This is gdb.info, produced by makeinfo version 4.13 from ./gdb.texinfo.

INFO-DIR-SECTION Software development
START-INFO-DIR-ENTRY
* Gdb: (gdb).                     The GNU debugger.
END-INFO-DIR-ENTRY

   Copyright (C) 1988-2013 Free Software Foundation, Inc.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Free Software" and "Free Software Needs Free
Documentation", with the Front-Cover Texts being "A GNU Manual," and
with the Back-Cover Texts as in (a) below.

   (a) The FSF's Back-Cover Text is: "You are free to copy and modify
this GNU Manual.  Buying copies from GNU Press supports the FSF in
developing GNU and promoting software freedom."

   This file documents the GNU debugger GDB.

   This is the Tenth Edition, of `Debugging with GDB: the GNU
Source-Level Debugger' for GDB (GDB) Version 7.6.

   Copyright (C) 1988-2013 Free Software Foundation, Inc.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Free Software" and "Free Software Needs Free
Documentation", with the Front-Cover Texts being "A GNU Manual," and
with the Back-Cover Texts as in (a) below.

   (a) The FSF's Back-Cover Text is: "You are free to copy and modify
this GNU Manual.  Buying copies from GNU Press supports the FSF in
developing GNU and promoting software freedom."


File: gdb.info,  Node: MiniDebugInfo,  Next: Index Files,  Prev: Separate Debug Files,  Up: GDB Files

18.3 Debugging information in a special section
===============================================

Some systems ship pre-built executables and libraries that have a
special `.gnu_debugdata' section.  This feature is called
"MiniDebugInfo".  This section holds an LZMA-compressed object and is
used to supply extra symbols for backtraces.

   The intent of this section is to provide extra minimal debugging
information for use in simple backtraces.  It is not intended to be a
replacement for full separate debugging information (*note Separate
Debug Files::).  The example below shows the intended use; however, GDB
does not currently put restrictions on what sort of debugging
information might be included in the section.

   GDB has support for this extension.  If the section exists, then it
is used provided that no other source of debugging information can be
found, and that GDB was configured with LZMA support.

   This section can be easily created using `objcopy' and other
standard utilities:

     # Extract the dynamic symbols from the main binary, there is no need
     # to also have these in the normal symbol table
     nm -D BINARY --format=posix --defined-only \
       | awk '{ print $1 }' | sort > dynsyms

     # Extract all the text (i.e. function) symbols from the debuginfo .
     nm BINARY --format=posix --defined-only \
       | awk '{ if ($2 == "T" || $2 == "t") print $1 }' \
       | sort > funcsyms

     # Keep all the function symbols not already in the dynamic symbol
     # table.
     comm -13 dynsyms funcsyms > keep_symbols

     # Copy the full debuginfo, keeping only a minimal set of symbols and
     # removing some unnecessary sections.
     objcopy -S --remove-section .gdb_index --remove-section .comment \
       --keep-symbols=keep_symbols BINARY mini_debuginfo

     # Inject the compressed data into the .gnu_debugdata section of the
     # original binary.
     xz mini_debuginfo
     objcopy --add-section .gnu_debugdata=mini_debuginfo.xz BINARY


File: gdb.info,  Node: Index Files,  Next: Symbol Errors,  Prev: MiniDebugInfo,  Up: GDB Files

18.4 Index Files Speed Up GDB
=============================

When GDB finds a symbol file, it scans the symbols in the file in order
to construct an internal symbol table.  This lets most GDB operations
work quickly--at the cost of a delay early on.  For large programs,
this delay can be quite lengthy, so GDB provides a way to build an
index, which speeds up startup.

   The index is stored as a section in the symbol file.  GDB can write
the index to a file, then you can put it into the symbol file using
`objcopy'.

   To create an index file, use the `save gdb-index' command:

`save gdb-index DIRECTORY'
     Create an index file for each symbol file currently known by GDB.
     Each file is named after its corresponding symbol file, with
     `.gdb-index' appended, and is written into the given DIRECTORY.

   Once you have created an index file you can merge it into your symbol
file, here named `symfile', using `objcopy':

     $ objcopy --add-section .gdb_index=symfile.gdb-index \
         --set-section-flags .gdb_index=readonly symfile symfile

   GDB will normally ignore older versions of `.gdb_index' sections
that have been deprecated.  Usually they are deprecated because they
are missing a new feature or have performance issues.  To tell GDB to
use a deprecated index section anyway specify `set
use-deprecated-index-sections on'.  The default is `off'.  This can
speed up startup, but may result in some functionality being lost.
*Note Index Section Format::.

   _Warning:_ Setting `use-deprecated-index-sections' to `on' must be
done before gdb reads the file.  The following will not work:

     $ gdb -ex "set use-deprecated-index-sections on" <program>

   Instead you must do, for example,

     $ gdb -iex "set use-deprecated-index-sections on" <program>

   There are currently some limitation on indices.  They only work when
for DWARF debugging information, not stabs.  And, they do not currently
work for programs using Ada.


File: gdb.info,  Node: Symbol Errors,  Next: Data Files,  Prev: Index Files,  Up: GDB Files

18.5 Errors Reading Symbol Files
================================

While reading a symbol file, GDB occasionally encounters 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 (*note
Optional Warnings and Messages: Messages/Warnings.).

   The messages currently printed, and their meanings, include:

`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 has trouble locating
     symbols in the source file whose symbols it is reading.  (You can
     often determine what source file is affected by specifying `set
     verbose on'.  *Note Optional Warnings and Messages:
     Messages/Warnings.)

`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
     uncomprehended information, in hexadecimal.

     GDB circumvents the error by ignoring this symbol information.
     This usually allows you to debug your program, though certain
     symbols are not 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.



File: gdb.info,  Node: Data Files,  Prev: Symbol Errors,  Up: GDB Files

18.6 GDB Data Files
===================

GDB will sometimes read an auxiliary data file.  These files are kept
in a directory known as the "data directory".

   You can set the data directory's name, and view the name GDB is
currently using.

`set data-directory DIRECTORY'
     Set the directory which GDB searches for auxiliary data files to
     DIRECTORY.

`show data-directory'
     Show the directory GDB searches for auxiliary data files.

