
17865 @item show output-radix
17866 Display the current default base for numeric display.
17868 @item set radix @r{[}@var{base}@r{]}
17872 These commands set and show the default base for both input and output
17873 of numbers. @code{set radix} sets the radix of input and output to
17874 the same base; without an argument, it resets the radix back to its
17875 default value of 10.
17880 @section Configuring the Current ABI
17882 @value{GDBN} can determine the @dfn{ABI} (Application Binary Interface) of your
17883 application automatically. However, sometimes you need to override its
17884 conclusions. Use these commands to manage @value{GDBN}'s view of the
17891 One @value{GDBN} configuration can debug binaries for multiple operating
17892 system targets, either via remote debugging or native emulation.
17893 @value{GDBN} will autodetect the @dfn{OS ABI} (Operating System ABI) in use,
17894 but you can override its conclusion using the @code{set osabi} command.
17895 One example where this is useful is in debugging of binaries which use
17896 an alternate C library (e.g.@: @sc{uClibc} for @sc{gnu}/Linux) which does
17897 not have the same identifying marks that the standard C library for your
17902 Show the OS ABI currently in use.
17905 With no argument, show the list of registered available OS ABI's.
17907 @item set osabi @var{abi}
17908 Set the current OS ABI to @var{abi}.
17911 @cindex float promotion
17913 Generally, the way that an argument of type @code{float} is passed to a
17914 function depends on whether the function is prototyped. For a prototyped
17915 (i.e.@: ANSI/ISO style) function, @code{float} arguments are passed unchanged,
17916 according to the architecture's convention for @code{float}. For unprototyped
17917 (i.e.@: K&R style) functions, @code{float} arguments are first promoted to type
17918 @code{double} and then passed.
17920 Unfortunately, some forms of debug information do not reliably indicate whether
17921 a function is prototyped. If @value{GDBN} calls a function that is not marked
17922 as prototyped, it consults @kbd{set coerce-float-to-double}.
17925 @kindex set coerce-float-to-double
17926 @item set coerce-float-to-double
17927 @itemx set coerce-float-to-double on
17928 Arguments of type @code{float} will be promoted to @code{double} when passed
17929 to an unprototyped function. This is the default setting.
17931 @item set coerce-float-to-double off
17932 Arguments of type @code{float} will be passed directly to unprototyped
17935 @kindex show coerce-float-to-double
17936 @item show coerce-float-to-double
17937 Show the current setting of promoting @code{float} to @code{double}.
17941 @kindex show cp-abi
17942 @value{GDBN} needs to know the ABI used for your program's C@t{++}
17943 objects. The correct C@t{++} ABI depends on which C@t{++} compiler was
17944 used to build your application. @value{GDBN} only fully supports
17945 programs with a single C@t{++} ABI; if your program contains code using
17946 multiple C@t{++} ABI's or if @value{GDBN} can not identify your
17947 program's ABI correctly, you can tell @value{GDBN} which ABI to use.
17948 Currently supported ABI's include ``gnu-v2'', for @code{g++} versions
17949 before 3.0, ``gnu-v3'', for @code{g++} versions 3.0 and later, and
17950 ``hpaCC'' for the HP ANSI C@t{++} compiler. Other C@t{++} compilers may
17951 use the ``gnu-v2'' or ``gnu-v3'' ABI's as well. The default setting is
17956 Show the C@t{++} ABI currently in use.
17959 With no argument, show the list of supported C@t{++} ABI's.
17961 @item set cp-abi @var{abi}
17962 @itemx set cp-abi auto
17963 Set the current C@t{++} ABI to @var{abi}, or return to automatic detection.
17966 @node Messages/Warnings
17967 @section Optional Warnings and Messages
17969 @cindex verbose operation
17970 @cindex optional warnings
17971 By default, @value{GDBN} is silent about its inner workings. If you are
17972 running on a slow machine, you may want to use the @code{set verbose}
17973 command. This makes @value{GDBN} tell you when it does a lengthy
17974 internal operation, so you will not think it has crashed.
17976 Currently, the messages controlled by @code{set verbose} are those
17977 which announce that the symbol table for a source file is being read;
17978 see @code{symbol-file} in @ref{Files, ,Commands to Specify Files}.
17981 @kindex set verbose
17982 @item set verbose on
17983 Enables @value{GDBN} output of certain informational messages.
17985 @item set verbose off
17986 Disables @value{GDBN} output of certain informational messages.
17988 @kindex show verbose
17990 Displays whether @code{set verbose} is on or off.
17993 By default, if @value{GDBN} encounters bugs in the symbol table of an
17994 object file, it is silent; but if you are debugging a compiler, you may
17995 find this information useful (@pxref{Symbol Errors, ,Errors Reading
18000 @kindex set complaints
18001 @item set complaints @var{limit}
18002 Permits @value{GDBN} to output @var{limit} complaints about each type of
18003 unusual symbols before becoming silent about the problem. Set
18004 @var{limit} to zero to suppress all complaints; set it to a large number
18005 to prevent complaints from being suppressed.
18007 @kindex show complaints
18008 @item show complaints
18009 Displays how many symbol complaints @value{GDBN} is permitted to produce.
18013 @anchor{confirmation requests}
18014 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
18015 lot of stupid questions to confirm certain commands. For example, if
18016 you try to run a program which is already running:
18020 The program being debugged has been started already.
18021 Start it from the beginning? (y or n)
18024 If you are willing to unflinchingly face the consequences of your own
18025 commands, you can disable this ``feature'':
18029 @kindex set confirm
18031 @cindex confirmation
18032 @cindex stupid questions
18033 @item set confirm off
18034 Disables confirmation requests.
18036 @item set confirm on
18037 Enables confirmation requests (the default).
18039 @kindex show confirm
18041 Displays state of confirmation requests.
18045 @cindex command tracing
18046 If you need to debug user-defined commands or sourced files you may find it
18047 useful to enable @dfn{command tracing}. In this mode each command will be
18048 printed as it is executed, prefixed with one or more @samp{+} symbols, the
18049 quantity denoting the call depth of each command.
18052 @kindex set trace-commands
18053 @cindex command scripts, debugging
18054 @item set trace-commands on
18055 Enable command tracing.
18056 @item set trace-commands off
18057 Disable command tracing.
18058 @item show trace-commands
18059 Display the current state of command tracing.
18062 @node Debugging Output
18063 @section Optional Messages about Internal Happenings
18064 @cindex optional debugging messages
18066 @value{GDBN} has commands that enable optional debugging messages from
18067 various @value{GDBN} subsystems; normally these commands are of
18068 interest to @value{GDBN} maintainers, or when reporting a bug. This
18069 section documents those commands.
18072 @kindex set exec-done-display
18073 @item set exec-done-display
18074 Turns on or off the notification of asynchronous commands'
18075 completion. When on, @value{GDBN} will print a message when an
18076 asynchronous command finishes its execution. The default is off.
18077 @kindex show exec-done-display
18078 @item show exec-done-display
18079 Displays the current setting of asynchronous command completion
18082 @cindex gdbarch debugging info
18083 @cindex architecture debugging info
18084 @item set debug arch
18085 Turns on or off display of gdbarch debugging info. The default is off
18087 @item show debug arch
18088 Displays the current state of displaying gdbarch debugging info.
18089 @item set debug aix-thread
18090 @cindex AIX threads
18091 Display debugging messages about inner workings of the AIX thread
18093 @item show debug aix-thread
18094 Show the current state of AIX thread debugging info display.
18095 @item set debug dwarf2-die
18096 @cindex DWARF2 DIEs
18097 Dump DWARF2 DIEs after they are read in.
18098 The value is the number of nesting levels to print.
18099 A value of zero turns off the display.
18100 @item show debug dwarf2-die
18101 Show the current state of DWARF2 DIE debugging.
18102 @item set debug displaced
18103 @cindex displaced stepping debugging info
18104 Turns on or off display of @value{GDBN} debugging info for the
18105 displaced stepping support. The default is off.
18106 @item show debug displaced
18107 Displays the current state of displaying @value{GDBN} debugging info
18108 related to displaced stepping.
18109 @item set debug event
18110 @cindex event debugging info
18111 Turns on or off display of @value{GDBN} event debugging info. The
18113 @item show debug event
18114 Displays the current state of displaying @value{GDBN} event debugging
18116 @item set debug expression
18117 @cindex expression debugging info
18118 Turns on or off display of debugging info about @value{GDBN}
18119 expression parsing. The default is off.
18120 @item show debug expression
18121 Displays the current state of displaying debugging info about
18122 @value{GDBN} expression parsing.
18123 @item set debug frame
18124 @cindex frame debugging info
18125 Turns on or off display of @value{GDBN} frame debugging info. The
18127 @item show debug frame
18128 Displays the current state of displaying @value{GDBN} frame debugging
18130 @item set debug gnu-nat
18131 @cindex @sc{gnu}/Hurd debug messages
18132 Turns on or off debugging messages from the @sc{gnu}/Hurd debug support.
18133 @item show debug gnu-nat
18134 Show the current state of @sc{gnu}/Hurd debugging messages.
18135 @item set debug infrun
18136 @cindex inferior debugging info
18137 Turns on or off display of @value{GDBN} debugging info for running the inferior.
18138 The default is off. @file{infrun.c} contains GDB's runtime state machine used
18139 for implementing operations such as single-stepping the inferior.
18140 @item show debug infrun
18141 Displays the current state of @value{GDBN} inferior debugging.
18142 @item set debug lin-lwp
18143 @cindex @sc{gnu}/Linux LWP debug messages
18144 @cindex Linux lightweight processes
18145 Turns on or off debugging messages from the Linux LWP debug support.
18146 @item show debug lin-lwp
18147 Show the current state of Linux LWP debugging messages.
18148 @item set debug lin-lwp-async
18149 @cindex @sc{gnu}/Linux LWP async debug messages
18150 @cindex Linux lightweight processes
18151 Turns on or off debugging messages from the Linux LWP async debug support.
18152 @item show debug lin-lwp-async
18153 Show the current state of Linux LWP async debugging messages.
18154 @item set debug observer
18155 @cindex observer debugging info
18156 Turns on or off display of @value{GDBN} observer debugging. This
18157 includes info such as the notification of observable events.
18158 @item show debug observer
18159 Displays the current state of observer debugging.
18160 @item set debug overload
18161 @cindex C@t{++} overload debugging info
18162 Turns on or off display of @value{GDBN} C@t{++} overload debugging
18163 info. This includes info such as ranking of functions, etc. The default
18165 @item show debug overload
18166 Displays the current state of displaying @value{GDBN} C@t{++} overload
18168 @cindex packets, reporting on stdout
18169 @cindex serial connections, debugging
18170 @cindex debug remote protocol
18171 @cindex remote protocol debugging
18172 @cindex display remote packets
18173 @item set debug remote
18174 Turns on or off display of reports on all packets sent back and forth across
18175 the serial line to the remote machine. The info is printed on the
18176 @value{GDBN} standard output stream. The default is off.
18177 @item show debug remote
18178 Displays the state of display of remote packets.
18179 @item set debug serial
18180 Turns on or off display of @value{GDBN} serial debugging info. The
18182 @item show debug serial
18183 Displays the current state of displaying @value{GDBN} serial debugging
18185 @item set debug solib-frv
18186 @cindex FR-V shared-library debugging
18187 Turns on or off debugging messages for FR-V shared-library code.
18188 @item show debug solib-frv
18189 Display the current state of FR-V shared-library code debugging
18191 @item set debug target
18192 @cindex target debugging info
18193 Turns on or off display of @value{GDBN} target debugging info. This info
18194 includes what is going on at the target level of GDB, as it happens. The
18195 default is 0. Set it to 1 to track events, and to 2 to also track the
18196 value of large memory transfers. Changes to this flag do not take effect
18197 until the next time you connect to a target or use the @code{run} command.
18198 @item show debug target
18199 Displays the current state of displaying @value{GDBN} target debugging
18201 @item set debug timestamp
18202 @cindex timestampping debugging info
18203 Turns on or off display of timestamps with @value{GDBN} debugging info.
18204 When enabled, seconds and microseconds are displayed before each debugging
18206 @item show debug timestamp
18207 Displays the current state of displaying timestamps with @value{GDBN}
18209 @item set debugvarobj
18210 @cindex variable object debugging info
18211 Turns on or off display of @value{GDBN} variable object debugging
18212 info. The default is off.
18213 @item show debugvarobj
18214 Displays the current state of displaying @value{GDBN} variable object
18216 @item set debug xml
18217 @cindex XML parser debugging
18218 Turns on or off debugging messages for built-in XML parsers.
18219 @item show debug xml
18220 Displays the current state of XML debugging messages.
18223 @node Extending GDB
18224 @chapter Extending @value{GDBN}
18225 @cindex extending GDB
18227 @value{GDBN} provides two mechanisms for extension. The first is based
18228 on composition of @value{GDBN} commands, and the second is based on the
18229 Python scripting language.
18232 * Sequences:: Canned Sequences of Commands
18233 * Python:: Scripting @value{GDBN} using Python
18237 @section Canned Sequences of Commands
18239 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
18240 Command Lists}), @value{GDBN} provides two ways to store sequences of
18241 commands for execution as a unit: user-defined commands and command
18245 * Define:: How to define your own commands
18246 * Hooks:: Hooks for user-defined commands
18247 * Command Files:: How to write scripts of commands to be stored in a file
18248 * Output:: Commands for controlled output
18252 @subsection User-defined Commands
18254 @cindex user-defined command
18255 @cindex arguments, to user-defined commands
18256 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
18257 which you assign a new name as a command. This is done with the
18258 @code{define} command. User commands may accept up to 10 arguments
18259 separated by whitespace. Arguments are accessed within the user command
18260 via @code{$arg0@dots{}$arg9}. A trivial example:
18264 print $arg0 + $arg1 + $arg2
18269 To execute the command use:
18276 This defines the command @code{adder}, which prints the sum of
18277 its three arguments. Note the arguments are text substitutions, so they may
18278 reference variables, use complex expressions, or even perform inferior
18281 @cindex argument count in user-defined commands
18282 @cindex how many arguments (user-defined commands)
18283 In addition, @code{$argc} may be used to find out how many arguments have
18284 been passed. This expands to a number in the range 0@dots{}10.
18289 print $arg0 + $arg1
18292 print $arg0 + $arg1 + $arg2
18300 @item define @var{commandname}
18301 Define a command named @var{commandname}. If there is already a command
18302 by that name, you are asked to confirm that you want to redefine it.
18303 @var{commandname} may be a bare command name consisting of letters,
18304 numbers, dashes, and underscores. It may also start with any predefined
18305 prefix command. For example, @samp{define target my-target} creates
18306 a user-defined @samp{target my-target} command.
18308 The definition of the command is made up of other @value{GDBN} command lines,
18309 which are given following the @code{define} command. The end of these
18310 commands is marked by a line containing @code{end}.
18313 @kindex end@r{ (user-defined commands)}
18314 @item document @var{commandname}
18315 Document the user-defined command @var{commandname}, so that it can be
18316 accessed by @code{help}. The command @var{commandname} must already be
18317 defined. This command reads lines of documentation just as @code{define}
18318 reads the lines of the command definition, ending with @code{end}.
18319 After the @code{document} command is finished, @code{help} on command
18320 @var{commandname} displays the documentation you have written.
18322 You may use the @code{document} command again to change the
18323 documentation of a command. Redefining the command with @code{define}
18324 does not change the documentation.
18326 @kindex dont-repeat
18327 @cindex don't repeat command
18329 Used inside a user-defined command, this tells @value{GDBN} that this
18330 command should not be repeated when the user hits @key{RET}
18331 (@pxref{Command Syntax, repeat last command}).
18333 @kindex help user-defined
18334 @item help user-defined
18335 List all user-defined commands, with the first line of the documentation
18340 @itemx show user @var{commandname}
18341 Display the @value{GDBN} commands used to define @var{commandname} (but
18342 not its documentation). If no @var{commandname} is given, display the
18343 definitions for all user-defined commands.
18345 @cindex infinite recursion in user-defined commands
18346 @kindex show max-user-call-depth
18347 @kindex set max-user-call-depth
18348 @item show max-user-call-depth
18349 @itemx set max-user-call-depth
18350 The value of @code{max-user-call-depth} controls how many recursion
18351 levels are allowed in user-defined commands before @value{GDBN} suspects an
18352 infinite recursion and aborts the command.
18355 In addition to the above commands, user-defined commands frequently
18356 use control flow commands, described in @ref{Command Files}.
18358 When user-defined commands are executed, the
18359 commands of the definition are not printed. An error in any command
18360 stops execution of the user-defined command.
18362 If used interactively, commands that would ask for confirmation proceed
18363 without asking when used inside a user-defined command. Many @value{GDBN}
18364 commands that normally print messages to say what they are doing omit the
18365 messages when used in a user-defined command.
18368 @subsection User-defined Command Hooks
18369 @cindex command hooks
18370 @cindex hooks, for commands
18371 @cindex hooks, pre-command
18374 You may define @dfn{hooks}, which are a special kind of user-defined
18375 command. Whenever you run the command @samp{foo}, if the user-defined
18376 command @samp{hook-foo} exists, it is executed (with no arguments)
18377 before that command.
18379 @cindex hooks, post-command
18381 A hook may also be defined which is run after the command you executed.
18382 Whenever you run the command @samp{foo}, if the user-defined command
18383 @samp{hookpost-foo} exists, it is executed (with no arguments) after
18384 that command. Post-execution hooks may exist simultaneously with
18385 pre-execution hooks, for the same command.
18387 It is valid for a hook to call the command which it hooks. If this
18388 occurs, the hook is not re-executed, thereby avoiding infinite recursion.
18390 @c It would be nice if hookpost could be passed a parameter indicating
18391 @c if the command it hooks executed properly or not. FIXME!
18393 @kindex stop@r{, a pseudo-command}
18394 In addition, a pseudo-command, @samp{stop} exists. Defining
18395 (@samp{hook-stop}) makes the associated commands execute every time
18396 execution stops in your program: before breakpoint commands are run,
18397 displays are printed, or the stack frame is printed.
18399 For example, to ignore @code{SIGALRM} signals while
18400 single-stepping, but treat them normally during normal execution,
18405 handle SIGALRM nopass
18409 handle SIGALRM pass
18412 define hook-continue
18413 handle SIGALRM pass
18417 As a further example, to hook at the beginning and end of the @code{echo}
18418 command, and to add extra text to the beginning and end of the message,
18426 define hookpost-echo
18430 (@value{GDBP}) echo Hello World
18431 <<<---Hello World--->>>
18436 You can define a hook for any single-word command in @value{GDBN}, but
18437 not for command aliases; you should define a hook for the basic command
18438 name, e.g.@: @code{backtrace} rather than @code{bt}.
18439 @c FIXME! So how does Joe User discover whether a command is an alias
18441 You can hook a multi-word command by adding @code{hook-} or
18442 @code{hookpost-} to the last word of the command, e.g.@:
18443 @samp{define target hook-remote} to add a hook to @samp{target remote}.
18445 If an error occurs during the execution of your hook, execution of
18446 @value{GDBN} commands stops and @value{GDBN} issues a prompt
18447 (before the command that you actually typed had a chance to run).
18449 If you try to define a hook which does not match any known command, you
18450 get a warning from the @code{define} command.
18452 @node Command Files
18453 @subsection Command Files
18455 @cindex command files
18456 @cindex scripting commands
18457 A command file for @value{GDBN} is a text file made of lines that are
18458 @value{GDBN} commands. Comments (lines starting with @kbd{#}) may
18459 also be included. An empty line in a command file does nothing; it
18460 does not mean to repeat the last command, as it would from the
18463 You can request the execution of a command file with the @code{source}
18468 @cindex execute commands from a file
18469 @item source [@code{-v}] @var{filename}
18470 Execute the command file @var{filename}.
18473 The lines in a command file are generally executed sequentially,
18474 unless the order of execution is changed by one of the
18475 @emph{flow-control commands} described below. The commands are not
18476 printed as they are executed. An error in any command terminates
18477 execution of the command file and control is returned to the console.
18479 @value{GDBN} searches for @var{filename} in the current directory and then
18480 on the search path (specified with the @samp{directory} command).
18482 If @code{-v}, for verbose mode, is given then @value{GDBN} displays
18483 each command as it is executed. The option must be given before
18484 @var{filename}, and is interpreted as part of the filename anywhere else.
18486 Commands that would ask for confirmation if used interactively proceed
18487 without asking when used in a command file. Many @value{GDBN} commands that
18488 normally print messages to say what they are doing omit the messages
18489 when called from command files.
18491 @value{GDBN} also accepts command input from standard input. In this
18492 mode, normal output goes to standard output and error output goes to
18493 standard error. Errors in a command file supplied on standard input do
18494 not terminate execution of the command file---execution continues with
18498 gdb < cmds > log 2>&1
18501 (The syntax above will vary depending on the shell used.) This example
18502 will execute commands from the file @file{cmds}. All output and errors
18503 would be directed to @file{log}.
18505 Since commands stored on command files tend to be more general than
18506 commands typed interactively, they frequently need to deal with
18507 complicated situations, such as different or unexpected values of
18508 variables and symbols, changes in how the program being debugged is
18509 built, etc. @value{GDBN} provides a set of flow-control commands to
18510 deal with these complexities. Using these commands, you can write
18511 complex scripts that loop over data structures, execute commands
18512 conditionally, etc.
18519 This command allows to include in your script conditionally executed
18520 commands. The @code{if} command takes a single argument, which is an
18521 expression to evaluate. It is followed by a series of commands that
18522 are executed only if the expression is true (its value is nonzero).
18523 There can then optionally be an @code{else} line, followed by a series
18524 of commands that are only executed if the expression was false. The
18525 end of the list is marked by a line containing @code{end}.
18529 This command allows to write loops. Its syntax is similar to
18530 @code{if}: the command takes a single argument, which is an expression
18531 to evaluate, and must be followed by the commands to execute, one per
18532 line, terminated by an @code{end}. These commands are called the
18533 @dfn{body} of the loop. The commands in the body of @code{while} are
18534 executed repeatedly as long as the expression evaluates to true.
18538 This command exits the @code{while} loop in whose body it is included.
18539 Execution of the script continues after that @code{while}s @code{end}
18542 @kindex loop_continue
18543 @item loop_continue
18544 This command skips the execution of the rest of the body of commands
18545 in the @code{while} loop in whose body it is included. Execution
18546 branches to the beginning of the @code{while} loop, where it evaluates
18547 the controlling expression.
18549 @kindex end@r{ (if/else/while commands)}
18551 Terminate the block of commands that are the body of @code{if},
18552 @code{else}, or @code{while} flow-control commands.
18557 @subsection Commands for Controlled Output
18559 During the execution of a command file or a user-defined command, normal
18560 @value{GDBN} output is suppressed; the only output that appears is what is
18561 explicitly printed by the commands in the definition. This section
18562 describes three commands useful for generating exactly the output you
18567 @item echo @var{text}
18568 @c I do not consider backslash-space a standard C escape sequence
18569 @c because it is not in ANSI.
18570 Print @var{text}. Nonprinting characters can be included in
18571 @var{text} using C escape sequences, such as @samp{\n} to print a
18572 newline. @strong{No newline is printed unless you specify one.}
18573 In addition to the standard C escape sequences, a backslash followed
18574 by a space stands for a space. This is useful for displaying a
18575 string with spaces at the beginning or the end, since leading and
18576 trailing spaces are otherwise trimmed from all arguments.
18577 To print @samp{@w{ }and foo =@w{ }}, use the command
18578 @samp{echo \@w{ }and foo = \@w{ }}.
18580 A backslash at the end of @var{text} can be used, as in C, to continue
18581 the command onto subsequent lines. For example,
18584 echo This is some text\n\
18585 which is continued\n\
18586 onto several lines.\n
18589 produces the same output as
18592 echo This is some text\n
18593 echo which is continued\n
18594 echo onto several lines.\n
18598 @item output @var{expression}
18599 Print the value of @var{expression} and nothing but that value: no
18600 newlines, no @samp{$@var{nn} = }. The value is not entered in the
18601 value history either. @xref{Expressions, ,Expressions}, for more information
18604 @item output/@var{fmt} @var{expression}
18605 Print the value of @var{expression} in format @var{fmt}. You can use
18606 the same formats as for @code{print}. @xref{Output Formats,,Output
18607 Formats}, for more information.
18610 @item printf @var{template}, @var{expressions}@dots{}
18611 Print the values of one or more @var{expressions} under the control of
18612 the string @var{template}. To print several values, make
18613 @var{expressions} be a comma-separated list of individual expressions,
18614 which may be either numbers or pointers. Their values are printed as
18615 specified by @var{template}, exactly as a C program would do by
18616 executing the code below:
18619 printf (@var{template}, @var{expressions}@dots{});
18622 As in @code{C} @code{printf}, ordinary characters in @var{template}
18623 are printed verbatim, while @dfn{conversion specification} introduced
18624 by the @samp{%} character cause subsequent @var{expressions} to be
18625 evaluated, their values converted and formatted according to type and
18626 style information encoded in the conversion specifications, and then
18629 For example, you can print two values in hex like this:
18632 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
18635 @code{printf} supports all the standard @code{C} conversion
18636 specifications, including the flags and modifiers between the @samp{%}
18637 character and the conversion letter, with the following exceptions:
18641 The argument-ordering modifiers, such as @samp{2$}, are not supported.
18644 The modifier @samp{*} is not supported for specifying precision or
18648 The @samp{'} flag (for separation of digits into groups according to
18649 @code{LC_NUMERIC'}) is not supported.
18652 The type modifiers @samp{hh}, @samp{j}, @samp{t}, and @samp{z} are not
18656 The conversion letter @samp{n} (as in @samp{%n}) is not supported.
18659 The conversion letters @samp{a} and @samp{A} are not supported.
18663 Note that the @samp{ll} type modifier is supported only if the
18664 underlying @code{C} implementation used to build @value{GDBN} supports
18665 the @code{long long int} type, and the @samp{L} type modifier is
18666 supported only if @code{long double} type is available.
18668 As in @code{C}, @code{printf} supports simple backslash-escape
18669 sequences, such as @code{\n}, @samp{\t}, @samp{\\}, @samp{\"},
18670 @samp{\a}, and @samp{\f}, that consist of backslash followed by a
18671 single character. Octal and hexadecimal escape sequences are not
18674 Additionally, @code{printf} supports conversion specifications for DFP
18675 (@dfn{Decimal Floating Point}) types using the following length modifiers
18676 together with a floating point specifier.
18681 @samp{H} for printing @code{Decimal32} types.
18684 @samp{D} for printing @code{Decimal64} types.
18687 @samp{DD} for printing @code{Decimal128} types.
18690 If the underlying @code{C} implementation used to build @value{GDBN} has
18691 support for the three length modifiers for DFP types, other modifiers
18692 such as width and precision will also be available for @value{GDBN} to use.
18694 In case there is no such @code{C} support, no additional modifiers will be
18695 available and the value will be printed in the standard way.
18697 Here's an example of printing DFP types using the above conversion letters:
18699 printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl
18705 @section Scripting @value{GDBN} using Python
18706 @cindex python scripting
18707 @cindex scripting with python
18709 You can script @value{GDBN} using the @uref{http://www.python.org/,
18710 Python programming language}. This feature is available only if
18711 @value{GDBN} was configured using @option{--with-python}.
18714 * Python Commands:: Accessing Python from @value{GDBN}.
18715 * Python API:: Accessing @value{GDBN} from Python.
18718 @node Python Commands
18719 @subsection Python Commands
18720 @cindex python commands
18721 @cindex commands to access python
18723 @value{GDBN} provides one command for accessing the Python interpreter,
18724 and one related setting:
18728 @item python @r{[}@var{code}@r{]}
18729 The @code{python} command can be used to evaluate Python code.
18731 If given an argument, the @code{python} command will evaluate the
18732 argument as a Python command. For example:
18735 (@value{GDBP}) python print 23
18739 If you do not provide an argument to @code{python}, it will act as a
18740 multi-line command, like @code{define}. In this case, the Python
18741 script is made up of subsequent command lines, given after the
18742 @code{python} command. This command list is terminated using a line
18743 containing @code{end}. For example:
18746 (@value{GDBP}) python
18748 End with a line saying just "end".
18754 @kindex maint set python print-stack
18755 @item maint set python print-stack
18756 By default, @value{GDBN} will print a stack trace when an error occurs
18757 in a Python script. This can be controlled using @code{maint set
18758 python print-stack}: if @code{on}, the default, then Python stack
18759 printing is enabled; if @code{off}, then Python stack printing is
18764 @subsection Python API
18766 @cindex programming in python
18768 @cindex python stdout
18769 @cindex python pagination
18770 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
18771 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
18772 A Python program which outputs to one of these streams may have its
18773 output interrupted by the user (@pxref{Screen Size}). In this
18774 situation, a Python @code{KeyboardInterrupt} exception is thrown.
18777 * Basic Python:: Basic Python Functions.
18778 * Exception Handling::
18779 * Auto-loading:: Automatically loading Python code.
18780 * Values From Inferior::
18781 * Types In Python:: Python representation of types.
18782 * Pretty Printing:: Pretty-printing values.
18783 * Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
18784 * Commands In Python:: Implementing new commands in Python.
18785 * Functions In Python:: Writing new convenience functions.
18786 * Objfiles In Python:: Object files.
18787 * Frames In Python:: Acessing inferior stack frames from Python.
18791 @subsubsection Basic Python
18793 @cindex python functions
18794 @cindex python module
18796 @value{GDBN} introduces a new Python module, named @code{gdb}. All
18797 methods and classes added by @value{GDBN} are placed in this module.
18798 @value{GDBN} automatically @code{import}s the @code{gdb} module for
18799 use in all scripts evaluated by the @code{python} command.
18801 @findex gdb.execute
18802 @defun execute command [from_tty]
18803 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
18804 If a GDB exception happens while @var{command} runs, it is
18805 translated as described in @ref{Exception Handling,,Exception Handling}.
18806 If no exceptions occur, this function returns @code{None}.
18808 @var{from_tty} specifies whether @value{GDBN} ought to consider this
18809 command as having originated from the user invoking it interactively.
18810 It must be a boolean value. If omitted, it defaults to @code{False}.
18813 @findex gdb.parameter
18814 @defun parameter parameter
18815 Return the value of a @value{GDBN} parameter. @var{parameter} is a
18816 string naming the parameter to look up; @var{parameter} may contain
18817 spaces if the parameter has a multi-part name. For example,
18818 @samp{print object} is a valid parameter name.
18820 If the named parameter does not exist, this function throws a
18821 @code{RuntimeError}. Otherwise, the parameter's value is converted to
18822 a Python value of the appropriate type, and returned.
18825 @findex gdb.history
18826 @defun history number
18827 Return a value from @value{GDBN}'s value history (@pxref{Value
18828 History}). @var{number} indicates which history element to return.
18829 If @var{number} is negative, then @value{GDBN} will take its absolute value
18830 and count backward from the last element (i.e., the most recent element) to
18831 find the value to return. If @var{number} is zero, then @value{GDBN} will
18832 return the most recent element. If the element specified by @var{number}
18833 doesn't exist in the value history, a @code{RuntimeError} exception will be
18836 If no exception is raised, the return value is always an instance of
18837 @code{gdb.Value} (@pxref{Values From Inferior}).
18841 @defun write string
18842 Print a string to @value{GDBN}'s paginated standard output stream.
18843 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
18844 call this function.
18849 Flush @value{GDBN}'s paginated standard output stream. Flushing
18850 @code{sys.stdout} or @code{sys.stderr} will automatically call this
18854 @node Exception Handling
18855 @subsubsection Exception Handling
18856 @cindex python exceptions
18857 @cindex exceptions, python
18859 When executing the @code{python} command, Python exceptions
18860 uncaught within the Python code are translated to calls to
18861 @value{GDBN} error-reporting mechanism. If the command that called
18862 @code{python} does not handle the error, @value{GDBN} will
18863 terminate it and print an error message containing the Python
18864 exception name, the associated value, and the Python call stack
18865 backtrace at the point where the exception was raised. Example:
18868 (@value{GDBP}) python print foo
18869 Traceback (most recent call last):
18870 File "<string>", line 1, in <module>
18871 NameError: name 'foo' is not defined
18874 @value{GDBN} errors that happen in @value{GDBN} commands invoked by Python
18875 code are converted to Python @code{RuntimeError} exceptions. User
18876 interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
18877 prompt) is translated to a Python @code{KeyboardInterrupt}
18878 exception. If you catch these exceptions in your Python code, your
18879 exception handler will see @code{RuntimeError} or
18880 @code{KeyboardInterrupt} as the exception type, the @value{GDBN} error
18881 message as its value, and the Python call stack backtrace at the
18882 Python statement closest to where the @value{GDBN} error occured as the
18886 @subsubsection Auto-loading
18887 @cindex auto-loading, Python
18889 When a new object file is read (for example, due to the @code{file}
18890 command, or because the inferior has loaded a shared library),
18891 @value{GDBN} will look for a file named @file{@var{objfile}-gdb.py},
18892 where @var{objfile} is the object file's real name, formed by ensuring
18893 that the file name is absolute, following all symlinks, and resolving
18894 @code{.} and @code{..} components. If this file exists and is
18895 readable, @value{GDBN} will evaluate it as a Python script.
18897 If this file does not exist, and if the parameter
18898 @code{debug-file-directory} is set (@pxref{Separate Debug Files}),
18899 then @value{GDBN} will use the file named
18900 @file{@var{debug-file-directory}/@var{real-name}}, where
18901 @var{real-name} is the object file's real name, as described above.
18903 Finally, if this file does not exist, then @value{GDBN} will look for
18904 a file named @file{@var{data-directory}/python/auto-load/@var{real-name}}, where
18905 @var{data-directory} is @value{GDBN}'s data directory (available via
18906 @code{show data-directory}, @pxref{Data Files}), and @var{real-name}
18907 is the object file's real name, as described above.
18909 When reading an auto-loaded file, @value{GDBN} sets the ``current
18910 objfile''. This is available via the @code{gdb.current_objfile}
18911 function (@pxref{Objfiles In Python}). This can be useful for
18912 registering objfile-specific pretty-printers.
18914 The auto-loading feature is useful for supplying application-specific
18915 debugging commands and scripts. You can enable or disable this
18916 feature, and view its current state.
18919 @kindex maint set python auto-load
18920 @item maint set python auto-load [yes|no]
18921 Enable or disable the Python auto-loading feature.
18923 @kindex show python auto-load
18924 @item show python auto-load
18925 Show whether Python auto-loading is enabled or disabled.
18928 @value{GDBN} does not track which files it has already auto-loaded.
18929 So, your @samp{-gdb.py} file should take care to ensure that it may be
18930 evaluated multiple times without error.
18932 @node Values From Inferior
18933 @subsubsection Values From Inferior
18934 @cindex values from inferior, with Python
18935 @cindex python, working with values from inferior
18937 @cindex @code{gdb.Value}
18938 @value{GDBN} provides values it obtains from the inferior program in
18939 an object of type @code{gdb.Value}. @value{GDBN} uses this object
18940 for its internal bookkeeping of the inferior's values, and for
18941 fetching values when necessary.
18943 Inferior values that are simple scalars can be used directly in
18944 Python expressions that are valid for the value's data type. Here's
18945 an example for an integer or floating-point value @code{some_val}:
18952 As result of this, @code{bar} will also be a @code{gdb.Value} object
18953 whose values are of the same type as those of @code{some_val}.
18955 Inferior values that are structures or instances of some class can
18956 be accessed using the Python @dfn{dictionary syntax}. For example, if
18957 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
18958 can access its @code{foo} element with:
18961 bar = some_val['foo']
18964 Again, @code{bar} will also be a @code{gdb.Value} object.
18966 The following attributes are provided:
18969 @defivar Value address
18970 If this object is addressable, this read-only attribute holds a
18971 @code{gdb.Value} object representing the address. Otherwise,
18972 this attribute holds @code{None}.
18975 @cindex optimized out value in Python
18976 @defivar Value is_optimized_out
18977 This read-only boolean attribute is true if the compiler optimized out
18978 this value, thus it is not available for fetching from the inferior.
18981 @defivar Value type
18982 The type of this @code{gdb.Value}. The value of this attribute is a
18983 @code{gdb.Type} object.
18987 The following methods are provided:
18990 @defmethod Value dereference
18991 For pointer data types, this method returns a new @code{gdb.Value} object
18992 whose contents is the object pointed to by the pointer. For example, if
18993 @code{foo} is a C pointer to an @code{int}, declared in your C program as
19000 then you can use the corresponding @code{gdb.Value} to access what
19001 @code{foo} points to like this:
19004 bar = foo.dereference ()
19007 The result @code{bar} will be a @code{gdb.Value} object holding the
19008 value pointed to by @code{foo}.
19011 @defmethod Value string @r{[}encoding@r{]} @r{[}errors@r{]} @r{[}length@r{]}
19012 If this @code{gdb.Value} represents a string, then this method
19013 converts the contents to a Python string. Otherwise, this method will
19014 throw an exception.
19016 Strings are recognized in a language-specific way; whether a given
19017 @code{gdb.Value} represents a string is determined by the current
19020 For C-like languages, a value is a string if it is a pointer to or an
19021 array of characters or ints. The string is assumed to be terminated
19022 by a zero of the appropriate width. However if the optional length
19023 argument is given, the string will be converted to that given length,
19024 ignoring any embedded zeros that the string may contain.
19026 If the optional @var{encoding} argument is given, it must be a string
19027 naming the encoding of the string in the @code{gdb.Value}, such as
19028 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
19029 the same encodings as the corresponding argument to Python's
19030 @code{string.decode} method, and the Python codec machinery will be used
19031 to convert the string. If @var{encoding} is not given, or if
19032 @var{encoding} is the empty string, then either the @code{target-charset}
19033 (@pxref{Character Sets}) will be used, or a language-specific encoding
19034 will be used, if the current language is able to supply one.
19036 The optional @var{errors} argument is the same as the corresponding
19037 argument to Python's @code{string.decode} method.
19039 If the optional @var{length} argument is given, the string will be
19040 fetched and converted to the given length.
19044 @node Types In Python
19045 @subsubsection Types In Python
19046 @cindex types in Python
19047 @cindex Python, working with types
19050 @value{GDBN} represents types from the inferior using the class
19053 The following type-related functions are available in the @code{gdb}
19056 @findex gdb.lookup_type
19057 @defun lookup_type name [block]
19058 This function looks up a type by name. @var{name} is the name of the
19059 type to look up. It must be a string.
19061 Ordinarily, this function will return an instance of @code{gdb.Type}.
19062 If the named type cannot be found, it will throw an exception.
19065 An instance of @code{Type} has the following attributes:
19069 The type code for this type. The type code will be one of the
19070 @code{TYPE_CODE_} constants defined below.
19073 @defivar Type sizeof
19074 The size of this type, in target @code{char} units. Usually, a
19075 target's @code{char} type will be an 8-bit byte. However, on some
19076 unusual platforms, this type may have a different size.
19080 The tag name for this type. The tag name is the name after
19081 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
19082 languages have this concept. If this type has no tag name, then
19083 @code{None} is returned.
19087 The following methods are provided:
19090 @defmethod Type fields
19091 For structure and union types, this method returns the fields. Range
19092 types have two fields, the minimum and maximum values. Enum types
19093 have one field per enum constant. Function and method types have one
19094 field per parameter. The base types of C@t{++} classes are also
19095 represented as fields. If the type has no fields, or does not fit
19096 into one of these categories, an empty sequence will be returned.
19098 Each field is an object, with some pre-defined attributes:
19101 This attribute is not available for @code{static} fields (as in
19102 C@t{++} or Java). For non-@code{static} fields, the value is the bit
19103 position of the field.
19106 The name of the field, or @code{None} for anonymous fields.
19109 This is @code{True} if the field is artificial, usually meaning that
19110 it was provided by the compiler and not the user. This attribute is
19111 always provided, and is @code{False} if the field is not artificial.
19114 If the field is packed, or is a bitfield, then this will have a
19115 non-zero value, which is the size of the field in bits. Otherwise,
19116 this will be zero; in this case the field's size is given by its type.
19119 The type of the field. This is usually an instance of @code{Type},
19120 but it can be @code{None} in some situations.
19124 @defmethod Type const
19125 Return a new @code{gdb.Type} object which represents a
19126 @code{const}-qualified variant of this type.
19129 @defmethod Type volatile
19130 Return a new @code{gdb.Type} object which represents a
19131 @code{volatile}-qualified variant of this type.
19134 @defmethod Type unqualified
19135 Return a new @code{gdb.Type} object which represents an unqualified
19136 variant of this type. That is, the result is neither @code{const} nor
19140 @defmethod Type reference
19141 Return a new @code{gdb.Type} object which represents a reference to this
19145 @defmethod Type strip_typedefs
19146 Return a new @code{gdb.Type} that represents the real type,
19147 after removing all layers of typedefs.
19150 @defmethod Type target
19151 Return a new @code{gdb.Type} object which represents the target type
19154 For a pointer type, the target type is the type of the pointed-to
19155 object. For an array type (meaning C-like arrays), the target type is
19156 the type of the elements of the array. For a function or method type,
19157 the target type is the type of the return value. For a complex type,
19158 the target type is the type of the elements. For a typedef, the
19159 target type is the aliased type.
19161 If the type does not have a target, this method will throw an
19165 @defmethod Type template_argument n
19166 If this @code{gdb.Type} is an instantiation of a template, this will
19167 return a new @code{gdb.Type} which represents the type of the
19168 @var{n}th template argument.
19170 If this @code{gdb.Type} is not a template type, this will throw an
19171 exception. Ordinarily, only C@t{++} code will have template types.
19173 @var{name} is searched for globally.
19178 Each type has a code, which indicates what category this type falls
19179 into. The available type categories are represented by constants
19180 defined in the @code{gdb} module:
19183 @findex TYPE_CODE_PTR
19184 @findex gdb.TYPE_CODE_PTR
19185 @item TYPE_CODE_PTR
19186 The type is a pointer.
19188 @findex TYPE_CODE_ARRAY
19189 @findex gdb.TYPE_CODE_ARRAY
19190 @item TYPE_CODE_ARRAY
19191 The type is an array.
19193 @findex TYPE_CODE_STRUCT
19194 @findex gdb.TYPE_CODE_STRUCT
19195 @item TYPE_CODE_STRUCT
19196 The type is a structure.
19198 @findex TYPE_CODE_UNION
19199 @findex gdb.TYPE_CODE_UNION
19200 @item TYPE_CODE_UNION
19201 The type is a union.
19203 @findex TYPE_CODE_ENUM
19204 @findex gdb.TYPE_CODE_ENUM
19205 @item TYPE_CODE_ENUM
19206 The type is an enum.
19208 @findex TYPE_CODE_FLAGS
19209 @findex gdb.TYPE_CODE_FLAGS
19210 @item TYPE_CODE_FLAGS
19211 A bit flags type, used for things such as status registers.
19213 @findex TYPE_CODE_FUNC
19214 @findex gdb.TYPE_CODE_FUNC
19215 @item TYPE_CODE_FUNC
19216 The type is a function.
19218 @findex TYPE_CODE_INT
19219 @findex gdb.TYPE_CODE_INT
19220 @item TYPE_CODE_INT
19221 The type is an integer type.
19223 @findex TYPE_CODE_FLT
19224 @findex gdb.TYPE_CODE_FLT
19225 @item TYPE_CODE_FLT
19226 A floating point type.
19228 @findex TYPE_CODE_VOID
19229 @findex gdb.TYPE_CODE_VOID
19230 @item TYPE_CODE_VOID
19231 The special type @code{void}.
19233 @findex TYPE_CODE_SET
19234 @findex gdb.TYPE_CODE_SET
19235 @item TYPE_CODE_SET
19238 @findex TYPE_CODE_RANGE
19239 @findex gdb.TYPE_CODE_RANGE
19240 @item TYPE_CODE_RANGE
19241 A range type, that is, an integer type with bounds.
19243 @findex TYPE_CODE_STRING
19244 @findex gdb.TYPE_CODE_STRING
19245 @item TYPE_CODE_STRING
19246 A string type. Note that this is only used for certain languages with
19247 language-defined string types; C strings are not represented this way.
19249 @findex TYPE_CODE_BITSTRING
19250 @findex gdb.TYPE_CODE_BITSTRING
19251 @item TYPE_CODE_BITSTRING
19254 @findex TYPE_CODE_ERROR
19255 @findex gdb.TYPE_CODE_ERROR
19256 @item TYPE_CODE_ERROR
19257 An unknown or erroneous type.
19259 @findex TYPE_CODE_METHOD
19260 @findex gdb.TYPE_CODE_METHOD
19261 @item TYPE_CODE_METHOD
19262 A method type, as found in C@t{++} or Java.
19264 @findex TYPE_CODE_METHODPTR
19265 @findex gdb.TYPE_CODE_METHODPTR
19266 @item TYPE_CODE_METHODPTR
19267 A pointer-to-member-function.
19269 @findex TYPE_CODE_MEMBERPTR
19270 @findex gdb.TYPE_CODE_MEMBERPTR
19271 @item TYPE_CODE_MEMBERPTR
19272 A pointer-to-member.
19274 @findex TYPE_CODE_REF
19275 @findex gdb.TYPE_CODE_REF
19276 @item TYPE_CODE_REF
19279 @findex TYPE_CODE_CHAR
19280 @findex gdb.TYPE_CODE_CHAR
19281 @item TYPE_CODE_CHAR
19284 @findex TYPE_CODE_BOOL
19285 @findex gdb.TYPE_CODE_BOOL
19286 @item TYPE_CODE_BOOL
19289 @findex TYPE_CODE_COMPLEX
19290 @findex gdb.TYPE_CODE_COMPLEX
19291 @item TYPE_CODE_COMPLEX
19292 A complex float type.
19294 @findex TYPE_CODE_TYPEDEF
19295 @findex gdb.TYPE_CODE_TYPEDEF
19296 @item TYPE_CODE_TYPEDEF
19297 A typedef to some other type.
19299 @findex TYPE_CODE_NAMESPACE
19300 @findex gdb.TYPE_CODE_NAMESPACE
19301 @item TYPE_CODE_NAMESPACE
19302 A C@t{++} namespace.
19304 @findex TYPE_CODE_DECFLOAT
19305 @findex gdb.TYPE_CODE_DECFLOAT
19306 @item TYPE_CODE_DECFLOAT
19307 A decimal floating point type.
19309 @findex TYPE_CODE_INTERNAL_FUNCTION
19310 @findex gdb.TYPE_CODE_INTERNAL_FUNCTION
19311 @item TYPE_CODE_INTERNAL_FUNCTION
19312 A function internal to @value{GDBN}. This is the type used to represent
19313 convenience functions.
19316 @node Pretty Printing
19317 @subsubsection Pretty Printing
19319 @value{GDBN} provides a mechanism to allow pretty-printing of values
19320 using Python code. The pretty-printer API allows application-specific
19321 code to greatly simplify the display of complex objects. This
19322 mechanism works for both MI and the CLI.
19324 For example, here is how a C@t{++} @code{std::string} looks without a
19328 (@value{GDBP}) print s
19330 static npos = 4294967295,
19332 <std::allocator<char>> = @{
19333 <__gnu_cxx::new_allocator<char>> = @{<No data fields>@}, <No data fields>@},
19334 members of std::basic_string<char, std::char_traits<char>, std::allocator<char> >::_Alloc_hider:
19335 _M_p = 0x804a014 "abcd"
19340 After a pretty-printer for @code{std::string} has been installed, only
19341 the contents are printed:
19344 (@value{GDBP}) print s
19348 A pretty-printer is just an object that holds a value and implements a
19349 specific interface, defined here.
19351 @defop Operation {pretty printer} children (self)
19352 @value{GDBN} will call this method on a pretty-printer to compute the
19353 children of the pretty-printer's value.
19355 This method must return an object conforming to the Python iterator
19356 protocol. Each item returned by the iterator must be a tuple holding
19357 two elements. The first element is the ``name'' of the child; the
19358 second element is the child's value. The value can be any Python
19359 object which is convertible to a @value{GDBN} value.
19361 This method is optional. If it does not exist, @value{GDBN} will act
19362 as though the value has no children.
19365 @defop Operation {pretty printer} display_hint (self)
19366 The CLI may call this method and use its result to change the
19367 formatting of a value. The result will also be supplied to an MI
19368 consumer as a @samp{displayhint} attribute of the variable being
19371 This method is optional. If it does exist, this method must return a
19374 Some display hints are predefined by @value{GDBN}:
19378 Indicate that the object being printed is ``array-like''. The CLI
19379 uses this to respect parameters such as @code{set print elements} and
19380 @code{set print array}.
19383 Indicate that the object being printed is ``map-like'', and that the
19384 children of this value can be assumed to alternate between keys and
19388 Indicate that the object being printed is ``string-like''. If the
19389 printer's @code{to_string} method returns a Python string of some
19390 kind, then @value{GDBN} will call its internal language-specific
19391 string-printing function to format the string. For the CLI this means
19392 adding quotation marks, possibly escaping some characters, respecting
19393 @code{set print elements}, and the like.
19397 @defop Operation {pretty printer} to_string (self)
19398 @value{GDBN} will call this method to display the string
19399 representation of the value passed to the object's constructor.
19401 When printing from the CLI, if the @code{to_string} method exists,
19402 then @value{GDBN} will prepend its result to the values returned by
19403 @code{children}. Exactly how this formatting is done is dependent on
19404 the display hint, and may change as more hints are added. Also,
19405 depending on the print settings (@pxref{Print Settings}), the CLI may
19406 print just the result of @code{to_string} in a stack trace, omitting
19407 the result of @code{children}.
19409 If this method returns a string, it is printed verbatim.
19411 Otherwise, if this method returns an instance of @code{gdb.Value},
19412 then @value{GDBN} prints this value. This may result in a call to
19413 another pretty-printer.
