1 \input texinfo @c -*-texinfo-*-
2 @c Copyright (c) 1988 1989 1990 1991 1992 1993 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 November 1993
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:: 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: Fred
277 Fish (releases 4.11, 4.10, 4.9), Stu Grossman and John Gilmore (releases
278 4.8, 4.7, 4.6, 4.5, 4.4), John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and
279 3.9); Jim Kingdon (releases 3.5, 3.4, 3.3); and Randy Smith (releases
280 3.2, 3.1, 3.0). As major maintainer of GDB for some period, each
281 contributed significantly to the structure, stability, and capabilities
282 of the entire debugger.
284 Richard Stallman, assisted at various times by Peter TerMaat, Chris
285 Hanson, and Richard Mlynarik, handled releases through 2.8.
288 Michael Tiemann is the author of most of the GNU C++ support in GDB,
289 with significant additional contributions from Per Bothner. James
290 Clark wrote the GNU C++ demangler. Early work on C++ was by Peter
291 TerMaat (who also did much general update work leading to release 3.0).
294 GDB 4 uses the BFD subroutine library to examine multiple
295 object-file formats; BFD was a joint project of David V.
296 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
298 David Johnson wrote the original COFF support; Pace Willison did
299 the original support for encapsulated COFF.
301 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
302 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
303 support. Jean-Daniel Fekete contributed Sun 386i support. Chris
304 Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki
305 Hasei contributed Sony/News OS 3 support. David Johnson contributed
306 Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support.
307 Keith Packard contributed NS32K support. Doug Rabson contributed
308 Acorn Risc Machine support. Chris Smith contributed Convex support
309 (and Fortran debugging). Jonathan Stone contributed Pyramid support.
310 Michael Tiemann contributed SPARC support. Tim Tucker contributed
311 support for the Gould NP1 and Gould Powernode. Pace Willison
312 contributed Intel 386 support. Jay Vosburgh contributed Symmetry
315 Rich Schaefer and Peter Schauer helped with support of SunOS shared
318 Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about
319 several machine instruction sets.
321 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped
322 develop remote debugging. Intel Corporation and Wind River Systems
323 contributed remote debugging modules for their products.
325 Brian Fox is the author of the readline libraries providing
326 command-line editing and command history.
328 Andrew Beers of SUNY Buffalo wrote the language-switching code,
330 the Modula-2 support,
332 and contributed the Languages chapter of this manual.
334 Fred Fish wrote most of the support for Unix System Vr4.
336 He also enhanced the command-completion support to cover C++ overloaded
340 Hitachi America, Ltd. sponsored the support for Hitachi microprocessors.
344 @unnumbered New Features since GDB Version 3.5
348 Using the new command @code{target}, you can select at runtime whether
349 you are debugging local files, local processes, standalone systems over
350 a serial port, or realtime systems over a TCP/IP connection. The
351 command @code{load} can download programs into a remote system. Serial
352 stubs are available for Motorola 680x0, Intel 80386, and Sparc remote
353 systems; GDB also supports debugging realtime processes running under
354 VxWorks, using SunRPC Remote Procedure Calls over TCP/IP to talk to a
355 debugger stub on the target system. Internally, GDB now uses a function
356 vector to mediate access to different targets; if you need to add your
357 own support for a remote protocol, this makes it much easier.
360 GDB now sports watchpoints as well as breakpoints. You can use a
361 watchpoint to stop execution whenever the value of an expression
362 changes, without having to predict a particular place in your program
363 where this may happen.
366 Commands that issue wide output now insert newlines at places designed
367 to make the output more readable.
369 @item Object Code Formats
370 GDB uses a new library called the Binary File Descriptor (BFD) Library
371 to permit it to switch dynamically, without reconfiguration or
372 recompilation, between different object-file formats. Formats currently
373 supported are COFF, ELF, a.out, Intel 960 b.out, MIPS ECOFF, HPPA SOM
374 (with stabs debugging), and S-records; files may be read as .o files,
375 archive libraries, or core dumps. BFD is available as a subroutine
376 library so that other programs may take advantage of it, and the other
377 GNU binary utilities are being converted to use it.
379 @item Configuration and Ports
380 Compile-time configuration (to select a particular architecture and
381 operating system) is much easier. The script @code{configure} now
382 allows you to configure GDB as either a native debugger or a
383 cross-debugger. @xref{Installing GDB}, for details on how to
387 The user interface to the GDB control variables is simpler,
388 and is consolidated in two commands, @code{set} and @code{show}. Output
389 lines are now broken at readable places, rather than overflowing onto
390 the next line. You can suppress output of machine-level addresses,
391 displaying only source language information.
394 GDB now supports C++ multiple inheritance (if used with a GCC
395 version 2 compiler), and also has limited support for C++ exception
396 handling, with the commands @code{catch} and @code{info catch}: GDB
397 can break when an exception is raised, before the stack is peeled back
398 to the exception handler's context.
402 GDB now has preliminary support for the GNU Modula-2 compiler, currently
403 under development at the State University of New York at Buffalo.
404 Coordinated development of both GDB and the GNU Modula-2 compiler will
405 continue. Other Modula-2 compilers are currently not supported, and
406 attempting to debug programs compiled with them will likely result in an
407 error as the symbol table of the executable is read in.
410 @item Command Rationalization
411 Many GDB commands have been renamed to make them easier to remember
412 and use. In particular, the subcommands of @code{info} and
413 @code{show}/@code{set} are grouped to make the former refer to the state
414 of your program, and the latter refer to the state of GDB itself.
415 @xref{Renamed Commands}, for details on what commands were renamed.
417 @item Shared Libraries
418 GDB 4 can debug programs and core files that use SunOS, SVR4, or IBM RS/6000
422 On some systems, GDB 4 has facilities to debug multi-thread programs.
425 GDB 4 has a reference card. @xref{Formatting Documentation,,Formatting
426 the Documentation}, for instructions about how to print it.
432 @chapter A Sample @value{GDBN} Session
434 You can use this manual at your leisure to read all about @value{GDBN}.
435 However, a handful of commands are enough to get started using the
436 debugger. This chapter illustrates those commands.
439 In this sample session, we emphasize user input like this: @b{input},
440 to make it easier to pick out from the surrounding output.
443 @c FIXME: this example may not be appropriate for some configs, where
444 @c FIXME...primary interest is in remote use.
446 One of the preliminary versions of GNU @code{m4} (a generic macro
447 processor) exhibits the following bug: sometimes, when we change its
448 quote strings from the default, the commands used to capture one macro
449 definition within another stop working. In the following short @code{m4}
450 session, we define a macro @code{foo} which expands to @code{0000}; we
451 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
452 same thing. However, when we change the open quote string to
453 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
454 procedure fails to define a new synonym @code{baz}:
463 @b{define(bar,defn(`foo'))}
467 @b{changequote(<QUOTE>,<UNQUOTE>)}
469 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
472 m4: End of input: 0: fatal error: EOF in string
476 Let us use @value{GDBN} to try to see what is going on.
479 $ @b{@value{GDBP} m4}
480 @c FIXME: this falsifies the exact text played out, to permit smallbook
481 @c FIXME... format to come out better.
482 GDB is free software and you are welcome to distribute copies
483 of it under certain conditions; type "show copying" to see
485 There is absolutely no warranty for GDB; type "show warranty"
487 GDB @value{GDBVN}, Copyright 1993 Free Software Foundation, Inc...
492 @value{GDBN} reads only enough symbol data to know where to find the rest when
493 needed; as a result, the first prompt comes up very quickly. We now
494 tell @value{GDBN} to use a narrower display width than usual, so that examples
495 will fit in this manual.
498 (@value{GDBP}) @b{set width 70}
502 We need to see how the @code{m4} built-in @code{changequote} works.
503 Having looked at the source, we know the relevant subroutine is
504 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
505 @code{break} command.
508 (@value{GDBP}) @b{break m4_changequote}
509 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
513 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
514 control; as long as control does not reach the @code{m4_changequote}
515 subroutine, the program runs as usual:
518 (@value{GDBP}) @b{run}
519 Starting program: /work/Editorial/gdb/gnu/m4/m4
527 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
528 suspends execution of @code{m4}, displaying information about the
529 context where it stops.
532 @b{changequote(<QUOTE>,<UNQUOTE>)}
534 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
536 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
540 Now we use the command @code{n} (@code{next}) to advance execution to
541 the next line of the current function.
545 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
550 @code{set_quotes} looks like a promising subroutine. We can go into it
551 by using the command @code{s} (@code{step}) instead of @code{next}.
552 @code{step} goes to the next line to be executed in @emph{any}
553 subroutine, so it steps into @code{set_quotes}.
557 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
559 530 if (lquote != def_lquote)
563 The display that shows the subroutine where @code{m4} is now
564 suspended (and its arguments) is called a stack frame display. It
565 shows a summary of the stack. We can use the @code{backtrace}
566 command (which can also be spelled @code{bt}), to see where we are
567 in the stack as a whole: the @code{backtrace} command displays a
568 stack frame for each active subroutine.
571 (@value{GDBP}) @b{bt}
572 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
574 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
576 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
577 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
579 #4 0x79dc in expand_input () at macro.c:40
580 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
584 We will step through a few more lines to see what happens. The first two
585 times, we can use @samp{s}; the next two times we use @code{n} to avoid
586 falling into the @code{xstrdup} subroutine.
590 0x3b5c 532 if (rquote != def_rquote)
592 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
593 def_lquote : xstrdup(lq);
595 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
598 538 len_lquote = strlen(rquote);
602 The last line displayed looks a little odd; we can examine the variables
603 @code{lquote} and @code{rquote} to see if they are in fact the new left
604 and right quotes we specified. We use the command @code{p}
605 (@code{print}) to see their values.
608 (@value{GDBP}) @b{p lquote}
609 $1 = 0x35d40 "<QUOTE>"
610 (@value{GDBP}) @b{p rquote}
611 $2 = 0x35d50 "<UNQUOTE>"
615 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
616 To look at some context, we can display ten lines of source
617 surrounding the current line with the @code{l} (@code{list}) command.
623 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
625 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
628 538 len_lquote = strlen(rquote);
629 539 len_rquote = strlen(lquote);
636 Let us step past the two lines that set @code{len_lquote} and
637 @code{len_rquote}, and then examine the values of those variables.
641 539 len_rquote = strlen(lquote);
644 (@value{GDBP}) @b{p len_lquote}
646 (@value{GDBP}) @b{p len_rquote}
651 That certainly looks wrong, assuming @code{len_lquote} and
652 @code{len_rquote} are meant to be the lengths of @code{lquote} and
653 @code{rquote} respectively. We can set them to better values using
654 the @code{p} command, since it can print the value of
655 any expression---and that expression can include subroutine calls and
659 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
661 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
666 Is that enough to fix the problem of using the new quotes with the
667 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
668 executing with the @code{c} (@code{continue}) command, and then try the
669 example that caused trouble initially:
675 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
682 Success! The new quotes now work just as well as the default ones. The
683 problem seems to have been just the two typos defining the wrong
684 lengths. We allow @code{m4} exit by giving it an EOF as input:
688 Program exited normally.
692 The message @samp{Program exited normally.} is from @value{GDBN}; it
693 indicates @code{m4} has finished executing. We can end our @value{GDBN}
694 session with the @value{GDBN} @code{quit} command.
697 (@value{GDBP}) @b{quit}
702 @chapter Getting In and Out of @value{GDBN}
704 This chapter discusses how to start @value{GDBN}, and how to get out of it.
705 (The essentials: type @samp{@value{GDBP}} to start GDB, and type @kbd{quit}
706 or @kbd{C-d} to exit.)
709 * Invoking GDB:: How to start @value{GDBN}
710 * Quitting GDB:: How to quit @value{GDBN}
711 * Shell Commands:: How to use shell commands inside @value{GDBN}
715 @section Invoking @value{GDBN}
718 For details on starting up @value{GDBP} as a
719 remote debugger attached to a Hitachi microprocessor, see @ref{Hitachi
720 Remote,,@value{GDBN} and Hitachi Microprocessors}.
723 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
724 @value{GDBN} reads commands from the terminal until you tell it to exit.
726 You can also run @code{@value{GDBP}} with a variety of arguments and options,
727 to specify more of your debugging environment at the outset.
730 The command-line options described here are designed
731 to cover a variety of situations; in some environments, some of these
732 options may effectively be unavailable.
735 The most usual way to start @value{GDBN} is with one argument,
736 specifying an executable program:
739 @value{GDBP} @var{program}
744 You can also start with both an executable program and a core file
748 @value{GDBP} @var{program} @var{core}
751 You can, instead, specify a process ID as a second argument, if you want
752 to debug a running process:
755 @value{GDBP} @var{program} 1234
759 would attach @value{GDBN} to process @code{1234} (unless you also have a file
760 named @file{1234}; @value{GDBN} does check for a core file first).
762 Taking advantage of the second command-line argument requires a fairly
763 complete operating system; when you use @value{GDBN} as a remote debugger
764 attached to a bare board, there may not be any notion of ``process'',
765 and there is often no way to get a core dump.
769 You can further control how @value{GDBN} starts up by using command-line
770 options. @value{GDBN} itself can remind you of the options available.
780 to display all available options and briefly describe their use
781 (@samp{@value{GDBP} -h} is a shorter equivalent).
783 All options and command line arguments you give are processed
784 in sequential order. The order makes a difference when the
785 @samp{-x} option is used.
791 * Remote Serial:: @value{GDBN} remote serial protocol
794 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
797 * UDI29K Remote:: The UDI protocol for AMD29K
798 * EB29K Remote:: The EBMON protocol for AMD29K
801 * VxWorks Remote:: @value{GDBN} and VxWorks
804 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
807 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
810 * MIPS Remote:: @value{GDBN} and MIPS boards
813 * Simulator:: Simulated CPU target
816 @c remnant makeinfo bug requires this blank line after *two* end-ifblahs:
818 * File Options:: Choosing files
819 * Mode Options:: Choosing modes
827 @subsection Choosing files
830 When @value{GDBN} starts, it reads any arguments other than options as
831 specifying an executable file and core file (or process ID). This is
832 the same as if the arguments were specified by the @samp{-se} and
833 @samp{-c} options respectively. (@value{GDBN} reads the first argument
834 that does not have an associated option flag as equivalent to the
835 @samp{-se} option followed by that argument; and the second argument
836 that does not have an associated option flag, if any, as equivalent to
837 the @samp{-c} option followed by that argument.)
840 When @value{GDBN} starts, it reads any argument other than options as
841 specifying an executable file. This is the same as if the argument was
842 specified by the @samp{-se} option.
845 Many options have both long and short forms; both are shown in the
846 following list. @value{GDBN} also recognizes the long forms if you truncate
847 them, so long as enough of the option is present to be unambiguous.
848 (If you prefer, you can flag option arguments with @samp{--} rather
849 than @samp{-}, though we illustrate the more usual convention.)
852 @item -symbols @var{file}
854 Read symbol table from file @var{file}.
856 @item -exec @var{file}
858 Use file @var{file} as the executable file to execute when
863 appropriate, and for examining pure data in conjunction with a core
868 Read symbol table from file @var{file} and use it as the executable
872 @item -core @var{file}
874 Use file @var{file} as a core dump to examine.
876 @item -c @var{number}
877 Connect to process ID @var{number}, as with the @code{attach} command
878 (unless there is a file in core-dump format named @var{number}, in which
879 case @samp{-c} specifies that file as a core dump to read).
882 @item -command @var{file}
884 Execute @value{GDBN} commands from file @var{file}. @xref{Command
885 Files,, Command files}.
887 @item -directory @var{directory}
888 @itemx -d @var{directory}
889 Add @var{directory} to the path to search for source files.
894 @emph{Warning: this option depends on operating system facilities that are not
895 supported on all systems.}@*
896 If memory-mapped files are available on your system through the @code{mmap}
897 system call, you can use this option
898 to have @value{GDBN} write the symbols from your
899 program into a reusable file in the current directory. If the program you are debugging is
900 called @file{/tmp/fred}, the mapped symbol file will be @file{./fred.syms}.
901 Future @value{GDBN} debugging sessions will notice the presence of this file,
902 and will quickly map in symbol information from it, rather than reading
903 the symbol table from the executable program.
905 @c FIXME! Really host, not target?
906 The @file{.syms} file is specific to the host machine where @value{GDBN}
907 is run. It holds an exact image of the internal @value{GDBN} symbol
908 table. It cannot be shared across multiple host platforms.
913 Read each symbol file's entire symbol table immediately, rather than
914 the default, which is to read it incrementally as it is needed.
915 This makes startup slower, but makes future operations faster.
919 The @code{-mapped} and @code{-readnow} options are typically combined in
920 order to build a @file{.syms} file that contains complete symbol
921 information. (@xref{Files,,Commands to specify files}, for information
922 on @file{.syms} files.) A simple GDB invocation to do nothing but build
923 a @file{.syms} file for future use is:
926 gdb -batch -nx -mapped -readnow programname
931 @subsection Choosing modes
933 You can run @value{GDBN} in various alternative modes---for example, in
934 batch mode or quiet mode.
939 Do not execute commands from any initialization files (normally called
940 @file{@value{GDBINIT}}). Normally, the commands in these files are
941 executed after all the command options and arguments have been
942 processed. @xref{Command Files,,Command files}.
946 ``Quiet''. Do not print the introductory and copyright messages. These
947 messages are also suppressed in batch mode.
950 Run in batch mode. Exit with status @code{0} after processing all the
951 command files specified with @samp{-x} (and all commands from
952 initialization files, if not inhibited with @samp{-n}). Exit with
953 nonzero status if an error occurs in executing the @value{GDBN} commands
954 in the command files.
956 Batch mode may be useful for running @value{GDBN} as a filter, for example to
957 download and run a program on another computer; in order to make this
958 more useful, the message
961 Program exited normally.
965 (which is ordinarily issued whenever a program running under @value{GDBN} control
966 terminates) is not issued when running in batch mode.
968 @item -cd @var{directory}
969 Run @value{GDBN} using @var{directory} as its working directory,
970 instead of the current directory.
973 @item -context @var{authentication}
974 When the Energize programming system starts up @value{GDBN}, it uses this
975 option to trigger an alternate mode of interaction.
976 @var{authentication} is a pair of numeric codes that identify @value{GDBN}
977 as a client in the Energize environment. Avoid this option when you run
978 @value{GDBN} directly from the command line. See @ref{Energize,,Using
979 @value{GDBN} with Energize} for more discussion of using @value{GDBN} with Energize.
985 Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN}
986 to output the full file name and line number in a standard,
987 recognizable fashion each time a stack frame is displayed (which
988 includes each time your program stops). This recognizable format looks
989 like two @samp{\032} characters, followed by the file name, line number
990 and character position separated by colons, and a newline. The
991 Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as
992 a signal to display the source code for the frame.
997 Set the line speed (baud rate or bits per second) of any serial
998 interface used by @value{GDBN} for remote debugging.
1000 @item -tty @var{device}
1001 Run using @var{device} for your program's standard input and output.
1002 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1007 @section Quitting @value{GDBN}
1008 @cindex exiting @value{GDBN}
1009 @cindex leaving @value{GDBN}
1015 To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or type
1016 an end-of-file character (usually @kbd{C-d}).
1020 An interrupt (often @kbd{C-c}) will not exit from @value{GDBN}, but rather
1021 will terminate the action of any @value{GDBN} command that is in progress and
1022 return to @value{GDBN} command level. It is safe to type the interrupt
1023 character at any time because @value{GDBN} does not allow it to take effect
1024 until a time when it is safe.
1027 If you have been using @value{GDBN} to control an attached process or
1028 device, you can release it with the @code{detach} command
1029 (@pxref{Attach, ,Debugging an already-running process}).
1032 @node Shell Commands
1033 @section Shell commands
1035 If you need to execute occasional shell commands during your
1036 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1037 just use the @code{shell} command.
1040 @item shell @var{command string}
1042 @cindex shell escape
1043 Invoke a the standard shell to execute @var{command string}.
1045 If it exists, the environment variable @code{SHELL} determines which
1046 shell to run. Otherwise @value{GDBN} uses @code{/bin/sh}.
1050 The utility @code{make} is often needed in development environments.
1051 You do not have to use the @code{shell} command for this purpose in
1055 @item make @var{make-args}
1057 @cindex calling make
1058 Execute the @code{make} program with the specified
1059 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1063 @chapter @value{GDBN} Commands
1065 You can abbreviate a @value{GDBN} command to the first few letters of the command
1066 name, if that abbreviation is unambiguous; and you can repeat certain
1067 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1068 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1069 show you the alternatives available, if there is more than one possibility).
1072 * Command Syntax:: How to give commands to @value{GDBN}
1073 * Completion:: Command completion
1074 * Help:: How to ask @value{GDBN} for help
1077 @node Command Syntax
1078 @section Command syntax
1080 A @value{GDBN} command is a single line of input. There is no limit on
1081 how long it can be. It starts with a command name, which is followed by
1082 arguments whose meaning depends on the command name. For example, the
1083 command @code{step} accepts an argument which is the number of times to
1084 step, as in @samp{step 5}. You can also use the @code{step} command
1085 with no arguments. Some command names do not allow any arguments.
1087 @cindex abbreviation
1088 @value{GDBN} command names may always be truncated if that abbreviation is
1089 unambiguous. Other possible command abbreviations are listed in the
1090 documentation for individual commands. In some cases, even ambiguous
1091 abbreviations are allowed; for example, @code{s} is specially defined as
1092 equivalent to @code{step} even though there are other commands whose
1093 names start with @code{s}. You can test abbreviations by using them as
1094 arguments to the @code{help} command.
1096 @cindex repeating commands
1098 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1099 repeat the previous command. Certain commands (for example, @code{run})
1100 will not repeat this way; these are commands for which unintentional
1101 repetition might cause trouble and which you are unlikely to want to
1104 The @code{list} and @code{x} commands, when you repeat them with
1105 @key{RET}, construct new arguments rather than repeating
1106 exactly as typed. This permits easy scanning of source or memory.
1108 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1109 output, in a way similar to the common utility @code{more}
1110 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1111 @key{RET} too many in this situation, @value{GDBN} disables command
1112 repetition after any command that generates this sort of display.
1116 Any text from a @kbd{#} to the end of the line is a comment; it does
1117 nothing. This is useful mainly in command files (@pxref{Command
1118 Files,,Command files}).
1121 @section Command completion
1124 @cindex word completion
1125 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1126 only one possibility; it can also show you what the valid possibilities
1127 are for the next word in a command, at any time. This works for @value{GDBN}
1128 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1130 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1131 of a word. If there is only one possibility, @value{GDBN} will fill in the
1132 word, and wait for you to finish the command (or press @key{RET} to
1133 enter it). For example, if you type
1135 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1136 @c complete accuracy in these examples; space introduced for clarity.
1137 @c If texinfo enhancements make it unnecessary, it would be nice to
1138 @c replace " @key" by "@key" in the following...
1140 (@value{GDBP}) info bre @key{TAB}
1144 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1145 the only @code{info} subcommand beginning with @samp{bre}:
1148 (@value{GDBP}) info breakpoints
1152 You can either press @key{RET} at this point, to run the @code{info
1153 breakpoints} command, or backspace and enter something else, if
1154 @samp{breakpoints} does not look like the command you expected. (If you
1155 were sure you wanted @code{info breakpoints} in the first place, you
1156 might as well just type @key{RET} immediately after @samp{info bre},
1157 to exploit command abbreviations rather than command completion).
1159 If there is more than one possibility for the next word when you press
1160 @key{TAB}, @value{GDBN} will sound a bell. You can either supply more
1161 characters and try again, or just press @key{TAB} a second time, and
1162 @value{GDBN} will display all the possible completions for that word. For
1163 example, you might want to set a breakpoint on a subroutine whose name
1164 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1165 just sounds the bell. Typing @key{TAB} again will display all the
1166 function names in your program that begin with those characters, for
1170 (@value{GDBP}) b make_ @key{TAB}
1171 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1172 make_a_section_from_file make_environ
1173 make_abs_section make_function_type
1174 make_blockvector make_pointer_type
1175 make_cleanup make_reference_type
1176 make_command make_symbol_completion_list
1177 (@value{GDBP}) b make_
1181 After displaying the available possibilities, @value{GDBN} copies your
1182 partial input (@samp{b make_} in the example) so you can finish the
1185 If you just want to see the list of alternatives in the first place, you
1186 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1187 means @kbd{@key{META} ?}. You can type this
1189 either by holding down a
1190 key designated as the @key{META} shift on your keyboard (if there is
1191 one) while typing @kbd{?}, or
1193 as @key{ESC} followed by @kbd{?}.
1195 @cindex quotes in commands
1196 @cindex completion of quoted strings
1197 Sometimes the string you need, while logically a ``word'', may contain
1198 parentheses or other characters that @value{GDBN} normally excludes from its
1199 notion of a word. To permit word completion to work in this situation,
1200 you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands.
1203 The most likely situation where you might need this is in typing the
1204 name of a C++ function. This is because C++ allows function overloading
1205 (multiple definitions of the same function, distinguished by argument
1206 type). For example, when you want to set a breakpoint you may need to
1207 distinguish whether you mean the version of @code{name} that takes an
1208 @code{int} parameter, @code{name(int)}, or the version that takes a
1209 @code{float} parameter, @code{name(float)}. To use the word-completion
1210 facilities in this situation, type a single quote @code{'} at the
1211 beginning of the function name. This alerts @value{GDBN} that it may need to
1212 consider more information than usual when you press @key{TAB} or
1213 @kbd{M-?} to request word completion:
1216 (@value{GDBP}) b 'bubble( @key{M-?}
1217 bubble(double,double) bubble(int,int)
1218 (@value{GDBP}) b 'bubble(
1221 In some cases, @value{GDBN} can tell that completing a name will require
1222 quotes. When this happens, @value{GDBN} will insert the quote for you (while
1223 completing as much as it can) if you do not type the quote in the first
1227 (@value{GDBP}) b bub @key{TAB}
1228 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1229 (@value{GDBP}) b 'bubble(
1233 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1234 you have not yet started typing the argument list when you ask for
1235 completion on an overloaded symbol.
1240 @section Getting help
1241 @cindex online documentation
1244 You can always ask @value{GDBN} itself for information on its commands, using the
1245 command @code{help}.
1251 You can use @code{help} (abbreviated @code{h}) with no arguments to
1252 display a short list of named classes of commands:
1256 List of classes of commands:
1258 running -- Running the program
1259 stack -- Examining the stack
1260 data -- Examining data
1261 breakpoints -- Making program stop at certain points
1262 files -- Specifying and examining files
1263 status -- Status inquiries
1264 support -- Support facilities
1265 user-defined -- User-defined commands
1266 aliases -- Aliases of other commands
1267 obscure -- Obscure features
1269 Type "help" followed by a class name for a list of
1270 commands in that class.
1271 Type "help" followed by command name for full
1273 Command name abbreviations are allowed if unambiguous.
1277 @item help @var{class}
1278 Using one of the general help classes as an argument, you can get a
1279 list of the individual commands in that class. For example, here is the
1280 help display for the class @code{status}:
1283 (@value{GDBP}) help status
1288 @c Line break in "show" line falsifies real output, but needed
1289 @c to fit in smallbook page size.
1290 show -- Generic command for showing things set
1292 info -- Generic command for printing status
1294 Type "help" followed by command name for full
1296 Command name abbreviations are allowed if unambiguous.
1300 @item help @var{command}
1301 With a command name as @code{help} argument, @value{GDBN} will display a
1302 short paragraph on how to use that command.
1305 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1306 and @code{show} to inquire about the state of your program, or the state
1307 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1308 manual introduces each of them in the appropriate context. The listings
1309 under @code{info} and under @code{show} in the Index point to
1310 all the sub-commands. @xref{Index}.
1317 This command (abbreviated @code{i}) is for describing the state of your
1318 program. For example, you can list the arguments given to your program
1319 with @code{info args}, list the registers currently in use with @code{info
1320 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1321 You can get a complete list of the @code{info} sub-commands with
1322 @w{@code{help info}}.
1326 In contrast, @code{show} is for describing the state of @value{GDBN} itself.
1327 You can change most of the things you can @code{show}, by using the
1328 related command @code{set}; for example, you can control what number
1329 system is used for displays with @code{set radix}, or simply inquire
1330 which is currently in use with @code{show radix}.
1333 To display all the settable parameters and their current
1334 values, you can use @code{show} with no arguments; you may also use
1335 @code{info set}. Both commands produce the same display.
1336 @c FIXME: "info set" violates the rule that "info" is for state of
1337 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1338 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1342 Here are three miscellaneous @code{show} subcommands, all of which are
1343 exceptional in lacking corresponding @code{set} commands:
1346 @kindex show version
1347 @cindex version number
1349 Show what version of @value{GDBN} is running. You should include this
1350 information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in
1351 use at your site, you may occasionally want to determine which version
1352 of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced,
1353 and old ones may wither away. The version number is also announced
1354 when you start @value{GDBN}.
1356 @kindex show copying
1358 Display information about permission for copying @value{GDBN}.
1360 @kindex show warranty
1362 Display the GNU ``NO WARRANTY'' statement.
1366 @chapter Running Programs Under @value{GDBN}
1368 When you run a program under @value{GDBN}, you must first generate
1369 debugging information when you compile it.
1371 You may start it with its arguments, if any, in an environment of your
1372 choice. You may redirect your program's input and output, debug an
1373 already running process, or kill a child process.
1377 * Compilation:: Compiling for debugging
1378 * Starting:: Starting your program
1380 * Arguments:: Your program's arguments
1381 * Environment:: Your program's environment
1382 * Working Directory:: Your program's working directory
1383 * Input/Output:: Your program's input and output
1384 * Attach:: Debugging an already-running process
1385 * Kill Process:: Killing the child process
1386 * Process Information:: Additional process information
1387 * Threads:: Debugging programs with multiple threads
1392 @section Compiling for debugging
1394 In order to debug a program effectively, you need to generate
1395 debugging information when you compile it. This debugging information
1396 is stored in the object file; it describes the data type of each
1397 variable or function and the correspondence between source line numbers
1398 and addresses in the executable code.
1400 To request debugging information, specify the @samp{-g} option when you run
1403 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1404 options together. Using those compilers, you cannot generate optimized
1405 executables containing debugging information.
1407 @value{NGCC}, the GNU C compiler, supports @samp{-g} with or without
1408 @samp{-O}, making it possible to debug optimized code. We recommend
1409 that you @emph{always} use @samp{-g} whenever you compile a program.
1410 You may think your program is correct, but there is no sense in pushing
1413 @cindex optimized code, debugging
1414 @cindex debugging optimized code
1415 When you debug a program compiled with @samp{-g -O}, remember that the
1416 optimizer is rearranging your code; the debugger will show you what is
1417 really there. Do not be too surprised when the execution path does not
1418 exactly match your source file! An extreme example: if you define a
1419 variable, but never use it, @value{GDBN} will never see that
1420 variable---because the compiler optimizes it out of existence.
1422 Some things do not work as well with @samp{-g -O} as with just
1423 @samp{-g}, particularly on machines with instruction scheduling. If in
1424 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1425 please report it as a bug (including a test case!).
