2 _dnl__ Copyright (c) 1988 1989 1990 1991 Free Software Foundation, Inc.
4 @setfilename _GDBP__.info
6 @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly.
8 @c NOTE: this manual is marked up for preprocessing with a collection
9 @c of m4 macros called "pretex.m4". If you see <_if__> and <_fi__>
10 @c scattered around the source, you have the full source before
11 @c preprocessing; if you don't, you have the source configured for
12 @c _HOST__ architectures (and you can of course get the full source,
13 @c with all configurations, from wherever you got this).
16 THIS IS THE SOURCE PRIOR TO PREPROCESSING. The full source needs to
17 be run through m4 before either tex- or info- formatting: for example,
19 m4 pretex.m4 none.m4 all.m4 gdb.texinfo >gdb-all.texinfo
21 will produce (assuming your path finds either GNU m4 >= 0.84, or SysV
22 m4; Berkeley won't do) a file suitable for formatting. See the text in
23 "pretex.m4" for a fuller explanation (and the macro definitions).
28 \def\$#1${{#1}} % Kluge: collect RCS revision info without $...$
29 \xdef\manvers{\$Revision$} % For use in headers, footers too
33 @c FOR UPDATES LEADING TO THIS DRAFT, GDB CHANGELOG CONSULTED BETWEEN:
34 @c Fri Sep 20 16:10:52 1991 John Gilmore (gnu at cygnus.com)
35 @c Sat Dec 22 02:51:40 1990 John Gilmore (gnu at cygint)
37 This file documents the GNU debugger _GDBN__.
39 Copyright (C) 1988, 1989, 1990, 1991 Free Software Foundation, Inc.
41 Permission is granted to make and distribute verbatim copies of
42 this manual provided the copyright notice and this permission notice
43 are preserved on all copies.
46 Permission is granted to process this file through TeX and print the
47 results, provided the printed document carries copying permission
48 notice identical to this one except for the removal of this paragraph
49 (this paragraph not being relevant to the printed manual).
52 Permission is granted to copy and distribute modified versions of this
53 manual under the conditions for verbatim copying, provided also that the
54 section entitled ``GNU General Public License'' is included exactly as
55 in the original, and provided that the entire resulting derived work is
56 distributed under the terms of a permission notice identical to this
59 Permission is granted to copy and distribute translations of this manual
60 into another language, under the above conditions for modified versions,
61 except that the section entitled ``GNU General Public License'' may be
62 included in a translation approved by the Free Software Foundation
63 instead of in the original English.
66 @setchapternewpage odd
68 @settitle Using _GDBN__ (<v>_GDB_VN__)
71 @settitle Using _GDBN__ <v>_GDB_VN__ (_HOST__)
78 @subtitle{A Guide to the GNU Source-Level Debugger}
80 @subtitle{On _HOST__ Systems}
83 @c Maybe crank this up to "Fourth Edition" when released at FSF
84 @c @subtitle Third Edition---_GDBN__ version _GDB_VN__
85 @subtitle _GDBN__ version _GDB_VN__
87 @author{Richard M. Stallman@qquad @hfill Free Software Foundation}
88 @author{Roland H. Pesch@qquad @hfill Cygnus Support}
92 \hfill rms\@ai.mit.edu, pesch\@cygnus.com\par
93 \hfill {\it Using _GDBN__}, \manvers\par
94 \hfill \TeX{}info \texinfoversion\par
98 @vskip 0pt plus 1filll
99 Copyright @copyright{} 1988, 1989, 1990, 1991 Free Software Foundation, Inc.
101 Permission is granted to make and distribute verbatim copies of
102 this manual provided the copyright notice and this permission notice
103 are preserved on all copies.
105 Permission is granted to copy and distribute modified versions of this
106 manual under the conditions for verbatim copying, provided also that the
107 section entitled ``GNU General Public License'' is included exactly as
108 in the original, and provided that the entire resulting derived work is
109 distributed under the terms of a permission notice identical to this
112 Permission is granted to copy and distribute translations of this manual
113 into another language, under the above conditions for modified versions,
114 except that the section entitled ``GNU General Public License'' may be
115 included in a translation approved by the Free Software Foundation
116 instead of in the original English.
120 @node Top, Summary, (dir), (dir)
122 This file describes version _GDB_VN__ of GDB, the GNU symbolic debugger.
126 * Summary:: Summary of _GDBN__
127 * New Features:: New Features in _GDBN__ version _GDB_VN__
128 * Sample Session:: A Sample _GDBN__ Session
129 * Invocation:: Getting In and Out of _GDBN__
130 * Commands:: _GDBN__ Commands
131 * Running:: Running Programs Under _GDBN__
132 * Stopping:: Stopping and Continuing
133 * Stack:: Examining the Stack
134 * Source:: Examining Source Files
135 * Data:: Examining Data
136 * Languages:: Using _GDBN__ with Different Languages
137 * Symbols:: Examining the Symbol Table
138 * Altering:: Altering Execution
139 * _GDBN__ Files:: _GDBN__'s Files
140 * Targets:: Specifying a Debugging Target
141 * Controlling _GDBN__:: Controlling _GDBN__
142 * Sequences:: Canned Sequences of Commands
143 * Emacs:: Using _GDBN__ under GNU Emacs
144 * _GDBN__ Bugs:: Reporting Bugs in _GDBN__
146 * Installing _GDBN__:: Installing _GDBN__
147 * Copying:: GNU GENERAL PUBLIC LICENSE
150 --- The Detailed Node Listing ---
154 * Free Software:: Free Software
155 * Contributors:: Contributors to _GDBN__
157 Getting In and Out of _GDBN__
159 * Starting _GDBN__:: Starting _GDBN__
160 * Leaving _GDBN__:: Leaving _GDBN__
161 * Shell Commands:: Shell Commands
165 * File Options:: Choosing Files
166 * Mode Options:: Choosing Modes
170 * Command Syntax:: Command Syntax
171 * Help:: Getting Help
173 Running Programs Under _GDBN__
175 * Compilation:: Compiling for Debugging
176 * Starting:: Starting your Program
177 * Arguments:: Your Program's Arguments
178 * Environment:: Your Program's Environment
179 * Working Directory:: Your Program's Working Directory
180 * Input/Output:: Your Program's Input and Output
181 * Attach:: Debugging an Already-Running Process
182 * Kill Process:: Killing the Child Process
184 Stopping and Continuing
186 * Breakpoints:: Breakpoints, Watchpoints, and Exceptions
187 * Continuing and Stepping:: Resuming Execution
190 Breakpoints, Watchpoints, and Exceptions
192 * Set Breaks:: Setting Breakpoints
193 * Set Watchpoints:: Setting Watchpoints
194 * Exception Handling:: Breakpoints and Exceptions
195 * Delete Breaks:: Deleting Breakpoints
196 * Disabling:: Disabling Breakpoints
197 * Conditions:: Break Conditions
198 * Break Commands:: Breakpoint Command Lists
199 * Breakpoint Menus:: Breakpoint Menus
200 * Error in Breakpoints:: ``Cannot insert breakpoints''
204 * Frames:: Stack Frames
205 * Backtrace:: Backtraces
206 * Selection:: Selecting a Frame
207 * Frame Info:: Information on a Frame
209 Examining Source Files
211 * List:: Printing Source Lines
212 * Search:: Searching Source Files
213 * Source Path:: Specifying Source Directories
214 * Machine Code:: Source and Machine Code
218 * Expressions:: Expressions
219 * Variables:: Program Variables
220 * Arrays:: Artificial Arrays
221 * Output formats:: Output formats
222 * Memory:: Examining Memory
223 * Auto Display:: Automatic Display
224 * Print Settings:: Print Settings
225 * Value History:: Value History
226 * Convenience Vars:: Convenience Variables
227 * Registers:: Registers
228 * Floating Point Hardware:: Floating Point Hardware
230 Using GDB with Different Languages
232 * Setting:: Switching between source languages
233 * Show:: Displaying the language
234 * Checks:: Type and Range checks
235 * Support:: Supported languages
237 Switching between source languages
239 * Manually:: Setting the working language manually
240 * Automatically:: Having GDB infer the source language
242 Type and range Checking
244 * Type Checking:: An overview of type checking
245 * Range Checking:: An overview of range checking
250 * Modula-2:: Modula-2
254 * C Operators:: C and C++ Operators
255 * C Constants:: C and C++ Constants
256 * Cplusplus expressions:: C++ Expressions
257 * C Defaults:: Default settings for C and C++
258 * C Checks:: C and C++ Type and Range Checks
259 * Debugging C:: _GDBN__ and C
260 * Debugging C plus plus:: Special features for C++
264 * M2 Operators:: Built-in operators
265 * Builtin Func/Proc:: Built-in Functions and Procedures
266 * M2 Constants:: Modula-2 Constants
267 * M2 Defaults:: Default settings for Modula-2
268 * Deviations:: Deviations from standard Modula-2
269 * M2 Checks:: Modula-2 Type and Range Checks
270 * M2 Scope:: The scope operators @code{::} and @code{.}
271 * GDB/M2:: GDB and Modula-2
275 * Assignment:: Assignment to Variables
276 * Jumping:: Continuing at a Different Address
277 * Signaling:: Giving the Program a Signal
278 * Returning:: Returning from a Function
279 * Calling:: Calling your Program's Functions
280 * Patching:: Patching your Program
284 * Files:: Commands to Specify Files
285 * Symbol Errors:: Errors Reading Symbol Files
287 Specifying a Debugging Target
289 * Active Targets:: Active Targets
290 * Target Commands:: Commands for Managing Targets
291 * Remote:: Remote Debugging
295 * i960-Nindy Remote:: _GDBN__ with a Remote i960 (Nindy)
296 * EB29K Remote:: _GDBN__ with a Remote EB29K
297 * VxWorks Remote:: _GDBN__ and VxWorks
299 _GDBN__ with a Remote i960 (Nindy)
301 * Nindy Startup:: Startup with Nindy
302 * Nindy Options:: Options for Nindy
303 * Nindy reset:: Nindy Reset Command
305 _GDBN__ with a Remote EB29K
307 * Comms (EB29K):: Communications Setup
308 * gdb-EB29K:: EB29K cross-debugging
309 * Remote Log:: Remote Log
313 * VxWorks connection:: Connecting to VxWorks
314 * VxWorks download:: VxWorks Download
315 * VxWorks attach:: Running Tasks
320 * Editing:: Command Editing
321 * History:: Command History
322 * Screen Size:: Screen Size
324 * Messages/Warnings:: Optional Warnings and Messages
326 Canned Sequences of Commands
328 * Define:: User-Defined Commands
329 * Command Files:: Command Files
330 * Output:: Commands for Controlled Output
332 Reporting Bugs in _GDBN__
334 * Bug Criteria:: Have You Found a Bug?
335 * Bug Reporting:: How to Report Bugs
339 * Subdirectories:: Configuration subdirectories
340 * Config Names:: Specifying names for hosts and targets
341 * configure Options:: Summary of options for configure
342 * Formatting Documentation:: How to format and print GDB documentation
345 @node Summary, New Features, Top, Top
346 @unnumbered Summary of _GDBN__
348 The purpose of a debugger such as _GDBN__ is to allow you to see what is
349 going on ``inside'' another program while it executes---or what another
350 program was doing at the moment it crashed.
352 _GDBN__ can do four main kinds of things (plus other things in support of
353 these) to help you catch bugs in the act:
357 Start your program, specifying anything that might affect its behavior.
360 Make your program stop on specified conditions.
363 Examine what has happened, when your program has stopped.
366 Change things in your program, so you can experiment with correcting the
367 effects of one bug and go on to learn about another.
370 You can use _GDBN__ to debug programs written in C, C++, and Modula-2.
371 Fortran support will be added when a GNU Fortran compiler is ready.
374 * Free Software:: Free Software
375 * Contributors:: Contributors to GDB
378 @node Free Software, Contributors, Summary, Summary
379 @unnumberedsec Free Software
380 _GDBN__ is @dfn{free software}, protected by the GNU General Public License (GPL).
381 The GPL gives you the freedom to copy or adapt a licensed
382 program---but every person getting a copy also gets with it the
383 freedom to modify that copy (which means that they must get access to
384 the source code), and the freedom to distribute further copies.
385 Typical software companies use copyrights to limit your freedoms; the
386 Free Software Foundation uses the GPL to preserve these freedoms.
388 Fundamentally, the General Public License is a license which says that
389 you have these freedoms and that you can't take these freedoms away
392 @c FIXME: (passim) go through all xrefs, expanding to use text headings
393 For full details, @pxref{Copying}.
394 @node Contributors, , Free Software, Summary
395 @unnumberedsec Contributors to GDB
397 Richard Stallman was the original author of GDB, and of many other GNU
398 programs. Many others have contributed to its development. This
399 section attempts to credit major contributors. One of the virtues of
400 free software is that everyone is free to contribute to it; with
401 regret, we cannot actually acknowledge everyone here. The file
402 @file{ChangeLog} in the GDB distribution approximates a blow-by-blow
405 Changes much prior to version 2.0 are lost in the mists of time.
408 @emph{Plea:} Additions to this section are particularly welcome. If you
409 or your friends (or enemies; let's be evenhanded) have been unfairly
410 omitted from this list, we would like to add your names!
413 So that they may not regard their long labor as thankless, we
414 particularly thank those who shepherded GDB through major releases: John
415 Gilmore (releases _GDB_VN__, 4.0); Jim Kingdon (releases 3.9, 3.5, 3.4, 3.3);
416 and Randy Smith (releases 3.2, 3.1, 3.0). As major maintainer of GDB
417 for some period, each contributed significantly to the structure,
418 stability, and capabilities of the entire debugger.
420 Richard Stallman, assisted at various times by Pete TerMaat, Chris
421 Hanson, and Richard Mlynarik, handled releases through 2.8.
423 Michael Tiemann is the author of most of the GNU C++ support in GDB,
424 with significant additional contributions from Per Bothner. James
425 Clark wrote the GNU C++ demangler. Early work on C++ was by Peter
426 TerMaat (who also did much general update work leading to release 3.0).
428 GDB _GDB_VN__ uses the BFD subroutine library to examine multiple
429 object-file formats; BFD was a joint project of V. Gumby
430 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
432 David Johnson wrote the original COFF support; Pace Willison did
433 the original support for encapsulated COFF.
435 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
436 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
437 support. Jean-Daniel Fekete contributed Sun 386i support. Chris
438 Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki
439 Hasei contributed Sony/News OS 3 support. David Johnson contributed
440 Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support.
441 Keith Packard contributed NS32K support. Doug Rabson contributed
442 Acorn Risc Machine support. Chris Smith contributed Convex support
443 (and Fortran debugging). Jonathan Stone contributed Pyramid support.
444 Michael Tiemann contributed SPARC support. Tim Tucker contributed
445 support for the Gould NP1 and Gould Powernode. Pace Willison
446 contributed Intel 386 support. Jay Vosburgh contributed Symmetry
449 Rich Schaefer and Peter Schauer helped with support of SunOS shared
452 Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about
453 several machine instruction sets.
455 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped
456 develop remote debugging. Intel Corporation and Wind River Systems
457 contributed remote debugging modules for their products.
459 Brian Fox is the author of the readline libraries providing
460 command-line editing and command history.
462 Andrew Beers of SUNY Buffalo wrote the language-switching code and
463 the Modula-2 support, and contributed the Languages chapter of this
466 @node New Features, Sample Session, Summary, Top
467 @unnumbered New Features since _GDBN__ version 3.5
471 Using the new command @code{target}, you can select at runtime whether
472 you are debugging local files, local processes, standalone systems over
473 a serial port, realtime systems over a TCP/IP connection, etc. The
474 command @code{load} can download programs into a remote system. Serial
475 stubs are available for Motorola 680x0 and Intel 80386 remote systems;
476 _GDBN__ also supports debugging realtime processes running under
477 VxWorks, using SunRPC Remote Procedure Calls over TCP/IP to talk to a
478 debugger stub on the target system. Internally, _GDBN__ now uses a
479 function vector to mediate access to different targets; if you need to
480 add your own support for a remote protocol, this makes it much easier.
483 _GDBN__ now sports watchpoints as well as breakpoints. You can use a
484 watchpoint to stop execution whenever the value of an expression
485 changes, without having to predict a particular place in your program
486 where this may happen.
489 Commands that issue wide output now insert newlines at places designed
490 to make the output more readable.
492 @item Object Code Formats
493 _GDBN__ uses a new library called the Binary File Descriptor (BFD)
494 Library to permit it to switch dynamically, without reconfiguration or
495 recompilation, between different object-file formats. Formats currently
496 supported are COFF, a.out, and the Intel 960 b.out; files may be read as
497 .o's, archive libraries, or core dumps. BFD is available as a
498 subroutine library so that other programs may take advantage of it, and
499 the other GNU binary utilities are being converted to use it.
501 @item Configuration and Ports
502 Compile-time configuration (to select a particular architecture and
503 operating system) is much easier. The script @code{configure} now
504 allows you to configure _GDBN__ as either a native debugger or a
505 cross-debugger. @xref{Installing _GDBN__} for details on how to
506 configure and on what architectures are now available.
509 The user interface to _GDBN__'s control variables has been simplified
510 and consolidated in two commands, @code{set} and @code{show}. Output
511 lines are now broken at readable places, rather than overflowing onto
512 the next line. You can suppress output of machine-level addresses,
513 displaying only source language information.
517 _GDBN__ now supports C++ multiple inheritance (if used with a GCC
518 version 2 compiler), and also has limited support for C++ exception
519 handling, with the commands @code{catch} and @code{info catch}: _GDBN__
520 can break when an exception is raised, before the stack is peeled back
521 to the exception handler's context.
524 _GDBN__ now has preliminary support for the GNU Modula-2 compiler,
525 currently under development at the State University of New York at
526 Buffalo. Coordinated development of both _GDBN__ and the GNU Modula-2
527 compiler will continue through the fall of 1991 and into 1992. Other
528 Modula-2 compilers are currently not supported, and attempting to debug
529 programs compiled with them will likely result in an error as the symbol
530 table of the executable is read in.
532 @item Command Rationalization
533 Many _GDBN__ commands have been renamed to make them easier to remember
534 and use. In particular, the subcommands of @code{info} and
535 @code{show}/@code{set} are grouped to make the former refer to the state
536 of your program, and the latter refer to the state of _GDBN__ itself.
537 @xref{Renamed Commands}, for details on what commands were renamed.
539 @item Shared Libraries
540 _GDBN__ _GDB_VN__ can debug programs and core files that use SunOS shared
544 _GDBN__ _GDB_VN__ has a reference card; @xref{Formatting Documentation} for
545 instructions on printing it.
547 @item Work in Progress
548 Kernel debugging for BSD and Mach systems; Tahoe and HPPA architecture
553 @node Sample Session, Invocation, New Features, Top
554 @chapter A Sample _GDBN__ Session
556 You can use this manual at your leisure to read all about _GDBN__.
557 However, a handful of commands are enough to get started using the
558 debugger. This chapter illustrates these commands.
561 In this sample session, we emphasize user input like this: @i{input},
562 to make it easier to pick out from the surrounding output.
565 @c FIXME: this example may not be appropriate for some configs, where
566 @c FIXME...primary interest is in remote use.
568 One of the preliminary versions of GNU @code{m4} (a generic macro
569 processor) exhibits the following bug: sometimes, when we change its
570 quote strings from the default, the commands used to capture one macro's
571 definition in another stop working. In the following short @code{m4}
572 session, we define a macro @code{foo} which expands to @code{0000}; we
573 then use the @code{m4} builtin @code{defn} to define @code{bar} as the
574 same thing. However, when we change the open quote string to
575 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
576 procedure fails to define a new synonym @code{baz}:
585 @i{define(bar,defn(`foo'))}
589 @i{changequote(<QUOTE>,<UNQUOTE>)}
591 @i{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
594 m4: End of input: 0: fatal error: EOF in string
598 Let's use _GDBN__ to try to see what's going on.
602 GDB is free software and you are welcome to distribute copies of it
603 under certain conditions; type "info copying" to see the conditions.
604 There is absolutely no warranty for GDB; type "info warranty" for details.
605 GDB _GDB_VN__, Copyright 1991 Free Software Foundation, Inc...
610 _GDBN__ reads only enough symbol data to know where to find the rest
611 when needed; as a result, the first prompt comes up very quickly. We
612 then tell _GDBN__ to use a narrower display width than usual, so
613 that examples will fit in this manual.
616 (_GDBP__) @i{set width 70}
620 Let's see how the @code{m4} builtin @code{changequote} works.
621 Having looked at the source, we know the relevant subroutine is
622 @code{m4_changequote}, so we set a breakpoint there with _GDBN__'s
623 @code{break} command.
626 (_GDBP__) @i{break m4_changequote}
627 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
631 Using the @code{run} command, we start @code{m4} running under _GDBN__
632 control; as long as control does not reach the @code{m4_changequote}
633 subroutine, the program runs as usual:
637 Starting program: /work/Editorial/gdb/gnu/m4/m4
645 To trigger the breakpoint, we call @code{changequote}. _GDBN__
646 suspends execution of @code{m4}, displaying information about the
647 context where it stops.
650 @i{changequote(<QUOTE>,<UNQUOTE>)}
652 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70) at builtin.c:879
653 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]), argc, 1, 3))
657 Now we use the command @code{n} (@code{next}) to advance execution to
658 the next line of the current function.
662 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1]) : nil,
666 @code{set_quotes} looks like a promising subroutine. We can go into it
667 by using the command @code{s} (@code{step}) instead of @code{next}.
668 @code{step} goes to the next line to be executed in @emph{any}
669 subroutine, so it steps into @code{set_quotes}.
673 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
675 530 if (lquote != def_lquote)
679 The summary display showing the subroutine where @code{m4} is now
680 suspended (and its arguments) is called a stack frame display. We can
681 use the @code{backtrace} command (which can also be spelled @code{bt}),
682 to see where we are in the stack: it displays a stack frame for each
687 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
689 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70) at builtin.c:882
690 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
691 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
693 #4 0x79dc in expand_input () at macro.c:40
694 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
698 Let's step through a few more lines to see what happens. The first two
699 times, we can use @samp{s}; the next two times we use @code{n} to avoid
700 falling into the @code{xstrdup} subroutine.
703 0x3b5c 532 if (rquote != def_rquote)
705 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? def_lquote :\
708 536 rquote = (rq == nil || *rq == '\0') ? def_rquote : xstrdup\
711 538 len_lquote = strlen(rquote);
715 The last line displayed looks a little odd; let's examine the variables
716 @code{lquote} and @code{rquote} to see if they are in fact the new left
717 and right quotes we specified. We can use the command @code{p}
718 (@code{print}) to see their values.
721 (_GDBP__) @i{p lquote}
722 $1 = 0x35d40 "<QUOTE>"
723 (_GDBP__) @i{p rquote}
724 $2 = 0x35d50 "<UNQUOTE>"
728 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
729 Let's look at some context; we can display ten lines of source
730 surrounding the current line, with the @code{l} (@code{list}) command.
736 535 lquote = (lq == nil || *lq == '\0') ? def_lquote : xstrdup\
738 536 rquote = (rq == nil || *rq == '\0') ? def_rquote : xstrdup\
741 538 len_lquote = strlen(rquote);
742 539 len_rquote = strlen(lquote);
749 Let's step past the two lines that set @code{len_lquote} and
750 @code{len_rquote}, and then examine the values of those variables.
754 539 len_rquote = strlen(lquote);
757 (_GDBP__) @i{p len_lquote}
759 (_GDBP__) @i{p len_rquote}
764 That certainly looks wrong, assuming @code{len_lquote} and
765 @code{len_rquote} are meant to be the lengths of @code{lquote} and
766 @code{rquote} respectively. Let's try setting them to better values.
767 We can use the @code{p} command for this, since it'll print the value of
768 any expression---and that expression can include subroutine calls and
772 (_GDBP__) p len_lquote=strlen(lquote)
774 (_GDBP__) p len_rquote=strlen(rquote)
779 Let's see if that fixes the problem of using the new quotes with the
780 @code{m4} built-in @code{defn}. We can allow @code{m4} to continue
781 executing with the @code{c} (@code{continue}) command, and then try the
782 example that caused trouble initially:
788 @i{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
795 Success! The new quotes now work just as well as the default ones. The
796 problem seems to have been just the two typos defining the wrong
797 lengths. We'll let @code{m4} exit by giving it an EOF as input.
801 Program exited normally.
805 The message @samp{Program exited normally.} is from _GDBN__; it
806 indicates @code{m4} has finished executing. We can end our _GDBN__
807 session with the _GDBN__ @code{quit} command.
811 _1__@end smallexample
813 @node Invocation, Commands, Sample Session, Top
814 @chapter Getting In and Out of _GDBN__
817 * Starting _GDBN__:: Starting _GDBN__
818 * Leaving _GDBN__:: Leaving _GDBN__
819 * Shell Commands:: Shell Commands
822 @node Starting _GDBN__, Leaving _GDBN__, Invocation, Invocation
823 @section Starting _GDBN__
825 _GDBN__ is invoked with the shell command @code{_GDBP__}. Once started,
826 it reads commands from the terminal until you tell it to exit.
828 You can run @code{_GDBP__} with no arguments or options; but the most
829 usual way to start _GDBN__ is with one argument or two, specifying an
830 executable program as the argument:
835 You can also start with both an executable program and a core file specified:
840 You can, instead, specify a process ID as a second argument, if you want
841 to debug a running process:
846 would attach _GDBN__ to process @code{1234} (unless you also have a file
847 named @file{1234}; _GDBN__ does check for a core file first).
850 You can further control how _GDBN__ starts up by using command-line
851 options. _GDBN__ itself can remind you of the options available:
856 will display all available options and briefly describe their use
857 (@samp{_GDBP__ -h} is a shorter equivalent).
859 All options and command line arguments you give are processed
860 in sequential order. The order makes a difference when the
861 @samp{-x} option is used.
864 * File Options:: Choosing Files
865 * Mode Options:: Choosing Modes
867 _include__(gdbinv-m.m4)_dnl__
871 @node File Options, Mode Options, Starting _GDBN__, Starting _GDBN__
872 @subsection Choosing Files
874 As shown above, any arguments other than options specify an executable
875 file and core file; that is, the first argument encountered with no
876 associated option flag is equivalent to a @samp{-se} option, and the
877 second, if any, is equivalent to a @samp{-c} option. Many options have
878 both long and short forms; both are shown here. The long forms are also
879 recognized if you truncate them, so long as enough of the option is
880 present to be unambiguous. (If you prefer, you can flag option
881 arguments with @samp{+} rather than @samp{-}, though we illustrate the
882 more usual convention.)
885 @item -symbols=@var{file}
887 Read symbol table from file @var{file}.
889 @item -exec=@var{file}
891 Use file @var{file} as the executable file to execute when
892 appropriate, and for examining pure data in conjunction with a core
896 Read symbol table from file @var{file} and use it as the executable
899 @item -core=@var{file}
901 Use file @var{file} as a core dump to examine.
903 @item -command=@var{file}
905 Execute _GDBN__ commands from file @var{file}. @xref{Command Files}.
907 @item -directory=@var{directory}
908 @itemx -d @var{directory}
909 Add @var{directory} to the path to search for source files.
913 @node Mode Options, Mode Options, File Options, Starting _GDBN__
916 @node Mode Options, , File Options, Starting _GDBN__
918 @subsection Choosing Modes
923 Do not execute commands from any @file{_GDBINIT__} initialization files.
924 Normally, the commands in these files are executed after all the
925 command options and arguments have been processed.
926 @xref{Command Files}.
930 ``Quiet''. Do not print the introductory and copyright messages. These
931 messages are also suppressed in batch mode.
934 Run in batch mode. Exit with status @code{0} after processing all the command
935 files specified with @samp{-x} (and @file{_GDBINIT__}, if not inhibited).
936 Exit with nonzero status if an error occurs in executing the _GDBN__
937 commands in the command files.
939 Batch mode may be useful for running _GDBN__ as a filter, for example to
940 download and run a program on another computer; in order to make this
941 more useful, the message
943 Program exited normally.
946 (which is ordinarily issued whenever a program running under _GDBN__ control
947 terminates) is not issued when running in batch mode.
949 @item -cd=@var{directory}
950 Run _GDBN__ using @var{directory} as its working directory,
951 instead of the current directory.
955 Emacs sets this option when it runs _GDBN__ as a subprocess. It tells _GDBN__
956 to output the full file name and line number in a standard,
957 recognizable fashion each time a stack frame is displayed (which
958 includes each time the program stops). This recognizable format looks
959 like two @samp{\032} characters, followed by the file name, line number
960 and character position separated by colons, and a newline. The
961 Emacs-to-_GDBN__ interface program uses the two @samp{\032} characters as
962 a signal to display the source code for the frame.
965 Set the line speed (baud rate or bits per second) of any serial
966 interface used by _GDBN__ for remote debugging.
968 @item -tty=@var{device}
969 Run using @var{device} for your program's standard input and output.
970 @c FIXME: kingdon thinks there's more to -tty. Investigate.
974 _include__(gdbinv-s.m4)
977 @node Leaving _GDBN__, Shell Commands, Starting _GDBN__, Invocation
978 @section Leaving _GDBN__
979 @cindex exiting _GDBN__
984 To exit _GDBN__, use the @code{quit} command (abbreviated @code{q}), or type
985 an end-of-file character (usually @kbd{C-d}).
989 An interrupt (often @kbd{C-c}) will not exit from _GDBN__, but rather
990 will terminate the action of any _GDBN__ command that is in progress and
991 return to _GDBN__ command level. It is safe to type the interrupt
992 character at any time because _GDBN__ does not allow it to take effect
993 until a time when it is safe.
995 If you've been using _GDBN__ to control an attached process or device,
996 you can release it with the @code{detach} command; @pxref{Attach}.
998 @node Shell Commands, , Leaving _GDBN__, Invocation
999 @section Shell Commands
1000 If you need to execute occasional shell commands during your
1001 debugging session, there's no need to leave or suspend _GDBN__; you can
1002 just use the @code{shell} command.
1005 @item shell @var{command string}
1007 @cindex shell escape
1008 Directs _GDBN__ to invoke an inferior shell to execute @var{command
1009 string}. If it exists, the environment variable @code{SHELL} is used
1010 for the name of the shell to run. Otherwise _GDBN__ uses
1014 The utility @code{make} is often needed in development environments.
1015 You don't have to use the @code{shell} command for this purpose in _GDBN__:
1018 @item make @var{make-args}
1020 @cindex calling make
1021 Causes _GDBN__ to execute an inferior @code{make} program with the specified
1022 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1025 @node Commands, Running, Invocation, Top
1026 @chapter _GDBN__ Commands
1029 * Command Syntax:: Command Syntax
1030 * Help:: Getting Help
1033 @node Command Syntax, Help, Commands, Commands
1034 @section Command Syntax
1035 A _GDBN__ command is a single line of input. There is no limit on how long
1036 it can be. It starts with a command name, which is followed by arguments
1037 whose meaning depends on the command name. For example, the command
1038 @code{step} accepts an argument which is the number of times to step,
1039 as in @samp{step 5}. You can also use the @code{step} command with
1040 no arguments. Some command names do not allow any arguments.
1042 @cindex abbreviation
1043 _GDBN__ command names may always be truncated if that abbreviation is
1044 unambiguous. Other possible command abbreviations are listed in the
1045 documentation for individual commands. In some cases, even ambiguous
1046 abbreviations are allowed; for example, @code{s} is specially defined as
1047 equivalent to @code{step} even though there are other commands whose
1048 names start with @code{s}. You can test abbreviations by using them as
1049 arguments to the @code{help} command.
