1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988 1989 1990 1991 1992 1993 1994 Free Software Foundation, Inc.
5 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
6 @c of @set vars. However, you can override filename with makeinfo -o.
12 @settitle Debugging with @value{GDBN}
15 @settitle Debugging with @value{GDBN} (@value{TARGET})
17 @setchapternewpage odd
28 @c readline appendices use @vindex
31 @c !!set GDB manual's edition---not the same as GDB version!
34 @c !!set GDB manual's revision date
35 @set DATE January 1994
37 @c GDB CHANGELOG CONSULTED BETWEEN:
38 @c Fri Oct 11 23:27:06 1991 John Gilmore (gnu at cygnus.com)
39 @c Sat Dec 22 02:51:40 1990 John Gilmore (gnu at cygint)
41 @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly.
44 @c This is a dir.info fragment to support semi-automated addition of
45 @c manuals to an info tree. zoo@cygnus.com is developing this facility.
48 * Gdb: (gdb). The GNU debugger.
55 This file documents the GNU debugger @value{GDBN}.
58 This is Edition @value{EDITION}, @value{DATE},
59 of @cite{Debugging with @value{GDBN}: the GNU Source-Level Debugger}
60 for GDB Version @value{GDBVN}.
62 Copyright (C) 1988, '89, '90, '91, '92, '93 Free Software Foundation, Inc.
64 Permission is granted to make and distribute verbatim copies of
65 this manual provided the copyright notice and this permission notice
66 are preserved on all copies.
69 Permission is granted to process this file through TeX and print the
70 results, provided the printed document carries copying permission
71 notice identical to this one except for the removal of this paragraph
72 (this paragraph not being relevant to the printed manual).
75 Permission is granted to copy and distribute modified versions of this
76 manual under the conditions for verbatim copying, provided also that the
77 entire resulting derived work is distributed under the terms of a
78 permission notice identical to this one.
80 Permission is granted to copy and distribute translations of this manual
81 into another language, under the above conditions for modified versions.
85 @title Debugging with @value{GDBN}
86 @subtitle The GNU Source-Level Debugger
88 @subtitle (@value{TARGET})
91 @subtitle Edition @value{EDITION}, for @value{GDBN} version @value{GDBVN}
92 @subtitle @value{DATE}
93 @author Richard M. Stallman and Roland H. Pesch
97 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@prep.ai.mit.edu.)\par
98 \hfill {\it Debugging with @value{GDBN}}\par
99 \hfill \TeX{}info \texinfoversion\par
100 \hfill pesch\@cygnus.com\par
104 @vskip 0pt plus 1filll
105 Copyright @copyright{} 1988, '89, '90, '91, '92, '93 Free Software
108 Published by the Free Software Foundation @*
109 675 Massachusetts Avenue, @*
110 Cambridge, MA 02139 USA @*
111 Printed copies are available for $20 each. @*
112 ISBN 1-882114-11-6 @*
114 Permission is granted to make and distribute verbatim copies of
115 this manual provided the copyright notice and this permission notice
116 are preserved on all copies.
118 Permission is granted to copy and distribute modified versions of this
119 manual under the conditions for verbatim copying, provided also that the
120 entire resulting derived work is distributed under the terms of a
121 permission notice identical to this one.
123 Permission is granted to copy and distribute translations of this manual
124 into another language, under the above conditions for modified versions.
130 @top Debugging with @value{GDBN}
132 This file describes @value{GDBN}, the GNU symbolic debugger.
134 This is Edition @value{EDITION}, @value{DATE}, for GDB Version @value{GDBVN}.
137 * Summary:: Summary of @value{GDBN}
139 * New Features:: New features since GDB version 3.5
142 * Sample Session:: A sample @value{GDBN} session
145 * Invocation:: Getting in and out of @value{GDBN}
146 * Commands:: @value{GDBN} commands
147 * Running:: Running programs under @value{GDBN}
148 * Stopping:: Stopping and continuing
149 * Stack:: Examining the stack
150 * Source:: Examining source files
151 * Data:: Examining data
153 * Languages:: Using @value{GDBN} with different languages
156 * C:: C language support
158 @c remnant makeinfo bug, blank line needed after two end-ifs?
160 * Symbols:: Examining the symbol table
161 * Altering:: Altering execution
162 * GDB Files:: @value{GDBN} files
163 * Targets:: Specifying a debugging target
164 * Controlling GDB:: Controlling @value{GDBN}
165 * Sequences:: Canned sequences of commands
167 * Emacs:: Using @value{GDBN} under GNU Emacs
170 * GDB Bugs:: Reporting bugs in @value{GDBN}
171 * Command Line Editing:: Facilities of the readline library
172 * Using History Interactively::
176 @ifclear PRECONFIGURED
177 * Formatting Documentation:: How to format and print GDB documentation
178 * Installing GDB:: Installing GDB
186 @unnumbered Summary of @value{GDBN}
188 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
189 going on ``inside'' another program while it executes---or what another
190 program was doing at the moment it crashed.
192 @value{GDBN} can do four main kinds of things (plus other things in support of
193 these) to help you catch bugs in the act:
197 Start your program, specifying anything that might affect its behavior.
200 Make your program stop on specified conditions.
203 Examine what has happened, when your program has stopped.
206 Change things in your program, so you can experiment with correcting the
207 effects of one bug and go on to learn about another.
211 You can use @value{GDBN} to debug programs written in C or C++.
212 @c "MOD2" used as a "miscellaneous languages" flag here.
213 @c This is acceptable while there is no real doc for Chill and Pascal.
215 For more information, see @ref{Support,,Supported languages}.
218 For more information, see @ref{C,,C and C++}.
220 Support for Modula-2 and Chill is partial. For information on Modula-2,
221 see @ref{Modula-2,,Modula-2}. There is no further documentation on Chill yet.
223 Debugging Pascal programs which use sets, subranges, file variables, or nested
224 functions does not currently work. @value{GDBN} does not support
225 entering expressions, printing values, or similar features using Pascal syntax.
229 @value{GDBN} can be used to debug programs written in Fortran, although
230 it does not yet support entering expressions, printing values, or
231 similar features using Fortran syntax. It may be necessary to refer to
232 some variables with a trailing underscore.
237 * Free Software:: Freely redistributable software
238 * Contributors:: Contributors to GDB
242 @unnumberedsec Free software
244 @value{GDBN} is @dfn{free software}, protected by the GNU General Public License
245 (GPL). The GPL gives you the freedom to copy or adapt a licensed
246 program---but every person getting a copy also gets with it the
247 freedom to modify that copy (which means that they must get access to
248 the source code), and the freedom to distribute further copies.
249 Typical software companies use copyrights to limit your freedoms; the
250 Free Software Foundation uses the GPL to preserve these freedoms.
252 Fundamentally, the General Public License is a license which says that
253 you have these freedoms and that you cannot take these freedoms away
257 @unnumberedsec Contributors to GDB
259 Richard Stallman was the original author of GDB, and of many other GNU
260 programs. Many others have contributed to its development. This
261 section attempts to credit major contributors. One of the virtues of
262 free software is that everyone is free to contribute to it; with
263 regret, we cannot actually acknowledge everyone here. The file
264 @file{ChangeLog} in the GDB distribution approximates a blow-by-blow
267 Changes much prior to version 2.0 are lost in the mists of time.
270 @emph{Plea:} Additions to this section are particularly welcome. If you
271 or your friends (or enemies, to be evenhanded) have been unfairly
272 omitted from this list, we would like to add your names!
275 So that they may not regard their long labor as thankless, we
276 particularly thank those who shepherded GDB through major releases:
277 Fred Fish (releases 4.12, 4.11, 4.10, and 4.9),
278 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4),
279 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
280 Jim Kingdon (releases 3.5, 3.4, and 3.3);
281 and Randy Smith (releases 3.2, 3.1, and 3.0).
282 As major maintainer of GDB for some period, each
283 contributed significantly to the structure, stability, and capabilities
284 of the entire debugger.
286 Richard Stallman, assisted at various times by Peter TerMaat, Chris
287 Hanson, and Richard Mlynarik, handled releases through 2.8.
290 Michael Tiemann is the author of most of the GNU C++ support in GDB,
291 with significant additional contributions from Per Bothner. James
292 Clark wrote the GNU C++ demangler. Early work on C++ was by Peter
293 TerMaat (who also did much general update work leading to release 3.0).
296 GDB 4 uses the BFD subroutine library to examine multiple
297 object-file formats; BFD was a joint project of David V.
298 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
300 David Johnson wrote the original COFF support; Pace Willison did
301 the original support for encapsulated COFF.
303 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
304 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
306 Jean-Daniel Fekete contributed Sun 386i support.
307 Chris Hanson improved the HP9000 support.
308 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
309 David Johnson contributed Encore Umax support.
310 Jyrki Kuoppala contributed Altos 3068 support.
311 Jeff Law contributed HP PA and SOM support.
312 Keith Packard contributed NS32K support.
313 Doug Rabson contributed Acorn Risc Machine support.
314 Bob Rusk contributed Harris Nighthawk CX-UX support.
315 Chris Smith contributed Convex support (and Fortran debugging).
316 Jonathan Stone contributed Pyramid support.
317 Michael Tiemann contributed SPARC support.
318 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
319 Pace Willison contributed Intel 386 support.
320 Jay Vosburgh contributed Symmetry support.
322 Rich Schaefer and Peter Schauer helped with support of SunOS shared
325 Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about
326 several machine instruction sets.
328 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped
329 develop remote debugging. Intel Corporation and Wind River Systems
330 contributed remote debugging modules for their products.
332 Brian Fox is the author of the readline libraries providing
333 command-line editing and command history.
335 Andrew Beers of SUNY Buffalo wrote the language-switching code,
337 the Modula-2 support,
339 and contributed the Languages chapter of this manual.
341 Fred Fish wrote most of the support for Unix System Vr4.
343 He also enhanced the command-completion support to cover C++ overloaded
347 Hitachi America, Ltd. sponsored the support for Hitachi microprocessors.
349 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
352 Stu Grossman wrote gdbserver.
354 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
355 nearly innumerable bug fixes and cleanups throughout GDB.
359 @unnumbered New Features since GDB Version 3.5
363 Using the new command @code{target}, you can select at runtime whether
364 you are debugging local files, local processes, standalone systems over
365 a serial port, or realtime systems over a TCP/IP connection. The
366 command @code{load} can download programs into a remote system. Serial
367 stubs are available for Motorola 680x0, Intel 80386, and Sparc remote
368 systems; GDB also supports debugging realtime processes running under
369 VxWorks, using SunRPC Remote Procedure Calls over TCP/IP to talk to a
370 debugger stub on the target system. Internally, GDB now uses a function
371 vector to mediate access to different targets; if you need to add your
372 own support for a remote protocol, this makes it much easier.
375 GDB now sports watchpoints as well as breakpoints. You can use a
376 watchpoint to stop execution whenever the value of an expression
377 changes, without having to predict a particular place in your program
378 where this may happen.
381 Commands that issue wide output now insert newlines at places designed
382 to make the output more readable.
384 @item Object Code Formats
385 GDB uses a new library called the Binary File Descriptor (BFD) Library
386 to permit it to switch dynamically, without reconfiguration or
387 recompilation, between different object-file formats. Formats currently
388 supported are COFF, ELF, a.out, Intel 960 b.out, MIPS ECOFF, HPPA SOM
389 (with stabs debugging), and S-records; files may be read as .o files,
390 archive libraries, or core dumps. BFD is available as a subroutine
391 library so that other programs may take advantage of it, and the other
392 GNU binary utilities are being converted to use it.
394 @item Configuration and Ports
395 Compile-time configuration (to select a particular architecture and
396 operating system) is much easier. The script @code{configure} now
397 allows you to configure GDB as either a native debugger or a
398 cross-debugger. @xref{Installing GDB}, for details on how to
402 The user interface to the GDB control variables is simpler,
403 and is consolidated in two commands, @code{set} and @code{show}. Output
404 lines are now broken at readable places, rather than overflowing onto
405 the next line. You can suppress output of machine-level addresses,
406 displaying only source language information.
409 GDB now supports C++ multiple inheritance (if used with a GCC
410 version 2 compiler), and also has limited support for C++ exception
411 handling, with the commands @code{catch} and @code{info catch}: GDB
412 can break when an exception is raised, before the stack is peeled back
413 to the exception handler's context.
417 GDB now has preliminary support for the GNU Modula-2 compiler, currently
418 under development at the State University of New York at Buffalo.
419 Coordinated development of both GDB and the GNU Modula-2 compiler will
420 continue. Other Modula-2 compilers are currently not supported, and
421 attempting to debug programs compiled with them will likely result in an
422 error as the symbol table of the executable is read in.
425 @item Command Rationalization
426 Many GDB commands have been renamed to make them easier to remember
427 and use. In particular, the subcommands of @code{info} and
428 @code{show}/@code{set} are grouped to make the former refer to the state
429 of your program, and the latter refer to the state of GDB itself.
430 @xref{Renamed Commands}, for details on what commands were renamed.
432 @item Shared Libraries
433 GDB 4 can debug programs and core files that use SunOS, SVR4, or IBM RS/6000
437 On some systems, GDB 4 has facilities to debug multi-thread programs.
440 GDB 4 has a reference card. @xref{Formatting Documentation,,Formatting
441 the Documentation}, for instructions about how to print it.
447 @chapter A Sample @value{GDBN} Session
449 You can use this manual at your leisure to read all about @value{GDBN}.
450 However, a handful of commands are enough to get started using the
451 debugger. This chapter illustrates those commands.
454 In this sample session, we emphasize user input like this: @b{input},
455 to make it easier to pick out from the surrounding output.
458 @c FIXME: this example may not be appropriate for some configs, where
459 @c FIXME...primary interest is in remote use.
461 One of the preliminary versions of GNU @code{m4} (a generic macro
462 processor) exhibits the following bug: sometimes, when we change its
463 quote strings from the default, the commands used to capture one macro
464 definition within another stop working. In the following short @code{m4}
465 session, we define a macro @code{foo} which expands to @code{0000}; we
466 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
467 same thing. However, when we change the open quote string to
468 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
469 procedure fails to define a new synonym @code{baz}:
478 @b{define(bar,defn(`foo'))}
482 @b{changequote(<QUOTE>,<UNQUOTE>)}
484 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
487 m4: End of input: 0: fatal error: EOF in string
491 Let us use @value{GDBN} to try to see what is going on.
494 $ @b{@value{GDBP} m4}
495 @c FIXME: this falsifies the exact text played out, to permit smallbook
496 @c FIXME... format to come out better.
497 GDB is free software and you are welcome to distribute copies
498 of it under certain conditions; type "show copying" to see
500 There is absolutely no warranty for GDB; type "show warranty"
502 GDB @value{GDBVN}, Copyright 1993 Free Software Foundation, Inc...
507 @value{GDBN} reads only enough symbol data to know where to find the
508 rest when needed; as a result, the first prompt comes up very quickly.
509 We now tell @value{GDBN} to use a narrower display width than usual, so
510 that examples fit in this manual.
513 (@value{GDBP}) @b{set width 70}
517 We need to see how the @code{m4} built-in @code{changequote} works.
518 Having looked at the source, we know the relevant subroutine is
519 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
520 @code{break} command.
523 (@value{GDBP}) @b{break m4_changequote}
524 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
528 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
529 control; as long as control does not reach the @code{m4_changequote}
530 subroutine, the program runs as usual:
533 (@value{GDBP}) @b{run}
534 Starting program: /work/Editorial/gdb/gnu/m4/m4
542 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
543 suspends execution of @code{m4}, displaying information about the
544 context where it stops.
547 @b{changequote(<QUOTE>,<UNQUOTE>)}
549 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
551 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
555 Now we use the command @code{n} (@code{next}) to advance execution to
556 the next line of the current function.
560 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
565 @code{set_quotes} looks like a promising subroutine. We can go into it
566 by using the command @code{s} (@code{step}) instead of @code{next}.
567 @code{step} goes to the next line to be executed in @emph{any}
568 subroutine, so it steps into @code{set_quotes}.
572 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
574 530 if (lquote != def_lquote)
578 The display that shows the subroutine where @code{m4} is now
579 suspended (and its arguments) is called a stack frame display. It
580 shows a summary of the stack. We can use the @code{backtrace}
581 command (which can also be spelled @code{bt}), to see where we are
582 in the stack as a whole: the @code{backtrace} command displays a
583 stack frame for each active subroutine.
586 (@value{GDBP}) @b{bt}
587 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
589 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
591 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
592 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
594 #4 0x79dc in expand_input () at macro.c:40
595 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
599 We step through a few more lines to see what happens. The first two
600 times, we can use @samp{s}; the next two times we use @code{n} to avoid
601 falling into the @code{xstrdup} subroutine.
605 0x3b5c 532 if (rquote != def_rquote)
607 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
608 def_lquote : xstrdup(lq);
610 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
613 538 len_lquote = strlen(rquote);
617 The last line displayed looks a little odd; we can examine the variables
618 @code{lquote} and @code{rquote} to see if they are in fact the new left
619 and right quotes we specified. We use the command @code{p}
620 (@code{print}) to see their values.
623 (@value{GDBP}) @b{p lquote}
624 $1 = 0x35d40 "<QUOTE>"
625 (@value{GDBP}) @b{p rquote}
626 $2 = 0x35d50 "<UNQUOTE>"
630 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
631 To look at some context, we can display ten lines of source
632 surrounding the current line with the @code{l} (@code{list}) command.
638 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
640 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
643 538 len_lquote = strlen(rquote);
644 539 len_rquote = strlen(lquote);
651 Let us step past the two lines that set @code{len_lquote} and
652 @code{len_rquote}, and then examine the values of those variables.
656 539 len_rquote = strlen(lquote);
659 (@value{GDBP}) @b{p len_lquote}
661 (@value{GDBP}) @b{p len_rquote}
666 That certainly looks wrong, assuming @code{len_lquote} and
667 @code{len_rquote} are meant to be the lengths of @code{lquote} and
668 @code{rquote} respectively. We can set them to better values using
669 the @code{p} command, since it can print the value of
670 any expression---and that expression can include subroutine calls and
674 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
676 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
681 Is that enough to fix the problem of using the new quotes with the
682 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
683 executing with the @code{c} (@code{continue}) command, and then try the
684 example that caused trouble initially:
690 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
697 Success! The new quotes now work just as well as the default ones. The
698 problem seems to have been just the two typos defining the wrong
699 lengths. We allow @code{m4} exit by giving it an EOF as input:
703 Program exited normally.
707 The message @samp{Program exited normally.} is from @value{GDBN}; it
708 indicates @code{m4} has finished executing. We can end our @value{GDBN}
709 session with the @value{GDBN} @code{quit} command.
712 (@value{GDBP}) @b{quit}
717 @chapter Getting In and Out of @value{GDBN}
719 This chapter discusses how to start @value{GDBN}, and how to get out of it.
720 (The essentials: type @samp{@value{GDBP}} to start GDB, and type @kbd{quit}
721 or @kbd{C-d} to exit.)
724 * Invoking GDB:: How to start @value{GDBN}
725 * Quitting GDB:: How to quit @value{GDBN}
726 * Shell Commands:: How to use shell commands inside @value{GDBN}
730 @section Invoking @value{GDBN}
733 For details on starting up @value{GDBP} as a
734 remote debugger attached to a Hitachi microprocessor, see @ref{Hitachi
735 Remote,,@value{GDBN} and Hitachi Microprocessors}.
738 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
739 @value{GDBN} reads commands from the terminal until you tell it to exit.
741 You can also run @code{@value{GDBP}} with a variety of arguments and options,
742 to specify more of your debugging environment at the outset.
745 The command-line options described here are designed
746 to cover a variety of situations; in some environments, some of these
747 options may effectively be unavailable.
750 The most usual way to start @value{GDBN} is with one argument,
751 specifying an executable program:
754 @value{GDBP} @var{program}
759 You can also start with both an executable program and a core file
763 @value{GDBP} @var{program} @var{core}
766 You can, instead, specify a process ID as a second argument, if you want
767 to debug a running process:
770 @value{GDBP} @var{program} 1234
774 would attach @value{GDBN} to process @code{1234} (unless you also have a file
775 named @file{1234}; @value{GDBN} does check for a core file first).
777 Taking advantage of the second command-line argument requires a fairly
778 complete operating system; when you use @value{GDBN} as a remote debugger
779 attached to a bare board, there may not be any notion of ``process'',
780 and there is often no way to get a core dump.
784 You can further control how @value{GDBN} starts up by using command-line
785 options. @value{GDBN} itself can remind you of the options available.
795 to display all available options and briefly describe their use
796 (@samp{@value{GDBP} -h} is a shorter equivalent).
798 All options and command line arguments you give are processed
799 in sequential order. The order makes a difference when the
800 @samp{-x} option is used.
806 * Remote Serial:: @value{GDBN} remote serial protocol
809 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
812 * UDI29K Remote:: The UDI protocol for AMD29K
813 * EB29K Remote:: The EBMON protocol for AMD29K
816 * VxWorks Remote:: @value{GDBN} and VxWorks
819 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
822 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
825 * MIPS Remote:: @value{GDBN} and MIPS boards
828 * Simulator:: Simulated CPU target
831 @c remnant makeinfo bug requires this blank line after *two* end-ifblahs:
833 * File Options:: Choosing files
834 * Mode Options:: Choosing modes
842 @subsection Choosing files
845 When @value{GDBN} starts, it reads any arguments other than options as
846 specifying an executable file and core file (or process ID). This is
847 the same as if the arguments were specified by the @samp{-se} and
848 @samp{-c} options respectively. (@value{GDBN} reads the first argument
849 that does not have an associated option flag as equivalent to the
850 @samp{-se} option followed by that argument; and the second argument
851 that does not have an associated option flag, if any, as equivalent to
852 the @samp{-c} option followed by that argument.)
855 When @value{GDBN} starts, it reads any argument other than options as
856 specifying an executable file. This is the same as if the argument was
857 specified by the @samp{-se} option.
860 Many options have both long and short forms; both are shown in the
861 following list. @value{GDBN} also recognizes the long forms if you truncate
862 them, so long as enough of the option is present to be unambiguous.
863 (If you prefer, you can flag option arguments with @samp{--} rather
864 than @samp{-}, though we illustrate the more usual convention.)
867 @item -symbols @var{file}
869 Read symbol table from file @var{file}.
871 @item -exec @var{file}
873 Use file @var{file} as the executable file to execute when
878 appropriate, and for examining pure data in conjunction with a core
883 Read symbol table from file @var{file} and use it as the executable
887 @item -core @var{file}
889 Use file @var{file} as a core dump to examine.
891 @item -c @var{number}
892 Connect to process ID @var{number}, as with the @code{attach} command
893 (unless there is a file in core-dump format named @var{number}, in which
894 case @samp{-c} specifies that file as a core dump to read).
897 @item -command @var{file}
899 Execute @value{GDBN} commands from file @var{file}. @xref{Command
900 Files,, Command files}.
902 @item -directory @var{directory}
903 @itemx -d @var{directory}
904 Add @var{directory} to the path to search for source files.
909 @emph{Warning: this option depends on operating system facilities that are not
910 supported on all systems.}@*
911 If memory-mapped files are available on your system through the @code{mmap}
912 system call, you can use this option
913 to have @value{GDBN} write the symbols from your
914 program into a reusable file in the current directory. If the program you are debugging is
915 called @file{/tmp/fred}, the mapped symbol file is @file{./fred.syms}.
916 Future @value{GDBN} debugging sessions notice the presence of this file,
917 and can quickly map in symbol information from it, rather than reading
918 the symbol table from the executable program.
920 @c FIXME! Really host, not target?
921 The @file{.syms} file is specific to the host machine where @value{GDBN}
922 is run. It holds an exact image of the internal @value{GDBN} symbol
923 table. It cannot be shared across multiple host platforms.
928 Read each symbol file's entire symbol table immediately, rather than
929 the default, which is to read it incrementally as it is needed.
930 This makes startup slower, but makes future operations faster.
934 The @code{-mapped} and @code{-readnow} options are typically combined in
935 order to build a @file{.syms} file that contains complete symbol
936 information. (@xref{Files,,Commands to specify files}, for information
937 on @file{.syms} files.) A simple GDB invocation to do nothing but build
938 a @file{.syms} file for future use is:
941 gdb -batch -nx -mapped -readnow programname
946 @subsection Choosing modes
948 You can run @value{GDBN} in various alternative modes---for example, in
949 batch mode or quiet mode.
954 Do not execute commands from any initialization files (normally called
955 @file{@value{GDBINIT}}). Normally, the commands in these files are
956 executed after all the command options and arguments have been
957 processed. @xref{Command Files,,Command files}.
961 ``Quiet''. Do not print the introductory and copyright messages. These
962 messages are also suppressed in batch mode.
965 Run in batch mode. Exit with status @code{0} after processing all the
966 command files specified with @samp{-x} (and all commands from
967 initialization files, if not inhibited with @samp{-n}). Exit with
968 nonzero status if an error occurs in executing the @value{GDBN} commands
969 in the command files.
971 Batch mode may be useful for running @value{GDBN} as a filter, for example to
972 download and run a program on another computer; in order to make this
973 more useful, the message
976 Program exited normally.
980 (which is ordinarily issued whenever a program running under @value{GDBN} control
981 terminates) is not issued when running in batch mode.
983 @item -cd @var{directory}
984 Run @value{GDBN} using @var{directory} as its working directory,
985 instead of the current directory.
988 @item -context @var{authentication}
989 When the Energize programming system starts up @value{GDBN}, it uses this
990 option to trigger an alternate mode of interaction.
991 @var{authentication} is a pair of numeric codes that identify @value{GDBN}
992 as a client in the Energize environment. Avoid this option when you run
993 @value{GDBN} directly from the command line. See @ref{Energize,,Using
994 @value{GDBN} with Energize} for more discussion of using @value{GDBN} with Energize.
1000 Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN}
1001 to output the full file name and line number in a standard,
1002 recognizable fashion each time a stack frame is displayed (which
1003 includes each time your program stops). This recognizable format looks
1004 like two @samp{\032} characters, followed by the file name, line number
1005 and character position separated by colons, and a newline. The
1006 Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as
1007 a signal to display the source code for the frame.
1012 Set the line speed (baud rate or bits per second) of any serial
1013 interface used by @value{GDBN} for remote debugging.
1015 @item -tty @var{device}
1016 Run using @var{device} for your program's standard input and output.
1017 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1022 @section Quitting @value{GDBN}
1023 @cindex exiting @value{GDBN}
1024 @cindex leaving @value{GDBN}
1030 To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or type
1031 an end-of-file character (usually @kbd{C-d}).
1035 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1036 terminates the action of any @value{GDBN} command that is in progress and
1037 returns to @value{GDBN} command level. It is safe to type the interrupt
1038 character at any time because @value{GDBN} does not allow it to take effect
1039 until a time when it is safe.
1042 If you have been using @value{GDBN} to control an attached process or
1043 device, you can release it with the @code{detach} command
1044 (@pxref{Attach, ,Debugging an already-running process}).
1047 @node Shell Commands
1048 @section Shell commands
1050 If you need to execute occasional shell commands during your
1051 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1052 just use the @code{shell} command.
1055 @item shell @var{command string}
1057 @cindex shell escape
1058 Invoke a the standard shell to execute @var{command string}.
1060 If it exists, the environment variable @code{SHELL} determines which
1061 shell to run. Otherwise @value{GDBN} uses @code{/bin/sh}.
1065 The utility @code{make} is often needed in development environments.
1066 You do not have to use the @code{shell} command for this purpose in
1070 @item make @var{make-args}
1072 @cindex calling make
1073 Execute the @code{make} program with the specified
1074 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1078 @chapter @value{GDBN} Commands
1080 You can abbreviate a @value{GDBN} command to the first few letters of the command
1081 name, if that abbreviation is unambiguous; and you can repeat certain
1082 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1083 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1084 show you the alternatives available, if there is more than one possibility).
1087 * Command Syntax:: How to give commands to @value{GDBN}
1088 * Completion:: Command completion
1089 * Help:: How to ask @value{GDBN} for help
1092 @node Command Syntax
1093 @section Command syntax
1095 A @value{GDBN} command is a single line of input. There is no limit on
1096 how long it can be. It starts with a command name, which is followed by
1097 arguments whose meaning depends on the command name. For example, the
1098 command @code{step} accepts an argument which is the number of times to
1099 step, as in @samp{step 5}. You can also use the @code{step} command
1100 with no arguments. Some command names do not allow any arguments.
1102 @cindex abbreviation
1103 @value{GDBN} command names may always be truncated if that abbreviation is
1104 unambiguous. Other possible command abbreviations are listed in the
1105 documentation for individual commands. In some cases, even ambiguous
1106 abbreviations are allowed; for example, @code{s} is specially defined as
1107 equivalent to @code{step} even though there are other commands whose
1108 names start with @code{s}. You can test abbreviations by using them as
1109 arguments to the @code{help} command.
1111 @cindex repeating commands
1113 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1114 repeat the previous command. Certain commands (for example, @code{run})
1115 will not repeat this way; these are commands whose unintentional
1116 repetition might cause trouble and which you are unlikely to want to
1119 The @code{list} and @code{x} commands, when you repeat them with
1120 @key{RET}, construct new arguments rather than repeating
1121 exactly as typed. This permits easy scanning of source or memory.
1123 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1124 output, in a way similar to the common utility @code{more}
1125 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1126 @key{RET} too many in this situation, @value{GDBN} disables command
1127 repetition after any command that generates this sort of display.
1131 Any text from a @kbd{#} to the end of the line is a comment; it does
1132 nothing. This is useful mainly in command files (@pxref{Command
1133 Files,,Command files}).
1136 @section Command completion
1139 @cindex word completion
1140 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1141 only one possibility; it can also show you what the valid possibilities
1142 are for the next word in a command, at any time. This works for @value{GDBN}
1143 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1145 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1146 of a word. If there is only one possibility, @value{GDBN} fills in the
1147 word, and waits for you to finish the command (or press @key{RET} to
1148 enter it). For example, if you type
1150 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1151 @c complete accuracy in these examples; space introduced for clarity.
1152 @c If texinfo enhancements make it unnecessary, it would be nice to
1153 @c replace " @key" by "@key" in the following...
1155 (@value{GDBP}) info bre @key{TAB}
1159 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1160 the only @code{info} subcommand beginning with @samp{bre}:
1163 (@value{GDBP}) info breakpoints
1167 You can either press @key{RET} at this point, to run the @code{info
1168 breakpoints} command, or backspace and enter something else, if
1169 @samp{breakpoints} does not look like the command you expected. (If you
1170 were sure you wanted @code{info breakpoints} in the first place, you
1171 might as well just type @key{RET} immediately after @samp{info bre},
1172 to exploit command abbreviations rather than command completion).
1174 If there is more than one possibility for the next word when you press
1175 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1176 characters and try again, or just press @key{TAB} a second time;
1177 @value{GDBN} displays all the possible completions for that word. For
1178 example, you might want to set a breakpoint on a subroutine whose name
1179 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1180 just sounds the bell. Typing @key{TAB} again displays all the
1181 function names in your program that begin with those characters, for
1185 (@value{GDBP}) b make_ @key{TAB}
1186 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1187 make_a_section_from_file make_environ
1188 make_abs_section make_function_type
1189 make_blockvector make_pointer_type
1190 make_cleanup make_reference_type
1191 make_command make_symbol_completion_list
1192 (@value{GDBP}) b make_
1196 After displaying the available possibilities, @value{GDBN} copies your
1197 partial input (@samp{b make_} in the example) so you can finish the
1200 If you just want to see the list of alternatives in the first place, you
1201 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1202 means @kbd{@key{META} ?}. You can type this
1204 either by holding down a
1205 key designated as the @key{META} shift on your keyboard (if there is
1206 one) while typing @kbd{?}, or
1208 as @key{ESC} followed by @kbd{?}.
1210 @cindex quotes in commands
1211 @cindex completion of quoted strings
1212 Sometimes the string you need, while logically a ``word'', may contain
1213 parentheses or other characters that @value{GDBN} normally excludes from its
1214 notion of a word. To permit word completion to work in this situation,
1215 you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands.