1427 Older versions of the GNU C compiler permitted a variant option
1428 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1429 format; if your GNU C compiler has this option, do not use it.
1433 @section Starting your program
1441 Use the @code{run} command to start your program under @value{GDBN}. You must
1442 first specify the program name
1446 with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and
1447 Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file}
1448 command (@pxref{Files, ,Commands to specify files}).
1453 If you are running your program in an execution environment that
1454 supports processes, @code{run} creates an inferior process and makes
1455 that process run your program. (In environments without processes,
1456 @code{run} jumps to the start of your program.)
1458 The execution of a program is affected by certain information it
1459 receives from its superior. @value{GDBN} provides ways to specify this
1460 information, which you must do @emph{before} starting your program. (You
1461 can change it after starting your program, but such changes will only affect
1462 your program the next time you start it.) This information may be
1463 divided into four categories:
1466 @item The @emph{arguments.}
1467 Specify the arguments to give your program as the arguments of the
1468 @code{run} command. If a shell is available on your target, the shell
1469 is used to pass the arguments, so that you may use normal conventions
1470 (such as wildcard expansion or variable substitution) in describing
1471 the arguments. In Unix systems, you can control which shell is used
1472 with the @code{SHELL} environment variable. @xref{Arguments, ,Your
1473 program's arguments}.
1475 @item The @emph{environment.}
1476 Your program normally inherits its environment from @value{GDBN}, but you can
1477 use the @value{GDBN} commands @code{set environment} and @code{unset
1478 environment} to change parts of the environment that will be given to
1479 your program. @xref{Environment, ,Your program's environment}.
1481 @item The @emph{working directory.}
1482 Your program inherits its working directory from @value{GDBN}. You can set
1483 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1484 @xref{Working Directory, ,Your program's working directory}.
1486 @item The @emph{standard input and output.}
1487 Your program normally uses the same device for standard input and
1488 standard output as @value{GDBN} is using. You can redirect input and output
1489 in the @code{run} command line, or you can use the @code{tty} command to
1490 set a different device for your program.
1491 @xref{Input/Output, ,Your program's input and output}.
1494 @emph{Warning:} While input and output redirection work, you cannot use
1495 pipes to pass the output of the program you are debugging to another
1496 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1501 When you issue the @code{run} command, your program begins to execute
1502 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1503 of how to arrange for your program to stop. Once your program has
1504 stopped, you may call functions in your program, using the @code{print}
1505 or @code{call} commands. @xref{Data, ,Examining Data}.
1507 If the modification time of your symbol file has changed since the
1508 last time @value{GDBN} read its symbols, @value{GDBN} will discard its symbol table and
1509 re-read it. When it does this, @value{GDBN} tries to retain your current
1514 @section Your program's arguments
1516 @cindex arguments (to your program)
1517 The arguments to your program can be specified by the arguments of the
1518 @code{run} command. They are passed to a shell, which expands wildcard
1519 characters and performs redirection of I/O, and thence to your program.
1520 Your @code{SHELL} environment variable (if it exists) specifies what
1521 shell @value{GDBN} if you do not define @code{SHELL}, @value{GDBN} uses
1524 @code{run} with no arguments uses the same arguments used by the previous
1525 @code{run}, or those set by the @code{set args} command.
1530 Specify the arguments to be used the next time your program is run. If
1531 @code{set args} has no arguments, @code{run} will execute your program
1532 with no arguments. Once you have run your program with arguments,
1533 using @code{set args} before the next @code{run} is the only way to run
1534 it again without arguments.
1538 Show the arguments to give your program when it is started.
1542 @section Your program's environment
1544 @cindex environment (of your program)
1545 The @dfn{environment} consists of a set of environment variables and
1546 their values. Environment variables conventionally record such things as
1547 your user name, your home directory, your terminal type, and your search
1548 path for programs to run. Usually you set up environment variables with
1549 the shell and they are inherited by all the other programs you run. When
1550 debugging, it can be useful to try running your program with a modified
1551 environment without having to start @value{GDBN} over again.
1554 @item path @var{directory}
1556 Add @var{directory} to the front of the @code{PATH} environment variable
1557 (the search path for executables), for both @value{GDBN} and your program.
1558 You may specify several directory names, separated by @samp{:} or
1559 whitespace. If @var{directory} is already in the path, it is moved to
1560 the front, so it will be searched sooner.
1562 You can use the string @samp{$cwd} to refer to whatever is the current
1563 working directory at the time @value{GDBN} searches the path. If you
1564 use @samp{.} instead, it refers to the directory where you executed the
1565 @code{path} command. @value{GDBN} replaces @samp{.} in the
1566 @var{directory} argument (with the current path) before adding
1567 @var{directory} to the search path.
1568 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1569 @c document that, since repeating it would be a no-op.
1573 Display the list of search paths for executables (the @code{PATH}
1574 environment variable).
1576 @item show environment @r{[}@var{varname}@r{]}
1577 @kindex show environment
1578 Print the value of environment variable @var{varname} to be given to
1579 your program when it starts. If you do not supply @var{varname},
1580 print the names and values of all environment variables to be given to
1581 your program. You can abbreviate @code{environment} as @code{env}.
1583 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1584 @kindex set environment
1585 Set environment variable @var{varname} to @var{value}. The value
1586 changes for your program only, not for @value{GDBN} itself. @var{value} may
1587 be any string; the values of environment variables are just strings, and
1588 any interpretation is supplied by your program itself. The @var{value}
1589 parameter is optional; if it is eliminated, the variable is set to a
1591 @c "any string" here does not include leading, trailing
1592 @c blanks. Gnu asks: does anyone care?
1594 For example, this command:
1601 tells a Unix program, when subsequently run, that its user is named
1602 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1603 are not actually required.)
1605 @item unset environment @var{varname}
1606 @kindex unset environment
1607 Remove variable @var{varname} from the environment to be passed to your
1608 program. This is different from @samp{set env @var{varname} =};
1609 @code{unset environment} removes the variable from the environment,
1610 rather than assigning it an empty value.
1613 @emph{Warning:} @value{GDBN} runs your program using the shell indicated
1614 by your @code{SHELL} environment variable if it exists (or
1615 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1616 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1617 @file{.bashrc} for BASH---any variables you set in that file will affect
1618 your program. You may wish to move setting of environment variables to
1619 files that are only run when you sign on, such as @file{.login} or
1622 @node Working Directory
1623 @section Your program's working directory
1625 @cindex working directory (of your program)
1626 Each time you start your program with @code{run}, it inherits its
1627 working directory from the current working directory of @value{GDBN}.
1628 The @value{GDBN} working directory is initially whatever it inherited
1629 from its parent process (typically the shell), but you can specify a new
1630 working directory in @value{GDBN} with the @code{cd} command.
1632 The @value{GDBN} working directory also serves as a default for the commands
1633 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1637 @item cd @var{directory}
1639 Set the @value{GDBN} working directory to @var{directory}.
1643 Print the @value{GDBN} working directory.
1647 @section Your program's input and output
1652 By default, the program you run under @value{GDBN} does input and output to
1653 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal to
1654 its own terminal modes to interact with you, but it records the terminal
1655 modes your program was using and switches back to them when you continue
1656 running your program.
1660 @kindex info terminal
1661 Displays information recorded by @value{GDBN} about the terminal modes your
1665 You can redirect your program's input and/or output using shell
1666 redirection with the @code{run} command. For example,
1673 starts your program, diverting its output to the file @file{outfile}.
1676 @cindex controlling terminal
1677 Another way to specify where your program should do input and output is
1678 with the @code{tty} command. This command accepts a file name as
1679 argument, and causes this file to be the default for future @code{run}
1680 commands. It also resets the controlling terminal for the child
1681 process, for future @code{run} commands. For example,
1688 directs that processes started with subsequent @code{run} commands
1689 default to do input and output on the terminal @file{/dev/ttyb} and have
1690 that as their controlling terminal.
1692 An explicit redirection in @code{run} overrides the @code{tty} command's
1693 effect on the input/output device, but not its effect on the controlling
1696 When you use the @code{tty} command or redirect input in the @code{run}
1697 command, only the input @emph{for your program} is affected. The input
1698 for @value{GDBN} still comes from your terminal.
1701 @section Debugging an already-running process
1706 @item attach @var{process-id}
1707 This command attaches to a running process---one that was started
1708 outside @value{GDBN}. (@code{info files} will show your active
1709 targets.) The command takes as argument a process ID. The usual way to
1710 find out the process-id of a Unix process is with the @code{ps} utility,
1711 or with the @samp{jobs -l} shell command.
1713 @code{attach} will not repeat if you press @key{RET} a second time after
1714 executing the command.
1717 To use @code{attach}, your program must be running in an environment
1718 which supports processes; for example, @code{attach} does not work for
1719 programs on bare-board targets that lack an operating system. You must
1720 also have permission to send the process a signal.
1722 When using @code{attach}, you should first use the @code{file} command
1723 to specify the program running in the process and load its symbol table.
1724 @xref{Files, ,Commands to Specify Files}.
1726 The first thing @value{GDBN} does after arranging to debug the specified
1727 process is to stop it. You can examine and modify an attached process
1728 with all the @value{GDBN} commands that are ordinarily available when you start
1729 processes with @code{run}. You can insert breakpoints; you can step and
1730 continue; you can modify storage. If you would rather the process
1731 continue running, you may use the @code{continue} command after
1732 attaching @value{GDBN} to the process.
1737 When you have finished debugging the attached process, you can use the
1738 @code{detach} command to release it from @value{GDBN} control. Detaching
1739 the process continues its execution. After the @code{detach} command,
1740 that process and @value{GDBN} become completely independent once more, and you
1741 are ready to @code{attach} another process or start one with @code{run}.
1742 @code{detach} will not repeat if you press @key{RET} again after
1743 executing the command.
1746 If you exit @value{GDBN} or use the @code{run} command while you have an attached
1747 process, you kill that process. By default, you will be asked for
1748 confirmation if you try to do either of these things; you can control
1749 whether or not you need to confirm by using the @code{set confirm} command
1750 (@pxref{Messages/Warnings, ,Optional warnings and messages}).
1754 @section Killing the child process
1759 Kill the child process in which your program is running under @value{GDBN}.
1762 This command is useful if you wish to debug a core dump instead of a
1763 running process. @value{GDBN} ignores any core dump file while your program
1767 On some operating systems, a program cannot be executed outside @value{GDBN}
1768 while you have breakpoints set on it inside @value{GDBN}. You can use the
1769 @code{kill} command in this situation to permit running your program
1770 outside the debugger.
1772 The @code{kill} command is also useful if you wish to recompile and
1773 relink your program, since on many systems it is impossible to modify an
1774 executable file while it is running in a process. In this case, when you
1775 next type @code{run}, @value{GDBN} will notice that the file has changed, and
1776 will re-read the symbol table (while trying to preserve your current
1777 breakpoint settings).
1779 @node Process Information
1780 @section Additional process information
1783 @cindex process image
1784 Some operating systems provide a facility called @samp{/proc} that can
1785 be used to examine the image of a running process using file-system
1786 subroutines. If @value{GDBN} is configured for an operating system with this
1787 facility, the command @code{info proc} is available to report on several
1788 kinds of information about the process running your program.
1793 Summarize available information about the process.
1795 @item info proc mappings
1796 @kindex info proc mappings
1797 Report on the address ranges accessible in the program, with information
1798 on whether your program may read, write, or execute each range.
1800 @item info proc times
1801 @kindex info proc times
1802 Starting time, user CPU time, and system CPU time for your program and
1806 @kindex info proc id
1807 Report on the process IDs related to your program: its own process ID,
1808 the ID of its parent, the process group ID, and the session ID.
1810 @item info proc status
1811 @kindex info proc status
1812 General information on the state of the process. If the process is
1813 stopped, this report includes the reason for stopping, and any signal
1817 Show all the above information about the process.
1821 @section Debugging programs with multiple threads
1823 @cindex threads of execution
1824 @cindex multiple threads
1825 @cindex switching threads
1826 In some operating systems, a single program may have more than one
1827 @dfn{thread} of execution. The precise semantics of threads differ from
1828 one operating system to another, but in general the threads of a single
1829 program are akin to multiple processes---except that they share one
1830 address space (that is, they can all examine and modify the same
1831 variables). On the other hand, each thread has its own registers and
1832 execution stack, and perhaps private memory.
1834 @value{GDBN} provides these facilities for debugging multi-thread
1838 @item automatic notification of new threads
1839 @item @samp{thread @var{threadno}}, a command to switch among threads
1840 @item @samp{info threads}, a command to inquire about existing threads
1841 @item thread-specific breakpoints
1845 @emph{Warning:} These facilities are not yet available on every
1846 @value{GDBN} configuration where the operating system supports threads.
1847 If your @value{GDBN} does not support threads, these commands have no
1848 effect. For example, a system without thread support shows no output
1849 from @samp{info threads}, and always rejects the @code{thread} command,
1853 (@value{GDBP}) info threads
1854 (@value{GDBP}) thread 1
1855 Thread ID 1 not known. Use the "info threads" command to
1856 see the IDs of currently known threads.
1858 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1859 @c doesn't support threads"?
1862 @cindex focus of debugging
1863 @cindex current thread
1864 The @value{GDBN} thread debugging facility allows you to observe all
1865 threads while your program runs---but whenever @value{GDBN} takes
1866 control, one thread in particular is always the focus of debugging.
1867 This thread is called the @dfn{current thread}. Debugging commands show
1868 program information from the perspective of the current thread.
1870 @kindex New @var{systag}
1871 @cindex thread identifier (system)
1872 @c FIXME-implementors!! It would be more helpful if the [New...] message
1873 @c included GDB's numeric thread handle, so you could just go to that
1874 @c thread without first checking `info threads'.
1875 Whenever @value{GDBN} detects a new thread in your program, it displays
1876 the target system's identification for the thread with a message in the
1877 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1878 whose form varies depending on the particular system. For example, on
1879 LynxOS, you might see
1882 [New process 35 thread 27]
1886 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
1887 the @var{systag} is simply something like @samp{process 368}, with no
1890 @c FIXME!! (1) Does the [New...] message appear even for the very first
1891 @c thread of a program, or does it only appear for the
1892 @c second---i.e., when it becomes obvious we have a multithread
1894 @c (2) *Is* there necessarily a first thread always? Or do some
1895 @c multithread systems permit starting a program with multiple
1896 @c threads ab initio?
1898 @cindex thread number
1899 @cindex thread identifier (GDB)
1900 For debugging purposes, @value{GDBN} associates its own thread
1901 number---always a single integer---with each thread in your program.
1905 @kindex info threads
1906 Display a summary of all threads currently in your
1907 program. @value{GDBN} displays for each thread (in this order):
1910 @item the thread number assigned by @value{GDBN}
1912 @item the target system's thread identifier (@var{systag})
1914 @item the current stack frame summary for that thread
1918 An asterisk @samp{*} to the left of the @value{GDBN} thread number
1919 indicates the current thread.
1923 @c end table here to get a little more width for example
1926 (@value{GDBP}) info threads
1927 3 process 35 thread 27 0x34e5 in sigpause ()
1928 2 process 35 thread 23 0x34e5 in sigpause ()
1929 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
1934 @item thread @var{threadno}
1935 @kindex thread @var{threadno}
1936 Make thread number @var{threadno} the current thread. The command
1937 argument @var{threadno} is the internal @value{GDBN} thread number, as
1938 shown in the first field of the @samp{info threads} display.
1939 @value{GDBN} responds by displaying the system identifier of the thread
1940 you selected, and its current stack frame summary:
1943 @c FIXME!! This example made up; find a GDB w/threads and get real one
1944 (@value{GDBP}) thread 2
1945 [Switching to process 35 thread 23]
1946 0x34e5 in sigpause ()
1950 As with the @samp{[New @dots{}]} message, the form of the text after
1951 @samp{Switching to} depends on your system's conventions for identifying
1955 @cindex automatic thread selection
1956 @cindex switching threads automatically
1957 @cindex threads, automatic switching
1958 Whenever @value{GDBN} stops your program, due to a breakpoint or a
1959 signal, it automatically selects the thread where that breakpoint or
1960 signal happened. @value{GDBN} alerts you to the context switch with a
1961 message of the form @samp{[Switching to @var{systag}]} to identify the
1964 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
1965 more information about how @value{GDBN} behaves when you stop and start
1966 programs with multiple threads.
1968 @xref{Set Watchpoints,,Setting watchpoints}, for information about
1969 watchpoints in programs with multiple threads.
1973 @chapter Stopping and Continuing
1975 The principal purposes of using a debugger are so that you can stop your
1976 program before it terminates; or so that, if your program runs into
1977 trouble, you can investigate and find out why.
1979 Inside @value{GDBN}, your program may stop for any of several reasons, such
1984 a breakpoint, or reaching a new line after a @value{GDBN}
1985 command such as @code{step}. You may then examine and change
1986 variables, set new breakpoints or remove old ones, and then continue
1987 execution. Usually, the messages shown by @value{GDBN} provide ample
1988 explanation of the status of your program---but you can also explicitly
1989 request this information at any time.
1993 @kindex info program
1994 Display information about the status of your program: whether it is
2004 * Breakpoints:: Breakpoints, watchpoints, and exceptions
2007 * Breakpoints:: Breakpoints and watchpoints
2009 @c Remnant makeinfo bug requires blank line after *successful* end-if in menu:
2011 * Continuing and Stepping:: Resuming execution
2016 * Thread Stops:: Stopping and starting multi-thread programs
2020 @c makeinfo node-defaulting requires adjacency of @node and sectioning cmds
2021 @c ...hence distribute @node Breakpoints over two possible @if expansions.
2025 @section Breakpoints, watchpoints, and exceptions
2029 @section Breakpoints and watchpoints
2033 A @dfn{breakpoint} makes your program stop whenever a certain point in
2034 the program is reached. For each breakpoint, you can add various
2035 conditions to control in finer detail whether your program will stop.
2036 You can set breakpoints with the @code{break} command and its variants
2037 (@pxref{Set Breaks, ,Setting breakpoints}), to specify the place where
2038 your program should stop by line number, function name or exact address
2041 In languages with exception handling (such as GNU C++), you can also set
2042 breakpoints where an exception is raised (@pxref{Exception Handling,,
2043 Breakpoints and exceptions}).
2047 @cindex memory tracing
2048 @cindex breakpoint on memory address
2049 @cindex breakpoint on variable modification
2050 A @dfn{watchpoint} is a special breakpoint that stops your program
2051 when the value of an expression changes. You must use a different
2052 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2053 watchpoints}), but aside from that, you can manage a watchpoint like
2054 any other breakpoint: you enable, disable, and delete both breakpoints
2055 and watchpoints using the same commands.
2057 You can arrange to have values from your program displayed automatically
2058 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2061 @cindex breakpoint numbers
2062 @cindex numbers for breakpoints
2063 @value{GDBN} assigns a number to each breakpoint or watchpoint when you
2064 create it; these numbers are successive integers starting with one. In
2065 many of the commands for controlling various features of breakpoints you
2066 use the breakpoint number to say which breakpoint you want to change.
2067 Each breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has
2068 no effect on your program until you enable it again.
2071 * Set Breaks:: Setting breakpoints
2072 * Set Watchpoints:: Setting watchpoints
2074 * Exception Handling:: Breakpoints and exceptions
2077 * Delete Breaks:: Deleting breakpoints
2078 * Disabling:: Disabling breakpoints
2079 * Conditions:: Break conditions
2080 * Break Commands:: Breakpoint command lists
2082 * Breakpoint Menus:: Breakpoint menus
2085 * Error in Breakpoints:: ``Cannot insert breakpoints''
2090 @subsection Setting breakpoints
2092 @c FIXME LMB what does GDB do if no code on line of breakpt?
2093 @c consider in particular declaration with/without initialization.
2095 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2100 @cindex latest breakpoint
2101 Breakpoints are set with the @code{break} command (abbreviated
2102 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2103 number of the beakpoint you've set most recently; see @ref{Convenience
2104 Vars,, Convenience variables}, for a discussion of what you can do with
2105 convenience variables.
2107 You have several ways to say where the breakpoint should go.
2110 @item break @var{function}
2111 Set a breakpoint at entry to function @var{function}.
2113 When using source languages that permit overloading of symbols, such as
2114 C++, @var{function} may refer to more than one possible place to break.
2115 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2118 @item break +@var{offset}
2119 @itemx break -@var{offset}
2120 Set a breakpoint some number of lines forward or back from the position
2121 at which execution stopped in the currently selected frame.
2123 @item break @var{linenum}
2124 Set a breakpoint at line @var{linenum} in the current source file.
2125 That file is the last file whose source text was printed. This
2126 breakpoint will stop your program just before it executes any of the
2129 @item break @var{filename}:@var{linenum}
2130 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2132 @item break @var{filename}:@var{function}
2133 Set a breakpoint at entry to function @var{function} found in file
2134 @var{filename}. Specifying a file name as well as a function name is
2135 superfluous except when multiple files contain similarly named
2138 @item break *@var{address}
2139 Set a breakpoint at address @var{address}. You can use this to set
2140 breakpoints in parts of your program which do not have debugging
2141 information or source files.
2144 When called without any arguments, @code{break} sets a breakpoint at
2145 the next instruction to be executed in the selected stack frame
2146 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2147 innermost, this will cause your program to stop as soon as control
2148 returns to that frame. This is similar to the effect of a
2149 @code{finish} command in the frame inside the selected frame---except
2150 that @code{finish} does not leave an active breakpoint. If you use
2151 @code{break} without an argument in the innermost frame, @value{GDBN} will stop
2152 the next time it reaches the current location; this may be useful
2155 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2156 least one instruction has been executed. If it did not do this, you
2157 would be unable to proceed past a breakpoint without first disabling the
2158 breakpoint. This rule applies whether or not the breakpoint already
2159 existed when your program stopped.
2161 @item break @dots{} if @var{cond}
2162 Set a breakpoint with condition @var{cond}; evaluate the expression
2163 @var{cond} each time the breakpoint is reached, and stop only if the
2164 value is nonzero---that is, if @var{cond} evaluates as true.
2165 @samp{@dots{}} stands for one of the possible arguments described
2166 above (or no argument) specifying where to break. @xref{Conditions,
2167 ,Break conditions}, for more information on breakpoint conditions.
2169 @item tbreak @var{args}
2171 Set a breakpoint enabled only for one stop. @var{args} are the
2172 same as for the @code{break} command, and the breakpoint is set in the same
2173 way, but the breakpoint is automatically disabled after the first time your
2174 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2176 @item rbreak @var{regex}
2178 @cindex regular expression
2179 @c FIXME what kind of regexp?
2180 Set breakpoints on all functions matching the regular expression
2181 @var{regex}. This command
2182 sets an unconditional breakpoint on all matches, printing a list of all
2183 breakpoints it set. Once these breakpoints are set, they are treated
2184 just like the breakpoints set with the @code{break} command. You can
2185 delete them, disable them, or make them conditional the same way as any
2189 When debugging C++ programs, @code{rbreak} is useful for setting
2190 breakpoints on overloaded functions that are not members of any special
2194 @kindex info breakpoints
2195 @cindex @code{$_} and @code{info breakpoints}
2196 @item info breakpoints @r{[}@var{n}@r{]}
2197 @itemx info break @r{[}@var{n}@r{]}
2198 @itemx info watchpoints @r{[}@var{n}@r{]}
2199 Print a table of all breakpoints and watchpoints set and not
2200 deleted, with the following columns for each breakpoint:
2203 @item Breakpoint Numbers
2205 Breakpoint or watchpoint.
2207 Whether the breakpoint is marked to be disabled or deleted when hit.
2208 @item Enabled or Disabled
2209 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2210 that are not enabled.
2212 Where the breakpoint is in your program, as a memory address
2214 Where the breakpoint is in the source for your program, as a file and
2219 If a breakpoint is conditional, @code{info break} shows the condition on
2220 the line following the affected breakpoint; breakpoint commands, if any,
2221 are listed after that.
2224 @code{info break} with a breakpoint
2225 number @var{n} as argument lists only that breakpoint. The
2226 convenience variable @code{$_} and the default examining-address for
2227 the @code{x} command are set to the address of the last breakpoint
2228 listed (@pxref{Memory, ,Examining memory}).
2231 @value{GDBN} allows you to set any number of breakpoints at the same place in
2232 your program. There is nothing silly or meaningless about this. When
2233 the breakpoints are conditional, this is even useful
2234 (@pxref{Conditions, ,Break conditions}).
2236 @cindex negative breakpoint numbers
2237 @cindex internal @value{GDBN} breakpoints
2238 @value{GDBN} itself sometimes sets breakpoints in your program for special
2239 purposes, such as proper handling of @code{longjmp} (in C programs).
2240 These internal breakpoints are assigned negative numbers, starting with
2241 @code{-1}; @samp{info breakpoints} does not display them.
2243 You can see these breakpoints with the @value{GDBN} maintenance command
2244 @samp{maint info breakpoints}.
2247 @kindex maint info breakpoints
2248 @item maint info breakpoints
2249 Using the same format as @samp{info breakpoints}, display both the
2250 breakpoints you've set explicitly, and those @value{GDBN} is using for
2251 internal purposes. Internal breakpoints are shown with negative
2252 breakpoint numbers. The type column identifies what kind of breakpoint
2257 Normal, explicitly set breakpoint.
2260 Normal, explicitly set watchpoint.
2263 Internal breakpoint, used to handle correctly stepping through
2264 @code{longjmp} calls.
2266 @item longjmp resume
2267 Internal breakpoint at the target of a @code{longjmp}.
2270 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2273 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2279 @node Set Watchpoints
2280 @subsection Setting watchpoints
2281 @cindex setting watchpoints
2283 You can use a watchpoint to stop execution whenever the value of an
2284 expression changes, without having to predict a particular place
2285 where this may happen.
2287 Watchpoints currently execute two orders of magnitude more slowly than
2288 other breakpoints, but this can be well worth it to catch errors where
2289 you have no clue what part of your program is the culprit. Some
2290 processors provide special hardware to support watchpoint evaluation; future
2291 releases of @value{GDBN} will use such hardware if it is available.
2295 @item watch @var{expr}
2296 Set a watchpoint for an expression.
2298 @kindex info watchpoints
2299 @item info watchpoints
2300 This command prints a list of watchpoints and breakpoints; it is the
2301 same as @code{info break}.
2306 @cindex watchpoints and threads
2307 @cindex threads and watchpoints
2308 @emph{Warning:} in multi-thread programs, watchpoints have only limited
2309 usefulness. With the current watchpoint implementation, @value{GDBN}
2310 can only watch the value of an expression @emph{in a single thread}. If
2311 you are confident that the expression can only change due to the current
2312 thread's activity (and if you are also confident that the same thread
2313 will remain current), then you can use watchpoints as usual. However,
2314 @value{GDBN} may not notice when a non-current thread's activity changes
2320 @node Exception Handling
2321 @subsection Breakpoints and exceptions
2322 @cindex exception handlers
2324 Some languages, such as GNU C++, implement exception handling. You can
2325 use @value{GDBN} to examine what caused your program to raise an exception,
2326 and to list the exceptions your program is prepared to handle at a
2327 given point in time.
2330 @item catch @var{exceptions}
2332 You can set breakpoints at active exception handlers by using the
2333 @code{catch} command. @var{exceptions} is a list of names of exceptions
2337 You can use @code{info catch} to list active exception handlers.
2338 @xref{Frame Info, ,Information about a frame}.
2340 There are currently some limitations to exception handling in @value{GDBN}.
2341 These will be corrected in a future release.
2345 If you call a function interactively, @value{GDBN} normally returns
2346 control to you when the function has finished executing. If the call
2347 raises an exception, however, the call may bypass the mechanism that
2348 returns control to you and cause your program to simply continue
2349 running until it hits a breakpoint, catches a signal that @value{GDBN} is
2350 listening for, or exits.
2352 You cannot raise an exception interactively.
2354 You cannot interactively install an exception handler.
2357 @cindex raise exceptions
2358 Sometimes @code{catch} is not the best way to debug exception handling:
2359 if you need to know exactly where an exception is raised, it is better to
2360 stop @emph{before} the exception handler is called, since that way you
2361 can see the stack before any unwinding takes place. If you set a
2362 breakpoint in an exception handler instead, it may not be easy to find
2363 out where the exception was raised.
2365 To stop just before an exception handler is called, you need some
2366 knowledge of the implementation. In the case of GNU C++, exceptions are
2367 raised by calling a library function named @code{__raise_exception}
2368 which has the following ANSI C interface:
2371 /* @var{addr} is where the exception identifier is stored.
2372 ID is the exception identifier. */
2373 void __raise_exception (void **@var{addr}, void *@var{id});
2377 To make the debugger catch all exceptions before any stack
2378 unwinding takes place, set a breakpoint on @code{__raise_exception}
2379 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2381 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2382 that depends on the value of @var{id}, you can stop your program when
2383 a specific exception is raised. You can use multiple conditional
2384 breakpoints to stop your program when any of a number of exceptions are
2389 @subsection Deleting breakpoints
2391 @cindex clearing breakpoints, watchpoints
2392 @cindex deleting breakpoints, watchpoints
2393 It is often necessary to eliminate a breakpoint or watchpoint once it
2394 has done its job and you no longer want your program to stop there. This
2395 is called @dfn{deleting} the breakpoint. A breakpoint that has been
2396 deleted no longer exists; it is forgotten.
2398 With the @code{clear} command you can delete breakpoints according to
2399 where they are in your program. With the @code{delete} command you can
2400 delete individual breakpoints or watchpoints by specifying their
2403 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2404 automatically ignores breakpoints on the first instruction to be executed
2405 when you continue execution without changing the execution address.
2410 Delete any breakpoints at the next instruction to be executed in the
2411 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2412 the innermost frame is selected, this is a good way to delete a
2413 breakpoint where your program just stopped.
2415 @item clear @var{function}
2416 @itemx clear @var{filename}:@var{function}
2417 Delete any breakpoints set at entry to the function @var{function}.
2419 @item clear @var{linenum}
2420 @itemx clear @var{filename}:@var{linenum}
2421 Delete any breakpoints set at or within the code of the specified line.
2423 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2424 @cindex delete breakpoints
2427 Delete the breakpoints or watchpoints of the numbers specified as
2428 arguments. If no argument is specified, delete all breakpoints (@value{GDBN}
2429 asks confirmation, unless you have @code{set confirm off}). You
2430 can abbreviate this command as @code{d}.
2434 @subsection Disabling breakpoints
2436 @cindex disabled breakpoints
2437 @cindex enabled breakpoints
2438 Rather than deleting a breakpoint or watchpoint, you might prefer to
2439 @dfn{disable} it. This makes the breakpoint inoperative as if it had
2440 been deleted, but remembers the information on the breakpoint so that
2441 you can @dfn{enable} it again later.
2443 You disable and enable breakpoints and watchpoints with the
2444 @code{enable} and @code{disable} commands, optionally specifying one or
2445 more breakpoint numbers as arguments. Use @code{info break} or
2446 @code{info watch} to print a list of breakpoints or watchpoints if you
2447 do not know which numbers to use.
2449 A breakpoint or watchpoint can have any of four different states of
2454 Enabled. The breakpoint will stop your program. A breakpoint set
2455 with the @code{break} command starts out in this state.