1051 @cindex repeating commands
1053 A blank line as input to _GDBN__ (typing just @key{RET}) means to
1054 repeat the previous command. Certain commands (for example, @code{run})
1055 will not repeat this way; these are commands for which unintentional
1056 repetition might cause trouble and which you are unlikely to want to
1059 The @code{list} and @code{x} commands, when you repeat them with
1060 @key{RET}, construct new arguments rather than repeating
1061 exactly as typed. This permits easy scanning of source or memory.
1063 _GDBN__ can also use @key{RET} in another way: to partition lengthy
1064 output, in a way similar to the common utility @code{more}
1065 (@pxref{Screen Size}). Since it's easy to press one @key{RET} too many
1066 in this situation, _GDBN__ disables command repetition after any command
1067 that generates this sort of display.
1071 A line of input starting with @kbd{#} is a comment; it does nothing.
1072 This is useful mainly in command files (@xref{Command Files}).
1074 @node Help, , Command Syntax, Commands
1075 @section Getting Help
1076 @cindex online documentation
1078 You can always ask _GDBN__ itself for information on its commands, using the
1079 command @code{help}.
1085 You can use @code{help} (abbreviated @code{h}) with no arguments to
1086 display a short list of named classes of commands:
1089 List of classes of commands:
1091 running -- Running the program
1092 stack -- Examining the stack
1093 data -- Examining data
1094 breakpoints -- Making program stop at certain points
1095 files -- Specifying and examining files
1096 status -- Status inquiries
1097 support -- Support facilities
1098 user-defined -- User-defined commands
1099 aliases -- Aliases of other commands
1100 obscure -- Obscure features
1102 Type "help" followed by a class name for a list of commands in that class.
1103 Type "help" followed by command name for full documentation.
1104 Command name abbreviations are allowed if unambiguous.
1108 @item help @var{class}
1109 Using one of the general help classes as an argument, you can get a
1110 list of the individual commands in that class. For example, here is the
1111 help display for the class @code{status}:
1113 (_GDBP__) help status
1118 show -- Generic command for showing things set with "set"
1119 info -- Generic command for printing status
1121 Type "help" followed by command name for full documentation.
1122 Command name abbreviations are allowed if unambiguous.
1126 @item help @var{command}
1127 With a command name as @code{help} argument, _GDBN__ will display a
1128 short paragraph on how to use that command.
1131 In addition to @code{help}, you can use the _GDBN__ commands @code{info}
1132 and @code{show} to inquire about the state of your program, or the state
1133 of _GDBN__ itself. Each command supports many topics of inquiry; this
1134 manual introduces each of them in the appropriate context. The listings
1135 under @code{info} and under @code{show} in the Index point to
1136 all the sub-commands.
1137 @c FIXME: @pxref{Index} used to be here, but even though it shows up in
1138 @c FIXME...the 'aux' file with a pageno the xref can't find it.
1145 This command (abbreviated @code{i}) is for describing the state of your
1146 program; for example, it can list the arguments given to your program
1147 (@code{info args}), the registers currently in use (@code{info
1148 registers}), or the breakpoints you've set (@code{info breakpoints}).
1149 You can get a complete list of the @code{info} sub-commands with
1150 @w{@code{help info}}.
1154 In contrast, @code{show} is for describing the state of _GDBN__ itself.
1155 You can change most of the things you can @code{show}, by using the
1156 related command @code{set}; for example, you can control what number
1157 system is used for displays with @code{set radix}, or simply inquire
1158 which is currently in use with @code{show radix}.
1161 To display all the settable parameters and their current
1162 values, you can use @code{show} with no arguments; you may also use
1163 @code{info set}. Both commands produce the same display.
1164 @c FIXME: "info set" violates the rule that "info" is for state of
1165 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1166 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1170 Here are three miscellaneous @code{show} subcommands, all of which are
1171 exceptional in lacking corresponding @code{set} commands:
1174 @kindex show version
1175 @cindex version number
1177 Show what version of _GDBN__ is running. You should include this
1178 information in _GDBN__ bug-reports. If multiple versions of _GDBN__ are
1179 in use at your site, you may occasionally want to make sure what version
1180 of _GDBN__ you're running; as _GDBN__ evolves, new commands are
1181 introduced, and old ones may wither away. The version number is also
1182 announced when you start _GDBN__ with no arguments.
1184 @kindex show copying
1186 Display information about permission for copying _GDBN__.
1188 @kindex show warranty
1190 Display the GNU ``NO WARRANTY'' statement.
1193 @node Running, Stopping, Commands, Top
1194 @chapter Running Programs Under _GDBN__
1197 * Compilation:: Compiling for Debugging
1198 * Starting:: Starting your Program
1199 * Arguments:: Your Program's Arguments
1200 * Environment:: Your Program's Environment
1201 * Working Directory:: Your Program's Working Directory
1202 * Input/Output:: Your Program's Input and Output
1203 * Attach:: Debugging an Already-Running Process
1204 * Kill Process:: Killing the Child Process
1207 @node Compilation, Starting, Running, Running
1208 @section Compiling for Debugging
1210 In order to debug a program effectively, you need to generate
1211 debugging information when you compile it. This debugging information
1212 is stored in the object file; it describes the data type of each
1213 variable or function and the correspondence between source line numbers
1214 and addresses in the executable code.
1216 To request debugging information, specify the @samp{-g} option when you run
1219 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1220 options together. Using those compilers, you cannot generate optimized
1221 executables containing debugging information.
1223 The GNU C compiler supports @samp{-g} with or without @samp{-O}, making it
1224 possible to debug optimized code. We recommend that you @emph{always} use
1225 @samp{-g} whenever you compile a program. You may think the program is
1226 correct, but there's no sense in pushing your luck.
1228 Some things do not work as well with @samp{-g -O} as with just
1229 @samp{-g}, particularly on machines with instruction scheduling. If in
1230 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1231 please report it as a bug (including a test case!).
1233 Older versions of the GNU C compiler permitted a variant option
1234 @samp{-gg} for debugging information. _GDBN__ no longer supports this
1235 format; if your GNU C compiler has this option, do not use it.
1238 @comment As far as I know, there are no cases in which _GDBN__ will
1239 @comment produce strange output in this case. (but no promises).
1240 If your program includes archives made with the @code{ar} program, and
1241 if the object files used as input to @code{ar} were compiled without the
1242 @samp{-g} option and have names longer than 15 characters, _GDBN__ will get
1243 confused reading the program's symbol table. No error message will be
1244 given, but _GDBN__ may behave strangely. The reason for this problem is a
1245 deficiency in the Unix archive file format, which cannot represent file
1246 names longer than 15 characters.
1248 To avoid this problem, compile the archive members with the @samp{-g}
1249 option or use shorter file names. Alternatively, use a version of GNU
1250 @code{ar} dated more recently than August 1989.
1254 @node Starting, Arguments, Compilation, Running
1255 @section Starting your Program
1262 Use the @code{run} command to start your program under _GDBN__. You
1263 must first specify the program name
1267 with an argument to _GDBN__
1268 (@pxref{Invocation}), or using the @code{file} or @code{exec-file}
1269 command (@pxref{Files}).
1273 On targets that support processes, @code{run} creates an inferior
1274 process and makes that process run your program. On other targets,
1275 @code{run} jumps to the start of the program.
1277 The execution of a program is affected by certain information it
1278 receives from its superior. _GDBN__ provides ways to specify this
1279 information, which you must do @i{before} starting the program. (You
1280 can change it after starting the program, but such changes will only affect
1281 the program the next time you start it.) This information may be
1282 divided into four categories:
1285 @item The @i{arguments.}
1286 You specify the arguments to give your program as the arguments of the
1287 @code{run} command. If a shell is available on your target, the shell
1288 is used to pass the arguments, so that you may use normal conventions
1289 (such as wildcard expansion or variable substitution) in
1290 describing the arguments. In Unix systems, you can control which shell
1291 is used with the @code{SHELL} environment variable. @xref{Arguments}.@refill
1293 @item The @i{environment.}
1294 Your program normally inherits its environment from _GDBN__, but you can
1295 use the _GDBN__ commands @code{set environment} and @code{unset
1296 environment} to change parts of the environment that will be given to
1297 the program. @xref{Environment}.@refill
1299 @item The @i{working directory.}
1300 Your program inherits its working directory from _GDBN__. You can set
1301 _GDBN__'s working directory with the @code{cd} command in _GDBN__.
1302 @xref{Working Directory}.
1304 @item The @i{standard input and output.}
1305 Your program normally uses the same device for standard input and
1306 standard output as _GDBN__ is using. You can redirect input and output
1307 in the @code{run} command line, or you can use the @code{tty} command to
1308 set a different device for your program.
1309 @xref{Input/Output}.
1312 @emph{Warning:} While input and output redirection work, you can't use
1313 pipes to pass the output of the program you're debugging to another
1314 program; if you attempt this, _GDBN__ is likely to wind up debugging the
1318 When you issue the @code{run} command, your program begins to execute
1319 immediately. @xref{Stopping}, for discussion of how to arrange for your
1320 program to stop. Once your program has been started by the @code{run}
1321 command (and then stopped), you may evaluate expressions that involve
1322 calls to functions in the inferior, using the @code{print} or
1323 @code{call} commands. @xref{Data}.
1325 If the modification time of your symbol file has changed since the last
1326 time _GDBN__ read its symbols, _GDBN__ will discard its symbol table and re-read
1327 it. In this process, it tries to retain your current breakpoints.
1329 @node Arguments, Environment, Starting, Running
1330 @section Your Program's Arguments
1332 @cindex arguments (to your program)
1333 The arguments to your program can be specified by the arguments of the
1334 @code{run} command. They are passed to a shell, which expands wildcard
1335 characters and performs redirection of I/O, and thence to the program.
1336 _GDBN__ uses the shell indicated by your environment variable
1337 @code{SHELL} if it exists; otherwise, _GDBN__ uses @code{/bin/sh}.
1339 @code{run} with no arguments uses the same arguments used by the previous
1340 @code{run}, or those set by the @code{set args} command.
1345 Specify the arguments to be used the next time your program is run. If
1346 @code{set args} has no arguments, @code{run} will execute your program
1347 with no arguments. Once you have run your program with arguments,
1348 using @code{set args} before the next @code{run} is the only way to run
1349 it again without arguments.
1353 Show the arguments to give your program when it is started.
1356 @node Environment, Working Directory, Arguments, Running
1357 @section Your Program's Environment
1359 @cindex environment (of your program)
1360 The @dfn{environment} consists of a set of environment variables and
1361 their values. Environment variables conventionally record such things as
1362 your user name, your home directory, your terminal type, and your search
1363 path for programs to run. Usually you set up environment variables with
1364 the shell and they are inherited by all the other programs you run. When
1365 debugging, it can be useful to try running the program with a modified
1366 environment without having to start _GDBN__ over again.
1369 @item path @var{directory}
1371 Add @var{directory} to the front of the @code{PATH} environment variable
1372 (the search path for executables), for both _GDBN__ and your program.
1373 You may specify several directory names, separated by @samp{:} or
1374 whitespace. If @var{directory} is already in the path, it is moved to
1375 the front, so it will be searched sooner.
1377 You can use the string @samp{$cwd} to refer to whatever is the current
1378 working directory at the time _GDBN__ searches the path. If you use
1379 @samp{.} instead, it refers to the directory where you executed the
1380 @code{path} command. _GDBN__ fills in the current path where needed in
1381 the @var{directory} argument, before adding it to the search path.
1382 @c 'path' is explicitly nonrepeatable, but RMS points out it's silly to
1383 @c document that, since repeating it would be a no-op.
1387 Display the list of search paths for executables (the @code{PATH}
1388 environment variable).
1390 @item show environment @r{[}@var{varname}@r{]}
1391 @kindex show environment
1392 Print the value of environment variable @var{varname} to be given to
1393 your program when it starts. If you don't supply @var{varname},
1394 print the names and values of all environment variables to be given to
1395 your program. You can abbreviate @code{environment} as @code{env}.
1397 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1398 @kindex set environment
1399 Sets environment variable @var{varname} to @var{value}. The value
1400 changes for your program only, not for _GDBN__ itself. @var{value} may
1401 be any string; the values of environment variables are just strings, and
1402 any interpretation is supplied by your program itself. The @var{value}
1403 parameter is optional; if it is eliminated, the variable is set to a
1405 @c "any string" here doesn't include leading, trailing
1406 @c blanks. Gnu asks: does anyone care?
1408 For example, this command:
1415 tells a Unix program, when subsequently run, that its user is named
1416 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1417 are not actually required.)
1419 @item unset environment @var{varname}
1420 @kindex unset environment
1421 Remove variable @var{varname} from the environment to be passed to your
1422 program. This is different from @samp{set env @var{varname} =};
1423 @code{unset environment} removes the variable from the environment,
1424 rather than assigning it an empty value.
1427 @node Working Directory, Input/Output, Environment, Running
1428 @section Your Program's Working Directory
1430 @cindex working directory (of your program)
1431 Each time you start your program with @code{run}, it inherits its
1432 working directory from the current working directory of _GDBN__. _GDBN__'s
1433 working directory is initially whatever it inherited from its parent
1434 process (typically the shell), but you can specify a new working
1435 directory in _GDBN__ with the @code{cd} command.
1437 The _GDBN__ working directory also serves as a default for the commands
1438 that specify files for _GDBN__ to operate on. @xref{Files}.
1441 @item cd @var{directory}
1443 Set _GDBN__'s working directory to @var{directory}.
1447 Print _GDBN__'s working directory.
1450 @node Input/Output, Attach, Working Directory, Running
1451 @section Your Program's Input and Output
1456 By default, the program you run under _GDBN__ does input and output to
1457 the same terminal that _GDBN__ uses. _GDBN__ switches the terminal to
1458 its own terminal modes to interact with you, but it records the terminal
1459 modes your program was using and switches back to them when you continue
1460 running your program.
1464 @kindex info terminal
1465 Displays _GDBN__'s recorded information about the terminal modes your
1469 You can redirect the program's input and/or output using shell
1470 redirection with the @code{run} command. For example,
1477 starts the program, diverting its output to the file @file{outfile}.
1480 @cindex controlling terminal
1481 Another way to specify where the program should do input and output is
1482 with the @code{tty} command. This command accepts a file name as
1483 argument, and causes this file to be the default for future @code{run}
1484 commands. It also resets the controlling terminal for the child
1485 process, for future @code{run} commands. For example,
1492 directs that processes started with subsequent @code{run} commands
1493 default to do input and output on the terminal @file{/dev/ttyb} and have
1494 that as their controlling terminal.
1496 An explicit redirection in @code{run} overrides the @code{tty} command's
1497 effect on the input/output device, but not its effect on the controlling
1500 When you use the @code{tty} command or redirect input in the @code{run}
1501 command, only the input @emph{for your program} is affected. The input
1502 for _GDBN__ still comes from your terminal.
1504 @node Attach, Kill Process, Input/Output, Running
1505 @section Debugging an Already-Running Process
1510 @item attach @var{process-id}
1512 attaches to a running process---one that was started outside _GDBN__.
1513 (@code{info files} will show your active targets.) The command takes as
1514 argument a process ID. The usual way to find out the process-id of
1515 a Unix process is with the @code{ps} utility, or with the @samp{jobs -l}
1518 @code{attach} will not repeat if you press @key{RET} a second time after
1519 executing the command.
1522 To use @code{attach}, you must be debugging in an environment which
1523 supports processes. You must also have permission to send the process a
1524 signal, and it must have the same effective user ID as the _GDBN__
1527 When using @code{attach}, you should first use the @code{file} command
1528 to specify the program running in the process and load its symbol table.
1531 The first thing _GDBN__ does after arranging to debug the specified
1532 process is to stop it. You can examine and modify an attached process
1533 with all the _GDBN__ commands that are ordinarily available when you start
1534 processes with @code{run}. You can insert breakpoints; you can step and
1535 continue; you can modify storage. If you would rather the process
1536 continue running, you may use the @code{continue} command after
1537 attaching _GDBN__ to the process.
1542 When you have finished debugging the attached process, you can use the
1543 @code{detach} command to release it from _GDBN__'s control. Detaching
1544 the process continues its execution. After the @code{detach} command,
1545 that process and _GDBN__ become completely independent once more, and you
1546 are ready to @code{attach} another process or start one with @code{run}.
1547 @code{detach} will not repeat if you press @key{RET} again after
1548 executing the command.
1551 If you exit _GDBN__ or use the @code{run} command while you have an attached
1552 process, you kill that process. By default, you will be asked for
1553 confirmation if you try to do either of these things; you can control
1554 whether or not you need to confirm by using the @code{set confirm} command
1555 (@pxref{Messages/Warnings}).
1557 @node Kill Process, , Attach, Running
1559 @section Killing the Child Process
1564 Kill the child process in which your program is running under _GDBN__.
1567 This command is useful if you wish to debug a core dump instead of a
1568 running process. _GDBN__ ignores any core dump file while your program
1572 On some operating systems, a program can't be executed outside _GDBN__
1573 while you have breakpoints set on it inside _GDBN__. You can use the
1574 @code{kill} command in this situation to permit running the program
1575 outside the debugger.
1577 The @code{kill} command is also useful if you wish to recompile and
1578 relink the program, since on many systems it is impossible to modify an
1579 executable file while it is running in a process. In this case, when you
1580 next type @code{run}, _GDBN__ will notice that the file has changed, and
1581 will re-read the symbol table (while trying to preserve your current
1582 breakpoint settings).
1584 @node Stopping, Stack, Running, Top
1585 @chapter Stopping and Continuing
1587 The principal purpose of using a debugger is so that you can stop your
1588 program before it terminates; or so that, if the program runs into
1589 trouble, you can investigate and find out why.
1591 Inside _GDBN__, your program may stop for any of several reasons, such
1592 as a signal, a breakpoint, or reaching a new line after a _GDBN__
1593 command such as @code{step}. You may then examine and change
1594 variables, set new breakpoints or remove old ones, and then continue
1595 execution. Usually, the messages shown by _GDBN__ provide ample
1596 explanation of the status of your program---but you can also explicitly
1597 request this information at any time.
1601 @kindex info program
1602 Display information about the status of your program: whether it is
1603 running or not, what process it is, and why it stopped.
1607 * Breakpoints:: Breakpoints, Watchpoints, and Exceptions
1608 * Continuing and Stepping:: Resuming Execution
1612 @node Breakpoints, Continuing and Stepping, Stopping, Stopping
1613 @section Breakpoints, Watchpoints, and Exceptions
1616 A @dfn{breakpoint} makes your program stop whenever a certain point in
1617 the program is reached. For each breakpoint, you can add various
1618 conditions to control in finer detail whether the program will stop.
1619 You can set breakpoints with the @code{break} command and its variants
1620 (@pxref{Set Breaks}), to specify the place where the program should stop
1621 by line number, function name or exact address in the program. In
1622 languages with exception handling (such as GNU C++), you can also set
1623 breakpoints where an exception is raised (@pxref{Exception Handling}).
1626 A @dfn{watchpoint} is a special breakpoint that stops your program when
1627 the value of an expression changes. You must use a different command to
1628 set watchpoints (@pxref{Set Watchpoints}), but aside from that, you can
1629 manage a watchpoint like any other breakpoint: you enable, disable, and
1630 delete both breakpoints and watchpoints using the same commands.
1632 Each breakpoint or watchpoint is assigned a number when it is created;
1633 these numbers are successive integers starting with one. In many of the
1634 commands for controlling various features of breakpoints you use the
1635 breakpoint number to say which breakpoint you want to change. Each
1636 breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has
1637 no effect on the program until you enable it again.
1640 * Set Breaks:: Setting Breakpoints
1641 * Set Watchpoints:: Setting Watchpoints
1642 * Exception Handling:: Breakpoints and Exceptions
1643 * Delete Breaks:: Deleting Breakpoints
1644 * Disabling:: Disabling Breakpoints
1645 * Conditions:: Break Conditions
1646 * Break Commands:: Breakpoint Command Lists
1647 * Breakpoint Menus:: Breakpoint Menus
1648 * Error in Breakpoints::
1651 @node Set Breaks, Set Watchpoints, Breakpoints, Breakpoints
1652 @subsection Setting Breakpoints
1656 Breakpoints are set with the @code{break} command (abbreviated @code{b}).
1658 You have several ways to say where the breakpoint should go.
1661 @item break @var{function}
1662 Set a breakpoint at entry to function @var{function}. When using source
1663 languages that permit overloading of symbols, such as C++,
1664 @var{function} may refer to more than one possible place to break.
1665 @xref{Breakpoint Menus}, for a discussion of that situation.
1667 @item break +@var{offset}
1668 @itemx break -@var{offset}
1669 Set a breakpoint some number of lines forward or back from the position
1670 at which execution stopped in the currently selected frame.
1672 @item break @var{linenum}
1673 Set a breakpoint at line @var{linenum} in the current source file.
1674 That file is the last file whose source text was printed. This
1675 breakpoint will stop the program just before it executes any of the
1678 @item break @var{filename}:@var{linenum}
1679 Set a breakpoint at line @var{linenum} in source file @var{filename}.
1681 @item break @var{filename}:@var{function}
1682 Set a breakpoint at entry to function @var{function} found in file
1683 @var{filename}. Specifying a file name as well as a function name is
1684 superfluous except when multiple files contain similarly named
1687 @item break *@var{address}
1688 Set a breakpoint at address @var{address}. You can use this to set
1689 breakpoints in parts of the program which do not have debugging
1690 information or source files.
1693 When called without any arguments, @code{break} sets a breakpoint at the
1694 next instruction to be executed in the selected stack frame
1695 (@pxref{Stack}). In any selected frame but the innermost, this will
1696 cause the program to stop as soon as control returns to that frame.
1697 This is similar to the effect of a @code{finish} command in the frame
1698 inside the selected frame---except that @code{finish} doesn't leave an
1699 active breakpoint. If you use @code{break} without an argument in the
1700 innermost frame, _GDBN__ will stop the next time it reaches the current
1701 location; this may be useful inside loops.
1703 _GDBN__ normally ignores breakpoints when it resumes execution, until at
1704 least one instruction has been executed. If it did not do this, you
1705 would be unable to proceed past a breakpoint without first disabling the
1706 breakpoint. This rule applies whether or not the breakpoint already
1707 existed when the program stopped.
1709 @item break @dots{} if @var{cond}
1710 Set a breakpoint with condition @var{cond}; evaluate the expression
1711 @var{cond} each time the breakpoint is reached, and stop only if the
1712 value is nonzero---that is, if @var{cond} evaluates as true.
1713 @samp{@dots{}} stands for one of the possible arguments described above
1714 (or no argument) specifying where to break. @xref{Conditions}, for more
1715 information on breakpoint conditions.
1717 @item tbreak @var{args}
1719 Set a breakpoint enabled only for one stop. @var{args} are the
1720 same as for the @code{break} command, and the breakpoint is set in the same
1721 way, but the breakpoint is automatically disabled the first time it
1722 is hit. @xref{Disabling}.
1724 @item rbreak @var{regex}
1726 @cindex regular expression
1727 Set breakpoints on all functions matching the regular expression
1728 @var{regex}. This command
1729 sets an unconditional breakpoint on all matches, printing a list of all
1730 breakpoints it set. Once these breakpoints are set, they are treated
1731 just like the breakpoints set with the @code{break} command. They can
1732 be deleted, disabled, made conditional, etc., in the standard ways.
1734 When debugging C++ programs, @code{rbreak} is useful for setting
1735 breakpoints on overloaded functions that are not members of any special
1738 @kindex info breakpoints
1739 @cindex @code{$_} and @code{info breakpoints}
1740 @item info breakpoints @r{[}@var{n}@r{]}
1741 @item info break @r{[}@var{n}@r{]}
1742 Print a list of all breakpoints (but not watchpoints) set and not
1743 deleted, showing their numbers, where in the program they are, and any
1744 special features in use for them. Disabled breakpoints are included in
1745 the list, but marked as disabled. @code{info break} with a breakpoint
1746 number @var{n} as argument lists only that breakpoint. The convenience
1747 variable @code{$_} and the default examining-address for the @code{x}
1748 command are set to the address of the last breakpoint listed
1749 (@pxref{Memory}). The equivalent command for watchpoints is @code{info
1752 _GDBN__ allows you to set any number of breakpoints at the same place in the
1753 program. There is nothing silly or meaningless about this. When the
1754 breakpoints are conditional, this is even useful (@pxref{Conditions}).
1756 @node Set Watchpoints, Exception Handling, Set Breaks, Breakpoints
1757 @subsection Setting Watchpoints
1758 @cindex setting watchpoints
1759 You can use a watchpoint to stop execution whenever the value of an
1760 expression changes, without having to predict a particular place
1761 where this may happen.
1763 Watchpoints currently execute two orders of magnitude more slowly than
1764 other breakpoints, but this can well be worth it to catch errors where
1765 you have no clue what part of your program is the culprit. Some
1766 processors provide special hardware to support watchpoint evaluation; future
1767 releases of _GDBN__ will use such hardware if it is available.
1771 @item watch @var{expr}
1772 Set a watchpoint for an expression.
1774 @kindex info watchpoints
1775 @item info watchpoints
1776 This command prints a list of watchpoints; it is otherwise similar to
1780 @node Exception Handling, Delete Breaks, Set Watchpoints, Breakpoints
1781 @subsection Breakpoints and Exceptions
1782 @cindex exception handlers
1784 Some languages, such as GNU C++, implement exception handling. You can
1785 use _GDBN__ to examine what caused the program to raise an exception,
1786 and to list the exceptions the program is prepared to handle at a
1787 given point in time.
1790 @item catch @var{exceptions}
1792 You can set breakpoints at active exception handlers by using the
1793 @code{catch} command. @var{exceptions} is a list of names of exceptions
1797 You can use @code{info catch} to list active exception handlers;
1800 There are currently some limitations to exception handling in _GDBN__.
1801 These will be corrected in a future release.
1805 If you call a function interactively, _GDBN__ normally returns
1806 control to you when the function has finished executing. If the call
1807 raises an exception, however, the call may bypass the mechanism that
1808 returns control to the user and cause the program to simply continue
1809 running until it hits a breakpoint, catches a signal that _GDBN__ is
1810 listening for, or exits.
1812 You cannot raise an exception interactively.
1814 You cannot interactively install an exception handler.
1817 @cindex raise exceptions
1818 Sometimes @code{catch} is not the best way to debug exception handling:
1819 if you need to know exactly where an exception is raised, it's better to
1820 stop @emph{before} the exception handler is called, since that way you
1821 can see the stack before any unwinding takes place. If you set a
1822 breakpoint in an exception handler instead, it may not be easy to find
1823 out where the exception was raised.
1825 To stop just before an exception handler is called, you need some
1826 knowledge of the implementation. In the case of GNU C++, exceptions are
1827 raised by calling a library function named @code{__raise_exception}
1828 which has the following ANSI C interface:
1831 /* @var{addr} is where the exception identifier is stored.
1832 ID is the exception identifier. */
1833 void __raise_exception (void **@var{addr}, void *@var{id});
1837 To make the debugger catch all exceptions before any stack
1838 unwinding takes place, set a breakpoint on @code{__raise_exception}
1839 (@pxref{Breakpoints}).
1841 With a conditional breakpoint (@xref{Conditions}) that depends on the
1842 value of @var{id}, you can stop your program when a specific exception
1843 is raised. You can use multiple conditional breakpoints to stop the
1844 program when any of a number of exceptions are raised.
1846 @node Delete Breaks, Disabling, Exception Handling, Breakpoints
1847 @subsection Deleting Breakpoints
1849 @cindex clearing breakpoints, watchpoints
1850 @cindex deleting breakpoints, watchpoints
1851 It is often necessary to eliminate a breakpoint or watchpoint once it
1852 has done its job and you no longer want the program to stop there. This
1853 is called @dfn{deleting} the breakpoint. A breakpoint that has been
1854 deleted no longer exists; it is forgotten.
1856 With the @code{clear} command you can delete breakpoints according to
1857 where they are in the program. With the @code{delete} command you can
1858 delete individual breakpoints or watchpoints by specifying their
1861 It is not necessary to delete a breakpoint to proceed past it. _GDBN__
1862 automatically ignores breakpoints on the first instruction to be executed
1863 when you continue execution without changing the execution address.
1868 Delete any breakpoints at the next instruction to be executed in the
1869 selected stack frame (@pxref{Selection}). When the innermost frame
1870 is selected, this is a good way to delete a breakpoint that the program
1873 @item clear @var{function}
1874 @itemx clear @var{filename}:@var{function}
1875 Delete any breakpoints set at entry to the function @var{function}.
1877 @item clear @var{linenum}
1878 @itemx clear @var{filename}:@var{linenum}
1879 Delete any breakpoints set at or within the code of the specified line.
1881 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
1882 @cindex delete breakpoints
1885 Delete the breakpoints or watchpoints of the numbers specified as
1886 arguments. If no argument is specified, delete all breakpoints (_GDBN__
1887 asks confirmation, unless you've @code{set confirm off}). You
1888 can abbreviate this command as @code{d}.
1891 @node Disabling, Conditions, Delete Breaks, Breakpoints
1892 @subsection Disabling Breakpoints
1894 @cindex disabled breakpoints
1895 @cindex enabled breakpoints
1896 Rather than deleting a breakpoint or watchpoint, you might prefer to
1897 @dfn{disable} it. This makes the breakpoint inoperative as if it had
1898 been deleted, but remembers the information on the breakpoint so that
1899 you can @dfn{enable} it again later.
1901 You disable and enable breakpoints and watchpoints with the
1902 @code{enable} and @code{disable} commands, optionally specifying one or
1903 more breakpoint numbers as arguments. Use @code{info break} or
1904 @code{info watch} to print a list of breakpoints or watchpoints if you
1905 don't know which numbers to use.
1907 A breakpoint or watchpoint can have any of four different states of
1912 Enabled. The breakpoint will stop the program. A breakpoint set
1913 with the @code{break} command starts out in this state.
1915 Disabled. The breakpoint has no effect on the program.
1917 Enabled once. The breakpoint will stop the program, but
1918 when it does so it will become disabled. A breakpoint set
1919 with the @code{tbreak} command starts out in this state.
1921 Enabled for deletion. The breakpoint will stop the program, but
1922 immediately after it does so it will be deleted permanently.
1925 You can use the following commands to enable or disable breakpoints and
1929 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
1930 @kindex disable breakpoints
1933 Disable the specified breakpoints---or all breakpoints, if none are
1934 listed. A disabled breakpoint has no effect but is not forgotten. All
1935 options such as ignore-counts, conditions and commands are remembered in
1936 case the breakpoint is enabled again later. You may abbreviate
1937 @code{disable} as @code{dis}.
1939 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
1940 @kindex enable breakpoints
1942 Enable the specified breakpoints (or all defined breakpoints). They
1943 become effective once again in stopping the program.
1945 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
1946 Enable the specified breakpoints temporarily. Each will be disabled
1947 again the next time it stops the program.
1949 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
1950 Enable the specified breakpoints to work once and then die. Each of
1951 the breakpoints will be deleted the next time it stops the program.
1954 Save for a breakpoint set with @code{tbreak} (@pxref{Set Breaks}),
1955 breakpoints that you set are initially enabled; subsequently, they become
1956 disabled or enabled only when you use one of the commands above. (The
1957 command @code{until} can set and delete a breakpoint of its own, but it
1958 will not change the state of your other breakpoints;
1959 @pxref{Continuing and Stepping}.)