1218 The most likely situation where you might need this is in typing the
1219 name of a C++ function. This is because C++ allows function overloading
1220 (multiple definitions of the same function, distinguished by argument
1221 type). For example, when you want to set a breakpoint you may need to
1222 distinguish whether you mean the version of @code{name} that takes an
1223 @code{int} parameter, @code{name(int)}, or the version that takes a
1224 @code{float} parameter, @code{name(float)}. To use the word-completion
1225 facilities in this situation, type a single quote @code{'} at the
1226 beginning of the function name. This alerts @value{GDBN} that it may need to
1227 consider more information than usual when you press @key{TAB} or
1228 @kbd{M-?} to request word completion:
1231 (@value{GDBP}) b 'bubble( @key{M-?}
1232 bubble(double,double) bubble(int,int)
1233 (@value{GDBP}) b 'bubble(
1236 In some cases, @value{GDBN} can tell that completing a name requires using
1237 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1238 completing as much as it can) if you do not type the quote in the first
1242 (@value{GDBP}) b bub @key{TAB}
1243 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1244 (@value{GDBP}) b 'bubble(
1248 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1249 you have not yet started typing the argument list when you ask for
1250 completion on an overloaded symbol.
1255 @section Getting help
1256 @cindex online documentation
1259 You can always ask @value{GDBN} itself for information on its commands, using the
1260 command @code{help}.
1266 You can use @code{help} (abbreviated @code{h}) with no arguments to
1267 display a short list of named classes of commands:
1271 List of classes of commands:
1273 running -- Running the program
1274 stack -- Examining the stack
1275 data -- Examining data
1276 breakpoints -- Making program stop at certain points
1277 files -- Specifying and examining files
1278 status -- Status inquiries
1279 support -- Support facilities
1280 user-defined -- User-defined commands
1281 aliases -- Aliases of other commands
1282 obscure -- Obscure features
1284 Type "help" followed by a class name for a list of
1285 commands in that class.
1286 Type "help" followed by command name for full
1288 Command name abbreviations are allowed if unambiguous.
1292 @item help @var{class}
1293 Using one of the general help classes as an argument, you can get a
1294 list of the individual commands in that class. For example, here is the
1295 help display for the class @code{status}:
1298 (@value{GDBP}) help status
1303 @c Line break in "show" line falsifies real output, but needed
1304 @c to fit in smallbook page size.
1305 show -- Generic command for showing things set
1307 info -- Generic command for printing status
1309 Type "help" followed by command name for full
1311 Command name abbreviations are allowed if unambiguous.
1315 @item help @var{command}
1316 With a command name as @code{help} argument, @value{GDBN} displays a
1317 short paragraph on how to use that command.
1320 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1321 and @code{show} to inquire about the state of your program, or the state
1322 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1323 manual introduces each of them in the appropriate context. The listings
1324 under @code{info} and under @code{show} in the Index point to
1325 all the sub-commands. @xref{Index}.
1332 This command (abbreviated @code{i}) is for describing the state of your
1333 program. For example, you can list the arguments given to your program
1334 with @code{info args}, list the registers currently in use with @code{info
1335 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1336 You can get a complete list of the @code{info} sub-commands with
1337 @w{@code{help info}}.
1341 In contrast, @code{show} is for describing the state of @value{GDBN} itself.
1342 You can change most of the things you can @code{show}, by using the
1343 related command @code{set}; for example, you can control what number
1344 system is used for displays with @code{set radix}, or simply inquire
1345 which is currently in use with @code{show radix}.
1348 To display all the settable parameters and their current
1349 values, you can use @code{show} with no arguments; you may also use
1350 @code{info set}. Both commands produce the same display.
1351 @c FIXME: "info set" violates the rule that "info" is for state of
1352 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1353 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1357 Here are three miscellaneous @code{show} subcommands, all of which are
1358 exceptional in lacking corresponding @code{set} commands:
1361 @kindex show version
1362 @cindex version number
1364 Show what version of @value{GDBN} is running. You should include this
1365 information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in
1366 use at your site, you may occasionally want to determine which version
1367 of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced,
1368 and old ones may wither away. The version number is also announced
1369 when you start @value{GDBN}.
1371 @kindex show copying
1373 Display information about permission for copying @value{GDBN}.
1375 @kindex show warranty
1377 Display the GNU ``NO WARRANTY'' statement.
1381 @chapter Running Programs Under @value{GDBN}
1383 When you run a program under @value{GDBN}, you must first generate
1384 debugging information when you compile it.
1386 You may start it with its arguments, if any, in an environment of your
1387 choice. You may redirect your program's input and output, debug an
1388 already running process, or kill a child process.
1392 * Compilation:: Compiling for debugging
1393 * Starting:: Starting your program
1395 * Arguments:: Your program's arguments
1396 * Environment:: Your program's environment
1397 * Working Directory:: Your program's working directory
1398 * Input/Output:: Your program's input and output
1399 * Attach:: Debugging an already-running process
1400 * Kill Process:: Killing the child process
1401 * Process Information:: Additional process information
1402 * Threads:: Debugging programs with multiple threads
1407 @section Compiling for debugging
1409 In order to debug a program effectively, you need to generate
1410 debugging information when you compile it. This debugging information
1411 is stored in the object file; it describes the data type of each
1412 variable or function and the correspondence between source line numbers
1413 and addresses in the executable code.
1415 To request debugging information, specify the @samp{-g} option when you run
1418 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1419 options together. Using those compilers, you cannot generate optimized
1420 executables containing debugging information.
1422 @value{NGCC}, the GNU C compiler, supports @samp{-g} with or without
1423 @samp{-O}, making it possible to debug optimized code. We recommend
1424 that you @emph{always} use @samp{-g} whenever you compile a program.
1425 You may think your program is correct, but there is no sense in pushing
1428 @cindex optimized code, debugging
1429 @cindex debugging optimized code
1430 When you debug a program compiled with @samp{-g -O}, remember that the
1431 optimizer is rearranging your code; the debugger shows you what is
1432 really there. Do not be too surprised when the execution path does not
1433 exactly match your source file! An extreme example: if you define a
1434 variable, but never use it, @value{GDBN} never sees that
1435 variable---because the compiler optimizes it out of existence.
1437 Some things do not work as well with @samp{-g -O} as with just
1438 @samp{-g}, particularly on machines with instruction scheduling. If in
1439 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1440 please report it as a bug (including a test case!).
1442 Older versions of the GNU C compiler permitted a variant option
1443 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1444 format; if your GNU C compiler has this option, do not use it.
1448 @section Starting your program
1456 Use the @code{run} command to start your program under @value{GDBN}. You must
1457 first specify the program name
1461 with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and
1462 Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file}
1463 command (@pxref{Files, ,Commands to specify files}).
1468 If you are running your program in an execution environment that
1469 supports processes, @code{run} creates an inferior process and makes
1470 that process run your program. (In environments without processes,
1471 @code{run} jumps to the start of your program.)
1473 The execution of a program is affected by certain information it
1474 receives from its superior. @value{GDBN} provides ways to specify this
1475 information, which you must do @emph{before} starting your program. (You
1476 can change it after starting your program, but such changes only affect
1477 your program the next time you start it.) This information may be
1478 divided into four categories:
1481 @item The @emph{arguments.}
1482 Specify the arguments to give your program as the arguments of the
1483 @code{run} command. If a shell is available on your target, the shell
1484 is used to pass the arguments, so that you may use normal conventions
1485 (such as wildcard expansion or variable substitution) in describing
1486 the arguments. In Unix systems, you can control which shell is used
1487 with the @code{SHELL} environment variable. @xref{Arguments, ,Your
1488 program's arguments}.
1490 @item The @emph{environment.}
1491 Your program normally inherits its environment from @value{GDBN}, but you can
1492 use the @value{GDBN} commands @code{set environment} and @code{unset
1493 environment} to change parts of the environment that affect
1494 your program. @xref{Environment, ,Your program's environment}.
1496 @item The @emph{working directory.}
1497 Your program inherits its working directory from @value{GDBN}. You can set
1498 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1499 @xref{Working Directory, ,Your program's working directory}.
1501 @item The @emph{standard input and output.}
1502 Your program normally uses the same device for standard input and
1503 standard output as @value{GDBN} is using. You can redirect input and output
1504 in the @code{run} command line, or you can use the @code{tty} command to
1505 set a different device for your program.
1506 @xref{Input/Output, ,Your program's input and output}.
1509 @emph{Warning:} While input and output redirection work, you cannot use
1510 pipes to pass the output of the program you are debugging to another
1511 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1516 When you issue the @code{run} command, your program begins to execute
1517 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1518 of how to arrange for your program to stop. Once your program has
1519 stopped, you may call functions in your program, using the @code{print}
1520 or @code{call} commands. @xref{Data, ,Examining Data}.
1522 If the modification time of your symbol file has changed since the last
1523 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1524 table, and reads it again. When it does this, @value{GDBN} tries to retain
1525 your current breakpoints.
1529 @section Your program's arguments
1531 @cindex arguments (to your program)
1532 The arguments to your program can be specified by the arguments of the
1533 @code{run} command. They are passed to a shell, which expands wildcard
1534 characters and performs redirection of I/O, and thence to your program.
1535 Your @code{SHELL} environment variable (if it exists) specifies what
1536 shell @value{GDBN} uses. If you do not define @code{SHELL},
1537 @value{GDBN} uses @code{/bin/sh}.
1539 @code{run} with no arguments uses the same arguments used by the previous
1540 @code{run}, or those set by the @code{set args} command.
1545 Specify the arguments to be used the next time your program is run. If
1546 @code{set args} has no arguments, @code{run} executes your program
1547 with no arguments. Once you have run your program with arguments,
1548 using @code{set args} before the next @code{run} is the only way to run
1549 it again without arguments.
1553 Show the arguments to give your program when it is started.
1557 @section Your program's environment
1559 @cindex environment (of your program)
1560 The @dfn{environment} consists of a set of environment variables and
1561 their values. Environment variables conventionally record such things as
1562 your user name, your home directory, your terminal type, and your search
1563 path for programs to run. Usually you set up environment variables with
1564 the shell and they are inherited by all the other programs you run. When
1565 debugging, it can be useful to try running your program with a modified
1566 environment without having to start @value{GDBN} over again.
1569 @item path @var{directory}
1571 Add @var{directory} to the front of the @code{PATH} environment variable
1572 (the search path for executables), for both @value{GDBN} and your program.
1573 You may specify several directory names, separated by @samp{:} or
1574 whitespace. If @var{directory} is already in the path, it is moved to
1575 the front, so it is searched sooner.
1577 You can use the string @samp{$cwd} to refer to whatever is the current
1578 working directory at the time @value{GDBN} searches the path. If you
1579 use @samp{.} instead, it refers to the directory where you executed the
1580 @code{path} command. @value{GDBN} replaces @samp{.} in the
1581 @var{directory} argument (with the current path) before adding
1582 @var{directory} to the search path.
1583 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1584 @c document that, since repeating it would be a no-op.
1588 Display the list of search paths for executables (the @code{PATH}
1589 environment variable).
1591 @item show environment @r{[}@var{varname}@r{]}
1592 @kindex show environment
1593 Print the value of environment variable @var{varname} to be given to
1594 your program when it starts. If you do not supply @var{varname},
1595 print the names and values of all environment variables to be given to
1596 your program. You can abbreviate @code{environment} as @code{env}.
1598 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1599 @kindex set environment
1600 Set environment variable @var{varname} to @var{value}. The value
1601 changes for your program only, not for @value{GDBN} itself. @var{value} may
1602 be any string; the values of environment variables are just strings, and
1603 any interpretation is supplied by your program itself. The @var{value}
1604 parameter is optional; if it is eliminated, the variable is set to a
1606 @c "any string" here does not include leading, trailing
1607 @c blanks. Gnu asks: does anyone care?
1609 For example, this command:
1616 tells a Unix program, when subsequently run, that its user is named
1617 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1618 are not actually required.)
1620 @item unset environment @var{varname}
1621 @kindex unset environment
1622 Remove variable @var{varname} from the environment to be passed to your
1623 program. This is different from @samp{set env @var{varname} =};
1624 @code{unset environment} removes the variable from the environment,
1625 rather than assigning it an empty value.
1628 @emph{Warning:} @value{GDBN} runs your program using the shell indicated
1629 by your @code{SHELL} environment variable if it exists (or
1630 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1631 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1632 @file{.bashrc} for BASH---any variables you set in that file affect
1633 your program. You may wish to move setting of environment variables to
1634 files that are only run when you sign on, such as @file{.login} or
1637 @node Working Directory
1638 @section Your program's working directory
1640 @cindex working directory (of your program)
1641 Each time you start your program with @code{run}, it inherits its
1642 working directory from the current working directory of @value{GDBN}.
1643 The @value{GDBN} working directory is initially whatever it inherited
1644 from its parent process (typically the shell), but you can specify a new
1645 working directory in @value{GDBN} with the @code{cd} command.
1647 The @value{GDBN} working directory also serves as a default for the commands
1648 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1652 @item cd @var{directory}
1654 Set the @value{GDBN} working directory to @var{directory}.
1658 Print the @value{GDBN} working directory.
1662 @section Your program's input and output
1667 By default, the program you run under @value{GDBN} does input and output to
1668 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal to
1669 its own terminal modes to interact with you, but it records the terminal
1670 modes your program was using and switches back to them when you continue
1671 running your program.
1675 @kindex info terminal
1676 Displays information recorded by @value{GDBN} about the terminal modes your
1680 You can redirect your program's input and/or output using shell
1681 redirection with the @code{run} command. For example,
1688 starts your program, diverting its output to the file @file{outfile}.
1691 @cindex controlling terminal
1692 Another way to specify where your program should do input and output is
1693 with the @code{tty} command. This command accepts a file name as
1694 argument, and causes this file to be the default for future @code{run}
1695 commands. It also resets the controlling terminal for the child
1696 process, for future @code{run} commands. For example,
1703 directs that processes started with subsequent @code{run} commands
1704 default to do input and output on the terminal @file{/dev/ttyb} and have
1705 that as their controlling terminal.
1707 An explicit redirection in @code{run} overrides the @code{tty} command's
1708 effect on the input/output device, but not its effect on the controlling
1711 When you use the @code{tty} command or redirect input in the @code{run}
1712 command, only the input @emph{for your program} is affected. The input
1713 for @value{GDBN} still comes from your terminal.
1716 @section Debugging an already-running process
1721 @item attach @var{process-id}
1722 This command attaches to a running process---one that was started
1723 outside @value{GDBN}. (@code{info files} shows your active
1724 targets.) The command takes as argument a process ID. The usual way to
1725 find out the process-id of a Unix process is with the @code{ps} utility,
1726 or with the @samp{jobs -l} shell command.
1728 @code{attach} does not repeat if you press @key{RET} a second time after
1729 executing the command.
1732 To use @code{attach}, your program must be running in an environment
1733 which supports processes; for example, @code{attach} does not work for
1734 programs on bare-board targets that lack an operating system. You must
1735 also have permission to send the process a signal.
1737 When using @code{attach}, you should first use the @code{file} command
1738 to specify the program running in the process and load its symbol table.
1739 @xref{Files, ,Commands to Specify Files}.
1741 The first thing @value{GDBN} does after arranging to debug the specified
1742 process is to stop it. You can examine and modify an attached process
1743 with all the @value{GDBN} commands that are ordinarily available when you start
1744 processes with @code{run}. You can insert breakpoints; you can step and
1745 continue; you can modify storage. If you would rather the process
1746 continue running, you may use the @code{continue} command after
1747 attaching @value{GDBN} to the process.
1752 When you have finished debugging the attached process, you can use the
1753 @code{detach} command to release it from @value{GDBN} control. Detaching
1754 the process continues its execution. After the @code{detach} command,
1755 that process and @value{GDBN} become completely independent once more, and you
1756 are ready to @code{attach} another process or start one with @code{run}.
1757 @code{detach} does not repeat if you press @key{RET} again after
1758 executing the command.
1761 If you exit @value{GDBN} or use the @code{run} command while you have an
1762 attached process, you kill that process. By default, @value{GDBN} asks
1763 for confirmation if you try to do either of these things; you can
1764 control whether or not you need to confirm by using the @code{set
1765 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1770 @section Killing the child process
1775 Kill the child process in which your program is running under @value{GDBN}.
1778 This command is useful if you wish to debug a core dump instead of a
1779 running process. @value{GDBN} ignores any core dump file while your program
1783 On some operating systems, a program cannot be executed outside @value{GDBN}
1784 while you have breakpoints set on it inside @value{GDBN}. You can use the
1785 @code{kill} command in this situation to permit running your program
1786 outside the debugger.
1788 The @code{kill} command is also useful if you wish to recompile and
1789 relink your program, since on many systems it is impossible to modify an
1790 executable file while it is running in a process. In this case, when you
1791 next type @code{run}, @value{GDBN} notices that the file has changed, and
1792 reads the symbol table again (while trying to preserve your current
1793 breakpoint settings).
1795 @node Process Information
1796 @section Additional process information
1799 @cindex process image
1800 Some operating systems provide a facility called @samp{/proc} that can
1801 be used to examine the image of a running process using file-system
1802 subroutines. If @value{GDBN} is configured for an operating system with this
1803 facility, the command @code{info proc} is available to report on several
1804 kinds of information about the process running your program.
1809 Summarize available information about the process.
1811 @item info proc mappings
1812 @kindex info proc mappings
1813 Report on the address ranges accessible in the program, with information
1814 on whether your program may read, write, or execute each range.
1816 @item info proc times
1817 @kindex info proc times
1818 Starting time, user CPU time, and system CPU time for your program and
1822 @kindex info proc id
1823 Report on the process IDs related to your program: its own process ID,
1824 the ID of its parent, the process group ID, and the session ID.
1826 @item info proc status
1827 @kindex info proc status
1828 General information on the state of the process. If the process is
1829 stopped, this report includes the reason for stopping, and any signal
1833 Show all the above information about the process.
1837 @section Debugging programs with multiple threads
1839 @cindex threads of execution
1840 @cindex multiple threads
1841 @cindex switching threads
1842 In some operating systems, a single program may have more than one
1843 @dfn{thread} of execution. The precise semantics of threads differ from
1844 one operating system to another, but in general the threads of a single
1845 program are akin to multiple processes---except that they share one
1846 address space (that is, they can all examine and modify the same
1847 variables). On the other hand, each thread has its own registers and
1848 execution stack, and perhaps private memory.
1850 @value{GDBN} provides these facilities for debugging multi-thread
1854 @item automatic notification of new threads
1855 @item @samp{thread @var{threadno}}, a command to switch among threads
1856 @item @samp{info threads}, a command to inquire about existing threads
1857 @item thread-specific breakpoints
1861 @emph{Warning:} These facilities are not yet available on every
1862 @value{GDBN} configuration where the operating system supports threads.
1863 If your @value{GDBN} does not support threads, these commands have no
1864 effect. For example, a system without thread support shows no output
1865 from @samp{info threads}, and always rejects the @code{thread} command,
1869 (@value{GDBP}) info threads
1870 (@value{GDBP}) thread 1
1871 Thread ID 1 not known. Use the "info threads" command to
1872 see the IDs of currently known threads.
1874 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1875 @c doesn't support threads"?
1878 @cindex focus of debugging
1879 @cindex current thread
1880 The @value{GDBN} thread debugging facility allows you to observe all
1881 threads while your program runs---but whenever @value{GDBN} takes
1882 control, one thread in particular is always the focus of debugging.
1883 This thread is called the @dfn{current thread}. Debugging commands show
1884 program information from the perspective of the current thread.
1886 @kindex New @var{systag}
1887 @cindex thread identifier (system)
1888 @c FIXME-implementors!! It would be more helpful if the [New...] message
1889 @c included GDB's numeric thread handle, so you could just go to that
1890 @c thread without first checking `info threads'.
1891 Whenever @value{GDBN} detects a new thread in your program, it displays
1892 the target system's identification for the thread with a message in the
1893 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1894 whose form varies depending on the particular system. For example, on
1895 LynxOS, you might see
1898 [New process 35 thread 27]
1902 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
1903 the @var{systag} is simply something like @samp{process 368}, with no
1906 @c FIXME!! (1) Does the [New...] message appear even for the very first
1907 @c thread of a program, or does it only appear for the
1908 @c second---i.e., when it becomes obvious we have a multithread
1910 @c (2) *Is* there necessarily a first thread always? Or do some
1911 @c multithread systems permit starting a program with multiple
1912 @c threads ab initio?
1914 @cindex thread number
1915 @cindex thread identifier (GDB)
1916 For debugging purposes, @value{GDBN} associates its own thread
1917 number---always a single integer---with each thread in your program.
1921 @kindex info threads
1922 Display a summary of all threads currently in your
1923 program. @value{GDBN} displays for each thread (in this order):
1926 @item the thread number assigned by @value{GDBN}
1928 @item the target system's thread identifier (@var{systag})
1930 @item the current stack frame summary for that thread
1934 An asterisk @samp{*} to the left of the @value{GDBN} thread number
1935 indicates the current thread.
1939 @c end table here to get a little more width for example
1942 (@value{GDBP}) info threads
1943 3 process 35 thread 27 0x34e5 in sigpause ()
1944 2 process 35 thread 23 0x34e5 in sigpause ()
1945 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
1950 @item thread @var{threadno}
1951 @kindex thread @var{threadno}
1952 Make thread number @var{threadno} the current thread. The command
1953 argument @var{threadno} is the internal @value{GDBN} thread number, as
1954 shown in the first field of the @samp{info threads} display.
1955 @value{GDBN} responds by displaying the system identifier of the thread
1956 you selected, and its current stack frame summary:
1959 @c FIXME!! This example made up; find a GDB w/threads and get real one
1960 (@value{GDBP}) thread 2
1961 [Switching to process 35 thread 23]
1962 0x34e5 in sigpause ()
1966 As with the @samp{[New @dots{}]} message, the form of the text after
1967 @samp{Switching to} depends on your system's conventions for identifying
1971 @cindex automatic thread selection
1972 @cindex switching threads automatically
1973 @cindex threads, automatic switching
1974 Whenever @value{GDBN} stops your program, due to a breakpoint or a
1975 signal, it automatically selects the thread where that breakpoint or
1976 signal happened. @value{GDBN} alerts you to the context switch with a
1977 message of the form @samp{[Switching to @var{systag}]} to identify the
1980 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
1981 more information about how @value{GDBN} behaves when you stop and start
1982 programs with multiple threads.
1984 @xref{Set Watchpoints,,Setting watchpoints}, for information about
1985 watchpoints in programs with multiple threads.
1989 @chapter Stopping and Continuing
1991 The principal purposes of using a debugger are so that you can stop your
1992 program before it terminates; or so that, if your program runs into
1993 trouble, you can investigate and find out why.
1995 Inside @value{GDBN}, your program may stop for any of several reasons, such
2000 a breakpoint, or reaching a new line after a @value{GDBN}
2001 command such as @code{step}. You may then examine and change
2002 variables, set new breakpoints or remove old ones, and then continue
2003 execution. Usually, the messages shown by @value{GDBN} provide ample
2004 explanation of the status of your program---but you can also explicitly
2005 request this information at any time.
2009 @kindex info program
2010 Display information about the status of your program: whether it is
2020 * Breakpoints:: Breakpoints, watchpoints, and exceptions
2023 * Breakpoints:: Breakpoints and watchpoints
2025 @c Remnant makeinfo bug requires blank line after *successful* end-if in menu:
2027 * Continuing and Stepping:: Resuming execution
2032 * Thread Stops:: Stopping and starting multi-thread programs
2036 @c makeinfo node-defaulting requires adjacency of @node and sectioning cmds
2037 @c ...hence distribute @node Breakpoints over two possible @if expansions.
2041 @section Breakpoints, watchpoints, and exceptions
2045 @section Breakpoints and watchpoints
2049 A @dfn{breakpoint} makes your program stop whenever a certain point in
2050 the program is reached. For each breakpoint, you can add
2051 conditions to control in finer detail whether your program stops.
2052 You can set breakpoints with the @code{break} command and its variants
2053 (@pxref{Set Breaks, ,Setting breakpoints}), to specify the place where
2054 your program should stop by line number, function name or exact address
2057 In languages with exception handling (such as GNU C++), you can also set
2058 breakpoints where an exception is raised (@pxref{Exception Handling,,
2059 Breakpoints and exceptions}).
2063 @cindex memory tracing
2064 @cindex breakpoint on memory address
2065 @cindex breakpoint on variable modification
2066 A @dfn{watchpoint} is a special breakpoint that stops your program
2067 when the value of an expression changes. You must use a different
2068 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2069 watchpoints}), but aside from that, you can manage a watchpoint like
2070 any other breakpoint: you enable, disable, and delete both breakpoints
2071 and watchpoints using the same commands.
2073 You can arrange to have values from your program displayed automatically
2074 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2077 @cindex breakpoint numbers
2078 @cindex numbers for breakpoints
2079 @value{GDBN} assigns a number to each breakpoint or watchpoint when you
2080 create it; these numbers are successive integers starting with one. In
2081 many of the commands for controlling various features of breakpoints you
2082 use the breakpoint number to say which breakpoint you want to change.
2083 Each breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has
2084 no effect on your program until you enable it again.
2087 * Set Breaks:: Setting breakpoints
2088 * Set Watchpoints:: Setting watchpoints
2090 * Exception Handling:: Breakpoints and exceptions
2093 * Delete Breaks:: Deleting breakpoints
2094 * Disabling:: Disabling breakpoints
2095 * Conditions:: Break conditions
2096 * Break Commands:: Breakpoint command lists
2098 * Breakpoint Menus:: Breakpoint menus
2101 * Error in Breakpoints:: ``Cannot insert breakpoints''
2106 @subsection Setting breakpoints
2108 @c FIXME LMB what does GDB do if no code on line of breakpt?
2109 @c consider in particular declaration with/without initialization.
2111 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2116 @cindex latest breakpoint
2117 Breakpoints are set with the @code{break} command (abbreviated
2118 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2119 number of the beakpoint you've set most recently; see @ref{Convenience
2120 Vars,, Convenience variables}, for a discussion of what you can do with
2121 convenience variables.
2123 You have several ways to say where the breakpoint should go.
2126 @item break @var{function}
2127 Set a breakpoint at entry to function @var{function}.
2129 When using source languages that permit overloading of symbols, such as
2130 C++, @var{function} may refer to more than one possible place to break.
2131 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2134 @item break +@var{offset}
2135 @itemx break -@var{offset}
2136 Set a breakpoint some number of lines forward or back from the position
2137 at which execution stopped in the currently selected frame.
2139 @item break @var{linenum}
2140 Set a breakpoint at line @var{linenum} in the current source file.
2141 That file is the last file whose source text was printed. This
2142 breakpoint stops your program just before it executes any of the
2145 @item break @var{filename}:@var{linenum}
2146 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2148 @item break @var{filename}:@var{function}
2149 Set a breakpoint at entry to function @var{function} found in file
2150 @var{filename}. Specifying a file name as well as a function name is
2151 superfluous except when multiple files contain similarly named
2154 @item break *@var{address}
2155 Set a breakpoint at address @var{address}. You can use this to set
2156 breakpoints in parts of your program which do not have debugging
2157 information or source files.
2160 When called without any arguments, @code{break} sets a breakpoint at
2161 the next instruction to be executed in the selected stack frame
2162 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2163 innermost, this makes your program stop as soon as control
2164 returns to that frame. This is similar to the effect of a
2165 @code{finish} command in the frame inside the selected frame---except
2166 that @code{finish} does not leave an active breakpoint. If you use
2167 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2168 the next time it reaches the current location; this may be useful
2171 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2172 least one instruction has been executed. If it did not do this, you
2173 would be unable to proceed past a breakpoint without first disabling the
2174 breakpoint. This rule applies whether or not the breakpoint already
2175 existed when your program stopped.
2177 @item break @dots{} if @var{cond}
2178 Set a breakpoint with condition @var{cond}; evaluate the expression
2179 @var{cond} each time the breakpoint is reached, and stop only if the
2180 value is nonzero---that is, if @var{cond} evaluates as true.
2181 @samp{@dots{}} stands for one of the possible arguments described
2182 above (or no argument) specifying where to break. @xref{Conditions,
2183 ,Break conditions}, for more information on breakpoint conditions.
2185 @item tbreak @var{args}
2187 Set a breakpoint enabled only for one stop. @var{args} are the
2188 same as for the @code{break} command, and the breakpoint is set in the same
2189 way, but the breakpoint is automatically deleted after the first time your
2190 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2192 @item rbreak @var{regex}
2194 @cindex regular expression
2195 @c FIXME what kind of regexp?
2196 Set breakpoints on all functions matching the regular expression
2197 @var{regex}. This command
2198 sets an unconditional breakpoint on all matches, printing a list of all
2199 breakpoints it set. Once these breakpoints are set, they are treated
2200 just like the breakpoints set with the @code{break} command. You can
2201 delete them, disable them, or make them conditional the same way as any
2205 When debugging C++ programs, @code{rbreak} is useful for setting
2206 breakpoints on overloaded functions that are not members of any special
2210 @kindex info breakpoints
2211 @cindex @code{$_} and @code{info breakpoints}
2212 @item info breakpoints @r{[}@var{n}@r{]}
2213 @itemx info break @r{[}@var{n}@r{]}
2214 @itemx info watchpoints @r{[}@var{n}@r{]}
2215 Print a table of all breakpoints and watchpoints set and not
2216 deleted, with the following columns for each breakpoint:
2219 @item Breakpoint Numbers
2221 Breakpoint or watchpoint.
2223 Whether the breakpoint is marked to be disabled or deleted when hit.
2224 @item Enabled or Disabled
2225 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2226 that are not enabled.
2228 Where the breakpoint is in your program, as a memory address
2230 Where the breakpoint is in the source for your program, as a file and
2235 If a breakpoint is conditional, @code{info break} shows the condition on
2236 the line following the affected breakpoint; breakpoint commands, if any,
2237 are listed after that.
2240 @code{info break} with a breakpoint
2241 number @var{n} as argument lists only that breakpoint. The
2242 convenience variable @code{$_} and the default examining-address for
2243 the @code{x} command are set to the address of the last breakpoint
2244 listed (@pxref{Memory, ,Examining memory}).
2247 @value{GDBN} allows you to set any number of breakpoints at the same place in
2248 your program. There is nothing silly or meaningless about this. When
2249 the breakpoints are conditional, this is even useful
2250 (@pxref{Conditions, ,Break conditions}).
2252 @cindex negative breakpoint numbers
2253 @cindex internal @value{GDBN} breakpoints
2254 @value{GDBN} itself sometimes sets breakpoints in your program for special
2255 purposes, such as proper handling of @code{longjmp} (in C programs).
2256 These internal breakpoints are assigned negative numbers, starting with
2257 @code{-1}; @samp{info breakpoints} does not display them.
2259 You can see these breakpoints with the @value{GDBN} maintenance command
2260 @samp{maint info breakpoints}.
2263 @kindex maint info breakpoints
2264 @item maint info breakpoints
2265 Using the same format as @samp{info breakpoints}, display both the
2266 breakpoints you've set explicitly, and those @value{GDBN} is using for
2267 internal purposes. Internal breakpoints are shown with negative
2268 breakpoint numbers. The type column identifies what kind of breakpoint
2273 Normal, explicitly set breakpoint.
2276 Normal, explicitly set watchpoint.
2279 Internal breakpoint, used to handle correctly stepping through
2280 @code{longjmp} calls.
2282 @item longjmp resume
2283 Internal breakpoint at the target of a @code{longjmp}.
2286 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2289 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2295 @node Set Watchpoints
2296 @subsection Setting watchpoints
2297 @cindex setting watchpoints
2299 You can use a watchpoint to stop execution whenever the value of an
2300 expression changes, without having to predict a particular place
2301 where this may happen.
2303 Watchpoints currently execute two orders of magnitude more slowly than
2304 other breakpoints, but this can be well worth it to catch errors where
2305 you have no clue what part of your program is the culprit.
2308 @c this "future releases" promise has been in too long, is getting
2309 @c embarrassing. But...
2310 @c FIXME: in future updates, check whether hardware watchpoints in on any
2311 @c platforms yet. As of 26jan94, they're very close on HPPA running
2312 @c Berkeley and on Irix 4.
