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diff --git a/gnu/usr.bin/gdb/doc/gdb.texinfo b/gnu/usr.bin/gdb/doc/gdb.texinfo new file mode 100644 index 000000000000..a2f293deb2a8 --- /dev/null +++ b/gnu/usr.bin/gdb/doc/gdb.texinfo @@ -0,0 +1,8591 @@ +\input texinfo @c -*-texinfo-*- +@c Copyright (c) 1988 1989 1990 1991 1992 1993 Free Software Foundation, Inc. +@c +@c %**start of header +@c makeinfo ignores cmds prev to setfilename, so its arg cannot make use +@c of @set vars. However, you can override filename with makeinfo -o. +@setfilename gdb.info +@c +@include gdb-cfg.texi +@c +@ifset GENERIC +@settitle Debugging with @value{GDBN} +@end ifset +@ifclear GENERIC +@settitle Debugging with @value{GDBN} (@value{TARGET}) +@end ifclear +@setchapternewpage odd +@c %**end of header + +@iftex +@c @smallbook +@c @cropmarks +@end iftex + +@finalout +@syncodeindex ky cp + +@c readline appendices use @vindex +@syncodeindex vr cp + +@c ===> NOTE! <== +@c Determine the edition number in *three* places by hand: +@c 1. First ifinfo section 2. title page 3. top node +@c To find the locations, search for !!set + +@c GDB CHANGELOG CONSULTED BETWEEN: +@c Fri Oct 11 23:27:06 1991 John Gilmore (gnu at cygnus.com) +@c Sat Dec 22 02:51:40 1990 John Gilmore (gnu at cygint) + +@c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly. + +@ifinfo +@c This is a dir.info fragment to support semi-automated addition of +@c manuals to an info tree. zoo@cygnus.com is developing this facility. +@format +START-INFO-DIR-ENTRY +* Gdb:: The GNU debugger. +END-INFO-DIR-ENTRY +@end format +@end ifinfo +@c +@c +@ifinfo +This file documents the GNU debugger @value{GDBN}. + +@c !!set edition, date, version +This is Edition 4.09, August 1993, +of @cite{Debugging with @value{GDBN}: the GNU Source-Level Debugger} +for GDB Version @value{GDBVN}. + +Copyright (C) 1988, '89, '90, '91, '92, '93 Free Software Foundation, Inc. + +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +@ignore +Permission is granted to process this file through TeX and print the +results, provided the printed document carries copying permission +notice identical to this one except for the removal of this paragraph +(this paragraph not being relevant to the printed manual). + +@end ignore +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided also that the +entire resulting derived work is distributed under the terms of a +permission notice identical to this one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions. +@end ifinfo + +@titlepage +@title Debugging with @value{GDBN} +@subtitle The GNU Source-Level Debugger +@ifclear GENERIC +@subtitle (@value{TARGET}) +@end ifclear +@sp 1 +@c !!set edition, date, version +@subtitle Edition 4.09, for @value{GDBN} version @value{GDBVN} +@subtitle August 1993 +@author Richard M. Stallman and Roland H. Pesch +@page +@tex +{\parskip=0pt +\hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@prep.ai.mit.edu.)\par +\hfill {\it Debugging with @value{GDBN}}\par +\hfill \TeX{}info \texinfoversion\par +\hfill pesch\@cygnus.com\par +} +@end tex + +@vskip 0pt plus 1filll +Copyright @copyright{} 1988, '89, '90, '91, '92, '93 Free Software +Foundation, Inc. +@sp 2 +Published by the Free Software Foundation @* +675 Massachusetts Avenue, @* +Cambridge, MA 02139 USA @* +Printed copies are available for $20 each. @* +ISBN 1-882114-11-6 @* + +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided also that the +entire resulting derived work is distributed under the terms of a +permission notice identical to this one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions. +@end titlepage +@page + +@ifinfo +@node Top +@top Debugging with @value{GDBN} + +This file describes @value{GDBN}, the GNU symbolic debugger. + +@c !!set edition, date, version +This is Edition 4.09, August 1993, for GDB Version @value{GDBVN}. + +@menu +* Summary:: Summary of @value{GDBN} +@ifset NOVEL +* New Features:: New features since GDB version 3.5 +@end ifset +@ifclear BARETARGET +* Sample Session:: A sample @value{GDBN} session +@end ifclear + +* Invocation:: Getting in and out of @value{GDBN} +* Commands:: @value{GDBN} commands +* Running:: Running programs under @value{GDBN} +* Stopping:: Stopping and continuing +* Stack:: Examining the stack +* Source:: Examining source files +* Data:: Examining data +@ifclear CONLY +* Languages:: Using @value{GDBN} with different languages +@end ifclear +@ifset CONLY +* C:: C language support +@end ifset +@c remnant makeinfo bug, blank line needed after two end-ifs? + +* Symbols:: Examining the symbol table +* Altering:: Altering execution +* GDB Files:: @value{GDBN} files +* Targets:: Specifying a debugging target +* Controlling GDB:: Controlling @value{GDBN} +* Sequences:: Canned sequences of commands +@ifclear DOSHOST +* Emacs:: Using @value{GDBN} under GNU Emacs +@end ifclear + +* GDB Bugs:: Reporting bugs in @value{GDBN} +* Command Line Editing:: Facilities of the readline library +* Using History Interactively:: +@ifset NOVEL +* Renamed Commands:: +@end ifset +@ifclear PRECONFIGURED +* Formatting Documentation:: How to format and print GDB documentation +* Installing GDB:: Installing GDB +@end ifclear + +* Index:: Index +@end menu +@end ifinfo + +@node Summary +@unnumbered Summary of @value{GDBN} + +The purpose of a debugger such as @value{GDBN} is to allow you to see what is +going on ``inside'' another program while it executes---or what another +program was doing at the moment it crashed. + +@value{GDBN} can do four main kinds of things (plus other things in support of +these) to help you catch bugs in the act: + +@itemize @bullet +@item +Start your program, specifying anything that might affect its behavior. + +@item +Make your program stop on specified conditions. + +@item +Examine what has happened, when your program has stopped. + +@item +Change things in your program, so you can experiment with correcting the +effects of one bug and go on to learn about another. +@end itemize + +@ifclear CONLY +@ifclear MOD2 +You can use @value{GDBN} to debug programs written in C or C++. +@end ifclear +@ifset MOD2 +You can use @value{GDBN} to debug programs written in C, C++, and +Modula-2. +@end ifset +@ifset FORTRAN +@cindex Fortran +@value{GDBN} can be used to debug programs written in Fortran, although +it does not yet support entering expressions, printing values, etc. +using Fortran syntax. It may be necessary to refer to some variables +with a trailing underscore. +@end ifset +@end ifclear + +@menu +* Free Software:: Freely redistributable software +* Contributors:: Contributors to GDB +@end menu + +@node Free Software +@unnumberedsec Free software + +@value{GDBN} is @dfn{free software}, protected by the GNU General Public License +(GPL). The GPL gives you the freedom to copy or adapt a licensed +program---but every person getting a copy also gets with it the +freedom to modify that copy (which means that they must get access to +the source code), and the freedom to distribute further copies. +Typical software companies use copyrights to limit your freedoms; the +Free Software Foundation uses the GPL to preserve these freedoms. + +Fundamentally, the General Public License is a license which says that +you have these freedoms and that you cannot take these freedoms away +from anyone else. + +@node Contributors +@unnumberedsec Contributors to GDB + +Richard Stallman was the original author of GDB, and of many other GNU +programs. Many others have contributed to its development. This +section attempts to credit major contributors. One of the virtues of +free software is that everyone is free to contribute to it; with +regret, we cannot actually acknowledge everyone here. The file +@file{ChangeLog} in the GDB distribution approximates a blow-by-blow +account. + +Changes much prior to version 2.0 are lost in the mists of time. + +@quotation +@emph{Plea:} Additions to this section are particularly welcome. If you +or your friends (or enemies, to be evenhanded) have been unfairly +omitted from this list, we would like to add your names! +@end quotation + +So that they may not regard their long labor as thankless, we +particularly thank those who shepherded GDB through major releases: Fred +Fish (releases 4.11, 4.10, 4.9), Stu Grossman and John Gilmore (releases +4.8, 4.7, 4.6, 4.5, 4.4), John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and +3.9); Jim Kingdon (releases 3.5, 3.4, 3.3); and Randy Smith (releases +3.2, 3.1, 3.0). As major maintainer of GDB for some period, each +contributed significantly to the structure, stability, and capabilities +of the entire debugger. + +Richard Stallman, assisted at various times by Peter TerMaat, Chris +Hanson, and Richard Mlynarik, handled releases through 2.8. + +@ifclear CONLY +Michael Tiemann is the author of most of the GNU C++ support in GDB, +with significant additional contributions from Per Bothner. James +Clark wrote the GNU C++ demangler. Early work on C++ was by Peter +TerMaat (who also did much general update work leading to release 3.0). +@end ifclear + +GDB 4 uses the BFD subroutine library to examine multiple +object-file formats; BFD was a joint project of David V. +Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore. + +David Johnson wrote the original COFF support; Pace Willison did +the original support for encapsulated COFF. + +Adam de Boor and Bradley Davis contributed the ISI Optimum V support. +Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS +support. Jean-Daniel Fekete contributed Sun 386i support. Chris +Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki +Hasei contributed Sony/News OS 3 support. David Johnson contributed +Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support. +Keith Packard contributed NS32K support. Doug Rabson contributed +Acorn Risc Machine support. Chris Smith contributed Convex support +(and Fortran debugging). Jonathan Stone contributed Pyramid support. +Michael Tiemann contributed SPARC support. Tim Tucker contributed +support for the Gould NP1 and Gould Powernode. Pace Willison +contributed Intel 386 support. Jay Vosburgh contributed Symmetry +support. + +Rich Schaefer and Peter Schauer helped with support of SunOS shared +libraries. + +Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about +several machine instruction sets. + +Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped +develop remote debugging. Intel Corporation and Wind River Systems +contributed remote debugging modules for their products. + +Brian Fox is the author of the readline libraries providing +command-line editing and command history. + +Andrew Beers of SUNY Buffalo wrote the language-switching code, +@ifset MOD2 +the Modula-2 support, +@end ifset +and contributed the Languages chapter of this manual. + +Fred Fish wrote most of the support for Unix System Vr4. +@ifclear CONLY +He also enhanced the command-completion support to cover C++ overloaded +symbols. +@end ifclear + +Hitachi America, Ltd. sponsored the support for Hitachi microprocessors. + +@ifset NOVEL +@node New Features +@unnumbered New Features since GDB Version 3.5 + +@table @emph +@item Targets +Using the new command @code{target}, you can select at runtime whether +you are debugging local files, local processes, standalone systems over +a serial port, realtime systems over a TCP/IP connection, etc. The +command @code{load} can download programs into a remote system. Serial +stubs are available for Motorola 680x0, Intel 80386, and Sparc remote +systems; GDB also supports debugging realtime processes running under +VxWorks, using SunRPC Remote Procedure Calls over TCP/IP to talk to a +debugger stub on the target system. Internally, GDB now uses a function +vector to mediate access to different targets; if you need to add your +own support for a remote protocol, this makes it much easier. + +@item Watchpoints +GDB now sports watchpoints as well as breakpoints. You can use a +watchpoint to stop execution whenever the value of an expression +changes, without having to predict a particular place in your program +where this may happen. + +@item Wide Output +Commands that issue wide output now insert newlines at places designed +to make the output more readable. + +@item Object Code Formats +GDB uses a new library called the Binary File Descriptor (BFD) Library +to permit it to switch dynamically, without reconfiguration or +recompilation, between different object-file formats. Formats currently +supported are COFF, ELF, a.out, Intel 960 b.out, MIPS ECOFF, HPPA SOM +(with stabs debugging), and S-records; files may be read as .o files, +archive libraries, or core dumps. BFD is available as a subroutine +library so that other programs may take advantage of it, and the other +GNU binary utilities are being converted to use it. + +@item Configuration and Ports +Compile-time configuration (to select a particular architecture and +operating system) is much easier. The script @code{configure} now +allows you to configure GDB as either a native debugger or a +cross-debugger. @xref{Installing GDB}, for details on how to +configure. + +@item Interaction +The user interface to the GDB control variables is simpler, +and is consolidated in two commands, @code{set} and @code{show}. Output +lines are now broken at readable places, rather than overflowing onto +the next line. You can suppress output of machine-level addresses, +displaying only source language information. + +@item C++ +GDB now supports C++ multiple inheritance (if used with a GCC +version 2 compiler), and also has limited support for C++ exception +handling, with the commands @code{catch} and @code{info catch}: GDB +can break when an exception is raised, before the stack is peeled back +to the exception handler's context. + +@ifset MOD2 +@item Modula-2 +GDB now has preliminary support for the GNU Modula-2 compiler, currently +under development at the State University of New York at Buffalo. +Coordinated development of both GDB and the GNU Modula-2 compiler will +continue. Other Modula-2 compilers are currently not supported, and +attempting to debug programs compiled with them will likely result in an +error as the symbol table of the executable is read in. +@end ifset + +@item Command Rationalization +Many GDB commands have been renamed to make them easier to remember +and use. In particular, the subcommands of @code{info} and +@code{show}/@code{set} are grouped to make the former refer to the state +of your program, and the latter refer to the state of GDB itself. +@xref{Renamed Commands}, for details on what commands were renamed. + +@item Shared Libraries +GDB 4 can debug programs and core files that use SunOS, SVR4, or IBM RS/6000 +shared libraries. + +@item Reference Card +GDB 4 has a reference card. @xref{Formatting Documentation,,Formatting +the Documentation}, for instructions about how to print it. +@end table +@end ifset + +@ifclear BARETARGET +@node Sample Session +@chapter A Sample @value{GDBN} Session + +You can use this manual at your leisure to read all about @value{GDBN}. +However, a handful of commands are enough to get started using the +debugger. This chapter illustrates those commands. + +@iftex +In this sample session, we emphasize user input like this: @b{input}, +to make it easier to pick out from the surrounding output. +@end iftex + +@c FIXME: this example may not be appropriate for some configs, where +@c FIXME...primary interest is in remote use. + +One of the preliminary versions of GNU @code{m4} (a generic macro +processor) exhibits the following bug: sometimes, when we change its +quote strings from the default, the commands used to capture one macro +definition within another stop working. In the following short @code{m4} +session, we define a macro @code{foo} which expands to @code{0000}; we +then use the @code{m4} built-in @code{defn} to define @code{bar} as the +same thing. However, when we change the open quote string to +@code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same +procedure fails to define a new synonym @code{baz}: + +@smallexample +$ @b{cd gnu/m4} +$ @b{./m4} +@b{define(foo,0000)} + +@b{foo} +0000 +@b{define(bar,defn(`foo'))} + +@b{bar} +0000 +@b{changequote(<QUOTE>,<UNQUOTE>)} + +@b{define(baz,defn(<QUOTE>foo<UNQUOTE>))} +@b{baz} +@b{C-d} +m4: End of input: 0: fatal error: EOF in string +@end smallexample + +@noindent +Let us use @value{GDBN} to try to see what is going on. + +@smallexample +$ @b{@value{GDBP} m4} +@c FIXME: this falsifies the exact text played out, to permit smallbook +@c FIXME... format to come out better. +GDB is free software and you are welcome to distribute copies + of it under certain conditions; type "show copying" to see + the conditions. +There is absolutely no warranty for GDB; type "show warranty" + for details. +GDB @value{GDBVN}, Copyright 1993 Free Software Foundation, Inc... +(@value{GDBP}) +@end smallexample + +@noindent +@value{GDBN} reads only enough symbol data to know where to find the rest when +needed; as a result, the first prompt comes up very quickly. We now +tell @value{GDBN} to use a narrower display width than usual, so that examples +will fit in this manual. + +@smallexample +(@value{GDBP}) @b{set width 70} +@end smallexample + +@noindent +We need to see how the @code{m4} built-in @code{changequote} works. +Having looked at the source, we know the relevant subroutine is +@code{m4_changequote}, so we set a breakpoint there with the @value{GDBN} +@code{break} command. + +@smallexample +(@value{GDBP}) @b{break m4_changequote} +Breakpoint 1 at 0x62f4: file builtin.c, line 879. +@end smallexample + +@noindent +Using the @code{run} command, we start @code{m4} running under @value{GDBN} +control; as long as control does not reach the @code{m4_changequote} +subroutine, the program runs as usual: + +@smallexample +(@value{GDBP}) @b{run} +Starting program: /work/Editorial/gdb/gnu/m4/m4 +@b{define(foo,0000)} + +@b{foo} +0000 +@end smallexample + +@noindent +To trigger the breakpoint, we call @code{changequote}. @value{GDBN} +suspends execution of @code{m4}, displaying information about the +context where it stops. + +@smallexample +@b{changequote(<QUOTE>,<UNQUOTE>)} + +Breakpoint 1, m4_changequote (argc=3, argv=0x33c70) + at builtin.c:879 +879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3)) +@end smallexample + +@noindent +Now we use the command @code{n} (@code{next}) to advance execution to +the next line of the current function. + +@smallexample +(@value{GDBP}) @b{n} +882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\ + : nil, +@end smallexample + +@noindent +@code{set_quotes} looks like a promising subroutine. We can go into it +by using the command @code{s} (@code{step}) instead of @code{next}. +@code{step} goes to the next line to be executed in @emph{any} +subroutine, so it steps into @code{set_quotes}. + +@smallexample +(@value{GDBP}) @b{s} +set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") + at input.c:530 +530 if (lquote != def_lquote) +@end smallexample + +@noindent +The display that shows the subroutine where @code{m4} is now +suspended (and its arguments) is called a stack frame display. It +shows a summary of the stack. We can use the @code{backtrace} +command (which can also be spelled @code{bt}), to see where we are +in the stack as a whole: the @code{backtrace} command displays a +stack frame for each active subroutine. + +@smallexample +(@value{GDBP}) @b{bt} +#0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") + at input.c:530 +#1 0x6344 in m4_changequote (argc=3, argv=0x33c70) + at builtin.c:882 +#2 0x8174 in expand_macro (sym=0x33320) at macro.c:242 +#3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30) + at macro.c:71 +#4 0x79dc in expand_input () at macro.c:40 +#5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195 +@end smallexample + +@noindent +We will step through a few more lines to see what happens. The first two +times, we can use @samp{s}; the next two times we use @code{n} to avoid +falling into the @code{xstrdup} subroutine. + +@smallexample +(@value{GDBP}) @b{s} +0x3b5c 532 if (rquote != def_rquote) +(@value{GDBP}) @b{s} +0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \ +def_lquote : xstrdup(lq); +(@value{GDBP}) @b{n} +536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ + : xstrdup(rq); +(@value{GDBP}) @b{n} +538 len_lquote = strlen(rquote); +@end smallexample + +@noindent +The last line displayed looks a little odd; we can examine the variables +@code{lquote} and @code{rquote} to see if they are in fact the new left +and right quotes we specified. We use the command @code{p} +(@code{print}) to see their values. + +@smallexample +(@value{GDBP}) @b{p lquote} +$1 = 0x35d40 "<QUOTE>" +(@value{GDBP}) @b{p rquote} +$2 = 0x35d50 "<UNQUOTE>" +@end smallexample + +@noindent +@code{lquote} and @code{rquote} are indeed the new left and right quotes. +To look at some context, we can display ten lines of source +surrounding the current line with the @code{l} (@code{list}) command. + +@smallexample +(@value{GDBP}) @b{l} +533 xfree(rquote); +534 +535 lquote = (lq == nil || *lq == '\0') ? def_lquote\ + : xstrdup (lq); +536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ + : xstrdup (rq); +537 +538 len_lquote = strlen(rquote); +539 len_rquote = strlen(lquote); +540 @} +541 +542 void +@end smallexample + +@noindent +Let us step past the two lines that set @code{len_lquote} and +@code{len_rquote}, and then examine the values of those variables. + +@smallexample +(@value{GDBP}) @b{n} +539 len_rquote = strlen(lquote); +(@value{GDBP}) @b{n} +540 @} +(@value{GDBP}) @b{p len_lquote} +$3 = 9 +(@value{GDBP}) @b{p len_rquote} +$4 = 7 +@end smallexample + +@noindent +That certainly looks wrong, assuming @code{len_lquote} and +@code{len_rquote} are meant to be the lengths of @code{lquote} and +@code{rquote} respectively. We can set them to better values using +the @code{p} command, since it can print the value of +any expression---and that expression can include subroutine calls and +assignments. + +@smallexample +(@value{GDBP}) @b{p len_lquote=strlen(lquote)} +$5 = 7 +(@value{GDBP}) @b{p len_rquote=strlen(rquote)} +$6 = 9 +@end smallexample + +@noindent +Is that enough to fix the problem of using the new quotes with the +@code{m4} built-in @code{defn}? We can allow @code{m4} to continue +executing with the @code{c} (@code{continue}) command, and then try the +example that caused trouble initially: + +@smallexample +(@value{GDBP}) @b{c} +Continuing. + +@b{define(baz,defn(<QUOTE>foo<UNQUOTE>))} + +baz +0000 +@end smallexample + +@noindent +Success! The new quotes now work just as well as the default ones. The +problem seems to have been just the two typos defining the wrong +lengths. We allow @code{m4} exit by giving it an EOF as input: + +@smallexample +@b{C-d} +Program exited normally. +@end smallexample + +@noindent +The message @samp{Program exited normally.} is from @value{GDBN}; it +indicates @code{m4} has finished executing. We can end our @value{GDBN} +session with the @value{GDBN} @code{quit} command. + +@smallexample +(@value{GDBP}) @b{quit} +@end smallexample +@end ifclear + +@node Invocation +@chapter Getting In and Out of @value{GDBN} + +This chapter discusses how to start @value{GDBN}, and how to get out of it. +(The essentials: type @samp{@value{GDBP}} to start GDB, and type @kbd{quit} +or @kbd{C-d} to exit.) + +@menu +* Invoking GDB:: How to start @value{GDBN} +* Quitting GDB:: How to quit @value{GDBN} +* Shell Commands:: How to use shell commands inside @value{GDBN} +@end menu + +@node Invoking GDB +@section Invoking @value{GDBN} + +@ifset H8EXCLUSIVE +For details on starting up @value{GDBP} as a +remote debugger attached to a Hitachi microprocessor, see @ref{Hitachi +Remote,,@value{GDBN} and Hitachi Microprocessors}. +@end ifset + +Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started, +@value{GDBN} reads commands from the terminal until you tell it to exit. + +You can also run @code{@value{GDBP}} with a variety of arguments and options, +to specify more of your debugging environment at the outset. + +@ifset GENERIC +The command-line options described here are designed +to cover a variety of situations; in some environments, some of these +options may effectively be unavailable. +@end ifset + +The most usual way to start @value{GDBN} is with one argument, +specifying an executable program: + +@example +@value{GDBP} @var{program} +@end example + +@ifclear BARETARGET +@noindent +You can also start with both an executable program and a core file +specified: + +@example +@value{GDBP} @var{program} @var{core} +@end example + +You can, instead, specify a process ID as a second argument, if you want +to debug a running process: + +@example +@value{GDBP} @var{program} 1234 +@end example + +@noindent +would attach @value{GDBN} to process @code{1234} (unless you also have a file +named @file{1234}; @value{GDBN} does check for a core file first). + +Taking advantage of the second command-line argument requires a fairly +complete operating system; when you use @value{GDBN} as a remote debugger +attached to a bare board, there may not be any notion of ``process'', +and there is often no way to get a core dump. +@end ifclear + +@noindent +You can further control how @value{GDBN} starts up by using command-line +options. @value{GDBN} itself can remind you of the options available. + +@noindent +Type + +@example +@value{GDBP} -help +@end example + +@noindent +to display all available options and briefly describe their use +(@samp{@value{GDBP} -h} is a shorter equivalent). + +All options and command line arguments you give are processed +in sequential order. The order makes a difference when the +@samp{-x} option is used. + + +@menu +@ifclear GENERIC +@ifset REMOTESTUB +* Remote Serial:: @value{GDBN} remote serial protocol +@end ifset +@ifset I960 +* i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy) +@end ifset +@ifset AMD29K +* UDI29K Remote:: @value{GDBN} and the UDI protocol for AMD29K +* EB29K Remote:: @value{GDBN} with a remote EB29K +@end ifset +@ifset VXWORKS +* VxWorks Remote:: @value{GDBN} and VxWorks +@end ifset +@ifset ST2000 +* ST2000 Remote:: @value{GDBN} with a Tandem ST2000 +@end ifset +@ifset H8 +* Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors +@end ifset +@ifset MIPS +* MIPS Remote:: @value{GDBN} and MIPS boards +@end ifset +@ifset SIMS +* Simulator:: Simulated CPU target +@end ifset +@end ifclear +@c remnant makeinfo bug requires this blank line after *two* end-ifblahs: + +* File Options:: Choosing files +* Mode Options:: Choosing modes +@end menu + +@ifclear GENERIC +@include remote.texi +@end ifclear + +@node File Options +@subsection Choosing files + +@ifclear BARETARGET +When @value{GDBN} starts, it reads any arguments other than options as +specifying an executable file and core file (or process ID). This is +the same as if the arguments were specified by the @samp{-se} and +@samp{-c} options respectively. (@value{GDBN} reads the first argument +that does not have an associated option flag as equivalent to the +@samp{-se} option followed by that argument; and the second argument +that does not have an associated option flag, if any, as equivalent to +the @samp{-c} option followed by that argument.) +@end ifclear +@ifset BARETARGET +When @value{GDBN} starts, it reads any argument other than options as +specifying an executable file. This is the same as if the argument was +specified by the @samp{-se} option. +@end ifset + +Many options have both long and short forms; both are shown in the +following list. @value{GDBN} also recognizes the long forms if you truncate +them, so long as enough of the option is present to be unambiguous. +(If you prefer, you can flag option arguments with @samp{--} rather +than @samp{-}, though we illustrate the more usual convention.) + +@table @code +@item -symbols @var{file} +@itemx -s @var{file} +Read symbol table from file @var{file}. + +@item -exec @var{file} +@itemx -e @var{file} +Use file @var{file} as the executable file to execute when +@ifset BARETARGET +appropriate. +@end ifset +@ifclear BARETARGET +appropriate, and for examining pure data in conjunction with a core +dump. +@end ifclear + +@item -se @var{file} +Read symbol table from file @var{file} and use it as the executable +file. + +@ifclear BARETARGET +@item -core @var{file} +@itemx -c @var{file} +Use file @var{file} as a core dump to examine. + +@item -c @var{number} +Connect to process ID @var{number}, as with the @code{attach} command +(unless there is a file in core-dump format named @var{number}, in which +case @samp{-c} specifies that file as a core dump to read). +@end ifclear + +@item -command @var{file} +@itemx -x @var{file} +Execute @value{GDBN} commands from file @var{file}. @xref{Command +Files,, Command files}. + +@item -directory @var{directory} +@itemx -d @var{directory} +Add @var{directory} to the path to search for source files. + +@ifclear BARETARGET +@item -m +@itemx -mapped +@emph{Warning: this option depends on operating system facilities that are not +supported on all systems.}@* +If memory-mapped files are available on your system through the @code{mmap} +system call, you can use this option +to have @value{GDBN} write the symbols from your +program into a reusable file in the current directory. If the program you are debugging is +called @file{/tmp/fred}, the mapped symbol file will be @file{./fred.syms}. +Future @value{GDBN} debugging sessions will notice the presence of this file, +and will quickly map in symbol information from it, rather than reading +the symbol table from the executable program. + +@c FIXME! Really host, not target? +The @file{.syms} file is specific to the host machine where @value{GDBN} +is run. It holds an exact image of the internal @value{GDBN} symbol +table. It cannot be shared across multiple host platforms. +@end ifclear + +@item -r +@itemx -readnow +Read each symbol file's entire symbol table immediately, rather than +the default, which is to read it incrementally as it is needed. +This makes startup slower, but makes future operations faster. +@end table + +@ifclear BARETARGET +The @code{-mapped} and @code{-readnow} options are typically combined in +order to build a @file{.syms} file that contains complete symbol +information. (@xref{Files,,Commands to specify files}, for information +on @file{.syms} files.) A simple GDB invocation to do nothing but build +a @file{.syms} file for future use is: + +@example + gdb -batch -nx -mapped -readnow programname +@end example +@end ifclear + +@node Mode Options +@subsection Choosing modes + +You can run @value{GDBN} in various alternative modes---for example, in +batch mode or quiet mode. + +@table @code +@item -nx +@itemx -n +Do not execute commands from any initialization files (normally called +@file{@value{GDBINIT}}). Normally, the commands in these files are +executed after all the command options and arguments have been +processed. @xref{Command Files,,Command files}. + +@item -quiet +@itemx -q +``Quiet''. Do not print the introductory and copyright messages. These +messages are also suppressed in batch mode. + +@item -batch +Run in batch mode. Exit with status @code{0} after processing all the +command files specified with @samp{-x} (and all commands from +initialization files, if not inhibited with @samp{-n}). Exit with +nonzero status if an error occurs in executing the @value{GDBN} commands +in the command files. + +Batch mode may be useful for running @value{GDBN} as a filter, for example to +download and run a program on another computer; in order to make this +more useful, the message + +@example +Program exited normally. +@end example + +@noindent +(which is ordinarily issued whenever a program running under @value{GDBN} control +terminates) is not issued when running in batch mode. + +@item -cd @var{directory} +Run @value{GDBN} using @var{directory} as its working directory, +instead of the current directory. + +@ifset LUCID +@item -context @var{authentication} +When the Energize programming system starts up @value{GDBN}, it uses this +option to trigger an alternate mode of interaction. +@var{authentication} is a pair of numeric codes that identify @value{GDBN} +as a client in the Energize environment. Avoid this option when you run +@value{GDBN} directly from the command line. See @ref{Energize,,Using +@value{GDBN} with Energize} for more discussion of using @value{GDBN} with Energize. +@end ifset + +@ifclear DOSHOST +@item -fullname +@itemx -f +Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN} +to output the full file name and line number in a standard, +recognizable fashion each time a stack frame is displayed (which +includes each time your program stops). This recognizable format looks +like two @samp{\032} characters, followed by the file name, line number +and character position separated by colons, and a newline. The +Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as +a signal to display the source code for the frame. +@end ifclear + +@ifset SERIAL +@item -b @var{bps} +Set the line speed (baud rate or bits per second) of any serial +interface used by @value{GDBN} for remote debugging. + +@item -tty @var{device} +Run using @var{device} for your program's standard input and output. +@c FIXME: kingdon thinks there is more to -tty. Investigate. +@end ifset +@end table + +@node Quitting GDB +@section Quitting @value{GDBN} +@cindex exiting @value{GDBN} +@cindex leaving @value{GDBN} + +@table @code +@item quit +@kindex quit +@kindex q +To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or type +an end-of-file character (usually @kbd{C-d}). +@end table + +@cindex interrupt +An interrupt (often @kbd{C-c}) will not exit from @value{GDBN}, but rather +will terminate the action of any @value{GDBN} command that is in progress and +return to @value{GDBN} command level. It is safe to type the interrupt +character at any time because @value{GDBN} does not allow it to take effect +until a time when it is safe. + +@ifclear BARETARGET +If you have been using @value{GDBN} to control an attached process or +device, you can release it with the @code{detach} command +(@pxref{Attach, ,Debugging an already-running process}). +@end ifclear + +@node Shell Commands +@section Shell commands + +If you need to execute occasional shell commands during your +debugging session, there is no need to leave or suspend @value{GDBN}; you can +just use the @code{shell} command. + +@table @code +@item shell @var{command string} +@kindex shell +@cindex shell escape +Invoke a the standard shell to execute @var{command string}. +@ifclear DOSHOST +If it exists, the environment variable @code{SHELL} determines which +shell to run. Otherwise @value{GDBN} uses @code{/bin/sh}. +@end ifclear +@end table + +The utility @code{make} is often needed in development environments. +You do not have to use the @code{shell} command for this purpose in +@value{GDBN}: + +@table @code +@item make @var{make-args} +@kindex make +@cindex calling make +Execute the @code{make} program with the specified +arguments. This is equivalent to @samp{shell make @var{make-args}}. +@end table + +@node Commands +@chapter @value{GDBN} Commands + +You can abbreviate a @value{GDBN} command to the first few letters of the command +name, if that abbreviation is unambiguous; and you can repeat certain +@value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB} +key to get @value{GDBN} to fill out the rest of a word in a command (or to +show you the alternatives available, if there is more than one possibility). + +@menu +* Command Syntax:: How to give commands to @value{GDBN} +* Completion:: Command completion +* Help:: How to ask @value{GDBN} for help +@end menu + +@node Command Syntax +@section Command syntax + +A @value{GDBN} command is a single line of input. There is no limit on +how long it can be. It starts with a command name, which is followed by +arguments whose meaning depends on the command name. For example, the +command @code{step} accepts an argument which is the number of times to +step, as in @samp{step 5}. You can also use the @code{step} command +with no arguments. Some command names do not allow any arguments. + +@cindex abbreviation +@value{GDBN} command names may always be truncated if that abbreviation is +unambiguous. Other possible command abbreviations are listed in the +documentation for individual commands. In some cases, even ambiguous +abbreviations are allowed; for example, @code{s} is specially defined as +equivalent to @code{step} even though there are other commands whose +names start with @code{s}. You can test abbreviations by using them as +arguments to the @code{help} command. + +@cindex repeating commands +@kindex RET +A blank line as input to @value{GDBN} (typing just @key{RET}) means to +repeat the previous command. Certain commands (for example, @code{run}) +will not repeat this way; these are commands for which unintentional +repetition might cause trouble and which you are unlikely to want to +repeat. + +The @code{list} and @code{x} commands, when you repeat them with +@key{RET}, construct new arguments rather than repeating +exactly as typed. This permits easy scanning of source or memory. + +@value{GDBN} can also use @key{RET} in another way: to partition lengthy +output, in a way similar to the common utility @code{more} +(@pxref{Screen Size,,Screen size}). Since it is easy to press one +@key{RET} too many in this situation, @value{GDBN} disables command +repetition after any command that generates this sort of display. + +@kindex # +@cindex comment +Any text from a @kbd{#} to the end of the line is a comment; it does +nothing. This is useful mainly in command files (@pxref{Command +Files,,Command files}). + +@node Completion +@section Command completion + +@cindex completion +@cindex word completion +@value{GDBN} can fill in the rest of a word in a command for you, if there is +only one possibility; it can also show you what the valid possibilities +are for the next word in a command, at any time. This works for @value{GDBN} +commands, @value{GDBN} subcommands, and the names of symbols in your program. + +Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest +of a word. If there is only one possibility, @value{GDBN} will fill in the +word, and wait for you to finish the command (or press @key{RET} to +enter it). For example, if you type + +@c FIXME "@key" does not distinguish its argument sufficiently to permit +@c complete accuracy in these examples; space introduced for clarity. +@c If texinfo enhancements make it unnecessary, it would be nice to +@c replace " @key" by "@key" in the following... +@example +(@value{GDBP}) info bre @key{TAB} +@end example + +@noindent +@value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is +the only @code{info} subcommand beginning with @samp{bre}: + +@example +(@value{GDBP}) info breakpoints +@end example + +@noindent +You can either press @key{RET} at this point, to run the @code{info +breakpoints} command, or backspace and enter something else, if +@samp{breakpoints} does not look like the command you expected. (If you +were sure you wanted @code{info breakpoints} in the first place, you +might as well just type @key{RET} immediately after @samp{info bre}, +to exploit command abbreviations rather than command completion). + +If there is more than one possibility for the next word when you press +@key{TAB}, @value{GDBN} will sound a bell. You can either supply more +characters and try again, or just press @key{TAB} a second time, and +@value{GDBN} will display all the possible completions for that word. For +example, you might want to set a breakpoint on a subroutine whose name +begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN} +just sounds the bell. Typing @key{TAB} again will display all the +function names in your program that begin with those characters, for +example: + +@example +(@value{GDBP}) b make_ @key{TAB} +@exdent @value{GDBN} sounds bell; press @key{TAB} again, to see: +make_a_section_from_file make_environ +make_abs_section make_function_type +make_blockvector make_pointer_type +make_cleanup make_reference_type +make_command make_symbol_completion_list +(@value{GDBP}) b make_ +@end example + +@noindent +After displaying the available possibilities, @value{GDBN} copies your +partial input (@samp{b make_} in the example) so you can finish the +command. + +If you just want to see the list of alternatives in the first place, you +can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?