1961 @node Conditions, Break Commands, Disabling, Breakpoints
1962 @subsection Break Conditions
1963 @cindex conditional breakpoints
1964 @cindex breakpoint conditions
1966 The simplest sort of breakpoint breaks every time the program reaches a
1967 specified place. You can also specify a @dfn{condition} for a
1968 breakpoint. A condition is just a Boolean expression in your
1969 programming language. (@xref{Expressions}). A breakpoint with a condition
1970 evaluates the expression each time the program reaches it, and the
1971 program stops only if the condition is @emph{true}.
1973 This is the converse of using assertions for program validation; in that
1974 situation, you want to stop when the assertion is violated---that is,
1975 when the condition is false. In C, if you want to test an assertion expressed
1976 by the condition @var{assert}, you should set the condition
1977 @samp{! @var{assert}} on the appropriate breakpoint.
1979 Conditions are also accepted for watchpoints; you may not need them,
1980 since a watchpoint is inspecting the value of an expression anyhow---but
1981 it might be simpler, say, to just set a watchpoint on a variable name,
1982 and specify a condition that tests whether the new value is an interesting
1985 Break conditions ca have side effects, and may even call functions in
1986 your program. This can be useful, for example, to activate functions
1987 that log program progress, or to use your own print functions to format
1988 special data structures. The effects are completely predictable unless
1989 there is another enabled breakpoint at the same address. (In that
1990 case, _GDBN__ might see the other breakpoint first and stop the program
1991 without checking the condition of this one.) Note that breakpoint
1992 commands are usually more convenient and flexible for the purpose of
1993 performing side effects when a breakpoint is reached
1994 (@pxref{Break Commands}).
1996 Break conditions can be specified when a breakpoint is set, by using
1997 @samp{if} in the arguments to the @code{break} command. @xref{Set Breaks}.
1998 They can also be changed at any time with the @code{condition} command.
1999 The @code{watch} command doesn't recognize the @code{if} keyword;
2000 @code{condition} is the only way to impose a further condition on a
2004 @item condition @var{bnum} @var{expression}
2006 Specify @var{expression} as the break condition for breakpoint or
2007 watchpoint number @var{bnum}. From now on, this breakpoint will stop
2008 the program only if the value of @var{expression} is true (nonzero, in
2009 C). When you use @code{condition}, _GDBN__ checks @var{expression}
2010 immediately for syntactic correctness, and to determine whether symbols
2011 in it have referents in the context of your breakpoint. _GDBN__ does
2012 not actually evaluate @var{expression} at the time the @code{condition}
2013 command is given, however. @xref{Expressions}.
2015 @item condition @var{bnum}
2016 Remove the condition from breakpoint number @var{bnum}. It becomes
2017 an ordinary unconditional breakpoint.
2020 @cindex ignore count (of breakpoint)
2021 A special case of a breakpoint condition is to stop only when the
2022 breakpoint has been reached a certain number of times. This is so
2023 useful that there is a special way to do it, using the @dfn{ignore
2024 count} of the breakpoint. Every breakpoint has an ignore count, which
2025 is an integer. Most of the time, the ignore count is zero, and
2026 therefore has no effect. But if the program reaches a breakpoint whose
2027 ignore count is positive, then instead of stopping, it just decrements
2028 the ignore count by one and continues. As a result, if the ignore count
2029 value is @var{n}, the breakpoint will not stop the next @var{n} times it
2033 @item ignore @var{bnum} @var{count}
2035 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
2036 The next @var{count} times the breakpoint is reached, your program's
2037 execution will not stop; other than to decrement the ignore count, _GDBN__
2040 To make the breakpoint stop the next time it is reached, specify
2043 @item continue @var{count}
2044 @itemx c @var{count}
2045 @itemx fg @var{count}
2046 @kindex continue @var{count}
2047 Continue execution of the program, setting the ignore count of the
2048 breakpoint that the program stopped at to @var{count} minus one.
2049 Thus, the program will not stop at this breakpoint until the
2050 @var{count}'th time it is reached.
2052 An argument to this command is meaningful only when the program stopped
2053 due to a breakpoint. At other times, the argument to @code{continue} is
2056 The synonym @code{fg} is provided purely for convenience, and has
2057 exactly the same behavior as other forms of the command.
2060 If a breakpoint has a positive ignore count and a condition, the condition
2061 is not checked. Once the ignore count reaches zero, the condition will
2064 You could achieve the effect of the ignore count with a
2065 condition such as _0__@w{@samp{$foo-- <= 0}}_1__ using a debugger convenience
2066 variable that is decremented each time. @xref{Convenience Vars}.
2068 @node Break Commands, Breakpoint Menus, Conditions, Breakpoints
2069 @subsection Breakpoint Command Lists
2071 @cindex breakpoint commands
2072 You can give any breakpoint (or watchpoint) a series of commands to
2073 execute when the program stops due to that breakpoint. For example, you
2074 might want to print the values of certain expressions, or enable other
2078 @item commands @r{[}@var{bnum}@r{]}
2079 @itemx @dots{} @var{command-list} @dots{}
2083 Specify a list of commands for breakpoint number @var{bnum}. The commands
2084 themselves appear on the following lines. Type a line containing just
2085 @code{end} to terminate the commands.
2087 To remove all commands from a breakpoint, type @code{commands} followed
2088 immediately by @code{end}; that is, give no commands.
2090 With no @var{bnum} argument, @code{commands} refers to the last
2091 breakpoint or watchpoint set (not to the breakpoint most recently
2095 Pressing @key{RET} as a means of repeating the last _GDBN__ command is
2096 disabled within a @var{command-list}.
2098 You can use breakpoint commands to start the program up again. Simply
2099 use the @code{continue} command, or @code{step}, or any other command
2100 that resumes execution. Subsequent commands in the command list are
2104 If the first command specified is @code{silent}, the usual message about
2105 stopping at a breakpoint is not printed. This may be desirable for
2106 breakpoints that are to print a specific message and then continue.
2107 If the remaining commands too print nothing, you will see no sign that
2108 the breakpoint was reached at all. @code{silent} is meaningful only
2109 at the beginning of a breakpoint command list.
2111 The commands @code{echo} and @code{output} that allow you to print precisely
2112 controlled output are often useful in silent breakpoints. @xref{Output}.
2114 For example, here is how you could use breakpoint commands to print the
2115 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
2128 One application for breakpoint commands is to compensate for one bug so
2129 you can test for another. Put a breakpoint just after the erroneous line
2130 of code, give it a condition to detect the case in which something
2131 erroneous has been done, and give it commands to assign correct values
2132 to any variables that need them. End with the @code{continue} command
2133 so that the program does not stop, and start with the @code{silent}
2134 command so that no output is produced. Here is an example:
2146 One deficiency in the operation of automatically continuing breakpoints
2147 under Unix appears when your program uses raw mode for the terminal.
2148 _GDBN__ switches back to its own terminal modes (not raw) before executing
2149 commands, and then must switch back to raw mode when your program is
2150 continued. This causes any pending terminal input to be lost.
2151 @c FIXME: revisit below when GNU sys avail.
2152 @c In the GNU system, this will be fixed by changing the behavior of
2155 Under Unix, you can get around this problem by writing actions into
2156 the breakpoint condition rather than in commands. For example
2159 condition 5 (x = y + 4), 0
2163 specifies a condition expression (@xref{Expressions}) that will change
2164 @code{x} as needed, then always have the value zero so the program will
2165 not stop. No input is lost here, because _GDBN__ evaluates break
2166 conditions without changing the terminal modes. When you want to have
2167 nontrivial conditions for performing the side effects, the operators
2168 @samp{&&}, @samp{||} and @samp{?@dots{}:} may be useful.
2170 @node Breakpoint Menus, Error in Breakpoints, Break Commands, Breakpoints
2171 @subsection Breakpoint Menus
2173 @cindex symbol overloading
2175 Some programming languages (notably C++) permit a single function name
2176 to be defined several times, for application in different contexts.
2177 This is called @dfn{overloading}. When a function name is overloaded,
2178 @samp{break @var{function}} is not enough to tell _GDBN__ where you
2179 want a breakpoint. _GDBN__ offers you a menu of numbered choices for
2180 different possible breakpoints, and waits for your selection with the
2181 prompt @samp{>}. The first two options are always @samp{[0] cancel}
2182 and @samp{[1] all}. Typing @kbd{1} sets a breakpoint at each
2183 definition of @var{function}, and typing @kbd{0} aborts the
2184 @code{break} command without setting any new breakpoints.
2186 For example, the following session excerpt shows an attempt to set a
2187 breakpoint at the overloaded symbol @code{String::after}.
2188 We choose three particular definitions of that function name:
2191 (_GDBP__) b String::after
2194 [2] file:String.cc; line number:867
2195 [3] file:String.cc; line number:860
2196 [4] file:String.cc; line number:875
2197 [5] file:String.cc; line number:853
2198 [6] file:String.cc; line number:846
2199 [7] file:String.cc; line number:735
2201 Breakpoint 1 at 0xb26c: file String.cc, line 867.
2202 Breakpoint 2 at 0xb344: file String.cc, line 875.
2203 Breakpoint 3 at 0xafcc: file String.cc, line 846.
2204 Multiple breakpoints were set.
2205 Use the "delete" command to delete unwanted breakpoints.
2210 @node Error in Breakpoints, , Breakpoint Menus, Breakpoints
2211 @subsection ``Cannot Insert Breakpoints''
2213 @c FIXME: "cannot insert breakpoints" error, v unclear.
2214 @c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91
2215 @c some light may be shed by looking at instances of
2216 @c ONE_PROCESS_WRITETEXT. But error seems possible otherwise
2217 @c too. pesch, 20sep91
2218 Under some operating systems, breakpoints cannot be used in a program if
2219 any other process is running that program. In this situation,
2220 attempting to run or continue a program with a breakpoint causes _GDBN__
2221 to stop the other process.
2223 When this happens, you have three ways to proceed:
2227 Remove or disable the breakpoints, then continue.
2230 Suspend _GDBN__, and copy the file containing the program to a new name.
2231 Resume _GDBN__ and use the @code{exec-file} command to specify that _GDBN__
2232 should run the program under that name. Then start the program again.
2234 @c FIXME: RMS commented here "Show example". Maybe when someone
2235 @c explains the first FIXME: in this section...
2238 Relink the program so that the text segment is nonsharable, using the
2239 linker option @samp{-N}. The operating system limitation may not apply
2240 to nonsharable executables.
2243 @node Continuing and Stepping, Signals, Breakpoints, Stopping
2244 @section Continuing and Stepping
2248 @cindex resuming execution
2249 @dfn{Continuing} means resuming program execution until your program
2250 completes normally. In contrast, @dfn{stepping} means resuming program
2251 execution for a very limited time: one line of source code, or one
2252 machine instruction. Either when continuing or when stepping, the
2253 program may stop even sooner, due to a breakpoint or to a signal. (If
2254 due to a signal, you may want to use @code{handle}, or use @samp{signal
2255 0} to resume execution; @pxref{Signals}.)
2258 @item continue @r{[}@var{ignore-count}@r{]}
2260 Resume program execution, at the address where the program last stopped;
2261 any breakpoints set at that address are bypassed. The optional argument
2262 @var{ignore-count} allows you to specify a further number of times to
2263 ignore a breakpoint at this location; its effect is like that of
2264 @code{ignore} (@pxref{Conditions}).
2266 To resume execution at a different place, you can use @code{return}
2267 (@pxref{Returning}) to go back to the calling function; or @code{jump}
2268 (@pxref{Jumping}) to go to an arbitrary location in your program.
2272 A typical technique for using stepping is to set a breakpoint
2273 (@pxref{Breakpoints}) at the beginning of the function or the section of
2274 the program in which a problem is believed to lie, run the program until
2275 it stops at that breakpoint, and then step through the suspect area,
2276 examining the variables that are interesting, until you see the problem
2283 Continue running the program until control reaches a different source
2284 line, then stop it and return control to _GDBN__. This command is
2285 abbreviated @code{s}.
2288 @emph{Warning:} If you use the @code{step} command while control is
2289 within a function that was compiled without debugging information,
2290 execution will proceed until control reaches another function.
2293 @item step @var{count}
2294 Continue running as in @code{step}, but do so @var{count} times. If a
2295 breakpoint is reached or a signal not related to stepping occurs before
2296 @var{count} steps, stepping stops right away.
2298 @item next @r{[}@var{count}@r{]}
2301 Continue to the next source line in the current (innermost) stack frame.
2302 Similar to @code{step}, but any function calls appearing within the line
2303 of code are executed without stopping. Execution stops when control
2304 reaches a different line of code at the stack level which was executing
2305 when the @code{next} command was given. This command is abbreviated
2308 An argument @var{count} is a repeat count, as for @code{step}.
2310 @code{next} within a function that lacks debugging information acts like
2311 @code{step}, but any function calls appearing within the code of the
2312 function are executed without stopping.
2316 Continue running until just after function in the selected stack frame
2317 returns. Print the returned value (if any).
2319 Contrast this with the @code{return} command (@pxref{Returning}).
2325 Continue running until a source line past the current line, in the
2326 current stack frame, is reached. This command is used to avoid single
2327 stepping through a loop more than once. It is like the @code{next}
2328 command, except that when @code{until} encounters a jump, it
2329 automatically continues execution until the program counter is greater
2330 than the address of the jump.
2332 This means that when you reach the end of a loop after single stepping
2333 though it, @code{until} will cause the program to continue execution
2334 until the loop is exited. In contrast, a @code{next} command at the end
2335 of a loop will simply step back to the beginning of the loop, which
2336 would force you to step through the next iteration.
2338 @code{until} always stops the program if it attempts to exit the current
2341 @code{until} may produce somewhat counterintuitive results if the order
2342 of machine code does not match the order of the source lines. For
2343 example, in the following excerpt from a debugging session, the @code{f}
2344 (@code{frame}) command shows that execution is stopped at line
2345 @code{206}; yet when we use @code{until}, we get to line @code{195}:
2349 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
2352 195 for ( ; argc > 0; NEXTARG) @{
2355 This happened because, for execution efficiency, the compiler had
2356 generated code for the loop closure test at the end, rather than the
2357 start, of the loop---even though the test in a C @code{for}-loop is
2358 written before the body of the loop. The @code{until} command appeared
2359 to step back to the beginning of the loop when it advanced to this
2360 expression; however, it has not really gone to an earlier
2361 statement---not in terms of the actual machine code.
2363 @code{until} with no argument works by means of single
2364 instruction stepping, and hence is slower than @code{until} with an
2367 @item until @var{location}
2368 @item u @var{location}
2369 Continue running the program until either the specified location is
2370 reached, or the current stack frame returns. @var{location}
2371 is any of the forms of argument acceptable to @code{break}
2372 (@pxref{Set Breaks}). This form of the command uses breakpoints, and
2373 hence is quicker than @code{until} without an argument.
2379 Execute one machine instruction, then stop and return to the debugger.
2381 It is often useful to do @samp{display/i $pc} when stepping by machine
2382 instructions. This will cause the next instruction to be executed to
2383 be displayed automatically at each stop. @xref{Auto Display}.
2385 An argument is a repeat count, as in @code{step}.
2391 Execute one machine instruction, but if it is a function call,
2392 proceed until the function returns.
2394 An argument is a repeat count, as in @code{next}.
2398 @node Signals, , Continuing and Stepping, Stopping
2402 A signal is an asynchronous event that can happen in a program. The
2403 operating system defines the possible kinds of signals, and gives each
2404 kind a name and a number. For example, in Unix @code{SIGINT} is the
2405 signal a program gets when you type an interrupt (often @kbd{C-c});
2406 @code{SIGSEGV} is the signal a program gets from referencing a place in
2407 memory far away from all the areas in use; @code{SIGALRM} occurs when
2408 the alarm clock timer goes off (which happens only if the program has
2409 requested an alarm).
2411 @cindex fatal signals
2412 Some signals, including @code{SIGALRM}, are a normal part of the
2413 functioning of the program. Others, such as @code{SIGSEGV}, indicate
2414 errors; these signals are @dfn{fatal} (kill the program immediately) if the
2415 program has not specified in advance some other way to handle the signal.
2416 @code{SIGINT} does not indicate an error in the program, but it is normally
2417 fatal so it can carry out the purpose of the interrupt: to kill the program.
2419 _GDBN__ has the ability to detect any occurrence of a signal in the program
2420 running under _GDBN__'s control. You can tell _GDBN__ in advance what to do for
2421 each kind of signal.
2423 @cindex handling signals
2424 Normally, _GDBN__ is set up to ignore non-erroneous signals like @code{SIGALRM}
2425 (so as not to interfere with their role in the functioning of the program)
2426 but to stop the program immediately whenever an error signal happens.
2427 You can change these settings with the @code{handle} command.
2431 @kindex info signals
2432 Print a table of all the kinds of signals and how _GDBN__ has been told to
2433 handle each one. You can use this to see the signal numbers of all
2434 the defined types of signals.
2436 @item handle @var{signal} @var{keywords}@dots{}
2438 Change the way _GDBN__ handles signal @var{signal}. @var{signal} can be the
2439 number of a signal or its name (with or without the @samp{SIG} at the
2440 beginning). The @var{keywords} say what change to make.
2444 The keywords allowed by the @code{handle} command can be abbreviated.
2445 Their full names are:
2449 _GDBN__ should not stop the program when this signal happens. It may
2450 still print a message telling you that the signal has come in.
2453 _GDBN__ should stop the program when this signal happens. This implies
2454 the @code{print} keyword as well.
2457 _GDBN__ should print a message when this signal happens.
2460 _GDBN__ should not mention the occurrence of the signal at all. This
2461 implies the @code{nostop} keyword as well.
2464 _GDBN__ should allow the program to see this signal; the program will be
2465 able to handle the signal, or may be terminated if the signal is fatal
2469 _GDBN__ should not allow the program to see this signal.
2473 When a signal has been set to stop the program, the program cannot see the
2474 signal until you continue. It will see the signal then, if @code{pass} is
2475 in effect for the signal in question @i{at that time}. In other words,
2476 after _GDBN__ reports a signal, you can use the @code{handle} command with
2477 @code{pass} or @code{nopass} to control whether that signal will be seen by
2478 the program when you later continue it.
2480 You can also use the @code{signal} command to prevent the program from
2481 seeing a signal, or cause it to see a signal it normally would not see,
2482 or to give it any signal at any time. For example, if the program stopped
2483 due to some sort of memory reference error, you might store correct
2484 values into the erroneous variables and continue, hoping to see more
2485 execution; but the program would probably terminate immediately as
2486 a result of the fatal signal once it sees the signal. To prevent this,
2487 you can continue with @samp{signal 0}. @xref{Signaling}.
2489 @node Stack, Source, Stopping, Top
2490 @chapter Examining the Stack
2492 When your program has stopped, the first thing you need to know is where it
2493 stopped and how it got there.
2496 Each time your program performs a function call, the information about
2497 where in the program the call was made from is saved in a block of data
2498 called a @dfn{stack frame}. The frame also contains the arguments of the
2499 call and the local variables of the function that was called. All the
2500 stack frames are allocated in a region of memory called the @dfn{call
2503 When your program stops, the _GDBN__ commands for examining the stack allow you
2504 to see all of this information.
2506 @cindex selected frame
2507 One of the stack frames is @dfn{selected} by _GDBN__ and many _GDBN__ commands
2508 refer implicitly to the selected frame. In particular, whenever you ask
2509 _GDBN__ for the value of a variable in the program, the value is found in the
2510 selected frame. There are special _GDBN__ commands to select whichever frame
2511 you are interested in.
2513 When the program stops, _GDBN__ automatically selects the currently executing
2514 frame and describes it briefly as the @code{frame} command does
2515 (@pxref{Frame Info}).
2518 * Frames:: Stack Frames
2519 * Backtrace:: Backtraces
2520 * Selection:: Selecting a Frame
2521 * Frame Info:: Information on a Frame
2524 @node Frames, Backtrace, Stack, Stack
2525 @section Stack Frames
2529 The call stack is divided up into contiguous pieces called @dfn{stack
2530 frames}, or @dfn{frames} for short; each frame is the data associated
2531 with one call to one function. The frame contains the arguments given
2532 to the function, the function's local variables, and the address at
2533 which the function is executing.
2535 @cindex initial frame
2536 @cindex outermost frame
2537 @cindex innermost frame
2538 When your program is started, the stack has only one frame, that of the
2539 function @code{main}. This is called the @dfn{initial} frame or the
2540 @dfn{outermost} frame. Each time a function is called, a new frame is
2541 made. Each time a function returns, the frame for that function invocation
2542 is eliminated. If a function is recursive, there can be many frames for
2543 the same function. The frame for the function in which execution is
2544 actually occurring is called the @dfn{innermost} frame. This is the most
2545 recently created of all the stack frames that still exist.
2547 @cindex frame pointer
2548 Inside your program, stack frames are identified by their addresses. A
2549 stack frame consists of many bytes, each of which has its own address; each
2550 kind of computer has a convention for choosing one of those bytes whose
2551 address serves as the address of the frame. Usually this address is kept
2552 in a register called the @dfn{frame pointer register} while execution is
2553 going on in that frame.
2555 @cindex frame number
2556 _GDBN__ assigns numbers to all existing stack frames, starting with
2557 zero for the innermost frame, one for the frame that called it,
2558 and so on upward. These numbers do not really exist in your program;
2559 they are assigned by _GDBN__ to give you a way of designating stack
2560 frames in _GDBN__ commands.
2562 @cindex frameless execution
2563 Some compilers allow functions to be compiled so that they operate
2564 without stack frames. (For example, the @code{_GCC__} option
2565 @samp{-fomit-frame-pointer} will generate functions without a frame.)
2566 This is occasionally done with heavily used library functions to save
2567 the frame setup time. _GDBN__ has limited facilities for dealing with
2568 these function invocations. If the innermost function invocation has no
2569 stack frame, _GDBN__ will nevertheless regard it as though it had a
2570 separate frame, which is numbered zero as usual, allowing correct
2571 tracing of the function call chain. However, _GDBN__ has no provision
2572 for frameless functions elsewhere in the stack.
2574 @node Backtrace, Selection, Frames, Stack
2577 A backtrace is a summary of how the program got where it is. It shows one
2578 line per frame, for many frames, starting with the currently executing
2579 frame (frame zero), followed by its caller (frame one), and on up the
2587 Print a backtrace of the entire stack: one line per frame for all
2588 frames in the stack.
2590 You can stop the backtrace at any time by typing the system interrupt
2591 character, normally @kbd{C-c}.
2593 @item backtrace @var{n}
2595 Similar, but print only the innermost @var{n} frames.
2597 @item backtrace -@var{n}
2599 Similar, but print only the outermost @var{n} frames.
2605 The names @code{where} and @code{info stack} (abbreviated @code{info s})
2606 are additional aliases for @code{backtrace}.
2608 Each line in the backtrace shows the frame number and the function name.
2609 The program counter value is also shown---unless you use @code{set
2610 print address off}. The backtrace also shows the source file name and
2611 line number, as well as the arguments to the function. The program
2612 counter value is omitted if it is at the beginning of the code for that
2615 Here is an example of a backtrace. It was made with the command
2616 @samp{bt 3}, so it shows the innermost three frames.
2620 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8) at builtin.c:993
2621 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
2622 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
2624 (More stack frames follow...)
2629 The display for frame zero doesn't begin with a program counter
2630 value, indicating that the program has stopped at the beginning of the
2631 code for line @code{993} of @code{builtin.c}.
2633 @node Selection, Frame Info, Backtrace, Stack
2634 @section Selecting a Frame
2636 Most commands for examining the stack and other data in the program work on
2637 whichever stack frame is selected at the moment. Here are the commands for
2638 selecting a stack frame; all of them finish by printing a brief description
2639 of the stack frame just selected.
2646 Select frame number @var{n}. Recall that frame zero is the innermost
2647 (currently executing) frame, frame one is the frame that called the
2648 innermost one, and so on. The highest-numbered frame is @code{main}'s
2651 @item frame @var{addr}
2653 Select the frame at address @var{addr}. This is useful mainly if the
2654 chaining of stack frames has been damaged by a bug, making it
2655 impossible for _GDBN__ to assign numbers properly to all frames. In
2656 addition, this can be useful when the program has multiple stacks and
2657 switches between them.
2660 On the SPARC architecture, @code{frame} needs two addresses to
2661 select an arbitrary frame: a frame pointer and a stack pointer.
2662 @c note to future updaters: this is conditioned on a flag
2663 @c FRAME_SPECIFICATION_DYADIC in the tm-*.h files, currently only used
2664 @c by SPARC, hence the specific attribution. Generalize or list all
2665 @c possibilities if more supported machines start doing this.
2670 Move @var{n} frames up the stack. For positive numbers @var{n}, this
2671 advances toward the outermost frame, to higher frame numbers, to frames
2672 that have existed longer. @var{n} defaults to one.
2677 Move @var{n} frames down the stack. For positive numbers @var{n}, this
2678 advances toward the innermost frame, to lower frame numbers, to frames
2679 that were created more recently. @var{n} defaults to one. You may
2680 abbreviate @code{down} as @code{do}.
2683 All of these commands end by printing two lines of output describing the
2684 frame. The first line shows the frame number, the function name, the
2685 arguments, and the source file and line number of execution in that
2686 frame. The second line shows the text of that source line. For
2691 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc) at env.c:10
2692 10 read_input_file (argv[i]);
2695 After such a printout, the @code{list} command with no arguments will print
2696 ten lines centered on the point of execution in the frame. @xref{List}.
2699 @item up-silently @var{n}
2700 @itemx down-silently @var{n}
2701 @kindex down-silently
2703 These two commands are variants of @code{up} and @code{down},
2704 respectively; they differ in that they do their work silently, without
2705 causing display of the new frame. They are intended primarily for use
2706 in _GDBN__ command scripts, where the output might be unnecessary and
2711 @node Frame Info, , Selection, Stack
2712 @section Information About a Frame
2714 There are several other commands to print information about the selected
2720 When used without any argument, this command does not change which frame
2721 is selected, but prints a brief description of the currently
2722 selected stack frame. It can be abbreviated @code{f}. With an
2723 argument, this command is used to select a stack frame (@pxref{Selection}).
2729 This command prints a verbose description of the selected stack frame,
2730 including the address of the frame, the addresses of the next frame down
2731 (called by this frame) and the next frame up (caller of this frame), the
2732 language that the source code corresponding to this frame was written in,
2733 the address of the frame's arguments, the program counter saved in it
2734 (the address of execution in the caller frame), and which registers
2735 were saved in the frame. The verbose description is useful when
2736 something has gone wrong that has made the stack format fail to fit
2737 the usual conventions.
2739 @item info frame @var{addr}
2740 @itemx info f @var{addr}
2741 Print a verbose description of the frame at address @var{addr},
2742 without selecting that frame. The selected frame remains unchanged by
2747 Print the arguments of the selected frame, each on a separate line.
2751 Print the local variables of the selected frame, each on a separate
2752 line. These are all variables declared static or automatic within all
2753 program blocks that execution in this frame is currently inside of.
2757 @cindex catch exceptions
2758 @cindex exception handlers
2759 Print a list of all the exception handlers that are active in the
2760 current stack frame at the current point of execution. To see other
2761 exception handlers, visit the associated frame (using the @code{up},
2762 @code{down}, or @code{frame} commands); then type @code{info catch}.
2763 @xref{Exception Handling}.
2766 @node Source, Data, Stack, Top
2767 @chapter Examining Source Files
2769 _GDBN__ can print parts of your program's source, since the debugging
2770 information recorded in your program tells _GDBN__ what source files
2771 were used to built it. When your program stops, _GDBN__ spontaneously
2772 prints the line where it stopped. Likewise, when you select a stack
2773 frame (@pxref{Selection}), _GDBN__ prints the line where execution in
2774 that frame has stopped. You can print other portions of source files by
2777 If you use _GDBN__ through its GNU Emacs interface, you may prefer to
2778 use Emacs facilities to view source; @pxref{Emacs}.
2781 * List:: Printing Source Lines
2782 * Search:: Searching Source Files
2783 * Source Path:: Specifying Source Directories
2784 * Machine Code:: Source and Machine Code
2787 @node List, Search, Source, Source
2788 @section Printing Source Lines
2792 To print lines from a source file, use the @code{list} command
2793 (abbreviated @code{l}). There are several ways to specify what part
2794 of the file you want to print.
2796 Here are the forms of the @code{list} command most commonly used:
2799 @item list @var{linenum}
2800 Print lines centered around line number @var{linenum} in the
2801 current source file.
2803 @item list @var{function}
2804 Print lines centered around the beginning of function
2808 Print more lines. If the last lines printed were printed with a
2809 @code{list} command, this prints lines following the last lines
2810 printed; however, if the last line printed was a solitary line printed
2811 as part of displaying a stack frame (@pxref{Stack}), this prints
2812 lines centered around that line.
2815 Print lines just before the lines last printed.
2818 By default, _GDBN__ prints ten source lines with any of these forms of
2819 the @code{list} command. You can change this using @code{set listsize}:
2822 @item set listsize @var{count}
2823 @kindex set listsize
2824 Make the @code{list} command display @var{count} source lines (unless
2825 the @code{list} argument explicitly specifies some other number).
2828 @kindex show listsize
2829 Display the number of lines that @code{list} will currently display by
2833 Repeating a @code{list} command with @key{RET} discards the argument,
2834 so it is equivalent to typing just @code{list}. This is more useful
2835 than listing the same lines again. An exception is made for an
2836 argument of @samp{-}; that argument is preserved in repetition so that
2837 each repetition moves up in the source file.
2840 In general, the @code{list} command expects you to supply zero, one or two
2841 @dfn{linespecs}. Linespecs specify source lines; there are several ways
2842 of writing them but the effect is always to specify some source line.
2843 Here is a complete description of the possible arguments for @code{list}:
2846 @item list @var{linespec}
2847 Print lines centered around the line specified by @var{linespec}.
2849 @item list @var{first},@var{last}
2850 Print lines from @var{first} to @var{last}. Both arguments are
2853 @item list ,@var{last}
2854 Print lines ending with @var{last}.
2856 @item list @var{first},
2857 Print lines starting with @var{first}.
2860 Print lines just after the lines last printed.
2863 Print lines just before the lines last printed.
2866 As described in the preceding table.
2869 Here are the ways of specifying a single source line---all the
2874 Specifies line @var{number} of the current source file.
2875 When a @code{list} command has two linespecs, this refers to
2876 the same source file as the first linespec.
2879 Specifies the line @var{offset} lines after the last line printed.
2880 When used as the second linespec in a @code{list} command that has
2881 two, this specifies the line @var{offset} lines down from the
2885 Specifies the line @var{offset} lines before the last line printed.
2887 @item @var{filename}:@var{number}
2888 Specifies line @var{number} in the source file @var{filename}.
2890 @item @var{function}
2891 @c FIXME: "of the open-brace" is C-centric. When we add other langs...
2892 Specifies the line of the open-brace that begins the body of the
2893 function @var{function}.
2895 @item @var{filename}:@var{function}
2896 Specifies the line of the open-brace that begins the body of the
2897 function @var{function} in the file @var{filename}. You only need the
2898 file name with a function name to avoid ambiguity when there are
2899 identically named functions in different source files.
2901 @item *@var{address}
2902 Specifies the line containing the program address @var{address}.
2903 @var{address} may be any expression.
