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ΓòÉΓòÉΓòÉ 1. Title page ΓòÉΓòÉΓòÉ

                               Debugging with GDB

                          The GNU Source-Level Debugger

                        Edition 4.06, for GDB version 4.7

                                  October 1992

                    by Richard M. Stallman and Roland H. Pesch

Copyright (C) 1988, 1989, 1990, 1991, 1992 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.

Permission is granted to copy and distribute modified versions of this manual
under the conditions for verbatim copying, provided also that the section
entitled ``GNU General Public License'' is included exactly as in the original,
and provided 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, except that
the section entitled ``GNU General Public License'' may be included in a
translation approved by the Free Software Foundation instead of in the original
English.


ΓòÉΓòÉΓòÉ 2. Top node: "Debugging with GDB" ΓòÉΓòÉΓòÉ

This file describes GDB, the GNU symbolic debugger.

This is Edition 4.06, October 1992, for GDB Version 4.7.


ΓòÉΓòÉΓòÉ 3. Summary of GDB ΓòÉΓòÉΓòÉ

The purpose of a debugger such as GDB 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.

GDB can do four main kinds of things (plus other things in support of these) to
help you catch bugs in the act:

o Start your program, specifying anything that might affect its behavior.

o Make your program stop on specified conditions.

o Examine what has happened, when your program has stopped.

o Change things in your program, so you can experiment with correcting the
  effects of one bug and go on to learn about another.

You can use GDB to debug programs written in C, C++, and Modula-2. Fortran
support will be added when a GNU Fortran compiler is ready.


ΓòÉΓòÉΓòÉ 3.1. Free Software ΓòÉΓòÉΓòÉ

GDB is 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.

For full details, see GNU GENERAL PUBLIC LICENSE.


ΓòÉΓòÉΓòÉ 3.2. Contributors to GDB ΓòÉΓòÉΓòÉ

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 `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.

Plea: Additions to this section are particularly welcome.  If you or your
friends (or enemies; let's be evenhanded) have been unfairly omitted from this
list, we would like to add your names!

So that they may not regard their long labor as thankless, we particularly
thank those who shepherded GDB through major releases: Stu Grossman and John
Gilmore (releases 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 Pete TerMaat, Chris Hanson, and
Richard Mlynarik, handled releases through 2.8.

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).

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 and the Modula-2
support, and contributed the Languages chapter of this manual.

Fred Fish wrote most of the support for Unix System Vr4, and enhanced the
command-completion support to cover C++ overloaded symbols.


ΓòÉΓòÉΓòÉ 4. New Features since GDB version 3.5 ΓòÉΓòÉΓòÉ

Targets
          Using the new command 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 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.

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.

Wide Output
          Commands that issue wide output now insert newlines at places
          designed to make the output more readable.

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, a.out, and the Intel 960 b.out; files
          may be read as .o's, 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.

Configuration and Ports
          Compile-time configuration (to select a particular architecture and
          operating system) is much easier.  The script configure now allows
          you to configure GDB as either a native debugger or a cross-debugger.
          See Installing GDB, for details on how to configure.

Interaction
          The user interface to GDB's control variables has been simplified and
          consolidated in two commands, set and 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.

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 catch and info catch: GDB can break when an
          exception is raised, before the stack is peeled back to the exception
          handler's context.

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 into 1992.  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.

Command Rationalization
          Many GDB commands have been renamed to make them easier to remember
          and use.  In particular, the subcommands of info and show/set are
          grouped to make the former refer to the state of your program, and
          the latter refer to the state of GDB itself. See Renamed Commands,
          for details on what commands were renamed.

Shared Libraries
          GDB 4 can debug programs and core files that use SunOS, SVR4, or IBM
          RS/6000 shared libraries.

Reference Card
          GDB 4 has a reference card. See Formatting the Documentation, for
          instructions to print it.

Work in Progress
          Kernel debugging for BSD and Mach systems; Tahoe and HPPA
          architecture support.


ΓòÉΓòÉΓòÉ 5. A Sample GDB Session ΓòÉΓòÉΓòÉ

You can use this manual at your leisure to read all about GDB. However, a
handful of commands are enough to get started using the debugger.  This chapter
illustrates these commands.

One of the preliminary versions of GNU 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's definition in another stop
working.  In the following short m4 session, we define a macro foo which
expands to 0000; we then use the m4 built-in defn to define bar as the same
thing.  However, when we change the open quote string to <QUOTE> and the close
quote string to <UNQUOTE>, the same procedure fails to define a new synonym
baz:

$ cd gnu/m4
$ ./m4
define(foo,0000)

foo
0000
define(bar,defn(`foo'))

bar
0000
changequote(<QUOTE>,<UNQUOTE>)

define(baz,defn(<QUOTE>foo<UNQUOTE>))
baz
C-d
m4: End of input: 0: fatal error: EOF in string

Let's use GDB to try to see what's going on.

$ gdb m4
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 4.7, Copyright 1992 Free Software Foundation, Inc...
(gdb)

GDB 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 GDB to use a
narrower display width than usual, so that examples will fit in this manual.

(gdb) set width 70

Let's see how the m4 built-in changequote works. Having looked at the source,
we know the relevant subroutine is m4_changequote, so we set a breakpoint there
with GDB's break command.

(gdb) break m4_changequote
Breakpoint 1 at 0x62f4: file builtin.c, line 879.

Using the run command, we start m4 running under GDB control; as long as
control does not reach the m4_changequote subroutine, the program runs as
usual:

(gdb) run
Starting program: /work/Editorial/gdb/gnu/m4/m4
define(foo,0000)

foo
0000

To trigger the breakpoint, we call changequote.  GDB suspends execution of m4,
displaying information about the context where it stops.

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))

Now we use the command n (next) to advance execution to the next line of the
current function.

(gdb) n
882         set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
 : nil,

set_quotes looks like a promising subroutine.  We can go into it by using the
command s (step) instead of next. step goes to the next line to be executed in
any subroutine, so it steps into set_quotes.

(gdb) s
set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
    at input.c:530
530         if (lquote != def_lquote)

The display that shows the subroutine where m4 is now suspended (and its
arguments) is called a stack frame display.  It shows a summary of the stack.
We can use the backtrace command (which can also be spelled bt), to see where
we are in the stack as a whole: the backtrace command displays a stack frame
for each active subroutine.

(gdb) 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

Let's step through a few more lines to see what happens.  The first two times,
we can use `s'; the next two times we use n to avoid falling into the xstrdup
subroutine.

(gdb) s
0x3b5c  532         if (rquote != def_rquote)
(gdb) s
0x3b80  535         lquote = (lq == nil || *lq == '\0') ?  \
def_lquote : xstrdup(lq);
(gdb) n
536         rquote = (rq == nil || *rq == '\0') ? def_rquote\
 : xstrdup(rq);
(gdb) n
538         len_lquote = strlen(rquote);

The last line displayed looks a little odd; let's examine the variables lquote
and rquote to see if they are in fact the new left and right quotes we
specified.  We can use the command p (print) to see their values.

(gdb) p lquote
$1 = 0x35d40 "<QUOTE>"
(gdb) p rquote
$2 = 0x35d50 "<UNQUOTE>"

lquote and rquote are indeed the new left and right quotes. Let's look at some
context; we can display ten lines of source surrounding the current line, with
the l (list) command.

(gdb) 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

Let's step past the two lines that set len_lquote and len_rquote, and then
examine the values of those variables.

(gdb) n
539         len_rquote = strlen(lquote);
(gdb) n
540     }
(gdb) p len_lquote
$3 = 9
(gdb) p len_rquote
$4 = 7

That certainly looks wrong, assuming len_lquote and len_rquote are meant to be
the lengths of lquote and rquote respectively.  Let's try setting them to
better values. We can use the p command for this, since it'll print the value
of any expression---and that expression can include subroutine calls and
assignments.

(gdb) p len_lquote=strlen(lquote)
$5 = 7
(gdb) p len_rquote=strlen(rquote)
$6 = 9

Let's see if that fixes the problem of using the new quotes with the m4
built-in defn.  We can allow m4 to continue executing with the c (continue)
command, and then try the example that caused trouble initially:

(gdb) c
Continuing.

define(baz,defn(<QUOTE>foo<UNQUOTE>))

baz
0000

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'll let m4 exit by giving it an EOF as input.

C-d
Program exited normally.

The message `Program exited normally.' is from GDB; it indicates m4 has
finished executing.  We can end our GDB session with the GDB quit command.

(gdb) quit


ΓòÉΓòÉΓòÉ 6. Getting In and Out of GDB ΓòÉΓòÉΓòÉ

This chapter discusses how to start GDB, and how to get out of it. (The
essentials: type `gdb' to start GDB, and type quit or C-d to exit.)


ΓòÉΓòÉΓòÉ 6.1. Starting GDB ΓòÉΓòÉΓòÉ

For details on starting up gdb as a remote debugger attached to a Hitachi
H8/300 board, see GDB and the Hitachi H8/300.

Start GDB by running the program gdb.  Once it's running, GDB reads commands
from the terminal until you tell it to exit.

You can also run gdb with a variety of arguments and options, to specify more
of your debugging environment at the outset.

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.

The most usual way to start GDB is with one argument, specifying an executable
program:

gdb program

You can also start with both an executable program and a core file specified:

gdb program core

You can, instead, specify a process ID as a second argument, if you want to
debug a running process:

gdb program 1234

would attach GDB to process 1234 (unless you also have a file named `1234'; GDB
does check for a core file first).

Taking advantage of the second command-line argument requires a fairly complete
operating system; when you use GDB 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.

You can further control how GDB starts up by using command-line options.  GDB
itself can remind you of the options available.

Type

gdb -help

to display all available options and briefly describe their use (`gdb -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 `-x' option is used.


ΓòÉΓòÉΓòÉ 6.1.1. Choosing Files ΓòÉΓòÉΓòÉ

When GDB 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 `-se' and `-c' options respectively.  (GDB
reads the first argument that does not have an associated option flag as
equivalent to the `-se' option followed by that argument; and the second
argument that does not have an associated option flag, if any, as equivalent to
the `-c' option followed by that argument.)

Many options have both long and short forms; both are shown in the following
list.  GDB 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 `--' rather than `-', though we illustrate the more usual
convention.)

-symbols=file
-s file
          Read symbol table from file file.

-exec=file
-e file
          Use file file as the executable file to execute when appropriate, and
          for examining pure data in conjunction with a core dump.

-se=file
          Read symbol table from file file and use it as the executable file.

-core=file
-c file
          Use file file as a core dump to examine.

-command=file
-x file
          Execute GDB commands from file file.  See Command Files.

-directory=directory
-d directory
          Add directory to the path to search for source files.

-m
-mapped
          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 mmap
          system call, you can use this option to have GDB write the symbols
          from your program into a reusable file in the current directory.  If
          the program you are debugging is called `/tmp/fred', the mapped
          symbol file will be `./fred.syms'. Future GDB 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.

          The `.syms' file is specific to the host machine on which GDB is run.
          It holds an exact image of GDB's internal symbol table.  It cannot be
          shared across multiple host platforms.

-r
-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.

The -mapped and -readnow options are typically combined in order to build a
`.syms' file that contains complete symbol information. A simple GDB invocation
to do nothing but build a `.syms' file for future use is:

        gdb -batch -nx -mapped -readnow programname


ΓòÉΓòÉΓòÉ 6.1.2. Choosing Modes ΓòÉΓòÉΓòÉ

You can run GDB in various alternative modes---for example, in batch mode or
quiet mode.

-nx
-n
          Do not execute commands from any `.gdbinit' initialization files.
          Normally, the commands in these files are executed after all the
          command options and arguments have been processed. See Command Files.

-quiet
-q
          ``Quiet''.  Do not print the introductory and copyright messages.
          These messages are also suppressed in batch mode.

-batch
          Run in batch mode.  Exit with status 0 after processing all the
          command files specified with `-x' (and `.gdbinit', if not inhibited).
          Exit with nonzero status if an error occurs in executing the GDB
          commands in the command files.

          Batch mode may be useful for running GDB as a filter, for example to
          download and run a program on another computer; in order to make this
          more useful, the message

                    Program exited normally.

          (which is ordinarily issued whenever a program running under GDB
          control terminates) is not issued when running in batch mode.

-cd=directory
          Run GDB using directory as its working directory, instead of the
          current directory.

-fullname
-f
          Emacs sets this option when it runs GDB as a subprocess.  It tells
          GDB 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 `\032' characters, followed by the file name, line
          number and character position separated by colons, and a newline.
          The Emacs-to-GDB interface program uses the two `\032' characters as
          a signal to display the source code for the frame.

-b bps
          Set the line speed (baud rate or bits per second) of any serial
          interface used by GDB for remote debugging.

-tty=device
          Run using device for your program's standard input and output.


ΓòÉΓòÉΓòÉ 6.2. Leaving GDB ΓòÉΓòÉΓòÉ

quit
          To exit GDB, use the quit command (abbreviated q), or type an
          end-of-file character (usually C-d).

An interrupt (often C-c) will not exit from GDB, but rather will terminate the
action of any GDB command that is in progress and return to GDB command level.
It is safe to type the interrupt character at any time because GDB does not
allow it to take effect until a time when it is safe.

If you have been using GDB to control an attached process or device, you can
release it with the detach command; see Debugging an Already-Running Process..


ΓòÉΓòÉΓòÉ 6.3. Shell Commands ΓòÉΓòÉΓòÉ

If you need to execute occasional shell commands during your debugging session,
there is no need to leave or suspend GDB; you can just use the shell command.

shell command string
          Directs GDB to invoke an inferior shell to execute command string.
          If it exists, the environment variable SHELL is used for the name of
          the shell to run.  Otherwise GDB uses /bin/sh.

The utility make is often needed in development environments. You do not have
to use the shell command for this purpose in GDB:

make make-args
          Causes GDB to execute an inferior make program with the specified
          arguments.  This is equivalent to `shell make make-args'.


ΓòÉΓòÉΓòÉ 7. GDB Commands ΓòÉΓòÉΓòÉ

You can abbreviate a GDB command to the first few letters of the command name,
if that abbreviation is unambiguous; and you can repeat certain GDB commands by
typing just RET.  You can also use the TAB key to get GDB to fill out the rest
of a word in a command (or to show you the alternatives available, if there's
more than one possibility).


ΓòÉΓòÉΓòÉ 7.1. Command Syntax ΓòÉΓòÉΓòÉ

A GDB 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 step accepts an
argument which is the number of times to step, as in `step 5'.  You can also
use the step command with no arguments.  Some command names do not allow any
arguments.

GDB 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, s is specially defined as equivalent to step even though there are
other commands whose names start with s.  You can test abbreviations by using
them as arguments to the help command.

A blank line as input to GDB (typing just RET) means to repeat the previous
command. Certain commands (for example, 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 list and x commands, when you repeat them with RET, construct new arguments
rather than repeating exactly as typed.  This permits easy scanning of source
or memory.

GDB can also use RET in another way: to partition lengthy output, in a way
similar to the common utility more (see Screen Size).  Since it is easy to
press one RET too many in this situation, GDB disables command repetition after
any command that generates this sort of display.

A line of input starting with # is a comment; it does nothing. This is useful
mainly in command files (see Command Files).


ΓòÉΓòÉΓòÉ 7.2. Command Completion ΓòÉΓòÉΓòÉ

GDB can fill in the rest of a word in a command for you, if there's 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 GDB commands, GDB subcommands,
and the names of symbols in your program.

Press the TAB key whenever you want GDB to fill out the rest of a word.  If
there's only one possibility, GDB will fill in the word, and wait for you to
finish the command (or press RET to enter it).  For example, if you type

(gdb) info bre TAB

GDB fills in the rest of the word `breakpoints', since that's the only info
subcommand beginning with `bre':

(gdb) info breakpoints

You can either press RET at this point, to run the info breakpoints command, or
backspace and enter something else, if `breakpoints' doesn't look like the
command you expected.  (If you were sure you wanted info breakpoints in the
first place, you might as well just type RET immediately after `info bre', to
exploit command abbreviations rather than command completion).

If there is more than one possibility for the next word when you press TAB, GDB
will sound a bell.  You can either supply more characters and try again, or
just press TAB a second time, and GDB 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 `make_', but when you type b make_TAB GDB just sounds
the bell.  Typing TAB again will display all the function names in your program
that begin with those characters, for example:

(gdb) b make_ TAB
GDB sounds bell; press 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
(GDBP__) b make_

After displaying the available possibilities, GDB copies your partial input (`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 M-? rather than pressing TAB twice. M-? means META ?.  You can type this
either by holding down a key designated as the META shift on your keyboard (if
there is one) while typing ?, or as ESC followed by ?.

Sometimes the string you need, while logically a ``word'', may contain
parentheses or other characters that GDB normally excludes from its notion of a
word.  To permit word completion to work in this situation, you may enclose
words in ' (single quote marks) in GDB commands.

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 name that takes an int parameter, name(int), or the
version that takes a float parameter, name(float).  To use the word-completion
facilities in this situation, type a single quote ' at the beginning of the
function name.  This alerts GDB that it may need to consider more information
than usual when you press TAB or M-? to request word completion:

(gdb) b 'bubble( M-?
bubble(double,double)    bubble(int,int)
(gdb) b 'bubble(

In some cases, GDB can tell that completing a name will require quotes.  When
this happens, GDB will insert the quote for you (while completing as much as it
can) if you do not type the quote in the first place:

(gdb) b bub TAB
GDB alters your input line to the following, and rings a bell:
(gdb) b 'bubble(

In general, GDB 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.


ΓòÉΓòÉΓòÉ 7.3. Getting Help ΓòÉΓòÉΓòÉ

You can always ask GDB itself for information on its commands, using the
command help.

help
h
          You can use help (abbreviated h) with no arguments to display a short
          list of named classes of commands:

                    (gdb) 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.
                    (gdb)

help 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 status:

                    (gdb) help status
                    Status inquiries.

                    List of commands:

                    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.
                    (gdb)

help command
          With a command name as help argument, GDB will display a short
          paragraph on how to use that command.

In addition to help, you can use the GDB commands info and show to inquire
about the state of your program, or the state of GDB itself.  Each command
supports many topics of inquiry; this manual introduces each of them in the
appropriate context.  The listings under info and under show in the Index point
to all the sub-commands.  See Index.

info
          This command (abbreviated i) is for describing the state of your
          program; for example, it can list the arguments given to your program
          (info args), the registers currently in use (info registers), or the
          breakpoints you have set (info breakpoints). You can get a complete
          list of the info sub-commands with help info.

show
          In contrast, show is for describing the state of GDB itself. You can
          change most of the things you can show, by using the related command
          set; for example, you can control what number system is used for
          displays with set radix, or simply inquire which is currently in use
          with show radix.

          To display all the settable parameters and their current values, you
          can use show with no arguments; you may also use info set.  Both
          commands produce the same display.

Here are three miscellaneous show subcommands, all of which are exceptional in
lacking corresponding set commands:

show version
          Show what version of GDB is running.  You should include this
          information in GDB bug-reports.  If multiple versions of GDB are in
          use at your site, you may occasionally want to make sure what version
          of GDB you are running; as GDB evolves, new commands are introduced,
          and old ones may wither away.  The version number is also announced
          when you start GDB with no arguments.

show copying
          Display information about permission for copying GDB.

show warranty
          Display the GNU ``NO WARRANTY'' statement.


ΓòÉΓòÉΓòÉ 8. Running Programs Under GDB ΓòÉΓòÉΓòÉ

To debug a program, you must run it under GDB.


ΓòÉΓòÉΓòÉ 8.1. Compiling for Debugging ΓòÉΓòÉΓòÉ

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 `-g' option when you run the
compiler.

Many C compilers are unable to handle the `-g' and `-O' options together.
Using those compilers, you cannot generate optimized executables containing
debugging information.

gcc, the GNU C compiler, supports `-g' with or without `-O', making it possible
to debug optimized code.  We recommend that you always use `-g' whenever you
compile a program. You may think your program is correct, but there is no sense
in pushing your luck.

When you debug a program compiled with `-g -O', remember that the optimizer is
rearranging your code; the debugger will show you what's really there.  Don't
be too surprised when the execution path doesn't exactly match your source
file!  An extreme example: if you define a variable, but never use it, GDB will
never see that variable---because the compiler optimizes it out of existence.

Some things do not work as well with `-g -O' as with just `-g', particularly on
machines with instruction scheduling.  If in doubt, recompile with `-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 `-gg' for
debugging information.  GDB no longer supports this format; if your GNU C
compiler has this option, do not use it.


ΓòÉΓòÉΓòÉ 8.2. Starting your Program ΓòÉΓòÉΓòÉ

run
r
          Use the run command to start your program under GDB.  You must first
          specify the program name (except on VxWorks) with an argument to GDB
          (see Getting In and Out of GDB), or by using the file or exec-file
          command ( see Commands to Specify Files).

If you are running your program in an execution environment that supports
processes, run creates an inferior process and makes that process run your
program.  (In environments without processes, run jumps to the start of your
program.)

The execution of a program is affected by certain information it receives from
its superior.  GDB provides ways to specify this information, which you must do
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:

The arguments.
          Specify the arguments to give your program as the arguments of the
          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 SHELL environment variable. See Your Program_s Arguments.

The environment.
          Your program normally inherits its environment from GDB, but you can
          use the GDB commands set environment and unset environment to change
          parts of the environment that will be given to your program.  See
          Your Program_s Environment.

The working directory.
          Your program inherits its working directory from GDB.  You can set
          GDB's working directory with the cd command in GDB. See Your
          Program_s Working Directory.

The standard input and output.
          Your program normally uses the same device for standard input and
          standard output as GDB is using.  You can redirect input and output
          in the run command line, or you can use the tty command to set a
          different device for your program. See Your Program_s Input and
          Output.