} +means @kbd{@key{META} ?}. You can type this +@ifclear DOSHOST +either by holding down a +key designated as the @key{META} shift on your keyboard (if there is +one) while typing @kbd{?}, or +@end ifclear +as @key{ESC} followed by @kbd{?}. + +@cindex quotes in commands +@cindex completion of quoted strings +Sometimes the string you need, while logically a ``word'', may contain +parentheses or other characters that @value{GDBN} normally excludes from its +notion of a word. To permit word completion to work in this situation, +you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands. + +@ifclear CONLY +The most likely situation where you might need this is in typing the +name of a C++ function. This is because C++ allows function overloading +(multiple definitions of the same function, distinguished by argument +type). For example, when you want to set a breakpoint you may need to +distinguish whether you mean the version of @code{name} that takes an +@code{int} parameter, @code{name(int)}, or the version that takes a +@code{float} parameter, @code{name(float)}. To use the word-completion +facilities in this situation, type a single quote @code{'} at the +beginning of the function name. This alerts @value{GDBN} that it may need to +consider more information than usual when you press @key{TAB} or +@kbd{M-?} to request word completion: + +@example +(@value{GDBP}) b 'bubble( @key{M-?} +bubble(double,double) bubble(int,int) +(@value{GDBP}) b 'bubble( +@end example + +In some cases, @value{GDBN} can tell that completing a name will require +quotes. When this happens, @value{GDBN} will insert the quote for you (while +completing as much as it can) if you do not type the quote in the first +place: + +@example +(@value{GDBP}) b bub @key{TAB} +@exdent @value{GDBN} alters your input line to the following, and rings a bell: +(@value{GDBP}) b 'bubble( +@end example + +@noindent +In general, @value{GDBN} can tell that a quote is needed (and inserts it) if +you have not yet started typing the argument list when you ask for +completion on an overloaded symbol. +@end ifclear + + +@node Help +@section Getting help +@cindex online documentation +@kindex help + +You can always ask @value{GDBN} itself for information on its commands, using the +command @code{help}. + +@table @code +@item help +@itemx h +@kindex h +You can use @code{help} (abbreviated @code{h}) with no arguments to +display a short list of named classes of commands: + +@smallexample +(@value{GDBP}) help +List of classes of commands: + +running -- Running the program +stack -- Examining the stack +data -- Examining data +breakpoints -- Making program stop at certain points +files -- Specifying and examining files +status -- Status inquiries +support -- Support facilities +user-defined -- User-defined commands +aliases -- Aliases of other commands +obscure -- Obscure features + +Type "help" followed by a class name for a list of +commands in that class. +Type "help" followed by command name for full +documentation. +Command name abbreviations are allowed if unambiguous. +(@value{GDBP}) +@end smallexample + +@item help @var{class} +Using one of the general help classes as an argument, you can get a +list of the individual commands in that class. For example, here is the +help display for the class @code{status}: + +@smallexample +(@value{GDBP}) help status +Status inquiries. + +List of commands: + +@c Line break in "show" line falsifies real output, but needed +@c to fit in smallbook page size. +show -- Generic command for showing things set + with "set" +info -- Generic command for printing status + +Type "help" followed by command name for full +documentation. +Command name abbreviations are allowed if unambiguous. +(@value{GDBP}) +@end smallexample + +@item help @var{command} +With a command name as @code{help} argument, @value{GDBN} will display a +short paragraph on how to use that command. +@end table + +In addition to @code{help}, you can use the @value{GDBN} commands @code{info} +and @code{show} to inquire about the state of your program, or the state +of @value{GDBN} itself. Each command supports many topics of inquiry; this +manual introduces each of them in the appropriate context. The listings +under @code{info} and under @code{show} in the Index point to +all the sub-commands. @xref{Index}. + +@c @group +@table @code +@item info +@kindex info +@kindex i +This command (abbreviated @code{i}) is for describing the state of your +program. For example, you can list the arguments given to your program +with @code{info args}, list the registers currently in use with @code{info +registers}, or list the breakpoints you have set with @code{info breakpoints}. +You can get a complete list of the @code{info} sub-commands with +@w{@code{help info}}. + +@kindex show +@item show +In contrast, @code{show} is for describing the state of @value{GDBN} itself. +You can change most of the things you can @code{show}, by using the +related command @code{set}; for example, you can control what number +system is used for displays with @code{set radix}, or simply inquire +which is currently in use with @code{show radix}. + +@kindex info set +To display all the settable parameters and their current +values, you can use @code{show} with no arguments; you may also use +@code{info set}. Both commands produce the same display. +@c FIXME: "info set" violates the rule that "info" is for state of +@c FIXME...program. Ck w/ GNU: "info set" to be called something else, +@c FIXME...or change desc of rule---eg "state of prog and debugging session"? +@end table +@c @end group + +Here are three miscellaneous @code{show} subcommands, all of which are +exceptional in lacking corresponding @code{set} commands: + +@table @code +@kindex show version +@cindex version number +@item show version +Show what version of @value{GDBN} is running. You should include this +information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in +use at your site, you may occasionally want to determine which version +of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced, +and old ones may wither away. The version number is also announced +when you start @value{GDBN}. + +@kindex show copying +@item show copying +Display information about permission for copying @value{GDBN}. + +@kindex show warranty +@item show warranty +Display the GNU ``NO WARRANTY'' statement. +@end table + +@node Running +@chapter Running Programs Under @value{GDBN} + +When you run a program under @value{GDBN}, you must first generate +debugging information when you compile it. +@ifclear BARETARGET +You may start it with its arguments, if any, in an environment of your +choice. You may redirect your program's input and output, debug an +already running process, or kill a child process. +@end ifclear + +@menu +* Compilation:: Compiling for debugging +* Starting:: Starting your program +@ifclear BARETARGET +* Arguments:: Your program's arguments +* Environment:: Your program's environment +* Working Directory:: Your program's working directory +* Input/Output:: Your program's input and output +* Attach:: Debugging an already-running process +* Kill Process:: Killing the child process +* Process Information:: Additional process information +@end ifclear +@end menu + +@node Compilation +@section Compiling for debugging + +In order to debug a program effectively, you need to generate +debugging information when you compile it. This debugging information +is stored in the object file; it describes the data type of each +variable or function and the correspondence between source line numbers +and addresses in the executable code. + +To request debugging information, specify the @samp{-g} option when you run +the compiler. + +Many C compilers are unable to handle the @samp{-g} and @samp{-O} +options together. Using those compilers, you cannot generate optimized +executables containing debugging information. + +@value{NGCC}, the GNU C compiler, supports @samp{-g} with or without +@samp{-O}, making it possible to debug optimized code. We recommend +that you @emph{always} use @samp{-g} whenever you compile a program. +You may think your program is correct, but there is no sense in pushing +your luck. + +@cindex optimized code, debugging +@cindex debugging optimized code +When you debug a program compiled with @samp{-g -O}, remember that the +optimizer is rearranging your code; the debugger will show you what is +really there. Do not be too surprised when the execution path does not +exactly match your source file! An extreme example: if you define a +variable, but never use it, @value{GDBN} will never see that +variable---because the compiler optimizes it out of existence. + +Some things do not work as well with @samp{-g -O} as with just +@samp{-g}, particularly on machines with instruction scheduling. If in +doubt, recompile with @samp{-g} alone, and if this fixes the problem, +please report it as a bug (including a test case!). + +Older versions of the GNU C compiler permitted a variant option +@w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this +format; if your GNU C compiler has this option, do not use it. + +@need 2000 +@node Starting +@section Starting your program +@cindex starting +@cindex running + +@table @code +@item run +@itemx r +@kindex run +Use the @code{run} command to start your program under @value{GDBN}. You must +first specify the program name +@ifset VXWORKS +(except on VxWorks) +@end ifset +with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and +Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file} +command (@pxref{Files, ,Commands to specify files}). + +@end table + +@ifclear BARETARGET +If you are running your program in an execution environment that +supports processes, @code{run} creates an inferior process and makes +that process run your program. (In environments without processes, +@code{run} jumps to the start of your program.) + +The execution of a program is affected by certain information it +receives from its superior. @value{GDBN} provides ways to specify this +information, which you must do @emph{before} starting your program. (You +can change it after starting your program, but such changes will only affect +your program the next time you start it.) This information may be +divided into four categories: + +@table @asis +@item The @emph{arguments.} +Specify the arguments to give your program as the arguments of the +@code{run} command. If a shell is available on your target, the shell +is used to pass the arguments, so that you may use normal conventions +(such as wildcard expansion or variable substitution) in describing +the arguments. In Unix systems, you can control which shell is used +with the @code{SHELL} environment variable. @xref{Arguments, ,Your +program's arguments}. + +@item The @emph{environment.} +Your program normally inherits its environment from @value{GDBN}, but you can +use the @value{GDBN} commands @code{set environment} and @code{unset +environment} to change parts of the environment that will be given to +your program. @xref{Environment, ,Your program's environment}. + +@item The @emph{working directory.} +Your program inherits its working directory from @value{GDBN}. You can set +the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}. +@xref{Working Directory, ,Your program's working directory}. + +@item The @emph{standard input and output.} +Your program normally uses the same device for standard input and +standard output as @value{GDBN} is using. You can redirect input and output +in the @code{run} command line, or you can use the @code{tty} command to +set a different device for your program. +@xref{Input/Output, ,Your program's input and output}. + +@cindex pipes +@emph{Warning:} While input and output redirection work, you cannot use +pipes to pass the output of the program you are debugging to another +program; if you attempt this, @value{GDBN} is likely to wind up debugging the +wrong program. +@end table +@end ifclear + +When you issue the @code{run} command, your program begins to execute +immediately. @xref{Stopping, ,Stopping and continuing}, for discussion +of how to arrange for your program to stop. Once your program has +stopped, you may call functions in your program, using the @code{print} +or @code{call} commands. @xref{Data, ,Examining Data}. + +If the modification time of your symbol file has changed since the +last time @value{GDBN} read its symbols, @value{GDBN} will discard its symbol table and +re-read it. When it does this, @value{GDBN} tries to retain your current +breakpoints. + +@ifclear BARETARGET +@node Arguments +@section Your program's arguments + +@cindex arguments (to your program) +The arguments to your program can be specified by the arguments of the +@code{run} command. They are passed to a shell, which expands wildcard +characters and performs redirection of I/O, and thence to your program. +Your @code{SHELL} environment variable (if it exists) specifies what +shell @value{GDBN} if you do not define @code{SHELL}, @value{GDBN} uses +@code{/bin/sh}. + +@code{run} with no arguments uses the same arguments used by the previous +@code{run}, or those set by the @code{set args} command. + +@kindex set args +@table @code +@item set args +Specify the arguments to be used the next time your program is run. If +@code{set args} has no arguments, @code{run} will execute your program +with no arguments. Once you have run your program with arguments, +using @code{set args} before the next @code{run} is the only way to run +it again without arguments. + +@item show args +@kindex show args +Show the arguments to give your program when it is started. +@end table + +@node Environment +@section Your program's environment + +@cindex environment (of your program) +The @dfn{environment} consists of a set of environment variables and +their values. Environment variables conventionally record such things as +your user name, your home directory, your terminal type, and your search +path for programs to run. Usually you set up environment variables with +the shell and they are inherited by all the other programs you run. When +debugging, it can be useful to try running your program with a modified +environment without having to start @value{GDBN} over again. + +@table @code +@item path @var{directory} +@kindex path +Add @var{directory} to the front of the @code{PATH} environment variable +(the search path for executables), for both @value{GDBN} and your program. +You may specify several directory names, separated by @samp{:} or +whitespace. If @var{directory} is already in the path, it is moved to +the front, so it will be searched sooner. + +You can use the string @samp{$cwd} to refer to whatever is the current +working directory at the time @value{GDBN} searches the path. If you +use @samp{.} instead, it refers to the directory where you executed the +@code{path} command. @value{GDBN} replaces @samp{.} in the +@var{directory} argument (with the current path) before adding +@var{directory} to the search path. +@c 'path' is explicitly nonrepeatable, but RMS points out it is silly to +@c document that, since repeating it would be a no-op. + +@item show paths +@kindex show paths +Display the list of search paths for executables (the @code{PATH} +environment variable). + +@item show environment @r{[}@var{varname}@r{]} +@kindex show environment +Print the value of environment variable @var{varname} to be given to +your program when it starts. If you do not supply @var{varname}, +print the names and values of all environment variables to be given to +your program. You can abbreviate @code{environment} as @code{env}. + +@item set environment @var{varname} @r{[}=@r{]} @var{value} +@kindex set environment +Set environment variable @var{varname} to @var{value}. The value +changes for your program only, not for @value{GDBN} itself. @var{value} may +be any string; the values of environment variables are just strings, and +any interpretation is supplied by your program itself. The @var{value} +parameter is optional; if it is eliminated, the variable is set to a +null value. +@c "any string" here does not include leading, trailing +@c blanks. Gnu asks: does anyone care? + +For example, this command: + +@example +set env USER = foo +@end example + +@noindent +tells a Unix program, when subsequently run, that its user is named +@samp{foo}. (The spaces around @samp{=} are used for clarity here; they +are not actually required.) + +@item unset environment @var{varname} +@kindex unset environment +Remove variable @var{varname} from the environment to be passed to your +program. This is different from @samp{set env @var{varname} =}; +@code{unset environment} removes the variable from the environment, +rather than assigning it an empty value. +@end table + +@emph{Warning:} @value{GDBN} runs your program using the shell indicated +by your @code{SHELL} environment variable if it exists (or +@code{/bin/sh} if not). If your @code{SHELL} variable names a shell +that runs an initialization file---such as @file{.cshrc} for C-shell, or +@file{.bashrc} for BASH---any variables you set in that file will affect +your program. You may wish to move setting of environment variables to +files that are only run when you sign on, such as @file{.login} or +@file{.profile}. + +@node Working Directory +@section Your program's working directory + +@cindex working directory (of your program) +Each time you start your program with @code{run}, it inherits its +working directory from the current working directory of @value{GDBN}. +The @value{GDBN} working directory is initially whatever it inherited +from its parent process (typically the shell), but you can specify a new +working directory in @value{GDBN} with the @code{cd} command. + +The @value{GDBN} working directory also serves as a default for the commands +that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to +specify files}. + +@table @code +@item cd @var{directory} +@kindex cd +Set the @value{GDBN} working directory to @var{directory}. + +@item pwd +@kindex pwd +Print the @value{GDBN} working directory. +@end table + +@node Input/Output +@section Your program's input and output + +@cindex redirection +@cindex i/o +@cindex terminal +By default, the program you run under @value{GDBN} does input and output to +the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal to +its own terminal modes to interact with you, but it records the terminal +modes your program was using and switches back to them when you continue +running your program. + +@table @code +@item info terminal +@kindex info terminal +Displays information recorded by @value{GDBN} about the terminal modes your +program is using. +@end table + +You can redirect your program's input and/or output using shell +redirection with the @code{run} command. For example, + +@example +run > outfile +@end example + +@noindent +starts your program, diverting its output to the file @file{outfile}. + +@kindex tty +@cindex controlling terminal +Another way to specify where your program should do input and output is +with the @code{tty} command. This command accepts a file name as +argument, and causes this file to be the default for future @code{run} +commands. It also resets the controlling terminal for the child +process, for future @code{run} commands. For example, + +@example +tty /dev/ttyb +@end example + +@noindent +directs that processes started with subsequent @code{run} commands +default to do input and output on the terminal @file{/dev/ttyb} and have +that as their controlling terminal. + +An explicit redirection in @code{run} overrides the @code{tty} command's +effect on the input/output device, but not its effect on the controlling +terminal. + +When you use the @code{tty} command or redirect input in the @code{run} +command, only the input @emph{for your program} is affected. The input +for @value{GDBN} still comes from your terminal. + +@node Attach +@section Debugging an already-running process +@kindex attach +@cindex attach + +@table @code +@item attach @var{process-id} +This command attaches to a running process---one that was started +outside @value{GDBN}. (@code{info files} will show your active +targets.) The command takes as argument a process ID. The usual way to +find out the process-id of a Unix process is with the @code{ps} utility, +or with the @samp{jobs -l} shell command. + +@code{attach} will not repeat if you press @key{RET} a second time after +executing the command. +@end table + +To use @code{attach}, your program must be running in an environment +which supports processes; for example, @code{attach} does not work for +programs on bare-board targets that lack an operating system. You must +also have permission to send the process a signal. + +When using @code{attach}, you should first use the @code{file} command +to specify the program running in the process and load its symbol table. +@xref{Files, ,Commands to Specify Files}. + +The first thing @value{GDBN} does after arranging to debug the specified +process is to stop it. You can examine and modify an attached process +with all the @value{GDBN} commands that are ordinarily available when you start +processes with @code{run}. You can insert breakpoints; you can step and +continue; you can modify storage. If you would rather the process +continue running, you may use the @code{continue} command after +attaching @value{GDBN} to the process. + +@table @code +@item detach +@kindex detach +When you have finished debugging the attached process, you can use the +@code{detach} command to release it from @value{GDBN} control. Detaching +the process continues its execution. After the @code{detach} command, +that process and @value{GDBN} become completely independent once more, and you +are ready to @code{attach} another process or start one with @code{run}. +@code{detach} will not repeat if you press @key{RET} again after +executing the command. +@end table + +If you exit @value{GDBN} or use the @code{run} command while you have an attached +process, you kill that process. By default, you will be asked for +confirmation if you try to do either of these things; you can control +whether or not you need to confirm by using the @code{set confirm} command +(@pxref{Messages/Warnings, ,Optional warnings and messages}). + +@node Kill Process +@c @group +@section Killing the child process + +@table @code +@item kill +@kindex kill +Kill the child process in which your program is running under @value{GDBN}. +@end table + +This command is useful if you wish to debug a core dump instead of a +running process. @value{GDBN} ignores any core dump file while your program +is running. +@c @end group + +On some operating systems, a program cannot be executed outside @value{GDBN} +while you have breakpoints set on it inside @value{GDBN}. You can use the +@code{kill} command in this situation to permit running your program +outside the debugger. + +The @code{kill} command is also useful if you wish to recompile and +relink your program, since on many systems it is impossible to modify an +executable file while it is running in a process. In this case, when you +next type @code{run}, @value{GDBN} will notice that the file has changed, and +will re-read the symbol table (while trying to preserve your current +breakpoint settings). + +@node Process Information +@section Additional process information + +@kindex /proc +@cindex process image +Some operating systems provide a facility called @samp{/proc} that can +be used to examine the image of a running process using file-system +subroutines. If @value{GDBN} is configured for an operating system with this +facility, the command @code{info proc} is available to report on several +kinds of information about the process running your program. + +@table @code +@item info proc +@kindex info proc +Summarize available information about the process. + +@item info proc mappings +@kindex info proc mappings +Report on the address ranges accessible in the program, with information +on whether your program may read, write, or execute each range. + +@item info proc times +@kindex info proc times +Starting time, user CPU time, and system CPU time for your program and +its children. + +@item info proc id +@kindex info proc id +Report on the process IDs related to your program: its own process ID, +the ID of its parent, the process group ID, and the session ID. + +@item info proc status +@kindex info proc status +General information on the state of the process. If the process is +stopped, this report includes the reason for stopping, and any signal +received. + +@item info proc all +Show all the above information about the process. +@end table +@end ifclear + +@node Stopping +@chapter Stopping and Continuing + +The principal purposes of using a debugger are so that you can stop your +program before it terminates; or so that, if your program runs into +trouble, you can investigate and find out why. + +Inside @value{GDBN}, your program may stop for any of several reasons, such +as +@ifclear BARETARGET +a signal, +@end ifclear +a breakpoint, or reaching a new line after a @value{GDBN} +command such as @code{step}. You may then examine and change +variables, set new breakpoints or remove old ones, and then continue +execution. Usually, the messages shown by @value{GDBN} provide ample +explanation of the status of your program---but you can also explicitly +request this information at any time. + +@table @code +@item info program +@kindex info program +Display information about the status of your program: whether it is +running or not, +@ifclear BARETARGET +what process it is, +@end ifclear +and why it stopped. +@end table + +@menu +@ifclear CONLY +* Breakpoints:: Breakpoints, watchpoints, and exceptions +@end ifclear +@ifset CONLY +* Breakpoints:: Breakpoints and watchpoints +@end ifset +@c Remnant makeinfo bug requires blank line after *successful* end-if in menu: + +* Continuing and Stepping:: Resuming execution +@ifset POSIX +* Signals:: Signals +@end ifset +@end menu + +@c makeinfo node-defaulting requires adjacency of @node and sectioning cmds +@c ...hence distribute @node Breakpoints over two possible @if expansions. +@c +@ifclear CONLY +@node Breakpoints +@section Breakpoints, watchpoints, and exceptions +@end ifclear +@ifset CONLY +@node Breakpoints +@section Breakpoints and watchpoints +@end ifset + +@cindex breakpoints +A @dfn{breakpoint} makes your program stop whenever a certain point in +the program is reached. For each breakpoint, you can add various +conditions to control in finer detail whether your program will stop. +You can set breakpoints with the @code{break} command and its variants +(@pxref{Set Breaks, ,Setting breakpoints}), to specify the place where +your program should stop by line number, function name or exact address +in the program. +@ifclear CONLY +In languages with exception handling (such as GNU C++), you can also set +breakpoints where an exception is raised (@pxref{Exception Handling, +,Breakpoints and exceptions}). +@end ifclear + +@cindex watchpoints +@cindex memory tracing +@cindex breakpoint on memory address +@cindex breakpoint on variable modification +A @dfn{watchpoint} is a special breakpoint that stops your program +when the value of an expression changes. You must use a different +command to set watchpoints (@pxref{Set Watchpoints, ,Setting +watchpoints}), but aside from that, you can manage a watchpoint like +any other breakpoint: you enable, disable, and delete both breakpoints +and watchpoints using the same commands. + +You can arrange to have values from your program displayed automatically +whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display, +,Automatic display}. + +@cindex breakpoint numbers +@cindex numbers for breakpoints +@value{GDBN} assigns a number to each breakpoint or watchpoint when you +create it; these numbers are successive integers starting with one. In +many of the commands for controlling various features of breakpoints you +use the breakpoint number to say which breakpoint you want to change. +Each breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has +no effect on your program until you enable it again. + +@menu +* Set Breaks:: Setting breakpoints +* Set Watchpoints:: Setting watchpoints +@ifclear CONLY +* Exception Handling:: Breakpoints and exceptions +@end ifclear + +* Delete Breaks:: Deleting breakpoints +* Disabling:: Disabling breakpoints +* Conditions:: Break conditions +* Break Commands:: Breakpoint command lists +@ifclear CONLY +* Breakpoint Menus:: Breakpoint menus +@end ifclear +@ifclear BARETARGET +* Error in Breakpoints:: ``Cannot insert breakpoints'' +@end ifclear +@end menu + +@node Set Breaks +@subsection Setting breakpoints + +@c FIXME LMB what does GDB do if no code on line of breakpt? +@c consider in particular declaration with/without initialization. +@c +@c FIXME 2 is there stuff on this already? break at fun start, already init? + +@kindex break +@kindex b +@kindex $bpnum +@cindex latest breakpoint +Breakpoints are set with the @code{break} command (abbreviated +@code{b}). The debugger convenience variable @samp{$bpnum} records the +number of the beakpoint you've set most recently; see @ref{Convenience +Vars,, Convenience variables}, for a discussion of what you can do with +convenience variables. + +You have several ways to say where the breakpoint should go. + +@table @code +@item break @var{function} +Set a breakpoint at entry to function @var{function}. +@ifclear CONLY +When using source languages that permit overloading of symbols, such as +C++, @var{function} may refer to more than one possible place to break. +@xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation. +@end ifclear + +@item break +@var{offset} +@itemx break -@var{offset} +Set a breakpoint some number of lines forward or back from the position +at which execution stopped in the currently selected frame. + +@item break @var{linenum} +Set a breakpoint at line @var{linenum} in the current source file. +That file is the last file whose source text was printed. This +breakpoint will stop your program just before it executes any of the +code on that line. + +@item break @var{filename}:@var{linenum} +Set a breakpoint at line @var{linenum} in source file @var{filename}. + +@item break @var{filename}:@var{function} +Set a breakpoint at entry to function @var{function} found in file +@var{filename}. Specifying a file name as well as a function name is +superfluous except when multiple files contain similarly named +functions. + +@item break *@var{address} +Set a breakpoint at address @var{address}. You can use this to set +breakpoints in parts of your program which do not have debugging +information or source files. + +@item break +When called without any arguments, @code{break} sets a breakpoint at +the next instruction to be executed in the selected stack frame +(@pxref{Stack, ,Examining the Stack}). In any selected frame but the +innermost, this will cause your program to stop as soon as control +returns to that frame. This is similar to the effect of a +@code{finish} command in the frame inside the selected frame---except +that @code{finish} does not leave an active breakpoint. If you use +@code{break} without an argument in the innermost frame, @value{GDBN} will stop +the next time it reaches the current location; this may be useful +inside loops. + +@value{GDBN} normally ignores breakpoints when it resumes execution, until at +least one instruction has been executed. If it did not do this, you +would be unable to proceed past a breakpoint without first disabling the +breakpoint. This rule applies whether or not the breakpoint already +existed when your program stopped. + +@item break @dots{} if @var{cond} +Set a breakpoint with condition @var{cond}; evaluate the expression +@var{cond} each time the breakpoint is reached, and stop only if the +value is nonzero---that is, if @var{cond} evaluates as true. +@samp{@dots{}} stands for one of the possible arguments described +above (or no argument) specifying where to break. @xref{Conditions, +,Break conditions}, for more information on breakpoint conditions. + +@item tbreak @var{args} +@kindex tbreak +Set a breakpoint enabled only for one stop. @var{args} are the +same as for the @code{break} command, and the breakpoint is set in the same +way, but the breakpoint is automatically disabled after the first time your +program stops there. @xref{Disabling, ,Disabling breakpoints}. + +@item rbreak @var{regex} +@kindex rbreak +@cindex regular expression +@c FIXME what kind of regexp? +Set breakpoints on all functions matching the regular expression +@var{regex}. This command +sets an unconditional breakpoint on all matches, printing a list of all +breakpoints it set. Once these breakpoints are set, they are treated +just like the breakpoints set with the @code{break} command. They can +be deleted, disabled, made conditional, etc., in the standard ways. + +@ifclear CONLY +When debugging C++ programs, @code{rbreak} is useful for setting +breakpoints on overloaded functions that are not members of any special +classes. +@end ifclear + +@kindex info breakpoints +@cindex @code{$_} and @code{info breakpoints} +@item info breakpoints @r{[}@var{n}@r{]} +@itemx info break @r{[}@var{n}@r{]} +@itemx info watchpoints @r{[}@var{n}@r{]} +Print a table of all breakpoints and watchpoints set and not +deleted, with the following columns for each breakpoint: + +@table @emph +@item Breakpoint Numbers +@item Type +Breakpoint or watchpoint. +@item Disposition +Whether the breakpoint is marked to be disabled or deleted when hit. +@item Enabled or Disabled +Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints +that are not enabled. +@item Address +Where the breakpoint is in your program, as a memory address +@item What +Where the breakpoint is in the source for your program, as a file and +line number. +@end table + +@noindent +If a breakpoint is conditional, @code{info break} shows the condition on +the line following the affected breakpoint; breakpoint commands, if any, +are listed after that. + +@noindent +@code{info break} with a breakpoint +number @var{n} as argument lists only that breakpoint. The +convenience variable @code{$_} and the default examining-address for +the @code{x} command are set to the address of the last breakpoint +listed (@pxref{Memory, ,Examining memory}). +@end table + +@value{GDBN} allows you to set any number of breakpoints at the same place in +your program. There is nothing silly or meaningless about this. When +the breakpoints are conditional, this is even useful +(@pxref{Conditions, ,Break conditions}). + +@cindex negative breakpoint numbers +@cindex internal @value{GDBN} breakpoints +@value{GDBN} itself sometimes sets breakpoints in your program for special +purposes, such as proper handling of @code{longjmp} (in C programs). +These internal breakpoints are assigned negative numbers, starting with +@code{-1}; @samp{info breakpoints} does not display them. + +You can see these breakpoints with the @value{GDBN} maintenance command +@samp{maint info breakpoints}. + +@table @code +@kindex maint info breakpoints +@item maint info breakpoints +Using the same format as @samp{info breakpoints}, display both the +breakpoints you've set explicitly, and those @value{GDBN} is using for +internal purposes. Internal breakpoints are shown with negative +breakpoint numbers. The type column identifies what kind of breakpoint +is shown: + +@table @code +@item breakpoint +Normal, explicitly set breakpoint. + +@item watchpoint +Normal, explicitly set watchpoint. + +@item longjmp +Internal breakpoint, used to handle correctly stepping through +@code{longjmp} calls. + +@item longjmp resume +Internal breakpoint at the target of a @code{longjmp}. + +@item until +Temporary internal breakpoint used by the @value{GDBN} @code{until} command. + +@item finish +Temporary internal breakpoint used by the @value{GDBN} @code{finish} command. +@end table + +@end table + + +@node Set Watchpoints +@subsection Setting watchpoints +@cindex setting watchpoints + +You can use a watchpoint to stop execution whenever the value of an +expression changes, without having to predict a particular place +where this may happen. + +Watchpoints currently execute two orders of magnitude more slowly than +other breakpoints, but this can be well worth it to catch errors where +you have no clue what part of your program is the culprit. Some +processors provide special hardware to support watchpoint evaluation; future +releases of @value{GDBN} will use such hardware if it is available. + +@table @code +@kindex watch +@item watch @var{expr} +Set a watchpoint for an expression. + +@kindex info watchpoints +@item info watchpoints +This command prints a list of watchpoints and breakpoints; it is the +same as @code{info break}. +@end table + +@ifclear CONLY +@node Exception Handling +@subsection Breakpoints and exceptions +@cindex exception handlers + +Some languages, such as GNU C++, implement exception handling. You can +use @value{GDBN} to examine what caused your program to raise an exception, +and to list the exceptions your program is prepared to handle at a +given point in time. + +@table @code +@item catch @var{exceptions} +@kindex catch +You can set breakpoints at active exception handlers by using the +@code{catch} command. @var{exceptions} is a list of names of exceptions +to catch. +@end table + +You can use @code{info catch} to list active exception handlers. +@xref{Frame Info, ,Information about a frame}. + +There are currently some limitations to exception handling in @value{GDBN}. +These will be corrected in a future release. + +@itemize @bullet +@item +If you call a function interactively, @value{GDBN} normally returns +control to you when the function has finished executing. If the call +raises an exception, however, the call may bypass the mechanism that +returns control to you and cause your program to simply continue +running until it hits a breakpoint, catches a signal that @value{GDBN} is +listening for, or exits. +@item +You cannot raise an exception interactively. +@item +You cannot