19415 If instead the method returns a Python value which is convertible to a
19416 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
19417 the resulting value. Again, this may result in a call to another
19418 pretty-printer. Python scalars (integers, floats, and booleans) and
19419 strings are convertible to @code{gdb.Value}; other types are not.
19421 If the result is not one of these types, an exception is raised.
19424 @node Selecting Pretty-Printers
19425 @subsubsection Selecting Pretty-Printers
19427 The Python list @code{gdb.pretty_printers} contains an array of
19428 functions that have been registered via addition as a pretty-printer.
19429 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
19432 A function on one of these lists is passed a single @code{gdb.Value}
19433 argument and should return a pretty-printer object conforming to the
19434 interface definition above (@pxref{Pretty Printing}). If a function
19435 cannot create a pretty-printer for the value, it should return
19438 @value{GDBN} first checks the @code{pretty_printers} attribute of each
19439 @code{gdb.Objfile} and iteratively calls each function in the list for
19440 that @code{gdb.Objfile} until it receives a pretty-printer object.
19441 After these lists have been exhausted, it tries the global
19442 @code{gdb.pretty-printers} list, again calling each function until an
19443 object is returned.
19445 The order in which the objfiles are searched is not specified. For a
19446 given list, functions are always invoked from the head of the list,
19447 and iterated over sequentially until the end of the list, or a printer
19448 object is returned.
19450 Here is an example showing how a @code{std::string} printer might be
19454 class StdStringPrinter:
19455 "Print a std::string"
19457 def __init__ (self, val):
19460 def to_string (self):
19461 return self.val['_M_dataplus']['_M_p']
19463 def display_hint (self):
19467 And here is an example showing how a lookup function for the printer
19468 example above might be written.
19471 def str_lookup_function (val):
19473 lookup_tag = val.type.tag
19474 regex = re.compile ("^std::basic_string<char,.*>$")
19475 if lookup_tag == None:
19477 if regex.match (lookup_tag):
19478 return StdStringPrinter (val)
19483 The example lookup function extracts the value's type, and attempts to
19484 match it to a type that it can pretty-print. If it is a type the
19485 printer can pretty-print, it will return a printer object. If not, it
19486 returns @code{None}.
19488 We recommend that you put your core pretty-printers into a Python
19489 package. If your pretty-printers are for use with a library, we
19490 further recommend embedding a version number into the package name.
19491 This practice will enable @value{GDBN} to load multiple versions of
19492 your pretty-printers at the same time, because they will have
19495 You should write auto-loaded code (@pxref{Auto-loading}) such that it
19496 can be evaluated multiple times without changing its meaning. An
19497 ideal auto-load file will consist solely of @code{import}s of your
19498 printer modules, followed by a call to a register pretty-printers with
19499 the current objfile.
19501 Taken as a whole, this approach will scale nicely to multiple
19502 inferiors, each potentially using a different library version.
19503 Embedding a version number in the Python package name will ensure that
19504 @value{GDBN} is able to load both sets of printers simultaneously.
19505 Then, because the search for pretty-printers is done by objfile, and
19506 because your auto-loaded code took care to register your library's
19507 printers with a specific objfile, @value{GDBN} will find the correct
19508 printers for the specific version of the library used by each
19511 To continue the @code{std::string} example (@pxref{Pretty Printing}),
19512 this code might appear in @code{gdb.libstdcxx.v6}:
19515 def register_printers (objfile):
19516 objfile.pretty_printers.add (str_lookup_function)
19520 And then the corresponding contents of the auto-load file would be:
19523 import gdb.libstdcxx.v6
19524 gdb.libstdcxx.v6.register_printers (gdb.current_objfile ())
19527 @node Commands In Python
19528 @subsubsection Commands In Python
19530 @cindex commands in python
19531 @cindex python commands
19532 You can implement new @value{GDBN} CLI commands in Python. A CLI
19533 command is implemented using an instance of the @code{gdb.Command}
19534 class, most commonly using a subclass.
19536 @defmethod Command __init__ name @var{command_class} @r{[}@var{completer_class}@r{]} @r{[}@var{prefix}@r{]}
19537 The object initializer for @code{Command} registers the new command
19538 with @value{GDBN}. This initializer is normally invoked from the
19539 subclass' own @code{__init__} method.
19541 @var{name} is the name of the command. If @var{name} consists of
19542 multiple words, then the initial words are looked for as prefix
19543 commands. In this case, if one of the prefix commands does not exist,
19544 an exception is raised.
19546 There is no support for multi-line commands.
19548 @var{command_class} should be one of the @samp{COMMAND_} constants
19549 defined below. This argument tells @value{GDBN} how to categorize the
19550 new command in the help system.
19552 @var{completer_class} is an optional argument. If given, it should be
19553 one of the @samp{COMPLETE_} constants defined below. This argument
19554 tells @value{GDBN} how to perform completion for this command. If not
19555 given, @value{GDBN} will attempt to complete using the object's
19556 @code{complete} method (see below); if no such method is found, an
19557 error will occur when completion is attempted.
19559 @var{prefix} is an optional argument. If @code{True}, then the new
19560 command is a prefix command; sub-commands of this command may be
19563 The help text for the new command is taken from the Python
19564 documentation string for the command's class, if there is one. If no
19565 documentation string is provided, the default value ``This command is
19566 not documented.'' is used.
19569 @cindex don't repeat Python command
19570 @defmethod Command dont_repeat
19571 By default, a @value{GDBN} command is repeated when the user enters a
19572 blank line at the command prompt. A command can suppress this
19573 behavior by invoking the @code{dont_repeat} method. This is similar
19574 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
19577 @defmethod Command invoke argument from_tty
19578 This method is called by @value{GDBN} when this command is invoked.
19580 @var{argument} is a string. It is the argument to the command, after
19581 leading and trailing whitespace has been stripped.
19583 @var{from_tty} is a boolean argument. When true, this means that the
19584 command was entered by the user at the terminal; when false it means
19585 that the command came from elsewhere.
19587 If this method throws an exception, it is turned into a @value{GDBN}
19588 @code{error} call. Otherwise, the return value is ignored.
19591 @cindex completion of Python commands
19592 @defmethod Command complete text word
19593 This method is called by @value{GDBN} when the user attempts
19594 completion on this command. All forms of completion are handled by
19595 this method, that is, the @key{TAB} and @key{M-?} key bindings
19596 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
19599 The arguments @var{text} and @var{word} are both strings. @var{text}
19600 holds the complete command line up to the cursor's location.
19601 @var{word} holds the last word of the command line; this is computed
19602 using a word-breaking heuristic.
19604 The @code{complete} method can return several values:
19607 If the return value is a sequence, the contents of the sequence are
19608 used as the completions. It is up to @code{complete} to ensure that the
19609 contents actually do complete the word. A zero-length sequence is
19610 allowed, it means that there were no completions available. Only
19611 string elements of the sequence are used; other elements in the
19612 sequence are ignored.
19615 If the return value is one of the @samp{COMPLETE_} constants defined
19616 below, then the corresponding @value{GDBN}-internal completion
19617 function is invoked, and its result is used.
19620 All other results are treated as though there were no available
19625 When a new command is registered, it must be declared as a member of
19626 some general class of commands. This is used to classify top-level
19627 commands in the on-line help system; note that prefix commands are not
19628 listed under their own category but rather that of their top-level
19629 command. The available classifications are represented by constants
19630 defined in the @code{gdb} module:
19633 @findex COMMAND_NONE
19634 @findex gdb.COMMAND_NONE
19636 The command does not belong to any particular class. A command in
19637 this category will not be displayed in any of the help categories.
19639 @findex COMMAND_RUNNING
19640 @findex gdb.COMMAND_RUNNING
19641 @item COMMAND_RUNNING
19642 The command is related to running the inferior. For example,
19643 @code{start}, @code{step}, and @code{continue} are in this category.
19644 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
19645 commands in this category.
19647 @findex COMMAND_DATA
19648 @findex gdb.COMMAND_DATA
19650 The command is related to data or variables. For example,
19651 @code{call}, @code{find}, and @code{print} are in this category. Type
19652 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
19655 @findex COMMAND_STACK
19656 @findex gdb.COMMAND_STACK
19657 @item COMMAND_STACK
19658 The command has to do with manipulation of the stack. For example,
19659 @code{backtrace}, @code{frame}, and @code{return} are in this
19660 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
19661 list of commands in this category.
19663 @findex COMMAND_FILES
19664 @findex gdb.COMMAND_FILES
19665 @item COMMAND_FILES
19666 This class is used for file-related commands. For example,
19667 @code{file}, @code{list} and @code{section} are in this category.
19668 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
19669 commands in this category.
19671 @findex COMMAND_SUPPORT
19672 @findex gdb.COMMAND_SUPPORT
19673 @item COMMAND_SUPPORT
19674 This should be used for ``support facilities'', generally meaning
19675 things that are useful to the user when interacting with @value{GDBN},
19676 but not related to the state of the inferior. For example,
19677 @code{help}, @code{make}, and @code{shell} are in this category. Type
19678 @kbd{help support} at the @value{GDBN} prompt to see a list of
19679 commands in this category.
19681 @findex COMMAND_STATUS
19682 @findex gdb.COMMAND_STATUS
19683 @item COMMAND_STATUS
19684 The command is an @samp{info}-related command, that is, related to the
19685 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
19686 and @code{show} are in this category. Type @kbd{help status} at the
19687 @value{GDBN} prompt to see a list of commands in this category.
19689 @findex COMMAND_BREAKPOINTS
19690 @findex gdb.COMMAND_BREAKPOINTS
19691 @item COMMAND_BREAKPOINTS
19692 The command has to do with breakpoints. For example, @code{break},
19693 @code{clear}, and @code{delete} are in this category. Type @kbd{help
19694 breakpoints} at the @value{GDBN} prompt to see a list of commands in
19697 @findex COMMAND_TRACEPOINTS
19698 @findex gdb.COMMAND_TRACEPOINTS
19699 @item COMMAND_TRACEPOINTS
19700 The command has to do with tracepoints. For example, @code{trace},
19701 @code{actions}, and @code{tfind} are in this category. Type
19702 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
19703 commands in this category.
19705 @findex COMMAND_OBSCURE
19706 @findex gdb.COMMAND_OBSCURE
19707 @item COMMAND_OBSCURE
19708 The command is only used in unusual circumstances, or is not of
19709 general interest to users. For example, @code{checkpoint},
19710 @code{fork}, and @code{stop} are in this category. Type @kbd{help
19711 obscure} at the @value{GDBN} prompt to see a list of commands in this
19714 @findex COMMAND_MAINTENANCE
19715 @findex gdb.COMMAND_MAINTENANCE
19716 @item COMMAND_MAINTENANCE
19717 The command is only useful to @value{GDBN} maintainers. The
19718 @code{maintenance} and @code{flushregs} commands are in this category.
19719 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
19720 commands in this category.
19723 A new command can use a predefined completion function, either by
19724 specifying it via an argument at initialization, or by returning it
19725 from the @code{complete} method. These predefined completion
19726 constants are all defined in the @code{gdb} module:
19729 @findex COMPLETE_NONE
19730 @findex gdb.COMPLETE_NONE
19731 @item COMPLETE_NONE
19732 This constant means that no completion should be done.
19734 @findex COMPLETE_FILENAME
19735 @findex gdb.COMPLETE_FILENAME
19736 @item COMPLETE_FILENAME
19737 This constant means that filename completion should be performed.
19739 @findex COMPLETE_LOCATION
19740 @findex gdb.COMPLETE_LOCATION
19741 @item COMPLETE_LOCATION
19742 This constant means that location completion should be done.
19743 @xref{Specify Location}.
19745 @findex COMPLETE_COMMAND
19746 @findex gdb.COMPLETE_COMMAND
19747 @item COMPLETE_COMMAND
19748 This constant means that completion should examine @value{GDBN}
19751 @findex COMPLETE_SYMBOL
19752 @findex gdb.COMPLETE_SYMBOL
19753 @item COMPLETE_SYMBOL
19754 This constant means that completion should be done using symbol names
19758 The following code snippet shows how a trivial CLI command can be
19759 implemented in Python:
19762 class HelloWorld (gdb.Command):
19763 """Greet the whole world."""
19765 def __init__ (self):
19766 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_OBSCURE)
19768 def invoke (self, arg, from_tty):
19769 print "Hello, World!"
19774 The last line instantiates the class, and is necessary to trigger the
19775 registration of the command with @value{GDBN}. Depending on how the
19776 Python code is read into @value{GDBN}, you may need to import the
19777 @code{gdb} module explicitly.
19779 @node Functions In Python
19780 @subsubsection Writing new convenience functions
19782 @cindex writing convenience functions
19783 @cindex convenience functions in python
19784 @cindex python convenience functions
19785 @tindex gdb.Function
19787 You can implement new convenience functions (@pxref{Convenience Vars})
19788 in Python. A convenience function is an instance of a subclass of the
19789 class @code{gdb.Function}.
19791 @defmethod Function __init__ name
19792 The initializer for @code{Function} registers the new function with
19793 @value{GDBN}. The argument @var{name} is the name of the function,
19794 a string. The function will be visible to the user as a convenience
19795 variable of type @code{internal function}, whose name is the same as
19796 the given @var{name}.
19798 The documentation for the new function is taken from the documentation
19799 string for the new class.
19802 @defmethod Function invoke @var{*args}
19803 When a convenience function is evaluated, its arguments are converted
19804 to instances of @code{gdb.Value}, and then the function's
19805 @code{invoke} method is called. Note that @value{GDBN} does not
19806 predetermine the arity of convenience functions. Instead, all
19807 available arguments are passed to @code{invoke}, following the
19808 standard Python calling convention. In particular, a convenience
19809 function can have default values for parameters without ill effect.
19811 The return value of this method is used as its value in the enclosing
19812 expression. If an ordinary Python value is returned, it is converted
19813 to a @code{gdb.Value} following the usual rules.
19816 The following code snippet shows how a trivial convenience function can
19817 be implemented in Python:
19820 class Greet (gdb.Function):
19821 """Return string to greet someone.
19822 Takes a name as argument."""
19824 def __init__ (self):
19825 super (Greet, self).__init__ ("greet")
19827 def invoke (self, name):
19828 return "Hello, %s!" % name.string ()
19833 The last line instantiates the class, and is necessary to trigger the
19834 registration of the function with @value{GDBN}. Depending on how the
19835 Python code is read into @value{GDBN}, you may need to import the
19836 @code{gdb} module explicitly.
19838 @node Objfiles In Python
19839 @subsubsection Objfiles In Python
19841 @cindex objfiles in python
19842 @tindex gdb.Objfile
19844 @value{GDBN} loads symbols for an inferior from various
19845 symbol-containing files (@pxref{Files}). These include the primary
19846 executable file, any shared libraries used by the inferior, and any
19847 separate debug info files (@pxref{Separate Debug Files}).
19848 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
19850 The following objfile-related functions are available in the
19853 @findex gdb.current_objfile
19854 @defun current_objfile
19855 When auto-loading a Python script (@pxref{Auto-loading}), @value{GDBN}
19856 sets the ``current objfile'' to the corresponding objfile. This
19857 function returns the current objfile. If there is no current objfile,
19858 this function returns @code{None}.
19861 @findex gdb.objfiles
19863 Return a sequence of all the objfiles current known to @value{GDBN}.
19864 @xref{Objfiles In Python}.
19867 Each objfile is represented by an instance of the @code{gdb.Objfile}
19870 @defivar Objfile filename
19871 The file name of the objfile as a string.
19874 @defivar Objfile pretty_printers
19875 The @code{pretty_printers} attribute is a list of functions. It is
19876 used to look up pretty-printers. A @code{Value} is passed to each
19877 function in order; if the function returns @code{None}, then the
19878 search continues. Otherwise, the return value should be an object
19879 which is used to format the value. @xref{Pretty Printing}, for more
19883 @node Frames In Python
19884 @subsubsection Acessing inferior stack frames from Python.
19886 @cindex frames in python
19887 When the debugged program stops, @value{GDBN} is able to analyze its call
19888 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
19889 represents a frame in the stack. A @code{gdb.Frame} object is only valid
19890 while its corresponding frame exists in the inferior's stack. If you try
19891 to use an invalid frame object, @value{GDBN} will throw a @code{RuntimeError}
19894 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
19898 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
19902 The following frame-related functions are available in the @code{gdb} module:
19904 @findex gdb.selected_frame
19905 @defun selected_frame
19906 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
19909 @defun frame_stop_reason_string reason
19910 Return a string explaining the reason why @value{GDBN} stopped unwinding
19911 frames, as expressed by the given @var{reason} code (an integer, see the
19912 @code{unwind_stop_reason} method further down in this section).
19915 A @code{gdb.Frame} object has the following methods:
19918 @defmethod Frame is_valid
19919 Returns true if the @code{gdb.Frame} object is valid, false if not.
19920 A frame object can become invalid if the frame it refers to doesn't
19921 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
19922 an exception if it is invalid at the time the method is called.
19925 @defmethod Frame name
19926 Returns the function name of the frame, or @code{None} if it can't be
19930 @defmethod Frame type
19931 Returns the type of the frame. The value can be one of
19932 @code{gdb.NORMAL_FRAME}, @code{gdb.DUMMY_FRAME}, @code{gdb.SIGTRAMP_FRAME}
19933 or @code{gdb.SENTINEL_FRAME}.
19936 @defmethod Frame unwind_stop_reason
19937 Return an integer representing the reason why it's not possible to find
19938 more frames toward the outermost frame. Use
19939 @code{gdb.frame_stop_reason_string} to convert the value returned by this
19940 function to a string.
19943 @defmethod Frame pc
19944 Returns the frame's resume address.
19947 @defmethod Frame older
19948 Return the frame that called this frame.
19951 @defmethod Frame newer
19952 Return the frame called by this frame.
19955 @defmethod Frame read_var variable
19956 Return the value of the given variable in this frame. @var{variable} must
19962 @chapter Command Interpreters
19963 @cindex command interpreters
19965 @value{GDBN} supports multiple command interpreters, and some command
19966 infrastructure to allow users or user interface writers to switch
19967 between interpreters or run commands in other interpreters.
19969 @value{GDBN} currently supports two command interpreters, the console
19970 interpreter (sometimes called the command-line interpreter or @sc{cli})
19971 and the machine interface interpreter (or @sc{gdb/mi}). This manual
19972 describes both of these interfaces in great detail.
19974 By default, @value{GDBN} will start with the console interpreter.
19975 However, the user may choose to start @value{GDBN} with another
19976 interpreter by specifying the @option{-i} or @option{--interpreter}
19977 startup options. Defined interpreters include:
19981 @cindex console interpreter
19982 The traditional console or command-line interpreter. This is the most often
19983 used interpreter with @value{GDBN}. With no interpreter specified at runtime,
19984 @value{GDBN} will use this interpreter.
19987 @cindex mi interpreter
19988 The newest @sc{gdb/mi} interface (currently @code{mi2}). Used primarily
19989 by programs wishing to use @value{GDBN} as a backend for a debugger GUI
19990 or an IDE. For more information, see @ref{GDB/MI, ,The @sc{gdb/mi}
19994 @cindex mi2 interpreter
19995 The current @sc{gdb/mi} interface.
19998 @cindex mi1 interpreter
19999 The @sc{gdb/mi} interface included in @value{GDBN} 5.1, 5.2, and 5.3.
20003 @cindex invoke another interpreter
20004 The interpreter being used by @value{GDBN} may not be dynamically
20005 switched at runtime. Although possible, this could lead to a very
20006 precarious situation. Consider an IDE using @sc{gdb/mi}. If a user
20007 enters the command "interpreter-set console" in a console view,
20008 @value{GDBN} would switch to using the console interpreter, rendering
20009 the IDE inoperable!
20011 @kindex interpreter-exec
20012 Although you may only choose a single interpreter at startup, you may execute
20013 commands in any interpreter from the current interpreter using the appropriate
20014 command. If you are running the console interpreter, simply use the
20015 @code{interpreter-exec} command:
20018 interpreter-exec mi "-data-list-register-names"
20021 @sc{gdb/mi} has a similar command, although it is only available in versions of
20022 @value{GDBN} which support @sc{gdb/mi} version 2 (or greater).
20025 @chapter @value{GDBN} Text User Interface
20027 @cindex Text User Interface
20030 * TUI Overview:: TUI overview
20031 * TUI Keys:: TUI key bindings
20032 * TUI Single Key Mode:: TUI single key mode
20033 * TUI Commands:: TUI-specific commands
20034 * TUI Configuration:: TUI configuration variables
20037 The @value{GDBN} Text User Interface (TUI) is a terminal
20038 interface which uses the @code{curses} library to show the source
20039 file, the assembly output, the program registers and @value{GDBN}
20040 commands in separate text windows. The TUI mode is supported only
20041 on platforms where a suitable version of the @code{curses} library
20044 @pindex @value{GDBTUI}
20045 The TUI mode is enabled by default when you invoke @value{GDBN} as
20046 either @samp{@value{GDBTUI}} or @samp{@value{GDBP} -tui}.
20047 You can also switch in and out of TUI mode while @value{GDBN} runs by
20048 using various TUI commands and key bindings, such as @kbd{C-x C-a}.
20049 @xref{TUI Keys, ,TUI Key Bindings}.
20052 @section TUI Overview
20054 In TUI mode, @value{GDBN} can display several text windows:
20058 This window is the @value{GDBN} command window with the @value{GDBN}
20059 prompt and the @value{GDBN} output. The @value{GDBN} input is still
20060 managed using readline.
20063 The source window shows the source file of the program. The current
20064 line and active breakpoints are displayed in this window.
20067 The assembly window shows the disassembly output of the program.
20070 This window shows the processor registers. Registers are highlighted
20071 when their values change.
20074 The source and assembly windows show the current program position
20075 by highlighting the current line and marking it with a @samp{>} marker.
20076 Breakpoints are indicated with two markers. The first marker
20077 indicates the breakpoint type:
20081 Breakpoint which was hit at least once.
20084 Breakpoint which was never hit.
20087 Hardware breakpoint which was hit at least once.
20090 Hardware breakpoint which was never hit.
20093 The second marker indicates whether the breakpoint is enabled or not:
20097 Breakpoint is enabled.
20100 Breakpoint is disabled.
20103 The source, assembly and register windows are updated when the current
20104 thread changes, when the frame changes, or when the program counter
20107 These windows are not all visible at the same time. The command
20108 window is always visible. The others can be arranged in several
20119 source and assembly,
20122 source and registers, or
20125 assembly and registers.
20128 A status line above the command window shows the following information:
20132 Indicates the current @value{GDBN} target.
20133 (@pxref{Targets, ,Specifying a Debugging Target}).
20136 Gives the current process or thread number.
20137 When no process is being debugged, this field is set to @code{No process}.
20140 Gives the current function name for the selected frame.
20141 The name is demangled if demangling is turned on (@pxref{Print Settings}).
20142 When there is no symbol corresponding to the current program counter,
20143 the string @code{??} is displayed.
20146 Indicates the current line number for the selected frame.
20147 When the current line number is not known, the string @code{??} is displayed.
20150 Indicates the current program counter address.
20154 @section TUI Key Bindings
20155 @cindex TUI key bindings
20157 The TUI installs several key bindings in the readline keymaps
20158 (@pxref{Command Line Editing}). The following key bindings
20159 are installed for both TUI mode and the @value{GDBN} standard mode.
20168 Enter or leave the TUI mode. When leaving the TUI mode,
20169 the curses window management stops and @value{GDBN} operates using
20170 its standard mode, writing on the terminal directly. When reentering
20171 the TUI mode, control is given back to the curses windows.
20172 The screen is then refreshed.
20176 Use a TUI layout with only one window. The layout will
20177 either be @samp{source} or @samp{assembly}. When the TUI mode
20178 is not active, it will switch to the TUI mode.
20180 Think of this key binding as the Emacs @kbd{C-x 1} binding.
20184 Use a TUI layout with at least two windows. When the current
20185 layout already has two windows, the next layout with two windows is used.
20186 When a new layout is chosen, one window will always be common to the
20187 previous layout and the new one.
20189 Think of it as the Emacs @kbd{C-x 2} binding.
20193 Change the active window. The TUI associates several key bindings
20194 (like scrolling and arrow keys) with the active window. This command
20195 gives the focus to the next TUI window.
20197 Think of it as the Emacs @kbd{C-x o} binding.
20201 Switch in and out of the TUI SingleKey mode that binds single
20202 keys to @value{GDBN} commands (@pxref{TUI Single Key Mode}).
20205 The following key bindings only work in the TUI mode:
20210 Scroll the active window one page up.
20214 Scroll the active window one page down.
20218 Scroll the active window one line up.
20222 Scroll the active window one line down.
20226 Scroll the active window one column left.
20230 Scroll the active window one column right.
20234 Refresh the screen.
20237 Because the arrow keys scroll the active window in the TUI mode, they
20238 are not available for their normal use by readline unless the command
20239 window has the focus. When another window is active, you must use
20240 other readline key bindings such as @kbd{C-p}, @kbd{C-n}, @kbd{C-b}
20241 and @kbd{C-f} to control the command window.
20243 @node TUI Single Key Mode
20244 @section TUI Single Key Mode
20245 @cindex TUI single key mode
20247 The TUI also provides a @dfn{SingleKey} mode, which binds several
20248 frequently used @value{GDBN} commands to single keys. Type @kbd{C-x s} to
20249 switch into this mode, where the following key bindings are used:
20252 @kindex c @r{(SingleKey TUI key)}
20256 @kindex d @r{(SingleKey TUI key)}
20260 @kindex f @r{(SingleKey TUI key)}
20264 @kindex n @r{(SingleKey TUI key)}
20268 @kindex q @r{(SingleKey TUI key)}
20270 exit the SingleKey mode.
20272 @kindex r @r{(SingleKey TUI key)}
20276 @kindex s @r{(SingleKey TUI key)}
20280 @kindex u @r{(SingleKey TUI key)}
20284 @kindex v @r{(SingleKey TUI key)}
20288 @kindex w @r{(SingleKey TUI key)}
20293 Other keys temporarily switch to the @value{GDBN} command prompt.
20294 The key that was pressed is inserted in the editing buffer so that
20295 it is possible to type most @value{GDBN} commands without interaction
20296 with the TUI SingleKey mode. Once the command is entered the TUI
20297 SingleKey mode is restored. The only way to permanently leave
20298 this mode is by typing @kbd{q} or @kbd{C-x s}.
20302 @section TUI-specific Commands
20303 @cindex TUI commands
20305 The TUI has specific commands to control the text windows.
20306 These commands are always available, even when @value{GDBN} is not in
20307 the TUI mode. When @value{GDBN} is in the standard mode, most
20308 of these commands will automatically switch to the TUI mode.
20313 List and give the size of all displayed windows.
20317 Display the next layout.
20320 Display the previous layout.
20323 Display the source window only.
20326 Display the assembly window only.
20329 Display the source and assembly window.
20332 Display the register window together with the source or assembly window.
20336 Make the next window active for scrolling.
20339 Make the previous window active for scrolling.
20342 Make the source window active for scrolling.
20345 Make the assembly window active for scrolling.
20348 Make the register window active for scrolling.
20351 Make the command window active for scrolling.
20355 Refresh the screen. This is similar to typing @kbd{C-L}.
20357 @item tui reg float
20359 Show the floating point registers in the register window.
20361 @item tui reg general
20362 Show the general registers in the register window.
20365 Show the next register group. The list of register groups as well as
20366 their order is target specific. The predefined register groups are the
20367 following: @code{general}, @code{float}, @code{system}, @code{vector},
20368 @code{all}, @code{save}, @code{restore}.
20370 @item tui reg system
20371 Show the system registers in the register window.
20375 Update the source window and the current execution point.
20377 @item winheight @var{name} +@var{count}
20378 @itemx winheight @var{name} -@var{count}
20380 Change the height of the window @var{name} by @var{count}
20381 lines. Positive counts increase the height, while negative counts
20384 @item tabset @var{nchars}
20386 Set the width of tab stops to be @var{nchars} characters.
20389 @node TUI Configuration
20390 @section TUI Configuration Variables
20391 @cindex TUI configuration variables
20393 Several configuration variables control the appearance of TUI windows.
20396 @item set tui border-kind @var{kind}
20397 @kindex set tui border-kind
20398 Select the border appearance for the source, assembly and register windows.
20399 The possible values are the following:
20402 Use a space character to draw the border.
20405 Use @sc{ascii} characters @samp{+}, @samp{-} and @samp{|} to draw the border.
20408 Use the Alternate Character Set to draw the border. The border is
20409 drawn using character line graphics if the terminal supports them.
20412 @item set tui border-mode @var{mode}
20413 @kindex set tui border-mode
20414 @itemx set tui active-border-mode @var{mode}
20415 @kindex set tui active-border-mode
20416 Select the display attributes for the borders of the inactive windows
20417 or the active window. The @var{mode} can be one of the following:
20420 Use normal attributes to display the border.
20426 Use reverse video mode.
20429 Use half bright mode.
20431 @item half-standout
20432 Use half bright and standout mode.
20435 Use extra bright or bold mode.
20437 @item bold-standout
20438 Use extra bright or bold and standout mode.
20443 @chapter Using @value{GDBN} under @sc{gnu} Emacs
20446 @cindex @sc{gnu} Emacs
20447 A special interface allows you to use @sc{gnu} Emacs to view (and
20448 edit) the source files for the program you are debugging with
20451 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
20452 executable file you want to debug as an argument. This command starts
20453 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
20454 created Emacs buffer.
20455 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
20457 Running @value{GDBN} under Emacs can be just like running @value{GDBN} normally except for two
20462 All ``terminal'' input and output goes through an Emacs buffer, called
20465 This applies both to @value{GDBN} commands and their output, and to the input
20466 and output done by the program you are debugging.
20468 This is useful because it means that you can copy the text of previous
20469 commands and input them again; you can even use parts of the output
20472 All the facilities of Emacs' Shell mode are available for interacting
20473 with your program. In particular, you can send signals the usual
20474 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
20478 @value{GDBN} displays source code through Emacs.
20480 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
20481 source file for that frame and puts an arrow (@samp{=>}) at the
20482 left margin of the current line. Emacs uses a separate buffer for
20483 source display, and splits the screen to show both your @value{GDBN} session
20486 Explicit @value{GDBN} @code{list} or search commands still produce output as
20487 usual, but you probably have no reason to use them from Emacs.
20490 We call this @dfn{text command mode}. Emacs 22.1, and later, also uses
20491 a graphical mode, enabled by default, which provides further buffers
20492 that can control the execution and describe the state of your program.
20493 @xref{GDB Graphical Interface,,, Emacs, The @sc{gnu} Emacs Manual}.
20495 If you specify an absolute file name when prompted for the @kbd{M-x
20496 gdb} argument, then Emacs sets your current working directory to where
20497 your program resides. If you only specify the file name, then Emacs
20498 sets your current working directory to to the directory associated
20499 with the previous buffer. In this case, @value{GDBN} may find your
20500 program by searching your environment's @code{PATH} variable, but on
20501 some operating systems it might not find the source. So, although the
20502 @value{GDBN} input and output session proceeds normally, the auxiliary
20503 buffer does not display the current source and line of execution.
20505 The initial working directory of @value{GDBN} is printed on the top
20506 line of the GUD buffer and this serves as a default for the commands
20507 that specify files for @value{GDBN} to operate on. @xref{Files,
20508 ,Commands to Specify Files}.
20510 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If you
20511 need to call @value{GDBN} by a different name (for example, if you
20512 keep several configurations around, with different names) you can
20513 customize the Emacs variable @code{gud-gdb-command-name} to run the
20516 In the GUD buffer, you can use these special Emacs commands in
20517 addition to the standard Shell mode commands:
20521 Describe the features of Emacs' GUD Mode.
20524 Execute to another source line, like the @value{GDBN} @code{step} command; also
20525 update the display window to show the current file and location.
20528 Execute to next source line in this function, skipping all function
20529 calls, like the @value{GDBN} @code{next} command. Then update the display window
20530 to show the current file and location.
20533 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
20534 display window accordingly.
20537 Execute until exit from the selected stack frame, like the @value{GDBN}
20538 @code{finish} command.
20541 Continue execution of your program, like the @value{GDBN} @code{continue}
20545 Go up the number of frames indicated by the numeric argument
20546 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
20547 like the @value{GDBN} @code{up} command.
20550 Go down the number of frames indicated by the numeric argument, like the
20551 @value{GDBN} @code{down} command.
20554 In any source file, the Emacs command @kbd{C-x @key{SPC}} (@code{gud-break})
20555 tells @value{GDBN} to set a breakpoint on the source line point is on.
20557 In text command mode, if you type @kbd{M-x speedbar}, Emacs displays a
20558 separate frame which shows a backtrace when the GUD buffer is current.
20559 Move point to any frame in the stack and type @key{RET} to make it
20560 become the current frame and display the associated source in the
20561 source buffer. Alternatively, click @kbd{Mouse-2} to make the
20562 selected frame become the current one. In graphical mode, the
20563 speedbar displays watch expressions.
20565 If you accidentally delete the source-display buffer, an easy way to get
20566 it back is to type the command @code{f} in the @value{GDBN} buffer, to
20567 request a frame display; when you run under Emacs, this recreates
20568 the source buffer if necessary to show you the context of the current
20571 The source files displayed in Emacs are in ordinary Emacs buffers
20572 which are visiting the source files in the usual way. You can edit
20573 the files with these buffers if you wish; but keep in mind that @value{GDBN}
20574 communicates with Emacs in terms of line numbers. If you add or
20575 delete lines from the text, the line numbers that @value{GDBN} knows cease
20576 to correspond properly with the code.
20578 A more detailed description of Emacs' interaction with @value{GDBN} is
20579 given in the Emacs manual (@pxref{Debuggers,,, Emacs, The @sc{gnu}
20582 @c The following dropped because Epoch is nonstandard. Reactivate
20583 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
20585 @kindex Emacs Epoch environment
20589 Version 18 of @sc{gnu} Emacs has a built-in window system
20590 called the @code{epoch}
20591 environment. Users of this environment can use a new command,
20592 @code{inspect} which performs identically to @code{print} except that
20593 each value is printed in its own window.
20598 @chapter The @sc{gdb/mi} Interface
20600 @unnumberedsec Function and Purpose
20602 @cindex @sc{gdb/mi}, its purpose
20603 @sc{gdb/mi} is a line based machine oriented text interface to
20604 @value{GDBN} and is activated by specifying using the
20605 @option{--interpreter} command line option (@pxref{Mode Options}). It
20606 is specifically intended to support the development of systems which
20607 use the debugger as just one small component of a larger system.
20609 This chapter is a specification of the @sc{gdb/mi} interface. It is written
20610 in the form of a reference manual.
20612 Note that @sc{gdb/mi} is still under construction, so some of the
20613 features described below are incomplete and subject to change
20614 (@pxref{GDB/MI Development and Front Ends, , @sc{gdb/mi} Development and Front Ends}).
20616 @unnumberedsec Notation and Terminology
20618 @cindex notational conventions, for @sc{gdb/mi}
20619 This chapter uses the following notation:
20623 @code{|} separates two alternatives.
20626 @code{[ @var{something} ]} indicates that @var{something} is optional:
20627 it may or may not be given.
20630 @code{( @var{group} )*} means that @var{group} inside the parentheses
20631 may repeat zero or more times.
20634 @code{( @var{group} )+} means that @var{group} inside the parentheses
20635 may repeat one or more times.
20638 @code{"@var{string}"} means a literal @var{string}.
20642 @heading Dependencies
20646 * GDB/MI General Design::
20647 * GDB/MI Command Syntax::
20648 * GDB/MI Compatibility with CLI::
20649 * GDB/MI Development and Front Ends::
20650 * GDB/MI Output Records::
20651 * GDB/MI Simple Examples::
20652 * GDB/MI Command Description Format::
20653 * GDB/MI Breakpoint Commands::
20654 * GDB/MI Program Context::
20655 * GDB/MI Thread Commands::
20656 * GDB/MI Program Execution::
20657 * GDB/MI Stack Manipulation::
20658 * GDB/MI Variable Objects::
20659 * GDB/MI Data Manipulation::
20660 * GDB/MI Tracepoint Commands::
20661 * GDB/MI Symbol Query::
20662 * GDB/MI File Commands::
20664 * GDB/MI Kod Commands::
20665 * GDB/MI Memory Overlay Commands::
20666 * GDB/MI Signal Handling Commands::
20668 * GDB/MI Target Manipulation::
20669 * GDB/MI File Transfer Commands::
20670 * GDB/MI Miscellaneous Commands::
20673 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
20674 @node GDB/MI General Design
20675 @section @sc{gdb/mi} General Design
20676 @cindex GDB/MI General Design
20678 Interaction of a @sc{GDB/MI} frontend with @value{GDBN} involves three
20679 parts---commands sent to @value{GDBN}, responses to those commands
20680 and notifications. Each command results in exactly one response,
20681 indicating either successful completion of the command, or an error.
20682 For the commands that do not resume the target, the response contains the
20683 requested information. For the commands that resume the target, the
20684 response only indicates whether the target was successfully resumed.
20685 Notifications is the mechanism for reporting changes in the state of the
20686 target, or in @value{GDBN} state, that cannot conveniently be associated with
20687 a command and reported as part of that command response.
20689 The important examples of notifications are:
20693 Exec notifications. These are used to report changes in
20694 target state---when a target is resumed, or stopped. It would not
20695 be feasible to include this information in response of resuming
20696 commands, because one resume commands can result in multiple events in
20697 different threads. Also, quite some time may pass before any event
20698 happens in the target, while a frontend needs to know whether the resuming
20699 command itself was successfully executed.
20702 Console output, and status notifications. Console output
20703 notifications are used to report output of CLI commands, as well as
20704 diagnostics for other commands. Status notifications are used to
20705 report the progress of a long-running operation. Naturally, including
20706 this information in command response would mean no output is produced
20707 until the command is finished, which is undesirable.
20710 General notifications. Commands may have various side effects on
20711 the @value{GDBN} or target state beyond their official purpose. For example,
20712 a command may change the selected thread. Although such changes can
20713 be included in command response, using notification allows for more
20714 orthogonal frontend design.
20718 There's no guarantee that whenever an MI command reports an error,
20719 @value{GDBN} or the target are in any specific state, and especially,
20720 the state is not reverted to the state before the MI command was
20721 processed. Therefore, whenever an MI command results in an error,
20722 we recommend that the frontend refreshes all the information shown in
20723 the user interface.
20727 * Context management::
20728 * Asynchronous and non-stop modes::
20732 @node Context management
20733 @subsection Context management
20735 In most cases when @value{GDBN} accesses the target, this access is
20736 done in context of a specific thread and frame (@pxref{Frames}).
20737 Often, even when accessing global data, the target requires that a thread
20738 be specified. The CLI interface maintains the selected thread and frame,
20739 and supplies them to target on each command. This is convenient,
20740 because a command line user would not want to specify that information
20741 explicitly on each command, and because user interacts with
20742 @value{GDBN} via a single terminal, so no confusion is possible as
20743 to what thread and frame are the current ones.
20745 In the case of MI, the concept of selected thread and frame is less
20746 useful. First, a frontend can easily remember this information
20747 itself. Second, a graphical frontend can have more than one window,
20748 each one used for debugging a different thread, and the frontend might
20749 want to access additional threads for internal purposes. This
20750 increases the risk that by relying on implicitly selected thread, the
20751 frontend may be operating on a wrong one. Therefore, each MI command
20752 should explicitly specify which thread and frame to operate on. To
20753 make it possible, each MI command accepts the @samp{--thread} and
20754 @samp{--frame} options, the value to each is @value{GDBN} identifier
20755 for thread and frame to operate on.
20757 Usually, each top-level window in a frontend allows the user to select
20758 a thread and a frame, and remembers the user selection for further
20759 operations. However, in some cases @value{GDBN} may suggest that the
20760 current thread be changed. For example, when stopping on a breakpoint
20761 it is reasonable to switch to the thread where breakpoint is hit. For
20762 another example, if the user issues the CLI @samp{thread} command via
20763 the frontend, it is desirable to change the frontend's selected thread to the
20764 one specified by user. @value{GDBN} communicates the suggestion to
20765 change current thread using the @samp{=thread-selected} notification.
20766 No such notification is available for the selected frame at the moment.
20768 Note that historically, MI shares the selected thread with CLI, so
20769 frontends used the @code{-thread-select} to execute commands in the
20770 right context. However, getting this to work right is cumbersome. The
20771 simplest way is for frontend to emit @code{-thread-select} command
20772 before every command. This doubles the number of commands that need
20773 to be sent. The alternative approach is to suppress @code{-thread-select}
20774 if the selected thread in @value{GDBN} is supposed to be identical to the
20775 thread the frontend wants to operate on. However, getting this
20776 optimization right can be tricky. In particular, if the frontend
20777 sends several commands to @value{GDBN}, and one of the commands changes the
20778 selected thread, then the behaviour of subsequent commands will
20779 change. So, a frontend should either wait for response from such
20780 problematic commands, or explicitly add @code{-thread-select} for
20781 all subsequent commands. No frontend is known to do this exactly
20782 right, so it is suggested to just always pass the @samp{--thread} and
20783 @samp{--frame} options.
20785 @node Asynchronous and non-stop modes
20786 @subsection Asynchronous command execution and non-stop mode
20788 On some targets, @value{GDBN} is capable of processing MI commands
20789 even while the target is running. This is called @dfn{asynchronous
20790 command execution} (@pxref{Background Execution}). The frontend may
20791 specify a preferrence for asynchronous execution using the
20792 @code{-gdb-set target-async 1} command, which should be emitted before
20793 either running the executable or attaching to the target. After the
20794 frontend has started the executable or attached to the target, it can
20795 find if asynchronous execution is enabled using the
20796 @code{-list-target-features} command.
20798 Even if @value{GDBN} can accept a command while target is running,
20799 many commands that access the target do not work when the target is
20800 running. Therefore, asynchronous command execution is most useful
20801 when combined with non-stop mode (@pxref{Non-Stop Mode}). Then,
20802 it is possible to examine the state of one thread, while other threads
20805 When a given thread is running, MI commands that try to access the
20806 target in the context of that thread may not work, or may work only on
20807 some targets. In particular, commands that try to operate on thread's
20808 stack will not work, on any target. Commands that read memory, or
20809 modify breakpoints, may work or not work, depending on the target. Note
20810 that even commands that operate on global state, such as @code{print},
20811 @code{set}, and breakpoint commands, still access the target in the
20812 context of a specific thread, so frontend should try to find a
20813 stopped thread and perform the operation on that thread (using the
20814 @samp{--thread} option).
20816 Which commands will work in the context of a running thread is
20817 highly target dependent. However, the two commands
20818 @code{-exec-interrupt}, to stop a thread, and @code{-thread-info},
20819 to find the state of a thread, will always work.
20821 @node Thread groups
20822 @subsection Thread groups
20823 @value{GDBN} may be used to debug several processes at the same time.
20824 On some platfroms, @value{GDBN} may support debugging of several
20825 hardware systems, each one having several cores with several different
20826 processes running on each core. This section describes the MI
20827 mechanism to support such debugging scenarios.
20829 The key observation is that regardless of the structure of the
20830 target, MI can have a global list of threads, because most commands that
20831 accept the @samp{--thread} option do not need to know what process that
20832 thread belongs to. Therefore, it is not necessary to introduce
20833 neither additional @samp{--process} option, nor an notion of the
20834 current process in the MI interface. The only strictly new feature
20835 that is required is the ability to find how the threads are grouped
20838 To allow the user to discover such grouping, and to support arbitrary
20839 hierarchy of machines/cores/processes, MI introduces the concept of a
20840 @dfn{thread group}. Thread group is a collection of threads and other
20841 thread groups. A thread group always has a string identifier, a type,
20842 and may have additional attributes specific to the type. A new
20843 command, @code{-list-thread-groups}, returns the list of top-level
20844 thread groups, which correspond to processes that @value{GDBN} is
20845 debugging at the moment. By passing an identifier of a thread group
20846 to the @code{-list-thread-groups} command, it is possible to obtain
20847 the members of specific thread group.
20849 To allow the user to easily discover processes, and other objects, he
20850 wishes to debug, a concept of @dfn{available thread group} is
20851 introduced. Available thread group is an thread group that
20852 @value{GDBN} is not debugging, but that can be attached to, using the
20853 @code{-target-attach} command. The list of available top-level thread
20854 groups can be obtained using @samp{-list-thread-groups --available}.
20855 In general, the content of a thread group may be only retrieved only
20856 after attaching to that thread group.
20858 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
20859 @node GDB/MI Command Syntax
20860 @section @sc{gdb/mi} Command Syntax
20863 * GDB/MI Input Syntax::
20864 * GDB/MI Output Syntax::
20867 @node GDB/MI Input Syntax
20868 @subsection @sc{gdb/mi} Input Syntax
20870 @cindex input syntax for @sc{gdb/mi}
20871 @cindex @sc{gdb/mi}, input syntax
20873 @item @var{command} @expansion{}
20874 @code{@var{cli-command} | @var{mi-command}}
20876 @item @var{cli-command} @expansion{}
20877 @code{[ @var{token} ] @var{cli-command} @var{nl}}, where
20878 @var{cli-command} is any existing @value{GDBN} CLI command.
20880 @item @var{mi-command} @expansion{}
20881 @code{[ @var{token} ] "-" @var{operation} ( " " @var{option} )*
20882 @code{[} " --" @code{]} ( " " @var{parameter} )* @var{nl}}
20884 @item @var{token} @expansion{}
20885 "any sequence of digits"
20887 @item @var{option} @expansion{}
20888 @code{"-" @var{parameter} [ " " @var{parameter} ]}
20890 @item @var{parameter} @expansion{}
20891 @code{@var{non-blank-sequence} | @var{c-string}}
20893 @item @var{operation} @expansion{}
20894 @emph{any of the operations described in this chapter}
20896 @item @var{non-blank-sequence} @expansion{}
20897 @emph{anything, provided it doesn't contain special characters such as
20898 "-", @var{nl}, """ and of course " "}
20900 @item @var{c-string} @expansion{}
20901 @code{""" @var{seven-bit-iso-c-string-content} """}
20903 @item @var{nl} @expansion{}
20912 The CLI commands are still handled by the @sc{mi} interpreter; their
20913 output is described below.
20916 The @code{@var{token}}, when present, is passed back when the command
20920 Some @sc{mi} commands accept optional arguments as part of the parameter
20921 list. Each option is identified by a leading @samp{-} (dash) and may be
20922 followed by an optional argument parameter. Options occur first in the
20923 parameter list and can be delimited from normal parameters using
20924 @samp{--} (this is useful when some parameters begin with a dash).
20931 We want easy access to the existing CLI syntax (for debugging).
20934 We want it to be easy to spot a @sc{mi} operation.
20937 @node GDB/MI Output Syntax
20938 @subsection @sc{gdb/mi} Output Syntax
20940 @cindex output syntax of @sc{gdb/mi}
20941 @cindex @sc{gdb/mi}, output syntax
20942 The output from @sc{gdb/mi} consists of zero or more out-of-band records
20943 followed, optionally, by a single result record. This result record
20944 is for the most recent command. The sequence of output records is
20945 terminated by @samp{(gdb)}.
20947 If an input command was prefixed with a @code{@var{token}} then the
20948 corresponding output for that command will also be prefixed by that same
20952 @item @var{output} @expansion{}
20953 @code{( @var{out-of-band-record} )* [ @var{result-record} ] "(gdb)" @var{nl}}
20955 @item @var{result-record} @expansion{}
20956 @code{ [ @var{token} ] "^" @var{result-class} ( "," @var{result} )* @var{nl}}
20958 @item @var{out-of-band-record} @expansion{}
20959 @code{@var{async-record} | @var{stream-record}}
20961 @item @var{async-record} @expansion{}
20962 @code{@var{exec-async-output} | @var{status-async-output} | @var{notify-async-output}}
20964 @item @var{exec-async-output} @expansion{}
20965 @code{[ @var{token} ] "*" @var{async-output}}
20967 @item @var{status-async-output} @expansion{}
20968 @code{[ @var{token} ] "+" @var{async-output}}
20970 @item @var{notify-async-output} @expansion{}
20971 @code{[ @var{token} ] "=" @var{async-output}}
20973 @item @var{async-output} @expansion{}
20974 @code{@var{async-class} ( "," @var{result} )* @var{nl}}
20976 @item @var{result-class} @expansion{}
20977 @code{"done" | "running" | "connected" | "error" | "exit"}
20979 @item @var{async-class} @expansion{}
20980 @code{"stopped" | @var{others}} (where @var{others} will be added
20981 depending on the needs---this is still in development).
20983 @item @var{result} @expansion{}
20984 @code{ @var{variable} "=" @var{value}}
20986 @item @var{variable} @expansion{}
20987 @code{ @var{string} }
20989 @item @var{value} @expansion{}
20990 @code{ @var{const} | @var{tuple} | @var{list} }
20992 @item @var{const} @expansion{}
20993 @code{@var{c-string}}
20995 @item @var{tuple} @expansion{}
20996 @code{ "@{@}" | "@{" @var{result} ( "," @var{result} )* "@}" }
20998 @item @var{list} @expansion{}
20999 @code{ "[]" | "[" @var{value} ( "," @var{value} )* "]" | "["
21000 @var{result} ( "," @var{result} )* "]" }
21002 @item @var{stream-record} @expansion{}
21003 @code{@var{console-stream-output} | @var{target-stream-output} | @var{log-stream-output}}
21005 @item @var{console-stream-output} @expansion{}
21006 @code{"~" @var{c-string}}
21008 @item @var{target-stream-output} @expansion{}
21009 @code{"@@" @var{c-string}}
21011 @item @var{log-stream-output} @expansion{}
21012 @code{"&" @var{c-string}}
21014 @item @var{nl} @expansion{}
21017 @item @var{token} @expansion{}
21018 @emph{any sequence of digits}.