2906 @node Search, Source Path, List, Source
2907 @section Searching Source Files
2909 @kindex reverse-search
2911 There are two commands for searching through the current source file for a
2915 @item forward-search @var{regexp}
2916 @itemx search @var{regexp}
2918 @kindex forward-search
2919 The command @samp{forward-search @var{regexp}} checks each line, starting
2920 with the one following the last line listed, for a match for @var{regexp}.
2921 It lists the line that is found. You can abbreviate the command name
2922 as @code{fo}. The synonym @samp{search @var{regexp}} is also supported.
2924 @item reverse-search @var{regexp}
2925 The command @samp{reverse-search @var{regexp}} checks each line, starting
2926 with the one before the last line listed and going backward, for a match
2927 for @var{regexp}. It lists the line that is found. You can abbreviate
2928 this command as @code{rev}.
2931 @node Source Path, Machine Code, Search, Source
2932 @section Specifying Source Directories
2935 @cindex directories for source files
2936 Executable programs sometimes do not record the directories of the source
2937 files from which they were compiled, just the names. Even when they do,
2938 the directories could be moved between the compilation and your debugging
2939 session. _GDBN__ has a list of directories to search for source files;
2940 this is called the @dfn{source path}. Each time _GDBN__ wants a source file,
2941 it tries all the directories in the list, in the order they are present
2942 in the list, until it finds a file with the desired name. Note that
2943 the executable search path is @emph{not} used for this purpose. Neither is
2944 the current working directory, unless it happens to be in the source
2947 If _GDBN__ can't find a source file in the source path, and the object
2948 program records a directory, _GDBN__ tries that directory too. If the
2949 source path is empty, and there is no record of the compilation
2950 directory, _GDBN__ will, as a last resort, look in the current
2953 Whenever you reset or rearrange the source path, _GDBN__ will clear out
2954 any information it has cached about where source files are found, where
2955 each line is in the file, etc.
2958 When you start _GDBN__, its source path is empty.
2959 To add other directories, use the @code{directory} command.
2962 @item directory @var{dirname} @dots{}
2963 Add directory @var{dirname} to the front of the source path. Several
2964 directory names may be given to this command, separated by @samp{:} or
2965 whitespace. You may specify a directory that is already in the source
2966 path; this moves it forward, so it will be searched sooner.
2968 You can use the string @samp{$cdir} to refer to the compilation
2969 directory (if one is recorded), and @samp{$cwd} to refer to the current
2970 working directory. @samp{$cwd} is not the same as @samp{.}---the former
2971 tracks the current working directory as it changes during your _GDBN__
2972 session, while the latter is immediately expanded to the current
2973 directory at the time you add an entry to the source path.
2976 Reset the source path to empty again. This requires confirmation.
2978 @c RET-repeat for @code{directory} is explicitly disabled, but since
2979 @c repeating it would be a no-op we don't say that. (thanks to RMS)
2981 @item show directories
2982 @kindex show directories
2983 Print the source path: show which directories it contains.
2986 If your source path is cluttered with directories that are no longer of
2987 interest, _GDBN__ may sometimes cause confusion by finding the wrong
2988 versions of source. You can correct the situation as follows:
2992 Use @code{directory} with no argument to reset the source path to empty.
2995 Use @code{directory} with suitable arguments to reinstall the
2996 directories you want in the source path. You can add all the
2997 directories in one command.
3000 @node Machine Code, , Source Path, Source
3001 @section Source and Machine Code
3002 You can use the command @code{info line} to map source lines to program
3003 addresses (and viceversa), and the command @code{disassemble} to display
3004 a range of addresses as machine instructions.
3007 @item info line @var{linespec}
3009 Print the starting and ending addresses of the compiled code for
3010 source line @var{linespec}. You can specify source lines in any of the
3011 ways understood by the @code{list} command (@pxref{List}).
3014 For example, we can use @code{info line} to inquire on where the object
3015 code for the first line of function @code{m4_changequote} lies:
3017 (_GDBP__) info line m4_changecom
3018 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
3022 We can also inquire (using @code{*@var{addr}} as the form for
3023 @var{linespec}) what source line covers a particular address:
3025 (_GDBP__) info line *0x63ff
3026 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
3029 @cindex @code{$_} and @code{info line}
3030 After @code{info line}, the default address for the @code{x}
3031 command is changed to the starting address of the line, so that
3032 @samp{x/i} is sufficient to begin examining the machine code
3033 (@pxref{Memory}). Also, this address is saved as the value of the
3034 convenience variable @code{$_} (@pxref{Convenience Vars}).
3039 This specialized command is provided to dump a range of memory as
3040 machine instructions. The default memory range is the function
3041 surrounding the program counter of the selected frame. A single
3042 argument to this command is a program counter value; the function
3043 surrounding this value will be dumped. Two arguments (separated by one
3044 or more spaces) specify a range of addresses (first inclusive, second
3045 exclusive) to be dumped.
3048 We can use @code{disassemble} to inspect the object code
3049 range shown in the last @code{info line} example:
3052 (_GDBP__) disas 0x63e4 0x6404
3053 Dump of assembler code from 0x63e4 to 0x6404:
3054 0x63e4 <builtin_init+5340>: ble 0x63f8 <builtin_init+5360>
3055 0x63e8 <builtin_init+5344>: sethi %hi(0x4c00), %o0
3056 0x63ec <builtin_init+5348>: ld [%i1+4], %o0
3057 0x63f0 <builtin_init+5352>: b 0x63fc <builtin_init+5364>
3058 0x63f4 <builtin_init+5356>: ld [%o0+4], %o0
3059 0x63f8 <builtin_init+5360>: or %o0, 0x1a4, %o0
3060 0x63fc <builtin_init+5364>: call 0x9288 <path_search>
3061 0x6400 <builtin_init+5368>: nop
3062 End of assembler dump.
3067 @node Data, Languages, Source, Top
3068 @chapter Examining Data
3070 @cindex printing data
3071 @cindex examining data
3074 @c "inspect" isn't quite a synonym if you're using Epoch, which we don't
3075 @c document because it's nonstandard... Under Epoch it displays in a
3076 @c different window or something like that.
3077 The usual way to examine data in your program is with the @code{print}
3078 command (abbreviated @code{p}), or its synonym @code{inspect}. It
3079 evaluates and prints the value of an expression of the language your
3080 program is written in (@pxref{Languages}). You type
3087 where @var{exp} is an expression (in the source language), and
3088 the value of @var{exp} is printed in a format appropriate to its data
3091 A more low-level way of examining data is with the @code{x} command.
3092 It examines data in memory at a specified address and prints it in a
3093 specified format. @xref{Memory}.
3095 If you're interested in information about types, or about how the fields
3096 of a struct or class are declared, use the @code{ptype @var{exp}}
3097 command rather than @code{print}. @xref{Symbols}.
3100 * Expressions:: Expressions
3101 * Variables:: Program Variables
3102 * Arrays:: Artificial Arrays
3103 * Output formats:: Output formats
3104 * Memory:: Examining Memory
3105 * Auto Display:: Automatic Display
3106 * Print Settings:: Print Settings
3107 * Value History:: Value History
3108 * Convenience Vars:: Convenience Variables
3109 * Registers:: Registers
3110 * Floating Point Hardware:: Floating Point Hardware
3113 @node Expressions, Variables, Data, Data
3114 @section Expressions
3117 @code{print} and many other _GDBN__ commands accept an expression and
3118 compute its value. Any kind of constant, variable or operator defined
3119 by the programming language you are using is legal in an expression in
3120 _GDBN__. This includes conditional expressions, function calls, casts
3121 and string constants. It unfortunately does not include symbols defined
3122 by preprocessor @code{#define} commands.
3124 Because C is so widespread, most of the expressions shown in examples in
3125 this manual are in C. @xref{Languages,, Using _GDBN__ with Different
3126 Languages}, for information on how to use expressions in other
3129 In this section, we discuss operators that you can use in _GDBN__
3130 expressions regardless of your programming language.
3132 Casts are supported in all languages, not just in C, because it is so
3133 useful to cast a number into a pointer so as to examine a structure
3134 at that address in memory.
3135 @c FIXME: casts supported---Mod2 true?
3137 _GDBN__ supports these operators in addition to those of programming
3142 @samp{@@} is a binary operator for treating parts of memory as arrays.
3143 @xref{Arrays}, for more information.
3146 @samp{::} allows you to specify a variable in terms of the file or
3147 function where it is defined. @xref{Variables}.
3149 @item @{@var{type}@} @var{addr}
3150 Refers to an object of type @var{type} stored at address @var{addr} in
3151 memory. @var{addr} may be any expression whose value is an integer or
3152 pointer (but parentheses are required around binary operators, just as in
3153 a cast). This construct is allowed regardless of what kind of data is
3154 normally supposed to reside at @var{addr}.@refill
3157 @node Variables, Arrays, Expressions, Data
3158 @section Program Variables
3160 The most common kind of expression to use is the name of a variable
3163 Variables in expressions are understood in the selected stack frame
3164 (@pxref{Selection}); they must either be global (or static) or be visible
3165 according to the scope rules of the programming language from the point of
3166 execution in that frame. This means that in the function
3181 the variable @code{a} is usable whenever the program is executing
3182 within the function @code{foo}, but the variable @code{b} is visible
3183 only while the program is executing inside the block in which @code{b}
3186 @cindex variable name conflict
3187 There is an exception: you can refer to a variable or function whose
3188 scope is a single source file even if the current execution point is not
3189 in this file. But it is possible to have more than one such variable or
3190 function with the same name (in different source files). If that happens,
3191 referring to that name has unpredictable effects. If you wish, you can
3192 specify a variable in a particular file, using the colon-colon notation:
3197 @var{file}::@var{variable}
3201 Here @var{file} is the name of the source file whose variable you want.
3203 @cindex C++ scope resolution
3204 This use of @samp{::} is very rarely in conflict with the very similar
3205 use of the same notation in C++. _GDBN__ also supports use of the C++
3206 scope resolution operator in _GDBN__ expressions.
3208 @cindex wrong values
3209 @cindex variable values, wrong
3211 @emph{Warning:} Occasionally, a local variable may appear to have the
3212 wrong value at certain points in a function---just after entry to the
3213 function, and just before exit. You may see this problem when you're
3214 stepping by machine instructions. This is because on most machines, it
3215 takes more than one instruction to set up a stack frame (including local
3216 variable definitions); if you're stepping by machine instructions,
3217 variables may appear to have the wrong values until the stack frame is
3218 completely built. On function exit, it usually also takes more than one
3219 machine instruction to destroy a stack frame; after you begin stepping
3220 through that group of instructions, local variable definitions may be
3224 @node Arrays, Output formats, Variables, Data
3225 @section Artificial Arrays
3227 @cindex artificial array
3229 It is often useful to print out several successive objects of the
3230 same type in memory; a section of an array, or an array of
3231 dynamically determined size for which only a pointer exists in the
3234 This can be done by constructing an @dfn{artificial array} with the
3235 binary operator @samp{@@}. The left operand of @samp{@@} should be
3236 the first element of the desired array, as an individual object.
3237 The right operand should be the desired length of the array. The result is
3238 an array value whose elements are all of the type of the left argument.
3239 The first element is actually the left argument; the second element
3240 comes from bytes of memory immediately following those that hold the
3241 first element, and so on. Here is an example. If a program says
3244 int *array = (int *) malloc (len * sizeof (int));
3248 you can print the contents of @code{array} with
3254 The left operand of @samp{@@} must reside in memory. Array values made
3255 with @samp{@@} in this way behave just like other arrays in terms of
3256 subscripting, and are coerced to pointers when used in expressions.
3257 Artificial arrays most often appear in expressions via the value history
3258 (@pxref{Value History}), after printing one out.)
3260 Sometimes the artificial array mechanism isn't quite enough; in
3261 moderately complex data structures, the elements of interest may not
3262 actually be adjacent---for example, if you're interested in the values
3263 of pointers in an array. One useful work-around in this situation is to
3264 use a convenience variable (@pxref{Convenience Vars}) as a counter in an
3265 expression that prints the first interesting value, and then repeat that
3266 expression via @key{RET}. For instance, suppose you have an array
3267 @code{dtab} of pointers to structures, and you're interested in the
3268 values of a field @code{fv} in each structure. Here's an example of
3269 what you might type:
3278 @node Output formats, Memory, Arrays, Data
3279 @section Output formats
3281 @cindex formatted output
3282 @cindex output formats
3283 By default, _GDBN__ prints a value according to its data type. Sometimes
3284 this is not what you want. For example, you might want to print a number
3285 in hex, or a pointer in decimal. Or you might want to view data in memory
3286 at a certain address as a character string or as an instruction. To do
3287 these things, specify an @dfn{output format} when you print a value.
3289 The simplest use of output formats is to say how to print a value
3290 already computed. This is done by starting the arguments of the
3291 @code{print} command with a slash and a format letter. The format
3292 letters supported are:
3296 Regard the bits of the value as an integer, and print the integer in
3300 Print as integer in signed decimal.
3303 Print as integer in unsigned decimal.
3306 Print as integer in octal.
3309 Print as integer in binary. The letter @samp{t} stands for ``two''.
3312 Print as an address, both absolute in hex and as an offset from the
3313 nearest preceding symbol. This format can be used to discover where (in
3314 what function) an unknown address is located:
3316 (_GDBP__) p/a 0x54320
3317 _0__$3 = 0x54320 <_initialize_vx+396>_1__
3322 Regard as an integer and print it as a character constant.
3325 Regard the bits of the value as a floating point number and print
3326 using typical floating point syntax.
3329 For example, to print the program counter in hex (@pxref{Registers}), type
3336 Note that no space is required before the slash; this is because command
3337 names in _GDBN__ cannot contain a slash.
3339 To reprint the last value in the value history with a different format,
3340 you can use the @code{print} command with just a format and no
3341 expression. For example, @samp{p/x} reprints the last value in hex.
3343 @node Memory, Auto Display, Output formats, Data
3344 @section Examining Memory
3346 @cindex examining memory
3349 @item x/@var{nfu} @var{expr}
3350 The command @code{x} (for `examine') can be used to examine memory
3351 without being constrained by your program's data types. You can specify
3352 the unit size @var{u} of memory to inspect, and a repeat count @var{n} of how
3353 many of those units to display. @code{x} understands the formats
3354 @var{f} used by @code{print}; two additional formats, @samp{s} (string)
3355 and @samp{i} (machine instruction) can be used without specifying a unit
3359 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
3360 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
3361 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
3362 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
3363 @pxref{Registers}) in hexadecimal (@samp{x}).
3365 Since the letters indicating unit sizes are all distinct from the
3366 letters specifying output formats, you don't have to remember whether
3367 unit size or format comes first; either order will work. The output
3368 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
3370 After the format specification, you supply an expression for the address
3371 where _GDBN__ is to begin reading from memory. The expression need not
3372 have a pointer value (though it may); it is always interpreted as an
3373 integer address of a byte of memory. @xref{Expressions} for more
3374 information on expressions.
3376 These are the memory units @var{u} you can specify with the @code{x}
3381 Examine individual bytes.
3384 Examine halfwords (two bytes each).
3387 Examine words (four bytes each).
3390 Many assemblers and cpu designers still use `word' for a 16-bit quantity,
3391 as a holdover from specific predecessor machines of the 1970's that really
3392 did use two-byte words. But more generally the term `word' has always
3393 referred to the size of quantity that a machine normally operates on and
3394 stores in its registers. This is 32 bits for all the machines that _GDBN__
3398 Examine giant words (8 bytes).
3401 You can combine these unit specifications with any of the formats
3402 described for @code{print}. @xref{Output formats}.
3404 @code{x} has two additional output specifications which derive the unit
3405 size from the data inspected:
3409 Print a null-terminated string of characters. Any explicitly specified
3410 unit size is ignored; instead, the unit is however many bytes it takes
3411 to reach a null character (including the null character).
3414 Print a machine instruction in assembler syntax (or nearly). Any
3415 specified unit size is ignored; the number of bytes in an instruction
3416 varies depending on the type of machine, the opcode and the addressing
3417 modes used. The command @code{disassemble} gives an alternative way of
3418 inspecting machine instructions. @xref{Machine Code}.
3421 If you omit either the format @var{f} or the unit size @var{u}, @code{x}
3422 will use the same one that was used last. If you don't use any letters
3423 or digits after the slash, you can omit the slash as well.
3425 You can also omit the address to examine. Then the address used is just
3426 after the last unit examined. This is why string and instruction
3427 formats actually compute a unit-size based on the data: so that the next
3428 string or instruction examined will start in the right place.
3430 When the @code{print} command shows a value that resides in memory,
3431 @code{print} also sets the default address for the @code{x} command.
3432 @code{info line} also sets the default for @code{x}, to the address of
3433 the start of the machine code for the specified line
3434 (@pxref{Machine Code}),
3435 and @code{info breakpoints} sets it to the address of the last
3436 breakpoint listed (@pxref{Set Breaks}).@refill
3438 When you use @key{RET} to repeat an @code{x} command, the address
3439 specified previously (if any) is ignored, so that the repeated command
3440 examines the successive locations in memory rather than the same ones.
3442 You can examine several consecutive units of memory with one command by
3443 writing a repeat-count after the slash (before the format letters, if
3444 any). Omitting the repeat count @var{n} displays one unit of the
3445 appropriate size. The repeat count must be a decimal integer. It has
3446 the same effect as repeating the @code{x} command @var{n} times except
3447 that the output may be more compact, with several units per line. For
3455 prints ten instructions starting with the one to be executed next in the
3456 selected frame. After doing this, you could print a further seven
3464 ---where the format and address are allowed to default.
3466 @cindex @code{$_}, @code{$__}, and value history
3467 The addresses and contents printed by the @code{x} command are not put
3468 in the value history because there is often too much of them and they
3469 would get in the way. Instead, _GDBN__ makes these values available for
3470 subsequent use in expressions as values of the convenience variables
3471 @code{$_} and @code{$__}. After an @code{x} command, the last address
3472 examined is available for use in expressions in the convenience variable
3473 @code{$_}. The contents of that address, as examined, are available in
3474 the convenience variable @code{$__}.
3476 If the @code{x} command has a repeat count, the address and contents saved
3477 are from the last memory unit printed; this is not the same as the last
3478 address printed if several units were printed on the last line of output.
3480 @node Auto Display, Print Settings, Memory, Data
3481 @section Automatic Display
3482 @cindex automatic display
3483 @cindex display of expressions
3485 If you find that you want to print the value of an expression frequently
3486 (to see how it changes), you might want to add it to the @dfn{automatic
3487 display list} so that _GDBN__ will print its value each time the program stops.
3488 Each expression added to the list is given a number to identify it;
3489 to remove an expression from the list, you specify that number.
3490 The automatic display looks like this:
3494 3: bar[5] = (struct hack *) 0x3804
3498 showing item numbers, expressions and their current values. As with
3499 displays you request manually using @code{x} or @code{print}, you can
3500 specify the output format you prefer; in fact, @code{display} decides
3501 whether to use @code{print} or @code{x} depending on how elaborate your
3502 format specification is---it uses @code{x} if you specify a unit size,
3503 or one of the two formats (@samp{i} and @samp{s}) that are only
3504 supported by @code{x}; otherwise it uses @code{print}.
3507 @item display @var{exp}
3509 Add the expression @var{exp} to the list of expressions to display
3510 each time the program stops. @xref{Expressions}.
3512 @code{display} will not repeat if you press @key{RET} again after using it.
3514 @item display/@var{fmt} @var{exp}
3515 For @var{fmt} specifying only a display format and not a size or
3516 count, add the expression @var{exp} to the auto-display list but
3517 arranges to display it each time in the specified format @var{fmt}.
3518 @xref{Output formats}.
3520 @item display/@var{fmt} @var{addr}
3521 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
3522 number of units, add the expression @var{addr} as a memory address to
3523 be examined each time the program stops. Examining means in effect
3524 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory}.
3527 For example, @samp{display/i $pc} can be helpful, to see the machine
3528 instruction about to be executed each time execution stops (@samp{$pc}
3529 is a common name for the program counter; @pxref{Registers}).
3532 @item undisplay @var{dnums}@dots{}
3533 @itemx delete display @var{dnums}@dots{}
3534 @kindex delete display
3536 Remove item numbers @var{dnums} from the list of expressions to display.
3538 @code{undisplay} will not repeat if you press @key{RET} after using it.
3539 (Otherwise you would just get the error @samp{No display number @dots{}}.)
3541 @item disable display @var{dnums}@dots{}
3542 @kindex disable display
3543 Disable the display of item numbers @var{dnums}. A disabled display
3544 item is not printed automatically, but is not forgotten. It may be
3545 enabled again later.
3547 @item enable display @var{dnums}@dots{}
3548 @kindex enable display
3549 Enable display of item numbers @var{dnums}. It becomes effective once
3550 again in auto display of its expression, until you specify otherwise.
3553 Display the current values of the expressions on the list, just as is
3554 done when the program stops.
3557 @kindex info display
3558 Print the list of expressions previously set up to display
3559 automatically, each one with its item number, but without showing the
3560 values. This includes disabled expressions, which are marked as such.
3561 It also includes expressions which would not be displayed right now
3562 because they refer to automatic variables not currently available.
3565 If a display expression refers to local variables, then it does not make
3566 sense outside the lexical context for which it was set up. Such an
3567 expression is disabled when execution enters a context where one of its
3568 variables is not defined. For example, if you give the command
3569 @code{display last_char} while inside a function with an argument
3570 @code{last_char}, then this argument will be displayed while the program
3571 continues to stop inside that function. When it stops elsewhere---where
3572 there is no variable @code{last_char}---display is disabled. The next time
3573 your program stops where @code{last_char} is meaningful, you can enable the
3574 display expression once again.
3576 @node Print Settings, Value History, Auto Display, Data
3577 @section Print Settings
3579 @cindex format options
3580 @cindex print settings
3581 _GDBN__ provides the following ways to control how arrays, structures,
3582 and symbols are printed.
3585 These settings are useful for debugging programs in any language:
3588 @item set print address
3589 @item set print address on
3590 @kindex set print address
3591 _GDBN__ will print memory addresses showing the location of stack
3592 traces, structure values, pointer values, breakpoints, and so forth,
3593 even when it also displays the contents of those addresses. The default
3594 is on. For example, this is what a stack frame display looks like, with
3595 @code{set print address on}:
3598 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
3600 530 if (lquote != def_lquote)
3603 @item set print address off
3604 Do not print addresses when displaying their contents. For example,
3605 this is the same stack frame displayed with @code{set print address off}:
3607 (_GDBP__) set print addr off
3609 #0 set_quotes (lq="<<", rq=">>") at input.c:530
3610 530 if (lquote != def_lquote)
3613 @item show print address
3614 @kindex show print address
3615 Show whether or not addresses are to be printed.
3617 @item set print array
3618 @itemx set print array on
3619 @kindex set print array
3620 _GDBN__ will pretty print arrays. This format is more convenient to read,
3621 but uses more space. The default is off.
3623 @item set print array off.
3624 Return to compressed format for arrays.
3626 @item show print array
3627 @kindex show print array
3628 Show whether compressed or pretty format is selected for displaying
3631 @item set print elements @var{number-of-elements}
3632 @kindex set print elements
3633 If _GDBN__ is printing a large array, it will stop printing after it has
3634 printed the number of elements set by the @code{set print elements} command.
3635 This limit also applies to the display of strings.
3637 @item show print elements
3638 @kindex show print elements
3639 Display the number of elements of a large array that _GDBN__ will print
3640 before losing patience.
3642 @item set print pretty on
3643 @kindex set print pretty
3644 Cause _GDBN__ to print structures in an indented format with one member per
3658 @item set print pretty off
3659 Cause _GDBN__ to print structures in a compact format, like this:
3662 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, meat \
3667 This is the default format.
3669 @item show print pretty
3670 @kindex show print pretty
3671 Show which format _GDBN__ will use to print structures.
3673 @item set print sevenbit-strings on
3674 @kindex set print sevenbit-strings
3675 Print using only seven-bit characters; if this option is set,
3676 _GDBN__ will display any eight-bit characters (in strings or character
3677 values) using the notation @code{\}@var{nnn}. For example, @kbd{M-a} is
3678 displayed as @code{\341}.
3680 @item set print sevenbit-strings off
3681 Print using either seven-bit or eight-bit characters, as required. This
3684 @item show print sevenbit-strings
3685 @kindex show print sevenbit-strings
3686 Show whether or not _GDBN__ will print only seven-bit characters.
3688 @item set print union on
3689 @kindex set print union
3690 Tell _GDBN__ to print unions which are contained in structures. This is the
3693 @item set print union off
3694 Tell _GDBN__ not to print unions which are contained in structures.
3696 @item show print union
3697 @kindex show print union
3698 Ask _GDBN__ whether or not it will print unions which are contained in
3701 For example, given the declarations
3704 typedef enum @{Tree, Bug@} Species;
3705 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
3706 typedef enum @{Caterpillar, Cocoon, Butterfly@} Bug_forms;
3716 struct thing foo = @{Tree, @{Acorn@}@};
3720 with @code{set print union on} in effect @samp{p foo} would print
3723 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
3727 and with @code{set print union off} in effect it would print
3730 $1 = @{it = Tree, form = @{...@}@}
3735 These settings are of interest when debugging C++ programs:
3738 @item set print demangle
3739 @itemx set print demangle on
3740 @kindex set print demangle
3741 Print C++ names in their source form rather than in the mangled form
3742 in which they are passed to the assembler and linker for type-safe linkage.
3745 @item show print demangle
3746 @kindex show print demangle
3747 Show whether C++ names will be printed in mangled or demangled form.
3749 @item set print asm-demangle
3750 @itemx set print asm-demangle on
3751 @kindex set print asm-demangle
3752 Print C++ names in their source form rather than their mangled form, even
3753 in assembler code printouts such as instruction disassemblies.
3756 @item show print asm-demangle
3757 @kindex show print asm-demangle
3758 Show whether C++ names in assembly listings will be printed in mangled
3761 @item set print object
3762 @itemx set print object on
3763 @kindex set print object
3764 When displaying a pointer to an object, identify the @emph{actual}
3765 (derived) type of the object rather than the @emph{declared} type, using
3766 the virtual function table.
3768 @item set print object off
3769 Display only the declared type of objects, without reference to the
3770 virtual function table. This is the default setting.
3772 @item show print object
3773 @kindex show print object
3774 Show whether actual, or declared, object types will be displayed.
3776 @item set print vtbl
3777 @itemx set print vtbl on
3778 @kindex set print vtbl
3779 Pretty print C++ virtual function tables. The default is off.
3781 @item set print vtbl off
3782 Do not pretty print C++ virtual function tables.
3784 @item show print vtbl
3785 @kindex show print vtbl
3786 Show whether C++ virtual function tables are pretty printed, or not.
3790 @node Value History, Convenience Vars, Print Settings, Data
3791 @section Value History
3793 @cindex value history
3794 Values printed by the @code{print} command are saved in _GDBN__'s @dfn{value
3795 history} so that you can refer to them in other expressions. Values are
3796 kept until the symbol table is re-read or discarded (for example with
3797 the @code{file} or @code{symbol-file} commands). When the symbol table
3798 changes, the value history is discarded, since the values may contain
3799 pointers back to the types defined in the symbol table.
3803 @cindex history number
3804 The values printed are given @dfn{history numbers} for you to refer to them
3805 by. These are successive integers starting with one. @code{print} shows you
3806 the history number assigned to a value by printing @samp{$@var{num} = }
3807 before the value; here @var{num} is the history number.
3809 To refer to any previous value, use @samp{$} followed by the value's
3810 history number. The way @code{print} labels its output is designed to
3811 remind you of this. Just @code{$} refers to the most recent value in
3812 the history, and @code{$$} refers to the value before that.
3813 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
3814 is the value just prior to @code{$$}, @code{$$1} is equivalent to
3815 @code{$$}, and @code{$$0} is equivalent to @code{$}.
3817 For example, suppose you have just printed a pointer to a structure and
3818 want to see the contents of the structure. It suffices to type
3824 If you have a chain of structures where the component @code{next} points
3825 to the next one, you can print the contents of the next one with this:
3832 You can print successive links in the chain by repeating this
3833 command---which you can do by just typing @key{RET}.
3835 Note that the history records values, not expressions. If the value of
3836 @code{x} is 4 and you type these commands:
3844 then the value recorded in the value history by the @code{print} command
3845 remains 4 even though the value of @code{x} has changed.
3850 Print the last ten values in the value history, with their item numbers.
3851 This is like @samp{p@ $$9} repeated ten times, except that @code{show
3852 values} does not change the history.
3854 @item show values @var{n}
3855 Print ten history values centered on history item number @var{n}.
3858 Print ten history values just after the values last printed. If no more
3859 values are available, produces no display.
3862 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
3863 same effect as @samp{show values +}.
3865 @node Convenience Vars, Registers, Value History, Data
3866 @section Convenience Variables
3868 @cindex convenience variables
3869 _GDBN__ provides @dfn{convenience variables} that you can use within
3870 _GDBN__ to hold on to a value and refer to it later. These variables
3871 exist entirely within _GDBN__; they are not part of your program, and
3872 setting a convenience variable has no direct effect on further execution
3873 of your program. That's why you can use them freely.
3875 Convenience variables are prefixed with @samp{$}. Any name preceded by
3876 @samp{$} can be used for a convenience variable, unless it is one of
3877 the predefined machine-specific register names (@pxref{Registers}).
3878 (Value history references, in contrast, are @emph{numbers} preceded
3879 by @samp{$}. @xref{Value History}.)
3881 You can save a value in a convenience variable with an assignment
3882 expression, just as you would set a variable in your program. Example:
3885 set $foo = *object_ptr
3889 would save in @code{$foo} the value contained in the object pointed to by
3892 Using a convenience variable for the first time creates it; but its value
3893 is @code{void} until you assign a new value. You can alter the value with
3894 another assignment at any time.
3896 Convenience variables have no fixed types. You can assign a convenience
3897 variable any type of value, including structures and arrays, even if
3898 that variable already has a value of a different type. The convenience
3899 variable, when used as an expression, has the type of its current value.
3902 @item show convenience
3903 @kindex show convenience
3904 Print a list of convenience variables used so far, and their values.
3905 Abbreviated @code{show con}.
3908 One of the ways to use a convenience variable is as a counter to be
3909 incremented or a pointer to be advanced. For example, to print
3910 a field from successive elements of an array of structures:
3914 print bar[$i++]->contents
3915 @i{@dots{} repeat that command by typing @key{RET}.}
3918 Some convenience variables are created automatically by _GDBN__ and given
3919 values likely to be useful.
3924 The variable @code{$_} is automatically set by the @code{x} command to
3925 the last address examined (@pxref{Memory}). Other commands which
3926 provide a default address for @code{x} to examine also set @code{$_}
3927 to that address; these commands include @code{info line} and @code{info
3928 breakpoint}. The type of @code{$_} is @code{void *} except when set by the
3929 @code{x} command, in which case it is a pointer to the type of @code{$__}.
3933 The variable @code{$__} is automatically set by the @code{x} command
3934 to the value found in the last address examined. Its type is chosen
3935 to match the format in which the data was printed.
3938 @node Registers, Floating Point Hardware, Convenience Vars, Data
3942 You can refer to machine register contents, in expressions, as variables
3943 with names starting with @samp{$}. The names of registers are different
3944 for each machine; use @code{info registers} to see the names used on
3948 @item info registers
3949 @kindex info registers
3950 Print the names and values of all registers except floating-point
3951 registers (in the selected stack frame).