2457 Disabled. The breakpoint has no effect on your program.
2459 Enabled once. The breakpoint will stop your program, but
2460 when it does so it will become disabled. A breakpoint set
2461 with the @code{tbreak} command starts out in this state.
2463 Enabled for deletion. The breakpoint will stop your program, but
2464 immediately after it does so it will be deleted permanently.
2467 You can use the following commands to enable or disable breakpoints and
2471 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2472 @kindex disable breakpoints
2475 Disable the specified breakpoints---or all breakpoints, if none are
2476 listed. A disabled breakpoint has no effect but is not forgotten. All
2477 options such as ignore-counts, conditions and commands are remembered in
2478 case the breakpoint is enabled again later. You may abbreviate
2479 @code{disable} as @code{dis}.
2481 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2482 @kindex enable breakpoints
2484 Enable the specified breakpoints (or all defined breakpoints). They
2485 become effective once again in stopping your program.
2487 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
2488 Enable the specified breakpoints temporarily. Each will be disabled
2489 again the next time it stops your program.
2491 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
2492 Enable the specified breakpoints to work once and then die. Each of
2493 the breakpoints will be deleted the next time it stops your program.
2496 Save for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2497 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2498 subsequently, they become disabled or enabled only when you use one of
2499 the commands above. (The command @code{until} can set and delete a
2500 breakpoint of its own, but it will not change the state of your other
2501 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2505 @subsection Break conditions
2506 @cindex conditional breakpoints
2507 @cindex breakpoint conditions
2509 @c FIXME what is scope of break condition expr? Context where wanted?
2510 @c in particular for a watchpoint?
2511 The simplest sort of breakpoint breaks every time your program reaches a
2512 specified place. You can also specify a @dfn{condition} for a
2513 breakpoint. A condition is just a Boolean expression in your
2514 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2515 a condition evaluates the expression each time your program reaches it,
2516 and your program stops only if the condition is @emph{true}.
2518 This is the converse of using assertions for program validation; in that
2519 situation, you want to stop when the assertion is violated---that is,
2520 when the condition is false. In C, if you want to test an assertion expressed
2521 by the condition @var{assert}, you should set the condition
2522 @samp{! @var{assert}} on the appropriate breakpoint.
2524 Conditions are also accepted for watchpoints; you may not need them,
2525 since a watchpoint is inspecting the value of an expression anyhow---but
2526 it might be simpler, say, to just set a watchpoint on a variable name,
2527 and specify a condition that tests whether the new value is an interesting
2530 Break conditions can have side effects, and may even call functions in
2531 your program. This can be useful, for example, to activate functions
2532 that log program progress, or to use your own print functions to
2533 format special data structures. The effects are completely predictable
2534 unless there is another enabled breakpoint at the same address. (In
2535 that case, @value{GDBN} might see the other breakpoint first and stop your
2536 program without checking the condition of this one.) Note that
2537 breakpoint commands are usually more convenient and flexible for the
2538 purpose of performing side effects when a breakpoint is reached
2539 (@pxref{Break Commands, ,Breakpoint command lists}).
2541 Break conditions can be specified when a breakpoint is set, by using
2542 @samp{if} in the arguments to the @code{break} command. @xref{Set
2543 Breaks, ,Setting breakpoints}. They can also be changed at any time
2544 with the @code{condition} command. The @code{watch} command does not
2545 recognize the @code{if} keyword; @code{condition} is the only way to
2546 impose a further condition on a watchpoint.
2549 @item condition @var{bnum} @var{expression}
2551 Specify @var{expression} as the break condition for breakpoint or
2552 watchpoint number @var{bnum}. From now on, this breakpoint will stop
2553 your program only if the value of @var{expression} is true (nonzero, in
2554 C). When you use @code{condition}, @value{GDBN} checks @var{expression}
2555 immediately for syntactic correctness, and to determine whether symbols
2556 in it have referents in the context of your breakpoint.
2557 @c FIXME so what does GDB do if there is no referent? Moreover, what
2558 @c about watchpoints?
2560 not actually evaluate @var{expression} at the time the @code{condition}
2561 command is given, however. @xref{Expressions, ,Expressions}.
2563 @item condition @var{bnum}
2564 Remove the condition from breakpoint number @var{bnum}. It becomes
2565 an ordinary unconditional breakpoint.
2568 @cindex ignore count (of breakpoint)
2569 A special case of a breakpoint condition is to stop only when the
2570 breakpoint has been reached a certain number of times. This is so
2571 useful that there is a special way to do it, using the @dfn{ignore
2572 count} of the breakpoint. Every breakpoint has an ignore count, which
2573 is an integer. Most of the time, the ignore count is zero, and
2574 therefore has no effect. But if your program reaches a breakpoint whose
2575 ignore count is positive, then instead of stopping, it just decrements
2576 the ignore count by one and continues. As a result, if the ignore count
2577 value is @var{n}, the breakpoint will not stop the next @var{n} times it
2581 @item ignore @var{bnum} @var{count}
2583 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
2584 The next @var{count} times the breakpoint is reached, your program's
2585 execution will not stop; other than to decrement the ignore count, @value{GDBN}
2588 To make the breakpoint stop the next time it is reached, specify
2591 When you use @code{continue} to resume execution of your program from a
2592 breakpoint, you can specify an ignore count directly as an argument to
2593 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
2594 Stepping,,Continuing and stepping}.
2596 If a breakpoint has a positive ignore count and a condition, the condition
2597 is not checked. Once the ignore count reaches zero, the condition will
2600 You could achieve the effect of the ignore count with a condition such
2601 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
2602 is decremented each time. @xref{Convenience Vars, ,Convenience
2606 @node Break Commands
2607 @subsection Breakpoint command lists
2609 @cindex breakpoint commands
2610 You can give any breakpoint (or watchpoint) a series of commands to
2611 execute when your program stops due to that breakpoint. For example, you
2612 might want to print the values of certain expressions, or enable other
2616 @item commands @r{[}@var{bnum}@r{]}
2617 @itemx @dots{} @var{command-list} @dots{}
2621 Specify a list of commands for breakpoint number @var{bnum}. The commands
2622 themselves appear on the following lines. Type a line containing just
2623 @code{end} to terminate the commands.
2625 To remove all commands from a breakpoint, type @code{commands} and
2626 follow it immediately with @code{end}; that is, give no commands.
2628 With no @var{bnum} argument, @code{commands} refers to the last
2629 breakpoint or watchpoint set (not to the breakpoint most recently
2633 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
2634 disabled within a @var{command-list}.
2636 You can use breakpoint commands to start your program up again. Simply
2637 use the @code{continue} command, or @code{step}, or any other command
2638 that resumes execution.
2640 Any other commands in the command list, after a command that resumes
2641 execution, are ignored. This is because any time you resume execution
2642 (even with a simple @code{next} or @code{step}), you may encounter
2643 another breakpoint---which could have its own command list, leading to
2644 ambiguities about which list to execute.
2647 If the first command you specify in a command list is @code{silent}, the
2648 usual message about stopping at a breakpoint is not printed. This may
2649 be desirable for breakpoints that are to print a specific message and
2650 then continue. If none of the remaining commands print anything, you
2651 will see no sign that the breakpoint was reached. @code{silent} is
2652 meaningful only at the beginning of a breakpoint command list.
2654 The commands @code{echo}, @code{output}, and @code{printf} allow you to
2655 print precisely controlled output, and are often useful in silent
2656 breakpoints. @xref{Output, ,Commands for controlled output}.
2658 For example, here is how you could use breakpoint commands to print the
2659 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
2665 printf "x is %d\n",x
2670 One application for breakpoint commands is to compensate for one bug so
2671 you can test for another. Put a breakpoint just after the erroneous line
2672 of code, give it a condition to detect the case in which something
2673 erroneous has been done, and give it commands to assign correct values
2674 to any variables that need them. End with the @code{continue} command
2675 so that your program does not stop, and start with the @code{silent}
2676 command so that no output is produced. Here is an example:
2688 @node Breakpoint Menus
2689 @subsection Breakpoint menus
2691 @cindex symbol overloading
2693 Some programming languages (notably C++) permit a single function name
2694 to be defined several times, for application in different contexts.
2695 This is called @dfn{overloading}. When a function name is overloaded,
2696 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
2697 a breakpoint. If you realize this will be a problem, you can use
2698 something like @samp{break @var{function}(@var{types})} to specify which
2699 particular version of the function you want. Otherwise, @value{GDBN} offers
2700 you a menu of numbered choices for different possible breakpoints, and
2701 waits for your selection with the prompt @samp{>}. The first two
2702 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
2703 sets a breakpoint at each definition of @var{function}, and typing
2704 @kbd{0} aborts the @code{break} command without setting any new
2707 For example, the following session excerpt shows an attempt to set a
2708 breakpoint at the overloaded symbol @code{String::after}.
2709 We choose three particular definitions of that function name:
2711 @c FIXME! This is likely to change to show arg type lists, at least
2713 (@value{GDBP}) b String::after
2716 [2] file:String.cc; line number:867
2717 [3] file:String.cc; line number:860
2718 [4] file:String.cc; line number:875
2719 [5] file:String.cc; line number:853
2720 [6] file:String.cc; line number:846
2721 [7] file:String.cc; line number:735
2723 Breakpoint 1 at 0xb26c: file String.cc, line 867.
2724 Breakpoint 2 at 0xb344: file String.cc, line 875.
2725 Breakpoint 3 at 0xafcc: file String.cc, line 846.
2726 Multiple breakpoints were set.
2727 Use the "delete" command to delete unwanted
2734 @node Error in Breakpoints
2735 @subsection ``Cannot insert breakpoints''
2737 @c FIXME: "cannot insert breakpoints" error, v unclear.
2738 @c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91
2739 @c some light may be shed by looking at instances of
2740 @c ONE_PROCESS_WRITETEXT. But error message seems possible otherwise
2741 @c too. pesch, 20sep91
2742 Under some operating systems, breakpoints cannot be used in a program if
2743 any other process is running that program. In this situation,
2744 attempting to run or continue a program with a breakpoint causes @value{GDBN}
2745 to stop the other process.
2747 When this happens, you have three ways to proceed:
2751 Remove or disable the breakpoints, then continue.
2754 Suspend @value{GDBN}, and copy the file containing your program to a new name.
2755 Resume @value{GDBN} and use the @code{exec-file} command to specify that @value{GDBN}
2756 should run your program under that name. Then start your program again.
2758 @c FIXME: RMS commented here "Show example". Maybe when someone
2759 @c explains the first FIXME: in this section...
2762 Relink your program so that the text segment is nonsharable, using the
2763 linker option @samp{-N}. The operating system limitation may not apply
2764 to nonsharable executables.
2768 @node Continuing and Stepping
2769 @section Continuing and stepping
2773 @cindex resuming execution
2774 @dfn{Continuing} means resuming program execution until your program
2775 completes normally. In contrast, @dfn{stepping} means executing just
2776 one more ``step'' of your program, where ``step'' may mean either one
2777 line of source code, or one machine instruction (depending on what
2778 particular command you use). Either when continuing
2779 or when stepping, your program may stop even sooner, due to
2784 a breakpoint or a signal. (If due to a signal, you may want to use
2785 @code{handle}, or use @samp{signal 0} to resume execution.
2786 @xref{Signals, ,Signals}.)
2790 @item continue @r{[}@var{ignore-count}@r{]}
2791 @itemx c @r{[}@var{ignore-count}@r{]}
2792 @itemx fg @r{[}@var{ignore-count}@r{]}
2796 Resume program execution, at the address where your program last stopped;
2797 any breakpoints set at that address are bypassed. The optional argument
2798 @var{ignore-count} allows you to specify a further number of times to
2799 ignore a breakpoint at this location; its effect is like that of
2800 @code{ignore} (@pxref{Conditions, ,Break conditions}).
2802 The argument @var{ignore-count} is meaningful only when your program
2803 stopped due to a breakpoint. At other times, the argument to
2804 @code{continue} is ignored.
2806 The synonyms @code{c} and @code{fg} are provided purely for convenience,
2807 and have exactly the same behavior as @code{continue}.
2810 To resume execution at a different place, you can use @code{return}
2811 (@pxref{Returning, ,Returning from a function}) to go back to the
2812 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
2813 different address}) to go to an arbitrary location in your program.
2815 A typical technique for using stepping is to set a breakpoint
2817 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions})
2820 (@pxref{Breakpoints, ,Breakpoints and watchpoints})
2823 beginning of the function or the section of your program where a
2824 problem is believed to lie, run your program until it stops at that
2825 breakpoint, and then step through the suspect area, examining the
2826 variables that are interesting, until you see the problem happen.
2832 Continue running your program until control reaches a different source
2833 line, then stop it and return control to @value{GDBN}. This command is
2834 abbreviated @code{s}.
2837 @emph{Warning:} If you use the @code{step} command while control is
2838 within a function that was compiled without debugging information,
2839 execution proceeds until control reaches a function that does have
2840 debugging information.
2843 @item step @var{count}
2844 Continue running as in @code{step}, but do so @var{count} times. If a
2845 breakpoint is reached,
2847 or a signal not related to stepping occurs before @var{count} steps,
2849 stepping stops right away.
2851 @item next @r{[}@var{count}@r{]}
2854 Continue to the next source line in the current (innermost) stack frame.
2855 Similar to @code{step}, but any function calls appearing within the line
2856 of code are executed without stopping. Execution stops when control
2857 reaches a different line of code at the stack level which was executing
2858 when the @code{next} command was given. This command is abbreviated
2861 An argument @var{count} is a repeat count, as for @code{step}.
2863 @code{next} within a function that lacks debugging information acts like
2864 @code{step}, but any function calls appearing within the code of the
2865 function are executed without stopping.
2869 Continue running until just after function in the selected stack frame
2870 returns. Print the returned value (if any).
2872 Contrast this with the @code{return} command (@pxref{Returning,
2873 ,Returning from a function}).
2879 Continue running until a source line past the current line, in the
2880 current stack frame, is reached. This command is used to avoid single
2881 stepping through a loop more than once. It is like the @code{next}
2882 command, except that when @code{until} encounters a jump, it
2883 automatically continues execution until the program counter is greater
2884 than the address of the jump.
2886 This means that when you reach the end of a loop after single stepping
2887 though it, @code{until} will cause your program to continue execution
2888 until the loop is exited. In contrast, a @code{next} command at the end
2889 of a loop will simply step back to the beginning of the loop, which
2890 would force you to step through the next iteration.
2892 @code{until} always stops your program if it attempts to exit the current
2895 @code{until} may produce somewhat counterintuitive results if the order
2896 of machine code does not match the order of the source lines. For
2897 example, in the following excerpt from a debugging session, the @code{f}
2898 (@code{frame}) command shows that execution is stopped at line
2899 @code{206}; yet when we use @code{until}, we get to line @code{195}:
2903 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
2905 (@value{GDBP}) until
2906 195 for ( ; argc > 0; NEXTARG) @{
2909 This happened because, for execution efficiency, the compiler had
2910 generated code for the loop closure test at the end, rather than the
2911 start, of the loop---even though the test in a C @code{for}-loop is
2912 written before the body of the loop. The @code{until} command appeared
2913 to step back to the beginning of the loop when it advanced to this
2914 expression; however, it has not really gone to an earlier
2915 statement---not in terms of the actual machine code.
2917 @code{until} with no argument works by means of single
2918 instruction stepping, and hence is slower than @code{until} with an
2921 @item until @var{location}
2922 @itemx u @var{location}
2923 Continue running your program until either the specified location is
2924 reached, or the current stack frame returns. @var{location} is any of
2925 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
2926 ,Setting breakpoints}). This form of the command uses breakpoints,
2927 and hence is quicker than @code{until} without an argument.
2933 Execute one machine instruction, then stop and return to the debugger.
2935 It is often useful to do @samp{display/i $pc} when stepping by machine
2936 instructions. This will cause the next instruction to be executed to
2937 be displayed automatically at each stop. @xref{Auto Display,
2938 ,Automatic display}.
2940 An argument is a repeat count, as in @code{step}.
2947 Execute one machine instruction, but if it is a function call,
2948 proceed until the function returns.
2950 An argument is a repeat count, as in @code{next}.
2958 A signal is an asynchronous event that can happen in a program. The
2959 operating system defines the possible kinds of signals, and gives each
2960 kind a name and a number. For example, in Unix @code{SIGINT} is the
2961 signal a program gets when you type an interrupt (often @kbd{C-c});
2962 @code{SIGSEGV} is the signal a program gets from referencing a place in
2963 memory far away from all the areas in use; @code{SIGALRM} occurs when
2964 the alarm clock timer goes off (which happens only if your program has
2965 requested an alarm).
2967 @cindex fatal signals
2968 Some signals, including @code{SIGALRM}, are a normal part of the
2969 functioning of your program. Others, such as @code{SIGSEGV}, indicate
2970 errors; these signals are @dfn{fatal} (kill your program immediately) if the
2971 program has not specified in advance some other way to handle the signal.
2972 @code{SIGINT} does not indicate an error in your program, but it is normally
2973 fatal so it can carry out the purpose of the interrupt: to kill the program.
2975 @value{GDBN} has the ability to detect any occurrence of a signal in your
2976 program. You can tell @value{GDBN} in advance what to do for each kind of
2979 @cindex handling signals
2980 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
2981 (so as not to interfere with their role in the functioning of your program)
2982 but to stop your program immediately whenever an error signal happens.
2983 You can change these settings with the @code{handle} command.
2987 @kindex info signals
2988 Print a table of all the kinds of signals and how @value{GDBN} has been told to
2989 handle each one. You can use this to see the signal numbers of all
2990 the defined types of signals.
2992 @item handle @var{signal} @var{keywords}@dots{}
2994 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can be the
2995 number of a signal or its name (with or without the @samp{SIG} at the
2996 beginning). The @var{keywords} say what change to make.
3000 The keywords allowed by the @code{handle} command can be abbreviated.
3001 Their full names are:
3005 @value{GDBN} should not stop your program when this signal happens. It may
3006 still print a message telling you that the signal has come in.
3009 @value{GDBN} should stop your program when this signal happens. This implies
3010 the @code{print} keyword as well.
3013 @value{GDBN} should print a message when this signal happens.
3016 @value{GDBN} should not mention the occurrence of the signal at all. This
3017 implies the @code{nostop} keyword as well.
3020 @value{GDBN} should allow your program to see this signal; your program will be
3021 able to handle the signal, or may be terminated if the signal is fatal
3025 @value{GDBN} should not allow your program to see this signal.
3029 When a signal stops your program, the signal is not visible until you
3030 continue. Your program will see the signal then, if @code{pass} is in
3031 effect for the signal in question @emph{at that time}. In other words,
3032 after @value{GDBN} reports a signal, you can use the @code{handle}
3033 command with @code{pass} or @code{nopass} to control whether that
3034 signal will be seen by your program when you later continue it.
3036 You can also use the @code{signal} command to prevent your program from
3037 seeing a signal, or cause it to see a signal it normally would not see,
3038 or to give it any signal at any time. For example, if your program stopped
3039 due to some sort of memory reference error, you might store correct
3040 values into the erroneous variables and continue, hoping to see more
3041 execution; but your program would probably terminate immediately as
3042 a result of the fatal signal once it saw the signal. To prevent this,
3043 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3049 @section Stopping and starting multi-thread programs
3051 When your program has multiple threads (@pxref{Threads,, Debugging
3052 programs with multiple threads}), you can choose whether to set
3053 breakpoints on all threads, or on a particular thread.
3056 @cindex breakpoints and threads
3057 @cindex thread breakpoints
3058 @kindex break @dots{} thread @var{threadno}
3059 @item break @var{linespec} thread @var{threadno}
3060 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3061 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3062 to specify that you only want @value{GDBN} to stop the program when a
3063 particular thread reaches this breakpoint. @var{threadno} is one of the
3064 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3065 column of the @samp{info threads} display.
3067 If you do not specify @samp{thread @var{threadno}} when you set a
3068 breakpoint, the breakpoint applies to @emph{all} threads of your
3071 You can use the @code{thread} qualifier on conditional breakpoints as
3072 well; in this case, place @samp{thread @var{threadno}} before the
3073 breakpoint condition, like this:
3076 (gdb) break frik.c:13 thread 28 if bartab > lim
3080 @cindex stopped threads
3081 @cindex threads, stopped
3082 Whenever your program stops under @value{GDBN} for any reason,
3083 @emph{all} threads of execution stop, not just the current thread. This
3084 allows you to examine the overall state of the program, including
3085 switching between threads, without worrying that things may change
3088 @cindex continuing threads
3089 @cindex threads, continuing
3090 Conversely, whenever you restart the program, @emph{all} threads start
3091 executing. @emph{This is true even when single-stepping} with commands
3092 like @code{step} or @code{next}.
3094 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3095 Since thread scheduling is up to your debugging target's operating
3096 system (not controlled by @value{GDBN}), other threads may
3097 execute more than one statement while the current thread completes a
3098 single step. Moreover, in general other threads stop in the middle of a
3099 statement, rather than at a clean statement boundary, when the program
3102 You might even find your program stopped in another thread after
3103 continuing or even single-stepping. This happens whenever some other
3104 thread runs into a breakpoint, a signal, or an exception before the
3105 first thread completes whatever you requested.
3109 @chapter Examining the Stack
3111 When your program has stopped, the first thing you need to know is where it
3112 stopped and how it got there.
3115 Each time your program performs a function call, the information about
3116 where in your program the call was made from is saved in a block of data
3117 called a @dfn{stack frame}. The frame also contains the arguments of the
3118 call and the local variables of the function that was called. All the
3119 stack frames are allocated in a region of memory called the @dfn{call
3122 When your program stops, the @value{GDBN} commands for examining the
3123 stack allow you to see all of this information.
3125 @cindex selected frame
3126 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3127 @value{GDBN} commands refer implicitly to the selected frame. In
3128 particular, whenever you ask @value{GDBN} for the value of a variable in
3129 your program, the value is found in the selected frame. There are
3130 special @value{GDBN} commands to select whichever frame you are
3133 When your program stops, @value{GDBN} automatically selects the
3134 currently executing frame and describes it briefly as the @code{frame}
3135 command does (@pxref{Frame Info, ,Information about a frame}).
3138 * Frames:: Stack frames
3139 * Backtrace:: Backtraces
3140 * Selection:: Selecting a frame
3141 * Frame Info:: Information on a frame
3143 * MIPS Stack:: MIPS machines and the function stack
3148 @section Stack frames
3152 The call stack is divided up into contiguous pieces called @dfn{stack
3153 frames}, or @dfn{frames} for short; each frame is the data associated
3154 with one call to one function. The frame contains the arguments given
3155 to the function, the function's local variables, and the address at
3156 which the function is executing.
3158 @cindex initial frame
3159 @cindex outermost frame
3160 @cindex innermost frame
3161 When your program is started, the stack has only one frame, that of the
3162 function @code{main}. This is called the @dfn{initial} frame or the
3163 @dfn{outermost} frame. Each time a function is called, a new frame is
3164 made. Each time a function returns, the frame for that function invocation
3165 is eliminated. If a function is recursive, there can be many frames for
3166 the same function. The frame for the function in which execution is
3167 actually occurring is called the @dfn{innermost} frame. This is the most
3168 recently created of all the stack frames that still exist.
3170 @cindex frame pointer
3171 Inside your program, stack frames are identified by their addresses. A
3172 stack frame consists of many bytes, each of which has its own address; each
3173 kind of computer has a convention for choosing one of those bytes whose
3174 address serves as the address of the frame. Usually this address is kept
3175 in a register called the @dfn{frame pointer register} while execution is
3176 going on in that frame.
3178 @cindex frame number
3179 @value{GDBN} assigns numbers to all existing stack frames, starting with
3180 zero for the innermost frame, one for the frame that called it,
3181 and so on upward. These numbers do not really exist in your program;
3182 they are assigned by @value{GDBN} to give you a way of designating stack
3183 frames in @value{GDBN} commands.
3185 @c below produces an acceptable overful hbox. --mew 13aug1993
3186 @cindex frameless execution
3187 Some compilers provide a way to compile functions so that they operate
3188 without stack frames. (For example, the @code{@value{GCC}} option
3189 @samp{-fomit-frame-pointer} will generate functions without a frame.)
3190 This is occasionally done with heavily used library functions to save
3191 the frame setup time. @value{GDBN} has limited facilities for dealing
3192 with these function invocations. If the innermost function invocation
3193 has no stack frame, @value{GDBN} will nevertheless regard it as though
3194 it had a separate frame, which is numbered zero as usual, allowing
3195 correct tracing of the function call chain. However, @value{GDBN} has
3196 no provision for frameless functions elsewhere in the stack.
3201 A backtrace is a summary of how your program got where it is. It shows one
3202 line per frame, for many frames, starting with the currently executing
3203 frame (frame zero), followed by its caller (frame one), and on up the
3211 Print a backtrace of the entire stack: one line per frame for all
3212 frames in the stack.
3214 You can stop the backtrace at any time by typing the system interrupt
3215 character, normally @kbd{C-c}.
3217 @item backtrace @var{n}
3219 Similar, but print only the innermost @var{n} frames.
3221 @item backtrace -@var{n}
3223 Similar, but print only the outermost @var{n} frames.
3229 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3230 are additional aliases for @code{backtrace}.
3232 Each line in the backtrace shows the frame number and the function name.
3233 The program counter value is also shown---unless you use @code{set
3234 print address off}. The backtrace also shows the source file name and
3235 line number, as well as the arguments to the function. The program
3236 counter value is omitted if it is at the beginning of the code for that
3239 Here is an example of a backtrace. It was made with the command
3240 @samp{bt 3}, so it shows the innermost three frames.
3244 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3246 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3247 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3249 (More stack frames follow...)
3254 The display for frame zero does not begin with a program counter
3255 value, indicating that your program has stopped at the beginning of the
3256 code for line @code{993} of @code{builtin.c}.
3259 @section Selecting a frame
3261 Most commands for examining the stack and other data in your program work on
3262 whichever stack frame is selected at the moment. Here are the commands for
3263 selecting a stack frame; all of them finish by printing a brief description
3264 of the stack frame just selected.
3271 Select frame number @var{n}. Recall that frame zero is the innermost
3272 (currently executing) frame, frame one is the frame that called the
3273 innermost one, and so on. The highest-numbered frame is the one for
3276 @item frame @var{addr}
3278 Select the frame at address @var{addr}. This is useful mainly if the
3279 chaining of stack frames has been damaged by a bug, making it
3280 impossible for @value{GDBN} to assign numbers properly to all frames. In
3281 addition, this can be useful when your program has multiple stacks and
3282 switches between them.
3285 On the SPARC architecture, @code{frame} needs two addresses to
3286 select an arbitrary frame: a frame pointer and a stack pointer.
3287 @c note to future updaters: this is conditioned on a flag
3288 @c FRAME_SPECIFICATION_DYADIC in the tm-*.h files, currently only used
3289 @c by SPARC, hence the specific attribution. Generalize or list all
3290 @c possibilities if more supported machines start doing this.
3295 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3296 advances toward the outermost frame, to higher frame numbers, to frames
3297 that have existed longer. @var{n} defaults to one.
3302 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3303 advances toward the innermost frame, to lower frame numbers, to frames
3304 that were created more recently. @var{n} defaults to one. You may
3305 abbreviate @code{down} as @code{do}.
3308 All of these commands end by printing two lines of output describing the
3309 frame. The first line shows the frame number, the function name, the
3310 arguments, and the source file and line number of execution in that
3311 frame. The second line shows the text of that source line.
3319 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3321 10 read_input_file (argv[i]);
3325 After such a printout, the @code{list} command with no arguments will
3326 print ten lines centered on the point of execution in the frame.
3327 @xref{List, ,Printing source lines}.
3330 @item up-silently @var{n}
3331 @itemx down-silently @var{n}
3332 @kindex down-silently
3334 These two commands are variants of @code{up} and @code{down},
3335 respectively; they differ in that they do their work silently, without
3336 causing display of the new frame. They are intended primarily for use
3337 in @value{GDBN} command scripts, where the output might be unnecessary and
3342 @section Information about a frame
3344 There are several other commands to print information about the selected
3350 When used without any argument, this command does not change which
3351 frame is selected, but prints a brief description of the currently
3352 selected stack frame. It can be abbreviated @code{f}. With an
3353 argument, this command is used to select a stack frame.
3354 @xref{Selection, ,Selecting a frame}.
3360 This command prints a verbose description of the selected stack frame,
3361 including the address of the frame, the addresses of the next frame down
3362 (called by this frame) and the next frame up (caller of this frame), the
3363 language that the source code corresponding to this frame was written in,
3364 the address of the frame's arguments, the program counter saved in it
3365 (the address of execution in the caller frame), and which registers
3366 were saved in the frame. The verbose description is useful when
3367 something has gone wrong that has made the stack format fail to fit
3368 the usual conventions.
3370 @item info frame @var{addr}
3371 @itemx info f @var{addr}
3372 Print a verbose description of the frame at address @var{addr},
3373 without selecting that frame. The selected frame remains unchanged by
3378 Print the arguments of the selected frame, each on a separate line.
3382 Print the local variables of the selected frame, each on a separate
3383 line. These are all variables (declared either static or automatic)
3384 accessible at the point of execution of the selected frame.
3389 @cindex catch exceptions
3390 @cindex exception handlers
3391 Print a list of all the exception handlers that are active in the
3392 current stack frame at the current point of execution. To see other
3393 exception handlers, visit the associated frame (using the @code{up},
3394 @code{down}, or @code{frame} commands); then type @code{info catch}.
3395 @xref{Exception Handling, ,Breakpoints and exceptions}.
3401 @section MIPS machines and the function stack
3403 @cindex stack on MIPS
3405 MIPS based computers use an unusual stack frame, which sometimes
3406 requires @value{GDBN} to search backward in the object code to find the
3407 beginning of a function.
3409 @cindex response time, MIPS debugging
3410 To improve response time (especially for embedded applications, where
3411 @value{GDBN} may be restricted to a slow serial line for this search)
3412 you may want to limit the size of this search, using one of these
3414 @c FIXME! So what happens when GDB does *not* find the beginning of a
3417 @cindex @code{heuristic-fence-post} (MIPS)
3419 @item set heuristic-fence-post @var{limit}
3420 Restrict @value{GDBN} to examining at most @var{limit} bytes in its search
3421 for the beginning of a function. A value of @code{0} (the default)
3422 means there is no limit.
3424 @item show heuristic-fence-post
3425 Display the current limit.
3429 These commands are available @emph{only} when @value{GDBN} is configured
3430 for debugging programs on MIPS processors.
3434 @chapter Examining Source Files
3436 @value{GDBN} can print parts of your program's source, since the debugging
3437 information recorded in the program tells @value{GDBN} what source files were
3438 used to build it. When your program stops, @value{GDBN} spontaneously prints
3439 the line where it stopped. Likewise, when you select a stack frame
3440 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3441 execution in that frame has stopped. You can print other portions of
3442 source files by explicit command.