interactively install an exception handler. +@end itemize + +@cindex raise exceptions +Sometimes @code{catch} is not the best way to debug exception handling: +if you need to know exactly where an exception is raised, it is better to +stop @emph{before} the exception handler is called, since that way you +can see the stack before any unwinding takes place. If you set a +breakpoint in an exception handler instead, it may not be easy to find +out where the exception was raised. + +To stop just before an exception handler is called, you need some +knowledge of the implementation. In the case of GNU C++, exceptions are +raised by calling a library function named @code{__raise_exception} +which has the following ANSI C interface: + +@example + /* @var{addr} is where the exception identifier is stored. + ID is the exception identifier. */ + void __raise_exception (void **@var{addr}, void *@var{id}); +@end example + +@noindent +To make the debugger catch all exceptions before any stack +unwinding takes place, set a breakpoint on @code{__raise_exception} +(@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}). + +With a conditional breakpoint (@pxref{Conditions, ,Break conditions}) +that depends on the value of @var{id}, you can stop your program when +a specific exception is raised. You can use multiple conditional +breakpoints to stop your program when any of a number of exceptions are +raised. +@end ifclear + +@node Delete Breaks +@subsection Deleting breakpoints + +@cindex clearing breakpoints, watchpoints +@cindex deleting breakpoints, watchpoints +It is often necessary to eliminate a breakpoint or watchpoint once it +has done its job and you no longer want your program to stop there. This +is called @dfn{deleting} the breakpoint. A breakpoint that has been +deleted no longer exists; it is forgotten. + +With the @code{clear} command you can delete breakpoints according to +where they are in your program. With the @code{delete} command you can +delete individual breakpoints or watchpoints by specifying their +breakpoint numbers. + +It is not necessary to delete a breakpoint to proceed past it. @value{GDBN} +automatically ignores breakpoints on the first instruction to be executed +when you continue execution without changing the execution address. + +@table @code +@item clear +@kindex clear +Delete any breakpoints at the next instruction to be executed in the +selected stack frame (@pxref{Selection, ,Selecting a frame}). When +the innermost frame is selected, this is a good way to delete a +breakpoint where your program just stopped. + +@item clear @var{function} +@itemx clear @var{filename}:@var{function} +Delete any breakpoints set at entry to the function @var{function}. + +@item clear @var{linenum} +@itemx clear @var{filename}:@var{linenum} +Delete any breakpoints set at or within the code of the specified line. + +@item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]} +@cindex delete breakpoints +@kindex delete +@kindex d +Delete the breakpoints or watchpoints of the numbers specified as +arguments. If no argument is specified, delete all breakpoints (@value{GDBN} +asks confirmation, unless you have @code{set confirm off}). You +can abbreviate this command as @code{d}. +@end table + +@node Disabling +@subsection Disabling breakpoints + +@cindex disabled breakpoints +@cindex enabled breakpoints +Rather than deleting a breakpoint or watchpoint, you might prefer to +@dfn{disable} it. This makes the breakpoint inoperative as if it had +been deleted, but remembers the information on the breakpoint so that +you can @dfn{enable} it again later. + +You disable and enable breakpoints and watchpoints with the +@code{enable} and @code{disable} commands, optionally specifying one or +more breakpoint numbers as arguments. Use @code{info break} or +@code{info watch} to print a list of breakpoints or watchpoints if you +do not know which numbers to use. + +A breakpoint or watchpoint can have any of four different states of +enablement: + +@itemize @bullet +@item +Enabled. The breakpoint will stop your program. A breakpoint set +with the @code{break} command starts out in this state. +@item +Disabled. The breakpoint has no effect on your program. +@item +Enabled once. The breakpoint will stop your program, but +when it does so it will become disabled. A breakpoint set +with the @code{tbreak} command starts out in this state. +@item +Enabled for deletion. The breakpoint will stop your program, but +immediately after it does so it will be deleted permanently. +@end itemize + +You can use the following commands to enable or disable breakpoints and +watchpoints: + +@table @code +@item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]} +@kindex disable breakpoints +@kindex disable +@kindex dis +Disable the specified breakpoints---or all breakpoints, if none are +listed. A disabled breakpoint has no effect but is not forgotten. All +options such as ignore-counts, conditions and commands are remembered in +case the breakpoint is enabled again later. You may abbreviate +@code{disable} as @code{dis}. + +@item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]} +@kindex enable breakpoints +@kindex enable +Enable the specified breakpoints (or all defined breakpoints). They +become effective once again in stopping your program. + +@item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{} +Enable the specified breakpoints temporarily. Each will be disabled +again the next time it stops your program. + +@item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{} +Enable the specified breakpoints to work once and then die. Each of +the breakpoints will be deleted the next time it stops your program. +@end table + +Save for a breakpoint set with @code{tbreak} (@pxref{Set Breaks, +,Setting breakpoints}), breakpoints that you set are initially enabled; +subsequently, they become disabled or enabled only when you use one of +the commands above. (The command @code{until} can set and delete a +breakpoint of its own, but it will not change the state of your other +breakpoints; see @ref{Continuing and Stepping, ,Continuing and +stepping}.) + +@node Conditions +@subsection Break conditions +@cindex conditional breakpoints +@cindex breakpoint conditions + +@c FIXME what is scope of break condition expr? Context where wanted? +@c in particular for a watchpoint? +The simplest sort of breakpoint breaks every time your program reaches a +specified place. You can also specify a @dfn{condition} for a +breakpoint. A condition is just a Boolean expression in your +programming language (@pxref{Expressions, ,Expressions}). A breakpoint with +a condition evaluates the expression each time your program reaches it, +and your program stops only if the condition is @emph{true}. + +This is the converse of using assertions for program validation; in that +situation, you want to stop when the assertion is violated---that is, +when the condition is false. In C, if you want to test an assertion expressed +by the condition @var{assert}, you should set the condition +@samp{! @var{assert}} on the appropriate breakpoint. + +Conditions are also accepted for watchpoints; you may not need them, +since a watchpoint is inspecting the value of an expression anyhow---but +it might be simpler, say, to just set a watchpoint on a variable name, +and specify a condition that tests whether the new value is an interesting +one. + +Break conditions can have side effects, and may even call functions in +your program. This can be useful, for example, to activate functions +that log program progress, or to use your own print functions to +format special data structures. The effects are completely predictable +unless there is another enabled breakpoint at the same address. (In +that case, @value{GDBN} might see the other breakpoint first and stop your +program without checking the condition of this one.) Note that +breakpoint commands are usually more convenient and flexible for the +purpose of performing side effects when a breakpoint is reached +(@pxref{Break Commands, ,Breakpoint command lists}). + +Break conditions can be specified when a breakpoint is set, by using +@samp{if} in the arguments to the @code{break} command. @xref{Set +Breaks, ,Setting breakpoints}. They can also be changed at any time +with the @code{condition} command. The @code{watch} command does not +recognize the @code{if} keyword; @code{condition} is the only way to +impose a further condition on a watchpoint. + +@table @code +@item condition @var{bnum} @var{expression} +@kindex condition +Specify @var{expression} as the break condition for breakpoint or +watchpoint number @var{bnum}. From now on, this breakpoint will stop +your program only if the value of @var{expression} is true (nonzero, in +C). When you use @code{condition}, @value{GDBN} checks @var{expression} +immediately for syntactic correctness, and to determine whether symbols +in it have referents in the context of your breakpoint. +@c FIXME so what does GDB do if there is no referent? Moreover, what +@c about watchpoints? +@value{GDBN} does +not actually evaluate @var{expression} at the time the @code{condition} +command is given, however. @xref{Expressions, ,Expressions}. + +@item condition @var{bnum} +Remove the condition from breakpoint number @var{bnum}. It becomes +an ordinary unconditional breakpoint. +@end table + +@cindex ignore count (of breakpoint) +A special case of a breakpoint condition is to stop only when the +breakpoint has been reached a certain number of times. This is so +useful that there is a special way to do it, using the @dfn{ignore +count} of the breakpoint. Every breakpoint has an ignore count, which +is an integer. Most of the time, the ignore count is zero, and +therefore has no effect. But if your program reaches a breakpoint whose +ignore count is positive, then instead of stopping, it just decrements +the ignore count by one and continues. As a result, if the ignore count +value is @var{n}, the breakpoint will not stop the next @var{n} times it +is reached. + +@table @code +@item ignore @var{bnum} @var{count} +@kindex ignore +Set the ignore count of breakpoint number @var{bnum} to @var{count}. +The next @var{count} times the breakpoint is reached, your program's +execution will not stop; other than to decrement the ignore count, @value{GDBN} +takes no action. + +To make the breakpoint stop the next time it is reached, specify +a count of zero. + +When you use @code{continue} to resume execution of your program from a +breakpoint, you can specify an ignore count directly as an argument to +@code{continue}, rather than using @code{ignore}. @xref{Continuing and +Stepping,,Continuing and stepping}. + +If a breakpoint has a positive ignore count and a condition, the condition +is not checked. Once the ignore count reaches zero, the condition will +be checked. + +You could achieve the effect of the ignore count with a condition such +as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that +is decremented each time. @xref{Convenience Vars, ,Convenience +variables}. +@end table + +@node Break Commands +@subsection Breakpoint command lists + +@cindex breakpoint commands +You can give any breakpoint (or watchpoint) a series of commands to +execute when your program stops due to that breakpoint. For example, you +might want to print the values of certain expressions, or enable other +breakpoints. + +@table @code +@item commands @r{[}@var{bnum}@r{]} +@itemx @dots{} @var{command-list} @dots{} +@itemx end +@kindex commands +@kindex end +Specify a list of commands for breakpoint number @var{bnum}. The commands +themselves appear on the following lines. Type a line containing just +@code{end} to terminate the commands. + +To remove all commands from a breakpoint, type @code{commands} and +follow it immediately with @code{end}; that is, give no commands. + +With no @var{bnum} argument, @code{commands} refers to the last +breakpoint or watchpoint set (not to the breakpoint most recently +encountered). +@end table + +Pressing @key{RET} as a means of repeating the last @value{GDBN} command is +disabled within a @var{command-list}. + +You can use breakpoint commands to start your program up again. Simply +use the @code{continue} command, or @code{step}, or any other command +that resumes execution. + +Any other commands in the command list, after a command that resumes +execution, are ignored. This is because any time you resume execution +(even with a simple @code{next} or @code{step}), you may encounter +another breakpoint---which could have its own command list, leading to +ambiguities about which list to execute. + +@kindex silent +If the first command you specify in a command list is @code{silent}, the +usual message about stopping at a breakpoint is not printed. This may +be desirable for breakpoints that are to print a specific message and +then continue. If none of the remaining commands print anything, you +will see no sign that the breakpoint was reached. @code{silent} is +meaningful only at the beginning of a breakpoint command list. + +The commands @code{echo}, @code{output}, and @code{printf} allow you to +print precisely controlled output, and are often useful in silent +breakpoints. @xref{Output, ,Commands for controlled output}. + +For example, here is how you could use breakpoint commands to print the +value of @code{x} at entry to @code{foo} whenever @code{x} is positive. + +@example +break foo if x>0 +commands +silent +printf "x is %d\n",x +cont +end +@end example + +One application for breakpoint commands is to compensate for one bug so +you can test for another. Put a breakpoint just after the erroneous line +of code, give it a condition to detect the case in which something +erroneous has been done, and give it commands to assign correct values +to any variables that need them. End with the @code{continue} command +so that your program does not stop, and start with the @code{silent} +command so that no output is produced. Here is an example: + +@example +break 403 +commands +silent +set x = y + 4 +cont +end +@end example + +@ifclear CONLY +@node Breakpoint Menus +@subsection Breakpoint menus +@cindex overloading +@cindex symbol overloading + +Some programming languages (notably C++) permit a single function name +to be defined several times, for application in different contexts. +This is called @dfn{overloading}. When a function name is overloaded, +@samp{break @var{function}} is not enough to tell @value{GDBN} where you want +a breakpoint. If you realize this will be a problem, you can use +something like @samp{break @var{function}(@var{types})} to specify which +particular version of the function you want. Otherwise, @value{GDBN} offers +you a menu of numbered choices for different possible breakpoints, and +waits for your selection with the prompt @samp{>}. The first two +options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1} +sets a breakpoint at each definition of @var{function}, and typing +@kbd{0} aborts the @code{break} command without setting any new +breakpoints. + +For example, the following session excerpt shows an attempt to set a +breakpoint at the overloaded symbol @code{String::after}. +We choose three particular definitions of that function name: + +@c FIXME! This is likely to change to show arg type lists, at least +@smallexample +(@value{GDBP}) b String::after +[0] cancel +[1] all +[2] file:String.cc; line number:867 +[3] file:String.cc; line number:860 +[4] file:String.cc; line number:875 +[5] file:String.cc; line number:853 +[6] file:String.cc; line number:846 +[7] file:String.cc; line number:735 +> 2 4 6 +Breakpoint 1 at 0xb26c: file String.cc, line 867. +Breakpoint 2 at 0xb344: file String.cc, line 875. +Breakpoint 3 at 0xafcc: file String.cc, line 846. +Multiple breakpoints were set. +Use the "delete" command to delete unwanted + breakpoints. +(@value{GDBP}) +@end smallexample +@end ifclear + +@ifclear BARETARGET +@node Error in Breakpoints +@subsection ``Cannot insert breakpoints'' + +@c FIXME: "cannot insert breakpoints" error, v unclear. +@c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91 +@c some light may be shed by looking at instances of +@c ONE_PROCESS_WRITETEXT. But error message seems possible otherwise +@c too. pesch, 20sep91 +Under some operating systems, breakpoints cannot be used in a program if +any other process is running that program. In this situation, +attempting to run or continue a program with a breakpoint causes @value{GDBN} +to stop the other process. + +When this happens, you have three ways to proceed: + +@enumerate +@item +Remove or disable the breakpoints, then continue. + +@item +Suspend @value{GDBN}, and copy the file containing your program to a new name. +Resume @value{GDBN} and use the @code{exec-file} command to specify that @value{GDBN} +should run your program under that name. Then start your program again. + +@c FIXME: RMS commented here "Show example". Maybe when someone +@c explains the first FIXME: in this section... + +@item +Relink your program so that the text segment is nonsharable, using the +linker option @samp{-N}. The operating system limitation may not apply +to nonsharable executables. +@end enumerate +@end ifclear + +@node Continuing and Stepping +@section Continuing and stepping + +@cindex stepping +@cindex continuing +@cindex resuming execution +@dfn{Continuing} means resuming program execution until your program +completes normally. In contrast, @dfn{stepping} means executing just +one more ``step'' of your program, where ``step'' may mean either one +line of source code, or one machine instruction (depending on what +particular command you use). Either when continuing +or when stepping, your program may stop even sooner, due to +@ifset BARETARGET +a breakpoint. +@end ifset +@ifclear BARETARGET +a breakpoint or a signal. (If due to a signal, you may want to use +@code{handle}, or use @samp{signal 0} to resume execution. +@xref{Signals, ,Signals}.) +@end ifclear + +@table @code +@item continue @r{[}@var{ignore-count}@r{]} +@itemx c @r{[}@var{ignore-count}@r{]} +@itemx fg @r{[}@var{ignore-count}@r{]} +@kindex continue +@kindex c +@kindex fg +Resume program execution, at the address where your program last stopped; +any breakpoints set at that address are bypassed. The optional argument +@var{ignore-count} allows you to specify a further number of times to +ignore a breakpoint at this location; its effect is like that of +@code{ignore} (@pxref{Conditions, ,Break conditions}). + +The argument @var{ignore-count} is meaningful only when your program +stopped due to a breakpoint. At other times, the argument to +@code{continue} is ignored. + +The synonyms @code{c} and @code{fg} are provided purely for convenience, +and have exactly the same behavior as @code{continue}. +@end table + +To resume execution at a different place, you can use @code{return} +(@pxref{Returning, ,Returning from a function}) to go back to the +calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a +different address}) to go to an arbitrary location in your program. + +A typical technique for using stepping is to set a breakpoint +@ifclear CONLY +(@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}) +@end ifclear +@ifset CONLY +(@pxref{Breakpoints, ,Breakpoints and watchpoints}) +@end ifset +at the +beginning of the function or the section of your program where a +problem is believed to lie, run your program until it stops at that +breakpoint, and then step through the suspect area, examining the +variables that are interesting, until you see the problem happen. + +@table @code +@item step +@kindex step +@kindex s +Continue running your program until control reaches a different source +line, then stop it and return control to @value{GDBN}. This command is +abbreviated @code{s}. + +@quotation +@emph{Warning:} If you use the @code{step} command while control is +within a function that was compiled without debugging information, +execution proceeds until control reaches a function that does have +debugging information. +@end quotation + +@item step @var{count} +Continue running as in @code{step}, but do so @var{count} times. If a +breakpoint is reached, +@ifclear BARETARGET +or a signal not related to stepping occurs before @var{count} steps, +@end ifclear +stepping stops right away. + +@item next @r{[}@var{count}@r{]} +@kindex next +@kindex n +Continue to the next source line in the current (innermost) stack frame. +Similar to @code{step}, but any function calls appearing within the line +of code are executed without stopping. Execution stops when control +reaches a different line of code at the stack level which was executing +when the @code{next} command was given. This command is abbreviated +@code{n}. + +An argument @var{count} is a repeat count, as for @code{step}. + +@code{next} within a function that lacks debugging information acts like +@code{step}, but any function calls appearing within the code of the +function are executed without stopping. + +@item finish +@kindex finish +Continue running until just after function in the selected stack frame +returns. Print the returned value (if any). + +Contrast this with the @code{return} command (@pxref{Returning, +,Returning from a function}). + +@item until +@kindex until +@itemx u +@kindex u +Continue running until a source line past the current line, in the +current stack frame, is reached. This command is used to avoid single +stepping through a loop more than once. It is like the @code{next} +command, except that when @code{until} encounters a jump, it +automatically continues execution until the program counter is greater +than the address of the jump. + +This means that when you reach the end of a loop after single stepping +though it, @code{until} will cause your program to continue execution +until the loop is exited. In contrast, a @code{next} command at the end +of a loop will simply step back to the beginning of the loop, which +would force you to step through the next iteration. + +@code{until} always stops your program if it attempts to exit the current +stack frame. + +@code{until} may produce somewhat counterintuitive results if the order +of machine code does not match the order of the source lines. For +example, in the following excerpt from a debugging session, the @code{f} +(@code{frame}) command shows that execution is stopped at line +@code{206}; yet when we use @code{until}, we get to line @code{195}: + +@example +(@value{GDBP}) f +#0 main (argc=4, argv=0xf7fffae8) at m4.c:206 +206 expand_input(); +(@value{GDBP}) until +195 for ( ; argc > 0; NEXTARG) @{ +@end example + +This happened because, for execution efficiency, the compiler had +generated code for the loop closure test at the end, rather than the +start, of the loop---even though the test in a C @code{for}-loop is +written before the body of the loop. The @code{until} command appeared +to step back to the beginning of the loop when it advanced to this +expression; however, it has not really gone to an earlier +statement---not in terms of the actual machine code. + +@code{until} with no argument works by means of single +instruction stepping, and hence is slower than @code{until} with an +argument. + +@item until @var{location} +@itemx u @var{location} +Continue running your program until either the specified location is +reached, or the current stack frame returns. @var{location} is any of +the forms of argument acceptable to @code{break} (@pxref{Set Breaks, +,Setting breakpoints}). This form of the command uses breakpoints, +and hence is quicker than @code{until} without an argument. + +@item stepi +@itemx si +@kindex stepi +@kindex si +Execute one machine instruction, then stop and return to the debugger. + +It is often useful to do @samp{display/i $pc} when stepping by machine +instructions. This will cause the next instruction to be executed to +be displayed automatically at each stop. @xref{Auto Display, +,Automatic display}. + +An argument is a repeat count, as in @code{step}. + +@need 750 +@item nexti +@itemx ni +@kindex nexti +@kindex ni +Execute one machine instruction, but if it is a function call, +proceed until the function returns. + +An argument is a repeat count, as in @code{next}. +@end table + +@ifset POSIX +@node Signals +@section Signals +@cindex signals + +A signal is an asynchronous event that can happen in a program. The +operating system defines the possible kinds of signals, and gives each +kind a name and a number. For example, in Unix @code{SIGINT} is the +signal a program gets when you type an interrupt (often @kbd{C-c}); +@code{SIGSEGV} is the signal a program gets from referencing a place in +memory far away from all the areas in use; @code{SIGALRM} occurs when +the alarm clock timer goes off (which happens only if your program has +requested an alarm). + +@cindex fatal signals +Some signals, including @code{SIGALRM}, are a normal part of the +functioning of your program. Others, such as @code{SIGSEGV}, indicate +errors; these signals are @dfn{fatal} (kill your program immediately) if the +program has not specified in advance some other way to handle the signal. +@code{SIGINT} does not indicate an error in your program, but it is normally +fatal so it can carry out the purpose of the interrupt: to kill the program. + +@value{GDBN} has the ability to detect any occurrence of a signal in your +program. You can tell @value{GDBN} in advance what to do for each kind of +signal. + +@cindex handling signals +Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM} +(so as not to interfere with their role in the functioning of your program) +but to stop your program immediately whenever an error signal happens. +You can change these settings with the @code{handle} command. + +@table @code +@item info signals +@kindex info signals +Print a table of all the kinds of signals and how @value{GDBN} has been told to +handle each one. You can use this to see the signal numbers of all +the defined types of signals. + +@item handle @var{signal} @var{keywords}@dots{} +@kindex handle +Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can be the +number of a signal or its name (with or without the @samp{SIG} at the +beginning). The @var{keywords} say what change to make. +@end table + +@c @group +The keywords allowed by the @code{handle} command can be abbreviated. +Their full names are: + +@table @code +@item nostop +@value{GDBN} should not stop your program when this signal happens. It may +still print a message telling you that the signal has come in. + +@item stop +@value{GDBN} should stop your program when this signal happens. This implies +the @code{print} keyword as well. + +@item print +@value{GDBN} should print a message when this signal happens. + +@item noprint +@value{GDBN} should not mention the occurrence of the signal at all. This +implies the @code{nostop} keyword as well. + +@item pass +@value{GDBN} should allow your program to see this signal; your program will be +able to handle the signal, or may be terminated if the signal is fatal +and not handled. + +@item nopass +@value{GDBN} should not allow your program to see this signal. +@end table +@c @end group + +When a signal stops your program, the signal is not visible until you +continue. Your program will see the signal then, if @code{pass} is in +effect for the signal in question @emph{at that time}. In other words, +after @value{GDBN} reports a signal, you can use the @code{handle} +command with @code{pass} or @code{nopass} to control whether that +signal will be seen by your program when you later continue it. + +You can also use the @code{signal} command to prevent your program from +seeing a signal, or cause it to see a signal it normally would not see, +or to give it any signal at any time. For example, if your program stopped +due to some sort of memory reference error, you might store correct +values into the erroneous variables and continue, hoping to see more +execution; but your program would probably terminate immediately as +a result of the fatal signal once it saw the signal. To prevent this, +you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your +program a signal}. +@end ifset + +@node Stack +@chapter Examining the Stack + +When your program has stopped, the first thing you need to know is where it +stopped and how it got there. + +@cindex call stack +Each time your program performs a function call, the information about +where in your program the call was made from is saved in a block of data +called a @dfn{stack frame}. The frame also contains the arguments of the +call and the local variables of the function that was called. All the +stack frames are allocated in a region of memory called the @dfn{call +stack}. + +When your program stops, the @value{GDBN} commands for examining the +stack allow you to see all of this information. + +@cindex selected frame +One of the stack frames is @dfn{selected} by @value{GDBN} and many +@value{GDBN} commands refer implicitly to the selected frame. In +particular, whenever you ask @value{GDBN} for the value of a variable in +your program, the value is found in the selected frame. There are +special @value{GDBN} commands to select whichever frame you are +interested in. + +When your program stops, @value{GDBN} automatically selects the +currently executing frame and describes it briefly as the @code{frame} +command does (@pxref{Frame Info, ,Information about a frame}). + +@menu +* Frames:: Stack frames +* Backtrace:: Backtraces +* Selection:: Selecting a frame +* Frame Info:: Information on a frame +@ifset MIPS +* MIPS Stack:: MIPS machines and the function stack +@end ifset +@end menu + +@node Frames +@section Stack frames + +@cindex frame +@cindex stack frame +The call stack is divided up into contiguous pieces called @dfn{stack +frames}, or @dfn{frames} for short; each frame is the data associated +with one call to one function. The frame contains the arguments given +to the function, the function's local variables, and the address at +which the function is executing. + +@cindex initial frame +@cindex outermost frame +@cindex innermost frame +When your program is started, the stack has only one frame, that of the +function @code{main}. This is called the @dfn{initial} frame or the +@dfn{outermost} frame. Each time a function is called, a new frame is +made. Each time a function returns, the frame for that function invocation +is eliminated. If a function is recursive, there can be many frames for +the same function. The frame for the function in which execution is +actually occurring is called the @dfn{innermost} frame. This is the most +recently created of all the stack frames that still exist. + +@cindex frame pointer +Inside your program, stack frames are identified by their addresses. A +stack frame consists of many bytes, each of which has its own address; each +kind of computer has a convention for choosing one of those bytes whose +address serves as the address of the frame. Usually this address is kept +in a register called the @dfn{frame pointer register} while execution is +going on in that frame. + +@cindex frame number +@value{GDBN} assigns numbers to all existing stack frames, starting with +zero for the innermost frame, one for the frame that called it, +and so on upward. These numbers do not really exist in your program; +they are assigned by @value{GDBN} to give you a way of designating stack +frames in @value{GDBN} commands. + +@c below produces an acceptable overful hbox. --mew 13aug1993 +@cindex frameless execution +Some compilers provide a way to compile functions so that they operate +without stack frames. (For example, the @code{@value{GCC}} option +@samp{-fomit-frame-pointer} will generate functions without a frame.) +This is occasionally done with heavily used library functions to save +the frame setup time. @value{GDBN} has limited facilities for dealing +with these function invocations. If the innermost function invocation +has no stack frame, @value{GDBN} will nevertheless regard it as though +it had a separate frame, which is numbered zero as usual, allowing +correct tracing of the function call chain. However, @value{GDBN} has +no provision for frameless functions elsewhere in the stack. + +@node Backtrace +@section Backtraces + +A backtrace is a summary of how your program got where it is. It shows one +line per frame, for many frames, starting with the currently executing +frame (frame zero), followed by its caller (frame one), and on up the +stack. + +@table @code +@item backtrace +@itemx bt +@kindex backtrace +@kindex bt +Print a backtrace of the entire stack: one line per frame for all +frames in the stack. + +You can stop the backtrace at any time by typing the system interrupt +character, normally @kbd{C-c}. + +@item backtrace @var{n} +@itemx bt @var{n} +Similar, but print only the innermost @var{n} frames. + +@item backtrace -@var{n} +@itemx bt -@var{n} +Similar, but print only the outermost @var{n} frames. +@end table + +@kindex where +@kindex info stack +@kindex info s +The names @code{where} and @code{info stack} (abbreviated @code{info s}) +are additional aliases for @code{backtrace}. + +Each line in the backtrace shows the frame number and the function name. +The program counter value is also shown---unless you use @code{set +print address off}. The backtrace also shows the source file name and +line number, as well as the arguments to the function. The program +counter value is omitted if it is at the beginning of the code for that +line number. + +Here is an example of a backtrace. It was made with the command +@samp{bt 3}, so it shows the innermost three frames. + +@smallexample +@group +#0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8) + at builtin.c:993 +#1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242 +#2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08) + at macro.c:71 +(More stack frames follow...) +@end group +@end smallexample + +@noindent +The display for frame zero does not begin with a program counter +value, indicating that your program has stopped at the beginning of the +code for line @code{993} of @code{builtin.c}. + +@node Selection +@section Selecting a frame + +Most commands for examining the stack and other data in your program work on +whichever stack frame is selected at the moment. Here are the commands for +selecting a stack frame; all of them finish by printing a brief description +of the stack frame just selected. + +@table @code +@item frame @var{n} +@itemx f @var{n} +@kindex frame +@kindex f +Select frame number @var{n}. Recall that frame zero is the innermost +(currently executing) frame, frame one is the frame that called the +innermost one, and so on. The highest-numbered frame is the one for +@code{main}. + +@item frame @var{addr} +@itemx f @var{addr} +Select the frame at address @var{addr}. This is useful mainly if the +chaining of stack frames has been damaged by a bug, making it +impossible for @value{GDBN} to assign numbers properly to all frames. In +addition, this can be useful when your program has multiple stacks and +switches between them. + +@ifset SPARC +On the SPARC architecture, @code{frame} needs two addresses to +select an arbitrary frame: a frame pointer and a stack pointer. +@c note to future updaters: this is conditioned on a flag +@c FRAME_SPECIFICATION_DYADIC in the tm-*.h files, currently only used +@c by SPARC, hence the specific attribution. Generalize or list all +@c possibilities if more supported machines start doing this. +@end ifset + +@item up @var{n} +@kindex up +Move @var{n} frames up the stack. For positive numbers @var{n}, this +advances toward the outermost frame, to higher frame numbers, to frames +that have existed longer. @var{n} defaults to one. + +@item down @var{n} +@kindex down +@kindex do +Move @var{n} frames down the stack. For positive numbers @var{n}, this +advances toward the innermost frame, to lower frame numbers, to frames +that were created more recently. @var{n} defaults to one. You may +abbreviate @code{down} as @code{do}. +@end table + +All of these commands end by printing two lines of output describing the +frame. The first line shows the frame number, the function name, the +arguments, and the source file and line number of execution in that +frame. The second line shows the text of that source line. + +For example: +@smallexample +@group +(@value{GDBP}) up +#1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc) + at env.c:10 +10 read_input_file (argv[i]); +@end group +@end smallexample + +After such a printout, the @code{list} command with no arguments will +print ten lines centered on the point of execution in the frame. +@xref{List, ,Printing source lines}. + +@table @code +@item up-silently @var{n} +@itemx down-silently @var{n} +@kindex down-silently +@kindex up-silently +These two commands are variants of @code{up} and @code{down}, +respectively; they differ in that they do their work silently, without +causing display of the new frame. They are intended primarily for use +in @value{GDBN} command scripts, where the output might be unnecessary and +distracting. +@end table + +@node Frame Info +@section Information about a frame + +There are several other commands to print information about the selected +stack frame. + +@table @code +@item frame +@itemx f +When used without any argument, this command does not change which +frame is selected, but prints a brief description of the currently +selected stack frame. It can be abbreviated @code{f}. With an +argument, this command is used to select a stack frame. +@xref{Selection, ,Selecting a frame}. + +@item info frame +@itemx info f +@kindex info frame +@kindex info f +This command prints a verbose description of the selected stack frame, +including the address of the frame, the addresses of the next frame down +(called by this frame) and the next frame up (caller of this frame), the +language that the source code corresponding to this frame was written in, +the address of the frame's arguments, the program counter saved in it +(the address of execution in the caller frame), and which registers +were saved in the frame. The verbose description is useful when +something has gone wrong that has made the stack format fail to fit +the usual conventions. + +@item info frame @var{addr} +@itemx info f @var{addr} +Print a verbose description of the frame at address @var{addr}, +without selecting that frame. The selected frame remains unchanged by +this command. + +@item info args +@kindex info args +Print the arguments of the selected frame, each on a separate line. + +@item info locals +@kindex info locals +Print the local variables of the selected frame, each on a separate +line. These are all variables (declared either static or automatic) +accessible at the point of execution of the selected frame. + +@ifclear CONLY +@item info catch +@kindex info catch +@cindex catch exceptions +@cindex exception handlers +Print a list of all the exception handlers that are active in the +current stack frame at the current point of execution. To see other +exception handlers, visit the associated frame (using the @code{up}, +@code{down}, or @code{frame} commands); then type @code{info catch}. +@xref{Exception Handling, ,Breakpoints and exceptions}. +@end ifclear +@end table + +@ifset MIPS +@node MIPS Stack +@section MIPS machines