   You can set the default data directory by using the configure-time
`--with-gdb-datadir' option.  If the data directory is inside GDB's
configured binary prefix (set with `--prefix' or `--exec-prefix'), then
the default data directory will be updated automatically if the
installed GDB is moved to a new location.

   The data directory may also be specified with the `--data-directory'
command line option.  *Note Mode Options::.


File: gdb.info,  Node: Targets,  Next: Remote Debugging,  Prev: GDB Files,  Up: Top

19 Specifying a Debugging Target
********************************

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 (*note Commands for Managing Targets:
Target Commands.).

   It is possible to build GDB for several different "target
architectures".  When GDB is built like that, you can choose one of the
available architectures with the `set architecture' command.

`set architecture ARCH'
     This command sets the current target architecture to ARCH.  The
     value of ARCH can be `"auto"', in addition to one of the supported
     architectures.

`show architecture'
     Show the current target architecture.

`set processor'
`processor'
     These are alias commands for, respectively, `set architecture' and
     `show architecture'.

* Menu:

* Active Targets::              Active targets
* Target Commands::             Commands for managing targets
* Byte Order::                  Choosing target byte order


File: gdb.info,  Node: Active Targets,  Next: Target Commands,  Up: Targets

19.1 Active Targets
===================

There are multiple classes of targets such as: processes, executable
files or recording sessions.  Core files belong to the process class,
making core file and process mutually exclusive.  Otherwise, GDB can
work concurrently on multiple active targets, one in each class.  This
allows you to (for example) start a process and inspect its activity,
while still having access to the executable file after the process
finishes.  Or if you start process recording (*note Reverse
Execution::) and `reverse-step' there, you are presented a virtual
layer of the recording target, while the process target remains stopped
at the chronologically last point of the process execution.

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


File: gdb.info,  Node: Target Commands,  Next: Byte Order,  Prev: Active Targets,  Up: Targets

19.2 Commands for Managing Targets
==================================

`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 does 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'
     (*note Commands to Specify Files: Files.).

`help target NAME'
     Describe a particular target, including any parameters necessary to
     select it.

`set gnutarget ARGS'
     GDB uses its own library BFD to read your files.  GDB knows
     whether it is reading an "executable", a "core", or a ".o" file;
     however, you can specify the file format with the `set gnutarget'
     command.  Unlike most `target' commands, with `gnutarget' the
     `target' refers to a program, not a machine.

          _Warning:_ To specify a file format with `set gnutarget', you
          must know the actual BFD name.

     *Note Commands to Specify Files: Files.

`show gnutarget'
     Use the `show gnutarget' command to display what file format
     `gnutarget' is set to read.  If you have not set `gnutarget', GDB
     will determine the file format for each file automatically, and
     `show gnutarget' displays `The current BFD target is "auto"'.

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

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

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

`target remote MEDIUM'
     A remote system connected to GDB via a serial line or network
     connection.  This command tells GDB to use its own remote protocol
     over MEDIUM for debugging.  *Note Remote Debugging::.

     For example, if you have a board connected to `/dev/ttya' on the
     machine running GDB, you could say:

          target remote /dev/ttya

     `target remote' supports the `load' command.  This is only useful
     if you have some other way of getting the stub to the target
     system, and you can put it somewhere in memory where it won't get
     clobbered by the download.

`target sim [SIMARGS] ...'
     Builtin CPU simulator.  GDB includes simulators for most
     architectures.  In general,
                  target sim
                  load
                  run
     works; however, you cannot assume that a specific memory map,
     device drivers, or even basic I/O is available, although some
     simulators do provide these.  For info about any
     processor-specific simulator details, see the appropriate section
     in *note Embedded Processors: Embedded Processors.


   Some configurations may include these targets as well:

`target nrom DEV'
     NetROM ROM emulator.  This target only supports downloading.


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

   Many remote targets require you to download the executable's code
once you've successfully established a connection.  You may wish to
control various aspects of this process.

`set hash'
     This command controls whether a hash mark `#' is displayed while
     downloading a file to the remote monitor.  If on, a hash mark is
     displayed after each S-record is successfully downloaded to the
     monitor.

`show hash'
     Show the current status of displaying the hash mark.

`set debug monitor'
     Enable or disable display of communications messages between GDB
     and the remote monitor.

`show debug monitor'
     Show the current status of displaying communications between GDB
     and the remote monitor.

`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 the FILENAME symbol table in GDB, like the
     `add-symbol-file' command.

     If your GDB does not have a `load' command, attempting to execute
     it gets the error message "`You can't do that when your target is
     ...'"

     The file is loaded at whatever address is specified in the
     executable.  For some object file formats, you can specify the
     load address when you link the program; for other formats, like
     a.out, the object file format specifies a fixed address.

     Depending on the remote side capabilities, GDB may be able to load
     programs into flash memory.

     `load' does not repeat if you press <RET> again after using it.


File: gdb.info,  Node: Byte Order,  Prev: Target Commands,  Up: Targets

19.3 Choosing Target Byte Order
===============================

Some types of processors, such as the MIPS, PowerPC, and Renesas SH,
offer the ability to run either big-endian or little-endian byte
orders.  Usually the executable or symbol will include a bit to
designate the endian-ness, and you will not need to worry about which
to use.  However, you may still find it useful to adjust GDB's idea of
processor endian-ness manually.

`set endian big'
     Instruct GDB to assume the target is big-endian.

`set endian little'
     Instruct GDB to assume the target is little-endian.

`set endian auto'
     Instruct GDB to use the byte order associated with the executable.

`show endian'
     Display GDB's current idea of the target byte order.


   Note that these commands merely adjust interpretation of symbolic
data on the host, and that they have absolutely no effect on the target
system.


File: gdb.info,  Node: Remote Debugging,  Next: Configurations,  Prev: Targets,  Up: Top

20 Debugging Remote Programs
****************************

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 runs on the remote system to communicate
with GDB.

   Other remote targets may be available in your configuration of GDB;
use `help target' to list them.