          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, GDB is likely to wind up debugging the
          wrong program.

When you issue the run command, your program begins to execute immediately.
See Stopping and Continuing, for discussion of how to arrange for your program
to stop.  Once your program has stopped, you may calls functions in your
program, using the print or call commands.  See Examining Data.

If the modification time of your symbol file has changed since the last time
GDB read its symbols, GDB will discard its symbol table and re-read it.  When
it does this, GDB tries to retain your current breakpoints.


ΓòÉΓòÉΓòÉ 8.3. Your Program's Arguments ΓòÉΓòÉΓòÉ

The arguments to your program can be specified by the arguments of the run
command.  They are passed to a shell, which expands wildcard characters and
performs redirection of I/O, and thence to your program. GDB uses the shell
indicated by your environment variable SHELL if it exists; otherwise, GDB uses
/bin/sh.

run with no arguments uses the same arguments used by the previous run, or
those set by the set args command.

set args
          Specify the arguments to be used the next time your program is run.
          If set args has no arguments, run will execute your program with no
          arguments.  Once you have run your program with arguments, using set
          args before the next run is the only way to run it again without
          arguments.

show args
          Show the arguments to give your program when it is started.


ΓòÉΓòÉΓòÉ 8.4. Your Program's Environment ΓòÉΓòÉΓòÉ

The 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 GDB
over again.

path directory
          Add directory to the front of the PATH environment variable (the
          search path for executables), for both GDB and your program. You may
          specify several directory names, separated by `:' or whitespace.  If
          directory is already in the path, it is moved to the front, so it
          will be searched sooner.

          You can use the string `$cwd' to refer to whatever is the current
          working directory at the time GDB searches the path.  If you use `.'
          instead, it refers to the directory where you executed the path
          command.  GDB fills in the current path where needed in the directory
          argument, before adding it to the search path.

show paths
          Display the list of search paths for executables (the PATH
          environment variable).

show environment [varname]
          Print the value of environment variable varname to be given to your
          program when it starts.  If you do not supply varname, print the
          names and values of all environment variables to be given to your
          program.  You can abbreviate environment as env.

set environment varname [=] value
          Sets environment variable varname to value.  The value changes for
          your program only, not for GDB itself.  value may be any string; the
          values of environment variables are just strings, and any
          interpretation is supplied by your program itself.  The value
          parameter is optional; if it is eliminated, the variable is set to a
          null value.

          For example, this command:

                    set env USER = foo

          tells a Unix program, when subsequently run, that its user is named
          `foo'.  (The spaces around `=' are used for clarity here; they are
          not actually required.)

unset environment varname
          Remove variable varname from the environment to be passed to your
          program.  This is different from `set env varname ='; unset
          environment removes the variable from the environment, rather than
          assigning it an empty value.


ΓòÉΓòÉΓòÉ 8.5. Your Program's Working Directory ΓòÉΓòÉΓòÉ

Each time you start your program with run, it inherits its working directory
from the current working directory of GDB.  GDB's working directory is
initially whatever it inherited from its parent process (typically the shell),
but you can specify a new working directory in GDB with the cd command.

The GDB working directory also serves as a default for the commands that
specify files for GDB to operate on. See Commands to Specify Files.

cd directory
          Set GDB's working directory to directory.

pwd
          Print GDB's working directory.


ΓòÉΓòÉΓòÉ 8.6. Your Program's Input and Output ΓòÉΓòÉΓòÉ

By default, the program you run under GDB does input and output to the same
terminal that GDB uses.  GDB 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.

info terminal
          Displays GDB's recorded information about the terminal modes your
          program is using.

You can redirect your program's input and/or output using shell redirection
with the run command.  For example,

run > outfile

starts your program, diverting its output to the file `outfile'.

Another way to specify where your program should do input and output is with
the tty command.  This command accepts a file name as argument, and causes this
file to be the default for future run commands.  It also resets the controlling
terminal for the child process, for future run commands.  For example,

tty /dev/ttyb

directs that processes started with subsequent run commands default to do input
and output on the terminal `/dev/ttyb' and have that as their controlling
terminal.

An explicit redirection in run overrides the tty command's effect on the
input/output device, but not its effect on the controlling terminal.

When you use the tty command or redirect input in the run command, only the
input for your program is affected.  The input for GDB still comes from your
terminal.


ΓòÉΓòÉΓòÉ 8.7. Debugging an Already-Running Process ΓòÉΓòÉΓòÉ

attach process-id
          This command attaches to a running process---one that was started
          outside GDB. (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 ps utility, or with the
          `jobs -l' shell command.

          attach will not repeat if you press RET a second time after executing
          the command.

To use attach, you must be debugging in an environment which supports
processes.  You must also have permission to send the process a signal, and it
must have the same effective user ID as the GDB process.

When using attach, you should first use the file command to specify the program
running in the process and load its symbol table. See Commands to Specify
Files.

The first thing GDB does after arranging to debug the specified process is to
stop it.  You can examine and modify an attached process with all the GDB
commands that are ordinarily available when you start processes with 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 continue command
after attaching GDB to the process.

detach
          When you have finished debugging the attached process, you can use
          the detach command to release it from GDB's control.  Detaching the
          process continues its execution.  After the detach command, that
          process and GDB become completely independent once more, and you are
          ready to attach another process or start one with run. detach will
          not repeat if you press RET again after executing the command.

If you exit GDB or use the 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 set confirm command (see Optional Warnings and Messages).


ΓòÉΓòÉΓòÉ 8.8. Killing the Child Process ΓòÉΓòÉΓòÉ

kill
          Kill the child process in which your program is running under GDB.

This command is useful if you wish to debug a core dump instead of a running
process.  GDB ignores any core dump file while your program is running.

On some operating systems, a program cannot be executed outside GDB while you
have breakpoints set on it inside GDB.  You can use the kill command in this
situation to permit running your program outside the debugger.

The 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 run, GDB
will notice that the file has changed, and will re-read the symbol table (while
trying to preserve your current breakpoint settings).


ΓòÉΓòÉΓòÉ 8.9. Additional Process Information ΓòÉΓòÉΓòÉ

Some operating systems provide a facility called `/proc' that can be used to
examine the image of a running process using file-system subroutines.  If GDB
is configured for an operating system with this facility, the command info proc
is available to report on several kinds of information about the process
running your program.

info proc
          Summarize available information about the process.

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.

info proc times
          Starting time, user CPU time, and system CPU time for your program
          and its children.

info proc id
          Report on the process ID's related to your program: its own process
          id, the id of its parent, the process group id, and the session id.

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.

info proc all
          Show all the above information about the process.


ΓòÉΓòÉΓòÉ 9. Stopping and Continuing ΓòÉΓòÉΓòÉ

The principal purpose of using a debugger is 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 GDB, your program may stop for any of several reasons, such as a signal,
a breakpoint, or reaching a new line after a GDB command such as step.  You may
then examine and change variables, set new breakpoints or remove old ones, and
then continue execution.  Usually, the messages shown by GDB provide ample
explanation of the status of your program---but you can also explicitly request
this information at any time.

info program
          Display information about the status of your program: whether it is
          running or not, what process it is, and why it stopped.


ΓòÉΓòÉΓòÉ 9.1. Breakpoints, Watchpoints, and Exceptions ΓòÉΓòÉΓòÉ

A 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
break command and its variants (see Setting Breakpoints), to specify the place
where your program should stop by line number, function name or exact address
in the program. In languages with exception handling (such as GNU C++), you can
also set breakpoints where an exception is raised ( see Breakpoints and
Exceptions).

A 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 (
see 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.

GDB 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 enabled or
disabled; if disabled, it has no effect on your program until you enable it
again.


ΓòÉΓòÉΓòÉ 9.1.1. Setting Breakpoints ΓòÉΓòÉΓòÉ

Breakpoints are set with the break command (abbreviated b).  The debugger
convenience variable `$bpnum' records the number of the beakpoint you've set
most recently; see Convenience Variables, for a discussion of what you can do
with convenience variables.

You have several ways to say where the breakpoint should go.

break function
          Set a breakpoint at entry to function function. When using source
          languages that permit overloading of symbols, such as C++, function
          may refer to more than one possible place to break. See Breakpoint
          Menus, for a discussion of that situation.

break +offset
break -offset
          Set a breakpoint some number of lines forward or back from the
          position at which execution stopped in the currently selected frame.

break linenum
          Set a breakpoint at line 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.

break filename:linenum
          Set a breakpoint at line linenum in source file filename.

break filename:function
          Set a breakpoint at entry to function function found in file
          filename.  Specifying a file name as well as a function name is
          superfluous except when multiple files contain similarly named
          functions.

break *address
          Set a breakpoint at address address.  You can use this to set
          breakpoints in parts of your program which do not have debugging
          information or source files.

break
          When called without any arguments, break sets a breakpoint at the
          next instruction to be executed in the selected stack frame (see
          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 finish command in the
          frame inside the selected frame---except that finish does not leave
          an active breakpoint.  If you use break without an argument in the
          innermost frame, GDB will stop the next time it reaches the current
          location; this may be useful inside loops.

          GDB 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.

break ... if cond
          Set a breakpoint with condition cond; evaluate the expression cond
          each time the breakpoint is reached, and stop only if the value is
          nonzero---that is, if cond evaluates as true. `...' stands for one of
          the possible arguments described above (or no argument) specifying
          where to break. See Break Conditions, for more information on
          breakpoint conditions.

tbreak args
          Set a breakpoint enabled only for one stop.  args are the same as for
          the 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.  See Disabling Breakpoints.

rbreak regex
          Set breakpoints on all functions matching the regular expression
          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 break
          command.  They can be deleted, disabled, made conditional, etc., in
          the standard ways.

          When debugging C++ programs, rbreak is useful for setting breakpoints
          on overloaded functions that are not members of any special classes.

info breakpoints [n]
info break [n]
info watchpoints [n]
          Print a table of all breakpoints and watchpoints set and not deleted,
          with the following columns for each breakpoint:

   Breakpoint Numbers

   Type
             Breakpoint or watchpoint.

   Disposition
             Whether the breakpoint is marked to be disabled or deleted when
             hit.

   Enabled or Disabled
             Enabled breakpoints are marked with `y'.  `n' marks breakpoints
             that are not enabled.

   Address
             Where the breakpoint is in your program, as a memory address

   What
             Where the breakpoint is in the source for your program, as a file
             and line number.

          Breakpoint commands, if any, are listed after the line for the
          corresponding breakpoint.

          info break with a breakpoint number n as argument lists only that
          breakpoint.  The convenience variable $_ and the default
          examining-address for the x command are set to the address of the
          last breakpoint listed (see Examining Memory).

GDB 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 (see Break Conditions).

GDB itself sometimes sets breakpoints in your program for special purposes,
such as proper handling of longjmp (in C programs). These internal breakpoints
are assigned negative numbers, starting with -1; `info breakpoints' does not
display them.

You can see these breakpoints with the GDB maintenance command `maint info
breakpoints'.

maint info breakpoints
          Using the same format as `info breakpoints', display both the
          breakpoints you've set explicitly, and those GDB is using for
          internal purposes.  Internal breakpoints are shown with negative
          breakpoint numbers.  The type column identifies what kind of
          breakpoint is shown:

   breakpoint
             Normal, explicitly set breakpoint.

   watchpoint
             Normal, explicitly set watchpoint.

   longjmp
             Internal breakpoint, used to handle correctly stepping through
             longjmp calls.

   longjmp resume
             Internal breakpoint at the target of a longjmp.

   until
             Temporary internal breakpoint used by the GDB until command.

   finish
             Temporary internal breakpoint used by the GDB finish command.


ΓòÉΓòÉΓòÉ 9.1.2. Setting Watchpoints ΓòÉΓòÉΓòÉ

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 well be 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 GDB will use such
hardware if it is available.

watch expr
          Set a watchpoint for an expression.

info watchpoints
          This command prints a list of watchpoints and breakpoints; it is the
          same as info break.


ΓòÉΓòÉΓòÉ 9.1.3. Breakpoints and Exceptions ΓòÉΓòÉΓòÉ

Some languages, such as GNU C++, implement exception handling.  You can use GDB
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.

catch exceptions
          You can set breakpoints at active exception handlers by using the
          catch command.  exceptions is a list of names of exceptions to catch.

You can use info catch to list active exception handlers. See Information About
a Frame.

There are currently some limitations to exception handling in GDB. These will
be corrected in a future release.

o If you call a function interactively, GDB 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 GDB is listening for, or exits.

o You cannot raise an exception interactively.

o You cannot interactively install an exception handler.

Sometimes 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 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 __raise_exception which has the following ANSI C
interface:

    /* addr is where the exception identifier is stored.
       ID is the exception identifier.  */
    void __raise_exception (void **addr, void *id);

To make the debugger catch all exceptions before any stack unwinding takes
place, set a breakpoint on __raise_exception (see Breakpoints Watchpoints and
Exceptions).

With a conditional breakpoint (see Break Conditions) that depends on the value
of 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.


ΓòÉΓòÉΓòÉ 9.1.4. Deleting Breakpoints ΓòÉΓòÉΓòÉ

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
deleting the breakpoint.  A breakpoint that has been deleted no longer exists;
it is forgotten.

With the clear command you can delete breakpoints according to where they are
in your program.  With the 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.  GDB
automatically ignores breakpoints on the first instruction to be executed when
you continue execution without changing the execution address.

clear
          Delete any breakpoints at the next instruction to be executed in the
          selected stack frame (see Selecting a Frame).  When the innermost
          frame is selected, this is a good way to delete a breakpoint where
          your program just stopped.

clear function
clear filename:function
          Delete any breakpoints set at entry to the function function.

clear linenum
clear filename:linenum
          Delete any breakpoints set at or within the code of the specified
          line.

delete [breakpoints] [bnums...]
          Delete the breakpoints or watchpoints of the numbers specified as
          arguments.  If no argument is specified, delete all breakpoints (GDB
          asks confirmation, unless you have set confirm off).  You can
          abbreviate this command as d.


ΓòÉΓòÉΓòÉ 9.1.5. Disabling Breakpoints ΓòÉΓòÉΓòÉ

Rather than deleting a breakpoint or watchpoint, you might prefer to disable
it.  This makes the breakpoint inoperative as if it had been deleted, but
remembers the information on the breakpoint so that you can enable it again
later.

You disable and enable breakpoints and watchpoints with the enable and disable
commands, optionally specifying one or more breakpoint numbers as arguments.
Use info break or 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:

o Enabled.  The breakpoint will stop your program.  A breakpoint set with the
  break command starts out in this state.

o Disabled.  The breakpoint has no effect on your program.

o Enabled once.  The breakpoint will stop your program, but when it does so it
  will become disabled.  A breakpoint set with the tbreak command starts out in
  this state.

o Enabled for deletion.  The breakpoint will stop your program, but immediately
  after it does so it will be deleted permanently.

You can use the following commands to enable or disable breakpoints and
watchpoints:

disable [breakpoints] [bnums...]
          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 disable as dis.

enable [breakpoints] [bnums...]
          Enable the specified breakpoints (or all defined breakpoints).  They
          become effective once again in stopping your program.

enable [breakpoints] once bnums...
          Enable the specified breakpoints temporarily.  Each will be disabled
          again the next time it stops your program.

enable [breakpoints] delete bnums...
          Enable the specified breakpoints to work once and then die.  Each of
          the breakpoints will be deleted the next time it stops your program.

Save for a breakpoint set with tbreak ( see 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 until can
set and delete a breakpoint of its own, but it will not change the state of
your other breakpoints; see Continuing and Stepping.)


ΓòÉΓòÉΓòÉ 9.1.6. Break Conditions ΓòÉΓòÉΓòÉ

The simplest sort of breakpoint breaks every time your program reaches a
specified place.  You can also specify a condition for a breakpoint.  A
condition is just a Boolean expression in your programming language (see
Expressions).  A breakpoint with a condition evaluates the expression each time
your program reaches it, and your program stops only if the condition is 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 assert, you should set the condition `! 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, GDB 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 (see
Breakpoint Command Lists).

Break conditions can be specified when a breakpoint is set, by using `if' in
the arguments to the break command. See Setting Breakpoints.  They can also be
changed at any time with the condition command.  The watch command does not
recognize the if keyword; condition is the only way to impose a further
condition on a watchpoint.

condition bnum expression
          Specify expression as the break condition for breakpoint or
          watchpoint number bnum.  From now on, this breakpoint will stop your
          program only if the value of expression is true (nonzero, in C).
          When you use condition, GDB checks expression immediately for
          syntactic correctness, and to determine whether symbols in it have
          referents in the context of your breakpoint. GDB does not actually
          evaluate expression at the time the condition command is given,
          however.  See Expressions.

condition bnum
          Remove the condition from breakpoint number bnum.  It becomes an
          ordinary unconditional 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 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 n, the breakpoint will not stop the next n times it is reached.

ignore bnum count
          Set the ignore count of breakpoint number bnum to count. The next
          count times the breakpoint is reached, your program's execution will
          not stop; other than to decrement the ignore count, GDB takes no
          action.

          To make the breakpoint stop the next time it is reached, specify a
          count of zero.

continue count
c count
fg count
          Continue execution of your program, setting the ignore count of the
          breakpoint where your program stopped to count minus one. Thus, your
          program will not stop at this breakpoint until the count'th time it
          is reached.

          An argument to this command is meaningful only when your program
          stopped due to a breakpoint.  At other times, the argument to
          continue is ignored.

          The synonym fg is provided purely for convenience, and has exactly
          the same behavior as other forms of the command.

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
`$foo-- <= 0' using a debugger convenience variable that is decremented each
time. See Convenience Variables.


ΓòÉΓòÉΓòÉ 9.1.7. Breakpoint Command Lists ΓòÉΓòÉΓòÉ

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.

commands [bnum]
... command-list ...
end
          Specify a list of commands for breakpoint number bnum.  The commands
          themselves appear on the following lines.  Type a line containing
          just end to terminate the commands.

          To remove all commands from a breakpoint, type commands and follow it
          immediately with end; that is, give no commands.

          With no bnum argument, commands refers to the last breakpoint or
          watchpoint set (not to the breakpoint most recently encountered).

Pressing RET as a means of repeating the last GDB command is disabled within a
command-list.

You can use breakpoint commands to start your program up again.  Simply use the
continue command, or step, or any other command that resumes execution.
Subsequent commands in the command list are ignored.

If the first command specified is 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 the remaining commands too print
nothing, you will see no sign that the breakpoint was reached at all.  silent
is meaningful only at the beginning of a breakpoint command list.

The commands echo and output that allow you to print precisely controlled
output are often useful in silent breakpoints. See Commands for Controlled
Output.

For example, here is how you could use breakpoint commands to print the value
of x at entry to foo whenever x is positive.

break foo if x>0
commands
silent
echo x is\040
output x
echo \n
cont
end

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 continue command so that your program does not stop, and start
with the silent command so that no output is produced.  Here is an example:

break 403
commands
silent
set x = y + 4
cont
end

One deficiency in the operation of automatically continuing breakpoints under
Unix appears when your program uses raw mode for the terminal. GDB switches
back to its own terminal modes (not raw) before executing commands, and then
must switch back to raw mode when your program is continued.  This causes any
pending terminal input to be lost.

Under Unix, you can get around this problem by writing actions into the
breakpoint condition rather than in commands.  For example

condition 5  (x = y + 4), 0

specifies a condition expression (see Expressions) that will change x as
needed, then always have the value zero so your program will not stop.  No
input is lost here, because GDB evaluates break conditions without changing the
terminal modes.  When you want to have nontrivial conditions for performing the
side effects, the operators `&&', `||' and `?...:' may be useful.


ΓòÉΓòÉΓòÉ 9.1.8. Breakpoint Menus ΓòÉΓòÉΓòÉ

Some programming languages (notably C++) permit a single function name to be
defined several times, for application in different contexts. This is called
overloading.  When a function name is overloaded, `break function' is not
enough to tell GDB where you want a breakpoint.  If you realize this will be a
problem, you can use something like `break function(types)' to specify which
particular version of the function you want.  Otherwise, GDB offers you a menu
of numbered choices for different possible breakpoints, and waits for your
selection with the prompt `>'.  The first two options are always `[0] cancel'
and `[1] all'.  Typing 1 sets a breakpoint at each definition of function, and
typing 0 aborts the break command without setting any new breakpoints.

For example, the following session excerpt shows an attempt to set a breakpoint
at the overloaded symbol String::after. We choose three particular definitions
of that function name:

(gdb) 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.
(gdb)


ΓòÉΓòÉΓòÉ 9.1.9. ``Cannot Insert Breakpoints'' ΓòÉΓòÉΓòÉ

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 GDB to stop the other process.

When this happens, you have three ways to proceed:

 1. Remove or disable the breakpoints, then continue.

 2. Suspend GDB, and copy the file containing your program to a new name.
    Resume GDB and use the exec-file command to specify that GDB should run
    your program under that name.  Then start your program again.

 3. Relink your program so that the text segment is nonsharable, using the
    linker option `-N'.  The operating system limitation may not apply to
    nonsharable executables.


ΓòÉΓòÉΓòÉ 9.2. Continuing and Stepping ΓòÉΓòÉΓòÉ

Continuing means resuming program execution until your program completes
normally.  In contrast, 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 a
breakpoint or to a signal.  (If due to a signal, you may want to use handle, or
use `signal 0' to resume execution. See Signals.)

continue [ignore-count]
          Resume program execution, at the address where your program last
          stopped; any breakpoints set at that address are bypassed.  The
          optional argument ignore-count allows you to specify a further number
          of times to ignore a breakpoint at this location; its effect is like
          that of ignore (see Break Conditions).

          To resume execution at a different place, you can use return (see
          Returning from a Function) to go back to the calling function; or
          jump ( see 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 (see Breakpoints
Watchpoints and Exceptions) 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.

step
          Continue running your program until control reaches a different
          source line, then stop it and return control to GDB.  This command is
          abbreviated s.