3445 If you use @value{GDBN} through its GNU Emacs interface, you may prefer to use
3446 Emacs facilities to view source; @pxref{Emacs, ,Using @value{GDBN} under GNU
3451 * List:: Printing source lines
3453 * Search:: Searching source files
3456 * Source Path:: Specifying source directories
3457 * Machine Code:: Source and machine code
3461 @section Printing source lines
3465 To print lines from a source file, use the @code{list} command
3466 (abbreviated @code{l}). There are several ways to specify what part
3467 of the file you want to print.
3469 Here are the forms of the @code{list} command most commonly used:
3472 @item list @var{linenum}
3473 Print lines centered around line number @var{linenum} in the
3474 current source file.
3476 @item list @var{function}
3477 Print lines centered around the beginning of function
3481 Print more lines. If the last lines printed were printed with a
3482 @code{list} command, this prints lines following the last lines
3483 printed; however, if the last line printed was a solitary line printed
3484 as part of displaying a stack frame (@pxref{Stack, ,Examining the
3485 Stack}), this prints lines centered around that line.
3488 Print lines just before the lines last printed.
3491 By default, @value{GDBN} prints ten source lines with any of these forms of
3492 the @code{list} command. You can change this using @code{set listsize}:
3495 @item set listsize @var{count}
3496 @kindex set listsize
3497 Make the @code{list} command display @var{count} source lines (unless
3498 the @code{list} argument explicitly specifies some other number).
3501 @kindex show listsize
3502 Display the number of lines that @code{list} will currently display by
3506 Repeating a @code{list} command with @key{RET} discards the argument,
3507 so it is equivalent to typing just @code{list}. This is more useful
3508 than listing the same lines again. An exception is made for an
3509 argument of @samp{-}; that argument is preserved in repetition so that
3510 each repetition moves up in the source file.
3513 In general, the @code{list} command expects you to supply zero, one or two
3514 @dfn{linespecs}. Linespecs specify source lines; there are several ways
3515 of writing them but the effect is always to specify some source line.
3516 Here is a complete description of the possible arguments for @code{list}:
3519 @item list @var{linespec}
3520 Print lines centered around the line specified by @var{linespec}.
3522 @item list @var{first},@var{last}
3523 Print lines from @var{first} to @var{last}. Both arguments are
3526 @item list ,@var{last}
3527 Print lines ending with @var{last}.
3529 @item list @var{first},
3530 Print lines starting with @var{first}.
3533 Print lines just after the lines last printed.
3536 Print lines just before the lines last printed.
3539 As described in the preceding table.
3542 Here are the ways of specifying a single source line---all the
3547 Specifies line @var{number} of the current source file.
3548 When a @code{list} command has two linespecs, this refers to
3549 the same source file as the first linespec.
3552 Specifies the line @var{offset} lines after the last line printed.
3553 When used as the second linespec in a @code{list} command that has
3554 two, this specifies the line @var{offset} lines down from the
3558 Specifies the line @var{offset} lines before the last line printed.
3560 @item @var{filename}:@var{number}
3561 Specifies line @var{number} in the source file @var{filename}.
3563 @item @var{function}
3564 @c FIXME: "of the open-brace" is C-centric. When we add other langs...
3565 Specifies the line of the open-brace that begins the body of the
3566 function @var{function}.
3568 @item @var{filename}:@var{function}
3569 Specifies the line of the open-brace that begins the body of the
3570 function @var{function} in the file @var{filename}. You only need the
3571 file name with a function name to avoid ambiguity when there are
3572 identically named functions in different source files.
3574 @item *@var{address}
3575 Specifies the line containing the program address @var{address}.
3576 @var{address} may be any expression.
3581 @section Searching source files
3583 @kindex reverse-search
3585 There are two commands for searching through the current source file for a
3589 @item forward-search @var{regexp}
3590 @itemx search @var{regexp}
3592 @kindex forward-search
3593 The command @samp{forward-search @var{regexp}} checks each line,
3594 starting with the one following the last line listed, for a match for
3595 @var{regexp}. It lists the line that is found. You can use
3596 synonym @samp{search @var{regexp}} or abbreviate the command name as
3599 @item reverse-search @var{regexp}
3600 The command @samp{reverse-search @var{regexp}} checks each line, starting
3601 with the one before the last line listed and going backward, for a match
3602 for @var{regexp}. It lists the line that is found. You can abbreviate
3603 this command as @code{rev}.
3608 @section Specifying source directories
3611 @cindex directories for source files
3612 Executable programs sometimes do not record the directories of the source
3613 files from which they were compiled, just the names. Even when they do,
3614 the directories could be moved between the compilation and your debugging
3615 session. @value{GDBN} has a list of directories to search for source files;
3616 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
3617 it tries all the directories in the list, in the order they are present
3618 in the list, until it finds a file with the desired name. Note that
3619 the executable search path is @emph{not} used for this purpose. Neither is
3620 the current working directory, unless it happens to be in the source
3623 If @value{GDBN} cannot find a source file in the source path, and the object
3624 program records a directory, @value{GDBN} tries that directory too. If the
3625 source path is empty, and there is no record of the compilation
3626 directory, @value{GDBN} will, as a last resort, look in the current
3629 Whenever you reset or rearrange the source path, @value{GDBN} will clear out
3630 any information it has cached about where source files are found and where
3631 each line is in the file.
3634 When you start @value{GDBN}, its source path is empty.
3635 To add other directories, use the @code{directory} command.
3638 @item directory @var{dirname} @dots{}
3639 Add directory @var{dirname} to the front of the source path. Several
3640 directory names may be given to this command, separated by @samp{:} or
3641 whitespace. You may specify a directory that is already in the source
3642 path; this moves it forward, so it will be searched sooner.
3648 @cindex compilation directory
3649 @cindex current directory
3650 @cindex working directory
3651 @cindex directory, current
3652 @cindex directory, compilation
3653 You can use the string @samp{$cdir} to refer to the compilation
3654 directory (if one is recorded), and @samp{$cwd} to refer to the current
3655 working directory. @samp{$cwd} is not the same as @samp{.}---the former
3656 tracks the current working directory as it changes during your @value{GDBN}
3657 session, while the latter is immediately expanded to the current
3658 directory at the time you add an entry to the source path.
3661 Reset the source path to empty again. This requires confirmation.
3663 @c RET-repeat for @code{directory} is explicitly disabled, but since
3664 @c repeating it would be a no-op we do not say that. (thanks to RMS)
3666 @item show directories
3667 @kindex show directories
3668 Print the source path: show which directories it contains.
3671 If your source path is cluttered with directories that are no longer of
3672 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
3673 versions of source. You can correct the situation as follows:
3677 Use @code{directory} with no argument to reset the source path to empty.
3680 Use @code{directory} with suitable arguments to reinstall the
3681 directories you want in the source path. You can add all the
3682 directories in one command.
3686 @section Source and machine code
3688 You can use the command @code{info line} to map source lines to program
3689 addresses (and vice versa), and the command @code{disassemble} to display
3690 a range of addresses as machine instructions.
3693 @item info line @var{linespec}
3695 Print the starting and ending addresses of the compiled code for
3696 source line @var{linespec}. You can specify source lines in any of
3697 the ways understood by the @code{list} command (@pxref{List, ,Printing
3701 For example, we can use @code{info line} to discover the location of
3702 the object code for the first line of function
3703 @code{m4_changequote}:
3706 (@value{GDBP}) info line m4_changecom
3707 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
3711 We can also inquire (using @code{*@var{addr}} as the form for
3712 @var{linespec}) what source line covers a particular address:
3714 (@value{GDBP}) info line *0x63ff
3715 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
3718 @cindex @code{$_} and @code{info line}
3719 After @code{info line}, the default address for the @code{x} command
3720 is changed to the starting address of the line, so that @samp{x/i} is
3721 sufficient to begin examining the machine code (@pxref{Memory,
3722 ,Examining memory}). Also, this address is saved as the value of the
3723 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
3729 @cindex assembly instructions
3730 @cindex instructions, assembly
3731 @cindex machine instructions
3732 @cindex listing machine instructions
3733 This specialized command dumps a range of memory as machine
3734 instructions. The default memory range is the function surrounding the
3735 program counter of the selected frame. A single argument to this
3736 command is a program counter value; the function surrounding this value
3737 will be dumped. Two arguments specify a range of addresses (first
3738 inclusive, second exclusive) to dump.
3741 @ifclear H8EXCLUSIVE
3742 We can use @code{disassemble} to inspect the object code
3743 range shown in the last @code{info line} example (the example
3744 shows SPARC machine instructions):
3748 (@value{GDBP}) disas 0x63e4 0x6404
3749 Dump of assembler code from 0x63e4 to 0x6404:
3750 0x63e4 <builtin_init+5340>: ble 0x63f8 <builtin_init+5360>
3751 0x63e8 <builtin_init+5344>: sethi %hi(0x4c00), %o0
3752 0x63ec <builtin_init+5348>: ld [%i1+4], %o0
3753 0x63f0 <builtin_init+5352>: b 0x63fc <builtin_init+5364>
3754 0x63f4 <builtin_init+5356>: ld [%o0+4], %o0
3755 0x63f8 <builtin_init+5360>: or %o0, 0x1a4, %o0
3756 0x63fc <builtin_init+5364>: call 0x9288 <path_search>
3757 0x6400 <builtin_init+5368>: nop
3758 End of assembler dump.
3763 For example, here is the beginning of the output for the
3764 disassembly of a function @code{fact}:
3768 (@value{GDBP}) disas fact
3769 Dump of assembler code for function fact:
3771 0x802c <fact>: 6d f2 mov.w r2,@@-r7
3772 0x802e <fact+2>: 6d f3 mov.w r3,@@-r7
3773 0x8030 <fact+4>: 6d f6 mov.w r6,@@-r7
3774 0x8032 <fact+6>: 0d 76 mov.w r7,r6
3775 0x8034 <fact+8>: 6f 70 00 08 mov.w @@(0x8,r7),r0
3776 0x8038 <fact+12> 19 11 sub.w r1,r1
3784 @chapter Examining Data
3786 @cindex printing data
3787 @cindex examining data
3790 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
3791 @c document because it is nonstandard... Under Epoch it displays in a
3792 @c different window or something like that.
3793 The usual way to examine data in your program is with the @code{print}
3794 command (abbreviated @code{p}), or its synonym @code{inspect}.
3796 It evaluates and prints the value of an expression of the language your
3797 program is written in (@pxref{Languages, ,Using @value{GDBN} with Different
3802 @item print @var{exp}
3803 @itemx print /@var{f} @var{exp}
3804 @var{exp} is an expression (in the source language). By default the
3805 value of @var{exp} is printed in a format appropriate to its data type;
3806 you can choose a different format by specifying @samp{/@var{f}}, where
3807 @var{f} is a letter specifying the format; @pxref{Output Formats,,Output
3811 @itemx print /@var{f}
3812 If you omit @var{exp}, @value{GDBN} displays the last value again (from the
3813 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
3814 conveniently inspect the same value in an alternative format.
3817 A more low-level way of examining data is with the @code{x} command.
3818 It examines data in memory at a specified address and prints it in a
3819 specified format. @xref{Memory, ,Examining memory}.
3821 If you are interested in information about types, or about how the fields
3826 are declared, use the @code{ptype @var{exp}}
3827 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}.
3830 * Expressions:: Expressions
3831 * Variables:: Program variables
3832 * Arrays:: Artificial arrays
3833 * Output Formats:: Output formats
3834 * Memory:: Examining memory
3835 * Auto Display:: Automatic display
3836 * Print Settings:: Print settings
3837 * Value History:: Value history
3838 * Convenience Vars:: Convenience variables
3839 * Registers:: Registers
3841 * Floating Point Hardware:: Floating point hardware
3846 @section Expressions
3849 @code{print} and many other @value{GDBN} commands accept an expression and
3850 compute its value. Any kind of constant, variable or operator defined
3851 by the programming language you are using is valid in an expression in
3852 @value{GDBN}. This includes conditional expressions, function calls, casts
3853 and string constants. It unfortunately does not include symbols defined
3854 by preprocessor @code{#define} commands.
3857 Because C is so widespread, most of the expressions shown in examples in
3858 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
3859 Languages}, for information on how to use expressions in other
3862 In this section, we discuss operators that you can use in @value{GDBN}
3863 expressions regardless of your programming language.
3865 Casts are supported in all languages, not just in C, because it is so
3866 useful to cast a number into a pointer so as to examine a structure
3867 at that address in memory.
3868 @c FIXME: casts supported---Mod2 true?
3871 @value{GDBN} supports these operators in addition to those of programming
3876 @samp{@@} is a binary operator for treating parts of memory as arrays.
3877 @xref{Arrays, ,Artificial arrays}, for more information.
3880 @samp{::} allows you to specify a variable in terms of the file or
3881 function where it is defined. @xref{Variables, ,Program variables}.
3883 @item @{@var{type}@} @var{addr}
3884 @cindex @{@var{type}@}
3885 @cindex type casting memory
3886 @cindex memory, viewing as typed object
3887 @cindex casts, to view memory
3888 Refers to an object of type @var{type} stored at address @var{addr} in
3889 memory. @var{addr} may be any expression whose value is an integer or
3890 pointer (but parentheses are required around binary operators, just as in
3891 a cast). This construct is allowed regardless of what kind of data is
3892 normally supposed to reside at @var{addr}.
3896 @section Program variables
3898 The most common kind of expression to use is the name of a variable
3901 Variables in expressions are understood in the selected stack frame
3902 (@pxref{Selection, ,Selecting a frame}); they must either be global
3903 (or static) or be visible according to the scope rules of the
3904 programming language from the point of execution in that frame. This
3905 means that in the function
3920 you can examine and use the variable @code{a} whenever your program is
3921 executing within the function @code{foo}, but you can only use or
3922 examine the variable @code{b} while your program is executing inside
3923 the block where @code{b} is declared.
3925 @cindex variable name conflict
3926 There is an exception: you can refer to a variable or function whose
3927 scope is a single source file even if the current execution point is not
3928 in this file. But it is possible to have more than one such variable or
3929 function with the same name (in different source files). If that
3930 happens, referring to that name has unpredictable effects. If you wish,
3931 you can specify a static variable in a particular function or file,
3932 using the colon-colon notation:
3936 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
3940 @var{file}::@var{variable}
3941 @var{function}::@var{variable}
3945 Here @var{file} or @var{function} is the name of the context for the
3946 static @var{variable}. In the case of file names, you can use quotes to
3947 make sure @value{GDBN} parses the file name as a single word---for example,
3948 to print a global value of @code{x} defined in @file{f2.c}:
3951 (@value{GDBP}) p 'f2.c'::x
3955 @cindex C++ scope resolution
3956 This use of @samp{::} is very rarely in conflict with the very similar
3957 use of the same notation in C++. @value{GDBN} also supports use of the C++
3958 scope resolution operator in @value{GDBN} expressions.
3959 @c FIXME: Um, so what happens in one of those rare cases where it's in
3963 @cindex wrong values
3964 @cindex variable values, wrong
3966 @emph{Warning:} Occasionally, a local variable may appear to have the
3967 wrong value at certain points in a function---just after entry to a new
3968 scope, and just before exit.
3970 You may see this problem when you are stepping by machine instructions.
3971 This is because on most machines, it takes more than one instruction to
3972 set up a stack frame (including local variable definitions); if you are
3973 stepping by machine instructions, variables may appear to have the wrong
3974 values until the stack frame is completely built. On exit, it usually
3975 also takes more than one machine instruction to destroy a stack frame;
3976 after you begin stepping through that group of instructions, local
3977 variable definitions may be gone.
3980 @section Artificial arrays
3982 @cindex artificial array
3984 It is often useful to print out several successive objects of the
3985 same type in memory; a section of an array, or an array of
3986 dynamically determined size for which only a pointer exists in the
3989 You can do this by referring to a contiguous span of memory as an
3990 @dfn{artificial array}, using the binary operator @samp{@@}. The left
3991 operand of @samp{@@} should be the first element of the desired array,
3992 as an individual object. The right operand should be the desired length
3993 of the array. The result is an array value whose elements are all of
3994 the type of the left argument. The first element is actually the left
3995 argument; the second element comes from bytes of memory immediately
3996 following those that hold the first element, and so on. Here is an
3997 example. If a program says
4000 int *array = (int *) malloc (len * sizeof (int));
4004 you can print the contents of @code{array} with
4010 The left operand of @samp{@@} must reside in memory. Array values made
4011 with @samp{@@} in this way behave just like other arrays in terms of
4012 subscripting, and are coerced to pointers when used in expressions.
4013 Artificial arrays most often appear in expressions via the value history
4014 (@pxref{Value History, ,Value history}), after printing one out.
4016 Sometimes the artificial array mechanism is not quite enough; in
4017 moderately complex data structures, the elements of interest may not
4018 actually be adjacent---for example, if you are interested in the values
4019 of pointers in an array. One useful work-around in this situation is
4020 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4021 variables}) as a counter in an expression that prints the first
4022 interesting value, and then repeat that expression via @key{RET}. For
4023 instance, suppose you have an array @code{dtab} of pointers to
4024 structures, and you are interested in the values of a field @code{fv}
4025 in each structure. Here is an example of what you might type:
4035 @node Output Formats
4036 @section Output formats
4038 @cindex formatted output
4039 @cindex output formats
4040 By default, @value{GDBN} prints a value according to its data type. Sometimes
4041 this is not what you want. For example, you might want to print a number
4042 in hex, or a pointer in decimal. Or you might want to view data in memory
4043 at a certain address as a character string or as an instruction. To do
4044 these things, specify an @dfn{output format} when you print a value.
4046 The simplest use of output formats is to say how to print a value
4047 already computed. This is done by starting the arguments of the
4048 @code{print} command with a slash and a format letter. The format
4049 letters supported are:
4053 Regard the bits of the value as an integer, and print the integer in
4057 Print as integer in signed decimal.
4060 Print as integer in unsigned decimal.
4063 Print as integer in octal.
4066 Print as integer in binary. The letter @samp{t} stands for ``two''.
4067 @footnote{@samp{b} cannot be used because these format letters are also
4068 used with the @code{x} command, where @samp{b} stands for ``byte'';
4069 @pxref{Memory,,Examining memory}.}
4072 Print as an address, both absolute in hex and as an offset from the
4073 nearest preceding symbol. This format can be used to discover where (in
4074 what function) an unknown address is located:
4077 (@value{GDBP}) p/a 0x54320
4078 $3 = 0x54320 <_initialize_vx+396>
4082 Regard as an integer and print it as a character constant.
4085 Regard the bits of the value as a floating point number and print
4086 using typical floating point syntax.
4089 For example, to print the program counter in hex (@pxref{Registers}), type
4096 Note that no space is required before the slash; this is because command
4097 names in @value{GDBN} cannot contain a slash.
4099 To reprint the last value in the value history with a different format,
4100 you can use the @code{print} command with just a format and no
4101 expression. For example, @samp{p/x} reprints the last value in hex.
4104 @section Examining memory
4106 You can use the command @code{x} (for ``examine'') to examine memory in
4107 any of several formats, independently of your program's data types.
4109 @cindex examining memory
4112 @item x/@var{nfu} @var{addr}
4115 Use the @code{x} command to examine memory.
4118 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4119 much memory to display and how to format it; @var{addr} is an
4120 expression giving the address where you want to start displaying memory.
4121 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4122 Several commands set convenient defaults for @var{addr}.
4125 @item @var{n}, the repeat count
4126 The repeat count is a decimal integer; the default is 1. It specifies
4127 how much memory (counting by units @var{u}) to display.
4128 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4131 @item @var{f}, the display format
4132 The display format is one of the formats used by @code{print},
4133 or @samp{s} (null-terminated string) or @samp{i} (machine instruction).
4134 The default is @samp{x} (hexadecimal) initially, or the format from the
4135 last time you used either @code{x} or @code{print}.
4137 @item @var{u}, the unit size
4138 The unit size is any of
4144 Halfwords (two bytes).
4146 Words (four bytes). This is the initial default.
4148 Giant words (eight bytes).
4151 Each time you specify a unit size with @code{x}, that size becomes the
4152 default unit the next time you use @code{x}. (For the @samp{s} and
4153 @samp{i} formats, the unit size is ignored and is normally not written.)
4155 @item @var{addr}, starting display address
4156 @var{addr} is the address where you want @value{GDBN} to begin displaying
4157 memory. The expression need not have a pointer value (though it may);
4158 it is always interpreted as an integer address of a byte of memory.
4159 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4160 @var{addr} is usually just after the last address examined---but several
4161 other commands also set the default address: @code{info breakpoints} (to
4162 the address of the last breakpoint listed), @code{info line} (to the
4163 starting address of a line), and @code{print} (if you use it to display
4164 a value from memory).
4167 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4168 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4169 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4170 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4171 @pxref{Registers}) in hexadecimal (@samp{x}).
4173 Since the letters indicating unit sizes are all distinct from the
4174 letters specifying output formats, you do not have to remember whether
4175 unit size or format comes first; either order will work. The output
4176 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4177 (However, the count @var{n} must come first; @samp{wx4} will not work.)
4179 Even though the unit size @var{u} is ignored for the formats @samp{s}
4180 and @samp{i}, you might still want to use a count @var{n}; for example,
4181 @samp{3i} specifies that you want to see three machine instructions,
4182 including any operands. The command @code{disassemble} gives an
4183 alternative way of inspecting machine instructions; @pxref{Machine
4184 Code,,Source and machine code}.
4186 All the defaults for the arguments to @code{x} are designed to make it
4187 easy to continue scanning memory with minimal specifications each time
4188 you use @code{x}. For example, after you have inspected three machine
4189 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4190 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4191 the repeat count @var{n} is used again; the other arguments default as
4192 for successive uses of @code{x}.
4194 @cindex @code{$_}, @code{$__}, and value history
4195 The addresses and contents printed by the @code{x} command are not saved
4196 in the value history because there is often too much of them and they
4197 would get in the way. Instead, @value{GDBN} makes these values available for
4198 subsequent use in expressions as values of the convenience variables
4199 @code{$_} and @code{$__}. After an @code{x} command, the last address
4200 examined is available for use in expressions in the convenience variable
4201 @code{$_}. The contents of that address, as examined, are available in
4202 the convenience variable @code{$__}.
4204 If the @code{x} command has a repeat count, the address and contents saved
4205 are from the last memory unit printed; this is not the same as the last
4206 address printed if several units were printed on the last line of output.
4209 @section Automatic display
4210 @cindex automatic display
4211 @cindex display of expressions
4213 If you find that you want to print the value of an expression frequently
4214 (to see how it changes), you might want to add it to the @dfn{automatic
4215 display list} so that @value{GDBN} will print its value each time your program stops.
4216 Each expression added to the list is given a number to identify it;
4217 to remove an expression from the list, you specify that number.
4218 The automatic display looks like this:
4222 3: bar[5] = (struct hack *) 0x3804
4226 This display shows item numbers, expressions and their current values. As with
4227 displays you request manually using @code{x} or @code{print}, you can
4228 specify the output format you prefer; in fact, @code{display} decides
4229 whether to use @code{print} or @code{x} depending on how elaborate your
4230 format specification is---it uses @code{x} if you specify a unit size,
4231 or one of the two formats (@samp{i} and @samp{s}) that are only
4232 supported by @code{x}; otherwise it uses @code{print}.
4235 @item display @var{exp}
4237 Add the expression @var{exp} to the list of expressions to display
4238 each time your program stops. @xref{Expressions, ,Expressions}.
4240 @code{display} will not repeat if you press @key{RET} again after using it.
4242 @item display/@var{fmt} @var{exp}
4243 For @var{fmt} specifying only a display format and not a size or
4244 count, add the expression @var{exp} to the auto-display list but
4245 arrange to display it each time in the specified format @var{fmt}.
4246 @xref{Output Formats,,Output formats}.
4248 @item display/@var{fmt} @var{addr}
4249 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4250 number of units, add the expression @var{addr} as a memory address to
4251 be examined each time your program stops. Examining means in effect
4252 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4255 For example, @samp{display/i $pc} can be helpful, to see the machine
4256 instruction about to be executed each time execution stops (@samp{$pc}
4257 is a common name for the program counter; @pxref{Registers}).
4260 @item undisplay @var{dnums}@dots{}
4261 @itemx delete display @var{dnums}@dots{}
4262 @kindex delete display
4264 Remove item numbers @var{dnums} from the list of expressions to display.
4266 @code{undisplay} will not repeat if you press @key{RET} after using it.
4267 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4269 @item disable display @var{dnums}@dots{}
4270 @kindex disable display
4271 Disable the display of item numbers @var{dnums}. A disabled display
4272 item is not printed automatically, but is not forgotten. It may be
4273 enabled again later.
4275 @item enable display @var{dnums}@dots{}
4276 @kindex enable display
4277 Enable display of item numbers @var{dnums}. It becomes effective once
4278 again in auto display of its expression, until you specify otherwise.
4281 Display the current values of the expressions on the list, just as is
4282 done when your program stops.
4285 @kindex info display
4286 Print the list of expressions previously set up to display
4287 automatically, each one with its item number, but without showing the
4288 values. This includes disabled expressions, which are marked as such.
4289 It also includes expressions which would not be displayed right now
4290 because they refer to automatic variables not currently available.
4293 If a display expression refers to local variables, then it does not make
4294 sense outside the lexical context for which it was set up. Such an
4295 expression is disabled when execution enters a context where one of its
4296 variables is not defined. For example, if you give the command
4297 @code{display last_char} while inside a function with an argument
4298 @code{last_char}, then this argument will be displayed while your program
4299 continues to stop inside that function. When it stops elsewhere---where
4300 there is no variable @code{last_char}---display is disabled. The next time
4301 your program stops where @code{last_char} is meaningful, you can enable the
4302 display expression once again.
4304 @node Print Settings
4305 @section Print settings
4307 @cindex format options
4308 @cindex print settings
4309 @value{GDBN} provides the following ways to control how arrays, structures,
4310 and symbols are printed.
4313 These settings are useful for debugging programs in any language:
4316 @item set print address
4317 @itemx set print address on
4318 @kindex set print address
4319 @value{GDBN} will print memory addresses showing the location of stack
4320 traces, structure values, pointer values, breakpoints, and so forth,
4321 even when it also displays the contents of those addresses. The default
4322 is on. For example, this is what a stack frame display looks like, with
4323 @code{set print address on}:
4328 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4330 530 if (lquote != def_lquote)
4334 @item set print address off
4335 Do not print addresses when displaying their contents. For example,
4336 this is the same stack frame displayed with @code{set print address off}:
4340 (@value{GDBP}) set print addr off
4342 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4343 530 if (lquote != def_lquote)
4347 You can use @samp{set print address off} to eliminate all machine
4348 dependent displays from the @value{GDBN} interface. For example, with
4349 @code{print address off}, you should get the same text for backtraces on
4350 all machines---whether or not they involve pointer arguments.
4352 @item show print address
4353 @kindex show print address
4354 Show whether or not addresses are to be printed.
4357 When @value{GDBN} prints a symbolic address, it normally prints the
4358 closest earlier symbol plus an offset. If that symbol does not uniquely
4359 identify the address (for example, it is a name whose scope is a single
4360 source file), you may need to disambiguate. One way to do this is with
4361 @code{info line}, for example @code{info line *0x4537}. Alternately,
4362 you can set @value{GDBN} to print the source file and line number when
4363 it prints a symbolic address:
4366 @item set print symbol-filename on
4367 @kindex set print symbol-filename
4368 Tell @value{GDBN} to print the source file name and line number of a
4369 symbol in the symbolic form of an address.
4371 @item set print symbol-filename off
4372 Do not print source file name and line number of a symbol. This is the
4375 @item show print symbol-filename
4376 @kindex show print symbol-filename
4377 Show whether or not @value{GDBN} will print the source file name and
4378 line number of a symbol in the symbolic form of an address.
4381 Also, you may wish to see the symbolic form only if the address being
4382 printed is reasonably close to the closest earlier symbol:
4385 @item set print max-symbolic-offset @var{max-offset}
4386 @kindex set print max-symbolic-offset
4387 Tell @value{GDBN} to only display the symbolic form of an address if the
4388 offset between the closest earlier symbol and the address is less than
4389 @var{max-offset}. The default is 0, which means to always print the
4390 symbolic form of an address, if any symbol precedes it.
4392 @item show print max-symbolic-offset
4393 @kindex show print max-symbolic-offset
4394 Ask how large the maximum offset is that @value{GDBN} will print in a
4399 @item set print array
4400 @itemx set print array on
4401 @kindex set print array
4402 @value{GDBN} will pretty-print arrays. This format is more convenient to read,
4403 but uses more space. The default is off.
4405 @item set print array off
4406 Return to compressed format for arrays.
4408 @item show print array
4409 @kindex show print array
4410 Show whether compressed or pretty format is selected for displaying
4413 @item set print elements @var{number-of-elements}
4414 @kindex set print elements
4415 If @value{GDBN} is printing a large array, it will stop printing after it has
4416 printed the number of elements set by the @code{set print elements} command.
4417 This limit also applies to the display of strings.
4418 Setting the number of elements to zero means that the printing is unlimited.
4420 @item show print elements
4421 @kindex show print elements
4422 Display the number of elements of a large array that @value{GDBN} will print
4423 before losing patience.
4425 @item set print pretty on
4426 @kindex set print pretty
4427 Cause @value{GDBN} to print structures in an indented format with one member per
4443 @item set print pretty off
4444 Cause @value{GDBN} to print structures in a compact format, like this:
4448 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
4449 meat = 0x54 "Pork"@}
4454 This is the default format.
4456 @item show print pretty
4457 @kindex show print pretty
4458 Show which format @value{GDBN} will use to print structures.
4460 @item set print sevenbit-strings on
4461 @kindex set print sevenbit-strings
4462 Print using only seven-bit characters; if this option is set,
4463 @value{GDBN} will display any eight-bit characters (in strings or character
4464 values) using the notation @code{\}@var{nnn}. For example, @kbd{M-a} is
4465 displayed as @code{\341}.
4467 @item set print sevenbit-strings off
4468 Print using either seven-bit or eight-bit characters, as required. This
4471 @item show print sevenbit-strings
4472 @kindex show print sevenbit-strings
4473 Show whether or not @value{GDBN} will print only seven-bit characters.
4475 @item set print union on
4476 @kindex set print union
4477 Tell @value{GDBN} to print unions which are contained in structures. This is the
4480 @item set print union off
4481 Tell @value{GDBN} not to print unions which are contained in structures.
4483 @item show print union
4484 @kindex show print union
4485 Ask @value{GDBN} whether or not it will print unions which are contained in
4488 For example, given the declarations
4491 typedef enum @{Tree, Bug@} Species;
4492 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
4493 typedef enum @{Caterpillar, Cocoon, Butterfly@}
4504 struct thing foo = @{Tree, @{Acorn@}@};
4508 with @code{set print union on} in effect @samp{p foo} would print
4511 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
4515 and with @code{set print union off} in effect it would print
4518 $1 = @{it = Tree, form = @{...@}@}
4525 These settings are of interest when debugging C++ programs:
4528 @item set print demangle
4529 @itemx set print demangle on
4530 @kindex set print demangle
4531 Print C++ names in their source form rather than in the encoded
4532 (``mangled'') form passed to the assembler and linker for type-safe
4533 linkage. The default is @samp{on}.