* Menu:

* Connecting::                  Connecting to a remote target
* File Transfer::               Sending files to a remote system
* Server::	                Using the gdbserver program
* Remote Configuration::        Remote configuration
* Remote Stub::                 Implementing a remote stub


File: gdb.info,  Node: Connecting,  Next: File Transfer,  Up: Remote Debugging

20.1 Connecting to a Remote Target
==================================

On the GDB host machine, you will need an unstripped copy of your
program, since GDB needs symbol and debugging information.  Start up
GDB as usual, using the name of the local copy of your program as the
first argument.

   GDB can communicate with the target over a serial line, or over an
IP network using TCP or UDP.  In each case, GDB uses the same protocol
for debugging your program; only the medium carrying the debugging
packets varies.  The `target remote' command establishes a connection
to the target.  Its arguments indicate which medium to use:

`target remote SERIAL-DEVICE'
     Use SERIAL-DEVICE to communicate with the target.  For example, to
     use a serial line connected to the device named `/dev/ttyb':

          target remote /dev/ttyb

     If you're using a serial line, you may want to give GDB the
     `--baud' option, or use the `set remotebaud' command (*note set
     remotebaud: Remote Configuration.) before the `target' command.

`target remote `HOST:PORT''
`target remote `tcp:HOST:PORT''
     Debug using a TCP connection to PORT on HOST.  The HOST may be
     either a host name or a numeric IP address; PORT must be a decimal
     number.  The HOST could be the target machine itself, if it is
     directly connected to the net, or it might be a terminal server
     which in turn has a serial line to the target.

     For example, to connect to port 2828 on a terminal server named
     `manyfarms':

          target remote manyfarms:2828

     If your remote target is actually running on the same machine as
     your debugger session (e.g. a simulator for your target running on
     the same host), you can omit the hostname.  For example, to
     connect to port 1234 on your local machine:

          target remote :1234
     Note that the colon is still required here.

`target remote `udp:HOST:PORT''
     Debug using UDP packets to PORT on HOST.  For example, to connect
     to UDP port 2828 on a terminal server named `manyfarms':

          target remote udp:manyfarms:2828

     When using a UDP connection for remote debugging, you should keep
     in mind that the `U' stands for "Unreliable".  UDP can silently
     drop packets on busy or unreliable networks, which will cause
     havoc with your debugging session.

`target remote | COMMAND'
     Run COMMAND in the background and communicate with it using a
     pipe.  The COMMAND is a shell command, to be parsed and expanded
     by the system's command shell, `/bin/sh'; it should expect remote
     protocol packets on its standard input, and send replies on its
     standard output.  You could use this to run a stand-alone simulator
     that speaks the remote debugging protocol, to make net connections
     using programs like `ssh', or for other similar tricks.

     If COMMAND closes its standard output (perhaps by exiting), GDB
     will try to send it a `SIGTERM' signal.  (If the program has
     already exited, this will have no effect.)


   Once the connection has been established, you can use all the usual
commands to examine and change data.  The remote program is already
running; you can use `step' and `continue', and you do not need to use
`run'.

   Whenever GDB is waiting for the remote program, if you type the
interrupt character (often `Ctrl-c'), GDB attempts to stop the program.
This may or may not succeed, depending in part on the hardware and the
serial drivers the remote system uses.  If you type the interrupt
character once again, GDB displays this prompt:

     Interrupted while waiting for the program.
     Give up (and stop debugging it)?  (y or n)

   If you type `y', GDB abandons the remote debugging session.  (If you
decide you want to try again later, you can use `target remote' again
to connect once more.)  If you type `n', GDB goes back to waiting.

`detach'
     When you have finished debugging the remote program, you can use
     the `detach' command to release it from GDB control.  Detaching
     from the target normally resumes its execution, but the results
     will depend on your particular remote stub.  After the `detach'
     command, GDB is free to connect to another target.

`disconnect'
     The `disconnect' command behaves like `detach', except that the
     target is generally not resumed.  It will wait for GDB (this
     instance or another one) to connect and continue debugging.  After
     the `disconnect' command, GDB is again free to connect to another
     target.

`monitor CMD'
     This command allows you to send arbitrary commands directly to the
     remote monitor.  Since GDB doesn't care about the commands it
     sends like this, this command is the way to extend GDB--you can
     add new commands that only the external monitor will understand
     and implement.


File: gdb.info,  Node: File Transfer,  Next: Server,  Prev: Connecting,  Up: Remote Debugging

20.2 Sending files to a remote system
=====================================

Some remote targets offer the ability to transfer files over the same
connection used to communicate with GDB.  This is convenient for
targets accessible through other means, e.g. GNU/Linux systems running
`gdbserver' over a network interface.  For other targets, e.g. embedded
devices with only a single serial port, this may be the only way to
upload or download files.

   Not all remote targets support these commands.

`remote put HOSTFILE TARGETFILE'
     Copy file HOSTFILE from the host system (the machine running GDB)
     to TARGETFILE on the target system.

`remote get TARGETFILE HOSTFILE'
     Copy file TARGETFILE from the target system to HOSTFILE on the
     host system.

`remote delete TARGETFILE'
     Delete TARGETFILE from the target system.



File: gdb.info,  Node: Server,  Next: Remote Configuration,  Prev: File Transfer,  Up: Remote Debugging

20.3 Using the `gdbserver' Program
==================================

`gdbserver' is a control program for Unix-like systems, which allows
you to connect your program with a remote GDB via `target remote'--but
without linking in the usual debugging stub.

   `gdbserver' is not a complete replacement for the debugging stubs,
because it requires essentially the same operating-system facilities
that GDB itself does.  In fact, a system that can run `gdbserver' to
connect to a remote GDB could also run GDB locally!  `gdbserver' is
sometimes useful nevertheless, because it is a much smaller program
than GDB itself.  It is also easier to port than all of GDB, so you may
be able to get started more quickly on a new system by using
`gdbserver'.  Finally, if you develop code for real-time systems, you
may find that the tradeoffs involved in real-time operation make it
more convenient to do as much development work as possible on another
system, for example by cross-compiling.  You can use `gdbserver' to
make a similar choice for debugging.

   GDB and `gdbserver' communicate via either a serial line or a TCP
connection, using the standard GDB remote serial protocol.

     _Warning:_ `gdbserver' does not have any built-in security.  Do
     not run `gdbserver' connected to any public network; a GDB
     connection to `gdbserver' provides access to the target system
     with the same privileges as the user running `gdbserver'.