21026 All output sequences end in a single line containing a period.
21029 The @code{@var{token}} is from the corresponding request. Note that
21030 for all async output, while the token is allowed by the grammar and
21031 may be output by future versions of @value{GDBN} for select async
21032 output messages, it is generally omitted. Frontends should treat
21033 all async output as reporting general changes in the state of the
21034 target and there should be no need to associate async output to any
21038 @cindex status output in @sc{gdb/mi}
21039 @var{status-async-output} contains on-going status information about the
21040 progress of a slow operation. It can be discarded. All status output is
21041 prefixed by @samp{+}.
21044 @cindex async output in @sc{gdb/mi}
21045 @var{exec-async-output} contains asynchronous state change on the target
21046 (stopped, started, disappeared). All async output is prefixed by
21050 @cindex notify output in @sc{gdb/mi}
21051 @var{notify-async-output} contains supplementary information that the
21052 client should handle (e.g., a new breakpoint information). All notify
21053 output is prefixed by @samp{=}.
21056 @cindex console output in @sc{gdb/mi}
21057 @var{console-stream-output} is output that should be displayed as is in the
21058 console. It is the textual response to a CLI command. All the console
21059 output is prefixed by @samp{~}.
21062 @cindex target output in @sc{gdb/mi}
21063 @var{target-stream-output} is the output produced by the target program.
21064 All the target output is prefixed by @samp{@@}.
21067 @cindex log output in @sc{gdb/mi}
21068 @var{log-stream-output} is output text coming from @value{GDBN}'s internals, for
21069 instance messages that should be displayed as part of an error log. All
21070 the log output is prefixed by @samp{&}.
21073 @cindex list output in @sc{gdb/mi}
21074 New @sc{gdb/mi} commands should only output @var{lists} containing
21080 @xref{GDB/MI Stream Records, , @sc{gdb/mi} Stream Records}, for more
21081 details about the various output records.
21083 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21084 @node GDB/MI Compatibility with CLI
21085 @section @sc{gdb/mi} Compatibility with CLI
21087 @cindex compatibility, @sc{gdb/mi} and CLI
21088 @cindex @sc{gdb/mi}, compatibility with CLI
21090 For the developers convenience CLI commands can be entered directly,
21091 but there may be some unexpected behaviour. For example, commands
21092 that query the user will behave as if the user replied yes, breakpoint
21093 command lists are not executed and some CLI commands, such as
21094 @code{if}, @code{when} and @code{define}, prompt for further input with
21095 @samp{>}, which is not valid MI output.
21097 This feature may be removed at some stage in the future and it is
21098 recommended that front ends use the @code{-interpreter-exec} command
21099 (@pxref{-interpreter-exec}).
21101 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21102 @node GDB/MI Development and Front Ends
21103 @section @sc{gdb/mi} Development and Front Ends
21104 @cindex @sc{gdb/mi} development
21106 The application which takes the MI output and presents the state of the
21107 program being debugged to the user is called a @dfn{front end}.
21109 Although @sc{gdb/mi} is still incomplete, it is currently being used
21110 by a variety of front ends to @value{GDBN}. This makes it difficult
21111 to introduce new functionality without breaking existing usage. This
21112 section tries to minimize the problems by describing how the protocol
21115 Some changes in MI need not break a carefully designed front end, and
21116 for these the MI version will remain unchanged. The following is a
21117 list of changes that may occur within one level, so front ends should
21118 parse MI output in a way that can handle them:
21122 New MI commands may be added.
21125 New fields may be added to the output of any MI command.
21128 The range of values for fields with specified values, e.g.,
21129 @code{in_scope} (@pxref{-var-update}) may be extended.
21131 @c The format of field's content e.g type prefix, may change so parse it
21132 @c at your own risk. Yes, in general?
21134 @c The order of fields may change? Shouldn't really matter but it might
21135 @c resolve inconsistencies.
21138 If the changes are likely to break front ends, the MI version level
21139 will be increased by one. This will allow the front end to parse the
21140 output according to the MI version. Apart from mi0, new versions of
21141 @value{GDBN} will not support old versions of MI and it will be the
21142 responsibility of the front end to work with the new one.
21144 @c Starting with mi3, add a new command -mi-version that prints the MI
21147 The best way to avoid unexpected changes in MI that might break your front
21148 end is to make your project known to @value{GDBN} developers and
21149 follow development on @email{gdb@@sourceware.org} and
21150 @email{gdb-patches@@sourceware.org}.
21151 @cindex mailing lists
21153 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21154 @node GDB/MI Output Records
21155 @section @sc{gdb/mi} Output Records
21158 * GDB/MI Result Records::
21159 * GDB/MI Stream Records::
21160 * GDB/MI Async Records::
21161 * GDB/MI Frame Information::
21164 @node GDB/MI Result Records
21165 @subsection @sc{gdb/mi} Result Records
21167 @cindex result records in @sc{gdb/mi}
21168 @cindex @sc{gdb/mi}, result records
21169 In addition to a number of out-of-band notifications, the response to a
21170 @sc{gdb/mi} command includes one of the following result indications:
21174 @item "^done" [ "," @var{results} ]
21175 The synchronous operation was successful, @code{@var{results}} are the return
21180 @c Is this one correct? Should it be an out-of-band notification?
21181 The asynchronous operation was successfully started. The target is
21186 @value{GDBN} has connected to a remote target.
21188 @item "^error" "," @var{c-string}
21190 The operation failed. The @code{@var{c-string}} contains the corresponding
21195 @value{GDBN} has terminated.
21199 @node GDB/MI Stream Records
21200 @subsection @sc{gdb/mi} Stream Records
21202 @cindex @sc{gdb/mi}, stream records
21203 @cindex stream records in @sc{gdb/mi}
21204 @value{GDBN} internally maintains a number of output streams: the console, the
21205 target, and the log. The output intended for each of these streams is
21206 funneled through the @sc{gdb/mi} interface using @dfn{stream records}.
21208 Each stream record begins with a unique @dfn{prefix character} which
21209 identifies its stream (@pxref{GDB/MI Output Syntax, , @sc{gdb/mi} Output
21210 Syntax}). In addition to the prefix, each stream record contains a
21211 @code{@var{string-output}}. This is either raw text (with an implicit new
21212 line) or a quoted C string (which does not contain an implicit newline).
21215 @item "~" @var{string-output}
21216 The console output stream contains text that should be displayed in the
21217 CLI console window. It contains the textual responses to CLI commands.
21219 @item "@@" @var{string-output}
21220 The target output stream contains any textual output from the running
21221 target. This is only present when GDB's event loop is truly
21222 asynchronous, which is currently only the case for remote targets.
21224 @item "&" @var{string-output}
21225 The log stream contains debugging messages being produced by @value{GDBN}'s
21229 @node GDB/MI Async Records
21230 @subsection @sc{gdb/mi} Async Records
21232 @cindex async records in @sc{gdb/mi}
21233 @cindex @sc{gdb/mi}, async records
21234 @dfn{Async} records are used to notify the @sc{gdb/mi} client of
21235 additional changes that have occurred. Those changes can either be a
21236 consequence of @sc{gdb/mi} commands (e.g., a breakpoint modified) or a result of
21237 target activity (e.g., target stopped).
21239 The following is the list of possible async records:
21243 @item *running,thread-id="@var{thread}"
21244 The target is now running. The @var{thread} field tells which
21245 specific thread is now running, and can be @samp{all} if all threads
21246 are running. The frontend should assume that no interaction with a
21247 running thread is possible after this notification is produced.
21248 The frontend should not assume that this notification is output
21249 only once for any command. @value{GDBN} may emit this notification
21250 several times, either for different threads, because it cannot resume
21251 all threads together, or even for a single thread, if the thread must
21252 be stepped though some code before letting it run freely.
21254 @item *stopped,reason="@var{reason}",thread-id="@var{id}",stopped-threads="@var{stopped}"
21255 The target has stopped. The @var{reason} field can have one of the
21259 @item breakpoint-hit
21260 A breakpoint was reached.
21261 @item watchpoint-trigger
21262 A watchpoint was triggered.
21263 @item read-watchpoint-trigger
21264 A read watchpoint was triggered.
21265 @item access-watchpoint-trigger
21266 An access watchpoint was triggered.
21267 @item function-finished
21268 An -exec-finish or similar CLI command was accomplished.
21269 @item location-reached
21270 An -exec-until or similar CLI command was accomplished.
21271 @item watchpoint-scope
21272 A watchpoint has gone out of scope.
21273 @item end-stepping-range
21274 An -exec-next, -exec-next-instruction, -exec-step, -exec-step-instruction or
21275 similar CLI command was accomplished.
21276 @item exited-signalled
21277 The inferior exited because of a signal.
21279 The inferior exited.
21280 @item exited-normally
21281 The inferior exited normally.
21282 @item signal-received
21283 A signal was received by the inferior.
21286 The @var{id} field identifies the thread that directly caused the stop
21287 -- for example by hitting a breakpoint. Depending on whether all-stop
21288 mode is in effect (@pxref{All-Stop Mode}), @value{GDBN} may either
21289 stop all threads, or only the thread that directly triggered the stop.
21290 If all threads are stopped, the @var{stopped} field will have the
21291 value of @code{"all"}. Otherwise, the value of the @var{stopped}
21292 field will be a list of thread identifiers. Presently, this list will
21293 always include a single thread, but frontend should be prepared to see
21294 several threads in the list.
21296 @item =thread-group-created,id="@var{id}"
21297 @itemx =thread-group-exited,id="@var{id}"
21298 A thread thread group either was attached to, or has exited/detached
21299 from. The @var{id} field contains the @value{GDBN} identifier of the
21302 @item =thread-created,id="@var{id}",group-id="@var{gid}"
21303 @itemx =thread-exited,id="@var{id}",group-id="@var{gid}"
21304 A thread either was created, or has exited. The @var{id} field
21305 contains the @value{GDBN} identifier of the thread. The @var{gid}
21306 field identifies the thread group this thread belongs to.
21308 @item =thread-selected,id="@var{id}"
21309 Informs that the selected thread was changed as result of the last
21310 command. This notification is not emitted as result of @code{-thread-select}
21311 command but is emitted whenever an MI command that is not documented
21312 to change the selected thread actually changes it. In particular,
21313 invoking, directly or indirectly (via user-defined command), the CLI
21314 @code{thread} command, will generate this notification.
21316 We suggest that in response to this notification, front ends
21317 highlight the selected thread and cause subsequent commands to apply to
21320 @item =library-loaded,...
21321 Reports that a new library file was loaded by the program. This
21322 notification has 4 fields---@var{id}, @var{target-name},
21323 @var{host-name}, and @var{symbols-loaded}. The @var{id} field is an
21324 opaque identifier of the library. For remote debugging case,
21325 @var{target-name} and @var{host-name} fields give the name of the
21326 library file on the target, and on the host respectively. For native
21327 debugging, both those fields have the same value. The
21328 @var{symbols-loaded} field reports if the debug symbols for this
21329 library are loaded.
21331 @item =library-unloaded,...
21332 Reports that a library was unloaded by the program. This notification
21333 has 3 fields---@var{id}, @var{target-name} and @var{host-name} with
21334 the same meaning as for the @code{=library-loaded} notification
21338 @node GDB/MI Frame Information
21339 @subsection @sc{gdb/mi} Frame Information
21341 Response from many MI commands includes an information about stack
21342 frame. This information is a tuple that may have the following
21347 The level of the stack frame. The innermost frame has the level of
21348 zero. This field is always present.
21351 The name of the function corresponding to the frame. This field may
21352 be absent if @value{GDBN} is unable to determine the function name.
21355 The code address for the frame. This field is always present.
21358 The name of the source files that correspond to the frame's code
21359 address. This field may be absent.
21362 The source line corresponding to the frames' code address. This field
21366 The name of the binary file (either executable or shared library) the
21367 corresponds to the frame's code address. This field may be absent.
21372 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21373 @node GDB/MI Simple Examples
21374 @section Simple Examples of @sc{gdb/mi} Interaction
21375 @cindex @sc{gdb/mi}, simple examples
21377 This subsection presents several simple examples of interaction using
21378 the @sc{gdb/mi} interface. In these examples, @samp{->} means that the
21379 following line is passed to @sc{gdb/mi} as input, while @samp{<-} means
21380 the output received from @sc{gdb/mi}.
21382 Note the line breaks shown in the examples are here only for
21383 readability, they don't appear in the real output.
21385 @subheading Setting a Breakpoint
21387 Setting a breakpoint generates synchronous output which contains detailed
21388 information of the breakpoint.
21391 -> -break-insert main
21392 <- ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
21393 enabled="y",addr="0x08048564",func="main",file="myprog.c",
21394 fullname="/home/nickrob/myprog.c",line="68",times="0"@}
21398 @subheading Program Execution
21400 Program execution generates asynchronous records and MI gives the
21401 reason that execution stopped.
21407 <- *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
21408 frame=@{addr="0x08048564",func="main",
21409 args=[@{name="argc",value="1"@},@{name="argv",value="0xbfc4d4d4"@}],
21410 file="myprog.c",fullname="/home/nickrob/myprog.c",line="68"@}
21415 <- *stopped,reason="exited-normally"
21419 @subheading Quitting @value{GDBN}
21421 Quitting @value{GDBN} just prints the result class @samp{^exit}.
21429 @subheading A Bad Command
21431 Here's what happens if you pass a non-existent command:
21435 <- ^error,msg="Undefined MI command: rubbish"
21440 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21441 @node GDB/MI Command Description Format
21442 @section @sc{gdb/mi} Command Description Format
21444 The remaining sections describe blocks of commands. Each block of
21445 commands is laid out in a fashion similar to this section.
21447 @subheading Motivation
21449 The motivation for this collection of commands.
21451 @subheading Introduction
21453 A brief introduction to this collection of commands as a whole.
21455 @subheading Commands
21457 For each command in the block, the following is described:
21459 @subsubheading Synopsis
21462 -command @var{args}@dots{}
21465 @subsubheading Result
21467 @subsubheading @value{GDBN} Command
21469 The corresponding @value{GDBN} CLI command(s), if any.
21471 @subsubheading Example
21473 Example(s) formatted for readability. Some of the described commands have
21474 not been implemented yet and these are labeled N.A.@: (not available).
21477 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21478 @node GDB/MI Breakpoint Commands
21479 @section @sc{gdb/mi} Breakpoint Commands
21481 @cindex breakpoint commands for @sc{gdb/mi}
21482 @cindex @sc{gdb/mi}, breakpoint commands
21483 This section documents @sc{gdb/mi} commands for manipulating
21486 @subheading The @code{-break-after} Command
21487 @findex -break-after
21489 @subsubheading Synopsis
21492 -break-after @var{number} @var{count}
21495 The breakpoint number @var{number} is not in effect until it has been
21496 hit @var{count} times. To see how this is reflected in the output of
21497 the @samp{-break-list} command, see the description of the
21498 @samp{-break-list} command below.
21500 @subsubheading @value{GDBN} Command
21502 The corresponding @value{GDBN} command is @samp{ignore}.
21504 @subsubheading Example
21509 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
21510 enabled="y",addr="0x000100d0",func="main",file="hello.c",
21511 fullname="/home/foo/hello.c",line="5",times="0"@}
21518 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
21519 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21520 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21521 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21522 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21523 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21524 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21525 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
21526 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
21527 line="5",times="0",ignore="3"@}]@}
21532 @subheading The @code{-break-catch} Command
21533 @findex -break-catch
21536 @subheading The @code{-break-commands} Command
21537 @findex -break-commands
21539 @subsubheading Synopsis
21542 -break-commands @var{number} [ @var{command1} ... @var{commandN} ]
21545 Specifies the CLI commands that should be executed when breakpoint
21546 @var{number} is hit. The parameters @var{command1} to @var{commandN}
21547 are the commands. If no command is specified, any previously-set
21548 commands are cleared. @xref{Break Commands}. Typical use of this
21549 functionality is tracing a program, that is, printing of values of
21550 some variables whenever breakpoint is hit and then continuing.
21552 @subsubheading @value{GDBN} Command
21554 The corresponding @value{GDBN} command is @samp{commands}.
21556 @subsubheading Example
21561 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
21562 enabled="y",addr="0x000100d0",func="main",file="hello.c",
21563 fullname="/home/foo/hello.c",line="5",times="0"@}
21565 -break-commands 1 "print v" "continue"
21570 @subheading The @code{-break-condition} Command
21571 @findex -break-condition
21573 @subsubheading Synopsis
21576 -break-condition @var{number} @var{expr}
21579 Breakpoint @var{number} will stop the program only if the condition in
21580 @var{expr} is true. The condition becomes part of the
21581 @samp{-break-list} output (see the description of the @samp{-break-list}
21584 @subsubheading @value{GDBN} Command
21586 The corresponding @value{GDBN} command is @samp{condition}.
21588 @subsubheading Example
21592 -break-condition 1 1
21596 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
21597 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21598 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21599 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21600 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21601 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21602 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21603 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
21604 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
21605 line="5",cond="1",times="0",ignore="3"@}]@}
21609 @subheading The @code{-break-delete} Command
21610 @findex -break-delete
21612 @subsubheading Synopsis
21615 -break-delete ( @var{breakpoint} )+
21618 Delete the breakpoint(s) whose number(s) are specified in the argument
21619 list. This is obviously reflected in the breakpoint list.
21621 @subsubheading @value{GDBN} Command
21623 The corresponding @value{GDBN} command is @samp{delete}.
21625 @subsubheading Example
21633 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
21634 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21635 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21636 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21637 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21638 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21639 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21644 @subheading The @code{-break-disable} Command
21645 @findex -break-disable
21647 @subsubheading Synopsis
21650 -break-disable ( @var{breakpoint} )+
21653 Disable the named @var{breakpoint}(s). The field @samp{enabled} in the
21654 break list is now set to @samp{n} for the named @var{breakpoint}(s).
21656 @subsubheading @value{GDBN} Command
21658 The corresponding @value{GDBN} command is @samp{disable}.
21660 @subsubheading Example
21668 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
21669 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21670 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21671 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21672 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21673 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21674 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21675 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="n",
21676 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
21677 line="5",times="0"@}]@}
21681 @subheading The @code{-break-enable} Command
21682 @findex -break-enable
21684 @subsubheading Synopsis
21687 -break-enable ( @var{breakpoint} )+
21690 Enable (previously disabled) @var{breakpoint}(s).
21692 @subsubheading @value{GDBN} Command
21694 The corresponding @value{GDBN} command is @samp{enable}.
21696 @subsubheading Example
21704 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
21705 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21706 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21707 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21708 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21709 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21710 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21711 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
21712 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
21713 line="5",times="0"@}]@}
21717 @subheading The @code{-break-info} Command
21718 @findex -break-info
21720 @subsubheading Synopsis
21723 -break-info @var{breakpoint}
21727 Get information about a single breakpoint.
21729 @subsubheading @value{GDBN} Command
21731 The corresponding @value{GDBN} command is @samp{info break @var{breakpoint}}.
21733 @subsubheading Example
21736 @subheading The @code{-break-insert} Command
21737 @findex -break-insert
21739 @subsubheading Synopsis
21742 -break-insert [ -t ] [ -h ] [ -f ] [ -d ]
21743 [ -c @var{condition} ] [ -i @var{ignore-count} ]
21744 [ -p @var{thread} ] [ @var{location} ]
21748 If specified, @var{location}, can be one of:
21755 @item filename:linenum
21756 @item filename:function
21760 The possible optional parameters of this command are:
21764 Insert a temporary breakpoint.
21766 Insert a hardware breakpoint.
21767 @item -c @var{condition}
21768 Make the breakpoint conditional on @var{condition}.
21769 @item -i @var{ignore-count}
21770 Initialize the @var{ignore-count}.
21772 If @var{location} cannot be parsed (for example if it
21773 refers to unknown files or functions), create a pending
21774 breakpoint. Without this flag, @value{GDBN} will report
21775 an error, and won't create a breakpoint, if @var{location}
21778 Create a disabled breakpoint.
21781 @subsubheading Result
21783 The result is in the form:
21786 ^done,bkpt=@{number="@var{number}",type="@var{type}",disp="del"|"keep",
21787 enabled="y"|"n",addr="@var{hex}",func="@var{funcname}",file="@var{filename}",
21788 fullname="@var{full_filename}",line="@var{lineno}",[thread="@var{threadno},]
21789 times="@var{times}"@}
21793 where @var{number} is the @value{GDBN} number for this breakpoint,
21794 @var{funcname} is the name of the function where the breakpoint was
21795 inserted, @var{filename} is the name of the source file which contains
21796 this function, @var{lineno} is the source line number within that file
21797 and @var{times} the number of times that the breakpoint has been hit
21798 (always 0 for -break-insert but may be greater for -break-info or -break-list
21799 which use the same output).
21801 Note: this format is open to change.
21802 @c An out-of-band breakpoint instead of part of the result?
21804 @subsubheading @value{GDBN} Command
21806 The corresponding @value{GDBN} commands are @samp{break}, @samp{tbreak},
21807 @samp{hbreak}, @samp{thbreak}, and @samp{rbreak}.
21809 @subsubheading Example
21814 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",
21815 fullname="/home/foo/recursive2.c,line="4",times="0"@}
21817 -break-insert -t foo
21818 ^done,bkpt=@{number="2",addr="0x00010774",file="recursive2.c",
21819 fullname="/home/foo/recursive2.c,line="11",times="0"@}
21822 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
21823 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21824 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21825 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21826 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21827 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21828 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21829 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
21830 addr="0x0001072c", func="main",file="recursive2.c",
21831 fullname="/home/foo/recursive2.c,"line="4",times="0"@},
21832 bkpt=@{number="2",type="breakpoint",disp="del",enabled="y",
21833 addr="0x00010774",func="foo",file="recursive2.c",
21834 fullname="/home/foo/recursive2.c",line="11",times="0"@}]@}
21836 -break-insert -r foo.*
21837 ~int foo(int, int);
21838 ^done,bkpt=@{number="3",addr="0x00010774",file="recursive2.c,
21839 "fullname="/home/foo/recursive2.c",line="11",times="0"@}
21843 @subheading The @code{-break-list} Command
21844 @findex -break-list
21846 @subsubheading Synopsis
21852 Displays the list of inserted breakpoints, showing the following fields:
21856 number of the breakpoint
21858 type of the breakpoint: @samp{breakpoint} or @samp{watchpoint}
21860 should the breakpoint be deleted or disabled when it is hit: @samp{keep}
21863 is the breakpoint enabled or no: @samp{y} or @samp{n}
21865 memory location at which the breakpoint is set
21867 logical location of the breakpoint, expressed by function name, file
21870 number of times the breakpoint has been hit
21873 If there are no breakpoints or watchpoints, the @code{BreakpointTable}
21874 @code{body} field is an empty list.
21876 @subsubheading @value{GDBN} Command
21878 The corresponding @value{GDBN} command is @samp{info break}.
21880 @subsubheading Example
21885 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
21886 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21887 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21888 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21889 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21890 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21891 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21892 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
21893 addr="0x000100d0",func="main",file="hello.c",line="5",times="0"@},
21894 bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
21895 addr="0x00010114",func="foo",file="hello.c",fullname="/home/foo/hello.c",
21896 line="13",times="0"@}]@}
21900 Here's an example of the result when there are no breakpoints:
21905 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
21906 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21907 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21908 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21909 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21910 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21911 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21916 @subheading The @code{-break-watch} Command
21917 @findex -break-watch
21919 @subsubheading Synopsis
21922 -break-watch [ -a | -r ]
21925 Create a watchpoint. With the @samp{-a} option it will create an
21926 @dfn{access} watchpoint, i.e., a watchpoint that triggers either on a
21927 read from or on a write to the memory location. With the @samp{-r}
21928 option, the watchpoint created is a @dfn{read} watchpoint, i.e., it will
21929 trigger only when the memory location is accessed for reading. Without
21930 either of the options, the watchpoint created is a regular watchpoint,
21931 i.e., it will trigger when the memory location is accessed for writing.
21932 @xref{Set Watchpoints, , Setting Watchpoints}.
21934 Note that @samp{-break-list} will report a single list of watchpoints and
21935 breakpoints inserted.
21937 @subsubheading @value{GDBN} Command
21939 The corresponding @value{GDBN} commands are @samp{watch}, @samp{awatch}, and
21942 @subsubheading Example
21944 Setting a watchpoint on a variable in the @code{main} function:
21949 ^done,wpt=@{number="2",exp="x"@}
21954 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="x"@},
21955 value=@{old="-268439212",new="55"@},
21956 frame=@{func="main",args=[],file="recursive2.c",
21957 fullname="/home/foo/bar/recursive2.c",line="5"@}
21961 Setting a watchpoint on a variable local to a function. @value{GDBN} will stop
21962 the program execution twice: first for the variable changing value, then
21963 for the watchpoint going out of scope.
21968 ^done,wpt=@{number="5",exp="C"@}
21973 *stopped,reason="watchpoint-trigger",
21974 wpt=@{number="5",exp="C"@},value=@{old="-276895068",new="3"@},
21975 frame=@{func="callee4",args=[],
21976 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
21977 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
21982 *stopped,reason="watchpoint-scope",wpnum="5",
21983 frame=@{func="callee3",args=[@{name="strarg",
21984 value="0x11940 \"A string argument.\""@}],
21985 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
21986 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
21990 Listing breakpoints and watchpoints, at different points in the program
21991 execution. Note that once the watchpoint goes out of scope, it is
21997 ^done,wpt=@{number="2",exp="C"@}
22000 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
22001 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
22002 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
22003 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
22004 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
22005 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
22006 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
22007 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
22008 addr="0x00010734",func="callee4",
22009 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22010 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c"line="8",times="1"@},
22011 bkpt=@{number="2",type="watchpoint",disp="keep",
22012 enabled="y",addr="",what="C",times="0"@}]@}
22017 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="C"@},
22018 value=@{old="-276895068",new="3"@},
22019 frame=@{func="callee4",args=[],
22020 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22021 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
22024 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
22025 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
22026 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
22027 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
22028 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
22029 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
22030 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
22031 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
22032 addr="0x00010734",func="callee4",
22033 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22034 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",times="1"@},
22035 bkpt=@{number="2",type="watchpoint",disp="keep",
22036 enabled="y",addr="",what="C",times="-5"@}]@}
22040 ^done,reason="watchpoint-scope",wpnum="2",
22041 frame=@{func="callee3",args=[@{name="strarg",
22042 value="0x11940 \"A string argument.\""@}],
22043 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22044 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
22047 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
22048 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
22049 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
22050 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
22051 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
22052 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
22053 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
22054 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
22055 addr="0x00010734",func="callee4",
22056 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22057 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",
22062 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22063 @node GDB/MI Program Context
22064 @section @sc{gdb/mi} Program Context
22066 @subheading The @code{-exec-arguments} Command
22067 @findex -exec-arguments
22070 @subsubheading Synopsis
22073 -exec-arguments @var{args}
22076 Set the inferior program arguments, to be used in the next
22079 @subsubheading @value{GDBN} Command
22081 The corresponding @value{GDBN} command is @samp{set args}.
22083 @subsubheading Example
22087 -exec-arguments -v word
22094 @subheading The @code{-exec-show-arguments} Command
22095 @findex -exec-show-arguments
22097 @subsubheading Synopsis
22100 -exec-show-arguments
22103 Print the arguments of the program.
22105 @subsubheading @value{GDBN} Command
22107 The corresponding @value{GDBN} command is @samp{show args}.
22109 @subsubheading Example
22114 @subheading The @code{-environment-cd} Command
22115 @findex -environment-cd
22117 @subsubheading Synopsis
22120 -environment-cd @var{pathdir}
22123 Set @value{GDBN}'s working directory.
22125 @subsubheading @value{GDBN} Command
22127 The corresponding @value{GDBN} command is @samp{cd}.
22129 @subsubheading Example
22133 -environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
22139 @subheading The @code{-environment-directory} Command
22140 @findex -environment-directory
22142 @subsubheading Synopsis
22145 -environment-directory [ -r ] [ @var{pathdir} ]+
22148 Add directories @var{pathdir} to beginning of search path for source files.
22149 If the @samp{-r} option is used, the search path is reset to the default
22150 search path. If directories @var{pathdir} are supplied in addition to the
22151 @samp{-r} option, the search path is first reset and then addition
22153 Multiple directories may be specified, separated by blanks. Specifying
22154 multiple directories in a single command
22155 results in the directories added to the beginning of the
22156 search path in the same order they were presented in the command.
22157 If blanks are needed as
22158 part of a directory name, double-quotes should be used around
22159 the name. In the command output, the path will show up separated
22160 by the system directory-separator character. The directory-separator
22161 character must not be used
22162 in any directory name.
22163 If no directories are specified, the current search path is displayed.
22165 @subsubheading @value{GDBN} Command
22167 The corresponding @value{GDBN} command is @samp{dir}.
22169 @subsubheading Example
22173 -environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
22174 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
22176 -environment-directory ""
22177 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
22179 -environment-directory -r /home/jjohnstn/src/gdb /usr/src
22180 ^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd"
22182 -environment-directory -r
22183 ^done,source-path="$cdir:$cwd"
22188 @subheading The @code{-environment-path} Command
22189 @findex -environment-path
22191 @subsubheading Synopsis
22194 -environment-path [ -r ] [ @var{pathdir} ]+
22197 Add directories @var{pathdir} to beginning of search path for object files.
22198 If the @samp{-r} option is used, the search path is reset to the original
22199 search path that existed at gdb start-up. If directories @var{pathdir} are
22200 supplied in addition to the
22201 @samp{-r} option, the search path is first reset and then addition
22203 Multiple directories may be specified, separated by blanks. Specifying
22204 multiple directories in a single command
22205 results in the directories added to the beginning of the
22206 search path in the same order they were presented in the command.
22207 If blanks are needed as
22208 part of a directory name, double-quotes should be used around
22209 the name. In the command output, the path will show up separated
22210 by the system directory-separator character. The directory-separator
22211 character must not be used
22212 in any directory name.
22213 If no directories are specified, the current path is displayed.
22216 @subsubheading @value{GDBN} Command
22218 The corresponding @value{GDBN} command is @samp{path}.
22220 @subsubheading Example
22225 ^done,path="/usr/bin"
22227 -environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb /bin
22228 ^done,path="/kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb:/bin:/usr/bin"
22230 -environment-path -r /usr/local/bin
22231 ^done,path="/usr/local/bin:/usr/bin"
22236 @subheading The @code{-environment-pwd} Command
22237 @findex -environment-pwd
22239 @subsubheading Synopsis
22245 Show the current working directory.
22247 @subsubheading @value{GDBN} Command
22249 The corresponding @value{GDBN} command is @samp{pwd}.
22251 @subsubheading Example
22256 ^done,cwd="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb"
22260 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22261 @node GDB/MI Thread Commands
22262 @section @sc{gdb/mi} Thread Commands
22265 @subheading The @code{-thread-info} Command
22266 @findex -thread-info
22268 @subsubheading Synopsis
22271 -thread-info [ @var{thread-id} ]
22274 Reports information about either a specific thread, if
22275 the @var{thread-id} parameter is present, or about all
22276 threads. When printing information about all threads,
22277 also reports the current thread.
22279 @subsubheading @value{GDBN} Command
22281 The @samp{info thread} command prints the same information
22284 @subsubheading Example
22289 @{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
22290 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]@},state="running"@},
22291 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
22292 frame=@{level="0",addr="0x0804891f",func="foo",args=[@{name="i",value="10"@}],
22293 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},state="running"@}],
22294 current-thread-id="1"
22298 The @samp{state} field may have the following values:
22302 The thread is stopped. Frame information is available for stopped
22306 The thread is running. There's no frame information for running
22311 @subheading The @code{-thread-list-ids} Command
22312 @findex -thread-list-ids
22314 @subsubheading Synopsis
22320 Produces a list of the currently known @value{GDBN} thread ids. At the
22321 end of the list it also prints the total number of such threads.
22323 This command is retained for historical reasons, the
22324 @code{-thread-info} command should be used instead.
22326 @subsubheading @value{GDBN} Command
22328 Part of @samp{info threads} supplies the same information.
22330 @subsubheading Example
22335 ^done,thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
22336 current-thread-id="1",number-of-threads="3"
22341 @subheading The @code{-thread-select} Command
22342 @findex -thread-select
22344 @subsubheading Synopsis
22347 -thread-select @var{threadnum}
22350 Make @var{threadnum} the current thread. It prints the number of the new
22351 current thread, and the topmost frame for that thread.
22353 This command is deprecated in favor of explicitly using the
22354 @samp{--thread} option to each command.
22356 @subsubheading @value{GDBN} Command
22358 The corresponding @value{GDBN} command is @samp{thread}.
22360 @subsubheading Example
22367 *stopped,reason="end-stepping-range",thread-id="2",line="187",
22368 file="../../../devo/gdb/testsuite/gdb.threads/linux-dp.c"
22372 thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
22373 number-of-threads="3"
22376 ^done,new-thread-id="3",
22377 frame=@{level="0",func="vprintf",
22378 args=[@{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""@},
22379 @{name="arg",value="0x2"@}],file="vprintf.c",line="31"@}
22383 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22384 @node GDB/MI Program Execution
22385 @section @sc{gdb/mi} Program Execution
22387 These are the asynchronous commands which generate the out-of-band
22388 record @samp{*stopped}. Currently @value{GDBN} only really executes
22389 asynchronously with remote targets and this interaction is mimicked in
22392 @subheading The @code{-exec-continue} Command
22393 @findex -exec-continue
22395 @subsubheading Synopsis
22398 -exec-continue [--all|--thread-group N]
22401 Resumes the execution of the inferior program until a breakpoint is
22402 encountered, or until the inferior exits. In all-stop mode
22403 (@pxref{All-Stop Mode}), may resume only one thread, or all threads,
22404 depending on the value of the @samp{scheduler-locking} variable. In
22405 non-stop mode (@pxref{Non-Stop Mode}), if the @samp{--all} is not
22406 specified, only the thread specified with the @samp{--thread} option
22407 (or current thread, if no @samp{--thread} is provided) is resumed. If
22408 @samp{--all} is specified, all threads will be resumed. The
22409 @samp{--all} option is ignored in all-stop mode. If the
22410 @samp{--thread-group} options is specified, then all threads in that
22411 thread group are resumed.
22413 @subsubheading @value{GDBN} Command
22415 The corresponding @value{GDBN} corresponding is @samp{continue}.
22417 @subsubheading Example
22424 *stopped,reason="breakpoint-hit",disp="keep",bkptno="2",frame=@{
22425 func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c",
22431 @subheading The @code{-exec-finish} Command
22432 @findex -exec-finish
22434 @subsubheading Synopsis
22440 Resumes the execution of the inferior program until the current
22441 function is exited. Displays the results returned by the function.
22443 @subsubheading @value{GDBN} Command
22445 The corresponding @value{GDBN} command is @samp{finish}.
22447 @subsubheading Example
22449 Function returning @code{void}.
22456 *stopped,reason="function-finished",frame=@{func="main",args=[],
22457 file="hello.c",fullname="/home/foo/bar/hello.c",line="7"@}
22461 Function returning other than @code{void}. The name of the internal
22462 @value{GDBN} variable storing the result is printed, together with the
22469 *stopped,reason="function-finished",frame=@{addr="0x000107b0",func="foo",
22470 args=[@{name="a",value="1"],@{name="b",value="9"@}@},
22471 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
22472 gdb-result-var="$1",return-value="0"
22477 @subheading The @code{-exec-interrupt} Command
22478 @findex -exec-interrupt
22480 @subsubheading Synopsis
22483 -exec-interrupt [--all|--thread-group N]
22486 Interrupts the background execution of the target. Note how the token
22487 associated with the stop message is the one for the execution command
22488 that has been interrupted. The token for the interrupt itself only
22489 appears in the @samp{^done} output. If the user is trying to
22490 interrupt a non-running program, an error message will be printed.
22492 Note that when asynchronous execution is enabled, this command is
22493 asynchronous just like other execution commands. That is, first the
22494 @samp{^done} response will be printed, and the target stop will be
22495 reported after that using the @samp{*stopped} notification.
22497 In non-stop mode, only the context thread is interrupted by default.
22498 All threads will be interrupted if the @samp{--all} option is
22499 specified. If the @samp{--thread-group} option is specified, all
22500 threads in that group will be interrupted.
22502 @subsubheading @value{GDBN} Command
22504 The corresponding @value{GDBN} command is @samp{interrupt}.
22506 @subsubheading Example
22517 111*stopped,signal-name="SIGINT",signal-meaning="Interrupt",
22518 frame=@{addr="0x00010140",func="foo",args=[],file="try.c",
22519 fullname="/home/foo/bar/try.c",line="13"@}
22524 ^error,msg="mi_cmd_exec_interrupt: Inferior not executing."
22528 @subheading The @code{-exec-jump} Command
22531 @subsubheading Synopsis
22534 -exec-jump @var{location}
22537 Resumes execution of the inferior program at the location specified by
22538 parameter. @xref{Specify Location}, for a description of the
22539 different forms of @var{location}.
22541 @subsubheading @value{GDBN} Command
22543 The corresponding @value{GDBN} command is @samp{jump}.
22545 @subsubheading Example
22548 -exec-jump foo.c:10
22549 *running,thread-id="all"
22554 @subheading The @code{-exec-next} Command
22557 @subsubheading Synopsis
22563 Resumes execution of the inferior program, stopping when the beginning
22564 of the next source line is reached.
22566 @subsubheading @value{GDBN} Command
22568 The corresponding @value{GDBN} command is @samp{next}.
22570 @subsubheading Example
22576 *stopped,reason="end-stepping-range",line="8",file="hello.c"
22581 @subheading The @code{-exec-next-instruction} Command
22582 @findex -exec-next-instruction
22584 @subsubheading Synopsis
22587 -exec-next-instruction
22590 Executes one machine instruction. If the instruction is a function
22591 call, continues until the function returns. If the program stops at an
22592 instruction in the middle of a source line, the address will be
22595 @subsubheading @value{GDBN} Command
22597 The corresponding @value{GDBN} command is @samp{nexti}.
22599 @subsubheading Example
22603 -exec-next-instruction
22607 *stopped,reason="end-stepping-range",
22608 addr="0x000100d4",line="5",file="hello.c"
22613 @subheading The @code{-exec-return} Command
22614 @findex -exec-return
22616 @subsubheading Synopsis
22622 Makes current function return immediately. Doesn't execute the inferior.
22623 Displays the new current frame.
22625 @subsubheading @value{GDBN} Command
22627 The corresponding @value{GDBN} command is @samp{return}.
22629 @subsubheading Example
22633 200-break-insert callee4
22634 200^done,bkpt=@{number="1",addr="0x00010734",
22635 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
22640 000*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
22641 frame=@{func="callee4",args=[],
22642 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22643 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
22649 111^done,frame=@{level="0",func="callee3",
22650 args=[@{name="strarg",
22651 value="0x11940 \"A string argument.\""@}],
22652 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22653 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
22658 @subheading The @code{-exec-run} Command
22661 @subsubheading Synopsis
22667 Starts execution of the inferior from the beginning. The inferior
22668 executes until either a breakpoint is encountered or the program
22669 exits. In the latter case the output will include an exit code, if
22670 the program has exited exceptionally.
22672 @subsubheading @value{GDBN} Command
22674 The corresponding @value{GDBN} command is @samp{run}.
22676 @subsubheading Examples
22681 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",line="4"@}
22686 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
22687 frame=@{func="main",args=[],file="recursive2.c",
22688 fullname="/home/foo/bar/recursive2.c",line="4"@}
22693 Program exited normally:
22701 *stopped,reason="exited-normally"
22706 Program exited exceptionally:
22714 *stopped,reason="exited",exit-code="01"
22718 Another way the program can terminate is if it receives a signal such as
22719 @code{SIGINT}. In this case, @sc{gdb/mi} displays this:
22723 *stopped,reason="exited-signalled",signal-name="SIGINT",
22724 signal-meaning="Interrupt"
22728 @c @subheading -exec-signal
22731 @subheading The @code{-exec-step} Command
22734 @subsubheading Synopsis
22740 Resumes execution of the inferior program, stopping when the beginning
22741 of the next source line is reached, if the next source line is not a
22742 function call. If it is, stop at the first instruction of the called
22745 @subsubheading @value{GDBN} Command
22747 The corresponding @value{GDBN} command is @samp{step}.
22749 @subsubheading Example
22751 Stepping into a function:
22757 *stopped,reason="end-stepping-range",
22758 frame=@{func="foo",args=[@{name="a",value="10"@},
22759 @{name="b",value="0"@}],file="recursive2.c",
22760 fullname="/home/foo/bar/recursive2.c",line="11"@}
22770 *stopped,reason="end-stepping-range",line="14",file="recursive2.c"
22775 @subheading The @code{-exec-step-instruction} Command
22776 @findex -exec-step-instruction
22778 @subsubheading Synopsis
22781 -exec-step-instruction
22784 Resumes the inferior which executes one machine instruction. The
22785 output, once @value{GDBN} has stopped, will vary depending on whether
22786 we have stopped in the middle of a source line or not. In the former
22787 case, the address at which the program stopped will be printed as
22790 @subsubheading @value{GDBN} Command
22792 The corresponding @value{GDBN} command is @samp{stepi}.
22794 @subsubheading Example
22798 -exec-step-instruction
22802 *stopped,reason="end-stepping-range",
22803 frame=@{func="foo",args=[],file="try.c",
22804 fullname="/home/foo/bar/try.c",line="10"@}
22806 -exec-step-instruction
22810 *stopped,reason="end-stepping-range",
22811 frame=@{addr="0x000100f4",func="foo",args=[],file="try.c",
22812 fullname="/home/foo/bar/try.c",line="10"@}
22817 @subheading The @code{-exec-until} Command
22818 @findex -exec-until
22820 @subsubheading Synopsis
22823 -exec-until [ @var{location} ]
22826 Executes the inferior until the @var{location} specified in the
22827 argument is reached. If there is no argument, the inferior executes
22828 until a source line greater than the current one is reached. The
22829 reason for stopping in this case will be @samp{location-reached}.
22831 @subsubheading @value{GDBN} Command
22833 The corresponding @value{GDBN} command is @samp{until}.
22835 @subsubheading Example
22839 -exec-until recursive2.c:6
22843 *stopped,reason="location-reached",frame=@{func="main",args=[],
22844 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="6"@}
22849 @subheading -file-clear
22850 Is this going away????
22853 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22854 @node GDB/MI Stack Manipulation
22855 @section @sc{gdb/mi} Stack Manipulation Commands
22858 @subheading The @code{-stack-info-frame} Command
22859 @findex -stack-info-frame
22861 @subsubheading Synopsis
22867 Get info on the selected frame.
22869 @subsubheading @value{GDBN} Command
22871 The corresponding @value{GDBN} command is @samp{info frame} or @samp{frame}
22872 (without arguments).
22874 @subsubheading Example
22879 ^done,frame=@{level="1",addr="0x0001076c",func="callee3",
22880 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22881 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@}
22885 @subheading The @code{-stack-info-depth} Command
22886 @findex -stack-info-depth
22888 @subsubheading Synopsis
22891 -stack-info-depth [ @var{max-depth} ]
22894 Return the depth of the stack. If the integer argument @var{max-depth}
22895 is specified, do not count beyond @var{max-depth} frames.
22897 @subsubheading @value{GDBN} Command
22899 There's no equivalent @value{GDBN} command.
22901 @subsubheading Example
22903 For a stack with frame levels 0 through 11:
22910 -stack-info-depth 4
22913 -stack-info-depth 12
22916 -stack-info-depth 11
22919 -stack-info-depth 13
22924 @subheading The @code{-stack-list-arguments} Command
22925 @findex -stack-list-arguments
22927 @subsubheading Synopsis
22930 -stack-list-arguments @var{show-values}
22931 [ @var{low-frame} @var{high-frame} ]
22934 Display a list of the arguments for the frames between @var{low-frame}
22935 and @var{high-frame} (inclusive). If @var{low-frame} and
22936 @var{high-frame} are not provided, list the arguments for the whole
22937 call stack. If the two arguments are equal, show the single frame
22938 at the corresponding level. It is an error if @var{low-frame} is
22939 larger than the actual number of frames. On the other hand,
22940 @var{high-frame} may be larger than the actual number of frames, in
22941 which case only existing frames will be returned.
22943 The @var{show-values} argument must have a value of 0 or 1. A value of
22944 0 means that only the names of the arguments are listed, a value of 1
22945 means that both names and values of the arguments are printed.
22947 @subsubheading @value{GDBN} Command
22949 @value{GDBN} does not have an equivalent command. @code{gdbtk} has a
22950 @samp{gdb_get_args} command which partially overlaps with the
22951 functionality of @samp{-stack-list-arguments}.
22953 @subsubheading Example
22960 frame=@{level="0",addr="0x00010734",func="callee4",
22961 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22962 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@},
22963 frame=@{level="1",addr="0x0001076c",func="callee3",
22964 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22965 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@},
22966 frame=@{level="2",addr="0x0001078c",func="callee2",
22967 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22968 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="22"@},
22969 frame=@{level="3",addr="0x000107b4",func="callee1",
22970 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22971 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="27"@},
22972 frame=@{level="4",addr="0x000107e0",func="main",
22973 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22974 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="32"@}]
22976 -stack-list-arguments 0
22979 frame=@{level="0",args=[]@},
22980 frame=@{level="1",args=[name="strarg"]@},
22981 frame=@{level="2",args=[name="intarg",name="strarg"]@},
22982 frame=@{level="3",args=[name="intarg",name="strarg",name="fltarg"]@},
22983 frame=@{level="4",args=[]@}]
22985 -stack-list-arguments 1
22988 frame=@{level="0",args=[]@},
22990 args=[@{name="strarg",value="0x11940 \"A string argument.\""@}]@},
22991 frame=@{level="2",args=[
22992 @{name="intarg",value="2"@},
22993 @{name="strarg",value="0x11940 \"A string argument.\""@}]@},
22994 @{frame=@{level="3",args=[
22995 @{name="intarg",value="2"@},
22996 @{name="strarg",value="0x11940 \"A string argument.\""@},
22997 @{name="fltarg",value="3.5"@}]@},
22998 frame=@{level="4",args=[]@}]
23000 -stack-list-arguments 0 2 2
23001 ^done,stack-args=[frame=@{level="2",args=[name="intarg",name="strarg"]@}]
23003 -stack-list-arguments 1 2 2
23004 ^done,stack-args=[frame=@{level="2",
23005 args=[@{name="intarg",value="2"@},
23006 @{name="strarg",value="0x11940 \"A string argument.\""@}]@}]
23010 @c @subheading -stack-list-exception-handlers
23013 @subheading The @code{-stack-list-frames} Command
23014 @findex -stack-list-frames
23016 @subsubheading Synopsis
23019 -stack-list-frames [ @var{low-frame} @var{high-frame} ]
23022 List the frames currently on the stack. For each frame it displays the
23027 The frame number, 0 being the topmost frame, i.e., the innermost function.
23029 The @code{$pc} value for that frame.
23033 File name of the source file where the function lives.
23035 Line number corresponding to the @code{$pc}.
23038 If invoked without arguments, this command prints a backtrace for the
23039 whole stack. If given two integer arguments, it shows the frames whose
23040 levels are between the two arguments (inclusive). If the two arguments
23041 are equal, it shows the single frame at the corresponding level. It is
23042 an error if @var{low-frame} is larger than the actual number of
23043 frames. On the other hand, @var{high-frame} may be larger than the
23044 actual number of frames, in which case only existing frames will be returned.
23046 @subsubheading @value{GDBN} Command
23048 The corresponding @value{GDBN} commands are @samp{backtrace} and @samp{where}.
23050 @subsubheading Example
23052 Full stack backtrace:
23058 [frame=@{level="0",addr="0x0001076c",func="foo",
23059 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11"@},
23060 frame=@{level="1",addr="0x000107a4",func="foo",
23061 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23062 frame=@{level="2",addr="0x000107a4",func="foo",
23063 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23064 frame=@{level="3",addr="0x000107a4",func="foo",
23065 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23066 frame=@{level="4",addr="0x000107a4",func="foo",
23067 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23068 frame=@{level="5",addr="0x000107a4",func="foo",
23069 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23070 frame=@{level="6",addr="0x000107a4",func="foo",
23071 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23072 frame=@{level="7",addr="0x000107a4",func="foo",
23073 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23074 frame=@{level="8",addr="0x000107a4",func="foo",
23075 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23076 frame=@{level="9",addr="0x000107a4",func="foo",
23077 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23078 frame=@{level="10",addr="0x000107a4",func="foo",
23079 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23080 frame=@{level="11",addr="0x00010738",func="main",
23081 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4"@}]
23085 Show frames between @var{low_frame} and @var{high_frame}:
23089 -stack-list-frames 3 5
23091 [frame=@{level="3",addr="0x000107a4",func="foo",
23092 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23093 frame=@{level="4",addr="0x000107a4",func="foo",
23094 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23095 frame=@{level="5",addr="0x000107a4",func="foo",
23096 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
23100 Show a single frame:
23104 -stack-list-frames 3 3
23106 [frame=@{level="3",addr="0x000107a4",func="foo",
23107 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
23112 @subheading The @code{-stack-list-locals} Command
23113 @findex -stack-list-locals
23115 @subsubheading Synopsis
23118 -stack-list-locals @var{print-values}
23121 Display the local variable names for the selected frame. If
23122 @var{print-values} is 0 or @code{--no-values}, print only the names of
23123 the variables; if it is 1 or @code{--all-values}, print also their
23124 values; and if it is 2 or @code{--simple-values}, print the name,
23125 type and value for simple data types and the name and type for arrays,
23126 structures and unions. In this last case, a frontend can immediately
23127 display the value of simple data types and create variable objects for
23128 other data types when the user wishes to explore their values in
23131 @subsubheading @value{GDBN} Command
23133 @samp{info locals} in @value{GDBN}, @samp{gdb_get_locals} in @code{gdbtk}.