4535 @item show print demangle
4536 @kindex show print demangle
4537 Show whether C++ names will be printed in mangled or demangled form.
4539 @item set print asm-demangle
4540 @itemx set print asm-demangle on
4541 @kindex set print asm-demangle
4542 Print C++ names in their source form rather than their mangled form, even
4543 in assembler code printouts such as instruction disassemblies.
4546 @item show print asm-demangle
4547 @kindex show print asm-demangle
4548 Show whether C++ names in assembly listings will be printed in mangled
4551 @item set demangle-style @var{style}
4552 @kindex set demangle-style
4553 @cindex C++ symbol decoding style
4554 @cindex symbol decoding style, C++
4555 Choose among several encoding schemes used by different compilers to
4556 represent C++ names. The choices for @var{style} are currently:
4560 Allow @value{GDBN} to choose a decoding style by inspecting your program.
4563 Decode based on the GNU C++ compiler (@code{g++}) encoding algorithm.
4566 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
4569 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
4570 @strong{Warning:} this setting alone is not sufficient to allow
4571 debugging @code{cfront}-generated executables. @value{GDBN} would
4572 require further enhancement to permit that.
4575 @item show demangle-style
4576 @kindex show demangle-style
4577 Display the encoding style currently in use for decoding C++ symbols.
4579 @item set print object
4580 @itemx set print object on
4581 @kindex set print object
4582 When displaying a pointer to an object, identify the @emph{actual}
4583 (derived) type of the object rather than the @emph{declared} type, using
4584 the virtual function table.
4586 @item set print object off
4587 Display only the declared type of objects, without reference to the
4588 virtual function table. This is the default setting.
4590 @item show print object
4591 @kindex show print object
4592 Show whether actual, or declared, object types will be displayed.
4594 @item set print vtbl
4595 @itemx set print vtbl on
4596 @kindex set print vtbl
4597 Pretty print C++ virtual function tables. The default is off.
4599 @item set print vtbl off
4600 Do not pretty print C++ virtual function tables.
4602 @item show print vtbl
4603 @kindex show print vtbl
4604 Show whether C++ virtual function tables are pretty printed, or not.
4609 @section Value history
4611 @cindex value history
4612 Values printed by the @code{print} command are saved in the @value{GDBN} @dfn{value
4613 history} so that you can refer to them in other expressions. Values are
4614 kept until the symbol table is re-read or discarded (for example with
4615 the @code{file} or @code{symbol-file} commands). When the symbol table
4616 changes, the value history is discarded, since the values may contain
4617 pointers back to the types defined in the symbol table.
4621 @cindex history number
4622 The values printed are given @dfn{history numbers} by which you can
4623 refer to them. These are successive integers starting with one.
4624 @code{print} shows you the history number assigned to a value by
4625 printing @samp{$@var{num} = } before the value; here @var{num} is the
4628 To refer to any previous value, use @samp{$} followed by the value's
4629 history number. The way @code{print} labels its output is designed to
4630 remind you of this. Just @code{$} refers to the most recent value in
4631 the history, and @code{$$} refers to the value before that.
4632 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
4633 is the value just prior to @code{$$}, @code{$$1} is equivalent to
4634 @code{$$}, and @code{$$0} is equivalent to @code{$}.
4636 For example, suppose you have just printed a pointer to a structure and
4637 want to see the contents of the structure. It suffices to type
4643 If you have a chain of structures where the component @code{next} points
4644 to the next one, you can print the contents of the next one with this:
4651 You can print successive links in the chain by repeating this
4652 command---which you can do by just typing @key{RET}.
4654 Note that the history records values, not expressions. If the value of
4655 @code{x} is 4 and you type these commands:
4663 then the value recorded in the value history by the @code{print} command
4664 remains 4 even though the value of @code{x} has changed.
4669 Print the last ten values in the value history, with their item numbers.
4670 This is like @samp{p@ $$9} repeated ten times, except that @code{show
4671 values} does not change the history.
4673 @item show values @var{n}
4674 Print ten history values centered on history item number @var{n}.
4677 Print ten history values just after the values last printed. If no more
4678 values are available, produces no display.
4681 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
4682 same effect as @samp{show values +}.
4684 @node Convenience Vars
4685 @section Convenience variables
4687 @cindex convenience variables
4688 @value{GDBN} provides @dfn{convenience variables} that you can use within
4689 @value{GDBN} to hold on to a value and refer to it later. These variables
4690 exist entirely within @value{GDBN}; they are not part of your program, and
4691 setting a convenience variable has no direct effect on further execution
4692 of your program. That is why you can use them freely.
4694 Convenience variables are prefixed with @samp{$}. Any name preceded by
4695 @samp{$} can be used for a convenience variable, unless it is one of
4696 the predefined machine-specific register names (@pxref{Registers}).
4697 (Value history references, in contrast, are @emph{numbers} preceded
4698 by @samp{$}. @xref{Value History, ,Value history}.)
4700 You can save a value in a convenience variable with an assignment
4701 expression, just as you would set a variable in your program.
4705 set $foo = *object_ptr
4709 would save in @code{$foo} the value contained in the object pointed to by
4712 Using a convenience variable for the first time creates it, but its
4713 value is @code{void} until you assign a new value. You can alter the
4714 value with another assignment at any time.
4716 Convenience variables have no fixed types. You can assign a convenience
4717 variable any type of value, including structures and arrays, even if
4718 that variable already has a value of a different type. The convenience
4719 variable, when used as an expression, has the type of its current value.
4722 @item show convenience
4723 @kindex show convenience
4724 Print a list of convenience variables used so far, and their values.
4725 Abbreviated @code{show con}.
4728 One of the ways to use a convenience variable is as a counter to be
4729 incremented or a pointer to be advanced. For example, to print
4730 a field from successive elements of an array of structures:
4734 print bar[$i++]->contents
4735 @i{@dots{} repeat that command by typing @key{RET}.}
4738 Some convenience variables are created automatically by @value{GDBN} and given
4739 values likely to be useful.
4744 The variable @code{$_} is automatically set by the @code{x} command to
4745 the last address examined (@pxref{Memory, ,Examining memory}). Other
4746 commands which provide a default address for @code{x} to examine also
4747 set @code{$_} to that address; these commands include @code{info line}
4748 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
4749 except when set by the @code{x} command, in which case it is a pointer
4750 to the type of @code{$__}.
4754 The variable @code{$__} is automatically set by the @code{x} command
4755 to the value found in the last address examined. Its type is chosen
4756 to match the format in which the data was printed.
4763 You can refer to machine register contents, in expressions, as variables
4764 with names starting with @samp{$}. The names of registers are different
4765 for each machine; use @code{info registers} to see the names used on
4769 @item info registers
4770 @kindex info registers
4771 Print the names and values of all registers except floating-point
4772 registers (in the selected stack frame).
4774 @item info all-registers
4775 @kindex info all-registers
4776 @cindex floating point registers
4777 Print the names and values of all registers, including floating-point
4780 @item info registers @var{regname} @dots{}
4781 Print the relativized value of each specified register @var{regname}.
4782 @var{regname} may be any register name valid on the machine you are using, with
4783 or without the initial @samp{$}.
4786 @value{GDBN} has four ``standard'' register names that are available (in
4787 expressions) on most machines---whenever they do not conflict with an
4788 architecture's canonical mnemonics for registers. The register names
4789 @code{$pc} and @code{$sp} are used for the program counter register and
4790 the stack pointer. @code{$fp} is used for a register that contains a
4791 pointer to the current stack frame, and @code{$ps} is used for a
4792 register that contains the processor status. For example,
4793 you could print the program counter in hex with
4800 or print the instruction to be executed next with
4807 or add four to the stack pointer@footnote{This is a way of removing
4808 one word from the stack, on machines where stacks grow downward in
4809 memory (most machines, nowadays). This assumes that the innermost
4810 stack frame is selected; setting @code{$sp} is not allowed when other
4811 stack frames are selected. To pop entire frames off the stack,
4812 regardless of machine architecture, use @code{return};
4813 @pxref{Returning, ,Returning from a function}.} with
4819 Whenever possible, these four standard register names are available on
4820 your machine even though the machine has different canonical mnemonics,
4821 so long as there is no conflict. The @code{info registers} command
4822 shows the canonical names. For example, on the SPARC, @code{info
4823 registers} displays the processor status register as @code{$psr} but you
4824 can also refer to it as @code{$ps}.
4826 @value{GDBN} always considers the contents of an ordinary register as an
4827 integer when the register is examined in this way. Some machines have
4828 special registers which can hold nothing but floating point; these
4829 registers are considered to have floating point values. There is no way
4830 to refer to the contents of an ordinary register as floating point value
4831 (although you can @emph{print} it as a floating point value with
4832 @samp{print/f $@var{regname}}).
4834 Some registers have distinct ``raw'' and ``virtual'' data formats. This
4835 means that the data format in which the register contents are saved by
4836 the operating system is not the same one that your program normally
4837 sees. For example, the registers of the 68881 floating point
4838 coprocessor are always saved in ``extended'' (raw) format, but all C
4839 programs expect to work with ``double'' (virtual) format. In such
4840 cases, @value{GDBN} normally works with the virtual format only (the format that
4841 makes sense for your program), but the @code{info registers} command
4842 prints the data in both formats.
4844 Normally, register values are relative to the selected stack frame
4845 (@pxref{Selection, ,Selecting a frame}). This means that you get the
4846 value that the register would contain if all stack frames farther in
4847 were exited and their saved registers restored. In order to see the
4848 true contents of hardware registers, you must select the innermost
4849 frame (with @samp{frame 0}).
4851 However, @value{GDBN} must deduce where registers are saved, from the machine
4852 code generated by your compiler. If some registers are not saved, or if
4853 @value{GDBN} is unable to locate the saved registers, the selected stack
4854 frame will make no difference.
4858 @item set rstack_high_address @var{address}
4859 @kindex set rstack_high_address
4860 @cindex AMD 29K register stack
4861 @cindex register stack, AMD29K
4862 On AMD 29000 family processors, registers are saved in a separate
4863 ``register stack''. There is no way for @value{GDBN} to determine the extent
4864 of this stack. Normally, @value{GDBN} just assumes that the stack is ``large
4865 enough''. This may result in @value{GDBN} referencing memory locations that
4866 do not exist. If necessary, you can get around this problem by
4867 specifying the ending address of the register stack with the @code{set
4868 rstack_high_address} command. The argument should be an address, which
4869 you will probably want to precede with @samp{0x} to specify in
4872 @item show rstack_high_address
4873 @kindex show rstack_high_address
4874 Display the current limit of the register stack, on AMD 29000 family
4880 @node Floating Point Hardware
4881 @section Floating point hardware
4882 @cindex floating point
4884 @c FIXME! Really host, not target?
4885 Depending on the host machine architecture, @value{GDBN} may be able to give
4886 you more information about the status of the floating point hardware.
4891 Display hardware-dependent information about the floating
4892 point unit. The exact contents and layout vary depending on the
4893 floating point chip; on some platforms, @samp{info float} is not
4896 @c FIXME: this is a cop-out. Try to get examples, explanations. Only
4897 @c FIXME...supported currently on arm's and 386's. Mark properly with
4898 @c FIXME... m4 macros to isolate general statements from hardware-dep,
4899 @c FIXME... at that point.
4904 @chapter Using @value{GDBN} with Different Languages
4908 Although programming languages generally have common aspects, they are
4909 rarely expressed in the same manner. For instance, in ANSI C,
4910 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
4911 Modula-2, it is accomplished by @code{p^}. Values can also be
4912 represented (and displayed) differently. Hex numbers in C are written
4913 like @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
4916 @cindex working language
4917 Language-specific information is built into @value{GDBN} for some languages,
4918 allowing you to express operations like the above in your program's
4919 native language, and allowing @value{GDBN} to output values in a manner
4920 consistent with the syntax of your program's native language. The
4921 language you use to build expressions, called the @dfn{working
4922 language}, can be selected manually, or @value{GDBN} can set it
4926 * Setting:: Switching between source languages
4927 * Show:: Displaying the language
4929 * Checks:: Type and range checks
4932 * Support:: Supported languages
4936 @section Switching between source languages
4938 There are two ways to control the working language---either have @value{GDBN}
4939 set it automatically, or select it manually yourself. You can use the
4940 @code{set language} command for either purpose. On startup, @value{GDBN}
4941 defaults to setting the language automatically.
4944 * Manually:: Setting the working language manually
4945 * Automatically:: Having @value{GDBN} infer the source language
4949 @subsection Setting the working language
4951 If you allow @value{GDBN} to set the language automatically,
4952 expressions are interpreted the same way in your debugging session and
4955 @kindex set language
4956 If you wish, you may set the language manually. To do this, issue the
4957 command @samp{set language @var{lang}}, where @var{lang} is the name of
4963 @code{c} or @code{modula-2}.
4965 For a list of the supported languages, type @samp{set language}.
4966 @c FIXME: rms: eventually this command should be "help set language".
4969 Setting the language manually prevents @value{GDBN} from updating the working
4970 language automatically. This can lead to confusion if you try
4971 to debug a program when the working language is not the same as the
4972 source language, when an expression is acceptable to both
4973 languages---but means different things. For instance, if the current
4974 source file were written in C, and @value{GDBN} was parsing Modula-2, a
4982 might not have the effect you intended. In C, this means to add
4983 @code{b} and @code{c} and place the result in @code{a}. The result
4984 printed would be the value of @code{a}. In Modula-2, this means to compare
4985 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
4989 @subsection Having @value{GDBN} infer the source language
4991 To have @value{GDBN} set the working language automatically, use @samp{set
4992 language local} or @samp{set language auto}. @value{GDBN} then infers the
4993 language that a program was written in by looking at the name of its
4994 source files, and examining their extensions:
4999 Modula-2 source file
5010 This information is recorded for each function or procedure in a source
5011 file. When your program stops in a frame (usually by encountering a
5012 breakpoint), @value{GDBN} sets the working language to the language recorded
5013 for the function in that frame. If the language for a frame is unknown
5014 (that is, if the function or block corresponding to the frame was
5015 defined in a source file that does not have a recognized extension), the
5016 current working language is not changed, and @value{GDBN} issues a warning.
5018 This may not seem necessary for most programs, which are written
5019 entirely in one source language. However, program modules and libraries
5020 written in one source language can be used by a main program written in
5021 a different source language. Using @samp{set language auto} in this
5022 case frees you from having to set the working language manually.
5025 @section Displaying the language
5027 The following commands will help you find out which language is the
5028 working language, and also what language source files were written in.
5030 @kindex show language
5035 Display the current working language. This is the
5036 language you can use with commands such as @code{print} to
5037 build and compute expressions that may involve variables in your program.
5040 Among the other information listed here (@pxref{Frame Info, ,Information
5041 about a frame}) is the source language for this frame. This is the
5042 language that will become the working language if you ever use an
5043 identifier that is in this frame.
5046 Among the other information listed here (@pxref{Symbols, ,Examining the
5047 Symbol Table}) is the source language of this source file.
5052 @section Type and range checking
5055 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
5056 checking are included, but they do not yet have any effect. This
5057 section documents the intended facilities.
5059 @c FIXME remove warning when type/range code added
5061 Some languages are designed to guard you against making seemingly common
5062 errors through a series of compile- and run-time checks. These include
5063 checking the type of arguments to functions and operators, and making
5064 sure mathematical overflows are caught at run time. Checks such as
5065 these help to ensure a program's correctness once it has been compiled
5066 by eliminating type mismatches, and providing active checks for range
5067 errors when your program is running.
5069 @value{GDBN} can check for conditions like the above if you wish.
5070 Although @value{GDBN} will not check the statements in your program, it
5071 can check expressions entered directly into @value{GDBN} for evaluation via
5072 the @code{print} command, for example. As with the working language,
5073 @value{GDBN} can also decide whether or not to check automatically based on
5074 your program's source language. @xref{Support, ,Supported languages},
5075 for the default settings of supported languages.
5078 * Type Checking:: An overview of type checking
5079 * Range Checking:: An overview of range checking
5082 @cindex type checking
5083 @cindex checks, type
5085 @subsection An overview of type checking
5087 Some languages, such as Modula-2, are strongly typed, meaning that the
5088 arguments to operators and functions have to be of the correct type,
5089 otherwise an error occurs. These checks prevent type mismatch
5090 errors from ever causing any run-time problems. For example,
5098 The second example fails because the @code{CARDINAL} 1 is not
5099 type-compatible with the @code{REAL} 2.3.
5101 For expressions you use in @value{GDBN} commands, you can tell the @value{GDBN}
5102 type checker to skip checking; to treat any mismatches as errors and
5103 abandon the expression; or only issue warnings when type mismatches
5104 occur, but evaluate the expression anyway. When you choose the last of
5105 these, @value{GDBN} evaluates expressions like the second example above, but
5106 also issues a warning.
5108 Even though you may turn type checking off, other type-based reasons may
5109 prevent @value{GDBN} from evaluating an expression. For instance, @value{GDBN} does not
5110 know how to add an @code{int} and a @code{struct foo}. These particular
5111 type errors have nothing to do with the language in use, and usually
5112 arise from expressions, such as the one described above, which make
5113 little sense to evaluate anyway.
5115 Each language defines to what degree it is strict about type. For
5116 instance, both Modula-2 and C require the arguments to arithmetical
5117 operators to be numbers. In C, enumerated types and pointers can be
5118 represented as numbers, so that they are valid arguments to mathematical
5119 operators. @xref{Support, ,Supported languages}, for further
5120 details on specific languages.
5122 @value{GDBN} provides some additional commands for controlling the type checker:
5125 @kindex set check type
5126 @kindex show check type
5128 @item set check type auto
5129 Set type checking on or off based on the current working language.
5130 @xref{Support, ,Supported languages}, for the default settings for
5133 @item set check type on
5134 @itemx set check type off
5135 Set type checking on or off, overriding the default setting for the
5136 current working language. Issue a warning if the setting does not
5137 match the language default. If any type mismatches occur in
5138 evaluating an expression while typechecking is on, @value{GDBN} prints a
5139 message and aborts evaluation of the expression.
5141 @item set check type warn
5142 Cause the type checker to issue warnings, but to always attempt to
5143 evaluate the expression. Evaluating the expression may still
5144 be impossible for other reasons. For example, @value{GDBN} cannot add
5145 numbers and structures.
5148 Show the current setting of the type checker, and whether or not @value{GDBN} is
5149 setting it automatically.
5152 @cindex range checking
5153 @cindex checks, range
5154 @node Range Checking
5155 @subsection An overview of range checking
5157 In some languages (such as Modula-2), it is an error to exceed the
5158 bounds of a type; this is enforced with run-time checks. Such range
5159 checking is meant to ensure program correctness by making sure
5160 computations do not overflow, or indices on an array element access do
5161 not exceed the bounds of the array.
5163 For expressions you use in @value{GDBN} commands, you can tell
5164 @value{GDBN} to treat range errors in one of three ways: ignore them,
5165 always treat them as errors and abandon the expression, or issue
5166 warnings but evaluate the expression anyway.
5168 A range error can result from numerical overflow, from exceeding an
5169 array index bound, or when you type a constant that is not a member
5170 of any type. Some languages, however, do not treat overflows as an
5171 error. In many implementations of C, mathematical overflow causes the
5172 result to ``wrap around'' to lower values---for example, if @var{m} is
5173 the largest integer value, and @var{s} is the smallest, then
5176 @var{m} + 1 @result{} @var{s}
5179 This, too, is specific to individual languages, and in some cases
5180 specific to individual compilers or machines. @xref{Support, ,
5181 Supported languages}, for further details on specific languages.
5183 @value{GDBN} provides some additional commands for controlling the range checker:
5186 @kindex set check range
5187 @kindex show check range
5189 @item set check range auto
5190 Set range checking on or off based on the current working language.
5191 @xref{Support, ,Supported languages}, for the default settings for
5194 @item set check range on
5195 @itemx set check range off
5196 Set range checking on or off, overriding the default setting for the
5197 current working language. A warning is issued if the setting does not
5198 match the language default. If a range error occurs, then a message
5199 is printed and evaluation of the expression is aborted.
5201 @item set check range warn
5202 Output messages when the @value{GDBN} range checker detects a range error,
5203 but attempt to evaluate the expression anyway. Evaluating the
5204 expression may still be impossible for other reasons, such as accessing
5205 memory that the process does not own (a typical example from many Unix
5209 Show the current setting of the range checker, and whether or not it is
5210 being set automatically by @value{GDBN}.
5215 @section Supported languages
5218 @value{GDBN} 4 supports C, C++, and Modula-2.
5221 @value{GDBN} 4 supports C, and C++.
5223 Some @value{GDBN} features may be used in expressions regardless of the
5224 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
5225 and the @samp{@{type@}addr} construct (@pxref{Expressions,
5226 ,Expressions}) can be used with the constructs of any supported
5229 The following sections detail to what degree each source language is
5230 supported by @value{GDBN}. These sections are not meant to be language
5231 tutorials or references, but serve only as a reference guide to what the
5232 @value{GDBN} expression parser will accept, and what input and output
5233 formats should look like for different languages. There are many good
5234 books written on each of these languages; please look to these for a
5235 language reference or tutorial.
5240 * Modula-2:: Modula-2
5244 @subsection C and C++
5246 @cindex expressions in C or C++
5248 Since C and C++ are so closely related, many features of @value{GDBN} apply
5249 to both languages. Whenever this is the case, we discuss both languages
5253 @c Cancel this below, under same condition, at end of this chapter!
5260 The C++ debugging facilities are jointly implemented by the GNU C++
5261 compiler and @value{GDBN}. Therefore, to debug your C++ code
5262 effectively, you must compile your C++ programs with the GNU C++
5263 compiler, @code{g++}.
5265 For best results when debugging C++ programs, use the stabs debugging
5266 format. You can select that format explicitly with the @code{g++}
5267 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
5268 @ref{Debugging Options,,Options for Debugging Your Program or GNU CC,
5269 gcc.info, Using GNU CC}, for more information.
5273 @chapter C Language Support
5275 @cindex expressions in C
5277 Information specific to the C language is built into @value{GDBN} so that you
5278 can use C expressions while degugging. This also permits @value{GDBN} to
5279 output values in a manner consistent with C conventions.
5282 * C Operators:: C operators
5283 * C Constants:: C constants
5284 * Debugging C:: @value{GDBN} and C
5289 * C Operators:: C and C++ operators
5290 * C Constants:: C and C++ constants
5291 * Cplus expressions:: C++ expressions
5292 * C Defaults:: Default settings for C and C++
5294 * C Checks:: C and C++ type and range checks
5297 * Debugging C:: @value{GDBN} and C
5298 * Debugging C plus plus:: Special features for C++
5303 @cindex C and C++ operators
5305 @subsubsection C and C++ operators
5310 @section C operators
5313 Operators must be defined on values of specific types. For instance,
5314 @code{+} is defined on numbers, but not on structures. Operators are
5315 often defined on groups of types.
5318 For the purposes of C and C++, the following definitions hold:
5323 @emph{Integral types} include @code{int} with any of its storage-class
5324 specifiers; @code{char}; and @code{enum}.
5327 @emph{Floating-point types} include @code{float} and @code{double}.
5330 @emph{Pointer types} include all types defined as @code{(@var{type}
5334 @emph{Scalar types} include all of the above.
5338 The following operators are supported. They are listed here
5339 in order of increasing precedence:
5343 The comma or sequencing operator. Expressions in a comma-separated list
5344 are evaluated from left to right, with the result of the entire
5345 expression being the last expression evaluated.
5348 Assignment. The value of an assignment expression is the value
5349 assigned. Defined on scalar types.
5352 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
5353 and translated to @w{@code{@var{a} = @var{a op b}}}.
5354 @w{@code{@var{op}=}} and @code{=} have the same precendence.
5355 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
5356 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
5359 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
5360 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
5364 Logical @sc{or}. Defined on integral types.
5367 Logical @sc{and}. Defined on integral types.
5370 Bitwise @sc{or}. Defined on integral types.
5373 Bitwise exclusive-@sc{or}. Defined on integral types.
5376 Bitwise @sc{and}. Defined on integral types.
5379 Equality and inequality. Defined on scalar types. The value of these
5380 expressions is 0 for false and non-zero for true.
5382 @item <@r{, }>@r{, }<=@r{, }>=
5383 Less than, greater than, less than or equal, greater than or equal.
5384 Defined on scalar types. The value of these expressions is 0 for false
5385 and non-zero for true.
5388 left shift, and right shift. Defined on integral types.
5391 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5394 Addition and subtraction. Defined on integral types, floating-point types and
5397 @item *@r{, }/@r{, }%
5398 Multiplication, division, and modulus. Multiplication and division are
5399 defined on integral and floating-point types. Modulus is defined on
5403 Increment and decrement. When appearing before a variable, the
5404 operation is performed before the variable is used in an expression;
5405 when appearing after it, the variable's value is used before the
5406 operation takes place.
5409 Pointer dereferencing. Defined on pointer types. Same precedence as
5413 Address operator. Defined on variables. Same precedence as @code{++}.
5416 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
5417 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
5418 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
5419 where a C++ reference variable (declared with @samp{&@var{ref}}) is
5424 Negative. Defined on integral and floating-point types. Same
5425 precedence as @code{++}.
5428 Logical negation. Defined on integral types. Same precedence as
5432 Bitwise complement operator. Defined on integral types. Same precedence as
5437 Structure member, and pointer-to-structure member. For convenience,
5438 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
5439 pointer based on the stored type information.
5440 Defined on @code{struct} and @code{union} data.
5443 Array indexing. @code{@var{a}[@var{i}]} is defined as
5444 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
5447 Function parameter list. Same precedence as @code{->}.
5451 C++ scope resolution operator. Defined on
5452 @code{struct}, @code{union}, and @code{class} types.
5460 represent the @value{GDBN} scope operator (@pxref{Expressions,
5463 Same precedence as @code{::}, above.
5468 @cindex C and C++ constants
5470 @subsubsection C and C++ constants
5472 @value{GDBN} allows you to express the constants of C and C++ in the
5478 @section C constants
5480 @value{GDBN} allows you to express the constants of C in the
5486 Integer constants are a sequence of digits. Octal constants are
5487 specified by a leading @samp{0} (ie. zero), and hexadecimal constants by
5488 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
5489 @samp{l}, specifying that the constant should be treated as a
5493 Floating point constants are a sequence of digits, followed by a decimal
5494 point, followed by a sequence of digits, and optionally followed by an
5495 exponent. An exponent is of the form:
5496 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
5497 sequence of digits. The @samp{+} is optional for positive exponents.
5500 Enumerated constants consist of enumerated identifiers, or their
5501 integral equivalents.
5504 Character constants are a single character surrounded by single quotes
5505 (@code{'}), or a number---the ordinal value of the corresponding character
5506 (usually its @sc{ASCII} value). Within quotes, the single character may
5507 be represented by a letter or by @dfn{escape sequences}, which are of
5508 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
5509 of the character's ordinal value; or of the form @samp{\@var{x}}, where
5510 @samp{@var{x}} is a predefined special character---for example,
5511 @samp{\n} for newline.
5514 String constants are a sequence of character constants surrounded
5515 by double quotes (@code{"}).
5518 Pointer constants are an integral value. You can also write pointers
5519 to constants using the C operator @samp{&}.
5522 Array constants are comma-separated lists surrounded by braces @samp{@{}
5523 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
5524 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
5525 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
5529 @node Cplus expressions
5530 @subsubsection C++ expressions
5532 @cindex expressions in C++
5533 @value{GDBN} expression handling has a number of extensions to
5534 interpret a significant subset of C++ expressions.
5536 @cindex C++ support, not in @sc{coff}
5537 @cindex @sc{coff} versus C++
5538 @cindex C++ and object formats
5539 @cindex object formats and C++
5540 @cindex a.out and C++
5541 @cindex @sc{ecoff} and C++
5542 @cindex @sc{xcoff} and C++
5543 @cindex @sc{elf}/stabs and C++
5544 @cindex @sc{elf}/@sc{dwarf} and C++
5546 @emph{Warning:} Most of these extensions depend on the use of additional
5547 debugging information in the symbol table, and thus require a rich,
5548 extendable object code format. In particular, if your system uses
5549 a.out, MIPS @sc{ecoff}, RS/6000 @sc{xcoff}, or Sun @sc{elf} with stabs
5550 extensions to the symbol table, these facilities are all available.
5551 Where the object code format is standard @sc{coff}, on the other hand,
5552 most of the C++ support in @value{GDBN} will @emph{not} work, nor can it.
5553 For the standard SVr4 debugging format, @sc{dwarf} in @sc{elf}, the
5554 standard is still evolving, so the C++ support in @value{GDBN} is still
5555 fragile; when this debugging format stabilizes, however, C++ support
5556 will also be available on systems that use it.
5561 @cindex member functions
5563 Member function calls are allowed; you can use expressions like
5566 count = aml->GetOriginal(x, y)
5570 @cindex namespace in C++
5572 While a member function is active (in the selected stack frame), your
5573 expressions have the same namespace available as the member function;
5574 that is, @value{GDBN} allows implicit references to the class instance
5575 pointer @code{this} following the same rules as C++.
5577 @cindex call overloaded functions
5578 @cindex type conversions in C++
5580 You can call overloaded functions; @value{GDBN} will resolve the function
5581 call to the right definition, with one restriction---you must use
5582 arguments of the type required by the function that you want to call.
5583 @value{GDBN} will not perform conversions requiring constructors or
5584 user-defined type operators.
5586 @cindex reference declarations
5588 @value{GDBN} understands variables declared as C++ references; you can use them in
5589 expressions just as you do in C++ source---they are automatically
5592 In the parameter list shown when @value{GDBN} displays a frame, the values of
5593 reference variables are not displayed (unlike other variables); this
5594 avoids clutter, since references are often used for large structures.
5595 The @emph{address} of a reference variable is always shown, unless
5596 you have specified @samp{set print address off}.
5599 @value{GDBN} supports the C++ name resolution operator @code{::}---your
5600 expressions can use it just as expressions in your program do. Since
5601 one scope may be defined in another, you can use @code{::} repeatedly if
5602 necessary, for example in an expression like
5603 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
5604 resolving name scope by reference to source files, in both C and C++
5605 debugging (@pxref{Variables, ,Program variables}).
5609 @subsubsection C and C++ defaults
5610 @cindex C and C++ defaults
5612 If you allow @value{GDBN} to set type and range checking automatically, they
5613 both default to @code{off} whenever the working language changes to
5614 C or C++. This happens regardless of whether you, or @value{GDBN},
5615 selected the working language.
5617 If you allow @value{GDBN} to set the language automatically, it sets the
5618 working language to C or C++ on entering code compiled from a source file
5619 whose name ends with @file{.c}, @file{.C}, or @file{.cc}.
5620 @xref{Automatically, ,Having @value{GDBN} infer the source language}, for
5624 @c Type checking is (a) primarily motivated by Modula-2, and (b)
5625 @c unimplemented. If (b) changes, it might make sense to let this node
5626 @c appear even if Mod-2 does not, but meanwhile ignore it. pesch 16jul93.