2313 Some processors provide special hardware to support watchpoint
2314 evaluation; future releases of @value{GDBN} will use such hardware if it
2320 @item watch @var{expr}
2321 Set a watchpoint for an expression.
2323 @kindex info watchpoints
2324 @item info watchpoints
2325 This command prints a list of watchpoints and breakpoints; it is the
2326 same as @code{info break}.
2331 @cindex watchpoints and threads
2332 @cindex threads and watchpoints
2333 @emph{Warning:} in multi-thread programs, watchpoints have only limited
2334 usefulness. With the current watchpoint implementation, @value{GDBN}
2335 can only watch the value of an expression @emph{in a single thread}. If
2336 you are confident that the expression can only change due to the current
2337 thread's activity (and if you are also confident that no other thread
2338 can become current), then you can use watchpoints as usual. However,
2339 @value{GDBN} may not notice when a non-current thread's activity changes
2345 @node Exception Handling
2346 @subsection Breakpoints and exceptions
2347 @cindex exception handlers
2349 Some languages, such as GNU C++, implement exception handling. You can
2350 use @value{GDBN} to examine what caused your program to raise an exception,
2351 and to list the exceptions your program is prepared to handle at a
2352 given point in time.
2355 @item catch @var{exceptions}
2357 You can set breakpoints at active exception handlers by using the
2358 @code{catch} command. @var{exceptions} is a list of names of exceptions
2362 You can use @code{info catch} to list active exception handlers.
2363 @xref{Frame Info, ,Information about a frame}.
2365 There are currently some limitations to exception handling in @value{GDBN}:
2369 If you call a function interactively, @value{GDBN} normally returns
2370 control to you when the function has finished executing. If the call
2371 raises an exception, however, the call may bypass the mechanism that
2372 returns control to you and cause your program to simply continue
2373 running until it hits a breakpoint, catches a signal that @value{GDBN} is
2374 listening for, or exits.
2377 You cannot raise an exception interactively.
2380 You cannot install an exception handler interactively.
2383 @cindex raise exceptions
2384 Sometimes @code{catch} is not the best way to debug exception handling:
2385 if you need to know exactly where an exception is raised, it is better to
2386 stop @emph{before} the exception handler is called, since that way you
2387 can see the stack before any unwinding takes place. If you set a
2388 breakpoint in an exception handler instead, it may not be easy to find
2389 out where the exception was raised.
2391 To stop just before an exception handler is called, you need some
2392 knowledge of the implementation. In the case of GNU C++, exceptions are
2393 raised by calling a library function named @code{__raise_exception}
2394 which has the following ANSI C interface:
2397 /* @var{addr} is where the exception identifier is stored.
2398 ID is the exception identifier. */
2399 void __raise_exception (void **@var{addr}, void *@var{id});
2403 To make the debugger catch all exceptions before any stack
2404 unwinding takes place, set a breakpoint on @code{__raise_exception}
2405 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2407 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2408 that depends on the value of @var{id}, you can stop your program when
2409 a specific exception is raised. You can use multiple conditional
2410 breakpoints to stop your program when any of a number of exceptions are
2415 @subsection Deleting breakpoints
2417 @cindex clearing breakpoints, watchpoints
2418 @cindex deleting breakpoints, watchpoints
2419 It is often necessary to eliminate a breakpoint or watchpoint once it
2420 has done its job and you no longer want your program to stop there. This
2421 is called @dfn{deleting} the breakpoint. A breakpoint that has been
2422 deleted no longer exists; it is forgotten.
2424 With the @code{clear} command you can delete breakpoints according to
2425 where they are in your program. With the @code{delete} command you can
2426 delete individual breakpoints or watchpoints by specifying their
2429 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2430 automatically ignores breakpoints on the first instruction to be executed
2431 when you continue execution without changing the execution address.
2436 Delete any breakpoints at the next instruction to be executed in the
2437 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2438 the innermost frame is selected, this is a good way to delete a
2439 breakpoint where your program just stopped.
2441 @item clear @var{function}
2442 @itemx clear @var{filename}:@var{function}
2443 Delete any breakpoints set at entry to the function @var{function}.
2445 @item clear @var{linenum}
2446 @itemx clear @var{filename}:@var{linenum}
2447 Delete any breakpoints set at or within the code of the specified line.
2449 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2450 @cindex delete breakpoints
2453 Delete the breakpoints or watchpoints of the numbers specified as
2454 arguments. If no argument is specified, delete all breakpoints (@value{GDBN}
2455 asks confirmation, unless you have @code{set confirm off}). You
2456 can abbreviate this command as @code{d}.
2460 @subsection Disabling breakpoints
2462 @cindex disabled breakpoints
2463 @cindex enabled breakpoints
2464 Rather than deleting a breakpoint or watchpoint, you might prefer to
2465 @dfn{disable} it. This makes the breakpoint inoperative as if it had
2466 been deleted, but remembers the information on the breakpoint so that
2467 you can @dfn{enable} it again later.
2469 You disable and enable breakpoints and watchpoints with the
2470 @code{enable} and @code{disable} commands, optionally specifying one or
2471 more breakpoint numbers as arguments. Use @code{info break} or
2472 @code{info watch} to print a list of breakpoints or watchpoints if you
2473 do not know which numbers to use.
2475 A breakpoint or watchpoint can have any of four different states of
2480 Enabled. The breakpoint stops your program. A breakpoint set
2481 with the @code{break} command starts out in this state.
2483 Disabled. The breakpoint has no effect on your program.
2485 Enabled once. The breakpoint stops your program, but then becomes
2486 disabled. A breakpoint set with the @code{tbreak} command starts out in
2489 Enabled for deletion. The breakpoint stops your program, but
2490 immediately after it does so it is deleted permanently.
2493 You can use the following commands to enable or disable breakpoints and
2497 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2498 @kindex disable breakpoints
2501 Disable the specified breakpoints---or all breakpoints, if none are
2502 listed. A disabled breakpoint has no effect but is not forgotten. All
2503 options such as ignore-counts, conditions and commands are remembered in
2504 case the breakpoint is enabled again later. You may abbreviate
2505 @code{disable} as @code{dis}.
2507 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2508 @kindex enable breakpoints
2510 Enable the specified breakpoints (or all defined breakpoints). They
2511 become effective once again in stopping your program.
2513 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
2514 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2515 of these breakpoints immediately after stopping your program.
2517 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
2518 Enable the specified breakpoints to work once, then die. @value{GDBN}
2519 deletes any of these breakpoints as soon as your program stops there.
2522 Save for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2523 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2524 subsequently, they become disabled or enabled only when you use one of
2525 the commands above. (The command @code{until} can set and delete a
2526 breakpoint of its own, but it does not change the state of your other
2527 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2531 @subsection Break conditions
2532 @cindex conditional breakpoints
2533 @cindex breakpoint conditions
2535 @c FIXME what is scope of break condition expr? Context where wanted?
2536 @c in particular for a watchpoint?
2537 The simplest sort of breakpoint breaks every time your program reaches a
2538 specified place. You can also specify a @dfn{condition} for a
2539 breakpoint. A condition is just a Boolean expression in your
2540 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2541 a condition evaluates the expression each time your program reaches it,
2542 and your program stops only if the condition is @emph{true}.
2544 This is the converse of using assertions for program validation; in that
2545 situation, you want to stop when the assertion is violated---that is,
2546 when the condition is false. In C, if you want to test an assertion expressed
2547 by the condition @var{assert}, you should set the condition
2548 @samp{! @var{assert}} on the appropriate breakpoint.
2550 Conditions are also accepted for watchpoints; you may not need them,
2551 since a watchpoint is inspecting the value of an expression anyhow---but
2552 it might be simpler, say, to just set a watchpoint on a variable name,
2553 and specify a condition that tests whether the new value is an interesting
2556 Break conditions can have side effects, and may even call functions in
2557 your program. This can be useful, for example, to activate functions
2558 that log program progress, or to use your own print functions to
2559 format special data structures. The effects are completely predictable
2560 unless there is another enabled breakpoint at the same address. (In
2561 that case, @value{GDBN} might see the other breakpoint first and stop your
2562 program without checking the condition of this one.) Note that
2563 breakpoint commands are usually more convenient and flexible for the
2564 purpose of performing side effects when a breakpoint is reached
2565 (@pxref{Break Commands, ,Breakpoint command lists}).
2567 Break conditions can be specified when a breakpoint is set, by using
2568 @samp{if} in the arguments to the @code{break} command. @xref{Set
2569 Breaks, ,Setting breakpoints}. They can also be changed at any time
2570 with the @code{condition} command. The @code{watch} command does not
2571 recognize the @code{if} keyword; @code{condition} is the only way to
2572 impose a further condition on a watchpoint.
2575 @item condition @var{bnum} @var{expression}
2577 Specify @var{expression} as the break condition for breakpoint or
2578 watchpoint number @var{bnum}. After you set a condition, breakpoint
2579 @var{bnum} stops your program only if the value of @var{expression} is
2580 true (nonzero, in C). When you use @code{condition}, @value{GDBN}
2581 checks @var{expression} immediately for syntactic correctness, and to
2582 determine whether symbols in it have referents in the context of your
2584 @c FIXME so what does GDB do if there is no referent? Moreover, what
2585 @c about watchpoints?
2587 not actually evaluate @var{expression} at the time the @code{condition}
2588 command is given, however. @xref{Expressions, ,Expressions}.
2590 @item condition @var{bnum}
2591 Remove the condition from breakpoint number @var{bnum}. It becomes
2592 an ordinary unconditional breakpoint.
2595 @cindex ignore count (of breakpoint)
2596 A special case of a breakpoint condition is to stop only when the
2597 breakpoint has been reached a certain number of times. This is so
2598 useful that there is a special way to do it, using the @dfn{ignore
2599 count} of the breakpoint. Every breakpoint has an ignore count, which
2600 is an integer. Most of the time, the ignore count is zero, and
2601 therefore has no effect. But if your program reaches a breakpoint whose
2602 ignore count is positive, then instead of stopping, it just decrements
2603 the ignore count by one and continues. As a result, if the ignore count
2604 value is @var{n}, the breakpoint does not stop the next @var{n} times
2605 your program reaches it.
2608 @item ignore @var{bnum} @var{count}
2610 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
2611 The next @var{count} times the breakpoint is reached, your program's
2612 execution does not stop; other than to decrement the ignore count, @value{GDBN}
2615 To make the breakpoint stop the next time it is reached, specify
2618 When you use @code{continue} to resume execution of your program from a
2619 breakpoint, you can specify an ignore count directly as an argument to
2620 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
2621 Stepping,,Continuing and stepping}.
2623 If a breakpoint has a positive ignore count and a condition, the
2624 condition is not checked. Once the ignore count reaches zero,
2625 @value{GDBN} resumes checking the condition.
2627 You could achieve the effect of the ignore count with a condition such
2628 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
2629 is decremented each time. @xref{Convenience Vars, ,Convenience
2633 @node Break Commands
2634 @subsection Breakpoint command lists
2636 @cindex breakpoint commands
2637 You can give any breakpoint (or watchpoint) a series of commands to
2638 execute when your program stops due to that breakpoint. For example, you
2639 might want to print the values of certain expressions, or enable other
2643 @item commands @r{[}@var{bnum}@r{]}
2644 @itemx @dots{} @var{command-list} @dots{}
2648 Specify a list of commands for breakpoint number @var{bnum}. The commands
2649 themselves appear on the following lines. Type a line containing just
2650 @code{end} to terminate the commands.
2652 To remove all commands from a breakpoint, type @code{commands} and
2653 follow it immediately with @code{end}; that is, give no commands.
2655 With no @var{bnum} argument, @code{commands} refers to the last
2656 breakpoint or watchpoint set (not to the breakpoint most recently
2660 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
2661 disabled within a @var{command-list}.
2663 You can use breakpoint commands to start your program up again. Simply
2664 use the @code{continue} command, or @code{step}, or any other command
2665 that resumes execution.
2667 Any other commands in the command list, after a command that resumes
2668 execution, are ignored. This is because any time you resume execution
2669 (even with a simple @code{next} or @code{step}), you may encounter
2670 another breakpoint---which could have its own command list, leading to
2671 ambiguities about which list to execute.
2674 If the first command you specify in a command list is @code{silent}, the
2675 usual message about stopping at a breakpoint is not printed. This may
2676 be desirable for breakpoints that are to print a specific message and
2677 then continue. If none of the remaining commands print anything, you
2678 see no sign that the breakpoint was reached. @code{silent} is
2679 meaningful only at the beginning of a breakpoint command list.
2681 The commands @code{echo}, @code{output}, and @code{printf} allow you to
2682 print precisely controlled output, and are often useful in silent
2683 breakpoints. @xref{Output, ,Commands for controlled output}.
2685 For example, here is how you could use breakpoint commands to print the
2686 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
2692 printf "x is %d\n",x
2697 One application for breakpoint commands is to compensate for one bug so
2698 you can test for another. Put a breakpoint just after the erroneous line
2699 of code, give it a condition to detect the case in which something
2700 erroneous has been done, and give it commands to assign correct values
2701 to any variables that need them. End with the @code{continue} command
2702 so that your program does not stop, and start with the @code{silent}
2703 command so that no output is produced. Here is an example:
2715 @node Breakpoint Menus
2716 @subsection Breakpoint menus
2718 @cindex symbol overloading
2720 Some programming languages (notably C++) permit a single function name
2721 to be defined several times, for application in different contexts.
2722 This is called @dfn{overloading}. When a function name is overloaded,
2723 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
2724 a breakpoint. If you realize this is a problem, you can use
2725 something like @samp{break @var{function}(@var{types})} to specify which
2726 particular version of the function you want. Otherwise, @value{GDBN} offers
2727 you a menu of numbered choices for different possible breakpoints, and
2728 waits for your selection with the prompt @samp{>}. The first two
2729 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
2730 sets a breakpoint at each definition of @var{function}, and typing
2731 @kbd{0} aborts the @code{break} command without setting any new
2734 For example, the following session excerpt shows an attempt to set a
2735 breakpoint at the overloaded symbol @code{String::after}.
2736 We choose three particular definitions of that function name:
2738 @c FIXME! This is likely to change to show arg type lists, at least
2740 (@value{GDBP}) b String::after
2743 [2] file:String.cc; line number:867
2744 [3] file:String.cc; line number:860
2745 [4] file:String.cc; line number:875
2746 [5] file:String.cc; line number:853
2747 [6] file:String.cc; line number:846
2748 [7] file:String.cc; line number:735
2750 Breakpoint 1 at 0xb26c: file String.cc, line 867.
2751 Breakpoint 2 at 0xb344: file String.cc, line 875.
2752 Breakpoint 3 at 0xafcc: file String.cc, line 846.
2753 Multiple breakpoints were set.
2754 Use the "delete" command to delete unwanted
2761 @node Error in Breakpoints
2762 @subsection ``Cannot insert breakpoints''
2764 @c FIXME: "cannot insert breakpoints" error, v unclear.
2765 @c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91
2766 @c some light may be shed by looking at instances of
2767 @c ONE_PROCESS_WRITETEXT. But error message seems possible otherwise
2768 @c too. pesch, 20sep91
2769 Under some operating systems, breakpoints cannot be used in a program if
2770 any other process is running that program. In this situation,
2771 attempting to run or continue a program with a breakpoint causes @value{GDBN}
2772 to stop the other process.
2774 When this happens, you have three ways to proceed:
2778 Remove or disable the breakpoints, then continue.
2781 Suspend @value{GDBN}, and copy the file containing your program to a new name.
2782 Resume @value{GDBN} and use the @code{exec-file} command to specify that @value{GDBN}
2783 should run your program under that name. Then start your program again.
2785 @c FIXME: RMS commented here "Show example". Maybe when someone
2786 @c explains the first FIXME: in this section...
2789 Relink your program so that the text segment is nonsharable, using the
2790 linker option @samp{-N}. The operating system limitation may not apply
2791 to nonsharable executables.
2795 @node Continuing and Stepping
2796 @section Continuing and stepping
2800 @cindex resuming execution
2801 @dfn{Continuing} means resuming program execution until your program
2802 completes normally. In contrast, @dfn{stepping} means executing just
2803 one more ``step'' of your program, where ``step'' may mean either one
2804 line of source code, or one machine instruction (depending on what
2805 particular command you use). Either when continuing
2806 or when stepping, your program may stop even sooner, due to
2811 a breakpoint or a signal. (If due to a signal, you may want to use
2812 @code{handle}, or use @samp{signal 0} to resume execution.
2813 @xref{Signals, ,Signals}.)
2817 @item continue @r{[}@var{ignore-count}@r{]}
2818 @itemx c @r{[}@var{ignore-count}@r{]}
2819 @itemx fg @r{[}@var{ignore-count}@r{]}
2823 Resume program execution, at the address where your program last stopped;
2824 any breakpoints set at that address are bypassed. The optional argument
2825 @var{ignore-count} allows you to specify a further number of times to
2826 ignore a breakpoint at this location; its effect is like that of
2827 @code{ignore} (@pxref{Conditions, ,Break conditions}).
2829 The argument @var{ignore-count} is meaningful only when your program
2830 stopped due to a breakpoint. At other times, the argument to
2831 @code{continue} is ignored.
2833 The synonyms @code{c} and @code{fg} are provided purely for convenience,
2834 and have exactly the same behavior as @code{continue}.
2837 To resume execution at a different place, you can use @code{return}
2838 (@pxref{Returning, ,Returning from a function}) to go back to the
2839 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
2840 different address}) to go to an arbitrary location in your program.
2842 A typical technique for using stepping is to set a breakpoint
2844 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions})
2847 (@pxref{Breakpoints, ,Breakpoints and watchpoints})
2850 beginning of the function or the section of your program where a
2851 problem is believed to lie, run your program until it stops at that
2852 breakpoint, and then step through the suspect area, examining the
2853 variables that are interesting, until you see the problem happen.
2859 Continue running your program until control reaches a different source
2860 line, then stop it and return control to @value{GDBN}. This command is
2861 abbreviated @code{s}.
2864 @c "without debugging information" is imprecise; actually "without line
2865 @c numbers in the debugging information". (gcc -g1 has debugging info but
2866 @c not line numbers). But it seems complex to try to make that
2867 @c distinction here.
2868 @emph{Warning:} If you use the @code{step} command while control is
2869 within a function that was compiled without debugging information,
2870 execution proceeds until control reaches a function that does have
2871 debugging information. Likewise, it will not step into a function which
2872 is compiled without debugging information. To step through functions
2873 without debugging information, use the @code{stepi} command, described
2877 @item step @var{count}
2878 Continue running as in @code{step}, but do so @var{count} times. If a
2879 breakpoint is reached,
2881 or a signal not related to stepping occurs before @var{count} steps,
2883 stepping stops right away.
2885 @item next @r{[}@var{count}@r{]}
2888 Continue to the next source line in the current (innermost) stack frame.
2889 Similar to @code{step}, but any function calls appearing within the line
2890 of code are executed without stopping. Execution stops when control
2891 reaches a different line of code at the stack level which was executing
2892 when the @code{next} command was given. This command is abbreviated
2895 An argument @var{count} is a repeat count, as for @code{step}.
2897 @code{next} within a function that lacks debugging information acts like
2898 @code{step}, but any function calls appearing within the code of the
2899 function are executed without stopping.
2903 Continue running until just after function in the selected stack frame
2904 returns. Print the returned value (if any).
2906 Contrast this with the @code{return} command (@pxref{Returning,
2907 ,Returning from a function}).
2913 Continue running until a source line past the current line, in the
2914 current stack frame, is reached. This command is used to avoid single
2915 stepping through a loop more than once. It is like the @code{next}
2916 command, except that when @code{until} encounters a jump, it
2917 automatically continues execution until the program counter is greater
2918 than the address of the jump.
2920 This means that when you reach the end of a loop after single stepping
2921 though it, @code{until} makes your program continue execution until it
2922 exits the loop. In contrast, a @code{next} command at the end of a loop
2923 simply steps back to the beginning of the loop, which forces you to step
2924 through the next iteration.
2926 @code{until} always stops your program if it attempts to exit the current
2929 @code{until} may produce somewhat counterintuitive results if the order
2930 of machine code does not match the order of the source lines. For
2931 example, in the following excerpt from a debugging session, the @code{f}
2932 (@code{frame}) command shows that execution is stopped at line
2933 @code{206}; yet when we use @code{until}, we get to line @code{195}:
2937 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
2939 (@value{GDBP}) until
2940 195 for ( ; argc > 0; NEXTARG) @{
2943 This happened because, for execution efficiency, the compiler had
2944 generated code for the loop closure test at the end, rather than the
2945 start, of the loop---even though the test in a C @code{for}-loop is
2946 written before the body of the loop. The @code{until} command appeared
2947 to step back to the beginning of the loop when it advanced to this
2948 expression; however, it has not really gone to an earlier
2949 statement---not in terms of the actual machine code.
2951 @code{until} with no argument works by means of single
2952 instruction stepping, and hence is slower than @code{until} with an
2955 @item until @var{location}
2956 @itemx u @var{location}
2957 Continue running your program until either the specified location is
2958 reached, or the current stack frame returns. @var{location} is any of
2959 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
2960 ,Setting breakpoints}). This form of the command uses breakpoints,
2961 and hence is quicker than @code{until} without an argument.
2967 Execute one machine instruction, then stop and return to the debugger.
2969 It is often useful to do @samp{display/i $pc} when stepping by machine
2970 instructions. This makes @value{GDBN} automatically display the next
2971 instruction to be executed, each time your program stops. @xref{Auto
2972 Display,, Automatic display}.
2974 An argument is a repeat count, as in @code{step}.
2981 Execute one machine instruction, but if it is a function call,
2982 proceed until the function returns.
2984 An argument is a repeat count, as in @code{next}.
2992 A signal is an asynchronous event that can happen in a program. The
2993 operating system defines the possible kinds of signals, and gives each
2994 kind a name and a number. For example, in Unix @code{SIGINT} is the
2995 signal a program gets when you type an interrupt (often @kbd{C-c});
2996 @code{SIGSEGV} is the signal a program gets from referencing a place in
2997 memory far away from all the areas in use; @code{SIGALRM} occurs when
2998 the alarm clock timer goes off (which happens only if your program has
2999 requested an alarm).
3001 @cindex fatal signals
3002 Some signals, including @code{SIGALRM}, are a normal part of the
3003 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3004 errors; these signals are @dfn{fatal} (kill your program immediately) if the
3005 program has not specified in advance some other way to handle the signal.
3006 @code{SIGINT} does not indicate an error in your program, but it is normally
3007 fatal so it can carry out the purpose of the interrupt: to kill the program.
3009 @value{GDBN} has the ability to detect any occurrence of a signal in your
3010 program. You can tell @value{GDBN} in advance what to do for each kind of
3013 @cindex handling signals
3014 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
3015 (so as not to interfere with their role in the functioning of your program)
3016 but to stop your program immediately whenever an error signal happens.
3017 You can change these settings with the @code{handle} command.
3021 @kindex info signals
3022 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3023 handle each one. You can use this to see the signal numbers of all
3024 the defined types of signals.
3026 @item handle @var{signal} @var{keywords}@dots{}
3028 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can be the
3029 number of a signal or its name (with or without the @samp{SIG} at the
3030 beginning). The @var{keywords} say what change to make.
3034 The keywords allowed by the @code{handle} command can be abbreviated.
3035 Their full names are:
3039 @value{GDBN} should not stop your program when this signal happens. It may
3040 still print a message telling you that the signal has come in.
3043 @value{GDBN} should stop your program when this signal happens. This implies
3044 the @code{print} keyword as well.
3047 @value{GDBN} should print a message when this signal happens.
3050 @value{GDBN} should not mention the occurrence of the signal at all. This
3051 implies the @code{nostop} keyword as well.
3054 @value{GDBN} should allow your program to see this signal; your program
3055 can handle the signal, or else it may terminate if the signal is fatal
3059 @value{GDBN} should not allow your program to see this signal.
3063 When a signal stops your program, the signal is not visible until you
3064 continue. Your program sees the signal then, if @code{pass} is in
3065 effect for the signal in question @emph{at that time}. In other words,
3066 after @value{GDBN} reports a signal, you can use the @code{handle}
3067 command with @code{pass} or @code{nopass} to control whether your
3068 program sees that signal when you continue.
3070 You can also use the @code{signal} command to prevent your program from
3071 seeing a signal, or cause it to see a signal it normally would not see,
3072 or to give it any signal at any time. For example, if your program stopped
3073 due to some sort of memory reference error, you might store correct
3074 values into the erroneous variables and continue, hoping to see more
3075 execution; but your program would probably terminate immediately as
3076 a result of the fatal signal once it saw the signal. To prevent this,
3077 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3083 @section Stopping and starting multi-thread programs
3085 When your program has multiple threads (@pxref{Threads,, Debugging
3086 programs with multiple threads}), you can choose whether to set
3087 breakpoints on all threads, or on a particular thread.
3090 @cindex breakpoints and threads
3091 @cindex thread breakpoints
3092 @kindex break @dots{} thread @var{threadno}
3093 @item break @var{linespec} thread @var{threadno}
3094 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3095 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3096 to specify that you only want @value{GDBN} to stop the program when a
3097 particular thread reaches this breakpoint. @var{threadno} is one of the
3098 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3099 column of the @samp{info threads} display.
3101 If you do not specify @samp{thread @var{threadno}} when you set a
3102 breakpoint, the breakpoint applies to @emph{all} threads of your
3105 You can use the @code{thread} qualifier on conditional breakpoints as
3106 well; in this case, place @samp{thread @var{threadno}} before the
3107 breakpoint condition, like this:
3110 (gdb) break frik.c:13 thread 28 if bartab > lim
3114 @cindex stopped threads
3115 @cindex threads, stopped
3116 Whenever your program stops under @value{GDBN} for any reason,
3117 @emph{all} threads of execution stop, not just the current thread. This
3118 allows you to examine the overall state of the program, including
3119 switching between threads, without worrying that things may change
3122 @cindex continuing threads
3123 @cindex threads, continuing
3124 Conversely, whenever you restart the program, @emph{all} threads start
3125 executing. @emph{This is true even when single-stepping} with commands
3126 like @code{step} or @code{next}.
3128 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3129 Since thread scheduling is up to your debugging target's operating
3130 system (not controlled by @value{GDBN}), other threads may
3131 execute more than one statement while the current thread completes a
3132 single step. Moreover, in general other threads stop in the middle of a
3133 statement, rather than at a clean statement boundary, when the program
3136 You might even find your program stopped in another thread after
3137 continuing or even single-stepping. This happens whenever some other
3138 thread runs into a breakpoint, a signal, or an exception before the
3139 first thread completes whatever you requested.
3143 @chapter Examining the Stack
3145 When your program has stopped, the first thing you need to know is where it
3146 stopped and how it got there.
3149 Each time your program performs a function call, the information about
3150 where in your program the call was made from is saved in a block of data
3151 called a @dfn{stack frame}. The frame also contains the arguments of the
3152 call and the local variables of the function that was called. All the
3153 stack frames are allocated in a region of memory called the @dfn{call
3156 When your program stops, the @value{GDBN} commands for examining the
3157 stack allow you to see all of this information.
3159 @cindex selected frame
3160 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3161 @value{GDBN} commands refer implicitly to the selected frame. In
3162 particular, whenever you ask @value{GDBN} for the value of a variable in
3163 your program, the value is found in the selected frame. There are
3164 special @value{GDBN} commands to select whichever frame you are
3167 When your program stops, @value{GDBN} automatically selects the
3168 currently executing frame and describes it briefly as the @code{frame}
3169 command does (@pxref{Frame Info, ,Information about a frame}).
3172 * Frames:: Stack frames
3173 * Backtrace:: Backtraces
3174 * Selection:: Selecting a frame
3175 * Frame Info:: Information on a frame
3177 * MIPS Stack:: MIPS machines and the function stack
3182 @section Stack frames
3186 The call stack is divided up into contiguous pieces called @dfn{stack
3187 frames}, or @dfn{frames} for short; each frame is the data associated
3188 with one call to one function. The frame contains the arguments given
3189 to the function, the function's local variables, and the address at
3190 which the function is executing.
3192 @cindex initial frame
3193 @cindex outermost frame
3194 @cindex innermost frame
3195 When your program is started, the stack has only one frame, that of the
3196 function @code{main}. This is called the @dfn{initial} frame or the
3197 @dfn{outermost} frame. Each time a function is called, a new frame is
3198 made. Each time a function returns, the frame for that function invocation
3199 is eliminated. If a function is recursive, there can be many frames for
3200 the same function. The frame for the function in which execution is
3201 actually occurring is called the @dfn{innermost} frame. This is the most
3202 recently created of all the stack frames that still exist.
3204 @cindex frame pointer
3205 Inside your program, stack frames are identified by their addresses. A
3206 stack frame consists of many bytes, each of which has its own address; each
3207 kind of computer has a convention for choosing one of those bytes whose
3208 address serves as the address of the frame. Usually this address is kept
3209 in a register called the @dfn{frame pointer register} while execution is
3210 going on in that frame.
3212 @cindex frame number
3213 @value{GDBN} assigns numbers to all existing stack frames, starting with
3214 zero for the innermost frame, one for the frame that called it,
3215 and so on upward. These numbers do not really exist in your program;
3216 they are assigned by @value{GDBN} to give you a way of designating stack
3217 frames in @value{GDBN} commands.
3219 @c below produces an acceptable overful hbox. --mew 13aug1993
3220 @cindex frameless execution
3221 Some compilers provide a way to compile functions so that they operate
3222 without stack frames. (For example, the @code{@value{GCC}} option
3223 @samp{-fomit-frame-pointer} generates functions without a frame.)
3224 This is occasionally done with heavily used library functions to save
3225 the frame setup time. @value{GDBN} has limited facilities for dealing
3226 with these function invocations. If the innermost function invocation
3227 has no stack frame, @value{GDBN} nevertheless regards it as though
3228 it had a separate frame, which is numbered zero as usual, allowing
3229 correct tracing of the function call chain. However, @value{GDBN} has
3230 no provision for frameless functions elsewhere in the stack.
3235 A backtrace is a summary of how your program got where it is. It shows one
3236 line per frame, for many frames, starting with the currently executing
3237 frame (frame zero), followed by its caller (frame one), and on up the
3245 Print a backtrace of the entire stack: one line per frame for all
3246 frames in the stack.
3248 You can stop the backtrace at any time by typing the system interrupt
3249 character, normally @kbd{C-c}.
3251 @item backtrace @var{n}
3253 Similar, but print only the innermost @var{n} frames.
3255 @item backtrace -@var{n}
3257 Similar, but print only the outermost @var{n} frames.
3263 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3264 are additional aliases for @code{backtrace}.
3266 Each line in the backtrace shows the frame number and the function name.
3267 The program counter value is also shown---unless you use @code{set
3268 print address off}. The backtrace also shows the source file name and
3269 line number, as well as the arguments to the function. The program
3270 counter value is omitted if it is at the beginning of the code for that
3273 Here is an example of a backtrace. It was made with the command
3274 @samp{bt 3}, so it shows the innermost three frames.
3278 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3280 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3281 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3283 (More stack frames follow...)
3288 The display for frame zero does not begin with a program counter
3289 value, indicating that your program has stopped at the beginning of the
3290 code for line @code{993} of @code{builtin.c}.
3293 @section Selecting a frame
3295 Most commands for examining the stack and other data in your program work on
3296 whichever stack frame is selected at the moment. Here are the commands for
3297 selecting a stack frame; all of them finish by printing a brief description
3298 of the stack frame just selected.
3305 Select frame number @var{n}. Recall that frame zero is the innermost
3306 (currently executing) frame, frame one is the frame that called the
3307 innermost one, and so on. The highest-numbered frame is the one for
3310 @item frame @var{addr}
3312 Select the frame at address @var{addr}. This is useful mainly if the
3313 chaining of stack frames has been damaged by a bug, making it
3314 impossible for @value{GDBN} to assign numbers properly to all frames. In
3315 addition, this can be useful when your program has multiple stacks and
3316 switches between them.
3318 @ifclear H8EXCLUSIVE
3319 On the SPARC architecture, @code{frame} needs two addresses to
3320 select an arbitrary frame: a frame pointer and a stack pointer.