23135 @subsubheading Example
23139 -stack-list-locals 0
23140 ^done,locals=[name="A",name="B",name="C"]
23142 -stack-list-locals --all-values
23143 ^done,locals=[@{name="A",value="1"@},@{name="B",value="2"@},
23144 @{name="C",value="@{1, 2, 3@}"@}]
23145 -stack-list-locals --simple-values
23146 ^done,locals=[@{name="A",type="int",value="1"@},
23147 @{name="B",type="int",value="2"@},@{name="C",type="int [3]"@}]
23152 @subheading The @code{-stack-select-frame} Command
23153 @findex -stack-select-frame
23155 @subsubheading Synopsis
23158 -stack-select-frame @var{framenum}
23161 Change the selected frame. Select a different frame @var{framenum} on
23164 This command in deprecated in favor of passing the @samp{--frame}
23165 option to every command.
23167 @subsubheading @value{GDBN} Command
23169 The corresponding @value{GDBN} commands are @samp{frame}, @samp{up},
23170 @samp{down}, @samp{select-frame}, @samp{up-silent}, and @samp{down-silent}.
23172 @subsubheading Example
23176 -stack-select-frame 2
23181 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
23182 @node GDB/MI Variable Objects
23183 @section @sc{gdb/mi} Variable Objects
23187 @subheading Motivation for Variable Objects in @sc{gdb/mi}
23189 For the implementation of a variable debugger window (locals, watched
23190 expressions, etc.), we are proposing the adaptation of the existing code
23191 used by @code{Insight}.
23193 The two main reasons for that are:
23197 It has been proven in practice (it is already on its second generation).
23200 It will shorten development time (needless to say how important it is
23204 The original interface was designed to be used by Tcl code, so it was
23205 slightly changed so it could be used through @sc{gdb/mi}. This section
23206 describes the @sc{gdb/mi} operations that will be available and gives some
23207 hints about their use.
23209 @emph{Note}: In addition to the set of operations described here, we
23210 expect the @sc{gui} implementation of a variable window to require, at
23211 least, the following operations:
23214 @item @code{-gdb-show} @code{output-radix}
23215 @item @code{-stack-list-arguments}
23216 @item @code{-stack-list-locals}
23217 @item @code{-stack-select-frame}
23222 @subheading Introduction to Variable Objects
23224 @cindex variable objects in @sc{gdb/mi}
23226 Variable objects are "object-oriented" MI interface for examining and
23227 changing values of expressions. Unlike some other MI interfaces that
23228 work with expressions, variable objects are specifically designed for
23229 simple and efficient presentation in the frontend. A variable object
23230 is identified by string name. When a variable object is created, the
23231 frontend specifies the expression for that variable object. The
23232 expression can be a simple variable, or it can be an arbitrary complex
23233 expression, and can even involve CPU registers. After creating a
23234 variable object, the frontend can invoke other variable object
23235 operations---for example to obtain or change the value of a variable
23236 object, or to change display format.
23238 Variable objects have hierarchical tree structure. Any variable object
23239 that corresponds to a composite type, such as structure in C, has
23240 a number of child variable objects, for example corresponding to each
23241 element of a structure. A child variable object can itself have
23242 children, recursively. Recursion ends when we reach
23243 leaf variable objects, which always have built-in types. Child variable
23244 objects are created only by explicit request, so if a frontend
23245 is not interested in the children of a particular variable object, no
23246 child will be created.
23248 For a leaf variable object it is possible to obtain its value as a
23249 string, or set the value from a string. String value can be also
23250 obtained for a non-leaf variable object, but it's generally a string
23251 that only indicates the type of the object, and does not list its
23252 contents. Assignment to a non-leaf variable object is not allowed.
23254 A frontend does not need to read the values of all variable objects each time
23255 the program stops. Instead, MI provides an update command that lists all
23256 variable objects whose values has changed since the last update
23257 operation. This considerably reduces the amount of data that must
23258 be transferred to the frontend. As noted above, children variable
23259 objects are created on demand, and only leaf variable objects have a
23260 real value. As result, gdb will read target memory only for leaf
23261 variables that frontend has created.
23263 The automatic update is not always desirable. For example, a frontend
23264 might want to keep a value of some expression for future reference,
23265 and never update it. For another example, fetching memory is
23266 relatively slow for embedded targets, so a frontend might want
23267 to disable automatic update for the variables that are either not
23268 visible on the screen, or ``closed''. This is possible using so
23269 called ``frozen variable objects''. Such variable objects are never
23270 implicitly updated.
23272 Variable objects can be either @dfn{fixed} or @dfn{floating}. For the
23273 fixed variable object, the expression is parsed when the variable
23274 object is created, including associating identifiers to specific
23275 variables. The meaning of expression never changes. For a floating
23276 variable object the values of variables whose names appear in the
23277 expressions are re-evaluated every time in the context of the current
23278 frame. Consider this example:
23283 struct work_state state;
23290 If a fixed variable object for the @code{state} variable is created in
23291 this function, and we enter the recursive call, the the variable
23292 object will report the value of @code{state} in the top-level
23293 @code{do_work} invocation. On the other hand, a floating variable
23294 object will report the value of @code{state} in the current frame.
23296 If an expression specified when creating a fixed variable object
23297 refers to a local variable, the variable object becomes bound to the
23298 thread and frame in which the variable object is created. When such
23299 variable object is updated, @value{GDBN} makes sure that the
23300 thread/frame combination the variable object is bound to still exists,
23301 and re-evaluates the variable object in context of that thread/frame.
23303 The following is the complete set of @sc{gdb/mi} operations defined to
23304 access this functionality:
23306 @multitable @columnfractions .4 .6
23307 @item @strong{Operation}
23308 @tab @strong{Description}
23310 @item @code{-var-create}
23311 @tab create a variable object
23312 @item @code{-var-delete}
23313 @tab delete the variable object and/or its children
23314 @item @code{-var-set-format}
23315 @tab set the display format of this variable
23316 @item @code{-var-show-format}
23317 @tab show the display format of this variable
23318 @item @code{-var-info-num-children}
23319 @tab tells how many children this object has
23320 @item @code{-var-list-children}
23321 @tab return a list of the object's children
23322 @item @code{-var-info-type}
23323 @tab show the type of this variable object
23324 @item @code{-var-info-expression}
23325 @tab print parent-relative expression that this variable object represents
23326 @item @code{-var-info-path-expression}
23327 @tab print full expression that this variable object represents
23328 @item @code{-var-show-attributes}
23329 @tab is this variable editable? does it exist here?
23330 @item @code{-var-evaluate-expression}
23331 @tab get the value of this variable
23332 @item @code{-var-assign}
23333 @tab set the value of this variable
23334 @item @code{-var-update}
23335 @tab update the variable and its children
23336 @item @code{-var-set-frozen}
23337 @tab set frozeness attribute
23340 In the next subsection we describe each operation in detail and suggest
23341 how it can be used.
23343 @subheading Description And Use of Operations on Variable Objects
23345 @subheading The @code{-var-create} Command
23346 @findex -var-create
23348 @subsubheading Synopsis
23351 -var-create @{@var{name} | "-"@}
23352 @{@var{frame-addr} | "*" | "@@"@} @var{expression}
23355 This operation creates a variable object, which allows the monitoring of
23356 a variable, the result of an expression, a memory cell or a CPU
23359 The @var{name} parameter is the string by which the object can be
23360 referenced. It must be unique. If @samp{-} is specified, the varobj
23361 system will generate a string ``varNNNNNN'' automatically. It will be
23362 unique provided that one does not specify @var{name} of that format.
23363 The command fails if a duplicate name is found.
23365 The frame under which the expression should be evaluated can be
23366 specified by @var{frame-addr}. A @samp{*} indicates that the current
23367 frame should be used. A @samp{@@} indicates that a floating variable
23368 object must be created.
23370 @var{expression} is any expression valid on the current language set (must not
23371 begin with a @samp{*}), or one of the following:
23375 @samp{*@var{addr}}, where @var{addr} is the address of a memory cell
23378 @samp{*@var{addr}-@var{addr}} --- a memory address range (TBD)
23381 @samp{$@var{regname}} --- a CPU register name
23384 @subsubheading Result
23386 This operation returns the name, number of children and the type of the
23387 object created. Type is returned as a string as the ones generated by
23388 the @value{GDBN} CLI. If a fixed variable object is bound to a
23389 specific thread, the thread is is also printed:
23392 name="@var{name}",numchild="@var{N}",type="@var{type}",thread-id="@var{M}"
23396 @subheading The @code{-var-delete} Command
23397 @findex -var-delete
23399 @subsubheading Synopsis
23402 -var-delete [ -c ] @var{name}
23405 Deletes a previously created variable object and all of its children.
23406 With the @samp{-c} option, just deletes the children.
23408 Returns an error if the object @var{name} is not found.
23411 @subheading The @code{-var-set-format} Command
23412 @findex -var-set-format
23414 @subsubheading Synopsis
23417 -var-set-format @var{name} @var{format-spec}
23420 Sets the output format for the value of the object @var{name} to be
23423 @anchor{-var-set-format}
23424 The syntax for the @var{format-spec} is as follows:
23427 @var{format-spec} @expansion{}
23428 @{binary | decimal | hexadecimal | octal | natural@}
23431 The natural format is the default format choosen automatically
23432 based on the variable type (like decimal for an @code{int}, hex
23433 for pointers, etc.).
23435 For a variable with children, the format is set only on the
23436 variable itself, and the children are not affected.
23438 @subheading The @code{-var-show-format} Command
23439 @findex -var-show-format
23441 @subsubheading Synopsis
23444 -var-show-format @var{name}
23447 Returns the format used to display the value of the object @var{name}.
23450 @var{format} @expansion{}
23455 @subheading The @code{-var-info-num-children} Command
23456 @findex -var-info-num-children
23458 @subsubheading Synopsis
23461 -var-info-num-children @var{name}
23464 Returns the number of children of a variable object @var{name}:
23471 @subheading The @code{-var-list-children} Command
23472 @findex -var-list-children
23474 @subsubheading Synopsis
23477 -var-list-children [@var{print-values}] @var{name}
23479 @anchor{-var-list-children}
23481 Return a list of the children of the specified variable object and
23482 create variable objects for them, if they do not already exist. With
23483 a single argument or if @var{print-values} has a value for of 0 or
23484 @code{--no-values}, print only the names of the variables; if
23485 @var{print-values} is 1 or @code{--all-values}, also print their
23486 values; and if it is 2 or @code{--simple-values} print the name and
23487 value for simple data types and just the name for arrays, structures
23490 For each child the following results are returned:
23495 Name of the variable object created for this child.
23498 The expression to be shown to the user by the front end to designate this child.
23499 For example this may be the name of a structure member.
23501 For C/C@t{++} structures there are several pseudo children returned to
23502 designate access qualifiers. For these pseudo children @var{exp} is
23503 @samp{public}, @samp{private}, or @samp{protected}. In this case the
23504 type and value are not present.
23507 Number of children this child has.
23510 The type of the child.
23513 If values were requested, this is the value.
23516 If this variable object is associated with a thread, this is the thread id.
23517 Otherwise this result is not present.
23520 If the variable object is frozen, this variable will be present with a value of 1.
23523 @subsubheading Example
23527 -var-list-children n
23528 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
23529 numchild=@var{n},type=@var{type}@},@r{(repeats N times)}]
23531 -var-list-children --all-values n
23532 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
23533 numchild=@var{n},value=@var{value},type=@var{type}@},@r{(repeats N times)}]
23537 @subheading The @code{-var-info-type} Command
23538 @findex -var-info-type
23540 @subsubheading Synopsis
23543 -var-info-type @var{name}
23546 Returns the type of the specified variable @var{name}. The type is
23547 returned as a string in the same format as it is output by the
23551 type=@var{typename}
23555 @subheading The @code{-var-info-expression} Command
23556 @findex -var-info-expression
23558 @subsubheading Synopsis
23561 -var-info-expression @var{name}
23564 Returns a string that is suitable for presenting this
23565 variable object in user interface. The string is generally
23566 not valid expression in the current language, and cannot be evaluated.
23568 For example, if @code{a} is an array, and variable object
23569 @code{A} was created for @code{a}, then we'll get this output:
23572 (gdb) -var-info-expression A.1
23573 ^done,lang="C",exp="1"
23577 Here, the values of @code{lang} can be @code{@{"C" | "C++" | "Java"@}}.
23579 Note that the output of the @code{-var-list-children} command also
23580 includes those expressions, so the @code{-var-info-expression} command
23583 @subheading The @code{-var-info-path-expression} Command
23584 @findex -var-info-path-expression
23586 @subsubheading Synopsis
23589 -var-info-path-expression @var{name}
23592 Returns an expression that can be evaluated in the current
23593 context and will yield the same value that a variable object has.
23594 Compare this with the @code{-var-info-expression} command, which
23595 result can be used only for UI presentation. Typical use of
23596 the @code{-var-info-path-expression} command is creating a
23597 watchpoint from a variable object.
23599 For example, suppose @code{C} is a C@t{++} class, derived from class
23600 @code{Base}, and that the @code{Base} class has a member called
23601 @code{m_size}. Assume a variable @code{c} is has the type of
23602 @code{C} and a variable object @code{C} was created for variable
23603 @code{c}. Then, we'll get this output:
23605 (gdb) -var-info-path-expression C.Base.public.m_size
23606 ^done,path_expr=((Base)c).m_size)
23609 @subheading The @code{-var-show-attributes} Command
23610 @findex -var-show-attributes
23612 @subsubheading Synopsis
23615 -var-show-attributes @var{name}
23618 List attributes of the specified variable object @var{name}:
23621 status=@var{attr} [ ( ,@var{attr} )* ]
23625 where @var{attr} is @code{@{ @{ editable | noneditable @} | TBD @}}.
23627 @subheading The @code{-var-evaluate-expression} Command
23628 @findex -var-evaluate-expression
23630 @subsubheading Synopsis
23633 -var-evaluate-expression [-f @var{format-spec}] @var{name}
23636 Evaluates the expression that is represented by the specified variable
23637 object and returns its value as a string. The format of the string
23638 can be specified with the @samp{-f} option. The possible values of
23639 this option are the same as for @code{-var-set-format}
23640 (@pxref{-var-set-format}). If the @samp{-f} option is not specified,
23641 the current display format will be used. The current display format
23642 can be changed using the @code{-var-set-format} command.
23648 Note that one must invoke @code{-var-list-children} for a variable
23649 before the value of a child variable can be evaluated.
23651 @subheading The @code{-var-assign} Command
23652 @findex -var-assign
23654 @subsubheading Synopsis
23657 -var-assign @var{name} @var{expression}
23660 Assigns the value of @var{expression} to the variable object specified
23661 by @var{name}. The object must be @samp{editable}. If the variable's
23662 value is altered by the assign, the variable will show up in any
23663 subsequent @code{-var-update} list.
23665 @subsubheading Example
23673 ^done,changelist=[@{name="var1",in_scope="true",type_changed="false"@}]
23677 @subheading The @code{-var-update} Command
23678 @findex -var-update
23680 @subsubheading Synopsis
23683 -var-update [@var{print-values}] @{@var{name} | "*"@}
23686 Reevaluate the expressions corresponding to the variable object
23687 @var{name} and all its direct and indirect children, and return the
23688 list of variable objects whose values have changed; @var{name} must
23689 be a root variable object. Here, ``changed'' means that the result of
23690 @code{-var-evaluate-expression} before and after the
23691 @code{-var-update} is different. If @samp{*} is used as the variable
23692 object names, all existing variable objects are updated, except
23693 for frozen ones (@pxref{-var-set-frozen}). The option
23694 @var{print-values} determines whether both names and values, or just
23695 names are printed. The possible values of this option are the same
23696 as for @code{-var-list-children} (@pxref{-var-list-children}). It is
23697 recommended to use the @samp{--all-values} option, to reduce the
23698 number of MI commands needed on each program stop.
23700 With the @samp{*} parameter, if a variable object is bound to a
23701 currently running thread, it will not be updated, without any
23704 @subsubheading Example
23711 -var-update --all-values var1
23712 ^done,changelist=[@{name="var1",value="3",in_scope="true",
23713 type_changed="false"@}]
23717 @anchor{-var-update}
23718 The field in_scope may take three values:
23722 The variable object's current value is valid.
23725 The variable object does not currently hold a valid value but it may
23726 hold one in the future if its associated expression comes back into
23730 The variable object no longer holds a valid value.
23731 This can occur when the executable file being debugged has changed,
23732 either through recompilation or by using the @value{GDBN} @code{file}
23733 command. The front end should normally choose to delete these variable
23737 In the future new values may be added to this list so the front should
23738 be prepared for this possibility. @xref{GDB/MI Development and Front Ends, ,@sc{GDB/MI} Development and Front Ends}.
23740 @subheading The @code{-var-set-frozen} Command
23741 @findex -var-set-frozen
23742 @anchor{-var-set-frozen}
23744 @subsubheading Synopsis
23747 -var-set-frozen @var{name} @var{flag}
23750 Set the frozenness flag on the variable object @var{name}. The
23751 @var{flag} parameter should be either @samp{1} to make the variable
23752 frozen or @samp{0} to make it unfrozen. If a variable object is
23753 frozen, then neither itself, nor any of its children, are
23754 implicitly updated by @code{-var-update} of
23755 a parent variable or by @code{-var-update *}. Only
23756 @code{-var-update} of the variable itself will update its value and
23757 values of its children. After a variable object is unfrozen, it is
23758 implicitly updated by all subsequent @code{-var-update} operations.
23759 Unfreezing a variable does not update it, only subsequent
23760 @code{-var-update} does.
23762 @subsubheading Example
23766 -var-set-frozen V 1
23771 @subheading The @code{-var-set-visualizer} command
23772 @findex -var-set-visualizer
23773 @anchor{-var-set-visualizer}
23775 @subsubheading Synopsis
23778 -var-set-visualizer @var{name} @var{visualizer}
23781 Set a visualizer for the variable object @var{name}.
23783 @var{visualizer} is the visualizer to use. The special value
23784 @samp{None} means to disable any visualizer in use.
23786 If not @samp{None}, @var{visualizer} must be a Python expression.
23787 This expression must evaluate to a callable object which accepts a
23788 single argument. @value{GDBN} will call this object with the value of
23789 the varobj @var{name} as an argument (this is done so that the same
23790 Python pretty-printing code can be used for both the CLI and MI).
23791 When called, this object must return an object which conforms to the
23792 pretty-printing interface (@pxref{Pretty Printing}).
23794 The pre-defined function @code{gdb.default_visualizer} may be used to
23795 select a visualizer by following the built-in process
23796 (@pxref{Selecting Pretty-Printers}). This is done automatically when
23797 a varobj is created, and so ordinarily is not needed.
23799 This feature is only available if Python support is enabled. The MI
23800 command @code{-list-features} (@pxref{GDB/MI Miscellaneous Commands})
23801 can be used to check this.
23803 @subsubheading Example
23805 Resetting the visualizer:
23809 -var-set-visualizer V None
23813 Reselecting the default (type-based) visualizer:
23817 -var-set-visualizer V gdb.default_visualizer
23821 Suppose @code{SomeClass} is a visualizer class. A lambda expression
23822 can be used to instantiate this class for a varobj:
23826 -var-set-visualizer V "lambda val: SomeClass()"
23830 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
23831 @node GDB/MI Data Manipulation
23832 @section @sc{gdb/mi} Data Manipulation
23834 @cindex data manipulation, in @sc{gdb/mi}
23835 @cindex @sc{gdb/mi}, data manipulation
23836 This section describes the @sc{gdb/mi} commands that manipulate data:
23837 examine memory and registers, evaluate expressions, etc.
23839 @c REMOVED FROM THE INTERFACE.
23840 @c @subheading -data-assign
23841 @c Change the value of a program variable. Plenty of side effects.
23842 @c @subsubheading GDB Command
23844 @c @subsubheading Example
23847 @subheading The @code{-data-disassemble} Command
23848 @findex -data-disassemble
23850 @subsubheading Synopsis
23854 [ -s @var{start-addr} -e @var{end-addr} ]
23855 | [ -f @var{filename} -l @var{linenum} [ -n @var{lines} ] ]
23863 @item @var{start-addr}
23864 is the beginning address (or @code{$pc})
23865 @item @var{end-addr}
23867 @item @var{filename}
23868 is the name of the file to disassemble
23869 @item @var{linenum}
23870 is the line number to disassemble around
23872 is the number of disassembly lines to be produced. If it is -1,
23873 the whole function will be disassembled, in case no @var{end-addr} is
23874 specified. If @var{end-addr} is specified as a non-zero value, and
23875 @var{lines} is lower than the number of disassembly lines between
23876 @var{start-addr} and @var{end-addr}, only @var{lines} lines are
23877 displayed; if @var{lines} is higher than the number of lines between
23878 @var{start-addr} and @var{end-addr}, only the lines up to @var{end-addr}
23881 is either 0 (meaning only disassembly) or 1 (meaning mixed source and
23885 @subsubheading Result
23887 The output for each instruction is composed of four fields:
23896 Note that whatever included in the instruction field, is not manipulated
23897 directly by @sc{gdb/mi}, i.e., it is not possible to adjust its format.
23899 @subsubheading @value{GDBN} Command
23901 There's no direct mapping from this command to the CLI.
23903 @subsubheading Example
23905 Disassemble from the current value of @code{$pc} to @code{$pc + 20}:
23909 -data-disassemble -s $pc -e "$pc + 20" -- 0
23912 @{address="0x000107c0",func-name="main",offset="4",
23913 inst="mov 2, %o0"@},
23914 @{address="0x000107c4",func-name="main",offset="8",
23915 inst="sethi %hi(0x11800), %o2"@},
23916 @{address="0x000107c8",func-name="main",offset="12",
23917 inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"@},
23918 @{address="0x000107cc",func-name="main",offset="16",
23919 inst="sethi %hi(0x11800), %o2"@},
23920 @{address="0x000107d0",func-name="main",offset="20",
23921 inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"@}]
23925 Disassemble the whole @code{main} function. Line 32 is part of
23929 -data-disassemble -f basics.c -l 32 -- 0
23931 @{address="0x000107bc",func-name="main",offset="0",
23932 inst="save %sp, -112, %sp"@},
23933 @{address="0x000107c0",func-name="main",offset="4",
23934 inst="mov 2, %o0"@},
23935 @{address="0x000107c4",func-name="main",offset="8",
23936 inst="sethi %hi(0x11800), %o2"@},
23938 @{address="0x0001081c",func-name="main",offset="96",inst="ret "@},
23939 @{address="0x00010820",func-name="main",offset="100",inst="restore "@}]
23943 Disassemble 3 instructions from the start of @code{main}:
23947 -data-disassemble -f basics.c -l 32 -n 3 -- 0
23949 @{address="0x000107bc",func-name="main",offset="0",
23950 inst="save %sp, -112, %sp"@},
23951 @{address="0x000107c0",func-name="main",offset="4",
23952 inst="mov 2, %o0"@},
23953 @{address="0x000107c4",func-name="main",offset="8",
23954 inst="sethi %hi(0x11800), %o2"@}]
23958 Disassemble 3 instructions from the start of @code{main} in mixed mode:
23962 -data-disassemble -f basics.c -l 32 -n 3 -- 1
23964 src_and_asm_line=@{line="31",
23965 file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
23966 testsuite/gdb.mi/basics.c",line_asm_insn=[
23967 @{address="0x000107bc",func-name="main",offset="0",
23968 inst="save %sp, -112, %sp"@}]@},
23969 src_and_asm_line=@{line="32",
23970 file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
23971 testsuite/gdb.mi/basics.c",line_asm_insn=[
23972 @{address="0x000107c0",func-name="main",offset="4",
23973 inst="mov 2, %o0"@},
23974 @{address="0x000107c4",func-name="main",offset="8",
23975 inst="sethi %hi(0x11800), %o2"@}]@}]
23980 @subheading The @code{-data-evaluate-expression} Command
23981 @findex -data-evaluate-expression
23983 @subsubheading Synopsis
23986 -data-evaluate-expression @var{expr}
23989 Evaluate @var{expr} as an expression. The expression could contain an
23990 inferior function call. The function call will execute synchronously.
23991 If the expression contains spaces, it must be enclosed in double quotes.
23993 @subsubheading @value{GDBN} Command
23995 The corresponding @value{GDBN} commands are @samp{print}, @samp{output}, and
23996 @samp{call}. In @code{gdbtk} only, there's a corresponding
23997 @samp{gdb_eval} command.
23999 @subsubheading Example
24001 In the following example, the numbers that precede the commands are the
24002 @dfn{tokens} described in @ref{GDB/MI Command Syntax, ,@sc{gdb/mi}
24003 Command Syntax}. Notice how @sc{gdb/mi} returns the same tokens in its
24007 211-data-evaluate-expression A
24010 311-data-evaluate-expression &A
24011 311^done,value="0xefffeb7c"
24013 411-data-evaluate-expression A+3
24016 511-data-evaluate-expression "A + 3"
24022 @subheading The @code{-data-list-changed-registers} Command
24023 @findex -data-list-changed-registers
24025 @subsubheading Synopsis
24028 -data-list-changed-registers
24031 Display a list of the registers that have changed.
24033 @subsubheading @value{GDBN} Command
24035 @value{GDBN} doesn't have a direct analog for this command; @code{gdbtk}
24036 has the corresponding command @samp{gdb_changed_register_list}.
24038 @subsubheading Example
24040 On a PPC MBX board:
24048 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame=@{
24049 func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c",
24052 -data-list-changed-registers
24053 ^done,changed-registers=["0","1","2","4","5","6","7","8","9",
24054 "10","11","13","14","15","16","17","18","19","20","21","22","23",
24055 "24","25","26","27","28","30","31","64","65","66","67","69"]
24060 @subheading The @code{-data-list-register-names} Command
24061 @findex -data-list-register-names
24063 @subsubheading Synopsis
24066 -data-list-register-names [ ( @var{regno} )+ ]
24069 Show a list of register names for the current target. If no arguments
24070 are given, it shows a list of the names of all the registers. If
24071 integer numbers are given as arguments, it will print a list of the
24072 names of the registers corresponding to the arguments. To ensure
24073 consistency between a register name and its number, the output list may
24074 include empty register names.
24076 @subsubheading @value{GDBN} Command
24078 @value{GDBN} does not have a command which corresponds to
24079 @samp{-data-list-register-names}. In @code{gdbtk} there is a
24080 corresponding command @samp{gdb_regnames}.
24082 @subsubheading Example
24084 For the PPC MBX board:
24087 -data-list-register-names
24088 ^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7",
24089 "r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18",
24090 "r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29",
24091 "r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9",
24092 "f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20",
24093 "f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31",
24094 "", "pc","ps","cr","lr","ctr","xer"]
24096 -data-list-register-names 1 2 3
24097 ^done,register-names=["r1","r2","r3"]
24101 @subheading The @code{-data-list-register-values} Command
24102 @findex -data-list-register-values
24104 @subsubheading Synopsis
24107 -data-list-register-values @var{fmt} [ ( @var{regno} )*]
24110 Display the registers' contents. @var{fmt} is the format according to
24111 which the registers' contents are to be returned, followed by an optional
24112 list of numbers specifying the registers to display. A missing list of
24113 numbers indicates that the contents of all the registers must be returned.
24115 Allowed formats for @var{fmt} are:
24132 @subsubheading @value{GDBN} Command
24134 The corresponding @value{GDBN} commands are @samp{info reg}, @samp{info
24135 all-reg}, and (in @code{gdbtk}) @samp{gdb_fetch_registers}.
24137 @subsubheading Example
24139 For a PPC MBX board (note: line breaks are for readability only, they
24140 don't appear in the actual output):
24144 -data-list-register-values r 64 65
24145 ^done,register-values=[@{number="64",value="0xfe00a300"@},
24146 @{number="65",value="0x00029002"@}]
24148 -data-list-register-values x
24149 ^done,register-values=[@{number="0",value="0xfe0043c8"@},
24150 @{number="1",value="0x3fff88"@},@{number="2",value="0xfffffffe"@},
24151 @{number="3",value="0x0"@},@{number="4",value="0xa"@},
24152 @{number="5",value="0x3fff68"@},@{number="6",value="0x3fff58"@},
24153 @{number="7",value="0xfe011e98"@},@{number="8",value="0x2"@},
24154 @{number="9",value="0xfa202820"@},@{number="10",value="0xfa202808"@},
24155 @{number="11",value="0x1"@},@{number="12",value="0x0"@},
24156 @{number="13",value="0x4544"@},@{number="14",value="0xffdfffff"@},
24157 @{number="15",value="0xffffffff"@},@{number="16",value="0xfffffeff"@},
24158 @{number="17",value="0xefffffed"@},@{number="18",value="0xfffffffe"@},
24159 @{number="19",value="0xffffffff"@},@{number="20",value="0xffffffff"@},
24160 @{number="21",value="0xffffffff"@},@{number="22",value="0xfffffff7"@},
24161 @{number="23",value="0xffffffff"@},@{number="24",value="0xffffffff"@},
24162 @{number="25",value="0xffffffff"@},@{number="26",value="0xfffffffb"@},
24163 @{number="27",value="0xffffffff"@},@{number="28",value="0xf7bfffff"@},
24164 @{number="29",value="0x0"@},@{number="30",value="0xfe010000"@},
24165 @{number="31",value="0x0"@},@{number="32",value="0x0"@},
24166 @{number="33",value="0x0"@},@{number="34",value="0x0"@},
24167 @{number="35",value="0x0"@},@{number="36",value="0x0"@},
24168 @{number="37",value="0x0"@},@{number="38",value="0x0"@},
24169 @{number="39",value="0x0"@},@{number="40",value="0x0"@},
24170 @{number="41",value="0x0"@},@{number="42",value="0x0"@},
24171 @{number="43",value="0x0"@},@{number="44",value="0x0"@},
24172 @{number="45",value="0x0"@},@{number="46",value="0x0"@},
24173 @{number="47",value="0x0"@},@{number="48",value="0x0"@},
24174 @{number="49",value="0x0"@},@{number="50",value="0x0"@},
24175 @{number="51",value="0x0"@},@{number="52",value="0x0"@},
24176 @{number="53",value="0x0"@},@{number="54",value="0x0"@},
24177 @{number="55",value="0x0"@},@{number="56",value="0x0"@},
24178 @{number="57",value="0x0"@},@{number="58",value="0x0"@},
24179 @{number="59",value="0x0"@},@{number="60",value="0x0"@},
24180 @{number="61",value="0x0"@},@{number="62",value="0x0"@},
24181 @{number="63",value="0x0"@},@{number="64",value="0xfe00a300"@},
24182 @{number="65",value="0x29002"@},@{number="66",value="0x202f04b5"@},
24183 @{number="67",value="0xfe0043b0"@},@{number="68",value="0xfe00b3e4"@},
24184 @{number="69",value="0x20002b03"@}]
24189 @subheading The @code{-data-read-memory} Command
24190 @findex -data-read-memory
24192 @subsubheading Synopsis
24195 -data-read-memory [ -o @var{byte-offset} ]
24196 @var{address} @var{word-format} @var{word-size}
24197 @var{nr-rows} @var{nr-cols} [ @var{aschar} ]
24204 @item @var{address}
24205 An expression specifying the address of the first memory word to be
24206 read. Complex expressions containing embedded white space should be
24207 quoted using the C convention.
24209 @item @var{word-format}
24210 The format to be used to print the memory words. The notation is the
24211 same as for @value{GDBN}'s @code{print} command (@pxref{Output Formats,
24214 @item @var{word-size}
24215 The size of each memory word in bytes.
24217 @item @var{nr-rows}
24218 The number of rows in the output table.
24220 @item @var{nr-cols}
24221 The number of columns in the output table.
24224 If present, indicates that each row should include an @sc{ascii} dump. The
24225 value of @var{aschar} is used as a padding character when a byte is not a
24226 member of the printable @sc{ascii} character set (printable @sc{ascii}
24227 characters are those whose code is between 32 and 126, inclusively).
24229 @item @var{byte-offset}
24230 An offset to add to the @var{address} before fetching memory.
24233 This command displays memory contents as a table of @var{nr-rows} by
24234 @var{nr-cols} words, each word being @var{word-size} bytes. In total,
24235 @code{@var{nr-rows} * @var{nr-cols} * @var{word-size}} bytes are read
24236 (returned as @samp{total-bytes}). Should less than the requested number
24237 of bytes be returned by the target, the missing words are identified
24238 using @samp{N/A}. The number of bytes read from the target is returned
24239 in @samp{nr-bytes} and the starting address used to read memory in
24242 The address of the next/previous row or page is available in
24243 @samp{next-row} and @samp{prev-row}, @samp{next-page} and
24246 @subsubheading @value{GDBN} Command
24248 The corresponding @value{GDBN} command is @samp{x}. @code{gdbtk} has
24249 @samp{gdb_get_mem} memory read command.
24251 @subsubheading Example
24253 Read six bytes of memory starting at @code{bytes+6} but then offset by
24254 @code{-6} bytes. Format as three rows of two columns. One byte per
24255 word. Display each word in hex.
24259 9-data-read-memory -o -6 -- bytes+6 x 1 3 2
24260 9^done,addr="0x00001390",nr-bytes="6",total-bytes="6",
24261 next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396",
24262 prev-page="0x0000138a",memory=[
24263 @{addr="0x00001390",data=["0x00","0x01"]@},
24264 @{addr="0x00001392",data=["0x02","0x03"]@},
24265 @{addr="0x00001394",data=["0x04","0x05"]@}]
24269 Read two bytes of memory starting at address @code{shorts + 64} and
24270 display as a single word formatted in decimal.
24274 5-data-read-memory shorts+64 d 2 1 1
24275 5^done,addr="0x00001510",nr-bytes="2",total-bytes="2",
24276 next-row="0x00001512",prev-row="0x0000150e",
24277 next-page="0x00001512",prev-page="0x0000150e",memory=[
24278 @{addr="0x00001510",data=["128"]@}]
24282 Read thirty two bytes of memory starting at @code{bytes+16} and format
24283 as eight rows of four columns. Include a string encoding with @samp{x}
24284 used as the non-printable character.
24288 4-data-read-memory bytes+16 x 1 8 4 x
24289 4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32",
24290 next-row="0x000013c0",prev-row="0x0000139c",
24291 next-page="0x000013c0",prev-page="0x00001380",memory=[
24292 @{addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"@},
24293 @{addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"@},
24294 @{addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"@},
24295 @{addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"@},
24296 @{addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"@},
24297 @{addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"@},
24298 @{addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"@},
24299 @{addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"@}]
24303 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24304 @node GDB/MI Tracepoint Commands
24305 @section @sc{gdb/mi} Tracepoint Commands
24307 The tracepoint commands are not yet implemented.
24309 @c @subheading -trace-actions
24311 @c @subheading -trace-delete
24313 @c @subheading -trace-disable
24315 @c @subheading -trace-dump
24317 @c @subheading -trace-enable
24319 @c @subheading -trace-exists
24321 @c @subheading -trace-find
24323 @c @subheading -trace-frame-number
24325 @c @subheading -trace-info
24327 @c @subheading -trace-insert
24329 @c @subheading -trace-list
24331 @c @subheading -trace-pass-count
24333 @c @subheading -trace-save
24335 @c @subheading -trace-start
24337 @c @subheading -trace-stop
24340 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24341 @node GDB/MI Symbol Query
24342 @section @sc{gdb/mi} Symbol Query Commands
24346 @subheading The @code{-symbol-info-address} Command
24347 @findex -symbol-info-address
24349 @subsubheading Synopsis
24352 -symbol-info-address @var{symbol}
24355 Describe where @var{symbol} is stored.
24357 @subsubheading @value{GDBN} Command
24359 The corresponding @value{GDBN} command is @samp{info address}.
24361 @subsubheading Example
24365 @subheading The @code{-symbol-info-file} Command
24366 @findex -symbol-info-file
24368 @subsubheading Synopsis
24374 Show the file for the symbol.
24376 @subsubheading @value{GDBN} Command
24378 There's no equivalent @value{GDBN} command. @code{gdbtk} has
24379 @samp{gdb_find_file}.
24381 @subsubheading Example
24385 @subheading The @code{-symbol-info-function} Command
24386 @findex -symbol-info-function
24388 @subsubheading Synopsis
24391 -symbol-info-function
24394 Show which function the symbol lives in.
24396 @subsubheading @value{GDBN} Command
24398 @samp{gdb_get_function} in @code{gdbtk}.
24400 @subsubheading Example
24404 @subheading The @code{-symbol-info-line} Command
24405 @findex -symbol-info-line
24407 @subsubheading Synopsis
24413 Show the core addresses of the code for a source line.
24415 @subsubheading @value{GDBN} Command
24417 The corresponding @value{GDBN} command is @samp{info line}.
24418 @code{gdbtk} has the @samp{gdb_get_line} and @samp{gdb_get_file} commands.
24420 @subsubheading Example
24424 @subheading The @code{-symbol-info-symbol} Command
24425 @findex -symbol-info-symbol
24427 @subsubheading Synopsis
24430 -symbol-info-symbol @var{addr}
24433 Describe what symbol is at location @var{addr}.
24435 @subsubheading @value{GDBN} Command
24437 The corresponding @value{GDBN} command is @samp{info symbol}.
24439 @subsubheading Example
24443 @subheading The @code{-symbol-list-functions} Command
24444 @findex -symbol-list-functions
24446 @subsubheading Synopsis
24449 -symbol-list-functions
24452 List the functions in the executable.
24454 @subsubheading @value{GDBN} Command
24456 @samp{info functions} in @value{GDBN}, @samp{gdb_listfunc} and
24457 @samp{gdb_search} in @code{gdbtk}.
24459 @subsubheading Example
24464 @subheading The @code{-symbol-list-lines} Command
24465 @findex -symbol-list-lines
24467 @subsubheading Synopsis
24470 -symbol-list-lines @var{filename}
24473 Print the list of lines that contain code and their associated program
24474 addresses for the given source filename. The entries are sorted in
24475 ascending PC order.
24477 @subsubheading @value{GDBN} Command
24479 There is no corresponding @value{GDBN} command.
24481 @subsubheading Example
24484 -symbol-list-lines basics.c
24485 ^done,lines=[@{pc="0x08048554",line="7"@},@{pc="0x0804855a",line="8"@}]
24491 @subheading The @code{-symbol-list-types} Command
24492 @findex -symbol-list-types
24494 @subsubheading Synopsis
24500 List all the type names.
24502 @subsubheading @value{GDBN} Command
24504 The corresponding commands are @samp{info types} in @value{GDBN},
24505 @samp{gdb_search} in @code{gdbtk}.
24507 @subsubheading Example
24511 @subheading The @code{-symbol-list-variables} Command
24512 @findex -symbol-list-variables
24514 @subsubheading Synopsis
24517 -symbol-list-variables
24520 List all the global and static variable names.
24522 @subsubheading @value{GDBN} Command
24524 @samp{info variables} in @value{GDBN}, @samp{gdb_search} in @code{gdbtk}.
24526 @subsubheading Example
24530 @subheading The @code{-symbol-locate} Command
24531 @findex -symbol-locate
24533 @subsubheading Synopsis
24539 @subsubheading @value{GDBN} Command
24541 @samp{gdb_loc} in @code{gdbtk}.
24543 @subsubheading Example
24547 @subheading The @code{-symbol-type} Command
24548 @findex -symbol-type
24550 @subsubheading Synopsis
24553 -symbol-type @var{variable}
24556 Show type of @var{variable}.
24558 @subsubheading @value{GDBN} Command
24560 The corresponding @value{GDBN} command is @samp{ptype}, @code{gdbtk} has
24561 @samp{gdb_obj_variable}.
24563 @subsubheading Example
24568 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24569 @node GDB/MI File Commands
24570 @section @sc{gdb/mi} File Commands
24572 This section describes the GDB/MI commands to specify executable file names
24573 and to read in and obtain symbol table information.
24575 @subheading The @code{-file-exec-and-symbols} Command
24576 @findex -file-exec-and-symbols
24578 @subsubheading Synopsis
24581 -file-exec-and-symbols @var{file}
24584 Specify the executable file to be debugged. This file is the one from
24585 which the symbol table is also read. If no file is specified, the
24586 command clears the executable and symbol information. If breakpoints
24587 are set when using this command with no arguments, @value{GDBN} will produce
24588 error messages. Otherwise, no output is produced, except a completion
24591 @subsubheading @value{GDBN} Command
24593 The corresponding @value{GDBN} command is @samp{file}.
24595 @subsubheading Example
24599 -file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
24605 @subheading The @code{-file-exec-file} Command
24606 @findex -file-exec-file
24608 @subsubheading Synopsis
24611 -file-exec-file @var{file}
24614 Specify the executable file to be debugged. Unlike
24615 @samp{-file-exec-and-symbols}, the symbol table is @emph{not} read
24616 from this file. If used without argument, @value{GDBN} clears the information
24617 about the executable file. No output is produced, except a completion
24620 @subsubheading @value{GDBN} Command
24622 The corresponding @value{GDBN} command is @samp{exec-file}.
24624 @subsubheading Example
24628 -file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
24635 @subheading The @code{-file-list-exec-sections} Command
24636 @findex -file-list-exec-sections
24638 @subsubheading Synopsis
24641 -file-list-exec-sections
24644 List the sections of the current executable file.
24646 @subsubheading @value{GDBN} Command
24648 The @value{GDBN} command @samp{info file} shows, among the rest, the same
24649 information as this command. @code{gdbtk} has a corresponding command
24650 @samp{gdb_load_info}.
24652 @subsubheading Example
24657 @subheading The @code{-file-list-exec-source-file} Command
24658 @findex -file-list-exec-source-file
24660 @subsubheading Synopsis
24663 -file-list-exec-source-file
24666 List the line number, the current source file, and the absolute path
24667 to the current source file for the current executable. The macro
24668 information field has a value of @samp{1} or @samp{0} depending on
24669 whether or not the file includes preprocessor macro information.
24671 @subsubheading @value{GDBN} Command
24673 The @value{GDBN} equivalent is @samp{info source}
24675 @subsubheading Example
24679 123-file-list-exec-source-file
24680 123^done,line="1",file="foo.c",fullname="/home/bar/foo.c,macro-info="1"
24685 @subheading The @code{-file-list-exec-source-files} Command
24686 @findex -file-list-exec-source-files
24688 @subsubheading Synopsis
24691 -file-list-exec-source-files
24694 List the source files for the current executable.
24696 It will always output the filename, but only when @value{GDBN} can find
24697 the absolute file name of a source file, will it output the fullname.
24699 @subsubheading @value{GDBN} Command
24701 The @value{GDBN} equivalent is @samp{info sources}.
24702 @code{gdbtk} has an analogous command @samp{gdb_listfiles}.
24704 @subsubheading Example
24707 -file-list-exec-source-files
24709 @{file=foo.c,fullname=/home/foo.c@},
24710 @{file=/home/bar.c,fullname=/home/bar.c@},
24711 @{file=gdb_could_not_find_fullpath.c@}]
24716 @subheading The @code{-file-list-shared-libraries} Command
24717 @findex -file-list-shared-libraries
24719 @subsubheading Synopsis
24722 -file-list-shared-libraries
24725 List the shared libraries in the program.
24727 @subsubheading @value{GDBN} Command
24729 The corresponding @value{GDBN} command is @samp{info shared}.
24731 @subsubheading Example
24735 @subheading The @code{-file-list-symbol-files} Command
24736 @findex -file-list-symbol-files
24738 @subsubheading Synopsis
24741 -file-list-symbol-files
24746 @subsubheading @value{GDBN} Command
24748 The corresponding @value{GDBN} command is @samp{info file} (part of it).
24750 @subsubheading Example
24755 @subheading The @code{-file-symbol-file} Command
24756 @findex -file-symbol-file
24758 @subsubheading Synopsis
24761 -file-symbol-file @var{file}
24764 Read symbol table info from the specified @var{file} argument. When
24765 used without arguments, clears @value{GDBN}'s symbol table info. No output is
24766 produced, except for a completion notification.
24768 @subsubheading @value{GDBN} Command
24770 The corresponding @value{GDBN} command is @samp{symbol-file}.
24772 @subsubheading Example
24776 -file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
24782 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24783 @node GDB/MI Memory Overlay Commands
24784 @section @sc{gdb/mi} Memory Overlay Commands
24786 The memory overlay commands are not implemented.
24788 @c @subheading -overlay-auto
24790 @c @subheading -overlay-list-mapping-state
24792 @c @subheading -overlay-list-overlays
24794 @c @subheading -overlay-map
24796 @c @subheading -overlay-off
24798 @c @subheading -overlay-on
24800 @c @subheading -overlay-unmap
24802 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24803 @node GDB/MI Signal Handling Commands
24804 @section @sc{gdb/mi} Signal Handling Commands
24806 Signal handling commands are not implemented.
24808 @c @subheading -signal-handle
24810 @c @subheading -signal-list-handle-actions
24812 @c @subheading -signal-list-signal-types
24816 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24817 @node GDB/MI Target Manipulation
24818 @section @sc{gdb/mi} Target Manipulation Commands
24821 @subheading The @code{-target-attach} Command
24822 @findex -target-attach
24824 @subsubheading Synopsis
24827 -target-attach @var{pid} | @var{gid} | @var{file}
24830 Attach to a process @var{pid} or a file @var{file} outside of
24831 @value{GDBN}, or a thread group @var{gid}. If attaching to a thread
24832 group, the id previously returned by
24833 @samp{-list-thread-groups --available} must be used.
24835 @subsubheading @value{GDBN} Command
24837 The corresponding @value{GDBN} command is @samp{attach}.
24839 @subsubheading Example
24843 =thread-created,id="1"
24844 *stopped,thread-id="1",frame=@{addr="0xb7f7e410",func="bar",args=[]@}
24850 @subheading The @code{-target-compare-sections} Command
24851 @findex -target-compare-sections
24853 @subsubheading Synopsis
24856 -target-compare-sections [ @var{section} ]
24859 Compare data of section @var{section} on target to the exec file.
24860 Without the argument, all sections are compared.
24862 @subsubheading @value{GDBN} Command
24864 The @value{GDBN} equivalent is @samp{compare-sections}.
24866 @subsubheading Example
24871 @subheading The @code{-target-detach} Command
24872 @findex -target-detach
24874 @subsubheading Synopsis
24877 -target-detach [ @var{pid} | @var{gid} ]
24880 Detach from the remote target which normally resumes its execution.
24881 If either @var{pid} or @var{gid} is specified, detaches from either
24882 the specified process, or specified thread group. There's no output.
24884 @subsubheading @value{GDBN} Command
24886 The corresponding @value{GDBN} command is @samp{detach}.
24888 @subsubheading Example
24898 @subheading The @code{-target-disconnect} Command
24899 @findex -target-disconnect
24901 @subsubheading Synopsis
24907 Disconnect from the remote target. There's no output and the target is
24908 generally not resumed.
24910 @subsubheading @value{GDBN} Command
24912 The corresponding @value{GDBN} command is @samp{disconnect}.
24914 @subsubheading Example
24924 @subheading The @code{-target-download} Command
24925 @findex -target-download
24927 @subsubheading Synopsis
24933 Loads the executable onto the remote target.
24934 It prints out an update message every half second, which includes the fields:
24938 The name of the section.
24940 The size of what has been sent so far for that section.
24942 The size of the section.
24944 The total size of what was sent so far (the current and the previous sections).
24946 The size of the overall executable to download.
24950 Each message is sent as status record (@pxref{GDB/MI Output Syntax, ,
24951 @sc{gdb/mi} Output Syntax}).
24953 In addition, it prints the name and size of the sections, as they are
24954 downloaded. These messages include the following fields:
24958 The name of the section.
24960 The size of the section.
24962 The size of the overall executable to download.
24966 At the end, a summary is printed.
24968 @subsubheading @value{GDBN} Command
24970 The corresponding @value{GDBN} command is @samp{load}.
24972 @subsubheading Example
24974 Note: each status message appears on a single line. Here the messages
24975 have been broken down so that they can fit onto a page.
24980 +download,@{section=".text",section-size="6668",total-size="9880"@}
24981 +download,@{section=".text",section-sent="512",section-size="6668",
24982 total-sent="512",total-size="9880"@}
24983 +download,@{section=".text",section-sent="1024",section-size="6668",
24984 total-sent="1024",total-size="9880"@}
24985 +download,@{section=".text",section-sent="1536",section-size="6668",
24986 total-sent="1536",total-size="9880"@}
24987 +download,@{section=".text",section-sent="2048",section-size="6668",
24988 total-sent="2048",total-size="9880"@}
24989 +download,@{section=".text",section-sent="2560",section-size="6668",
24990 total-sent="2560",total-size="9880"@}
24991 +download,@{section=".text",section-sent="3072",section-size="6668",
24992 total-sent="3072",total-size="9880"@}
24993 +download,@{section=".text",section-sent="3584",section-size="6668",
24994 total-sent="3584",total-size="9880"@}
24995 +download,@{section=".text",section-sent="4096",section-size="6668",
24996 total-sent="4096",total-size="9880"@}
24997 +download,@{section=".text",section-sent="4608",section-size="6668",
24998 total-sent="4608",total-size="9880"@}
24999 +download,@{section=".text",section-sent="5120",section-size="6668",
25000 total-sent="5120",total-size="9880"@}
25001 +download,@{section=".text",section-sent="5632",section-size="6668",
25002 total-sent="5632",total-size="9880"@}
25003 +download,@{section=".text",section-sent="6144",section-size="6668",
25004 total-sent="6144",total-size="9880"@}
25005 +download,@{section=".text",section-sent="6656",section-size="6668",
25006 total-sent="6656",total-size="9880"@}
25007 +download,@{section=".init",section-size="28",total-size="9880"@}
25008 +download,@{section=".fini",section-size="28",total-size="9880"@}
25009 +download,@{section=".data",section-size="3156",total-size="9880"@}
25010 +download,@{section=".data",section-sent="512",section-size="3156",
25011 total-sent="7236",total-size="9880"@}
25012 +download,@{section=".data",section-sent="1024",section-size="3156",
25013 total-sent="7748",total-size="9880"@}
25014 +download,@{section=".data",section-sent="1536",section-size="3156",
25015 total-sent="8260",total-size="9880"@}
25016 +download,@{section=".data",section-sent="2048",section-size="3156",
25017 total-sent="8772",total-size="9880"@}
25018 +download,@{section=".data",section-sent="2560",section-size="3156",
25019 total-sent="9284",total-size="9880"@}
25020 +download,@{section=".data",section-sent="3072",section-size="3156",
25021 total-sent="9796",total-size="9880"@}
25022 ^done,address="0x10004",load-size="9880",transfer-rate="6586",
25029 @subheading The @code{-target-exec-status} Command
25030 @findex -target-exec-status
25032 @subsubheading Synopsis
25035 -target-exec-status
25038 Provide information on the state of the target (whether it is running or
25039 not, for instance).