and the function stack + +@cindex stack on MIPS +@cindex MIPS stack +MIPS based computers use an unusual stack frame, which sometimes +requires @value{GDBN} to search backward in the object code to find the +beginning of a function. + +@cindex response time, MIPS debugging +To improve response time (especially for embedded applications, where +@value{GDBN} may be restricted to a slow serial line for this search) +you may want to limit the size of this search, using one of these +commands: +@c FIXME! So what happens when GDB does *not* find the beginning of a +@c function? + +@cindex @code{heuristic-fence-post} (MIPS) +@table @code +@item set heuristic-fence-post @var{limit} +Restrict @var{GDBN} to examining at most @var{limit} bytes in its search +for the beginning of a function. A value of @code{0} (the default) +means there is no limit. + +@item show heuristic-fence-post +Display the current limit. +@end table + +@noindent +These commands are available @emph{only} when @value{GDBN} is configured +for debugging programs on MIPS processors. +@end ifset + +@node Source +@chapter Examining Source Files + +@value{GDBN} can print parts of your program's source, since the debugging +information recorded in the program tells @value{GDBN} what source files were +used to build it. When your program stops, @value{GDBN} spontaneously prints +the line where it stopped. Likewise, when you select a stack frame +(@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where +execution in that frame has stopped. You can print other portions of +source files by explicit command. + +@ifclear DOSHOST +If you use @value{GDBN} through its GNU Emacs interface, you may prefer to use +Emacs facilities to view source; @pxref{Emacs, ,Using @value{GDBN} under GNU +Emacs}. +@end ifclear + +@menu +* List:: Printing source lines +@ifclear DOSHOST +* Search:: Searching source files +@end ifclear + +* Source Path:: Specifying source directories +* Machine Code:: Source and machine code +@end menu + +@node List +@section Printing source lines + +@kindex list +@kindex l +To print lines from a source file, use the @code{list} command +(abbreviated @code{l}). There are several ways to specify what part +of the file you want to print. + +Here are the forms of the @code{list} command most commonly used: + +@table @code +@item list @var{linenum} +Print lines centered around line number @var{linenum} in the +current source file. + +@item list @var{function} +Print lines centered around the beginning of function +@var{function}. + +@item list +Print more lines. If the last lines printed were printed with a +@code{list} command, this prints lines following the last lines +printed; however, if the last line printed was a solitary line printed +as part of displaying a stack frame (@pxref{Stack, ,Examining the +Stack}), this prints lines centered around that line. + +@item list - +Print lines just before the lines last printed. +@end table + +By default, @value{GDBN} prints ten source lines with any of these forms of +the @code{list} command. You can change this using @code{set listsize}: + +@table @code +@item set listsize @var{count} +@kindex set listsize +Make the @code{list} command display @var{count} source lines (unless +the @code{list} argument explicitly specifies some other number). + +@item show listsize +@kindex show listsize +Display the number of lines that @code{list} will currently display by +default. +@end table + +Repeating a @code{list} command with @key{RET} discards the argument, +so it is equivalent to typing just @code{list}. This is more useful +than listing the same lines again. An exception is made for an +argument of @samp{-}; that argument is preserved in repetition so that +each repetition moves up in the source file. + +@cindex linespec +In general, the @code{list} command expects you to supply zero, one or two +@dfn{linespecs}. Linespecs specify source lines; there are several ways +of writing them but the effect is always to specify some source line. +Here is a complete description of the possible arguments for @code{list}: + +@table @code +@item list @var{linespec} +Print lines centered around the line specified by @var{linespec}. + +@item list @var{first},@var{last} +Print lines from @var{first} to @var{last}. Both arguments are +linespecs. + +@item list ,@var{last} +Print lines ending with @var{last}. + +@item list @var{first}, +Print lines starting with @var{first}. + +@item list + +Print lines just after the lines last printed. + +@item list - +Print lines just before the lines last printed. + +@item list +As described in the preceding table. +@end table + +Here are the ways of specifying a single source line---all the +kinds of linespec. + +@table @code +@item @var{number} +Specifies line @var{number} of the current source file. +When a @code{list} command has two linespecs, this refers to +the same source file as the first linespec. + +@item +@var{offset} +Specifies the line @var{offset} lines after the last line printed. +When used as the second linespec in a @code{list} command that has +two, this specifies the line @var{offset} lines down from the +first linespec. + +@item -@var{offset} +Specifies the line @var{offset} lines before the last line printed. + +@item @var{filename}:@var{number} +Specifies line @var{number} in the source file @var{filename}. + +@item @var{function} +@c FIXME: "of the open-brace" is C-centric. When we add other langs... +Specifies the line of the open-brace that begins the body of the +function @var{function}. + +@item @var{filename}:@var{function} +Specifies the line of the open-brace that begins the body of the +function @var{function} in the file @var{filename}. You only need the +file name with a function name to avoid ambiguity when there are +identically named functions in different source files. + +@item *@var{address} +Specifies the line containing the program address @var{address}. +@var{address} may be any expression. +@end table + +@ifclear DOSHOST +@node Search +@section Searching source files +@cindex searching +@kindex reverse-search + +There are two commands for searching through the current source file for a +regular expression. + +@table @code +@item forward-search @var{regexp} +@itemx search @var{regexp} +@kindex search +@kindex forward-search +The command @samp{forward-search @var{regexp}} checks each line, +starting with the one following the last line listed, for a match for +@var{regexp}. It lists the line that is found. You can use +synonym @samp{search @var{regexp}} or abbreviate the command name as +@code{fo}. + +@item reverse-search @var{regexp} +The command @samp{reverse-search @var{regexp}} checks each line, starting +with the one before the last line listed and going backward, for a match +for @var{regexp}. It lists the line that is found. You can abbreviate +this command as @code{rev}. +@end table +@end ifclear + +@node Source Path +@section Specifying source directories + +@cindex source path +@cindex directories for source files +Executable programs sometimes do not record the directories of the source +files from which they were compiled, just the names. Even when they do, +the directories could be moved between the compilation and your debugging +session. @value{GDBN} has a list of directories to search for source files; +this is called the @dfn{source path}. Each time @value{GDBN} wants a source file, +it tries all the directories in the list, in the order they are present +in the list, until it finds a file with the desired name. Note that +the executable search path is @emph{not} used for this purpose. Neither is +the current working directory, unless it happens to be in the source +path. + +If @value{GDBN} cannot find a source file in the source path, and the object +program records a directory, @value{GDBN} tries that directory too. If the +source path is empty, and there is no record of the compilation +directory, @value{GDBN} will, as a last resort, look in the current +directory. + +Whenever you reset or rearrange the source path, @value{GDBN} will clear out +any information it has cached about where source files are found, where +each line is in the file, etc. + +@kindex directory +When you start @value{GDBN}, its source path is empty. +To add other directories, use the @code{directory} command. + +@table @code +@item directory @var{dirname} @dots{} +Add directory @var{dirname} to the front of the source path. Several +directory names may be given to this command, separated by @samp{:} or +whitespace. You may specify a directory that is already in the source +path; this moves it forward, so it will be searched sooner. + +@kindex cdir +@kindex cwd +@kindex $cdir +@kindex $cwd +@cindex compilation directory +@cindex current directory +@cindex working directory +@cindex directory, current +@cindex directory, compilation +You can use the string @samp{$cdir} to refer to the compilation +directory (if one is recorded), and @samp{$cwd} to refer to the current +working directory. @samp{$cwd} is not the same as @samp{.}---the former +tracks the current working directory as it changes during your @value{GDBN} +session, while the latter is immediately expanded to the current +directory at the time you add an entry to the source path. + +@item directory +Reset the source path to empty again. This requires confirmation. + +@c RET-repeat for @code{directory} is explicitly disabled, but since +@c repeating it would be a no-op we do not say that. (thanks to RMS) + +@item show directories +@kindex show directories +Print the source path: show which directories it contains. +@end table + +If your source path is cluttered with directories that are no longer of +interest, @value{GDBN} may sometimes cause confusion by finding the wrong +versions of source. You can correct the situation as follows: + +@enumerate +@item +Use @code{directory} with no argument to reset the source path to empty. + +@item +Use @code{directory} with suitable arguments to reinstall the +directories you want in the source path. You can add all the +directories in one command. +@end enumerate + +@node Machine Code +@section Source and machine code + +You can use the command @code{info line} to map source lines to program +addresses (and vice versa), and the command @code{disassemble} to display +a range of addresses as machine instructions. + +@table @code +@item info line @var{linespec} +@kindex info line +Print the starting and ending addresses of the compiled code for +source line @var{linespec}. You can specify source lines in any of +the ways understood by the @code{list} command (@pxref{List, ,Printing +source lines}). +@end table + +For example, we can use @code{info line} to discover the location of +the object code for the first line of function +@code{m4_changequote}: + +@smallexample +(@value{GDBP}) info line m4_changecom +Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350. +@end smallexample + +@noindent +We can also inquire (using @code{*@var{addr}} as the form for +@var{linespec}) what source line covers a particular address: +@smallexample +(@value{GDBP}) info line *0x63ff +Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404. +@end smallexample + +@cindex @code{$_} and @code{info line} +After @code{info line}, the default address for the @code{x} command +is changed to the starting address of the line, so that @samp{x/i} is +sufficient to begin examining the machine code (@pxref{Memory, +,Examining memory}). Also, this address is saved as the value of the +convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience +variables}). + +@table @code +@kindex disassemble +@item disassemble +@cindex assembly instructions +@cindex instructions, assembly +@cindex machine instructions +@cindex listing machine instructions +This specialized command dumps a range of memory as machine +instructions. The default memory range is the function surrounding the +program counter of the selected frame. A single argument to this +command is a program counter value; the function surrounding this value +will be dumped. Two arguments specify a range of addresses (first +inclusive, second exclusive) to dump. +@end table + +@ifclear H8EXCLUSIVE +We can use @code{disassemble} to inspect the object code +range shown in the last @code{info line} example (the example +shows SPARC machine instructions): + + +@smallexample +(@value{GDBP}) disas 0x63e4 0x6404 +Dump of assembler code from 0x63e4 to 0x6404: +0x63e4 <builtin_init+5340>: ble 0x63f8 <builtin_init+5360> +0x63e8 <builtin_init+5344>: sethi %hi(0x4c00), %o0 +0x63ec <builtin_init+5348>: ld [%i1+4], %o0 +0x63f0 <builtin_init+5352>: b 0x63fc <builtin_init+5364> +0x63f4 <builtin_init+5356>: ld [%o0+4], %o0 +0x63f8 <builtin_init+5360>: or %o0, 0x1a4, %o0 +0x63fc <builtin_init+5364>: call 0x9288 <path_search> +0x6400 <builtin_init+5368>: nop +End of assembler dump. +@end smallexample +@end ifclear + +@ifset H8EXCLUSIVE +For example, here is the beginning of the output for the +disassembly of a function @code{fact}: + + +@smallexample +(@value{GDBP}) disas fact +Dump of assembler code for function fact: +to 0x808c: +0x802c <fact>: 6d f2 mov.w r2,@@-r7 +0x802e <fact+2>: 6d f3 mov.w r3,@@-r7 +0x8030 <fact+4>: 6d f6 mov.w r6,@@-r7 +0x8032 <fact+6>: 0d 76 mov.w r7,r6 +0x8034 <fact+8>: 6f 70 00 08 mov.w @@(0x8,r7),r0 +0x8038 <fact+12> 19 11 sub.w r1,r1 + . + . + . +@end smallexample +@end ifset + +@node Data +@chapter Examining Data + +@cindex printing data +@cindex examining data +@kindex print +@kindex inspect +@c "inspect" is not quite a synonym if you are using Epoch, which we do not +@c document because it is nonstandard... Under Epoch it displays in a +@c different window or something like that. +The usual way to examine data in your program is with the @code{print} +command (abbreviated @code{p}), or its synonym @code{inspect}. +@ifclear CONLY +It evaluates and prints the value of an expression of the language your +program is written in (@pxref{Languages, ,Using @value{GDBN} with Different +Languages}). +@end ifclear + +@table @code +@item print @var{exp} +@itemx print /@var{f} @var{exp} +@var{exp} is an expression (in the source language). By default the +value of @var{exp} is printed in a format appropriate to its data type; +you can choose a different format by specifying @samp{/@var{f}}, where +@var{f} is a letter specifying the format; @pxref{Output Formats,,Output +formats}. + +@item print +@itemx print /@var{f} +If you omit @var{exp}, @value{GDBN} displays the last value again (from the +@dfn{value history}; @pxref{Value History, ,Value history}). This allows you to +conveniently inspect the same value in an alternative format. +@end table + +A more low-level way of examining data is with the @code{x} command. +It examines data in memory at a specified address and prints it in a +specified format. @xref{Memory, ,Examining memory}. + +If you are interested in information about types, or about how the fields +of a struct +@ifclear CONLY +or class +@end ifclear +are declared, use the @code{ptype @var{exp}} +command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}. + +@menu +* Expressions:: Expressions +* Variables:: Program variables +* Arrays:: Artificial arrays +* Output Formats:: Output formats +* Memory:: Examining memory +* Auto Display:: Automatic display +* Print Settings:: Print settings +* Value History:: Value history +* Convenience Vars:: Convenience variables +* Registers:: Registers +@ifclear HAVE-FLOAT +* Floating Point Hardware:: Floating point hardware +@end ifclear +@end menu + +@node Expressions +@section Expressions + +@cindex expressions +@code{print} and many other @value{GDBN} commands accept an expression and +compute its value. Any kind of constant, variable or operator defined +by the programming language you are using is valid in an expression in +@value{GDBN}. This includes conditional expressions, function calls, casts +and string constants. It unfortunately does not include symbols defined +by preprocessor @code{#define} commands. + +@ifclear CONLY +Because C is so widespread, most of the expressions shown in examples in +this manual are in C. @xref{Languages, , Using @value{GDBN} with Different +Languages}, for information on how to use expressions in other +languages. + +In this section, we discuss operators that you can use in @value{GDBN} +expressions regardless of your programming language. + +Casts are supported in all languages, not just in C, because it is so +useful to cast a number into a pointer so as to examine a structure +at that address in memory. +@c FIXME: casts supported---Mod2 true? +@end ifclear + +@value{GDBN} supports these operators in addition to those of programming +languages: + +@table @code +@item @@ +@samp{@@} is a binary operator for treating parts of memory as arrays. +@xref{Arrays, ,Artificial arrays}, for more information. + +@item :: +@samp{::} allows you to specify a variable in terms of the file or +function where it is defined. @xref{Variables, ,Program variables}. + +@item @{@var{type}@} @var{addr} +@cindex @{@var{type}@} +@cindex type casting memory +@cindex memory, viewing as typed object +@cindex casts, to view memory +Refers to an object of type @var{type} stored at address @var{addr} in +memory. @var{addr} may be any expression whose value is an integer or +pointer (but parentheses are required around binary operators, just as in +a cast). This construct is allowed regardless of what kind of data is +normally supposed to reside at @var{addr}. +@end table + +@node Variables +@section Program variables + +The most common kind of expression to use is the name of a variable +in your program. + +Variables in expressions are understood in the selected stack frame +(@pxref{Selection, ,Selecting a frame}); they must either be global +(or static) or be visible according to the scope rules of the +programming language from the point of execution in that frame. This +means that in the function + +@example +foo (a) + int a; +@{ + bar (a); + @{ + int b = test (); + bar (b); + @} +@} +@end example + +@noindent +you can examine and use the variable @code{a} whenever your program is +executing within the function @code{foo}, but you can only use or +examine the variable @code{b} while your program is executing inside +the block where @code{b} is declared. + +@cindex variable name conflict +There is an exception: you can refer to a variable or function whose +scope is a single source file even if the current execution point is not +in this file. But it is possible to have more than one such variable or +function with the same name (in different source files). If that +happens, referring to that name has unpredictable effects. If you wish, +you can specify a static variable in a particular function or file, +using the colon-colon notation: + +@cindex colon-colon +@iftex +@c info cannot cope with a :: index entry, but why deprive hard copy readers? +@kindex :: +@end iftex +@example +@var{file}::@var{variable} +@var{function}::@var{variable} +@end example + +@noindent +Here @var{file} or @var{function} is the name of the context for the +static @var{variable}. In the case of file names, you can use quotes to +make sure @value{GDBN} parses the file name as a single word---for example, +to print a global value of @code{x} defined in @file{f2.c}: + +@example +(@value{GDBP}) p 'f2.c'::x +@end example + +@ifclear CONLY +@cindex C++ scope resolution +This use of @samp{::} is very rarely in conflict with the very similar +use of the same notation in C++. @value{GDBN} also supports use of the C++ +scope resolution operator in @value{GDBN} expressions. +@c FIXME: Um, so what happens in one of those rare cases where it's in +@c conflict?? --mew +@end ifclear + +@cindex wrong values +@cindex variable values, wrong +@quotation +@emph{Warning:} Occasionally, a local variable may appear to have the +wrong value at certain points in a function---just after entry to a new +scope, and just before exit. +@end quotation +You may see this problem when you are stepping by machine instructions. +This is because on most machines, it takes more than one instruction to +set up a stack frame (including local variable definitions); if you are +stepping by machine instructions, variables may appear to have the wrong +values until the stack frame is completely built. On exit, it usually +also takes more than one machine instruction to destroy a stack frame; +after you begin stepping through that group of instructions, local +variable definitions may be gone. + +@node Arrays +@section Artificial arrays + +@cindex artificial array +@kindex @@ +It is often useful to print out several successive objects of the +same type in memory; a section of an array, or an array of +dynamically determined size for which only a pointer exists in the +program. + +You can do this by referring to a contiguous span of memory as an +@dfn{artificial array}, using the binary operator @samp{@@}. The left +operand of @samp{@@} should be the first element of the desired array, +as an individual object. The right operand should be the desired length +of the array. The result is an array value whose elements are all of +the type of the left argument. The first element is actually the left +argument; the second element comes from bytes of memory immediately +following those that hold the first element, and so on. Here is an +example. If a program says + +@example +int *array = (int *) malloc (len * sizeof (int)); +@end example + +@noindent +you can print the contents of @code{array} with + +@example +p *array@@len +@end example + +The left operand of @samp{@@} must reside in memory. Array values made +with @samp{@@} in this way behave just like other arrays in terms of +subscripting, and are coerced to pointers when used in expressions. +Artificial arrays most often appear in expressions via the value history +(@pxref{Value History, ,Value history}), after printing one out. + +Sometimes the artificial array mechanism is not quite enough; in +moderately complex data structures, the elements of interest may not +actually be adjacent---for example, if you are interested in the values +of pointers in an array. One useful work-around in this situation is +to use a convenience variable (@pxref{Convenience Vars, ,Convenience +variables}) as a counter in an expression that prints the first +interesting value, and then repeat that expression via @key{RET}. For +instance, suppose you have an array @code{dtab} of pointers to +structures, and you are interested in the values of a field @code{fv} +in each structure. Here is an example of what you might type: + +@example +set $i = 0 +p dtab[$i++]->fv +@key{RET} +@key{RET} +@dots{} +@end example + +@node Output Formats +@section Output formats + +@cindex formatted output +@cindex output formats +By default, @value{GDBN} prints a value according to its data type. Sometimes +this is not what you want. For example, you might want to print a number +in hex, or a pointer in decimal. Or you might want to view data in memory +at a certain address as a character string or as an instruction. To do +these things, specify an @dfn{output format} when you print a value. + +The simplest use of output formats is to say how to print a value +already computed. This is done by starting the arguments of the +@code{print} command with a slash and a format letter. The format +letters supported are: + +@table @code +@item x +Regard the bits of the value as an integer, and print the integer in +hexadecimal. + +@item d +Print as integer in signed decimal. + +@item u +Print as integer in unsigned decimal. + +@item o +Print as integer in octal. + +@item t +Print as integer in binary. The letter @samp{t} stands for ``two''. +@footnote{@samp{b} cannot be used because these format letters are also +used with the @code{x} command, where @samp{b} stands for ``byte''; +@pxref{Memory,,Examining memory}.} + +@item a +Print as an address, both absolute in hex and as an offset from the +nearest preceding symbol. This format can be used to discover where (in +what function) an unknown address is located: + +@example +(@value{GDBP}) p/a 0x54320 +$3 = 0x54320 <_initialize_vx+396> +@end example + +@item c +Regard as an integer and print it as a character constant. + +@item f +Regard the bits of the value as a floating point number and print +using typical floating point syntax. +@end table + +For example, to print the program counter in hex (@pxref{Registers}), type + +@example +p/x $pc +@end example + +@noindent +Note that no space is required before the slash; this is because command +names in @value{GDBN} cannot contain a slash. + +To reprint the last value in the value history with a different format, +you can use the @code{print} command with just a format and no +expression. For example, @samp{p/x} reprints the last value in hex. + +@node Memory +@section Examining memory + +You can use the command @code{x} (for ``examine'') to examine memory in +any of several formats, independently of your program's data types. + +@cindex examining memory +@table @code +@kindex x +@item x/@var{nfu} @var{addr} +@itemx x @var{addr} +@itemx x +Use the @code{x} command to examine memory. +@end table + +@var{n}, @var{f}, and @var{u} are all optional parameters that specify how +much memory to display and how to format it; @var{addr} is an +expression giving the address where you want to start displaying memory. +If you use defaults for @var{nfu}, you need not type the slash @samp{/}. +Several commands set convenient defaults for @var{addr}. + +@table @r +@item @var{n}, the repeat count +The repeat count is a decimal integer; the default is 1. It specifies +how much memory (counting by units @var{u}) to display. +@c This really is **decimal**; unaffected by 'set radix' as of GDB +@c 4.1.2. + +@item @var{f}, the display format +The display format is one of the formats used by @code{print}, +or @samp{s} (null-terminated string) or @samp{i} (machine instruction). +The default is @samp{x} (hexadecimal) initially, or the format from the +last time you used either @code{x} or @code{print}. + +@item @var{u}, the unit size +The unit size is any of + +@table @code +@item b +Bytes. +@item h +Halfwords (two bytes). +@item w +Words (four bytes). This is the initial default. +@item g +Giant words (eight bytes). +@end table + +Each time you specify a unit size with @code{x}, that size becomes the +default unit the next time you use @code{x}. (For the @samp{s} and +@samp{i} formats, the unit size is ignored and is normally not written.) + +@item @var{addr}, starting display address +@var{addr} is the address where you want @value{GDBN} to begin displaying +memory. The expression need not have a pointer value (though it may); +it is always interpreted as an integer address of a byte of memory. +@xref{Expressions, ,Expressions}, for more information on expressions. The default for +@var{addr} is usually just after the last address examined---but several +other commands also set the default address: @code{info breakpoints} (to +the address of the last breakpoint listed), @code{info line} (to the +starting address of a line), and @code{print} (if you use it to display +a value from memory). +@end table + +For example, @samp{x/3uh 0x54320} is a request to display three halfwords +(@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}), +starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four +words (@samp{w}) of memory above the stack pointer (here, @samp{$sp}; +@pxref{Registers}) in hexadecimal (@samp{x}). + +Since the letters indicating unit sizes are all distinct from the +letters specifying output formats, you do not have to remember whether +unit size or format comes first; either order will work. The output +specifications @samp{4xw} and @samp{4wx} mean exactly the same thing. +(However, the count @var{n} must come first; @samp{wx4} will not work.) + +Even though the unit size @var{u} is ignored for the formats @samp{s} +and @samp{i}, you might still want to use a count @var{n}; for example, +@samp{3i} specifies that you want to see three machine instructions, +including any operands. The command @code{disassemble} gives an +alternative way of inspecting machine instructions; @pxref{Machine +Code,,Source and machine code}. + +All the defaults for the arguments to @code{x} are designed to make it +easy to continue scanning memory with minimal specifications each time +you use @code{x}. For example, after you have inspected three machine +instructions with @samp{x/3i @var{addr}}, you can inspect the next seven +with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command, +the repeat count @var{n} is used again; the other arguments default as +for successive uses of @code{x}. + +@cindex @code{$_}, @code{$__}, and value history +The addresses and contents printed by the @code{x} command are not saved +in the value history because there is often too much of them and they +would get in the way. Instead, @value{GDBN} makes these values available for +subsequent use in expressions as values of the convenience variables +@code{$_} and @code{$__}. After an @code{x} command, the last address +examined is available for use in expressions in the convenience variable +@code{$_}. The contents of that address, as examined, are available in +the convenience variable @code{$__}. + +If the @code{x} command has a repeat count, the address and contents saved +are from the last memory unit printed; this is not the same as the last +address printed if several units were printed on the last line of output. + +@node Auto Display +@section Automatic display +@cindex automatic display +@cindex display of expressions + +If you find that you want to print the value of an expression frequently +(to see how it changes), you might want to add it to the @dfn{automatic +display list} so that @value{GDBN} will print its value each time your program stops. +Each expression added to the list is given a number to identify it; +to remove an expression from the list, you specify that number. +The automatic display looks like this: + +@example +2: foo = 38 +3: bar[5] = (struct hack *) 0x3804 +@end example + +@noindent +This display shows item numbers, expressions and their current values. As with +displays you request manually using @code{x} or @code{print}, you can +specify the output format you prefer; in fact, @code{display} decides +whether to use @code{print} or @code{x} depending on how elaborate your +format specification is---it uses @code{x} if you specify a unit size, +or one of the two formats (@samp{i} and @samp{s}) that are only +supported by @code{x}; otherwise it uses @code{print}. + +@table @code +@item display @var{exp} +@kindex display +Add the expression @var{exp} to the list of expressions to display +each time your program stops. @xref{Expressions, ,Expressions}. + +@code{display} will not repeat if you press @key{RET} again after using it. + +@item display/@var{fmt} @var{exp} +For @var{fmt} specifying only a display format and not a size or +count, add the expression @var{exp} to the auto-display list but +arrange to display it each time in the specified format @var{fmt}. +@xref{Output Formats,,Output formats}. + +@item display/@var{fmt} @var{addr} +For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a +number of units, add the expression @var{addr} as a memory address to +be examined each time your program stops. Examining means in effect +doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}. +@end table + +For example, @samp{display/i $pc} can be helpful, to see the machine +instruction about to be executed each time execution stops (@samp{$pc} +is a common name for the program counter; @pxref{Registers}). + +@table @code +@item undisplay @var{dnums}@dots{} +@itemx delete display @var{dnums}@dots{} +@kindex delete display +@kindex undisplay +Remove item numbers @var{dnums} from the list of expressions to display. + +@code{undisplay} will not repeat if you press @key{RET} after using it. +(Otherwise you would just get the error @samp{No display number @dots{}}.) + +@item disable display @var{dnums}@dots{} +@kindex disable display +Disable the display of item numbers @var{dnums}. A disabled display +item is not printed automatically, but is not forgotten. It may be +enabled again later. + +@item enable display @var{dnums}@dots{} +@kindex enable display +Enable display of item numbers @var{dnums}. It becomes effective once +again in auto display of its expression, until you specify otherwise. + +@item display +Display the current values of the expressions on the list, just as is +done when your program stops. + +@item info display +@kindex info display +Print the list of expressions previously set up to display +automatically, each one with its item number, but without showing the +values. This includes disabled expressions, which are marked as such. +It also includes expressions which would not be displayed right now +because they refer to automatic variables not currently available. +@end table + +If a display expression refers to local variables, then it does not make +sense outside the lexical context for which it was set up. Such an +expression is disabled when execution enters a context where one of its +variables is not defined. For example, if you give the command +@code{display last_char} while inside a function with an argument +@code{last_char}, then this argument will be displayed while your program +continues to stop inside that function. When it stops elsewhere---where +there is no variable @code{last_char}---display is disabled. The next time +your program stops where @code{last_char} is meaningful, you can enable the +display expression once again. + +@node Print Settings +@section Print settings + +@cindex format options +@cindex print settings +@value{GDBN} provides the following ways to control how arrays, structures, +and symbols are printed. + +@noindent +These settings are useful for debugging programs in any language: + +@table @code +@item set print address +@itemx set print address on +@kindex set print address +@value{GDBN} will print memory addresses showing the location of stack +traces, structure values, pointer values, breakpoints, and so forth, +even when it also displays the contents of those addresses. The default +is on. For example, this is what a stack frame display looks like, with +@code{set print address on}: + +@smallexample +@group +(@value{GDBP}) f +#0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>") + at input.c:530 +530 if (lquote != def_lquote) +@end group +@end smallexample + +@item set print address off +Do not print addresses when displaying their contents. For example, +this is the same stack frame displayed with @code{set print address off}: + +@smallexample +@group +(@value{GDBP}) set print addr off +(@value{GDBP}) f +#0 set_quotes (lq="<<", rq=">>") at input.c:530 +530 if (lquote != def_lquote) +@end group +@end smallexample + +You can use @samp{set print address off} to eliminate all machine +dependent displays from the @value{GDBN} interface. For example, with +@code{print address off}, you should get the same text for backtraces on +all machines---whether or not they involve pointer arguments. + +@item show print address +@kindex show print address +Show whether or not addresses are to be printed. +@end table + +When @value{GDBN} prints a symbolic address, it normally prints the +closest earlier symbol plus an offset. If that symbol does not uniquely +identify the address (for example, it is a name whose scope is a single +source file), you may need to disambiguate. One way to do this is with +@code{info line}, for example @code{info line *0x4537}. Alternately, +you can set @value{GDBN} to print the source file and line number when +it prints a symbolic address: + +@table @code +@item set print symbol-filename on +@kindex set print symbol-filename +Tell @value{GDBN} to print the source file name and line number of a +symbol in the symbolic form of an address. + +@item set print symbol-filename off +Do not print source file name and line number of a symbol. This is the +default. + +@item show print symbol-filename +@kindex show print symbol-filename +Show whether or not @value{GDBN} will print the source file name and +line number of a symbol in the symbolic form of an address. +@end table + +Also, you may wish to see the symbolic form only if the address being +printed is reasonably close to the closest earlier symbol: + +@table @code +@item set print max-symbolic-offset @var{max-offset} +@kindex set print max-symbolic-offset +Tell @value{GDBN} to only display the symbolic form of an address if the +offset between the closest earlier symbol and the address is less than +@var{max-offset}. The default is 0, which means to always print the +symbolic form of an address, if any symbol precedes it. + +@item show print max-symbolic-offset +@kindex show print max-symbolic-offset +Ask how large the maximum offset is that @value{GDBN} will print in a +symbolic address. +@end table + +@table @code +@item set print array +@itemx set print array on +@kindex set print array +@value{GDBN} will pretty-print arrays. This format is more convenient to read, +but uses more space. The default is off. + +@item set print array off +Return to compressed format for arrays. + +@item show print array +@kindex show print array +Show whether compressed or pretty format is selected for displaying +arrays. + +@item set print elements @var{number-of-elements} +@kindex set print elements +If @value{GDBN} is printing a large array, it will stop printing after it has +printed the number of elements set by the @code{set print elements} command. +This limit also applies to the display of strings. +Setting the number of elements to zero means that the printing is unlimited. + +@item show print elements +@kindex show print elements +Display the number of elements of a large array that @value{GDBN} will print +before losing patience. + +@item set print pretty on +@kindex set print pretty +Cause @value{GDBN} to print structures in an indented format with one member per +line, like this: + +@smallexample +@group +$1 = @{ + next = 0x0, + flags = @{ + sweet = 1, + sour = 1 + @}, + meat = 0x54 "Pork" +@} +@end group +@end smallexample + +@item set print pretty off +Cause @value{GDBN} to print structures in a compact format, like this: + +@smallexample +@group +$1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \ +meat = 0x54 "Pork"@} +@end group +@end smallexample + +@noindent +This is the default format. + +@item show print pretty +@kindex show print pretty +Show which format @value{GDBN} will use to print structures. + +@item set print sevenbit-strings on +@kindex set print sevenbit-strings +Print using only seven-bit characters; if this option is set, +@value{GDBN} will display any eight-bit characters (in strings or character +values) using the notation @code{\}@var{nnn}. For example, @kbd{M-a} is +displayed as @code{\341}. + +@item set print sevenbit-strings off +Print using either seven-bit or eight-bit characters, as required. This +is the default. + +@item show print sevenbit-strings +@kindex show print sevenbit-strings +Show whether or not @value{GDBN} will print only seven-bit characters. + +@item set print union on +@kindex set print union +Tell @value{GDBN} to print unions which are contained in structures. This is the +default setting. + +@item set print union off +Tell @value{GDBN} not to print unions which are contained in structures. + +@item show print union +@kindex show print union +Ask @value{GDBN} whether or not it will print unions which are contained in +structures. + +For example, given the declarations + +@smallexample +typedef enum @{Tree, Bug@} Species; +typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms; +typedef enum @{Caterpillar, Cocoon, Butterfly@} + Bug_forms; + +struct thing @{ + Species it; + union @{ + Tree_forms tree; + Bug_forms bug; + @} form; +@}; + +struct thing foo = @{Tree, @{Acorn@}@}; +@end smallexample + +@noindent +with @code{set print union on} in effect @samp{p foo} would print + +@smallexample +$1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@} +@end smallexample + +@noindent +and with @code{set print union off} in effect it would print + +@smallexample +$1 = @{it = Tree, form = @{...