20.3.1 Running `gdbserver'
--------------------------

Run `gdbserver' on the target system.  You need a copy of the program
you want to debug, including any libraries it requires.  `gdbserver'
does not need your program's symbol table, so you can strip the program
if necessary to save space.  GDB on the host system does all the symbol
handling.

   To use the server, you must tell it how to communicate with GDB; the
name of your program; and the arguments for your program.  The usual
syntax is:

     target> gdbserver COMM PROGRAM [ ARGS ... ]

   COMM is either a device name (to use a serial line), or a TCP
hostname and portnumber, or `-' or `stdio' to use stdin/stdout of
`gdbserver'.  For example, to debug Emacs with the argument `foo.txt'
and communicate with GDB over the serial port `/dev/com1':

     target> gdbserver /dev/com1 emacs foo.txt

   `gdbserver' waits passively for the host GDB to communicate with it.

   To use a TCP connection instead of a serial line:

     target> gdbserver host:2345 emacs foo.txt

   The only difference from the previous example is the first argument,
specifying that you are communicating with the host GDB via TCP.  The
`host:2345' argument means that `gdbserver' is to expect a TCP
connection from machine `host' to local TCP port 2345.  (Currently, the
`host' part is ignored.)  You can choose any number you want for the
port number as long as it does not conflict with any TCP ports already
in use on the target system (for example, `23' is reserved for
`telnet').(1)  You must use the same port number with the host GDB
`target remote' command.

   The `stdio' connection is useful when starting `gdbserver' with ssh:

     (gdb) target remote | ssh -T hostname gdbserver - hello

   The `-T' option to ssh is provided because we don't need a remote
pty, and we don't want escape-character handling.  Ssh does this by
default when a command is provided, the flag is provided to make it
explicit.  You could elide it if you want to.

   Programs started with stdio-connected gdbserver have `/dev/null' for
`stdin', and `stdout',`stderr' are sent back to gdb for display through
a pipe connected to gdbserver.  Both `stdout' and `stderr' use the same
pipe.

20.3.1.1 Attaching to a Running Program
.......................................

On some targets, `gdbserver' can also attach to running programs.  This
is accomplished via the `--attach' argument.  The syntax is:

     target> gdbserver --attach COMM PID

   PID is the process ID of a currently running process.  It isn't
necessary to point `gdbserver' at a binary for the running process.

   You can debug processes by name instead of process ID if your target
has the `pidof' utility:

     target> gdbserver --attach COMM `pidof PROGRAM`

   In case more than one copy of PROGRAM is running, or PROGRAM has
multiple threads, most versions of `pidof' support the `-s' option to
only return the first process ID.

20.3.1.2 Multi-Process Mode for `gdbserver'
...........................................

When you connect to `gdbserver' using `target remote', `gdbserver'
debugs the specified program only once.  When the program exits, or you
detach from it, GDB closes the connection and `gdbserver' exits.

   If you connect using `target extended-remote', `gdbserver' enters
multi-process mode.  When the debugged program exits, or you detach
from it, GDB stays connected to `gdbserver' even though no program is
running.  The `run' and `attach' commands instruct `gdbserver' to run
or attach to a new program.  The `run' command uses `set remote
exec-file' (*note set remote exec-file::) to select the program to run.
Command line arguments are supported, except for wildcard expansion and
I/O redirection (*note Arguments::).

   To start `gdbserver' without supplying an initial command to run or
process ID to attach, use the `--multi' command line option.  Then you
can connect using `target extended-remote' and start the program you
want to debug.

   In multi-process mode `gdbserver' does not automatically exit unless
you use the option `--once'.  You can terminate it by using `monitor
exit' (*note Monitor Commands for gdbserver::).  Note that the
conditions under which `gdbserver' terminates depend on how GDB
connects to it (`target remote' or `target extended-remote').  The
`--multi' option to `gdbserver' has no influence on that.

20.3.1.3 TCP port allocation lifecycle of `gdbserver'
.....................................................

This section applies only when `gdbserver' is run to listen on a TCP
port.

   `gdbserver' normally terminates after all of its debugged processes
have terminated in `target remote' mode.  On the other hand, for `target
extended-remote', `gdbserver' stays running even with no processes left.
GDB normally terminates the spawned debugged process on its exit, which
normally also terminates `gdbserver' in the `target remote' mode.
Therefore, when the connection drops unexpectedly, and GDB cannot ask
`gdbserver' to kill its debugged processes, `gdbserver' stays running
even in the `target remote' mode.

   When `gdbserver' stays running, GDB can connect to it again later.
Such reconnecting is useful for features like *note disconnected
tracing::.  For completeness, at most one GDB can be connected at a
time.

   By default, `gdbserver' keeps the listening TCP port open, so that
additional connections are possible.  However, if you start `gdbserver'
with the `--once' option, it will stop listening for any further
connection attempts after connecting to the first GDB session.  This
means no further connections to `gdbserver' will be possible after the
first one.  It also means `gdbserver' will terminate after the first
connection with remote GDB has closed, even for unexpectedly closed
connections and even in the `target extended-remote' mode.  The
`--once' option allows reusing the same port number for connecting to
multiple instances of `gdbserver' running on the same host, since each
instance closes its port after the first connection.

20.3.1.4 Other Command-Line Arguments for `gdbserver'
.....................................................

The `--debug' option tells `gdbserver' to display extra status
information about the debugging process.  The `--remote-debug' option
tells `gdbserver' to display remote protocol debug output.  These
options are intended for `gdbserver' development and for bug reports to
the developers.

   The `--wrapper' option specifies a wrapper to launch programs for
debugging.  The option should be followed by the name of the wrapper,
then any command-line arguments to pass to the wrapper, then `--'
indicating the end of the wrapper arguments.

   `gdbserver' runs the specified wrapper program with a combined
command line including the wrapper arguments, then the name of the
program to debug, then any arguments to the program.  The wrapper runs
until it executes your program, and then GDB gains control.

   You can use any program that eventually calls `execve' with its
arguments as a wrapper.  Several standard Unix utilities do this, e.g.
`env' and `nohup'.  Any Unix shell script ending with `exec "$@"' will
also work.