25041 @subsubheading @value{GDBN} Command
25043 There's no equivalent @value{GDBN} command.
25045 @subsubheading Example
25049 @subheading The @code{-target-list-available-targets} Command
25050 @findex -target-list-available-targets
25052 @subsubheading Synopsis
25055 -target-list-available-targets
25058 List the possible targets to connect to.
25060 @subsubheading @value{GDBN} Command
25062 The corresponding @value{GDBN} command is @samp{help target}.
25064 @subsubheading Example
25068 @subheading The @code{-target-list-current-targets} Command
25069 @findex -target-list-current-targets
25071 @subsubheading Synopsis
25074 -target-list-current-targets
25077 Describe the current target.
25079 @subsubheading @value{GDBN} Command
25081 The corresponding information is printed by @samp{info file} (among
25084 @subsubheading Example
25088 @subheading The @code{-target-list-parameters} Command
25089 @findex -target-list-parameters
25091 @subsubheading Synopsis
25094 -target-list-parameters
25100 @subsubheading @value{GDBN} Command
25104 @subsubheading Example
25108 @subheading The @code{-target-select} Command
25109 @findex -target-select
25111 @subsubheading Synopsis
25114 -target-select @var{type} @var{parameters @dots{}}
25117 Connect @value{GDBN} to the remote target. This command takes two args:
25121 The type of target, for instance @samp{remote}, etc.
25122 @item @var{parameters}
25123 Device names, host names and the like. @xref{Target Commands, ,
25124 Commands for Managing Targets}, for more details.
25127 The output is a connection notification, followed by the address at
25128 which the target program is, in the following form:
25131 ^connected,addr="@var{address}",func="@var{function name}",
25132 args=[@var{arg list}]
25135 @subsubheading @value{GDBN} Command
25137 The corresponding @value{GDBN} command is @samp{target}.
25139 @subsubheading Example
25143 -target-select remote /dev/ttya
25144 ^connected,addr="0xfe00a300",func="??",args=[]
25148 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25149 @node GDB/MI File Transfer Commands
25150 @section @sc{gdb/mi} File Transfer Commands
25153 @subheading The @code{-target-file-put} Command
25154 @findex -target-file-put
25156 @subsubheading Synopsis
25159 -target-file-put @var{hostfile} @var{targetfile}
25162 Copy file @var{hostfile} from the host system (the machine running
25163 @value{GDBN}) to @var{targetfile} on the target system.
25165 @subsubheading @value{GDBN} Command
25167 The corresponding @value{GDBN} command is @samp{remote put}.
25169 @subsubheading Example
25173 -target-file-put localfile remotefile
25179 @subheading The @code{-target-file-get} Command
25180 @findex -target-file-get
25182 @subsubheading Synopsis
25185 -target-file-get @var{targetfile} @var{hostfile}
25188 Copy file @var{targetfile} from the target system to @var{hostfile}
25189 on the host system.
25191 @subsubheading @value{GDBN} Command
25193 The corresponding @value{GDBN} command is @samp{remote get}.
25195 @subsubheading Example
25199 -target-file-get remotefile localfile
25205 @subheading The @code{-target-file-delete} Command
25206 @findex -target-file-delete
25208 @subsubheading Synopsis
25211 -target-file-delete @var{targetfile}
25214 Delete @var{targetfile} from the target system.
25216 @subsubheading @value{GDBN} Command
25218 The corresponding @value{GDBN} command is @samp{remote delete}.
25220 @subsubheading Example
25224 -target-file-delete remotefile
25230 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25231 @node GDB/MI Miscellaneous Commands
25232 @section Miscellaneous @sc{gdb/mi} Commands
25234 @c @subheading -gdb-complete
25236 @subheading The @code{-gdb-exit} Command
25239 @subsubheading Synopsis
25245 Exit @value{GDBN} immediately.
25247 @subsubheading @value{GDBN} Command
25249 Approximately corresponds to @samp{quit}.
25251 @subsubheading Example
25261 @subheading The @code{-exec-abort} Command
25262 @findex -exec-abort
25264 @subsubheading Synopsis
25270 Kill the inferior running program.
25272 @subsubheading @value{GDBN} Command
25274 The corresponding @value{GDBN} command is @samp{kill}.
25276 @subsubheading Example
25281 @subheading The @code{-gdb-set} Command
25284 @subsubheading Synopsis
25290 Set an internal @value{GDBN} variable.
25291 @c IS THIS A DOLLAR VARIABLE? OR SOMETHING LIKE ANNOTATE ?????
25293 @subsubheading @value{GDBN} Command
25295 The corresponding @value{GDBN} command is @samp{set}.
25297 @subsubheading Example
25307 @subheading The @code{-gdb-show} Command
25310 @subsubheading Synopsis
25316 Show the current value of a @value{GDBN} variable.
25318 @subsubheading @value{GDBN} Command
25320 The corresponding @value{GDBN} command is @samp{show}.
25322 @subsubheading Example
25331 @c @subheading -gdb-source
25334 @subheading The @code{-gdb-version} Command
25335 @findex -gdb-version
25337 @subsubheading Synopsis
25343 Show version information for @value{GDBN}. Used mostly in testing.
25345 @subsubheading @value{GDBN} Command
25347 The @value{GDBN} equivalent is @samp{show version}. @value{GDBN} by
25348 default shows this information when you start an interactive session.
25350 @subsubheading Example
25352 @c This example modifies the actual output from GDB to avoid overfull
25358 ~Copyright 2000 Free Software Foundation, Inc.
25359 ~GDB is free software, covered by the GNU General Public License, and
25360 ~you are welcome to change it and/or distribute copies of it under
25361 ~ certain conditions.
25362 ~Type "show copying" to see the conditions.
25363 ~There is absolutely no warranty for GDB. Type "show warranty" for
25365 ~This GDB was configured as
25366 "--host=sparc-sun-solaris2.5.1 --target=ppc-eabi".
25371 @subheading The @code{-list-features} Command
25372 @findex -list-features
25374 Returns a list of particular features of the MI protocol that
25375 this version of gdb implements. A feature can be a command,
25376 or a new field in an output of some command, or even an
25377 important bugfix. While a frontend can sometimes detect presence
25378 of a feature at runtime, it is easier to perform detection at debugger
25381 The command returns a list of strings, with each string naming an
25382 available feature. Each returned string is just a name, it does not
25383 have any internal structure. The list of possible feature names
25389 (gdb) -list-features
25390 ^done,result=["feature1","feature2"]
25393 The current list of features is:
25396 @item frozen-varobjs
25397 Indicates presence of the @code{-var-set-frozen} command, as well
25398 as possible presense of the @code{frozen} field in the output
25399 of @code{-varobj-create}.
25400 @item pending-breakpoints
25401 Indicates presence of the @option{-f} option to the @code{-break-insert} command.
25403 Indicates presence of Python scripting support, Python-based
25404 pretty-printing commands, and possible presence of the
25405 @samp{display_hint} field in the output of @code{-var-list-children}
25407 Indicates presence of the @code{-thread-info} command.
25411 @subheading The @code{-list-target-features} Command
25412 @findex -list-target-features
25414 Returns a list of particular features that are supported by the
25415 target. Those features affect the permitted MI commands, but
25416 unlike the features reported by the @code{-list-features} command, the
25417 features depend on which target GDB is using at the moment. Whenever
25418 a target can change, due to commands such as @code{-target-select},
25419 @code{-target-attach} or @code{-exec-run}, the list of target features
25420 may change, and the frontend should obtain it again.
25424 (gdb) -list-features
25425 ^done,result=["async"]
25428 The current list of features is:
25432 Indicates that the target is capable of asynchronous command
25433 execution, which means that @value{GDBN} will accept further commands
25434 while the target is running.
25438 @subheading The @code{-list-thread-groups} Command
25439 @findex -list-thread-groups
25441 @subheading Synopsis
25444 -list-thread-groups [ --available ] [ @var{group} ]
25447 When used without the @var{group} parameter, lists top-level thread
25448 groups that are being debugged. When used with the @var{group}
25449 parameter, the children of the specified group are listed. The
25450 children can be either threads, or other groups. At present,
25451 @value{GDBN} will not report both threads and groups as children at
25452 the same time, but it may change in future.
25454 With the @samp{--available} option, instead of reporting groups that
25455 are been debugged, GDB will report all thread groups available on the
25456 target. Using the @samp{--available} option together with @var{group}
25459 @subheading Example
25463 -list-thread-groups
25464 ^done,groups=[@{id="17",type="process",pid="yyy",num_children="2"@}]
25465 -list-thread-groups 17
25466 ^done,threads=[@{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
25467 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]@},state="running"@},
25468 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
25469 frame=@{level="0",addr="0x0804891f",func="foo",args=[@{name="i",value="10"@}],
25470 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},state="running"@}]]
25473 @subheading The @code{-interpreter-exec} Command
25474 @findex -interpreter-exec
25476 @subheading Synopsis
25479 -interpreter-exec @var{interpreter} @var{command}
25481 @anchor{-interpreter-exec}
25483 Execute the specified @var{command} in the given @var{interpreter}.
25485 @subheading @value{GDBN} Command
25487 The corresponding @value{GDBN} command is @samp{interpreter-exec}.
25489 @subheading Example
25493 -interpreter-exec console "break main"
25494 &"During symbol reading, couldn't parse type; debugger out of date?.\n"
25495 &"During symbol reading, bad structure-type format.\n"
25496 ~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n"
25501 @subheading The @code{-inferior-tty-set} Command
25502 @findex -inferior-tty-set
25504 @subheading Synopsis
25507 -inferior-tty-set /dev/pts/1
25510 Set terminal for future runs of the program being debugged.
25512 @subheading @value{GDBN} Command
25514 The corresponding @value{GDBN} command is @samp{set inferior-tty} /dev/pts/1.
25516 @subheading Example
25520 -inferior-tty-set /dev/pts/1
25525 @subheading The @code{-inferior-tty-show} Command
25526 @findex -inferior-tty-show
25528 @subheading Synopsis
25534 Show terminal for future runs of program being debugged.
25536 @subheading @value{GDBN} Command
25538 The corresponding @value{GDBN} command is @samp{show inferior-tty}.
25540 @subheading Example
25544 -inferior-tty-set /dev/pts/1
25548 ^done,inferior_tty_terminal="/dev/pts/1"
25552 @subheading The @code{-enable-timings} Command
25553 @findex -enable-timings
25555 @subheading Synopsis
25558 -enable-timings [yes | no]
25561 Toggle the printing of the wallclock, user and system times for an MI
25562 command as a field in its output. This command is to help frontend
25563 developers optimize the performance of their code. No argument is
25564 equivalent to @samp{yes}.
25566 @subheading @value{GDBN} Command
25570 @subheading Example
25578 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
25579 addr="0x080484ed",func="main",file="myprog.c",
25580 fullname="/home/nickrob/myprog.c",line="73",times="0"@},
25581 time=@{wallclock="0.05185",user="0.00800",system="0.00000"@}
25589 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
25590 frame=@{addr="0x080484ed",func="main",args=[@{name="argc",value="1"@},
25591 @{name="argv",value="0xbfb60364"@}],file="myprog.c",
25592 fullname="/home/nickrob/myprog.c",line="73"@}
25597 @chapter @value{GDBN} Annotations
25599 This chapter describes annotations in @value{GDBN}. Annotations were
25600 designed to interface @value{GDBN} to graphical user interfaces or other
25601 similar programs which want to interact with @value{GDBN} at a
25602 relatively high level.
25604 The annotation mechanism has largely been superseded by @sc{gdb/mi}
25608 This is Edition @value{EDITION}, @value{DATE}.
25612 * Annotations Overview:: What annotations are; the general syntax.
25613 * Server Prefix:: Issuing a command without affecting user state.
25614 * Prompting:: Annotations marking @value{GDBN}'s need for input.
25615 * Errors:: Annotations for error messages.
25616 * Invalidation:: Some annotations describe things now invalid.
25617 * Annotations for Running::
25618 Whether the program is running, how it stopped, etc.
25619 * Source Annotations:: Annotations describing source code.
25622 @node Annotations Overview
25623 @section What is an Annotation?
25624 @cindex annotations
25626 Annotations start with a newline character, two @samp{control-z}
25627 characters, and the name of the annotation. If there is no additional
25628 information associated with this annotation, the name of the annotation
25629 is followed immediately by a newline. If there is additional
25630 information, the name of the annotation is followed by a space, the
25631 additional information, and a newline. The additional information
25632 cannot contain newline characters.
25634 Any output not beginning with a newline and two @samp{control-z}
25635 characters denotes literal output from @value{GDBN}. Currently there is
25636 no need for @value{GDBN} to output a newline followed by two
25637 @samp{control-z} characters, but if there was such a need, the
25638 annotations could be extended with an @samp{escape} annotation which
25639 means those three characters as output.
25641 The annotation @var{level}, which is specified using the
25642 @option{--annotate} command line option (@pxref{Mode Options}), controls
25643 how much information @value{GDBN} prints together with its prompt,
25644 values of expressions, source lines, and other types of output. Level 0
25645 is for no annotations, level 1 is for use when @value{GDBN} is run as a
25646 subprocess of @sc{gnu} Emacs, level 3 is the maximum annotation suitable
25647 for programs that control @value{GDBN}, and level 2 annotations have
25648 been made obsolete (@pxref{Limitations, , Limitations of the Annotation
25649 Interface, annotate, GDB's Obsolete Annotations}).
25652 @kindex set annotate
25653 @item set annotate @var{level}
25654 The @value{GDBN} command @code{set annotate} sets the level of
25655 annotations to the specified @var{level}.
25657 @item show annotate
25658 @kindex show annotate
25659 Show the current annotation level.
25662 This chapter describes level 3 annotations.
25664 A simple example of starting up @value{GDBN} with annotations is:
25667 $ @kbd{gdb --annotate=3}
25669 Copyright 2003 Free Software Foundation, Inc.
25670 GDB is free software, covered by the GNU General Public License,
25671 and you are welcome to change it and/or distribute copies of it
25672 under certain conditions.
25673 Type "show copying" to see the conditions.
25674 There is absolutely no warranty for GDB. Type "show warranty"
25676 This GDB was configured as "i386-pc-linux-gnu"
25687 Here @samp{quit} is input to @value{GDBN}; the rest is output from
25688 @value{GDBN}. The three lines beginning @samp{^Z^Z} (where @samp{^Z}
25689 denotes a @samp{control-z} character) are annotations; the rest is
25690 output from @value{GDBN}.
25692 @node Server Prefix
25693 @section The Server Prefix
25694 @cindex server prefix
25696 If you prefix a command with @samp{server } then it will not affect
25697 the command history, nor will it affect @value{GDBN}'s notion of which
25698 command to repeat if @key{RET} is pressed on a line by itself. This
25699 means that commands can be run behind a user's back by a front-end in
25700 a transparent manner.
25702 The @code{server } prefix does not affect the recording of values into
25703 the value history; to print a value without recording it into the
25704 value history, use the @code{output} command instead of the
25705 @code{print} command.
25707 Using this prefix also disables confirmation requests
25708 (@pxref{confirmation requests}).
25711 @section Annotation for @value{GDBN} Input
25713 @cindex annotations for prompts
25714 When @value{GDBN} prompts for input, it annotates this fact so it is possible
25715 to know when to send output, when the output from a given command is
25718 Different kinds of input each have a different @dfn{input type}. Each
25719 input type has three annotations: a @code{pre-} annotation, which
25720 denotes the beginning of any prompt which is being output, a plain
25721 annotation, which denotes the end of the prompt, and then a @code{post-}
25722 annotation which denotes the end of any echo which may (or may not) be
25723 associated with the input. For example, the @code{prompt} input type
25724 features the following annotations:
25732 The input types are
25735 @findex pre-prompt annotation
25736 @findex prompt annotation
25737 @findex post-prompt annotation
25739 When @value{GDBN} is prompting for a command (the main @value{GDBN} prompt).
25741 @findex pre-commands annotation
25742 @findex commands annotation
25743 @findex post-commands annotation
25745 When @value{GDBN} prompts for a set of commands, like in the @code{commands}
25746 command. The annotations are repeated for each command which is input.
25748 @findex pre-overload-choice annotation
25749 @findex overload-choice annotation
25750 @findex post-overload-choice annotation
25751 @item overload-choice
25752 When @value{GDBN} wants the user to select between various overloaded functions.
25754 @findex pre-query annotation
25755 @findex query annotation
25756 @findex post-query annotation
25758 When @value{GDBN} wants the user to confirm a potentially dangerous operation.
25760 @findex pre-prompt-for-continue annotation
25761 @findex prompt-for-continue annotation
25762 @findex post-prompt-for-continue annotation
25763 @item prompt-for-continue
25764 When @value{GDBN} is asking the user to press return to continue. Note: Don't
25765 expect this to work well; instead use @code{set height 0} to disable
25766 prompting. This is because the counting of lines is buggy in the
25767 presence of annotations.
25772 @cindex annotations for errors, warnings and interrupts
25774 @findex quit annotation
25779 This annotation occurs right before @value{GDBN} responds to an interrupt.
25781 @findex error annotation
25786 This annotation occurs right before @value{GDBN} responds to an error.
25788 Quit and error annotations indicate that any annotations which @value{GDBN} was
25789 in the middle of may end abruptly. For example, if a
25790 @code{value-history-begin} annotation is followed by a @code{error}, one
25791 cannot expect to receive the matching @code{value-history-end}. One
25792 cannot expect not to receive it either, however; an error annotation
25793 does not necessarily mean that @value{GDBN} is immediately returning all the way
25796 @findex error-begin annotation
25797 A quit or error annotation may be preceded by
25803 Any output between that and the quit or error annotation is the error
25806 Warning messages are not yet annotated.
25807 @c If we want to change that, need to fix warning(), type_error(),
25808 @c range_error(), and possibly other places.
25811 @section Invalidation Notices
25813 @cindex annotations for invalidation messages
25814 The following annotations say that certain pieces of state may have
25818 @findex frames-invalid annotation
25819 @item ^Z^Zframes-invalid
25821 The frames (for example, output from the @code{backtrace} command) may
25824 @findex breakpoints-invalid annotation
25825 @item ^Z^Zbreakpoints-invalid
25827 The breakpoints may have changed. For example, the user just added or
25828 deleted a breakpoint.
25831 @node Annotations for Running
25832 @section Running the Program
25833 @cindex annotations for running programs
25835 @findex starting annotation
25836 @findex stopping annotation
25837 When the program starts executing due to a @value{GDBN} command such as
25838 @code{step} or @code{continue},
25844 is output. When the program stops,
25850 is output. Before the @code{stopped} annotation, a variety of
25851 annotations describe how the program stopped.
25854 @findex exited annotation
25855 @item ^Z^Zexited @var{exit-status}
25856 The program exited, and @var{exit-status} is the exit status (zero for
25857 successful exit, otherwise nonzero).
25859 @findex signalled annotation
25860 @findex signal-name annotation
25861 @findex signal-name-end annotation
25862 @findex signal-string annotation
25863 @findex signal-string-end annotation
25864 @item ^Z^Zsignalled
25865 The program exited with a signal. After the @code{^Z^Zsignalled}, the
25866 annotation continues:
25872 ^Z^Zsignal-name-end
25876 ^Z^Zsignal-string-end
25881 where @var{name} is the name of the signal, such as @code{SIGILL} or
25882 @code{SIGSEGV}, and @var{string} is the explanation of the signal, such
25883 as @code{Illegal Instruction} or @code{Segmentation fault}.
25884 @var{intro-text}, @var{middle-text}, and @var{end-text} are for the
25885 user's benefit and have no particular format.
25887 @findex signal annotation
25889 The syntax of this annotation is just like @code{signalled}, but @value{GDBN} is
25890 just saying that the program received the signal, not that it was
25891 terminated with it.
25893 @findex breakpoint annotation
25894 @item ^Z^Zbreakpoint @var{number}
25895 The program hit breakpoint number @var{number}.
25897 @findex watchpoint annotation
25898 @item ^Z^Zwatchpoint @var{number}
25899 The program hit watchpoint number @var{number}.
25902 @node Source Annotations
25903 @section Displaying Source
25904 @cindex annotations for source display
25906 @findex source annotation
25907 The following annotation is used instead of displaying source code:
25910 ^Z^Zsource @var{filename}:@var{line}:@var{character}:@var{middle}:@var{addr}
25913 where @var{filename} is an absolute file name indicating which source
25914 file, @var{line} is the line number within that file (where 1 is the
25915 first line in the file), @var{character} is the character position
25916 within the file (where 0 is the first character in the file) (for most
25917 debug formats this will necessarily point to the beginning of a line),
25918 @var{middle} is @samp{middle} if @var{addr} is in the middle of the
25919 line, or @samp{beg} if @var{addr} is at the beginning of the line, and
25920 @var{addr} is the address in the target program associated with the
25921 source which is being displayed. @var{addr} is in the form @samp{0x}
25922 followed by one or more lowercase hex digits (note that this does not
25923 depend on the language).
25925 @node JIT Interface
25926 @chapter JIT Compilation Interface
25927 @cindex just-in-time compilation
25928 @cindex JIT compilation interface
25930 This chapter documents @value{GDBN}'s @dfn{just-in-time} (JIT) compilation
25931 interface. A JIT compiler is a program or library that generates native
25932 executable code at runtime and executes it, usually in order to achieve good
25933 performance while maintaining platform independence.
25935 Programs that use JIT compilation are normally difficult to debug because
25936 portions of their code are generated at runtime, instead of being loaded from
25937 object files, which is where @value{GDBN} normally finds the program's symbols
25938 and debug information. In order to debug programs that use JIT compilation,
25939 @value{GDBN} has an interface that allows the program to register in-memory
25940 symbol files with @value{GDBN} at runtime.
25942 If you are using @value{GDBN} to debug a program that uses this interface, then
25943 it should work transparently so long as you have not stripped the binary. If
25944 you are developing a JIT compiler, then the interface is documented in the rest
25945 of this chapter. At this time, the only known client of this interface is the
25948 Broadly speaking, the JIT interface mirrors the dynamic loader interface. The
25949 JIT compiler communicates with @value{GDBN} by writing data into a global
25950 variable and calling a fuction at a well-known symbol. When @value{GDBN}
25951 attaches, it reads a linked list of symbol files from the global variable to
25952 find existing code, and puts a breakpoint in the function so that it can find
25953 out about additional code.
25956 * Declarations:: Relevant C struct declarations
25957 * Registering Code:: Steps to register code
25958 * Unregistering Code:: Steps to unregister code
25962 @section JIT Declarations
25964 These are the relevant struct declarations that a C program should include to
25965 implement the interface:
25975 struct jit_code_entry
25977 struct jit_code_entry *next_entry;
25978 struct jit_code_entry *prev_entry;
25979 const char *symfile_addr;
25980 uint64_t symfile_size;
25983 struct jit_descriptor
25986 /* This type should be jit_actions_t, but we use uint32_t
25987 to be explicit about the bitwidth. */
25988 uint32_t action_flag;
25989 struct jit_code_entry *relevant_entry;
25990 struct jit_code_entry *first_entry;
25993 /* GDB puts a breakpoint in this function. */
25994 void __attribute__((noinline)) __jit_debug_register_code() @{ @};
25996 /* Make sure to specify the version statically, because the
25997 debugger may check the version before we can set it. */
25998 struct jit_descriptor __jit_debug_descriptor = @{ 1, 0, 0, 0 @};
26001 If the JIT is multi-threaded, then it is important that the JIT synchronize any
26002 modifications to this global data properly, which can easily be done by putting
26003 a global mutex around modifications to these structures.
26005 @node Registering Code
26006 @section Registering Code
26008 To register code with @value{GDBN}, the JIT should follow this protocol:
26012 Generate an object file in memory with symbols and other desired debug
26013 information. The file must include the virtual addresses of the sections.
26016 Create a code entry for the file, which gives the start and size of the symbol
26020 Add it to the linked list in the JIT descriptor.
26023 Point the relevant_entry field of the descriptor at the entry.
26026 Set @code{action_flag} to @code{JIT_REGISTER} and call
26027 @code{__jit_debug_register_code}.
26030 When @value{GDBN} is attached and the breakpoint fires, @value{GDBN} uses the
26031 @code{relevant_entry} pointer so it doesn't have to walk the list looking for
26032 new code. However, the linked list must still be maintained in order to allow
26033 @value{GDBN} to attach to a running process and still find the symbol files.
26035 @node Unregistering Code
26036 @section Unregistering Code
26038 If code is freed, then the JIT should use the following protocol:
26042 Remove the code entry corresponding to the code from the linked list.
26045 Point the @code{relevant_entry} field of the descriptor at the code entry.
26048 Set @code{action_flag} to @code{JIT_UNREGISTER} and call
26049 @code{__jit_debug_register_code}.
26052 If the JIT frees or recompiles code without unregistering it, then @value{GDBN}
26053 and the JIT will leak the memory used for the associated symbol files.
26056 @chapter Reporting Bugs in @value{GDBN}
26057 @cindex bugs in @value{GDBN}
26058 @cindex reporting bugs in @value{GDBN}
26060 Your bug reports play an essential role in making @value{GDBN} reliable.
26062 Reporting a bug may help you by bringing a solution to your problem, or it
26063 may not. But in any case the principal function of a bug report is to help
26064 the entire community by making the next version of @value{GDBN} work better. Bug
26065 reports are your contribution to the maintenance of @value{GDBN}.
26067 In order for a bug report to serve its purpose, you must include the
26068 information that enables us to fix the bug.
26071 * Bug Criteria:: Have you found a bug?
26072 * Bug Reporting:: How to report bugs
26076 @section Have You Found a Bug?
26077 @cindex bug criteria
26079 If you are not sure whether you have found a bug, here are some guidelines:
26082 @cindex fatal signal
26083 @cindex debugger crash
26084 @cindex crash of debugger
26086 If the debugger gets a fatal signal, for any input whatever, that is a
26087 @value{GDBN} bug. Reliable debuggers never crash.
26089 @cindex error on valid input
26091 If @value{GDBN} produces an error message for valid input, that is a
26092 bug. (Note that if you're cross debugging, the problem may also be
26093 somewhere in the connection to the target.)
26095 @cindex invalid input
26097 If @value{GDBN} does not produce an error message for invalid input,
26098 that is a bug. However, you should note that your idea of
26099 ``invalid input'' might be our idea of ``an extension'' or ``support
26100 for traditional practice''.
26103 If you are an experienced user of debugging tools, your suggestions
26104 for improvement of @value{GDBN} are welcome in any case.
26107 @node Bug Reporting
26108 @section How to Report Bugs
26109 @cindex bug reports
26110 @cindex @value{GDBN} bugs, reporting
26112 A number of companies and individuals offer support for @sc{gnu} products.
26113 If you obtained @value{GDBN} from a support organization, we recommend you
26114 contact that organization first.
26116 You can find contact information for many support companies and
26117 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
26119 @c should add a web page ref...
26122 @ifset BUGURL_DEFAULT
26123 In any event, we also recommend that you submit bug reports for
26124 @value{GDBN}. The preferred method is to submit them directly using
26125 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
26126 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
26129 @strong{Do not send bug reports to @samp{info-gdb}, or to
26130 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
26131 not want to receive bug reports. Those that do have arranged to receive
26134 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
26135 serves as a repeater. The mailing list and the newsgroup carry exactly
26136 the same messages. Often people think of posting bug reports to the
26137 newsgroup instead of mailing them. This appears to work, but it has one
26138 problem which can be crucial: a newsgroup posting often lacks a mail
26139 path back to the sender. Thus, if we need to ask for more information,
26140 we may be unable to reach you. For this reason, it is better to send
26141 bug reports to the mailing list.
26143 @ifclear BUGURL_DEFAULT
26144 In any event, we also recommend that you submit bug reports for
26145 @value{GDBN} to @value{BUGURL}.
26149 The fundamental principle of reporting bugs usefully is this:
26150 @strong{report all the facts}. If you are not sure whether to state a
26151 fact or leave it out, state it!
26153 Often people omit facts because they think they know what causes the
26154 problem and assume that some details do not matter. Thus, you might
26155 assume that the name of the variable you use in an example does not matter.
26156 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
26157 stray memory reference which happens to fetch from the location where that
26158 name is stored in memory; perhaps, if the name were different, the contents
26159 of that location would fool the debugger into doing the right thing despite
26160 the bug. Play it safe and give a specific, complete example. That is the
26161 easiest thing for you to do, and the most helpful.
26163 Keep in mind that the purpose of a bug report is to enable us to fix the
26164 bug. It may be that the bug has been reported previously, but neither
26165 you nor we can know that unless your bug report is complete and
26168 Sometimes people give a few sketchy facts and ask, ``Does this ring a
26169 bell?'' Those bug reports are useless, and we urge everyone to
26170 @emph{refuse to respond to them} except to chide the sender to report
26173 To enable us to fix the bug, you should include all these things:
26177 The version of @value{GDBN}. @value{GDBN} announces it if you start
26178 with no arguments; you can also print it at any time using @code{show
26181 Without this, we will not know whether there is any point in looking for
26182 the bug in the current version of @value{GDBN}.
26185 The type of machine you are using, and the operating system name and
26189 What compiler (and its version) was used to compile @value{GDBN}---e.g.@:
26190 ``@value{GCC}--2.8.1''.
26193 What compiler (and its version) was used to compile the program you are
26194 debugging---e.g.@: ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
26195 C Compiler''. For @value{NGCC}, you can say @kbd{@value{GCC} --version}
26196 to get this information; for other compilers, see the documentation for
26200 The command arguments you gave the compiler to compile your example and
26201 observe the bug. For example, did you use @samp{-O}? To guarantee
26202 you will not omit something important, list them all. A copy of the
26203 Makefile (or the output from make) is sufficient.
26205 If we were to try to guess the arguments, we would probably guess wrong
26206 and then we might not encounter the bug.
26209 A complete input script, and all necessary source files, that will
26213 A description of what behavior you observe that you believe is
26214 incorrect. For example, ``It gets a fatal signal.''
26216 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
26217 will certainly notice it. But if the bug is incorrect output, we might
26218 not notice unless it is glaringly wrong. You might as well not give us
26219 a chance to make a mistake.
26221 Even if the problem you experience is a fatal signal, you should still
26222 say so explicitly. Suppose something strange is going on, such as, your
26223 copy of @value{GDBN} is out of synch, or you have encountered a bug in
26224 the C library on your system. (This has happened!) Your copy might
26225 crash and ours would not. If you told us to expect a crash, then when
26226 ours fails to crash, we would know that the bug was not happening for
26227 us. If you had not told us to expect a crash, then we would not be able
26228 to draw any conclusion from our observations.
26231 @cindex recording a session script
26232 To collect all this information, you can use a session recording program
26233 such as @command{script}, which is available on many Unix systems.
26234 Just run your @value{GDBN} session inside @command{script} and then
26235 include the @file{typescript} file with your bug report.
26237 Another way to record a @value{GDBN} session is to run @value{GDBN}
26238 inside Emacs and then save the entire buffer to a file.
26241 If you wish to suggest changes to the @value{GDBN} source, send us context
26242 diffs. If you even discuss something in the @value{GDBN} source, refer to
26243 it by context, not by line number.
26245 The line numbers in our development sources will not match those in your
26246 sources. Your line numbers would convey no useful information to us.
26250 Here are some things that are not necessary:
26254 A description of the envelope of the bug.
26256 Often people who encounter a bug spend a lot of time investigating
26257 which changes to the input file will make the bug go away and which
26258 changes will not affect it.
26260 This is often time consuming and not very useful, because the way we
26261 will find the bug is by running a single example under the debugger
26262 with breakpoints, not by pure deduction from a series of examples.
26263 We recommend that you save your time for something else.
26265 Of course, if you can find a simpler example to report @emph{instead}
26266 of the original one, that is a convenience for us. Errors in the
26267 output will be easier to spot, running under the debugger will take
26268 less time, and so on.
26270 However, simplification is not vital; if you do not want to do this,
26271 report the bug anyway and send us the entire test case you used.
26274 A patch for the bug.
26276 A patch for the bug does help us if it is a good one. But do not omit
26277 the necessary information, such as the test case, on the assumption that
26278 a patch is all we need. We might see problems with your patch and decide
26279 to fix the problem another way, or we might not understand it at all.
26281 Sometimes with a program as complicated as @value{GDBN} it is very hard to
26282 construct an example that will make the program follow a certain path
26283 through the code. If you do not send us the example, we will not be able
26284 to construct one, so we will not be able to verify that the bug is fixed.
26286 And if we cannot understand what bug you are trying to fix, or why your
26287 patch should be an improvement, we will not install it. A test case will
26288 help us to understand.
26291 A guess about what the bug is or what it depends on.
26293 Such guesses are usually wrong. Even we cannot guess right about such
26294 things without first using the debugger to find the facts.
26297 @c The readline documentation is distributed with the readline code
26298 @c and consists of the two following files:
26300 @c inc-hist.texinfo
26301 @c Use -I with makeinfo to point to the appropriate directory,
26302 @c environment var TEXINPUTS with TeX.
26303 @include rluser.texi
26304 @include inc-hist.texinfo
26307 @node Formatting Documentation
26308 @appendix Formatting Documentation
26310 @cindex @value{GDBN} reference card
26311 @cindex reference card
26312 The @value{GDBN} 4 release includes an already-formatted reference card, ready
26313 for printing with PostScript or Ghostscript, in the @file{gdb}
26314 subdirectory of the main source directory@footnote{In
26315 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
26316 release.}. If you can use PostScript or Ghostscript with your printer,
26317 you can print the reference card immediately with @file{refcard.ps}.
26319 The release also includes the source for the reference card. You
26320 can format it, using @TeX{}, by typing:
26326 The @value{GDBN} reference card is designed to print in @dfn{landscape}
26327 mode on US ``letter'' size paper;
26328 that is, on a sheet 11 inches wide by 8.5 inches
26329 high. You will need to specify this form of printing as an option to
26330 your @sc{dvi} output program.
26332 @cindex documentation
26334 All the documentation for @value{GDBN} comes as part of the machine-readable
26335 distribution. The documentation is written in Texinfo format, which is
26336 a documentation system that uses a single source file to produce both
26337 on-line information and a printed manual. You can use one of the Info
26338 formatting commands to create the on-line version of the documentation
26339 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
26341 @value{GDBN} includes an already formatted copy of the on-line Info
26342 version of this manual in the @file{gdb} subdirectory. The main Info
26343 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
26344 subordinate files matching @samp{gdb.info*} in the same directory. If
26345 necessary, you can print out these files, or read them with any editor;
26346 but they are easier to read using the @code{info} subsystem in @sc{gnu}
26347 Emacs or the standalone @code{info} program, available as part of the
26348 @sc{gnu} Texinfo distribution.
26350 If you want to format these Info files yourself, you need one of the
26351 Info formatting programs, such as @code{texinfo-format-buffer} or
26354 If you have @code{makeinfo} installed, and are in the top level
26355 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
26356 version @value{GDBVN}), you can make the Info file by typing:
26363 If you want to typeset and print copies of this manual, you need @TeX{},
26364 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
26365 Texinfo definitions file.
26367 @TeX{} is a typesetting program; it does not print files directly, but
26368 produces output files called @sc{dvi} files. To print a typeset
26369 document, you need a program to print @sc{dvi} files. If your system
26370 has @TeX{} installed, chances are it has such a program. The precise
26371 command to use depends on your system; @kbd{lpr -d} is common; another
26372 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
26373 require a file name without any extension or a @samp{.dvi} extension.
26375 @TeX{} also requires a macro definitions file called
26376 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
26377 written in Texinfo format. On its own, @TeX{} cannot either read or
26378 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
26379 and is located in the @file{gdb-@var{version-number}/texinfo}
26382 If you have @TeX{} and a @sc{dvi} printer program installed, you can
26383 typeset and print this manual. First switch to the @file{gdb}
26384 subdirectory of the main source directory (for example, to
26385 @file{gdb-@value{GDBVN}/gdb}) and type:
26391 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
26393 @node Installing GDB
26394 @appendix Installing @value{GDBN}
26395 @cindex installation
26398 * Requirements:: Requirements for building @value{GDBN}
26399 * Running Configure:: Invoking the @value{GDBN} @file{configure} script
26400 * Separate Objdir:: Compiling @value{GDBN} in another directory
26401 * Config Names:: Specifying names for hosts and targets
26402 * Configure Options:: Summary of options for configure
26403 * System-wide configuration:: Having a system-wide init file
26407 @section Requirements for Building @value{GDBN}
26408 @cindex building @value{GDBN}, requirements for
26410 Building @value{GDBN} requires various tools and packages to be available.
26411 Other packages will be used only if they are found.
26413 @heading Tools/Packages Necessary for Building @value{GDBN}
26415 @item ISO C90 compiler
26416 @value{GDBN} is written in ISO C90. It should be buildable with any
26417 working C90 compiler, e.g.@: GCC.
26421 @heading Tools/Packages Optional for Building @value{GDBN}
26425 @value{GDBN} can use the Expat XML parsing library. This library may be
26426 included with your operating system distribution; if it is not, you
26427 can get the latest version from @url{http://expat.sourceforge.net}.
26428 The @file{configure} script will search for this library in several
26429 standard locations; if it is installed in an unusual path, you can
26430 use the @option{--with-libexpat-prefix} option to specify its location.
26436 Remote protocol memory maps (@pxref{Memory Map Format})
26438 Target descriptions (@pxref{Target Descriptions})
26440 Remote shared library lists (@pxref{Library List Format})
26442 MS-Windows shared libraries (@pxref{Shared Libraries})
26446 @cindex compressed debug sections
26447 @value{GDBN} will use the @samp{zlib} library, if available, to read
26448 compressed debug sections. Some linkers, such as GNU gold, are capable
26449 of producing binaries with compressed debug sections. If @value{GDBN}
26450 is compiled with @samp{zlib}, it will be able to read the debug
26451 information in such binaries.
26453 The @samp{zlib} library is likely included with your operating system
26454 distribution; if it is not, you can get the latest version from
26455 @url{http://zlib.net}.
26458 @value{GDBN}'s features related to character sets (@pxref{Character
26459 Sets}) require a functioning @code{iconv} implementation. If you are
26460 on a GNU system, then this is provided by the GNU C Library. Some
26461 other systems also provide a working @code{iconv}.
26463 On systems with @code{iconv}, you can install GNU Libiconv. If you
26464 have previously installed Libiconv, you can use the
26465 @option{--with-libiconv-prefix} option to configure.
26467 @value{GDBN}'s top-level @file{configure} and @file{Makefile} will
26468 arrange to build Libiconv if a directory named @file{libiconv} appears
26469 in the top-most source directory. If Libiconv is built this way, and
26470 if the operating system does not provide a suitable @code{iconv}
26471 implementation, then the just-built library will automatically be used
26472 by @value{GDBN}. One easy way to set this up is to download GNU
26473 Libiconv, unpack it, and then rename the directory holding the
26474 Libiconv source code to @samp{libiconv}.
26477 @node Running Configure
26478 @section Invoking the @value{GDBN} @file{configure} Script
26479 @cindex configuring @value{GDBN}
26480 @value{GDBN} comes with a @file{configure} script that automates the process
26481 of preparing @value{GDBN} for installation; you can then use @code{make} to
26482 build the @code{gdb} program.
26484 @c irrelevant in info file; it's as current as the code it lives with.
26485 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
26486 look at the @file{README} file in the sources; we may have improved the
26487 installation procedures since publishing this manual.}
26490 The @value{GDBN} distribution includes all the source code you need for
26491 @value{GDBN} in a single directory, whose name is usually composed by
26492 appending the version number to @samp{gdb}.
26494 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
26495 @file{gdb-@value{GDBVN}} directory. That directory contains:
26498 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
26499 script for configuring @value{GDBN} and all its supporting libraries
26501 @item gdb-@value{GDBVN}/gdb
26502 the source specific to @value{GDBN} itself
26504 @item gdb-@value{GDBVN}/bfd
26505 source for the Binary File Descriptor library
26507 @item gdb-@value{GDBVN}/include
26508 @sc{gnu} include files
26510 @item gdb-@value{GDBVN}/libiberty
26511 source for the @samp{-liberty} free software library
26513 @item gdb-@value{GDBVN}/opcodes
26514 source for the library of opcode tables and disassemblers
26516 @item gdb-@value{GDBVN}/readline
26517 source for the @sc{gnu} command-line interface
26519 @item gdb-@value{GDBVN}/glob
26520 source for the @sc{gnu} filename pattern-matching subroutine
26522 @item gdb-@value{GDBVN}/mmalloc
26523 source for the @sc{gnu} memory-mapped malloc package
26526 The simplest way to configure and build @value{GDBN} is to run @file{configure}
26527 from the @file{gdb-@var{version-number}} source directory, which in
26528 this example is the @file{gdb-@value{GDBVN}} directory.
26530 First switch to the @file{gdb-@var{version-number}} source directory
26531 if you are not already in it; then run @file{configure}. Pass the
26532 identifier for the platform on which @value{GDBN} will run as an
26538 cd gdb-@value{GDBVN}
26539 ./configure @var{host}
26544 where @var{host} is an identifier such as @samp{sun4} or
26545 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
26546 (You can often leave off @var{host}; @file{configure} tries to guess the
26547 correct value by examining your system.)
26549 Running @samp{configure @var{host}} and then running @code{make} builds the
26550 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
26551 libraries, then @code{gdb} itself. The configured source files, and the
26552 binaries, are left in the corresponding source directories.
26555 @file{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
26556 system does not recognize this automatically when you run a different
26557 shell, you may need to run @code{sh} on it explicitly:
26560 sh configure @var{host}
26563 If you run @file{configure} from a directory that contains source
26564 directories for multiple libraries or programs, such as the
26565 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN},
26567 creates configuration files for every directory level underneath (unless
26568 you tell it not to, with the @samp{--norecursion} option).
26570 You should run the @file{configure} script from the top directory in the
26571 source tree, the @file{gdb-@var{version-number}} directory. If you run
26572 @file{configure} from one of the subdirectories, you will configure only
26573 that subdirectory. That is usually not what you want. In particular,
26574 if you run the first @file{configure} from the @file{gdb} subdirectory
26575 of the @file{gdb-@var{version-number}} directory, you will omit the
26576 configuration of @file{bfd}, @file{readline}, and other sibling
26577 directories of the @file{gdb} subdirectory. This leads to build errors
26578 about missing include files such as @file{bfd/bfd.h}.
26580 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
26581 However, you should make sure that the shell on your path (named by
26582 the @samp{SHELL} environment variable) is publicly readable. Remember
26583 that @value{GDBN} uses the shell to start your program---some systems refuse to
26584 let @value{GDBN} debug child processes whose programs are not readable.
26586 @node Separate Objdir
26587 @section Compiling @value{GDBN} in Another Directory
26589 If you want to run @value{GDBN} versions for several host or target machines,
26590 you need a different @code{gdb} compiled for each combination of
26591 host and target. @file{configure} is designed to make this easy by
26592 allowing you to generate each configuration in a separate subdirectory,
26593 rather than in the source directory. If your @code{make} program
26594 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
26595 @code{make} in each of these directories builds the @code{gdb}
26596 program specified there.
26598 To build @code{gdb} in a separate directory, run @file{configure}
26599 with the @samp{--srcdir} option to specify where to find the source.
26600 (You also need to specify a path to find @file{configure}
26601 itself from your working directory. If the path to @file{configure}
26602 would be the same as the argument to @samp{--srcdir}, you can leave out
26603 the @samp{--srcdir} option; it is assumed.)
26605 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
26606 separate directory for a Sun 4 like this:
26610 cd gdb-@value{GDBVN}
26613 ../gdb-@value{GDBVN}/configure sun4
26618 When @file{configure} builds a configuration using a remote source
26619 directory, it creates a tree for the binaries with the same structure
26620 (and using the same names) as the tree under the source directory. In
26621 the example, you'd find the Sun 4 library @file{libiberty.a} in the
26622 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
26623 @file{gdb-sun4/gdb}.
26625 Make sure that your path to the @file{configure} script has just one
26626 instance of @file{gdb} in it. If your path to @file{configure} looks
26627 like @file{../gdb-@value{GDBVN}/gdb/configure}, you are configuring only
26628 one subdirectory of @value{GDBN}, not the whole package. This leads to
26629 build errors about missing include files such as @file{bfd/bfd.h}.
26631 One popular reason to build several @value{GDBN} configurations in separate
26632 directories is to configure @value{GDBN} for cross-compiling (where
26633 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
26634 programs that run on another machine---the @dfn{target}).
26635 You specify a cross-debugging target by
26636 giving the @samp{--target=@var{target}} option to @file{configure}.
26638 When you run @code{make} to build a program or library, you must run
26639 it in a configured directory---whatever directory you were in when you
26640 called @file{configure} (or one of its subdirectories).
26642 The @code{Makefile} that @file{configure} generates in each source
26643 directory also runs recursively. If you type @code{make} in a source
26644 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
26645 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
26646 will build all the required libraries, and then build GDB.
26648 When you have multiple hosts or targets configured in separate
26649 directories, you can run @code{make} on them in parallel (for example,
26650 if they are NFS-mounted on each of the hosts); they will not interfere
26654 @section Specifying Names for Hosts and Targets
26656 The specifications used for hosts and targets in the @file{configure}
26657 script are based on a three-part naming scheme, but some short predefined
26658 aliases are also supported. The full naming scheme encodes three pieces
26659 of information in the following pattern:
26662 @var{architecture}-@var{vendor}-@var{os}
26665 For example, you can use the alias @code{sun4} as a @var{host} argument,
26666 or as the value for @var{target} in a @code{--target=@var{target}}
26667 option. The equivalent full name is @samp{sparc-sun-sunos4}.
26669 The @file{configure} script accompanying @value{GDBN} does not provide
26670 any query facility to list all supported host and target names or
26671 aliases. @file{configure} calls the Bourne shell script
26672 @code{config.sub} to map abbreviations to full names; you can read the
26673 script, if you wish, or you can use it to test your guesses on
26674 abbreviations---for example:
26677 % sh config.sub i386-linux
26679 % sh config.sub alpha-linux
26680 alpha-unknown-linux-gnu
26681 % sh config.sub hp9k700
26683 % sh config.sub sun4
26684 sparc-sun-sunos4.1.1
26685 % sh config.sub sun3
26686 m68k-sun-sunos4.1.1
26687 % sh config.sub i986v
26688 Invalid configuration `i986v': machine `i986v' not recognized
26692 @code{config.sub} is also distributed in the @value{GDBN} source
26693 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
26695 @node Configure Options
26696 @section @file{configure} Options
26698 Here is a summary of the @file{configure} options and arguments that
26699 are most often useful for building @value{GDBN}. @file{configure} also has
26700 several other options not listed here. @inforef{What Configure
26701 Does,,configure.info}, for a full explanation of @file{configure}.
26704 configure @r{[}--help@r{]}
26705 @r{[}--prefix=@var{dir}@r{]}
26706 @r{[}--exec-prefix=@var{dir}@r{]}
26707 @r{[}--srcdir=@var{dirname}@r{]}
26708 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
26709 @r{[}--target=@var{target}@r{]}
26714 You may introduce options with a single @samp{-} rather than
26715 @samp{--} if you prefer; but you may abbreviate option names if you use
26720 Display a quick summary of how to invoke @file{configure}.
26722 @item --prefix=@var{dir}
26723 Configure the source to install programs and files under directory
26726 @item --exec-prefix=@var{dir}
26727 Configure the source to install programs under directory
26730 @c avoid splitting the warning from the explanation:
26732 @item --srcdir=@var{dirname}
26733 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
26734 @code{make} that implements the @code{VPATH} feature.}@*
26735 Use this option to make configurations in directories separate from the
26736 @value{GDBN} source directories. Among other things, you can use this to
26737 build (or maintain) several configurations simultaneously, in separate
26738 directories. @file{configure} writes configuration-specific files in
26739 the current directory, but arranges for them to use the source in the
26740 directory @var{dirname}. @file{configure} creates directories under
26741 the working directory in parallel to the source directories below
26744 @item --norecursion
26745 Configure only the directory level where @file{configure} is executed; do not
26746 propagate configuration to subdirectories.
26748 @item --target=@var{target}
26749 Configure @value{GDBN} for cross-debugging programs running on the specified
26750 @var{target}. Without this option, @value{GDBN} is configured to debug
26751 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
26753 There is no convenient way to generate a list of all available targets.
26755 @item @var{host} @dots{}
26756 Configure @value{GDBN} to run on the specified @var{host}.
26758 There is no convenient way to generate a list of all available hosts.
26761 There are many other options available as well, but they are generally
26762 needed for special purposes only.
26764 @node System-wide configuration
26765 @section System-wide configuration and settings
26766 @cindex system-wide init file
26768 @value{GDBN} can be configured to have a system-wide init file;
26769 this file will be read and executed at startup (@pxref{Startup, , What
26770 @value{GDBN} does during startup}).