@}@} +@end smallexample +@end table + +@ifclear CONLY +@need 1000 +@noindent +These settings are of interest when debugging C++ programs: + +@table @code +@item set print demangle +@itemx set print demangle on +@kindex set print demangle +Print C++ names in their source form rather than in the encoded +(``mangled'') form passed to the assembler and linker for type-safe +linkage. The default is @samp{on}. + +@item show print demangle +@kindex show print demangle +Show whether C++ names will be printed in mangled or demangled form. + +@item set print asm-demangle +@itemx set print asm-demangle on +@kindex set print asm-demangle +Print C++ names in their source form rather than their mangled form, even +in assembler code printouts such as instruction disassemblies. +The default is off. + +@item show print asm-demangle +@kindex show print asm-demangle +Show whether C++ names in assembly listings will be printed in mangled +or demangled form. + +@item set demangle-style @var{style} +@kindex set demangle-style +@cindex C++ symbol decoding style +@cindex symbol decoding style, C++ +Choose among several encoding schemes used by different compilers to +represent C++ names. The choices for @var{style} are currently: + +@table @code +@item auto +Allow @value{GDBN} to choose a decoding style by inspecting your program. + +@item gnu +Decode based on the GNU C++ compiler (@code{g++}) encoding algorithm. + +@item lucid +Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm. + +@item arm +Decode using the algorithm in the @cite{C++ Annotated Reference Manual}. +@strong{Warning:} this setting alone is not sufficient to allow +debugging @code{cfront}-generated executables. @value{GDBN} would +require further enhancement to permit that. +@end table + +@item show demangle-style +@kindex show demangle-style +Display the encoding style currently in use for decoding C++ symbols. + +@item set print object +@itemx set print object on +@kindex set print object +When displaying a pointer to an object, identify the @emph{actual} +(derived) type of the object rather than the @emph{declared} type, using +the virtual function table. + +@item set print object off +Display only the declared type of objects, without reference to the +virtual function table. This is the default setting. + +@item show print object +@kindex show print object +Show whether actual, or declared, object types will be displayed. + +@item set print vtbl +@itemx set print vtbl on +@kindex set print vtbl +Pretty print C++ virtual function tables. The default is off. + +@item set print vtbl off +Do not pretty print C++ virtual function tables. + +@item show print vtbl +@kindex show print vtbl +Show whether C++ virtual function tables are pretty printed, or not. +@end table +@end ifclear + +@node Value History +@section Value history + +@cindex value history +Values printed by the @code{print} command are saved in the @value{GDBN} @dfn{value +history} so that you can refer to them in other expressions. Values are +kept until the symbol table is re-read or discarded (for example with +the @code{file} or @code{symbol-file} commands). When the symbol table +changes, the value history is discarded, since the values may contain +pointers back to the types defined in the symbol table. + +@cindex @code{$} +@cindex @code{$$} +@cindex history number +The values printed are given @dfn{history numbers} by which you can +refer to them. These are successive integers starting with one. +@code{print} shows you the history number assigned to a value by +printing @samp{$@var{num} = } before the value; here @var{num} is the +history number. + +To refer to any previous value, use @samp{$} followed by the value's +history number. The way @code{print} labels its output is designed to +remind you of this. Just @code{$} refers to the most recent value in +the history, and @code{$$} refers to the value before that. +@code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2} +is the value just prior to @code{$$}, @code{$$1} is equivalent to +@code{$$}, and @code{$$0} is equivalent to @code{$}. + +For example, suppose you have just printed a pointer to a structure and +want to see the contents of the structure. It suffices to type + +@example +p *$ +@end example + +If you have a chain of structures where the component @code{next} points +to the next one, you can print the contents of the next one with this: + +@example +p *$.next +@end example + +@noindent +You can print successive links in the chain by repeating this +command---which you can do by just typing @key{RET}. + +Note that the history records values, not expressions. If the value of +@code{x} is 4 and you type these commands: + +@example +print x +set x=5 +@end example + +@noindent +then the value recorded in the value history by the @code{print} command +remains 4 even though the value of @code{x} has changed. + +@table @code +@kindex show values +@item show values +Print the last ten values in the value history, with their item numbers. +This is like @samp{p@ $$9} repeated ten times, except that @code{show +values} does not change the history. + +@item show values @var{n} +Print ten history values centered on history item number @var{n}. + +@item show values + +Print ten history values just after the values last printed. If no more +values are available, produces no display. +@end table + +Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the +same effect as @samp{show values +}. + +@node Convenience Vars +@section Convenience variables + +@cindex convenience variables +@value{GDBN} provides @dfn{convenience variables} that you can use within +@value{GDBN} to hold on to a value and refer to it later. These variables +exist entirely within @value{GDBN}; they are not part of your program, and +setting a convenience variable has no direct effect on further execution +of your program. That is why you can use them freely. + +Convenience variables are prefixed with @samp{$}. Any name preceded by +@samp{$} can be used for a convenience variable, unless it is one of +the predefined machine-specific register names (@pxref{Registers}). +(Value history references, in contrast, are @emph{numbers} preceded +by @samp{$}. @xref{Value History, ,Value history}.) + +You can save a value in a convenience variable with an assignment +expression, just as you would set a variable in your program. +For example: + +@example +set $foo = *object_ptr +@end example + +@noindent +would save in @code{$foo} the value contained in the object pointed to by +@code{object_ptr}. + +Using a convenience variable for the first time creates it, but its +value is @code{void} until you assign a new value. You can alter the +value with another assignment at any time. + +Convenience variables have no fixed types. You can assign a convenience +variable any type of value, including structures and arrays, even if +that variable already has a value of a different type. The convenience +variable, when used as an expression, has the type of its current value. + +@table @code +@item show convenience +@kindex show convenience +Print a list of convenience variables used so far, and their values. +Abbreviated @code{show con}. +@end table + +One of the ways to use a convenience variable is as a counter to be +incremented or a pointer to be advanced. For example, to print +a field from successive elements of an array of structures: + +@example +set $i = 0 +print bar[$i++]->contents +@i{@dots{} repeat that command by typing @key{RET}.} +@end example + +Some convenience variables are created automatically by @value{GDBN} and given +values likely to be useful. + +@table @code +@item $_ +@kindex $_ +The variable @code{$_} is automatically set by the @code{x} command to +the last address examined (@pxref{Memory, ,Examining memory}). Other +commands which provide a default address for @code{x} to examine also +set @code{$_} to that address; these commands include @code{info line} +and @code{info breakpoint}. The type of @code{$_} is @code{void *} +except when set by the @code{x} command, in which case it is a pointer +to the type of @code{$__}. + +@item $__ +@kindex $__ +The variable @code{$__} is automatically set by the @code{x} command +to the value found in the last address examined. Its type is chosen +to match the format in which the data was printed. +@end table + +@node Registers +@section Registers + +@cindex registers +You can refer to machine register contents, in expressions, as variables +with names starting with @samp{$}. The names of registers are different +for each machine; use @code{info registers} to see the names used on +your machine. + +@table @code +@item info registers +@kindex info registers +Print the names and values of all registers except floating-point +registers (in the selected stack frame). + +@item info all-registers +@kindex info all-registers +@cindex floating point registers +Print the names and values of all registers, including floating-point +registers. + +@item info registers @var{regname} @dots{} +Print the relativized value of each specified register @var{regname}. +@var{regname} may be any register name valid on the machine you are using, with +or without the initial @samp{$}. +@end table + +@value{GDBN} has four ``standard'' register names that are available (in +expressions) on most machines---whenever they do not conflict with an +architecture's canonical mnemonics for registers. The register names +@code{$pc} and @code{$sp} are used for the program counter register and +the stack pointer. @code{$fp} is used for a register that contains a +pointer to the current stack frame, and @code{$ps} is used for a +register that contains the processor status. For example, +you could print the program counter in hex with + +@example +p/x $pc +@end example + +@noindent +or print the instruction to be executed next with + +@example +x/i $pc +@end example + +@noindent +or add four to the stack pointer@footnote{This is a way of removing +one word from the stack, on machines where stacks grow downward in +memory (most machines, nowadays). This assumes that the innermost +stack frame is selected; setting @code{$sp} is not allowed when other +stack frames are selected. To pop entire frames off the stack, +regardless of machine architecture, use @code{return}; +@pxref{Returning, ,Returning from a function}.} with + +@example +set $sp += 4 +@end example + +Whenever possible, these four standard register names are available on +your machine even though the machine has different canonical mnemonics, +so long as there is no conflict. The @code{info registers} command +shows the canonical names. For example, on the SPARC, @code{info +registers} displays the processor status register as @code{$psr} but you +can also refer to it as @code{$ps}. + +@value{GDBN} always considers the contents of an ordinary register as an +integer when the register is examined in this way. Some machines have +special registers which can hold nothing but floating point; these +registers are considered to have floating point values. There is no way +to refer to the contents of an ordinary register as floating point value +(although you can @emph{print} it as a floating point value with +@samp{print/f $@var{regname}}). + +Some registers have distinct ``raw'' and ``virtual'' data formats. This +means that the data format in which the register contents are saved by +the operating system is not the same one that your program normally +sees. For example, the registers of the 68881 floating point +coprocessor are always saved in ``extended'' (raw) format, but all C +programs expect to work with ``double'' (virtual) format. In such +cases, @value{GDBN} normally works with the virtual format only (the format that +makes sense for your program), but the @code{info registers} command +prints the data in both formats. + +Normally, register values are relative to the selected stack frame +(@pxref{Selection, ,Selecting a frame}). This means that you get the +value that the register would contain if all stack frames farther in +were exited and their saved registers restored. In order to see the +true contents of hardware registers, you must select the innermost +frame (with @samp{frame 0}). + +However, @value{GDBN} must deduce where registers are saved, from the machine +code generated by your compiler. If some registers are not saved, or if +@value{GDBN} is unable to locate the saved registers, the selected stack +frame will make no difference. + +@ifset AMD29K +@table @code +@item set rstack_high_address @var{address} +@kindex set rstack_high_address +@cindex AMD 29K register stack +@cindex register stack, AMD29K +On AMD 29000 family processors, registers are saved in a separate +``register stack''. There is no way for @value{GDBN} to determine the extent +of this stack. Normally, @value{GDBN} just assumes that the stack is ``large +enough''. This may result in @value{GDBN} referencing memory locations that +do not exist. If necessary, you can get around this problem by +specifying the ending address of the register stack with the @code{set +rstack_high_address} command. The argument should be an address, which +you will probably want to precede with @samp{0x} to specify in +hexadecimal. + +@item show rstack_high_address +@kindex show rstack_high_address +Display the current limit of the register stack, on AMD 29000 family +processors. +@end table +@end ifset + +@ifclear HAVE-FLOAT +@node Floating Point Hardware +@section Floating point hardware +@cindex floating point + +@c FIXME! Really host, not target? +Depending on the host machine architecture, @value{GDBN} may be able to give +you more information about the status of the floating point hardware. + +@table @code +@item info float +@kindex info float +Display hardware-dependent information about the floating +point unit. The exact contents and layout vary depending on the +floating point chip; on some platforms, @samp{info float} is not +available at all. +@end table +@c FIXME: this is a cop-out. Try to get examples, explanations. Only +@c FIXME...supported currently on arm's and 386's. Mark properly with +@c FIXME... m4 macros to isolate general statements from hardware-dep, +@c FIXME... at that point. +@end ifclear + +@ifclear CONLY +@node Languages +@chapter Using @value{GDBN} with Different Languages +@cindex languages + +@ifset MOD2 +Although programming languages generally have common aspects, they are +rarely expressed in the same manner. For instance, in ANSI C, +dereferencing a pointer @code{p} is accomplished by @code{*p}, but in +Modula-2, it is accomplished by @code{p^}. Values can also be +represented (and displayed) differently. Hex numbers in C are written +like @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}. +@end ifset + +@cindex working language +Language-specific information is built into @value{GDBN} for some languages, +allowing you to express operations like the above in your program's +native language, and allowing @value{GDBN} to output values in a manner +consistent with the syntax of your program's native language. The +language you use to build expressions, called the @dfn{working +language}, can be selected manually, or @value{GDBN} can set it +automatically. + +@menu +* Setting:: Switching between source languages +* Show:: Displaying the language +@ifset MOD2 +* Checks:: Type and range checks +@end ifset + +* Support:: Supported languages +@end menu + +@node Setting +@section Switching between source languages + +There are two ways to control the working language---either have @value{GDBN} +set it automatically, or select it manually yourself. You can use the +@code{set language} command for either purpose. On startup, @value{GDBN} +defaults to setting the language automatically. + +@menu +* Manually:: Setting the working language manually +* Automatically:: Having @value{GDBN} infer the source language +@end menu + +@node Manually +@subsection Setting the working language + +If you allow @value{GDBN} to set the language automatically, +expressions are interpreted the same way in your debugging session and +your program. + +@kindex set language +If you wish, you may set the language manually. To do this, issue the +command @samp{set language @var{lang}}, where @var{lang} is the name of +a language, such as +@ifclear MOD2 +@code{c}. +@end ifclear +@ifset MOD2 +@code{c} or @code{modula-2}. +@end ifset +For a list of the supported languages, type @samp{set language}. +@c FIXME: rms: eventually this command should be "help set language". + +@ifset MOD2 +Setting the language manually prevents @value{GDBN} from updating the working +language automatically. This can lead to confusion if you try +to debug a program when the working language is not the same as the +source language, when an expression is acceptable to both +languages---but means different things. For instance, if the current +source file were written in C, and @value{GDBN} was parsing Modula-2, a +command such as: + +@example +print a = b + c +@end example + +@noindent +might not have the effect you intended. In C, this means to add +@code{b} and @code{c} and place the result in @code{a}. The result +printed would be the value of @code{a}. In Modula-2, this means to compare +@code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value. +@end ifset + +@node Automatically +@subsection Having @value{GDBN} infer the source language + +To have @value{GDBN} set the working language automatically, use @samp{set +language local} or @samp{set language auto}. @value{GDBN} then infers the +language that a program was written in by looking at the name of its +source files, and examining their extensions: + +@table @file +@ifset MOD2 +@item *.mod +Modula-2 source file +@end ifset + +@item *.c +C source file + +@item *.C +@itemx *.cc +C++ source file +@end table + +This information is recorded for each function or procedure in a source +file. When your program stops in a frame (usually by encountering a +breakpoint), @value{GDBN} sets the working language to the language recorded +for the function in that frame. If the language for a frame is unknown +(that is, if the function or block corresponding to the frame was +defined in a source file that does not have a recognized extension), the +current working language is not changed, and @value{GDBN} issues a warning. + +This may not seem necessary for most programs, which are written +entirely in one source language. However, program modules and libraries +written in one source language can be used by a main program written in +a different source language. Using @samp{set language auto} in this +case frees you from having to set the working language manually. + +@node Show +@section Displaying the language + +The following commands will help you find out which language is the +working language, and also what language source files were written in. + +@kindex show language +@kindex info frame +@kindex info source +@table @code +@item show language +Display the current working language. This is the +language you can use with commands such as @code{print} to +build and compute expressions that may involve variables in your program. + +@item info frame +Among the other information listed here (@pxref{Frame Info, ,Information +about a frame}) is the source language for this frame. This is the +language that will become the working language if you ever use an +identifier that is in this frame. + +@item info source +Among the other information listed here (@pxref{Symbols, ,Examining the +Symbol Table}) is the source language of this source file. +@end table + +@ifset MOD2 +@node Checks +@section Type and range checking + +@quotation +@emph{Warning:} In this release, the @value{GDBN} commands for type and range +checking are included, but they do not yet have any effect. This +section documents the intended facilities. +@end quotation +@c FIXME remove warning when type/range code added + +Some languages are designed to guard you against making seemingly common +errors through a series of compile- and run-time checks. These include +checking the type of arguments to functions and operators, and making +sure mathematical overflows are caught at run time. Checks such as +these help to ensure a program's correctness once it has been compiled +by eliminating type mismatches, and providing active checks for range +errors when your program is running. + +@value{GDBN} can check for conditions like the above if you wish. +Although @value{GDBN} will not check the statements in your program, it +can check expressions entered directly into @value{GDBN} for evaluation via +the @code{print} command, for example. As with the working language, +@value{GDBN} can also decide whether or not to check automatically based on +your program's source language. @xref{Support, ,Supported languages}, +for the default settings of supported languages. + +@menu +* Type Checking:: An overview of type checking +* Range Checking:: An overview of range checking +@end menu + +@cindex type checking +@cindex checks, type +@node Type Checking +@subsection An overview of type checking + +Some languages, such as Modula-2, are strongly typed, meaning that the +arguments to operators and functions have to be of the correct type, +otherwise an error occurs. These checks prevent type mismatch +errors from ever causing any run-time problems. For example, + +@example +1 + 2 @result{} 3 +@exdent but +@error{} 1 + 2.3 +@end example + +The second example fails because the @code{CARDINAL} 1 is not +type-compatible with the @code{REAL} 2.3. + +For expressions you use in @value{GDBN} commands, you can tell the @value{GDBN} +type checker to skip checking; to treat any mismatches as errors and +abandon the expression; or only issue warnings when type mismatches +occur, but evaluate the expression anyway. When you choose the last of +these, @value{GDBN} evaluates expressions like the second example above, but +also issues a warning. + +Even though you may turn type checking off, other type-based reasons may +prevent @value{GDBN} from evaluating an expression. For instance, @value{GDBN} does not +know how to add an @code{int} and a @code{struct foo}. These particular +type errors have nothing to do with the language in use, and usually +arise from expressions, such as the one described above, which make +little sense to evaluate anyway. + +Each language defines to what degree it is strict about type. For +instance, both Modula-2 and C require the arguments to arithmetical +operators to be numbers. In C, enumerated types and pointers can be +represented as numbers, so that they are valid arguments to mathematical +operators. @xref{Support, ,Supported languages}, for further +details on specific languages. + +@value{GDBN} provides some additional commands for controlling the type checker: + +@kindex set check +@kindex set check type +@kindex show check type +@table @code +@item set check type auto +Set type checking on or off based on the current working language. +@xref{Support, ,Supported languages}, for the default settings for +each language. + +@item set check type on +@itemx set check type off +Set type checking on or off, overriding the default setting for the +current working language. Issue a warning if the setting does not +match the language default. If any type mismatches occur in +evaluating an expression while typechecking is on, @value{GDBN} prints a +message and aborts evaluation of the expression. + +@item set check type warn +Cause the type checker to issue warnings, but to always attempt to +evaluate the expression. Evaluating the expression may still +be impossible for other reasons. For example, @value{GDBN} cannot add +numbers and structures. + +@item show type +Show the current setting of the type checker, and whether or not @value{GDBN} is +setting it automatically. +@end table + +@cindex range checking +@cindex checks, range +@node Range Checking +@subsection An overview of range checking + +In some languages (such as Modula-2), it is an error to exceed the +bounds of a type; this is enforced with run-time checks. Such range +checking is meant to ensure program correctness by making sure +computations do not overflow, or indices on an array element access do +not exceed the bounds of the array. + +For expressions you use in @value{GDBN} commands, you can tell +@value{GDBN} to treat range errors in one of three ways: ignore them, +always treat them as errors and abandon the expression, or issue +warnings but evaluate the expression anyway. + +A range error can result from numerical overflow, from exceeding an +array index bound, or when you type a constant that is not a member +of any type. Some languages, however, do not treat overflows as an +error. In many implementations of C, mathematical overflow causes the +result to ``wrap around'' to lower values---for example, if @var{m} is +the largest integer value, and @var{s} is the smallest, then + +@example +@var{m} + 1 @result{} @var{s} +@end example + +This, too, is specific to individual languages, and in some cases +specific to individual compilers or machines. @xref{Support, , +Supported languages}, for further details on specific languages. + +@value{GDBN} provides some additional commands for controlling the range checker: + +@kindex set check +@kindex set check range +@kindex show check range +@table @code +@item set check range auto +Set range checking on or off based on the current working language. +@xref{Support, ,Supported languages}, for the default settings for +each language. + +@item set check range on +@itemx set check range off +Set range checking on or off, overriding the default setting for the +current working language. A warning is issued if the setting does not +match the language default. If a range error occurs, then a message +is printed and evaluation of the expression is aborted. + +@item set check range warn +Output messages when the @value{GDBN} range checker detects a range error, +but attempt to evaluate the expression anyway. Evaluating the +expression may still be impossible for other reasons, such as accessing +memory that the process does not own (a typical example from many Unix +systems). + +@item show range +Show the current setting of the range checker, and whether or not it is +being set automatically by @value{GDBN}. +@end table +@end ifset + +@node Support +@section Supported languages + +@ifset MOD2 +@value{GDBN} 4 supports C, C++, and Modula-2. +@end ifset +@ifclear MOD2 +@value{GDBN} 4 supports C, and C++. +@end ifclear +Some @value{GDBN} features may be used in expressions regardless of the +language you use: the @value{GDBN} @code{@@} and @code{::} operators, +and the @samp{@{type@}addr} construct (@pxref{Expressions, +,Expressions}) can be used with the constructs of any supported +language. + +The following sections detail to what degree each source language is +supported by @value{GDBN}. These sections are not meant to be language +tutorials or references, but serve only as a reference guide to what the +@value{GDBN} expression parser will accept, and what input and output +formats should look like for different languages. There are many good +books written on each of these languages; please look to these for a +language reference or tutorial. + +@ifset MOD2 +@menu +* C:: C and C++ +* Modula-2:: Modula-2 +@end menu + +@node C +@subsection C and C++ +@cindex C and C++ +@cindex expressions in C or C++ + +Since C and C++ are so closely related, many features of @value{GDBN} apply +to both languages. Whenever this is the case, we discuss both languages +together. +@end ifset +@ifclear MOD2 +@c Cancel this below, under same condition, at end of this chapter! +@raisesections +@end ifclear + +@cindex C++ +@kindex g++ +@cindex GNU C++ +The C++ debugging facilities are jointly implemented by the GNU C++ +compiler and @value{GDBN}. Therefore, to debug your C++ code effectively, +you must compile your C++ programs with the GNU C++ compiler, +@code{g++}. +@end ifclear +@ifset CONLY +@node C +@chapter C Language Support +@cindex C language +@cindex expressions in C + +Information specific to the C language is built into @value{GDBN} so that you +can use C expressions while degugging. This also permits @value{GDBN} to +output values in a manner consistent with C conventions. + +@menu +* C Operators:: C operators +* C Constants:: C constants +* Debugging C:: @value{GDBN} and C +@end menu +@end ifset +@ifclear CONLY +@menu +* C Operators:: C and C++ operators +* C Constants:: C and C++ constants +* Cplus expressions:: C++ expressions +* C Defaults:: Default settings for C and C++ +@ifset MOD2 +* C Checks:: C and C++ type and range checks +@end ifset + +* Debugging C:: @value{GDBN} and C +* Debugging C plus plus:: Special features for C++ +@end menu +@end ifclear + +@ifclear CONLY +@cindex C and C++ operators +@node C Operators +@subsubsection C and C++ operators +@end ifclear +@ifset CONLY +@cindex C operators +@node C Operators +@section C operators +@end ifset + +Operators must be defined on values of specific types. For instance, +@code{+} is defined on numbers, but not on structures. Operators are +often defined on groups of types. + +@ifclear CONLY +For the purposes of C and C++, the following definitions hold: +@end ifclear + +@itemize @bullet +@item +@emph{Integral types} include @code{int} with any of its storage-class +specifiers; @code{char}; and @code{enum}. + +@item +@emph{Floating-point types} include @code{float} and @code{double}. + +@item +@emph{Pointer types} include all types defined as @code{(@var{type} +*)}. + +@item +@emph{Scalar types} include all of the above. +@end itemize + +@noindent +The following operators are supported. They are listed here +in order of increasing precedence: + +@table @code +@item , +The comma or sequencing operator. Expressions in a comma-separated list +are evaluated from left to right, with the result of the entire +expression being the last expression evaluated. + +@item = +Assignment. The value of an assignment expression is the value +assigned. Defined on scalar types. + +@item @var{op}= +Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}}, +and translated to @w{@code{@var{a} = @var{a op b}}}. +@w{@code{@var{op}=}} and @code{=} have the same precendence. +@var{op} is any one of the operators @code{|}, @code{^}, @code{&}, +@code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}. + +@item ?: +The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought +of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an +integral type. + +@item || +Logical @sc{or}. Defined on integral types. + +@item && +Logical @sc{and}. Defined on integral types. + +@item | +Bitwise @sc{or}. Defined on integral types. + +@item ^ +Bitwise exclusive-@sc{or}. Defined on integral types. + +@item & +Bitwise @sc{and}. Defined on integral types. + +@item ==@r{, }!= +Equality and inequality. Defined on scalar types. The value of these +expressions is 0 for false and non-zero for true. + +@item <@r{, }>@r{, }<=@r{, }>= +Less than, greater than, less than or equal, greater than or equal. +Defined on scalar types. The value of these expressions is 0 for false +and non-zero for true. + +@item <<@r{, }>> +left shift, and right shift. Defined on integral types. + +@item @@ +The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}). + +@item +@r{, }- +Addition and subtraction. Defined on integral types, floating-point types and +pointer types. + +@item *@r{, }/@r{, }% +Multiplication, division, and modulus. Multiplication and division are +defined on integral and floating-point types. Modulus is defined on +integral types. + +@item ++@r{, }-- +Increment and decrement. When appearing before a variable, the +operation is performed before the variable is used in an expression; +when appearing after it, the variable's value is used before the +operation takes place. + +@item * +Pointer dereferencing. Defined on pointer types. Same precedence as +@code{++}. + +@item & +Address operator. Defined on variables. Same precedence as @code{++}. + +@ifclear CONLY +For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is +allowed in the C++ language itself: you can use @samp{&(&@var{ref})} +(or, if you prefer, simply @samp{&&@var{ref}}) to examine the address +where a C++ reference variable (declared with @samp{&@var{ref}}) is +stored. +@end ifclear + +@item - +Negative. Defined on integral and floating-point types. Same +precedence as @code{++}. + +@item ! +Logical negation. Defined on integral types. Same precedence as +@code{++}. + +@item ~ +Bitwise complement operator. Defined on integral types. Same precedence as +@code{++}. + + +@item .@r{, }-> +Structure member, and pointer-to-structure member. For convenience, +@value{GDBN} regards the two as equivalent, choosing whether to dereference a +pointer based on the stored type information. +Defined on @code{struct} and @code{union} data. + +@item [] +Array indexing. @code{@var{a}[@var{i}]} is defined as +@code{*(@var{a}+@var{i})}. Same precedence as @code{->}. + +@item () +Function parameter list. Same precedence as @code{->}. + +@ifclear CONLY +@item :: +C++ scope resolution operator. Defined on +@code{struct}, @code{union}, and @code{class} types. +@end ifclear + +@item :: +Doubled colons +@ifclear CONLY +also +@end ifclear +represent the @value{GDBN} scope operator (@pxref{Expressions, +,Expressions}). +@ifclear CONLY +Same precedence as @code{::}, above. +@end ifclear +@end table + +@ifclear CONLY +@cindex C and C++ constants +@node C Constants +@subsubsection C and C++ constants + +@value{GDBN} allows you to express the constants of C and C++ in the +following ways: +@end ifclear +@ifset CONLY +@cindex C constants +@node C Constants +@section C constants + +@value{GDBN} allows you to express the constants of C in the +following ways: +@end ifset + +@itemize @bullet +@item +Integer constants are a sequence of digits. Octal constants are +specified by a leading @samp{0} (ie. zero), and hexadecimal constants by +a leading @samp{0x} or @samp{0X}. Constants may also end with a letter +@samp{l}, specifying that the constant should be treated as a +@code{long} value. + +@item +Floating point constants are a sequence of digits, followed by a decimal +point, followed by a sequence of digits, and optionally followed by an +exponent. An exponent is of the form: +@samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another +sequence of digits. The @samp{+} is optional for positive exponents. + +@item +Enumerated constants consist of enumerated identifiers, or their +integral equivalents. + +@item +Character constants are a single character surrounded by single quotes +(@code{'}), or a number---the ordinal value of the corresponding character +(usually its @sc{ASCII} value). Within quotes, the single character may +be represented by a letter or by @dfn{escape sequences}, which are of +the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation +of the character's ordinal value; or of the form @samp{\@var{x}}, where +@samp{@var{x}} is a predefined special character---for example, +@samp{\n} for newline. + +@item +String constants are a sequence of character constants surrounded +by double quotes (@code{"}). + +@item +Pointer constants are an integral value. You can also write pointers +to constants using the C operator @samp{&}. + +@item +Array constants are comma-separated lists surrounded by braces @samp{@{} +and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of +integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array, +and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers. +@end itemize + +@ifclear CONLY +@node Cplus expressions +@subsubsection C++ expressions + +@cindex expressions in C++ +@value{GDBN} expression handling has a number of extensions to +interpret a significant subset of C++ expressions. + +@cindex C++ support, not in @sc{coff} +@cindex @sc{coff} versus C++ +@cindex C++ and object formats +@cindex object formats and C++ +@cindex a.out and C++ +@cindex @sc{ecoff} and C++ +@cindex @sc{xcoff} and C++ +@cindex @sc{elf}/stabs and C++ +@cindex @sc{elf}/@sc{dwarf} and C++ +@quotation +@emph{Warning:} Most of these extensions depend on the use of additional +debugging information in the symbol table, and thus require a rich, +extendable object code format. In particular, if your system uses +a.out, MIPS @sc{ecoff}, RS/6000 @sc{xcoff}, or Sun @sc{elf} with stabs +extensions to the symbol table, these facilities are all available. +Where the object code format is standard @sc{coff}, on the other hand, +most of the C++ support in @value{GDBN} will @emph{not} work, nor can it. +For the standard SVr4 debugging format, @sc{dwarf} in @sc{elf}, the +standard is still evolving, so the C++ support in @value{GDBN} is still +fragile; when this debugging format stabilizes, however, C++ support +will also be available on systems that use it. +@end quotation + +@enumerate + +@cindex member functions +@item +Member function calls are allowed; you can use expressions like + +@example +count = aml->GetOriginal(x, y) +@end example + +@kindex this +@cindex namespace in C++ +@item +While a member function is active (in the selected stack frame), your +expressions have the same namespace available as the member function; +that is, @value{GDBN} allows implicit references to the class instance +pointer @code{this} following the same rules as C++. + +@cindex call overloaded functions +@cindex type conversions in C++ +@item +You can call overloaded functions; @value{GDBN} will resolve the function +call to the right definition, with one restriction---you must use +arguments of the type required by the function that you want to call. +@value{GDBN} will not perform conversions requiring constructors or +user-defined type operators. + +@cindex reference declarations +@item +@value{GDBN} understands variables declared as C++ references; you can use them in +expressions just as you do in C++ source---they are automatically +dereferenced. + +In the parameter list shown when @value{GDBN} displays a frame, the values of +reference variables are not displayed (unlike other variables); this +avoids clutter, since references are often used for large structures. +The @emph{address} of a reference variable is always shown, unless +you have specified @samp{set print address off}. + +@item +@value{GDBN} supports the C++ name resolution operator @code{::}---your +expressions can use it just as expressions in your program do. Since +one scope may be defined in another, you can use @code{::} repeatedly if +necessary, for example in an expression like +@samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows +resolving name scope by reference to source files, in both C and C++ +debugging (@pxref{Variables, ,Program variables}). +@end enumerate + +@node C Defaults +@subsubsection C and C++ defaults +@cindex C and C++ defaults + +If you allow @value{GDBN} to set type and range checking automatically, they +both default to @code{off} whenever the working language changes to +C or C++. This happens regardless of whether you, or @value{GDBN}, +selected the working language. + +If you allow @value{GDBN} to set the language automatically, it sets the +working language to C or C++ on entering code compiled from a source file +whose name ends with @file{.c}, @file{.C}, or @file{.cc}. +@xref{Automatically, ,Having @value{GDBN} infer the source language}, for +further details. + +@ifset MOD2 +@c Type checking is (a) primarily motivated by Modula-2, and (b) +@c unimplemented. If (b) changes, it might make sense to let this node +@c appear even if Mod-2 does not, but meanwhile ignore it. pesch 16jul93. +@node C Checks +@subsubsection C and C++ type and range checks +@cindex C and C++ checks + +By default, when @value{GDBN} parses C or C++ expressions, type checking +is not used. However, if you turn type checking on, @value{GDBN} will +consider two variables type equivalent if: + +@itemize @bullet +@item +The two variables are structured and have the same structure, union, or +enumerated tag. + +@item +Two two variables have the same type name, or types that have been +declared equivalent through @code{typedef}. + +@ignore +@c leaving this out because neither J Gilmore nor R Pesch understand it. +@c FIXME--beers? +@item +The two @code{struct}, @code{union}, or @code{enum} variables are +declared in the same declaration. (Note: this may not be true for all C +compilers.) +@end ignore +@end itemize + +Range checking, if turned on, is done on mathematical operations. Array +indices are not checked, since they are often used to index a pointer +that is not itself an array. +@end ifset +@end ifclear + +@ifclear CONLY +@node Debugging C +@subsubsection @value{GDBN} and C +@end ifclear +@ifset CONLY +@node Debugging C +@section @value{GDBN} and C +@end ifset + +The @code{set print union} and @code{show print union} commands apply to +the @code{union} type. When set to @samp{on}, any @code{union} that is +inside a @code{struct} +@ifclear CONLY +or @code{class} +@end ifclear +will also be printed. +Otherwise, it will appear as @samp{@{...