          Warning: If you use the step command while control is within a
          function that was compiled without debugging information, execution
          will proceed until control reaches another function.

step count
          Continue running as in step, but do so count times.  If a breakpoint
          is reached or a signal not related to stepping occurs before count
          steps, stepping stops right away.

next [count]
          Continue to the next source line in the current (innermost) stack
          frame. Similar to 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 next command was given.  This command is
          abbreviated n.

          An argument count is a repeat count, as for step.

          next within a function that lacks debugging information acts like
          step, but any function calls appearing within the code of the
          function are executed without stopping.

finish
          Continue running until just after function in the selected stack
          frame returns.  Print the returned value (if any).

          Contrast this with the return command ( see Returning from a
          Function).

until

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 next
          command, except that when 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, until will cause your program to continue
          execution until the loop is exited.  In contrast, a 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.

          until always stops your program if it attempts to exit the current
          stack frame.

          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 f
          (frame) command shows that execution is stopped at line 206; yet when
          we use until, we get to line 195:

                    (gdb) f
                    #0  main (argc=4, argv=0xf7fffae8) at m4.c:206
                    206                 expand_input();
                    (gdb) until
                    195             for ( ; argc > 0; NEXTARG) {

          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 for-loop is written
          before the body of the loop.  The 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.

          until with no argument works by means of single instruction stepping,
          and hence is slower than until with an argument.

until location

u location
          Continue running your program until either the specified location is
          reached, or the current stack frame returns.  location is any of the
          forms of argument acceptable to break ( see Setting Breakpoints).
          This form of the command uses breakpoints, and hence is quicker than
          until without an argument.

stepi
si
          Execute one machine instruction, then stop and return to the
          debugger.

          It is often useful to do `display/i $pc' when stepping by machine
          instructions.  This will cause the next instruction to be executed to
          be displayed automatically at each stop. See Automatic Display.

          An argument is a repeat count, as in step.

nexti
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 next.


ΓòÉΓòÉΓòÉ 9.3. Signals ΓòÉΓòÉΓòÉ

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 SIGINT is the signal a program gets when you type
an interrupt (often C-c); SIGSEGV is the signal a program gets from referencing
a place in memory far away from all the areas in use; SIGALRM occurs when the
alarm clock timer goes off (which happens only if your program has requested an
alarm).

Some signals, including SIGALRM, are a normal part of the functioning of your
program.  Others, such as SIGSEGV, indicate errors; these signals are fatal
(kill your program immediately) if the program has not specified in advance
some other way to handle the signal. 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.

GDB has the ability to detect any occurrence of a signal in your program.  You
can tell GDB in advance what to do for each kind of signal.

Normally, GDB is set up to ignore non-erroneous signals like 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 handle command.

info signals
          Print a table of all the kinds of signals and how GDB has been told
          to handle each one.  You can use this to see the signal numbers of
          all the defined types of signals.

handle signal keywords...
          Change the way GDB handles signal signal.  signal can be the number
          of a signal or its name (with or without the `SIG' at the beginning).
          The keywords say what change to make.

The keywords allowed by the handle command can be abbreviated. Their full names
are:

nostop
          GDB should not stop your program when this signal happens.  It may
          still print a message telling you that the signal has come in.

stop
          GDB should stop your program when this signal happens.  This implies
          the print keyword as well.

print
          GDB should print a message when this signal happens.

noprint
          GDB should not mention the occurrence of the signal at all.  This
          implies the nostop keyword as well.

pass
          GDB 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.

nopass
          GDB should not allow your program to see this signal.

When a signal has been set to stop your program, your program cannot see the
signal until you continue.  It will see the signal then, if pass is in effect
for the signal in question at that time.  In other words, after GDB reports a
signal, you can use the handle command with pass or nopass to control whether
that signal will be seen by your program when you later continue it.

You can also use the 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 `signal 0'. See Giving your
Program a Signal.


ΓòÉΓòÉΓòÉ 10. Examining the Stack ΓòÉΓòÉΓòÉ

When your program has stopped, the first thing you need to know is where it
stopped and how it got there.

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 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 call stack.

When your program stops, the GDB commands for examining the stack allow you to
see all of this information.

One of the stack frames is selected by GDB and many GDB commands refer
implicitly to the selected frame.  In particular, whenever you ask GDB for the
value of a variable in your program, the value is found in the selected frame.
There are special GDB commands to select whichever frame you are interested in.

When your program stops, GDB automatically selects the currently executing
frame and describes it briefly as the frame command does (see Information About
a Frame).


ΓòÉΓòÉΓòÉ 10.1. Stack Frames ΓòÉΓòÉΓòÉ

The call stack is divided up into contiguous pieces called stack frames, or
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.

When your program is started, the stack has only one frame, that of the
function main.  This is called the initial frame or the 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 innermost
frame.  This is the most recently created of all the stack frames that still
exist.

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 frame pointer register while execution is going on in that frame.

GDB 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 GDB to give
you a way of designating stack frames in GDB commands.

Some compilers allow functions to be compiled so that they operate without
stack frames.  (For example, the gcc option `-fomit-frame-pointer' will
generate functions without a frame.) This is occasionally done with heavily
used library functions to save the frame setup time.  GDB has limited
facilities for dealing with these function invocations.  If the innermost
function invocation has no stack frame, GDB 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, GDB has no provision for
frameless functions elsewhere in the stack.


ΓòÉΓòÉΓòÉ 10.2. Backtraces ΓòÉΓòÉΓòÉ

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.

backtrace
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 C-c.

backtrace n
bt n
          Similar, but print only the innermost n frames.

backtrace -n
bt -n
          Similar, but print only the outermost n frames.

The names where and info stack (abbreviated info s) are additional aliases for
backtrace.

Each line in the backtrace shows the frame number and the function name. The
program counter value is also shown---unless you use 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 `bt 3', so it
shows the innermost three frames.

#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...)

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
993 of builtin.c.


ΓòÉΓòÉΓòÉ 10.3. Selecting a Frame ΓòÉΓòÉΓòÉ

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.

frame n
f n
          Select frame number 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 main's
          frame.

frame addr
f addr
          Select the frame at address addr.  This is useful mainly if the
          chaining of stack frames has been damaged by a bug, making it
          impossible for GDB to assign numbers properly to all frames.  In
          addition, this can be useful when your program has multiple stacks
          and switches between them.

          On the SPARC architecture, frame needs two addresses to select an
          arbitrary frame: a frame pointer and a stack pointer.

up n
          Move n frames up the stack.  For positive numbers n, this advances
          toward the outermost frame, to higher frame numbers, to frames that
          have existed longer.  n defaults to one.

down n
          Move n frames down the stack.  For positive numbers n, this advances
          toward the innermost frame, to lower frame numbers, to frames that
          were created more recently.  n defaults to one.  You may abbreviate
          down as do.

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:

(gdb) up
#1  0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
    at env.c:10
10              read_input_file (argv[i]);

After such a printout, the list command with no arguments will print ten lines
centered on the point of execution in the frame. See Printing Source Lines.

up-silently n
down-silently n
          These two commands are variants of up and 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 GDB command
          scripts, where the output might be unnecessary and distracting.


ΓòÉΓòÉΓòÉ 10.4. Information About a Frame ΓòÉΓòÉΓòÉ

There are several other commands to print information about the selected stack
frame.

frame
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 f.  With an argument,
          this command is used to select a stack frame (see Selecting a Frame).

info frame
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.

info frame addr
info f addr
          Print a verbose description of the frame at address addr, without
          selecting that frame.  The selected frame remains unchanged by this
          command.

info args
          Print the arguments of the selected frame, each on a separate line.

info locals
          Print the local variables of the selected frame, each on a separate
          line.  These are all variables declared static or automatic within
          all program blocks that execution in this frame is currently inside
          of.

info catch
          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 up, down,
          or frame commands); then type info catch. See Breakpoints and
          Exceptions.


ΓòÉΓòÉΓòÉ 11. Examining Source Files ΓòÉΓòÉΓòÉ

GDB can print parts of your program's source, since the debugging information
recorded in your program tells GDB what source files were used to build it.
When your program stops, GDB spontaneously prints the line where it stopped.
Likewise, when you select a stack frame (see Selecting a Frame), GDB prints the
line where execution in that frame has stopped.  You can print other portions
of source files by explicit command.

If you use GDB through its GNU Emacs interface, you may prefer to use Emacs
facilities to view source; see Using GDB under GNU Emacs.


ΓòÉΓòÉΓòÉ 11.1. Printing Source Lines ΓòÉΓòÉΓòÉ

To print lines from a source file, use the list command (abbreviated l).  There
are several ways to specify what part of the file you want to print.

Here are the forms of the list command most commonly used:

list linenum
          Print lines centered around line number linenum in the current source
          file.

list function
          Print lines centered around the beginning of function function.

list
          Print more lines.  If the last lines printed were printed with a 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 ( see Examining the Stack), this prints
          lines centered around that line.

list -
          Print lines just before the lines last printed.

By default, GDB prints ten source lines with any of these forms of the list
command.  You can change this using set listsize:

set listsize count
          Make the list command display count source lines (unless the list
          argument explicitly specifies some other number).

show listsize
          Display the number of lines that list will currently display by
          default.

Repeating a list command with RET discards the argument, so it is equivalent to
typing just list.  This is more useful than listing the same lines again.  An
exception is made for an argument of `-'; that argument is preserved in
repetition so that each repetition moves up in the source file.

In general, the list command expects you to supply zero, one or two 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 list:

list linespec
          Print lines centered around the line specified by linespec.

list first,last
          Print lines from first to last.  Both arguments are linespecs.

list ,last
          Print lines ending with last.

list first,
          Print lines starting with first.

list +
          Print lines just after the lines last printed.

list -
          Print lines just before the lines last printed.

list
          As described in the preceding table.

Here are the ways of specifying a single source line---all the kinds of
linespec.

number
          Specifies line number of the current source file. When a list command
          has two linespecs, this refers to the same source file as the first
          linespec.

+offset
          Specifies the line offset lines after the last line printed. When
          used as the second linespec in a list command that has two, this
          specifies the line offset lines down from the first linespec.

-offset
          Specifies the line offset lines before the last line printed.

filename:number
          Specifies line number in the source file filename.

function
          Specifies the line of the open-brace that begins the body of the
          function function.

filename:function
          Specifies the line of the open-brace that begins the body of the
          function function in the file filename.  You only need the file name
          with a function name to avoid ambiguity when there are identically
          named functions in different source files.

*address
          Specifies the line containing the program address address. address
          may be any expression.


ΓòÉΓòÉΓòÉ 11.2. Searching Source Files ΓòÉΓòÉΓòÉ

There are two commands for searching through the current source file for a
regular expression.

forward-search regexp
search regexp
          The command `forward-search regexp' checks each line, starting with
          the one following the last line listed, for a match for regexp.  It
          lists the line that is found.  You can use synonym `search regexp' or
          abbreviate the command name as fo.

reverse-search regexp
          The command `reverse-search regexp' checks each line, starting with
          the one before the last line listed and going backward, for a match
          for regexp.  It lists the line that is found.  You can abbreviate
          this command as rev.


ΓòÉΓòÉΓòÉ 11.3. Specifying Source Directories ΓòÉΓòÉΓòÉ

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.
GDB has a list of directories to search for source files; this is called the
source path.  Each time GDB 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 not used for
this purpose.  Neither is the current working directory, unless it happens to
be in the source path.

If GDB cannot find a source file in the source path, and the object program
records a directory, GDB tries that directory too.  If the source path is
empty, and there is no record of the compilation directory, GDB will, as a last
resort, look in the current directory.

Whenever you reset or rearrange the source path, GDB will clear out any
information it has cached about where source files are found, where each line
is in the file, etc.

When you start GDB, its source path is empty. To add other directories, use the
directory command.

directory dirname ...
          Add directory dirname to the front of the source path.  Several
          directory names may be given to this command, separated by `:' or
          whitespace.  You may specify a directory that is already in the
          source path; this moves it forward, so it will be searched sooner.

          You can use the string `$cdir' to refer to the compilation directory
          (if one is recorded), and `$cwd' to refer to the current working
          directory.  `$cwd' is not the same as `.'---the former tracks the
          current working directory as it changes during your GDB session,
          while the latter is immediately expanded to the current directory at
          the time you add an entry to the source path.

directory
          Reset the source path to empty again.  This requires confirmation.

show directories
          Print the source path: show which directories it contains.

If your source path is cluttered with directories that are no longer of
interest, GDB may sometimes cause confusion by finding the wrong versions of
source.  You can correct the situation as follows:

 1. Use directory with no argument to reset the source path to empty.

 2. Use directory with suitable arguments to reinstall the directories you want
    in the source path.  You can add all the directories in one command.


ΓòÉΓòÉΓòÉ 11.4. Source and Machine Code ΓòÉΓòÉΓòÉ

You can use the command info line to map source lines to program addresses (and
viceversa), and the command disassemble to display a range of addresses as
machine instructions.

info line linespec
          Print the starting and ending addresses of the compiled code for
          source line linespec.  You can specify source lines in any of the
          ways understood by the list command ( see Printing Source Lines).

For example, we can use info line to discover the location of the object code
for the first line of function m4_changequote:

(gdb) info line m4_changecom
Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.

We can also inquire (using *addr as the form for linespec) what source line
covers a particular address:

(gdb) info line *0x63ff
Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.

After info line, the default address for the x command is changed to the
starting address of the line, so that `x/i' is sufficient to begin examining
the machine code ( see Examining Memory).  Also, this address is saved as the
value of the convenience variable $_ ( see Convenience Variables).

disassemble
          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.

We can use disassemble to inspect the object code range shown in the last info
line example (the example shows SPARC machine instructions):

(gdb) 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.

For example, here is the beginning of the output for the disassembly of a
function fact:

(gdb) 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
 .
 .
 .


ΓòÉΓòÉΓòÉ 12. Examining Data ΓòÉΓòÉΓòÉ

The usual way to examine data in your program is with the print command
(abbreviated p), or its synonym inspect. It evaluates and prints the value of
an expression of the language your program is written in ( see Using GDB with
Different Languages).

print exp
print /f exp
          exp is an expression (in the source language).  By default the value
          of exp is printed in a format appropriate to its data type; you can
          choose a different format by specifying `/f', where f is a letter
          specifying the format; see Output formats.

print
print /f
          If you omit exp, GDB displays the last value again (from the value
          history; see Value History).  This allows you to conveniently inspect
          the same value in an alternative format.

A more low-level way of examining data is with the x command. It examines data
in memory at a specified address and prints it in a specified format.  See
Examining Memory.

If you are interested in information about types, or about how the fields of a
struct or class are declared, use the ptype exp command rather than print. See
Examining the Symbol Table.


ΓòÉΓòÉΓòÉ 12.1. Expressions ΓòÉΓòÉΓòÉ

print and many other GDB commands accept an expression and compute its value.
Any kind of constant, variable or operator defined by the programming language
you are using is legal in an expression in GDB.  This includes conditional
expressions, function calls, casts and string constants.  It unfortunately does
not include symbols defined by preprocessor #define commands.

Because C is so widespread, most of the expressions shown in examples in this
manual are in C. See Using GDB with Different Languages, for information on how
to use expressions in other languages.

In this section, we discuss operators that you can use in GDB 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.

GDB supports these operators in addition to those of programming languages:

@
          `@' is a binary operator for treating parts of memory as arrays. See
          Artificial Arrays, for more information.

::
          `::' allows you to specify a variable in terms of the file or
          function where it is defined.  See Program Variables.

{type} addr
          Refers to an object of type type stored at address addr in memory.
          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 addr.


ΓòÉΓòÉΓòÉ 12.2. Program Variables ΓòÉΓòÉΓòÉ

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 (see
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

foo (a)
     int a;
{
  bar (a);
  {
    int b = test ();
    bar (b);
  }
}

the variable a is usable whenever your program is executing within the function
foo, but the variable b is visible only while your program is executing inside
the block in which b is declared.

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:

file::variable
function::variable

Here file or function is the name of the context for the static variable.  In
the case of file names, you can use quotes to make sure GDB parses the file
name as a single word---for example, to print a global value of x defined in
`f2.c':

(gdb) p 'f2.c'::x

This use of `::' is very rarely in conflict with the very similar use of the
same notation in C++.  GDB also supports use of the C++ scope resolution
operator in GDB expressions.

Warning: Occasionally, a local variable may appear to have the wrong value at
certain points in a function---just after entry to the function, and just
before exit.  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 function 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.


ΓòÉΓòÉΓòÉ 12.3. Artificial Arrays ΓòÉΓòÉΓòÉ

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.

This can be done by constructing an artificial array with the binary operator
`@'.  The left operand of `@' 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

int *array = (int *) malloc (len * sizeof (int));

you can print the contents of array with

p *array@len

The left operand of `@' must reside in memory.  Array values made with `@' 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 (see 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 ( see Convenience Variables) as a counter in an expression that prints
the first interesting value, and then repeat that expression via RET.  For
instance, suppose you have an array dtab of pointers to structures, and you are
interested in the values of a field fv in each structure.  Here is an example
of what you might type:

set $i = 0
p dtab[$i++]->fv
RET
RET
...


ΓòÉΓòÉΓòÉ 12.4. Output formats ΓòÉΓòÉΓòÉ

By default, GDB 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 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 print command with a
slash and a format letter.  The format letters supported are:

x
          Regard the bits of the value as an integer, and print the integer in
          hexadecimal.

d
          Print as integer in signed decimal.

u
          Print as integer in unsigned decimal.

o
          Print as integer in octal.

t
          Print as integer in binary.  The letter `t' stands for ``two''.

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:

                    (gdb) p/a 0x54320
                    $3 = 0x54320 <_initialize_vx+396>

c
          Regard as an integer and print it as a character constant.

f
          Regard the bits of the value as a floating point number and print
          using typical floating point syntax.

For example, to print the program counter in hex (see Registers), type

p/x $pc

Note that no space is required before the slash; this is because command names
in GDB cannot contain a slash.

To reprint the last value in the value history with a different format, you can
use the print command with just a format and no expression.  For example, `p/x'
reprints the last value in hex.


ΓòÉΓòÉΓòÉ 12.5. Examining Memory ΓòÉΓòÉΓòÉ

You can use the command x (for ``examine'') to examine memory in any of several
formats, independently of your program's data types.

x/nfu addr
x addr
x
          Use the command x to examine memory.

n, f, and u are all optional parameters that specify how much memory to display
and how to format it; addr is an expression giving the address where you want
to start displaying memory. If you use defaults for nfu, you need not type the
slash `/'. Several commands set convenient defaults for addr.

n, the repeat count
          The repeat count is a decimal integer; the default is 1.  It
          specifies how much memory (counting by units u) to display.

f, the display format
          The display format is one of the formats used by print, or `s'
          (null-terminated string) or `i' (machine instruction). The default is
          `x' (hexadecimal) initially, or the format from the last time you
          used either x or print.

u, the unit size
          The unit size is any of

   b
             Bytes.

   h
             Halfwords (two bytes).

   w
             Words (four bytes).  This is the initial default.

   g
             Giant words (eight bytes).

          Each time you specify a unit size with x, that size becomes the
          default unit the next time you use x.  (For the `s' and `i' formats,
          the unit size is ignored and is normally not written.)

addr, starting display address
          addr is the address where you want GDB 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. See
          Expressions, for more information on expressions.  The default for
          addr is usually just after the last address examined---but several
          other commands also set the default address: info breakpoints (to the
          address of the last breakpoint listed), info line (to the starting
          address of a line), and print (if you use it to display a value from
          memory).

For example, `x/3uh 0x54320' is a request to display three halfwords (h) of
memory, formatted as unsigned decimal integers (`u'), starting at address
0x54320.  `x/4xw $sp' prints the four words (`w') of memory above the stack
pointer (here, `$sp'; see Registers) in hexadecimal (`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 `4xw'
and `4wx' mean exactly the same thing. (However, the count n must come first;
`wx4' will not work.)

Even though the unit size u is ignored for the formats `s' and `i', you might
still want to use a count n; for example, `3i' specifies that you want to see
three machine instructions, including any operands.  The command disassemble
gives an alternative way of inspecting machine instructions; see Machine Code.

All the defaults for the arguments to x are designed to make it easy to
continue scanning memory with minimal specifications each time you use x.  For
example, after you have inspected three machine instructions with `x/3i addr',
you can inspect the next seven with just `x/7'.  If you use RET to repeat the x
command, the repeat count n is used again; the other arguments default as for
successive uses of x.

The addresses and contents printed by the 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, GDB makes these values available for subsequent use in expressions as
values of the convenience variables $_ and $__.  After an x command, the last
address examined is available for use in expressions in the convenience
variable $_.  The contents of that address, as examined, are available in the
convenience variable $__.

If the 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.


ΓòÉΓòÉΓòÉ 12.6. Automatic Display ΓòÉΓòÉΓòÉ

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 automatic display list so
that GDB 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:

2: foo = 38
3: bar[5] = (struct hack *) 0x3804

showing item numbers, expressions and their current values.  As with displays
you request manually using x or print, you can specify the output format you
prefer; in fact, display decides whether to use print or x depending on how
elaborate your format specification is---it uses x if you specify a unit size,
or one of the two formats (`i' and `s') that are only supported by x; otherwise
it uses print.

display exp
          Add the expression exp to the list of expressions to display each
          time your program stops.  See Expressions.

          display will not repeat if you press RET again after using it.

display/fmt exp
          For fmt specifying only a display format and not a size or count, add
          the expression exp to the auto-display list but arranges to display
          it each time in the specified format fmt. See Output formats.

display/fmt addr
          For fmt `i' or `s', or including a unit-size or a number of units,
          add the expression addr as a memory address to be examined each time
          your program stops.  Examining means in effect doing `x/fmt addr'.
          See Examining Memory.