26772 Here is the corresponding configure option:
26775 @item --with-system-gdbinit=@var{file}
26776 Specify that the default location of the system-wide init file is
26780 If @value{GDBN} has been configured with the option @option{--prefix=$prefix},
26781 it may be subject to relocation. Two possible cases:
26785 If the default location of this init file contains @file{$prefix},
26786 it will be subject to relocation. Suppose that the configure options
26787 are @option{--prefix=$prefix --with-system-gdbinit=$prefix/etc/gdbinit};
26788 if @value{GDBN} is moved from @file{$prefix} to @file{$install}, the system
26789 init file is looked for as @file{$install/etc/gdbinit} instead of
26790 @file{$prefix/etc/gdbinit}.
26793 By contrast, if the default location does not contain the prefix,
26794 it will not be relocated. E.g.@: if @value{GDBN} has been configured with
26795 @option{--prefix=/usr/local --with-system-gdbinit=/usr/share/gdb/gdbinit},
26796 then @value{GDBN} will always look for @file{/usr/share/gdb/gdbinit},
26797 wherever @value{GDBN} is installed.
26800 @node Maintenance Commands
26801 @appendix Maintenance Commands
26802 @cindex maintenance commands
26803 @cindex internal commands
26805 In addition to commands intended for @value{GDBN} users, @value{GDBN}
26806 includes a number of commands intended for @value{GDBN} developers,
26807 that are not documented elsewhere in this manual. These commands are
26808 provided here for reference. (For commands that turn on debugging
26809 messages, see @ref{Debugging Output}.)
26812 @kindex maint agent
26813 @kindex maint agent-eval
26814 @item maint agent @var{expression}
26815 @itemx maint agent-eval @var{expression}
26816 Translate the given @var{expression} into remote agent bytecodes.
26817 This command is useful for debugging the Agent Expression mechanism
26818 (@pxref{Agent Expressions}). The @samp{agent} version produces an
26819 expression useful for data collection, such as by tracepoints, while
26820 @samp{maint agent-eval} produces an expression that evaluates directly
26821 to a result. For instance, a collection expression for @code{globa +
26822 globb} will include bytecodes to record four bytes of memory at each
26823 of the addresses of @code{globa} and @code{globb}, while discarding
26824 the result of the addition, while an evaluation expression will do the
26825 addition and return the sum.
26827 @kindex maint info breakpoints
26828 @item @anchor{maint info breakpoints}maint info breakpoints
26829 Using the same format as @samp{info breakpoints}, display both the
26830 breakpoints you've set explicitly, and those @value{GDBN} is using for
26831 internal purposes. Internal breakpoints are shown with negative
26832 breakpoint numbers. The type column identifies what kind of breakpoint
26837 Normal, explicitly set breakpoint.
26840 Normal, explicitly set watchpoint.
26843 Internal breakpoint, used to handle correctly stepping through
26844 @code{longjmp} calls.
26846 @item longjmp resume
26847 Internal breakpoint at the target of a @code{longjmp}.
26850 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
26853 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
26856 Shared library events.
26860 @kindex set displaced-stepping
26861 @kindex show displaced-stepping
26862 @cindex displaced stepping support
26863 @cindex out-of-line single-stepping
26864 @item set displaced-stepping
26865 @itemx show displaced-stepping
26866 Control whether or not @value{GDBN} will do @dfn{displaced stepping}
26867 if the target supports it. Displaced stepping is a way to single-step
26868 over breakpoints without removing them from the inferior, by executing
26869 an out-of-line copy of the instruction that was originally at the
26870 breakpoint location. It is also known as out-of-line single-stepping.
26873 @item set displaced-stepping on
26874 If the target architecture supports it, @value{GDBN} will use
26875 displaced stepping to step over breakpoints.
26877 @item set displaced-stepping off
26878 @value{GDBN} will not use displaced stepping to step over breakpoints,
26879 even if such is supported by the target architecture.
26881 @cindex non-stop mode, and @samp{set displaced-stepping}
26882 @item set displaced-stepping auto
26883 This is the default mode. @value{GDBN} will use displaced stepping
26884 only if non-stop mode is active (@pxref{Non-Stop Mode}) and the target
26885 architecture supports displaced stepping.
26888 @kindex maint check-symtabs
26889 @item maint check-symtabs
26890 Check the consistency of psymtabs and symtabs.
26892 @kindex maint cplus first_component
26893 @item maint cplus first_component @var{name}
26894 Print the first C@t{++} class/namespace component of @var{name}.
26896 @kindex maint cplus namespace
26897 @item maint cplus namespace
26898 Print the list of possible C@t{++} namespaces.
26900 @kindex maint demangle
26901 @item maint demangle @var{name}
26902 Demangle a C@t{++} or Objective-C mangled @var{name}.
26904 @kindex maint deprecate
26905 @kindex maint undeprecate
26906 @cindex deprecated commands
26907 @item maint deprecate @var{command} @r{[}@var{replacement}@r{]}
26908 @itemx maint undeprecate @var{command}
26909 Deprecate or undeprecate the named @var{command}. Deprecated commands
26910 cause @value{GDBN} to issue a warning when you use them. The optional
26911 argument @var{replacement} says which newer command should be used in
26912 favor of the deprecated one; if it is given, @value{GDBN} will mention
26913 the replacement as part of the warning.
26915 @kindex maint dump-me
26916 @item maint dump-me
26917 @cindex @code{SIGQUIT} signal, dump core of @value{GDBN}
26918 Cause a fatal signal in the debugger and force it to dump its core.
26919 This is supported only on systems which support aborting a program
26920 with the @code{SIGQUIT} signal.
26922 @kindex maint internal-error
26923 @kindex maint internal-warning
26924 @item maint internal-error @r{[}@var{message-text}@r{]}
26925 @itemx maint internal-warning @r{[}@var{message-text}@r{]}
26926 Cause @value{GDBN} to call the internal function @code{internal_error}
26927 or @code{internal_warning} and hence behave as though an internal error
26928 or internal warning has been detected. In addition to reporting the
26929 internal problem, these functions give the user the opportunity to
26930 either quit @value{GDBN} or create a core file of the current
26931 @value{GDBN} session.
26933 These commands take an optional parameter @var{message-text} that is
26934 used as the text of the error or warning message.
26936 Here's an example of using @code{internal-error}:
26939 (@value{GDBP}) @kbd{maint internal-error testing, 1, 2}
26940 @dots{}/maint.c:121: internal-error: testing, 1, 2
26941 A problem internal to GDB has been detected. Further
26942 debugging may prove unreliable.
26943 Quit this debugging session? (y or n) @kbd{n}
26944 Create a core file? (y or n) @kbd{n}
26948 @cindex @value{GDBN} internal error
26949 @cindex internal errors, control of @value{GDBN} behavior
26951 @kindex maint set internal-error
26952 @kindex maint show internal-error
26953 @kindex maint set internal-warning
26954 @kindex maint show internal-warning
26955 @item maint set internal-error @var{action} [ask|yes|no]
26956 @itemx maint show internal-error @var{action}
26957 @itemx maint set internal-warning @var{action} [ask|yes|no]
26958 @itemx maint show internal-warning @var{action}
26959 When @value{GDBN} reports an internal problem (error or warning) it
26960 gives the user the opportunity to both quit @value{GDBN} and create a
26961 core file of the current @value{GDBN} session. These commands let you
26962 override the default behaviour for each particular @var{action},
26963 described in the table below.
26967 You can specify that @value{GDBN} should always (yes) or never (no)
26968 quit. The default is to ask the user what to do.
26971 You can specify that @value{GDBN} should always (yes) or never (no)
26972 create a core file. The default is to ask the user what to do.
26975 @kindex maint packet
26976 @item maint packet @var{text}
26977 If @value{GDBN} is talking to an inferior via the serial protocol,
26978 then this command sends the string @var{text} to the inferior, and
26979 displays the response packet. @value{GDBN} supplies the initial
26980 @samp{$} character, the terminating @samp{#} character, and the
26983 @kindex maint print architecture
26984 @item maint print architecture @r{[}@var{file}@r{]}
26985 Print the entire architecture configuration. The optional argument
26986 @var{file} names the file where the output goes.
26988 @kindex maint print c-tdesc
26989 @item maint print c-tdesc
26990 Print the current target description (@pxref{Target Descriptions}) as
26991 a C source file. The created source file can be used in @value{GDBN}
26992 when an XML parser is not available to parse the description.
26994 @kindex maint print dummy-frames
26995 @item maint print dummy-frames
26996 Prints the contents of @value{GDBN}'s internal dummy-frame stack.
26999 (@value{GDBP}) @kbd{b add}
27001 (@value{GDBP}) @kbd{print add(2,3)}
27002 Breakpoint 2, add (a=2, b=3) at @dots{}
27004 The program being debugged stopped while in a function called from GDB.
27006 (@value{GDBP}) @kbd{maint print dummy-frames}
27007 0x1a57c80: pc=0x01014068 fp=0x0200bddc sp=0x0200bdd6
27008 top=0x0200bdd4 id=@{stack=0x200bddc,code=0x101405c@}
27009 call_lo=0x01014000 call_hi=0x01014001
27013 Takes an optional file parameter.
27015 @kindex maint print registers
27016 @kindex maint print raw-registers
27017 @kindex maint print cooked-registers
27018 @kindex maint print register-groups
27019 @item maint print registers @r{[}@var{file}@r{]}
27020 @itemx maint print raw-registers @r{[}@var{file}@r{]}
27021 @itemx maint print cooked-registers @r{[}@var{file}@r{]}
27022 @itemx maint print register-groups @r{[}@var{file}@r{]}
27023 Print @value{GDBN}'s internal register data structures.
27025 The command @code{maint print raw-registers} includes the contents of
27026 the raw register cache; the command @code{maint print cooked-registers}
27027 includes the (cooked) value of all registers; and the command
27028 @code{maint print register-groups} includes the groups that each
27029 register is a member of. @xref{Registers,, Registers, gdbint,
27030 @value{GDBN} Internals}.
27032 These commands take an optional parameter, a file name to which to
27033 write the information.
27035 @kindex maint print reggroups
27036 @item maint print reggroups @r{[}@var{file}@r{]}
27037 Print @value{GDBN}'s internal register group data structures. The
27038 optional argument @var{file} tells to what file to write the
27041 The register groups info looks like this:
27044 (@value{GDBP}) @kbd{maint print reggroups}
27057 This command forces @value{GDBN} to flush its internal register cache.
27059 @kindex maint print objfiles
27060 @cindex info for known object files
27061 @item maint print objfiles
27062 Print a dump of all known object files. For each object file, this
27063 command prints its name, address in memory, and all of its psymtabs
27066 @kindex maint print statistics
27067 @cindex bcache statistics
27068 @item maint print statistics
27069 This command prints, for each object file in the program, various data
27070 about that object file followed by the byte cache (@dfn{bcache})
27071 statistics for the object file. The objfile data includes the number
27072 of minimal, partial, full, and stabs symbols, the number of types
27073 defined by the objfile, the number of as yet unexpanded psym tables,
27074 the number of line tables and string tables, and the amount of memory
27075 used by the various tables. The bcache statistics include the counts,
27076 sizes, and counts of duplicates of all and unique objects, max,
27077 average, and median entry size, total memory used and its overhead and
27078 savings, and various measures of the hash table size and chain
27081 @kindex maint print target-stack
27082 @cindex target stack description
27083 @item maint print target-stack
27084 A @dfn{target} is an interface between the debugger and a particular
27085 kind of file or process. Targets can be stacked in @dfn{strata},
27086 so that more than one target can potentially respond to a request.
27087 In particular, memory accesses will walk down the stack of targets
27088 until they find a target that is interested in handling that particular
27091 This command prints a short description of each layer that was pushed on
27092 the @dfn{target stack}, starting from the top layer down to the bottom one.
27094 @kindex maint print type
27095 @cindex type chain of a data type
27096 @item maint print type @var{expr}
27097 Print the type chain for a type specified by @var{expr}. The argument
27098 can be either a type name or a symbol. If it is a symbol, the type of
27099 that symbol is described. The type chain produced by this command is
27100 a recursive definition of the data type as stored in @value{GDBN}'s
27101 data structures, including its flags and contained types.
27103 @kindex maint set dwarf2 max-cache-age
27104 @kindex maint show dwarf2 max-cache-age
27105 @item maint set dwarf2 max-cache-age
27106 @itemx maint show dwarf2 max-cache-age
27107 Control the DWARF 2 compilation unit cache.
27109 @cindex DWARF 2 compilation units cache
27110 In object files with inter-compilation-unit references, such as those
27111 produced by the GCC option @samp{-feliminate-dwarf2-dups}, the DWARF 2
27112 reader needs to frequently refer to previously read compilation units.
27113 This setting controls how long a compilation unit will remain in the
27114 cache if it is not referenced. A higher limit means that cached
27115 compilation units will be stored in memory longer, and more total
27116 memory will be used. Setting it to zero disables caching, which will
27117 slow down @value{GDBN} startup, but reduce memory consumption.
27119 @kindex maint set profile
27120 @kindex maint show profile
27121 @cindex profiling GDB
27122 @item maint set profile
27123 @itemx maint show profile
27124 Control profiling of @value{GDBN}.
27126 Profiling will be disabled until you use the @samp{maint set profile}
27127 command to enable it. When you enable profiling, the system will begin
27128 collecting timing and execution count data; when you disable profiling or
27129 exit @value{GDBN}, the results will be written to a log file. Remember that
27130 if you use profiling, @value{GDBN} will overwrite the profiling log file
27131 (often called @file{gmon.out}). If you have a record of important profiling
27132 data in a @file{gmon.out} file, be sure to move it to a safe location.
27134 Configuring with @samp{--enable-profiling} arranges for @value{GDBN} to be
27135 compiled with the @samp{-pg} compiler option.
27137 @kindex maint set show-debug-regs
27138 @kindex maint show show-debug-regs
27139 @cindex hardware debug registers
27140 @item maint set show-debug-regs
27141 @itemx maint show show-debug-regs
27142 Control whether to show variables that mirror the hardware debug
27143 registers. Use @code{ON} to enable, @code{OFF} to disable. If
27144 enabled, the debug registers values are shown when @value{GDBN} inserts or
27145 removes a hardware breakpoint or watchpoint, and when the inferior
27146 triggers a hardware-assisted breakpoint or watchpoint.
27148 @kindex maint space
27149 @cindex memory used by commands
27151 Control whether to display memory usage for each command. If set to a
27152 nonzero value, @value{GDBN} will display how much memory each command
27153 took, following the command's own output. This can also be requested
27154 by invoking @value{GDBN} with the @option{--statistics} command-line
27155 switch (@pxref{Mode Options}).
27158 @cindex time of command execution
27160 Control whether to display the execution time for each command. If
27161 set to a nonzero value, @value{GDBN} will display how much time it
27162 took to execute each command, following the command's own output.
27163 The time is not printed for the commands that run the target, since
27164 there's no mechanism currently to compute how much time was spend
27165 by @value{GDBN} and how much time was spend by the program been debugged.
27166 it's not possibly currently
27167 This can also be requested by invoking @value{GDBN} with the
27168 @option{--statistics} command-line switch (@pxref{Mode Options}).
27170 @kindex maint translate-address
27171 @item maint translate-address @r{[}@var{section}@r{]} @var{addr}
27172 Find the symbol stored at the location specified by the address
27173 @var{addr} and an optional section name @var{section}. If found,
27174 @value{GDBN} prints the name of the closest symbol and an offset from
27175 the symbol's location to the specified address. This is similar to
27176 the @code{info address} command (@pxref{Symbols}), except that this
27177 command also allows to find symbols in other sections.
27179 If section was not specified, the section in which the symbol was found
27180 is also printed. For dynamically linked executables, the name of
27181 executable or shared library containing the symbol is printed as well.
27185 The following command is useful for non-interactive invocations of
27186 @value{GDBN}, such as in the test suite.
27189 @item set watchdog @var{nsec}
27190 @kindex set watchdog
27191 @cindex watchdog timer
27192 @cindex timeout for commands
27193 Set the maximum number of seconds @value{GDBN} will wait for the
27194 target operation to finish. If this time expires, @value{GDBN}
27195 reports and error and the command is aborted.
27197 @item show watchdog
27198 Show the current setting of the target wait timeout.
27201 @node Remote Protocol
27202 @appendix @value{GDBN} Remote Serial Protocol
27207 * Stop Reply Packets::
27208 * General Query Packets::
27209 * Register Packet Format::
27210 * Tracepoint Packets::
27211 * Host I/O Packets::
27213 * Notification Packets::
27214 * Remote Non-Stop::
27215 * Packet Acknowledgment::
27217 * File-I/O Remote Protocol Extension::
27218 * Library List Format::
27219 * Memory Map Format::
27225 There may be occasions when you need to know something about the
27226 protocol---for example, if there is only one serial port to your target
27227 machine, you might want your program to do something special if it
27228 recognizes a packet meant for @value{GDBN}.
27230 In the examples below, @samp{->} and @samp{<-} are used to indicate
27231 transmitted and received data, respectively.
27233 @cindex protocol, @value{GDBN} remote serial
27234 @cindex serial protocol, @value{GDBN} remote
27235 @cindex remote serial protocol
27236 All @value{GDBN} commands and responses (other than acknowledgments
27237 and notifications, see @ref{Notification Packets}) are sent as a
27238 @var{packet}. A @var{packet} is introduced with the character
27239 @samp{$}, the actual @var{packet-data}, and the terminating character
27240 @samp{#} followed by a two-digit @var{checksum}:
27243 @code{$}@var{packet-data}@code{#}@var{checksum}
27247 @cindex checksum, for @value{GDBN} remote
27249 The two-digit @var{checksum} is computed as the modulo 256 sum of all
27250 characters between the leading @samp{$} and the trailing @samp{#} (an
27251 eight bit unsigned checksum).
27253 Implementors should note that prior to @value{GDBN} 5.0 the protocol
27254 specification also included an optional two-digit @var{sequence-id}:
27257 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
27260 @cindex sequence-id, for @value{GDBN} remote
27262 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
27263 has never output @var{sequence-id}s. Stubs that handle packets added
27264 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
27266 When either the host or the target machine receives a packet, the first
27267 response expected is an acknowledgment: either @samp{+} (to indicate
27268 the package was received correctly) or @samp{-} (to request
27272 -> @code{$}@var{packet-data}@code{#}@var{checksum}
27277 The @samp{+}/@samp{-} acknowledgments can be disabled
27278 once a connection is established.
27279 @xref{Packet Acknowledgment}, for details.
27281 The host (@value{GDBN}) sends @var{command}s, and the target (the
27282 debugging stub incorporated in your program) sends a @var{response}. In
27283 the case of step and continue @var{command}s, the response is only sent
27284 when the operation has completed, and the target has again stopped all
27285 threads in all attached processes. This is the default all-stop mode
27286 behavior, but the remote protocol also supports @value{GDBN}'s non-stop
27287 execution mode; see @ref{Remote Non-Stop}, for details.
27289 @var{packet-data} consists of a sequence of characters with the
27290 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
27293 @cindex remote protocol, field separator
27294 Fields within the packet should be separated using @samp{,} @samp{;} or
27295 @samp{:}. Except where otherwise noted all numbers are represented in
27296 @sc{hex} with leading zeros suppressed.
27298 Implementors should note that prior to @value{GDBN} 5.0, the character
27299 @samp{:} could not appear as the third character in a packet (as it
27300 would potentially conflict with the @var{sequence-id}).
27302 @cindex remote protocol, binary data
27303 @anchor{Binary Data}
27304 Binary data in most packets is encoded either as two hexadecimal
27305 digits per byte of binary data. This allowed the traditional remote
27306 protocol to work over connections which were only seven-bit clean.
27307 Some packets designed more recently assume an eight-bit clean
27308 connection, and use a more efficient encoding to send and receive
27311 The binary data representation uses @code{7d} (@sc{ascii} @samp{@}})
27312 as an escape character. Any escaped byte is transmitted as the escape
27313 character followed by the original character XORed with @code{0x20}.
27314 For example, the byte @code{0x7d} would be transmitted as the two
27315 bytes @code{0x7d 0x5d}. The bytes @code{0x23} (@sc{ascii} @samp{#}),
27316 @code{0x24} (@sc{ascii} @samp{$}), and @code{0x7d} (@sc{ascii}
27317 @samp{@}}) must always be escaped. Responses sent by the stub
27318 must also escape @code{0x2a} (@sc{ascii} @samp{*}), so that it
27319 is not interpreted as the start of a run-length encoded sequence
27322 Response @var{data} can be run-length encoded to save space.
27323 Run-length encoding replaces runs of identical characters with one
27324 instance of the repeated character, followed by a @samp{*} and a
27325 repeat count. The repeat count is itself sent encoded, to avoid
27326 binary characters in @var{data}: a value of @var{n} is sent as
27327 @code{@var{n}+29}. For a repeat count greater or equal to 3, this
27328 produces a printable @sc{ascii} character, e.g.@: a space (@sc{ascii}
27329 code 32) for a repeat count of 3. (This is because run-length
27330 encoding starts to win for counts 3 or more.) Thus, for example,
27331 @samp{0* } is a run-length encoding of ``0000'': the space character
27332 after @samp{*} means repeat the leading @code{0} @w{@code{32 - 29 =
27335 The printable characters @samp{#} and @samp{$} or with a numeric value
27336 greater than 126 must not be used. Runs of six repeats (@samp{#}) or
27337 seven repeats (@samp{$}) can be expanded using a repeat count of only
27338 five (@samp{"}). For example, @samp{00000000} can be encoded as
27341 The error response returned for some packets includes a two character
27342 error number. That number is not well defined.
27344 @cindex empty response, for unsupported packets
27345 For any @var{command} not supported by the stub, an empty response
27346 (@samp{$#00}) should be returned. That way it is possible to extend the
27347 protocol. A newer @value{GDBN} can tell if a packet is supported based
27350 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
27351 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
27357 The following table provides a complete list of all currently defined
27358 @var{command}s and their corresponding response @var{data}.
27359 @xref{File-I/O Remote Protocol Extension}, for details about the File
27360 I/O extension of the remote protocol.
27362 Each packet's description has a template showing the packet's overall
27363 syntax, followed by an explanation of the packet's meaning. We
27364 include spaces in some of the templates for clarity; these are not
27365 part of the packet's syntax. No @value{GDBN} packet uses spaces to
27366 separate its components. For example, a template like @samp{foo
27367 @var{bar} @var{baz}} describes a packet beginning with the three ASCII
27368 bytes @samp{foo}, followed by a @var{bar}, followed directly by a
27369 @var{baz}. @value{GDBN} does not transmit a space character between the
27370 @samp{foo} and the @var{bar}, or between the @var{bar} and the
27373 @cindex @var{thread-id}, in remote protocol
27374 @anchor{thread-id syntax}
27375 Several packets and replies include a @var{thread-id} field to identify
27376 a thread. Normally these are positive numbers with a target-specific
27377 interpretation, formatted as big-endian hex strings. A @var{thread-id}
27378 can also be a literal @samp{-1} to indicate all threads, or @samp{0} to
27381 In addition, the remote protocol supports a multiprocess feature in
27382 which the @var{thread-id} syntax is extended to optionally include both
27383 process and thread ID fields, as @samp{p@var{pid}.@var{tid}}.
27384 The @var{pid} (process) and @var{tid} (thread) components each have the
27385 format described above: a positive number with target-specific
27386 interpretation formatted as a big-endian hex string, literal @samp{-1}
27387 to indicate all processes or threads (respectively), or @samp{0} to
27388 indicate an arbitrary process or thread. Specifying just a process, as
27389 @samp{p@var{pid}}, is equivalent to @samp{p@var{pid}.-1}. It is an
27390 error to specify all processes but a specific thread, such as
27391 @samp{p-1.@var{tid}}. Note that the @samp{p} prefix is @emph{not} used
27392 for those packets and replies explicitly documented to include a process
27393 ID, rather than a @var{thread-id}.
27395 The multiprocess @var{thread-id} syntax extensions are only used if both
27396 @value{GDBN} and the stub report support for the @samp{multiprocess}
27397 feature using @samp{qSupported}. @xref{multiprocess extensions}, for
27400 Note that all packet forms beginning with an upper- or lower-case
27401 letter, other than those described here, are reserved for future use.
27403 Here are the packet descriptions.
27408 @cindex @samp{!} packet
27409 @anchor{extended mode}
27410 Enable extended mode. In extended mode, the remote server is made
27411 persistent. The @samp{R} packet is used to restart the program being
27417 The remote target both supports and has enabled extended mode.
27421 @cindex @samp{?} packet
27422 Indicate the reason the target halted. The reply is the same as for
27423 step and continue. This packet has a special interpretation when the
27424 target is in non-stop mode; see @ref{Remote Non-Stop}.
27427 @xref{Stop Reply Packets}, for the reply specifications.
27429 @item A @var{arglen},@var{argnum},@var{arg},@dots{}
27430 @cindex @samp{A} packet
27431 Initialized @code{argv[]} array passed into program. @var{arglen}
27432 specifies the number of bytes in the hex encoded byte stream
27433 @var{arg}. See @code{gdbserver} for more details.
27438 The arguments were set.
27444 @cindex @samp{b} packet
27445 (Don't use this packet; its behavior is not well-defined.)
27446 Change the serial line speed to @var{baud}.
27448 JTC: @emph{When does the transport layer state change? When it's
27449 received, or after the ACK is transmitted. In either case, there are
27450 problems if the command or the acknowledgment packet is dropped.}
27452 Stan: @emph{If people really wanted to add something like this, and get
27453 it working for the first time, they ought to modify ser-unix.c to send
27454 some kind of out-of-band message to a specially-setup stub and have the
27455 switch happen "in between" packets, so that from remote protocol's point
27456 of view, nothing actually happened.}
27458 @item B @var{addr},@var{mode}
27459 @cindex @samp{B} packet
27460 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
27461 breakpoint at @var{addr}.
27463 Don't use this packet. Use the @samp{Z} and @samp{z} packets instead
27464 (@pxref{insert breakpoint or watchpoint packet}).
27467 @cindex @samp{bc} packet
27468 Backward continue. Execute the target system in reverse. No parameter.
27469 @xref{Reverse Execution}, for more information.
27472 @xref{Stop Reply Packets}, for the reply specifications.
27475 @cindex @samp{bs} packet
27476 Backward single step. Execute one instruction in reverse. No parameter.
27477 @xref{Reverse Execution}, for more information.
27480 @xref{Stop Reply Packets}, for the reply specifications.
27482 @item c @r{[}@var{addr}@r{]}
27483 @cindex @samp{c} packet
27484 Continue. @var{addr} is address to resume. If @var{addr} is omitted,
27485 resume at current address.
27488 @xref{Stop Reply Packets}, for the reply specifications.
27490 @item C @var{sig}@r{[};@var{addr}@r{]}
27491 @cindex @samp{C} packet
27492 Continue with signal @var{sig} (hex signal number). If
27493 @samp{;@var{addr}} is omitted, resume at same address.
27496 @xref{Stop Reply Packets}, for the reply specifications.
27499 @cindex @samp{d} packet
27502 Don't use this packet; instead, define a general set packet
27503 (@pxref{General Query Packets}).
27507 @cindex @samp{D} packet
27508 The first form of the packet is used to detach @value{GDBN} from the
27509 remote system. It is sent to the remote target
27510 before @value{GDBN} disconnects via the @code{detach} command.
27512 The second form, including a process ID, is used when multiprocess
27513 protocol extensions are enabled (@pxref{multiprocess extensions}), to
27514 detach only a specific process. The @var{pid} is specified as a
27515 big-endian hex string.
27525 @item F @var{RC},@var{EE},@var{CF};@var{XX}
27526 @cindex @samp{F} packet
27527 A reply from @value{GDBN} to an @samp{F} packet sent by the target.
27528 This is part of the File-I/O protocol extension. @xref{File-I/O
27529 Remote Protocol Extension}, for the specification.
27532 @anchor{read registers packet}
27533 @cindex @samp{g} packet
27534 Read general registers.
27538 @item @var{XX@dots{}}
27539 Each byte of register data is described by two hex digits. The bytes
27540 with the register are transmitted in target byte order. The size of
27541 each register and their position within the @samp{g} packet are
27542 determined by the @value{GDBN} internal gdbarch functions
27543 @code{DEPRECATED_REGISTER_RAW_SIZE} and @code{gdbarch_register_name}. The
27544 specification of several standard @samp{g} packets is specified below.
27549 @item G @var{XX@dots{}}
27550 @cindex @samp{G} packet
27551 Write general registers. @xref{read registers packet}, for a
27552 description of the @var{XX@dots{}} data.
27562 @item H @var{c} @var{thread-id}
27563 @cindex @samp{H} packet
27564 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
27565 @samp{G}, et.al.). @var{c} depends on the operation to be performed: it
27566 should be @samp{c} for step and continue operations, @samp{g} for other
27567 operations. The thread designator @var{thread-id} has the format and
27568 interpretation described in @ref{thread-id syntax}.
27579 @c 'H': How restrictive (or permissive) is the thread model. If a
27580 @c thread is selected and stopped, are other threads allowed
27581 @c to continue to execute? As I mentioned above, I think the
27582 @c semantics of each command when a thread is selected must be
27583 @c described. For example:
27585 @c 'g': If the stub supports threads and a specific thread is
27586 @c selected, returns the register block from that thread;
27587 @c otherwise returns current registers.
27589 @c 'G' If the stub supports threads and a specific thread is
27590 @c selected, sets the registers of the register block of
27591 @c that thread; otherwise sets current registers.
27593 @item i @r{[}@var{addr}@r{[},@var{nnn}@r{]]}
27594 @anchor{cycle step packet}
27595 @cindex @samp{i} packet
27596 Step the remote target by a single clock cycle. If @samp{,@var{nnn}} is
27597 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
27598 step starting at that address.
27601 @cindex @samp{I} packet
27602 Signal, then cycle step. @xref{step with signal packet}. @xref{cycle
27606 @cindex @samp{k} packet
27609 FIXME: @emph{There is no description of how to operate when a specific
27610 thread context has been selected (i.e.@: does 'k' kill only that
27613 @item m @var{addr},@var{length}
27614 @cindex @samp{m} packet
27615 Read @var{length} bytes of memory starting at address @var{addr}.
27616 Note that @var{addr} may not be aligned to any particular boundary.
27618 The stub need not use any particular size or alignment when gathering
27619 data from memory for the response; even if @var{addr} is word-aligned
27620 and @var{length} is a multiple of the word size, the stub is free to
27621 use byte accesses, or not. For this reason, this packet may not be
27622 suitable for accessing memory-mapped I/O devices.
27623 @cindex alignment of remote memory accesses
27624 @cindex size of remote memory accesses
27625 @cindex memory, alignment and size of remote accesses
27629 @item @var{XX@dots{}}
27630 Memory contents; each byte is transmitted as a two-digit hexadecimal
27631 number. The reply may contain fewer bytes than requested if the
27632 server was able to read only part of the region of memory.
27637 @item M @var{addr},@var{length}:@var{XX@dots{}}
27638 @cindex @samp{M} packet
27639 Write @var{length} bytes of memory starting at address @var{addr}.
27640 @var{XX@dots{}} is the data; each byte is transmitted as a two-digit
27641 hexadecimal number.
27648 for an error (this includes the case where only part of the data was
27653 @cindex @samp{p} packet
27654 Read the value of register @var{n}; @var{n} is in hex.
27655 @xref{read registers packet}, for a description of how the returned
27656 register value is encoded.
27660 @item @var{XX@dots{}}
27661 the register's value
27665 Indicating an unrecognized @var{query}.
27668 @item P @var{n@dots{}}=@var{r@dots{}}
27669 @anchor{write register packet}
27670 @cindex @samp{P} packet
27671 Write register @var{n@dots{}} with value @var{r@dots{}}. The register
27672 number @var{n} is in hexadecimal, and @var{r@dots{}} contains two hex
27673 digits for each byte in the register (target byte order).
27683 @item q @var{name} @var{params}@dots{}
27684 @itemx Q @var{name} @var{params}@dots{}
27685 @cindex @samp{q} packet
27686 @cindex @samp{Q} packet
27687 General query (@samp{q}) and set (@samp{Q}). These packets are
27688 described fully in @ref{General Query Packets}.
27691 @cindex @samp{r} packet
27692 Reset the entire system.
27694 Don't use this packet; use the @samp{R} packet instead.
27697 @cindex @samp{R} packet
27698 Restart the program being debugged. @var{XX}, while needed, is ignored.
27699 This packet is only available in extended mode (@pxref{extended mode}).
27701 The @samp{R} packet has no reply.
27703 @item s @r{[}@var{addr}@r{]}
27704 @cindex @samp{s} packet
27705 Single step. @var{addr} is the address at which to resume. If
27706 @var{addr} is omitted, resume at same address.
27709 @xref{Stop Reply Packets}, for the reply specifications.
27711 @item S @var{sig}@r{[};@var{addr}@r{]}
27712 @anchor{step with signal packet}
27713 @cindex @samp{S} packet
27714 Step with signal. This is analogous to the @samp{C} packet, but
27715 requests a single-step, rather than a normal resumption of execution.
27718 @xref{Stop Reply Packets}, for the reply specifications.
27720 @item t @var{addr}:@var{PP},@var{MM}
27721 @cindex @samp{t} packet
27722 Search backwards starting at address @var{addr} for a match with pattern
27723 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4 bytes.
27724 @var{addr} must be at least 3 digits.
27726 @item T @var{thread-id}
27727 @cindex @samp{T} packet
27728 Find out if the thread @var{thread-id} is alive. @xref{thread-id syntax}.
27733 thread is still alive
27739 Packets starting with @samp{v} are identified by a multi-letter name,
27740 up to the first @samp{;} or @samp{?} (or the end of the packet).
27742 @item vAttach;@var{pid}
27743 @cindex @samp{vAttach} packet
27744 Attach to a new process with the specified process ID @var{pid}.
27745 The process ID is a
27746 hexadecimal integer identifying the process. In all-stop mode, all
27747 threads in the attached process are stopped; in non-stop mode, it may be
27748 attached without being stopped if that is supported by the target.
27750 @c In non-stop mode, on a successful vAttach, the stub should set the
27751 @c current thread to a thread of the newly-attached process. After
27752 @c attaching, GDB queries for the attached process's thread ID with qC.
27753 @c Also note that, from a user perspective, whether or not the
27754 @c target is stopped on attach in non-stop mode depends on whether you
27755 @c use the foreground or background version of the attach command, not
27756 @c on what vAttach does; GDB does the right thing with respect to either
27757 @c stopping or restarting threads.
27759 This packet is only available in extended mode (@pxref{extended mode}).
27765 @item @r{Any stop packet}
27766 for success in all-stop mode (@pxref{Stop Reply Packets})
27768 for success in non-stop mode (@pxref{Remote Non-Stop})
27771 @item vCont@r{[};@var{action}@r{[}:@var{thread-id}@r{]]}@dots{}
27772 @cindex @samp{vCont} packet
27773 Resume the inferior, specifying different actions for each thread.
27774 If an action is specified with no @var{thread-id}, then it is applied to any
27775 threads that don't have a specific action specified; if no default action is
27776 specified then other threads should remain stopped in all-stop mode and
27777 in their current state in non-stop mode.
27778 Specifying multiple
27779 default actions is an error; specifying no actions is also an error.
27780 Thread IDs are specified using the syntax described in @ref{thread-id syntax}.
27782 Currently supported actions are:
27788 Continue with signal @var{sig}. The signal @var{sig} should be two hex digits.
27792 Step with signal @var{sig}. The signal @var{sig} should be two hex digits.
27796 Stop with signal @var{sig}. The signal @var{sig} should be two hex digits.
27799 The optional argument @var{addr} normally associated with the
27800 @samp{c}, @samp{C}, @samp{s}, and @samp{S} packets is
27801 not supported in @samp{vCont}.
27803 The @samp{t} and @samp{T} actions are only relevant in non-stop mode
27804 (@pxref{Remote Non-Stop}) and may be ignored by the stub otherwise.
27805 A stop reply should be generated for any affected thread not already stopped.
27806 When a thread is stopped by means of a @samp{t} action,
27807 the corresponding stop reply should indicate that the thread has stopped with
27808 signal @samp{0}, regardless of whether the target uses some other signal
27809 as an implementation detail.
27812 @xref{Stop Reply Packets}, for the reply specifications.
27815 @cindex @samp{vCont?} packet
27816 Request a list of actions supported by the @samp{vCont} packet.
27820 @item vCont@r{[};@var{action}@dots{}@r{]}
27821 The @samp{vCont} packet is supported. Each @var{action} is a supported
27822 command in the @samp{vCont} packet.
27824 The @samp{vCont} packet is not supported.
27827 @item vFile:@var{operation}:@var{parameter}@dots{}
27828 @cindex @samp{vFile} packet
27829 Perform a file operation on the target system. For details,
27830 see @ref{Host I/O Packets}.
27832 @item vFlashErase:@var{addr},@var{length}
27833 @cindex @samp{vFlashErase} packet
27834 Direct the stub to erase @var{length} bytes of flash starting at
27835 @var{addr}. The region may enclose any number of flash blocks, but
27836 its start and end must fall on block boundaries, as indicated by the
27837 flash block size appearing in the memory map (@pxref{Memory Map
27838 Format}). @value{GDBN} groups flash memory programming operations
27839 together, and sends a @samp{vFlashDone} request after each group; the
27840 stub is allowed to delay erase operation until the @samp{vFlashDone}
27841 packet is received.
27843 The stub must support @samp{vCont} if it reports support for
27844 multiprocess extensions (@pxref{multiprocess extensions}). Note that in
27845 this case @samp{vCont} actions can be specified to apply to all threads
27846 in a process by using the @samp{p@var{pid}.-1} form of the
27857 @item vFlashWrite:@var{addr}:@var{XX@dots{}}
27858 @cindex @samp{vFlashWrite} packet
27859 Direct the stub to write data to flash address @var{addr}. The data
27860 is passed in binary form using the same encoding as for the @samp{X}
27861 packet (@pxref{Binary Data}). The memory ranges specified by
27862 @samp{vFlashWrite} packets preceding a @samp{vFlashDone} packet must
27863 not overlap, and must appear in order of increasing addresses
27864 (although @samp{vFlashErase} packets for higher addresses may already
27865 have been received; the ordering is guaranteed only between
27866 @samp{vFlashWrite} packets). If a packet writes to an address that was
27867 neither erased by a preceding @samp{vFlashErase} packet nor by some other
27868 target-specific method, the results are unpredictable.
27876 for vFlashWrite addressing non-flash memory
27882 @cindex @samp{vFlashDone} packet
27883 Indicate to the stub that flash programming operation is finished.
27884 The stub is permitted to delay or batch the effects of a group of
27885 @samp{vFlashErase} and @samp{vFlashWrite} packets until a
27886 @samp{vFlashDone} packet is received. The contents of the affected
27887 regions of flash memory are unpredictable until the @samp{vFlashDone}
27888 request is completed.
27890 @item vKill;@var{pid}
27891 @cindex @samp{vKill} packet
27892 Kill the process with the specified process ID. @var{pid} is a
27893 hexadecimal integer identifying the process. This packet is used in
27894 preference to @samp{k} when multiprocess protocol extensions are
27895 supported; see @ref{multiprocess extensions}.
27905 @item vRun;@var{filename}@r{[};@var{argument}@r{]}@dots{}
27906 @cindex @samp{vRun} packet
27907 Run the program @var{filename}, passing it each @var{argument} on its
27908 command line. The file and arguments are hex-encoded strings. If
27909 @var{filename} is an empty string, the stub may use a default program
27910 (e.g.@: the last program run). The program is created in the stopped
27913 @c FIXME: What about non-stop mode?
27915 This packet is only available in extended mode (@pxref{extended mode}).
27921 @item @r{Any stop packet}
27922 for success (@pxref{Stop Reply Packets})
27926 @anchor{vStopped packet}
27927 @cindex @samp{vStopped} packet
27929 In non-stop mode (@pxref{Remote Non-Stop}), acknowledge a previous stop
27930 reply and prompt for the stub to report another one.
27934 @item @r{Any stop packet}
27935 if there is another unreported stop event (@pxref{Stop Reply Packets})
27937 if there are no unreported stop events
27940 @item X @var{addr},@var{length}:@var{XX@dots{}}
27942 @cindex @samp{X} packet
27943 Write data to memory, where the data is transmitted in binary.
27944 @var{addr} is address, @var{length} is number of bytes,
27945 @samp{@var{XX}@dots{}} is binary data (@pxref{Binary Data}).
27955 @item z @var{type},@var{addr},@var{length}
27956 @itemx Z @var{type},@var{addr},@var{length}
27957 @anchor{insert breakpoint or watchpoint packet}
27958 @cindex @samp{z} packet
27959 @cindex @samp{Z} packets
27960 Insert (@samp{Z}) or remove (@samp{z}) a @var{type} breakpoint or
27961 watchpoint starting at address @var{address} and covering the next
27962 @var{length} bytes.
27964 Each breakpoint and watchpoint packet @var{type} is documented
27967 @emph{Implementation notes: A remote target shall return an empty string
27968 for an unrecognized breakpoint or watchpoint packet @var{type}. A
27969 remote target shall support either both or neither of a given
27970 @samp{Z@var{type}@dots{}} and @samp{z@var{type}@dots{}} packet pair. To
27971 avoid potential problems with duplicate packets, the operations should
27972 be implemented in an idempotent way.}
27974 @item z0,@var{addr},@var{length}
27975 @itemx Z0,@var{addr},@var{length}
27976 @cindex @samp{z0} packet
27977 @cindex @samp{Z0} packet
27978 Insert (@samp{Z0}) or remove (@samp{z0}) a memory breakpoint at address
27979 @var{addr} of size @var{length}.
27981 A memory breakpoint is implemented by replacing the instruction at
27982 @var{addr} with a software breakpoint or trap instruction. The
27983 @var{length} is used by targets that indicates the size of the
27984 breakpoint (in bytes) that should be inserted (e.g., the @sc{arm} and
27985 @sc{mips} can insert either a 2 or 4 byte breakpoint).
27987 @emph{Implementation note: It is possible for a target to copy or move
27988 code that contains memory breakpoints (e.g., when implementing
27989 overlays). The behavior of this packet, in the presence of such a
27990 target, is not defined.}
28002 @item z1,@var{addr},@var{length}
28003 @itemx Z1,@var{addr},@var{length}
28004 @cindex @samp{z1} packet
28005 @cindex @samp{Z1} packet
28006 Insert (@samp{Z1}) or remove (@samp{z1}) a hardware breakpoint at
28007 address @var{addr} of size @var{length}.
28009 A hardware breakpoint is implemented using a mechanism that is not
28010 dependant on being able to modify the target's memory.
28012 @emph{Implementation note: A hardware breakpoint is not affected by code
28025 @item z2,@var{addr},@var{length}
28026 @itemx Z2,@var{addr},@var{length}
28027 @cindex @samp{z2} packet
28028 @cindex @samp{Z2} packet
28029 Insert (@samp{Z2}) or remove (@samp{z2}) a write watchpoint.
28041 @item z3,@var{addr},@var{length}
28042 @itemx Z3,@var{addr},@var{length}
28043 @cindex @samp{z3} packet
28044 @cindex @samp{Z3} packet
28045 Insert (@samp{Z3}) or remove (@samp{z3}) a read watchpoint.
28057 @item z4,@var{addr},@var{length}
28058 @itemx Z4,@var{addr},@var{length}
28059 @cindex @samp{z4} packet
28060 @cindex @samp{Z4} packet
28061 Insert (@samp{Z4}) or remove (@samp{z4}) an access watchpoint.
28075 @node Stop Reply Packets
28076 @section Stop Reply Packets
28077 @cindex stop reply packets
28079 The @samp{C}, @samp{c}, @samp{S}, @samp{s}, @samp{vCont},
28080 @samp{vAttach}, @samp{vRun}, @samp{vStopped}, and @samp{?} packets can
28081 receive any of the below as a reply. Except for @samp{?}
28082 and @samp{vStopped}, that reply is only returned
28083 when the target halts. In the below the exact meaning of @dfn{signal
28084 number} is defined by the header @file{include/gdb/signals.h} in the
28085 @value{GDBN} source code.
28087 As in the description of request packets, we include spaces in the
28088 reply templates for clarity; these are not part of the reply packet's
28089 syntax. No @value{GDBN} stop reply packet uses spaces to separate its
28095 The program received signal number @var{AA} (a two-digit hexadecimal
28096 number). This is equivalent to a @samp{T} response with no
28097 @var{n}:@var{r} pairs.
28099 @item T @var{AA} @var{n1}:@var{r1};@var{n2}:@var{r2};@dots{}
28100 @cindex @samp{T} packet reply
28101 The program received signal number @var{AA} (a two-digit hexadecimal
28102 number). This is equivalent to an @samp{S} response, except that the
28103 @samp{@var{n}:@var{r}} pairs can carry values of important registers
28104 and other information directly in the stop reply packet, reducing
28105 round-trip latency. Single-step and breakpoint traps are reported
28106 this way. Each @samp{@var{n}:@var{r}} pair is interpreted as follows:
28110 If @var{n} is a hexadecimal number, it is a register number, and the
28111 corresponding @var{r} gives that register's value. @var{r} is a
28112 series of bytes in target byte order, with each byte given by a
28113 two-digit hex number.
28116 If @var{n} is @samp{thread}, then @var{r} is the @var{thread-id} of
28117 the stopped thread, as specified in @ref{thread-id syntax}.
28120 If @var{n} is a recognized @dfn{stop reason}, it describes a more
28121 specific event that stopped the target. The currently defined stop
28122 reasons are listed below. @var{aa} should be @samp{05}, the trap
28123 signal. At most one stop reason should be present.
28126 Otherwise, @value{GDBN} should ignore this @samp{@var{n}:@var{r}} pair
28127 and go on to the next; this allows us to extend the protocol in the
28131 The currently defined stop reasons are:
28137 The packet indicates a watchpoint hit, and @var{r} is the data address, in
28140 @cindex shared library events, remote reply
28142 The packet indicates that the loaded libraries have changed.
28143 @value{GDBN} should use @samp{qXfer:libraries:read} to fetch a new
28144 list of loaded libraries. @var{r} is ignored.
28146 @cindex replay log events, remote reply
28148 The packet indicates that the target cannot continue replaying
28149 logged execution events, because it has reached the end (or the
28150 beginning when executing backward) of the log. The value of @var{r}
28151 will be either @samp{begin} or @samp{end}. @xref{Reverse Execution},
28152 for more information.
28158 @itemx W @var{AA} ; process:@var{pid}
28159 The process exited, and @var{AA} is the exit status. This is only
28160 applicable to certain targets.
28162 The second form of the response, including the process ID of the exited
28163 process, can be used only when @value{GDBN} has reported support for
28164 multiprocess protocol extensions; see @ref{multiprocess extensions}.
28165 The @var{pid} is formatted as a big-endian hex string.
28168 @itemx X @var{AA} ; process:@var{pid}
28169 The process terminated with signal @var{AA}.
28171 The second form of the response, including the process ID of the
28172 terminated process, can be used only when @value{GDBN} has reported
28173 support for multiprocess protocol extensions; see @ref{multiprocess
28174 extensions}. The @var{pid} is formatted as a big-endian hex string.
28176 @item O @var{XX}@dots{}
28177 @samp{@var{XX}@dots{}} is hex encoding of @sc{ascii} data, to be
28178 written as the program's console output. This can happen at any time
28179 while the program is running and the debugger should continue to wait
28180 for @samp{W}, @samp{T}, etc. This reply is not permitted in non-stop mode.
28182 @item F @var{call-id},@var{parameter}@dots{}
28183 @var{call-id} is the identifier which says which host system call should
28184 be called. This is just the name of the function. Translation into the
28185 correct system call is only applicable as it's defined in @value{GDBN}.
28186 @xref{File-I/O Remote Protocol Extension}, for a list of implemented
28189 @samp{@var{parameter}@dots{}} is a list of parameters as defined for
28190 this very system call.
28192 The target replies with this packet when it expects @value{GDBN} to
28193 call a host system call on behalf of the target. @value{GDBN} replies
28194 with an appropriate @samp{F} packet and keeps up waiting for the next
28195 reply packet from the target. The latest @samp{C}, @samp{c}, @samp{S}
28196 or @samp{s} action is expected to be continued. @xref{File-I/O Remote
28197 Protocol Extension}, for more details.
28201 @node General Query Packets
28202 @section General Query Packets
28203 @cindex remote query requests
28205 Packets starting with @samp{q} are @dfn{general query packets};
28206 packets starting with @samp{Q} are @dfn{general set packets}. General
28207 query and set packets are a semi-unified form for retrieving and
28208 sending information to and from the stub.
28210 The initial letter of a query or set packet is followed by a name
28211 indicating what sort of thing the packet applies to. For example,
28212 @value{GDBN} may use a @samp{qSymbol} packet to exchange symbol
28213 definitions with the stub. These packet names follow some
28218 The name must not contain commas, colons or semicolons.
28220 Most @value{GDBN} query and set packets have a leading upper case
28223 The names of custom vendor packets should use a company prefix, in
28224 lower case, followed by a period. For example, packets designed at
28225 the Acme Corporation might begin with @samp{qacme.foo} (for querying
28226 foos) or @samp{Qacme.bar} (for setting bars).