@}}. + +The @code{@@} operator aids in the debugging of dynamic arrays, formed +with pointers and a memory allocation function. @xref{Expressions, +,Expressions}. + +@ifclear CONLY +@node Debugging C plus plus +@subsubsection @value{GDBN} features for C++ + +@cindex commands for C++ +Some @value{GDBN} commands are particularly useful with C++, and some are +designed specifically for use with C++. Here is a summary: + +@table @code +@cindex break in overloaded functions +@item @r{breakpoint menus} +When you want a breakpoint in a function whose name is overloaded, +@value{GDBN} breakpoint menus help you specify which function definition +you want. @xref{Breakpoint Menus,,Breakpoint menus}. + +@cindex overloading in C++ +@item rbreak @var{regex} +Setting breakpoints using regular expressions is helpful for setting +breakpoints on overloaded functions that are not members of any special +classes. +@xref{Set Breaks, ,Setting breakpoints}. + +@cindex C++ exception handling +@item catch @var{exceptions} +@itemx info catch +Debug C++ exception handling using these commands. @xref{Exception +Handling, ,Breakpoints and exceptions}. + +@cindex inheritance +@item ptype @var{typename} +Print inheritance relationships as well as other information for type +@var{typename}. +@xref{Symbols, ,Examining the Symbol Table}. + +@cindex C++ symbol display +@item set print demangle +@itemx show print demangle +@itemx set print asm-demangle +@itemx show print asm-demangle +Control whether C++ symbols display in their source form, both when +displaying code as C++ source and when displaying disassemblies. +@xref{Print Settings, ,Print settings}. + +@item set print object +@itemx show print object +Choose whether to print derived (actual) or declared types of objects. +@xref{Print Settings, ,Print settings}. + +@item set print vtbl +@itemx show print vtbl +Control the format for printing virtual function tables. +@xref{Print Settings, ,Print settings}. + +@item @r{Overloaded symbol names} +You can specify a particular definition of an overloaded symbol, using +the same notation that is used to declare such symbols in C++: type +@code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can +also use the @value{GDBN} command-line word completion facilities to list the +available choices, or to finish the type list for you. +@xref{Completion,, Command completion}, for details on how to do this. +@end table +@ifclear MOD2 +@c cancels "raisesections" under same conditions near bgn of chapter +@lowersections +@end ifclear + +@ifset MOD2 +@node Modula-2 +@subsection Modula-2 +@cindex Modula-2 + +The extensions made to @value{GDBN} to support Modula-2 only support +output from the GNU Modula-2 compiler (which is currently being +developed). Other Modula-2 compilers are not currently supported, and +attempting to debug executables produced by them will most likely +result in an error as @value{GDBN} reads in the executable's symbol +table. + +@cindex expressions in Modula-2 +@menu +* M2 Operators:: Built-in operators +* Built-In Func/Proc:: Built-in functions and procedures +* M2 Constants:: Modula-2 constants +* M2 Defaults:: Default settings for Modula-2 +* Deviations:: Deviations from standard Modula-2 +* M2 Checks:: Modula-2 type and range checks +* M2 Scope:: The scope operators @code{::} and @code{.} +* GDB/M2:: @value{GDBN} and Modula-2 +@end menu + +@node M2 Operators +@subsubsection Operators +@cindex Modula-2 operators + +Operators must be defined on values of specific types. For instance, +@code{+} is defined on numbers, but not on structures. Operators are +often defined on groups of types. For the purposes of Modula-2, the +following definitions hold: + +@itemize @bullet + +@item +@emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and +their subranges. + +@item +@emph{Character types} consist of @code{CHAR} and its subranges. + +@item +@emph{Floating-point types} consist of @code{REAL}. + +@item +@emph{Pointer types} consist of anything declared as @code{POINTER TO +@var{type}}. + +@item +@emph{Scalar types} consist of all of the above. + +@item +@emph{Set types} consist of @code{SET} and @code{BITSET} types. + +@item +@emph{Boolean types} consist of @code{BOOLEAN}. +@end itemize + +@noindent +The following operators are supported, and appear in order of +increasing precedence: + +@table @code +@item , +Function argument or array index separator. + +@item := +Assignment. The value of @var{var} @code{:=} @var{value} is +@var{value}. + +@item <@r{, }> +Less than, greater than on integral, floating-point, or enumerated +types. + +@item <=@r{, }>= +Less than, greater than, less than or equal to, greater than or equal to +on integral, floating-point and enumerated types, or set inclusion on +set types. Same precedence as @code{<}. + +@item =@r{, }<>@r{, }# +Equality and two ways of expressing inequality, valid on scalar types. +Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is +available for inequality, since @code{#} conflicts with the script +comment character. + +@item IN +Set membership. Defined on set types and the types of their members. +Same precedence as @code{<}. + +@item OR +Boolean disjunction. Defined on boolean types. + +@item AND@r{, }& +Boolean conjuction. Defined on boolean types. + +@item @@ +The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}). + +@item +@r{, }- +Addition and subtraction on integral and floating-point types, or union +and difference on set types. + +@item * +Multiplication on integral and floating-point types, or set intersection +on set types. + +@item / +Division on floating-point types, or symmetric set difference on set +types. Same precedence as @code{*}. + +@item DIV@r{, }MOD +Integer division and remainder. Defined on integral types. Same +precedence as @code{*}. + +@item - +Negative. Defined on @code{INTEGER} and @code{REAL} data. + +@item ^ +Pointer dereferencing. Defined on pointer types. + +@item NOT +Boolean negation. Defined on boolean types. Same precedence as +@code{^}. + +@item . +@code{RECORD} field selector. Defined on @code{RECORD} data. Same +precedence as @code{^}. + +@item [] +Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}. + +@item () +Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence +as @code{^}. + +@item ::@r{, }. +@value{GDBN} and Modula-2 scope operators. +@end table + +@quotation +@emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN} +will treat the use of the operator @code{IN}, or the use of operators +@code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#}, +@code{<=}, and @code{>=} on sets as an error. +@end quotation + +@cindex Modula-2 built-ins +@node Built-In Func/Proc +@subsubsection Built-in functions and procedures + +Modula-2 also makes available several built-in procedures and functions. +In describing these, the following metavariables are used: + +@table @var + +@item a +represents an @code{ARRAY} variable. + +@item c +represents a @code{CHAR} constant or variable. + +@item i +represents a variable or constant of integral type. + +@item m +represents an identifier that belongs to a set. Generally used in the +same function with the metavariable @var{s}. The type of @var{s} should +be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}). + +@item n +represents a variable or constant of integral or floating-point type. + +@item r +represents a variable or constant of floating-point type. + +@item t +represents a type. + +@item v +represents a variable. + +@item x +represents a variable or constant of one of many types. See the +explanation of the function for details. +@end table + +All Modula-2 built-in procedures also return a result, described below. + +@table @code +@item ABS(@var{n}) +Returns the absolute value of @var{n}. + +@item CAP(@var{c}) +If @var{c} is a lower case letter, it returns its upper case +equivalent, otherwise it returns its argument + +@item CHR(@var{i}) +Returns the character whose ordinal value is @var{i}. + +@item DEC(@var{v}) +Decrements the value in the variable @var{v}. Returns the new value. + +@item DEC(@var{v},@var{i}) +Decrements the value in the variable @var{v} by @var{i}. Returns the +new value. + +@item EXCL(@var{m},@var{s}) +Removes the element @var{m} from the set @var{s}. Returns the new +set. + +@item FLOAT(@var{i}) +Returns the floating point equivalent of the integer @var{i}. + +@item HIGH(@var{a}) +Returns the index of the last member of @var{a}. + +@item INC(@var{v}) +Increments the value in the variable @var{v}. Returns the new value. + +@item INC(@var{v},@var{i}) +Increments the value in the variable @var{v} by @var{i}. Returns the +new value. + +@item INCL(@var{m},@var{s}) +Adds the element @var{m} to the set @var{s} if it is not already +there. Returns the new set. + +@item MAX(@var{t}) +Returns the maximum value of the type @var{t}. + +@item MIN(@var{t}) +Returns the minimum value of the type @var{t}. + +@item ODD(@var{i}) +Returns boolean TRUE if @var{i} is an odd number. + +@item ORD(@var{x}) +Returns the ordinal value of its argument. For example, the ordinal +value of a character is its ASCII value (on machines supporting the +ASCII character set). @var{x} must be of an ordered type, which include +integral, character and enumerated types. + +@item SIZE(@var{x}) +Returns the size of its argument. @var{x} can be a variable or a type. + +@item TRUNC(@var{r}) +Returns the integral part of @var{r}. + +@item VAL(@var{t},@var{i}) +Returns the member of the type @var{t} whose ordinal value is @var{i}. +@end table + +@quotation +@emph{Warning:} Sets and their operations are not yet supported, so +@value{GDBN} will treat the use of procedures @code{INCL} and @code{EXCL} as +an error. +@end quotation + +@cindex Modula-2 constants +@node M2 Constants +@subsubsection Constants + +@value{GDBN} allows you to express the constants of Modula-2 in the following +ways: + +@itemize @bullet + +@item +Integer constants are simply a sequence of digits. When used in an +expression, a constant is interpreted to be type-compatible with the +rest of the expression. Hexadecimal integers are specified by a +trailing @samp{H}, and octal integers by a trailing @samp{B}. + +@item +Floating point constants appear as a sequence of digits, followed by a +decimal point and another sequence of digits. An optional exponent can +then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where +@samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the +digits of the floating point constant must be valid decimal (base 10) +digits. + +@item +Character constants consist of a single character enclosed by a pair of +like quotes, either single (@code{'}) or double (@code{"}). They may +also be expressed by their ordinal value (their ASCII value, usually) +followed by a @samp{C}. + +@item +String constants consist of a sequence of characters enclosed by a +pair of like quotes, either single (@code{'}) or double (@code{"}). +Escape sequences in the style of C are also allowed. @xref{C +Constants, ,C and C++ constants}, for a brief explanation of escape +sequences. + +@item +Enumerated constants consist of an enumerated identifier. + +@item +Boolean constants consist of the identifiers @code{TRUE} and +@code{FALSE}. + +@item +Pointer constants consist of integral values only. + +@item +Set constants are not yet supported. +@end itemize + +@node M2 Defaults +@subsubsection Modula-2 defaults +@cindex Modula-2 defaults + +If type and range checking are set automatically by @value{GDBN}, they +both default to @code{on} whenever the working language changes to +Modula-2. This happens regardless of whether you, or @value{GDBN}, +selected the working language. + +If you allow @value{GDBN} to set the language automatically, then entering +code compiled from a file whose name ends with @file{.mod} will set the +working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set +the language automatically}, for further details. + +@node Deviations +@subsubsection Deviations from standard Modula-2 +@cindex Modula-2, deviations from + +A few changes have been made to make Modula-2 programs easier to debug. +This is done primarily via loosening its type strictness: + +@itemize @bullet +@item +Unlike in standard Modula-2, pointer constants can be formed by +integers. This allows you to modify pointer variables during +debugging. (In standard Modula-2, the actual address contained in a +pointer variable is hidden from you; it can only be modified +through direct assignment to another pointer variable or expression that +returned a pointer.) + +@item +C escape sequences can be used in strings and characters to represent +non-printable characters. @value{GDBN} will print out strings with these +escape sequences embedded. Single non-printable characters are +printed using the @samp{CHR(@var{nnn})} format. + +@item +The assignment operator (@code{:=}) returns the value of its right-hand +argument. + +@item +All built-in procedures both modify @emph{and} return their argument. +@end itemize + +@node M2 Checks +@subsubsection Modula-2 type and range checks +@cindex Modula-2 checks + +@quotation +@emph{Warning:} in this release, @value{GDBN} does not yet perform type or +range checking. +@end quotation +@c FIXME remove warning when type/range checks added + +@value{GDBN} considers two Modula-2 variables type equivalent if: + +@itemize @bullet +@item +They are of types that have been declared equivalent via a @code{TYPE +@var{t1} = @var{t2}} statement + +@item +They have been declared on the same line. (Note: This is true of the +GNU Modula-2 compiler, but it may not be true of other compilers.) +@end itemize + +As long as type checking is enabled, any attempt to combine variables +whose types are not equivalent is an error. + +Range checking is done on all mathematical operations, assignment, array +index bounds, and all built-in functions and procedures. + +@node M2 Scope +@subsubsection The scope operators @code{::} and @code{.} +@cindex scope +@kindex . +@cindex colon, doubled as scope operator +@ifinfo +@kindex colon-colon +@c Info cannot handle :: but TeX can. +@end ifinfo +@iftex +@kindex :: +@end iftex + +There are a few subtle differences between the Modula-2 scope operator +(@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have +similar syntax: + +@example + +@var{module} . @var{id} +@var{scope} :: @var{id} +@end example + +@noindent +where @var{scope} is the name of a module or a procedure, +@var{module} the name of a module, and @var{id} is any declared +identifier within your program, except another module. + +Using the @code{::} operator makes @value{GDBN} search the scope +specified by @var{scope} for the identifier @var{id}. If it is not +found in the specified scope, then @value{GDBN} will search all scopes +enclosing the one specified by @var{scope}. + +Using the @code{.} operator makes @value{GDBN} search the current scope for +the identifier specified by @var{id} that was imported from the +definition module specified by @var{module}. With this operator, it is +an error if the identifier @var{id} was not imported from definition +module @var{module}, or if @var{id} is not an identifier in +@var{module}. + +@node GDB/M2 +@subsubsection @value{GDBN} and Modula-2 + +Some @value{GDBN} commands have little use when debugging Modula-2 programs. +Five subcommands of @code{set print} and @code{show print} apply +specifically to C and C++: @samp{vtbl}, @samp{demangle}, +@samp{asm-demangle}, @samp{object}, and @samp{union}. The first four +apply to C++, and the last to the C @code{union} type, which has no direct +analogue in Modula-2. + +The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available +while using any language, is not useful with Modula-2. Its +intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be +created in Modula-2 as they can in C or C++. However, because an +address can be specified by an integral constant, the construct +@samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions}) + +@cindex @code{#} in Modula-2 +In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is +interpreted as the beginning of a comment. Use @code{<>} instead. + +@end ifset +@end ifclear + +@node Symbols +@chapter Examining the Symbol Table + +The commands described in this section allow you to inquire about the +symbols (names of variables, functions and types) defined in your +program. This information is inherent in the text of your program and +does not change as your program executes. @value{GDBN} finds it in your +program's symbol table, in the file indicated when you started @value{GDBN} +(@pxref{File Options, ,Choosing files}), or by one of the +file-management commands (@pxref{Files, ,Commands to specify files}). + +@c FIXME! This might be intentionally specific to C and C++; if so, move +@c to someplace in C section of lang chapter. +@cindex symbol names +@cindex names of symbols +@cindex quoting names +Occasionally, you may need to refer to symbols that contain unusual +characters, which @value{GDBN} ordinarily treats as word delimiters. The +most frequent case is in referring to static variables in other +source files (@pxref{Variables,,Program variables}). File names +are recorded in object files as debugging symbols, but @value{GDBN} would +ordinarily parse a typical file name, like @file{foo.c}, as the three words +@samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize +@samp{foo.c} as a single symbol, enclose it in single quotes; for example, + +@example +p 'foo.c'::x +@end example + +@noindent +looks up the value of @code{x} in the scope of the file @file{foo.c}. + +@table @code +@item info address @var{symbol} +@kindex info address +Describe where the data for @var{symbol} is stored. For a register +variable, this says which register it is kept in. For a non-register +local variable, this prints the stack-frame offset at which the variable +is always stored. + +Note the contrast with @samp{print &@var{symbol}}, which does not work +at all for a register variable, and for a stack local variable prints +the exact address of the current instantiation of the variable. + +@item whatis @var{exp} +@kindex whatis +Print the data type of expression @var{exp}. @var{exp} is not +actually evaluated, and any side-effecting operations (such as +assignments or function calls) inside it do not take place. +@xref{Expressions, ,Expressions}. + +@item whatis +Print the data type of @code{$}, the last value in the value history. + +@item ptype @var{typename} +@kindex ptype +Print a description of data type @var{typename}. @var{typename} may be +the name of a type, or for C code it may have the form +@ifclear CONLY +@samp{class @var{class-name}}, +@end ifclear +@samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or +@samp{enum @var{enum-tag}}. + +@item ptype @var{exp} +@itemx ptype +Print a description of the type of expression @var{exp}. @code{ptype} +differs from @code{whatis} by printing a detailed description, instead +of just the name of the type. + +For example, for this variable declaration: + +@example +struct complex @{double real; double imag;@} v; +@end example + +@noindent +the two commands give this output: + +@example +@group +(@value{GDBP}) whatis v +type = struct complex +(@value{GDBP}) ptype v +type = struct complex @{ + double real; + double imag; +@} +@end group +@end example + +@noindent +As with @code{whatis}, using @code{ptype} without an argument refers to +the type of @code{$}, the last value in the value history. + +@item info types @var{regexp} +@itemx info types +@kindex info types +Print a brief description of all types whose name matches @var{regexp} +(or all types in your program, if you supply no argument). Each +complete typename is matched as though it were a complete line; thus, +@samp{i type value} gives information on all types in your program whose +name includes the string @code{value}, but @samp{i type ^value$} gives +information only on types whose complete name is @code{value}. + +This command differs from @code{ptype} in two ways: first, like +@code{whatis}, it does not print a detailed description; second, it +lists all source files where a type is defined. + +@item info source +@kindex info source +Show the name of the current source file---that is, the source file for +the function containing the current point of execution---and the language +it was written in. + +@item info sources +@kindex info sources +Print the names of all source files in your program for which there is +debugging information, organized into two lists: files whose symbols +have already been read, and files whose symbols will be read when needed. + +@item info functions +@kindex info functions +Print the names and data types of all defined functions. + +@item info functions @var{regexp} +Print the names and data types of all defined functions +whose names contain a match for regular expression @var{regexp}. +Thus, @samp{info fun step} finds all functions whose names +include @code{step}; @samp{info fun ^step} finds those whose names +start with @code{step}. + +@item info variables +@kindex info variables +Print the names and data types of all variables that are declared +outside of functions (i.e., excluding local variables). + +@item info variables @var{regexp} +Print the names and data types of all variables (except for local +variables) whose names contain a match for regular expression +@var{regexp}. + +@ignore +This was never implemented. +@item info methods +@itemx info methods @var{regexp} +@kindex info methods +The @code{info methods} command permits the user to examine all defined +methods within C++ program, or (with the @var{regexp} argument) a +specific set of methods found in the various C++ classes. Many +C++ classes provide a large number of methods. Thus, the output +from the @code{ptype} command can be overwhelming and hard to use. The +@code{info-methods} command filters the methods, printing only those +which match the regular-expression @var{regexp}. +@end ignore + +@item maint print symbols @var{filename} +@itemx maint print psymbols @var{filename} +@itemx maint print msymbols @var{filename} +@kindex maint print symbols +@cindex symbol dump +@kindex maint print psymbols +@cindex partial symbol dump +Write a dump of debugging symbol data into the file @var{filename}. +These commands are used to debug the @value{GDBN} symbol-reading code. Only +symbols with debugging data are included. If you use @samp{maint print +symbols}, @value{GDBN} includes all the symbols for which it has already +collected full details: that is, @var{filename} reflects symbols for +only those files whose symbols @value{GDBN} has read. You can use the +command @code{info sources} to find out which files these are. If you +use @samp{maint print psymbols} instead, the dump shows information about +symbols that @value{GDBN} only knows partially---that is, symbols defined in +files that @value{GDBN} has skimmed, but not yet read completely. Finally, +@samp{maint print msymbols} dumps just the minimal symbol information +required for each object file from which @value{GDBN} has read some symbols. +@xref{Files, ,Commands to specify files}, for a discussion of how +@value{GDBN} reads symbols (in the description of @code{symbol-file}). +@end table + +@node Altering +@chapter Altering Execution + +Once you think you have found an error in your program, you might want to +find out for certain whether correcting the apparent error would lead to +correct results in the rest of the run. You can find the answer by +experiment, using the @value{GDBN} features for altering execution of the +program. + +For example, you can store new values into variables or memory +locations, +@ifclear BARETARGET +give your program a signal, restart it +@end ifclear +@ifset BARETARGET +restart your program +@end ifset +at a different address, or even return prematurely from a function to +its caller. + +@menu +* Assignment:: Assignment to variables +* Jumping:: Continuing at a different address +@ifclear BARETARGET +* Signaling:: Giving your program a signal +@end ifclear + +* Returning:: Returning from a function +* Calling:: Calling your program's functions +* Patching:: Patching your program +@end menu + +@node Assignment +@section Assignment to variables + +@cindex assignment +@cindex setting variables +To alter the value of a variable, evaluate an assignment expression. +@xref{Expressions, ,Expressions}. For example, + +@example +print x=4 +@end example + +@noindent +stores the value 4 into the variable @code{x}, and then prints the +value of the assignment expression (which is 4). +@ifclear CONLY +@xref{Languages, ,Using @value{GDBN} with Different Languages}, for more +information on operators in supported languages. +@end ifclear + +@kindex set variable +@cindex variables, setting +If you are not interested in seeing the value of the assignment, use the +@code{set} command instead of the @code{print} command. @code{set} is +really the same as @code{print} except that the expression's value is +not printed and is not put in the value history (@pxref{Value History, +,Value history}). The expression is evaluated only for its effects. + +If the beginning of the argument string of the @code{set} command +appears identical to a @code{set} subcommand, use the @code{set +variable} command instead of just @code{set}. This command is identical +to @code{set} except for its lack of subcommands. For example, if +your program has a variable @code{width}, you get +an error if you try to set a new value with just @samp{set width=13}, +because @value{GDBN} has the command @code{set width}: + +@example +(@value{GDBP}) whatis width +type = double +(@value{GDBP}) p width +$4 = 13 +(@value{GDBP}) set width=47 +Invalid syntax in expression. +@end example + +@noindent +The invalid expression, of course, is @samp{=47}. In +order to actually set the program's variable @code{width}, use + +@example +(@value{GDBP}) set var width=47 +@end example + +@value{GDBN} allows more implicit conversions in assignments than C; you can +freely store an integer value into a pointer variable or vice versa, +and you can convert any structure to any other structure that is the +same length or shorter. +@comment FIXME: how do structs align/pad in these conversions? +@comment /pesch@cygnus.com 18dec1990 + +To store values into arbitrary places in memory, use the @samp{@{@dots{}@}} +construct to generate a value of specified type at a specified address +(@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers +to memory location @code{0x83040} as an integer (which implies a certain size +and representation in memory), and + +@example +set @{int@}0x83040 = 4 +@end example + +@noindent +stores the value 4 into that memory location. + +@node Jumping +@section Continuing at a different address + +Ordinarily, when you continue your program, you do so at the place where +it stopped, with the @code{continue} command. You can instead continue at +an address of your own choosing, with the following commands: + +@table @code +@item jump @var{linespec} +@kindex jump +Resume execution at line @var{linespec}. Execution will stop +immediately if there is a breakpoint there. @xref{List, ,Printing +source lines}, for a description of the different forms of +@var{linespec}. + +The @code{jump} command does not change the current stack frame, or +the stack pointer, or the contents of any memory location or any +register other than the program counter. If line @var{linespec} is in +a different function from the one currently executing, the results may +be bizarre if the two functions expect different patterns of arguments or +of local variables. For this reason, the @code{jump} command requests +confirmation if the specified line is not in the function currently +executing. However, even bizarre results are predictable if you are +well acquainted with the machine-language code of your program. + +@item jump *@var{address} +Resume execution at the instruction at address @var{address}. +@end table + +You can get much the same effect as the @code{jump} command by storing a +new value into the register @code{$pc}. The difference is that this +does not start your program running; it only changes the address where it +@emph{will} run when it is continued. For example, + +@example +set $pc = 0x485 +@end example + +@noindent +causes the next @code{continue} command or stepping command to execute at +address @code{0x485}, rather than at the address where your program stopped. +@xref{Continuing and Stepping, ,Continuing and stepping}. + +The most common occasion to use the @code{jump} command is to back up, +perhaps with more breakpoints set, over a portion of a program that has +already executed, in order to examine its execution in more detail. + +@ifclear BARETARGET +@c @group +@node Signaling +@section Giving your program a signal + +@table @code +@item signal @var{signal} +@kindex signal +Resume execution where your program stopped, but immediately give it the +signal @var{signal}. @var{signal} can be the name or the number of a +signal. For example, on many systems @code{signal 2} and @code{signal +SIGINT} are both ways of sending an interrupt signal. + +Alternatively, if @var{signal} is zero, continue execution without +giving a signal. This is useful when your program stopped on account of +a signal and would ordinary see the signal when resumed with the +@code{continue} command; @samp{signal 0} causes it to resume without a +signal. + +@code{signal} does not repeat when you press @key{RET} a second time +after executing the command. +@end table +@c @end group + +Invoking the @code{signal} command is not the same as invoking the +@code{kill} utility from the shell. Sending a signal with @code{kill} +causes @value{GDBN} to decide what to do with the signal depending on +the signal handling tables (@pxref{Signals}). The @code{signal} command +passes the signal directly to your program. + +@end ifclear + +@node Returning +@section Returning from a function + +@table @code +@item return +@itemx return @var{expression} +@cindex returning from a function +@kindex return +You can cancel execution of a function call with the @code{return} +command. If you give an +@var{expression} argument, its value is used as the function's return +value. +@end table + +When you use @code{return}, @value{GDBN} discards the selected stack frame +(and all frames within it). You can think of this as making the +discarded frame return prematurely. If you wish to specify a value to +be returned, give that value as the argument to @code{return}. + +This pops the selected stack frame (@pxref{Selection, ,Selecting a +frame}), and any other frames inside of it, leaving its caller as the +innermost remaining frame. That frame becomes selected. The +specified value is stored in the registers used for returning values +of functions. + +The @code{return} command does not resume execution; it leaves the +program stopped in the state that would exist if the function had just +returned. In contrast, the @code{finish} command (@pxref{Continuing +and Stepping, ,Continuing and stepping}) resumes execution until the +selected stack frame returns naturally. + +@node Calling +@section Calling program functions + +@cindex calling functions +@kindex call +@table @code +@item call @var{expr} +Evaluate the expression @var{expr} without displaying @code{void} +returned values. +@end table + +You can use this variant of the @code{print} command if you want to +execute a function from your program, but without cluttering the output +with @code{void} returned values. The result is printed and saved in +the value history, if it is not void. + +@node Patching +@section Patching programs +@cindex patching binaries +@cindex writing into executables +@ifclear BARETARGET +@cindex writing into corefiles +@end ifclear + +By default, @value{GDBN} opens the file containing your program's executable +code +@ifclear BARETARGET +(or the corefile) +@end ifclear +read-only. This prevents accidental alterations +to machine code; but it also prevents you from intentionally patching +your program's binary. + +If you'd like to be able to patch the binary, you can specify that +explicitly with the @code{set write} command. For example, you might +want to turn on internal debugging flags, or even to make emergency +repairs. + +@table @code +@item set write on +@itemx set write off +@kindex set write +If you specify @samp{set write on}, @value{GDBN} will open executable +@ifclear BARETARGET +and core +@end ifclear +files for both reading and writing; if you specify @samp{set write +off} (the default), @value{GDBN} will open them read-only. + +If you have already loaded a file, you must load it again (using the +@code{exec-file} +@ifclear BARETARGET +or @code{core-file} +@end ifclear +command) after changing @code{set write}, for your new setting to take +effect. + +@item show write +@kindex show write +Display whether executable files +@ifclear BARETARGET +and core files +@end ifclear +will be opened for writing as well as reading. +@end table + +@node GDB Files +@chapter @value{GDBN} Files + +@value{GDBN} needs to know the file name of the program to be debugged, both in +order to read its symbol table and in order to start your program. +@ifclear BARETARGET +To debug a core dump of a previous run, you must also tell @value{GDBN} +the name of the core dump file. +@end ifclear + +@menu +* Files:: Commands to specify files +* Symbol Errors:: Errors reading symbol files +@end menu + +@node Files +@section Commands to specify files +@cindex symbol table + +@ifclear BARETARGET +@cindex core dump file +The usual way to specify executable and core dump file names is with +the command arguments given when you start @value{GDBN} (@pxref{Invocation, +,Getting In and Out of @value{GDBN}}. +@end ifclear +@ifset BARETARGET +The usual way to specify an executable file name is with +the command argument given when you start @value{GDBN}, (@pxref{Invocation, +,Getting In and Out of @value{GDBN}}. +@end ifset + +Occasionally it is necessary to change to a different file during a +@value{GDBN} session. Or you may run @value{GDBN} and forget to specify +a file you want to use. In these situations the @value{GDBN} commands +to specify new files are useful. + +@table @code +@item file @var{filename} +@cindex executable file +@kindex file +Use @var{filename} as the program to be debugged. It is read for its +symbols and for the contents of pure memory. It is also the program +executed when you use the @code{run} command. If you do not specify a +directory and the file is not found in the @value{GDBN} working directory, @value{GDBN} +uses the environment variable @code{PATH} as a list of directories to +search, just as the shell does when looking for a program to run. You +can change the value of this variable, for both @value{GDBN} and your program, +using the @code{path} command. + +On systems with memory-mapped files, an auxiliary symbol table file +@file{@var{filename}.syms} may be available for @var{filename}. If it +is, @value{GDBN} will map in the symbol table from +@file{@var{filename}.syms}, starting up more quickly. See the +descriptions of the options @samp{-mapped} and @samp{-readnow} (available +on the command line, and with the commands @code{file}, @code{symbol-file}, +or @code{add-symbol-file}), for more information. + +@item file +@code{file} with no argument makes @value{GDBN} discard any information it +has on both executable file and the symbol table. + +@item exec-file @r{[} @var{filename} @r{]} +@kindex exec-file +Specify that the program to be run (but not the symbol table) is found +in @var{filename}. @value{GDBN} will search the environment variable @code{PATH} +if necessary to locate your program. Omitting @var{filename} means to +discard information on the executable file. + +@item symbol-file @r{[} @var{filename} @r{]} +@kindex symbol-file +Read symbol table information from file @var{filename}. @code{PATH} is +searched when necessary. Use the @code{file} command to get both symbol +table and program to run from the same file. + +@code{symbol-file} with no argument clears out @value{GDBN} information on your +program's symbol table. + +The @code{symbol-file} command causes @value{GDBN} to forget the contents of its +convenience variables, the value history, and all breakpoints and +auto-display expressions. This is because they may contain pointers to +the internal data recording symbols and data types, which are part of +the old symbol table data being discarded inside @value{GDBN}. + +@code{symbol-file} will