3953 @item info all-registers
3954 @kindex info all-registers
3955 @cindex floating point registers
3956 Print the names and values of all registers, including floating-point
3959 @item info registers @var{regname}
3960 Print the relativized value of register @var{regname}. @var{regname}
3961 may be any register name valid on the machine you are using, with
3962 or without the initial @samp{$}.
3965 The register names @code{$pc} and @code{$sp} are used on most machines
3966 for the program counter register and the stack pointer. For example,
3967 you could print the program counter in hex with
3973 or print the instruction to be executed next with
3979 or add four to the stack pointer with
3985 The last is a way of removing one word from the stack, on machines where
3986 stacks grow downward in memory (most machines, nowadays). This assumes
3987 that the innermost stack frame is selected; setting @code{$sp} is
3988 not allowed when other stack frames are selected. (To pop entire frames
3989 off the stack, regardless of machine architecture, use @code{return};
3992 Often @code{$fp} is used for a register that contains a pointer to the
3993 current stack frame, and @code{$ps} is sometimes used for a register
3994 that contains the processor status. These standard register names may
3995 be available on your machine even though the @code{info registers}
3996 command shows other names. For example, on the SPARC, @code{info
3997 registers} displays the processor status register as @code{$psr} but you
3998 can also refer to it as @code{$ps}.
4000 _GDBN__ always considers the contents of an ordinary register as an
4001 integer when the register is examined in this way. Some machines have
4002 special registers which can hold nothing but floating point; these
4003 registers are considered to have floating point values. There is no way
4004 to refer to the contents of an ordinary register as floating point value
4005 (although you can @emph{print} it as a floating point value with
4006 @samp{print/f $@var{regname}}).
4008 Some registers have distinct ``raw'' and ``virtual'' data formats. This
4009 means that the data format in which the register contents are saved by
4010 the operating system is not the same one that your program normally
4011 sees. For example, the registers of the 68881 floating point
4012 coprocessor are always saved in ``extended'' (raw) format, but all C
4013 programs expect to work with ``double'' (virtual) format. In such
4014 cases, _GDBN__ normally works with the virtual format only (the format that
4015 makes sense for your program), but the @code{info registers} command
4016 prints the data in both formats.
4018 Normally, register values are relative to the selected stack frame
4019 (@pxref{Selection}). This means that you get the value that the
4020 register would contain if all stack frames farther in were exited and
4021 their saved registers restored. In order to see the true contents of
4022 hardware registers, you must select the innermost frame (with
4025 However, _GDBN__ must deduce where registers are saved, from the machine
4026 code generated by your compiler. If some registers are not saved, or if
4027 _GDBN__ is unable to locate the saved registers, the selected stack
4028 frame will make no difference.
4030 @node Floating Point Hardware, , Registers, Data
4031 @section Floating Point Hardware
4032 @cindex floating point
4033 Depending on the host machine architecture, _GDBN__ may be able to give
4034 you more information about the status of the floating point hardware.
4039 If available, provides hardware-dependent information about the floating
4040 point unit. The exact contents and layout vary depending on the
4041 floating point chip.
4043 @c FIXME: this is a cop-out. Try to get examples, explanations. Only
4044 @c FIXME...supported currently on arm's and 386's. Mark properly with
4045 @c FIXME... m4 macros to isolate general statements from hardware-dep,
4046 @c FIXME... at that point.
4048 @node Languages, Symbols, Data, Top
4049 @chapter Using _GDBN__ with Different Languages
4052 Although programming languages generally have common aspects, they are
4053 rarely expressed in the same manner. For instance, in ANSI C,
4054 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
4055 Modula-2, it is accomplished by @code{p^}. Values can also be
4056 represented (and displayed) differently. Hex numbers in C are written
4057 like @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
4059 @cindex working language
4060 Language-specific information is built into _GDBN__ for some languages,
4061 allowing you to express operations like the above in the program's
4062 native language, and allowing _GDBN__ to output values in a manner
4063 consistent with the syntax of the program's native language. The
4064 language you use to build expressions, called the @dfn{working
4065 language}, can be selected manually, or _GDBN__ can set it
4069 * Setting:: Switching between source languages
4070 * Show:: Displaying the language
4071 * Checks:: Type and Range checks
4072 * Support:: Supported languages
4075 @node Setting, Show, Languages, Languages
4076 @section Switching between source languages
4078 There are two ways to control the working language---either have _GDBN__
4079 set it automatically, or select it manually yourself. You can use the
4080 @code{set language} command for either purpose. On startup, _GDBN__
4081 defaults to setting the language automatically.
4084 * Manually:: Setting the working language manually
4085 * Automatically:: Having _GDBN__ infer the source language
4088 @node Manually, Automatically, Setting, Setting
4089 @subsection Setting the working language
4091 @kindex set language
4092 To set the language, issue the command @samp{set language @var{lang}},
4093 where @var{lang} is the name of a language: @code{c} or @code{modula-2}.
4094 For a list of the supported languages, type @samp{set language}.
4096 Setting the language manually prevents _GDBN__ from updating the working
4097 language automatically. This can lead to confusion if you try
4098 to debug a program when the working language is not the same as the
4099 source language, when an expression is acceptable to both
4100 languages---but means different things. For instance, if the current
4101 source file were written in C, and _GDBN__ was parsing Modula-2, a
4109 might not have the effect you intended. In C, this means to add
4110 @code{b} and @code{c} and place the result in @code{a}. The result
4111 printed would be the value of @code{a}. In Modula-2, this means to compare
4112 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
4114 If you allow _GDBN__ to set the language automatically, then
4115 you can count on expressions evaluating the same way in your debugging
4116 session and in your program.
4118 @node Automatically, , Manually, Setting
4119 @subsection Having _GDBN__ infer the source language
4121 To have _GDBN__ set the working language automatically, use @samp{set
4122 language local} or @samp{set language auto}. _GDBN__ then infers the
4123 language that a program was written in by looking at the name of its
4124 source files, and examining their extensions:
4128 Modula-2 source file
4132 C or C++ source file.
4135 This information is recorded for each function or procedure in a source
4136 file. When your program stops in a frame (usually by encountering a
4137 breakpoint), _GDBN__ sets the working language to the language recorded
4138 for the function in that frame. If the language for a frame is unknown
4139 (that is, if the function or block corresponding to the frame was
4140 defined in a source file that does not have a recognized extension), the
4141 current working language is not changed, and _GDBN__ issues a warning.
4143 This may not seem necessary for most programs, which are written
4144 entirely in one source language. However, program modules and libraries
4145 written in one source language can be used by a main program written in
4146 a different source language. Using @samp{set language auto} in this
4147 case frees you from having to set the working language manually.
4149 @node Show, Checks, Setting, Languages
4150 @section Displaying the language
4152 The following commands will help you find out which language is the
4153 working language, and also what language source files were written in.
4155 @kindex show language
4160 Display the current working language. This is the
4161 language you can use with commands such as @code{print} to
4162 build and compute expressions that may involve variables in the program.
4165 Among the other information listed here (@pxref{Frame Info,,Information
4166 about a Frame}) is the source language for this frame. This is the
4167 language that will become the working language if you ever use an
4168 identifier that is in this frame.
4171 Among the other information listed here (@pxref{Symbols,,Examining the
4172 Symbol Table}) is the source language of this source file.
4176 @node Checks, Support, Show, Languages
4177 @section Type and range Checking
4180 @emph{Warning:} In this release, the _GDBN__ commands for type and range
4181 checking are included, but they do not yet have any effect. This
4182 section documents the intended facilities.
4184 @c FIXME remove warning when type/range code added
4186 Some languages are designed to guard you against making seemingly common
4187 errors through a series of compile- and run-time checks. These include
4188 checking the type of arguments to functions and operators, and making
4189 sure mathematical overflows are caught at run time. Checks such as
4190 these help to ensure a program's correctness once it has been compiled
4191 by eliminating type mismatches, and providing active checks for range
4192 errors when the program is running.
4194 _GDBN__ can check for conditions like the above if you wish.
4195 Although _GDBN__ will not check the statements in your program, it
4196 can check expressions entered directly into _GDBN__ for evaluation via
4197 the @code{print} command, for example. As with the working language,
4198 _GDBN__ can also decide whether or not to check automatically based on
4199 the source language of the program being debugged.
4200 @xref{Support,,Supported Languages}, for the default settings
4201 of supported languages.
4204 * Type Checking:: An overview of type checking
4205 * Range Checking:: An overview of range checking
4208 @cindex type checking
4209 @cindex checks, type
4210 @node Type Checking, Range Checking, Checks, Checks
4211 @subsection An overview of type checking
4213 Some languages, such as Modula-2, are strongly typed, meaning that the
4214 arguments to operators and functions have to be of the correct type,
4215 otherwise an error occurs. These checks prevent type mismatch
4216 errors from ever causing any run-time problems. For example,
4223 The second example fails because the @code{CARDINAL} 1 is not
4224 type-compatible with the @code{REAL} 2.3.
4226 For expressions you use in _GDBN__ commands, you can tell the _GDBN__
4227 type checker to skip checking; to treat any mismatches as errors and
4228 abandon the expression; or only issue warnings when type mismatches
4229 occur, but evaluate the expression anyway. When you choose the last of
4230 these, _GDBN__ evaluates expressions like the second example above, but
4231 also issues a warning.
4233 Even though you may turn type checking off, other type-based reasons may
4234 prevent _GDBN__ from evaluating an expression. For instance, _GDBN__ does not
4235 know how to add an @code{int} and a @code{struct foo}. These particular
4236 type errors have nothing to do with the language in use, and usually
4237 arise from expressions, such as the one described above, which make
4238 little sense to evaluate anyway.
4240 Each language defines to what degree it is strict about type. For
4241 instance, both Modula-2 and C require the arguments to arithmetical
4242 operators to be numbers. In C, enumerated types and pointers can be
4243 represented as numbers, so that they are valid arguments to mathematical
4244 operators. @xref{Support,,Supported Languages}, for futher
4245 details on specific languages.
4247 _GDBN__ provides some additional commands for controlling the type checker:
4250 @kindex set check type
4251 @kindex show check type
4253 @item set check type auto
4254 Set type checking on or off based on the current working language.
4255 @xref{Support,,Supported Languages}, for the default settings for
4258 @item set check type on
4259 @itemx set check type off
4260 Set type checking on or off, overriding the default setting for the
4261 current working language. Issue a warning if the setting does not
4262 match the language's default. If any type mismatches occur in
4263 evaluating an expression while typechecking is on, _GDBN__ prints a
4264 message and aborts evaluation of the expression.
4266 @item set check type warn
4267 Cause the type checker to issue warnings, but to always attempt to
4268 evaluate the expression. Evaluating the expression may still
4269 be impossible for other reasons. For example, _GDBN__ cannot add
4270 numbers and structures.
4273 Show the current setting of the type checker, and whether or not _GDBN__ is
4274 setting it automatically.
4277 @cindex range checking
4278 @cindex checks, range
4279 @node Range Checking, , Type Checking, Checks
4280 @subsection An overview of Range Checking
4282 In some languages (such as Modula-2), it is an error to exceed the
4283 bounds of a type; this is enforced with run-time checks. Such range
4284 checking is meant to ensure program correctness by making sure
4285 computations do not overflow, or indices on an array element access do
4286 not exceed the bounds of the array.
4288 For expressions you use in _GDBN__ commands, you can tell _GDBN__ to
4289 ignore range errors; to always treat them as errors and abandon the
4290 expression; or to issue warnings when a range error occurs but evaluate
4291 the expression anyway.
4293 A range error can result from numerical overflow, from exceeding an
4294 array index bound, or when you type in a constant that is not a member
4295 of any type. Some languages, however, do not treat overflows as an
4296 error. In many implementations of C, mathematical overflow causes the
4297 result to ``wrap around'' to lower values---for example, if @var{m} is
4298 the largest integer value, and @var{s} is the smallest, then
4300 @var{m} + 1 @result{} @var{s}
4303 This, too, is specific to individual languages, and in some cases
4304 specific to individual compilers or machines. @xref{Support,,
4305 Supported Languages}, for further details on specific languages.
4307 _GDBN__ provides some additional commands for controlling the range checker:
4310 @kindex set check range
4311 @kindex show check range
4313 @item set check range auto
4314 Set range checking on or off based on the current working language.
4315 @xref{Support,,Supported Languages}, for the default settings for
4318 @item set check range on
4319 @itemx set check range off
4320 Set range checking on or off, overriding the default setting for the
4321 current working language. A warning is issued if the setting does not
4322 match the language's default. If a range error occurs, then a message
4323 is printed and evaluation of the expression is aborted.
4325 @item set check range warn
4326 Output messages when the _GDBN__ range checker detects a range error,
4327 but attempt to evaluate the expression anyway. Evaluating the
4328 expression may still be impossible for other reasons, such as accessing
4329 memory that the process does not own (a typical example from many UNIX
4333 Show the current setting of the range checker, and whether or not it is
4334 being set automatically by _GDBN__.
4337 @node Support, , Checks, Languages
4338 @section Supported Languages
4340 _GDBN__ _GDB_VN__ supports C, C++, and Modula-2. The syntax for C and C++ is
4341 so closely related that _GDBN__ does not distinguish the two. Some
4342 _GDBN__ features may be used in expressions regardless of the language
4343 you use: the _GDBN__ @code{@@} and @code{::} operators, and the
4344 @samp{@{type@}addr} construct (@pxref{Expressions}) can be used with the constructs of
4345 any of the supported languages.
4347 The following sections detail to what degree each of these
4348 source languages is supported by _GDBN__. These sections are
4349 not meant to be language tutorials or references, but serve only as a
4350 reference guide to what the _GDBN__ expression parser will accept, and
4351 what input and output formats should look like for different languages.
4352 There are many good books written on each of these languages; please
4353 look to these for a language reference or tutorial.
4357 * Modula-2:: Modula-2
4360 @node C, Modula-2, Support, Support
4361 @subsection C and C++
4364 @cindex expressions in C or C++
4365 Since C and C++ are so closely related, _GDBN__ does not distinguish
4366 between them when interpreting the expressions recognized in _GDBN__
4372 The C++ debugging facilities are jointly implemented by the GNU C++
4373 compiler and _GDBN__. Therefore, to debug your C++ code effectively,
4374 you must compile your C++ programs with the GNU C++ compiler,
4379 * C Operators:: C and C++ Operators
4380 * C Constants:: C and C++ Constants
4381 * Cplusplus expressions:: C++ Expressions
4382 * C Defaults:: Default settings for C and C++
4383 * C Checks:: C and C++ Type and Range Checks
4384 * Debugging C:: _GDBN__ and C
4385 * Debugging C plus plus:: Special features for C++
4388 @cindex C and C++ operators
4389 @node C Operators, C Constants, C, C
4390 @subsubsection C and C++ Operators
4392 Operators must be defined on values of specific types. For instance,
4393 @code{+} is defined on numbers, but not on structures. Operators are
4394 often defined on groups of types. For the purposes of C and C++, the
4395 following definitions hold:
4399 @emph{Integral types} include @code{int} with any of its storage-class
4400 specifiers, @code{char}, and @code{enum}s.
4403 @emph{Floating-point types} include @code{float} and @code{double}.
4406 @emph{Pointer types} include all types defined as @code{(@var{type}
4410 @emph{Scalar types} include all of the above.
4415 The following operators are supported. They are listed here
4416 in order of increasing precedence:
4421 The comma or sequencing operator. Expressions in a comma-separated list
4422 are evaluated from left to right, with the result of the entire
4423 expression being the last expression evaluated.
4426 Assignment. The value of an assignment expression is the value
4427 assigned. Defined on scalar types.
4430 Used in an expression of the form @var{a} @var{op}@code{=} @var{b}, and
4431 translated to @var{a} @code{=} @var{a op b}. @var{op}@code{=} and
4432 @code{=} have the same precendence. @var{op} is any one of the
4433 operators @code{|}, @code{^}, @code{&}, @code{<<}, @code{>>}, @code{+},
4434 @code{-}, @code{*}, @code{/}, @code{%}.
4437 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
4438 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
4442 Logical OR. Defined on integral types.
4445 Logical AND. Defined on integral types.
4448 Bitwise OR. Defined on integral types.
4451 Bitwise exclusive-OR. Defined on integral types.
4454 Bitwise AND. Defined on integral types.
4457 Equality and inequality. Defined on scalar types. The value of these
4458 expressions is 0 for false and non-zero for true.
4460 @item <@r{, }>@r{, }<=@r{, }>=
4461 Less than, greater than, less than or equal, greater than or equal.
4462 Defined on scalar types. The value of these expressions is 0 for false
4463 and non-zero for true.
4466 left shift, and right shift. Defined on integral types.
4469 The _GDBN__ ``artificial array'' operator (@pxref{Expressions}).
4472 Addition and subtraction. Defined on integral types, floating-point types and
4475 @item *@r{, }/@r{, }%
4476 Multiplication, division, and modulus. Multiplication and division are
4477 defined on integral and floating-point types. Modulus is defined on
4481 Increment and decrement. When appearing before a variable, the
4482 operation is performed before the variable is used in an expression;
4483 when appearing after it, the variable's value is used before the
4484 operation takes place.
4487 Pointer dereferencing. Defined on pointer types. Same precedence as
4491 Address operator. Defined on variables. Same precedence as @code{++}.
4494 Negative. Defined on integral and floating-point types. Same
4495 precedence as @code{++}.
4498 Logical negation. Defined on integral types. Same precedence as
4502 Bitwise complement operator. Defined on integral types. Same precedence as
4506 Structure member, and pointer-to-structure member. For convenience,
4507 _GDBN__ regards the two as equivalent, choosing whether to dereference a
4508 pointer based on the stored type information.
4509 Defined on @code{struct}s and @code{union}s.
4512 Array indexing. @code{@var{a}[@var{i}]} is defined as
4513 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
4516 Function parameter list. Same precedence as @code{->}.
4519 C++ scope resolution operator. Defined on
4520 @code{struct}, @code{union}, and @code{class} types.
4523 The _GDBN__ scope operator (@pxref{Expressions}). Same precedence as
4524 @code{::}, above. _1__
4527 @cindex C and C++ constants
4528 @node C Constants, Cplusplus expressions, C Operators, C
4529 @subsubsection C and C++ Constants
4531 _GDBN__ allows you to express the constants of C and C++ in the
4537 Integer constants are a sequence of digits. Octal constants are
4538 specified by a leading @samp{0} (ie. zero), and hexadecimal constants by
4539 a leading @samp{0x} or @samp{0X}. Constants may also end with an
4540 @samp{l}, specifying that the constant should be treated as a
4544 Floating point constants are a sequence of digits, followed by a decimal
4545 point, followed by a sequence of digits, and optionally followed by an
4546 exponent. An exponent is of the form:
4547 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
4548 sequence of digits. The @samp{+} is optional for positive exponents.
4551 Enumerated constants consist of enumerated identifiers, or their
4552 integral equivalents.
4555 Character constants are a single character surrounded by single quotes
4556 (@code{'}), or a number---the ordinal value of the corresponding character
4557 (usually its @sc{ASCII} value). Within quotes, the single character may
4558 be represented by a letter or by @dfn{escape sequences}, which are of
4559 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
4560 of the character's ordinal value; or of the form @samp{\@var{x}}, where
4561 @samp{@var{x}} is a predefined special character---for example,
4562 @samp{\n} for newline.
4565 String constants are a sequence of character constants surrounded
4566 by double quotes (@code{"}).
4569 Pointer constants are an integral value.
4574 @node Cplusplus expressions, C Defaults, C Constants, C
4575 @subsubsection C++ Expressions
4577 @cindex expressions in C++
4578 _GDBN__'s expression handling has the following extensions to
4579 interpret a significant subset of C++ expressions:
4583 @cindex member functions
4585 Member function calls are allowed; you can use expressions like
4587 count = aml->GetOriginal(x, y)
4591 @cindex namespace in C++
4593 While a member function is active (in the selected stack frame), your
4594 expressions have the same namespace available as the member function;
4595 that is, _GDBN__ allows implicit references to the class instance
4596 pointer @code{this} following the same rules as C++.
4598 @cindex call overloaded functions
4599 @cindex type conversions in C++
4601 You can call overloaded functions; _GDBN__ will resolve the function
4602 call to the right definition, with one restriction---you must use
4603 arguments of the type required by the function that you want to call.
4604 _GDBN__ will not perform conversions requiring constructors or
4605 user-defined type operators.
4607 @cindex reference declarations
4609 _GDBN__ understands variables declared as C++ references; you can use them in
4610 expressions just as you do in C++ source---they are automatically
4613 In the parameter list shown when _GDBN__ displays a frame, the values of
4614 reference variables are not displayed (unlike other variables); this
4615 avoids clutter, since references are often used for large structures.
4616 The @emph{address} of a reference variable is always shown, unless
4617 you've specified @samp{set print address off}.
4621 _GDBN__ supports the C++ name resolution operator @code{::}---your
4622 expressions can use it just as expressions in your program do. Since
4623 one scope may be defined in another, you can use @code{::} repeatedly if
4624 necessary, for example in an expression like
4625 @samp{@var{scope1}::@var{scope2}::@var{name}}. _GDBN__ also allows
4626 resolving name scope by reference to source files, in both C and C++
4627 debugging; @pxref{Variables}.
4632 @node C Defaults, C Checks, Cplusplus expressions, C
4633 @subsubsection C and C++ Defaults
4634 @cindex C and C++ defaults
4636 If you allow _GDBN__ to set type and range checking automatically, they
4637 both default to @code{off} whenever the working language changes to
4638 C/C++. This happens regardless of whether you, or _GDBN__,
4639 selected the working language.
4641 If you allow _GDBN__ to set the language automatically, it sets the
4642 working language to C/C++ on entering code compiled from a source file
4643 whose name ends with @file{.c} or @file{.cc}.
4644 @xref{Automatically,,Having _GDBN__ infer the source language}, for
4647 @node C Checks, Debugging C, C Defaults, C
4648 @subsubsection C and C++ Type and Range Checks
4649 @cindex C and C++ checks
4652 @emph{Warning:} in this release, _GDBN__ does not yet perform type or
4655 @c FIXME remove warning when type/range checks added
4657 By default, when _GDBN__ parses C or C++ expressions, type checking
4658 is not used. However, if you turn type checking on, _GDBN__ will
4659 consider two variables type equivalent if:
4663 The two variables are structured and have the same structure, union, or
4667 Two two variables have the same type name, or types that have been
4668 declared equivalent through @code{typedef}.
4671 @c leaving this out because neither J Gilmore nor R Pesch understand it.
4674 The two @code{struct}, @code{union}, or @code{enum} variables are
4675 declared in the same declaration. (Note: this may not be true for all C
4681 Range checking, if turned on, is done on mathematical operations. Array
4682 indices are not checked, since they are often used to index a pointer
4683 that is not itself an array.
4685 @node Debugging C, Debugging C plus plus, C Checks, C
4686 @subsubsection _GDBN__ and C
4688 The @code{set print union} and @code{show print union} commands apply to
4689 the @code{union} type. When set to @samp{on}, any @code{union} that is
4690 inside a @code{struct} or @code{class} will also be printed.
4691 Otherwise, it will appear as @samp{@{...@}}.
4693 The @code{@@} operator aids in the debugging of dynamic arrays, formed
4694 with pointers and a memory allocation function. (@pxref{Expressions})
4696 @node Debugging C plus plus, , Debugging C, C
4697 @subsubsection _GDBN__ Commands for C++
4699 @cindex commands for C++
4700 Some _GDBN__ commands are particularly useful with C++, and some are
4701 designed specifically for use with C++. Here is a summary:
4704 @cindex break in overloaded functions
4705 @item @r{breakpoint menus}
4706 When you want a breakpoint in a function whose name is overloaded,
4707 _GDBN__'s breakpoint menus help you specify which function definition
4708 you want. @xref{Breakpoint Menus}.
4710 @cindex overloading in C++
4711 @item rbreak @var{regex}
4712 Setting breakpoints using regular expressions is helpful for setting
4713 breakpoints on overloaded functions that are not members of any special
4717 @cindex C++ exception handling
4718 @item catch @var{exceptions}
4720 Debug C++ exception handling using these commands. @xref{Exception Handling}.
4723 @item ptype @var{typename}
4724 Print inheritance relationships as well as other information for type
4728 @cindex C++ symbol display
4729 @item set print demangle
4730 @itemx show print demangle
4731 @itemx set print asm-demangle
4732 @itemx show print asm-demangle
4733 Control whether C++ symbols display in their source form, both when
4734 displaying code as C++ source and when displaying disassemblies.
4735 @xref{Print Settings}.
4737 @item set print object
4738 @itemx show print object
4739 Choose whether to print derived (actual) or declared types of objects.
4740 @xref{Print Settings}.
4742 @item set print vtbl
4743 @itemx show print vtbl
4744 Control the format for printing virtual function tables.
4745 @xref{Print Settings}.
4750 @node Modula-2, , C, Support
4751 @subsection Modula-2
4754 The extensions made to _GDBN__ to support Modula-2 support output
4755 from the GNU Modula-2 compiler (which is currently being developed).
4756 Other Modula-2 compilers are not currently supported, and attempting to
4757 debug executables produced by them will most likely result in an error
4758 as _GDBN__ reads in the executable's symbol table.
4760 @cindex expressions in Modula-2
4762 * M2 Operators:: Built-in operators
4763 * Builtin Func/Proc:: Built-in Functions and Procedures
4764 * M2 Constants:: Modula-2 Constants
4765 * M2 Defaults:: Default settings for Modula-2
4766 * Deviations:: Deviations from standard Modula-2
4767 * M2 Checks:: Modula-2 Type and Range Checks
4768 * M2 Scope:: The scope operators @code{::} and @code{.}
4769 * GDB/M2:: _GDBN__ and Modula-2
4772 @node M2 Operators, Builtin Func/Proc, Modula-2, Modula-2
4773 @subsubsection Operators
4774 @cindex Modula-2 operators
4776 Operators must be defined on values of specific types. For instance,
4777 @code{+} is defined on numbers, but not on structures. Operators are
4778 often defined on groups of types. For the purposes of Modula-2, the
4779 following definitions hold:
4784 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
4788 @emph{Character types} consist of @code{CHAR} and its subranges.
4791 @emph{Floating-point types} consist of @code{REAL}.
4794 @emph{Pointer types} consist of anything declared as @code{POINTER TO
4798 @emph{Scalar types} consist of all of the above.
4801 @emph{Set types} consist of @code{SET}s and @code{BITSET}s.
4804 @emph{Boolean types} consist of @code{BOOLEAN}.
4809 The following operators are supported, and appear in order of
4810 increasing precedence:
4815 Function argument or array index separator.
4818 Assignment. The value of @var{var} @code{:=} @var{value} is
4822 Less than, greater than on integral, floating-point, or enumerated
4826 Less than, greater than, less than or equal to, greater than or equal to
4827 on integral, floating-point and enumerated types, or set inclusion on
4828 set types. Same precedence as @code{<}.
4830 @item =@r{, }<>@r{, }#
4831 Equality and two ways of expressing inequality, valid on scalar types.
4832 Same precedence as @code{<}. In _GDBN__ scripts, only @code{<>} is
4833 available for inequality, since @code{#} conflicts with the script
4837 Set membership. Defined on set types and the types of their members.
4838 Same precedence as @code{<}.
4841 Boolean disjunction. Defined on boolean types.
4844 Boolean conjuction. Defined on boolean types.
4847 The _GDBN__ ``artificial array'' operator (@pxref{Expressions}).
4850 Addition and subtraction on integral and floating-point types, or union
4851 and difference on set types.
4854 Multiplication on integral and floating-point types, or set intersection
4858 Division on floating-point types, or symmetric set difference on set
4859 types. Same precedence as @code{*}.
4862 Integer division and remainder. Defined on integral types. Same
4863 precedence as @code{*}.
4866 Negative. Defined on @code{INTEGER}s and @code{REAL}s.
4869 Pointer dereferencing. Defined on pointer types.
4872 Boolean negation. Defined on boolean types. Same precedence as
4876 @code{RECORD} field selector. Defined on @code{RECORD}s. Same
4877 precedence as @code{^}.
4880 Array indexing. Defined on @code{ARRAY}s. Same precedence as @code{^}.
4883 Procedure argument list. Defined on @code{PROCEDURE}s. Same precedence
4887 _GDBN__ and Modula-2 scope operators.
4892 @emph{Warning:} Sets and their operations are not yet supported, so _GDBN__
4893 will treat the use of the operator @code{IN}, or the use of operators
4894 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
4895 @code{<=}, and @code{>=} on sets as an error.
4899 @cindex Modula-2 builtins
4900 @node Builtin Func/Proc, M2 Constants, M2 Operators, Modula-2
4901 @subsubsection Built-in Functions and Procedures
4903 Modula-2 also makes available several built-in procedures and functions.
4904 In describing these, the following metavariables are used:
4909 represents an @code{ARRAY} variable.
4912 represents a @code{CHAR} constant or variable.
4915 represents a variable or constant of integral type.
4918 represents an identifier that belongs to a set. Generally used in the
4919 same function with the metavariable @var{s}. The type of @var{s} should
4920 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}.
4923 represents a variable or constant of integral or floating-point type.
4926 represents a variable or constant of floating-point type.
4932 represents a variable.
4935 represents a variable or constant of one of many types. See the
4936 explanation of the function for details.
4940 All Modula-2 built-in procedures also return a result, described below.
4944 Returns the absolute value of @var{n}.
4947 If @var{c} is a lower case letter, it returns its upper case
4948 equivalent, otherwise it returns its argument
4951 Returns the character whose ordinal value is @var{i}.
4954 Decrements the value in the variable @var{v}. Returns the new value.
4956 @item DEC(@var{v},@var{i})
4957 Decrements the value in the variable @var{v} by @var{i}. Returns the
4960 @item EXCL(@var{m},@var{s})
4961 Removes the element @var{m} from the set @var{s}. Returns the new
4964 @item FLOAT(@var{i})
4965 Returns the floating point equivalent of the integer @var{i}.
4968 Returns the index of the last member of @var{a}.
4971 Increments the value in the variable @var{v}. Returns the new value.
4973 @item INC(@var{v},@var{i})
4974 Increments the value in the variable @var{v} by @var{i}. Returns the
4977 @item INCL(@var{m},@var{s})
4978 Adds the element @var{m} to the set @var{s} if it is not already
4979 there. Returns the new set.
4982 Returns the maximum value of the type @var{t}.
4985 Returns the minimum value of the type @var{t}.
4988 Returns boolean TRUE if @var{i} is an odd number.
4991 Returns the ordinal value of its argument. For example, the ordinal
4992 value of a character is its ASCII value (on machines supporting the
4993 ASCII character set). @var{x} must be of an ordered type, which include
4994 integral, character and enumerated types.
4997 Returns the size of its argument. @var{x} can be a variable or a type.
4999 @item TRUNC(@var{r})
5000 Returns the integral part of @var{r}.
5002 @item VAL(@var{t},@var{i})
5003 Returns the member of the type @var{t} whose ordinal value is @var{i}.
5007 @emph{Warning:} Sets and their operations are not yet supported, so
5008 _GDBN__ will treat the use of procedures @code{INCL} and @code{EXCL} as
5012 @cindex Modula-2 constants
5013 @node M2 Constants, M2 Defaults, Builtin Func/Proc, Modula-2
5014 @subsubsection Constants
5016 _GDBN__ allows you to express the constants of Modula-2 in the following
5022 Integer constants are simply a sequence of digits. When used in an
5023 expression, a constant is interpreted to be type-compatible with the
5024 rest of the expression. Hexadecimal integers are specified by a
5025 trailing @samp{H}, and octal integers by a trailing @samp{B}.