For example, `display/i $pc' can be helpful, to see the machine instruction
about to be executed each time execution stops (`$pc' is a common name for the
program counter; see Registers).

undisplay dnums...
delete display dnums...
          Remove item numbers dnums from the list of expressions to display.

          undisplay will not repeat if you press RET after using it. (Otherwise
          you would just get the error `No display number ...'.)

disable display dnums...
          Disable the display of item numbers dnums.  A disabled display item
          is not printed automatically, but is not forgotten.  It may be
          enabled again later.

enable display dnums...
          Enable display of item numbers dnums.  It becomes effective once
          again in auto display of its expression, until you specify otherwise.

display
          Display the current values of the expressions on the list, just as is
          done when your program stops.

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.

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 display last_char while inside a
function with an argument 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 last_char---display is disabled.  The
next time your program stops where last_char is meaningful, you can enable the
display expression once again.


ΓòÉΓòÉΓòÉ 12.7. Print Settings ΓòÉΓòÉΓòÉ

GDB provides the following ways to control how arrays, structures, and symbols
are printed.

These settings are useful for debugging programs in any language:

set print address

set print address on
          GDB 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 set print address on:

                    (gdb) f
                    #0  set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
                        at input.c:530
                    530         if (lquote != def_lquote)

set print address off
          Do not print addresses when displaying their contents.  For example,
          this is the same stack frame displayed with set print address off:

                    (gdb) set print addr off
                    (gdb) f
                    #0  set_quotes (lq="<<", rq=">>") at input.c:530
                    530         if (lquote != def_lquote)

show print address
          Show whether or not addresses are to be printed.

set print array
set print array on
          GDB will pretty print arrays.  This format is more convenient to
          read, but uses more space.  The default is off.

set print array off.
          Return to compressed format for arrays.

show print array
          Show whether compressed or pretty format is selected for displaying
          arrays.

set print elements number-of-elements
          If GDB is printing a large array, it will stop printing after it has
          printed the number of elements set by the set print elements command.
          This limit also applies to the display of strings.

show print elements
          Display the number of elements of a large array that GDB will print
          before losing patience.

set print pretty on
          Cause GDB to print structures in an indented format with one member
          per line, like this:

                    $1 = {
                      next = 0x0,
                      flags = {
                        sweet = 1,
                        sour = 1
                      },
                      meat = 0x54 "Pork"
                    }

set print pretty off
          Cause GDB to print structures in a compact format, like this:

                    $1 = {next = 0x0, flags = {sweet = 1, sour = 1}, \
                    meat = 0x54 "Pork"}

          This is the default format.

show print pretty
          Show which format GDB will use to print structures.

set print sevenbit-strings on
          Print using only seven-bit characters; if this option is set, GDB
          will display any eight-bit characters (in strings or character
          values) using the notation \nnn.  For example, M-a is displayed as
          \341.

set print sevenbit-strings off
          Print using either seven-bit or eight-bit characters, as required.
          This is the default.

show print sevenbit-strings
          Show whether or not GDB will print only seven-bit characters.

set print union on
          Tell GDB to print unions which are contained in structures.  This is
          the default setting.

set print union off
          Tell GDB not to print unions which are contained in structures.

show print union
          Ask GDB whether or not it will print unions which are contained in
          structures.

          For example, given the declarations

                    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}};

          with set print union on in effect `p foo' would print

                    $1 = {it = Tree, form = {tree = Acorn, bug = Cocoon}}

          and with set print union off in effect it would print

                    $1 = {it = Tree, form = {...}}

These settings are of interest when debugging C++ programs:

set print demangle
set print demangle on
          Print C++ names in their source form rather than in the mangled form
          in which they are passed to the assembler and linker for type-safe
          linkage. The default is on.

show print demangle
          Show whether C++ names will be printed in mangled or demangled form.

set print asm-demangle
set print asm-demangle on
          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.

show print asm-demangle
          Show whether C++ names in assembly listings will be printed in
          mangled or demangled form.

set print object
set print object on
          When displaying a pointer to an object, identify the actual (derived)
          type of the object rather than the declared type, using the virtual
          function table.

set print object off
          Display only the declared type of objects, without reference to the
          virtual function table.  This is the default setting.

show print object
          Show whether actual, or declared, object types will be displayed.

set print vtbl
set print vtbl on
          Pretty print C++ virtual function tables.  The default is off.

set print vtbl off
          Do not pretty print C++ virtual function tables.

show print vtbl
          Show whether C++ virtual function tables are pretty printed, or not.


ΓòÉΓòÉΓòÉ 12.8. Value History ΓòÉΓòÉΓòÉ

Values printed by the print command are saved in GDB's 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 file or 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.

The values printed are given history numbers for you to refer to them by.
These are successive integers starting with one.  print shows you the history
number assigned to a value by printing `$num = ' before the value; here num is
the history number.

To refer to any previous value, use `$' followed by the value's history number.
The way print labels its output is designed to remind you of this.  Just $
refers to the most recent value in the history, and $$ refers to the value
before that. $$n refers to the nth value from the end; $$2 is the value just
prior to $$, $$1 is equivalent to $$, and $$0 is equivalent to $.

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

p *$

If you have a chain of structures where the component next points to the next
one, you can print the contents of the next one with this:

p *$.next

You can print successive links in the chain by repeating this command---which
you can do by just typing RET.

Note that the history records values, not expressions.  If the value of x is 4
and you type these commands:

print x
set x=5

then the value recorded in the value history by the print command remains 4
even though the value of x has changed.

show values
          Print the last ten values in the value history, with their item
          numbers. This is like `p@ $$9' repeated ten times, except that show
          values does not change the history.

show values n
          Print ten history values centered on history item number n.

show values +
          Print ten history values just after the values last printed.  If no
          more values are available, produces no display.

Pressing RET to repeat show values n has exactly the same effect as `show
values +'.


ΓòÉΓòÉΓòÉ 12.9. Convenience Variables ΓòÉΓòÉΓòÉ

GDB provides convenience variables that you can use within GDB to hold on to a
value and refer to it later.  These variables exist entirely within GDB; 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 `$'.  Any name preceded by `$' can be
used for a convenience variable, unless it is one of the predefined
machine-specific register names (see Registers). (Value history references, in
contrast, are numbers preceded by `$'.  See 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.  Example:

set $foo = *object_ptr

would save in $foo the value contained in the object pointed to by object_ptr.

Using a convenience variable for the first time creates it; but its value is
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.

show convenience
          Print a list of convenience variables used so far, and their values.
          Abbreviated show con.

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:

set $i = 0
print bar[$i++]->contents
... repeat that command by typing RET.

Some convenience variables are created automatically by GDB and given values
likely to be useful.

$_
          The variable $_ is automatically set by the x command to the last
          address examined (see Examining Memory).  Other commands which
          provide a default address for x to examine also set $_ to that
          address; these commands include info line and info breakpoint.  The
          type of $_ is void * except when set by the x command, in which case
          it is a pointer to the type of $__.

$__
          The variable $__ is automatically set by the 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.


ΓòÉΓòÉΓòÉ 12.10. Registers ΓòÉΓòÉΓòÉ

You can refer to machine register contents, in expressions, as variables with
names starting with `$'.  The names of registers are different for each
machine; use info registers to see the names used on your machine.

info registers
          Print the names and values of all registers except floating-point
          registers (in the selected stack frame).

info all-registers
          Print the names and values of all registers, including floating-point
          registers.

info registers regname ...
          Print the relativized value of each specified register regname.
          regname may be any register name valid on the machine you are using,
          with or without the initial `$'.

GDB 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 $pc and $sp are used for the
program counter register and the stack pointer.  $fp is used for a register
that contains a pointer to the current stack frame, and $ps is used for a
register that contains the processor status.  For example, you could print the
program counter in hex with

p/x $pc

or print the instruction to be executed next with

x/i $pc

or add four to the stack pointer  (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
$sp is not allowed when other stack frames are selected.  To pop entire frames
off the stack, regardless of machine architecture, use return; see Returning
from a Function.)  with

set $sp += 4

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 info registers command shows the canonical names.
For example, on the SPARC, info registers displays the processor status
register as $psr but you can also refer to it as $ps.

GDB 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 print it as a
floating point value with `print/f $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, GDB normally works with the virtual format
only (the format that makes sense for your program), but the info registers
command prints the data in both formats.

Normally, register values are relative to the selected stack frame (see
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 `frame 0').

However, GDB must deduce where registers are saved, from the machine code
generated by your compiler.  If some registers are not saved, or if GDB is
unable to locate the saved registers, the selected stack frame will make no
difference.

set rstack_high_address address
          On AMD 29000 family processors, registers are saved in a separate
          ``register stack''.  There is no way for GDB to determine the extent
          of this stack.  Normally, GDB just assumes that the stack is ``large
          enough''.  This may result in GDB referencing memory locations that
          don't exist.  If necessary, you can get around this problem by
          specifying the ending address of the register stack with the set
          rstack_high_address command.  The argument should be an address,
          which you will probably want to precede with `0x' to specify in
          hexadecimal.

show rstack_high_address
          Display the current limit of the register stack, on AMD 29000 family
          processors.


ΓòÉΓòÉΓòÉ 12.11. Floating Point Hardware ΓòÉΓòÉΓòÉ

Depending on the host machine architecture, GDB may be able to give you more
information about the status of the floating point hardware.

info float
          If available, provides hardware-dependent information about the
          floating point unit.  The exact contents and layout vary depending on
          the floating point chip.


ΓòÉΓòÉΓòÉ 13. Using GDB with Different Languages ΓòÉΓòÉΓòÉ

Although programming languages generally have common aspects, they are rarely
expressed in the same manner.  For instance, in ANSI C, dereferencing a pointer
p is accomplished by *p, but in Modula-2, it is accomplished by p^.  Values can
also be represented (and displayed) differently.  Hex numbers in C are written
like `0x1ae', while in Modula-2 they appear as `1AEH'.

Language-specific information is built into GDB for some languages, allowing
you to express operations like the above in your program's native language, and
allowing GDB 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 working language, can be selected manually, or GDB can set it
automatically.


ΓòÉΓòÉΓòÉ 13.1. Switching between source languages ΓòÉΓòÉΓòÉ

There are two ways to control the working language---either have GDB set it
automatically, or select it manually yourself.  You can use the set language
command for either purpose.  On startup, GDB defaults to setting the language
automatically.


ΓòÉΓòÉΓòÉ 13.1.1. Setting the working language ΓòÉΓòÉΓòÉ

To set the language, issue the command `set language lang', where lang is the
name of a language: c or modula-2. For a list of the supported languages, type
`set language'.

Setting the language manually prevents GDB 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 GDB was parsing Modula-2, a
command such as:

print a = b + c

might not have the effect you intended.  In C, this means to add b and c and
place the result in a.  The result printed would be the value of a.  In
Modula-2, this means to compare a to the result of b+c, yielding a BOOLEAN
value.

If you allow GDB to set the language automatically, then you can count on
expressions evaluating the same way in your debugging session and in your
program.


ΓòÉΓòÉΓòÉ 13.1.2. Having GDB infer the source language ΓòÉΓòÉΓòÉ

To have GDB set the working language automatically, use `set language local' or
`set language auto'.  GDB then infers the language that a program was written
in by looking at the name of its source files, and examining their extensions:

`*.mod'
          Modula-2 source file

`*.c'
          C source file

`*.C'
`*.cc'
          C++ source file

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), GDB
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
GDB 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 `set language auto' in this case frees you from having to set
the working language manually.


ΓòÉΓòÉΓòÉ 13.2. Displaying the language ΓòÉΓòÉΓòÉ

The following commands will help you find out which language is the working
language, and also what language source files were written in.

show language
          Display the current working language.  This is the language you can
          use with commands such as print to build and compute expressions that
          may involve variables in your program.

info frame
          Among the other information listed here ( see 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.

info source
          Among the other information listed here ( see Examining the Symbol
          Table) is the source language of this source file.


ΓòÉΓòÉΓòÉ 13.3. Type and range Checking ΓòÉΓòÉΓòÉ

Warning: In this release, the GDB commands for type and range checking are
included, but they do not yet have any effect.  This section documents the
intended facilities.

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.

GDB can check for conditions like the above if you wish. Although GDB will not
check the statements in your program, it can check expressions entered directly
into GDB for evaluation via the print command, for example.  As with the
working language, GDB can also decide whether or not to check automatically
based on your program's source language.  See Supported Languages, for the
default settings of supported languages.


ΓòÉΓòÉΓòÉ 13.3.1. An overview of type checking ΓòÉΓòÉΓòÉ

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,

1 + 2 => 3
but
error--> 1 + 2.3

The second example fails because the CARDINAL 1 is not type-compatible with the
REAL 2.3.

For expressions you use in GDB commands, you can tell the GDB 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, GDB 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 GDB from evaluating an expression.  For instance, GDB does not know how
to add an int and a 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.  See Supported
Languages, for further details on specific languages.

GDB provides some additional commands for controlling the type checker:

set check type auto
          Set type checking on or off based on the current working language.
          See Supported Languages, for the default settings for each language.

set check type on
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's default.  If any type mismatches occur in
          evaluating an expression while typechecking is on, GDB prints a
          message and aborts evaluation of the expression.

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, GDB cannot add numbers
          and structures.

show type
          Show the current setting of the type checker, and whether or not GDB
          is setting it automatically.


ΓòÉΓòÉΓòÉ 13.3.2. An overview of Range Checking ΓòÉΓòÉΓòÉ

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 GDB commands, you can tell GDB to ignore range
errors; to always treat them as errors and abandon the expression; or to issue
warnings when a range error occurs but evaluate the expression anyway.

A range error can result from numerical overflow, from exceeding an array index
bound, or when you type in 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 m is the largest integer value, and
s is the smallest, then

m + 1 => s

This, too, is specific to individual languages, and in some cases specific to
individual compilers or machines. See Supported Languages, for further details
on specific languages.

GDB provides some additional commands for controlling the range checker:

set check range auto
          Set range checking on or off based on the current working language.
          See Supported Languages, for the default settings for each language.

set check range on
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's default.  If a range error occurs, then a
          message is printed and evaluation of the expression is aborted.

set check range warn
          Output messages when the GDB 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).

show range
          Show the current setting of the range checker, and whether or not it
          is being set automatically by GDB.


ΓòÉΓòÉΓòÉ 13.4. Supported Languages ΓòÉΓòÉΓòÉ

GDB 4 supports C, C++, and Modula-2.  Some GDB features may be used in
expressions regardless of the language you use: the GDB @ and :: operators, and
the `{type}addr' construct (see Expressions) can be used with the constructs of
any of the supported languages.

The following sections detail to what degree each of these source languages is
supported by GDB.  These sections are not meant to be language tutorials or
references, but serve only as a reference guide to what the GDB 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.


ΓòÉΓòÉΓòÉ 13.4.1. C and C++ ΓòÉΓòÉΓòÉ

Since C and C++ are so closely related, many features of GDB apply to both
languages.  Whenever this is the case, we discuss both languages together.

The C++ debugging facilities are jointly implemented by the GNU C++ compiler
and GDB.  Therefore, to debug your C++ code effectively, you must compile your
C++ programs with the GNU C++ compiler, g++.


ΓòÉΓòÉΓòÉ 13.4.1.1. C and C++ Operators ΓòÉΓòÉΓòÉ

Operators must be defined on values of specific types.  For instance, + is
defined on numbers, but not on structures.  Operators are often defined on
groups of types.

For the purposes of C and C++, the following definitions hold:

o Integral types include int with any of its storage-class specifiers, char,
  and enums.

o Floating-point types include float and double.

o Pointer types include all types defined as (type *).

o Scalar types include all of the above.

The following operators are supported.  They are listed here in order of
increasing precedence:

,
          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.

=
          Assignment.  The value of an assignment expression is the value
          assigned.  Defined on scalar types.

op=
          Used in an expression of the form a op= b, and translated to a = a op
          b. op= and = have the same precendence. op is any one of the
          operators |, ^, &, <<, >>, +, -, *, /, %.

?:
          The ternary operator.  a ? b : c can be thought of as:  if a then b
          else c.  a should be of an integral type.

||
          Logical or.  Defined on integral types.

&&
          Logical and.  Defined on integral types.

|
          Bitwise or.  Defined on integral types.

^
          Bitwise exclusive-or.  Defined on integral types.

&
          Bitwise and.  Defined on integral types.

==, !=
          Equality and inequality.  Defined on scalar types.  The value of
          these expressions is 0 for false and non-zero for true.

<, >, <=, >=
          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.

<<, >>
          left shift, and right shift.  Defined on integral types.

@
          The GDB ``artificial array'' operator (see Expressions).

+, -
          Addition and subtraction.  Defined on integral types, floating-point
          types and pointer types.

*, /, %
          Multiplication, division, and modulus.  Multiplication and division
          are defined on integral and floating-point types.  Modulus is defined
          on integral types.

++, --
          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.

*
          Pointer dereferencing.  Defined on pointer types.  Same precedence as
          ++.

&
          Address operator.  Defined on variables.  Same precedence as ++.

          For debugging C++, GDB implements a use of `&' beyond what's allowed
          in the C++ language itself: you can use `&(&ref)' (or, if you prefer,
          simply `&&ref' to examine the address where a C++ reference variable
          (declared with `&ref') is stored.

-
          Negative.  Defined on integral and floating-point types.  Same
          precedence as ++.

!
          Logical negation.  Defined on integral types.  Same precedence as ++.

~
          Bitwise complement operator.  Defined on integral types.  Same
          precedence as ++.

., ->
          Structure member, and pointer-to-structure member.  For convenience,
          GDB regards the two as equivalent, choosing whether to dereference a
          pointer based on the stored type information. Defined on structs and
          unions.

[]
          Array indexing.  a[i] is defined as *(a+i).  Same precedence as ->.

()
          Function parameter list.  Same precedence as ->.

::
          C++ scope resolution operator.  Defined on struct, union, and class
          types.

::
          The GDB scope operator (see Expressions). Same precedence as ::,
          above.


ΓòÉΓòÉΓòÉ 13.4.1.2. C and C++ Constants ΓòÉΓòÉΓòÉ

GDB allows you to express the constants of C and C++ in the following ways:

o Integer constants are a sequence of digits.  Octal constants are specified by
  a leading `0' (ie. zero), and hexadecimal constants by a leading `0x' or
  `0X'.  Constants may also end with a letter `l', specifying that the constant
  should be treated as a long value.

o 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: `e[[+]|-]nnn', where nnn is another
  sequence of digits.  The `+' is optional for positive exponents.

o Enumerated constants consist of enumerated identifiers, or their integral
  equivalents.

o Character constants are a single character surrounded by single quotes ('),
  or a number---the ordinal value of the corresponding character (usually its
  ASCII value).  Within quotes, the single character may be represented by a
  letter or by escape sequences, which are of the form `\nnn', where nnn is the
  octal representation of the character's ordinal value; or of the form `\x',
  where `x' is a predefined special character---for example, `\n' for newline.

o String constants are a sequence of character constants surrounded by double
  quotes (").

o Pointer constants are an integral value.


ΓòÉΓòÉΓòÉ 13.4.1.3. C++ Expressions ΓòÉΓòÉΓòÉ

GDB's expression handling has a number of extensions to interpret a significant
subset of C++ expressions.

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 ecoff, RS/6000
xcoff, or Sun elf with stabs extensions to the symbol table, these facilities
are all available. Where the object code format is standard coff, on the other
hand, most of the C++ support in GDB will not work, nor can it. For the
standard SVr4 debugging format, dwarf in elf, the standard is still evolving,
so the C++ support in GDB is still fragile; when this debugging format
stabilizes, however, C++ support will also be available on systems that use it.

 1. Member function calls are allowed; you can use expressions like

        count = aml->GetOriginal(x, y)

 2. While a member function is active (in the selected stack frame), your
    expressions have the same namespace available as the member function; that
    is, GDB allows implicit references to the class instance pointer this
    following the same rules as C++.

 3. You can call overloaded functions; GDB 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. GDB will not perform
    conversions requiring constructors or user-defined type operators.

 4. GDB 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 GDB 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 address
    of a reference variable is always shown, unless you have specified `set
    print address off'.

 5. GDB supports the C++ name resolution operator ::---your expressions can use
    it just as expressions in your program do.  Since one scope may be defined
    in another, you can use :: repeatedly if necessary, for example in an
    expression like `scope1::scope2::name'.  GDB also allows resolving name
    scope by reference to source files, in both C and C++ debugging (see
    Program Variables).


ΓòÉΓòÉΓòÉ 13.4.1.4. C and C++ Defaults ΓòÉΓòÉΓòÉ

If you allow GDB to set type and range checking automatically, they both
default to off whenever the working language changes to C or C++.  This happens
regardless of whether you, or GDB, selected the working language.

If you allow GDB 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 `.c', `.C', or `.cc'. See Having GDB infer the source language, for
further details.


ΓòÉΓòÉΓòÉ 13.4.1.5. C and C++ Type and Range Checks ΓòÉΓòÉΓòÉ

Warning: in this release, GDB does not yet perform type or range checking.

By default, when GDB parses C or C++ expressions, type checking is not used.
However, if you turn type checking on, GDB will consider two variables type
equivalent if:

o The two variables are structured and have the same structure, union, or
  enumerated tag.

o Two two variables have the same type name, or types that have been declared
  equivalent through typedef.

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.


ΓòÉΓòÉΓòÉ 13.4.1.6. GDB and C ΓòÉΓòÉΓòÉ

The set print union and show print union commands apply to the union type.
When set to `on', any union that is inside a struct or class will also be
printed. Otherwise, it will appear as `{...}'.