   For example, you can use `env' to pass an environment variable to
the debugged program, without setting the variable in `gdbserver''s
environment:

     $ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog

20.3.2 Connecting to `gdbserver'
--------------------------------

Run GDB on the host system.

   First make sure you have the necessary symbol files.  Load symbols
for your application using the `file' command before you connect.  Use
`set sysroot' to locate target libraries (unless your GDB was compiled
with the correct sysroot using `--with-sysroot').

   The symbol file and target libraries must exactly match the
executable and libraries on the target, with one exception: the files
on the host system should not be stripped, even if the files on the
target system are.  Mismatched or missing files will lead to confusing
results during debugging.  On GNU/Linux targets, mismatched or missing
files may also prevent `gdbserver' from debugging multi-threaded
programs.

   Connect to your target (*note Connecting to a Remote Target:
Connecting.).  For TCP connections, you must start up `gdbserver' prior
to using the `target remote' command.  Otherwise you may get an error
whose text depends on the host system, but which usually looks
something like `Connection refused'.  Don't use the `load' command in
GDB when using `gdbserver', since the program is already on the target.

20.3.3 Monitor Commands for `gdbserver'
---------------------------------------

During a GDB session using `gdbserver', you can use the `monitor'
command to send special requests to `gdbserver'.  Here are the
available commands.

`monitor help'
     List the available monitor commands.

`monitor set debug 0'
`monitor set debug 1'
     Disable or enable general debugging messages.

`monitor set remote-debug 0'
`monitor set remote-debug 1'
     Disable or enable specific debugging messages associated with the
     remote protocol (*note Remote Protocol::).

`monitor set libthread-db-search-path [PATH]'
     When this command is issued, PATH is a colon-separated list of
     directories to search for `libthread_db' (*note set
     libthread-db-search-path: Threads.).  If you omit PATH,
     `libthread-db-search-path' will be reset to its default value.

     The special entry `$pdir' for `libthread-db-search-path' is not
     supported in `gdbserver'.

`monitor exit'
     Tell gdbserver to exit immediately.  This command should be
     followed by `disconnect' to close the debugging session.
     `gdbserver' will detach from any attached processes and kill any
     processes it created.  Use `monitor exit' to terminate `gdbserver'
     at the end of a multi-process mode debug session.


20.3.4 Tracepoints support in `gdbserver'
-----------------------------------------

On some targets, `gdbserver' supports tracepoints, fast tracepoints and
static tracepoints.

   For fast or static tracepoints to work, a special library called the
"in-process agent" (IPA), must be loaded in the inferior process.  This
library is built and distributed as an integral part of `gdbserver'.
In addition, support for static tracepoints requires building the
in-process agent library with static tracepoints support.  At present,
the UST (LTTng Userspace Tracer, `http://lttng.org/ust') tracing engine
is supported.  This support is automatically available if UST
development headers are found in the standard include path when
`gdbserver' is built, or if `gdbserver' was explicitly configured using
`--with-ust' to point at such headers.  You can explicitly disable the
support using `--with-ust=no'.

   There are several ways to load the in-process agent in your program:

`Specifying it as dependency at link time'
     You can link your program dynamically with the in-process agent
     library.  On most systems, this is accomplished by adding
     `-linproctrace' to the link command.

`Using the system's preloading mechanisms'
     You can force loading the in-process agent at startup time by using
     your system's support for preloading shared libraries.  Many Unixes
     support the concept of preloading user defined libraries.  In most
     cases, you do that by specifying `LD_PRELOAD=libinproctrace.so' in
     the environment.  See also the description of `gdbserver''s
     `--wrapper' command line option.

`Using GDB to force loading the agent at run time'
     On some systems, you can force the inferior to load a shared
     library, by calling a dynamic loader function in the inferior that
     takes care of dynamically looking up and loading a shared library.
     On most Unix systems, the function is `dlopen'.  You'll use the
     `call' command for that.  For example:

          (gdb) call dlopen ("libinproctrace.so", ...)

     Note that on most Unix systems, for the `dlopen' function to be
     available, the program needs to be linked with `-ldl'.

   On systems that have a userspace dynamic loader, like most Unix
systems, when you connect to `gdbserver' using `target remote', you'll
find that the program is stopped at the dynamic loader's entry point,
and no shared library has been loaded in the program's address space
yet, including the in-process agent.  In that case, before being able
to use any of the fast or static tracepoints features, you need to let
the loader run and load the shared libraries.  The simplest way to do
that is to run the program to the main procedure.  E.g., if debugging a
C or C++ program, start `gdbserver' like so:

     $ gdbserver :9999 myprogram

   Start GDB and connect to `gdbserver' like so, and run to main:

     $ gdb myprogram
     (gdb) target remote myhost:9999
     0x00007f215893ba60 in ?? () from /lib64/ld-linux-x86-64.so.2
     (gdb) b main
     (gdb) continue

   The in-process tracing agent library should now be loaded into the
process; you can confirm it with the `info sharedlibrary' command,
which will list `libinproctrace.so' as loaded in the process.  You are
now ready to install fast tracepoints, list static tracepoint markers,
probe static tracepoints markers, and start tracing.

   ---------- Footnotes ----------

   (1) If you choose a port number that conflicts with another service,
`gdbserver' prints an error message and exits.


File: gdb.info,  Node: Remote Configuration,  Next: Remote Stub,  Prev: Server,  Up: Remote Debugging

20.4 Remote Configuration
=========================

This section documents the configuration options available when
debugging remote programs.  For the options related to the File I/O
extensions of the remote protocol, see *note system-call-allowed:
system.

`set remoteaddresssize BITS'
     Set the maximum size of address in a memory packet to the specified
     number of bits.  GDB will mask off the address bits above that
     number, when it passes addresses to the remote target.  The
     default value is the number of bits in the target's address.

`show remoteaddresssize'
     Show the current value of remote address size in bits.

`set remotebaud N'
     Set the baud rate for the remote serial I/O to N baud.  The value
     is used to set the speed of the serial port used for debugging
     remote targets.

`show remotebaud'
     Show the current speed of the remote connection.