3322 On the MIPS and Alpha architecture, it needs two addresses: a stack
3323 pointer and a program counter.
3325 On the 29k architecture, it needs three addresses: a register stack
3326 pointer, a program counter, and a memory stack pointer.
3327 @c note to future updaters: this is conditioned on a flag
3328 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3329 @c as of 27 Jan 1994.
3334 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3335 advances toward the outermost frame, to higher frame numbers, to frames
3336 that have existed longer. @var{n} defaults to one.
3341 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3342 advances toward the innermost frame, to lower frame numbers, to frames
3343 that were created more recently. @var{n} defaults to one. You may
3344 abbreviate @code{down} as @code{do}.
3347 All of these commands end by printing two lines of output describing the
3348 frame. The first line shows the frame number, the function name, the
3349 arguments, and the source file and line number of execution in that
3350 frame. The second line shows the text of that source line.
3358 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3360 10 read_input_file (argv[i]);
3364 After such a printout, the @code{list} command with no arguments
3365 prints ten lines centered on the point of execution in the frame.
3366 @xref{List, ,Printing source lines}.
3369 @item up-silently @var{n}
3370 @itemx down-silently @var{n}
3371 @kindex down-silently
3373 These two commands are variants of @code{up} and @code{down},
3374 respectively; they differ in that they do their work silently, without
3375 causing display of the new frame. They are intended primarily for use
3376 in @value{GDBN} command scripts, where the output might be unnecessary and
3381 @section Information about a frame
3383 There are several other commands to print information about the selected
3389 When used without any argument, this command does not change which
3390 frame is selected, but prints a brief description of the currently
3391 selected stack frame. It can be abbreviated @code{f}. With an
3392 argument, this command is used to select a stack frame.
3393 @xref{Selection, ,Selecting a frame}.
3399 This command prints a verbose description of the selected stack frame,
3400 including the address of the frame, the addresses of the next frame down
3401 (called by this frame) and the next frame up (caller of this frame), the
3402 language that the source code corresponding to this frame was written in,
3403 the address of the frame's arguments, the program counter saved in it
3404 (the address of execution in the caller frame), and which registers
3405 were saved in the frame. The verbose description is useful when
3406 something has gone wrong that has made the stack format fail to fit
3407 the usual conventions.
3409 @item info frame @var{addr}
3410 @itemx info f @var{addr}
3411 Print a verbose description of the frame at address @var{addr}, without
3412 selecting that frame. The selected frame remains unchanged by this
3413 command. This requires the same kind of address (more than one for some
3414 architectures) that you specify in the @code{frame} command.
3415 @xref{Selection, ,Selecting a frame}.
3419 Print the arguments of the selected frame, each on a separate line.
3423 Print the local variables of the selected frame, each on a separate
3424 line. These are all variables (declared either static or automatic)
3425 accessible at the point of execution of the selected frame.
3430 @cindex catch exceptions
3431 @cindex exception handlers
3432 Print a list of all the exception handlers that are active in the
3433 current stack frame at the current point of execution. To see other
3434 exception handlers, visit the associated frame (using the @code{up},
3435 @code{down}, or @code{frame} commands); then type @code{info catch}.
3436 @xref{Exception Handling, ,Breakpoints and exceptions}.
3442 @section MIPS machines and the function stack
3444 @cindex stack on MIPS
3446 MIPS based computers use an unusual stack frame, which sometimes
3447 requires @value{GDBN} to search backward in the object code to find the
3448 beginning of a function.
3450 @cindex response time, MIPS debugging
3451 To improve response time (especially for embedded applications, where
3452 @value{GDBN} may be restricted to a slow serial line for this search)
3453 you may want to limit the size of this search, using one of these
3455 @c FIXME! So what happens when GDB does *not* find the beginning of a
3458 @cindex @code{heuristic-fence-post} (MIPS)
3460 @item set heuristic-fence-post @var{limit}
3461 Restrict @value{GDBN} to examining at most @var{limit} bytes in its search
3462 for the beginning of a function. A value of @code{0} (the default)
3463 means there is no limit.
3465 @item show heuristic-fence-post
3466 Display the current limit.
3470 These commands are available @emph{only} when @value{GDBN} is configured
3471 for debugging programs on MIPS processors.
3475 @chapter Examining Source Files
3477 @value{GDBN} can print parts of your program's source, since the debugging
3478 information recorded in the program tells @value{GDBN} what source files were
3479 used to build it. When your program stops, @value{GDBN} spontaneously prints
3480 the line where it stopped. Likewise, when you select a stack frame
3481 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3482 execution in that frame has stopped. You can print other portions of
3483 source files by explicit command.
3486 If you use @value{GDBN} through its GNU Emacs interface, you may prefer to use
3487 Emacs facilities to view source; @pxref{Emacs, ,Using @value{GDBN} under GNU
3492 * List:: Printing source lines
3494 * Search:: Searching source files
3497 * Source Path:: Specifying source directories
3498 * Machine Code:: Source and machine code
3502 @section Printing source lines
3506 To print lines from a source file, use the @code{list} command
3507 (abbreviated @code{l}). There are several ways to specify what part
3508 of the file you want to print.
3510 Here are the forms of the @code{list} command most commonly used:
3513 @item list @var{linenum}
3514 Print lines centered around line number @var{linenum} in the
3515 current source file.
3517 @item list @var{function}
3518 Print lines centered around the beginning of function
3522 Print more lines. If the last lines printed were printed with a
3523 @code{list} command, this prints lines following the last lines
3524 printed; however, if the last line printed was a solitary line printed
3525 as part of displaying a stack frame (@pxref{Stack, ,Examining the
3526 Stack}), this prints lines centered around that line.
3529 Print lines just before the lines last printed.
3532 By default, @value{GDBN} prints ten source lines with any of these forms of
3533 the @code{list} command. You can change this using @code{set listsize}:
3536 @item set listsize @var{count}
3537 @kindex set listsize
3538 Make the @code{list} command display @var{count} source lines (unless
3539 the @code{list} argument explicitly specifies some other number).
3542 @kindex show listsize
3543 Display the number of lines that @code{list} prints.
3546 Repeating a @code{list} command with @key{RET} discards the argument,
3547 so it is equivalent to typing just @code{list}. This is more useful
3548 than listing the same lines again. An exception is made for an
3549 argument of @samp{-}; that argument is preserved in repetition so that
3550 each repetition moves up in the source file.
3553 In general, the @code{list} command expects you to supply zero, one or two
3554 @dfn{linespecs}. Linespecs specify source lines; there are several ways
3555 of writing them but the effect is always to specify some source line.
3556 Here is a complete description of the possible arguments for @code{list}:
3559 @item list @var{linespec}
3560 Print lines centered around the line specified by @var{linespec}.
3562 @item list @var{first},@var{last}
3563 Print lines from @var{first} to @var{last}. Both arguments are
3566 @item list ,@var{last}
3567 Print lines ending with @var{last}.
3569 @item list @var{first},
3570 Print lines starting with @var{first}.
3573 Print lines just after the lines last printed.
3576 Print lines just before the lines last printed.
3579 As described in the preceding table.
3582 Here are the ways of specifying a single source line---all the
3587 Specifies line @var{number} of the current source file.
3588 When a @code{list} command has two linespecs, this refers to
3589 the same source file as the first linespec.
3592 Specifies the line @var{offset} lines after the last line printed.
3593 When used as the second linespec in a @code{list} command that has
3594 two, this specifies the line @var{offset} lines down from the
3598 Specifies the line @var{offset} lines before the last line printed.
3600 @item @var{filename}:@var{number}
3601 Specifies line @var{number} in the source file @var{filename}.
3603 @item @var{function}
3604 @c FIXME: "of the open-brace" is C-centric. When we add other langs...
3605 Specifies the line of the open-brace that begins the body of the
3606 function @var{function}.
3608 @item @var{filename}:@var{function}
3609 Specifies the line of the open-brace that begins the body of the
3610 function @var{function} in the file @var{filename}. You only need the
3611 file name with a function name to avoid ambiguity when there are
3612 identically named functions in different source files.
3614 @item *@var{address}
3615 Specifies the line containing the program address @var{address}.
3616 @var{address} may be any expression.
3621 @section Searching source files
3623 @kindex reverse-search
3625 There are two commands for searching through the current source file for a
3629 @item forward-search @var{regexp}
3630 @itemx search @var{regexp}
3632 @kindex forward-search
3633 The command @samp{forward-search @var{regexp}} checks each line,
3634 starting with the one following the last line listed, for a match for
3635 @var{regexp}. It lists the line that is found. You can use
3636 synonym @samp{search @var{regexp}} or abbreviate the command name as
3639 @item reverse-search @var{regexp}
3640 The command @samp{reverse-search @var{regexp}} checks each line, starting
3641 with the one before the last line listed and going backward, for a match
3642 for @var{regexp}. It lists the line that is found. You can abbreviate
3643 this command as @code{rev}.
3648 @section Specifying source directories
3651 @cindex directories for source files
3652 Executable programs sometimes do not record the directories of the source
3653 files from which they were compiled, just the names. Even when they do,
3654 the directories could be moved between the compilation and your debugging
3655 session. @value{GDBN} has a list of directories to search for source files;
3656 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
3657 it tries all the directories in the list, in the order they are present
3658 in the list, until it finds a file with the desired name. Note that
3659 the executable search path is @emph{not} used for this purpose. Neither is
3660 the current working directory, unless it happens to be in the source
3663 If @value{GDBN} cannot find a source file in the source path, and the
3664 object program records a directory, @value{GDBN} tries that directory
3665 too. If the source path is empty, and there is no record of the
3666 compilation directory, @value{GDBN} looks in the current directory as a
3669 Whenever you reset or rearrange the source path, @value{GDBN} clears out
3670 any information it has cached about where source files are found and where
3671 each line is in the file.
3674 When you start @value{GDBN}, its source path is empty.
3675 To add other directories, use the @code{directory} command.
3678 @item directory @var{dirname} @dots{}
3679 Add directory @var{dirname} to the front of the source path. Several
3680 directory names may be given to this command, separated by @samp{:} or
3681 whitespace. You may specify a directory that is already in the source
3682 path; this moves it forward, so @value{GDBN} searches it sooner.
3688 @cindex compilation directory
3689 @cindex current directory
3690 @cindex working directory
3691 @cindex directory, current
3692 @cindex directory, compilation
3693 You can use the string @samp{$cdir} to refer to the compilation
3694 directory (if one is recorded), and @samp{$cwd} to refer to the current
3695 working directory. @samp{$cwd} is not the same as @samp{.}---the former
3696 tracks the current working directory as it changes during your @value{GDBN}
3697 session, while the latter is immediately expanded to the current
3698 directory at the time you add an entry to the source path.
3701 Reset the source path to empty again. This requires confirmation.
3703 @c RET-repeat for @code{directory} is explicitly disabled, but since
3704 @c repeating it would be a no-op we do not say that. (thanks to RMS)
3706 @item show directories
3707 @kindex show directories
3708 Print the source path: show which directories it contains.
3711 If your source path is cluttered with directories that are no longer of
3712 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
3713 versions of source. You can correct the situation as follows:
3717 Use @code{directory} with no argument to reset the source path to empty.
3720 Use @code{directory} with suitable arguments to reinstall the
3721 directories you want in the source path. You can add all the
3722 directories in one command.
3726 @section Source and machine code
3728 You can use the command @code{info line} to map source lines to program
3729 addresses (and vice versa), and the command @code{disassemble} to display
3730 a range of addresses as machine instructions.
3733 @item info line @var{linespec}
3735 Print the starting and ending addresses of the compiled code for
3736 source line @var{linespec}. You can specify source lines in any of
3737 the ways understood by the @code{list} command (@pxref{List, ,Printing
3741 For example, we can use @code{info line} to discover the location of
3742 the object code for the first line of function
3743 @code{m4_changequote}:
3746 (@value{GDBP}) info line m4_changecom
3747 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
3751 We can also inquire (using @code{*@var{addr}} as the form for
3752 @var{linespec}) what source line covers a particular address:
3754 (@value{GDBP}) info line *0x63ff
3755 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
3758 @cindex @code{$_} and @code{info line}
3759 After @code{info line}, the default address for the @code{x} command
3760 is changed to the starting address of the line, so that @samp{x/i} is
3761 sufficient to begin examining the machine code (@pxref{Memory,
3762 ,Examining memory}). Also, this address is saved as the value of the
3763 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
3769 @cindex assembly instructions
3770 @cindex instructions, assembly
3771 @cindex machine instructions
3772 @cindex listing machine instructions
3773 This specialized command dumps a range of memory as machine
3774 instructions. The default memory range is the function surrounding the
3775 program counter of the selected frame. A single argument to this
3776 command is a program counter value; @value{GDBN} dumps the function
3777 surrounding this value. Two arguments specify a range of addresses
3778 (first inclusive, second exclusive) to dump.
3781 @ifclear H8EXCLUSIVE
3782 We can use @code{disassemble} to inspect the object code
3783 range shown in the last @code{info line} example (the example
3784 shows SPARC machine instructions):
3788 (@value{GDBP}) disas 0x63e4 0x6404
3789 Dump of assembler code from 0x63e4 to 0x6404:
3790 0x63e4 <builtin_init+5340>: ble 0x63f8 <builtin_init+5360>
3791 0x63e8 <builtin_init+5344>: sethi %hi(0x4c00), %o0
3792 0x63ec <builtin_init+5348>: ld [%i1+4], %o0
3793 0x63f0 <builtin_init+5352>: b 0x63fc <builtin_init+5364>
3794 0x63f4 <builtin_init+5356>: ld [%o0+4], %o0
3795 0x63f8 <builtin_init+5360>: or %o0, 0x1a4, %o0
3796 0x63fc <builtin_init+5364>: call 0x9288 <path_search>
3797 0x6400 <builtin_init+5368>: nop
3798 End of assembler dump.
3803 For example, here is the beginning of the output for the
3804 disassembly of a function @code{fact}:
3808 (@value{GDBP}) disas fact
3809 Dump of assembler code for function fact:
3811 0x802c <fact>: 6d f2 mov.w r2,@@-r7
3812 0x802e <fact+2>: 6d f3 mov.w r3,@@-r7
3813 0x8030 <fact+4>: 6d f6 mov.w r6,@@-r7
3814 0x8032 <fact+6>: 0d 76 mov.w r7,r6
3815 0x8034 <fact+8>: 6f 70 00 08 mov.w @@(0x8,r7),r0
3816 0x8038 <fact+12> 19 11 sub.w r1,r1
3824 @chapter Examining Data
3826 @cindex printing data
3827 @cindex examining data
3830 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
3831 @c document because it is nonstandard... Under Epoch it displays in a
3832 @c different window or something like that.
3833 The usual way to examine data in your program is with the @code{print}
3834 command (abbreviated @code{p}), or its synonym @code{inspect}.
3836 It evaluates and prints the value of an expression of the language your
3837 program is written in (@pxref{Languages, ,Using @value{GDBN} with Different
3842 @item print @var{exp}
3843 @itemx print /@var{f} @var{exp}
3844 @var{exp} is an expression (in the source language). By default the
3845 value of @var{exp} is printed in a format appropriate to its data type;
3846 you can choose a different format by specifying @samp{/@var{f}}, where
3847 @var{f} is a letter specifying the format; @pxref{Output Formats,,Output
3851 @itemx print /@var{f}
3852 If you omit @var{exp}, @value{GDBN} displays the last value again (from the
3853 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
3854 conveniently inspect the same value in an alternative format.
3857 A more low-level way of examining data is with the @code{x} command.
3858 It examines data in memory at a specified address and prints it in a
3859 specified format. @xref{Memory, ,Examining memory}.
3861 If you are interested in information about types, or about how the fields
3866 are declared, use the @code{ptype @var{exp}}
3867 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}.
3870 * Expressions:: Expressions
3871 * Variables:: Program variables
3872 * Arrays:: Artificial arrays
3873 * Output Formats:: Output formats
3874 * Memory:: Examining memory
3875 * Auto Display:: Automatic display
3876 * Print Settings:: Print settings
3877 * Value History:: Value history
3878 * Convenience Vars:: Convenience variables
3879 * Registers:: Registers
3881 * Floating Point Hardware:: Floating point hardware
3886 @section Expressions
3889 @code{print} and many other @value{GDBN} commands accept an expression and
3890 compute its value. Any kind of constant, variable or operator defined
3891 by the programming language you are using is valid in an expression in
3892 @value{GDBN}. This includes conditional expressions, function calls, casts
3893 and string constants. It unfortunately does not include symbols defined
3894 by preprocessor @code{#define} commands.
3897 Because C is so widespread, most of the expressions shown in examples in
3898 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
3899 Languages}, for information on how to use expressions in other
3902 In this section, we discuss operators that you can use in @value{GDBN}
3903 expressions regardless of your programming language.
3905 Casts are supported in all languages, not just in C, because it is so
3906 useful to cast a number into a pointer so as to examine a structure
3907 at that address in memory.
3908 @c FIXME: casts supported---Mod2 true?
3911 @value{GDBN} supports these operators in addition to those of programming
3916 @samp{@@} is a binary operator for treating parts of memory as arrays.
3917 @xref{Arrays, ,Artificial arrays}, for more information.
3920 @samp{::} allows you to specify a variable in terms of the file or
3921 function where it is defined. @xref{Variables, ,Program variables}.
3923 @item @{@var{type}@} @var{addr}
3924 @cindex @{@var{type}@}
3925 @cindex type casting memory
3926 @cindex memory, viewing as typed object
3927 @cindex casts, to view memory
3928 Refers to an object of type @var{type} stored at address @var{addr} in
3929 memory. @var{addr} may be any expression whose value is an integer or
3930 pointer (but parentheses are required around binary operators, just as in
3931 a cast). This construct is allowed regardless of what kind of data is
3932 normally supposed to reside at @var{addr}.
3936 @section Program variables
3938 The most common kind of expression to use is the name of a variable
3941 Variables in expressions are understood in the selected stack frame
3942 (@pxref{Selection, ,Selecting a frame}); they must either be global
3943 (or static) or be visible according to the scope rules of the
3944 programming language from the point of execution in that frame. This
3945 means that in the function
3960 you can examine and use the variable @code{a} whenever your program is
3961 executing within the function @code{foo}, but you can only use or
3962 examine the variable @code{b} while your program is executing inside
3963 the block where @code{b} is declared.
3965 @cindex variable name conflict
3966 There is an exception: you can refer to a variable or function whose
3967 scope is a single source file even if the current execution point is not
3968 in this file. But it is possible to have more than one such variable or
3969 function with the same name (in different source files). If that
3970 happens, referring to that name has unpredictable effects. If you wish,
3971 you can specify a static variable in a particular function or file,
3972 using the colon-colon notation:
3976 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
3980 @var{file}::@var{variable}
3981 @var{function}::@var{variable}
3985 Here @var{file} or @var{function} is the name of the context for the
3986 static @var{variable}. In the case of file names, you can use quotes to
3987 make sure @value{GDBN} parses the file name as a single word---for example,
3988 to print a global value of @code{x} defined in @file{f2.c}:
3991 (@value{GDBP}) p 'f2.c'::x
3995 @cindex C++ scope resolution
3996 This use of @samp{::} is very rarely in conflict with the very similar
3997 use of the same notation in C++. @value{GDBN} also supports use of the C++
3998 scope resolution operator in @value{GDBN} expressions.
3999 @c FIXME: Um, so what happens in one of those rare cases where it's in
4003 @cindex wrong values
4004 @cindex variable values, wrong
4006 @emph{Warning:} Occasionally, a local variable may appear to have the
4007 wrong value at certain points in a function---just after entry to a new
4008 scope, and just before exit.
4010 You may see this problem when you are stepping by machine instructions.
4011 This is because on most machines, it takes more than one instruction to
4012 set up a stack frame (including local variable definitions); if you are
4013 stepping by machine instructions, variables may appear to have the wrong
4014 values until the stack frame is completely built. On exit, it usually
4015 also takes more than one machine instruction to destroy a stack frame;
4016 after you begin stepping through that group of instructions, local
4017 variable definitions may be gone.
4020 @section Artificial arrays
4022 @cindex artificial array
4024 It is often useful to print out several successive objects of the
4025 same type in memory; a section of an array, or an array of
4026 dynamically determined size for which only a pointer exists in the
4029 You can do this by referring to a contiguous span of memory as an
4030 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4031 operand of @samp{@@} should be the first element of the desired array,
4032 as an individual object. The right operand should be the desired length
4033 of the array. The result is an array value whose elements are all of
4034 the type of the left argument. The first element is actually the left
4035 argument; the second element comes from bytes of memory immediately
4036 following those that hold the first element, and so on. Here is an
4037 example. If a program says
4040 int *array = (int *) malloc (len * sizeof (int));
4044 you can print the contents of @code{array} with
4050 The left operand of @samp{@@} must reside in memory. Array values made
4051 with @samp{@@} in this way behave just like other arrays in terms of
4052 subscripting, and are coerced to pointers when used in expressions.
4053 Artificial arrays most often appear in expressions via the value history
4054 (@pxref{Value History, ,Value history}), after printing one out.
4056 Sometimes the artificial array mechanism is not quite enough; in
4057 moderately complex data structures, the elements of interest may not
4058 actually be adjacent---for example, if you are interested in the values
4059 of pointers in an array. One useful work-around in this situation is
4060 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4061 variables}) as a counter in an expression that prints the first
4062 interesting value, and then repeat that expression via @key{RET}. For
4063 instance, suppose you have an array @code{dtab} of pointers to
4064 structures, and you are interested in the values of a field @code{fv}
4065 in each structure. Here is an example of what you might type:
4075 @node Output Formats
4076 @section Output formats
4078 @cindex formatted output
4079 @cindex output formats
4080 By default, @value{GDBN} prints a value according to its data type. Sometimes
4081 this is not what you want. For example, you might want to print a number
4082 in hex, or a pointer in decimal. Or you might want to view data in memory
4083 at a certain address as a character string or as an instruction. To do
4084 these things, specify an @dfn{output format} when you print a value.
4086 The simplest use of output formats is to say how to print a value
4087 already computed. This is done by starting the arguments of the
4088 @code{print} command with a slash and a format letter. The format
4089 letters supported are:
4093 Regard the bits of the value as an integer, and print the integer in
4097 Print as integer in signed decimal.
4100 Print as integer in unsigned decimal.
4103 Print as integer in octal.
4106 Print as integer in binary. The letter @samp{t} stands for ``two''.
4107 @footnote{@samp{b} cannot be used because these format letters are also
4108 used with the @code{x} command, where @samp{b} stands for ``byte'';
4109 @pxref{Memory,,Examining memory}.}
4112 @cindex unknown address, locating
4113 Print as an address, both absolute in hexadecimal and as an offset from
4114 the nearest preceding symbol. You can use this format used to discover
4115 where (in what function) an unknown address is located:
4118 (@value{GDBP}) p/a 0x54320
4119 $3 = 0x54320 <_initialize_vx+396>
4123 Regard as an integer and print it as a character constant.
4126 Regard the bits of the value as a floating point number and print
4127 using typical floating point syntax.
4130 For example, to print the program counter in hex (@pxref{Registers}), type
4137 Note that no space is required before the slash; this is because command
4138 names in @value{GDBN} cannot contain a slash.
4140 To reprint the last value in the value history with a different format,
4141 you can use the @code{print} command with just a format and no
4142 expression. For example, @samp{p/x} reprints the last value in hex.
4145 @section Examining memory
4147 You can use the command @code{x} (for ``examine'') to examine memory in
4148 any of several formats, independently of your program's data types.
4150 @cindex examining memory
4153 @item x/@var{nfu} @var{addr}
4156 Use the @code{x} command to examine memory.
4159 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4160 much memory to display and how to format it; @var{addr} is an
4161 expression giving the address where you want to start displaying memory.
4162 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4163 Several commands set convenient defaults for @var{addr}.
4166 @item @var{n}, the repeat count
4167 The repeat count is a decimal integer; the default is 1. It specifies
4168 how much memory (counting by units @var{u}) to display.
4169 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4172 @item @var{f}, the display format
4173 The display format is one of the formats used by @code{print},
4174 or @samp{s} (null-terminated string) or @samp{i} (machine instruction).
4175 The default is @samp{x} (hexadecimal) initially, or the format from the
4176 last time you used either @code{x} or @code{print}.
4178 @item @var{u}, the unit size
4179 The unit size is any of
4185 Halfwords (two bytes).
4187 Words (four bytes). This is the initial default.
4189 Giant words (eight bytes).
4192 Each time you specify a unit size with @code{x}, that size becomes the
4193 default unit the next time you use @code{x}. (For the @samp{s} and
4194 @samp{i} formats, the unit size is ignored and is normally not written.)
4196 @item @var{addr}, starting display address
4197 @var{addr} is the address where you want @value{GDBN} to begin displaying
4198 memory. The expression need not have a pointer value (though it may);
4199 it is always interpreted as an integer address of a byte of memory.
4200 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4201 @var{addr} is usually just after the last address examined---but several
4202 other commands also set the default address: @code{info breakpoints} (to
4203 the address of the last breakpoint listed), @code{info line} (to the
4204 starting address of a line), and @code{print} (if you use it to display
4205 a value from memory).
4208 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4209 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4210 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4211 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4212 @pxref{Registers}) in hexadecimal (@samp{x}).
4214 Since the letters indicating unit sizes are all distinct from the
4215 letters specifying output formats, you do not have to remember whether
4216 unit size or format comes first; either order works. The output
4217 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4218 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4220 Even though the unit size @var{u} is ignored for the formats @samp{s}
4221 and @samp{i}, you might still want to use a count @var{n}; for example,
4222 @samp{3i} specifies that you want to see three machine instructions,
4223 including any operands. The command @code{disassemble} gives an
4224 alternative way of inspecting machine instructions; @pxref{Machine
4225 Code,,Source and machine code}.
4227 All the defaults for the arguments to @code{x} are designed to make it
4228 easy to continue scanning memory with minimal specifications each time
4229 you use @code{x}. For example, after you have inspected three machine
4230 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4231 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4232 the repeat count @var{n} is used again; the other arguments default as
4233 for successive uses of @code{x}.
4235 @cindex @code{$_}, @code{$__}, and value history
4236 The addresses and contents printed by the @code{x} command are not saved
4237 in the value history because there is often too much of them and they
4238 would get in the way. Instead, @value{GDBN} makes these values available for
4239 subsequent use in expressions as values of the convenience variables
4240 @code{$_} and @code{$__}. After an @code{x} command, the last address
4241 examined is available for use in expressions in the convenience variable
4242 @code{$_}. The contents of that address, as examined, are available in
4243 the convenience variable @code{$__}.
4245 If the @code{x} command has a repeat count, the address and contents saved
4246 are from the last memory unit printed; this is not the same as the last
4247 address printed if several units were printed on the last line of output.
4250 @section Automatic display
4251 @cindex automatic display
4252 @cindex display of expressions
4254 If you find that you want to print the value of an expression frequently
4255 (to see how it changes), you might want to add it to the @dfn{automatic
4256 display list} so that @value{GDBN} prints its value each time your program stops.
4257 Each expression added to the list is given a number to identify it;
4258 to remove an expression from the list, you specify that number.
4259 The automatic display looks like this:
4263 3: bar[5] = (struct hack *) 0x3804
4267 This display shows item numbers, expressions and their current values. As with
4268 displays you request manually using @code{x} or @code{print}, you can
4269 specify the output format you prefer; in fact, @code{display} decides
4270 whether to use @code{print} or @code{x} depending on how elaborate your
4271 format specification is---it uses @code{x} if you specify a unit size,
4272 or one of the two formats (@samp{i} and @samp{s}) that are only
4273 supported by @code{x}; otherwise it uses @code{print}.
4276 @item display @var{exp}
4278 Add the expression @var{exp} to the list of expressions to display
4279 each time your program stops. @xref{Expressions, ,Expressions}.
4281 @code{display} does not repeat if you press @key{RET} again after using it.
4283 @item display/@var{fmt} @var{exp}
4284 For @var{fmt} specifying only a display format and not a size or
4285 count, add the expression @var{exp} to the auto-display list but
4286 arrange to display it each time in the specified format @var{fmt}.
4287 @xref{Output Formats,,Output formats}.
4289 @item display/@var{fmt} @var{addr}
4290 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4291 number of units, add the expression @var{addr} as a memory address to
4292 be examined each time your program stops. Examining means in effect
4293 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4296 For example, @samp{display/i $pc} can be helpful, to see the machine
4297 instruction about to be executed each time execution stops (@samp{$pc}
4298 is a common name for the program counter; @pxref{Registers}).
4301 @item undisplay @var{dnums}@dots{}
4302 @itemx delete display @var{dnums}@dots{}
4303 @kindex delete display
4305 Remove item numbers @var{dnums} from the list of expressions to display.
4307 @code{undisplay} does not repeat if you press @key{RET} after using it.
4308 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4310 @item disable display @var{dnums}@dots{}
4311 @kindex disable display
4312 Disable the display of item numbers @var{dnums}. A disabled display
4313 item is not printed automatically, but is not forgotten. It may be
4314 enabled again later.
4316 @item enable display @var{dnums}@dots{}
4317 @kindex enable display
4318 Enable display of item numbers @var{dnums}. It becomes effective once
4319 again in auto display of its expression, until you specify otherwise.
4322 Display the current values of the expressions on the list, just as is
4323 done when your program stops.
4326 @kindex info display
4327 Print the list of expressions previously set up to display
4328 automatically, each one with its item number, but without showing the
4329 values. This includes disabled expressions, which are marked as such.
4330 It also includes expressions which would not be displayed right now
4331 because they refer to automatic variables not currently available.
4334 If a display expression refers to local variables, then it does not make
4335 sense outside the lexical context for which it was set up. Such an
4336 expression is disabled when execution enters a context where one of its
4337 variables is not defined. For example, if you give the command
4338 @code{display last_char} while inside a function with an argument
4339 @code{last_char}, @value{GDBN} displays this argument while your program
4340 continues to stop inside that function. When it stops elsewhere---where
4341 there is no variable @code{last_char}---the display is disabled
4342 automatically. The next time your program stops where @code{last_char}
4343 is meaningful, you can enable the display expression once again.
4345 @node Print Settings
4346 @section Print settings
4348 @cindex format options
4349 @cindex print settings
4350 @value{GDBN} provides the following ways to control how arrays, structures,
4351 and symbols are printed.
4354 These settings are useful for debugging programs in any language:
4357 @item set print address
4358 @itemx set print address on
4359 @kindex set print address
4360 @value{GDBN} prints memory addresses showing the location of stack
4361 traces, structure values, pointer values, breakpoints, and so forth,
4362 even when it also displays the contents of those addresses. The default
4363 is @code{on}. For example, this is what a stack frame display looks like, with
4364 @code{set print address on}:
4369 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4371 530 if (lquote != def_lquote)
4375 @item set print address off
4376 Do not print addresses when displaying their contents. For example,
4377 this is the same stack frame displayed with @code{set print address off}:
4381 (@value{GDBP}) set print addr off
4383 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4384 530 if (lquote != def_lquote)
4388 You can use @samp{set print address off} to eliminate all machine
4389 dependent displays from the @value{GDBN} interface. For example, with
4390 @code{print address off}, you should get the same text for backtraces on
4391 all machines---whether or not they involve pointer arguments.
4393 @item show print address
4394 @kindex show print address
4395 Show whether or not addresses are to be printed.
4398 When @value{GDBN} prints a symbolic address, it normally prints the
4399 closest earlier symbol plus an offset. If that symbol does not uniquely
4400 identify the address (for example, it is a name whose scope is a single
4401 source file), you may need to disambiguate. One way to do this is with
4402 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4403 you can set @value{GDBN} to print the source file and line number when
4404 it prints a symbolic address:
4407 @item set print symbol-filename on
4408 @kindex set print symbol-filename
4409 Tell @value{GDBN} to print the source file name and line number of a
4410 symbol in the symbolic form of an address.
4412 @item set print symbol-filename off
4413 Do not print source file name and line number of a symbol. This is the
4416 @item show print symbol-filename
4417 @kindex show print symbol-filename
4418 Show whether or not @value{GDBN} will print the source file name and
4419 line number of a symbol in the symbolic form of an address.