The @ operator aids in the debugging of dynamic arrays, formed with pointers
and a memory allocation function.  (see Expressions)


ΓòÉΓòÉΓòÉ 13.4.1.7. GDB Features for C++ ΓòÉΓòÉΓòÉ

Some GDB commands are particularly useful with C++, and some are designed
specifically for use with C++.  Here is a summary:

breakpoint menus
          When you want a breakpoint in a function whose name is overloaded,
          GDB's breakpoint menus help you specify which function definition you
          want.  See Breakpoint Menus.

rbreak regex
          Setting breakpoints using regular expressions is helpful for setting
          breakpoints on overloaded functions that are not members of any
          special classes. See Setting Breakpoints.

catch exceptions
info catch
          Debug C++ exception handling using these commands. See Breakpoints
          and Exceptions.

ptype typename
          Print inheritance relationships as well as other information for type
          typename. See Examining the Symbol Table.

set print demangle
show print demangle
set print asm-demangle
show print asm-demangle
          Control whether C++ symbols display in their source form, both when
          displaying code as C++ source and when displaying disassemblies. See
          Print Settings.

set print object
show print object
          Choose whether to print derived (actual) or declared types of
          objects. See Print Settings.

set print vtbl
show print vtbl
          Control the format for printing virtual function tables. See Print
          Settings.

Overloaded symbol names
          You can specify a particular definition of an overloaded symbol,
          using the same notation that's used to declare such symbols in C++:
          type symbol(types) rather than just symbol.  You can also use GDB's
          command-line word completion facilities to list the available
          choices, or to finish the type list for you. See Command Completion,
          for details on how to do this.


ΓòÉΓòÉΓòÉ 13.4.2. Modula-2 ΓòÉΓòÉΓòÉ

The extensions made to GDB to support Modula-2 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 GDB reads in the
executable's symbol table.


ΓòÉΓòÉΓòÉ 13.4.2.1. Operators ΓòÉΓòÉΓòÉ

Operators must be defined on values of specific types.  For instance, + 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:

o Integral types consist of INTEGER, CARDINAL, and their subranges.

o Character types consist of CHAR and its subranges.

o Floating-point types consist of REAL.

o Pointer types consist of anything declared as POINTER TO type.

o Scalar types consist of all of the above.

o Set types consist of SETs and BITSETs.

o Boolean types consist of BOOLEAN.

The following operators are supported, and appear in order of increasing
precedence:

,
          Function argument or array index separator.

:=
          Assignment.  The value of var := value is value.

<, >
          Less than, greater than on integral, floating-point, or enumerated
          types.

<=, >=
          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 <.

=, <>, #
          Equality and two ways of expressing inequality, valid on scalar
          types. Same precedence as <.  In GDB scripts, only <> is available
          for inequality, since # conflicts with the script comment character.

IN
          Set membership.  Defined on set types and the types of their members.
          Same precedence as <.

OR
          Boolean disjunction.  Defined on boolean types.

AND, &
          Boolean conjuction.  Defined on boolean types.

@
          The GDB ``artificial array'' operator (see Expressions).

+, -
          Addition and subtraction on integral and floating-point types, or
          union and difference on set types.

*
          Multiplication on integral and floating-point types, or set
          intersection on set types.

/
          Division on floating-point types, or symmetric set difference on set
          types.  Same precedence as *.

DIV, MOD
          Integer division and remainder.  Defined on integral types.  Same
          precedence as *.

-
          Negative. Defined on INTEGERs and REALs.

^
          Pointer dereferencing.  Defined on pointer types.

NOT
          Boolean negation.  Defined on boolean types.  Same precedence as ^.

.
          RECORD field selector.  Defined on RECORDs.  Same precedence as ^.

[]
          Array indexing.  Defined on ARRAYs.  Same precedence as ^.

()
          Procedure argument list.  Defined on PROCEDUREs.  Same precedence as
          ^.

::, .
          GDB and Modula-2 scope operators.

Warning: Sets and their operations are not yet supported, so GDB will treat the
use of the operator IN, or the use of operators +, -, *, /, =, , <>, #, <=, and
>= on sets as an error.


ΓòÉΓòÉΓòÉ 13.4.2.2. Built-in Functions and Procedures ΓòÉΓòÉΓòÉ

Modula-2 also makes available several built-in procedures and functions. In
describing these, the following metavariables are used:

a
          represents an ARRAY variable.

c
          represents a CHAR constant or variable.

i
          represents a variable or constant of integral type.

m
          represents an identifier that belongs to a set.  Generally used in
          the same function with the metavariable s.  The type of s should be
          SET OF mtype (where mtype is the type of m.

n
          represents a variable or constant of integral or floating-point type.

r
          represents a variable or constant of floating-point type.

t
          represents a type.

v
          represents a variable.

x
          represents a variable or constant of one of many types.  See the
          explanation of the function for details.

All Modula-2 built-in procedures also return a result, described below.

ABS(n)
          Returns the absolute value of n.

CAP(c)
          If c is a lower case letter, it returns its upper case equivalent,
          otherwise it returns its argument

CHR(i)
          Returns the character whose ordinal value is i.

DEC(v)
          Decrements the value in the variable v.  Returns the new value.

DEC(v,i)
          Decrements the value in the variable v by i.  Returns the new value.

EXCL(m,s)
          Removes the element m from the set s.  Returns the new set.

FLOAT(i)
          Returns the floating point equivalent of the integer i.

HIGH(a)
          Returns the index of the last member of a.

INC(v)
          Increments the value in the variable v.  Returns the new value.

INC(v,i)
          Increments the value in the variable v by i.  Returns the new value.

INCL(m,s)
          Adds the element m to the set s if it is not already there.  Returns
          the new set.

MAX(t)
          Returns the maximum value of the type t.

MIN(t)
          Returns the minimum value of the type t.

ODD(i)
          Returns boolean TRUE if i is an odd number.

ORD(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).  x must be of an ordered type, which include
          integral, character and enumerated types.

SIZE(x)
          Returns the size of its argument.  x can be a variable or a type.

TRUNC(r)
          Returns the integral part of r.

VAL(t,i)
          Returns the member of the type t whose ordinal value is i.

Warning:  Sets and their operations are not yet supported, so GDB will treat
the use of procedures INCL and EXCL as an error.


ΓòÉΓòÉΓòÉ 13.4.2.3. Constants ΓòÉΓòÉΓòÉ

GDB allows you to express the constants of Modula-2 in the following ways:

o 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 `H', and
  octal integers by a trailing `B'.

o 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 `E[+|-]nnn', where `[+|-]nnn' is the desired
  exponent.  All of the digits of the floating point constant must be valid
  decimal (base 10) digits.

o Character constants consist of a single character enclosed by a pair of like
  quotes, either single (') or double (").  They may also be expressed by their
  ordinal value (their ASCII value, usually) followed by a `C'.

o String constants consist of a sequence of characters enclosed by a pair of
  like quotes, either single (') or double ("). Escape sequences in the style
  of C are also allowed. See C and C++ Constants, for a brief explanation of
  escape sequences.

o Enumerated constants consist of an enumerated identifier.

o Boolean constants consist of the identifiers TRUE and FALSE.

o Pointer constants consist of integral values only.

o Set constants are not yet supported.


ΓòÉΓòÉΓòÉ 13.4.2.4. Modula-2 Defaults ΓòÉΓòÉΓòÉ

If type and range checking are set automatically by GDB, they both default to
on whenever the working language changes to Modula-2.  This happens regardless
of whether you, or GDB, selected the working language.

If you allow GDB to set the language automatically, then entering code compiled
from a file whose name ends with `.mod' will set the working language to
Modula-2. See Having GDB set the language automatically, for further details.


ΓòÉΓòÉΓòÉ 13.4.2.5. Deviations from Standard Modula-2 ΓòÉΓòÉΓòÉ

A few changes have been made to make Modula-2 programs easier to debug. This is
done primarily via loosening its type strictness:

o 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.)

o C escape sequences can be used in strings and characters to represent
  non-printable characters.  GDB will print out strings with these escape
  sequences embedded.  Single non-printable characters are printed using the
  `CHR(nnn)' format.

o The assignment operator (:=) returns the value of its right-hand argument.

o All built-in procedures both modify and return their argument.


ΓòÉΓòÉΓòÉ 13.4.2.6. Modula-2 Type and Range Checks ΓòÉΓòÉΓòÉ

Warning: in this release, GDB does not yet perform type or range checking.

GDB considers two Modula-2 variables type equivalent if:

o They are of types that have been declared equivalent via a TYPE t1 = t2
  statement

o 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.)

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.


ΓòÉΓòÉΓòÉ 13.4.2.7. The scope operators :: and . ΓòÉΓòÉΓòÉ

There are a few subtle differences between the Modula-2 scope operator

(.) and the GDB scope operator (::).  The two have similar syntax:


module . id
scope :: id

where scope is the name of a module or a procedure, module the name of a
module, and id is any declared identifier within your program, except another
module.

Using the :: operator makes GDB search the scope specified by scope for the
identifier id.  If it is not found in the specified scope, then GDB will search
all scopes enclosing the one specified by scope.

Using the . operator makes GDB search the current scope for the identifier
specified by id that was imported from the definition module specified by
module.  With this operator, it is an error if the identifier id was not
imported from definition module module, or if id is not an identifier in
module.


ΓòÉΓòÉΓòÉ 13.4.2.8. GDB and Modula-2 ΓòÉΓòÉΓòÉ

Some GDB commands have little use when debugging Modula-2 programs. Five
subcommands of set print and show print apply specifically to C and C++:
`vtbl', `demangle', `asm-demangle', `object', and `union'.  The first four
apply to C++, and the last to C's union type, which has no direct analogue in
Modula-2.

The @ operator (see Expressions), while available while using any language, is
not useful with Modula-2.  Its intent is to aid the debugging of 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
`{type}adrexp' is still useful.  (see Expressions)

In GDB scripts, the Modula-2 inequality operator # is interpreted as the
beginning of a comment.  Use <> instead.


ΓòÉΓòÉΓòÉ 14. Examining the Symbol Table ΓòÉΓòÉΓòÉ

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.  GDB finds it in your program's symbol table, in the file
indicated when you started GDB (see Choosing Files), or by one of the
file-management commands (see Commands to Specify Files).

Occasionally, you may need to refer to symbols that contain unusual characters,
which GDB ordinarily treats as word delimiters.  The most frequent case is in
referring to static variables in other source files (see Program Variables).
File names are recorded in object files as debugging symbols, but GDB would
ordinarily parse a typical file name, like `foo.c', as the three words `foo'
`.' `c'.  To allow GDB to recognize `foo.c' as a single symbol, enclose it in
single quotes; for example,

p 'foo.c'::x

looks up the value of x in the scope of the file `foo.c'.

info address symbol
          Describe where the data for 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 `print &symbol', which does not work at all
          for a register variables, and for a stack local variable prints the
          exact address of the current instantiation of the variable.

whatis exp
          Print the data type of expression exp.  exp is not actually
          evaluated, and any side-effecting operations (such as assignments or
          function calls) inside it do not take place. See Expressions.

whatis
          Print the data type of $, the last value in the value history.

ptype typename
          Print a description of data type typename.  typename may be the name
          of a type, or for C code it may have the form `struct struct-tag',
          `union union-tag' or `enum enum-tag'.

ptype exp
ptype
          Print a description of the type of expression exp.  ptype differs
          from whatis by printing a detailed description, instead of just the
          name of the type.  For example, if your program declares a variable
          as

                    struct complex {double real; double imag;} v;

          compare the output of the two commands:

                    (gdb) whatis v
                    type = struct complex
                    (gdb) ptype v
                    type = struct complex {
                        double real;
                        double imag;
                    }

          As with whatis, using ptype without an argument refers to the type of
          $, the last value in the value history.

info types regexp
info types
          Print a brief description of all types whose name matches 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, `i type
          value' gives information on all types in your program whose name
          includes the string value, but `i type ^value$' gives information
          only on types whose complete name is value.

          This command differs from ptype in two ways: first, like whatis, it
          does not print a detailed description; second, it lists all source
          files where a type is defined.

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.

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.

info functions
          Print the names and data types of all defined functions.

info functions regexp
          Print the names and data types of all defined functions whose names
          contain a match for regular expression regexp. Thus, `info fun step'
          finds all functions whose names include step; `info fun ^step' finds
          those whose names start with step.

info variables
          Print the names and data types of all variables that are declared
          outside of functions (i.e., excluding local variables).

info variables regexp
          Print the names and data types of all variables (except for local
          variables) whose names contain a match for regular expression regexp.

maint print symbols filename
maint print psymbols filename
maint print msymbols filename
          Write a dump of debugging symbol data into the file filename. These
          commands are used to debug the GDB symbol-reading code.  Only symbols
          with debugging data are included.  If you use `maint print symbols',
          GDB includes all the symbols for which it has already collected full
          details: that is, filename reflects symbols for only those files
          whose symbols GDB has read.  You can use the command info sources to
          find out which files these are.  If you use `maint print psymbols'
          instead, the dump shows information about symbols that GDB only knows
          partially---that is, symbols defined in files that GDB has skimmed,
          but not yet read completely.  Finally, `maint print msymbols' dumps
          just the minimal symbol information required for each object file
          from which GDB has read some symbols. The description of symbol-file
          explains how GDB reads symbols; both info source and symbol-file are
          described in Commands to Specify Files.


ΓòÉΓòÉΓòÉ 15. Altering Execution ΓòÉΓòÉΓòÉ

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 GDB features for altering execution of the program.

For example, you can store new values into variables or memory locations, give
your program a signal, restart it at a different address, or even return
prematurely from a function to its caller.


ΓòÉΓòÉΓòÉ 15.1. Assignment to Variables ΓòÉΓòÉΓòÉ

To alter the value of a variable, evaluate an assignment expression. See
Expressions.  For example,

print x=4

stores the value 4 into the variable x, and then prints the value of the
assignment expression (which is 4). See Using GDB with Different Languages, for
more information on operators in supported languages.

If you are not interested in seeing the value of the assignment, use the set
command instead of the print command.  set is really the same as print except
that the expression's value is not printed and is not put in the value history
(see Value History).  The expression is evaluated only for its effects.

If the beginning of the argument string of the set command appears identical to
a set subcommand, use the set variable command instead of just set.  This
command is identical to set except for its lack of subcommands.  For example, a
program might well have a variable width---which leads to an error if we try to
set a new value with just `set width=13', as we might if set width did not
happen to be a GDB command:

(gdb) whatis width
type = double
(gdb) p width
$4 = 13
(gdb) set width=47
Invalid syntax in expression.

The invalid expression, of course, is `=47'.  What we can do in order to
actually set our program's variable width is

(gdb) set var width=47

GDB allows more implicit conversions in assignments than C; you can freely
store an integer value into a pointer variable or vice versa, and any structure
can be converted to any other structure that is the same length or shorter.

To store values into arbitrary places in memory, use the `{...}' construct to
generate a value of specified type at a specified address (see Expressions).
For example, {int}0x83040 refers to memory location 0x83040 as an integer
(which implies a certain size and representation in memory), and

set {int}0x83040 = 4

stores the value 4 into that memory location.


ΓòÉΓòÉΓòÉ 15.2. Continuing at a Different Address ΓòÉΓòÉΓòÉ

Ordinarily, when you continue your program, you do so at the place where it
stopped, with the continue command.  You can instead continue at an address of
your own choosing, with the following commands:

jump linespec
          Resume execution at line linespec.  Execution will stop immediately
          if there is a breakpoint there. See Printing Source Lines, for a
          description of the different forms of linespec.

          The 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 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 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.

jump *address
          Resume execution at the instruction at address address.

You can get much the same effect as the jump command by storing a new value
into the register $pc.  The difference is that this does not start your program
running; it only changes the address where it will run when it is continued.
For example,

set $pc = 0x485

causes the next continue command or stepping command to execute at address
0x485, rather than at the address where your program stopped. See Continuing
and Stepping.

The most common occasion to use the 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.


ΓòÉΓòÉΓòÉ 15.3. Giving your program a Signal ΓòÉΓòÉΓòÉ

signal signalnum
          Resume execution where your program stopped, but give it immediately
          the signal number signalnum.

          Alternatively, if signalnum 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
          continue command; `signal 0' causes it to resume without a signal.

          signal does not repeat when you press RET a second time after
          executing the command.


ΓòÉΓòÉΓòÉ 15.4. Returning from a Function ΓòÉΓòÉΓòÉ

return
return expression
          You can cancel execution of a function call with the return command.
          If you give an expression argument, its value is used as the
          function's return value.

When you use return, GDB 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 return.

This pops the selected stack frame ( see 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 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
finish command ( see Continuing and Stepping) resumes execution until the
selected stack frame returns naturally.


ΓòÉΓòÉΓòÉ 15.5. Calling your Program's Functions ΓòÉΓòÉΓòÉ

call expr
          Evaluate the expression expr without displaying void returned values.

You can use this variant of the print command if you want to execute a function
from your program, but without cluttering the output with void returned values.
The result is printed and saved in the value history, if it is not void.


ΓòÉΓòÉΓòÉ 15.6. Patching your Program ΓòÉΓòÉΓòÉ

By default, GDB opens the file containing your program's executable code (or
the corefile) 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 set write command.  For example, you might want to turn on internal
debugging flags, or even to make emergency repairs.

set write on
set write off
          If you specify `set write on', GDB will open executable and core
          files for both reading and writing; if you specify `set write off'
          (the default), GDB will open them read-only.

          If you have already loaded a file, you must load it again (using the
          exec-file or core-file command) after changing set write, for your
          new setting to take effect.

show write
          Display whether executable files and core files will be opened for
          writing as well as reading.


ΓòÉΓòÉΓòÉ 16. GDB's Files ΓòÉΓòÉΓòÉ

GDB 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. To debug a core dump
of a previous run, GDB must be told the file name of the core dump.


ΓòÉΓòÉΓòÉ 16.1. Commands to Specify Files ΓòÉΓòÉΓòÉ

The usual way to specify executable and core dump file names is with the
command arguments given when you start GDB, ( see Getting In and Out of GDB.

Occasionally it is necessary to change to a different file during a GDB
session.  Or you may run GDB and forget to specify a file you want to use.  In
these situations the GDB commands to specify new files are useful.

file filename
          Use 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 run command.  If you do not specify a
          directory and the file is not found in GDB's working directory, GDB
          uses the environment variable 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 GDB and your
          program, using the path command.

          On systems with memory-mapped files, an auxiliary symbol table file
          `filename.syms' may be available for filename.  If it is, GDB will
          map in the symbol table from `filename.syms', starting up more
          quickly.  See the descriptions of the options `-mapped' and
          `-readnow' (available on the command line, and with the commands
          file, symbol-file, or add-symbol-file), for more information.

file
          file with no argument makes GDB discard any information it has on
          both executable file and the symbol table.

exec-file [ filename ]
          Specify that the program to be run (but not the symbol table) is
          found in filename.  GDB will search the environment variable PATH if
          necessary to locate your program.  Omitting filename means to discard
          information on the executable file.

symbol-file [ filename ]
          Read symbol table information from file filename.  PATH is searched
          when necessary.  Use the file command to get both symbol table and
          program to run from the same file.

          symbol-file with no argument clears out GDB's information on your
          program's symbol table.

          The symbol-file command causes GDB 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 GDB.

          symbol-file will not repeat if you press RET again after executing it
          once.

          When GDB 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 gcc you
          can generate debugging information for optimized code.

          On some kinds of object files, the 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 GDB 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 set verbose command can turn these pauses into
          messages if desired. See Optional Warnings and Messages.)

          When the symbol table is stored in COFF format, symbol-file does read
          the symbol table data in full right away.  We have not implemented
          the two-stage strategy for COFF yet.

symbol-file filename [ -readnow ] [ -mapped ]
file filename [ -readnow ] [ -mapped ]
          You can override the GDB two-stage strategy for reading symbol tables
          by using the `-readnow' option with any of the commands that load
          symbol table information, if you want to be sure GDB has the entire
          symbol table available.

          If memory-mapped files are available on your system through the mmap
          system call, you can use another option, `-mapped', to cause GDB to
          write the symbols for your program into a reusable file.  Future GDB
          debugging sessions will map in symbol information from this auxiliary
          symbol file (if the program hasn't changed), rather than spending
          time reading the symbol table from the executable program.  Using the
          `-mapped' option has the same effect as starting GDB with the
          `-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 .syms file is specific to the host machine on which GDB is run.
          It holds an exact image of GDB's internal symbol table.  It cannot be
          shared across multiple host platforms.

          The auxiliary symbol file for a program called myprog is called
          `myprog.syms'.  Once this file exists (so long as it is newer than
          the corresponding executable), GDB will always attempt to use it when
          you debug myprog; no special options or commands are needed.

core-file [ filename ]
          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; GDB
          can access the executable file itself for other parts.

          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 GDB.  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 kill command (see
          Killing the Child Process).

load filename
          Depending on what remote debugging facilities are configured into
          GDB, the load command may be available.  Where it exists, it is meant
          to make filename (an executable) available for debugging on the
          remote system---by downloading, or dynamic linking, for example. load
          also records filename's symbol table in GDB, like the add-symbol-file
          command.

          If load is not available on your GDB, attempting to execute it gets
          the error message ``You can't do that when your target is ...''

          On VxWorks, load will dynamically link filename on the current target
          system as well as adding its symbols in GDB.

          With the Nindy interface to an Intel 960 board, load will download
          filename to the 960 as well as adding its symbols in GDB.

          When you select remote debugging to a Hitachi H8/300 board ( see GDB
          and the Hitachi H8/300), the load command downloads your program to
          the H8/300 and also opens it as the current executable target for GDB
          on your host (like the file command).

          load will not repeat if you press RET again after using it.

add-symbol-file filename address
add-symbol-file filename address [ -readnow ] [ -mapped ]
          The add-symbol-file command reads additional symbol table information
          from the file filename.  You would use this command when filename has
          been dynamically loaded (by some other means) into the program that
          is running.  address should be the memory address at which the file
          has been loaded; GDB cannot figure this out for itself.