`set remotebreak'
     If set to on, GDB sends a `BREAK' signal to the remote when you
     type `Ctrl-c' to interrupt the program running on the remote.  If
     set to off, GDB sends the `Ctrl-C' character instead.  The default
     is off, since most remote systems expect to see `Ctrl-C' as the
     interrupt signal.

`show remotebreak'
     Show whether GDB sends `BREAK' or `Ctrl-C' to interrupt the remote
     program.

`set remoteflow on'
`set remoteflow off'
     Enable or disable hardware flow control (`RTS'/`CTS') on the
     serial port used to communicate to the remote target.

`show remoteflow'
     Show the current setting of hardware flow control.

`set remotelogbase BASE'
     Set the base (a.k.a. radix) of logging serial protocol
     communications to BASE.  Supported values of BASE are: `ascii',
     `octal', and `hex'.  The default is `ascii'.

`show remotelogbase'
     Show the current setting of the radix for logging remote serial
     protocol.

`set remotelogfile FILE'
     Record remote serial communications on the named FILE.  The
     default is not to record at all.

`show remotelogfile.'
     Show the current setting  of the file name on which to record the
     serial communications.

`set remotetimeout NUM'
     Set the timeout limit to wait for the remote target to respond to
     NUM seconds.  The default is 2 seconds.

`show remotetimeout'
     Show the current number of seconds to wait for the remote target
     responses.

`set remote hardware-watchpoint-limit LIMIT'
`set remote hardware-breakpoint-limit LIMIT'
     Restrict GDB to using LIMIT remote hardware breakpoint or
     watchpoints.  A limit of -1, the default, is treated as unlimited.

`set remote hardware-watchpoint-length-limit LIMIT'
     Restrict GDB to using LIMIT bytes for the maximum length of a
     remote hardware watchpoint.  A limit of -1, the default, is treated
     as unlimited.

`show remote hardware-watchpoint-length-limit'
     Show the current limit (in bytes) of the maximum length of a
     remote hardware watchpoint.

`set remote exec-file FILENAME'
`show remote exec-file'
     Select the file used for `run' with `target extended-remote'.
     This should be set to a filename valid on the target system.  If
     it is not set, the target will use a default filename (e.g. the
     last program run).

`set remote interrupt-sequence'
     Allow the user to select one of `Ctrl-C', a `BREAK' or `BREAK-g'
     as the sequence to the remote target in order to interrupt the
     execution.  `Ctrl-C' is a default.  Some system prefers `BREAK'
     which is high level of serial line for some certain time.  Linux
     kernel prefers `BREAK-g', a.k.a Magic SysRq g.  It is `BREAK'
     signal followed by character `g'.

`show interrupt-sequence'
     Show which of `Ctrl-C', `BREAK' or `BREAK-g' is sent by GDB to
     interrupt the remote program.  `BREAK-g' is BREAK signal followed
     by `g' and also known as Magic SysRq g.

`set remote interrupt-on-connect'
     Specify whether interrupt-sequence is sent to remote target when
     GDB connects to it.  This is mostly needed when you debug Linux
     kernel.  Linux kernel expects `BREAK' followed by `g' which is
     known as Magic SysRq g in order to connect GDB.

`show interrupt-on-connect'
     Show whether interrupt-sequence is sent to remote target when GDB
     connects to it.

`set tcp auto-retry on'
     Enable auto-retry for remote TCP connections.  This is useful if
     the remote debugging agent is launched in parallel with GDB; there
     is a race condition because the agent may not become ready to
     accept the connection before GDB attempts to connect.  When
     auto-retry is enabled, if the initial attempt to connect fails,
     GDB reattempts to establish the connection using the timeout
     specified by `set tcp connect-timeout'.

`set tcp auto-retry off'
     Do not auto-retry failed TCP connections.

`show tcp auto-retry'
     Show the current auto-retry setting.

`set tcp connect-timeout SECONDS'
     Set the timeout for establishing a TCP connection to the remote
     target to SECONDS.  The timeout affects both polling to retry
     failed connections (enabled by `set tcp auto-retry on') and
     waiting for connections that are merely slow to complete, and
     represents an approximate cumulative value.

`show tcp connect-timeout'
     Show the current connection timeout setting.

   The GDB remote protocol autodetects the packets supported by your
debugging stub.  If you need to override the autodetection, you can use
these commands to enable or disable individual packets.  Each packet
can be set to `on' (the remote target supports this packet), `off' (the
remote target does not support this packet), or `auto' (detect remote
target support for this packet).  They all default to `auto'.  For more
information about each packet, see *note Remote Protocol::.

   During normal use, you should not have to use any of these commands.
If you do, that may be a bug in your remote debugging stub, or a bug in
GDB.  You may want to report the problem to the GDB developers.

   For each packet NAME, the command to enable or disable the packet is
`set remote NAME-packet'.  The available settings are:

Command Name         Remote Packet           Related Features
`fetch-register'     `p'                     `info registers'
`set-register'       `P'                     `set'
`binary-download'    `X'                     `load', `set'
`read-aux-vector'    `qXfer:auxv:read'       `info auxv'
`symbol-lookup'      `qSymbol'               Detecting
                                             multiple threads
`attach'             `vAttach'               `attach'
`verbose-resume'     `vCont'                 Stepping or
                                             resuming multiple
                                             threads
`run'                `vRun'                  `run'
`software-breakpoint'`Z0'                    `break'
`hardware-breakpoint'`Z1'                    `hbreak'
`write-watchpoint'   `Z2'                    `watch'
`read-watchpoint'    `Z3'                    `rwatch'
`access-watchpoint'  `Z4'                    `awatch'
`target-features'    `qXfer:features:read'   `set architecture'
`library-info'       `qXfer:libraries:read'  `info
                                             sharedlibrary'
`memory-map'         `qXfer:memory-map:read' `info mem'
`read-sdata-object'  `qXfer:sdata:read'      `print $_sdata'
`read-spu-object'    `qXfer:spu:read'        `info spu'
`write-spu-object'   `qXfer:spu:write'       `info spu'
`read-siginfo-object'`qXfer:siginfo:read'    `print $_siginfo'
`write-siginfo-object'`qXfer:siginfo:write'   `set $_siginfo'
`threads'            `qXfer:threads:read'    `info threads'
`get-thread-local-   `qGetTLSAddr'           Displaying
storage-address'                             `__thread'
                                             variables
`get-thread-information-block-address'`qGetTIBAddr'           Display
                                             MS-Windows Thread
                                             Information Block.
`search-memory'      `qSearch:memory'        `find'
`supported-packets'  `qSupported'            Remote
                                             communications
                                             parameters
`pass-signals'       `QPassSignals'          `handle SIGNAL'
`program-signals'    `QProgramSignals'       `handle SIGNAL'
`hostio-close-packet'`vFile:close'           `remote get',
                                             `remote put'
`hostio-open-packet' `vFile:open'            `remote get',
                                             `remote put'
`hostio-pread-packet'`vFile:pread'           `remote get',
                                             `remote put'
`hostio-pwrite-packet'`vFile:pwrite'          `remote get',
                                             `remote put'
`hostio-unlink-packet'`vFile:unlink'          `remote delete'
`hostio-readlink-packet'`vFile:readlink'        Host I/O
`noack-packet'       `QStartNoAckMode'       Packet
                                             acknowledgment
`osdata'             `qXfer:osdata:read'     `info os'
`query-attached'     `qAttached'             Querying remote
                                             process attach
                                             state.
`trace-buffer-size'  `QTBuffer:size'         `set
                                             trace-buffer-size'
`traceframe-info'    `qXfer:traceframe-info:read'Traceframe info
`install-in-trace'   `InstallInTrace'        Install
                                             tracepoint in
                                             tracing
`disable-randomization'`QDisableRandomization' `set
                                             disable-randomization'
`conditional-breakpoints-packet'`Z0 and Z1'             `Support for
                                             target-side
                                             breakpoint
                                             condition
                                             evaluation'


File: gdb.info,  Node: Remote Stub,  Prev: Remote Configuration,  Up: Remote Debugging

20.5 Implementing a Remote Stub
===============================

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.)

   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. 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
     (*note Specifying a Debugging Target: Targets.).

_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".

     On certain remote targets, you can use an auxiliary program
     `gdbserver' instead of linking a stub into your program.  *Note
     Using the `gdbserver' Program: Server, for details.

   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:

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

`m68k-stub.c'
     For Motorola 680x0 architectures.

`sh-stub.c'
     For Renesas SH architectures.

`sparc-stub.c'
     For SPARC architectures.

`sparcl-stub.c'
     For Fujitsu SPARCLITE architectures.


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

* Menu:

* Stub Contents::       What the stub can do for you
* Bootstrapping::       What you must do for the stub
* Debug Session::       Putting it all together


File: gdb.info,  Node: Stub Contents,  Next: Bootstrapping,  Up: Remote Stub

20.5.1 What the Stub Can Do for You
-----------------------------------

The debugging stub for your architecture supplies these three
subroutines:

`set_debug_traps'
     This routine arranges for `handle_exception' to run when your
     program stops.  You must call this subroutine explicitly in your
     program's startup code.

`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 transfers control to
     `handle_exception'--in effect, 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 gets 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.


File: gdb.info,  Node: Bootstrapping,  Next: Debug Session,  Prev: Stub Contents,  Up: Remote Stub

20.5.2 What You Must Do for the Stub
------------------------------------

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.

   First of all you need to tell the stub how to communicate with the
serial port.

`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.

   If you want GDB to be able to stop your program while it is running,
you need to use an interrupt-driven serial driver, and arrange for it
to stop when it receives a `^C' (`\003', the control-C character).
That is the character which GDB uses to tell the remote system to stop.

   Getting the debugging target to return the proper status to GDB
probably requires changes to the standard stub; one quick and dirty way
is to just execute a breakpoint instruction (the "dirty" part is that
GDB reports a `SIGTRAP' instead of a `SIGINT').

   Other routines you need to supply are:

`void exceptionHandler (int EXCEPTION_NUMBER, void *EXCEPTION_ADDRESS)'
     Write this function to install EXCEPTION_ADDRESS in the exception
     handling tables.  You need to do this because the stub does not
     have any way of knowing what the exception handling tables on your
     target system are like (for example, the processor's table might
     be in ROM, containing entries which point to a table in RAM).
     EXCEPTION_NUMBER is the exception number which should be changed;
     its meaning is architecture-dependent (for example, different
     numbers might represent divide by zero, misaligned access, etc).
     When this exception occurs, control should be transferred directly
     to EXCEPTION_ADDRESS, and the processor state (stack, registers,
     and so on) should be just as it is when a processor exception
     occurs.  So if you want to use a jump instruction to reach
     EXCEPTION_ADDRESS, it should be a simple jump, not a jump to
     subroutine.

     For the 386, EXCEPTION_ADDRESS should be installed as an interrupt
     gate so that interrupts are masked while the handler runs.  The
     gate should be at privilege level 0 (the most privileged level).
     The SPARC and 68k stubs are able to mask interrupts themselves
     without help from `exceptionHandler'.

`void flush_i_cache()'
     On SPARC and SPARCLITE only, 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 varies 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.


File: gdb.info,  Node: Debug Session,  Prev: Bootstrapping,  Up: Remote Stub

20.5.3 Putting it All Together
------------------------------

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

  1. Make sure you have defined the supporting low-level routines
     (*note What You Must Do for the Stub: Bootstrapping.):
          `getDebugChar', `putDebugChar',
          `flush_i_cache', `memset', `exceptionHandler'.

  2. Insert these lines in your program's startup code, before the main
     procedure is called:

          set_debug_traps();
          breakpoint();

     On some machines, when a breakpoint trap is raised, the hardware
     automatically makes the PC point to the instruction after the
     breakpoint.  If your machine doesn't do that, you may need to
     adjust `handle_exception' to arrange for it to return to the
     instruction after the breakpoint on this first invocation, so that
     your program doesn't keep hitting the initial breakpoint instead
     of making progress.

  3. For the 680x0 stub only, you need to provide a variable called
     `exceptionHook'.  Normally you just use:

          void (*exceptionHook)() = 0;

     but if before calling `set_debug_traps', you set it to point to a
     function in your program, that function is called when `GDB'
     continues after stopping on a trap (for example, bus error).  The
     function indicated by `exceptionHook' is called with one
     parameter: an `int' which is the exception number.