4422 Another situation where it is helpful to show symbol filenames and line
4423 numbers is when disassembling code; @value{GDBN} shows you the line
4424 number and source file that corresponds to each instruction.
4426 Also, you may wish to see the symbolic form only if the address being
4427 printed is reasonably close to the closest earlier symbol:
4430 @item set print max-symbolic-offset @var{max-offset}
4431 @kindex set print max-symbolic-offset
4432 Tell @value{GDBN} to only display the symbolic form of an address if the
4433 offset between the closest earlier symbol and the address is less than
4434 @var{max-offset}. The default is 0, which means to always print the
4435 symbolic form of an address, if any symbol precedes it.
4437 @item show print max-symbolic-offset
4438 @kindex show print max-symbolic-offset
4439 Ask how large the maximum offset is that @value{GDBN} prints in a
4443 @cindex wild pointer, interpreting
4444 @cindex pointer, finding referent
4445 If you have a pointer and you are not sure where it points, try
4446 @samp{set print symbol-filename on}. Then you can determine the name
4447 and source file location of the variable where it points, using
4448 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
4449 For example, here @value{GDBN} shows that a variable @code{ptt} points
4450 at another variable @code{t}, defined in @file{hi2.c}:
4453 (@value{GDBP}) set print symbol-filename on
4454 (@value{GDBP}) p/a ptt
4455 $4 = 0xe008 <t in hi2.c>
4459 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
4460 does not show the symbol name and filename of the referent, even with
4461 the appropriate @code{set print} options turned on.
4464 Other settings control how different kinds of objects are printed:
4467 @item set print array
4468 @itemx set print array on
4469 @kindex set print array
4470 Pretty-print arrays. This format is more convenient to read,
4471 but uses more space. The default is off.
4473 @item set print array off
4474 Return to compressed format for arrays.
4476 @item show print array
4477 @kindex show print array
4478 Show whether compressed or pretty format is selected for displaying
4481 @item set print elements @var{number-of-elements}
4482 @kindex set print elements
4483 If @value{GDBN} is printing a large array, it stops printing after it has
4484 printed the number of elements set by the @code{set print elements} command.
4485 This limit also applies to the display of strings.
4486 Setting the number of elements to zero means that the printing is unlimited.
4488 @item show print elements
4489 @kindex show print elements
4490 Display the number of elements of a large array that @value{GDBN} prints
4491 before losing patience.
4493 @item set print pretty on
4494 @kindex set print pretty
4495 Cause @value{GDBN} to print structures in an indented format with one member per
4511 @item set print pretty off
4512 Cause @value{GDBN} to print structures in a compact format, like this:
4516 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
4517 meat = 0x54 "Pork"@}
4522 This is the default format.
4524 @item show print pretty
4525 @kindex show print pretty
4526 Show which format @value{GDBN} is using to print structures.
4528 @item set print sevenbit-strings on
4529 @kindex set print sevenbit-strings
4530 Print using only seven-bit characters; if this option is set,
4531 @value{GDBN} displays any eight-bit characters (in strings or
4532 character values) using the notation @code{\}@var{nnn}. This setting is
4533 best if you are working in English (@sc{ascii}) and you use the
4534 high-order bit of characters as a marker or ``meta'' bit.
4536 @item set print sevenbit-strings off
4537 Print full eight-bit characters. This allows the use of more
4538 international character sets, and is the default.
4540 @item show print sevenbit-strings
4541 @kindex show print sevenbit-strings
4542 Show whether or not @value{GDBN} is printing only seven-bit characters.
4544 @item set print union on
4545 @kindex set print union
4546 Tell @value{GDBN} to print unions which are contained in structures. This is the
4549 @item set print union off
4550 Tell @value{GDBN} not to print unions which are contained in structures.
4552 @item show print union
4553 @kindex show print union
4554 Ask @value{GDBN} whether or not it will print unions which are contained in
4557 For example, given the declarations
4560 typedef enum @{Tree, Bug@} Species;
4561 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
4562 typedef enum @{Caterpillar, Cocoon, Butterfly@}
4573 struct thing foo = @{Tree, @{Acorn@}@};
4577 with @code{set print union on} in effect @samp{p foo} would print
4580 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
4584 and with @code{set print union off} in effect it would print
4587 $1 = @{it = Tree, form = @{...@}@}
4594 These settings are of interest when debugging C++ programs:
4597 @item set print demangle
4598 @itemx set print demangle on
4599 @kindex set print demangle
4600 Print C++ names in their source form rather than in the encoded
4601 (``mangled'') form passed to the assembler and linker for type-safe
4602 linkage. The default is @samp{on}.
4604 @item show print demangle
4605 @kindex show print demangle
4606 Show whether C++ names are printed in mangled or demangled form.
4608 @item set print asm-demangle
4609 @itemx set print asm-demangle on
4610 @kindex set print asm-demangle
4611 Print C++ names in their source form rather than their mangled form, even
4612 in assembler code printouts such as instruction disassemblies.
4615 @item show print asm-demangle
4616 @kindex show print asm-demangle
4617 Show whether C++ names in assembly listings are printed in mangled
4620 @item set demangle-style @var{style}
4621 @kindex set demangle-style
4622 @cindex C++ symbol decoding style
4623 @cindex symbol decoding style, C++
4624 Choose among several encoding schemes used by different compilers to
4625 represent C++ names. The choices for @var{style} are currently:
4629 Allow @value{GDBN} to choose a decoding style by inspecting your program.
4632 Decode based on the GNU C++ compiler (@code{g++}) encoding algorithm.
4635 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
4638 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
4639 @strong{Warning:} this setting alone is not sufficient to allow
4640 debugging @code{cfront}-generated executables. @value{GDBN} would
4641 require further enhancement to permit that.
4644 @item show demangle-style
4645 @kindex show demangle-style
4646 Display the encoding style currently in use for decoding C++ symbols.
4648 @item set print object
4649 @itemx set print object on
4650 @kindex set print object
4651 When displaying a pointer to an object, identify the @emph{actual}
4652 (derived) type of the object rather than the @emph{declared} type, using
4653 the virtual function table.
4655 @item set print object off
4656 Display only the declared type of objects, without reference to the
4657 virtual function table. This is the default setting.
4659 @item show print object
4660 @kindex show print object
4661 Show whether actual, or declared, object types are displayed.
4663 @item set print vtbl
4664 @itemx set print vtbl on
4665 @kindex set print vtbl
4666 Pretty print C++ virtual function tables. The default is off.
4668 @item set print vtbl off
4669 Do not pretty print C++ virtual function tables.
4671 @item show print vtbl
4672 @kindex show print vtbl
4673 Show whether C++ virtual function tables are pretty printed, or not.
4678 @section Value history
4680 @cindex value history
4681 Values printed by the @code{print} command are saved in the @value{GDBN} @dfn{value
4682 history} so that you can refer to them in other expressions. Values are
4683 kept until the symbol table is re-read or discarded (for example with
4684 the @code{file} or @code{symbol-file} commands). When the symbol table
4685 changes, the value history is discarded, since the values may contain
4686 pointers back to the types defined in the symbol table.
4690 @cindex history number
4691 The values printed are given @dfn{history numbers} by which you can
4692 refer to them. These are successive integers starting with one.
4693 @code{print} shows you the history number assigned to a value by
4694 printing @samp{$@var{num} = } before the value; here @var{num} is the
4697 To refer to any previous value, use @samp{$} followed by the value's
4698 history number. The way @code{print} labels its output is designed to
4699 remind you of this. Just @code{$} refers to the most recent value in
4700 the history, and @code{$$} refers to the value before that.
4701 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
4702 is the value just prior to @code{$$}, @code{$$1} is equivalent to
4703 @code{$$}, and @code{$$0} is equivalent to @code{$}.
4705 For example, suppose you have just printed a pointer to a structure and
4706 want to see the contents of the structure. It suffices to type
4712 If you have a chain of structures where the component @code{next} points
4713 to the next one, you can print the contents of the next one with this:
4720 You can print successive links in the chain by repeating this
4721 command---which you can do by just typing @key{RET}.
4723 Note that the history records values, not expressions. If the value of
4724 @code{x} is 4 and you type these commands:
4732 then the value recorded in the value history by the @code{print} command
4733 remains 4 even though the value of @code{x} has changed.
4738 Print the last ten values in the value history, with their item numbers.
4739 This is like @samp{p@ $$9} repeated ten times, except that @code{show
4740 values} does not change the history.
4742 @item show values @var{n}
4743 Print ten history values centered on history item number @var{n}.
4746 Print ten history values just after the values last printed. If no more
4747 values are available, produces no display.
4750 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
4751 same effect as @samp{show values +}.
4753 @node Convenience Vars
4754 @section Convenience variables
4756 @cindex convenience variables
4757 @value{GDBN} provides @dfn{convenience variables} that you can use within
4758 @value{GDBN} to hold on to a value and refer to it later. These variables
4759 exist entirely within @value{GDBN}; they are not part of your program, and
4760 setting a convenience variable has no direct effect on further execution
4761 of your program. That is why you can use them freely.
4763 Convenience variables are prefixed with @samp{$}. Any name preceded by
4764 @samp{$} can be used for a convenience variable, unless it is one of
4765 the predefined machine-specific register names (@pxref{Registers}).
4766 (Value history references, in contrast, are @emph{numbers} preceded
4767 by @samp{$}. @xref{Value History, ,Value history}.)
4769 You can save a value in a convenience variable with an assignment
4770 expression, just as you would set a variable in your program.
4774 set $foo = *object_ptr
4778 would save in @code{$foo} the value contained in the object pointed to by
4781 Using a convenience variable for the first time creates it, but its
4782 value is @code{void} until you assign a new value. You can alter the
4783 value with another assignment at any time.
4785 Convenience variables have no fixed types. You can assign a convenience
4786 variable any type of value, including structures and arrays, even if
4787 that variable already has a value of a different type. The convenience
4788 variable, when used as an expression, has the type of its current value.
4791 @item show convenience
4792 @kindex show convenience
4793 Print a list of convenience variables used so far, and their values.
4794 Abbreviated @code{show con}.
4797 One of the ways to use a convenience variable is as a counter to be
4798 incremented or a pointer to be advanced. For example, to print
4799 a field from successive elements of an array of structures:
4803 print bar[$i++]->contents
4804 @i{@dots{} repeat that command by typing @key{RET}.}
4807 Some convenience variables are created automatically by @value{GDBN} and given
4808 values likely to be useful.
4813 The variable @code{$_} is automatically set by the @code{x} command to
4814 the last address examined (@pxref{Memory, ,Examining memory}). Other
4815 commands which provide a default address for @code{x} to examine also
4816 set @code{$_} to that address; these commands include @code{info line}
4817 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
4818 except when set by the @code{x} command, in which case it is a pointer
4819 to the type of @code{$__}.
4823 The variable @code{$__} is automatically set by the @code{x} command
4824 to the value found in the last address examined. Its type is chosen
4825 to match the format in which the data was printed.
4832 You can refer to machine register contents, in expressions, as variables
4833 with names starting with @samp{$}. The names of registers are different
4834 for each machine; use @code{info registers} to see the names used on
4838 @item info registers
4839 @kindex info registers
4840 Print the names and values of all registers except floating-point
4841 registers (in the selected stack frame).
4843 @item info all-registers
4844 @kindex info all-registers
4845 @cindex floating point registers
4846 Print the names and values of all registers, including floating-point
4849 @item info registers @var{regname} @dots{}
4850 Print the relativized value of each specified register @var{regname}.
4851 @var{regname} may be any register name valid on the machine you are using, with
4852 or without the initial @samp{$}.
4855 @value{GDBN} has four ``standard'' register names that are available (in
4856 expressions) on most machines---whenever they do not conflict with an
4857 architecture's canonical mnemonics for registers. The register names
4858 @code{$pc} and @code{$sp} are used for the program counter register and
4859 the stack pointer. @code{$fp} is used for a register that contains a
4860 pointer to the current stack frame, and @code{$ps} is used for a
4861 register that contains the processor status. For example,
4862 you could print the program counter in hex with
4869 or print the instruction to be executed next with
4876 or add four to the stack pointer@footnote{This is a way of removing
4877 one word from the stack, on machines where stacks grow downward in
4878 memory (most machines, nowadays). This assumes that the innermost
4879 stack frame is selected; setting @code{$sp} is not allowed when other
4880 stack frames are selected. To pop entire frames off the stack,
4881 regardless of machine architecture, use @code{return};
4882 @pxref{Returning, ,Returning from a function}.} with
4888 Whenever possible, these four standard register names are available on
4889 your machine even though the machine has different canonical mnemonics,
4890 so long as there is no conflict. The @code{info registers} command
4891 shows the canonical names. For example, on the SPARC, @code{info
4892 registers} displays the processor status register as @code{$psr} but you
4893 can also refer to it as @code{$ps}.
4895 @value{GDBN} always considers the contents of an ordinary register as an
4896 integer when the register is examined in this way. Some machines have
4897 special registers which can hold nothing but floating point; these
4898 registers are considered to have floating point values. There is no way
4899 to refer to the contents of an ordinary register as floating point value
4900 (although you can @emph{print} it as a floating point value with
4901 @samp{print/f $@var{regname}}).
4903 Some registers have distinct ``raw'' and ``virtual'' data formats. This
4904 means that the data format in which the register contents are saved by
4905 the operating system is not the same one that your program normally
4906 sees. For example, the registers of the 68881 floating point
4907 coprocessor are always saved in ``extended'' (raw) format, but all C
4908 programs expect to work with ``double'' (virtual) format. In such
4909 cases, @value{GDBN} normally works with the virtual format only (the format that
4910 makes sense for your program), but the @code{info registers} command
4911 prints the data in both formats.
4913 Normally, register values are relative to the selected stack frame
4914 (@pxref{Selection, ,Selecting a frame}). This means that you get the
4915 value that the register would contain if all stack frames farther in
4916 were exited and their saved registers restored. In order to see the
4917 true contents of hardware registers, you must select the innermost
4918 frame (with @samp{frame 0}).
4920 However, @value{GDBN} must deduce where registers are saved, from the machine
4921 code generated by your compiler. If some registers are not saved, or if
4922 @value{GDBN} is unable to locate the saved registers, the selected stack
4923 frame makes no difference.
4927 @item set rstack_high_address @var{address}
4928 @kindex set rstack_high_address
4929 @cindex AMD 29K register stack
4930 @cindex register stack, AMD29K
4931 On AMD 29000 family processors, registers are saved in a separate
4932 ``register stack''. There is no way for @value{GDBN} to determine the extent
4933 of this stack. Normally, @value{GDBN} just assumes that the stack is ``large
4934 enough''. This may result in @value{GDBN} referencing memory locations that
4935 do not exist. If necessary, you can get around this problem by
4936 specifying the ending address of the register stack with the @code{set
4937 rstack_high_address} command. The argument should be an address, which
4938 you probably want to precede with @samp{0x} to specify in
4941 @item show rstack_high_address
4942 @kindex show rstack_high_address
4943 Display the current limit of the register stack, on AMD 29000 family
4949 @node Floating Point Hardware
4950 @section Floating point hardware
4951 @cindex floating point
4953 @c FIXME! Really host, not target?
4954 Depending on the host machine architecture, @value{GDBN} may be able to give
4955 you more information about the status of the floating point hardware.
4960 Display hardware-dependent information about the floating
4961 point unit. The exact contents and layout vary depending on the
4962 floating point chip; on some platforms, @samp{info float} is not
4965 @c FIXME: this is a cop-out. Try to get examples, explanations. Only
4966 @c FIXME...supported currently on arm's and 386's. Mark properly with
4967 @c FIXME... m4 macros to isolate general statements from hardware-dep,
4968 @c FIXME... at that point.
4973 @chapter Using @value{GDBN} with Different Languages
4977 Although programming languages generally have common aspects, they are
4978 rarely expressed in the same manner. For instance, in ANSI C,
4979 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
4980 Modula-2, it is accomplished by @code{p^}. Values can also be
4981 represented (and displayed) differently. Hex numbers in C are written
4982 like @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
4985 @cindex working language
4986 Language-specific information is built into @value{GDBN} for some languages,
4987 allowing you to express operations like the above in your program's
4988 native language, and allowing @value{GDBN} to output values in a manner
4989 consistent with the syntax of your program's native language. The
4990 language you use to build expressions, called the @dfn{working
4991 language}, can be selected manually, or @value{GDBN} can set it
4995 * Setting:: Switching between source languages
4996 * Show:: Displaying the language
4998 * Checks:: Type and range checks
5001 * Support:: Supported languages
5005 @section Switching between source languages
5007 There are two ways to control the working language---either have @value{GDBN}
5008 set it automatically, or select it manually yourself. You can use the
5009 @code{set language} command for either purpose. On startup, @value{GDBN}
5010 defaults to setting the language automatically.
5013 * Manually:: Setting the working language manually
5014 * Automatically:: Having @value{GDBN} infer the source language
5018 @subsection Setting the working language
5020 If you allow @value{GDBN} to set the language automatically,
5021 expressions are interpreted the same way in your debugging session and
5024 @kindex set language
5025 If you wish, you may set the language manually. To do this, issue the
5026 command @samp{set language @var{lang}}, where @var{lang} is the name of
5032 @code{c} or @code{modula-2}.
5034 For a list of the supported languages, type @samp{set language}.
5035 @c FIXME: rms: eventually this command should be "help set language".
5038 Setting the language manually prevents @value{GDBN} from updating the working
5039 language automatically. This can lead to confusion if you try
5040 to debug a program when the working language is not the same as the
5041 source language, when an expression is acceptable to both
5042 languages---but means different things. For instance, if the current
5043 source file were written in C, and @value{GDBN} was parsing Modula-2, a
5051 might not have the effect you intended. In C, this means to add
5052 @code{b} and @code{c} and place the result in @code{a}. The result
5053 printed would be the value of @code{a}. In Modula-2, this means to compare
5054 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
5058 @subsection Having @value{GDBN} infer the source language
5060 To have @value{GDBN} set the working language automatically, use @samp{set
5061 language local} or @samp{set language auto}. @value{GDBN} then infers the
5062 language that a program was written in by looking at the name of its
5063 source files, and examining their extensions:
5068 Modula-2 source file
5079 This information is recorded for each function or procedure in a source
5080 file. When your program stops in a frame (usually by encountering a
5081 breakpoint), @value{GDBN} sets the working language to the language recorded
5082 for the function in that frame. If the language for a frame is unknown
5083 (that is, if the function or block corresponding to the frame was
5084 defined in a source file that does not have a recognized extension), the
5085 current working language is not changed, and @value{GDBN} issues a warning.
5087 This may not seem necessary for most programs, which are written
5088 entirely in one source language. However, program modules and libraries
5089 written in one source language can be used by a main program written in
5090 a different source language. Using @samp{set language auto} in this
5091 case frees you from having to set the working language manually.
5094 @section Displaying the language
5096 The following commands help you find out which language is the
5097 working language, and also what language source files were written in.
5099 @kindex show language
5104 Display the current working language. This is the
5105 language you can use with commands such as @code{print} to
5106 build and compute expressions that may involve variables in your program.
5109 Among the other information listed here (@pxref{Frame Info, ,Information
5110 about a frame}) is the source language for this frame. This
5111 language becomes the working language if you use an
5112 identifier from this frame.
5115 Among the other information listed here (@pxref{Symbols, ,Examining the
5116 Symbol Table}) is the source language of this source file.
5121 @section Type and range checking
5124 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
5125 checking are included, but they do not yet have any effect. This
5126 section documents the intended facilities.
5128 @c FIXME remove warning when type/range code added
5130 Some languages are designed to guard you against making seemingly common
5131 errors through a series of compile- and run-time checks. These include
5132 checking the type of arguments to functions and operators, and making
5133 sure mathematical overflows are caught at run time. Checks such as
5134 these help to ensure a program's correctness once it has been compiled
5135 by eliminating type mismatches, and providing active checks for range
5136 errors when your program is running.
5138 @value{GDBN} can check for conditions like the above if you wish.
5139 Although @value{GDBN} does not check the statements in your program, it
5140 can check expressions entered directly into @value{GDBN} for evaluation via
5141 the @code{print} command, for example. As with the working language,
5142 @value{GDBN} can also decide whether or not to check automatically based on
5143 your program's source language. @xref{Support, ,Supported languages},
5144 for the default settings of supported languages.
5147 * Type Checking:: An overview of type checking
5148 * Range Checking:: An overview of range checking
5151 @cindex type checking
5152 @cindex checks, type
5154 @subsection An overview of type checking
5156 Some languages, such as Modula-2, are strongly typed, meaning that the
5157 arguments to operators and functions have to be of the correct type,
5158 otherwise an error occurs. These checks prevent type mismatch
5159 errors from ever causing any run-time problems. For example,
5167 The second example fails because the @code{CARDINAL} 1 is not
5168 type-compatible with the @code{REAL} 2.3.
5170 For expressions you use in @value{GDBN} commands, you can tell the @value{GDBN}
5171 type checker to skip checking; to treat any mismatches as errors and
5172 abandon the expression; or only issue warnings when type mismatches
5173 occur, but evaluate the expression anyway. When you choose the last of
5174 these, @value{GDBN} evaluates expressions like the second example above, but
5175 also issues a warning.
5177 Even though you may turn type checking off, other type-based reasons may
5178 prevent @value{GDBN} from evaluating an expression. For instance, @value{GDBN} does not
5179 know how to add an @code{int} and a @code{struct foo}. These particular
5180 type errors have nothing to do with the language in use, and usually
5181 arise from expressions, such as the one described above, which make
5182 little sense to evaluate anyway.
5184 Each language defines to what degree it is strict about type. For
5185 instance, both Modula-2 and C require the arguments to arithmetical
5186 operators to be numbers. In C, enumerated types and pointers can be
5187 represented as numbers, so that they are valid arguments to mathematical
5188 operators. @xref{Support, ,Supported languages}, for further
5189 details on specific languages.
5191 @value{GDBN} provides some additional commands for controlling the type checker:
5194 @kindex set check type
5195 @kindex show check type
5197 @item set check type auto
5198 Set type checking on or off based on the current working language.
5199 @xref{Support, ,Supported languages}, for the default settings for
5202 @item set check type on
5203 @itemx set check type off
5204 Set type checking on or off, overriding the default setting for the
5205 current working language. Issue a warning if the setting does not
5206 match the language default. If any type mismatches occur in
5207 evaluating an expression while typechecking is on, @value{GDBN} prints a
5208 message and aborts evaluation of the expression.
5210 @item set check type warn
5211 Cause the type checker to issue warnings, but to always attempt to
5212 evaluate the expression. Evaluating the expression may still
5213 be impossible for other reasons. For example, @value{GDBN} cannot add
5214 numbers and structures.
5217 Show the current setting of the type checker, and whether or not @value{GDBN} is
5218 setting it automatically.
5221 @cindex range checking
5222 @cindex checks, range
5223 @node Range Checking
5224 @subsection An overview of range checking
5226 In some languages (such as Modula-2), it is an error to exceed the
5227 bounds of a type; this is enforced with run-time checks. Such range
5228 checking is meant to ensure program correctness by making sure
5229 computations do not overflow, or indices on an array element access do
5230 not exceed the bounds of the array.
5232 For expressions you use in @value{GDBN} commands, you can tell
5233 @value{GDBN} to treat range errors in one of three ways: ignore them,
5234 always treat them as errors and abandon the expression, or issue
5235 warnings but evaluate the expression anyway.
5237 A range error can result from numerical overflow, from exceeding an
5238 array index bound, or when you type a constant that is not a member
5239 of any type. Some languages, however, do not treat overflows as an
5240 error. In many implementations of C, mathematical overflow causes the
5241 result to ``wrap around'' to lower values---for example, if @var{m} is
5242 the largest integer value, and @var{s} is the smallest, then
5245 @var{m} + 1 @result{} @var{s}
5248 This, too, is specific to individual languages, and in some cases
5249 specific to individual compilers or machines. @xref{Support, ,
5250 Supported languages}, for further details on specific languages.
5252 @value{GDBN} provides some additional commands for controlling the range checker:
5255 @kindex set check range
5256 @kindex show check range
5258 @item set check range auto
5259 Set range checking on or off based on the current working language.
5260 @xref{Support, ,Supported languages}, for the default settings for
5263 @item set check range on
5264 @itemx set check range off
5265 Set range checking on or off, overriding the default setting for the
5266 current working language. A warning is issued if the setting does not
5267 match the language default. If a range error occurs, then a message
5268 is printed and evaluation of the expression is aborted.
5270 @item set check range warn
5271 Output messages when the @value{GDBN} range checker detects a range error,
5272 but attempt to evaluate the expression anyway. Evaluating the
5273 expression may still be impossible for other reasons, such as accessing
5274 memory that the process does not own (a typical example from many Unix
5278 Show the current setting of the range checker, and whether or not it is
5279 being set automatically by @value{GDBN}.
5284 @section Supported languages
5287 @value{GDBN} 4 supports C, C++, and Modula-2.
5290 @value{GDBN} 4 supports C, and C++.
5292 Some @value{GDBN} features may be used in expressions regardless of the
5293 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
5294 and the @samp{@{type@}addr} construct (@pxref{Expressions,
5295 ,Expressions}) can be used with the constructs of any supported
5298 The following sections detail to what degree each source language is
5299 supported by @value{GDBN}. These sections are not meant to be language
5300 tutorials or references, but serve only as a reference guide to what the
5301 @value{GDBN} expression parser accepts, and what input and output
5302 formats should look like for different languages. There are many good
5303 books written on each of these languages; please look to these for a
5304 language reference or tutorial.
5309 * Modula-2:: Modula-2
5313 @subsection C and C++
5315 @cindex expressions in C or C++
5317 Since C and C++ are so closely related, many features of @value{GDBN} apply
5318 to both languages. Whenever this is the case, we discuss both languages
5322 @c Cancel this below, under same condition, at end of this chapter!
5329 The C++ debugging facilities are jointly implemented by the GNU C++
5330 compiler and @value{GDBN}. Therefore, to debug your C++ code
5331 effectively, you must compile your C++ programs with the GNU C++
5332 compiler, @code{g++}.
5334 For best results when debugging C++ programs, use the stabs debugging
5335 format. You can select that format explicitly with the @code{g++}
5336 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
5337 @ref{Debugging Options,,Options for Debugging Your Program or GNU CC,
5338 gcc.info, Using GNU CC}, for more information.
5342 @chapter C Language Support
5344 @cindex expressions in C
5346 Information specific to the C language is built into @value{GDBN} so that you
5347 can use C expressions while degugging. This also permits @value{GDBN} to
5348 output values in a manner consistent with C conventions.
5351 * C Operators:: C operators
5352 * C Constants:: C constants
5353 * Debugging C:: @value{GDBN} and C
5358 * C Operators:: C and C++ operators
5359 * C Constants:: C and C++ constants
5360 * Cplus expressions:: C++ expressions
5361 * C Defaults:: Default settings for C and C++
5363 * C Checks:: C and C++ type and range checks
5366 * Debugging C:: @value{GDBN} and C
5367 * Debugging C plus plus:: Special features for C++
5372 @cindex C and C++ operators
5374 @subsubsection C and C++ operators
5379 @section C operators
5382 Operators must be defined on values of specific types. For instance,
5383 @code{+} is defined on numbers, but not on structures. Operators are
5384 often defined on groups of types.
5387 For the purposes of C and C++, the following definitions hold:
5392 @emph{Integral types} include @code{int} with any of its storage-class
5393 specifiers; @code{char}; and @code{enum}.
5396 @emph{Floating-point types} include @code{float} and @code{double}.
5399 @emph{Pointer types} include all types defined as @code{(@var{type}
5403 @emph{Scalar types} include all of the above.
5407 The following operators are supported. They are listed here
5408 in order of increasing precedence:
5412 The comma or sequencing operator. Expressions in a comma-separated list
5413 are evaluated from left to right, with the result of the entire
5414 expression being the last expression evaluated.
5417 Assignment. The value of an assignment expression is the value
5418 assigned. Defined on scalar types.
5421 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
5422 and translated to @w{@code{@var{a} = @var{a op b}}}.
5423 @w{@code{@var{op}=}} and @code{=} have the same precendence.
5424 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
5425 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
5428 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
5429 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
5433 Logical @sc{or}. Defined on integral types.
5436 Logical @sc{and}. Defined on integral types.
5439 Bitwise @sc{or}. Defined on integral types.
5442 Bitwise exclusive-@sc{or}. Defined on integral types.
5445 Bitwise @sc{and}. Defined on integral types.
5448 Equality and inequality. Defined on scalar types. The value of these
5449 expressions is 0 for false and non-zero for true.
5451 @item <@r{, }>@r{, }<=@r{, }>=
5452 Less than, greater than, less than or equal, greater than or equal.
5453 Defined on scalar types. The value of these expressions is 0 for false
5454 and non-zero for true.
5457 left shift, and right shift. Defined on integral types.
5460 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5463 Addition and subtraction. Defined on integral types, floating-point types and
5466 @item *@r{, }/@r{, }%
5467 Multiplication, division, and modulus. Multiplication and division are
5468 defined on integral and floating-point types. Modulus is defined on
5472 Increment and decrement. When appearing before a variable, the
5473 operation is performed before the variable is used in an expression;
5474 when appearing after it, the variable's value is used before the
5475 operation takes place.
5478 Pointer dereferencing. Defined on pointer types. Same precedence as
5482 Address operator. Defined on variables. Same precedence as @code{++}.
5485 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
5486 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
5487 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
5488 where a C++ reference variable (declared with @samp{&@var{ref}}) is
5493 Negative. Defined on integral and floating-point types. Same
5494 precedence as @code{++}.
5497 Logical negation. Defined on integral types. Same precedence as
5501 Bitwise complement operator. Defined on integral types. Same precedence as
5506 Structure member, and pointer-to-structure member. For convenience,
5507 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
5508 pointer based on the stored type information.
5509 Defined on @code{struct} and @code{union} data.
5512 Array indexing. @code{@var{a}[@var{i}]} is defined as
5513 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
5516 Function parameter list. Same precedence as @code{->}.
5520 C++ scope resolution operator. Defined on
5521 @code{struct}, @code{union}, and @code{class} types.
5529 represent the @value{GDBN} scope operator (@pxref{Expressions,
5532 Same precedence as @code{::}, above.
5537 @cindex C and C++ constants
5539 @subsubsection C and C++ constants
5541 @value{GDBN} allows you to express the constants of C and C++ in the
5547 @section C constants
5549 @value{GDBN} allows you to express the constants of C in the
5555 Integer constants are a sequence of digits. Octal constants are
5556 specified by a leading @samp{0} (ie. zero), and hexadecimal constants by
5557 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
5558 @samp{l}, specifying that the constant should be treated as a
5562 Floating point constants are a sequence of digits, followed by a decimal
5563 point, followed by a sequence of digits, and optionally followed by an
5564 exponent. An exponent is of the form:
5565 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
5566 sequence of digits. The @samp{+} is optional for positive exponents.
5569 Enumerated constants consist of enumerated identifiers, or their
5570 integral equivalents.
5573 Character constants are a single character surrounded by single quotes
5574 (@code{'}), or a number---the ordinal value of the corresponding character
5575 (usually its @sc{ASCII} value). Within quotes, the single character may
5576 be represented by a letter or by @dfn{escape sequences}, which are of
5577 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
5578 of the character's ordinal value; or of the form @samp{\@var{x}}, where
5579 @samp{@var{x}} is a predefined special character---for example,
5580 @samp{\n} for newline.
5583 String constants are a sequence of character constants surrounded
5584 by double quotes (@code{"}).
5587 Pointer constants are an integral value. You can also write pointers
5588 to constants using the C operator @samp{&}.
5591 Array constants are comma-separated lists surrounded by braces @samp{@{}
5592 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
5593 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
5594 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
5598 @node Cplus expressions
5599 @subsubsection C++ expressions
5601 @cindex expressions in C++
5602 @value{GDBN} expression handling has a number of extensions to
5603 interpret a significant subset of C++ expressions.
5605 @cindex C++ support, not in @sc{coff}
5606 @cindex @sc{coff} versus C++
5607 @cindex C++ and object formats
5608 @cindex object formats and C++
5609 @cindex a.out and C++
5610 @cindex @sc{ecoff} and C++
5611 @cindex @sc{xcoff} and C++
5612 @cindex @sc{elf}/stabs and C++
5613 @cindex @sc{elf}/@sc{dwarf} and C++
5614 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
5615 @c periodically whether this has happened...