5028 Floating point constants appear as a sequence of digits, followed by a
5029 decimal point and another sequence of digits. An optional exponent can
5030 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
5031 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
5032 digits of the floating point constant must be valid decimal (base 10)
5036 Character constants consist of a single character enclosed by a pair of
5037 like quotes, either single (@code{'}) or double (@code{"}). They may
5038 also be expressed by their ordinal value (their ASCII value, usually)
5039 followed by a @samp{C}.
5042 String constants consist of a sequence of characters enclosed by a pair
5043 of like quotes, either single (@code{'}) or double (@code{"}). Escape
5044 sequences in the style of C are also allowed. @xref{C Constants}, for a
5045 brief explanation of escape sequences.
5048 Enumerated constants consist of an enumerated identifier.
5051 Boolean constants consist of the identifiers @code{TRUE} and
5055 Pointer constants consist of integral values only.
5058 Set constants are not yet supported.
5062 @node M2 Defaults, Deviations, M2 Constants, Modula-2
5063 @subsubsection Modula-2 Defaults
5064 @cindex Modula-2 defaults
5066 If type and range checking are set automatically by _GDBN__, they
5067 both default to @code{on} whenever the working language changes to
5068 Modula-2. This happens regardless of whether you, or _GDBN__,
5069 selected the working language.
5071 If you allow _GDBN__ to set the language automatically, then entering
5072 code compiled from a file whose name ends with @file{.mod} will set the
5073 working language to Modula-2. @xref{Automatically,,Having _GDBN__ set
5074 the language automatically}, for further details.
5076 @node Deviations, M2 Checks, M2 Defaults, Modula-2
5077 @subsubsection Deviations from Standard Modula-2
5078 @cindex Modula-2, deviations from
5080 A few changes have been made to make Modula-2 programs easier to debug.
5081 This is done primarily via loosening its type strictness:
5085 Unlike in standard Modula-2, pointer constants can be formed by
5086 integers. This allows you to modify pointer variables during
5087 debugging. (In standard Modula-2, the actual address contained in a
5088 pointer variable is hidden from you; it can only be modified
5089 through direct assignment to another pointer variable or expression that
5090 returned a pointer.)
5093 C escape sequences can be used in strings and characters to represent
5094 non-printable characters. _GDBN__ will print out strings with these
5095 escape sequences embedded. Single non-printable characters are
5096 printed using the @samp{CHR(@var{nnn})} format.
5099 The assignment operator (@code{:=}) returns the value of its right-hand
5103 All builtin procedures both modify @emph{and} return their argument.
5107 @node M2 Checks, M2 Scope, Deviations, Modula-2
5108 @subsubsection Modula-2 Type and Range Checks
5109 @cindex Modula-2 checks
5112 @emph{Warning:} in this release, _GDBN__ does not yet perform type or
5115 @c FIXME remove warning when type/range checks added
5117 _GDBN__ considers two Modula-2 variables type equivalent if:
5121 They are of types that have been declared equivalent via a @code{TYPE
5122 @var{t1} = @var{t2}} statement
5125 They have been declared on the same line. (Note: This is true of the
5126 GNU Modula-2 compiler, but it may not be true of other compilers.)
5130 As long as type checking is enabled, any attempt to combine variables
5131 whose types are not equivalent is an error.
5133 Range checking is done on all mathematical operations, assignment, array
5134 index bounds, and all builtin functions and procedures.
5136 @node M2 Scope, GDB/M2, M2 Checks, Modula-2
5137 @subsubsection The scope operators @code{::} and @code{.}
5142 There are a few subtle differences between the Modula-2 scope operator
5143 (@code{.}) and the _GDBN__ scope operator (@code{::}). The two have
5148 @var{module} . @var{id}
5149 @var{scope} :: @var{id}
5154 where @var{scope} is the name of a module or a procedure,
5155 @var{module} the name of a module, and @var{id} is any delcared
5156 identifier within the program, except another module.
5158 Using the @code{::} operator makes _GDBN__ search the scope
5159 specified by @var{scope} for the identifier @var{id}. If it is not
5160 found in the specified scope, then _GDBN__ will search all scopes
5161 enclosing the one specified by @var{scope}.
5163 Using the @code{.} operator makes _GDBN__ search the current scope for
5164 the identifier specified by @var{id} that was imported from the
5165 definition module specified by @var{module}. With this operator, it is
5166 an error if the identifier @var{id} was not imported from definition
5167 module @var{module}, or if @var{id} is not an identifier in
5170 @node GDB/M2, , M2 Scope, Modula-2
5171 @subsubsection _GDBN__ and Modula-2
5173 Some _GDBN__ commands have little use when debugging Modula-2 programs.
5174 Five subcommands of @code{set print} and @code{show print} apply
5175 specifically to C and C++: @samp{vtbl}, @samp{demangle},
5176 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
5177 apply to C++, and the last to C's @code{union} type, which has no direct
5178 analogue in Modula-2.
5180 The @code{@@} operator (@pxref{Expressions}), while available
5181 while using any language, is not useful with Modula-2. Its
5182 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
5183 created in Modula-2 as they can in C or C++. However, because an
5184 address can be specified by an integral constant, the construct
5185 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions})
5188 @cindex @code{#} in Modula-2
5189 In _GDBN__ scripts, the Modula-2 inequality operator @code{#} is
5190 interpreted as the beginning of a comment. Use @code{<>} instead.
5194 @node Symbols, Altering, Languages, Top
5195 @chapter Examining the Symbol Table
5197 The commands described in this section allow you to inquire about the
5198 symbols (names of variables, functions and types) defined in your
5199 program. This information is inherent in the text of your program and
5200 does not change as the program executes. _GDBN__ finds it in your
5201 program's symbol table, in the file indicated when you started _GDBN__
5202 (@pxref{File Options}), or by one of the file-management commands
5206 @item info address @var{symbol}
5207 @kindex info address
5208 Describe where the data for @var{symbol} is stored. For a register
5209 variable, this says which register it is kept in. For a non-register
5210 local variable, this prints the stack-frame offset at which the variable
5213 Note the contrast with @samp{print &@var{symbol}}, which does not work
5214 at all for a register variables, and for a stack local variable prints
5215 the exact address of the current instantiation of the variable.
5217 @item whatis @var{exp}
5219 Print the data type of expression @var{exp}. @var{exp} is not
5220 actually evaluated, and any side-effecting operations (such as
5221 assignments or function calls) inside it do not take place.
5225 Print the data type of @code{$}, the last value in the value history.
5227 @item ptype @var{typename}
5229 Print a description of data type @var{typename}. @var{typename} may be
5230 the name of a type, or for C code it may have the form
5231 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
5232 @samp{enum @var{enum-tag}}.@refill
5234 @item ptype @var{exp}
5235 Print a description of the type of expression @var{exp}. @code{ptype}
5236 differs from @code{whatis} by printing a detailed description, instead of just
5237 the name of the type. For example, if your program declares a variable
5240 struct complex @{double real; double imag;@} v;
5243 compare the output of the two commands:
5246 type = struct complex
5248 type = struct complex @{
5254 @item info types @var{regexp}
5257 Print a brief description of all types whose name matches @var{regexp}
5258 (or all types in your program, if you supply no argument). Each
5259 complete typename is matched as though it were a complete line; thus,
5260 @samp{i type value} gives information on all types in your program whose
5261 name includes the string @code{value}, but @samp{i type ^value$} gives
5262 information only on types whose complete name is @code{value}.
5264 This command differs from @code{ptype} in two ways: first, like
5265 @code{whatis}, it does not print a detailed description; second, it
5266 lists all source files where a type is defined.
5270 Show the name of the current source file---that is, the source file for
5271 the function containing the current point of execution---and the language
5275 @kindex info sources
5276 Print the names of all source files in the program for which there is
5277 debugging information, organized into two lists: files whose symbols
5278 have already been read, and files whose symbols will be read when needed.
5280 @item info functions
5281 @kindex info functions
5282 Print the names and data types of all defined functions.
5284 @item info functions @var{regexp}
5285 Print the names and data types of all defined functions
5286 whose names contain a match for regular expression @var{regexp}.
5287 Thus, @samp{info fun step} finds all functions whose names
5288 include @code{step}; @samp{info fun ^step} finds those whose names
5289 start with @code{step}.
5291 @item info variables
5292 @kindex info variables
5293 Print the names and data types of all variables that are declared
5294 outside of functions (i.e., excluding local variables).
5296 @item info variables @var{regexp}
5297 Print the names and data types of all variables (except for local
5298 variables) whose names contain a match for regular expression
5303 This was never implemented.
5305 @itemx info methods @var{regexp}
5306 @kindex info methods
5307 The @code{info methods} command permits the user to examine all defined
5308 methods within C++ program, or (with the @var{regexp} argument) a
5309 specific set of methods found in the various C++ classes. Many
5310 C++ classes provide a large number of methods. Thus, the output
5311 from the @code{ptype} command can be overwhelming and hard to use. The
5312 @code{info-methods} command filters the methods, printing only those
5313 which match the regular-expression @var{regexp}.
5316 @item printsyms @var{filename}
5318 Write a dump of debugging symbol data into the file
5319 @var{filename}. Only symbols with debugging data are included. _GDBN__
5320 includes all the symbols it already knows about: that is, @var{filename}
5321 reflects symbols for only those files whose symbols _GDBN__ has read.
5322 You can find out which files these are using the command @code{info
5323 files}. The description of @code{symbol-file} describes how _GDBN__
5324 reads symbols; both commands are described under @ref{Files}.
5327 @node Altering, _GDBN__ Files, Symbols, Top
5328 @chapter Altering Execution
5330 Once you think you have found an error in the program, you might want to
5331 find out for certain whether correcting the apparent error would lead to
5332 correct results in the rest of the run. You can find the answer by
5333 experiment, using the _GDBN__ features for altering execution of the
5336 For example, you can store new values into variables or memory
5337 locations, give the program a signal, restart it at a different address,
5338 or even return prematurely from a function to its caller.
5341 * Assignment:: Assignment to Variables
5342 * Jumping:: Continuing at a Different Address
5343 * Signaling:: Giving the Program a Signal
5344 * Returning:: Returning from a Function
5345 * Calling:: Calling your Program's Functions
5346 * Patching:: Patching your Program
5349 @node Assignment, Jumping, Altering, Altering
5350 @section Assignment to Variables
5353 @cindex setting variables
5354 To alter the value of a variable, evaluate an assignment expression.
5355 @xref{Expressions}. For example,
5362 would store the value 4 into the variable @code{x}, and then print the
5363 value of the assignment expression (which is 4). @xref{Languages}, for
5364 more information on operators in supported languages.
5366 @kindex set variable
5367 @cindex variables, setting
5368 If you are not interested in seeing the value of the assignment, use the
5369 @code{set} command instead of the @code{print} command. @code{set} is
5370 really the same as @code{print} except that the expression's value is not
5371 printed and is not put in the value history (@pxref{Value History}). The
5372 expression is evaluated only for its effects.
5374 If the beginning of the argument string of the @code{set} command
5375 appears identical to a @code{set} subcommand, use the @code{set
5376 variable} command instead of just @code{set}. This command is identical
5377 to @code{set} except for its lack of subcommands. For example, a
5378 program might well have a variable @code{width}---which leads to
5379 an error if we try to set a new value with just @samp{set width=13}, as
5380 we might if @code{set width} didn't happen to be a _GDBN__ command:
5382 (_GDBP__) whatis width
5386 (_GDBP__) set width=47
5387 Invalid syntax in expression.
5390 The invalid expression, of course, is @samp{=47}. What we can do in
5391 order to actually set our program's variable @code{width} is
5393 (_GDBP__) set var width=47
5396 _GDBN__ allows more implicit conversions in assignments than C does; you can
5397 freely store an integer value into a pointer variable or vice versa, and
5398 any structure can be converted to any other structure that is the same
5400 @comment FIXME: how do structs align/pad in these conversions?
5401 @comment /pesch@cygnus.com 18dec1990
5403 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
5404 construct to generate a value of specified type at a specified address
5405 (@pxref{Expressions}). For example, @code{@{int@}0x83040} refers
5406 to memory location @code{0x83040} as an integer (which implies a certain size
5407 and representation in memory), and
5410 set @{int@}0x83040 = 4
5414 stores the value 4 into that memory location.
5416 @node Jumping, Signaling, Assignment, Altering
5417 @section Continuing at a Different Address
5419 Ordinarily, when you continue the program, you do so at the place where
5420 it stopped, with the @code{continue} command. You can instead continue at
5421 an address of your own choosing, with the following commands:
5424 @item jump @var{linespec}
5426 Resume execution at line @var{linespec}. Execution will stop
5427 immediately if there is a breakpoint there. @xref{List} for a
5428 description of the different forms of @var{linespec}.
5430 The @code{jump} command does not change the current stack frame, or
5431 the stack pointer, or the contents of any memory location or any
5432 register other than the program counter. If line @var{linespec} is in
5433 a different function from the one currently executing, the results may
5434 be bizarre if the two functions expect different patterns of arguments or
5435 of local variables. For this reason, the @code{jump} command requests
5436 confirmation if the specified line is not in the function currently
5437 executing. However, even bizarre results are predictable if you are
5438 well acquainted with the machine-language code of the program.
5440 @item jump *@var{address}
5441 Resume execution at the instruction at address @var{address}.
5444 You can get much the same effect as the @code{jump} command by storing a
5445 new value into the register @code{$pc}. The difference is that this
5446 does not start the program running; it only changes the address where it
5447 @emph{will} run when it is continued. For example,
5454 causes the next @code{continue} command or stepping command to execute at
5455 address 0x485, rather than at the address where the program stopped.
5456 @xref{Continuing and Stepping}.
5458 The most common occasion to use the @code{jump} command is to back up,
5459 perhaps with more breakpoints set, over a portion of a program that has
5460 already executed, in order to examine its execution in more detail.
5462 @node Signaling, Returning, Jumping, Altering
5464 @section Giving the Program a Signal
5467 @item signal @var{signalnum}
5469 Resume execution where the program stopped, but give it immediately the
5470 signal number @var{signalnum}.
5472 Alternatively, if @var{signalnum} is zero, continue execution without
5473 giving a signal. This is useful when the program stopped on account of
5474 a signal and would ordinary see the signal when resumed with the
5475 @code{continue} command; @samp{signal 0} causes it to resume without a
5478 @code{signal} does not repeat when you press @key{RET} a second time
5479 after executing the command.
5483 @node Returning, Calling, Signaling, Altering
5484 @section Returning from a Function
5488 @itemx return @var{expression}
5489 @cindex returning from a function
5491 You can cancel execution of a function call with the @code{return}
5492 command. If you give an
5493 @var{expression} argument, its value is used as the function's return
5497 When you use @code{return}, _GDBN__ discards the selected stack frame
5498 (and all frames within it). You can think of this as making the
5499 discarded frame return prematurely. If you wish to specify a value to
5500 be returned, give that value as the argument to @code{return}.
5502 This pops the selected stack frame (@pxref{Selection}), and any other
5503 frames inside of it, leaving its caller as the innermost remaining
5504 frame. That frame becomes selected. The specified value is stored in
5505 the registers used for returning values of functions.
5507 The @code{return} command does not resume execution; it leaves the
5508 program stopped in the state that would exist if the function had just
5509 returned. In contrast, the @code{finish} command
5510 (@pxref{Continuing and Stepping})
5511 resumes execution until the selected stack frame returns naturally.@refill
5513 @node Calling, Patching, Returning, Altering
5514 @section Calling your Program's Functions
5516 @cindex calling functions
5519 @item call @var{expr}
5520 Evaluate the expression @var{expr} without displaying @code{void}
5524 You can use this variant of the @code{print} command if you want to
5525 execute a function from your program, but without cluttering the output
5526 with @code{void} returned values. The result is printed and saved in
5527 the value history, if it is not void.
5529 @node Patching, , Calling, Altering
5530 @section Patching your Program
5531 @cindex patching binaries
5532 @cindex writing into executables
5533 @cindex writing into corefiles
5534 By default, _GDBN__ opens the file containing your program's executable
5535 code (or the corefile) read-only. This prevents accidental alterations
5536 to machine code; but it also prevents you from intentionally patching
5537 your program's binary.
5539 If you'd like to be able to patch the binary, you can specify that
5540 explicitly with the @code{set write} command. For example, you might
5541 want to turn on internal debugging flags, or even to make emergency
5546 @itemx set write off
5548 If you specify @samp{set write on}, _GDBN__ will open executable and
5549 core files for both reading and writing; if you specify @samp{set write
5550 off} (the default), _GDBN__ will open them read-only.
5552 If you've already loaded a file, you must load it
5553 again (using the @code{exec-file} or @code{core-file} command) after
5554 changing @code{set write}, for your new setting to take effect.
5558 Display whether executable files and core files will be opened for
5559 writing as well as reading.
5563 @node _GDBN__ Files, Targets, Altering, Top
5564 @chapter _GDBN__'s Files
5567 * Files:: Commands to Specify Files
5568 * Symbol Errors:: Errors Reading Symbol Files
5571 @node Files, Symbol Errors, _GDBN__ Files, _GDBN__ Files
5572 @section Commands to Specify Files
5573 @cindex core dump file
5574 @cindex symbol table
5575 _GDBN__ needs to know the file name of the program to be debugged, both in
5576 order to read its symbol table and in order to start the program. To
5577 debug a core dump of a previous run, _GDBN__ must be told the file name of
5580 The usual way to specify the executable and core dump file names is with
5581 the command arguments given when you start _GDBN__, as discussed in
5584 Occasionally it is necessary to change to a different file during a
5585 _GDBN__ session. Or you may run _GDBN__ and forget to specify the files you
5586 want to use. In these situations the _GDBN__ commands to specify new files
5590 @item file @var{filename}
5591 @cindex executable file
5593 Use @var{filename} as the program to be debugged. It is read for its
5594 symbols and for the contents of pure memory. It is also the program
5595 executed when you use the @code{run} command. If you do not specify a
5596 directory and the file is not found in _GDBN__'s working directory,
5598 _GDBN__ uses the environment variable @code{PATH} as a list of
5599 directories to search, just as the shell does when looking for a program
5600 to run. You can change the value of this variable, for both _GDBN__ and
5601 your program, using the @code{path} command.
5603 @code{file} with no argument makes _GDBN__ discard any information it
5604 has on both executable file and the symbol table.
5606 @item exec-file @var{filename}
5608 Specify that the program to be run (but not the symbol table) is found
5609 in @var{filename}. _GDBN__ will search the environment variable @code{PATH}
5610 if necessary to locate the program.
5612 @item symbol-file @var{filename}
5614 Read symbol table information from file @var{filename}. @code{PATH} is
5615 searched when necessary. Use the @code{file} command to get both symbol
5616 table and program to run from the same file.
5618 @code{symbol-file} with no argument clears out _GDBN__'s information on your
5619 program's symbol table.
5621 The @code{symbol-file} command causes _GDBN__ to forget the contents of its
5622 convenience variables, the value history, and all breakpoints and
5623 auto-display expressions. This is because they may contain pointers to
5624 the internal data recording symbols and data types, which are part of
5625 the old symbol table data being discarded inside _GDBN__.
5627 @code{symbol-file} will not repeat if you press @key{RET} again after
5630 On some kinds of object files, the @code{symbol-file} command does not
5631 actually read the symbol table in full right away. Instead, it scans
5632 the symbol table quickly to find which source files and which symbols
5633 are present. The details are read later, one source file at a time,
5634 when they are needed.
5636 The purpose of this two-stage reading strategy is to make _GDBN__ start up
5637 faster. For the most part, it is invisible except for occasional pauses
5638 while the symbol table details for a particular source file are being
5639 read. (The @code{set verbose} command can turn these pauses into
5640 messages if desired. @xref{Messages/Warnings}).
5642 When the symbol table is stored in COFF format, @code{symbol-file} does
5643 read the symbol table data in full right away. We haven't implemented
5644 the two-stage strategy for COFF yet.
5646 When _GDBN__ is configured for a particular environment, it will
5647 understand debugging information in whatever format is the standard
5648 generated for that environment; you may use either a GNU compiler, or
5649 other compilers that adhere to the local conventions. Best results are
5650 usually obtained from GNU compilers; for example, using @code{_GCC__}
5651 you can generate debugging information for optimized code.
5653 @item core-file @var{filename}
5654 @itemx core @var{filename}
5657 Specify the whereabouts of a core dump file to be used as the ``contents
5658 of memory''. Traditionally, core files contain only some parts of the
5659 address space of the process that generated them; _GDBN__ can access the
5660 executable file itself for other parts.
5662 @code{core-file} with no argument specifies that no core file is
5665 Note that the core file is ignored when your program is actually running
5666 under _GDBN__. So, if you have been running the program and you wish to
5667 debug a core file instead, you must kill the subprocess in which the
5668 program is running. To do this, use the @code{kill} command
5669 (@pxref{Kill Process}).
5671 @item load @var{filename}
5674 Depending on what remote debugging facilities are configured into
5675 _GDBN__, the @code{load} command may be available. Where it exists, it
5676 is meant to make @var{filename} (an executable) available for debugging
5677 on the remote system---by downloading, or dynamic linking, for example.
5678 @code{load} also records @var{filename}'s symbol table in _GDBN__, like
5679 the @code{add-symbol-file} command.
5681 If @code{load} is not available on your _GDBN__, attempting to execute
5682 it gets the error message ``@code{You can't do that when your target is
5687 On VxWorks, @code{load} will dynamically link @var{filename} on the
5688 current target system as well as adding its symbols in _GDBN__.
5692 @cindex download to Nindy-960
5693 With the Nindy interface to an Intel 960 board, @code{load} will
5694 download @var{filename} to the 960 as well as adding its symbols in
5698 @code{load} will not repeat if you press @key{RET} again after using it.
5700 @item add-symbol-file @var{filename} @var{address}
5701 @kindex add-symbol-file
5702 @cindex dynamic linking
5703 The @code{add-symbol-file} command reads additional symbol table information
5704 from the file @var{filename}. You would use this command when @var{filename}
5705 has been dynamically loaded (by some other means) into the program that
5706 is running. @var{address} should be the memory address at which the
5707 file has been loaded; _GDBN__ cannot figure this out for itself.
5709 The symbol table of the file @var{filename} is added to the symbol table
5710 originally read with the @code{symbol-file} command. You can use the
5711 @code{add-symbol-file} command any number of times; the new symbol data thus
5712 read keeps adding to the old. To discard all old symbol data instead,
5713 use the @code{symbol-file} command.
5715 @code{add-symbol-file} will not repeat if you press @key{RET} after using it.
5721 @code{info files} and @code{info target} are synonymous; both print the
5722 current targets (@pxref{Targets}), including the names of the executable
5723 and core dump files currently in use by _GDBN__, and the files from
5724 which symbols were loaded. The command @code{help targets} lists all
5725 possible targets rather than current ones.
5729 All file-specifying commands allow both absolute and relative file names
5730 as arguments. _GDBN__ always converts the file name to an absolute path
5731 name and remembers it that way.
5733 @cindex shared libraries
5735 _GDBN__ supports the SunOS shared library format. _GDBN__ automatically
5736 loads symbol definitions from shared libraries when you use the
5737 @code{run} command, or when you examine a core file. (Before you issue
5738 the @code{run} command, _GDBN__ won't understand references to a
5739 function in a shared library, however---unless you're debugging a core
5741 @c FIXME: next _GDBN__ release should permit some refs to undef
5742 @c FIXME...symbols---eg in a break cmd---assuming they're from a shared lib
5746 @itemx info sharedlibrary
5747 @kindex info sharedlibrary
5749 Print the names of the shared libraries which are currently loaded.
5751 @item sharedlibrary @var{regex}
5752 @itemx share @var{regex}
5753 @kindex sharedlibrary
5755 This is an obsolescent command; you can use it to explicitly
5756 load shared object library symbols for files matching a UNIX regular
5757 expression, but as with files loaded automatically, it will only load
5758 shared libraries required by your program for a core file or after
5759 typing @code{run}. If @var{regex} is omitted all shared libraries
5760 required by your program are loaded.
5763 @node Symbol Errors, , Files, _GDBN__ Files
5764 @section Errors Reading Symbol Files
5765 While reading a symbol file, _GDBN__ will occasionally encounter
5766 problems, such as symbol types it does not recognize, or known bugs in
5767 compiler output. By default, _GDBN__ does not notify you of such
5768 problems, since they're relatively common and primarily of interest to
5769 people debugging compilers. If you are interested in seeing information
5770 about ill-constructed symbol tables, you can either ask _GDBN__ to print
5771 only one message about each such type of problem, no matter how many
5772 times the problem occurs; or you can ask _GDBN__ to print more messages,
5773 to see how many times the problems occur, with the @code{set complaints}
5774 command (@xref{Messages/Warnings}).
5776 The messages currently printed, and their meanings, are:
5779 @item inner block not inside outer block in @var{symbol}
5781 The symbol information shows where symbol scopes begin and end
5782 (such as at the start of a function or a block of statements). This
5783 error indicates that an inner scope block is not fully contained
5784 in its outer scope blocks.
5786 _GDBN__ circumvents the problem by treating the inner block as if it had
5787 the same scope as the outer block. In the error message, @var{symbol}
5788 may be shown as ``@code{(don't know)}'' if the outer block is not a
5791 @item block at @var{address} out of order
5793 The symbol information for symbol scope blocks should occur in
5794 order of increasing addresses. This error indicates that it does not
5797 _GDBN__ does not circumvent this problem, and will have trouble locating
5798 symbols in the source file whose symbols being read. (You can often
5799 determine what source file is affected by specifying @code{set verbose
5800 on}. @xref{Messages/Warnings}.)
5802 @item bad block start address patched
5804 The symbol information for a symbol scope block has a start address
5805 smaller than the address of the preceding source line. This is known
5806 to occur in the SunOS 4.1.1 (and earlier) C compiler.
5808 _GDBN__ circumvents the problem by treating the symbol scope block as
5809 starting on the previous source line.
5811 @item bad string table offset in symbol @var{n}
5814 Symbol number @var{n} contains a pointer into the string table which is
5815 larger than the size of the string table.
5817 _GDBN__ circumvents the problem by considering the symbol to have the
5818 name @code{foo}, which may cause other problems if many symbols end up
5821 @item unknown symbol type @code{0x@var{nn}}
5823 The symbol information contains new data types that _GDBN__ does not yet
5824 know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood
5825 information, in hexadecimal.
5827 _GDBN__ circumvents the error by ignoring this symbol information. This
5828 will usually allow the program to be debugged, though certain symbols
5829 will not be accessible. If you encounter such a problem and feel like
5830 debugging it, you can debug @code{_GDBP__} with itself, breakpoint on
5831 @code{complain}, then go up to the function @code{read_dbx_symtab} and
5832 examine @code{*bufp} to see the symbol.
5834 @item stub type has NULL name
5835 _GDBN__ could not find the full definition for a struct or class.
5838 @c this is #if 0'd in dbxread.c as of (at least!) 17 may 1991
5839 @item const/volatile indicator missing, got '@var{X}'
5841 The symbol information for a C++ member function is missing some
5842 information that the compiler should have output for it.
5845 @item C++ type mismatch between compiler and debugger
5847 _GDBN__ could not parse a type specification output by the compiler
5848 for some C++ object.
5852 @node Targets, Controlling _GDBN__, _GDBN__ Files, Top
5853 @chapter Specifying a Debugging Target
5854 @cindex debugging target
5856 A @dfn{target} is an interface between the debugger and a particular
5857 kind of file or process.
5859 Often, you will be able to run _GDBN__ in the same host environment as the
5860 program you are debugging; in that case, the debugging target can just be
5861 specified as a side effect of the @code{file} or @code{core} commands.
5862 When you need more flexibility---for example, running _GDBN__ on a
5863 physically separate host, controlling standalone systems over a
5864 serial port, or realtime systems over a TCP/IP connection---you can use
5865 the @code{target} command.
5868 * Active Targets:: Active Targets
5869 * Target Commands:: Commands for Managing Targets
5870 * Remote:: Remote Debugging
5873 @node Active Targets, Target Commands, Targets, Targets
5874 @section Active Targets
5875 @cindex stacking targets
5876 @cindex active targets
5877 @cindex multiple targets
5879 Targets are managed in three @dfn{strata} that correspond to different
5880 classes of target: processes, core files, and executable files. This
5881 allows you to (for example) start a process and inspect its activity
5882 without abandoning your work on a core file.
5884 More than one target can potentially respond to a request. In
5885 particular, when you access memory _GDBN__ will examine the three strata of
5886 targets until it finds a target that can handle that particular address.
5887 Strata are always examined in a fixed order: first a process if there is
5888 one, then a core file if there is one, and finally an executable file if
5889 there is one of those.
5891 When you specify a new target in a given stratum, it replaces any target
5892 previously in that stratum.
5894 To get rid of a target without replacing it, use the @code{detach}
5895 command. The related command @code{attach} provides you with a way of
5896 choosing a particular running process as a new target. @xref{Attach}.
5898 @node Target Commands, Remote, Active Targets, Targets
5899 @section Commands for Managing Targets
5902 @item target @var{type} @var{parameters}
5903 Connects the _GDBN__ host environment to a target machine or process. A
5904 target is typically a protocol for talking to debugging facilities. You
5905 use the argument @var{type} to specify the type or protocol of the
5908 Further @var{parameters} are interpreted by the target protocol, but
5909 typically include things like device names or host names to connect
5910 with, process numbers, and baud rates.
5912 The @code{target} command will not repeat if you press @key{RET} again
5913 after executing the command.
5917 Displays the names of all targets available. To display targets
5918 currently selected, use either @code{info target} or @code{info files}
5921 @item help target @var{name}
5922 Describe a particular target, including any parameters necessary to
5926 Here are some common targets (available, or not, depending on the _GDBN__
5930 @item target exec @var{prog}
5932 An executable file. @samp{target exec @var{prog}} is the same as
5933 @samp{exec-file @var{prog}}.
5935 @item target core @var{filename}
5937 A core dump file. @samp{target core @var{filename}} is the same as
5938 @samp{core-file @var{filename}}.
5940 @item target remote @var{dev}
5941 @kindex target remote
5942 Remote serial target in _GDBN__-specific protocol. The argument @var{dev}
5943 specifies what serial device to use for the connection (e.g.
5944 @file{/dev/ttya}). @xref{Remote}.
5947 @item target amd-eb @var{dev} @var{speed} @var{PROG}
5948 @kindex target amd-eb
5950 Remote PC-resident AMD EB29K board, attached over serial lines.
5951 @var{dev} is the serial device, as for @code{target remote};
5952 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
5953 name of the program to be debugged, as it appears to DOS on the PC.
5954 @xref{EB29K Remote}.
5958 @item target nindy @var{devicename}
5959 @kindex target nindy
5960 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
5961 the name of the serial device to use for the connection, e.g.
5962 @file{/dev/ttya}. @xref{i960-Nindy Remote}.
5966 @item target vxworks @var{machinename}
5967 @kindex target vxworks
5968 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
5969 is the target system's machine name or IP address.
5970 @xref{VxWorks Remote}.
5975 Different targets are available on different configurations of _GDBN__; your
5976 configuration may have more or fewer targets.