28229 The name of a query or set packet should be separated from any
28230 parameters by a @samp{:}; the parameters themselves should be
28231 separated by @samp{,} or @samp{;}. Stubs must be careful to match the
28232 full packet name, and check for a separator or the end of the packet,
28233 in case two packet names share a common prefix. New packets should not begin
28234 with @samp{qC}, @samp{qP}, or @samp{qL}@footnote{The @samp{qP} and @samp{qL}
28235 packets predate these conventions, and have arguments without any terminator
28236 for the packet name; we suspect they are in widespread use in places that
28237 are difficult to upgrade. The @samp{qC} packet has no arguments, but some
28238 existing stubs (e.g.@: RedBoot) are known to not check for the end of the
28241 Like the descriptions of the other packets, each description here
28242 has a template showing the packet's overall syntax, followed by an
28243 explanation of the packet's meaning. We include spaces in some of the
28244 templates for clarity; these are not part of the packet's syntax. No
28245 @value{GDBN} packet uses spaces to separate its components.
28247 Here are the currently defined query and set packets:
28252 @cindex current thread, remote request
28253 @cindex @samp{qC} packet
28254 Return the current thread ID.
28258 @item QC @var{thread-id}
28259 Where @var{thread-id} is a thread ID as documented in
28260 @ref{thread-id syntax}.
28261 @item @r{(anything else)}
28262 Any other reply implies the old thread ID.
28265 @item qCRC:@var{addr},@var{length}
28266 @cindex CRC of memory block, remote request
28267 @cindex @samp{qCRC} packet
28268 Compute the CRC checksum of a block of memory using CRC-32 defined in
28269 IEEE 802.3. The CRC is computed byte at a time, taking the most
28270 significant bit of each byte first. The initial pattern code
28271 @code{0xffffffff} is used to ensure leading zeros affect the CRC.
28273 @emph{Note:} This is the same CRC used in validating separate debug
28274 files (@pxref{Separate Debug Files, , Debugging Information in Separate
28275 Files}). However the algorithm is slightly different. When validating
28276 separate debug files, the CRC is computed taking the @emph{least}
28277 significant bit of each byte first, and the final result is inverted to
28278 detect trailing zeros.
28283 An error (such as memory fault)
28284 @item C @var{crc32}
28285 The specified memory region's checksum is @var{crc32}.
28289 @itemx qsThreadInfo
28290 @cindex list active threads, remote request
28291 @cindex @samp{qfThreadInfo} packet
28292 @cindex @samp{qsThreadInfo} packet
28293 Obtain a list of all active thread IDs from the target (OS). Since there
28294 may be too many active threads to fit into one reply packet, this query
28295 works iteratively: it may require more than one query/reply sequence to
28296 obtain the entire list of threads. The first query of the sequence will
28297 be the @samp{qfThreadInfo} query; subsequent queries in the
28298 sequence will be the @samp{qsThreadInfo} query.
28300 NOTE: This packet replaces the @samp{qL} query (see below).
28304 @item m @var{thread-id}
28306 @item m @var{thread-id},@var{thread-id}@dots{}
28307 a comma-separated list of thread IDs
28309 (lower case letter @samp{L}) denotes end of list.
28312 In response to each query, the target will reply with a list of one or
28313 more thread IDs, separated by commas.
28314 @value{GDBN} will respond to each reply with a request for more thread
28315 ids (using the @samp{qs} form of the query), until the target responds
28316 with @samp{l} (lower-case el, for @dfn{last}).
28317 Refer to @ref{thread-id syntax}, for the format of the @var{thread-id}
28320 @item qGetTLSAddr:@var{thread-id},@var{offset},@var{lm}
28321 @cindex get thread-local storage address, remote request
28322 @cindex @samp{qGetTLSAddr} packet
28323 Fetch the address associated with thread local storage specified
28324 by @var{thread-id}, @var{offset}, and @var{lm}.
28326 @var{thread-id} is the thread ID associated with the
28327 thread for which to fetch the TLS address. @xref{thread-id syntax}.
28329 @var{offset} is the (big endian, hex encoded) offset associated with the
28330 thread local variable. (This offset is obtained from the debug
28331 information associated with the variable.)
28333 @var{lm} is the (big endian, hex encoded) OS/ABI-specific encoding of the
28334 the load module associated with the thread local storage. For example,
28335 a @sc{gnu}/Linux system will pass the link map address of the shared
28336 object associated with the thread local storage under consideration.
28337 Other operating environments may choose to represent the load module
28338 differently, so the precise meaning of this parameter will vary.
28342 @item @var{XX}@dots{}
28343 Hex encoded (big endian) bytes representing the address of the thread
28344 local storage requested.
28347 An error occurred. @var{nn} are hex digits.
28350 An empty reply indicates that @samp{qGetTLSAddr} is not supported by the stub.
28353 @item qL @var{startflag} @var{threadcount} @var{nextthread}
28354 Obtain thread information from RTOS. Where: @var{startflag} (one hex
28355 digit) is one to indicate the first query and zero to indicate a
28356 subsequent query; @var{threadcount} (two hex digits) is the maximum
28357 number of threads the response packet can contain; and @var{nextthread}
28358 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
28359 returned in the response as @var{argthread}.
28361 Don't use this packet; use the @samp{qfThreadInfo} query instead (see above).
28365 @item qM @var{count} @var{done} @var{argthread} @var{thread}@dots{}
28366 Where: @var{count} (two hex digits) is the number of threads being
28367 returned; @var{done} (one hex digit) is zero to indicate more threads
28368 and one indicates no further threads; @var{argthreadid} (eight hex
28369 digits) is @var{nextthread} from the request packet; @var{thread}@dots{}
28370 is a sequence of thread IDs from the target. @var{threadid} (eight hex
28371 digits). See @code{remote.c:parse_threadlist_response()}.
28375 @cindex section offsets, remote request
28376 @cindex @samp{qOffsets} packet
28377 Get section offsets that the target used when relocating the downloaded
28382 @item Text=@var{xxx};Data=@var{yyy}@r{[};Bss=@var{zzz}@r{]}
28383 Relocate the @code{Text} section by @var{xxx} from its original address.
28384 Relocate the @code{Data} section by @var{yyy} from its original address.
28385 If the object file format provides segment information (e.g.@: @sc{elf}
28386 @samp{PT_LOAD} program headers), @value{GDBN} will relocate entire
28387 segments by the supplied offsets.
28389 @emph{Note: while a @code{Bss} offset may be included in the response,
28390 @value{GDBN} ignores this and instead applies the @code{Data} offset
28391 to the @code{Bss} section.}
28393 @item TextSeg=@var{xxx}@r{[};DataSeg=@var{yyy}@r{]}
28394 Relocate the first segment of the object file, which conventionally
28395 contains program code, to a starting address of @var{xxx}. If
28396 @samp{DataSeg} is specified, relocate the second segment, which
28397 conventionally contains modifiable data, to a starting address of
28398 @var{yyy}. @value{GDBN} will report an error if the object file
28399 does not contain segment information, or does not contain at least
28400 as many segments as mentioned in the reply. Extra segments are
28401 kept at fixed offsets relative to the last relocated segment.
28404 @item qP @var{mode} @var{thread-id}
28405 @cindex thread information, remote request
28406 @cindex @samp{qP} packet
28407 Returns information on @var{thread-id}. Where: @var{mode} is a hex
28408 encoded 32 bit mode; @var{thread-id} is a thread ID
28409 (@pxref{thread-id syntax}).
28411 Don't use this packet; use the @samp{qThreadExtraInfo} query instead
28414 Reply: see @code{remote.c:remote_unpack_thread_info_response()}.
28418 @cindex non-stop mode, remote request
28419 @cindex @samp{QNonStop} packet
28421 Enter non-stop (@samp{QNonStop:1}) or all-stop (@samp{QNonStop:0}) mode.
28422 @xref{Remote Non-Stop}, for more information.
28427 The request succeeded.
28430 An error occurred. @var{nn} are hex digits.
28433 An empty reply indicates that @samp{QNonStop} is not supported by
28437 This packet is not probed by default; the remote stub must request it,
28438 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28439 Use of this packet is controlled by the @code{set non-stop} command;
28440 @pxref{Non-Stop Mode}.
28442 @item QPassSignals: @var{signal} @r{[};@var{signal}@r{]}@dots{}
28443 @cindex pass signals to inferior, remote request
28444 @cindex @samp{QPassSignals} packet
28445 @anchor{QPassSignals}
28446 Each listed @var{signal} should be passed directly to the inferior process.
28447 Signals are numbered identically to continue packets and stop replies
28448 (@pxref{Stop Reply Packets}). Each @var{signal} list item should be
28449 strictly greater than the previous item. These signals do not need to stop
28450 the inferior, or be reported to @value{GDBN}. All other signals should be
28451 reported to @value{GDBN}. Multiple @samp{QPassSignals} packets do not
28452 combine; any earlier @samp{QPassSignals} list is completely replaced by the
28453 new list. This packet improves performance when using @samp{handle
28454 @var{signal} nostop noprint pass}.
28459 The request succeeded.
28462 An error occurred. @var{nn} are hex digits.
28465 An empty reply indicates that @samp{QPassSignals} is not supported by
28469 Use of this packet is controlled by the @code{set remote pass-signals}
28470 command (@pxref{Remote Configuration, set remote pass-signals}).
28471 This packet is not probed by default; the remote stub must request it,
28472 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28474 @item qRcmd,@var{command}
28475 @cindex execute remote command, remote request
28476 @cindex @samp{qRcmd} packet
28477 @var{command} (hex encoded) is passed to the local interpreter for
28478 execution. Invalid commands should be reported using the output
28479 string. Before the final result packet, the target may also respond
28480 with a number of intermediate @samp{O@var{output}} console output
28481 packets. @emph{Implementors should note that providing access to a
28482 stubs's interpreter may have security implications}.
28487 A command response with no output.
28489 A command response with the hex encoded output string @var{OUTPUT}.
28491 Indicate a badly formed request.
28493 An empty reply indicates that @samp{qRcmd} is not recognized.
28496 (Note that the @code{qRcmd} packet's name is separated from the
28497 command by a @samp{,}, not a @samp{:}, contrary to the naming
28498 conventions above. Please don't use this packet as a model for new
28501 @item qSearch:memory:@var{address};@var{length};@var{search-pattern}
28502 @cindex searching memory, in remote debugging
28503 @cindex @samp{qSearch:memory} packet
28504 @anchor{qSearch memory}
28505 Search @var{length} bytes at @var{address} for @var{search-pattern}.
28506 @var{address} and @var{length} are encoded in hex.
28507 @var{search-pattern} is a sequence of bytes, hex encoded.
28512 The pattern was not found.
28514 The pattern was found at @var{address}.
28516 A badly formed request or an error was encountered while searching memory.
28518 An empty reply indicates that @samp{qSearch:memory} is not recognized.
28521 @item QStartNoAckMode
28522 @cindex @samp{QStartNoAckMode} packet
28523 @anchor{QStartNoAckMode}
28524 Request that the remote stub disable the normal @samp{+}/@samp{-}
28525 protocol acknowledgments (@pxref{Packet Acknowledgment}).
28530 The stub has switched to no-acknowledgment mode.
28531 @value{GDBN} acknowledges this reponse,
28532 but neither the stub nor @value{GDBN} shall send or expect further
28533 @samp{+}/@samp{-} acknowledgments in the current connection.
28535 An empty reply indicates that the stub does not support no-acknowledgment mode.
28538 @item qSupported @r{[}:@var{gdbfeature} @r{[};@var{gdbfeature}@r{]}@dots{} @r{]}
28539 @cindex supported packets, remote query
28540 @cindex features of the remote protocol
28541 @cindex @samp{qSupported} packet
28542 @anchor{qSupported}
28543 Tell the remote stub about features supported by @value{GDBN}, and
28544 query the stub for features it supports. This packet allows
28545 @value{GDBN} and the remote stub to take advantage of each others'
28546 features. @samp{qSupported} also consolidates multiple feature probes
28547 at startup, to improve @value{GDBN} performance---a single larger
28548 packet performs better than multiple smaller probe packets on
28549 high-latency links. Some features may enable behavior which must not
28550 be on by default, e.g.@: because it would confuse older clients or
28551 stubs. Other features may describe packets which could be
28552 automatically probed for, but are not. These features must be
28553 reported before @value{GDBN} will use them. This ``default
28554 unsupported'' behavior is not appropriate for all packets, but it
28555 helps to keep the initial connection time under control with new
28556 versions of @value{GDBN} which support increasing numbers of packets.
28560 @item @var{stubfeature} @r{[};@var{stubfeature}@r{]}@dots{}
28561 The stub supports or does not support each returned @var{stubfeature},
28562 depending on the form of each @var{stubfeature} (see below for the
28565 An empty reply indicates that @samp{qSupported} is not recognized,
28566 or that no features needed to be reported to @value{GDBN}.
28569 The allowed forms for each feature (either a @var{gdbfeature} in the
28570 @samp{qSupported} packet, or a @var{stubfeature} in the response)
28574 @item @var{name}=@var{value}
28575 The remote protocol feature @var{name} is supported, and associated
28576 with the specified @var{value}. The format of @var{value} depends
28577 on the feature, but it must not include a semicolon.
28579 The remote protocol feature @var{name} is supported, and does not
28580 need an associated value.
28582 The remote protocol feature @var{name} is not supported.
28584 The remote protocol feature @var{name} may be supported, and
28585 @value{GDBN} should auto-detect support in some other way when it is
28586 needed. This form will not be used for @var{gdbfeature} notifications,
28587 but may be used for @var{stubfeature} responses.
28590 Whenever the stub receives a @samp{qSupported} request, the
28591 supplied set of @value{GDBN} features should override any previous
28592 request. This allows @value{GDBN} to put the stub in a known
28593 state, even if the stub had previously been communicating with
28594 a different version of @value{GDBN}.
28596 The following values of @var{gdbfeature} (for the packet sent by @value{GDBN})
28601 This feature indicates whether @value{GDBN} supports multiprocess
28602 extensions to the remote protocol. @value{GDBN} does not use such
28603 extensions unless the stub also reports that it supports them by
28604 including @samp{multiprocess+} in its @samp{qSupported} reply.
28605 @xref{multiprocess extensions}, for details.
28608 Stubs should ignore any unknown values for
28609 @var{gdbfeature}. Any @value{GDBN} which sends a @samp{qSupported}
28610 packet supports receiving packets of unlimited length (earlier
28611 versions of @value{GDBN} may reject overly long responses). Additional values
28612 for @var{gdbfeature} may be defined in the future to let the stub take
28613 advantage of new features in @value{GDBN}, e.g.@: incompatible
28614 improvements in the remote protocol---the @samp{multiprocess} feature is
28615 an example of such a feature. The stub's reply should be independent
28616 of the @var{gdbfeature} entries sent by @value{GDBN}; first @value{GDBN}
28617 describes all the features it supports, and then the stub replies with
28618 all the features it supports.
28620 Similarly, @value{GDBN} will silently ignore unrecognized stub feature
28621 responses, as long as each response uses one of the standard forms.
28623 Some features are flags. A stub which supports a flag feature
28624 should respond with a @samp{+} form response. Other features
28625 require values, and the stub should respond with an @samp{=}
28628 Each feature has a default value, which @value{GDBN} will use if
28629 @samp{qSupported} is not available or if the feature is not mentioned
28630 in the @samp{qSupported} response. The default values are fixed; a
28631 stub is free to omit any feature responses that match the defaults.
28633 Not all features can be probed, but for those which can, the probing
28634 mechanism is useful: in some cases, a stub's internal
28635 architecture may not allow the protocol layer to know some information
28636 about the underlying target in advance. This is especially common in
28637 stubs which may be configured for multiple targets.
28639 These are the currently defined stub features and their properties:
28641 @multitable @columnfractions 0.35 0.2 0.12 0.2
28642 @c NOTE: The first row should be @headitem, but we do not yet require
28643 @c a new enough version of Texinfo (4.7) to use @headitem.
28645 @tab Value Required
28649 @item @samp{PacketSize}
28654 @item @samp{qXfer:auxv:read}
28659 @item @samp{qXfer:features:read}
28664 @item @samp{qXfer:libraries:read}
28669 @item @samp{qXfer:memory-map:read}
28674 @item @samp{qXfer:spu:read}
28679 @item @samp{qXfer:spu:write}
28684 @item @samp{qXfer:siginfo:read}
28689 @item @samp{qXfer:siginfo:write}
28694 @item @samp{QNonStop}
28699 @item @samp{QPassSignals}
28704 @item @samp{QStartNoAckMode}
28709 @item @samp{multiprocess}
28714 @item @samp{ConditionalTracepoints}
28721 These are the currently defined stub features, in more detail:
28724 @cindex packet size, remote protocol
28725 @item PacketSize=@var{bytes}
28726 The remote stub can accept packets up to at least @var{bytes} in
28727 length. @value{GDBN} will send packets up to this size for bulk
28728 transfers, and will never send larger packets. This is a limit on the
28729 data characters in the packet, including the frame and checksum.
28730 There is no trailing NUL byte in a remote protocol packet; if the stub
28731 stores packets in a NUL-terminated format, it should allow an extra
28732 byte in its buffer for the NUL. If this stub feature is not supported,
28733 @value{GDBN} guesses based on the size of the @samp{g} packet response.
28735 @item qXfer:auxv:read
28736 The remote stub understands the @samp{qXfer:auxv:read} packet
28737 (@pxref{qXfer auxiliary vector read}).
28739 @item qXfer:features:read
28740 The remote stub understands the @samp{qXfer:features:read} packet
28741 (@pxref{qXfer target description read}).
28743 @item qXfer:libraries:read
28744 The remote stub understands the @samp{qXfer:libraries:read} packet
28745 (@pxref{qXfer library list read}).
28747 @item qXfer:memory-map:read
28748 The remote stub understands the @samp{qXfer:memory-map:read} packet
28749 (@pxref{qXfer memory map read}).
28751 @item qXfer:spu:read
28752 The remote stub understands the @samp{qXfer:spu:read} packet
28753 (@pxref{qXfer spu read}).
28755 @item qXfer:spu:write
28756 The remote stub understands the @samp{qXfer:spu:write} packet
28757 (@pxref{qXfer spu write}).
28759 @item qXfer:siginfo:read
28760 The remote stub understands the @samp{qXfer:siginfo:read} packet
28761 (@pxref{qXfer siginfo read}).
28763 @item qXfer:siginfo:write
28764 The remote stub understands the @samp{qXfer:siginfo:write} packet
28765 (@pxref{qXfer siginfo write}).
28768 The remote stub understands the @samp{QNonStop} packet
28769 (@pxref{QNonStop}).
28772 The remote stub understands the @samp{QPassSignals} packet
28773 (@pxref{QPassSignals}).
28775 @item QStartNoAckMode
28776 The remote stub understands the @samp{QStartNoAckMode} packet and
28777 prefers to operate in no-acknowledgment mode. @xref{Packet Acknowledgment}.
28780 @anchor{multiprocess extensions}
28781 @cindex multiprocess extensions, in remote protocol
28782 The remote stub understands the multiprocess extensions to the remote
28783 protocol syntax. The multiprocess extensions affect the syntax of
28784 thread IDs in both packets and replies (@pxref{thread-id syntax}), and
28785 add process IDs to the @samp{D} packet and @samp{W} and @samp{X}
28786 replies. Note that reporting this feature indicates support for the
28787 syntactic extensions only, not that the stub necessarily supports
28788 debugging of more than one process at a time. The stub must not use
28789 multiprocess extensions in packet replies unless @value{GDBN} has also
28790 indicated it supports them in its @samp{qSupported} request.
28792 @item qXfer:osdata:read
28793 The remote stub understands the @samp{qXfer:osdata:read} packet
28794 ((@pxref{qXfer osdata read}).
28796 @item ConditionalTracepoints
28797 The remote stub accepts and implements conditional expressions defined
28798 for tracepoints (@pxref{Tracepoint Conditions}).
28803 @cindex symbol lookup, remote request
28804 @cindex @samp{qSymbol} packet
28805 Notify the target that @value{GDBN} is prepared to serve symbol lookup
28806 requests. Accept requests from the target for the values of symbols.
28811 The target does not need to look up any (more) symbols.
28812 @item qSymbol:@var{sym_name}
28813 The target requests the value of symbol @var{sym_name} (hex encoded).
28814 @value{GDBN} may provide the value by using the
28815 @samp{qSymbol:@var{sym_value}:@var{sym_name}} message, described
28819 @item qSymbol:@var{sym_value}:@var{sym_name}
28820 Set the value of @var{sym_name} to @var{sym_value}.
28822 @var{sym_name} (hex encoded) is the name of a symbol whose value the
28823 target has previously requested.
28825 @var{sym_value} (hex) is the value for symbol @var{sym_name}. If
28826 @value{GDBN} cannot supply a value for @var{sym_name}, then this field
28832 The target does not need to look up any (more) symbols.
28833 @item qSymbol:@var{sym_name}
28834 The target requests the value of a new symbol @var{sym_name} (hex
28835 encoded). @value{GDBN} will continue to supply the values of symbols
28836 (if available), until the target ceases to request them.
28841 @xref{Tracepoint Packets}.
28843 @item qThreadExtraInfo,@var{thread-id}
28844 @cindex thread attributes info, remote request
28845 @cindex @samp{qThreadExtraInfo} packet
28846 Obtain a printable string description of a thread's attributes from
28847 the target OS. @var{thread-id} is a thread ID;
28848 see @ref{thread-id syntax}. This
28849 string may contain anything that the target OS thinks is interesting
28850 for @value{GDBN} to tell the user about the thread. The string is
28851 displayed in @value{GDBN}'s @code{info threads} display. Some
28852 examples of possible thread extra info strings are @samp{Runnable}, or
28853 @samp{Blocked on Mutex}.
28857 @item @var{XX}@dots{}
28858 Where @samp{@var{XX}@dots{}} is a hex encoding of @sc{ascii} data,
28859 comprising the printable string containing the extra information about
28860 the thread's attributes.
28863 (Note that the @code{qThreadExtraInfo} packet's name is separated from
28864 the command by a @samp{,}, not a @samp{:}, contrary to the naming
28865 conventions above. Please don't use this packet as a model for new
28873 @xref{Tracepoint Packets}.
28875 @item qXfer:@var{object}:read:@var{annex}:@var{offset},@var{length}
28876 @cindex read special object, remote request
28877 @cindex @samp{qXfer} packet
28878 @anchor{qXfer read}
28879 Read uninterpreted bytes from the target's special data area
28880 identified by the keyword @var{object}. Request @var{length} bytes
28881 starting at @var{offset} bytes into the data. The content and
28882 encoding of @var{annex} is specific to @var{object}; it can supply
28883 additional details about what data to access.
28885 Here are the specific requests of this form defined so far. All
28886 @samp{qXfer:@var{object}:read:@dots{}} requests use the same reply
28887 formats, listed below.
28890 @item qXfer:auxv:read::@var{offset},@var{length}
28891 @anchor{qXfer auxiliary vector read}
28892 Access the target's @dfn{auxiliary vector}. @xref{OS Information,
28893 auxiliary vector}. Note @var{annex} must be empty.
28895 This packet is not probed by default; the remote stub must request it,
28896 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28898 @item qXfer:features:read:@var{annex}:@var{offset},@var{length}
28899 @anchor{qXfer target description read}
28900 Access the @dfn{target description}. @xref{Target Descriptions}. The
28901 annex specifies which XML document to access. The main description is
28902 always loaded from the @samp{target.xml} annex.
28904 This packet is not probed by default; the remote stub must request it,
28905 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28907 @item qXfer:libraries:read:@var{annex}:@var{offset},@var{length}
28908 @anchor{qXfer library list read}
28909 Access the target's list of loaded libraries. @xref{Library List Format}.
28910 The annex part of the generic @samp{qXfer} packet must be empty
28911 (@pxref{qXfer read}).
28913 Targets which maintain a list of libraries in the program's memory do
28914 not need to implement this packet; it is designed for platforms where
28915 the operating system manages the list of loaded libraries.
28917 This packet is not probed by default; the remote stub must request it,
28918 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28920 @item qXfer:memory-map:read::@var{offset},@var{length}
28921 @anchor{qXfer memory map read}
28922 Access the target's @dfn{memory-map}. @xref{Memory Map Format}. The
28923 annex part of the generic @samp{qXfer} packet must be empty
28924 (@pxref{qXfer read}).
28926 This packet is not probed by default; the remote stub must request it,
28927 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28929 @item qXfer:siginfo:read::@var{offset},@var{length}
28930 @anchor{qXfer siginfo read}
28931 Read contents of the extra signal information on the target
28932 system. The annex part of the generic @samp{qXfer} packet must be
28933 empty (@pxref{qXfer read}).
28935 This packet is not probed by default; the remote stub must request it,
28936 by supplying an appropriate @samp{qSupported} response
28937 (@pxref{qSupported}).
28939 @item qXfer:spu:read:@var{annex}:@var{offset},@var{length}
28940 @anchor{qXfer spu read}
28941 Read contents of an @code{spufs} file on the target system. The
28942 annex specifies which file to read; it must be of the form
28943 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
28944 in the target process, and @var{name} identifes the @code{spufs} file
28945 in that context to be accessed.
28947 This packet is not probed by default; the remote stub must request it,
28948 by supplying an appropriate @samp{qSupported} response
28949 (@pxref{qSupported}).
28951 @item qXfer:osdata:read::@var{offset},@var{length}
28952 @anchor{qXfer osdata read}
28953 Access the target's @dfn{operating system information}.
28954 @xref{Operating System Information}.
28961 Data @var{data} (@pxref{Binary Data}) has been read from the
28962 target. There may be more data at a higher address (although
28963 it is permitted to return @samp{m} even for the last valid
28964 block of data, as long as at least one byte of data was read).
28965 @var{data} may have fewer bytes than the @var{length} in the
28969 Data @var{data} (@pxref{Binary Data}) has been read from the target.
28970 There is no more data to be read. @var{data} may have fewer bytes
28971 than the @var{length} in the request.
28974 The @var{offset} in the request is at the end of the data.
28975 There is no more data to be read.
28978 The request was malformed, or @var{annex} was invalid.
28981 The offset was invalid, or there was an error encountered reading the data.
28982 @var{nn} is a hex-encoded @code{errno} value.
28985 An empty reply indicates the @var{object} string was not recognized by
28986 the stub, or that the object does not support reading.
28989 @item qXfer:@var{object}:write:@var{annex}:@var{offset}:@var{data}@dots{}
28990 @cindex write data into object, remote request
28991 @anchor{qXfer write}
28992 Write uninterpreted bytes into the target's special data area
28993 identified by the keyword @var{object}, starting at @var{offset} bytes
28994 into the data. @var{data}@dots{} is the binary-encoded data
28995 (@pxref{Binary Data}) to be written. The content and encoding of @var{annex}
28996 is specific to @var{object}; it can supply additional details about what data
28999 Here are the specific requests of this form defined so far. All
29000 @samp{qXfer:@var{object}:write:@dots{}} requests use the same reply
29001 formats, listed below.
29004 @item qXfer:siginfo:write::@var{offset}:@var{data}@dots{}
29005 @anchor{qXfer siginfo write}
29006 Write @var{data} to the extra signal information on the target system.
29007 The annex part of the generic @samp{qXfer} packet must be
29008 empty (@pxref{qXfer write}).
29010 This packet is not probed by default; the remote stub must request it,
29011 by supplying an appropriate @samp{qSupported} response
29012 (@pxref{qSupported}).
29014 @item qXfer:spu:write:@var{annex}:@var{offset}:@var{data}@dots{}
29015 @anchor{qXfer spu write}
29016 Write @var{data} to an @code{spufs} file on the target system. The
29017 annex specifies which file to write; it must be of the form
29018 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
29019 in the target process, and @var{name} identifes the @code{spufs} file
29020 in that context to be accessed.
29022 This packet is not probed by default; the remote stub must request it,
29023 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
29029 @var{nn} (hex encoded) is the number of bytes written.
29030 This may be fewer bytes than supplied in the request.
29033 The request was malformed, or @var{annex} was invalid.
29036 The offset was invalid, or there was an error encountered writing the data.
29037 @var{nn} is a hex-encoded @code{errno} value.
29040 An empty reply indicates the @var{object} string was not
29041 recognized by the stub, or that the object does not support writing.
29044 @item qXfer:@var{object}:@var{operation}:@dots{}
29045 Requests of this form may be added in the future. When a stub does
29046 not recognize the @var{object} keyword, or its support for
29047 @var{object} does not recognize the @var{operation} keyword, the stub
29048 must respond with an empty packet.
29050 @item qAttached:@var{pid}
29051 @cindex query attached, remote request
29052 @cindex @samp{qAttached} packet
29053 Return an indication of whether the remote server attached to an
29054 existing process or created a new process. When the multiprocess
29055 protocol extensions are supported (@pxref{multiprocess extensions}),
29056 @var{pid} is an integer in hexadecimal format identifying the target
29057 process. Otherwise, @value{GDBN} will omit the @var{pid} field and
29058 the query packet will be simplified as @samp{qAttached}.
29060 This query is used, for example, to know whether the remote process
29061 should be detached or killed when a @value{GDBN} session is ended with
29062 the @code{quit} command.
29067 The remote server attached to an existing process.
29069 The remote server created a new process.
29071 A badly formed request or an error was encountered.
29076 @node Register Packet Format
29077 @section Register Packet Format
29079 The following @code{g}/@code{G} packets have previously been defined.
29080 In the below, some thirty-two bit registers are transferred as
29081 sixty-four bits. Those registers should be zero/sign extended (which?)
29082 to fill the space allocated. Register bytes are transferred in target
29083 byte order. The two nibbles within a register byte are transferred
29084 most-significant - least-significant.
29090 All registers are transferred as thirty-two bit quantities in the order:
29091 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
29092 registers; fsr; fir; fp.
29096 All registers are transferred as sixty-four bit quantities (including
29097 thirty-two bit registers such as @code{sr}). The ordering is the same
29102 @node Tracepoint Packets
29103 @section Tracepoint Packets
29104 @cindex tracepoint packets
29105 @cindex packets, tracepoint
29107 Here we describe the packets @value{GDBN} uses to implement
29108 tracepoints (@pxref{Tracepoints}).
29112 @item QTDP:@var{n}:@var{addr}:@var{ena}:@var{step}:@var{pass}[:X@var{len},@var{bytes}]@r{[}-@r{]}
29113 Create a new tracepoint, number @var{n}, at @var{addr}. If @var{ena}
29114 is @samp{E}, then the tracepoint is enabled; if it is @samp{D}, then
29115 the tracepoint is disabled. @var{step} is the tracepoint's step
29116 count, and @var{pass} is its pass count. If an @samp{X} is present,
29117 it introduces a tracepoint condition, which consists of a hexadecimal
29118 length, followed by a comma and hex-encoded bytes, in a manner similar
29119 to action encodings as described below. If the trailing @samp{-} is
29120 present, further @samp{QTDP} packets will follow to specify this
29121 tracepoint's actions.
29126 The packet was understood and carried out.
29128 The packet was not recognized.
29131 @item QTDP:-@var{n}:@var{addr}:@r{[}S@r{]}@var{action}@dots{}@r{[}-@r{]}
29132 Define actions to be taken when a tracepoint is hit. @var{n} and
29133 @var{addr} must be the same as in the initial @samp{QTDP} packet for
29134 this tracepoint. This packet may only be sent immediately after
29135 another @samp{QTDP} packet that ended with a @samp{-}. If the
29136 trailing @samp{-} is present, further @samp{QTDP} packets will follow,
29137 specifying more actions for this tracepoint.
29139 In the series of action packets for a given tracepoint, at most one
29140 can have an @samp{S} before its first @var{action}. If such a packet
29141 is sent, it and the following packets define ``while-stepping''
29142 actions. Any prior packets define ordinary actions --- that is, those
29143 taken when the tracepoint is first hit. If no action packet has an
29144 @samp{S}, then all the packets in the series specify ordinary
29145 tracepoint actions.
29147 The @samp{@var{action}@dots{}} portion of the packet is a series of
29148 actions, concatenated without separators. Each action has one of the
29154 Collect the registers whose bits are set in @var{mask}. @var{mask} is
29155 a hexadecimal number whose @var{i}'th bit is set if register number
29156 @var{i} should be collected. (The least significant bit is numbered
29157 zero.) Note that @var{mask} may be any number of digits long; it may
29158 not fit in a 32-bit word.
29160 @item M @var{basereg},@var{offset},@var{len}
29161 Collect @var{len} bytes of memory starting at the address in register
29162 number @var{basereg}, plus @var{offset}. If @var{basereg} is
29163 @samp{-1}, then the range has a fixed address: @var{offset} is the
29164 address of the lowest byte to collect. The @var{basereg},
29165 @var{offset}, and @var{len} parameters are all unsigned hexadecimal
29166 values (the @samp{-1} value for @var{basereg} is a special case).
29168 @item X @var{len},@var{expr}
29169 Evaluate @var{expr}, whose length is @var{len}, and collect memory as
29170 it directs. @var{expr} is an agent expression, as described in
29171 @ref{Agent Expressions}. Each byte of the expression is encoded as a
29172 two-digit hex number in the packet; @var{len} is the number of bytes
29173 in the expression (and thus one-half the number of hex digits in the
29178 Any number of actions may be packed together in a single @samp{QTDP}
29179 packet, as long as the packet does not exceed the maximum packet
29180 length (400 bytes, for many stubs). There may be only one @samp{R}
29181 action per tracepoint, and it must precede any @samp{M} or @samp{X}
29182 actions. Any registers referred to by @samp{M} and @samp{X} actions
29183 must be collected by a preceding @samp{R} action. (The
29184 ``while-stepping'' actions are treated as if they were attached to a
29185 separate tracepoint, as far as these restrictions are concerned.)
29190 The packet was understood and carried out.
29192 The packet was not recognized.
29195 @item QTFrame:@var{n}
29196 Select the @var{n}'th tracepoint frame from the buffer, and use the
29197 register and memory contents recorded there to answer subsequent
29198 request packets from @value{GDBN}.
29200 A successful reply from the stub indicates that the stub has found the
29201 requested frame. The response is a series of parts, concatenated
29202 without separators, describing the frame we selected. Each part has
29203 one of the following forms:
29207 The selected frame is number @var{n} in the trace frame buffer;
29208 @var{f} is a hexadecimal number. If @var{f} is @samp{-1}, then there
29209 was no frame matching the criteria in the request packet.
29212 The selected trace frame records a hit of tracepoint number @var{t};
29213 @var{t} is a hexadecimal number.
29217 @item QTFrame:pc:@var{addr}
29218 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
29219 currently selected frame whose PC is @var{addr};
29220 @var{addr} is a hexadecimal number.
29222 @item QTFrame:tdp:@var{t}
29223 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
29224 currently selected frame that is a hit of tracepoint @var{t}; @var{t}
29225 is a hexadecimal number.
29227 @item QTFrame:range:@var{start}:@var{end}
29228 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
29229 currently selected frame whose PC is between @var{start} (inclusive)
29230 and @var{end} (exclusive); @var{start} and @var{end} are hexadecimal
29233 @item QTFrame:outside:@var{start}:@var{end}
29234 Like @samp{QTFrame:range:@var{start}:@var{end}}, but select the first
29235 frame @emph{outside} the given range of addresses.
29238 Begin the tracepoint experiment. Begin collecting data from tracepoint
29239 hits in the trace frame buffer.
29242 End the tracepoint experiment. Stop collecting trace frames.
29245 Clear the table of tracepoints, and empty the trace frame buffer.
29247 @item QTro:@var{start1},@var{end1}:@var{start2},@var{end2}:@dots{}
29248 Establish the given ranges of memory as ``transparent''. The stub
29249 will answer requests for these ranges from memory's current contents,
29250 if they were not collected as part of the tracepoint hit.
29252 @value{GDBN} uses this to mark read-only regions of memory, like those
29253 containing program code. Since these areas never change, they should
29254 still have the same contents they did when the tracepoint was hit, so
29255 there's no reason for the stub to refuse to provide their contents.
29258 Ask the stub if there is a trace experiment running right now.
29263 There is no trace experiment running.
29265 There is a trace experiment running.
29271 @node Host I/O Packets
29272 @section Host I/O Packets
29273 @cindex Host I/O, remote protocol
29274 @cindex file transfer, remote protocol
29276 The @dfn{Host I/O} packets allow @value{GDBN} to perform I/O
29277 operations on the far side of a remote link. For example, Host I/O is
29278 used to upload and download files to a remote target with its own
29279 filesystem. Host I/O uses the same constant values and data structure
29280 layout as the target-initiated File-I/O protocol. However, the
29281 Host I/O packets are structured differently. The target-initiated
29282 protocol relies on target memory to store parameters and buffers.
29283 Host I/O requests are initiated by @value{GDBN}, and the
29284 target's memory is not involved. @xref{File-I/O Remote Protocol
29285 Extension}, for more details on the target-initiated protocol.
29287 The Host I/O request packets all encode a single operation along with
29288 its arguments. They have this format:
29292 @item vFile:@var{operation}: @var{parameter}@dots{}
29293 @var{operation} is the name of the particular request; the target
29294 should compare the entire packet name up to the second colon when checking
29295 for a supported operation. The format of @var{parameter} depends on
29296 the operation. Numbers are always passed in hexadecimal. Negative
29297 numbers have an explicit minus sign (i.e.@: two's complement is not
29298 used). Strings (e.g.@: filenames) are encoded as a series of
29299 hexadecimal bytes. The last argument to a system call may be a
29300 buffer of escaped binary data (@pxref{Binary Data}).
29304 The valid responses to Host I/O packets are:
29308 @item F @var{result} [, @var{errno}] [; @var{attachment}]
29309 @var{result} is the integer value returned by this operation, usually
29310 non-negative for success and -1 for errors. If an error has occured,
29311 @var{errno} will be included in the result. @var{errno} will have a
29312 value defined by the File-I/O protocol (@pxref{Errno Values}). For
29313 operations which return data, @var{attachment} supplies the data as a
29314 binary buffer. Binary buffers in response packets are escaped in the
29315 normal way (@pxref{Binary Data}). See the individual packet
29316 documentation for the interpretation of @var{result} and
29320 An empty response indicates that this operation is not recognized.
29324 These are the supported Host I/O operations:
29327 @item vFile:open: @var{pathname}, @var{flags}, @var{mode}
29328 Open a file at @var{pathname} and return a file descriptor for it, or
29329 return -1 if an error occurs. @var{pathname} is a string,
29330 @var{flags} is an integer indicating a mask of open flags
29331 (@pxref{Open Flags}), and @var{mode} is an integer indicating a mask
29332 of mode bits to use if the file is created (@pxref{mode_t Values}).
29333 @xref{open}, for details of the open flags and mode values.
29335 @item vFile:close: @var{fd}
29336 Close the open file corresponding to @var{fd} and return 0, or
29337 -1 if an error occurs.
29339 @item vFile:pread: @var{fd}, @var{count}, @var{offset}
29340 Read data from the open file corresponding to @var{fd}. Up to
29341 @var{count} bytes will be read from the file, starting at @var{offset}
29342 relative to the start of the file. The target may read fewer bytes;
29343 common reasons include packet size limits and an end-of-file
29344 condition. The number of bytes read is returned. Zero should only be
29345 returned for a successful read at the end of the file, or if
29346 @var{count} was zero.
29348 The data read should be returned as a binary attachment on success.
29349 If zero bytes were read, the response should include an empty binary
29350 attachment (i.e.@: a trailing semicolon). The return value is the
29351 number of target bytes read; the binary attachment may be longer if
29352 some characters were escaped.
29354 @item vFile:pwrite: @var{fd}, @var{offset}, @var{data}
29355 Write @var{data} (a binary buffer) to the open file corresponding
29356 to @var{fd}. Start the write at @var{offset} from the start of the
29357 file. Unlike many @code{write} system calls, there is no
29358 separate @var{count} argument; the length of @var{data} in the
29359 packet is used. @samp{vFile:write} returns the number of bytes written,
29360 which may be shorter than the length of @var{data}, or -1 if an
29363 @item vFile:unlink: @var{pathname}
29364 Delete the file at @var{pathname} on the target. Return 0,
29365 or -1 if an error occurs. @var{pathname} is a string.
29370 @section Interrupts
29371 @cindex interrupts (remote protocol)
29373 When a program on the remote target is running, @value{GDBN} may
29374 attempt to interrupt it by sending a @samp{Ctrl-C} or a @code{BREAK},
29375 control of which is specified via @value{GDBN}'s @samp{remotebreak}
29376 setting (@pxref{set remotebreak}).
29378 The precise meaning of @code{BREAK} is defined by the transport
29379 mechanism and may, in fact, be undefined. @value{GDBN} does not
29380 currently define a @code{BREAK} mechanism for any of the network
29381 interfaces except for TCP, in which case @value{GDBN} sends the
29382 @code{telnet} BREAK sequence.
29384 @samp{Ctrl-C}, on the other hand, is defined and implemented for all
29385 transport mechanisms. It is represented by sending the single byte
29386 @code{0x03} without any of the usual packet overhead described in
29387 the Overview section (@pxref{Overview}). When a @code{0x03} byte is
29388 transmitted as part of a packet, it is considered to be packet data
29389 and does @emph{not} represent an interrupt. E.g., an @samp{X} packet
29390 (@pxref{X packet}), used for binary downloads, may include an unescaped
29391 @code{0x03} as part of its packet.
29393 Stubs are not required to recognize these interrupt mechanisms and the
29394 precise meaning associated with receipt of the interrupt is
29395 implementation defined. If the target supports debugging of multiple
29396 threads and/or processes, it should attempt to interrupt all
29397 currently-executing threads and processes.
29398 If the stub is successful at interrupting the
29399 running program, it should send one of the stop
29400 reply packets (@pxref{Stop Reply Packets}) to @value{GDBN} as a result
29401 of successfully stopping the program in all-stop mode, and a stop reply
29402 for each stopped thread in non-stop mode.
29403 Interrupts received while the
29404 program is stopped are discarded.
29406 @node Notification Packets
29407 @section Notification Packets
29408 @cindex notification packets
29409 @cindex packets, notification
29411 The @value{GDBN} remote serial protocol includes @dfn{notifications},
29412 packets that require no acknowledgment. Both the GDB and the stub
29413 may send notifications (although the only notifications defined at
29414 present are sent by the stub). Notifications carry information
29415 without incurring the round-trip latency of an acknowledgment, and so
29416 are useful for low-impact communications where occasional packet loss
29419 A notification packet has the form @samp{% @var{data} #
29420 @var{checksum}}, where @var{data} is the content of the notification,
29421 and @var{checksum} is a checksum of @var{data}, computed and formatted
29422 as for ordinary @value{GDBN} packets. A notification's @var{data}
29423 never contains @samp{$}, @samp{%} or @samp{#} characters. Upon
29424 receiving a notification, the recipient sends no @samp{+} or @samp{-}
29425 to acknowledge the notification's receipt or to report its corruption.
29427 Every notification's @var{data} begins with a name, which contains no
29428 colon characters, followed by a colon character.
29430 Recipients should silently ignore corrupted notifications and
29431 notifications they do not understand. Recipients should restart
29432 timeout periods on receipt of a well-formed notification, whether or
29433 not they understand it.
29435 Senders should only send the notifications described here when this
29436 protocol description specifies that they are permitted. In the
29437 future, we may extend the protocol to permit existing notifications in
29438 new contexts; this rule helps older senders avoid confusing newer
29441 (Older versions of @value{GDBN} ignore bytes received until they see
29442 the @samp{$} byte that begins an ordinary packet, so new stubs may
29443 transmit notifications without fear of confusing older clients. There
29444 are no notifications defined for @value{GDBN} to send at the moment, but we
29445 assume that most older stubs would ignore them, as well.)
29447 The following notification packets from the stub to @value{GDBN} are
29451 @item Stop: @var{reply}
29452 Report an asynchronous stop event in non-stop mode.
29453 The @var{reply} has the form of a stop reply, as
29454 described in @ref{Stop Reply Packets}. Refer to @ref{Remote Non-Stop},
29455 for information on how these notifications are acknowledged by
29459 @node Remote Non-Stop
29460 @section Remote Protocol Support for Non-Stop Mode
29462 @value{GDBN}'s remote protocol supports non-stop debugging of
29463 multi-threaded programs, as described in @ref{Non-Stop Mode}. If the stub
29464 supports non-stop mode, it should report that to @value{GDBN} by including
29465 @samp{QNonStop+} in its @samp{qSupported} response (@pxref{qSupported}).
29467 @value{GDBN} typically sends a @samp{QNonStop} packet only when
29468 establishing a new connection with the stub. Entering non-stop mode
29469 does not alter the state of any currently-running threads, but targets
29470 must stop all threads in any already-attached processes when entering
29471 all-stop mode. @value{GDBN} uses the @samp{?} packet as necessary to
29472 probe the target state after a mode change.
29474 In non-stop mode, when an attached process encounters an event that
29475 would otherwise be reported with a stop reply, it uses the
29476 asynchronous notification mechanism (@pxref{Notification Packets}) to
29477 inform @value{GDBN}. In contrast to all-stop mode, where all threads
29478 in all processes are stopped when a stop reply is sent, in non-stop
29479 mode only the thread reporting the stop event is stopped. That is,
29480 when reporting a @samp{S} or @samp{T} response to indicate completion
29481 of a step operation, hitting a breakpoint, or a fault, only the
29482 affected thread is stopped; any other still-running threads continue
29483 to run. When reporting a @samp{W} or @samp{X} response, all running
29484 threads belonging to other attached processes continue to run.
29486 Only one stop reply notification at a time may be pending; if
29487 additional stop events occur before @value{GDBN} has acknowledged the
29488 previous notification, they must be queued by the stub for later
29489 synchronous transmission in response to @samp{vStopped} packets from
29490 @value{GDBN}. Because the notification mechanism is unreliable,
29491 the stub is permitted to resend a stop reply notification
29492 if it believes @value{GDBN} may not have received it. @value{GDBN}
29493 ignores additional stop reply notifications received before it has
29494 finished processing a previous notification and the stub has completed
29495 sending any queued stop events.
29497 Otherwise, @value{GDBN} must be prepared to receive a stop reply
29498 notification at any time. Specifically, they may appear when
29499 @value{GDBN} is not otherwise reading input from the stub, or when
29500 @value{GDBN} is expecting to read a normal synchronous response or a
29501 @samp{+}/@samp{-} acknowledgment to a packet it has sent.
29502 Notification packets are distinct from any other communication from
29503 the stub so there is no ambiguity.
29505 After receiving a stop reply notification, @value{GDBN} shall
29506 acknowledge it by sending a @samp{vStopped} packet (@pxref{vStopped packet})
29507 as a regular, synchronous request to the stub. Such acknowledgment
29508 is not required to happen immediately, as @value{GDBN} is permitted to
29509 send other, unrelated packets to the stub first, which the stub should
29512 Upon receiving a @samp{vStopped} packet, if the stub has other queued
29513 stop events to report to @value{GDBN}, it shall respond by sending a
29514 normal stop reply response. @value{GDBN} shall then send another
29515 @samp{vStopped} packet to solicit further responses; again, it is
29516 permitted to send other, unrelated packets as well which the stub
29517 should process normally.
29519 If the stub receives a @samp{vStopped} packet and there are no
29520 additional stop events to report, the stub shall return an @samp{OK}
29521 response. At this point, if further stop events occur, the stub shall
29522 send a new stop reply notification, @value{GDBN} shall accept the
29523 notification, and the process shall be repeated.
29525 In non-stop mode, the target shall respond to the @samp{?} packet as
29526 follows. First, any incomplete stop reply notification/@samp{vStopped}
29527 sequence in progress is abandoned. The target must begin a new
29528 sequence reporting stop events for all stopped threads, whether or not
29529 it has previously reported those events to @value{GDBN}. The first
29530 stop reply is sent as a synchronous reply to the @samp{?} packet, and
29531 subsequent stop replies are sent as responses to @samp{vStopped} packets
29532 using the mechanism described above. The target must not send
29533 asynchronous stop reply notifications until the sequence is complete.
29534 If all threads are running when the target receives the @samp{?} packet,
29535 or if the target is not attached to any process, it shall respond
29538 @node Packet Acknowledgment
29539 @section Packet Acknowledgment
29541 @cindex acknowledgment, for @value{GDBN} remote
29542 @cindex packet acknowledgment, for @value{GDBN} remote
29543 By default, when either the host or the target machine receives a packet,
29544 the first response expected is an acknowledgment: either @samp{+} (to indicate
29545 the package was received correctly) or @samp{-} (to request retransmission).
29546 This mechanism allows the @value{GDBN} remote protocol to operate over
29547 unreliable transport mechanisms, such as a serial line.
29549 In cases where the transport mechanism is itself reliable (such as a pipe or
29550 TCP connection), the @samp{+}/@samp{-} acknowledgments are redundant.
29551 It may be desirable to disable them in that case to reduce communication
29552 overhead, or for other reasons. This can be accomplished by means of the
29553 @samp{QStartNoAckMode} packet; @pxref{QStartNoAckMode}.
29555 When in no-acknowledgment mode, neither the stub nor @value{GDBN} shall send or
29556 expect @samp{+}/@samp{-} protocol acknowledgments. The packet
29557 and response format still includes the normal checksum, as described in
29558 @ref{Overview}, but the checksum may be ignored by the receiver.
29560 If the stub supports @samp{QStartNoAckMode} and prefers to operate in
29561 no-acknowledgment mode, it should report that to @value{GDBN}
29562 by including @samp{QStartNoAckMode+} in its response to @samp{qSupported};
29563 @pxref{qSupported}.
29564 If @value{GDBN} also supports @samp{QStartNoAckMode} and it has not been
29565 disabled via the @code{set remote noack-packet off} command
29566 (@pxref{Remote Configuration}),
29567 @value{GDBN} may then send a @samp{QStartNoAckMode} packet to the stub.
29568 Only then may the stub actually turn off packet acknowledgments.
29569 @value{GDBN} sends a final @samp{+} acknowledgment of the stub's @samp{OK}
29570 response, which can be safely ignored by the stub.