5617 @emph{Warning:} @value{GDBN} can only debug C++ code if you compile with
5618 the GNU C++ compiler. Moreover, C++ debugging depends on the use of
5619 additional debugging information in the symbol table, and thus requires
5620 special support. @value{GDBN} has this support @emph{only} with the
5621 stabs debug format. In particular, if your compiler generates a.out,
5622 MIPS @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions
5623 to the symbol table, these facilities are all available. (With GNU CC,
5624 you can use the @samp{-gstabs} option to request stabs debugging
5625 extensions explicitly.) Where the object code format is standard
5626 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C++
5627 support in @value{GDBN} does @emph{not} work.
5632 @cindex member functions
5634 Member function calls are allowed; you can use expressions like
5637 count = aml->GetOriginal(x, y)
5641 @cindex namespace in C++
5643 While a member function is active (in the selected stack frame), your
5644 expressions have the same namespace available as the member function;
5645 that is, @value{GDBN} allows implicit references to the class instance
5646 pointer @code{this} following the same rules as C++.
5648 @cindex call overloaded functions
5649 @cindex type conversions in C++
5651 You can call overloaded functions; @value{GDBN} resolves the function
5652 call to the right definition, with one restriction---you must use
5653 arguments of the type required by the function that you want to call.
5654 @value{GDBN} does not perform conversions requiring constructors or
5655 user-defined type operators.
5657 @cindex reference declarations
5659 @value{GDBN} understands variables declared as C++ references; you can use them in
5660 expressions just as you do in C++ source---they are automatically
5663 In the parameter list shown when @value{GDBN} displays a frame, the values of
5664 reference variables are not displayed (unlike other variables); this
5665 avoids clutter, since references are often used for large structures.
5666 The @emph{address} of a reference variable is always shown, unless
5667 you have specified @samp{set print address off}.
5670 @value{GDBN} supports the C++ name resolution operator @code{::}---your
5671 expressions can use it just as expressions in your program do. Since
5672 one scope may be defined in another, you can use @code{::} repeatedly if
5673 necessary, for example in an expression like
5674 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
5675 resolving name scope by reference to source files, in both C and C++
5676 debugging (@pxref{Variables, ,Program variables}).
5680 @subsubsection C and C++ defaults
5681 @cindex C and C++ defaults
5683 If you allow @value{GDBN} to set type and range checking automatically, they
5684 both default to @code{off} whenever the working language changes to
5685 C or C++. This happens regardless of whether you, or @value{GDBN},
5686 selected the working language.
5688 If you allow @value{GDBN} to set the language automatically, it sets the
5689 working language to C or C++ on entering code compiled from a source file
5690 whose name ends with @file{.c}, @file{.C}, or @file{.cc}.
5691 @xref{Automatically, ,Having @value{GDBN} infer the source language}, for
5695 @c Type checking is (a) primarily motivated by Modula-2, and (b)
5696 @c unimplemented. If (b) changes, it might make sense to let this node
5697 @c appear even if Mod-2 does not, but meanwhile ignore it. pesch 16jul93.
5699 @subsubsection C and C++ type and range checks
5700 @cindex C and C++ checks
5702 By default, when @value{GDBN} parses C or C++ expressions, type checking
5703 is not used. However, if you turn type checking on, @value{GDBN}
5704 considers two variables type equivalent if:
5708 The two variables are structured and have the same structure, union, or
5712 Two two variables have the same type name, or types that have been
5713 declared equivalent through @code{typedef}.
5716 @c leaving this out because neither J Gilmore nor R Pesch understand it.
5719 The two @code{struct}, @code{union}, or @code{enum} variables are
5720 declared in the same declaration. (Note: this may not be true for all C
5725 Range checking, if turned on, is done on mathematical operations. Array
5726 indices are not checked, since they are often used to index a pointer
5727 that is not itself an array.
5733 @subsubsection @value{GDBN} and C
5737 @section @value{GDBN} and C
5740 The @code{set print union} and @code{show print union} commands apply to
5741 the @code{union} type. When set to @samp{on}, any @code{union} that is
5742 inside a @code{struct}
5747 Otherwise, it appears as @samp{@{...@}}.
5749 The @code{@@} operator aids in the debugging of dynamic arrays, formed
5750 with pointers and a memory allocation function. @xref{Expressions,
5754 @node Debugging C plus plus
5755 @subsubsection @value{GDBN} features for C++
5757 @cindex commands for C++
5758 Some @value{GDBN} commands are particularly useful with C++, and some are
5759 designed specifically for use with C++. Here is a summary:
5762 @cindex break in overloaded functions
5763 @item @r{breakpoint menus}
5764 When you want a breakpoint in a function whose name is overloaded,
5765 @value{GDBN} breakpoint menus help you specify which function definition
5766 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
5768 @cindex overloading in C++
5769 @item rbreak @var{regex}
5770 Setting breakpoints using regular expressions is helpful for setting
5771 breakpoints on overloaded functions that are not members of any special
5773 @xref{Set Breaks, ,Setting breakpoints}.
5775 @cindex C++ exception handling
5776 @item catch @var{exceptions}
5778 Debug C++ exception handling using these commands. @xref{Exception
5779 Handling, ,Breakpoints and exceptions}.
5782 @item ptype @var{typename}
5783 Print inheritance relationships as well as other information for type
5785 @xref{Symbols, ,Examining the Symbol Table}.
5787 @cindex C++ symbol display
5788 @item set print demangle
5789 @itemx show print demangle
5790 @itemx set print asm-demangle
5791 @itemx show print asm-demangle
5792 Control whether C++ symbols display in their source form, both when
5793 displaying code as C++ source and when displaying disassemblies.
5794 @xref{Print Settings, ,Print settings}.
5796 @item set print object
5797 @itemx show print object
5798 Choose whether to print derived (actual) or declared types of objects.
5799 @xref{Print Settings, ,Print settings}.
5801 @item set print vtbl
5802 @itemx show print vtbl
5803 Control the format for printing virtual function tables.
5804 @xref{Print Settings, ,Print settings}.
5806 @item @r{Overloaded symbol names}
5807 You can specify a particular definition of an overloaded symbol, using
5808 the same notation that is used to declare such symbols in C++: type
5809 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
5810 also use the @value{GDBN} command-line word completion facilities to list the
5811 available choices, or to finish the type list for you.
5812 @xref{Completion,, Command completion}, for details on how to do this.
5815 @c cancels "raisesections" under same conditions near bgn of chapter
5821 @subsection Modula-2
5824 The extensions made to @value{GDBN} to support Modula-2 only support
5825 output from the GNU Modula-2 compiler (which is currently being
5826 developed). Other Modula-2 compilers are not currently supported, and
5827 attempting to debug executables produced by them is most likely
5828 to give an error as @value{GDBN} reads in the executable's symbol
5831 @cindex expressions in Modula-2
5833 * M2 Operators:: Built-in operators
5834 * Built-In Func/Proc:: Built-in functions and procedures
5835 * M2 Constants:: Modula-2 constants
5836 * M2 Defaults:: Default settings for Modula-2
5837 * Deviations:: Deviations from standard Modula-2
5838 * M2 Checks:: Modula-2 type and range checks
5839 * M2 Scope:: The scope operators @code{::} and @code{.}
5840 * GDB/M2:: @value{GDBN} and Modula-2
5844 @subsubsection Operators
5845 @cindex Modula-2 operators
5847 Operators must be defined on values of specific types. For instance,
5848 @code{+} is defined on numbers, but not on structures. Operators are
5849 often defined on groups of types. For the purposes of Modula-2, the
5850 following definitions hold:
5855 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
5859 @emph{Character types} consist of @code{CHAR} and its subranges.
5862 @emph{Floating-point types} consist of @code{REAL}.
5865 @emph{Pointer types} consist of anything declared as @code{POINTER TO
5869 @emph{Scalar types} consist of all of the above.
5872 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
5875 @emph{Boolean types} consist of @code{BOOLEAN}.
5879 The following operators are supported, and appear in order of
5880 increasing precedence:
5884 Function argument or array index separator.
5887 Assignment. The value of @var{var} @code{:=} @var{value} is
5891 Less than, greater than on integral, floating-point, or enumerated
5895 Less than, greater than, less than or equal to, greater than or equal to
5896 on integral, floating-point and enumerated types, or set inclusion on
5897 set types. Same precedence as @code{<}.
5899 @item =@r{, }<>@r{, }#
5900 Equality and two ways of expressing inequality, valid on scalar types.
5901 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
5902 available for inequality, since @code{#} conflicts with the script
5906 Set membership. Defined on set types and the types of their members.
5907 Same precedence as @code{<}.
5910 Boolean disjunction. Defined on boolean types.
5913 Boolean conjuction. Defined on boolean types.
5916 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5919 Addition and subtraction on integral and floating-point types, or union
5920 and difference on set types.
5923 Multiplication on integral and floating-point types, or set intersection
5927 Division on floating-point types, or symmetric set difference on set
5928 types. Same precedence as @code{*}.
5931 Integer division and remainder. Defined on integral types. Same
5932 precedence as @code{*}.
5935 Negative. Defined on @code{INTEGER} and @code{REAL} data.
5938 Pointer dereferencing. Defined on pointer types.
5941 Boolean negation. Defined on boolean types. Same precedence as
5945 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
5946 precedence as @code{^}.
5949 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
5952 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
5956 @value{GDBN} and Modula-2 scope operators.
5960 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
5961 treats the use of the operator @code{IN}, or the use of operators
5962 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
5963 @code{<=}, and @code{>=} on sets as an error.
5966 @cindex Modula-2 built-ins
5967 @node Built-In Func/Proc
5968 @subsubsection Built-in functions and procedures
5970 Modula-2 also makes available several built-in procedures and functions.
5971 In describing these, the following metavariables are used:
5976 represents an @code{ARRAY} variable.
5979 represents a @code{CHAR} constant or variable.
5982 represents a variable or constant of integral type.
5985 represents an identifier that belongs to a set. Generally used in the
5986 same function with the metavariable @var{s}. The type of @var{s} should
5987 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
5990 represents a variable or constant of integral or floating-point type.
5993 represents a variable or constant of floating-point type.
5999 represents a variable.
6002 represents a variable or constant of one of many types. See the
6003 explanation of the function for details.
6006 All Modula-2 built-in procedures also return a result, described below.
6010 Returns the absolute value of @var{n}.
6013 If @var{c} is a lower case letter, it returns its upper case
6014 equivalent, otherwise it returns its argument
6017 Returns the character whose ordinal value is @var{i}.
6020 Decrements the value in the variable @var{v}. Returns the new value.
6022 @item DEC(@var{v},@var{i})
6023 Decrements the value in the variable @var{v} by @var{i}. Returns the
6026 @item EXCL(@var{m},@var{s})
6027 Removes the element @var{m} from the set @var{s}. Returns the new
6030 @item FLOAT(@var{i})
6031 Returns the floating point equivalent of the integer @var{i}.
6034 Returns the index of the last member of @var{a}.
6037 Increments the value in the variable @var{v}. Returns the new value.
6039 @item INC(@var{v},@var{i})
6040 Increments the value in the variable @var{v} by @var{i}. Returns the
6043 @item INCL(@var{m},@var{s})
6044 Adds the element @var{m} to the set @var{s} if it is not already
6045 there. Returns the new set.
6048 Returns the maximum value of the type @var{t}.
6051 Returns the minimum value of the type @var{t}.
6054 Returns boolean TRUE if @var{i} is an odd number.
6057 Returns the ordinal value of its argument. For example, the ordinal
6058 value of a character is its ASCII value (on machines supporting the
6059 ASCII character set). @var{x} must be of an ordered type, which include
6060 integral, character and enumerated types.
6063 Returns the size of its argument. @var{x} can be a variable or a type.
6065 @item TRUNC(@var{r})
6066 Returns the integral part of @var{r}.
6068 @item VAL(@var{t},@var{i})
6069 Returns the member of the type @var{t} whose ordinal value is @var{i}.
6073 @emph{Warning:} Sets and their operations are not yet supported, so
6074 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
6078 @cindex Modula-2 constants
6080 @subsubsection Constants
6082 @value{GDBN} allows you to express the constants of Modula-2 in the following
6088 Integer constants are simply a sequence of digits. When used in an
6089 expression, a constant is interpreted to be type-compatible with the
6090 rest of the expression. Hexadecimal integers are specified by a
6091 trailing @samp{H}, and octal integers by a trailing @samp{B}.
6094 Floating point constants appear as a sequence of digits, followed by a
6095 decimal point and another sequence of digits. An optional exponent can
6096 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
6097 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
6098 digits of the floating point constant must be valid decimal (base 10)
6102 Character constants consist of a single character enclosed by a pair of
6103 like quotes, either single (@code{'}) or double (@code{"}). They may
6104 also be expressed by their ordinal value (their ASCII value, usually)
6105 followed by a @samp{C}.
6108 String constants consist of a sequence of characters enclosed by a
6109 pair of like quotes, either single (@code{'}) or double (@code{"}).
6110 Escape sequences in the style of C are also allowed. @xref{C
6111 Constants, ,C and C++ constants}, for a brief explanation of escape
6115 Enumerated constants consist of an enumerated identifier.
6118 Boolean constants consist of the identifiers @code{TRUE} and
6122 Pointer constants consist of integral values only.
6125 Set constants are not yet supported.
6129 @subsubsection Modula-2 defaults
6130 @cindex Modula-2 defaults
6132 If type and range checking are set automatically by @value{GDBN}, they
6133 both default to @code{on} whenever the working language changes to
6134 Modula-2. This happens regardless of whether you, or @value{GDBN},
6135 selected the working language.
6137 If you allow @value{GDBN} to set the language automatically, then entering
6138 code compiled from a file whose name ends with @file{.mod} sets the
6139 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
6140 the language automatically}, for further details.
6143 @subsubsection Deviations from standard Modula-2
6144 @cindex Modula-2, deviations from
6146 A few changes have been made to make Modula-2 programs easier to debug.
6147 This is done primarily via loosening its type strictness:
6151 Unlike in standard Modula-2, pointer constants can be formed by
6152 integers. This allows you to modify pointer variables during
6153 debugging. (In standard Modula-2, the actual address contained in a
6154 pointer variable is hidden from you; it can only be modified
6155 through direct assignment to another pointer variable or expression that
6156 returned a pointer.)
6159 C escape sequences can be used in strings and characters to represent
6160 non-printable characters. @value{GDBN} prints out strings with these
6161 escape sequences embedded. Single non-printable characters are
6162 printed using the @samp{CHR(@var{nnn})} format.
6165 The assignment operator (@code{:=}) returns the value of its right-hand
6169 All built-in procedures both modify @emph{and} return their argument.
6173 @subsubsection Modula-2 type and range checks
6174 @cindex Modula-2 checks
6177 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
6180 @c FIXME remove warning when type/range checks added
6182 @value{GDBN} considers two Modula-2 variables type equivalent if:
6186 They are of types that have been declared equivalent via a @code{TYPE
6187 @var{t1} = @var{t2}} statement
6190 They have been declared on the same line. (Note: This is true of the
6191 GNU Modula-2 compiler, but it may not be true of other compilers.)
6194 As long as type checking is enabled, any attempt to combine variables
6195 whose types are not equivalent is an error.
6197 Range checking is done on all mathematical operations, assignment, array
6198 index bounds, and all built-in functions and procedures.
6201 @subsubsection The scope operators @code{::} and @code{.}
6204 @cindex colon, doubled as scope operator
6207 @c Info cannot handle :: but TeX can.
6213 There are a few subtle differences between the Modula-2 scope operator
6214 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
6219 @var{module} . @var{id}
6220 @var{scope} :: @var{id}
6224 where @var{scope} is the name of a module or a procedure,
6225 @var{module} the name of a module, and @var{id} is any declared
6226 identifier within your program, except another module.
6228 Using the @code{::} operator makes @value{GDBN} search the scope
6229 specified by @var{scope} for the identifier @var{id}. If it is not
6230 found in the specified scope, then @value{GDBN} searches all scopes
6231 enclosing the one specified by @var{scope}.
6233 Using the @code{.} operator makes @value{GDBN} search the current scope for
6234 the identifier specified by @var{id} that was imported from the
6235 definition module specified by @var{module}. With this operator, it is
6236 an error if the identifier @var{id} was not imported from definition
6237 module @var{module}, or if @var{id} is not an identifier in
6241 @subsubsection @value{GDBN} and Modula-2
6243 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
6244 Five subcommands of @code{set print} and @code{show print} apply
6245 specifically to C and C++: @samp{vtbl}, @samp{demangle},
6246 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
6247 apply to C++, and the last to the C @code{union} type, which has no direct
6248 analogue in Modula-2.
6250 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
6251 while using any language, is not useful with Modula-2. Its
6252 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
6253 created in Modula-2 as they can in C or C++. However, because an
6254 address can be specified by an integral constant, the construct
6255 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions})
6257 @cindex @code{#} in Modula-2
6258 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
6259 interpreted as the beginning of a comment. Use @code{<>} instead.
6265 @chapter Examining the Symbol Table
6267 The commands described in this section allow you to inquire about the
6268 symbols (names of variables, functions and types) defined in your
6269 program. This information is inherent in the text of your program and
6270 does not change as your program executes. @value{GDBN} finds it in your
6271 program's symbol table, in the file indicated when you started @value{GDBN}
6272 (@pxref{File Options, ,Choosing files}), or by one of the
6273 file-management commands (@pxref{Files, ,Commands to specify files}).
6275 @c FIXME! This might be intentionally specific to C and C++; if so, move
6276 @c to someplace in C section of lang chapter.
6277 @cindex symbol names
6278 @cindex names of symbols
6279 @cindex quoting names
6280 Occasionally, you may need to refer to symbols that contain unusual
6281 characters, which @value{GDBN} ordinarily treats as word delimiters. The
6282 most frequent case is in referring to static variables in other
6283 source files (@pxref{Variables,,Program variables}). File names
6284 are recorded in object files as debugging symbols, but @value{GDBN} would
6285 ordinarily parse a typical file name, like @file{foo.c}, as the three words
6286 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
6287 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
6294 looks up the value of @code{x} in the scope of the file @file{foo.c}.
6297 @item info address @var{symbol}
6298 @kindex info address
6299 Describe where the data for @var{symbol} is stored. For a register
6300 variable, this says which register it is kept in. For a non-register
6301 local variable, this prints the stack-frame offset at which the variable
6304 Note the contrast with @samp{print &@var{symbol}}, which does not work
6305 at all for a register variable, and for a stack local variable prints
6306 the exact address of the current instantiation of the variable.
6308 @item whatis @var{exp}
6310 Print the data type of expression @var{exp}. @var{exp} is not
6311 actually evaluated, and any side-effecting operations (such as
6312 assignments or function calls) inside it do not take place.
6313 @xref{Expressions, ,Expressions}.
6316 Print the data type of @code{$}, the last value in the value history.
6318 @item ptype @var{typename}
6320 Print a description of data type @var{typename}. @var{typename} may be
6321 the name of a type, or for C code it may have the form
6323 @samp{class @var{class-name}},
6325 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
6326 @samp{enum @var{enum-tag}}.
6328 @item ptype @var{exp}
6330 Print a description of the type of expression @var{exp}. @code{ptype}
6331 differs from @code{whatis} by printing a detailed description, instead
6332 of just the name of the type.
6334 For example, for this variable declaration:
6337 struct complex @{double real; double imag;@} v;
6341 the two commands give this output:
6345 (@value{GDBP}) whatis v
6346 type = struct complex
6347 (@value{GDBP}) ptype v
6348 type = struct complex @{
6356 As with @code{whatis}, using @code{ptype} without an argument refers to
6357 the type of @code{$}, the last value in the value history.
6359 @item info types @var{regexp}
6362 Print a brief description of all types whose name matches @var{regexp}
6363 (or all types in your program, if you supply no argument). Each
6364 complete typename is matched as though it were a complete line; thus,
6365 @samp{i type value} gives information on all types in your program whose
6366 name includes the string @code{value}, but @samp{i type ^value$} gives
6367 information only on types whose complete name is @code{value}.
6369 This command differs from @code{ptype} in two ways: first, like
6370 @code{whatis}, it does not print a detailed description; second, it
6371 lists all source files where a type is defined.
6375 Show the name of the current source file---that is, the source file for
6376 the function containing the current point of execution---and the language
6380 @kindex info sources
6381 Print the names of all source files in your program for which there is
6382 debugging information, organized into two lists: files whose symbols
6383 have already been read, and files whose symbols will be read when needed.
6385 @item info functions
6386 @kindex info functions
6387 Print the names and data types of all defined functions.
6389 @item info functions @var{regexp}
6390 Print the names and data types of all defined functions
6391 whose names contain a match for regular expression @var{regexp}.
6392 Thus, @samp{info fun step} finds all functions whose names
6393 include @code{step}; @samp{info fun ^step} finds those whose names
6394 start with @code{step}.
6396 @item info variables
6397 @kindex info variables
6398 Print the names and data types of all variables that are declared
6399 outside of functions (i.e., excluding local variables).
6401 @item info variables @var{regexp}
6402 Print the names and data types of all variables (except for local
6403 variables) whose names contain a match for regular expression
6407 This was never implemented.
6409 @itemx info methods @var{regexp}
6410 @kindex info methods
6411 The @code{info methods} command permits the user to examine all defined
6412 methods within C++ program, or (with the @var{regexp} argument) a
6413 specific set of methods found in the various C++ classes. Many
6414 C++ classes provide a large number of methods. Thus, the output
6415 from the @code{ptype} command can be overwhelming and hard to use. The
6416 @code{info-methods} command filters the methods, printing only those
6417 which match the regular-expression @var{regexp}.
6420 @item maint print symbols @var{filename}
6421 @itemx maint print psymbols @var{filename}
6422 @itemx maint print msymbols @var{filename}
6423 @kindex maint print symbols
6425 @kindex maint print psymbols
6426 @cindex partial symbol dump
6427 Write a dump of debugging symbol data into the file @var{filename}.
6428 These commands are used to debug the @value{GDBN} symbol-reading code. Only
6429 symbols with debugging data are included. If you use @samp{maint print
6430 symbols}, @value{GDBN} includes all the symbols for which it has already
6431 collected full details: that is, @var{filename} reflects symbols for
6432 only those files whose symbols @value{GDBN} has read. You can use the
6433 command @code{info sources} to find out which files these are. If you
6434 use @samp{maint print psymbols} instead, the dump shows information about
6435 symbols that @value{GDBN} only knows partially---that is, symbols defined in
6436 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
6437 @samp{maint print msymbols} dumps just the minimal symbol information
6438 required for each object file from which @value{GDBN} has read some symbols.
6439 @xref{Files, ,Commands to specify files}, for a discussion of how
6440 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
6444 @chapter Altering Execution
6446 Once you think you have found an error in your program, you might want to
6447 find out for certain whether correcting the apparent error would lead to
6448 correct results in the rest of the run. You can find the answer by
6449 experiment, using the @value{GDBN} features for altering execution of the
6452 For example, you can store new values into variables or memory
6455 give your program a signal, restart it
6458 restart your program
6460 at a different address, or even return prematurely from a function to
6464 * Assignment:: Assignment to variables
6465 * Jumping:: Continuing at a different address
6467 * Signaling:: Giving your program a signal
6470 * Returning:: Returning from a function
6471 * Calling:: Calling your program's functions
6472 * Patching:: Patching your program
6476 @section Assignment to variables
6479 @cindex setting variables
6480 To alter the value of a variable, evaluate an assignment expression.
6481 @xref{Expressions, ,Expressions}. For example,
6488 stores the value 4 into the variable @code{x}, and then prints the
6489 value of the assignment expression (which is 4).
6491 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
6492 information on operators in supported languages.
6495 @kindex set variable
6496 @cindex variables, setting
6497 If you are not interested in seeing the value of the assignment, use the
6498 @code{set} command instead of the @code{print} command. @code{set} is
6499 really the same as @code{print} except that the expression's value is
6500 not printed and is not put in the value history (@pxref{Value History,
6501 ,Value history}). The expression is evaluated only for its effects.
6503 If the beginning of the argument string of the @code{set} command
6504 appears identical to a @code{set} subcommand, use the @code{set
6505 variable} command instead of just @code{set}. This command is identical
6506 to @code{set} except for its lack of subcommands. For example, if
6507 your program has a variable @code{width}, you get
6508 an error if you try to set a new value with just @samp{set width=13},
6509 because @value{GDBN} has the command @code{set width}:
6512 (@value{GDBP}) whatis width
6514 (@value{GDBP}) p width
6516 (@value{GDBP}) set width=47
6517 Invalid syntax in expression.
6521 The invalid expression, of course, is @samp{=47}. In
6522 order to actually set the program's variable @code{width}, use
6525 (@value{GDBP}) set var width=47
6528 @value{GDBN} allows more implicit conversions in assignments than C; you can
6529 freely store an integer value into a pointer variable or vice versa,
6530 and you can convert any structure to any other structure that is the
6531 same length or shorter.
6532 @comment FIXME: how do structs align/pad in these conversions?
6533 @comment /pesch@cygnus.com 18dec1990
6535 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
6536 construct to generate a value of specified type at a specified address
6537 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
6538 to memory location @code{0x83040} as an integer (which implies a certain size
6539 and representation in memory), and
6542 set @{int@}0x83040 = 4
6546 stores the value 4 into that memory location.
6549 @section Continuing at a different address
6551 Ordinarily, when you continue your program, you do so at the place where
6552 it stopped, with the @code{continue} command. You can instead continue at
6553 an address of your own choosing, with the following commands:
6556 @item jump @var{linespec}
6558 Resume execution at line @var{linespec}. Execution stops again
6559 immediately if there is a breakpoint there. @xref{List, ,Printing
6560 source lines}, for a description of the different forms of
6563 The @code{jump} command does not change the current stack frame, or
6564 the stack pointer, or the contents of any memory location or any
6565 register other than the program counter. If line @var{linespec} is in
6566 a different function from the one currently executing, the results may
6567 be bizarre if the two functions expect different patterns of arguments or
6568 of local variables. For this reason, the @code{jump} command requests
6569 confirmation if the specified line is not in the function currently
6570 executing. However, even bizarre results are predictable if you are
6571 well acquainted with the machine-language code of your program.
6573 @item jump *@var{address}
6574 Resume execution at the instruction at address @var{address}.
6577 You can get much the same effect as the @code{jump} command by storing a
6578 new value into the register @code{$pc}. The difference is that this
6579 does not start your program running; it only changes the address where it
6580 @emph{will} run when you continue. For example,
6587 makes the next @code{continue} command or stepping command execute at
6588 address @code{0x485}, rather than at the address where your program stopped.
6589 @xref{Continuing and Stepping, ,Continuing and stepping}.
6591 The most common occasion to use the @code{jump} command is to back up,
6592 perhaps with more breakpoints set, over a portion of a program that has
6593 already executed, in order to examine its execution in more detail.
6598 @section Giving your program a signal
6601 @item signal @var{signal}
6603 Resume execution where your program stopped, but immediately give it the
6604 signal @var{signal}. @var{signal} can be the name or the number of a
6605 signal. For example, on many systems @code{signal 2} and @code{signal
6606 SIGINT} are both ways of sending an interrupt signal.
6608 Alternatively, if @var{signal} is zero, continue execution without
6609 giving a signal. This is useful when your program stopped on account of
6610 a signal and would ordinary see the signal when resumed with the
6611 @code{continue} command; @samp{signal 0} causes it to resume without a
6614 @code{signal} does not repeat when you press @key{RET} a second time
6615 after executing the command.
6619 Invoking the @code{signal} command is not the same as invoking the
6620 @code{kill} utility from the shell. Sending a signal with @code{kill}
6621 causes @value{GDBN} to decide what to do with the signal depending on
6622 the signal handling tables (@pxref{Signals}). The @code{signal} command
6623 passes the signal directly to your program.
6628 @section Returning from a function
6632 @itemx return @var{expression}
6633 @cindex returning from a function
6635 You can cancel execution of a function call with the @code{return}
6636 command. If you give an
6637 @var{expression} argument, its value is used as the function's return
6641 When you use @code{return}, @value{GDBN} discards the selected stack frame
6642 (and all frames within it). You can think of this as making the
6643 discarded frame return prematurely. If you wish to specify a value to
6644 be returned, give that value as the argument to @code{return}.
6646 This pops the selected stack frame (@pxref{Selection, ,Selecting a
6647 frame}), and any other frames inside of it, leaving its caller as the
6648 innermost remaining frame. That frame becomes selected. The
6649 specified value is stored in the registers used for returning values
6652 The @code{return} command does not resume execution; it leaves the
6653 program stopped in the state that would exist if the function had just
6654 returned. In contrast, the @code{finish} command (@pxref{Continuing
6655 and Stepping, ,Continuing and stepping}) resumes execution until the
6656 selected stack frame returns naturally.
6659 @section Calling program functions
6661 @cindex calling functions
6664 @item call @var{expr}
6665 Evaluate the expression @var{expr} without displaying @code{void}
6669 You can use this variant of the @code{print} command if you want to
6670 execute a function from your program, but without cluttering the output
6671 with @code{void} returned values. The result is printed and saved in
6672 the value history, if it is not void.
6675 @section Patching programs
6676 @cindex patching binaries
6677 @cindex writing into executables
6679 @cindex writing into corefiles
6682 By default, @value{GDBN} opens the file containing your program's executable
6687 read-only. This prevents accidental alterations
6688 to machine code; but it also prevents you from intentionally patching
6689 your program's binary.
6691 If you'd like to be able to patch the binary, you can specify that
6692 explicitly with the @code{set write} command. For example, you might
6693 want to turn on internal debugging flags, or even to make emergency
6698 @itemx set write off
6700 If you specify @samp{set write on}, @value{GDBN} opens executable
6704 files for both reading and writing; if you specify @samp{set write
6705 off} (the default), @value{GDBN} opens them read-only.
6707 If you have already loaded a file, you must load it again (using the
6712 command) after changing @code{set write}, for your new setting to take
6717 Display whether executable files
6721 are opened for writing as well as reading.
6725 @chapter @value{GDBN} Files
6727 @value{GDBN} needs to know the file name of the program to be debugged, both in
6728 order to read its symbol table and in order to start your program.
6730 To debug a core dump of a previous run, you must also tell @value{GDBN}
6731 the name of the core dump file.
6735 * Files:: Commands to specify files
6736 * Symbol Errors:: Errors reading symbol files
6740 @section Commands to specify files
6741 @cindex symbol table
6744 @cindex core dump file
6745 The usual way to specify executable and core dump file names is with
6746 the command arguments given when you start @value{GDBN} (@pxref{Invocation,
6747 ,Getting In and Out of @value{GDBN}}.
6750 The usual way to specify an executable file name is with
6751 the command argument given when you start @value{GDBN}, (@pxref{Invocation,
6752 ,Getting In and Out of @value{GDBN}}.
6755 Occasionally it is necessary to change to a different file during a
6756 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
6757 a file you want to use. In these situations the @value{GDBN} commands
6758 to specify new files are useful.
6761 @item file @var{filename}
6762 @cindex executable file
6764 Use @var{filename} as the program to be debugged. It is read for its
6765 symbols and for the contents of pure memory. It is also the program
6766 executed when you use the @code{run} command. If you do not specify a
6767 directory and the file is not found in the @value{GDBN} working directory, @value{GDBN}
6768 uses the environment variable @code{PATH} as a list of directories to
6769 search, just as the shell does when looking for a program to run. You
6770 can change the value of this variable, for both @value{GDBN} and your program,
6771 using the @code{path} command.
6773 On systems with memory-mapped files, an auxiliary file
6774 @file{@var{filename}.syms} may hold symbol table information for
6775 @var{filename}. If so, @value{GDBN} maps in the symbol table from
6776 @file{@var{filename}.syms}, starting up more quickly. See the
6777 descriptions of the options @samp{-mapped} and @samp{-readnow}
6778 (available on the command line, and with the commands @code{file},
6779 @code{symbol-file}, or @code{add-symbol-file}), for more information.