5979 @node Remote, , Target Commands, Targets
5980 @section Remote Debugging
5981 @cindex remote debugging
5985 _include__(gdbinv-m.m4)<>_dnl__
5989 If you are trying to debug a program running on a machine that can't run
5990 _GDBN__ in the usual way, it is often useful to use remote debugging. For
5991 example, you might use remote debugging on an operating system kernel, or on
5992 a small system which does not have a general purpose operating system
5993 powerful enough to run a full-featured debugger.
5995 Some configurations of _GDBN__ have special serial or TCP/IP interfaces
5996 to make this work with particular debugging targets. In addition,
5997 _GDBN__ comes with a generic serial protocol (specific to _GDBN__, but
5998 not specific to any particular target system) which you can use if you
5999 write the remote stubs---the code that will run on the remote system to
6000 communicate with _GDBN__.
6002 To use the _GDBN__ remote serial protocol, the program to be debugged on
6003 the remote machine needs to contain a debugging stub which talks to
6004 _GDBN__ over the serial line. Several working remote stubs are
6005 distributed with _GDBN__; see the @file{README} file in the _GDBN__
6006 distribution for more information.
6008 For details of this communication protocol, see the comments in the
6009 _GDBN__ source file @file{remote.c}.
6011 To start remote debugging, first run _GDBN__ and specify as an executable file
6012 the program that is running in the remote machine. This tells _GDBN__ how
6013 to find the program's symbols and the contents of its pure text. Then
6014 establish communication using the @code{target remote} command with a device
6015 name as an argument. For example:
6018 target remote /dev/ttyb
6022 if the serial line is connected to the device named @file{/dev/ttyb}. This
6023 will stop the remote machine if it is not already stopped.
6025 Now you can use all the usual commands to examine and change data and to
6026 step and continue the remote program.
6028 To resume the remote program and stop debugging it, use the @code{detach}
6031 Other remote targets may be available in your
6032 configuration of _GDBN__; use @code{help targets} to list them.
6035 @c Text on starting up GDB in various specific cases; it goes up front
6036 @c in manuals configured for any of those particular situations, here
6038 _include__(gdbinv-s.m4)
6041 @node Controlling _GDBN__, Sequences, Targets, Top
6042 @chapter Controlling _GDBN__
6044 You can alter many aspects of _GDBN__'s interaction with you by using
6045 the @code{set} command. For commands controlling how _GDBN__ displays
6046 data, @pxref{Print Settings}; other settings are described here.
6050 * Editing:: Command Editing
6051 * History:: Command History
6052 * Screen Size:: Screen Size
6054 * Messages/Warnings:: Optional Warnings and Messages
6057 @node Prompt, Editing, Controlling _GDBN__, Controlling _GDBN__
6060 _GDBN__ indicates its readiness to read a command by printing a string
6061 called the @dfn{prompt}. This string is normally @samp{(_GDBP__)}. You
6062 can change the prompt string with the @code{set prompt} command. For
6063 instance, when debugging _GDBN__ with _GDBN__, it is useful to change
6064 the prompt in one of the _GDBN__<>s so that you can always tell which
6065 one you are talking to.
6068 @item set prompt @var{newprompt}
6070 Directs _GDBN__ to use @var{newprompt} as its prompt string henceforth.
6073 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
6076 @node Editing, History, Prompt, Controlling _GDBN__
6077 @section Command Editing
6079 @cindex command line editing
6080 _GDBN__ reads its input commands via the @dfn{readline} interface. This
6081 GNU library provides consistent behavior for programs which provide a
6082 command line interface to the user. Advantages are @code{emacs}-style
6083 or @code{vi}-style inline editing of commands, @code{csh}-like history
6084 substitution, and a storage and recall of command history across
6087 You may control the behavior of command line editing in _GDBN__ with the
6094 @itemx set editing on
6095 Enable command line editing (enabled by default).
6097 @item set editing off
6098 Disable command line editing.
6100 @kindex show editing
6102 Show whether command line editing is enabled.
6105 @node History, Screen Size, Editing, Controlling _GDBN__
6106 @section Command History
6108 @cindex history substitution
6109 @cindex history file
6110 @kindex set history filename
6111 @item set history filename @var{fname}
6112 Set the name of the _GDBN__ command history file to @var{fname}. This is
6113 the file from which _GDBN__ will read an initial command history
6114 list or to which it will write this list when it exits. This list is
6115 accessed through history expansion or through the history
6116 command editing characters listed below. This file defaults to the
6117 value of the environment variable @code{GDBHISTFILE}, or to
6118 @file{./.gdb_history} if this variable is not set.
6120 @cindex history save
6121 @kindex set history save
6122 @item set history save
6123 @itemx set history save on
6124 Record command history in a file, whose name may be specified with the
6125 @code{set history filename} command. By default, this option is disabled.
6127 @item set history save off
6128 Stop recording command history in a file.
6130 @cindex history size
6131 @kindex set history size
6132 @item set history size @var{size}
6133 Set the number of commands which _GDBN__ will keep in its history list.
6134 This defaults to the value of the environment variable
6135 @code{HISTSIZE}, or to 256 if this variable is not set.
6138 @cindex history expansion
6139 History expansion assigns special meaning to the character @kbd{!}.
6141 (@xref{Event Designators}.)
6143 Since @kbd{!} is also the logical not operator in C, history expansion
6144 is off by default. If you decide to enable history expansion with the
6145 @code{set history expansion on} command, you may sometimes need to
6146 follow @kbd{!} (when it is used as logical not, in an expression) with
6147 a space or a tab to prevent it from being expanded. The readline
6148 history facilities will not attempt substitution on the strings
6149 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
6151 The commands to control history expansion are:
6155 @kindex set history expansion
6156 @item set history expansion on
6157 @itemx set history expansion
6158 Enable history expansion. History expansion is off by default.
6160 @item set history expansion off
6161 Disable history expansion.
6163 The readline code comes with more complete documentation of
6164 editing and history expansion features. Users unfamiliar with @code{emacs}
6165 or @code{vi} may wish to read it.
6167 @xref{Command Line Editing}.
6171 @kindex show history
6173 @itemx show history filename
6174 @itemx show history save
6175 @itemx show history size
6176 @itemx show history expansion
6177 These commands display the state of the _GDBN__ history parameters.
6178 @code{show history} by itself displays all four states.
6184 @kindex show commands
6186 Display the last ten commands in the command history.
6188 @item show commands @var{n}
6189 Print ten commands centered on command number @var{n}.
6191 @item show commands +
6192 Print ten commands just after the commands last printed.
6196 @node Screen Size, Numbers, History, Controlling _GDBN__
6197 @section Screen Size
6198 @cindex size of screen
6199 @cindex pauses in output
6200 Certain commands to _GDBN__ may produce large amounts of information
6201 output to the screen. To help you read all of it, _GDBN__ pauses and
6202 asks you for input at the end of each page of output. Type @key{RET}
6203 when you want to continue the output. _GDBN__ also uses the screen
6204 width setting to determine when to wrap lines of output. Depending on
6205 what is being printed, it tries to break the line at a readable place,
6206 rather than simply letting it overflow onto the following line.
6208 Normally _GDBN__ knows the size of the screen from the termcap data base
6209 together with the value of the @code{TERM} environment variable and the
6210 @code{stty rows} and @code{stty cols} settings. If this is not correct,
6211 you can override it with the @code{set height} and @code{set
6215 @item set height @var{lpp}
6217 @itemx set width @var{cpl}
6223 These @code{set} commands specify a screen height of @var{lpp} lines and
6224 a screen width of @var{cpl} characters. The associated @code{show}
6225 commands display the current settings.
6227 If you specify a height of zero lines, _GDBN__ will not pause during output
6228 no matter how long the output is. This is useful if output is to a file
6229 or to an editor buffer.
6232 @node Numbers, Messages/Warnings, Screen Size, Controlling _GDBN__
6234 @cindex number representation
6235 @cindex entering numbers
6236 You can always enter numbers in octal, decimal, or hexadecimal in _GDBN__ by
6237 the usual conventions: octal numbers begin with @samp{0}, decimal
6238 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
6239 Numbers that begin with none of these are, by default, entered in base
6240 10; likewise, the default display for numbers---when no particular
6241 format is specified---is base 10. You can change the default base for
6242 both input and output with the @code{set radix} command.
6246 @item set radix @var{base}
6247 Set the default base for numeric input and display. Supported choices
6248 for @var{base} are decimal 2, 8, 10, 16. @var{base} must itself be
6249 specified either unambiguously or using the current default radix; for
6260 will set the base to decimal. On the other hand, @samp{set radix 10}
6261 will leave the radix unchanged no matter what it was.
6265 Display the current default base for numeric input and display.
6269 @node Messages/Warnings, , Numbers, Controlling _GDBN__
6270 @section Optional Warnings and Messages
6271 By default, _GDBN__ is silent about its inner workings. If you are running
6272 on a slow machine, you may want to use the @code{set verbose} command.
6273 It will make _GDBN__ tell you when it does a lengthy internal operation, so
6274 you won't think it has crashed.
6276 Currently, the messages controlled by @code{set verbose} are those which
6277 announce that the symbol table for a source file is being read
6278 (@pxref{Files}, in the description of the command
6279 @code{symbol-file}).
6280 @c The following is the right way to do it, but emacs 18.55 doesn't support
6281 @c @ref, and neither the emacs lisp manual version of texinfmt or makeinfo
6284 see @code{symbol-file} in @ref{Files}).
6289 @item set verbose on
6290 Enables _GDBN__'s output of certain informational messages.
6292 @item set verbose off
6293 Disables _GDBN__'s output of certain informational messages.
6295 @kindex show verbose
6297 Displays whether @code{set verbose} is on or off.
6300 By default, if _GDBN__ encounters bugs in the symbol table of an object
6301 file, it is silent; but if you are debugging a compiler, you may find
6302 this information useful (@pxref{Symbol Errors}).
6305 @kindex set complaints
6306 @item set complaints @var{limit}
6307 Permits _GDBN__ to output @var{limit} complaints about each type of unusual
6308 symbols before becoming silent about the problem. Set @var{limit} to
6309 zero to suppress all complaints; set it to a large number to prevent
6310 complaints from being suppressed.
6312 @kindex show complaints
6313 @item show complaints
6314 Displays how many symbol complaints _GDBN__ is permitted to produce.
6317 By default, _GDBN__ is cautious, and asks what sometimes seem to be a
6318 lot of stupid questions to confirm certain commands. For example, if
6319 you try to run a program which is already running:
6322 The program being debugged has been started already.
6323 Start it from the beginning? (y or n)
6326 If you're willing to unflinchingly face the consequences of your own
6327 commands, you can disable this ``feature'':
6332 @cindex confirmation
6333 @cindex stupid questions
6334 @item set confirm off
6335 Disables confirmation requests.
6337 @item set confirm on
6338 Enables confirmation requests (the default).
6341 @kindex show confirm
6342 Displays state of confirmation requests.
6345 @c FIXME this doesn't really belong here. But where *does* it belong?
6346 @cindex reloading symbols
6347 Some systems allow individual object files that make up your program to
6348 be replaced without stopping and restarting your program.
6350 For example, in VxWorks you can simply recompile a defective object file
6351 and keep on running.
6353 If you're running on one of these systems, you can allow _GDBN__ to
6354 reload the symbols for automatically relinked modules:@refill
6356 @kindex set symbol-reloading
6357 @item set symbol-reloading on
6358 Replace symbol definitions for the corresponding source file when an
6359 object file with a particular name is seen again.
6361 @item set symbol-reloading off
6362 Don't replace symbol definitions when re-encountering object files of
6363 the same name. This is the default state; if you're not running on a
6364 system that permits automatically relinking modules, you should leave
6365 @code{symbol-reloading} off, since otherwise _GDBN__ may discard symbols
6366 when linking large programs, that may contain several modules (from
6367 different directories or libraries) with the same name.
6369 @item show symbol-reloading
6370 Show the current @code{on} or @code{off} setting.
6373 @node Sequences, Emacs, Controlling _GDBN__, Top
6374 @chapter Canned Sequences of Commands
6376 Aside from breakpoint commands (@pxref{Break Commands}), _GDBN__ provides two
6377 ways to store sequences of commands for execution as a unit:
6378 user-defined commands and command files.
6381 * Define:: User-Defined Commands
6382 * Command Files:: Command Files
6383 * Output:: Commands for Controlled Output
6386 @node Define, Command Files, Sequences, Sequences
6387 @section User-Defined Commands
6389 @cindex user-defined command
6390 A @dfn{user-defined command} is a sequence of _GDBN__ commands to which you
6391 assign a new name as a command. This is done with the @code{define}
6395 @item define @var{commandname}
6397 Define a command named @var{commandname}. If there is already a command
6398 by that name, you are asked to confirm that you want to redefine it.
6400 The definition of the command is made up of other _GDBN__ command lines,
6401 which are given following the @code{define} command. The end of these
6402 commands is marked by a line containing @code{end}.
6404 @item document @var{commandname}
6406 Give documentation to the user-defined command @var{commandname}. The
6407 command @var{commandname} must already be defined. This command reads
6408 lines of documentation just as @code{define} reads the lines of the
6409 command definition, ending with @code{end}. After the @code{document}
6410 command is finished, @code{help} on command @var{commandname} will print
6411 the documentation you have specified.
6413 You may use the @code{document} command again to change the
6414 documentation of a command. Redefining the command with @code{define}
6415 does not change the documentation.
6417 @item help user-defined
6418 @kindex help user-defined
6419 List all user-defined commands, with the first line of the documentation
6423 @itemx info user @var{commandname}
6425 Display the _GDBN__ commands used to define @var{commandname} (but not its
6426 documentation). If no @var{commandname} is given, display the
6427 definitions for all user-defined commands.
6430 User-defined commands do not take arguments. When they are executed, the
6431 commands of the definition are not printed. An error in any command
6432 stops execution of the user-defined command.
6434 Commands that would ask for confirmation if used interactively proceed
6435 without asking when used inside a user-defined command. Many _GDBN__ commands
6436 that normally print messages to say what they are doing omit the messages
6437 when used in a user-defined command.
6439 @node Command Files, Output, Define, Sequences
6440 @section Command Files
6442 @cindex command files
6443 A command file for _GDBN__ is a file of lines that are _GDBN__ commands. Comments
6444 (lines starting with @kbd{#}) may also be included. An empty line in a
6445 command file does nothing; it does not mean to repeat the last command, as
6446 it would from the terminal.
6449 @cindex @file{_GDBINIT__}
6450 When you start _GDBN__, it automatically executes commands from its
6451 @dfn{init files}. These are files named @file{_GDBINIT__}. _GDBN__
6452 reads the init file (if any) in your home directory and then the init
6453 file (if any) in the current working directory. (The init files are not
6454 executed if you use the @samp{-nx} option; @pxref{Mode Options}.) You
6455 can also request the execution of a command file with the @code{source}
6459 @item source @var{filename}
6461 Execute the command file @var{filename}.
6464 The lines in a command file are executed sequentially. They are not
6465 printed as they are executed. An error in any command terminates execution
6466 of the command file.
6468 Commands that would ask for confirmation if used interactively proceed
6469 without asking when used in a command file. Many _GDBN__ commands that
6470 normally print messages to say what they are doing omit the messages
6471 when called from command files.
6473 @node Output, , Command Files, Sequences
6474 @section Commands for Controlled Output
6476 During the execution of a command file or a user-defined command, normal
6477 _GDBN__ output is suppressed; the only output that appears is what is
6478 explicitly printed by the commands in the definition. This section
6479 describes three commands useful for generating exactly the output you
6483 @item echo @var{text}
6485 @c I don't consider backslash-space a standard C escape sequence
6486 @c because it's not in ANSI.
6487 Print @var{text}. Nonprinting characters can be included in @var{text}
6488 using C escape sequences, such as @samp{\n} to print a newline. @b{No
6489 newline will be printed unless you specify one.} In addition to the
6490 standard C escape sequences, a backslash followed by a space stands for a
6491 space. This is useful for outputting a string with spaces at the
6492 beginning or the end, since leading and trailing spaces are otherwise
6493 trimmed from all arguments. Thus, to print @samp{@ and foo =@ }, use the
6494 command @samp{echo \@ and foo = \@ }.
6495 @c FIXME: verify hard copy actually issues enspaces for '@ '! Will this
6498 A backslash at the end of @var{text} can be used, as in C, to continue
6499 the command onto subsequent lines. For example,
6502 echo This is some text\n\
6503 which is continued\n\
6504 onto several lines.\n
6507 produces the same output as
6510 echo This is some text\n
6511 echo which is continued\n
6512 echo onto several lines.\n
6515 @item output @var{expression}
6517 Print the value of @var{expression} and nothing but that value: no
6518 newlines, no @samp{$@var{nn} = }. The value is not entered in the
6519 value history either. @xref{Expressions} for more information on
6522 @item output/@var{fmt} @var{expression}
6523 Print the value of @var{expression} in format @var{fmt}. You can use
6524 the same formats as for @code{print}; @pxref{Output formats}, for more
6527 @item printf @var{string}, @var{expressions}@dots{}
6529 Print the values of the @var{expressions} under the control of
6530 @var{string}. The @var{expressions} are separated by commas and may
6531 be either numbers or pointers. Their values are printed as specified
6532 by @var{string}, exactly as if the program were to execute
6535 printf (@var{string}, @var{expressions}@dots{});
6538 For example, you can print two values in hex like this:
6541 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
6544 The only backslash-escape sequences that you can use in the format
6545 string are the simple ones that consist of backslash followed by a
6549 @node Emacs, _GDBN__ Bugs, Sequences, Top
6550 @chapter Using _GDBN__ under GNU Emacs
6553 A special interface allows you to use GNU Emacs to view (and
6554 edit) the source files for the program you are debugging with
6557 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
6558 executable file you want to debug as an argument. This command starts
6559 _GDBN__ as a subprocess of Emacs, with input and output through a newly
6560 created Emacs buffer.
6562 Using _GDBN__ under Emacs is just like using _GDBN__ normally except for two
6567 All ``terminal'' input and output goes through the Emacs buffer.
6570 This applies both to _GDBN__ commands and their output, and to the input
6571 and output done by the program you are debugging.
6573 This is useful because it means that you can copy the text of previous
6574 commands and input them again; you can even use parts of the output
6577 All the facilities of Emacs' Shell mode are available for interacting
6578 with your program. In particular, you can send signals the usual
6579 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
6584 _GDBN__ displays source code through Emacs.
6587 Each time _GDBN__ displays a stack frame, Emacs automatically finds the
6588 source file for that frame and puts an arrow (_0__@samp{=>}_1__) at the
6589 left margin of the current line. Emacs uses a separate buffer for
6590 source display, and splits the window to show both your _GDBN__ session
6593 Explicit _GDBN__ @code{list} or search commands still produce output as
6594 usual, but you probably will have no reason to use them.
6597 @emph{Warning:} If the directory where your program resides is not your
6598 current directory, it can be easy to confuse Emacs about the location of
6599 the source files, in which case the auxiliary display buffer will not
6600 appear to show your source. _GDBN__ can find programs by searching your
6601 environment's @code{PATH} variable, so the _GDBN__ input and output
6602 session will proceed normally; but Emacs doesn't get enough information
6603 back from _GDBN__ to locate the source files in this situation. To
6604 avoid this problem, either start _GDBN__ mode from the directory where
6605 your program resides, or specify a full path name when prompted for the
6606 @kbd{M-x gdb} argument.
6608 A similar confusion can result if you use the _GDBN__ @code{file} command to
6609 switch to debugging a program in some other location, from an existing
6610 _GDBN__ buffer in Emacs.
6613 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
6614 you need to call _GDBN__ by a different name (for example, if you keep
6615 several configurations around, with different names) you can set the
6616 Emacs variable @code{gdb-command-name}; for example,
6618 (setq gdb-command-name "mygdb")
6621 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
6622 in your @file{.emacs} file) will make Emacs call the program named
6623 ``@code{mygdb}'' instead.
6625 In the _GDBN__ I/O buffer, you can use these special Emacs commands in
6626 addition to the standard Shell mode commands:
6630 Describe the features of Emacs' _GDBN__ Mode.
6633 Execute to another source line, like the _GDBN__ @code{step} command; also
6634 update the display window to show the current file and location.
6637 Execute to next source line in this function, skipping all function
6638 calls, like the _GDBN__ @code{next} command. Then update the display window
6639 to show the current file and location.
6642 Execute one instruction, like the _GDBN__ @code{stepi} command; update
6643 display window accordingly.
6646 Execute to next instruction, using the _GDBN__ @code{nexti} command; update
6647 display window accordingly.
6650 Execute until exit from the selected stack frame, like the _GDBN__
6651 @code{finish} command.
6654 Continue execution of the program, like the _GDBN__ @code{continue}
6655 command. @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
6658 Go up the number of frames indicated by the numeric argument
6659 (@pxref{Arguments, , Numeric Arguments, emacs, The GNU Emacs Manual}),
6660 like the _GDBN__ @code{up} command. @emph{Warning:} In Emacs v19, this
6661 command is @kbd{C-c C-u}.@refill
6664 Go down the number of frames indicated by the numeric argument, like the
6665 _GDBN__ @code{down} command. @emph{Warning:} In Emacs v19, this command
6669 Read the number where the cursor is positioned, and insert it at the end
6670 of the _GDBN__ I/O buffer. For example, if you wish to disassemble code
6671 around an address that was displayed earlier, type @kbd{disassemble};
6672 then move the cursor to the address display, and pick up the
6673 argument for @code{disassemble} by typing @kbd{C-x &}.
6675 You can customize this further on the fly by defining elements of the list
6676 @code{gdb-print-command}; once it is defined, you can format or
6677 otherwise process numbers picked up by @kbd{C-x &} before they are
6678 inserted. A numeric argument to @kbd{C-x &} will both indicate that you
6679 wish special formatting, and act as an index to pick an element of the
6680 list. If the list element is a string, the number to be inserted is
6681 formatted using the Emacs function @code{format}; otherwise the number
6682 is passed as an argument to the corresponding list element.
6686 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
6687 tells _GDBN__ to set a breakpoint on the source line point is on.
6689 If you accidentally delete the source-display buffer, an easy way to get
6690 it back is to type the command @code{f} in the _GDBN__ buffer, to
6691 request a frame display; when you run under Emacs, this will recreate
6692 the source buffer if necessary to show you the context of the current
6695 The source files displayed in Emacs are in ordinary Emacs buffers
6696 which are visiting the source files in the usual way. You can edit
6697 the files with these buffers if you wish; but keep in mind that _GDBN__
6698 communicates with Emacs in terms of line numbers. If you add or
6699 delete lines from the text, the line numbers that _GDBN__ knows will cease
6700 to correspond properly to the code.
6702 @c The following dropped because Epoch is nonstandard. Reactivate
6703 @c if/when v19 does something similar. ---pesch@cygnus.com 19dec1990
6705 @kindex emacs epoch environment
6709 Version 18 of Emacs has a built-in window system called the @code{epoch}
6710 environment. Users of this environment can use a new command,
6711 @code{inspect} which performs identically to @code{print} except that
6712 each value is printed in its own window.
6715 @node _GDBN__ Bugs, Renamed Commands, Emacs, Top
6716 @chapter Reporting Bugs in _GDBN__
6717 @cindex Bugs in _GDBN__
6718 @cindex Reporting Bugs in _GDBN__
6720 Your bug reports play an essential role in making _GDBN__ reliable.
6722 Reporting a bug may help you by bringing a solution to your problem, or it
6723 may not. But in any case the principal function of a bug report is to help
6724 the entire community by making the next version of _GDBN__ work better. Bug
6725 reports are your contribution to the maintenance of _GDBN__.
6727 In order for a bug report to serve its purpose, you must include the
6728 information that enables us to fix the bug.
6731 * Bug Criteria:: Have You Found a Bug?
6732 * Bug Reporting:: How to Report Bugs
6735 @node Bug Criteria, Bug Reporting, _GDBN__ Bugs, _GDBN__ Bugs
6736 @section Have You Found a Bug?
6737 @cindex Bug Criteria
6739 If you are not sure whether you have found a bug, here are some guidelines:
6743 @cindex Fatal Signal
6745 If the debugger gets a fatal signal, for any input whatever, that is a
6746 _GDBN__ bug. Reliable debuggers never crash.
6749 @cindex error on Valid Input
6750 If _GDBN__ produces an error message for valid input, that is a bug.
6753 @cindex Invalid Input
6754 If _GDBN__ does not produce an error message for invalid input,
6755 that is a bug. However, you should note that your idea of
6756 ``invalid input'' might be our idea of ``an extension'' or ``support
6757 for traditional practice''.
6760 If you are an experienced user of debugging tools, your suggestions
6761 for improvement of _GDBN__ are welcome in any case.
6764 @node Bug Reporting, , Bug Criteria, _GDBN__ Bugs
6765 @section How to Report Bugs
6767 @cindex _GDBN__ Bugs, Reporting
6769 A number of companies and individuals offer support for GNU products.
6770 If you obtained _GDBN__ from a support organization, we recommend you
6771 contact that organization first.
6773 Contact information for many support companies and individuals is
6774 available in the file @file{etc/SERVICE} in the GNU Emacs distribution.
6776 In any event, we also recommend that you send bug reports for _GDBN__ to one
6780 bug-gdb@@prep.ai.mit.edu
6781 @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb
6784 @strong{Do not send bug reports to @samp{info-gdb}, or to
6785 @samp{help-gdb}, or to any newsgroups.} Most users of _GDBN__ do not want to
6786 receive bug reports. Those that do, have arranged to receive @samp{bug-gdb}.
6788 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
6789 serves as a repeater. The mailing list and the newsgroup carry exactly
6790 the same messages. Often people think of posting bug reports to the
6791 newsgroup instead of mailing them. This appears to work, but it has one
6792 problem which can be crucial: a newsgroup posting often lacks a mail
6793 path back to the sender. Thus, if we need to ask for more information,
6794 we may be unable to reach you. For this reason, it is better to send
6795 bug reports to the mailing list.
6797 As a last resort, send bug reports on paper to:
6801 Free Software Foundation
6806 The fundamental principle of reporting bugs usefully is this:
6807 @strong{report all the facts}. If you are not sure whether to state a
6808 fact or leave it out, state it!
6810 Often people omit facts because they think they know what causes the
6811 problem and assume that some details don't matter. Thus, you might
6812 assume that the name of the variable you use in an example does not matter.
6813 Well, probably it doesn't, but one cannot be sure. Perhaps the bug is a
6814 stray memory reference which happens to fetch from the location where that
6815 name is stored in memory; perhaps, if the name were different, the contents
6816 of that location would fool the debugger into doing the right thing despite
6817 the bug. Play it safe and give a specific, complete example. That is the
6818 easiest thing for you to do, and the most helpful.
6820 Keep in mind that the purpose of a bug report is to enable us to fix
6821 the bug if it is new to us. It isn't as important what happens if
6822 the bug is already known. Therefore, always write your bug reports on
6823 the assumption that the bug has not been reported previously.
6825 Sometimes people give a few sketchy facts and ask, ``Does this ring a
6826 bell?'' Those bug reports are useless, and we urge everyone to
6827 @emph{refuse to respond to them} except to chide the sender to report
6830 To enable us to fix the bug, you should include all these things:
6834 The version of _GDBN__. _GDBN__ announces it if you start with no
6835 arguments; you can also print it at any time using @code{show version}.
6837 Without this, we won't know whether there is any point in looking for
6838 the bug in the current version of _GDBN__.
6841 A complete input script, and all necessary source files, that will
6845 What compiler (and its version) was used to compile _GDBN__---e.g.
6849 The command arguments you gave the compiler to compile your example and
6850 observe the bug. For example, did you use @samp{-O}? To guarantee
6851 you won't omit something important, list them all.
6853 If we were to try to guess the arguments, we would probably guess wrong
6854 and then we might not encounter the bug.
6857 The type of machine you are using, and the operating system name and
6861 A description of what behavior you observe that you believe is
6862 incorrect. For example, ``It gets a fatal signal.''
6864 Of course, if the bug is that _GDBN__ gets a fatal signal, then we will
6865 certainly notice it. But if the bug is incorrect output, we might not
6866 notice unless it is glaringly wrong. We are human, after all. You
6867 might as well not give us a chance to make a mistake.
6869 Even if the problem you experience is a fatal signal, you should still
6870 say so explicitly. Suppose something strange is going on, such as,
6871 your copy of _GDBN__ is out of synch, or you have encountered a
6872 bug in the C library on your system. (This has happened!) Your copy
6873 might crash and ours would not. If you told us to expect a crash,
6874 then when ours fails to crash, we would know that the bug was not
6875 happening for us. If you had not told us to expect a crash, then we
6876 would not be able to draw any conclusion from our observations.
6879 If you wish to suggest changes to the _GDBN__ source, send us context
6880 diffs. If you even discuss something in the _GDBN__ source, refer to
6881 it by context, not by line number.
6883 The line numbers in our development sources won't match those in your
6884 sources. Your line numbers would convey no useful information to us.
6888 Here are some things that are not necessary:
6892 A description of the envelope of the bug.
6894 Often people who encounter a bug spend a lot of time investigating
6895 which changes to the input file will make the bug go away and which
6896 changes will not affect it.
6898 This is often time consuming and not very useful, because the way we
6899 will find the bug is by running a single example under the debugger
6900 with breakpoints, not by pure deduction from a series of examples.
6901 We recommend that you save your time for something else.
6903 Of course, if you can find a simpler example to report @emph{instead}
6904 of the original one, that is a convenience for us. Errors in the
6905 output will be easier to spot, running under the debugger will take
6908 However, simplification is not vital; if you don't want to do this,
6909 report the bug anyway and send us the entire test case you used.
6912 A patch for the bug.
6914 A patch for the bug does help us if it is a good one. But don't omit
6915 the necessary information, such as the test case, on the assumption that
6916 a patch is all we need. We might see problems with your patch and decide
6917 to fix the problem another way, or we might not understand it at all.
6919 Sometimes with a program as complicated as _GDBN__ it is very hard to
6920 construct an example that will make the program follow a certain path
6921 through the code. If you don't send us the example, we won't be able
6922 to construct one, so we won't be able to verify that the bug is fixed.
6924 And if we can't understand what bug you are trying to fix, or why your
6925 patch should be an improvement, we won't install it. A test case will
6926 help us to understand.
6929 A guess about what the bug is or what it depends on.
6931 Such guesses are usually wrong. Even we can't guess right about such
6932 things without first using the debugger to find the facts.