29572 Note that @code{set remote noack-packet} command only affects negotiation
29573 between @value{GDBN} and the stub when subsequent connections are made;
29574 it does not affect the protocol acknowledgment state for any current
29576 Since @samp{+}/@samp{-} acknowledgments are enabled by default when a
29577 new connection is established,
29578 there is also no protocol request to re-enable the acknowledgments
29579 for the current connection, once disabled.
29584 Example sequence of a target being re-started. Notice how the restart
29585 does not get any direct output:
29590 @emph{target restarts}
29593 <- @code{T001:1234123412341234}
29597 Example sequence of a target being stepped by a single instruction:
29600 -> @code{G1445@dots{}}
29605 <- @code{T001:1234123412341234}
29609 <- @code{1455@dots{}}
29613 @node File-I/O Remote Protocol Extension
29614 @section File-I/O Remote Protocol Extension
29615 @cindex File-I/O remote protocol extension
29618 * File-I/O Overview::
29619 * Protocol Basics::
29620 * The F Request Packet::
29621 * The F Reply Packet::
29622 * The Ctrl-C Message::
29624 * List of Supported Calls::
29625 * Protocol-specific Representation of Datatypes::
29627 * File-I/O Examples::
29630 @node File-I/O Overview
29631 @subsection File-I/O Overview
29632 @cindex file-i/o overview
29634 The @dfn{File I/O remote protocol extension} (short: File-I/O) allows the
29635 target to use the host's file system and console I/O to perform various
29636 system calls. System calls on the target system are translated into a
29637 remote protocol packet to the host system, which then performs the needed
29638 actions and returns a response packet to the target system.
29639 This simulates file system operations even on targets that lack file systems.
29641 The protocol is defined to be independent of both the host and target systems.
29642 It uses its own internal representation of datatypes and values. Both
29643 @value{GDBN} and the target's @value{GDBN} stub are responsible for
29644 translating the system-dependent value representations into the internal
29645 protocol representations when data is transmitted.
29647 The communication is synchronous. A system call is possible only when
29648 @value{GDBN} is waiting for a response from the @samp{C}, @samp{c}, @samp{S}
29649 or @samp{s} packets. While @value{GDBN} handles the request for a system call,
29650 the target is stopped to allow deterministic access to the target's
29651 memory. Therefore File-I/O is not interruptible by target signals. On
29652 the other hand, it is possible to interrupt File-I/O by a user interrupt
29653 (@samp{Ctrl-C}) within @value{GDBN}.
29655 The target's request to perform a host system call does not finish
29656 the latest @samp{C}, @samp{c}, @samp{S} or @samp{s} action. That means,
29657 after finishing the system call, the target returns to continuing the
29658 previous activity (continue, step). No additional continue or step
29659 request from @value{GDBN} is required.
29662 (@value{GDBP}) continue
29663 <- target requests 'system call X'
29664 target is stopped, @value{GDBN} executes system call
29665 -> @value{GDBN} returns result
29666 ... target continues, @value{GDBN} returns to wait for the target
29667 <- target hits breakpoint and sends a Txx packet
29670 The protocol only supports I/O on the console and to regular files on
29671 the host file system. Character or block special devices, pipes,
29672 named pipes, sockets or any other communication method on the host
29673 system are not supported by this protocol.
29675 File I/O is not supported in non-stop mode.
29677 @node Protocol Basics
29678 @subsection Protocol Basics
29679 @cindex protocol basics, file-i/o
29681 The File-I/O protocol uses the @code{F} packet as the request as well
29682 as reply packet. Since a File-I/O system call can only occur when
29683 @value{GDBN} is waiting for a response from the continuing or stepping target,
29684 the File-I/O request is a reply that @value{GDBN} has to expect as a result
29685 of a previous @samp{C}, @samp{c}, @samp{S} or @samp{s} packet.
29686 This @code{F} packet contains all information needed to allow @value{GDBN}
29687 to call the appropriate host system call:
29691 A unique identifier for the requested system call.
29694 All parameters to the system call. Pointers are given as addresses
29695 in the target memory address space. Pointers to strings are given as
29696 pointer/length pair. Numerical values are given as they are.
29697 Numerical control flags are given in a protocol-specific representation.
29701 At this point, @value{GDBN} has to perform the following actions.
29705 If the parameters include pointer values to data needed as input to a
29706 system call, @value{GDBN} requests this data from the target with a
29707 standard @code{m} packet request. This additional communication has to be
29708 expected by the target implementation and is handled as any other @code{m}
29712 @value{GDBN} translates all value from protocol representation to host
29713 representation as needed. Datatypes are coerced into the host types.
29716 @value{GDBN} calls the system call.
29719 It then coerces datatypes back to protocol representation.
29722 If the system call is expected to return data in buffer space specified
29723 by pointer parameters to the call, the data is transmitted to the
29724 target using a @code{M} or @code{X} packet. This packet has to be expected
29725 by the target implementation and is handled as any other @code{M} or @code{X}
29730 Eventually @value{GDBN} replies with another @code{F} packet which contains all
29731 necessary information for the target to continue. This at least contains
29738 @code{errno}, if has been changed by the system call.
29745 After having done the needed type and value coercion, the target continues
29746 the latest continue or step action.
29748 @node The F Request Packet
29749 @subsection The @code{F} Request Packet
29750 @cindex file-i/o request packet
29751 @cindex @code{F} request packet
29753 The @code{F} request packet has the following format:
29756 @item F@var{call-id},@var{parameter@dots{}}
29758 @var{call-id} is the identifier to indicate the host system call to be called.
29759 This is just the name of the function.
29761 @var{parameter@dots{}} are the parameters to the system call.
29762 Parameters are hexadecimal integer values, either the actual values in case
29763 of scalar datatypes, pointers to target buffer space in case of compound
29764 datatypes and unspecified memory areas, or pointer/length pairs in case
29765 of string parameters. These are appended to the @var{call-id} as a
29766 comma-delimited list. All values are transmitted in ASCII
29767 string representation, pointer/length pairs separated by a slash.
29773 @node The F Reply Packet
29774 @subsection The @code{F} Reply Packet
29775 @cindex file-i/o reply packet
29776 @cindex @code{F} reply packet
29778 The @code{F} reply packet has the following format:
29782 @item F@var{retcode},@var{errno},@var{Ctrl-C flag};@var{call-specific attachment}
29784 @var{retcode} is the return code of the system call as hexadecimal value.
29786 @var{errno} is the @code{errno} set by the call, in protocol-specific
29788 This parameter can be omitted if the call was successful.
29790 @var{Ctrl-C flag} is only sent if the user requested a break. In this
29791 case, @var{errno} must be sent as well, even if the call was successful.
29792 The @var{Ctrl-C flag} itself consists of the character @samp{C}:
29799 or, if the call was interrupted before the host call has been performed:
29806 assuming 4 is the protocol-specific representation of @code{EINTR}.
29811 @node The Ctrl-C Message
29812 @subsection The @samp{Ctrl-C} Message
29813 @cindex ctrl-c message, in file-i/o protocol
29815 If the @samp{Ctrl-C} flag is set in the @value{GDBN}
29816 reply packet (@pxref{The F Reply Packet}),
29817 the target should behave as if it had
29818 gotten a break message. The meaning for the target is ``system call
29819 interrupted by @code{SIGINT}''. Consequentially, the target should actually stop
29820 (as with a break message) and return to @value{GDBN} with a @code{T02}
29823 It's important for the target to know in which
29824 state the system call was interrupted. There are two possible cases:
29828 The system call hasn't been performed on the host yet.
29831 The system call on the host has been finished.
29835 These two states can be distinguished by the target by the value of the
29836 returned @code{errno}. If it's the protocol representation of @code{EINTR}, the system
29837 call hasn't been performed. This is equivalent to the @code{EINTR} handling
29838 on POSIX systems. In any other case, the target may presume that the
29839 system call has been finished --- successfully or not --- and should behave
29840 as if the break message arrived right after the system call.
29842 @value{GDBN} must behave reliably. If the system call has not been called
29843 yet, @value{GDBN} may send the @code{F} reply immediately, setting @code{EINTR} as
29844 @code{errno} in the packet. If the system call on the host has been finished
29845 before the user requests a break, the full action must be finished by
29846 @value{GDBN}. This requires sending @code{M} or @code{X} packets as necessary.
29847 The @code{F} packet may only be sent when either nothing has happened
29848 or the full action has been completed.
29851 @subsection Console I/O
29852 @cindex console i/o as part of file-i/o
29854 By default and if not explicitly closed by the target system, the file
29855 descriptors 0, 1 and 2 are connected to the @value{GDBN} console. Output
29856 on the @value{GDBN} console is handled as any other file output operation
29857 (@code{write(1, @dots{})} or @code{write(2, @dots{})}). Console input is handled
29858 by @value{GDBN} so that after the target read request from file descriptor
29859 0 all following typing is buffered until either one of the following
29864 The user types @kbd{Ctrl-c}. The behaviour is as explained above, and the
29866 system call is treated as finished.
29869 The user presses @key{RET}. This is treated as end of input with a trailing
29873 The user types @kbd{Ctrl-d}. This is treated as end of input. No trailing
29874 character (neither newline nor @samp{Ctrl-D}) is appended to the input.
29878 If the user has typed more characters than fit in the buffer given to
29879 the @code{read} call, the trailing characters are buffered in @value{GDBN} until
29880 either another @code{read(0, @dots{})} is requested by the target, or debugging
29881 is stopped at the user's request.
29884 @node List of Supported Calls
29885 @subsection List of Supported Calls
29886 @cindex list of supported file-i/o calls
29903 @unnumberedsubsubsec open
29904 @cindex open, file-i/o system call
29909 int open(const char *pathname, int flags);
29910 int open(const char *pathname, int flags, mode_t mode);
29914 @samp{Fopen,@var{pathptr}/@var{len},@var{flags},@var{mode}}
29917 @var{flags} is the bitwise @code{OR} of the following values:
29921 If the file does not exist it will be created. The host
29922 rules apply as far as file ownership and time stamps
29926 When used with @code{O_CREAT}, if the file already exists it is
29927 an error and open() fails.
29930 If the file already exists and the open mode allows
29931 writing (@code{O_RDWR} or @code{O_WRONLY} is given) it will be
29932 truncated to zero length.
29935 The file is opened in append mode.
29938 The file is opened for reading only.
29941 The file is opened for writing only.
29944 The file is opened for reading and writing.
29948 Other bits are silently ignored.
29952 @var{mode} is the bitwise @code{OR} of the following values:
29956 User has read permission.
29959 User has write permission.
29962 Group has read permission.
29965 Group has write permission.
29968 Others have read permission.
29971 Others have write permission.
29975 Other bits are silently ignored.
29978 @item Return value:
29979 @code{open} returns the new file descriptor or -1 if an error
29986 @var{pathname} already exists and @code{O_CREAT} and @code{O_EXCL} were used.
29989 @var{pathname} refers to a directory.
29992 The requested access is not allowed.
29995 @var{pathname} was too long.
29998 A directory component in @var{pathname} does not exist.
30001 @var{pathname} refers to a device, pipe, named pipe or socket.
30004 @var{pathname} refers to a file on a read-only filesystem and
30005 write access was requested.
30008 @var{pathname} is an invalid pointer value.
30011 No space on device to create the file.
30014 The process already has the maximum number of files open.
30017 The limit on the total number of files open on the system
30021 The call was interrupted by the user.
30027 @unnumberedsubsubsec close
30028 @cindex close, file-i/o system call
30037 @samp{Fclose,@var{fd}}
30039 @item Return value:
30040 @code{close} returns zero on success, or -1 if an error occurred.
30046 @var{fd} isn't a valid open file descriptor.
30049 The call was interrupted by the user.
30055 @unnumberedsubsubsec read
30056 @cindex read, file-i/o system call
30061 int read(int fd, void *buf, unsigned int count);
30065 @samp{Fread,@var{fd},@var{bufptr},@var{count}}
30067 @item Return value:
30068 On success, the number of bytes read is returned.
30069 Zero indicates end of file. If count is zero, read
30070 returns zero as well. On error, -1 is returned.
30076 @var{fd} is not a valid file descriptor or is not open for
30080 @var{bufptr} is an invalid pointer value.
30083 The call was interrupted by the user.
30089 @unnumberedsubsubsec write
30090 @cindex write, file-i/o system call
30095 int write(int fd, const void *buf, unsigned int count);
30099 @samp{Fwrite,@var{fd},@var{bufptr},@var{count}}
30101 @item Return value:
30102 On success, the number of bytes written are returned.
30103 Zero indicates nothing was written. On error, -1
30110 @var{fd} is not a valid file descriptor or is not open for
30114 @var{bufptr} is an invalid pointer value.
30117 An attempt was made to write a file that exceeds the
30118 host-specific maximum file size allowed.
30121 No space on device to write the data.
30124 The call was interrupted by the user.
30130 @unnumberedsubsubsec lseek
30131 @cindex lseek, file-i/o system call
30136 long lseek (int fd, long offset, int flag);
30140 @samp{Flseek,@var{fd},@var{offset},@var{flag}}
30142 @var{flag} is one of:
30146 The offset is set to @var{offset} bytes.
30149 The offset is set to its current location plus @var{offset}
30153 The offset is set to the size of the file plus @var{offset}
30157 @item Return value:
30158 On success, the resulting unsigned offset in bytes from
30159 the beginning of the file is returned. Otherwise, a
30160 value of -1 is returned.
30166 @var{fd} is not a valid open file descriptor.
30169 @var{fd} is associated with the @value{GDBN} console.
30172 @var{flag} is not a proper value.
30175 The call was interrupted by the user.
30181 @unnumberedsubsubsec rename
30182 @cindex rename, file-i/o system call
30187 int rename(const char *oldpath, const char *newpath);
30191 @samp{Frename,@var{oldpathptr}/@var{len},@var{newpathptr}/@var{len}}
30193 @item Return value:
30194 On success, zero is returned. On error, -1 is returned.
30200 @var{newpath} is an existing directory, but @var{oldpath} is not a
30204 @var{newpath} is a non-empty directory.
30207 @var{oldpath} or @var{newpath} is a directory that is in use by some
30211 An attempt was made to make a directory a subdirectory
30215 A component used as a directory in @var{oldpath} or new
30216 path is not a directory. Or @var{oldpath} is a directory
30217 and @var{newpath} exists but is not a directory.
30220 @var{oldpathptr} or @var{newpathptr} are invalid pointer values.
30223 No access to the file or the path of the file.
30227 @var{oldpath} or @var{newpath} was too long.
30230 A directory component in @var{oldpath} or @var{newpath} does not exist.
30233 The file is on a read-only filesystem.
30236 The device containing the file has no room for the new
30240 The call was interrupted by the user.
30246 @unnumberedsubsubsec unlink
30247 @cindex unlink, file-i/o system call
30252 int unlink(const char *pathname);
30256 @samp{Funlink,@var{pathnameptr}/@var{len}}
30258 @item Return value:
30259 On success, zero is returned. On error, -1 is returned.
30265 No access to the file or the path of the file.
30268 The system does not allow unlinking of directories.
30271 The file @var{pathname} cannot be unlinked because it's
30272 being used by another process.
30275 @var{pathnameptr} is an invalid pointer value.
30278 @var{pathname} was too long.
30281 A directory component in @var{pathname} does not exist.
30284 A component of the path is not a directory.
30287 The file is on a read-only filesystem.
30290 The call was interrupted by the user.
30296 @unnumberedsubsubsec stat/fstat
30297 @cindex fstat, file-i/o system call
30298 @cindex stat, file-i/o system call
30303 int stat(const char *pathname, struct stat *buf);
30304 int fstat(int fd, struct stat *buf);
30308 @samp{Fstat,@var{pathnameptr}/@var{len},@var{bufptr}}@*
30309 @samp{Ffstat,@var{fd},@var{bufptr}}
30311 @item Return value:
30312 On success, zero is returned. On error, -1 is returned.
30318 @var{fd} is not a valid open file.
30321 A directory component in @var{pathname} does not exist or the
30322 path is an empty string.
30325 A component of the path is not a directory.
30328 @var{pathnameptr} is an invalid pointer value.
30331 No access to the file or the path of the file.
30334 @var{pathname} was too long.
30337 The call was interrupted by the user.
30343 @unnumberedsubsubsec gettimeofday
30344 @cindex gettimeofday, file-i/o system call
30349 int gettimeofday(struct timeval *tv, void *tz);
30353 @samp{Fgettimeofday,@var{tvptr},@var{tzptr}}
30355 @item Return value:
30356 On success, 0 is returned, -1 otherwise.
30362 @var{tz} is a non-NULL pointer.
30365 @var{tvptr} and/or @var{tzptr} is an invalid pointer value.
30371 @unnumberedsubsubsec isatty
30372 @cindex isatty, file-i/o system call
30377 int isatty(int fd);
30381 @samp{Fisatty,@var{fd}}
30383 @item Return value:
30384 Returns 1 if @var{fd} refers to the @value{GDBN} console, 0 otherwise.
30390 The call was interrupted by the user.
30395 Note that the @code{isatty} call is treated as a special case: it returns
30396 1 to the target if the file descriptor is attached
30397 to the @value{GDBN} console, 0 otherwise. Implementing through system calls
30398 would require implementing @code{ioctl} and would be more complex than
30403 @unnumberedsubsubsec system
30404 @cindex system, file-i/o system call
30409 int system(const char *command);
30413 @samp{Fsystem,@var{commandptr}/@var{len}}
30415 @item Return value:
30416 If @var{len} is zero, the return value indicates whether a shell is
30417 available. A zero return value indicates a shell is not available.
30418 For non-zero @var{len}, the value returned is -1 on error and the
30419 return status of the command otherwise. Only the exit status of the
30420 command is returned, which is extracted from the host's @code{system}
30421 return value by calling @code{WEXITSTATUS(retval)}. In case
30422 @file{/bin/sh} could not be executed, 127 is returned.
30428 The call was interrupted by the user.
30433 @value{GDBN} takes over the full task of calling the necessary host calls
30434 to perform the @code{system} call. The return value of @code{system} on
30435 the host is simplified before it's returned
30436 to the target. Any termination signal information from the child process
30437 is discarded, and the return value consists
30438 entirely of the exit status of the called command.
30440 Due to security concerns, the @code{system} call is by default refused
30441 by @value{GDBN}. The user has to allow this call explicitly with the
30442 @code{set remote system-call-allowed 1} command.
30445 @item set remote system-call-allowed
30446 @kindex set remote system-call-allowed
30447 Control whether to allow the @code{system} calls in the File I/O
30448 protocol for the remote target. The default is zero (disabled).
30450 @item show remote system-call-allowed
30451 @kindex show remote system-call-allowed
30452 Show whether the @code{system} calls are allowed in the File I/O
30456 @node Protocol-specific Representation of Datatypes
30457 @subsection Protocol-specific Representation of Datatypes
30458 @cindex protocol-specific representation of datatypes, in file-i/o protocol
30461 * Integral Datatypes::
30463 * Memory Transfer::
30468 @node Integral Datatypes
30469 @unnumberedsubsubsec Integral Datatypes
30470 @cindex integral datatypes, in file-i/o protocol
30472 The integral datatypes used in the system calls are @code{int},
30473 @code{unsigned int}, @code{long}, @code{unsigned long},
30474 @code{mode_t}, and @code{time_t}.
30476 @code{int}, @code{unsigned int}, @code{mode_t} and @code{time_t} are
30477 implemented as 32 bit values in this protocol.
30479 @code{long} and @code{unsigned long} are implemented as 64 bit types.
30481 @xref{Limits}, for corresponding MIN and MAX values (similar to those
30482 in @file{limits.h}) to allow range checking on host and target.
30484 @code{time_t} datatypes are defined as seconds since the Epoch.
30486 All integral datatypes transferred as part of a memory read or write of a
30487 structured datatype e.g.@: a @code{struct stat} have to be given in big endian
30490 @node Pointer Values
30491 @unnumberedsubsubsec Pointer Values
30492 @cindex pointer values, in file-i/o protocol
30494 Pointers to target data are transmitted as they are. An exception
30495 is made for pointers to buffers for which the length isn't
30496 transmitted as part of the function call, namely strings. Strings
30497 are transmitted as a pointer/length pair, both as hex values, e.g.@:
30504 which is a pointer to data of length 18 bytes at position 0x1aaf.
30505 The length is defined as the full string length in bytes, including
30506 the trailing null byte. For example, the string @code{"hello world"}
30507 at address 0x123456 is transmitted as
30513 @node Memory Transfer
30514 @unnumberedsubsubsec Memory Transfer
30515 @cindex memory transfer, in file-i/o protocol
30517 Structured data which is transferred using a memory read or write (for
30518 example, a @code{struct stat}) is expected to be in a protocol-specific format
30519 with all scalar multibyte datatypes being big endian. Translation to
30520 this representation needs to be done both by the target before the @code{F}
30521 packet is sent, and by @value{GDBN} before
30522 it transfers memory to the target. Transferred pointers to structured
30523 data should point to the already-coerced data at any time.
30527 @unnumberedsubsubsec struct stat
30528 @cindex struct stat, in file-i/o protocol
30530 The buffer of type @code{struct stat} used by the target and @value{GDBN}
30531 is defined as follows:
30535 unsigned int st_dev; /* device */
30536 unsigned int st_ino; /* inode */
30537 mode_t st_mode; /* protection */
30538 unsigned int st_nlink; /* number of hard links */
30539 unsigned int st_uid; /* user ID of owner */
30540 unsigned int st_gid; /* group ID of owner */
30541 unsigned int st_rdev; /* device type (if inode device) */
30542 unsigned long st_size; /* total size, in bytes */
30543 unsigned long st_blksize; /* blocksize for filesystem I/O */
30544 unsigned long st_blocks; /* number of blocks allocated */
30545 time_t st_atime; /* time of last access */
30546 time_t st_mtime; /* time of last modification */
30547 time_t st_ctime; /* time of last change */
30551 The integral datatypes conform to the definitions given in the
30552 appropriate section (see @ref{Integral Datatypes}, for details) so this
30553 structure is of size 64 bytes.
30555 The values of several fields have a restricted meaning and/or
30561 A value of 0 represents a file, 1 the console.
30564 No valid meaning for the target. Transmitted unchanged.
30567 Valid mode bits are described in @ref{Constants}. Any other
30568 bits have currently no meaning for the target.
30573 No valid meaning for the target. Transmitted unchanged.
30578 These values have a host and file system dependent
30579 accuracy. Especially on Windows hosts, the file system may not
30580 support exact timing values.
30583 The target gets a @code{struct stat} of the above representation and is
30584 responsible for coercing it to the target representation before
30587 Note that due to size differences between the host, target, and protocol
30588 representations of @code{struct stat} members, these members could eventually
30589 get truncated on the target.
30591 @node struct timeval
30592 @unnumberedsubsubsec struct timeval
30593 @cindex struct timeval, in file-i/o protocol
30595 The buffer of type @code{struct timeval} used by the File-I/O protocol
30596 is defined as follows:
30600 time_t tv_sec; /* second */
30601 long tv_usec; /* microsecond */
30605 The integral datatypes conform to the definitions given in the
30606 appropriate section (see @ref{Integral Datatypes}, for details) so this
30607 structure is of size 8 bytes.
30610 @subsection Constants
30611 @cindex constants, in file-i/o protocol
30613 The following values are used for the constants inside of the
30614 protocol. @value{GDBN} and target are responsible for translating these
30615 values before and after the call as needed.
30626 @unnumberedsubsubsec Open Flags
30627 @cindex open flags, in file-i/o protocol
30629 All values are given in hexadecimal representation.
30641 @node mode_t Values
30642 @unnumberedsubsubsec mode_t Values
30643 @cindex mode_t values, in file-i/o protocol
30645 All values are given in octal representation.
30662 @unnumberedsubsubsec Errno Values
30663 @cindex errno values, in file-i/o protocol
30665 All values are given in decimal representation.
30690 @code{EUNKNOWN} is used as a fallback error value if a host system returns
30691 any error value not in the list of supported error numbers.
30694 @unnumberedsubsubsec Lseek Flags
30695 @cindex lseek flags, in file-i/o protocol
30704 @unnumberedsubsubsec Limits
30705 @cindex limits, in file-i/o protocol
30707 All values are given in decimal representation.
30710 INT_MIN -2147483648
30712 UINT_MAX 4294967295
30713 LONG_MIN -9223372036854775808
30714 LONG_MAX 9223372036854775807
30715 ULONG_MAX 18446744073709551615
30718 @node File-I/O Examples
30719 @subsection File-I/O Examples
30720 @cindex file-i/o examples
30722 Example sequence of a write call, file descriptor 3, buffer is at target
30723 address 0x1234, 6 bytes should be written:
30726 <- @code{Fwrite,3,1234,6}
30727 @emph{request memory read from target}
30730 @emph{return "6 bytes written"}
30734 Example sequence of a read call, file descriptor 3, buffer is at target
30735 address 0x1234, 6 bytes should be read:
30738 <- @code{Fread,3,1234,6}
30739 @emph{request memory write to target}
30740 -> @code{X1234,6:XXXXXX}
30741 @emph{return "6 bytes read"}
30745 Example sequence of a read call, call fails on the host due to invalid
30746 file descriptor (@code{EBADF}):
30749 <- @code{Fread,3,1234,6}
30753 Example sequence of a read call, user presses @kbd{Ctrl-c} before syscall on
30757 <- @code{Fread,3,1234,6}
30762 Example sequence of a read call, user presses @kbd{Ctrl-c} after syscall on
30766 <- @code{Fread,3,1234,6}
30767 -> @code{X1234,6:XXXXXX}
30771 @node Library List Format
30772 @section Library List Format
30773 @cindex library list format, remote protocol
30775 On some platforms, a dynamic loader (e.g.@: @file{ld.so}) runs in the
30776 same process as your application to manage libraries. In this case,
30777 @value{GDBN} can use the loader's symbol table and normal memory
30778 operations to maintain a list of shared libraries. On other
30779 platforms, the operating system manages loaded libraries.
30780 @value{GDBN} can not retrieve the list of currently loaded libraries
30781 through memory operations, so it uses the @samp{qXfer:libraries:read}
30782 packet (@pxref{qXfer library list read}) instead. The remote stub
30783 queries the target's operating system and reports which libraries
30786 The @samp{qXfer:libraries:read} packet returns an XML document which
30787 lists loaded libraries and their offsets. Each library has an
30788 associated name and one or more segment or section base addresses,
30789 which report where the library was loaded in memory.
30791 For the common case of libraries that are fully linked binaries, the
30792 library should have a list of segments. If the target supports
30793 dynamic linking of a relocatable object file, its library XML element
30794 should instead include a list of allocated sections. The segment or
30795 section bases are start addresses, not relocation offsets; they do not
30796 depend on the library's link-time base addresses.
30798 @value{GDBN} must be linked with the Expat library to support XML
30799 library lists. @xref{Expat}.
30801 A simple memory map, with one loaded library relocated by a single
30802 offset, looks like this:
30806 <library name="/lib/libc.so.6">
30807 <segment address="0x10000000"/>
30812 Another simple memory map, with one loaded library with three
30813 allocated sections (.text, .data, .bss), looks like this:
30817 <library name="sharedlib.o">
30818 <section address="0x10000000"/>
30819 <section address="0x20000000"/>
30820 <section address="0x30000000"/>
30825 The format of a library list is described by this DTD:
30828 <!-- library-list: Root element with versioning -->
30829 <!ELEMENT library-list (library)*>
30830 <!ATTLIST library-list version CDATA #FIXED "1.0">
30831 <!ELEMENT library (segment*, section*)>
30832 <!ATTLIST library name CDATA #REQUIRED>
30833 <!ELEMENT segment EMPTY>
30834 <!ATTLIST segment address CDATA #REQUIRED>
30835 <!ELEMENT section EMPTY>
30836 <!ATTLIST section address CDATA #REQUIRED>
30839 In addition, segments and section descriptors cannot be mixed within a
30840 single library element, and you must supply at least one segment or
30841 section for each library.
30843 @node Memory Map Format
30844 @section Memory Map Format
30845 @cindex memory map format
30847 To be able to write into flash memory, @value{GDBN} needs to obtain a
30848 memory map from the target. This section describes the format of the
30851 The memory map is obtained using the @samp{qXfer:memory-map:read}
30852 (@pxref{qXfer memory map read}) packet and is an XML document that
30853 lists memory regions.
30855 @value{GDBN} must be linked with the Expat library to support XML
30856 memory maps. @xref{Expat}.
30858 The top-level structure of the document is shown below:
30861 <?xml version="1.0"?>
30862 <!DOCTYPE memory-map
30863 PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
30864 "http://sourceware.org/gdb/gdb-memory-map.dtd">
30870 Each region can be either:
30875 A region of RAM starting at @var{addr} and extending for @var{length}
30879 <memory type="ram" start="@var{addr}" length="@var{length}"/>
30884 A region of read-only memory:
30887 <memory type="rom" start="@var{addr}" length="@var{length}"/>
30892 A region of flash memory, with erasure blocks @var{blocksize}
30896 <memory type="flash" start="@var{addr}" length="@var{length}">
30897 <property name="blocksize">@var{blocksize}</property>
30903 Regions must not overlap. @value{GDBN} assumes that areas of memory not covered
30904 by the memory map are RAM, and uses the ordinary @samp{M} and @samp{X}
30905 packets to write to addresses in such ranges.
30907 The formal DTD for memory map format is given below:
30910 <!-- ................................................... -->
30911 <!-- Memory Map XML DTD ................................ -->
30912 <!-- File: memory-map.dtd .............................. -->
30913 <!-- .................................... .............. -->
30914 <!-- memory-map.dtd -->
30915 <!-- memory-map: Root element with versioning -->
30916 <!ELEMENT memory-map (memory | property)>
30917 <!ATTLIST memory-map version CDATA #FIXED "1.0.0">
30918 <!ELEMENT memory (property)>
30919 <!-- memory: Specifies a memory region,
30920 and its type, or device. -->
30921 <!ATTLIST memory type CDATA #REQUIRED
30922 start CDATA #REQUIRED
30923 length CDATA #REQUIRED
30924 device CDATA #IMPLIED>
30925 <!-- property: Generic attribute tag -->
30926 <!ELEMENT property (#PCDATA | property)*>
30927 <!ATTLIST property name CDATA #REQUIRED>
30930 @include agentexpr.texi
30932 @node Target Descriptions
30933 @appendix Target Descriptions
30934 @cindex target descriptions
30936 @strong{Warning:} target descriptions are still under active development,
30937 and the contents and format may change between @value{GDBN} releases.
30938 The format is expected to stabilize in the future.
30940 One of the challenges of using @value{GDBN} to debug embedded systems
30941 is that there are so many minor variants of each processor
30942 architecture in use. It is common practice for vendors to start with
30943 a standard processor core --- ARM, PowerPC, or MIPS, for example ---
30944 and then make changes to adapt it to a particular market niche. Some
30945 architectures have hundreds of variants, available from dozens of
30946 vendors. This leads to a number of problems:
30950 With so many different customized processors, it is difficult for
30951 the @value{GDBN} maintainers to keep up with the changes.
30953 Since individual variants may have short lifetimes or limited
30954 audiences, it may not be worthwhile to carry information about every
30955 variant in the @value{GDBN} source tree.
30957 When @value{GDBN} does support the architecture of the embedded system
30958 at hand, the task of finding the correct architecture name to give the
30959 @command{set architecture} command can be error-prone.
30962 To address these problems, the @value{GDBN} remote protocol allows a
30963 target system to not only identify itself to @value{GDBN}, but to
30964 actually describe its own features. This lets @value{GDBN} support
30965 processor variants it has never seen before --- to the extent that the
30966 descriptions are accurate, and that @value{GDBN} understands them.
30968 @value{GDBN} must be linked with the Expat library to support XML
30969 target descriptions. @xref{Expat}.
30972 * Retrieving Descriptions:: How descriptions are fetched from a target.
30973 * Target Description Format:: The contents of a target description.
30974 * Predefined Target Types:: Standard types available for target
30976 * Standard Target Features:: Features @value{GDBN} knows about.
30979 @node Retrieving Descriptions
30980 @section Retrieving Descriptions
30982 Target descriptions can be read from the target automatically, or
30983 specified by the user manually. The default behavior is to read the
30984 description from the target. @value{GDBN} retrieves it via the remote
30985 protocol using @samp{qXfer} requests (@pxref{General Query Packets,
30986 qXfer}). The @var{annex} in the @samp{qXfer} packet will be
30987 @samp{target.xml}. The contents of the @samp{target.xml} annex are an
30988 XML document, of the form described in @ref{Target Description
30991 Alternatively, you can specify a file to read for the target description.
30992 If a file is set, the target will not be queried. The commands to
30993 specify a file are:
30996 @cindex set tdesc filename
30997 @item set tdesc filename @var{path}
30998 Read the target description from @var{path}.
31000 @cindex unset tdesc filename
31001 @item unset tdesc filename
31002 Do not read the XML target description from a file. @value{GDBN}
31003 will use the description supplied by the current target.
31005 @cindex show tdesc filename
31006 @item show tdesc filename
31007 Show the filename to read for a target description, if any.
31011 @node Target Description Format
31012 @section Target Description Format
31013 @cindex target descriptions, XML format
31015 A target description annex is an @uref{http://www.w3.org/XML/, XML}
31016 document which complies with the Document Type Definition provided in
31017 the @value{GDBN} sources in @file{gdb/features/gdb-target.dtd}. This
31018 means you can use generally available tools like @command{xmllint} to
31019 check that your feature descriptions are well-formed and valid.
31020 However, to help people unfamiliar with XML write descriptions for
31021 their targets, we also describe the grammar here.
31023 Target descriptions can identify the architecture of the remote target
31024 and (for some architectures) provide information about custom register
31025 sets. They can also identify the OS ABI of the remote target.
31026 @value{GDBN} can use this information to autoconfigure for your
31027 target, or to warn you if you connect to an unsupported target.
31029 Here is a simple target description:
31032 <target version="1.0">
31033 <architecture>i386:x86-64</architecture>
31038 This minimal description only says that the target uses
31039 the x86-64 architecture.
31041 A target description has the following overall form, with [ ] marking
31042 optional elements and @dots{} marking repeatable elements. The elements
31043 are explained further below.
31046 <?xml version="1.0"?>
31047 <!DOCTYPE target SYSTEM "gdb-target.dtd">
31048 <target version="1.0">
31049 @r{[}@var{architecture}@r{]}
31050 @r{[}@var{osabi}@r{]}
31051 @r{[}@var{compatible}@r{]}
31052 @r{[}@var{feature}@dots{}@r{]}
31057 The description is generally insensitive to whitespace and line
31058 breaks, under the usual common-sense rules. The XML version
31059 declaration and document type declaration can generally be omitted
31060 (@value{GDBN} does not require them), but specifying them may be
31061 useful for XML validation tools. The @samp{version} attribute for
31062 @samp{<target>} may also be omitted, but we recommend
31063 including it; if future versions of @value{GDBN} use an incompatible
31064 revision of @file{gdb-target.dtd}, they will detect and report
31065 the version mismatch.
31067 @subsection Inclusion
31068 @cindex target descriptions, inclusion
31071 @cindex <xi:include>
31074 It can sometimes be valuable to split a target description up into
31075 several different annexes, either for organizational purposes, or to
31076 share files between different possible target descriptions. You can
31077 divide a description into multiple files by replacing any element of
31078 the target description with an inclusion directive of the form:
31081 <xi:include href="@var{document}"/>
31085 When @value{GDBN} encounters an element of this form, it will retrieve
31086 the named XML @var{document}, and replace the inclusion directive with
31087 the contents of that document. If the current description was read
31088 using @samp{qXfer}, then so will be the included document;
31089 @var{document} will be interpreted as the name of an annex. If the
31090 current description was read from a file, @value{GDBN} will look for
31091 @var{document} as a file in the same directory where it found the
31092 original description.
31094 @subsection Architecture
31095 @cindex <architecture>
31097 An @samp{<architecture>} element has this form:
31100 <architecture>@var{arch}</architecture>
31103 @var{arch} is one of the architectures from the set accepted by
31104 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
31107 @cindex @code{<osabi>}
31109 This optional field was introduced in @value{GDBN} version 7.0.
31110 Previous versions of @value{GDBN} ignore it.
31112 An @samp{<osabi>} element has this form:
31115 <osabi>@var{abi-name}</osabi>
31118 @var{abi-name} is an OS ABI name from the same selection accepted by
31119 @w{@code{set osabi}} (@pxref{ABI, ,Configuring the Current ABI}).
31121 @subsection Compatible Architecture
31122 @cindex @code{<compatible>}
31124 This optional field was introduced in @value{GDBN} version 7.0.
31125 Previous versions of @value{GDBN} ignore it.
31127 A @samp{<compatible>} element has this form:
31130 <compatible>@var{arch}</compatible>
31133 @var{arch} is one of the architectures from the set accepted by
31134 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
31136 A @samp{<compatible>} element is used to specify that the target
31137 is able to run binaries in some other than the main target architecture
31138 given by the @samp{<architecture>} element. For example, on the
31139 Cell Broadband Engine, the main architecture is @code{powerpc:common}
31140 or @code{powerpc:common64}, but the system is able to run binaries
31141 in the @code{spu} architecture as well. The way to describe this
31142 capability with @samp{<compatible>} is as follows:
31145 <architecture>powerpc:common</architecture>
31146 <compatible>spu</compatible>
31149 @subsection Features
31152 Each @samp{<feature>} describes some logical portion of the target
31153 system. Features are currently used to describe available CPU
31154 registers and the types of their contents. A @samp{<feature>} element
31158 <feature name="@var{name}">
31159 @r{[}@var{type}@dots{}@r{]}
31165 Each feature's name should be unique within the description. The name
31166 of a feature does not matter unless @value{GDBN} has some special
31167 knowledge of the contents of that feature; if it does, the feature
31168 should have its standard name. @xref{Standard Target Features}.
31172 Any register's value is a collection of bits which @value{GDBN} must
31173 interpret. The default interpretation is a two's complement integer,
31174 but other types can be requested by name in the register description.
31175 Some predefined types are provided by @value{GDBN} (@pxref{Predefined
31176 Target Types}), and the description can define additional composite types.
31178 Each type element must have an @samp{id} attribute, which gives
31179 a unique (within the containing @samp{<feature>}) name to the type.
31180 Types must be defined before they are used.
31183 Some targets offer vector registers, which can be treated as arrays
31184 of scalar elements. These types are written as @samp{<vector>} elements,
31185 specifying the array element type, @var{type}, and the number of elements,
31189 <vector id="@var{id}" type="@var{type}" count="@var{count}"/>
31193 If a register's value is usefully viewed in multiple ways, define it
31194 with a union type containing the useful representations. The
31195 @samp{<union>} element contains one or more @samp{<field>} elements,
31196 each of which has a @var{name} and a @var{type}:
31199 <union id="@var{id}">
31200 <field name="@var{name}" type="@var{type}"/>
31205 @subsection Registers
31208 Each register is represented as an element with this form:
31211 <reg name="@var{name}"
31212 bitsize="@var{size}"
31213 @r{[}regnum="@var{num}"@r{]}
31214 @r{[}save-restore="@var{save-restore}"@r{]}
31215 @r{[}type="@var{type}"@r{]}
31216 @r{[}group="@var{group}"@r{]}/>
31220 The components are as follows:
31225 The register's name; it must be unique within the target description.
31228 The register's size, in bits.
31231 The register's number. If omitted, a register's number is one greater
31232 than that of the previous register (either in the current feature or in
31233 a preceeding feature); the first register in the target description
31234 defaults to zero. This register number is used to read or write
31235 the register; e.g.@: it is used in the remote @code{p} and @code{P}
31236 packets, and registers appear in the @code{g} and @code{G} packets
31237 in order of increasing register number.
31240 Whether the register should be preserved across inferior function
31241 calls; this must be either @code{yes} or @code{no}. The default is
31242 @code{yes}, which is appropriate for most registers except for
31243 some system control registers; this is not related to the target's
31247 The type of the register. @var{type} may be a predefined type, a type
31248 defined in the current feature, or one of the special types @code{int}
31249 and @code{float}. @code{int} is an integer type of the correct size
31250 for @var{bitsize}, and @code{float} is a floating point type (in the
31251 architecture's normal floating point format) of the correct size for
31252 @var{bitsize}. The default is @code{int}.
31255 The register group to which this register belongs. @var{group} must
31256 be either @code{general}, @code{float}, or @code{vector}. If no
31257 @var{group} is specified, @value{GDBN} will not display the register
31258 in @code{info registers}.
31262 @node Predefined Target Types
31263 @section Predefined Target Types
31264 @cindex target descriptions, predefined types
31266 Type definitions in the self-description can build up composite types
31267 from basic building blocks, but can not define fundamental types. Instead,
31268 standard identifiers are provided by @value{GDBN} for the fundamental
31269 types. The currently supported types are:
31278 Signed integer types holding the specified number of bits.
31285 Unsigned integer types holding the specified number of bits.
31289 Pointers to unspecified code and data. The program counter and
31290 any dedicated return address register may be marked as code
31291 pointers; printing a code pointer converts it into a symbolic
31292 address. The stack pointer and any dedicated address registers
31293 may be marked as data pointers.
31296 Single precision IEEE floating point.
31299 Double precision IEEE floating point.
31302 The 12-byte extended precision format used by ARM FPA registers.
31306 @node Standard Target Features
31307 @section Standard Target Features
31308 @cindex target descriptions, standard features
31310 A target description must contain either no registers or all the
31311 target's registers. If the description contains no registers, then
31312 @value{GDBN} will assume a default register layout, selected based on
31313 the architecture. If the description contains any registers, the
31314 default layout will not be used; the standard registers must be
31315 described in the target description, in such a way that @value{GDBN}
31316 can recognize them.
31318 This is accomplished by giving specific names to feature elements
31319 which contain standard registers. @value{GDBN} will look for features
31320 with those names and verify that they contain the expected registers;
31321 if any known feature is missing required registers, or if any required
31322 feature is missing, @value{GDBN} will reject the target
31323 description. You can add additional registers to any of the
31324 standard features --- @value{GDBN} will display them just as if
31325 they were added to an unrecognized feature.
31327 This section lists the known features and their expected contents.
31328 Sample XML documents for these features are included in the
31329 @value{GDBN} source tree, in the directory @file{gdb/features}.
31331 Names recognized by @value{GDBN} should include the name of the
31332 company or organization which selected the name, and the overall
31333 architecture to which the feature applies; so e.g.@: the feature
31334 containing ARM core registers is named @samp{org.gnu.gdb.arm.core}.
31336 The names of registers are not case sensitive for the purpose
31337 of recognizing standard features, but @value{GDBN} will only display
31338 registers using the capitalization used in the description.
31344 * PowerPC Features::
31349 @subsection ARM Features
31350 @cindex target descriptions, ARM features
31352 The @samp{org.gnu.gdb.arm.core} feature is required for ARM targets.
31353 It should contain registers @samp{r0} through @samp{r13}, @samp{sp},
31354 @samp{lr}, @samp{pc}, and @samp{cpsr}.
31356 The @samp{org.gnu.gdb.arm.fpa} feature is optional. If present, it
31357 should contain registers @samp{f0} through @samp{f7} and @samp{fps}.
31359 The @samp{org.gnu.gdb.xscale.iwmmxt} feature is optional. If present,
31360 it should contain at least registers @samp{wR0} through @samp{wR15} and
31361 @samp{wCGR0} through @samp{wCGR3}. The @samp{wCID}, @samp{wCon},
31362 @samp{wCSSF}, and @samp{wCASF} registers are optional.
31364 The @samp{org.gnu.gdb.arm.vfp} feature is optional. If present, it
31365 should contain at least registers @samp{d0} through @samp{d15}. If
31366 they are present, @samp{d16} through @samp{d31} should also be included.
31367 @value{GDBN} will synthesize the single-precision registers from
31368 halves of the double-precision registers.
31370 The @samp{org.gnu.gdb.arm.neon} feature is optional. It does not
31371 need to contain registers; it instructs @value{GDBN} to display the
31372 VFP double-precision registers as vectors and to synthesize the
31373 quad-precision registers from pairs of double-precision registers.
31374 If this feature is present, @samp{org.gnu.gdb.arm.vfp} must also
31375 be present and include 32 double-precision registers.
31377 @node MIPS Features
31378 @subsection MIPS Features
31379 @cindex target descriptions, MIPS features
31381 The @samp{org.gnu.gdb.mips.cpu} feature is required for MIPS targets.
31382 It should contain registers @samp{r0} through @samp{r31}, @samp{lo},
31383 @samp{hi}, and @samp{pc}. They may be 32-bit or 64-bit depending
31386 The @samp{org.gnu.gdb.mips.cp0} feature is also required. It should
31387 contain at least the @samp{status}, @samp{badvaddr}, and @samp{cause}
31388 registers. They may be 32-bit or 64-bit depending on the target.
31390 The @samp{org.gnu.gdb.mips.fpu} feature is currently required, though
31391 it may be optional in a future version of @value{GDBN}. It should
31392 contain registers @samp{f0} through @samp{f31}, @samp{fcsr}, and
31393 @samp{fir}. They may be 32-bit or 64-bit depending on the target.
31395 The @samp{org.gnu.gdb.mips.linux} feature is optional. It should
31396 contain a single register, @samp{restart}, which is used by the
31397 Linux kernel to control restartable syscalls.
31399 @node M68K Features
31400 @subsection M68K Features
31401 @cindex target descriptions, M68K features
31404 @item @samp{org.gnu.gdb.m68k.core}
31405 @itemx @samp{org.gnu.gdb.coldfire.core}
31406 @itemx @samp{org.gnu.gdb.fido.core}
31407 One of those features must be always present.
31408 The feature that is present determines which flavor of m68k is
31409 used. The feature that is present should contain registers
31410 @samp{d0} through @samp{d7}, @samp{a0} through @samp{a5}, @samp{fp},
31411 @samp{sp}, @samp{ps} and @samp{pc}.
31413 @item @samp{org.gnu.gdb.coldfire.fp}
31414 This feature is optional. If present, it should contain registers
31415 @samp{fp0} through @samp{fp7}, @samp{fpcontrol}, @samp{fpstatus} and
31419 @node PowerPC Features
31420 @subsection PowerPC Features
31421 @cindex target descriptions, PowerPC features
31423 The @samp{org.gnu.gdb.power.core} feature is required for PowerPC
31424 targets. It should contain registers @samp{r0} through @samp{r31},
31425 @samp{pc}, @samp{msr}, @samp{cr}, @samp{lr}, @samp{ctr}, and
31426 @samp{xer}. They may be 32-bit or 64-bit depending on the target.
31428 The @samp{org.gnu.gdb.power.fpu} feature is optional. It should
31429 contain registers @samp{f0} through @samp{f31} and @samp{fpscr}.
31431 The @samp{org.gnu.gdb.power.altivec} feature is optional. It should
31432 contain registers @samp{vr0} through @samp{vr31}, @samp{vscr},
31435 The @samp{org.gnu.gdb.power.vsx} feature is optional. It should
31436 contain registers @samp{vs0h} through @samp{vs31h}. @value{GDBN}
31437 will combine these registers with the floating point registers
31438 (@samp{f0} through @samp{f31}) and the altivec registers (@samp{vr0}
31439 through @samp{vr31}) to present the 128-bit wide registers @samp{vs0}
31440 through @samp{vs63}, the set of vector registers for POWER7.
31442 The @samp{org.gnu.gdb.power.spe} feature is optional. It should
31443 contain registers @samp{ev0h} through @samp{ev31h}, @samp{acc}, and
31444 @samp{spefscr}. SPE targets should provide 32-bit registers in
31445 @samp{org.gnu.gdb.power.core} and provide the upper halves in
31446 @samp{ev0h} through @samp{ev31h}. @value{GDBN} will combine
31447 these to present registers @samp{ev0} through @samp{ev31} to the
31450 @node Operating System Information
31451 @appendix Operating System Information
31452 @cindex operating system information
31458 Users of @value{GDBN} often wish to obtain information about the state of
31459 the operating system running on the target---for example the list of
31460 processes, or the list of open files. This section describes the
31461 mechanism that makes it possible. This mechanism is similar to the
31462 target features mechanism (@pxref{Target Descriptions}), but focuses
31463 on a different aspect of target.
31465 Operating system information is retrived from the target via the
31466 remote protocol, using @samp{qXfer} requests (@pxref{qXfer osdata
31467 read}). The object name in the request should be @samp{osdata}, and
31468 the @var{annex} identifies the data to be fetched.
31471 @appendixsection Process list
31472 @cindex operating system information, process list
31474 When requesting the process list, the @var{annex} field in the
31475 @samp{qXfer} request should be @samp{processes}. The returned data is
31476 an XML document. The formal syntax of this document is defined in
31477 @file{gdb/features/osdata.dtd}.
31479 An example document is:
31482 <?xml version="1.0"?>
31483 <!DOCTYPE target SYSTEM "osdata.dtd">
31484 <osdata type="processes">
31486 <column name="pid">1</column>
31487 <column name="user">root</column>
31488 <column name="command">/sbin/init</column>
31493 Each item should include a column whose name is @samp{pid}. The value
31494 of that column should identify the process on the target. The
31495 @samp{user} and @samp{command} columns are optional, and will be
31496 displayed by @value{GDBN}. Target may provide additional columns,
31497 which @value{GDBN} currently ignores.
31511 % I think something like @colophon should be in texinfo. In the
31513 \long\def\colophon{\hbox to0pt{}\vfill
31514 \centerline{The body of this manual is set in}
31515 \centerline{\fontname\tenrm,}
31516 \centerline{with headings in {\bf\fontname\tenbf}}
31517 \centerline{and examples in {\tt\fontname\tentt}.}
31518 \centerline{{\it\fontname\tenit\/},}
31519 \centerline{{\bf\fontname\tenbf}, and}
31520 \centerline{{\sl\fontname\tensl\/}}
31521 \centerline{are used for emphasis.}\vfill}
31523 % Blame: doc@cygnus.com, 1991.