not repeat if you press @key{RET} again after +executing it once. + +When @value{GDBN} is configured for a particular environment, it will +understand debugging information in whatever format is the standard +generated for that environment; you may use either a GNU compiler, or +other compilers that adhere to the local conventions. Best results are +usually obtained from GNU compilers; for example, using @code{@value{GCC}} +you can generate debugging information for optimized code. + +On some kinds of object files, the @code{symbol-file} command does not +normally read the symbol table in full right away. Instead, it scans +the symbol table quickly to find which source files and which symbols +are present. The details are read later, one source file at a time, +as they are needed. + +The purpose of this two-stage reading strategy is to make @value{GDBN} start up +faster. For the most part, it is invisible except for occasional +pauses while the symbol table details for a particular source file are +being read. (The @code{set verbose} command can turn these pauses +into messages if desired. @xref{Messages/Warnings, ,Optional warnings +and messages}.) + +We have not implemented the two-stage strategy for COFF yet. When the +symbol table is stored in COFF format, @code{symbol-file} reads the +symbol table data in full right away. + +@item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]} +@itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]} +@kindex readnow +@cindex reading symbols immediately +@cindex symbols, reading immediately +@kindex mapped +@cindex memory-mapped symbol file +@cindex saving symbol table +You can override the @value{GDBN} two-stage strategy for reading symbol +tables by using the @samp{-readnow} option with any of the commands that +load symbol table information, if you want to be sure @value{GDBN} has the +entire symbol table available. + +@ifclear BARETARGET +If memory-mapped files are available on your system through the +@code{mmap} system call, you can use another option, @samp{-mapped}, to +cause @value{GDBN} to write the symbols for your program into a reusable +file. Future @value{GDBN} debugging sessions will map in symbol information +from this auxiliary symbol file (if the program has not changed), rather +than spending time reading the symbol table from the executable +program. Using the @samp{-mapped} option has the same effect as +starting @value{GDBN} with the @samp{-mapped} command-line option. + +You can use both options together, to make sure the auxiliary symbol +file has all the symbol information for your program. + +The auxiliary symbol file for a program called @var{myprog} is called +@samp{@var{myprog}.syms}. Once this file exists (so long as it is newer +than the corresponding executable), @value{GDBN} will always attempt to use +it when you debug @var{myprog}; no special options or commands are +needed. + +The @file{.syms} file is specific to the host machine where you run +@value{GDBN}. It holds an exact image of the internal @value{GDBN} +symbol table. It cannot be shared across multiple host platforms. + +@c FIXME: for now no mention of directories, since this seems to be in +@c flux. 13mar1992 status is that in theory GDB would look either in +@c current dir or in same dir as myprog; but issues like competing +@c GDB's, or clutter in system dirs, mean that in practice right now +@c only current dir is used. FFish says maybe a special GDB hierarchy +@c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol +@c files. + +@item core-file @r{[} @var{filename} @r{]} +@kindex core +@kindex core-file +Specify the whereabouts of a core dump file to be used as the ``contents +of memory''. Traditionally, core files contain only some parts of the +address space of the process that generated them; @value{GDBN} can access the +executable file itself for other parts. + +@code{core-file} with no argument specifies that no core file is +to be used. + +Note that the core file is ignored when your program is actually running +under @value{GDBN}. So, if you have been running your program and you wish to +debug a core file instead, you must kill the subprocess in which the +program is running. To do this, use the @code{kill} command +(@pxref{Kill Process, ,Killing the child process}). +@end ifclear + +@item load @var{filename} +@kindex load +@ifset GENERIC +Depending on what remote debugging facilities are configured into +@value{GDBN}, the @code{load} command may be available. Where it exists, it +is meant to make @var{filename} (an executable) available for debugging +on the remote system---by downloading, or dynamic linking, for example. +@code{load} also records the @var{filename} symbol table in @value{GDBN}, like +the @code{add-symbol-file} command. + +If your @value{GDBN} does not have a @code{load} command, attempting to +execute it gets the error message ``@code{You can't do that when your +target is @dots{}}'' +@end ifset + +The file is loaded at whatever address is specified in the executable. +For some object file formats, like a.out, the object file format fixes +the address and so it won't necessarily match the address you gave to +the linker. + +@ifset VXWORKS +On VxWorks, @code{load} will dynamically link @var{filename} on the +current target system as well as adding its symbols in @value{GDBN}. +@end ifset + +@ifset I960 +@cindex download to Nindy-960 +With the Nindy interface to an Intel 960 board, @code{load} will +download @var{filename} to the 960 as well as adding its symbols in +@value{GDBN}. +@end ifset + +@ifset H8 +@cindex download to H8/300 or H8/500 +@cindex H8/300 or H8/500 download +@cindex download to Hitachi SH +@cindex Hitachi SH download +When you select remote debugging to a Hitachi SH, H8/300, or H8/500 board +(@pxref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}), +the @code{load} command downloads your program to the Hitachi board and also +opens it as the current executable target for @value{GDBN} on your host +(like the @code{file} command). +@end ifset + +@code{load} will not repeat if you press @key{RET} again after using it. + +@ifclear BARETARGET +@item add-symbol-file @var{filename} @var{address} +@itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]} +@kindex add-symbol-file +@cindex dynamic linking +The @code{add-symbol-file} command reads additional symbol table information +from the file @var{filename}. You would use this command when @var{filename} +has been dynamically loaded (by some other means) into the program that +is running. @var{address} should be the memory address at which the +file has been loaded; @value{GDBN} cannot figure this out for itself. +You can specify @var{address} as an expression. + +The symbol table of the file @var{filename} is added to the symbol table +originally read with the @code{symbol-file} command. You can use the +@code{add-symbol-file} command any number of times; the new symbol data thus +read keeps adding to the old. To discard all old symbol data instead, +use the @code{symbol-file} command. + +@code{add-symbol-file} will not repeat if you press @key{RET} after using it. + +You can use the @samp{-mapped} and @samp{-readnow} options just as with +the @code{symbol-file} command, to change how @value{GDBN} manages the symbol +table information for @var{filename}. +@end ifclear + +@item info files +@itemx info target +@kindex info files +@kindex info target +@code{info files} and @code{info target} are synonymous; both print +the current target (@pxref{Targets, ,Specifying a Debugging Target}), +including the +@ifclear BARETARGET +names of the executable and core dump files +@end ifclear +@ifset BARETARGET +name of the executable file +@end ifset +currently in use by @value{GDBN}, and the files from which symbols were +loaded. The command @code{help targets} lists all possible targets +rather than current ones. +@end table + +All file-specifying commands allow both absolute and relative file names +as arguments. @value{GDBN} always converts the file name to an absolute path +name and remembers it that way. + +@ifclear BARETARGET +@cindex shared libraries +@value{GDBN} supports SunOS, SVR4, and IBM RS/6000 shared libraries. +@value{GDBN} automatically loads symbol definitions from shared libraries +when you use the @code{run} command, or when you examine a core file. +(Before you issue the @code{run} command, @value{GDBN} will not understand +references to a function in a shared library, however---unless you are +debugging a core file). +@c FIXME: next @value{GDBN} release should permit some refs to undef +@c FIXME...symbols---eg in a break cmd---assuming they are from a shared lib + +@table @code +@item info share +@itemx info sharedlibrary +@kindex info sharedlibrary +@kindex info share +Print the names of the shared libraries which are currently loaded. + +@item sharedlibrary @var{regex} +@itemx share @var{regex} +@kindex sharedlibrary +@kindex share +This is an obsolescent command; you can use it to explicitly load shared +object library symbols for files matching a Unix regular expression, but +as with files loaded automatically, it will only load shared libraries +required by your program for a core file or after typing @code{run}. If +@var{regex} is omitted all shared libraries required by your program are +loaded. +@end table +@end ifclear + +@node Symbol Errors +@section Errors reading symbol files + +While reading a symbol file, @value{GDBN} will occasionally encounter problems, +such as symbol types it does not recognize, or known bugs in compiler +output. By default, @value{GDBN} does not notify you of such problems, since +they are relatively common and primarily of interest to people +debugging compilers. If you are interested in seeing information +about ill-constructed symbol tables, you can either ask @value{GDBN} to print +only one message about each such type of problem, no matter how many +times the problem occurs; or you can ask @value{GDBN} to print more messages, +to see how many times the problems occur, with the @code{set +complaints} command (@pxref{Messages/Warnings, ,Optional warnings and +messages}). + +The messages currently printed, and their meanings, include: + +@table @code +@item inner block not inside outer block in @var{symbol} + +The symbol information shows where symbol scopes begin and end +(such as at the start of a function or a block of statements). This +error indicates that an inner scope block is not fully contained +in its outer scope blocks. + +@value{GDBN} circumvents the problem by treating the inner block as if it had +the same scope as the outer block. In the error message, @var{symbol} +may be shown as ``@code{(don't know)}'' if the outer block is not a +function. + +@item block at @var{address} out of order + +The symbol information for symbol scope blocks should occur in +order of increasing addresses. This error indicates that it does not +do so. + +@value{GDBN} does not circumvent this problem, and will have trouble +locating symbols in the source file whose symbols it is reading. (You +can often determine what source file is affected by specifying +@code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and +messages}.) + +@item bad block start address patched + +The symbol information for a symbol scope block has a start address +smaller than the address of the preceding source line. This is known +to occur in the SunOS 4.1.1 (and earlier) C compiler. + +@value{GDBN} circumvents the problem by treating the symbol scope block as +starting on the previous source line. + +@item bad string table offset in symbol @var{n} + +@cindex foo +Symbol number @var{n} contains a pointer into the string table which is +larger than the size of the string table. + +@value{GDBN} circumvents the problem by considering the symbol to have the +name @code{foo}, which may cause other problems if many symbols end up +with this name. + +@item unknown symbol type @code{0x@var{nn}} + +The symbol information contains new data types that @value{GDBN} does not yet +know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood +information, in hexadecimal. + +@value{GDBN} circumvents the error by ignoring this symbol information. This +will usually allow your program to be debugged, though certain symbols +will not be accessible. If you encounter such a problem and feel like +debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on +@code{complain}, then go up to the function @code{read_dbx_symtab} and +examine @code{*bufp} to see the symbol. + +@item stub type has NULL name +@value{GDBN} could not find the full definition for +@ifclear CONLY +a struct or class. +@end ifclear +@ifset CONLY +a struct. +@end ifset + +@ifclear CONLY +@item const/volatile indicator missing (ok if using g++ v1.x), got@dots{} + +The symbol information for a C++ member function is missing some +information that recent versions of the compiler should have output +for it. +@end ifclear + +@item info mismatch between compiler and debugger + +@value{GDBN} could not parse a type specification output by the compiler. +@end table + +@node Targets +@chapter Specifying a Debugging Target +@cindex debugging target +@kindex target + +A @dfn{target} is the execution environment occupied by your program. +@ifclear BARETARGET +Often, @value{GDBN} runs in the same host environment as your program; in +that case, the debugging target is specified as a side effect when you +use the @code{file} or @code{core} commands. When you need more +flexibility---for example, running @value{GDBN} on a physically separate +host, or controlling a standalone system over a serial port or a +realtime system over a TCP/IP connection---you +@end ifclear +@ifset BARETARGET +You +@end ifset +can use the @code{target} command to specify one of the target types +configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing +targets}). + +@menu +* Active Targets:: Active targets +* Target Commands:: Commands for managing targets +* Remote:: Remote debugging +@end menu + +@node Active Targets +@section Active targets +@cindex stacking targets +@cindex active targets +@cindex multiple targets + +@ifclear BARETARGET +There are three classes of targets: processes, core files, and +executable files. @value{GDBN} can work concurrently on up to three active +targets, one in each class. This allows you to (for example) start a +process and inspect its activity without abandoning your work on a core +file. + +For example, if you execute @samp{gdb a.out}, then the executable file +@code{a.out} is the only active target. If you designate a core file as +well---presumably from a prior run that crashed and coredumped---then +@value{GDBN} has two active targets and will use them in tandem, looking +first in the corefile target, then in the executable file, to satisfy +requests for memory addresses. (Typically, these two classes of target +are complementary, since core files contain only a program's +read-write memory---variables and so on---plus machine status, while +executable files contain only the program text and initialized data.) +@end ifclear + +When you type @code{run}, your executable file becomes an active process +target as well. When a process target is active, all @value{GDBN} commands +requesting memory addresses refer to that target; addresses in an +@ifclear BARETARGET +active core file or +@end ifclear +executable file target are obscured while the process +target is active. + +@ifset BARETARGET +Use the @code{exec-file} command to select a +new executable target (@pxref{Files, ,Commands to specify +files}). +@end ifset +@ifclear BARETARGET +Use the @code{core-file} and @code{exec-file} commands to select a +new core file or executable target (@pxref{Files, ,Commands to specify +files}). To specify as a target a process that is already running, use +the @code{attach} command (@pxref{Attach, ,Debugging an +already-running process}). +@end ifclear + +@node Target Commands +@section Commands for managing targets + +@table @code +@item target @var{type} @var{parameters} +Connects the @value{GDBN} host environment to a target +@ifset BARETARGET +machine. +@end ifset +@ifclear BARETARGET +machine or process. A target is typically a protocol for talking to +debugging facilities. You use the argument @var{type} to specify the +type or protocol of the target machine. + +Further @var{parameters} are interpreted by the target protocol, but +typically include things like device names or host names to connect +with, process numbers, and baud rates. +@end ifclear + +The @code{target} command will not repeat if you press @key{RET} again +after executing the command. + +@item help target +@kindex help target +Displays the names of all targets available. To display targets +currently selected, use either @code{info target} or @code{info files} +(@pxref{Files, ,Commands to specify files}). + +@item help target @var{name} +Describe a particular target, including any parameters necessary to +select it. +@end table + +Here are some common targets (available, or not, depending on the GDB +configuration): + +@table @code +@item target exec @var{program} +@kindex target exec +An executable file. @samp{target exec @var{program}} is the same as +@samp{exec-file @var{program}}. + +@ifclear BARETARGET +@item target core @var{filename} +@kindex target core +A core dump file. @samp{target core @var{filename}} is the same as +@samp{core-file @var{filename}}. +@end ifclear + +@ifset REMOTESTUB +@item target remote @var{dev} +@kindex target remote +Remote serial target in GDB-specific protocol. The argument @var{dev} +specifies what serial device to use for the connection (e.g. +@file{/dev/ttya}). @xref{Remote, ,Remote debugging}. +@end ifset + +@ifset SIMS +@item target sim +@kindex target sim +CPU simulator. @xref{Simulator,,Simulated CPU Target}. +@end ifset + +@ifset AMD29K +@item target udi @var{keyword} +@kindex target udi +Remote AMD29K target, using the AMD UDI protocol. The @var{keyword} +argument specifies which 29K board or simulator to use. @xref{UDI29K +Remote,,@value{GDBN} and the UDI protocol for AMD29K}. + +@item target amd-eb @var{dev} @var{speed} @var{PROG} +@kindex target amd-eb +@cindex AMD EB29K +Remote PC-resident AMD EB29K board, attached over serial lines. +@var{dev} is the serial device, as for @code{target remote}; +@var{speed} allows you to specify the linespeed; and @var{PROG} is the +name of the program to be debugged, as it appears to DOS on the PC. +@xref{EB29K Remote, ,@value{GDBN} with a remote EB29K}. + +@end ifset +@ifset H8 +@item target hms +@kindex target hms +A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host. +@ifclear H8EXCLUSIVE +@c Unix only, not currently of interest for H8-only manual +Use special commands @code{device} and @code{speed} to control the serial +line and the communications speed used. +@end ifclear +@xref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}. + +@end ifset +@ifset I960 +@item target nindy @var{devicename} +@kindex target nindy +An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is +the name of the serial device to use for the connection, e.g. +@file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}. + +@end ifset +@ifset ST2000 +@item target st2000 @var{dev} @var{speed} +@kindex target st2000 +A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev} +is the name of the device attached to the ST2000 serial line; +@var{speed} is the communication line speed. The arguments are not used +if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet. +@xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}. + +@end ifset +@ifset VXWORKS +@item target vxworks @var{machinename} +@kindex target vxworks +A VxWorks system, attached via TCP/IP. The argument @var{machinename} +is the target system's machine name or IP address. +@xref{VxWorks Remote, ,@value{GDBN} and VxWorks}. +@end ifset +@end table + +@ifset GENERIC +Different targets are available on different configurations of @value{GDBN}; your +configuration may have more or fewer targets. +@end ifset + +@node Remote +@section Remote debugging +@cindex remote debugging + +If you are trying to debug a program running on a machine that cannot run +GDB in the usual way, it is often useful to use remote debugging. For +example, you might use remote debugging on an operating system kernel, or on +a small system which does not have a general purpose operating system +powerful enough to run a full-featured debugger. + +Some configurations of GDB have special serial or TCP/IP interfaces +to make this work with particular debugging targets. In addition, +GDB comes with a generic serial protocol (specific to GDB, but +not specific to any particular target system) which you can use if you +write the remote stubs---the code that will run on the remote system to +communicate with GDB. + +Other remote targets may be available in your +configuration of GDB; use @code{help targets} to list them. + +@ifset GENERIC +@c Text on starting up GDB in various specific cases; it goes up front +@c in manuals configured for any of those particular situations, here +@c otherwise. +@menu +@ifset REMOTESTUB +* Remote Serial:: @value{GDBN} remote serial protocol +@end ifset +@ifset I960 +* i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy) +@end ifset +@ifset AMD29K +* UDI29K Remote:: @value{GDBN} and the UDI protocol for AMD29K +* EB29K Remote:: @value{GDBN} with a remote EB29K +@end ifset +@ifset VXWORKS +* VxWorks Remote:: @value{GDBN} and VxWorks +@end ifset +@ifset ST2000 +* ST2000 Remote:: @value{GDBN} with a Tandem ST2000 +@end ifset +@ifset H8 +* Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors +@end ifset +@ifset MIPS +* MIPS Remote:: @value{GDBN} and MIPS boards +@end ifset +@ifset SIMS +* Simulator:: Simulated CPU target +@end ifset +@end menu + +@include remote.texi +@end ifset + +@node Controlling GDB +@chapter Controlling @value{GDBN} + +You can alter the way @value{GDBN} interacts with you by using +the @code{set} command. For commands controlling how @value{GDBN} displays +data, @pxref{Print Settings, ,Print settings}; other settings are described here. + +@menu +* Prompt:: Prompt +* Editing:: Command editing +* History:: Command history +* Screen Size:: Screen size +* Numbers:: Numbers +* Messages/Warnings:: Optional warnings and messages +@end menu + +@node Prompt +@section Prompt +@cindex prompt + +@value{GDBN} indicates its readiness to read a command by printing a string +called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You +can change the prompt string with the @code{set prompt} command. For +instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change +the prompt in one of the @value{GDBN} sessions so that you can always tell which +one you are talking to. + +@table @code +@item set prompt @var{newprompt} +@kindex set prompt +Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth. +@kindex show prompt +@item show prompt +Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}} +@end table + +@node Editing +@section Command editing +@cindex readline +@cindex command line editing + +@value{GDBN} reads its input commands via the @dfn{readline} interface. This +GNU library provides consistent behavior for programs which provide a +command line interface to the user. Advantages are @code{emacs}-style +or @code{vi}-style inline editing of commands, @code{csh}-like history +substitution, and a storage and recall of command history across +debugging sessions. + +You may control the behavior of command line editing in @value{GDBN} with the +command @code{set}. + +@table @code +@kindex set editing +@cindex editing +@item set editing +@itemx set editing on +Enable command line editing (enabled by default). + +@item set editing off +Disable command line editing. + +@kindex show editing +@item show editing +Show whether command line editing is enabled. +@end table + +@node History +@section Command history + +@value{GDBN} can keep track of the commands you type during your +debugging sessions, so that you can be certain of precisely what +happened. Use these commands to manage the @value{GDBN} command +history facility. + +@table @code +@cindex history substitution +@cindex history file +@kindex set history filename +@item set history filename @var{fname} +Set the name of the @value{GDBN} command history file to @var{fname}. This is +the file from which @value{GDBN} will read an initial command history +list or to which it will write this list when it exits. This list is +accessed through history expansion or through the history +command editing characters listed below. This file defaults to the +value of the environment variable @code{GDBHISTFILE}, or to +@file{./.gdb_history} if this variable is not set. + +@cindex history save +@kindex set history save +@item set history save +@itemx set history save on +Record command history in a file, whose name may be specified with the +@code{set history filename} command. By default, this option is disabled. + +@item set history save off +Stop recording command history in a file. + +@cindex history size +@kindex set history size +@item set history size @var{size} +Set the number of commands which @value{GDBN} will keep in its history list. +This defaults to the value of the environment variable +@code{HISTSIZE}, or to 256 if this variable is not set. +@end table + +@cindex history expansion +History expansion assigns special meaning to the character @kbd{!}. +@ifset have-readline-appendices +@xref{Event Designators}. +@end ifset + +Since @kbd{!} is also the logical not operator in C, history expansion +is off by default. If you decide to enable history expansion with the +@code{set history expansion on} command, you may sometimes need to +follow @kbd{!} (when it is used as logical not, in an expression) with +a space or a tab to prevent it from being expanded. The readline +history facilities will not attempt substitution on the strings +@kbd{!=} and @kbd{!(}, even when history expansion is enabled. + +The commands to control history expansion are: + +@table @code + +@kindex set history expansion +@item set history expansion on +@itemx set history expansion +Enable history expansion. History expansion is off by default. + +@item set history expansion off +Disable history expansion. + +The readline code comes with more complete documentation of +editing and history expansion features. Users unfamiliar with @code{emacs} +or @code{vi} may wish to read it. +@ifset have-readline-appendices +@xref{Command Line Editing}. +@end ifset + +@c @group +@kindex show history +@item show history +@itemx show history filename +@itemx show history save +@itemx show history size +@itemx show history expansion +These commands display the state of the @value{GDBN} history parameters. +@code{show history} by itself displays all four states. +@c @end group +@end table + +@table @code +@kindex show commands +@item show commands +Display the last ten commands in the command history. + +@item show commands @var{n} +Print ten commands centered on command number @var{n}. + +@item show commands + +Print ten commands just after the commands last printed. +@end table + +@node Screen Size +@section Screen size +@cindex size of screen +@cindex pauses in output + +Certain commands to @value{GDBN} may produce large amounts of +information output to the screen. To help you read all of it, +@value{GDBN} pauses and asks you for input at the end of each page of +output. Type @key{RET} when you want to continue the output, or @kbd{q} +to discard the remaining output. Also, the screen width setting +determines when to wrap lines of output. Depending on what is being +printed, @value{GDBN} tries to break the line at a readable place, +rather than simply letting it overflow onto the following line. + +Normally @value{GDBN} knows the size of the screen from the termcap data base +together with the value of the @code{TERM} environment variable and the +@code{stty rows} and @code{stty cols} settings. If this is not correct, +you can override it with the @code{set height} and @code{set +width} commands: + +@table @code +@item set height @var{lpp} +@itemx show height +@itemx set width @var{cpl} +@itemx show width +@kindex set height +@kindex set width +@kindex show width +@kindex show height +These @code{set} commands specify a screen height of @var{lpp} lines and +a screen width of @var{cpl} characters. The associated @code{show} +commands display the current settings. + +If you specify a height of zero lines, @value{GDBN} will not pause during output +no matter how long the output is. This is useful if output is to a file +or to an editor buffer. + +Likewise, you can specify @samp{set width 0} to prevent @value{GDBN} +from wrapping its output. +@end table + +@node Numbers +@section Numbers +@cindex number representation +@cindex entering numbers + +You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by +the usual conventions: octal numbers begin with @samp{0}, decimal +numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}. +Numbers that begin with none of these are, by default, entered in base +10; likewise, the default display for numbers---when no particular +format is specified---is base 10. You can change the default base for +both input and output with the @code{set radix} command. + +@table @code +@kindex set radix +@item set radix @var{base} +Set the default base for numeric input and display. Supported choices +for @var{base} are decimal 8, 10, or 16. @var{base} must itself be +specified either unambiguously or using the current default radix; for +example, any of + +@example +set radix 012 +set radix 10. +set radix 0xa +@end example + +@noindent +will set the base to decimal. On the other hand, @samp{set radix 10} +will leave the radix unchanged no matter what it was. + +@kindex show radix +@item show radix +Display the current default base for numeric input and display. +@end table + +@node Messages/Warnings +@section Optional warnings and messages + +By default, @value{GDBN} is silent about its inner workings. If you are running +on a slow machine, you may want to use the @code{set verbose} command. +It will make @value{GDBN} tell you when it does a lengthy internal operation, so +you will not think it has crashed. + +Currently, the messages controlled by @code{set verbose} are those +which announce that the symbol table for a source file is being read; +see @code{symbol-file} in @ref{Files, ,Commands to specify files}. + +@table @code +@kindex set verbose +@item set verbose on +Enables @value{GDBN} output of certain informational messages. + +@item set verbose off +Disables @value{GDBN} output of certain informational messages. + +@kindex show verbose +@item show verbose +Displays whether @code{set verbose} is on or off. +@end table + +By default, if @value{GDBN} encounters bugs in the symbol table of an object +file, it is silent; but if you are debugging a compiler, you may find +this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}). + +@table @code +@kindex set complaints +@item set complaints @var{limit} +Permits @value{GDBN} to output @var{limit} complaints about each type of unusual +symbols before becoming silent about the problem. Set @var{limit} to +zero to suppress all complaints; set it to a large number to prevent +complaints from being suppressed. + +@kindex show complaints +@item show complaints +Displays how many symbol complaints @value{GDBN} is permitted to produce. +@end table + +By default, @value{GDBN} is cautious, and asks what sometimes seems to be a +lot of stupid questions to confirm certain commands. For example, if +you try to run a program which is already running: + +@example +(@value{GDBP}) run +The program being debugged has been started already. +Start it from the beginning? (y or n) +@end example + +If you are willing to unflinchingly face the consequences of your own +commands, you can disable this ``feature'': + +@table @code +@kindex set confirm +@cindex flinching +@cindex confirmation +@cindex stupid questions +@item set confirm off +Disables confirmation requests. + +@item set confirm on +Enables confirmation requests (the default). + +@item show confirm +@kindex show confirm +Displays state of confirmation requests. +@end table + +@c FIXME this does not really belong here. But where *does* it belong? +@cindex reloading symbols +Some systems allow individual object files that make up your program to +be replaced without stopping and restarting your program. +@ifset VXWORKS +For example, in VxWorks you can simply recompile a defective object file +and keep on running. +@end ifset +If you are running on one of these systems, you can allow @value{GDBN} to +reload the symbols for automatically relinked modules: + +@table @code +@kindex set symbol-reloading +@item set symbol-reloading on +Replace symbol definitions for the corresponding source file when an +object file with a particular name is seen again. + +@item set symbol-reloading off +Do not replace symbol definitions when re-encountering object files of +the same name. This is the default state; if you are not running on a +system that permits automatically relinking modules, you should leave +@code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols +when linking large programs, that may contain several modules (from +different directories or libraries) with the same name. + +@item show symbol-reloading +Show the current @code{on} or @code{off} setting. +@end table + +@node Sequences +@chapter Canned Sequences of Commands + +Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint +command lists}), @value{GDBN} provides two ways to store sequences of commands +for execution as a unit: user-defined commands and command files. + +@menu +* Define:: User-defined commands +* Hooks:: User-defined command hooks +* Command Files:: Command files +* Output:: Commands for controlled output +@end menu + +@node Define +@section User-defined commands + +@cindex user-defined command +A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which you +assign a new name as a command. This is done with the @code{define} +command. + +@table @code +@item define @var{commandname} +@kindex define +Define a command named @var{commandname}. If there is already a command +by that name, you are asked to confirm that you want to redefine it. + +The definition of the command is made up of other @value{GDBN} command lines, +which are given following the @code{define} command. The end of these +commands is marked by a line containing @code{end}. + +@item document @var{commandname} +@kindex document +Give documentation to the user-defined command @var{commandname}. The +command @var{commandname} must already be defined. This command reads +lines of documentation just as @code{define} reads the lines of the +command definition, ending with @code{end}. After the @code{document} +command is finished, @code{help} on command @var{commandname} will print +the documentation you have specified. + +You may use the @code{document} command again to change the +documentation of a command. Redefining the command with @code{define} +does not change the documentation. + +@item help user-defined +@kindex help user-defined +List all user-defined commands, with the first line of the documentation +(if any) for each. + +@item show user +@itemx show user @var{commandname} +@kindex show user +Display the @value{GDBN} commands used to define @var{commandname} (but not its +documentation). If no @var{commandname} is given, display the +definitions for all user-defined commands. +@end table + +User-defined commands do not take arguments. When they are executed, the +commands of the definition are not printed. An error in any command +stops execution of the user-defined command. + +Commands that would ask for confirmation if used interactively proceed +without asking when used inside a user-defined command. Many @value{GDBN} commands +that normally print messages to say what they are doing omit the messages +when used in a user-defined command. + +@node Hooks +@section User-defined command hooks +@cindex command files + +You may define @emph{hooks}, which are a special kind of user-defined +command. Whenever you run the command @samp{foo}, if the user-defined +command @samp{hook-foo} exists, it is executed (with no arguments) +before that command. + +In addition, a pseudo-command, @samp{stop} exists. Defining +(@samp{hook-stop}) makes the associated commands execute every time +execution stops in your program: before breakpoint commands are run, +displays are printed, or the stack frame is printed. + +@ifclear BARETARGET +For example, to ignore @code{SIGALRM} signals while +single-stepping, but treat them normally during normal execution, +you could define: + +@example +define hook-stop +handle SIGALRM nopass +end + +define hook-run +handle SIGALRM pass +end + +define hook-continue +handle SIGLARM pass +end +@end example +@end ifclear + +You can define a hook for any single-word command in @value{GDBN}, but +not for command aliases; you should define a hook for the basic command +name, e.g. @code{backtrace} rather than @code{bt}. +@c FIXME! So how does Joe User discover whether a command is an alias +@c or not? +If an error occurs during the execution of your hook, execution of +@value{GDBN} commands stops and @value{GDBN} issues a prompt +(before the command that you actually typed had a chance to run). + +If you try to define a hook which does not match any known command, you +will get a warning from the @code{define} command. + +@node Command Files +@section Command files + +@cindex command files +A command file for @value{GDBN} is a file of lines that are @value{GDBN} commands. Comments +(lines starting with @kbd{#}) may also be included. An empty line in a +command file does nothing; it does not mean to repeat the last command, as +it would from the terminal. + +@cindex init file +@cindex @file{@value{GDBINIT}} +When you start @value{GDBN}, it automatically executes commands from its +@dfn{init files}. These are files named @file{@value{GDBINIT}}. @value{GDBN} reads +the init file (if any) in your home directory and then the init file +(if any) in the current working directory. (The init files are not +executed if you use the @samp{-nx} option; @pxref{Mode Options, +,Choosing modes}.) + +@ifset GENERIC +@cindex init file name +On some configurations of @value{GDBN}, the init file is known by a +different name (these are typically environments where a specialized +form of GDB may need to coexist with other forms, hence a different name +for the specialized version's init file). These are the environments +with special init file names: + +@itemize @bullet +@kindex .vxgdbinit +@item +VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit} + +@kindex .os68gdbinit +@item +OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit} + +@kindex .esgdbinit +@item +ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit} +@end itemize +@end ifset + +You can also request the execution of a command file with the +@code{source} command: + +@table @code +@item source @var{filename} +@kindex source +Execute the command file @var{filename}. +@end table + +The lines in a command file are executed sequentially. They are not +printed as they are executed. An error in any command terminates execution +of the command file. + +Commands that would ask for confirmation if used interactively proceed +without asking when used in a command file. Many @value{GDBN} commands that +normally print messages to say what they are doing omit the messages +when called from command files. + +@node Output +@section Commands for controlled output + +During the execution of a command file or a user-defined command, normal +@value{GDBN} output is suppressed; the only output that appears is what is +explicitly printed by the commands in the definition. This section +describes three commands useful for generating exactly the output you +want. + +@table @code +@item echo @var{text} +@kindex echo +@c I do not consider backslash-space a standard C escape sequence +@c because it is not in ANSI. +Print @var{text}. Nonprinting characters can be included in +@var{text} using C escape sequences, such as @samp{\n} to print a +newline. @strong{No newline will be printed unless you specify one.