5628 @subsubsection C and C++ type and range checks
5629 @cindex C and C++ checks
5631 By default, when @value{GDBN} parses C or C++ expressions, type checking
5632 is not used. However, if you turn type checking on, @value{GDBN} will
5633 consider two variables type equivalent if:
5637 The two variables are structured and have the same structure, union, or
5641 Two two variables have the same type name, or types that have been
5642 declared equivalent through @code{typedef}.
5645 @c leaving this out because neither J Gilmore nor R Pesch understand it.
5648 The two @code{struct}, @code{union}, or @code{enum} variables are
5649 declared in the same declaration. (Note: this may not be true for all C
5654 Range checking, if turned on, is done on mathematical operations. Array
5655 indices are not checked, since they are often used to index a pointer
5656 that is not itself an array.
5662 @subsubsection @value{GDBN} and C
5666 @section @value{GDBN} and C
5669 The @code{set print union} and @code{show print union} commands apply to
5670 the @code{union} type. When set to @samp{on}, any @code{union} that is
5671 inside a @code{struct}
5675 will also be printed.
5676 Otherwise, it will appear as @samp{@{...@}}.
5678 The @code{@@} operator aids in the debugging of dynamic arrays, formed
5679 with pointers and a memory allocation function. @xref{Expressions,
5683 @node Debugging C plus plus
5684 @subsubsection @value{GDBN} features for C++
5686 @cindex commands for C++
5687 Some @value{GDBN} commands are particularly useful with C++, and some are
5688 designed specifically for use with C++. Here is a summary:
5691 @cindex break in overloaded functions
5692 @item @r{breakpoint menus}
5693 When you want a breakpoint in a function whose name is overloaded,
5694 @value{GDBN} breakpoint menus help you specify which function definition
5695 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
5697 @cindex overloading in C++
5698 @item rbreak @var{regex}
5699 Setting breakpoints using regular expressions is helpful for setting
5700 breakpoints on overloaded functions that are not members of any special
5702 @xref{Set Breaks, ,Setting breakpoints}.
5704 @cindex C++ exception handling
5705 @item catch @var{exceptions}
5707 Debug C++ exception handling using these commands. @xref{Exception
5708 Handling, ,Breakpoints and exceptions}.
5711 @item ptype @var{typename}
5712 Print inheritance relationships as well as other information for type
5714 @xref{Symbols, ,Examining the Symbol Table}.
5716 @cindex C++ symbol display
5717 @item set print demangle
5718 @itemx show print demangle
5719 @itemx set print asm-demangle
5720 @itemx show print asm-demangle
5721 Control whether C++ symbols display in their source form, both when
5722 displaying code as C++ source and when displaying disassemblies.
5723 @xref{Print Settings, ,Print settings}.
5725 @item set print object
5726 @itemx show print object
5727 Choose whether to print derived (actual) or declared types of objects.
5728 @xref{Print Settings, ,Print settings}.
5730 @item set print vtbl
5731 @itemx show print vtbl
5732 Control the format for printing virtual function tables.
5733 @xref{Print Settings, ,Print settings}.
5735 @item @r{Overloaded symbol names}
5736 You can specify a particular definition of an overloaded symbol, using
5737 the same notation that is used to declare such symbols in C++: type
5738 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
5739 also use the @value{GDBN} command-line word completion facilities to list the
5740 available choices, or to finish the type list for you.
5741 @xref{Completion,, Command completion}, for details on how to do this.
5744 @c cancels "raisesections" under same conditions near bgn of chapter
5750 @subsection Modula-2
5753 The extensions made to @value{GDBN} to support Modula-2 only support
5754 output from the GNU Modula-2 compiler (which is currently being
5755 developed). Other Modula-2 compilers are not currently supported, and
5756 attempting to debug executables produced by them will most likely
5757 result in an error as @value{GDBN} reads in the executable's symbol
5760 @cindex expressions in Modula-2
5762 * M2 Operators:: Built-in operators
5763 * Built-In Func/Proc:: Built-in functions and procedures
5764 * M2 Constants:: Modula-2 constants
5765 * M2 Defaults:: Default settings for Modula-2
5766 * Deviations:: Deviations from standard Modula-2
5767 * M2 Checks:: Modula-2 type and range checks
5768 * M2 Scope:: The scope operators @code{::} and @code{.}
5769 * GDB/M2:: @value{GDBN} and Modula-2
5773 @subsubsection Operators
5774 @cindex Modula-2 operators
5776 Operators must be defined on values of specific types. For instance,
5777 @code{+} is defined on numbers, but not on structures. Operators are
5778 often defined on groups of types. For the purposes of Modula-2, the
5779 following definitions hold:
5784 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
5788 @emph{Character types} consist of @code{CHAR} and its subranges.
5791 @emph{Floating-point types} consist of @code{REAL}.
5794 @emph{Pointer types} consist of anything declared as @code{POINTER TO
5798 @emph{Scalar types} consist of all of the above.
5801 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
5804 @emph{Boolean types} consist of @code{BOOLEAN}.
5808 The following operators are supported, and appear in order of
5809 increasing precedence:
5813 Function argument or array index separator.
5816 Assignment. The value of @var{var} @code{:=} @var{value} is
5820 Less than, greater than on integral, floating-point, or enumerated
5824 Less than, greater than, less than or equal to, greater than or equal to
5825 on integral, floating-point and enumerated types, or set inclusion on
5826 set types. Same precedence as @code{<}.
5828 @item =@r{, }<>@r{, }#
5829 Equality and two ways of expressing inequality, valid on scalar types.
5830 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
5831 available for inequality, since @code{#} conflicts with the script
5835 Set membership. Defined on set types and the types of their members.
5836 Same precedence as @code{<}.
5839 Boolean disjunction. Defined on boolean types.
5842 Boolean conjuction. Defined on boolean types.
5845 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5848 Addition and subtraction on integral and floating-point types, or union
5849 and difference on set types.
5852 Multiplication on integral and floating-point types, or set intersection
5856 Division on floating-point types, or symmetric set difference on set
5857 types. Same precedence as @code{*}.
5860 Integer division and remainder. Defined on integral types. Same
5861 precedence as @code{*}.
5864 Negative. Defined on @code{INTEGER} and @code{REAL} data.
5867 Pointer dereferencing. Defined on pointer types.
5870 Boolean negation. Defined on boolean types. Same precedence as
5874 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
5875 precedence as @code{^}.
5878 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
5881 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
5885 @value{GDBN} and Modula-2 scope operators.
5889 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
5890 will treat the use of the operator @code{IN}, or the use of operators
5891 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
5892 @code{<=}, and @code{>=} on sets as an error.
5895 @cindex Modula-2 built-ins
5896 @node Built-In Func/Proc
5897 @subsubsection Built-in functions and procedures
5899 Modula-2 also makes available several built-in procedures and functions.
5900 In describing these, the following metavariables are used:
5905 represents an @code{ARRAY} variable.
5908 represents a @code{CHAR} constant or variable.
5911 represents a variable or constant of integral type.
5914 represents an identifier that belongs to a set. Generally used in the
5915 same function with the metavariable @var{s}. The type of @var{s} should
5916 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
5919 represents a variable or constant of integral or floating-point type.
5922 represents a variable or constant of floating-point type.
5928 represents a variable.
5931 represents a variable or constant of one of many types. See the
5932 explanation of the function for details.
5935 All Modula-2 built-in procedures also return a result, described below.
5939 Returns the absolute value of @var{n}.
5942 If @var{c} is a lower case letter, it returns its upper case
5943 equivalent, otherwise it returns its argument
5946 Returns the character whose ordinal value is @var{i}.
5949 Decrements the value in the variable @var{v}. Returns the new value.
5951 @item DEC(@var{v},@var{i})
5952 Decrements the value in the variable @var{v} by @var{i}. Returns the
5955 @item EXCL(@var{m},@var{s})
5956 Removes the element @var{m} from the set @var{s}. Returns the new
5959 @item FLOAT(@var{i})
5960 Returns the floating point equivalent of the integer @var{i}.
5963 Returns the index of the last member of @var{a}.
5966 Increments the value in the variable @var{v}. Returns the new value.
5968 @item INC(@var{v},@var{i})
5969 Increments the value in the variable @var{v} by @var{i}. Returns the
5972 @item INCL(@var{m},@var{s})
5973 Adds the element @var{m} to the set @var{s} if it is not already
5974 there. Returns the new set.
5977 Returns the maximum value of the type @var{t}.
5980 Returns the minimum value of the type @var{t}.
5983 Returns boolean TRUE if @var{i} is an odd number.
5986 Returns the ordinal value of its argument. For example, the ordinal
5987 value of a character is its ASCII value (on machines supporting the
5988 ASCII character set). @var{x} must be of an ordered type, which include
5989 integral, character and enumerated types.
5992 Returns the size of its argument. @var{x} can be a variable or a type.
5994 @item TRUNC(@var{r})
5995 Returns the integral part of @var{r}.
5997 @item VAL(@var{t},@var{i})
5998 Returns the member of the type @var{t} whose ordinal value is @var{i}.
6002 @emph{Warning:} Sets and their operations are not yet supported, so
6003 @value{GDBN} will treat the use of procedures @code{INCL} and @code{EXCL} as
6007 @cindex Modula-2 constants
6009 @subsubsection Constants
6011 @value{GDBN} allows you to express the constants of Modula-2 in the following
6017 Integer constants are simply a sequence of digits. When used in an
6018 expression, a constant is interpreted to be type-compatible with the
6019 rest of the expression. Hexadecimal integers are specified by a
6020 trailing @samp{H}, and octal integers by a trailing @samp{B}.
6023 Floating point constants appear as a sequence of digits, followed by a
6024 decimal point and another sequence of digits. An optional exponent can
6025 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
6026 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
6027 digits of the floating point constant must be valid decimal (base 10)
6031 Character constants consist of a single character enclosed by a pair of
6032 like quotes, either single (@code{'}) or double (@code{"}). They may
6033 also be expressed by their ordinal value (their ASCII value, usually)
6034 followed by a @samp{C}.
6037 String constants consist of a sequence of characters enclosed by a
6038 pair of like quotes, either single (@code{'}) or double (@code{"}).
6039 Escape sequences in the style of C are also allowed. @xref{C
6040 Constants, ,C and C++ constants}, for a brief explanation of escape
6044 Enumerated constants consist of an enumerated identifier.
6047 Boolean constants consist of the identifiers @code{TRUE} and
6051 Pointer constants consist of integral values only.
6054 Set constants are not yet supported.
6058 @subsubsection Modula-2 defaults
6059 @cindex Modula-2 defaults
6061 If type and range checking are set automatically by @value{GDBN}, they
6062 both default to @code{on} whenever the working language changes to
6063 Modula-2. This happens regardless of whether you, or @value{GDBN},
6064 selected the working language.
6066 If you allow @value{GDBN} to set the language automatically, then entering
6067 code compiled from a file whose name ends with @file{.mod} will set the
6068 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
6069 the language automatically}, for further details.
6072 @subsubsection Deviations from standard Modula-2
6073 @cindex Modula-2, deviations from
6075 A few changes have been made to make Modula-2 programs easier to debug.
6076 This is done primarily via loosening its type strictness:
6080 Unlike in standard Modula-2, pointer constants can be formed by
6081 integers. This allows you to modify pointer variables during
6082 debugging. (In standard Modula-2, the actual address contained in a
6083 pointer variable is hidden from you; it can only be modified
6084 through direct assignment to another pointer variable or expression that
6085 returned a pointer.)
6088 C escape sequences can be used in strings and characters to represent
6089 non-printable characters. @value{GDBN} will print out strings with these
6090 escape sequences embedded. Single non-printable characters are
6091 printed using the @samp{CHR(@var{nnn})} format.
6094 The assignment operator (@code{:=}) returns the value of its right-hand
6098 All built-in procedures both modify @emph{and} return their argument.
6102 @subsubsection Modula-2 type and range checks
6103 @cindex Modula-2 checks
6106 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
6109 @c FIXME remove warning when type/range checks added
6111 @value{GDBN} considers two Modula-2 variables type equivalent if:
6115 They are of types that have been declared equivalent via a @code{TYPE
6116 @var{t1} = @var{t2}} statement
6119 They have been declared on the same line. (Note: This is true of the
6120 GNU Modula-2 compiler, but it may not be true of other compilers.)
6123 As long as type checking is enabled, any attempt to combine variables
6124 whose types are not equivalent is an error.
6126 Range checking is done on all mathematical operations, assignment, array
6127 index bounds, and all built-in functions and procedures.
6130 @subsubsection The scope operators @code{::} and @code{.}
6133 @cindex colon, doubled as scope operator
6136 @c Info cannot handle :: but TeX can.
6142 There are a few subtle differences between the Modula-2 scope operator
6143 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
6148 @var{module} . @var{id}
6149 @var{scope} :: @var{id}
6153 where @var{scope} is the name of a module or a procedure,
6154 @var{module} the name of a module, and @var{id} is any declared
6155 identifier within your program, except another module.
6157 Using the @code{::} operator makes @value{GDBN} search the scope
6158 specified by @var{scope} for the identifier @var{id}. If it is not
6159 found in the specified scope, then @value{GDBN} will search all scopes
6160 enclosing the one specified by @var{scope}.
6162 Using the @code{.} operator makes @value{GDBN} search the current scope for
6163 the identifier specified by @var{id} that was imported from the
6164 definition module specified by @var{module}. With this operator, it is
6165 an error if the identifier @var{id} was not imported from definition
6166 module @var{module}, or if @var{id} is not an identifier in
6170 @subsubsection @value{GDBN} and Modula-2
6172 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
6173 Five subcommands of @code{set print} and @code{show print} apply
6174 specifically to C and C++: @samp{vtbl}, @samp{demangle},
6175 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
6176 apply to C++, and the last to the C @code{union} type, which has no direct
6177 analogue in Modula-2.
6179 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
6180 while using any language, is not useful with Modula-2. Its
6181 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
6182 created in Modula-2 as they can in C or C++. However, because an
6183 address can be specified by an integral constant, the construct
6184 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions})
6186 @cindex @code{#} in Modula-2
6187 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
6188 interpreted as the beginning of a comment. Use @code{<>} instead.
6194 @chapter Examining the Symbol Table
6196 The commands described in this section allow you to inquire about the
6197 symbols (names of variables, functions and types) defined in your
6198 program. This information is inherent in the text of your program and
6199 does not change as your program executes. @value{GDBN} finds it in your
6200 program's symbol table, in the file indicated when you started @value{GDBN}
6201 (@pxref{File Options, ,Choosing files}), or by one of the
6202 file-management commands (@pxref{Files, ,Commands to specify files}).
6204 @c FIXME! This might be intentionally specific to C and C++; if so, move
6205 @c to someplace in C section of lang chapter.
6206 @cindex symbol names
6207 @cindex names of symbols
6208 @cindex quoting names
6209 Occasionally, you may need to refer to symbols that contain unusual
6210 characters, which @value{GDBN} ordinarily treats as word delimiters. The
6211 most frequent case is in referring to static variables in other
6212 source files (@pxref{Variables,,Program variables}). File names
6213 are recorded in object files as debugging symbols, but @value{GDBN} would
6214 ordinarily parse a typical file name, like @file{foo.c}, as the three words
6215 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
6216 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
6223 looks up the value of @code{x} in the scope of the file @file{foo.c}.
6226 @item info address @var{symbol}
6227 @kindex info address
6228 Describe where the data for @var{symbol} is stored. For a register
6229 variable, this says which register it is kept in. For a non-register
6230 local variable, this prints the stack-frame offset at which the variable
6233 Note the contrast with @samp{print &@var{symbol}}, which does not work
6234 at all for a register variable, and for a stack local variable prints
6235 the exact address of the current instantiation of the variable.
6237 @item whatis @var{exp}
6239 Print the data type of expression @var{exp}. @var{exp} is not
6240 actually evaluated, and any side-effecting operations (such as
6241 assignments or function calls) inside it do not take place.
6242 @xref{Expressions, ,Expressions}.
6245 Print the data type of @code{$}, the last value in the value history.
6247 @item ptype @var{typename}
6249 Print a description of data type @var{typename}. @var{typename} may be
6250 the name of a type, or for C code it may have the form
6252 @samp{class @var{class-name}},
6254 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
6255 @samp{enum @var{enum-tag}}.
6257 @item ptype @var{exp}
6259 Print a description of the type of expression @var{exp}. @code{ptype}
6260 differs from @code{whatis} by printing a detailed description, instead
6261 of just the name of the type.
6263 For example, for this variable declaration:
6266 struct complex @{double real; double imag;@} v;
6270 the two commands give this output:
6274 (@value{GDBP}) whatis v
6275 type = struct complex
6276 (@value{GDBP}) ptype v
6277 type = struct complex @{
6285 As with @code{whatis}, using @code{ptype} without an argument refers to
6286 the type of @code{$}, the last value in the value history.
6288 @item info types @var{regexp}
6291 Print a brief description of all types whose name matches @var{regexp}
6292 (or all types in your program, if you supply no argument). Each
6293 complete typename is matched as though it were a complete line; thus,
6294 @samp{i type value} gives information on all types in your program whose
6295 name includes the string @code{value}, but @samp{i type ^value$} gives
6296 information only on types whose complete name is @code{value}.
6298 This command differs from @code{ptype} in two ways: first, like
6299 @code{whatis}, it does not print a detailed description; second, it
6300 lists all source files where a type is defined.
6304 Show the name of the current source file---that is, the source file for
6305 the function containing the current point of execution---and the language
6309 @kindex info sources
6310 Print the names of all source files in your program for which there is
6311 debugging information, organized into two lists: files whose symbols
6312 have already been read, and files whose symbols will be read when needed.
6314 @item info functions
6315 @kindex info functions
6316 Print the names and data types of all defined functions.
6318 @item info functions @var{regexp}
6319 Print the names and data types of all defined functions
6320 whose names contain a match for regular expression @var{regexp}.
6321 Thus, @samp{info fun step} finds all functions whose names
6322 include @code{step}; @samp{info fun ^step} finds those whose names
6323 start with @code{step}.
6325 @item info variables
6326 @kindex info variables
6327 Print the names and data types of all variables that are declared
6328 outside of functions (i.e., excluding local variables).
6330 @item info variables @var{regexp}
6331 Print the names and data types of all variables (except for local
6332 variables) whose names contain a match for regular expression
6336 This was never implemented.
6338 @itemx info methods @var{regexp}
6339 @kindex info methods
6340 The @code{info methods} command permits the user to examine all defined
6341 methods within C++ program, or (with the @var{regexp} argument) a
6342 specific set of methods found in the various C++ classes. Many
6343 C++ classes provide a large number of methods. Thus, the output
6344 from the @code{ptype} command can be overwhelming and hard to use. The
6345 @code{info-methods} command filters the methods, printing only those
6346 which match the regular-expression @var{regexp}.
6349 @item maint print symbols @var{filename}
6350 @itemx maint print psymbols @var{filename}
6351 @itemx maint print msymbols @var{filename}
6352 @kindex maint print symbols
6354 @kindex maint print psymbols
6355 @cindex partial symbol dump
6356 Write a dump of debugging symbol data into the file @var{filename}.
6357 These commands are used to debug the @value{GDBN} symbol-reading code. Only
6358 symbols with debugging data are included. If you use @samp{maint print
6359 symbols}, @value{GDBN} includes all the symbols for which it has already
6360 collected full details: that is, @var{filename} reflects symbols for
6361 only those files whose symbols @value{GDBN} has read. You can use the
6362 command @code{info sources} to find out which files these are. If you
6363 use @samp{maint print psymbols} instead, the dump shows information about
6364 symbols that @value{GDBN} only knows partially---that is, symbols defined in
6365 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
6366 @samp{maint print msymbols} dumps just the minimal symbol information
6367 required for each object file from which @value{GDBN} has read some symbols.
6368 @xref{Files, ,Commands to specify files}, for a discussion of how
6369 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
6373 @chapter Altering Execution
6375 Once you think you have found an error in your program, you might want to
6376 find out for certain whether correcting the apparent error would lead to
6377 correct results in the rest of the run. You can find the answer by
6378 experiment, using the @value{GDBN} features for altering execution of the
6381 For example, you can store new values into variables or memory
6384 give your program a signal, restart it
6387 restart your program
6389 at a different address, or even return prematurely from a function to
6393 * Assignment:: Assignment to variables
6394 * Jumping:: Continuing at a different address
6396 * Signaling:: Giving your program a signal
6399 * Returning:: Returning from a function
6400 * Calling:: Calling your program's functions
6401 * Patching:: Patching your program
6405 @section Assignment to variables
6408 @cindex setting variables
6409 To alter the value of a variable, evaluate an assignment expression.
6410 @xref{Expressions, ,Expressions}. For example,
6417 stores the value 4 into the variable @code{x}, and then prints the
6418 value of the assignment expression (which is 4).
6420 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
6421 information on operators in supported languages.
6424 @kindex set variable
6425 @cindex variables, setting
6426 If you are not interested in seeing the value of the assignment, use the
6427 @code{set} command instead of the @code{print} command. @code{set} is
6428 really the same as @code{print} except that the expression's value is
6429 not printed and is not put in the value history (@pxref{Value History,
6430 ,Value history}). The expression is evaluated only for its effects.
6432 If the beginning of the argument string of the @code{set} command
6433 appears identical to a @code{set} subcommand, use the @code{set
6434 variable} command instead of just @code{set}. This command is identical
6435 to @code{set} except for its lack of subcommands. For example, if
6436 your program has a variable @code{width}, you get
6437 an error if you try to set a new value with just @samp{set width=13},
6438 because @value{GDBN} has the command @code{set width}:
6441 (@value{GDBP}) whatis width
6443 (@value{GDBP}) p width
6445 (@value{GDBP}) set width=47
6446 Invalid syntax in expression.
6450 The invalid expression, of course, is @samp{=47}. In
6451 order to actually set the program's variable @code{width}, use
6454 (@value{GDBP}) set var width=47
6457 @value{GDBN} allows more implicit conversions in assignments than C; you can
6458 freely store an integer value into a pointer variable or vice versa,
6459 and you can convert any structure to any other structure that is the
6460 same length or shorter.
6461 @comment FIXME: how do structs align/pad in these conversions?
6462 @comment /pesch@cygnus.com 18dec1990
6464 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
6465 construct to generate a value of specified type at a specified address
6466 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
6467 to memory location @code{0x83040} as an integer (which implies a certain size
6468 and representation in memory), and
6471 set @{int@}0x83040 = 4
6475 stores the value 4 into that memory location.
6478 @section Continuing at a different address
6480 Ordinarily, when you continue your program, you do so at the place where
6481 it stopped, with the @code{continue} command. You can instead continue at
6482 an address of your own choosing, with the following commands:
6485 @item jump @var{linespec}
6487 Resume execution at line @var{linespec}. Execution will stop
6488 immediately if there is a breakpoint there. @xref{List, ,Printing
6489 source lines}, for a description of the different forms of
6492 The @code{jump} command does not change the current stack frame, or
6493 the stack pointer, or the contents of any memory location or any
6494 register other than the program counter. If line @var{linespec} is in
6495 a different function from the one currently executing, the results may
6496 be bizarre if the two functions expect different patterns of arguments or
6497 of local variables. For this reason, the @code{jump} command requests
6498 confirmation if the specified line is not in the function currently
6499 executing. However, even bizarre results are predictable if you are
6500 well acquainted with the machine-language code of your program.
6502 @item jump *@var{address}
6503 Resume execution at the instruction at address @var{address}.
6506 You can get much the same effect as the @code{jump} command by storing a
6507 new value into the register @code{$pc}. The difference is that this
6508 does not start your program running; it only changes the address where it
6509 @emph{will} run when it is continued. For example,
6516 causes the next @code{continue} command or stepping command to execute at
6517 address @code{0x485}, rather than at the address where your program stopped.
6518 @xref{Continuing and Stepping, ,Continuing and stepping}.
6520 The most common occasion to use the @code{jump} command is to back up,
6521 perhaps with more breakpoints set, over a portion of a program that has
6522 already executed, in order to examine its execution in more detail.
6527 @section Giving your program a signal
6530 @item signal @var{signal}
6532 Resume execution where your program stopped, but immediately give it the
6533 signal @var{signal}. @var{signal} can be the name or the number of a
6534 signal. For example, on many systems @code{signal 2} and @code{signal
6535 SIGINT} are both ways of sending an interrupt signal.
6537 Alternatively, if @var{signal} is zero, continue execution without
6538 giving a signal. This is useful when your program stopped on account of
6539 a signal and would ordinary see the signal when resumed with the
6540 @code{continue} command; @samp{signal 0} causes it to resume without a
6543 @code{signal} does not repeat when you press @key{RET} a second time
6544 after executing the command.
6548 Invoking the @code{signal} command is not the same as invoking the
6549 @code{kill} utility from the shell. Sending a signal with @code{kill}
6550 causes @value{GDBN} to decide what to do with the signal depending on
6551 the signal handling tables (@pxref{Signals}). The @code{signal} command
6552 passes the signal directly to your program.
6557 @section Returning from a function
6561 @itemx return @var{expression}
6562 @cindex returning from a function
6564 You can cancel execution of a function call with the @code{return}
6565 command. If you give an
6566 @var{expression} argument, its value is used as the function's return
6570 When you use @code{return}, @value{GDBN} discards the selected stack frame
6571 (and all frames within it). You can think of this as making the
6572 discarded frame return prematurely. If you wish to specify a value to
6573 be returned, give that value as the argument to @code{return}.
6575 This pops the selected stack frame (@pxref{Selection, ,Selecting a
6576 frame}), and any other frames inside of it, leaving its caller as the
6577 innermost remaining frame. That frame becomes selected. The
6578 specified value is stored in the registers used for returning values
6581 The @code{return} command does not resume execution; it leaves the
6582 program stopped in the state that would exist if the function had just
6583 returned. In contrast, the @code{finish} command (@pxref{Continuing
6584 and Stepping, ,Continuing and stepping}) resumes execution until the
6585 selected stack frame returns naturally.
6588 @section Calling program functions
6590 @cindex calling functions
6593 @item call @var{expr}
6594 Evaluate the expression @var{expr} without displaying @code{void}
6598 You can use this variant of the @code{print} command if you want to
6599 execute a function from your program, but without cluttering the output
6600 with @code{void} returned values. The result is printed and saved in
6601 the value history, if it is not void.
6604 @section Patching programs
6605 @cindex patching binaries
6606 @cindex writing into executables
6608 @cindex writing into corefiles
6611 By default, @value{GDBN} opens the file containing your program's executable
6616 read-only. This prevents accidental alterations
6617 to machine code; but it also prevents you from intentionally patching
6618 your program's binary.
6620 If you'd like to be able to patch the binary, you can specify that
6621 explicitly with the @code{set write} command. For example, you might
6622 want to turn on internal debugging flags, or even to make emergency
6627 @itemx set write off
6629 If you specify @samp{set write on}, @value{GDBN} will open executable
6633 files for both reading and writing; if you specify @samp{set write
6634 off} (the default), @value{GDBN} will open them read-only.
6636 If you have already loaded a file, you must load it again (using the
6641 command) after changing @code{set write}, for your new setting to take
6646 Display whether executable files
6650 will be opened for writing as well as reading.
6654 @chapter @value{GDBN} Files
6656 @value{GDBN} needs to know the file name of the program to be debugged, both in
6657 order to read its symbol table and in order to start your program.
6659 To debug a core dump of a previous run, you must also tell @value{GDBN}
6660 the name of the core dump file.
6664 * Files:: Commands to specify files
6665 * Symbol Errors:: Errors reading symbol files
6669 @section Commands to specify files
6670 @cindex symbol table
6673 @cindex core dump file
6674 The usual way to specify executable and core dump file names is with
6675 the command arguments given when you start @value{GDBN} (@pxref{Invocation,
6676 ,Getting In and Out of @value{GDBN}}.
6679 The usual way to specify an executable file name is with
6680 the command argument given when you start @value{GDBN}, (@pxref{Invocation,
6681 ,Getting In and Out of @value{GDBN}}.
6684 Occasionally it is necessary to change to a different file during a
6685 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
6686 a file you want to use. In these situations the @value{GDBN} commands
6687 to specify new files are useful.
6690 @item file @var{filename}
6691 @cindex executable file
6693 Use @var{filename} as the program to be debugged. It is read for its
6694 symbols and for the contents of pure memory. It is also the program
6695 executed when you use the @code{run} command. If you do not specify a
6696 directory and the file is not found in the @value{GDBN} working directory, @value{GDBN}
6697 uses the environment variable @code{PATH} as a list of directories to
6698 search, just as the shell does when looking for a program to run. You
6699 can change the value of this variable, for both @value{GDBN} and your program,
6700 using the @code{path} command.
6702 On systems with memory-mapped files, an auxiliary symbol table file
6703 @file{@var{filename}.syms} may be available for @var{filename}. If it
6704 is, @value{GDBN} will map in the symbol table from
6705 @file{@var{filename}.syms}, starting up more quickly. See the
6706 descriptions of the options @samp{-mapped} and @samp{-readnow} (available
6707 on the command line, and with the commands @code{file}, @code{symbol-file},
6708 or @code{add-symbol-file}), for more information.
6711 @code{file} with no argument makes @value{GDBN} discard any information it
6712 has on both executable file and the symbol table.
6714 @item exec-file @r{[} @var{filename} @r{]}
6716 Specify that the program to be run (but not the symbol table) is found
6717 in @var{filename}. @value{GDBN} will search the environment variable @code{PATH}
6718 if necessary to locate your program. Omitting @var{filename} means to
6719 discard information on the executable file.
6721 @item symbol-file @r{[} @var{filename} @r{]}
6723 Read symbol table information from file @var{filename}. @code{PATH} is
6724 searched when necessary. Use the @code{file} command to get both symbol
6725 table and program to run from the same file.
6727 @code{symbol-file} with no argument clears out @value{GDBN} information on your
6728 program's symbol table.
6730 The @code{symbol-file} command causes @value{GDBN} to forget the contents of its
6731 convenience variables, the value history, and all breakpoints and
6732 auto-display expressions. This is because they may contain pointers to
6733 the internal data recording symbols and data types, which are part of
6734 the old symbol table data being discarded inside @value{GDBN}.
6736 @code{symbol-file} will not repeat if you press @key{RET} again after
6739 When @value{GDBN} is configured for a particular environment, it will
6740 understand debugging information in whatever format is the standard
6741 generated for that environment; you may use either a GNU compiler, or
6742 other compilers that adhere to the local conventions. Best results are
6743 usually obtained from GNU compilers; for example, using @code{@value{GCC}}
6744 you can generate debugging information for optimized code.
6746 On some kinds of object files, the @code{symbol-file} command does not
6747 normally read the symbol table in full right away. Instead, it scans
6748 the symbol table quickly to find which source files and which symbols
6749 are present. The details are read later, one source file at a time,
6752 The purpose of this two-stage reading strategy is to make @value{GDBN} start up
6753 faster. For the most part, it is invisible except for occasional
6754 pauses while the symbol table details for a particular source file are
6755 being read. (The @code{set verbose} command can turn these pauses
6756 into messages if desired. @xref{Messages/Warnings, ,Optional warnings
6759 We have not implemented the two-stage strategy for COFF yet. When the
6760 symbol table is stored in COFF format, @code{symbol-file} reads the
6761 symbol table data in full right away.