6936 @include rdl-apps.texi
6939 @node Renamed Commands, Installing _GDBN__, _GDBN__ Bugs, Top
6940 @appendix Renamed Commands
6942 The following commands were renamed in _GDBN__ 4.0, in order to make the
6943 command set as a whole more consistent and easier to use and remember:
6946 @kindex delete environment
6947 @kindex info copying
6948 @kindex info convenience
6949 @kindex info directories
6950 @kindex info editing
6951 @kindex info history
6952 @kindex info targets
6954 @kindex info version
6955 @kindex info warranty
6956 @kindex set addressprint
6957 @kindex set arrayprint
6958 @kindex set prettyprint
6959 @kindex set screen-height
6960 @kindex set screen-width
6961 @kindex set unionprint
6962 @kindex set vtblprint
6963 @kindex set demangle
6964 @kindex set asm-demangle
6965 @kindex set sevenbit-strings
6966 @kindex set array-max
6968 @kindex set history write
6969 @kindex show addressprint
6970 @kindex show arrayprint
6971 @kindex show prettyprint
6972 @kindex show screen-height
6973 @kindex show screen-width
6974 @kindex show unionprint
6975 @kindex show vtblprint
6976 @kindex show demangle
6977 @kindex show asm-demangle
6978 @kindex show sevenbit-strings
6979 @kindex show array-max
6980 @kindex show caution
6981 @kindex show history write
6986 OLD COMMAND NEW COMMAND
6987 --------------- -------------------------------
6988 add-syms add-symbol-file
6989 delete environment unset environment
6990 info convenience show convenience
6991 info copying show copying
6992 info directories show directories
6993 info editing show commands
6994 info history show values
6995 info targets help target
6996 info values show values
6997 info version show version
6998 info warranty show warranty
6999 set/show addressprint set/show print address
7000 set/show array-max set/show print elements
7001 set/show arrayprint set/show print array
7002 set/show asm-demangle set/show print asm-demangle
7003 set/show caution set/show confirm
7004 set/show demangle set/show print demangle
7005 set/show history write set/show history save
7006 set/show prettyprint set/show print pretty
7007 set/show screen-height set/show height
7008 set/show screen-width set/show width
7009 set/show sevenbit-strings set/show print sevenbit-strings
7010 set/show unionprint set/show print union
7011 set/show vtblprint set/show print vtbl
7013 unset [No longer an alias for delete]
7018 \vskip \parskip\vskip \baselineskip
7019 \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr
7020 {\bf Old Command} &&{\bf New Command}\cr
7021 add-syms &&add-symbol-file\cr
7022 delete environment &&unset environment\cr
7023 info convenience &&show convenience\cr
7024 info copying &&show copying\cr
7025 info directories &&show directories \cr
7026 info editing &&show commands\cr
7027 info history &&show values\cr
7028 info targets &&help target\cr
7029 info values &&show values\cr
7030 info version &&show version\cr
7031 info warranty &&show warranty\cr
7032 set{\rm / }show addressprint &&set{\rm / }show print address\cr
7033 set{\rm / }show array-max &&set{\rm / }show print elements\cr
7034 set{\rm / }show arrayprint &&set{\rm / }show print array\cr
7035 set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr
7036 set{\rm / }show caution &&set{\rm / }show confirm\cr
7037 set{\rm / }show demangle &&set{\rm / }show print demangle\cr
7038 set{\rm / }show history write &&set{\rm / }show history save\cr
7039 set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr
7040 set{\rm / }show screen-height &&set{\rm / }show height\cr
7041 set{\rm / }show screen-width &&set{\rm / }show width\cr
7042 set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr
7043 set{\rm / }show unionprint &&set{\rm / }show print union\cr
7044 set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr
7046 unset &&\rm(No longer an alias for delete)\cr
7050 @node Installing _GDBN__, Copying, Renamed Commands, Top
7051 @appendix Installing _GDBN__
7052 @cindex configuring _GDBN__
7053 @cindex installation
7055 _GDBN__ comes with a @code{configure} script that automates the process
7056 of preparing _GDBN__ for installation; you can then use @code{make} to
7057 build the @code{_GDBP__} program.
7059 The _GDBP__ distribution includes all the source code you need for
7060 _GDBP__ in a single directory @file{gdb-_GDB_VN__}. That directory in turn
7064 @item gdb-_GDB_VN__/configure
7065 Overall script for configuring _GDBN__ and all its supporting libraries.
7067 @item gdb-_GDB_VN__/gdb
7068 the source specific to _GDBN__ itself
7070 @item gdb-_GDB_VN__/bfd
7071 source for the Binary File Descriptor Library
7073 @item gdb-_GDB_VN__/include
7076 @item gdb-_GDB_VN__/libiberty
7077 source for the @samp{-liberty} free software library
7079 @item gdb-_GDB_VN__/readline
7080 source for the GNU command-line interface
7083 Each of these directories has its own @code{configure} script, which are
7084 used by the overall @code{configure} script in @file{gdb-_GDB_VN__}.
7086 It is most convenient to run @code{configure} from the @file{gdb-_GDB_VN__}
7087 directory. The simplest way to configure and build _GDBN__ is the
7091 ./configure @var{host}
7095 where @var{host} is something like @samp{sun4} or @samp{decstation}, that
7096 identifies the platform where _GDBN__ will run. This builds the three
7097 libraries @file{bfd}, @file{readline}, and @file{libiberty}, then
7098 @code{gdb} itself. The configured source files, and the binaries, are
7099 left in the corresponding source directories.
7101 You can install @code{_GDBP__} anywhere; it has no hardwired paths. However,
7102 you should make sure that the shell on your path (named by the
7103 @samp{SHELL} environment variable) is publicly readable; some systems
7104 refuse to let _GDBN__ debug child processes whose programs are not
7105 readable, and _GDBN__ uses the shell to start your program.
7108 * Subdirectories:: Configuration subdirectories
7109 * Config Names:: Specifying names for hosts and targets
7110 * configure Options:: Summary of options for configure
7111 * Formatting Documentation:: How to format and print _GDBN__ documentation
7115 @node Subdirectories, Config Names, Installing _GDBN__, Installing _GDBN__
7116 @section Configuration Subdirectories
7117 If you want to run _GDBN__ versions for several host or target machines,
7118 you'll need a different _GDBP__ compiled for each combination of host
7119 and target. @code{configure} is designed to make this easy by allowing
7120 you to generate each configuration in a separate subdirectory. If your
7121 @code{make} program handles the @samp{VPATH} feature (GNU @code{make}
7122 does), running @code{make} in each of these directories then builds the
7123 _GDBP__ program specified there.
7125 @code{configure} creates these subdirectories for you when you
7126 simultaneously specify several configurations; but it's a good habit
7127 even for a single configuration. You can specify the use of
7128 subdirectories using the @samp{+subdirs} option (abbreviated
7129 @samp{+sub}). For example, you can build _GDBN__ on a Sun 4 as follows:
7134 ./configure +sub sun4
7135 cd Host-sparc-sun-sunos4/Target-sparc-sun-sunos4
7140 When @code{configure} uses subdirectories to build programs or
7141 libraries, it creates nested directories
7142 @file{Host-@var{host}/Target-@var{target}}. (As you see in the example,
7143 the names used for @var{host} and @var{target} may be expanded from your
7144 @code{configure} argument; @pxref{Config Names}). @code{configure} uses
7145 these two directory levels because _GDBN__ can be configured for
7146 cross-compiling: _GDBN__ can run on one machine (the host) while
7147 debugging programs that run on another machine (the target). You
7148 specify cross-debugging targets by giving the
7149 @samp{+target=@var{target}} option to @code{configure}. Specifying only
7150 hosts still gives you two levels of subdirectory for each host, with the
7151 same configuration suffix on both; that is, if you give any number of
7152 hosts but no targets, _GDBN__ will be configured for native debugging on
7153 each host. On the other hand, whenever you specify both hosts and
7154 targets on the same command line, @code{configure} creates all
7155 combinations of the hosts and targets you list.@refill
7157 When you run @code{make} to build a program or library, you must run it
7158 in a configured directory. If you made a single configuration,
7159 without subdirectories, run @code{make} in the source directory.
7160 If you have @file{Host-@var{host}/Target-@var{target}} subdirectories,
7161 run @code{make} in those subdirectories.
7163 Each @code{configure} and @code{Makefile} under each source directory
7164 runs recursively, so that typing @code{make} in @file{gdb-_GDB_VN__} (or in a
7165 @file{gdb-_GDB_VN__/Host-@var{host}/Target-@var{target}} subdirectory)
7166 builds all the required libraries, then _GDBN__.@refill
7168 If you run @code{configure} from a directory (such as @file{gdb-_GDB_VN__}) that
7169 contains source directories for multiple libraries or programs,
7170 @code{configure} creates the @file{Host-@var{host}/Target-@var{target}}
7171 subdirectories in each library or program's source directory. For
7175 configure sun4 +target=vxworks960
7178 creates the following directories:
7180 gdb-_GDB_VN__/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks
7181 gdb-_GDB_VN__/bfd/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks
7182 gdb-_GDB_VN__/gdb/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks
7183 gdb-_GDB_VN__/libiberty/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks
7184 gdb-_GDB_VN__/readline/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks
7187 The @code{Makefile} in
7189 gdb-_GDB_VN__/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks
7192 will @code{cd} to the appropriate lower-level directories, for example:
7194 gdb-_GDB_VN__/bfd/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks
7197 building each in turn.
7199 When you have multiple hosts or targets configured, you can run
7200 @code{make} on them in parallel (for example, if they are NFS-mounted on
7201 each of the hosts); they will not interfere with each other.
7205 @c FIXME isn't there something kinder, gentler than @page?
7208 @node Config Names, configure Options, Subdirectories, Installing _GDBN__
7209 @section Specifying Names for Hosts and Targets
7211 The specifications used for hosts and targets in the @code{configure}
7212 script are based on a three-part naming scheme, but some short predefined
7213 aliases are also supported. The full naming scheme encodes three pieces
7214 of information in the following pattern:
7216 @var{architecture}-@var{vendor}-@var{os}
7219 For example, you can use the alias @code{sun4} as a @var{host} argument
7220 or in a @code{+target=@var{target}} option, but the full name of that
7221 configuration specifies that the architecture is @samp{sparc}, the
7222 vendor is @samp{sun}, and the operating system is @samp{sunos4}.
7225 @c I know this is ugly, but @group is useless except in examples now...
7226 @c (using texinfo 2.52 or so)
7230 The following table shows all the architectures, hosts, and OS prefixes
7231 that @code{configure} recognizes in _GDBN__ _GDB_VN__. Entries in the ``OS
7232 prefix'' column ending in a @samp{*} may be followed by a release number.
7237 ARCHITECTURE VENDOR OS prefix
7238 ------------+-------------+-------------
7241 a29k | amdahl | amigados
7242 alliant | aout | aout
7247 h8300 | bout | dynix*
7250 i960 | convergent | irix*
7251 m68000 | convex | isc*
7254 mips | encore | newsos*
7255 ns32k | gould | nindy*
7258 rs6000 | intel | sco*
7260 sparc | little | svr4
7262 tron | motorola | sysv*
7278 @emph{Warning:} Many combinations of architecture, vendor, and OS are
7282 @c FIXME: this table is probably screwed in @smallbook. Try setting
7283 @c FIXME...smallbook fonts?
7286 \vskip \baselineskip
7287 \halign{\hskip\parindent\tt #\hfil &\qquad#&\tt #\hfil &\qquad#&\tt
7288 #\hfil &\qquad\qquad\it #\hfil\cr
7289 {\bf Architecture} &&{\bf Vendor} &&{\bf OS prefix}\cr
7290 \multispan5\hrulefill\cr
7291 580 && altos && aix* \cr
7292 a29k && amdahl && amigados\cr
7293 alliant && aout && aout \cr
7294 arm && apollo && bout \cr
7295 c1 && att && bsd* \cr
7296 c2 && bull && coff \cr
7297 cray2 && bcs && ctix* \cr
7298 h8300 && bout && dynix* \cr
7299 i386 && cbm && esix* \cr
7300 i860 && coff && hpux* &Warning: \cr
7301 i960 && convergent && irix* &Many combinations \cr
7302 m68000 && convex && isc* &of architecture, vendor \cr
7303 m68k && cray && kern &and OS are untested. \cr
7304 m88k && dec && mach* \cr
7305 mips && encore && newsos* \cr
7306 ns32k && gould && nindy* \cr
7307 pyramid && hp && none \cr
7308 romp && ibm && osf* \cr
7309 rs6000 && intel && sco* \cr
7310 rtpc && isi && sunos* \cr
7311 sparc && little && svr4 \cr
7312 tahoe && mips && sym* \cr
7313 tron && motorola && sysv* \cr
7314 vax && ncr && ultrix* \cr
7315 xmp && next && unicos \cr
7316 ymp && none && unos* \cr
7319 && sequent && vms* \cr
7320 && sgi && vxworks*\cr
7329 The @code{configure} script accompanying _GDBN__ _GDB_VN__ does not provide
7330 any query facility to list all supported host and target names or
7331 aliases. @code{configure} calls the Bourne shell script
7332 @code{config.sub} to map abbreviations to full names; you can read the
7333 script, if you wish, or you can use it to test your guesses on
7334 abbreviations---for example:
7336 % sh config.sub sun4
7338 % sh config.sub sun3
7340 % sh config.sub decstation
7342 % sh config.sub hp300bsd
7344 % sh config.sub i386v
7346 % sh config.sub i486v
7347 *** No vendor: configuration `i486v' not recognized
7350 @node configure Options, Formatting Documentation, Config Names, Installing _GDBN__
7351 @section @code{configure} Options
7353 Here is a summary of all the @code{configure} options and arguments that
7354 you might use for building _GDBN__:
7357 configure @r{[}+destdir=@var{dir}@r{]} @r{[}+subdirs@r{]} @r{[}+norecur@r{]} @r{[}+rm@r{]}
7358 @r{[}+target=@var{target}@dots{}@r{]} @var{host}@dots{}
7361 You may introduce options with the character @samp{-} rather than
7362 @samp{+} if you prefer; but you may abbreviate option names if you use
7366 @item +destdir=@var{dir}
7367 @var{dir} is an installation directory @emph{path prefix}. After you
7368 configure with this option, @code{make install} will install _GDBN__ as
7369 @file{@var{dir}/bin/_GDBP__}, and the libraries in @file{@var{dir}/lib}.
7370 If you specify @samp{+destdir=/usr/local}, for example, @code{make
7371 install} creates @file{/usr/local/bin/gdb}.@refill
7374 Write configuration specific files in subdirectories of the form
7376 Host-@var{host}/Target-@var{target}
7379 (and configure the @code{Makefile} to write binaries there too).
7380 Without this option, if you specify only one configuration for _GDBN__,
7381 @code{configure} will use the same directory for source, configured
7382 files, and binaries. This option is used automatically if you specify
7383 more than one @var{host} or more than one @samp{+target=@var{target}}
7384 option on the @code{configure} command line.
7387 Configure only the directory where @code{configure} is executed; do not
7388 propagate configuration to subdirectories.
7391 Remove the configuration that the other arguments specify.
7393 @c This doesn't work (yet if ever). FIXME.
7394 @c @item +parse=@var{lang} @dots{}
7395 @c Configure the _GDBN__ expression parser to parse the listed languages.
7396 @c @samp{all} configures _GDBN__ for all supported languages. To get a
7397 @c list of all supported languages, omit the argument. Without this
7398 @c option, _GDBN__ is configured to parse all supported languages.
7400 @item +target=@var{target} @dots{}
7401 Configure _GDBN__ for cross-debugging programs running on each specified
7402 @var{target}. You may specify as many @samp{+target} options as you
7403 wish. Without this option, _GDBN__ is configured to debug programs that
7404 run on the same machine (@var{host}) as _GDBN__ itself.
7406 There is no convenient way to generate a list of all available targets.
7408 @item @var{host} @dots{}
7409 Configure _GDBN__ to run on each specified @var{host}. You may specify as
7410 many host names as you wish.
7412 There is no convenient way to generate a list of all available hosts.
7416 @code{configure} accepts other options, for compatibility with
7417 configuring other GNU tools recursively; but these are the only
7418 options that affect _GDBN__ or its supporting libraries.
7420 @node Formatting Documentation, , configure Options, Installing _GDBN__
7421 @section Formatting the Documentation
7423 @cindex _GDBN__ reference card
7424 @cindex reference card
7425 The _GDBN__ _GDB_VN__ release includes an already-formatted reference card,
7426 ready for printing on a PostScript printer, as @file{gdb-_GDB_VN__/gdb/refcard.ps}.
7427 It uses the most common PostScript fonts: the Times family, Courier, and
7428 Symbol. If you have a PostScript printer, you can print the reference
7429 card by just sending @file{refcard.ps} to the printer.
7431 The release also includes the online Info version of this manual already
7432 formatted: the main Info file is @file{gdb-_GDB_VN__/gdb/gdb.info}, and it
7433 refers to subordinate files matching @samp{gdb.info*} in the same
7436 If you want to make these Info files yourself from the _GDBN__ manual's
7437 source, you need the GNU @code{makeinfo} program. Once you have it, you
7440 cd gdb-_GDB_VN__/gdb
7444 to make the Info file.
7446 If you want to format and print copies of the manual, you need several
7450 @TeX{}, the public domain typesetting program written by Donald Knuth,
7451 must be installed on your system and available through your execution
7454 @file{gdb-_GDB_VN__/texinfo}: @TeX{} macros defining the GNU
7455 Documentation Format.
7457 @emph{A @sc{dvi} output program.} @TeX{} doesn't actually make marks on
7458 paper; it produces output files called @sc{dvi} files. If your system
7459 has @TeX{} installed, chances are it has a program for printing out
7460 these files; one popular example is @code{dvips}, which can print
7461 @sc{dvi} files on PostScript printers.
7464 Once you have these things, you can type
7466 cd gdb-_GDB_VN__/gdb
7470 to format the text of this manual, and print it with the usual output
7471 method for @TeX{} @sc{dvi} files at your site.
7473 If you want to print the reference card, but don't have a PostScript
7474 printer, or you want to use Computer Modern fonts instead,
7475 you can still print it if you have @TeX{}. Format the reference card by typing
7477 cd gdb-_GDB_VN__/gdb
7482 The _GDBN__ reference card is designed to print in landscape mode on US
7483 ``letter'' size paper; that is, on a sheet 11 inches wide by 8.5 inches
7484 high. You will need to specify this form of printing as an option to
7485 your @sc{dvi} output program.
7488 @node Copying, Index, Installing _GDBN__, Top
7489 @unnumbered GNU GENERAL PUBLIC LICENSE
7490 @center Version 2, June 1991
7493 Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc.
7494 675 Mass Ave, Cambridge, MA 02139, USA
7496 Everyone is permitted to copy and distribute verbatim copies
7497 of this license document, but changing it is not allowed.
7500 @unnumberedsec Preamble
7502 The licenses for most software are designed to take away your
7503 freedom to share and change it. By contrast, the GNU General Public
7504 License is intended to guarantee your freedom to share and change free
7505 software---to make sure the software is free for all its users. This
7506 General Public License applies to most of the Free Software
7507 Foundation's software and to any other program whose authors commit to
7508 using it. (Some other Free Software Foundation software is covered by
7509 the GNU Library General Public License instead.) You can apply it to
7512 When we speak of free software, we are referring to freedom, not
7513 price. Our General Public Licenses are designed to make sure that you
7514 have the freedom to distribute copies of free software (and charge for
7515 this service if you wish), that you receive source code or can get it
7516 if you want it, that you can change the software or use pieces of it
7517 in new free programs; and that you know you can do these things.
7519 To protect your rights, we need to make restrictions that forbid
7520 anyone to deny you these rights or to ask you to surrender the rights.
7521 These restrictions translate to certain responsibilities for you if you
7522 distribute copies of the software, or if you modify it.
7524 For example, if you distribute copies of such a program, whether
7525 gratis or for a fee, you must give the recipients all the rights that
7526 you have. You must make sure that they, too, receive or can get the
7527 source code. And you must show them these terms so they know their
7530 We protect your rights with two steps: (1) copyright the software, and
7531 (2) offer you this license which gives you legal permission to copy,
7532 distribute and/or modify the software.
7534 Also, for each author's protection and ours, we want to make certain
7535 that everyone understands that there is no warranty for this free
7536 software. If the software is modified by someone else and passed on, we
7537 want its recipients to know that what they have is not the original, so
7538 that any problems introduced by others will not reflect on the original
7539 authors' reputations.
7541 Finally, any free program is threatened constantly by software
7542 patents. We wish to avoid the danger that redistributors of a free
7543 program will individually obtain patent licenses, in effect making the
7544 program proprietary. To prevent this, we have made it clear that any
7545 patent must be licensed for everyone's free use or not licensed at all.
7547 The precise terms and conditions for copying, distribution and
7548 modification follow.
7551 @unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
7554 @center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
7559 This License applies to any program or other work which contains
7560 a notice placed by the copyright holder saying it may be distributed
7561 under the terms of this General Public License. The ``Program'', below,
7562 refers to any such program or work, and a ``work based on the Program''
7563 means either the Program or any derivative work under copyright law:
7564 that is to say, a work containing the Program or a portion of it,
7565 either verbatim or with modifications and/or translated into another
7566 language. (Hereinafter, translation is included without limitation in
7567 the term ``modification''.) Each licensee is addressed as ``you''.
7569 Activities other than copying, distribution and modification are not
7570 covered by this License; they are outside its scope. The act of
7571 running the Program is not restricted, and the output from the Program
7572 is covered only if its contents constitute a work based on the
7573 Program (independent of having been made by running the Program).
7574 Whether that is true depends on what the Program does.
7577 You may copy and distribute verbatim copies of the Program's
7578 source code as you receive it, in any medium, provided that you
7579 conspicuously and appropriately publish on each copy an appropriate
7580 copyright notice and disclaimer of warranty; keep intact all the
7581 notices that refer to this License and to the absence of any warranty;
7582 and give any other recipients of the Program a copy of this License
7583 along with the Program.
7585 You may charge a fee for the physical act of transferring a copy, and
7586 you may at your option offer warranty protection in exchange for a fee.
7589 You may modify your copy or copies of the Program or any portion
7590 of it, thus forming a work based on the Program, and copy and
7591 distribute such modifications or work under the terms of Section 1
7592 above, provided that you also meet all of these conditions:
7596 You must cause the modified files to carry prominent notices
7597 stating that you changed the files and the date of any change.
7600 You must cause any work that you distribute or publish, that in
7601 whole or in part contains or is derived from the Program or any
7602 part thereof, to be licensed as a whole at no charge to all third
7603 parties under the terms of this License.
7606 If the modified program normally reads commands interactively
7607 when run, you must cause it, when started running for such
7608 interactive use in the most ordinary way, to print or display an
7609 announcement including an appropriate copyright notice and a
7610 notice that there is no warranty (or else, saying that you provide
7611 a warranty) and that users may redistribute the program under
7612 these conditions, and telling the user how to view a copy of this
7613 License. (Exception: if the Program itself is interactive but
7614 does not normally print such an announcement, your work based on
7615 the Program is not required to print an announcement.)
7618 These requirements apply to the modified work as a whole. If
7619 identifiable sections of that work are not derived from the Program,
7620 and can be reasonably considered independent and separate works in
7621 themselves, then this License, and its terms, do not apply to those
7622 sections when you distribute them as separate works. But when you
7623 distribute the same sections as part of a whole which is a work based
7624 on the Program, the distribution of the whole must be on the terms of
7625 this License, whose permissions for other licensees extend to the
7626 entire whole, and thus to each and every part regardless of who wrote it.
7628 Thus, it is not the intent of this section to claim rights or contest
7629 your rights to work written entirely by you; rather, the intent is to
7630 exercise the right to control the distribution of derivative or
7631 collective works based on the Program.
7633 In addition, mere aggregation of another work not based on the Program
7634 with the Program (or with a work based on the Program) on a volume of
7635 a storage or distribution medium does not bring the other work under
7636 the scope of this License.
7639 You may copy and distribute the Program (or a work based on it,
7640 under Section 2) in object code or executable form under the terms of
7641 Sections 1 and 2 above provided that you also do one of the following:
7645 Accompany it with the complete corresponding machine-readable
7646 source code, which must be distributed under the terms of Sections
7647 1 and 2 above on a medium customarily used for software interchange; or,
7650 Accompany it with a written offer, valid for at least three
7651 years, to give any third party, for a charge no more than your
7652 cost of physically performing source distribution, a complete
7653 machine-readable copy of the corresponding source code, to be
7654 distributed under the terms of Sections 1 and 2 above on a medium
7655 customarily used for software interchange; or,
7658 Accompany it with the information you received as to the offer
7659 to distribute corresponding source code. (This alternative is
7660 allowed only for noncommercial distribution and only if you
7661 received the program in object code or executable form with such
7662 an offer, in accord with Subsection b above.)
7665 The source code for a work means the preferred form of the work for
7666 making modifications to it. For an executable work, complete source
7667 code means all the source code for all modules it contains, plus any
7668 associated interface definition files, plus the scripts used to
7669 control compilation and installation of the executable. However, as a
7670 special exception, the source code distributed need not include
7671 anything that is normally distributed (in either source or binary
7672 form) with the major components (compiler, kernel, and so on) of the
7673 operating system on which the executable runs, unless that component
7674 itself accompanies the executable.
7676 If distribution of executable or object code is made by offering
7677 access to copy from a designated place, then offering equivalent
7678 access to copy the source code from the same place counts as
7679 distribution of the source code, even though third parties are not
7680 compelled to copy the source along with the object code.
7683 You may not copy, modify, sublicense, or distribute the Program
7684 except as expressly provided under this License. Any attempt
7685 otherwise to copy, modify, sublicense or distribute the Program is
7686 void, and will automatically terminate your rights under this License.
7687 However, parties who have received copies, or rights, from you under
7688 this License will not have their licenses terminated so long as such
7689 parties remain in full compliance.
7692 You are not required to accept this License, since you have not
7693 signed it. However, nothing else grants you permission to modify or
7694 distribute the Program or its derivative works. These actions are
7695 prohibited by law if you do not accept this License. Therefore, by
7696 modifying or distributing the Program (or any work based on the
7697 Program), you indicate your acceptance of this License to do so, and
7698 all its terms and conditions for copying, distributing or modifying
7699 the Program or works based on it.
7702 Each time you redistribute the Program (or any work based on the
7703 Program), the recipient automatically receives a license from the
7704 original licensor to copy, distribute or modify the Program subject to
7705 these terms and conditions. You may not impose any further
7706 restrictions on the recipients' exercise of the rights granted herein.
7707 You are not responsible for enforcing compliance by third parties to
7711 If, as a consequence of a court judgment or allegation of patent
7712 infringement or for any other reason (not limited to patent issues),
7713 conditions are imposed on you (whether by court order, agreement or
7714 otherwise) that contradict the conditions of this License, they do not
7715 excuse you from the conditions of this License. If you cannot
7716 distribute so as to satisfy simultaneously your obligations under this
7717 License and any other pertinent obligations, then as a consequence you
7718 may not distribute the Program at all. For example, if a patent
7719 license would not permit royalty-free redistribution of the Program by
7720 all those who receive copies directly or indirectly through you, then
7721 the only way you could satisfy both it and this License would be to
7722 refrain entirely from distribution of the Program.
7724 If any portion of this section is held invalid or unenforceable under
7725 any particular circumstance, the balance of the section is intended to
7726 apply and the section as a whole is intended to apply in other
7729 It is not the purpose of this section to induce you to infringe any
7730 patents or other property right claims or to contest validity of any
7731 such claims; this section has the sole purpose of protecting the
7732 integrity of the free software distribution system, which is
7733 implemented by public license practices. Many people have made
7734 generous contributions to the wide range of software distributed
7735 through that system in reliance on consistent application of that
7736 system; it is up to the author/donor to decide if he or she is willing
7737 to distribute software through any other system and a licensee cannot
7740 This section is intended to make thoroughly clear what is believed to
7741 be a consequence of the rest of this License.
7744 If the distribution and/or use of the Program is restricted in
7745 certain countries either by patents or by copyrighted interfaces, the
7746 original copyright holder who places the Program under this License
7747 may add an explicit geographical distribution limitation excluding
7748 those countries, so that distribution is permitted only in or among
7749 countries not thus excluded. In such case, this License incorporates
7750 the limitation as if written in the body of this License.
7753 The Free Software Foundation may publish revised and/or new versions
7754 of the General Public License from time to time. Such new versions will
7755 be similar in spirit to the present version, but may differ in detail to
7756 address new problems or concerns.
7758 Each version is given a distinguishing version number. If the Program
7759 specifies a version number of this License which applies to it and ``any
7760 later version'', you have the option of following the terms and conditions
7761 either of that version or of any later version published by the Free
7762 Software Foundation. If the Program does not specify a version number of
7763 this License, you may choose any version ever published by the Free Software
7767 If you wish to incorporate parts of the Program into other free
7768 programs whose distribution conditions are different, write to the author
7769 to ask for permission. For software which is copyrighted by the Free
7770 Software Foundation, write to the Free Software Foundation; we sometimes
7771 make exceptions for this. Our decision will be guided by the two goals
7772 of preserving the free status of all derivatives of our free software and
7773 of promoting the sharing and reuse of software generally.
7776 @heading NO WARRANTY
7783 BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
7784 FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN
7785 OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
7786 PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
7787 OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
7788 MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS
7789 TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE
7790 PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
7791 REPAIR OR CORRECTION.
7794 IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
7795 WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
7796 REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
7797 INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
7798 OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
7799 TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
7800 YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
7801 PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
7802 POSSIBILITY OF SUCH DAMAGES.
7806 @heading END OF TERMS AND CONDITIONS
7809 @center END OF TERMS AND CONDITIONS
7813 @unnumberedsec Applying These Terms to Your New Programs
7815 If you develop a new program, and you want it to be of the greatest
7816 possible use to the public, the best way to achieve this is to make it
7817 free software which everyone can redistribute and change under these terms.
7819 To do so, attach the following notices to the program. It is safest
7820 to attach them to the start of each source file to most effectively
7821 convey the exclusion of warranty; and each file should have at least
7822 the ``copyright'' line and a pointer to where the full notice is found.
7825 @var{one line to give the program's name and a brief idea of what it does.}
7826 Copyright (C) 19@var{yy} @var{name of author}
7828 This program is free software; you can redistribute it and/or modify
7829 it under the terms of the GNU General Public License as published by
7830 the Free Software Foundation; either version 2 of the License, or
7831 (at your option) any later version.
7833 This program is distributed in the hope that it will be useful,
7834 but WITHOUT ANY WARRANTY; without even the implied warranty of
7835 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
7836 GNU General Public License for more details.
7838 You should have received a copy of the GNU General Public License
7839 along with this program; if not, write to the Free Software
7840 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
7843 Also add information on how to contact you by electronic and paper mail.
7845 If the program is interactive, make it output a short notice like this
7846 when it starts in an interactive mode:
7849 Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author}
7850 Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
7851 This is free software, and you are welcome to redistribute it
7852 under certain conditions; type `show c' for details.
7855 The hypothetical commands @samp{show w} and @samp{show c} should show
7856 the appropriate parts of the General Public License. Of course, the
7857 commands you use may be called something other than @samp{show w} and
7858 @samp{show c}; they could even be mouse-clicks or menu items---whatever
7861 You should also get your employer (if you work as a programmer) or your
7862 school, if any, to sign a ``copyright disclaimer'' for the program, if
7863 necessary. Here is a sample; alter the names:
7866 Yoyodyne, Inc., hereby disclaims all copyright interest in the program
7867 `Gnomovision' (which makes passes at compilers) written by James Hacker.
7869 @var{signature of Ty Coon}, 1 April 1989
7870 Ty Coon, President of Vice
7873 This General Public License does not permit incorporating your program into
7874 proprietary programs. If your program is a subroutine library, you may
7875 consider it more useful to permit linking proprietary applications with the
7876 library. If this is what you want to do, use the GNU Library General
7877 Public License instead of this License.
7880 @node Index, , Copying, Top
7886 % I think something like @colophon should be in texinfo. In the
7888 \long\def\colophon{\hbox to0pt{}\vfill
7889 \centerline{The body of this manual is set in}
7890 \centerline{\fontname\tenrm,}
7891 \centerline{with headings in {\bf\fontname\tenbf}}
7892 \centerline{and examples in {\tt\fontname\tentt}.}
7893 \centerline{{\it\fontname\tenit\/} and}
7894 \centerline{{\sl\fontname\tensl\/}}
7895 \centerline{are used for emphasis.}\vfill}
7897 % Blame: pesch@cygnus.com, 28mar91.