          The symbol table of the file filename is added to the symbol table
          originally read with the symbol-file command.  You can use the
          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 symbol-file command.

          add-symbol-file will not repeat if you press RET after using it.

          You can use the `-mapped' and `-readnow' options just as with the
          symbol-file command, to change how GDB manages the symbol table
          information for filename.

info files
info target
          info files and info target are synonymous; both print the current
          targets (see Specifying a Debugging Target), including the names of
          the executable and core dump files currently in use by GDB, and the
          files from which symbols were loaded.  The command help targets lists
          all possible targets rather than current ones.

All file-specifying commands allow both absolute and relative file names as
arguments.  GDB always converts the file name to an absolute path name and
remembers it that way.

GDB supports SunOS, SVR4, and IBM RS/6000 shared libraries. GDB automatically
loads symbol definitions from shared libraries when you use the run command, or
when you examine a core file. (Before you issue the run command, GDB will not
understand references to a function in a shared library, however---unless you
are debugging a core file).

info share
info sharedlibrary
          Print the names of the shared libraries which are currently loaded.

sharedlibrary regex
share regex
          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 run.  If regex is omitted all shared libraries required by
          your program are loaded.


ΓòÉΓòÉΓòÉ 16.2. Errors Reading Symbol Files ΓòÉΓòÉΓòÉ

While reading a symbol file, GDB will occasionally encounter problems, such as
symbol types it does not recognize, or known bugs in compiler output.  By
default, GDB 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 GDB to print only one message about each such type of problem, no
matter how many times the problem occurs; or you can ask GDB to print more
messages, to see how many times the problems occur, with the set complaints
command ( see Optional Warnings and Messages).

The messages currently printed, and their meanings, are:

inner block not inside outer block in 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.

          GDB circumvents the problem by treating the inner block as if it had
          the same scope as the outer block.  In the error message, symbol may
          be shown as ``(don't know)'' if the outer block is not a function.

block at 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.

          GDB does not circumvent this problem, and will have trouble locating
          symbols in the source file whose symbols being read.  (You can often
          determine what source file is affected by specifying set verbose on.
          See Optional Warnings and Messages.)

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.

          GDB circumvents the problem by treating the symbol scope block as
          starting on the previous source line.

bad string table offset in symbol n
          Symbol number n contains a pointer into the string table which is
          larger than the size of the string table.

          GDB circumvents the problem by considering the symbol to have the
          name foo, which may cause other problems if many symbols end up with
          this name.

unknown symbol type 0xnn
          The symbol information contains new data types that GDB does not yet
          know how to read.  0xnn is the symbol type of the misunderstood
          information, in hexadecimal.

          GDB 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 gdb with itself, breakpoint on
          complain, then go up to the function read_dbx_symtab and examine
          *bufp to see the symbol.

stub type has NULL name
          GDB could not find the full definition for a struct or class.

const/volatile indicator missing (ok if using g++ v1.x), got...
          The symbol information for a C++ member function is missing some
          information that recent versions of the compiler should have output
          for it.

info mismatch between compiler and debugger
          GDB could not parse a type specification output by the compiler.


ΓòÉΓòÉΓòÉ 17. Specifying a Debugging Target ΓòÉΓòÉΓòÉ

A target is the execution environment occupied by your program. Often, GDB 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 file or core commands.
When you need more flexibility---for example, running GDB on a physically
separate host, or controlling a standalone system over a serial port or a
realtime system over a TCP/IP connection---you can use the target command to
specify one of the target types configured for GDB ( see Commands for Managing
Targets).


ΓòÉΓòÉΓòÉ 17.1. Active Targets ΓòÉΓòÉΓòÉ

There are three classes of targets: processes, core files, and executable
files.  GDB 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.

If, for example, you execute `gdb a.out', then the executable file 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 GDB 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.)

When you type run, your executable file becomes an active process target as
well.  When a process target is active, all GDB commands requesting memory
addresses refer to that target; addresses in an active core file or executable
file target are obscured while the process target is active.

Use the core-file and exec-file commands to select a new core file or
executable target ( see Commands to Specify Files).  To specify as a target a
process that is already running, use the attach command ( see Debugging an
Already-Running Process.).


ΓòÉΓòÉΓòÉ 17.2. Commands for Managing Targets ΓòÉΓòÉΓòÉ

target type parameters
          Connects the GDB host environment to a target machine or process.  A
          target is typically a protocol for talking to debugging facilities.
          You use the argument type to specify the type or protocol of the
          target machine.

          Further 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.

          The target command will not repeat if you press RET again after
          executing the command.

help target
          Displays the names of all targets available.  To display targets
          currently selected, use either info target or info files (see
          Commands to Specify Files).

help target name
          Describe a particular target, including any parameters necessary to
          select it.

Here are some common targets (available, or not, depending on the GDB
configuration):

target exec prog
          An executable file.  `target exec prog' is the same as `exec-file
          prog'.

target core filename
          A core dump file.  `target core filename' is the same as `core-file
          filename'.

target remote dev
          Remote serial target in GDB-specific protocol.  The argument dev
          specifies what serial device to use for the connection (e.g.
          `/dev/ttya'). See Remote Debugging.

target amd-eb dev speed PROG
          Remote PC-resident AMD EB29K board, attached over serial lines. dev
          is the serial device, as for target remote; speed allows you to
          specify the linespeed; and PROG is the name of the program to be
          debugged, as it appears to DOS on the PC. See GDB with a Remote
          EB29K.

target hms
          A Hitachi H8/300 board, attached via serial line to your host.  Use
          special commands device and speed to control the serial line and the
          communications speed used. See GDB and the Hitachi H8/300.

target nindy devicename
          An Intel 960 board controlled by a Nindy Monitor.  devicename is the
          name of the serial device to use for the connection, e.g.
          `/dev/ttya'.  See GDB with a Remote i960 (Nindy).

target st2000 dev speed
          A Tandem ST2000 phone switch, running Tandem's STDBUG protocol.  dev
          is the name of the device attached to the ST2000 serial line; speed
          is the communication line speed.  The arguments are not used if GDB
          is configured to connect to the ST2000 using TCP or Telnet. See GDB
          with a Tandem ST2000.

target vxworks machinename
          A VxWorks system, attached via TCP/IP.  The argument machinename is
          the target system's machine name or IP address. See GDB and VxWorks.

Different targets are available on different configurations of GDB; your
configuration may have more or fewer targets.


ΓòÉΓòÉΓòÉ 17.3. Remote Debugging ΓòÉΓòÉΓòÉ

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 help
targets to list them.


ΓòÉΓòÉΓòÉ 17.3.1. The GDB remote serial protocol ΓòÉΓòÉΓòÉ

To debug a program running on another machine (the debugging target machine),
you must first arrange for all the usual prerequisites for the program to run
by itself.  For example, for a C program, you need

 1. A startup routine to set up the C runtime environment; these usually have a
    name like `crt0'.  The startup routine may be supplied by your hardware
    supplier, or you may have to write your own.

 2. You probably need a C subroutine library to support your program's
    subroutine calls, notably managing input and output.

 3. A way of getting your program to the other machine---for example, a
    download program.  These are often supplied by the hardware manufacturer,
    but you may have to write your own from hardware documentation.

The next step is to arrange for your program to use a serial port to
communicate with the machine where GDB is running (the host machine).  In
general terms, the scheme looks like this:

On the host,
          GDB already understands how to use this protocol; when everything
          else is set up, you can simply use the `target remote' command (see
          Specifying a Debugging Target).

On the target,
          you must link with your program a few special-purpose subroutines
          that implement the GDB remote serial protocol.  The file containing
          these subroutines is called  a debugging stub.

The debugging stub is specific to the architecture of the remote machine; for
example, use `sparc-stub.c' to debug programs on sparc boards.

These working remote stubs are distributed with GDB:

sparc-stub.c
          For sparc architectures.

m68k-stub.c
          For Motorola 680x0 architectures.

i386-stub.c
          For Intel 386 and compatible architectures.

The `README' file in the GDB distribution may list other recently added stubs.


ΓòÉΓòÉΓòÉ 17.3.1.1. What the stub can do for you ΓòÉΓòÉΓòÉ

The debugging stub for your architecture supplies these three subroutines:

set_debug_traps
          This routine arranges to transfer control to handle_exception when
          your program stops.  You must call this subroutine explicitly near
          the beginning of your program.

handle_exception
          This is the central workhorse, but your program never calls it
          explicitly---the setup code arranges for handle_exception to run when
          a trap is triggered.

          handle_exception takes control when your program stops during
          execution (for example, on a breakpoint), and mediates communications
          with GDB on the host machine.  This is where the communications
          protocol is implemented; handle_exception acts as the GDB
          representative on the target machine; it begins by sending summary
          information on the state of your program, then continues to execute,
          retrieving and transmitting any information GDB needs, until you
          execute a GDB command that makes your program resume; at that point,
          handle_exception returns control to your own code on the target
          machine.

breakpoint
          Use this auxiliary subroutine to make your program contain a
          breakpoint.  Depending on the particular situation, this may be the
          only way for GDB to get control.  For instance, if your target
          machine has some sort of interrupt button, you won't need to call
          this; pressing the interrupt button will transfer control to
          handle_exception---in efect, to GDB.  On some machines, simply
          receiving characters on the serial port may also trigger a trap;
          again, in that situation, you don't need to call breakpoint from your
          own program---simply running `target remote' from the host GDB
          session will get control.

          Call breakpoint if none of these is true, or if you simply want to
          make certain your program stops at a predetermined point for the
          start of your debugging session.


ΓòÉΓòÉΓòÉ 17.3.1.2. What you must do for the stub ΓòÉΓòÉΓòÉ

The debugging stubs that come with GDB are set up for a particular chip
architecture, but they have no information about the rest of your debugging
target machine.  To allow the stub to work, you must supply these special
low-level subroutines:

int getDebugChar()
          Write this subroutine to read a single character from the serial
          port. It may be identical to getchar for your target system; a
          different name is used to allow you to distinguish the two if you
          wish.

void putDebugChar(int)
          Write this subroutine to write a single character to the serial port.
          It may be identical to putchar for your target system; a different
          name is used to allow you to distinguish the two if you wish.

void flush_i_cache()
          Write this subroutine to flush the instruction cache, if any, on your
          target machine.  If there is no instruction cache, this subroutine
          may be a no-op.

          On target machines that have instruction caches, GDB requires this
          function to make certain that the state of your program is stable.

You must also make sure this library routine is available:

void *memset(void *, int, int)
          This is the standard library function memset that sets an area of
          memory to a known value.  If you have one of the free versions of
          libc.a, memset can be found there; otherwise, you must either obtain
          it from your hardware manufacturer, or write your own.

If you do not use the GNU C compiler, you may need other standard library
subroutines as well; this will vary from one stub to another, but in general
the stubs are likely to use any of the common library subroutines which gcc
generates as inline code.


ΓòÉΓòÉΓòÉ 17.3.1.3. Putting it all together ΓòÉΓòÉΓòÉ

In summary, when your program is ready to debug, you must follow these steps.

 1. Make sure you have the supporting low-level routines: getDebugChar,
    putDebugChar, flush_i_cache, memset.

 2. Insert these lines near the top of your program:

        set_debug_traps();
        breakpoint();

 3. Compile and link together: your program, the GDB debugging stub for your
    target architecture, and the supporting subroutines.

 4. Make sure you have a serial connection between your target machine and the
    GDB host, and identify the serial port used for this on the host.

 5. Download your program to your target machine (or get it there by whatever
    means the manufacturer provides), and start it.

 6. To start remote debugging, run GDB on the host machine, and specify as an
    executable file the program that is running in the remote machine. This
    tells GDB how to find your program's symbols and the contents of its pure
    text.

    Then establish communication using the target remote command. Its argument
    is the name of the device you're using to control the target machine.  For
    example:

        target remote /dev/ttyb

    if the serial line is connected to the device named `/dev/ttyb'.

Now you can use all the usual commands to examine and change data and to step
and continue the remote program.

To resume the remote program and stop debugging it, use the detach command.


ΓòÉΓòÉΓòÉ 17.3.1.4. Outline of the communication protocol ΓòÉΓòÉΓòÉ

The stub files provided with GDB implement the target side of the communication
protocol, and the GDB side is implemented in the GDB source file `remote.c'.
Normally, you can simply allow these subroutines to communicate, and ignore the
details.  (If you're implementing your own stub file, you can still ignore the
details: start with one of the existing stub files.  `sparc-stub.c' is the best
organized, and therefore the easiest to read.)

However, there may be occasions when you need to know something about the
protocol---for example, if there is only one serial port to your target
machine, you might want your program to do something special if it recognizes a
packet meant for GDB.

All GDB commands and responses (other than acknowledgements, which are single
characters) are sent as a packet which includes a checksum.  A packet is
introduced with the character `$', and ends with the character `#' followed by
a two-digit checksum:

$packet info#checksum

checksum is computed as the modulo 256 sum of the packet info characters.

When either the host or the target machine receives a packet, the first
response expected is an acknowledgement: a single character, either `+' (to
indicate the package was received correctly) or `-' (to request
retransmission).

The host (GDB) sends commands, and the target (the debugging stub incorporated
in your program) sends data in response.  The target also sends data when your
program stops.

Command packets are distinguished by their first character, which identifies
the kind of command.

These are the commands currently supported:

g
          Requests the values of CPU registers.

G
          Sets the values of CPU registers.

maddr,count
          Read count bytes at location addr.

Maddr,count:...
          Write count bytes at location addr.

c
caddr
          Resume execution at the current address (or at addr if supplied).

s
saddr
          Step the target program for one instruction, from either the current
          program counter or from addr if supplied.

k
          Kill the target program.

?
          Report the most recent signal.  To allow you to take advantage of the
          GDB signal handling commands, one of the functions of the debugging
          stub is to report CPU traps as the corresponding POSIX signal values.

If you have trouble with the serial connection, you can use the command set
remotedebug.  This makes GDB report on all packets sent back and forth across
the serial line to the remote machine.  The packet-debugging information is
printed on the GDB standard output stream.  set remotedebug off turns it off,
and show remotedebug will show you its current state.


ΓòÉΓòÉΓòÉ 17.3.2. GDB with a Remote i960 (Nindy) ΓòÉΓòÉΓòÉ

Nindy is a ROM Monitor program for Intel 960 target systems.  When GDB is
configured to control a remote Intel 960 using Nindy, you can tell GDB how to
connect to the 960 in several ways:

o Through command line options specifying serial port, version of the Nindy
  protocol, and communications speed;

o By responding to a prompt on startup;

o By using the target command at any point during your GDB session.  See
  Commands for Managing Targets.


ΓòÉΓòÉΓòÉ 17.3.2.1. Startup with Nindy ΓòÉΓòÉΓòÉ

If you simply start gdb without using any command-line options, you are
prompted for what serial port to use, before you reach the ordinary GDB prompt:

Attach /dev/ttyNN -- specify NN, or "quit" to quit:

Respond to the prompt with whatever suffix (after `/dev/tty') identifies the
serial port you want to use.  You can, if you choose, simply start up with no
Nindy connection by responding to the prompt with an empty line.  If you do
this, and later wish to attach to Nindy, use target (see Commands for Managing
Targets).


ΓòÉΓòÉΓòÉ 17.3.2.2. Options for Nindy ΓòÉΓòÉΓòÉ

These are the startup options for beginning your GDB session with a Nindy-960
board attached:

-r port
          Specify the serial port name of a serial interface to be used to
          connect to the target system.  This option is only available when GDB
          is configured for the Intel 960 target architecture.  You may specify
          port as any of: a full pathname (e.g. `-r /dev/ttya'), a device name
          in `/dev' (e.g. `-r ttya'), or simply the unique suffix for a
          specific tty (e.g. `-r a').

-O
          (An uppercase letter ``O'', not a zero.)  Specify that GDB should use
          the ``old'' Nindy monitor protocol to connect to the target system.
          This option is only available when GDB is configured for the Intel
          960 target architecture.

          Warning: if you specify `-O', but are actually trying to connect to a
          target system that expects the newer protocol, the connection will
          fail, appearing to be a speed mismatch.  GDB will repeatedly attempt
          to reconnect at several different line speeds.  You can abort this
          process with an interrupt.

-brk
          Specify that GDB should first send a BREAK signal to the target
          system, in an attempt to reset it, before connecting to a Nindy
          target.

          Warning: Many target systems do not have the hardware that this
          requires; it only works with a few boards.

The standard `-b' option controls the line speed used on the serial port.


ΓòÉΓòÉΓòÉ 17.3.2.3. Nindy Reset Command ΓòÉΓòÉΓòÉ

reset
          For a Nindy target, this command sends a ``break'' to the remote
          target system; this is only useful if the target has been equipped
          with a circuit to perform a hard reset (or some other interesting
          action) when a break is detected.


ΓòÉΓòÉΓòÉ 17.3.3. GDB with a Remote EB29K ΓòÉΓòÉΓòÉ

To use GDB from a Unix system to run programs on AMD's EB29K board in a PC, you
must first connect a serial cable between the PC and a serial port on the Unix
system.  In the following, we assume you've hooked the cable between the PC's
`COM1' port and `/dev/ttya' on the Unix system.


ΓòÉΓòÉΓòÉ 17.3.3.1. Communications Setup ΓòÉΓòÉΓòÉ

The next step is to set up the PC's port, by doing something like the following
in DOS on the PC:

C:\> MODE com1:9600,n,8,1,none

This example---run on an MS DOS 4.0 system---sets the PC port to 9600 bps, no
parity, eight data bits, one stop bit, and no ``retry'' action; you must match
the communications parameters when establishing the Unix end of the connection
as well.

To give control of the PC to the Unix side of the serial line, type the
following at the DOS console:

C:\> CTTY com1

(Later, if you wish to return control to the DOS console, you can use the
command CTTY con---but you must send it over the device that had control, in
our example over the `COM1' serial line).

From the Unix host, use a communications program such as tip or cu to
communicate with the PC; for example,

cu -s 9600 -l /dev/ttya

The cu options shown specify, respectively, the linespeed and the serial port
to use.  If you use tip instead, your command line may look something like the
following:

tip -9600 /dev/ttya

Your system may define a different name where our example uses `/dev/ttya' as
the argument to tip.  The communications parameters, including which port to
use, are associated with the tip argument in the ``remote'' descriptions
file---normally the system table `/etc/remote'.

Using the tip or cu connection, change the DOS working directory to the
directory containing a copy of your 29K program, then start the PC program
EBMON (an EB29K control program supplied with your board by AMD).  You should
see an initial display from EBMON similar to the one that follows, ending with
the EBMON prompt `#'---

C:\> G:

G:\> CD \usr\joe\work29k

G:\USR\JOE\WORK29K> EBMON
Am29000 PC Coprocessor Board Monitor, version 3.0-18
Copyright 1990 Advanced Micro Devices, Inc.
Written by Gibbons and Associates, Inc.

Enter '?' or 'H' for help

PC Coprocessor Type   = EB29K
I/O Base              = 0x208
Memory Base           = 0xd0000

Data Memory Size      = 2048KB
Available I-RAM Range = 0x8000 to 0x1fffff
Available D-RAM Range = 0x80002000 to 0x801fffff

PageSize              = 0x400
Register Stack Size   = 0x800
Memory Stack Size     = 0x1800

CPU PRL               = 0x3
Am29027 Available     = No
Byte Write Available  = Yes

# ~.

Then exit the cu or tip program (done in the example by typing ~. at the EBMON
prompt).  EBMON will keep running, ready for GDB to take over.

For this example, we've assumed what is probably the most convenient way to
make sure the same 29K program is on both the PC and the Unix system: a PC/NFS
connection that establishes ``drive G:'' on the PC as a file system on the Unix
host.  If you do not have PC/NFS or something similar connecting the two
systems, you must arrange some other way---perhaps floppy-disk transfer---of
getting the 29K program from the Unix system to the PC; GDB will not download
it over the serial line.


ΓòÉΓòÉΓòÉ 17.3.3.2. EB29K cross-debugging ΓòÉΓòÉΓòÉ

Finally, cd to the directory containing an image of your 29K program on the
Unix system, and start GDB---specifying as argument the name of your 29K
program:

cd /usr/joe/work29k
gdb myfoo

Now you can use the target command:

target amd-eb /dev/ttya 9600 MYFOO

In this example, we've assumed your program is in a file called `myfoo'.  Note
that the filename given as the last argument to target amd-eb should be the
name of the program as it appears to DOS. In our example this is simply MYFOO,
but in general it can include a DOS path, and depending on your transfer
mechanism may not resemble the name on the Unix side.

At this point, you can set any breakpoints you wish; when you are ready to see
your program run on the 29K board, use the GDB command run.

To stop debugging the remote program, use the GDB detach command.

To return control of the PC to its console, use tip or cu once again, after
your GDB session has concluded, to attach to EBMON.  You can then type the
command q to shut down EBMON, returning control to the DOS command-line
interpreter. Type CTTY con to return command input to the main DOS console, and
type ~. to leave tip or cu.


ΓòÉΓòÉΓòÉ 17.3.3.3. Remote Log ΓòÉΓòÉΓòÉ

The target amd-eb command creates a file `eb.log' in the current working
directory, to help debug problems with the connection. `eb.log' records all the
output from EBMON, including echoes of the commands sent to it.  Running `tail
-f' on this file in another window often helps to understand trouble with
EBMON, or unexpected events on the PC side of the connection.