6782 @code{file} with no argument makes @value{GDBN} discard any information it
6783 has on both executable file and the symbol table.
6785 @item exec-file @r{[} @var{filename} @r{]}
6787 Specify that the program to be run (but not the symbol table) is found
6788 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
6789 if necessary to locate your program. Omitting @var{filename} means to
6790 discard information on the executable file.
6792 @item symbol-file @r{[} @var{filename} @r{]}
6794 Read symbol table information from file @var{filename}. @code{PATH} is
6795 searched when necessary. Use the @code{file} command to get both symbol
6796 table and program to run from the same file.
6798 @code{symbol-file} with no argument clears out @value{GDBN} information on your
6799 program's symbol table.
6801 The @code{symbol-file} command causes @value{GDBN} to forget the contents of its
6802 convenience variables, the value history, and all breakpoints and
6803 auto-display expressions. This is because they may contain pointers to
6804 the internal data recording symbols and data types, which are part of
6805 the old symbol table data being discarded inside @value{GDBN}.
6807 @code{symbol-file} does not repeat if you press @key{RET} again after
6810 When @value{GDBN} is configured for a particular environment, it
6811 understands debugging information in whatever format is the standard
6812 generated for that environment; you may use either a GNU compiler, or
6813 other compilers that adhere to the local conventions. Best results are
6814 usually obtained from GNU compilers; for example, using @code{@value{GCC}}
6815 you can generate debugging information for optimized code.
6817 On some kinds of object files, the @code{symbol-file} command does not
6818 normally read the symbol table in full right away. Instead, it scans
6819 the symbol table quickly to find which source files and which symbols
6820 are present. The details are read later, one source file at a time,
6823 The purpose of this two-stage reading strategy is to make @value{GDBN} start up
6824 faster. For the most part, it is invisible except for occasional
6825 pauses while the symbol table details for a particular source file are
6826 being read. (The @code{set verbose} command can turn these pauses
6827 into messages if desired. @xref{Messages/Warnings, ,Optional warnings
6830 We have not implemented the two-stage strategy for COFF yet. When the
6831 symbol table is stored in COFF format, @code{symbol-file} reads the
6832 symbol table data in full right away.
6834 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6835 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6837 @cindex reading symbols immediately
6838 @cindex symbols, reading immediately
6840 @cindex memory-mapped symbol file
6841 @cindex saving symbol table
6842 You can override the @value{GDBN} two-stage strategy for reading symbol
6843 tables by using the @samp{-readnow} option with any of the commands that
6844 load symbol table information, if you want to be sure @value{GDBN} has the
6845 entire symbol table available.
6848 If memory-mapped files are available on your system through the
6849 @code{mmap} system call, you can use another option, @samp{-mapped}, to
6850 cause @value{GDBN} to write the symbols for your program into a reusable
6851 file. Future @value{GDBN} debugging sessions map in symbol information
6852 from this auxiliary symbol file (if the program has not changed), rather
6853 than spending time reading the symbol table from the executable
6854 program. Using the @samp{-mapped} option has the same effect as
6855 starting @value{GDBN} with the @samp{-mapped} command-line option.
6857 You can use both options together, to make sure the auxiliary symbol
6858 file has all the symbol information for your program.
6860 The auxiliary symbol file for a program called @var{myprog} is called
6861 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
6862 than the corresponding executable), @value{GDBN} always attempts to use
6863 it when you debug @var{myprog}; no special options or commands are
6866 The @file{.syms} file is specific to the host machine where you run
6867 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
6868 symbol table. It cannot be shared across multiple host platforms.
6870 @c FIXME: for now no mention of directories, since this seems to be in
6871 @c flux. 13mar1992 status is that in theory GDB would look either in
6872 @c current dir or in same dir as myprog; but issues like competing
6873 @c GDB's, or clutter in system dirs, mean that in practice right now
6874 @c only current dir is used. FFish says maybe a special GDB hierarchy
6875 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
6878 @item core-file @r{[} @var{filename} @r{]}
6881 Specify the whereabouts of a core dump file to be used as the ``contents
6882 of memory''. Traditionally, core files contain only some parts of the
6883 address space of the process that generated them; @value{GDBN} can access the
6884 executable file itself for other parts.
6886 @code{core-file} with no argument specifies that no core file is
6889 Note that the core file is ignored when your program is actually running
6890 under @value{GDBN}. So, if you have been running your program and you wish to
6891 debug a core file instead, you must kill the subprocess in which the
6892 program is running. To do this, use the @code{kill} command
6893 (@pxref{Kill Process, ,Killing the child process}).
6896 @item load @var{filename}
6899 Depending on what remote debugging facilities are configured into
6900 @value{GDBN}, the @code{load} command may be available. Where it exists, it
6901 is meant to make @var{filename} (an executable) available for debugging
6902 on the remote system---by downloading, or dynamic linking, for example.
6903 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
6904 the @code{add-symbol-file} command.
6906 If your @value{GDBN} does not have a @code{load} command, attempting to
6907 execute it gets the error message ``@code{You can't do that when your
6908 target is @dots{}}''
6911 The file is loaded at whatever address is specified in the executable.
6912 For some object file formats, you can specify the load address when you
6913 link the program; for other formats, like a.out, the object file format
6914 specifies a fixed address.
6915 @c FIXME! This would be a good place for an xref to the GNU linker doc.
6918 On VxWorks, @code{load} links @var{filename} dynamically on the
6919 current target system as well as adding its symbols in @value{GDBN}.
6923 @cindex download to Nindy-960
6924 With the Nindy interface to an Intel 960 board, @code{load}
6925 downloads @var{filename} to the 960 as well as adding its symbols in
6930 @cindex download to H8/300 or H8/500
6931 @cindex H8/300 or H8/500 download
6932 @cindex download to Hitachi SH
6933 @cindex Hitachi SH download
6934 When you select remote debugging to a Hitachi SH, H8/300, or H8/500 board
6935 (@pxref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}),
6936 the @code{load} command downloads your program to the Hitachi board and also
6937 opens it as the current executable target for @value{GDBN} on your host
6938 (like the @code{file} command).
6941 @code{load} does not repeat if you press @key{RET} again after using it.
6944 @item add-symbol-file @var{filename} @var{address}
6945 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6946 @kindex add-symbol-file
6947 @cindex dynamic linking
6948 The @code{add-symbol-file} command reads additional symbol table information
6949 from the file @var{filename}. You would use this command when @var{filename}
6950 has been dynamically loaded (by some other means) into the program that
6951 is running. @var{address} should be the memory address at which the
6952 file has been loaded; @value{GDBN} cannot figure this out for itself.
6953 You can specify @var{address} as an expression.
6955 The symbol table of the file @var{filename} is added to the symbol table
6956 originally read with the @code{symbol-file} command. You can use the
6957 @code{add-symbol-file} command any number of times; the new symbol data thus
6958 read keeps adding to the old. To discard all old symbol data instead,
6959 use the @code{symbol-file} command.
6961 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
6963 You can use the @samp{-mapped} and @samp{-readnow} options just as with
6964 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
6965 table information for @var{filename}.
6972 @code{info files} and @code{info target} are synonymous; both print
6973 the current target (@pxref{Targets, ,Specifying a Debugging Target}),
6976 names of the executable and core dump files
6979 name of the executable file
6981 currently in use by @value{GDBN}, and the files from which symbols were
6982 loaded. The command @code{help target} lists all possible targets
6983 rather than current ones.
6986 All file-specifying commands allow both absolute and relative file names
6987 as arguments. @value{GDBN} always converts the file name to an absolute file
6988 name and remembers it that way.
6991 @cindex shared libraries
6992 @value{GDBN} supports SunOS, SVr4, Irix 5, and IBM RS/6000 shared libraries.
6993 @value{GDBN} automatically loads symbol definitions from shared libraries
6994 when you use the @code{run} command, or when you examine a core file.
6995 (Before you issue the @code{run} command, @value{GDBN} does not understand
6996 references to a function in a shared library, however---unless you are
6997 debugging a core file).
6998 @c FIXME: some @value{GDBN} release may permit some refs to undef
6999 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
7000 @c FIXME...lib; check this from time to time when updating manual
7004 @itemx info sharedlibrary
7005 @kindex info sharedlibrary
7007 Print the names of the shared libraries which are currently loaded.
7009 @item sharedlibrary @var{regex}
7010 @itemx share @var{regex}
7011 @kindex sharedlibrary
7013 This is an obsolescent command; you can use it to explicitly load shared
7014 object library symbols for files matching a Unix regular expression, but
7015 as with files loaded automatically, it only loads shared libraries
7016 required by your program for a core file or after typing @code{run}. If
7017 @var{regex} is omitted all shared libraries required by your program are
7023 @section Errors reading symbol files
7025 While reading a symbol file, @value{GDBN} occasionally encounters problems,
7026 such as symbol types it does not recognize, or known bugs in compiler
7027 output. By default, @value{GDBN} does not notify you of such problems, since
7028 they are relatively common and primarily of interest to people
7029 debugging compilers. If you are interested in seeing information
7030 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
7031 only one message about each such type of problem, no matter how many
7032 times the problem occurs; or you can ask @value{GDBN} to print more messages,
7033 to see how many times the problems occur, with the @code{set
7034 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
7037 The messages currently printed, and their meanings, include:
7040 @item inner block not inside outer block in @var{symbol}
7042 The symbol information shows where symbol scopes begin and end
7043 (such as at the start of a function or a block of statements). This
7044 error indicates that an inner scope block is not fully contained
7045 in its outer scope blocks.
7047 @value{GDBN} circumvents the problem by treating the inner block as if it had
7048 the same scope as the outer block. In the error message, @var{symbol}
7049 may be shown as ``@code{(don't know)}'' if the outer block is not a
7052 @item block at @var{address} out of order
7054 The symbol information for symbol scope blocks should occur in
7055 order of increasing addresses. This error indicates that it does not
7058 @value{GDBN} does not circumvent this problem, and has trouble
7059 locating symbols in the source file whose symbols it is reading. (You
7060 can often determine what source file is affected by specifying
7061 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
7064 @item bad block start address patched
7066 The symbol information for a symbol scope block has a start address
7067 smaller than the address of the preceding source line. This is known
7068 to occur in the SunOS 4.1.1 (and earlier) C compiler.
7070 @value{GDBN} circumvents the problem by treating the symbol scope block as
7071 starting on the previous source line.
7073 @item bad string table offset in symbol @var{n}
7076 Symbol number @var{n} contains a pointer into the string table which is
7077 larger than the size of the string table.
7079 @value{GDBN} circumvents the problem by considering the symbol to have the
7080 name @code{foo}, which may cause other problems if many symbols end up
7083 @item unknown symbol type @code{0x@var{nn}}
7085 The symbol information contains new data types that @value{GDBN} does not yet
7086 know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood
7087 information, in hexadecimal.
7089 @value{GDBN} circumvents the error by ignoring this symbol information. This
7090 usually allows you to debug your program, though certain symbols
7091 are not accessible. If you encounter such a problem and feel like
7092 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on
7093 @code{complain}, then go up to the function @code{read_dbx_symtab} and
7094 examine @code{*bufp} to see the symbol.
7096 @item stub type has NULL name
7097 @value{GDBN} could not find the full definition for
7106 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
7108 The symbol information for a C++ member function is missing some
7109 information that recent versions of the compiler should have output
7113 @item info mismatch between compiler and debugger
7115 @value{GDBN} could not parse a type specification output by the compiler.
7119 @chapter Specifying a Debugging Target
7120 @cindex debugging target
7123 A @dfn{target} is the execution environment occupied by your program.
7125 Often, @value{GDBN} runs in the same host environment as your program; in
7126 that case, the debugging target is specified as a side effect when you
7127 use the @code{file} or @code{core} commands. When you need more
7128 flexibility---for example, running @value{GDBN} on a physically separate
7129 host, or controlling a standalone system over a serial port or a
7130 realtime system over a TCP/IP connection---you
7135 can use the @code{target} command to specify one of the target types
7136 configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing
7140 * Active Targets:: Active targets
7141 * Target Commands:: Commands for managing targets
7142 * Remote:: Remote debugging
7145 @node Active Targets
7146 @section Active targets
7147 @cindex stacking targets
7148 @cindex active targets
7149 @cindex multiple targets
7152 There are three classes of targets: processes, core files, and
7153 executable files. @value{GDBN} can work concurrently on up to three active
7154 targets, one in each class. This allows you to (for example) start a
7155 process and inspect its activity without abandoning your work on a core
7158 For example, if you execute @samp{gdb a.out}, then the executable file
7159 @code{a.out} is the only active target. If you designate a core file as
7160 well---presumably from a prior run that crashed and coredumped---then
7161 @value{GDBN} has two active targets and uses them in tandem, looking
7162 first in the corefile target, then in the executable file, to satisfy
7163 requests for memory addresses. (Typically, these two classes of target
7164 are complementary, since core files contain only a program's
7165 read-write memory---variables and so on---plus machine status, while
7166 executable files contain only the program text and initialized data.)
7169 When you type @code{run}, your executable file becomes an active process
7170 target as well. When a process target is active, all @value{GDBN} commands
7171 requesting memory addresses refer to that target; addresses in an
7175 executable file target are obscured while the process
7179 Use the @code{exec-file} command to select a
7180 new executable target (@pxref{Files, ,Commands to specify
7184 Use the @code{core-file} and @code{exec-file} commands to select a
7185 new core file or executable target (@pxref{Files, ,Commands to specify
7186 files}). To specify as a target a process that is already running, use
7187 the @code{attach} command (@pxref{Attach, ,Debugging an
7188 already-running process}).
7191 @node Target Commands
7192 @section Commands for managing targets
7195 @item target @var{type} @var{parameters}
7196 Connects the @value{GDBN} host environment to a target
7201 machine or process. A target is typically a protocol for talking to
7202 debugging facilities. You use the argument @var{type} to specify the
7203 type or protocol of the target machine.
7205 Further @var{parameters} are interpreted by the target protocol, but
7206 typically include things like device names or host names to connect
7207 with, process numbers, and baud rates.
7210 The @code{target} command does not repeat if you press @key{RET} again
7211 after executing the command.
7215 Displays the names of all targets available. To display targets
7216 currently selected, use either @code{info target} or @code{info files}
7217 (@pxref{Files, ,Commands to specify files}).
7219 @item help target @var{name}
7220 Describe a particular target, including any parameters necessary to
7224 Here are some common targets (available, or not, depending on the GDB
7228 @item target exec @var{program}
7230 An executable file. @samp{target exec @var{program}} is the same as
7231 @samp{exec-file @var{program}}.
7234 @item target core @var{filename}
7236 A core dump file. @samp{target core @var{filename}} is the same as
7237 @samp{core-file @var{filename}}.
7241 @item target remote @var{dev}
7242 @kindex target remote
7243 Remote serial target in GDB-specific protocol. The argument @var{dev}
7244 specifies what serial device to use for the connection (e.g.
7245 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}.
7251 CPU simulator. @xref{Simulator,,Simulated CPU Target}.
7255 @item target udi @var{keyword}
7257 Remote AMD29K target, using the AMD UDI protocol. The @var{keyword}
7258 argument specifies which 29K board or simulator to use. @xref{UDI29K
7259 Remote,,The UDI protocol for AMD29K}.
7261 @item target amd-eb @var{dev} @var{speed} @var{PROG}
7262 @kindex target amd-eb
7264 Remote PC-resident AMD EB29K board, attached over serial lines.
7265 @var{dev} is the serial device, as for @code{target remote};
7266 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
7267 name of the program to be debugged, as it appears to DOS on the PC.
7268 @xref{EB29K Remote, ,The EBMON protocol for AMD29K}.
7274 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
7275 @ifclear H8EXCLUSIVE
7276 @c Unix only, not currently of interest for H8-only manual
7277 Use special commands @code{device} and @code{speed} to control the serial
7278 line and the communications speed used.
7280 @xref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}.
7284 @item target nindy @var{devicename}
7285 @kindex target nindy
7286 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
7287 the name of the serial device to use for the connection, e.g.
7288 @file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}.
7292 @item target st2000 @var{dev} @var{speed}
7293 @kindex target st2000
7294 A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev}
7295 is the name of the device attached to the ST2000 serial line;
7296 @var{speed} is the communication line speed. The arguments are not used
7297 if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet.
7298 @xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}.
7302 @item target vxworks @var{machinename}
7303 @kindex target vxworks
7304 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
7305 is the target system's machine name or IP address.
7306 @xref{VxWorks Remote, ,@value{GDBN} and VxWorks}.
7311 Different targets are available on different configurations of @value{GDBN}; your
7312 configuration may have more or fewer targets.
7316 @section Remote debugging
7317 @cindex remote debugging
7319 If you are trying to debug a program running on a machine that cannot run
7320 GDB in the usual way, it is often useful to use remote debugging. For
7321 example, you might use remote debugging on an operating system kernel, or on
7322 a small system which does not have a general purpose operating system
7323 powerful enough to run a full-featured debugger.
7325 Some configurations of GDB have special serial or TCP/IP interfaces
7326 to make this work with particular debugging targets. In addition,
7327 GDB comes with a generic serial protocol (specific to GDB, but
7328 not specific to any particular target system) which you can use if you
7329 write the remote stubs---the code that runs on the remote system to
7330 communicate with GDB.
7332 Other remote targets may be available in your
7333 configuration of GDB; use @code{help target} to list them.
7336 @c Text on starting up GDB in various specific cases; it goes up front
7337 @c in manuals configured for any of those particular situations, here
7341 * Remote Serial:: @value{GDBN} remote serial protocol
7344 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
7347 * UDI29K Remote:: The UDI protocol for AMD29K
7348 * EB29K Remote:: The EBMON protocol for AMD29K
7351 * VxWorks Remote:: @value{GDBN} and VxWorks
7354 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
7357 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
7360 * MIPS Remote:: @value{GDBN} and MIPS boards
7363 * Simulator:: Simulated CPU target
7367 @include remote.texi
7370 @node Controlling GDB
7371 @chapter Controlling @value{GDBN}
7373 You can alter the way @value{GDBN} interacts with you by using
7374 the @code{set} command. For commands controlling how @value{GDBN} displays
7375 data, @pxref{Print Settings, ,Print settings}; other settings are described here.
7379 * Editing:: Command editing
7380 * History:: Command history
7381 * Screen Size:: Screen size
7383 * Messages/Warnings:: Optional warnings and messages
7390 @value{GDBN} indicates its readiness to read a command by printing a string
7391 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
7392 can change the prompt string with the @code{set prompt} command. For
7393 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
7394 the prompt in one of the @value{GDBN} sessions so that you can always tell which
7395 one you are talking to.
7398 @item set prompt @var{newprompt}
7400 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
7403 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
7407 @section Command editing
7409 @cindex command line editing
7411 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
7412 GNU library provides consistent behavior for programs which provide a
7413 command line interface to the user. Advantages are @code{emacs}-style
7414 or @code{vi}-style inline editing of commands, @code{csh}-like history
7415 substitution, and a storage and recall of command history across
7418 You may control the behavior of command line editing in @value{GDBN} with the
7425 @itemx set editing on
7426 Enable command line editing (enabled by default).
7428 @item set editing off
7429 Disable command line editing.
7431 @kindex show editing
7433 Show whether command line editing is enabled.
7437 @section Command history
7439 @value{GDBN} can keep track of the commands you type during your
7440 debugging sessions, so that you can be certain of precisely what
7441 happened. Use these commands to manage the @value{GDBN} command
7445 @cindex history substitution
7446 @cindex history file
7447 @kindex set history filename
7449 @item set history filename @var{fname}
7450 Set the name of the @value{GDBN} command history file to @var{fname}.
7451 This is the file where @value{GDBN} reads an initial command history
7452 list, and where it writes the command history from this session when it
7453 exits. You can access this list through history expansion or through
7454 the history command editing characters listed below. This file defaults
7455 to the value of the environment variable @code{GDBHISTFILE}, or to
7456 @file{./.gdb_history} if this variable is not set.
7458 @cindex history save
7459 @kindex set history save
7460 @item set history save
7461 @itemx set history save on
7462 Record command history in a file, whose name may be specified with the
7463 @code{set history filename} command. By default, this option is disabled.
7465 @item set history save off
7466 Stop recording command history in a file.
7468 @cindex history size
7469 @kindex set history size
7470 @item set history size @var{size}
7471 Set the number of commands which @value{GDBN} keeps in its history list.
7472 This defaults to the value of the environment variable
7473 @code{HISTSIZE}, or to 256 if this variable is not set.
7476 @cindex history expansion
7477 History expansion assigns special meaning to the character @kbd{!}.
7478 @ifset have-readline-appendices
7479 @xref{Event Designators}.
7482 Since @kbd{!} is also the logical not operator in C, history expansion
7483 is off by default. If you decide to enable history expansion with the
7484 @code{set history expansion on} command, you may sometimes need to
7485 follow @kbd{!} (when it is used as logical not, in an expression) with
7486 a space or a tab to prevent it from being expanded. The readline
7487 history facilities do not attempt substitution on the strings
7488 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
7490 The commands to control history expansion are:
7494 @kindex set history expansion
7495 @item set history expansion on
7496 @itemx set history expansion
7497 Enable history expansion. History expansion is off by default.
7499 @item set history expansion off
7500 Disable history expansion.
7502 The readline code comes with more complete documentation of
7503 editing and history expansion features. Users unfamiliar with @code{emacs}
7504 or @code{vi} may wish to read it.
7505 @ifset have-readline-appendices
7506 @xref{Command Line Editing}.
7510 @kindex show history
7512 @itemx show history filename
7513 @itemx show history save
7514 @itemx show history size
7515 @itemx show history expansion
7516 These commands display the state of the @value{GDBN} history parameters.
7517 @code{show history} by itself displays all four states.
7522 @kindex show commands
7524 Display the last ten commands in the command history.
7526 @item show commands @var{n}
7527 Print ten commands centered on command number @var{n}.
7529 @item show commands +
7530 Print ten commands just after the commands last printed.
7534 @section Screen size
7535 @cindex size of screen
7536 @cindex pauses in output
7538 Certain commands to @value{GDBN} may produce large amounts of
7539 information output to the screen. To help you read all of it,
7540 @value{GDBN} pauses and asks you for input at the end of each page of
7541 output. Type @key{RET} when you want to continue the output, or @kbd{q}
7542 to discard the remaining output. Also, the screen width setting
7543 determines when to wrap lines of output. Depending on what is being
7544 printed, @value{GDBN} tries to break the line at a readable place,
7545 rather than simply letting it overflow onto the following line.
7547 Normally @value{GDBN} knows the size of the screen from the termcap data base
7548 together with the value of the @code{TERM} environment variable and the
7549 @code{stty rows} and @code{stty cols} settings. If this is not correct,
7550 you can override it with the @code{set height} and @code{set
7554 @item set height @var{lpp}
7556 @itemx set width @var{cpl}
7562 These @code{set} commands specify a screen height of @var{lpp} lines and
7563 a screen width of @var{cpl} characters. The associated @code{show}
7564 commands display the current settings.
7566 If you specify a height of zero lines, @value{GDBN} does not pause during output
7567 no matter how long the output is. This is useful if output is to a file
7568 or to an editor buffer.
7570 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
7571 from wrapping its output.
7576 @cindex number representation
7577 @cindex entering numbers
7579 You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by
7580 the usual conventions: octal numbers begin with @samp{0}, decimal
7581 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
7582 Numbers that begin with none of these are, by default, entered in base
7583 10; likewise, the default display for numbers---when no particular
7584 format is specified---is base 10. You can change the default base for
7585 both input and output with the @code{set radix} command.
7589 @item set radix @var{base}
7590 Set the default base for numeric input and display. Supported choices
7591 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
7592 specified either unambiguously or using the current default radix; for
7602 sets the base to decimal. On the other hand, @samp{set radix 10}
7603 leaves the radix unchanged no matter what it was.
7607 Display the current default base for numeric input and display.
7610 @node Messages/Warnings
7611 @section Optional warnings and messages
7613 By default, @value{GDBN} is silent about its inner workings. If you are running
7614 on a slow machine, you may want to use the @code{set verbose} command.
7615 It makes @value{GDBN} tell you when it does a lengthy internal operation, so
7616 you will not think it has crashed.
7618 Currently, the messages controlled by @code{set verbose} are those
7619 which announce that the symbol table for a source file is being read;
7620 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
7624 @item set verbose on
7625 Enables @value{GDBN} output of certain informational messages.
7627 @item set verbose off
7628 Disables @value{GDBN} output of certain informational messages.
7630 @kindex show verbose
7632 Displays whether @code{set verbose} is on or off.
7635 By default, if @value{GDBN} encounters bugs in the symbol table of an object
7636 file, it is silent; but if you are debugging a compiler, you may find
7637 this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}).
7640 @kindex set complaints
7641 @item set complaints @var{limit}
7642 Permits @value{GDBN} to output @var{limit} complaints about each type of unusual
7643 symbols before becoming silent about the problem. Set @var{limit} to
7644 zero to suppress all complaints; set it to a large number to prevent
7645 complaints from being suppressed.
7647 @kindex show complaints
7648 @item show complaints
7649 Displays how many symbol complaints @value{GDBN} is permitted to produce.
7652 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
7653 lot of stupid questions to confirm certain commands. For example, if
7654 you try to run a program which is already running:
7658 The program being debugged has been started already.
7659 Start it from the beginning? (y or n)
7662 If you are willing to unflinchingly face the consequences of your own
7663 commands, you can disable this ``feature'':
7668 @cindex confirmation
7669 @cindex stupid questions
7670 @item set confirm off
7671 Disables confirmation requests.
7673 @item set confirm on
7674 Enables confirmation requests (the default).
7677 @kindex show confirm
7678 Displays state of confirmation requests.
7681 @c FIXME this does not really belong here. But where *does* it belong?
7682 @cindex reloading symbols
7683 Some systems allow individual object files that make up your program to
7684 be replaced without stopping and restarting your program.
7686 For example, in VxWorks you can simply recompile a defective object file
7687 and keep on running.
7689 If you are running on one of these systems, you can allow @value{GDBN} to
7690 reload the symbols for automatically relinked modules:
7693 @kindex set symbol-reloading
7694 @item set symbol-reloading on
7695 Replace symbol definitions for the corresponding source file when an
7696 object file with a particular name is seen again.
7698 @item set symbol-reloading off
7699 Do not replace symbol definitions when re-encountering object files of
7700 the same name. This is the default state; if you are not running on a
7701 system that permits automatically relinking modules, you should leave
7702 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
7703 when linking large programs, that may contain several modules (from
7704 different directories or libraries) with the same name.
7706 @item show symbol-reloading
7707 Show the current @code{on} or @code{off} setting.
7711 @chapter Canned Sequences of Commands
7713 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
7714 command lists}), @value{GDBN} provides two ways to store sequences of commands
7715 for execution as a unit: user-defined commands and command files.
7718 * Define:: User-defined commands
7719 * Hooks:: User-defined command hooks
7720 * Command Files:: Command files
7721 * Output:: Commands for controlled output
7725 @section User-defined commands
7727 @cindex user-defined command
7728 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which you
7729 assign a new name as a command. This is done with the @code{define}
7733 @item define @var{commandname}
7735 Define a command named @var{commandname}. If there is already a command
7736 by that name, you are asked to confirm that you want to redefine it.
7738 The definition of the command is made up of other @value{GDBN} command lines,
7739 which are given following the @code{define} command. The end of these
7740 commands is marked by a line containing @code{end}.
7742 @item document @var{commandname}
7744 Give documentation to the user-defined command @var{commandname}. The
7745 command @var{commandname} must already be defined. This command reads
7746 lines of documentation just as @code{define} reads the lines of the
7747 command definition, ending with @code{end}. After the @code{document}
7748 command is finished, @code{help} on command @var{commandname} displays
7749 the documentation you have specified.
7751 You may use the @code{document} command again to change the
7752 documentation of a command. Redefining the command with @code{define}
7753 does not change the documentation.
7755 @item help user-defined
7756 @kindex help user-defined
7757 List all user-defined commands, with the first line of the documentation
7761 @itemx show user @var{commandname}
7763 Display the @value{GDBN} commands used to define @var{commandname} (but not its
7764 documentation). If no @var{commandname} is given, display the
7765 definitions for all user-defined commands.
7768 User-defined commands do not take arguments. When they are executed, the
7769 commands of the definition are not printed. An error in any command
7770 stops execution of the user-defined command.
7772 Commands that would ask for confirmation if used interactively proceed
7773 without asking when used inside a user-defined command. Many @value{GDBN} commands
7774 that normally print messages to say what they are doing omit the messages
7775 when used in a user-defined command.
7778 @section User-defined command hooks
7779 @cindex command files
7781 You may define @emph{hooks}, which are a special kind of user-defined
7782 command. Whenever you run the command @samp{foo}, if the user-defined
7783 command @samp{hook-foo} exists, it is executed (with no arguments)
7784 before that command.
7786 In addition, a pseudo-command, @samp{stop} exists. Defining
7787 (@samp{hook-stop}) makes the associated commands execute every time
7788 execution stops in your program: before breakpoint commands are run,
7789 displays are printed, or the stack frame is printed.
7792 For example, to ignore @code{SIGALRM} signals while
7793 single-stepping, but treat them normally during normal execution,
7798 handle SIGALRM nopass
7805 define hook-continue
7811 You can define a hook for any single-word command in @value{GDBN}, but
7812 not for command aliases; you should define a hook for the basic command
7813 name, e.g. @code{backtrace} rather than @code{bt}.
7814 @c FIXME! So how does Joe User discover whether a command is an alias
7816 If an error occurs during the execution of your hook, execution of
7817 @value{GDBN} commands stops and @value{GDBN} issues a prompt
7818 (before the command that you actually typed had a chance to run).
7820 If you try to define a hook which does not match any known command, you
7821 get a warning from the @code{define} command.
7824 @section Command files
7826 @cindex command files
7827 A command file for @value{GDBN} is a file of lines that are @value{GDBN} commands. Comments
7828 (lines starting with @kbd{#}) may also be included. An empty line in a
7829 command file does nothing; it does not mean to repeat the last command, as
7830 it would from the terminal.
7833 @cindex @file{@value{GDBINIT}}
7834 When you start @value{GDBN}, it automatically executes commands from its
7835 @dfn{init files}. These are files named @file{@value{GDBINIT}}.
7836 @value{GDBN} reads the init file (if any) in your home directory, then
7837 processes command line options and operands, and then reads the init
7838 file (if any) in the current working directory. This is so the init
7839 file in your home directory can set options (such as @code{set
7840 complaints}) which affect the processing of the command line options and
7841 operands. The init files are not executed if you use the @samp{-nx}
7842 option; @pxref{Mode Options, ,Choosing modes}.
7845 @cindex init file name
7846 On some configurations of @value{GDBN}, the init file is known by a
7847 different name (these are typically environments where a specialized
7848 form of GDB may need to coexist with other forms, hence a different name
7849 for the specialized version's init file). These are the environments
7850 with special init file names:
7855 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
7857 @kindex .os68gdbinit
7859 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
7863 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
7867 You can also request the execution of a command file with the
7868 @code{source} command:
7871 @item source @var{filename}
7873 Execute the command file @var{filename}.
7876 The lines in a command file are executed sequentially. They are not
7877 printed as they are executed. An error in any command terminates execution
7878 of the command file.
7880 Commands that would ask for confirmation if used interactively proceed
7881 without asking when used in a command file. Many @value{GDBN} commands that
7882 normally print messages to say what they are doing omit the messages
7883 when called from command files.
7886 @section Commands for controlled output
7888 During the execution of a command file or a user-defined command, normal
7889 @value{GDBN} output is suppressed; the only output that appears is what is
7890 explicitly printed by the commands in the definition. This section
7891 describes three commands useful for generating exactly the output you
7895 @item echo @var{text}
7897 @c I do not consider backslash-space a standard C escape sequence
7898 @c because it is not in ANSI.
7899 Print @var{text}. Nonprinting characters can be included in
7900 @var{text} using C escape sequences, such as @samp{\n} to print a
7901 newline. @strong{No newline is printed unless you specify one.}
7902 In addition to the standard C escape sequences, a backslash followed
7903 by a space stands for a space. This is useful for displaying a
7904 string with spaces at the beginning or the end, since leading and
7905 trailing spaces are otherwise trimmed from all arguments.