6763 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6764 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6766 @cindex reading symbols immediately
6767 @cindex symbols, reading immediately
6769 @cindex memory-mapped symbol file
6770 @cindex saving symbol table
6771 You can override the @value{GDBN} two-stage strategy for reading symbol
6772 tables by using the @samp{-readnow} option with any of the commands that
6773 load symbol table information, if you want to be sure @value{GDBN} has the
6774 entire symbol table available.
6777 If memory-mapped files are available on your system through the
6778 @code{mmap} system call, you can use another option, @samp{-mapped}, to
6779 cause @value{GDBN} to write the symbols for your program into a reusable
6780 file. Future @value{GDBN} debugging sessions will map in symbol information
6781 from this auxiliary symbol file (if the program has not changed), rather
6782 than spending time reading the symbol table from the executable
6783 program. Using the @samp{-mapped} option has the same effect as
6784 starting @value{GDBN} with the @samp{-mapped} command-line option.
6786 You can use both options together, to make sure the auxiliary symbol
6787 file has all the symbol information for your program.
6789 The auxiliary symbol file for a program called @var{myprog} is called
6790 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
6791 than the corresponding executable), @value{GDBN} will always attempt to use
6792 it when you debug @var{myprog}; no special options or commands are
6795 The @file{.syms} file is specific to the host machine where you run
6796 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
6797 symbol table. It cannot be shared across multiple host platforms.
6799 @c FIXME: for now no mention of directories, since this seems to be in
6800 @c flux. 13mar1992 status is that in theory GDB would look either in
6801 @c current dir or in same dir as myprog; but issues like competing
6802 @c GDB's, or clutter in system dirs, mean that in practice right now
6803 @c only current dir is used. FFish says maybe a special GDB hierarchy
6804 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
6807 @item core-file @r{[} @var{filename} @r{]}
6810 Specify the whereabouts of a core dump file to be used as the ``contents
6811 of memory''. Traditionally, core files contain only some parts of the
6812 address space of the process that generated them; @value{GDBN} can access the
6813 executable file itself for other parts.
6815 @code{core-file} with no argument specifies that no core file is
6818 Note that the core file is ignored when your program is actually running
6819 under @value{GDBN}. So, if you have been running your program and you wish to
6820 debug a core file instead, you must kill the subprocess in which the
6821 program is running. To do this, use the @code{kill} command
6822 (@pxref{Kill Process, ,Killing the child process}).
6825 @item load @var{filename}
6828 Depending on what remote debugging facilities are configured into
6829 @value{GDBN}, the @code{load} command may be available. Where it exists, it
6830 is meant to make @var{filename} (an executable) available for debugging
6831 on the remote system---by downloading, or dynamic linking, for example.
6832 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
6833 the @code{add-symbol-file} command.
6835 If your @value{GDBN} does not have a @code{load} command, attempting to
6836 execute it gets the error message ``@code{You can't do that when your
6837 target is @dots{}}''
6840 The file is loaded at whatever address is specified in the executable.
6841 For some object file formats, you can specify the load address when you
6842 link the program; for other formats, like a.out, the object file format
6843 specifies a fixed address.
6844 @c FIXME! This would be a good place for an xref to the GNU linker doc.
6847 On VxWorks, @code{load} will dynamically link @var{filename} on the
6848 current target system as well as adding its symbols in @value{GDBN}.
6852 @cindex download to Nindy-960
6853 With the Nindy interface to an Intel 960 board, @code{load} will
6854 download @var{filename} to the 960 as well as adding its symbols in
6859 @cindex download to H8/300 or H8/500
6860 @cindex H8/300 or H8/500 download
6861 @cindex download to Hitachi SH
6862 @cindex Hitachi SH download
6863 When you select remote debugging to a Hitachi SH, H8/300, or H8/500 board
6864 (@pxref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}),
6865 the @code{load} command downloads your program to the Hitachi board and also
6866 opens it as the current executable target for @value{GDBN} on your host
6867 (like the @code{file} command).
6870 @code{load} will not repeat if you press @key{RET} again after using it.
6873 @item add-symbol-file @var{filename} @var{address}
6874 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6875 @kindex add-symbol-file
6876 @cindex dynamic linking
6877 The @code{add-symbol-file} command reads additional symbol table information
6878 from the file @var{filename}. You would use this command when @var{filename}
6879 has been dynamically loaded (by some other means) into the program that
6880 is running. @var{address} should be the memory address at which the
6881 file has been loaded; @value{GDBN} cannot figure this out for itself.
6882 You can specify @var{address} as an expression.
6884 The symbol table of the file @var{filename} is added to the symbol table
6885 originally read with the @code{symbol-file} command. You can use the
6886 @code{add-symbol-file} command any number of times; the new symbol data thus
6887 read keeps adding to the old. To discard all old symbol data instead,
6888 use the @code{symbol-file} command.
6890 @code{add-symbol-file} will not repeat if you press @key{RET} after using it.
6892 You can use the @samp{-mapped} and @samp{-readnow} options just as with
6893 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
6894 table information for @var{filename}.
6901 @code{info files} and @code{info target} are synonymous; both print
6902 the current target (@pxref{Targets, ,Specifying a Debugging Target}),
6905 names of the executable and core dump files
6908 name of the executable file
6910 currently in use by @value{GDBN}, and the files from which symbols were
6911 loaded. The command @code{help targets} lists all possible targets
6912 rather than current ones.
6915 All file-specifying commands allow both absolute and relative file names
6916 as arguments. @value{GDBN} always converts the file name to an absolute path
6917 name and remembers it that way.
6920 @cindex shared libraries
6921 @value{GDBN} supports SunOS, SVR4, and IBM RS/6000 shared libraries.
6922 @value{GDBN} automatically loads symbol definitions from shared libraries
6923 when you use the @code{run} command, or when you examine a core file.
6924 (Before you issue the @code{run} command, @value{GDBN} will not understand
6925 references to a function in a shared library, however---unless you are
6926 debugging a core file).
6927 @c FIXME: next @value{GDBN} release should permit some refs to undef
6928 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared lib
6932 @itemx info sharedlibrary
6933 @kindex info sharedlibrary
6935 Print the names of the shared libraries which are currently loaded.
6937 @item sharedlibrary @var{regex}
6938 @itemx share @var{regex}
6939 @kindex sharedlibrary
6941 This is an obsolescent command; you can use it to explicitly load shared
6942 object library symbols for files matching a Unix regular expression, but
6943 as with files loaded automatically, it will only load shared libraries
6944 required by your program for a core file or after typing @code{run}. If
6945 @var{regex} is omitted all shared libraries required by your program are
6951 @section Errors reading symbol files
6953 While reading a symbol file, @value{GDBN} will occasionally encounter problems,
6954 such as symbol types it does not recognize, or known bugs in compiler
6955 output. By default, @value{GDBN} does not notify you of such problems, since
6956 they are relatively common and primarily of interest to people
6957 debugging compilers. If you are interested in seeing information
6958 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
6959 only one message about each such type of problem, no matter how many
6960 times the problem occurs; or you can ask @value{GDBN} to print more messages,
6961 to see how many times the problems occur, with the @code{set
6962 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
6965 The messages currently printed, and their meanings, include:
6968 @item inner block not inside outer block in @var{symbol}
6970 The symbol information shows where symbol scopes begin and end
6971 (such as at the start of a function or a block of statements). This
6972 error indicates that an inner scope block is not fully contained
6973 in its outer scope blocks.
6975 @value{GDBN} circumvents the problem by treating the inner block as if it had
6976 the same scope as the outer block. In the error message, @var{symbol}
6977 may be shown as ``@code{(don't know)}'' if the outer block is not a
6980 @item block at @var{address} out of order
6982 The symbol information for symbol scope blocks should occur in
6983 order of increasing addresses. This error indicates that it does not
6986 @value{GDBN} does not circumvent this problem, and will have trouble
6987 locating symbols in the source file whose symbols it is reading. (You
6988 can often determine what source file is affected by specifying
6989 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
6992 @item bad block start address patched
6994 The symbol information for a symbol scope block has a start address
6995 smaller than the address of the preceding source line. This is known
6996 to occur in the SunOS 4.1.1 (and earlier) C compiler.
6998 @value{GDBN} circumvents the problem by treating the symbol scope block as
6999 starting on the previous source line.
7001 @item bad string table offset in symbol @var{n}
7004 Symbol number @var{n} contains a pointer into the string table which is
7005 larger than the size of the string table.
7007 @value{GDBN} circumvents the problem by considering the symbol to have the
7008 name @code{foo}, which may cause other problems if many symbols end up
7011 @item unknown symbol type @code{0x@var{nn}}
7013 The symbol information contains new data types that @value{GDBN} does not yet
7014 know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood
7015 information, in hexadecimal.
7017 @value{GDBN} circumvents the error by ignoring this symbol information. This
7018 will usually allow your program to be debugged, though certain symbols
7019 will not be accessible. If you encounter such a problem and feel like
7020 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on
7021 @code{complain}, then go up to the function @code{read_dbx_symtab} and
7022 examine @code{*bufp} to see the symbol.
7024 @item stub type has NULL name
7025 @value{GDBN} could not find the full definition for
7034 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
7036 The symbol information for a C++ member function is missing some
7037 information that recent versions of the compiler should have output
7041 @item info mismatch between compiler and debugger
7043 @value{GDBN} could not parse a type specification output by the compiler.
7047 @chapter Specifying a Debugging Target
7048 @cindex debugging target
7051 A @dfn{target} is the execution environment occupied by your program.
7053 Often, @value{GDBN} runs in the same host environment as your program; in
7054 that case, the debugging target is specified as a side effect when you
7055 use the @code{file} or @code{core} commands. When you need more
7056 flexibility---for example, running @value{GDBN} on a physically separate
7057 host, or controlling a standalone system over a serial port or a
7058 realtime system over a TCP/IP connection---you
7063 can use the @code{target} command to specify one of the target types
7064 configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing
7068 * Active Targets:: Active targets
7069 * Target Commands:: Commands for managing targets
7070 * Remote:: Remote debugging
7073 @node Active Targets
7074 @section Active targets
7075 @cindex stacking targets
7076 @cindex active targets
7077 @cindex multiple targets
7080 There are three classes of targets: processes, core files, and
7081 executable files. @value{GDBN} can work concurrently on up to three active
7082 targets, one in each class. This allows you to (for example) start a
7083 process and inspect its activity without abandoning your work on a core
7086 For example, if you execute @samp{gdb a.out}, then the executable file
7087 @code{a.out} is the only active target. If you designate a core file as
7088 well---presumably from a prior run that crashed and coredumped---then
7089 @value{GDBN} has two active targets and will use them in tandem, looking
7090 first in the corefile target, then in the executable file, to satisfy
7091 requests for memory addresses. (Typically, these two classes of target
7092 are complementary, since core files contain only a program's
7093 read-write memory---variables and so on---plus machine status, while
7094 executable files contain only the program text and initialized data.)
7097 When you type @code{run}, your executable file becomes an active process
7098 target as well. When a process target is active, all @value{GDBN} commands
7099 requesting memory addresses refer to that target; addresses in an
7103 executable file target are obscured while the process
7107 Use the @code{exec-file} command to select a
7108 new executable target (@pxref{Files, ,Commands to specify
7112 Use the @code{core-file} and @code{exec-file} commands to select a
7113 new core file or executable target (@pxref{Files, ,Commands to specify
7114 files}). To specify as a target a process that is already running, use
7115 the @code{attach} command (@pxref{Attach, ,Debugging an
7116 already-running process}).
7119 @node Target Commands
7120 @section Commands for managing targets
7123 @item target @var{type} @var{parameters}
7124 Connects the @value{GDBN} host environment to a target
7129 machine or process. A target is typically a protocol for talking to
7130 debugging facilities. You use the argument @var{type} to specify the
7131 type or protocol of the target machine.
7133 Further @var{parameters} are interpreted by the target protocol, but
7134 typically include things like device names or host names to connect
7135 with, process numbers, and baud rates.
7138 The @code{target} command will not repeat if you press @key{RET} again
7139 after executing the command.
7143 Displays the names of all targets available. To display targets
7144 currently selected, use either @code{info target} or @code{info files}
7145 (@pxref{Files, ,Commands to specify files}).
7147 @item help target @var{name}
7148 Describe a particular target, including any parameters necessary to
7152 Here are some common targets (available, or not, depending on the GDB
7156 @item target exec @var{program}
7158 An executable file. @samp{target exec @var{program}} is the same as
7159 @samp{exec-file @var{program}}.
7162 @item target core @var{filename}
7164 A core dump file. @samp{target core @var{filename}} is the same as
7165 @samp{core-file @var{filename}}.
7169 @item target remote @var{dev}
7170 @kindex target remote
7171 Remote serial target in GDB-specific protocol. The argument @var{dev}
7172 specifies what serial device to use for the connection (e.g.
7173 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}.
7179 CPU simulator. @xref{Simulator,,Simulated CPU Target}.
7183 @item target udi @var{keyword}
7185 Remote AMD29K target, using the AMD UDI protocol. The @var{keyword}
7186 argument specifies which 29K board or simulator to use. @xref{UDI29K
7187 Remote,,The UDI protocol for AMD29K}.
7189 @item target amd-eb @var{dev} @var{speed} @var{PROG}
7190 @kindex target amd-eb
7192 Remote PC-resident AMD EB29K board, attached over serial lines.
7193 @var{dev} is the serial device, as for @code{target remote};
7194 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
7195 name of the program to be debugged, as it appears to DOS on the PC.
7196 @xref{EB29K Remote, ,The EBMON protocol for AMD29K}.
7202 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
7203 @ifclear H8EXCLUSIVE
7204 @c Unix only, not currently of interest for H8-only manual
7205 Use special commands @code{device} and @code{speed} to control the serial
7206 line and the communications speed used.
7208 @xref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}.
7212 @item target nindy @var{devicename}
7213 @kindex target nindy
7214 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
7215 the name of the serial device to use for the connection, e.g.
7216 @file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}.
7220 @item target st2000 @var{dev} @var{speed}
7221 @kindex target st2000
7222 A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev}
7223 is the name of the device attached to the ST2000 serial line;
7224 @var{speed} is the communication line speed. The arguments are not used
7225 if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet.
7226 @xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}.
7230 @item target vxworks @var{machinename}
7231 @kindex target vxworks
7232 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
7233 is the target system's machine name or IP address.
7234 @xref{VxWorks Remote, ,@value{GDBN} and VxWorks}.
7239 Different targets are available on different configurations of @value{GDBN}; your
7240 configuration may have more or fewer targets.
7244 @section Remote debugging
7245 @cindex remote debugging
7247 If you are trying to debug a program running on a machine that cannot run
7248 GDB in the usual way, it is often useful to use remote debugging. For
7249 example, you might use remote debugging on an operating system kernel, or on
7250 a small system which does not have a general purpose operating system
7251 powerful enough to run a full-featured debugger.
7253 Some configurations of GDB have special serial or TCP/IP interfaces
7254 to make this work with particular debugging targets. In addition,
7255 GDB comes with a generic serial protocol (specific to GDB, but
7256 not specific to any particular target system) which you can use if you
7257 write the remote stubs---the code that will run on the remote system to
7258 communicate with GDB.
7260 Other remote targets may be available in your
7261 configuration of GDB; use @code{help targets} to list them.
7264 @c Text on starting up GDB in various specific cases; it goes up front
7265 @c in manuals configured for any of those particular situations, here
7269 * Remote Serial:: @value{GDBN} remote serial protocol
7272 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
7275 * UDI29K Remote:: The UDI protocol for AMD29K
7276 * EB29K Remote:: The EBMON protocol for AMD29K
7279 * VxWorks Remote:: @value{GDBN} and VxWorks
7282 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
7285 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
7288 * MIPS Remote:: @value{GDBN} and MIPS boards
7291 * Simulator:: Simulated CPU target
7295 @include remote.texi
7298 @node Controlling GDB
7299 @chapter Controlling @value{GDBN}
7301 You can alter the way @value{GDBN} interacts with you by using
7302 the @code{set} command. For commands controlling how @value{GDBN} displays
7303 data, @pxref{Print Settings, ,Print settings}; other settings are described here.
7307 * Editing:: Command editing
7308 * History:: Command history
7309 * Screen Size:: Screen size
7311 * Messages/Warnings:: Optional warnings and messages
7318 @value{GDBN} indicates its readiness to read a command by printing a string
7319 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
7320 can change the prompt string with the @code{set prompt} command. For
7321 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
7322 the prompt in one of the @value{GDBN} sessions so that you can always tell which
7323 one you are talking to.
7326 @item set prompt @var{newprompt}
7328 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
7331 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
7335 @section Command editing
7337 @cindex command line editing
7339 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
7340 GNU library provides consistent behavior for programs which provide a
7341 command line interface to the user. Advantages are @code{emacs}-style
7342 or @code{vi}-style inline editing of commands, @code{csh}-like history
7343 substitution, and a storage and recall of command history across
7346 You may control the behavior of command line editing in @value{GDBN} with the
7353 @itemx set editing on
7354 Enable command line editing (enabled by default).
7356 @item set editing off
7357 Disable command line editing.
7359 @kindex show editing
7361 Show whether command line editing is enabled.
7365 @section Command history
7367 @value{GDBN} can keep track of the commands you type during your
7368 debugging sessions, so that you can be certain of precisely what
7369 happened. Use these commands to manage the @value{GDBN} command
7373 @cindex history substitution
7374 @cindex history file
7375 @kindex set history filename
7376 @item set history filename @var{fname}
7377 Set the name of the @value{GDBN} command history file to @var{fname}. This is
7378 the file from which @value{GDBN} will read an initial command history
7379 list or to which it will write this list when it exits. This list is
7380 accessed through history expansion or through the history
7381 command editing characters listed below. This file defaults to the
7382 value of the environment variable @code{GDBHISTFILE}, or to
7383 @file{./.gdb_history} if this variable is not set.
7385 @cindex history save
7386 @kindex set history save
7387 @item set history save
7388 @itemx set history save on
7389 Record command history in a file, whose name may be specified with the
7390 @code{set history filename} command. By default, this option is disabled.
7392 @item set history save off
7393 Stop recording command history in a file.
7395 @cindex history size
7396 @kindex set history size
7397 @item set history size @var{size}
7398 Set the number of commands which @value{GDBN} will keep in its history list.
7399 This defaults to the value of the environment variable
7400 @code{HISTSIZE}, or to 256 if this variable is not set.
7403 @cindex history expansion
7404 History expansion assigns special meaning to the character @kbd{!}.
7405 @ifset have-readline-appendices
7406 @xref{Event Designators}.
7409 Since @kbd{!} is also the logical not operator in C, history expansion
7410 is off by default. If you decide to enable history expansion with the
7411 @code{set history expansion on} command, you may sometimes need to
7412 follow @kbd{!} (when it is used as logical not, in an expression) with
7413 a space or a tab to prevent it from being expanded. The readline
7414 history facilities will not attempt substitution on the strings
7415 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
7417 The commands to control history expansion are:
7421 @kindex set history expansion
7422 @item set history expansion on
7423 @itemx set history expansion
7424 Enable history expansion. History expansion is off by default.
7426 @item set history expansion off
7427 Disable history expansion.
7429 The readline code comes with more complete documentation of
7430 editing and history expansion features. Users unfamiliar with @code{emacs}
7431 or @code{vi} may wish to read it.
7432 @ifset have-readline-appendices
7433 @xref{Command Line Editing}.
7437 @kindex show history
7439 @itemx show history filename
7440 @itemx show history save
7441 @itemx show history size
7442 @itemx show history expansion
7443 These commands display the state of the @value{GDBN} history parameters.
7444 @code{show history} by itself displays all four states.
7449 @kindex show commands
7451 Display the last ten commands in the command history.
7453 @item show commands @var{n}
7454 Print ten commands centered on command number @var{n}.
7456 @item show commands +
7457 Print ten commands just after the commands last printed.
7461 @section Screen size
7462 @cindex size of screen
7463 @cindex pauses in output
7465 Certain commands to @value{GDBN} may produce large amounts of
7466 information output to the screen. To help you read all of it,
7467 @value{GDBN} pauses and asks you for input at the end of each page of
7468 output. Type @key{RET} when you want to continue the output, or @kbd{q}
7469 to discard the remaining output. Also, the screen width setting
7470 determines when to wrap lines of output. Depending on what is being
7471 printed, @value{GDBN} tries to break the line at a readable place,
7472 rather than simply letting it overflow onto the following line.
7474 Normally @value{GDBN} knows the size of the screen from the termcap data base
7475 together with the value of the @code{TERM} environment variable and the
7476 @code{stty rows} and @code{stty cols} settings. If this is not correct,
7477 you can override it with the @code{set height} and @code{set
7481 @item set height @var{lpp}
7483 @itemx set width @var{cpl}
7489 These @code{set} commands specify a screen height of @var{lpp} lines and
7490 a screen width of @var{cpl} characters. The associated @code{show}
7491 commands display the current settings.
7493 If you specify a height of zero lines, @value{GDBN} will not pause during output
7494 no matter how long the output is. This is useful if output is to a file
7495 or to an editor buffer.
7497 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
7498 from wrapping its output.
7503 @cindex number representation
7504 @cindex entering numbers
7506 You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by
7507 the usual conventions: octal numbers begin with @samp{0}, decimal
7508 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
7509 Numbers that begin with none of these are, by default, entered in base
7510 10; likewise, the default display for numbers---when no particular
7511 format is specified---is base 10. You can change the default base for
7512 both input and output with the @code{set radix} command.
7516 @item set radix @var{base}
7517 Set the default base for numeric input and display. Supported choices
7518 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
7519 specified either unambiguously or using the current default radix; for
7529 will set the base to decimal. On the other hand, @samp{set radix 10}
7530 will leave the radix unchanged no matter what it was.
7534 Display the current default base for numeric input and display.
7537 @node Messages/Warnings
7538 @section Optional warnings and messages
7540 By default, @value{GDBN} is silent about its inner workings. If you are running
7541 on a slow machine, you may want to use the @code{set verbose} command.
7542 It will make @value{GDBN} tell you when it does a lengthy internal operation, so
7543 you will not think it has crashed.
7545 Currently, the messages controlled by @code{set verbose} are those
7546 which announce that the symbol table for a source file is being read;
7547 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
7551 @item set verbose on
7552 Enables @value{GDBN} output of certain informational messages.
7554 @item set verbose off
7555 Disables @value{GDBN} output of certain informational messages.
7557 @kindex show verbose
7559 Displays whether @code{set verbose} is on or off.
7562 By default, if @value{GDBN} encounters bugs in the symbol table of an object
7563 file, it is silent; but if you are debugging a compiler, you may find
7564 this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}).
7567 @kindex set complaints
7568 @item set complaints @var{limit}
7569 Permits @value{GDBN} to output @var{limit} complaints about each type of unusual
7570 symbols before becoming silent about the problem. Set @var{limit} to
7571 zero to suppress all complaints; set it to a large number to prevent
7572 complaints from being suppressed.
7574 @kindex show complaints
7575 @item show complaints
7576 Displays how many symbol complaints @value{GDBN} is permitted to produce.
7579 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
7580 lot of stupid questions to confirm certain commands. For example, if
7581 you try to run a program which is already running:
7585 The program being debugged has been started already.
7586 Start it from the beginning? (y or n)
7589 If you are willing to unflinchingly face the consequences of your own
7590 commands, you can disable this ``feature'':
7595 @cindex confirmation
7596 @cindex stupid questions
7597 @item set confirm off
7598 Disables confirmation requests.
7600 @item set confirm on
7601 Enables confirmation requests (the default).
7604 @kindex show confirm
7605 Displays state of confirmation requests.
7608 @c FIXME this does not really belong here. But where *does* it belong?
7609 @cindex reloading symbols
7610 Some systems allow individual object files that make up your program to
7611 be replaced without stopping and restarting your program.
7613 For example, in VxWorks you can simply recompile a defective object file
7614 and keep on running.
7616 If you are running on one of these systems, you can allow @value{GDBN} to
7617 reload the symbols for automatically relinked modules:
7620 @kindex set symbol-reloading
7621 @item set symbol-reloading on
7622 Replace symbol definitions for the corresponding source file when an
7623 object file with a particular name is seen again.
7625 @item set symbol-reloading off
7626 Do not replace symbol definitions when re-encountering object files of
7627 the same name. This is the default state; if you are not running on a
7628 system that permits automatically relinking modules, you should leave
7629 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
7630 when linking large programs, that may contain several modules (from
7631 different directories or libraries) with the same name.
7633 @item show symbol-reloading
7634 Show the current @code{on} or @code{off} setting.
7638 @chapter Canned Sequences of Commands
7640 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
7641 command lists}), @value{GDBN} provides two ways to store sequences of commands
7642 for execution as a unit: user-defined commands and command files.
7645 * Define:: User-defined commands
7646 * Hooks:: User-defined command hooks
7647 * Command Files:: Command files
7648 * Output:: Commands for controlled output
7652 @section User-defined commands
7654 @cindex user-defined command
7655 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which you
7656 assign a new name as a command. This is done with the @code{define}
7660 @item define @var{commandname}
7662 Define a command named @var{commandname}. If there is already a command
7663 by that name, you are asked to confirm that you want to redefine it.
7665 The definition of the command is made up of other @value{GDBN} command lines,
7666 which are given following the @code{define} command. The end of these
7667 commands is marked by a line containing @code{end}.
7669 @item document @var{commandname}
7671 Give documentation to the user-defined command @var{commandname}. The
7672 command @var{commandname} must already be defined. This command reads
7673 lines of documentation just as @code{define} reads the lines of the
7674 command definition, ending with @code{end}. After the @code{document}
7675 command is finished, @code{help} on command @var{commandname} will print
7676 the documentation you have specified.
7678 You may use the @code{document} command again to change the
7679 documentation of a command. Redefining the command with @code{define}
7680 does not change the documentation.
7682 @item help user-defined
7683 @kindex help user-defined
7684 List all user-defined commands, with the first line of the documentation
7688 @itemx show user @var{commandname}
7690 Display the @value{GDBN} commands used to define @var{commandname} (but not its
7691 documentation). If no @var{commandname} is given, display the
7692 definitions for all user-defined commands.
7695 User-defined commands do not take arguments. When they are executed, the
7696 commands of the definition are not printed. An error in any command
7697 stops execution of the user-defined command.
7699 Commands that would ask for confirmation if used interactively proceed
7700 without asking when used inside a user-defined command. Many @value{GDBN} commands
7701 that normally print messages to say what they are doing omit the messages
7702 when used in a user-defined command.
7705 @section User-defined command hooks
7706 @cindex command files
7708 You may define @emph{hooks}, which are a special kind of user-defined
7709 command. Whenever you run the command @samp{foo}, if the user-defined
7710 command @samp{hook-foo} exists, it is executed (with no arguments)
7711 before that command.
7713 In addition, a pseudo-command, @samp{stop} exists. Defining
7714 (@samp{hook-stop}) makes the associated commands execute every time
7715 execution stops in your program: before breakpoint commands are run,
7716 displays are printed, or the stack frame is printed.
7719 For example, to ignore @code{SIGALRM} signals while
7720 single-stepping, but treat them normally during normal execution,
7725 handle SIGALRM nopass
7732 define hook-continue
7738 You can define a hook for any single-word command in @value{GDBN}, but
7739 not for command aliases; you should define a hook for the basic command
7740 name, e.g. @code{backtrace} rather than @code{bt}.
7741 @c FIXME! So how does Joe User discover whether a command is an alias
7743 If an error occurs during the execution of your hook, execution of
7744 @value{GDBN} commands stops and @value{GDBN} issues a prompt
7745 (before the command that you actually typed had a chance to run).
7747 If you try to define a hook which does not match any known command, you
7748 will get a warning from the @code{define} command.
7751 @section Command files
7753 @cindex command files
7754 A command file for @value{GDBN} is a file of lines that are @value{GDBN} commands. Comments
7755 (lines starting with @kbd{#}) may also be included. An empty line in a
7756 command file does nothing; it does not mean to repeat the last command, as
7757 it would from the terminal.
7760 @cindex @file{@value{GDBINIT}}
7761 When you start @value{GDBN}, it automatically executes commands from its
7762 @dfn{init files}. These are files named @file{@value{GDBINIT}}.
7763 @value{GDBN} reads the init file (if any) in your home directory, then
7764 processes command line options and operands, and then reads the init
7765 file (if any) in the current working directory. This is so the init
7766 file in your home directory can set options (such as @code{set
7767 complaints}) which affect the processing of the command line options and
7768 operands. The init files are not executed if you use the @samp{-nx}
7769 option; @pxref{Mode Options, ,Choosing modes}.
7772 @cindex init file name
7773 On some configurations of @value{GDBN}, the init file is known by a
7774 different name (these are typically environments where a specialized
7775 form of GDB may need to coexist with other forms, hence a different name
7776 for the specialized version's init file). These are the environments
7777 with special init file names:
7782 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
7784 @kindex .os68gdbinit
7786 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
7790 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
7794 You can also request the execution of a command file with the
7795 @code{source} command:
7798 @item source @var{filename}
7800 Execute the command file @var{filename}.
7803 The lines in a command file are executed sequentially. They are not
7804 printed as they are executed. An error in any command terminates execution
7805 of the command file.
7807 Commands that would ask for confirmation if used interactively proceed
7808 without asking when used in a command file. Many @value{GDBN} commands that
7809 normally print messages to say what they are doing omit the messages
7810 when called from command files.
7813 @section Commands for controlled output
7815 During the execution of a command file or a user-defined command, normal
7816 @value{GDBN} output is suppressed; the only output that appears is what is
7817 explicitly printed by the commands in the definition. This section
7818 describes three commands useful for generating exactly the output you
7822 @item echo @var{text}
7824 @c I do not consider backslash-space a standard C escape sequence
7825 @c because it is not in ANSI.
7826 Print @var{text}. Nonprinting characters can be included in
7827 @var{text} using C escape sequences, such as @samp{\n} to print a
7828 newline. @strong{No newline will be printed unless you specify one.}
7829 In addition to the standard C escape sequences, a backslash followed
7830 by a space stands for a space. This is useful for displaying a
7831 string with spaces at the beginning or the end, since leading and
7832 trailing spaces are otherwise trimmed from all arguments.
7833 To print @samp{@w{ }and foo =@w{ }}, use the command
7834 @samp{echo \@w{ }and foo = \@w{ }}.
7836 A backslash at the end of @var{text} can be used, as in C, to continue
7837 the command onto subsequent lines. For example,
7840 echo This is some text\n\
7841 which is continued\n\
7842 onto several lines.\n
7845 produces the same output as
7848 echo This is some text\n
7849 echo which is continued\n
7850 echo onto several lines.\n
7853 @item output @var{expression}
7855 Print the value of @var{expression} and nothing but that value: no
7856 newlines, no @samp{$@var{nn} = }. The value is not entered in the
7857 value history either. @xref{Expressions, ,Expressions}, for more information on
7860 @item output/@var{fmt} @var{expression}
7861 Print the value of @var{expression} in format @var{fmt}. You can use
7862 the same formats as for @code{print}. @xref{Output Formats,,Output
7863 formats}, for more information.