ΓòÉΓòÉΓòÉ 17.3.4. GDB with a Tandem ST2000 ΓòÉΓòÉΓòÉ

To connect your ST2000 to the host system, see the manufacturer's manual.  Once
the ST2000 is physically attached, you can run

target st2000 dev speed

to establish it as your debugging environment.

The load and attach commands are not defined for this target; you must load
your program into the ST2000 as you normally would for standalone operation.
GDB will read debugging information (such as symbols) from a separate,
debugging version of the program available on your host computer.

These auxiliary GDB commands are available to help you with the ST2000
environment:

st2000 command
          Send a command to the STDBUG monitor.  See the manufacturer's manual
          for available commands.

connect
          Connect the controlling terminal to the STDBUG command monitor.  When
          you are done interacting with STDBUG, typing either of two character
          sequences will get you back to the GDB command prompt: RET~. (Return,
          followed by tilde and period) or RET~C-d (Return, followed by tilde
          and control-D).


ΓòÉΓòÉΓòÉ 17.3.5. GDB and VxWorks ΓòÉΓòÉΓòÉ

GDB enables developers to spawn and debug tasks running on networked VxWorks
targets from a Unix host.  Already-running tasks spawned from the VxWorks shell
can also be debugged.  GDB uses code that runs on both the UNIX host and on the
VxWorks target.  The program gdb is installed and executed on the UNIX host.

The following information on connecting to VxWorks was current when this manual
was produced; newer releases of VxWorks may use revised procedures.

The remote debugging interface (RDB) routines are installed and executed on the
VxWorks target.  These routines are included in the VxWorks library `rdb.a' and
are incorporated into the system image when source-level debugging is enabled
in the VxWorks configuration.

If you wish, you can define INCLUDE_RDB in the VxWorks configuration file
`configAll.h' to include the RDB interface routines and spawn the source
debugging task tRdbTask when VxWorks is booted.  For more information on
configuring and remaking VxWorks, see the manufacturer's manual.

Once you have included the RDB interface in your VxWorks system image and set
your Unix execution search path to find GDB, you are ready to run GDB.  From
your UNIX host, type:

% gdb

GDB will come up showing the prompt:

(gdb)


ΓòÉΓòÉΓòÉ 17.3.5.1. Connecting to VxWorks ΓòÉΓòÉΓòÉ

The GDB command target lets you connect to a VxWorks target on the network.  To
connect to a target whose host name is ``tt'', type:

(gdb) target vxworks tt

GDB will display a message similar to the following:

Attaching remote machine across net... Success!

GDB will then attempt to read the symbol tables of any object modules loaded
into the VxWorks target since it was last booted.  GDB locates these files by
searching the directories listed in the command search path (see Your Program_s
Environment); if it fails to find an object file, it will display a message
such as:

prog.o: No such file or directory.

This will cause the target command to abort.  When this happens, you should add
the appropriate directory to the search path, with the GDB command path, and
execute the target command again.


ΓòÉΓòÉΓòÉ 17.3.5.2. VxWorks Download ΓòÉΓòÉΓòÉ

If you have connected to the VxWorks target and you want to debug an object
that has not yet been loaded, you can use the GDB load command to download a
file from UNIX to VxWorks incrementally.  The object file given as an argument
to the load command is actually opened twice: first by the VxWorks target in
order to download the code, then by GDB in order to read the symbol table.
This can lead to problems if the current working directories on the two systems
differ. It is simplest to set the working directory on both systems to the
directory in which the object file resides, and then to reference the file by
its name, without any path.  Thus, to load a program `prog.o', residing in
`wherever/vw/demo/rdb', on VxWorks type:

-> cd "wherever/vw/demo/rdb"

On GDB type:

(gdb) cd wherever/vw/demo/rdb
(gdb) load prog.o

GDB will display a response similar to the following:

Reading symbol data from wherever/vw/demo/rdb/prog.o... done.

You can also use the load command to reload an object module after editing and
recompiling the corresponding source file.  Note that this will cause GDB to
delete all currently-defined breakpoints, auto-displays, and convenience
variables, and to clear the value history.  (This is necessary in order to
preserve the integrity of debugger data structures that reference the target
system's symbol table.)


ΓòÉΓòÉΓòÉ 17.3.5.3. Running Tasks ΓòÉΓòÉΓòÉ

You can also attach to an existing task using the attach command as follows:

(gdb) attach task

where task is the VxWorks hexadecimal task ID.  The task can be running or
suspended when you attach to it.  If running, it will be suspended at the time
of attachment.


ΓòÉΓòÉΓòÉ 17.3.6. GDB and the Hitachi H8/300 ΓòÉΓòÉΓòÉ

GDB needs to know these things to talk to your H8/300:

 1. that you want to use `target hms', the remote debugging interface for the
    H8/300 (this is the default when GDB is configured specifically for the
    H8/300);

 2. what serial device connects your host to your H8/300 (the first serial
    device available on your host is the default);
GDB depends on an auxiliary terminate-and-stay-resident program

called asynctsr to communicate with the H8/300 development board through a PC
serial port.  You must also use the DOS mode command to set up the serial port
on the DOS side.

The following sample session illustrates the steps needed to start a program
under GDB control on your H8/300.  The example uses a sample H8/300 program
called `t.x'.

First hook up your H8/300 development board.  In this example, we use a board
attached to serial port COM2; if you use a different serial port, substitute
its name in the argument of the mode command. When you call asynctsr, the
auxiliary comms program used by the degugger, you give it just the numeric part
of the serial port's name; for example, `asyncstr 2' below runs asyncstr on
COM2.

(eg-C:\H8300\TEST) mode com2:9600,n,8,1,p

Resident portion of MODE loaded

COM2: 9600, n, 8, 1, p

(eg-C:\H8300\TEST) asynctsr 2

Warning: We have noticed a bug in PC-NFS that conflicts with asynctsr.  If you
also run PC-NFS on your DOS host, you may need to disable it, or even boot
without it, to use asynctsr to control your H8/300 board.

Now that serial communications are set up, and the H8/300 is connected, you can
start up GDB.  Call gdb with the name of your program as the argument.  gdb
prompts you, as usual, with the prompt `(gdb)'.  Use two special commands to
begin your debugging session: `target hms' to specify cross-debugging to the
Hitachi board, and the load command to download your program to the board. load
displays the names of the program's sections, and a `*' for each 2K of data
downloaded.  (If you want to refresh GDB data on symbols or on the executable
file without downloading, use the GDB commands file or symbol-file.  These
commands, and load itself, are described in Commands to Specify Files.)

(eg-C:\H8300\TEST) gdb t.x
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 4.7, Copyright 1992 Free Software Foundation, Inc...
(gdb) target hms
Connected to remote H8/300 HMS system.
(gdb) load t.x
.text   : 0x8000 .. 0xabde ***********
.data   : 0xabde .. 0xad30 *
.stack  : 0xf000 .. 0xf014 *

At this point, you're ready to run or debug your program.  From here on, you
can use all the usual GDB commands.  The break command sets breakpoints; the
run command starts your program; print or x display data; the continue command
resumes execution after stopping at a breakpoint.  You can use the help command
at any time to find out more about GDB commands.

Remember, however, that operating system facilities aren't available on your
H8/300; for example, if your program hangs, you can't send an interrupt---but
you can press the reset switch!

Use the reset button on the H8/300 board

o to interrupt your program (don't use ctl-C on the DOS host---it has no way to
  pass an interrupt signal to the H8/300); and

o to return to the GDB command prompt after your program finishes normally.
  The communications protocol provides no other way for GDB to detect program
  completion.

In either case, GDB will see the effect of a reset on the H8/300 board as a
``normal exit'' of your program.


ΓòÉΓòÉΓòÉ 18. Controlling GDB ΓòÉΓòÉΓòÉ

You can alter many aspects of GDB's interaction with you by using the set
command.  For commands controlling how GDB displays data, see Print Settings;
other settings are described here.


ΓòÉΓòÉΓòÉ 18.1. Prompt ΓòÉΓòÉΓòÉ

GDB indicates its readiness to read a command by printing a string called the
prompt.  This string is normally `(gdb)'.  You can change the prompt string
with the set prompt command.  For instance, when debugging GDB with GDB, it is
useful to change the prompt in one of the GDBs so that you can always tell
which one you are talking to.

set prompt newprompt
          Directs GDB to use newprompt as its prompt string henceforth.

show prompt
          Prints a line of the form: `Gdb's prompt is: your-prompt'


ΓòÉΓòÉΓòÉ 18.2. Command Editing ΓòÉΓòÉΓòÉ

GDB reads its input commands via the readline interface.  This GNU library
provides consistent behavior for programs which provide a command line
interface to the user.  Advantages are emacs-style or vi-style inline editing
of commands, 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 GDB with the command
set.

set editing
set editing on
          Enable command line editing (enabled by default).

set editing off
          Disable command line editing.

show editing
          Show whether command line editing is enabled.


ΓòÉΓòÉΓòÉ 18.3. Command History ΓòÉΓòÉΓòÉ

set history filename fname
          Set the name of the GDB command history file to fname.  This is the
          file from which GDB 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 GDBHISTFILE, or to `./.gdb_history' if this
          variable is not set.

set history save
set history save on
          Record command history in a file, whose name may be specified with
          the set history filename command.  By default, this option is
          disabled.

set history save off
          Stop recording command history in a file.

set history size size
          Set the number of commands which GDB will keep in its history list.
          This defaults to the value of the environment variable HISTSIZE, or
          to 256 if this variable is not set.

History expansion assigns special meaning to the character !. Since ! is also
the logical not operator in C, history expansion is off by default. If you
decide to enable history expansion with the set history expansion on command,
you may sometimes need to follow ! (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 != and
!(, even when history expansion is enabled.

The commands to control history expansion are:

set history expansion on
set history expansion
          Enable history expansion.  History expansion is off by default.

set history expansion off
          Disable history expansion.

          The readline code comes with more complete documentation of editing
          and history expansion features.  Users unfamiliar with emacs or vi
          may wish to read it.

show history
show history filename
show history save
show history size
show history expansion
          These commands display the state of the GDB history parameters. show
          history by itself displays all four states.

show commands
          Display the last ten commands in the command history.

show commands n
          Print ten commands centered on command number n.

show commands +
          Print ten commands just after the commands last printed.


ΓòÉΓòÉΓòÉ 18.4. Screen Size ΓòÉΓòÉΓòÉ

Certain commands to GDB may produce large amounts of information output to the
screen.  To help you read all of it, GDB pauses and asks you for input at the
end of each page of output.  Type RET when you want to continue the output.
GDB also uses the screen width setting to determine when to wrap lines of
output.  Depending on what is being printed, it tries to break the line at a
readable place, rather than simply letting it overflow onto the following line.

Normally GDB knows the size of the screen from the termcap data base together
with the value of the TERM environment variable and the stty rows and stty cols
settings. If this is not correct, you can override it with the set height and
set width commands:

set height lpp
show height
set width cpl
show width
          These set commands specify a screen height of lpp lines and a screen
          width of cpl characters.  The associated show commands display the
          current settings.

          If you specify a height of zero lines, GDB 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.


ΓòÉΓòÉΓòÉ 18.5. Numbers ΓòÉΓòÉΓòÉ

You can always enter numbers in octal, decimal, or hexadecimal in GDB by the
usual conventions: octal numbers begin with `0', decimal numbers end with `.',
and hexadecimal numbers begin with `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 set radix command.

set radix base
          Set the default base for numeric input and display.  Supported
          choices for base are decimal 2, 8, 10, 16.  base must itself be
          specified either unambiguously or using the current default radix;
          for example, any of

                    set radix 1010
                    set radix 012
                    set radix 10.
                    set radix 0xa

          will set the base to decimal.  On the other hand, `set radix 10' will
          leave the radix unchanged no matter what it was.

show radix
          Display the current default base for numeric input and display.


ΓòÉΓòÉΓòÉ 18.6. Optional Warnings and Messages ΓòÉΓòÉΓòÉ

By default, GDB is silent about its inner workings.  If you are running on a
slow machine, you may want to use the set verbose command. It will make GDB
tell you when it does a lengthy internal operation, so you will not think it
has crashed.

Currently, the messages controlled by set verbose are those which announce that
the symbol table for a source file is being read; see symbol-file in Commands
to Specify Files.

set verbose on
          Enables GDB's output of certain informational messages.

set verbose off
          Disables GDB's output of certain informational messages.

show verbose
          Displays whether set verbose is on or off.

By default, if GDB 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 (see Errors Reading Symbol Files).

set complaints limit
          Permits GDB to output limit complaints about each type of unusual
          symbols before becoming silent about the problem.  Set limit to zero
          to suppress all complaints; set it to a large number to prevent
          complaints from being suppressed.

show complaints
          Displays how many symbol complaints GDB is permitted to produce.

By default, GDB 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:

(gdb) run
The program being debugged has been started already.
Start it from the beginning? (y or n)

If you are willing to unflinchingly face the consequences of your own commands,
you can disable this ``feature'':

set confirm off
          Disables confirmation requests.

set confirm on
          Enables confirmation requests (the default).

show confirm
          Displays state of confirmation requests.

Some systems allow individual object files that make up your program to be
replaced without stopping and restarting your program. For example, in VxWorks
you can simply recompile a defective object file and keep on running. If you
are running on one of these systems, you can allow GDB to reload the symbols
for automatically relinked modules:

set symbol-reloading on
          Replace symbol definitions for the corresponding source file when an
          object file with a particular name is seen again.

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 symbol-reloading off, since otherwise GDB may discard symbols
          when linking large programs, that may contain several modules (from
          different directories or libraries) with the same name.

show symbol-reloading
          Show the current on or off setting.


ΓòÉΓòÉΓòÉ 19. Canned Sequences of Commands ΓòÉΓòÉΓòÉ

Aside from breakpoint commands ( see Breakpoint Command Lists), GDB provides
two ways to store sequences of commands for execution as a unit: user-defined
commands and command files.


ΓòÉΓòÉΓòÉ 19.1. User-Defined Commands ΓòÉΓòÉΓòÉ

A user-defined command is a sequence of GDB commands to which you assign a new
name as a command.  This is done with the define command.

define commandname
          Define a command named 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 GDB command lines,
          which are given following the define command.  The end of these
          commands is marked by a line containing end.

document commandname
          Give documentation to the user-defined command commandname.  The
          command commandname must already be defined.  This command reads
          lines of documentation just as define reads the lines of the command
          definition, ending with end.  After the document command is finished,
          help on command commandname will print the documentation you have
          specified.

          You may use the document command again to change the documentation of
          a command.  Redefining the command with define does not change the
          documentation.

help user-defined
          List all user-defined commands, with the first line of the
          documentation (if any) for each.

show user
show user commandname
          Display the GDB commands used to define commandname (but not its
          documentation).  If no commandname is given, display the definitions
          for all user-defined commands.

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 GDB commands that
normally print messages to say what they are doing omit the messages when used
in a user-defined command.


ΓòÉΓòÉΓòÉ 19.2. User-Defined Command Hooks ΓòÉΓòÉΓòÉ

You may define hooks, which are a special kind of user-defined command.
Whenever you run the command `foo', if the user-defined command `hook-foo'
exists, it is executed (with no arguments) before that command.

In addition, a pseudo-command, `stop' exists.  Hooking this command will cause
your hook to be executed every time execution stops in the inferior program,
before breakpoint commands are run, displays are printed, or the stack frame is
printed.

For example, to cause SIGALRM signals to be ignored while single-stepping, but
cause them to be resumed during normal execution, you could do:

define hook-stop
handle SIGALRM nopass
end

define hook-run
handle SIGALRM pass
end

define hook-continue
handle SIGLARM pass
end

Any single-word command in GDB can be hooked.  Aliases for other commands
cannot be hooked (you should hook the basic command name, e.g. backtrace rather
than bt).  If an error occurs during the execution of your hook, execution of
GDB commands stops and you are returned to the GDB prompt (before the command
that you actually typed had a chance to run).

If you try to define a hook which doesn't match any known command, you will get
a warning from the define command.


ΓòÉΓòÉΓòÉ 19.3. Command Files ΓòÉΓòÉΓòÉ

A command file for GDB is a file of lines that are GDB commands.  Comments
(lines starting with #) 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.

When you start GDB, it automatically executes commands from its init files.
These are files named `.gdbinit'.  GDB 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 `-nx' option; see
Choosing Modes.)  You can also request the execution of a command file with the
source command:

source filename
          Execute the command file filename.

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 GDB commands that normally print
messages to say what they are doing omit the messages when called from command
files.


ΓòÉΓòÉΓòÉ 19.4. Commands for Controlled Output ΓòÉΓòÉΓòÉ

During the execution of a command file or a user-defined command, normal GDB
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.

echo text
          Print text.  Nonprinting characters can be included in text using C
          escape sequences, such as `\n' to print a newline.  *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 outputting a string with spaces at the beginning
          or the end, since leading and trailing spaces are otherwise trimmed
          from all arguments. To print `and foo =', use the command `echo \and
          foo = \'.

          A backslash at the end of text can be used, as in C, to continue the
          command onto subsequent lines.  For example,

                    echo This is some text\n\
                    which is continued\n\
                    onto several lines.\n

          produces the same output as

                    echo This is some text\n
                    echo which is continued\n
                    echo onto several lines.\n

output expression
          Print the value of expression and nothing but that value: no
          newlines, no `$nn = '.  The value is not entered in the value history
          either.  See Expressions, for more information on expressions.

output/fmt expression
          Print the value of expression in format fmt.  You can use the same
          formats as for print; see Output formats, for more information.

printf string, expressions...
          Print the values of the expressions under the control of string.  The
          expressions are separated by commas and may be either numbers or
          pointers.  Their values are printed as specified by string, exactly
          as if your program were to execute

                    printf (string, expressions...);

          For example, you can print two values in hex like this:

                    printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo

          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.


ΓòÉΓòÉΓòÉ 20. Using GDB under GNU Emacs ΓòÉΓòÉΓòÉ

A special interface allows you to use GNU Emacs to view (and edit) the source
files for the program you are debugging with GDB.

To use this interface, use the command M-x gdb in Emacs.  Give the executable
file you want to debug as an argument.  This command starts GDB as a subprocess
of Emacs, with input and output through a newly created Emacs buffer.

Using GDB under Emacs is just like using GDB normally except for two things:

o All ``terminal'' input and output goes through the Emacs buffer.

This applies both to GDB 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, C-c
C-c for an interrupt, C-c C-z for a stop.

o GDB displays source code through Emacs.

Each time GDB displays a stack frame, Emacs automatically finds the source file
for that frame and puts an arrow (`=>') at the left margin of the current line.
Emacs uses a separate buffer for source display, and splits the window to show
both your GDB session and the source.

Explicit GDB list or search commands still produce output as usual, but you
probably will have no reason to use them.

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.  GDB can find programs by searching your environment's PATH variable,
so the GDB input and output session will proceed normally; but Emacs does not
get enough information back from GDB to locate the source files in this
situation.  To avoid this problem, either start GDB mode from the directory
where your program resides, or specify a full path name when prompted for the
M-x gdb argument.

A similar confusion can result if you use the GDB file command to switch to
debugging a program in some other location, from an existing GDB buffer in
Emacs.

By default, M-x gdb calls the program called `gdb'.  If you need to call GDB by
a different name (for example, if you keep several configurations around, with
different names) you can set the Emacs variable gdb-command-name; for example,

(setq gdb-command-name "mygdb")

(preceded by ESC ESC, or typed in the *scratch* buffer, or in your `.emacs'
file) will make Emacs call the program named ``mygdb'' instead.

In the GDB I/O buffer, you can use these special Emacs commands in addition to
the standard Shell mode commands:

C-h m
          Describe the features of Emacs' GDB Mode.

M-s
          Execute to another source line, like the GDB step command; also
          update the display window to show the current file and location.

M-n
          Execute to next source line in this function, skipping all function
          calls, like the GDB next command.  Then update the display window to
          show the current file and location.

M-i
          Execute one instruction, like the GDB stepi command; update display
          window accordingly.

M-x gdb-nexti
          Execute to next instruction, using the GDB nexti command; update
          display window accordingly.

C-c C-f
          Execute until exit from the selected stack frame, like the GDB finish
          command.

M-c
          Continue execution of your program, like the GDB continue command.

          Warning: In Emacs v19, this command is C-c C-p.

M-u
          Go up the number of frames indicated by the numeric argument (see
          Numeric Arguments), like the GDB up command.

          Warning: In Emacs v19, this command is C-c C-u.

M-d
          Go down the number of frames indicated by the numeric argument, like
          the GDB down command.

          Warning: In Emacs v19, this command is C-c C-d.

C-x &
          Read the number where the cursor is positioned, and insert it at the
          end of the GDB I/O buffer.  For example, if you wish to disassemble
          code around an address that was displayed earlier, type disassemble;
          then move the cursor to the address display, and pick up the argument
          for disassemble by typing C-x &.

          You can customize this further on the fly by defining elements of the
          list gdb-print-command; once it is defined, you can format or
          otherwise process numbers picked up by C-x & before they are
          inserted.  A numeric argument to 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 format; otherwise the number is
          passed as an argument to the corresponding list element.

In any source file, the Emacs command C-x SPC (gdb-break) tells GDB 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 f in the GDB 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 GDB communicates with Emacs in terms
of line numbers.  If you add or delete lines from the text, the line numbers
that GDB knows will cease to correspond properly to the code.


ΓòÉΓòÉΓòÉ 21. Reporting Bugs in GDB ΓòÉΓòÉΓòÉ

Your bug reports play an essential role in making GDB 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 GDB work better.  Bug reports
are your contribution to the maintenance of GDB.

In order for a bug report to serve its purpose, you must include the
information that enables us to fix the bug.