7906 To print @samp{@w{ }and foo =@w{ }}, use the command
7907 @samp{echo \@w{ }and foo = \@w{ }}.
7909 A backslash at the end of @var{text} can be used, as in C, to continue
7910 the command onto subsequent lines. For example,
7913 echo This is some text\n\
7914 which is continued\n\
7915 onto several lines.\n
7918 produces the same output as
7921 echo This is some text\n
7922 echo which is continued\n
7923 echo onto several lines.\n
7926 @item output @var{expression}
7928 Print the value of @var{expression} and nothing but that value: no
7929 newlines, no @samp{$@var{nn} = }. The value is not entered in the
7930 value history either. @xref{Expressions, ,Expressions}, for more information on
7933 @item output/@var{fmt} @var{expression}
7934 Print the value of @var{expression} in format @var{fmt}. You can use
7935 the same formats as for @code{print}. @xref{Output Formats,,Output
7936 formats}, for more information.
7938 @item printf @var{string}, @var{expressions}@dots{}
7940 Print the values of the @var{expressions} under the control of
7941 @var{string}. The @var{expressions} are separated by commas and may be
7942 either numbers or pointers. Their values are printed as specified by
7943 @var{string}, exactly as if your program were to execute the C
7947 printf (@var{string}, @var{expressions}@dots{});
7950 For example, you can print two values in hex like this:
7953 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
7956 The only backslash-escape sequences that you can use in the format
7957 string are the simple ones that consist of backslash followed by a
7963 @chapter Using @value{GDBN} under GNU Emacs
7966 A special interface allows you to use GNU Emacs to view (and
7967 edit) the source files for the program you are debugging with
7970 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
7971 executable file you want to debug as an argument. This command starts
7972 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
7973 created Emacs buffer.
7975 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
7980 All ``terminal'' input and output goes through the Emacs buffer.
7983 This applies both to @value{GDBN} commands and their output, and to the input
7984 and output done by the program you are debugging.
7986 This is useful because it means that you can copy the text of previous
7987 commands and input them again; you can even use parts of the output
7990 All the facilities of Emacs' Shell mode are available for interacting
7991 with your program. In particular, you can send signals the usual
7992 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
7997 @value{GDBN} displays source code through Emacs.
8000 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
8001 source file for that frame and puts an arrow (@samp{=>}) at the
8002 left margin of the current line. Emacs uses a separate buffer for
8003 source display, and splits the screen to show both your @value{GDBN} session
8006 Explicit @value{GDBN} @code{list} or search commands still produce output as
8007 usual, but you probably have no reason to use them from Emacs.
8010 @emph{Warning:} If the directory where your program resides is not your
8011 current directory, it can be easy to confuse Emacs about the location of
8012 the source files, in which case the auxiliary display buffer does not
8013 appear to show your source. @value{GDBN} can find programs by searching your
8014 environment's @code{PATH} variable, so the @value{GDBN} input and output
8015 session proceeds normally; but Emacs does not get enough information
8016 back from @value{GDBN} to locate the source files in this situation. To
8017 avoid this problem, either start @value{GDBN} mode from the directory where
8018 your program resides, or specify an absolute file name when prompted for the
8019 @kbd{M-x gdb} argument.
8021 A similar confusion can result if you use the @value{GDBN} @code{file} command to
8022 switch to debugging a program in some other location, from an existing
8023 @value{GDBN} buffer in Emacs.
8026 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
8027 you need to call @value{GDBN} by a different name (for example, if you keep
8028 several configurations around, with different names) you can set the
8029 Emacs variable @code{gdb-command-name}; for example,
8032 (setq gdb-command-name "mygdb")
8036 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
8037 in your @file{.emacs} file) makes Emacs call the program named
8038 ``@code{mygdb}'' instead.
8040 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
8041 addition to the standard Shell mode commands:
8045 Describe the features of Emacs' @value{GDBN} Mode.
8048 Execute to another source line, like the @value{GDBN} @code{step} command; also
8049 update the display window to show the current file and location.
8052 Execute to next source line in this function, skipping all function
8053 calls, like the @value{GDBN} @code{next} command. Then update the display window
8054 to show the current file and location.
8057 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
8058 display window accordingly.
8061 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
8062 display window accordingly.
8065 Execute until exit from the selected stack frame, like the @value{GDBN}
8066 @code{finish} command.
8069 Continue execution of your program, like the @value{GDBN} @code{continue}
8072 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
8075 Go up the number of frames indicated by the numeric argument
8076 (@pxref{Arguments, , Numeric Arguments, emacs, The GNU Emacs Manual}),
8077 like the @value{GDBN} @code{up} command.
8079 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
8082 Go down the number of frames indicated by the numeric argument, like the
8083 @value{GDBN} @code{down} command.
8085 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
8088 Read the number where the cursor is positioned, and insert it at the end
8089 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
8090 around an address that was displayed earlier, type @kbd{disassemble};
8091 then move the cursor to the address display, and pick up the
8092 argument for @code{disassemble} by typing @kbd{C-x &}.
8094 You can customize this further by defining elements of the list
8095 @code{gdb-print-command}; once it is defined, you can format or
8096 otherwise process numbers picked up by @kbd{C-x &} before they are
8097 inserted. A numeric argument to @kbd{C-x &} indicates that you
8098 wish special formatting, and also acts as an index to pick an element of the
8099 list. If the list element is a string, the number to be inserted is
8100 formatted using the Emacs function @code{format}; otherwise the number
8101 is passed as an argument to the corresponding list element.
8104 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
8105 tells @value{GDBN} to set a breakpoint on the source line point is on.
8107 If you accidentally delete the source-display buffer, an easy way to get
8108 it back is to type the command @code{f} in the @value{GDBN} buffer, to
8109 request a frame display; when you run under Emacs, this recreates
8110 the source buffer if necessary to show you the context of the current
8113 The source files displayed in Emacs are in ordinary Emacs buffers
8114 which are visiting the source files in the usual way. You can edit
8115 the files with these buffers if you wish; but keep in mind that @value{GDBN}
8116 communicates with Emacs in terms of line numbers. If you add or
8117 delete lines from the text, the line numbers that @value{GDBN} knows cease
8118 to correspond properly with the code.
8120 @c The following dropped because Epoch is nonstandard. Reactivate
8121 @c if/when v19 does something similar. ---pesch@cygnus.com 19dec1990
8123 @kindex emacs epoch environment
8127 Version 18 of Emacs has a built-in window system called the @code{epoch}
8128 environment. Users of this environment can use a new command,
8129 @code{inspect} which performs identically to @code{print} except that
8130 each value is printed in its own window.
8136 @chapter Using @value{GDBN} with Energize
8139 The Energize Programming System is an integrated development environment
8140 that includes a point-and-click interface to many programming tools.
8141 When you use @value{GDBN} in this environment, you can use the standard
8142 Energize graphical interface to drive @value{GDBN}; you can also, if you
8143 choose, type @value{GDBN} commands as usual in a debugging window. Even if
8144 you use the graphical interface, the debugging window (which uses Emacs,
8145 and resembles the standard Emacs interface to @value{GDBN}) displays the
8146 equivalent commands, so that the history of your debugging session is
8149 When Energize starts up a @value{GDBN} session, it uses one of the
8150 command-line options @samp{-energize} or @samp{-cadillac} (``cadillac''
8151 is the name of the communications protocol used by the Energize system).
8152 This option makes @value{GDBN} run as one of the tools in the Energize Tool
8153 Set: it sends all output to the Energize kernel, and accept input from
8156 See the user manual for the Energize Programming System for
8157 information on how to use the Energize graphical interface and the other
8158 development tools that Energize integrates with @value{GDBN}.
8163 @chapter Reporting Bugs in @value{GDBN}
8164 @cindex bugs in @value{GDBN}
8165 @cindex reporting bugs in @value{GDBN}
8167 Your bug reports play an essential role in making @value{GDBN} reliable.
8169 Reporting a bug may help you by bringing a solution to your problem, or it
8170 may not. But in any case the principal function of a bug report is to help
8171 the entire community by making the next version of @value{GDBN} work better. Bug
8172 reports are your contribution to the maintenance of @value{GDBN}.
8174 In order for a bug report to serve its purpose, you must include the
8175 information that enables us to fix the bug.
8178 * Bug Criteria:: Have you found a bug?
8179 * Bug Reporting:: How to report bugs
8183 @section Have you found a bug?
8184 @cindex bug criteria
8186 If you are not sure whether you have found a bug, here are some guidelines:
8190 @cindex fatal signal
8191 @cindex debugger crash
8192 @cindex crash of debugger
8193 If the debugger gets a fatal signal, for any input whatever, that is a
8194 @value{GDBN} bug. Reliable debuggers never crash.
8197 @cindex error on valid input
8198 If @value{GDBN} produces an error message for valid input, that is a bug.
8201 @cindex invalid input
8202 If @value{GDBN} does not produce an error message for invalid input,
8203 that is a bug. However, you should note that your idea of
8204 ``invalid input'' might be our idea of ``an extension'' or ``support
8205 for traditional practice''.
8208 If you are an experienced user of debugging tools, your suggestions
8209 for improvement of @value{GDBN} are welcome in any case.
8213 @section How to report bugs
8215 @cindex @value{GDBN} bugs, reporting
8217 A number of companies and individuals offer support for GNU products.
8218 If you obtained @value{GDBN} from a support organization, we recommend you
8219 contact that organization first.
8221 You can find contact information for many support companies and
8222 individuals in the file @file{etc/SERVICE} in the GNU Emacs
8225 In any event, we also recommend that you send bug reports for @value{GDBN} to one
8229 bug-gdb@@prep.ai.mit.edu
8230 @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb
8233 @strong{Do not send bug reports to @samp{info-gdb}, or to
8234 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do not want to
8235 receive bug reports. Those that do, have arranged to receive @samp{bug-gdb}.
8237 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
8238 serves as a repeater. The mailing list and the newsgroup carry exactly
8239 the same messages. Often people think of posting bug reports to the
8240 newsgroup instead of mailing them. This appears to work, but it has one
8241 problem which can be crucial: a newsgroup posting often lacks a mail
8242 path back to the sender. Thus, if we need to ask for more information,
8243 we may be unable to reach you. For this reason, it is better to send
8244 bug reports to the mailing list.
8246 As a last resort, send bug reports on paper to:
8250 Free Software Foundation
8255 The fundamental principle of reporting bugs usefully is this:
8256 @strong{report all the facts}. If you are not sure whether to state a
8257 fact or leave it out, state it!
8259 Often people omit facts because they think they know what causes the
8260 problem and assume that some details do not matter. Thus, you might
8261 assume that the name of the variable you use in an example does not matter.
8262 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
8263 stray memory reference which happens to fetch from the location where that
8264 name is stored in memory; perhaps, if the name were different, the contents
8265 of that location would fool the debugger into doing the right thing despite
8266 the bug. Play it safe and give a specific, complete example. That is the
8267 easiest thing for you to do, and the most helpful.
8269 Keep in mind that the purpose of a bug report is to enable us to fix
8270 the bug if it is new to us. It is not as important as what happens if
8271 the bug is already known. Therefore, always write your bug reports on
8272 the assumption that the bug has not been reported previously.
8274 Sometimes people give a few sketchy facts and ask, ``Does this ring a
8275 bell?'' Those bug reports are useless, and we urge everyone to
8276 @emph{refuse to respond to them} except to chide the sender to report
8279 To enable us to fix the bug, you should include all these things:
8283 The version of @value{GDBN}. @value{GDBN} announces it if you start with no
8284 arguments; you can also print it at any time using @code{show version}.
8286 Without this, we will not know whether there is any point in looking for
8287 the bug in the current version of @value{GDBN}.
8290 The type of machine you are using, and the operating system name and
8294 What compiler (and its version) was used to compile @value{GDBN}---e.g.
8295 ``@value{GCC}--2.0''.
8298 What compiler (and its version) was used to compile the program you
8299 are debugging---e.g. ``@value{GCC}--2.0''.
8302 The command arguments you gave the compiler to compile your example and
8303 observe the bug. For example, did you use @samp{-O}? To guarantee
8304 you will not omit something important, list them all. A copy of the
8305 Makefile (or the output from make) is sufficient.
8307 If we were to try to guess the arguments, we would probably guess wrong
8308 and then we might not encounter the bug.
8311 A complete input script, and all necessary source files, that will
8315 A description of what behavior you observe that you believe is
8316 incorrect. For example, ``It gets a fatal signal.''
8318 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we will
8319 certainly notice it. But if the bug is incorrect output, we might not
8320 notice unless it is glaringly wrong. We are human, after all. You
8321 might as well not give us a chance to make a mistake.
8323 Even if the problem you experience is a fatal signal, you should still
8324 say so explicitly. Suppose something strange is going on, such as,
8325 your copy of @value{GDBN} is out of synch, or you have encountered a
8326 bug in the C library on your system. (This has happened!) Your copy
8327 might crash and ours would not. If you told us to expect a crash,
8328 then when ours fails to crash, we would know that the bug was not
8329 happening for us. If you had not told us to expect a crash, then we
8330 would not be able to draw any conclusion from our observations.
8333 If you wish to suggest changes to the @value{GDBN} source, send us context
8334 diffs. If you even discuss something in the @value{GDBN} source, refer to
8335 it by context, not by line number.
8337 The line numbers in our development sources will not match those in your
8338 sources. Your line numbers would convey no useful information to us.
8341 Here are some things that are not necessary:
8345 A description of the envelope of the bug.
8347 Often people who encounter a bug spend a lot of time investigating
8348 which changes to the input file will make the bug go away and which
8349 changes will not affect it.
8351 This is often time consuming and not very useful, because the way we
8352 will find the bug is by running a single example under the debugger
8353 with breakpoints, not by pure deduction from a series of examples.
8354 We recommend that you save your time for something else.
8356 Of course, if you can find a simpler example to report @emph{instead}
8357 of the original one, that is a convenience for us. Errors in the
8358 output will be easier to spot, running under the debugger will take
8359 less time, and so on.
8361 However, simplification is not vital; if you do not want to do this,
8362 report the bug anyway and send us the entire test case you used.
8365 A patch for the bug.
8367 A patch for the bug does help us if it is a good one. But do not omit
8368 the necessary information, such as the test case, on the assumption that
8369 a patch is all we need. We might see problems with your patch and decide
8370 to fix the problem another way, or we might not understand it at all.
8372 Sometimes with a program as complicated as @value{GDBN} it is very hard to
8373 construct an example that will make the program follow a certain path
8374 through the code. If you do not send us the example, we will not be able
8375 to construct one, so we will not be able to verify that the bug is fixed.
8377 And if we cannot understand what bug you are trying to fix, or why your
8378 patch should be an improvement, we will not install it. A test case will
8379 help us to understand.
8382 A guess about what the bug is or what it depends on.
8384 Such guesses are usually wrong. Even we cannot guess right about such
8385 things without first using the debugger to find the facts.
8388 @c The readline documentation is distributed with the readline code
8389 @c and consists of the two following files:
8392 @c Use -I with makeinfo to point to the appropriate directory,
8393 @c environment var TEXINPUTS with TeX.
8394 @include rluser.texinfo
8395 @include inc-hist.texi
8398 @node Renamed Commands
8399 @appendix Renamed Commands
8401 The following commands were renamed in GDB 4, in order to make the
8402 command set as a whole more consistent and easier to use and remember:
8405 @kindex delete environment
8406 @kindex info copying
8407 @kindex info convenience
8408 @kindex info directories
8409 @kindex info editing
8410 @kindex info history
8411 @kindex info targets
8413 @kindex info version
8414 @kindex info warranty
8415 @kindex set addressprint
8416 @kindex set arrayprint
8417 @kindex set prettyprint
8418 @kindex set screen-height
8419 @kindex set screen-width
8420 @kindex set unionprint
8421 @kindex set vtblprint
8422 @kindex set demangle
8423 @kindex set asm-demangle
8424 @kindex set sevenbit-strings
8425 @kindex set array-max
8427 @kindex set history write
8428 @kindex show addressprint
8429 @kindex show arrayprint
8430 @kindex show prettyprint
8431 @kindex show screen-height
8432 @kindex show screen-width
8433 @kindex show unionprint
8434 @kindex show vtblprint
8435 @kindex show demangle
8436 @kindex show asm-demangle
8437 @kindex show sevenbit-strings
8438 @kindex show array-max
8439 @kindex show caution
8440 @kindex show history write
8445 @c END TEXI2ROFF-KILL
8447 OLD COMMAND NEW COMMAND
8449 --------------- -------------------------------
8450 @c END TEXI2ROFF-KILL
8451 add-syms add-symbol-file
8452 delete environment unset environment
8453 info convenience show convenience
8454 info copying show copying
8455 info directories show directories
8456 info editing show commands
8457 info history show values
8458 info targets help target
8459 info values show values
8460 info version show version
8461 info warranty show warranty
8462 set/show addressprint set/show print address
8463 set/show array-max set/show print elements
8464 set/show arrayprint set/show print array
8465 set/show asm-demangle set/show print asm-demangle
8466 set/show caution set/show confirm
8467 set/show demangle set/show print demangle
8468 set/show history write set/show history save
8469 set/show prettyprint set/show print pretty
8470 set/show screen-height set/show height
8471 set/show screen-width set/show width
8472 set/show sevenbit-strings set/show print sevenbit-strings
8473 set/show unionprint set/show print union
8474 set/show vtblprint set/show print vtbl
8476 unset [No longer an alias for delete]
8482 \vskip \parskip\vskip \baselineskip
8483 \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr
8484 {\bf Old Command} &&{\bf New Command}\cr
8485 add-syms &&add-symbol-file\cr
8486 delete environment &&unset environment\cr
8487 info convenience &&show convenience\cr
8488 info copying &&show copying\cr
8489 info directories &&show directories \cr
8490 info editing &&show commands\cr
8491 info history &&show values\cr
8492 info targets &&help target\cr
8493 info values &&show values\cr
8494 info version &&show version\cr
8495 info warranty &&show warranty\cr
8496 set{\rm / }show addressprint &&set{\rm / }show print address\cr
8497 set{\rm / }show array-max &&set{\rm / }show print elements\cr
8498 set{\rm / }show arrayprint &&set{\rm / }show print array\cr
8499 set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr
8500 set{\rm / }show caution &&set{\rm / }show confirm\cr
8501 set{\rm / }show demangle &&set{\rm / }show print demangle\cr
8502 set{\rm / }show history write &&set{\rm / }show history save\cr
8503 set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr
8504 set{\rm / }show screen-height &&set{\rm / }show height\cr
8505 set{\rm / }show screen-width &&set{\rm / }show width\cr
8506 set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr
8507 set{\rm / }show unionprint &&set{\rm / }show print union\cr
8508 set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr
8510 unset &&\rm(No longer an alias for delete)\cr
8513 @c END TEXI2ROFF-KILL
8516 @ifclear PRECONFIGURED
8517 @node Formatting Documentation
8518 @appendix Formatting Documentation
8520 @cindex GDB reference card
8521 @cindex reference card
8522 The GDB 4 release includes an already-formatted reference card, ready
8523 for printing with PostScript or Ghostscript, in the @file{gdb}
8524 subdirectory of the main source directory@footnote{In
8525 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
8526 release.}. If you can use PostScript or Ghostscript with your printer,
8527 you can print the reference card immediately with @file{refcard.ps}.
8529 The release also includes the source for the reference card. You
8530 can format it, using @TeX{}, by typing:
8536 The GDB reference card is designed to print in landscape mode on US
8537 ``letter'' size paper; that is, on a sheet 11 inches wide by 8.5 inches
8538 high. You will need to specify this form of printing as an option to
8539 your @sc{dvi} output program.
8541 @cindex documentation
8543 All the documentation for GDB comes as part of the machine-readable
8544 distribution. The documentation is written in Texinfo format, which is
8545 a documentation system that uses a single source file to produce both
8546 on-line information and a printed manual. You can use one of the Info
8547 formatting commands to create the on-line version of the documentation
8548 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
8550 GDB includes an already formatted copy of the on-line Info version of
8551 this manual in the @file{gdb} subdirectory. The main Info file is
8552 @file{gdb-@var{version-number}/gdb/gdb.info}, and it refers to
8553 subordinate files matching @samp{gdb.info*} in the same directory. If
8554 necessary, you can print out these files, or read them with any editor;
8555 but they are easier to read using the @code{info} subsystem in GNU Emacs
8556 or the standalone @code{info} program, available as part of the GNU
8557 Texinfo distribution.
8559 If you want to format these Info files yourself, you need one of the
8560 Info formatting programs, such as @code{texinfo-format-buffer} or
8563 If you have @code{makeinfo} installed, and are in the top level GDB
8564 source directory (@file{gdb-@value{GDBVN}}, in the case of version @value{GDBVN}), you can
8565 make the Info file by typing:
8572 If you want to typeset and print copies of this manual, you need @TeX{},
8573 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
8574 Texinfo definitions file.
8576 @TeX{} is a typesetting program; it does not print files directly, but
8577 produces output files called @sc{dvi} files. To print a typeset
8578 document, you need a program to print @sc{dvi} files. If your system
8579 has @TeX{} installed, chances are it has such a program. The precise
8580 command to use depends on your system; @kbd{lpr -d} is common; another
8581 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
8582 require a file name without any extension or a @samp{.dvi} extension.
8584 @TeX{} also requires a macro definitions file called
8585 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
8586 written in Texinfo format. On its own, @TeX{} cannot read, much less
8587 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
8588 and is located in the @file{gdb-@var{version-number}/texinfo}
8591 If you have @TeX{} and a @sc{dvi} printer program installed, you can
8592 typeset and print this manual. First switch to the the @file{gdb}
8593 subdirectory of the main source directory (for example, to
8594 @file{gdb-@value{GDBVN}/gdb}) and then type:
8600 @node Installing GDB
8601 @appendix Installing GDB
8602 @cindex configuring GDB
8603 @cindex installation
8605 GDB comes with a @code{configure} script that automates the process
8606 of preparing GDB for installation; you can then use @code{make} to
8607 build the @code{gdb} program.
8609 @c irrelevant in info file; it's as current as the code it lives with.
8610 @footnote{If you have a more recent version of GDB than @value{GDBVN},
8611 look at the @file{README} file in the sources; we may have improved the
8612 installation procedures since publishing this manual.}
8615 The GDB distribution includes all the source code you need for GDB in
8616 a single directory, whose name is usually composed by appending the
8617 version number to @samp{gdb}.
8619 For example, the GDB version @value{GDBVN} distribution is in the
8620 @file{gdb-@value{GDBVN}} directory. That directory contains:
8623 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
8624 script for configuring GDB and all its supporting libraries.
8626 @item gdb-@value{GDBVN}/gdb
8627 the source specific to GDB itself
8629 @item gdb-@value{GDBVN}/bfd
8630 source for the Binary File Descriptor library
8632 @item gdb-@value{GDBVN}/include
8635 @item gdb-@value{GDBVN}/libiberty
8636 source for the @samp{-liberty} free software library
8638 @item gdb-@value{GDBVN}/opcodes
8639 source for the library of opcode tables and disassemblers
8641 @item gdb-@value{GDBVN}/readline
8642 source for the GNU command-line interface
8644 @item gdb-@value{GDBVN}/glob
8645 source for the GNU filename pattern-matching subroutine
8647 @item gdb-@value{GDBVN}/mmalloc
8648 source for the GNU memory-mapped malloc package
8651 The simplest way to configure and build GDB is to run @code{configure}
8652 from the @file{gdb-@var{version-number}} source directory, which in
8653 this example is the @file{gdb-@value{GDBVN}} directory.
8655 First switch to the @file{gdb-@var{version-number}} source directory
8656 if you are not already in it; then run @code{configure}. Pass the
8657 identifier for the platform on which GDB will run as an
8663 cd gdb-@value{GDBVN}
8664 ./configure @var{host}
8669 where @var{host} is an identifier such as @samp{sun4} or
8670 @samp{decstation}, that identifies the platform where GDB will run.
8671 (You can often leave off @var{host}; @code{configure} tries to guess the
8672 correct value by examining your system.)
8674 Running @samp{configure @var{host}} and then running @code{make} builds the
8675 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
8676 libraries, then @code{gdb} itself. The configured source files, and the
8677 binaries, are left in the corresponding source directories.
8679 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
8680 system does not recognize this automatically when you run a different
8681 shell, you may need to run @code{sh} on it explicitly:
8684 sh configure @var{host}
8687 If you run @code{configure} from a directory that contains source
8688 directories for multiple libraries or programs, such as the
8689 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
8690 creates configuration files for every directory level underneath (unless
8691 you tell it not to, with the @samp{--norecursion} option).
8693 You can run the @code{configure} script from any of the
8694 subordinate directories in the GDB distribution if you only want to
8695 configure that subdirectory, but be sure to specify a path to it.
8697 For example, with version @value{GDBVN}, type the following to configure only
8698 the @code{bfd} subdirectory:
8702 cd gdb-@value{GDBVN}/bfd
8703 ../configure @var{host}
8707 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
8708 However, you should make sure that the shell on your path (named by
8709 the @samp{SHELL} environment variable) is publicly readable. Remember
8710 that GDB uses the shell to start your program---some systems refuse to
8711 let GDB debug child processes whose programs are not readable.
8714 * Separate Objdir:: Compiling GDB in another directory
8715 * Config Names:: Specifying names for hosts and targets
8716 * configure Options:: Summary of options for configure
8719 @node Separate Objdir
8720 @section Compiling GDB in another directory
8722 If you want to run GDB versions for several host or target machines,
8723 you need a different @code{gdb} compiled for each combination of
8724 host and target. @code{configure} is designed to make this easy by
8725 allowing you to generate each configuration in a separate subdirectory,
8726 rather than in the source directory. If your @code{make} program
8727 handles the @samp{VPATH} feature (GNU @code{make} does), running
8728 @code{make} in each of these directories builds the @code{gdb}
8729 program specified there.
8731 To build @code{gdb} in a separate directory, run @code{configure}
8732 with the @samp{--srcdir} option to specify where to find the source.
8733 (You also need to specify a path to find @code{configure}
8734 itself from your working directory. If the path to @code{configure}
8735 would be the same as the argument to @samp{--srcdir}, you can leave out
8736 the @samp{--srcdir} option; it is assumed.)
8738 For example, with version @value{GDBVN}, you can build GDB in a separate
8739 directory for a Sun 4 like this:
8743 cd gdb-@value{GDBVN}
8746 ../gdb-@value{GDBVN}/configure sun4
8751 When @code{configure} builds a configuration using a remote source
8752 directory, it creates a tree for the binaries with the same structure
8753 (and using the same names) as the tree under the source directory. In
8754 the example, you'd find the Sun 4 library @file{libiberty.a} in the
8755 directory @file{gdb-sun4/libiberty}, and GDB itself in
8756 @file{gdb-sun4/gdb}.
8758 One popular reason to build several GDB configurations in separate
8759 directories is to configure GDB for cross-compiling (where GDB
8760 runs on one machine---the host---while debugging programs that run on
8761 another machine---the target). You specify a cross-debugging target by
8762 giving the @samp{--target=@var{target}} option to @code{configure}.
8764 When you run @code{make} to build a program or library, you must run
8765 it in a configured directory---whatever directory you were in when you
8766 called @code{configure} (or one of its subdirectories).
8768 The @code{Makefile} that @code{configure} generates in each source
8769 directory also runs recursively. If you type @code{make} in a source
8770 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
8771 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
8772 will build all the required libraries, and then build GDB.
8774 When you have multiple hosts or targets configured in separate
8775 directories, you can run @code{make} on them in parallel (for example,
8776 if they are NFS-mounted on each of the hosts); they will not interfere
8780 @section Specifying names for hosts and targets
8782 The specifications used for hosts and targets in the @code{configure}
8783 script are based on a three-part naming scheme, but some short predefined
8784 aliases are also supported. The full naming scheme encodes three pieces
8785 of information in the following pattern:
8788 @var{architecture}-@var{vendor}-@var{os}
8791 For example, you can use the alias @code{sun4} as a @var{host} argument,
8792 or as the value for @var{target} in a @code{--target=@var{target}}
8793 option. The equivalent full name is @samp{sparc-sun-sunos4}.
8795 The @code{configure} script accompanying GDB does not provide
8796 any query facility to list all supported host and target names or
8797 aliases. @code{configure} calls the Bourne shell script
8798 @code{config.sub} to map abbreviations to full names; you can read the
8799 script, if you wish, or you can use it to test your guesses on
8800 abbreviations---for example:
8803 % sh config.sub sun4
8804 sparc-sun-sunos4.1.1
8805 % sh config.sub sun3
8807 % sh config.sub decstation
8809 % sh config.sub hp300bsd
8811 % sh config.sub i386v
8813 % sh config.sub i786v
8814 Invalid configuration `i786v': machine `i786v' not recognized
8818 @code{config.sub} is also distributed in the GDB source
8819 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
8821 @node configure Options
8822 @section @code{configure} options
8824 Here is a summary of the @code{configure} options and arguments that
8825 are most often useful for building @value{GDBN}. @code{configure} also has
8826 several other options not listed here. @inforef{What Configure
8827 Does,,configure.info}, for a full explanation of @code{configure}.
8828 @c FIXME: Would this be more, or less, useful as an xref (ref to printed
8829 @c manual in the printed manual, ref to info file only from the info file)?
8832 configure @r{[}--help@r{]}
8833 @r{[}--prefix=@var{dir}@r{]}
8834 @r{[}--srcdir=@var{dirname}@r{]}
8835 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
8836 @r{[}--target=@var{target}@r{]} @var{host}
8840 You may introduce options with a single @samp{-} rather than
8841 @samp{--} if you prefer; but you may abbreviate option names if you use
8846 Display a quick summary of how to invoke @code{configure}.
8848 @item -prefix=@var{dir}
8849 Configure the source to install programs and files under directory
8852 @c avoid splitting the warning from the explanation:
8854 @item --srcdir=@var{dirname}
8855 @strong{Warning: using this option requires GNU @code{make}, or another
8856 @code{make} that implements the @code{VPATH} feature.}@*
8857 Use this option to make configurations in directories separate from the
8858 GDB source directories. Among other things, you can use this to
8859 build (or maintain) several configurations simultaneously, in separate
8860 directories. @code{configure} writes configuration specific files in
8861 the current directory, but arranges for them to use the source in the
8862 directory @var{dirname}. @code{configure} creates directories under
8863 the working directory in parallel to the source directories below
8867 Configure only the directory level where @code{configure} is executed; do not
8868 propagate configuration to subdirectories.
8871 @emph{Remove} files otherwise built during configuration.
8873 @c This does not work (yet if ever). FIXME.
8874 @c @item --parse=@var{lang} @dots{}
8875 @c Configure the GDB expression parser to parse the listed languages.
8876 @c @samp{all} configures GDB for all supported languages. To get a
8877 @c list of all supported languages, omit the argument. Without this
8878 @c option, GDB is configured to parse all supported languages.
8880 @item --target=@var{target}
8881 Configure GDB for cross-debugging programs running on the specified
8882 @var{target}. Without this option, GDB is configured to debug
8883 programs that run on the same machine (@var{host}) as GDB itself.
8885 There is no convenient way to generate a list of all available targets.
8887 @item @var{host} @dots{}
8888 Configure GDB to run on the specified @var{host}.
8890 There is no convenient way to generate a list of all available hosts.
8894 @code{configure} accepts other options, for compatibility with
8895 configuring other GNU tools recursively; but these are the only
8896 options that affect GDB or its supporting libraries.
8905 % I think something like @colophon should be in texinfo. In the
8907 \long\def\colophon{\hbox to0pt{}\vfill
8908 \centerline{The body of this manual is set in}
8909 \centerline{\fontname\tenrm,}
8910 \centerline{with headings in {\bf\fontname\tenbf}}
8911 \centerline{and examples in {\tt\fontname\tentt}.}
8912 \centerline{{\it\fontname\tenit\/},}
8913 \centerline{{\bf\fontname\tenbf}, and}
8914 \centerline{{\sl\fontname\tensl\/}}
8915 \centerline{are used for emphasis.}\vfill}
8917 % Blame: pesch@cygnus.com, 1991.