7865 @item printf @var{string}, @var{expressions}@dots{}
7867 Print the values of the @var{expressions} under the control of
7868 @var{string}. The @var{expressions} are separated by commas and may be
7869 either numbers or pointers. Their values are printed as specified by
7870 @var{string}, exactly as if your program were to execute the C
7874 printf (@var{string}, @var{expressions}@dots{});
7877 For example, you can print two values in hex like this:
7880 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
7883 The only backslash-escape sequences that you can use in the format
7884 string are the simple ones that consist of backslash followed by a
7890 @chapter Using @value{GDBN} under GNU Emacs
7893 A special interface allows you to use GNU Emacs to view (and
7894 edit) the source files for the program you are debugging with
7897 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
7898 executable file you want to debug as an argument. This command starts
7899 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
7900 created Emacs buffer.
7902 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
7907 All ``terminal'' input and output goes through the Emacs buffer.
7910 This applies both to @value{GDBN} commands and their output, and to the input
7911 and output done by the program you are debugging.
7913 This is useful because it means that you can copy the text of previous
7914 commands and input them again; you can even use parts of the output
7917 All the facilities of Emacs' Shell mode are available for interacting
7918 with your program. In particular, you can send signals the usual
7919 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
7924 @value{GDBN} displays source code through Emacs.
7927 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
7928 source file for that frame and puts an arrow (@samp{=>}) at the
7929 left margin of the current line. Emacs uses a separate buffer for
7930 source display, and splits the screen to show both your @value{GDBN} session
7933 Explicit @value{GDBN} @code{list} or search commands still produce output as
7934 usual, but you probably will have no reason to use them.
7937 @emph{Warning:} If the directory where your program resides is not your
7938 current directory, it can be easy to confuse Emacs about the location of
7939 the source files, in which case the auxiliary display buffer will not
7940 appear to show your source. @value{GDBN} can find programs by searching your
7941 environment's @code{PATH} variable, so the @value{GDBN} input and output
7942 session will proceed normally; but Emacs does not get enough information
7943 back from @value{GDBN} to locate the source files in this situation. To
7944 avoid this problem, either start @value{GDBN} mode from the directory where
7945 your program resides, or specify a full path name when prompted for the
7946 @kbd{M-x gdb} argument.
7948 A similar confusion can result if you use the @value{GDBN} @code{file} command to
7949 switch to debugging a program in some other location, from an existing
7950 @value{GDBN} buffer in Emacs.
7953 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
7954 you need to call @value{GDBN} by a different name (for example, if you keep
7955 several configurations around, with different names) you can set the
7956 Emacs variable @code{gdb-command-name}; for example,
7959 (setq gdb-command-name "mygdb")
7963 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
7964 in your @file{.emacs} file) will make Emacs call the program named
7965 ``@code{mygdb}'' instead.
7967 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
7968 addition to the standard Shell mode commands:
7972 Describe the features of Emacs' @value{GDBN} Mode.
7975 Execute to another source line, like the @value{GDBN} @code{step} command; also
7976 update the display window to show the current file and location.
7979 Execute to next source line in this function, skipping all function
7980 calls, like the @value{GDBN} @code{next} command. Then update the display window
7981 to show the current file and location.
7984 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
7985 display window accordingly.
7988 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
7989 display window accordingly.
7992 Execute until exit from the selected stack frame, like the @value{GDBN}
7993 @code{finish} command.
7996 Continue execution of your program, like the @value{GDBN} @code{continue}
7999 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
8002 Go up the number of frames indicated by the numeric argument
8003 (@pxref{Arguments, , Numeric Arguments, emacs, The GNU Emacs Manual}),
8004 like the @value{GDBN} @code{up} command.
8006 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
8009 Go down the number of frames indicated by the numeric argument, like the
8010 @value{GDBN} @code{down} command.
8012 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
8015 Read the number where the cursor is positioned, and insert it at the end
8016 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
8017 around an address that was displayed earlier, type @kbd{disassemble};
8018 then move the cursor to the address display, and pick up the
8019 argument for @code{disassemble} by typing @kbd{C-x &}.
8021 You can customize this further by defining elements of the list
8022 @code{gdb-print-command}; once it is defined, you can format or
8023 otherwise process numbers picked up by @kbd{C-x &} before they are
8024 inserted. A numeric argument to @kbd{C-x &} will both indicate that you
8025 wish special formatting, and act as an index to pick an element of the
8026 list. If the list element is a string, the number to be inserted is
8027 formatted using the Emacs function @code{format}; otherwise the number
8028 is passed as an argument to the corresponding list element.
8031 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
8032 tells @value{GDBN} to set a breakpoint on the source line point is on.
8034 If you accidentally delete the source-display buffer, an easy way to get
8035 it back is to type the command @code{f} in the @value{GDBN} buffer, to
8036 request a frame display; when you run under Emacs, this will recreate
8037 the source buffer if necessary to show you the context of the current
8040 The source files displayed in Emacs are in ordinary Emacs buffers
8041 which are visiting the source files in the usual way. You can edit
8042 the files with these buffers if you wish; but keep in mind that @value{GDBN}
8043 communicates with Emacs in terms of line numbers. If you add or
8044 delete lines from the text, the line numbers that @value{GDBN} knows will cease
8045 to correspond properly with the code.
8047 @c The following dropped because Epoch is nonstandard. Reactivate
8048 @c if/when v19 does something similar. ---pesch@cygnus.com 19dec1990
8050 @kindex emacs epoch environment
8054 Version 18 of Emacs has a built-in window system called the @code{epoch}
8055 environment. Users of this environment can use a new command,
8056 @code{inspect} which performs identically to @code{print} except that
8057 each value is printed in its own window.
8063 @chapter Using @value{GDBN} with Energize
8066 The Energize Programming System is an integrated development environment
8067 that includes a point-and-click interface to many programming tools.
8068 When you use @value{GDBN} in this environment, you can use the standard
8069 Energize graphical interface to drive @value{GDBN}; you can also, if you
8070 choose, type @value{GDBN} commands as usual in a debugging window. Even if
8071 you use the graphical interface, the debugging window (which uses Emacs,
8072 and resembles the standard Emacs interface to @value{GDBN}) displays the
8073 equivalent commands, so that the history of your debugging session is
8076 When Energize starts up a @value{GDBN} session, it uses one of the
8077 command-line options @samp{-energize} or @samp{-cadillac} (``cadillac''
8078 is the name of the communications protocol used by the Energize system).
8079 This option makes @value{GDBN} run as one of the tools in the Energize Tool
8080 Set: it sends all output to the Energize kernel, and accept input from
8083 See the user manual for the Energize Programming System for
8084 information on how to use the Energize graphical interface and the other
8085 development tools that Energize integrates with @value{GDBN}.
8090 @chapter Reporting Bugs in @value{GDBN}
8091 @cindex bugs in @value{GDBN}
8092 @cindex reporting bugs in @value{GDBN}
8094 Your bug reports play an essential role in making @value{GDBN} reliable.
8096 Reporting a bug may help you by bringing a solution to your problem, or it
8097 may not. But in any case the principal function of a bug report is to help
8098 the entire community by making the next version of @value{GDBN} work better. Bug
8099 reports are your contribution to the maintenance of @value{GDBN}.
8101 In order for a bug report to serve its purpose, you must include the
8102 information that enables us to fix the bug.
8105 * Bug Criteria:: Have you found a bug?
8106 * Bug Reporting:: How to report bugs
8110 @section Have you found a bug?
8111 @cindex bug criteria
8113 If you are not sure whether you have found a bug, here are some guidelines:
8117 @cindex fatal signal
8118 @cindex debugger crash
8119 @cindex crash of debugger
8120 If the debugger gets a fatal signal, for any input whatever, that is a
8121 @value{GDBN} bug. Reliable debuggers never crash.
8124 @cindex error on valid input
8125 If @value{GDBN} produces an error message for valid input, that is a bug.
8128 @cindex invalid input
8129 If @value{GDBN} does not produce an error message for invalid input,
8130 that is a bug. However, you should note that your idea of
8131 ``invalid input'' might be our idea of ``an extension'' or ``support
8132 for traditional practice''.
8135 If you are an experienced user of debugging tools, your suggestions
8136 for improvement of @value{GDBN} are welcome in any case.
8140 @section How to report bugs
8142 @cindex @value{GDBN} bugs, reporting
8144 A number of companies and individuals offer support for GNU products.
8145 If you obtained @value{GDBN} from a support organization, we recommend you
8146 contact that organization first.
8148 You can find contact information for many support companies and
8149 individuals in the file @file{etc/SERVICE} in the GNU Emacs
8152 In any event, we also recommend that you send bug reports for @value{GDBN} to one
8156 bug-gdb@@prep.ai.mit.edu
8157 @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb
8160 @strong{Do not send bug reports to @samp{info-gdb}, or to
8161 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do not want to
8162 receive bug reports. Those that do, have arranged to receive @samp{bug-gdb}.
8164 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
8165 serves as a repeater. The mailing list and the newsgroup carry exactly
8166 the same messages. Often people think of posting bug reports to the
8167 newsgroup instead of mailing them. This appears to work, but it has one
8168 problem which can be crucial: a newsgroup posting often lacks a mail
8169 path back to the sender. Thus, if we need to ask for more information,
8170 we may be unable to reach you. For this reason, it is better to send
8171 bug reports to the mailing list.
8173 As a last resort, send bug reports on paper to:
8177 Free Software Foundation
8182 The fundamental principle of reporting bugs usefully is this:
8183 @strong{report all the facts}. If you are not sure whether to state a
8184 fact or leave it out, state it!
8186 Often people omit facts because they think they know what causes the
8187 problem and assume that some details do not matter. Thus, you might
8188 assume that the name of the variable you use in an example does not matter.
8189 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
8190 stray memory reference which happens to fetch from the location where that
8191 name is stored in memory; perhaps, if the name were different, the contents
8192 of that location would fool the debugger into doing the right thing despite
8193 the bug. Play it safe and give a specific, complete example. That is the
8194 easiest thing for you to do, and the most helpful.
8196 Keep in mind that the purpose of a bug report is to enable us to fix
8197 the bug if it is new to us. It is not as important as what happens if
8198 the bug is already known. Therefore, always write your bug reports on
8199 the assumption that the bug has not been reported previously.
8201 Sometimes people give a few sketchy facts and ask, ``Does this ring a
8202 bell?'' Those bug reports are useless, and we urge everyone to
8203 @emph{refuse to respond to them} except to chide the sender to report
8206 To enable us to fix the bug, you should include all these things:
8210 The version of @value{GDBN}. @value{GDBN} announces it if you start with no
8211 arguments; you can also print it at any time using @code{show version}.
8213 Without this, we will not know whether there is any point in looking for
8214 the bug in the current version of @value{GDBN}.
8217 The type of machine you are using, and the operating system name and
8221 What compiler (and its version) was used to compile @value{GDBN}---e.g.
8222 ``@value{GCC}--2.0''.
8225 What compiler (and its version) was used to compile the program you
8226 are debugging---e.g. ``@value{GCC}--2.0''.
8229 The command arguments you gave the compiler to compile your example and
8230 observe the bug. For example, did you use @samp{-O}? To guarantee
8231 you will not omit something important, list them all. A copy of the
8232 Makefile (or the output from make) is sufficient.
8234 If we were to try to guess the arguments, we would probably guess wrong
8235 and then we might not encounter the bug.
8238 A complete input script, and all necessary source files, that will
8242 A description of what behavior you observe that you believe is
8243 incorrect. For example, ``It gets a fatal signal.''
8245 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we will
8246 certainly notice it. But if the bug is incorrect output, we might not
8247 notice unless it is glaringly wrong. We are human, after all. You
8248 might as well not give us a chance to make a mistake.
8250 Even if the problem you experience is a fatal signal, you should still
8251 say so explicitly. Suppose something strange is going on, such as,
8252 your copy of @value{GDBN} is out of synch, or you have encountered a
8253 bug in the C library on your system. (This has happened!) Your copy
8254 might crash and ours would not. If you told us to expect a crash,
8255 then when ours fails to crash, we would know that the bug was not
8256 happening for us. If you had not told us to expect a crash, then we
8257 would not be able to draw any conclusion from our observations.
8260 If you wish to suggest changes to the @value{GDBN} source, send us context
8261 diffs. If you even discuss something in the @value{GDBN} source, refer to
8262 it by context, not by line number.
8264 The line numbers in our development sources will not match those in your
8265 sources. Your line numbers would convey no useful information to us.
8268 Here are some things that are not necessary:
8272 A description of the envelope of the bug.
8274 Often people who encounter a bug spend a lot of time investigating
8275 which changes to the input file will make the bug go away and which
8276 changes will not affect it.
8278 This is often time consuming and not very useful, because the way we
8279 will find the bug is by running a single example under the debugger
8280 with breakpoints, not by pure deduction from a series of examples.
8281 We recommend that you save your time for something else.
8283 Of course, if you can find a simpler example to report @emph{instead}
8284 of the original one, that is a convenience for us. Errors in the
8285 output will be easier to spot, running under the debugger will take
8286 less time, and so on.
8288 However, simplification is not vital; if you do not want to do this,
8289 report the bug anyway and send us the entire test case you used.
8292 A patch for the bug.
8294 A patch for the bug does help us if it is a good one. But do not omit
8295 the necessary information, such as the test case, on the assumption that
8296 a patch is all we need. We might see problems with your patch and decide
8297 to fix the problem another way, or we might not understand it at all.
8299 Sometimes with a program as complicated as @value{GDBN} it is very hard to
8300 construct an example that will make the program follow a certain path
8301 through the code. If you do not send us the example, we will not be able
8302 to construct one, so we will not be able to verify that the bug is fixed.
8304 And if we cannot understand what bug you are trying to fix, or why your
8305 patch should be an improvement, we will not install it. A test case will
8306 help us to understand.
8309 A guess about what the bug is or what it depends on.
8311 Such guesses are usually wrong. Even we cannot guess right about such
8312 things without first using the debugger to find the facts.
8315 @c The readline documentation is distributed with the readline code
8316 @c and consists of the two following files:
8319 @c Use -I with makeinfo to point to the appropriate directory,
8320 @c environment var TEXINPUTS with TeX.
8321 @include rluser.texinfo
8322 @include inc-hist.texi
8325 @node Renamed Commands
8326 @appendix Renamed Commands
8328 The following commands were renamed in GDB 4, in order to make the
8329 command set as a whole more consistent and easier to use and remember:
8332 @kindex delete environment
8333 @kindex info copying
8334 @kindex info convenience
8335 @kindex info directories
8336 @kindex info editing
8337 @kindex info history
8338 @kindex info targets
8340 @kindex info version
8341 @kindex info warranty
8342 @kindex set addressprint
8343 @kindex set arrayprint
8344 @kindex set prettyprint
8345 @kindex set screen-height
8346 @kindex set screen-width
8347 @kindex set unionprint
8348 @kindex set vtblprint
8349 @kindex set demangle
8350 @kindex set asm-demangle
8351 @kindex set sevenbit-strings
8352 @kindex set array-max
8354 @kindex set history write
8355 @kindex show addressprint
8356 @kindex show arrayprint
8357 @kindex show prettyprint
8358 @kindex show screen-height
8359 @kindex show screen-width
8360 @kindex show unionprint
8361 @kindex show vtblprint
8362 @kindex show demangle
8363 @kindex show asm-demangle
8364 @kindex show sevenbit-strings
8365 @kindex show array-max
8366 @kindex show caution
8367 @kindex show history write
8372 @c END TEXI2ROFF-KILL
8374 OLD COMMAND NEW COMMAND
8376 --------------- -------------------------------
8377 @c END TEXI2ROFF-KILL
8378 add-syms add-symbol-file
8379 delete environment unset environment
8380 info convenience show convenience
8381 info copying show copying
8382 info directories show directories
8383 info editing show commands
8384 info history show values
8385 info targets help target
8386 info values show values
8387 info version show version
8388 info warranty show warranty
8389 set/show addressprint set/show print address
8390 set/show array-max set/show print elements
8391 set/show arrayprint set/show print array
8392 set/show asm-demangle set/show print asm-demangle
8393 set/show caution set/show confirm
8394 set/show demangle set/show print demangle
8395 set/show history write set/show history save
8396 set/show prettyprint set/show print pretty
8397 set/show screen-height set/show height
8398 set/show screen-width set/show width
8399 set/show sevenbit-strings set/show print sevenbit-strings
8400 set/show unionprint set/show print union
8401 set/show vtblprint set/show print vtbl
8403 unset [No longer an alias for delete]
8409 \vskip \parskip\vskip \baselineskip
8410 \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr
8411 {\bf Old Command} &&{\bf New Command}\cr
8412 add-syms &&add-symbol-file\cr
8413 delete environment &&unset environment\cr
8414 info convenience &&show convenience\cr
8415 info copying &&show copying\cr
8416 info directories &&show directories \cr
8417 info editing &&show commands\cr
8418 info history &&show values\cr
8419 info targets &&help target\cr
8420 info values &&show values\cr
8421 info version &&show version\cr
8422 info warranty &&show warranty\cr
8423 set{\rm / }show addressprint &&set{\rm / }show print address\cr
8424 set{\rm / }show array-max &&set{\rm / }show print elements\cr
8425 set{\rm / }show arrayprint &&set{\rm / }show print array\cr
8426 set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr
8427 set{\rm / }show caution &&set{\rm / }show confirm\cr
8428 set{\rm / }show demangle &&set{\rm / }show print demangle\cr
8429 set{\rm / }show history write &&set{\rm / }show history save\cr
8430 set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr
8431 set{\rm / }show screen-height &&set{\rm / }show height\cr
8432 set{\rm / }show screen-width &&set{\rm / }show width\cr
8433 set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr
8434 set{\rm / }show unionprint &&set{\rm / }show print union\cr
8435 set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr
8437 unset &&\rm(No longer an alias for delete)\cr
8440 @c END TEXI2ROFF-KILL
8443 @ifclear PRECONFIGURED
8444 @node Formatting Documentation
8445 @appendix Formatting Documentation
8447 @cindex GDB reference card
8448 @cindex reference card
8449 The GDB 4 release includes an already-formatted reference card, ready
8450 for printing with PostScript or GhostScript, in the @file{gdb}
8451 subdirectory of the main source directory@footnote{In
8452 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
8453 release.}. If you can use PostScript or GhostScript with your printer,
8454 you can print the reference card immediately with @file{refcard.ps}.
8456 The release also includes the source for the reference card. You
8457 can format it, using @TeX{}, by typing:
8463 The GDB reference card is designed to print in landscape mode on US
8464 ``letter'' size paper; that is, on a sheet 11 inches wide by 8.5 inches
8465 high. You will need to specify this form of printing as an option to
8466 your @sc{dvi} output program.
8468 @cindex documentation
8470 All the documentation for GDB comes as part of the machine-readable
8471 distribution. The documentation is written in Texinfo format, which is
8472 a documentation system that uses a single source file to produce both
8473 on-line information and a printed manual. You can use one of the Info
8474 formatting commands to create the on-line version of the documentation
8475 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
8477 GDB includes an already formatted copy of the on-line Info version of
8478 this manual in the @file{gdb} subdirectory. The main Info file is
8479 @file{gdb-@var{version-number}/gdb/gdb.info}, and it refers to
8480 subordinate files matching @samp{gdb.info*} in the same directory. If
8481 necessary, you can print out these files, or read them with any editor;
8482 but they are easier to read using the @code{info} subsystem in GNU Emacs
8483 or the standalone @code{info} program, available as part of the GNU
8484 Texinfo distribution.
8486 If you want to format these Info files yourself, you need one of the
8487 Info formatting programs, such as @code{texinfo-format-buffer} or
8490 If you have @code{makeinfo} installed, and are in the top level GDB
8491 source directory (@file{gdb-@value{GDBVN}}, in the case of version @value{GDBVN}), you can
8492 make the Info file by typing:
8499 If you want to typeset and print copies of this manual, you need @TeX{},
8500 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
8501 Texinfo definitions file.
8503 @TeX{} is a typesetting program; it does not print files directly, but
8504 produces output files called @sc{dvi} files. To print a typeset
8505 document, you need a program to print @sc{dvi} files. If your system
8506 has @TeX{} installed, chances are it has such a program. The precise
8507 command to use depends on your system; @kbd{lpr -d} is common; another
8508 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
8509 require a file name without any extension or a @samp{.dvi} extension.
8511 @TeX{} also requires a macro definitions file called
8512 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
8513 written in Texinfo format. On its own, @TeX{} cannot read, much less
8514 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
8515 and is located in the @file{gdb-@var{version-number}/texinfo}
8518 If you have @TeX{} and a @sc{dvi} printer program installed, you can
8519 typeset and print this manual. First switch to the the @file{gdb}
8520 subdirectory of the main source directory (for example, to
8521 @file{gdb-@value{GDBVN}/gdb}) and then type:
8527 @node Installing GDB
8528 @appendix Installing GDB
8529 @cindex configuring GDB
8530 @cindex installation
8532 GDB comes with a @code{configure} script that automates the process
8533 of preparing GDB for installation; you can then use @code{make} to
8534 build the @code{gdb} program.
8536 @c irrelevant in info file; it's as current as the code it lives with.
8537 @footnote{If you have a more recent version of GDB than @value{GDBVN},
8538 look at the @file{README} file in the sources; we may have improved the
8539 installation procedures since publishing this manual.}
8542 The GDB distribution includes all the source code you need for GDB in
8543 a single directory, whose name is usually composed by appending the
8544 version number to @samp{gdb}.
8546 For example, the GDB version @value{GDBVN} distribution is in the
8547 @file{gdb-@value{GDBVN}} directory. That directory contains:
8550 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
8551 script for configuring GDB and all its supporting libraries.
8553 @item gdb-@value{GDBVN}/gdb
8554 the source specific to GDB itself
8556 @item gdb-@value{GDBVN}/bfd
8557 source for the Binary File Descriptor library
8559 @item gdb-@value{GDBVN}/include
8562 @item gdb-@value{GDBVN}/libiberty
8563 source for the @samp{-liberty} free software library
8565 @item gdb-@value{GDBVN}/opcodes
8566 source for the library of opcode tables and disassemblers
8568 @item gdb-@value{GDBVN}/readline
8569 source for the GNU command-line interface
8571 @item gdb-@value{GDBVN}/glob
8572 source for the GNU filename pattern-matching subroutine
8574 @item gdb-@value{GDBVN}/mmalloc
8575 source for the GNU memory-mapped malloc package
8578 The simplest way to configure and build GDB is to run @code{configure}
8579 from the @file{gdb-@var{version-number}} source directory, which in
8580 this example is the @file{gdb-@value{GDBVN}} directory.
8582 First switch to the @file{gdb-@var{version-number}} source directory
8583 if you are not already in it; then run @code{configure}. Pass the
8584 identifier for the platform on which GDB will run as an
8590 cd gdb-@value{GDBVN}
8591 ./configure @var{host}
8596 where @var{host} is an identifier such as @samp{sun4} or
8597 @samp{decstation}, that identifies the platform where GDB will run.
8598 (You can often leave off @var{host}; @code{configure} tries to guess the
8599 correct value by examining your system.)
8601 Running @samp{configure @var{host}} and then running @code{make} builds the
8602 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
8603 libraries, then @code{gdb} itself. The configured source files, and the
8604 binaries, are left in the corresponding source directories.
8606 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
8607 system does not recognize this automatically when you run a different
8608 shell, you may need to run @code{sh} on it explicitly:
8611 sh configure @var{host}
8614 If you run @code{configure} from a directory that contains source
8615 directories for multiple libraries or programs, such as the
8616 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
8617 creates configuration files for every directory level underneath (unless
8618 you tell it not to, with the @samp{--norecursion} option).
8620 You can run the @code{configure} script from any of the
8621 subordinate directories in the GDB distribution if you only want to
8622 configure that subdirectory, but be sure to specify a path to it.
8624 For example, with version @value{GDBVN}, type the following to configure only
8625 the @code{bfd} subdirectory:
8629 cd gdb-@value{GDBVN}/bfd
8630 ../configure @var{host}
8634 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
8635 However, you should make sure that the shell on your path (named by
8636 the @samp{SHELL} environment variable) is publicly readable. Remember
8637 that GDB uses the shell to start your program---some systems refuse to
8638 let GDB debug child processes whose programs are not readable.
8641 * Separate Objdir:: Compiling GDB in another directory
8642 * Config Names:: Specifying names for hosts and targets
8643 * configure Options:: Summary of options for configure
8646 @node Separate Objdir
8647 @section Compiling GDB in another directory
8649 If you want to run GDB versions for several host or target machines,
8650 you need a different @code{gdb} compiled for each combination of
8651 host and target. @code{configure} is designed to make this easy by
8652 allowing you to generate each configuration in a separate subdirectory,
8653 rather than in the source directory. If your @code{make} program
8654 handles the @samp{VPATH} feature (GNU @code{make} does), running
8655 @code{make} in each of these directories builds the @code{gdb}
8656 program specified there.
8658 To build @code{gdb} in a separate directory, run @code{configure}
8659 with the @samp{--srcdir} option to specify where to find the source.
8660 (You also need to specify a path to find @code{configure}
8661 itself from your working directory. If the path to @code{configure}
8662 would be the same as the argument to @samp{--srcdir}, you can leave out
8663 the @samp{--srcdir} option; it will be assumed.)
8665 For example, with version @value{GDBVN}, you can build GDB in a separate
8666 directory for a Sun 4 like this:
8670 cd gdb-@value{GDBVN}
8673 ../gdb-@value{GDBVN}/configure sun4
8678 When @code{configure} builds a configuration using a remote source
8679 directory, it creates a tree for the binaries with the same structure
8680 (and using the same names) as the tree under the source directory. In
8681 the example, you'd find the Sun 4 library @file{libiberty.a} in the
8682 directory @file{gdb-sun4/libiberty}, and GDB itself in
8683 @file{gdb-sun4/gdb}.
8685 One popular reason to build several GDB configurations in separate
8686 directories is to configure GDB for cross-compiling (where GDB
8687 runs on one machine---the host---while debugging programs that run on
8688 another machine---the target). You specify a cross-debugging target by
8689 giving the @samp{--target=@var{target}} option to @code{configure}.
8691 When you run @code{make} to build a program or library, you must run
8692 it in a configured directory---whatever directory you were in when you
8693 called @code{configure} (or one of its subdirectories).
8695 The @code{Makefile} that @code{configure} generates in each source
8696 directory also runs recursively. If you type @code{make} in a source
8697 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
8698 directory configured with @samp{--srcdir=@var{path}/gdb-@value{GDBVN}}), you
8699 will build all the required libraries, and then build GDB.
8701 When you have multiple hosts or targets configured in separate
8702 directories, you can run @code{make} on them in parallel (for example,
8703 if they are NFS-mounted on each of the hosts); they will not interfere
8707 @section Specifying names for hosts and targets
8709 The specifications used for hosts and targets in the @code{configure}
8710 script are based on a three-part naming scheme, but some short predefined
8711 aliases are also supported. The full naming scheme encodes three pieces
8712 of information in the following pattern:
8715 @var{architecture}-@var{vendor}-@var{os}
8718 For example, you can use the alias @code{sun4} as a @var{host} argument,
8719 or as the value for @var{target} in a @code{--target=@var{target}}
8720 option. The equivalent full name is @samp{sparc-sun-sunos4}.
8722 The @code{configure} script accompanying GDB does not provide
8723 any query facility to list all supported host and target names or
8724 aliases. @code{configure} calls the Bourne shell script
8725 @code{config.sub} to map abbreviations to full names; you can read the
8726 script, if you wish, or you can use it to test your guesses on
8727 abbreviations---for example:
8730 % sh config.sub sun4
8731 sparc-sun-sunos4.1.1
8732 % sh config.sub sun3
8734 % sh config.sub decstation
8736 % sh config.sub hp300bsd
8738 % sh config.sub i386v
8740 % sh config.sub i786v
8741 Invalid configuration `i786v': machine `i786v' not recognized
8745 @code{config.sub} is also distributed in the GDB source
8746 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
8748 @node configure Options
8749 @section @code{configure} options
8751 Here is a summary of the @code{configure} options and arguments that
8752 are most often useful for building @value{GDBN}. @code{configure} also has
8753 several other options not listed here. @inforef{What Configure
8754 Does,,configure.info}, for a full explanation of @code{configure}.
8755 @c FIXME: Would this be more, or less, useful as an xref (ref to printed
8756 @c manual in the printed manual, ref to info file only from the info file)?
8759 configure @r{[}--help@r{]}
8760 @r{[}--prefix=@var{dir}@r{]}
8761 @r{[}--srcdir=@var{path}@r{]}
8762 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
8763 @r{[}--target=@var{target}@r{]} @var{host}
8767 You may introduce options with a single @samp{-} rather than
8768 @samp{--} if you prefer; but you may abbreviate option names if you use
8773 Display a quick summary of how to invoke @code{configure}.
8775 @item -prefix=@var{dir}
8776 Configure the source to install programs and files under directory
8779 @c avoid splitting the warning from the explanation:
8781 @item --srcdir=@var{path}
8782 @strong{Warning: using this option requires GNU @code{make}, or another
8783 @code{make} that implements the @code{VPATH} feature.}@*
8784 Use this option to make configurations in directories separate from the
8785 GDB source directories. Among other things, you can use this to
8786 build (or maintain) several configurations simultaneously, in separate
8787 directories. @code{configure} writes configuration specific files in
8788 the current directory, but arranges for them to use the source in the
8789 directory @var{path}. @code{configure} will create directories under
8790 the working directory in parallel to the source directories below
8794 Configure only the directory level where @code{configure} is executed; do not
8795 propagate configuration to subdirectories.
8798 @emph{Remove} files otherwise built during configuration.
8800 @c This does not work (yet if ever). FIXME.
8801 @c @item --parse=@var{lang} @dots{}
8802 @c Configure the GDB expression parser to parse the listed languages.
8803 @c @samp{all} configures GDB for all supported languages. To get a
8804 @c list of all supported languages, omit the argument. Without this
8805 @c option, GDB is configured to parse all supported languages.
8807 @item --target=@var{target}
8808 Configure GDB for cross-debugging programs running on the specified
8809 @var{target}. Without this option, GDB is configured to debug
8810 programs that run on the same machine (@var{host}) as GDB itself.
8812 There is no convenient way to generate a list of all available targets.
8814 @item @var{host} @dots{}
8815 Configure GDB to run on the specified @var{host}.
8817 There is no convenient way to generate a list of all available hosts.
8821 @code{configure} accepts other options, for compatibility with
8822 configuring other GNU tools recursively; but these are the only
8823 options that affect GDB or its supporting libraries.
8832 % I think something like @colophon should be in texinfo. In the
8834 \long\def\colophon{\hbox to0pt{}\vfill
8835 \centerline{The body of this manual is set in}
8836 \centerline{\fontname\tenrm,}
8837 \centerline{with headings in {\bf\fontname\tenbf}}
8838 \centerline{and examples in {\tt\fontname\tentt}.}
8839 \centerline{{\it\fontname\tenit\/},}
8840 \centerline{{\bf\fontname\tenbf}, and}
8841 \centerline{{\sl\fontname\tensl\/}}
8842 \centerline{are used for emphasis.}\vfill}
8844 % Blame: pesch@cygnus.com, 1991.