ΓòÉΓòÉΓòÉ 21.1. Have You Found a Bug? ΓòÉΓòÉΓòÉ

If you are not sure whether you have found a bug, here are some guidelines:

o If the debugger gets a fatal signal, for any input whatever, that is a GDB
  bug.  Reliable debuggers never crash.

o If GDB produces an error message for valid input, that is a bug.

o If GDB 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''.

o If you are an experienced user of debugging tools, your suggestions for
  improvement of GDB are welcome in any case.


ΓòÉΓòÉΓòÉ 21.2. How to Report Bugs ΓòÉΓòÉΓòÉ

A number of companies and individuals offer support for GNU products. If you
obtained GDB from a support organization, we recommend you contact that
organization first.

Contact information for many support companies and individuals is available in
the file `etc/SERVICE' in the GNU Emacs distribution.

In any event, we also recommend that you send bug reports for GDB to one of
these addresses:

[e-mail]
{ucbvax|mit-eddie|uunet}!prep.ai.mit.edu!bug-gdb

*Do not send bug reports to `info-gdb', or to `help-gdb', or to any
newsgroups.* Most users of GDB do not want to receive bug reports.  Those that
do, have arranged to receive `bug-gdb'.

The mailing list `bug-gdb' has a newsgroup `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:

GNU Debugger Bugs
Free Software Foundation
545 Tech Square
Cambridge, MA 02139

The fundamental principle of reporting bugs usefully is this: *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 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:

o The version of GDB.  GDB announces it if you start with no arguments; you can
  also print it at any time using show version.

  Without this, we will not know whether there is any point in looking for the
  bug in the current version of GDB.

o The type of machine you are using, and the operating system name and version
  number.

o What compiler (and its version) was used to compile GDB---e.g. ``gcc-2.0''.

o What compiler (and its version) was used to compile the program you are
  debugging---e.g.  ``gcc-2.0''.

o The command arguments you gave the compiler to compile your example and
  observe the bug.  For example, did you use `-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.

o A complete input script, and all necessary source files, that will reproduce
  the bug.

o 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 GDB 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 GDB
  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.

o If you wish to suggest changes to the GDB source, send us context diffs.  If
  you even discuss something in the GDB 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.

Here are some things that are not necessary:

o 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 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.

o 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 GDB 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.

o 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.


ΓòÉΓòÉΓòÉ 22. Renamed Commands ΓòÉΓòÉΓòÉ

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:

OLD COMMAND               NEW COMMAND
---------------           -------------------------------
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]


ΓòÉΓòÉΓòÉ 23. Formatting the Documentation ΓòÉΓòÉΓòÉ

The GDB 4 release includes an already-formatted reference card, ready for
printing with PostScript or GhostScript, in the `gdb' subdirectory of the main
source directory---in `gdb-4.7/gdb/refcard.ps' of the version 4.7 release. If
you can use PostScript or GhostScript with your printer, you can print the
reference card immediately with `refcard.ps'.

The release also includes the source for the reference card.  You can format
it, using TeX, by typing:

make refcard.dvi

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 dvi output program.

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
texi2roff) to typeset the printed version.

GDB includes an already formatted copy of the on-line Info version of this
manual in the `gdb' subdirectory.  The main Info file is
`gdb-version-number/gdb/gdb.info', and it refers to subordinate files matching
`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 info
subsystem in GNU Emacs or the standalone 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 texinfo-format-buffer or makeinfo.

If you have makeinfo installed, and are in the top level GDB source directory
(`gdb-4.7', in the case of version 4.7), you can make the Info file by typing:

cd gdb
make gdb.info

If you want to typeset and print copies of this manual, you need TeX, a
printing program such as lpr, and `texinfo.tex', the Texinfo definitions file.

TeX is typesetting program; it does not print files directly, but produces
output files called dvi files.  To print a typeset document, you need a program
to print dvi files.  If your system has TeX installed, chances are it has such
a program.  The precise command to use depends on your system; lpr -d is
common; another is dvips.  The dvi print command may require a file name
without any extension or a `.dvi' extension.

TeX also requires a macro definitions file called `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.  `texinfo.tex' is distributed
with GDB and is located in the `gdb-version-number/texinfo' directory.

If you have TeX and a dvi printer program installed, you can typeset and print
this manual.  First switch to the the `gdb' subdirectory of the main source
directory (for example, to `gdb-4.7/gdb') and then type:

make gdb.dvi


ΓòÉΓòÉΓòÉ 24. Installing GDB ΓòÉΓòÉΓòÉ

GDB comes with a configure script that automates the process of preparing GDB
for installation; you can then use make to build the program.

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
`gdb'.

For example, the GDB version 4.7 distribution is in the `gdb-4.7' directory.
That directory contains:

gdb-4.7/configure (and supporting files)
          script for configuring GDB and all its supporting libraries.

gdb-4.7/gdb
          the source specific to GDB itself

gdb-4.7/bfd
          source for the Binary File Descriptor library

gdb-4.7/include
          GNU include files

gdb-4.7/libiberty
          source for the `-liberty' free software library

gdb-4.7/opcodes
          source for the library of opcode tables and disassemblers

gdb-4.7/readline
          source for the GNU command-line interface

gdb-4.7/glob
          source for the GNU filename pattern-matching subroutine

gdb-4.7/mmalloc
          source for the GNU memory-mapped malloc package

The simplest way to configure and build GDB is to run configure from the
`gdb-version-number' source directory, which in this example is the `gdb-4.7'
directory.

First switch to the `gdb-version-number' source directory if you are not
already in it; then run configure.  Pass the identifier for the platform on
which GDB will run as an argument.

For example:

cd gdb-4.7
./configure host
make

where host is an identifier such as `sun4' or `decstation', that identifies the
platform where GDB will run.

Running `configure host' followed by make builds the `bfd', `readline',
`mmalloc', and `libiberty' libraries, then gdb itself.  The configured source
files, and the binaries, are left in the corresponding source directories.

configure is a Bourne-shell (/bin/sh) script; if your system does not recognize
this automatically when you run a different shell, you may need to run sh on it
explicitly:

sh configure host

If you run configure from a directory that contains source directories for
multiple libraries or programs, such as the `gdb-4.7' source directory for
version 4.7, configure creates configuration files for every directory level
underneath (unless you tell it not to, with the `--norecursion' option).

You can run the 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 4.7, type the following to configure only the bfd
subdirectory:

cd gdb-4.7/bfd
../configure host

You can install gdb anywhere; it has no hardwired paths. However, you should
make sure that the shell on your path (named by the `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.


ΓòÉΓòÉΓòÉ 24.1. Compiling GDB in Another Directory ΓòÉΓòÉΓòÉ

If you want to run GDB versions for several host or target machines, you'll
need a different gdb compiled for each combination of host and target.
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 make program handles the `VPATH' feature (GNU make does), running make
in each of these directories then builds the gdb program specified there.

To build gdb in a separate directory, run configure with the `--srcdir' option
to specify where to find the source. (You'll also need to specify a path to
find configure itself from your working directory.  If the path to configure
would be the same as the argument to `--srcdir', you can leave out the
`--srcdir' option; it will be assumed.)

For example, with version 4.7, you can build GDB in a separate directory for a
Sun 4 like this:

cd gdb-4.7
mkdir ../gdb-sun4
cd ../gdb-sun4
../gdb-4.7/configure sun4
make

When 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 `libiberty.a' in the directory `gdb-sun4/libiberty', and GDB
itself in `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 `--target=target' option to
configure.

When you run make to build a program or library, you must run it in a
configured directory---whatever directory you were in when you called configure
(or one of its subdirectories).

The Makefile generated by configure for each source directory also runs
recursively.  If you type make in a source directory such as `gdb-4.7' (or in a
separate configured directory configured with `--srcdir=path/gdb-4.7'), you
will build all the required libraries, then build GDB.

When you have multiple hosts or targets configured in separate directories, you
can run make on them in parallel (for example, if they are NFS-mounted on each
of the hosts); they will not interfere with each other.


ΓòÉΓòÉΓòÉ 24.2. Specifying Names for Hosts and Targets ΓòÉΓòÉΓòÉ

The specifications used for hosts and targets in the 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:

architecture-vendor-os

For example, you can use the alias sun4 as a host argument or in a
--target=target option, but the equivalent full name is `sparc-sun-sunos4'.

The configure script accompanying GDB does not provide any query facility to
list all supported host and target names or aliases.  configure calls the
Bourne shell script 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:

% sh config.sub sun4
sparc-sun-sunos411
% sh config.sub sun3
m68k-sun-sunos411
% sh config.sub decstation
mips-dec-ultrix42
% 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

config.sub is also distributed in the GDB source directory (`gdb-4.7', for
version 4.7).


ΓòÉΓòÉΓòÉ 24.3. configure Options ΓòÉΓòÉΓòÉ

Here is a summary of the configure options and arguments that are most often
useful for building GDB.  configure also has several other options not listed
here.  See Info file What Configure Does,,configure.info, for a full
explanation of configure.

configure [--help]
          [--prefix=dir]
          [--srcdir=path]
          [--norecursion] [--rm]
          [--target=target] host

You may introduce options with a single `-' rather than `--' if you prefer; but
you may abbreviate option names if you use `--'.

--help
          Display a quick summary of how to invoke configure.

-prefix=dir
          Configure the source to install programs and files under directory
          `dir'.

--srcdir=path
          *Warning: using this option requires GNU make, or another make that
          implements the 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.  configure writes configuration specific files
          in the current directory, but arranges for them to use the source in
          the directory path.  configure will create directories under the
          working directory in parallel to the source directories below path.

--norecursion
          Configure only the directory level where configure is executed; do
          not propagate configuration to subdirectories.

--rm
          Remove the configuration that the other arguments specify.

--target=target
          Configure GDB for cross-debugging programs running on the specified
          target.  Without this option, GDB is configured to debug programs
          that run on the same machine (host) as GDB itself.

          There is no convenient way to generate a list of all available
          targets.

host ...
          Configure GDB to run on the specified host.

          There is no convenient way to generate a list of all available hosts.

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.


ΓòÉΓòÉΓòÉ 25. GNU GENERAL PUBLIC LICENSE ΓòÉΓòÉΓòÉ

                              Version 2, June 1991

Copyright (C) 1989, 1991 Free Software Foundation, Inc.
675 Mass Ave, Cambridge, MA 02139, USA

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.


ΓòÉΓòÉΓòÉ 25.1. Preamble ΓòÉΓòÉΓòÉ

 The licenses for most software are designed to take away your freedom to share
and change it.  By contrast, the GNU General Public License is intended to
guarantee your freedom to share and change free software---to make sure the
software is free for all its users.  This General Public License applies to
most of the Free Software Foundation's software and to any other program whose
authors commit to using it.  (Some other Free Software Foundation software is
covered by the GNU Library General Public License instead.)  You can apply it
to your programs, too.

 When we speak of free software, we are referring to freedom, not price.  Our
General Public Licenses are designed to make sure that you have the freedom to
distribute copies of free software (and charge for this service if you wish),
that you receive source code or can get it if you want it, that you can change
the software or use pieces of it in new free programs; and that you know you
can do these things.

 To protect your rights, we need to make restrictions that forbid anyone to
deny you these rights or to ask you to surrender the rights. These restrictions
translate to certain responsibilities for you if you distribute copies of the
software, or if you modify it.

 For example, if you distribute copies of such a program, whether gratis or for
a fee, you must give the recipients all the rights that you have.  You must
make sure that they, too, receive or can get the source code.  And you must
show them these terms so they know their rights.

 We protect your rights with two steps: (1) copyright the software, and (2)
offer you this license which gives you legal permission to copy, distribute
and/or modify the software.

 Also, for each author's protection and ours, we want to make certain that
everyone understands that there is no warranty for this free software.  If the
software is modified by someone else and passed on, we want its recipients to
know that what they have is not the original, so that any problems introduced
by others will not reflect on the original authors' reputations.

 Finally, any free program is threatened constantly by software patents.  We
wish to avoid the danger that redistributors of a free program will
individually obtain patent licenses, in effect making the program proprietary.
To prevent this, we have made it clear that any patent must be licensed for
everyone's free use or not licensed at all.

 The precise terms and conditions for copying, distribution and modification
follow.

         TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

 1. This License applies to any program or other work which contains a notice
    placed by the copyright holder saying it may be distributed under the terms
    of this General Public License.  The ``Program'', below, refers to any such
    program or work, and a ``work based on the Program'' means either the
    Program or any derivative work under copyright law: that is to say, a work
    containing the Program or a portion of it, either verbatim or with
    modifications and/or translated into another language.  (Hereinafter,
    translation is included without limitation in the term ``modification''.)
    Each licensee is addressed as ``you''.

    Activities other than copying, distribution and modification are not
    covered by this License; they are outside its scope.  The act of running
    the Program is not restricted, and the output from the Program is covered
    only if its contents constitute a work based on the Program (independent of
    having been made by running the Program). Whether that is true depends on
    what the Program does.

 2. You may copy and distribute verbatim copies of the Program's source code as
    you receive it, in any medium, provided that you conspicuously and
    appropriately publish on each copy an appropriate copyright notice and
    disclaimer of warranty; keep intact all the notices that refer to this
    License and to the absence of any warranty; and give any other recipients
    of the Program a copy of this License along with the Program.

    You may charge a fee for the physical act of transferring a copy, and you
    may at your option offer warranty protection in exchange for a fee.

 3. You may modify your copy or copies of the Program or any portion of it,
    thus forming a work based on the Program, and copy and distribute such
    modifications or work under the terms of Section 1 above, provided that you
    also meet all of these conditions:

    a. You must cause the modified files to carry prominent notices stating
       that you changed the files and the date of any change.

    b. You must cause any work that you distribute or publish, that in whole or
       in part contains or is derived from the Program or any part thereof, to
       be licensed as a whole at no charge to all third parties under the terms
       of this License.

    c. If the modified program normally reads commands interactively when run,
       you must cause it, when started running for such interactive use in the
       most ordinary way, to print or display an announcement including an
       appropriate copyright notice and a notice that there is no warranty (or
       else, saying that you provide a warranty) and that users may
       redistribute the program under these conditions, and telling the user
       how to view a copy of this License.  (Exception: if the Program itself
       is interactive but does not normally print such an announcement, your
       work based on the Program is not required to print an announcement.)

    These requirements apply to the modified work as a whole.  If identifiable
    sections of that work are not derived from the Program, and can be
    reasonably considered independent and separate works in themselves, then
    this License, and its terms, do not apply to those sections when you
    distribute them as separate works.  But when you distribute the same
    sections as part of a whole which is a work based on the Program, the
    distribution of the whole must be on the terms of this License, whose
    permissions for other licensees extend to the entire whole, and thus to
    each and every part regardless of who wrote it.

    Thus, it is not the intent of this section to claim rights or contest your
    rights to work written entirely by you; rather, the intent is to exercise
    the right to control the distribution of derivative or collective works
    based on the Program.

    In addition, mere aggregation of another work not based on the Program with
    the Program (or with a work based on the Program) on a volume of a storage
    or distribution medium does not bring the other work under the scope of
    this License.

 4. You may copy and distribute the Program (or a work based on it, under
    Section 2) in object code or executable form under the terms of Sections 1
    and 2 above provided that you also do one of the following:

    a. Accompany it with the complete corresponding machine-readable source
       code, which must be distributed under the terms of Sections 1 and 2
       above on a medium customarily used for software interchange; or,

    b. Accompany it with a written offer, valid for at least three years, to
       give any third party, for a charge no more than your cost of physically
       performing source distribution, a complete machine-readable copy of the
       corresponding source code, to be distributed under the terms of Sections
       1 and 2 above on a medium customarily used for software interchange; or,

    c. Accompany it with the information you received as to the offer to
       distribute corresponding source code.  (This alternative is allowed only
       for noncommercial distribution and only if you received the program in
       object code or executable form with such an offer, in accord with
       Subsection b above.)

    The source code for a work means the preferred form of the work for making
    modifications to it.  For an executable work, complete source code means
    all the source code for all modules it contains, plus any associated
    interface definition files, plus the scripts used to control compilation
    and installation of the executable.  However, as a special exception, the
    source code distributed need not include anything that is normally
    distributed (in either source or binary form) with the major components
    (compiler, kernel, and so on) of the operating system on which the
    executable runs, unless that component itself accompanies the executable.

    If distribution of executable or object code is made by offering access to
    copy from a designated place, then offering equivalent access to copy the
    source code from the same place counts as distribution of the source code,
    even though third parties are not compelled to copy the source along with
    the object code.

 5. You may not copy, modify, sublicense, or distribute the Program except as
    expressly provided under this License.  Any attempt otherwise to copy,
    modify, sublicense or distribute the Program is void, and will
    automatically terminate your rights under this License. However, parties
    who have received copies, or rights, from you under this License will not
    have their licenses terminated so long as such parties remain in full
    compliance.

 6. You are not required to accept this License, since you have not signed it.
    However, nothing else grants you permission to modify or distribute the
    Program or its derivative works.  These actions are prohibited by law if
    you do not accept this License.  Therefore, by modifying or distributing
    the Program (or any work based on the Program), you indicate your
    acceptance of this License to do so, and all its terms and conditions for
    copying, distributing or modifying the Program or works based on it.

 7. Each time you redistribute the Program (or any work based on the Program),
    the recipient automatically receives a license from the original licensor
    to copy, distribute or modify the Program subject to these terms and
    conditions.  You may not impose any further restrictions on the recipients'
    exercise of the rights granted herein. You are not responsible for
    enforcing compliance by third parties to this License.

 8. If, as a consequence of a court judgment or allegation of patent
    infringement or for any other reason (not limited to patent issues),
    conditions are imposed on you (whether by court order, agreement or
    otherwise) that contradict the conditions of this License, they do not
    excuse you from the conditions of this License.  If you cannot distribute
    so as to satisfy simultaneously your obligations under this License and any
    other pertinent obligations, then as a consequence you may not distribute
    the Program at all.  For example, if a patent license would not permit
    royalty-free redistribution of the Program by all those who receive copies
    directly or indirectly through you, then the only way you could satisfy
    both it and this License would be to refrain entirely from distribution of
    the Program.

    If any portion of this section is held invalid or unenforceable under any
    particular circumstance, the balance of the section is intended to apply
    and the section as a whole is intended to apply in other circumstances.

    It is not the purpose of this section to induce you to infringe any patents
    or other property right claims or to contest validity of any such claims;
    this section has the sole purpose of protecting the integrity of the free
    software distribution system, which is implemented by public license
    practices.  Many people have made generous contributions to the wide range
    of software distributed through that system in reliance on consistent
    application of that system; it is up to the author/donor to decide if he or
    she is willing to distribute software through any other system and a
    licensee cannot impose that choice.

    This section is intended to make thoroughly clear what is believed to be a
    consequence of the rest of this License.

 9. If the distribution and/or use of the Program is restricted in certain
    countries either by patents or by copyrighted interfaces, the original
    copyright holder who places the Program under this License may add an
    explicit geographical distribution limitation excluding those countries, so
    that distribution is permitted only in or among countries not thus
    excluded.  In such case, this License incorporates the limitation as if
    written in the body of this License.

10. The Free Software Foundation may publish revised and/or new versions of the
    General Public License from time to time.  Such new versions will be
    similar in spirit to the present version, but may differ in detail to
    address new problems or concerns.

    Each version is given a distinguishing version number.  If the Program
    specifies a version number of this License which applies to it and ``any
    later version'', you have the option of following the terms and conditions
    either of that version or of any later version published by the Free
    Software Foundation.  If the Program does not specify a version number of
    this License, you may choose any version ever published by the Free
    Software Foundation.

11. If you wish to incorporate parts of the Program into other free programs
    whose distribution conditions are different, write to the author to ask for
    permission.  For software which is copyrighted by the Free Software
    Foundation, write to the Free Software Foundation; we sometimes make
    exceptions for this.  Our decision will be guided by the two goals of
    preserving the free status of all derivatives of our free software and of
    promoting the sharing and reuse of software generally.

                                     NO WARRANTY

12. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR
    THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
    OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
    PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER
    EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
    OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK
    AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
    PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
    REPAIR OR CORRECTION.

13. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL
    ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE
    THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
    GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
    USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
    DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
    PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
    EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGES.

                           END OF TERMS AND CONDITIONS


ΓòÉΓòÉΓòÉ 25.2. Applying These Terms to Your New Programs ΓòÉΓòÉΓòÉ

 If you develop a new program, and you want it to be of the greatest possible
use to the public, the best way to achieve this is to make it free software
which everyone can redistribute and change under these terms.

 To do so, attach the following notices to the program.  It is safest to attach
them to the start of each source file to most effectively convey the exclusion
of warranty; and each file should have at least the ``copyright'' line and a
pointer to where the full notice is found.

one line to give the program's name and an idea of what it does.
Copyright (C) 19yy  name of author

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the
Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this when it
starts in an interactive mode:

Gnomovision version 69, Copyright (C) 19yy name of author
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'.  This is free software, and you are welcome
to redistribute it under certain conditions; type `show c'
for details.

The hypothetical commands `show w' and `show c' should show the appropriate
parts of the General Public License.  Of course, the commands you use may be
called something other than `show w' and `show c'; they could even be
mouse-clicks or menu items---whatever suits your program.

You should also get your employer (if you work as a programmer) or your school,
if any, to sign a ``copyright disclaimer'' for the program, if necessary.  Here
is a sample; alter the names:

Yoyodyne, Inc., hereby disclaims all copyright
interest in the program `Gnomovision'
(which makes passes at compilers) written
by James Hacker.

signature of Ty Coon, 1 April 1989
Ty Coon, President of Vice

This General Public License does not permit incorporating your program into
proprietary programs.  If your program is a subroutine library, you may
consider it more useful to permit linking proprietary applications with the
library.  If this is what you want to do, use the GNU Library General Public
License instead of this License.


ΓòÉΓòÉΓòÉ 26. Index ΓòÉΓòÉΓòÉ

Sorry, no cp index