} +In addition to the standard C escape sequences, a backslash followed +by a space stands for a space. This is useful for displaying a +string with spaces at the beginning or the end, since leading and +trailing spaces are otherwise trimmed from all arguments. +To print @samp{@w{ }and foo =@w{ }}, use the command +@samp{echo \@w{ }and foo = \@w{ }}. + +A backslash at the end of @var{text} can be used, as in C, to continue +the command onto subsequent lines. For example, + +@example +echo This is some text\n\ +which is continued\n\ +onto several lines.\n +@end example + +produces the same output as + +@example +echo This is some text\n +echo which is continued\n +echo onto several lines.\n +@end example + +@item output @var{expression} +@kindex output +Print the value of @var{expression} and nothing but that value: no +newlines, no @samp{$@var{nn} = }. The value is not entered in the +value history either. @xref{Expressions, ,Expressions}, for more information on +expressions. + +@item output/@var{fmt} @var{expression} +Print the value of @var{expression} in format @var{fmt}. You can use +the same formats as for @code{print}. @xref{Output Formats,,Output +formats}, for more information. + +@item printf @var{string}, @var{expressions}@dots{} +@kindex printf +Print the values of the @var{expressions} under the control of +@var{string}. The @var{expressions} are separated by commas and may be +either numbers or pointers. Their values are printed as specified by +@var{string}, exactly as if your program were to execute the C +subroutine + +@example +printf (@var{string}, @var{expressions}@dots{}); +@end example + +For example, you can print two values in hex like this: + +@smallexample +printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo +@end smallexample + +The only backslash-escape sequences that you can use in the format +string are the simple ones that consist of backslash followed by a +letter. +@end table + +@ifclear DOSHOST +@node Emacs +@chapter Using @value{GDBN} under GNU Emacs + +@cindex emacs +A special interface allows you to use GNU Emacs to view (and +edit) the source files for the program you are debugging with +@value{GDBN}. + +To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the +executable file you want to debug as an argument. This command starts +@value{GDBN} as a subprocess of Emacs, with input and output through a newly +created Emacs buffer. + +Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two +things: + +@itemize @bullet +@item +All ``terminal'' input and output goes through the Emacs buffer. +@end itemize + +This applies both to @value{GDBN} commands and their output, and to the input +and output done by the program you are debugging. + +This is useful because it means that you can copy the text of previous +commands and input them again; you can even use parts of the output +in this way. + +All the facilities of Emacs' Shell mode are available for interacting +with your program. In particular, you can send signals the usual +way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a +stop. + +@itemize @bullet +@item +@value{GDBN} displays source code through Emacs. +@end itemize + +Each time @value{GDBN} displays a stack frame, Emacs automatically finds the +source file for that frame and puts an arrow (@samp{=>}) at the +left margin of the current line. Emacs uses a separate buffer for +source display, and splits the screen to show both your @value{GDBN} session +and the source. + +Explicit @value{GDBN} @code{list} or search commands still produce output as +usual, but you probably will have no reason to use them. + +@quotation +@emph{Warning:} If the directory where your program resides is not your +current directory, it can be easy to confuse Emacs about the location of +the source files, in which case the auxiliary display buffer will not +appear to show your source. @value{GDBN} can find programs by searching your +environment's @code{PATH} variable, so the @value{GDBN} input and output +session will proceed normally; but Emacs does not get enough information +back from @value{GDBN} to locate the source files in this situation. To +avoid this problem, either start @value{GDBN} mode from the directory where +your program resides, or specify a full path name when prompted for the +@kbd{M-x gdb} argument. + +A similar confusion can result if you use the @value{GDBN} @code{file} command to +switch to debugging a program in some other location, from an existing +@value{GDBN} buffer in Emacs. +@end quotation + +By default, @kbd{M-x gdb} calls the program called @file{gdb}. If +you need to call @value{GDBN} by a different name (for example, if you keep +several configurations around, with different names) you can set the +Emacs variable @code{gdb-command-name}; for example, + +@example +(setq gdb-command-name "mygdb") +@end example + +@noindent +(preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or +in your @file{.emacs} file) will make Emacs call the program named +``@code{mygdb}'' instead. + +In the @value{GDBN} I/O buffer, you can use these special Emacs commands in +addition to the standard Shell mode commands: + +@table @kbd +@item C-h m +Describe the features of Emacs' @value{GDBN} Mode. + +@item M-s +Execute to another source line, like the @value{GDBN} @code{step} command; also +update the display window to show the current file and location. + +@item M-n +Execute to next source line in this function, skipping all function +calls, like the @value{GDBN} @code{next} command. Then update the display window +to show the current file and location. + +@item M-i +Execute one instruction, like the @value{GDBN} @code{stepi} command; update +display window accordingly. + +@item M-x gdb-nexti +Execute to next instruction, using the @value{GDBN} @code{nexti} command; update +display window accordingly. + +@item C-c C-f +Execute until exit from the selected stack frame, like the @value{GDBN} +@code{finish} command. + +@item M-c +Continue execution of your program, like the @value{GDBN} @code{continue} +command. + +@emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}. + +@item M-u +Go up the number of frames indicated by the numeric argument +(@pxref{Arguments, , Numeric Arguments, emacs, The GNU Emacs Manual}), +like the @value{GDBN} @code{up} command. + +@emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}. + +@item M-d +Go down the number of frames indicated by the numeric argument, like the +@value{GDBN} @code{down} command. + +@emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}. + +@item C-x & +Read the number where the cursor is positioned, and insert it at the end +of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code +around an address that was displayed earlier, type @kbd{disassemble}; +then move the cursor to the address display, and pick up the +argument for @code{disassemble} by typing @kbd{C-x &}. + +You can customize this further by defining elements of the list +@code{gdb-print-command}; once it is defined, you can format or +otherwise process numbers picked up by @kbd{C-x &} before they are +inserted. A numeric argument to @kbd{C-x &} will both indicate that you +wish special formatting, and act as an index to pick an element of the +list. If the list element is a string, the number to be inserted is +formatted using the Emacs function @code{format}; otherwise the number +is passed as an argument to the corresponding list element. +@end table + +In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break}) +tells @value{GDBN} to set a breakpoint on the source line point is on. + +If you accidentally delete the source-display buffer, an easy way to get +it back is to type the command @code{f} in the @value{GDBN} buffer, to +request a frame display; when you run under Emacs, this will recreate +the source buffer if necessary to show you the context of the current +frame. + +The source files displayed in Emacs are in ordinary Emacs buffers +which are visiting the source files in the usual way. You can edit +the files with these buffers if you wish; but keep in mind that @value{GDBN} +communicates with Emacs in terms of line numbers. If you add or +delete lines from the text, the line numbers that @value{GDBN} knows will cease +to correspond properly with the code. + +@c The following dropped because Epoch is nonstandard. Reactivate +@c if/when v19 does something similar. ---pesch@cygnus.com 19dec1990 +@ignore +@kindex emacs epoch environment +@kindex epoch +@kindex inspect + +Version 18 of Emacs has a built-in window system called the @code{epoch} +environment. Users of this environment can use a new command, +@code{inspect} which performs identically to @code{print} except that +each value is printed in its own window. +@end ignore +@end ifclear + +@ifset LUCID +@node Energize +@chapter Using @value{GDBN} with Energize + +@cindex Energize +The Energize Programming System is an integrated development environment +that includes a point-and-click interface to many programming tools. +When you use @value{GDBN} in this environment, you can use the standard +Energize graphical interface to drive @value{GDBN}; you can also, if you +choose, type @value{GDBN} commands as usual in a debugging window. Even if +you use the graphical interface, the debugging window (which uses Emacs, +and resembles the standard Emacs interface to @value{GDBN}) displays the +equivalent commands, so that the history of your debugging session is +properly reflected. + +When Energize starts up a @value{GDBN} session, it uses one of the +command-line options @samp{-energize} or @samp{-cadillac} (``cadillac'' +is the name of the communications protocol used by the Energize system). +This option makes @value{GDBN} run as one of the tools in the Energize Tool +Set: it sends all output to the Energize kernel, and accept input from +it as well. + +See the user manual for the Energize Programming System for +information on how to use the Energize graphical interface and the other +development tools that Energize integrates with @value{GDBN}. + +@end ifset + +@node GDB Bugs +@chapter Reporting Bugs in @value{GDBN} +@cindex bugs in @value{GDBN} +@cindex reporting bugs in @value{GDBN} + +Your bug reports play an essential role in making @value{GDBN} reliable. + +Reporting a bug may help you by bringing a solution to your problem, or it +may not. But in any case the principal function of a bug report is to help +the entire community by making the next version of @value{GDBN} work better. Bug +reports are your contribution to the maintenance of @value{GDBN}. + +In order for a bug report to serve its purpose, you must include the +information that enables us to fix the bug. + +@menu +* Bug Criteria:: Have you found a bug? +* Bug Reporting:: How to report bugs +@end menu + +@node Bug Criteria +@section Have you found a bug? +@cindex bug criteria + +If you are not sure whether you have found a bug, here are some guidelines: + +@itemize @bullet +@item +@cindex fatal signal +@cindex debugger crash +@cindex crash of debugger +If the debugger gets a fatal signal, for any input whatever, that is a +@value{GDBN} bug. Reliable debuggers never crash. + +@item +@cindex error on valid input +If @value{GDBN} produces an error message for valid input, that is a bug. + +@item +@cindex invalid input +If @value{GDBN} does not produce an error message for invalid input, +that is a bug. However, you should note that your idea of +``invalid input'' might be our idea of ``an extension'' or ``support +for traditional practice''. + +@item +If you are an experienced user of debugging tools, your suggestions +for improvement of @value{GDBN} are welcome in any case. +@end itemize + +@node Bug Reporting +@section How to report bugs +@cindex bug reports +@cindex @value{GDBN} bugs, reporting + +A number of companies and individuals offer support for GNU products. +If you obtained @value{GDBN} from a support organization, we recommend you +contact that organization first. + +You can find contact information for many support companies and +individuals in the file @file{etc/SERVICE} in the GNU Emacs +distribution. + +In any event, we also recommend that you send bug reports for @value{GDBN} to one +of these addresses: + +@example +bug-gdb@@prep.ai.mit.edu +@{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb +@end example + +@strong{Do not send bug reports to @samp{info-gdb}, or to +@samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do not want to +receive bug reports. Those that do, have arranged to receive @samp{bug-gdb}. + +The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which +serves as a repeater. The mailing list and the newsgroup carry exactly +the same messages. Often people think of posting bug reports to the +newsgroup instead of mailing them. This appears to work, but it has one +problem which can be crucial: a newsgroup posting often lacks a mail +path back to the sender. Thus, if we need to ask for more information, +we may be unable to reach you. For this reason, it is better to send +bug reports to the mailing list. + +As a last resort, send bug reports on paper to: + +@example +GNU Debugger Bugs +Free Software Foundation +545 Tech Square +Cambridge, MA 02139 +@end example + +The fundamental principle of reporting bugs usefully is this: +@strong{report all the facts}. If you are not sure whether to state a +fact or leave it out, state it! + +Often people omit facts because they think they know what causes the +problem and assume that some details do not matter. Thus, you might +assume that the name of the variable you use in an example does not matter. +Well, probably it does not, but one cannot be sure. Perhaps the bug is a +stray memory reference which happens to fetch from the location where that +name is stored in memory; perhaps, if the name were different, the contents +of that location would fool the debugger into doing the right thing despite +the bug. Play it safe and give a specific, complete example. That is the +easiest thing for you to do, and the most helpful. + +Keep in mind that the purpose of a bug report is to enable us to fix +the bug if it is new to us. It is not as important as what happens if +the bug is already known. Therefore, always write your bug reports on +the assumption that the bug has not been reported previously. + +Sometimes people give a few sketchy facts and ask, ``Does this ring a +bell?'' Those bug reports are useless, and we urge everyone to +@emph{refuse to respond to them} except to chide the sender to report +bugs properly. + +To enable us to fix the bug, you should include all these things: + +@itemize @bullet +@item +The version of @value{GDBN}. @value{GDBN} announces it if you start with no +arguments; you can also print it at any time using @code{show version}. + +Without this, we will not know whether there is any point in looking for +the bug in the current version of @value{GDBN}. + +@item +The type of machine you are using, and the operating system name and +version number. + +@item +What compiler (and its version) was used to compile @value{GDBN}---e.g. +``@value{GCC}--2.0''. + +@item +What compiler (and its version) was used to compile the program you +are debugging---e.g. ``@value{GCC}--2.0''. + +@item +The command arguments you gave the compiler to compile your example and +observe the bug. For example, did you use @samp{-O}? To guarantee +you will not omit something important, list them all. A copy of the +Makefile (or the output from make) is sufficient. + +If we were to try to guess the arguments, we would probably guess wrong +and then we might not encounter the bug. + +@item +A complete input script, and all necessary source files, that will +reproduce the bug. + +@item +A description of what behavior you observe that you believe is +incorrect. For example, ``It gets a fatal signal.'' + +Of course, if the bug is that @value{GDBN} gets a fatal signal, then we will +certainly notice it. But if the bug is incorrect output, we might not +notice unless it is glaringly wrong. We are human, after all. You +might as well not give us a chance to make a mistake. + +Even if the problem you experience is a fatal signal, you should still +say so explicitly. Suppose something strange is going on, such as, +your copy of @value{GDBN} is out of synch, or you have encountered a +bug in the C library on your system. (This has happened!) Your copy +might crash and ours would not. If you told us to expect a crash, +then when ours fails to crash, we would know that the bug was not +happening for us. If you had not told us to expect a crash, then we +would not be able to draw any conclusion from our observations. + +@item +If you wish to suggest changes to the @value{GDBN} source, send us context +diffs. If you even discuss something in the @value{GDBN} source, refer to +it by context, not by line number. + +The line numbers in our development sources will not match those in your +sources. Your line numbers would convey no useful information to us. +@end itemize + +Here are some things that are not necessary: + +@itemize @bullet +@item +A description of the envelope of the bug. + +Often people who encounter a bug spend a lot of time investigating +which changes to the input file will make the bug go away and which +changes will not affect it. + +This is often time consuming and not very useful, because the way we +will find the bug is by running a single example under the debugger +with breakpoints, not by pure deduction from a series of examples. +We recommend that you save your time for something else. + +Of course, if you can find a simpler example to report @emph{instead} +of the original one, that is a convenience for us. Errors in the +output will be easier to spot, running under the debugger will take +less time, etc. + +However, simplification is not vital; if you do not want to do this, +report the bug anyway and send us the entire test case you used. + +@item +A patch for the bug. + +A patch for the bug does help us if it is a good one. But do not omit +the necessary information, such as the test case, on the assumption that +a patch is all we need. We might see problems with your patch and decide +to fix the problem another way, or we might not understand it at all. + +Sometimes with a program as complicated as @value{GDBN} it is very hard to +construct an example that will make the program follow a certain path +through the code. If you do not send us the example, we will not be able +to construct one, so we will not be able to verify that the bug is fixed. + +And if we cannot understand what bug you are trying to fix, or why your +patch should be an improvement, we will not install it. A test case will +help us to understand. + +@item +A guess about what the bug is or what it depends on. + +Such guesses are usually wrong. Even we cannot guess right about such +things without first using the debugger to find the facts. +@end itemize + +@c The readline documentation is distributed with the readline code +@c and consists of the two following files: +@c rluser.texinfo +@c inc-hist.texi +@c Use -I with makeinfo to point to the appropriate directory, +@c environment var TEXINPUTS with TeX. +@include rluser.texinfo +@include inc-hist.texi + +@ifset NOVEL +@node Renamed Commands +@appendix Renamed Commands + +The following commands were renamed in GDB 4, in order to make the +command set as a whole more consistent and easier to use and remember: + +@kindex add-syms +@kindex delete environment +@kindex info copying +@kindex info convenience +@kindex info directories +@kindex info editing +@kindex info history +@kindex info targets +@kindex info values +@kindex info version +@kindex info warranty +@kindex set addressprint +@kindex set arrayprint +@kindex set prettyprint +@kindex set screen-height +@kindex set screen-width +@kindex set unionprint +@kindex set vtblprint +@kindex set demangle +@kindex set asm-demangle +@kindex set sevenbit-strings +@kindex set array-max +@kindex set caution +@kindex set history write +@kindex show addressprint +@kindex show arrayprint +@kindex show prettyprint +@kindex show screen-height +@kindex show screen-width +@kindex show unionprint +@kindex show vtblprint +@kindex show demangle +@kindex show asm-demangle +@kindex show sevenbit-strings +@kindex show array-max +@kindex show caution +@kindex show history write +@kindex unset + +@c TEXI2ROFF-KILL +@ifinfo +@c END TEXI2ROFF-KILL +@example +OLD COMMAND NEW COMMAND +@c TEXI2ROFF-KILL +--------------- ------------------------------- +@c END TEXI2ROFF-KILL +add-syms add-symbol-file +delete environment unset environment +info convenience show convenience +info copying show copying +info directories show directories +info editing show commands +info history show values +info targets help target +info values show values +info version show version +info warranty show warranty +set/show addressprint set/show print address +set/show array-max set/show print elements +set/show arrayprint set/show print array +set/show asm-demangle set/show print asm-demangle +set/show caution set/show confirm +set/show demangle set/show print demangle +set/show history write set/show history save +set/show prettyprint set/show print pretty +set/show screen-height set/show height +set/show screen-width set/show width +set/show sevenbit-strings set/show print sevenbit-strings +set/show unionprint set/show print union +set/show vtblprint set/show print vtbl + +unset [No longer an alias for delete] +@end example +@c TEXI2ROFF-KILL +@end ifinfo + +@tex +\vskip \parskip\vskip \baselineskip +\halign{\tt #\hfil &\qquad#&\tt #\hfil\cr +{\bf Old Command} &&{\bf New Command}\cr +add-syms &&add-symbol-file\cr +delete environment &&unset environment\cr +info convenience &&show convenience\cr +info copying &&show copying\cr +info directories &&show directories \cr +info editing &&show commands\cr +info history &&show values\cr +info targets &&help target\cr +info values &&show values\cr +info version &&show version\cr +info warranty &&show warranty\cr +set{\rm / }show addressprint &&set{\rm / }show print address\cr +set{\rm / }show array-max &&set{\rm / }show print elements\cr +set{\rm / }show arrayprint &&set{\rm / }show print array\cr +set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr +set{\rm / }show caution &&set{\rm / }show confirm\cr +set{\rm / }show demangle &&set{\rm / }show print demangle\cr +set{\rm / }show history write &&set{\rm / }show history save\cr +set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr +set{\rm / }show screen-height &&set{\rm / }show height\cr +set{\rm / }show screen-width &&set{\rm / }show width\cr +set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr +set{\rm / }show unionprint &&set{\rm / }show print union\cr +set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr +\cr +unset &&\rm(No longer an alias for delete)\cr +} +@end tex +@c END TEXI2ROFF-KILL +@end ifset + +@ifclear PRECONFIGURED +@node Formatting Documentation +@appendix Formatting Documentation + +@cindex GDB reference card +@cindex reference card +The GDB 4 release includes an already-formatted reference card, ready +for printing with PostScript or GhostScript, in the @file{gdb} +subdirectory of the main source directory@footnote{In +@file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN} +release.}. If you can use PostScript or GhostScript with your printer, +you can print the reference card immediately with @file{refcard.ps}. + +The release also includes the source for the reference card. You +can format it, using @TeX{}, by typing: + +@example +make refcard.dvi +@end example + +The GDB reference card is designed to print in landscape mode on US +``letter'' size paper; that is, on a sheet 11 inches wide by 8.5 inches +high. You will need to specify this form of printing as an option to +your @sc{dvi} output program. + +@cindex documentation + +All the documentation for GDB comes as part of the machine-readable +distribution. The documentation is written in Texinfo format, which is +a documentation system that uses a single source file to produce both +on-line information and a printed manual. You can use one of the Info +formatting commands to create the on-line version of the documentation +and @TeX{} (or @code{texi2roff}) to typeset the printed version. + +GDB includes an already formatted copy of the on-line Info version of +this manual in the @file{gdb} subdirectory. The main Info file is +@file{gdb-@var{version-number}/gdb/gdb.info}, and it refers to +subordinate files matching @samp{gdb.info*} in the same directory. If +necessary, you can print out these files, or read them with any editor; +but they are easier to read using the @code{info} subsystem in GNU Emacs +or the standalone @code{info} program, available as part of the GNU +Texinfo distribution. + +If you want to format these Info files yourself, you need one of the +Info formatting programs, such as @code{texinfo-format-buffer} or +@code{makeinfo}. + +If you have @code{makeinfo} installed, and are in the top level GDB +source directory (@file{gdb-@value{GDBVN}}, in the case of version @value{GDBVN}), you can +make the Info file by typing: + +@example +cd gdb +make gdb.info +@end example + +If you want to typeset and print copies of this manual, you need @TeX{}, +a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the +Texinfo definitions file. + +@TeX{} is a typesetting program; it does not print files directly, but +produces output files called @sc{dvi} files. To print a typeset +document, you need a program to print @sc{dvi} files. If your system +has @TeX{} installed, chances are it has such a program. The precise +command to use depends on your system; @kbd{lpr -d} is common; another +(for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may +require a file name without any extension or a @samp{.dvi} extension. + +@TeX{} also requires a macro definitions file called +@file{texinfo.tex}. This file tells @TeX{} how to typeset a document +written in Texinfo format. On its own, @TeX{} cannot read, much less +typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB +and is located in the @file{gdb-@var{version-number}/texinfo} +directory. + +If you have @TeX{} and a @sc{dvi} printer program installed, you can +typeset and print this manual. First switch to the the @file{gdb} +subdirectory of the main source directory (for example, to +@file{gdb-@value{GDBVN}/gdb}) and then type: + +@example +make gdb.dvi +@end example + +@node Installing GDB +@appendix Installing GDB +@cindex configuring GDB +@cindex installation + +GDB comes with a @code{configure} script that automates the process +of preparing GDB for installation; you can then use @code{make} to +build the @code{gdb} program. +@iftex +@c irrelevant in info file; it's as current as the code it lives with. +@footnote{If you have a more recent version of GDB than @value{GDBVN}, +look at the @file{README} file in the sources; we may have improved the +installation procedures since publishing this manual.} +@end iftex + +The GDB distribution includes all the source code you need for GDB in +a single directory, whose name is usually composed by appending the +version number to @samp{gdb}. + +For example, the GDB version @value{GDBVN} distribution is in the +@file{gdb-@value{GDBVN}} directory. That directory contains: + +@table @code +@item gdb-@value{GDBVN}/configure @r{(and supporting files)} +script for configuring GDB and all its supporting libraries. + +@item gdb-@value{GDBVN}/gdb +the source specific to GDB itself + +@item gdb-@value{GDBVN}/bfd +source for the Binary File Descriptor library + +@item gdb-@value{GDBVN}/include +GNU include files + +@item gdb-@value{GDBVN}/libiberty +source for the @samp{-liberty} free software library + +@item gdb-@value{GDBVN}/opcodes +source for the library of opcode tables and disassemblers + +@item gdb-@value{GDBVN}/readline +source for the GNU command-line interface + +@item gdb-@value{GDBVN}/glob +source for the GNU filename pattern-matching subroutine + +@item gdb-@value{GDBVN}/mmalloc +source for the GNU memory-mapped malloc package +@end table + +The simplest way to configure and build GDB is to run @code{configure} +from the @file{gdb-@var{version-number}} source directory, which in +this example is the @file{gdb-@value{GDBVN}} directory. + +First switch to the @file{gdb-@var{version-number}} source directory +if you are not already in it; then run @code{configure}. Pass the +identifier for the platform on which GDB will run as an +argument. + +For example: + +@example +cd gdb-@value{GDBVN} +./configure @var{host} +make +@end example + +@noindent +where @var{host} is an identifier such as @samp{sun4} or +@samp{decstation}, that identifies the platform where GDB will run. +(You can often leave off @var{host}; @code{configure} tries to guess the +correct value by examining your system.) + +Running @samp{configure @var{host}} and then running @code{make} builds the +@file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty} +libraries, then @code{gdb} itself. The configured source files, and the +binaries, are left in the corresponding source directories. + +@code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your +system does not recognize this automatically when you run a different +shell, you may need to run @code{sh} on it explicitly: + +@example +sh configure @var{host} +@end example + +If you run @code{configure} from a directory that contains source +directories for multiple libraries or programs, such as the +@file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure} +creates configuration files for every directory level underneath (unless +you tell it not to, with the @samp{--norecursion} option). + +You can run the @code{configure} script from any of the +subordinate directories in the GDB distribution if you only want to +configure that subdirectory, but be sure to specify a path to it. + +For example, with version @value{GDBVN}, type the following to configure only +the @code{bfd} subdirectory: + +@example +@group +cd gdb-@value{GDBVN}/bfd +../configure @var{host} +@end group +@end example + +You can install @code{@value{GDBP}} anywhere; it has no hardwired paths. +However, you should make sure that the shell on your path (named by +the @samp{SHELL} environment variable) is publicly readable. Remember +that GDB uses the shell to start your program---some systems refuse to +let GDB debug child processes whose programs are not readable. + +@menu +* Separate Objdir:: Compiling GDB in another directory +* Config Names:: Specifying names for hosts and targets +* configure Options:: Summary of options for configure +@end menu + +@node Separate Objdir +@section Compiling GDB in another directory + +If you want to run GDB versions for several host or target machines, +you need a different @code{gdb} compiled for each combination of +host and target. @code{configure} is designed to make this easy by +allowing you to generate each configuration in a separate subdirectory, +rather than in the source directory. If your @code{make} program +handles the @samp{VPATH} feature (GNU @code{make} does), running +@code{make} in each of these directories builds the @code{gdb} +program specified there. + +To build @code{gdb} in a separate directory, run @code{configure} +with the @samp{--srcdir} option to specify where to find the source. +(You also need to specify a path to find @code{configure} +itself from your working directory. If the path to @code{configure} +would be the same as the argument to @samp{--srcdir}, you can leave out +the @samp{--srcdir} option; it will be assumed.) + +For example, with version @value{GDBVN}, you can build GDB in a separate +directory for a Sun 4 like this: + +@example +@group +cd gdb-@value{GDBVN} +mkdir ../gdb-sun4 +cd ../gdb-sun4 +../gdb-@value{GDBVN}/configure sun4 +make +@end group +@end example + +When @code{configure} builds a configuration using a remote source +directory, it creates a tree for the binaries with the same structure +(and using the same names) as the tree under the source directory. In +the example, you'd find the Sun 4 library @file{libiberty.a} in the +directory @file{gdb-sun4/libiberty}, and GDB itself in +@file{gdb-sun4/gdb}. + +One popular reason to build several GDB configurations in separate +directories is to configure GDB for cross-compiling (where GDB +runs on one machine---the host---while debugging programs that run on +another machine---the target). You specify a cross-debugging target by +giving the @samp{--target=@var{target}} option to @code{configure}. + +When you run @code{make} to build a program or library, you must run +it in a configured directory---whatever directory you were in when you +called @code{configure} (or one of its subdirectories). + +The @code{Makefile} that @code{configure} generates in each source +directory also runs recursively. If you type @code{make} in a source +directory such as @file{gdb-@value{GDBVN}} (or in a separate configured +directory configured with @samp{--srcdir=@var{path}/gdb-@value{GDBVN}}), you +will build all the required libraries, and then build GDB. + +When you have multiple hosts or targets configured in separate +directories, you can run @code{make} on them in parallel (for example, +if they are NFS-mounted on each of the hosts); they will not interfere +with each other. + +@node Config Names +@section Specifying names for hosts and targets + +The specifications used for hosts and targets in the @code{configure} +script are based on a three-part naming scheme, but some short predefined +aliases are also supported. The full naming scheme encodes three pieces +of information in the following pattern: + +@example +@var{architecture}-@var{vendor}-@var{os} +@end example + +For example, you can use the alias @code{sun4} as a @var{host} argument, +or as the value for @var{target} in a @code{--target=@var{target}} +option. The equivalent full name is @samp{sparc-sun-sunos4}. + +The @code{configure} script accompanying GDB does not provide +any query facility to list all supported host and target names or +aliases. @code{configure} calls the Bourne shell script +@code{config.sub} to map abbreviations to full names; you can read the +script, if you wish, or you can use it to test your guesses on +abbreviations---for example: + +@smallexample +% sh config.sub sun4 +sparc-sun-sunos4.1.1 +% sh config.sub sun3 +m68k-sun-sunos4.1.1 +% sh config.sub decstation +mips-dec-ultrix4.2 +% sh config.sub hp300bsd +m68k-hp-bsd +% sh config.sub i386v +i386-unknown-sysv +% sh config.sub i786v +Invalid configuration `i786v': machine `i786v' not recognized +@end smallexample + +@noindent +@code{config.sub} is also distributed in the GDB source +directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}). + +@node configure Options +@section @code{configure} options + +Here is a summary of the @code{configure} options and arguments that +are most often useful for building @value{GDBN}. @code{configure} also has +several other options not listed here. @inforef{What Configure +Does,,configure.info}, for a full explanation of @code{configure}. +@c FIXME: Would this be more, or less, useful as an xref (ref to printed +@c manual in the printed manual, ref to info file only from the info file)? + +@example +configure @r{[}--help@r{]} + @r{[}--prefix=@var{dir}@r{]} + @r{[}--srcdir=@var{path}@r{]} + @r{[}--norecursion@r{]} @r{[}--rm@r{]} + @r{[}--target=@var{target}@r{]} @var{host} +@end example + +@noindent +You may introduce options with a single @samp{-} rather than +@samp{--} if you prefer; but you may abbreviate option names if you use +@samp{--}. + +@table @code +@item --help +Display a quick summary of how to invoke @code{configure}. + +@item -prefix=@var{dir} +Configure the source to install programs and files under directory +@file{@var{dir}}. + +@item --srcdir=@var{path} +@strong{Warning: using this option requires GNU @code{make}, or another +@code{make} that implements the @code{VPATH} feature.}@* +Use this option to make configurations in directories separate from the +GDB source directories. Among other things, you can use this to +build (or maintain) several configurations simultaneously, in separate +directories. @code{configure} writes configuration specific files in +the current directory, but arranges for them to use the source in the +directory @var{path}. @code{configure} will create directories under +the working directory in parallel to the source directories below +@var{path}. + +@item --norecursion +Configure only the directory level where @code{configure} is executed; do not +propagate configuration to subdirectories. + +@item --rm +@emph{Remove} files otherwise built during configuration. + +@c This does not work (yet if ever). FIXME. +@c @item --parse=@var{lang} @dots{} +@c Configure the GDB expression parser to parse the listed languages. +@c @samp{all} configures GDB for all supported languages. To get a +@c list of all supported languages, omit the argument. Without this +@c option, GDB is configured to parse all supported languages. + +@item --target=@var{target} +Configure GDB for cross-debugging programs running on the specified +@var{target}. Without this option, GDB is configured to debug +programs that run on the same machine (@var{host}) as GDB itself. + +There is no convenient way to generate a list of all available targets. + +@item @var{host} @dots{} +Configure GDB to run on the specified @var{host}. + +There is no convenient way to generate a list of all available hosts. +@end table + +@noindent +@code{configure} accepts other options, for compatibility with +configuring other GNU tools recursively; but these are the only +options that affect GDB or its supporting libraries. +@end ifclear + +@node Index +@unnumbered Index + +@printindex cp + +@tex +% I think something like @colophon should be in texinfo. In the +% meantime: +\long\def\colophon{\hbox to0pt{}\vfill +\centerline{The body of this manual is set in} +\centerline{\fontname\tenrm,} +\centerline{with headings in {\bf\fontname\tenbf}} +\centerline{and examples in {\tt\fontname\tentt}.} +\centerline{{\it\fontname\tenit\/},} +\centerline{{\bf\fontname\tenbf}, and} +\centerline{{\sl\fontname\tensl\/}} +\centerline{are used for emphasis.}\vfill} +\page\colophon +% Blame: pesch@cygnus.com, 1991. +@end tex + +@contents +@bye |