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

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

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

  7. Start GDB on the host, and connect to the target (*note Connecting
     to a Remote Target: Connecting.).



File: gdb.info,  Node: Configurations,  Next: Controlling GDB,  Prev: Remote Debugging,  Up: Top

21 Configuration-Specific Information
*************************************

While nearly all GDB commands are available for all native and cross
versions of the debugger, there are some exceptions.  This chapter
describes things that are only available in certain configurations.

   There are three major categories of configurations: native
configurations, where the host and target are the same, embedded
operating system configurations, which are usually the same for several
different processor architectures, and bare embedded processors, which
are quite different from each other.

* Menu:

* Native::
* Embedded OS::
* Embedded Processors::
* Architectures::


File: gdb.info,  Node: Native,  Next: Embedded OS,  Up: Configurations

21.1 Native
===========

This section describes details specific to particular native
configurations.

* Menu:

* HP-UX::                       HP-UX
* BSD libkvm Interface::	Debugging BSD kernel memory images
* SVR4 Process Information::    SVR4 process information
* DJGPP Native::                Features specific to the DJGPP port
* Cygwin Native::		Features specific to the Cygwin port
* Hurd Native::                 Features specific to GNU Hurd
* Darwin::			Features specific to Darwin


File: gdb.info,  Node: HP-UX,  Next: BSD libkvm Interface,  Up: Native

21.1.1 HP-UX
------------

On HP-UX systems, if you refer to a function or variable name that
begins with a dollar sign, GDB searches for a user or system name
first, before it searches for a convenience variable.


File: gdb.info,  Node: BSD libkvm Interface,  Next: SVR4 Process Information,  Prev: HP-UX,  Up: Native

21.1.2 BSD libkvm Interface
---------------------------

BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory
interface that provides a uniform interface for accessing kernel virtual
memory images, including live systems and crash dumps.  GDB uses this
interface to allow you to debug live kernels and kernel crash dumps on
many native BSD configurations.  This is implemented as a special `kvm'
debugging target.  For debugging a live system, load the currently
running kernel into GDB and connect to the `kvm' target:

     (gdb) target kvm

   For debugging crash dumps, provide the file name of the crash dump
as an argument:

     (gdb) target kvm /var/crash/bsd.0

   Once connected to the `kvm' target, the following commands are
available:

`kvm pcb'
     Set current context from the "Process Control Block" (PCB) address.

`kvm proc'
     Set current context from proc address.  This command isn't
     available on modern FreeBSD systems.


File: gdb.info,  Node: SVR4 Process Information,  Next: DJGPP Native,  Prev: BSD libkvm Interface,  Up: Native

21.1.3 SVR4 Process Information
-------------------------------

Many versions of SVR4 and compatible 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 information about the
process running your program, or about any process running on your
system.  This includes, as of this writing, GNU/Linux, OSF/1 (Digital
Unix), Solaris, and Irix, but not HP-UX, for example.

   This command may also work on core files that were created on a
system that has the `/proc' facility.

`info proc'
`info proc PROCESS-ID'
     Summarize available information about any running process.  If a
     process ID is specified by PROCESS-ID, display information about
     that process; otherwise display information about the program being
     debugged.  The summary includes the debugged process ID, the
     command line used to invoke it, its current working directory, and
     its executable file's absolute file name.

     On some systems, PROCESS-ID can be of the form `[PID]/TID' which
     specifies a certain thread ID within a process.  If the optional
     PID part is missing, it means a thread from the process being
     debugged (the leading `/' still needs to be present, or else GDB
     will interpret the number as a process ID rather than a thread ID).

`info proc cmdline'
     Show the original command line of the process.  This command is
     specific to GNU/Linux.

`info proc cwd'
     Show the current working directory of the process.  This command is
     specific to GNU/Linux.

`info proc exe'
     Show the name of executable of the process.  This command is
     specific to GNU/Linux.

`info proc mappings'
     Report the memory address space ranges accessible in the program,
     with information on whether the process has read, write, or
     execute access rights to each range.  On GNU/Linux systems, each
     memory range includes the object file which is mapped to that
     range, instead of the memory access rights to that range.

`info proc stat'
`info proc status'
     These subcommands are specific to GNU/Linux systems.  They show
     the process-related information, including the user ID and group
     ID; how many threads are there in the process; its virtual memory
     usage; the signals that are pending, blocked, and ignored; its
     TTY; its consumption of system and user time; its stack size; its
     `nice' value; etc.  For more information, see the `proc' man page
     (type `man 5 proc' from your shell prompt).

`info proc all'
     Show all the information about the process described under all of
     the above `info proc' subcommands.

`set procfs-trace'
     This command enables and disables tracing of `procfs' API calls.

`show procfs-trace'
     Show the current state of `procfs' API call tracing.

`set procfs-file FILE'
     Tell GDB to write `procfs' API trace to the named FILE.  GDB
     appends the trace info to the previous contents of the file.  The
     default is to display the trace on the standard output.

`show procfs-file'
     Show the file to which `procfs' API trace is written.

`proc-trace-entry'
`proc-trace-exit'
`proc-untrace-entry'
`proc-untrace-exit'
     These commands enable and disable tracing of entries into and exits
     from the `syscall' interface.

`info pidlist'
     For QNX Neutrino only, this command displays the list of all the
     processes and all the threads within each process.

`info meminfo'
     For QNX Neutrino only, this command displays the list of all
     mapinfos.


File: gdb.info,  Node: DJGPP Native,  Next: Cygwin Native,  Prev: SVR4 Process Information,  Up: Native

21.1.4 Features for Debugging DJGPP Programs
--------------------------------------------

DJGPP is a port of the GNU development tools to MS-DOS and MS-Windows.
DJGPP programs are 32-bit protected-mode programs that use the "DPMI"
(DOS Protected-Mode Interface) API to run on top of real-mode DOS
systems and their emulations.

   GDB supports native debugging of DJGPP programs, and defines a few
commands specific to the DJGPP port.  This subsection describes those
commands.

`info dos'
     This is a prefix of DJGPP-specific commands which print
     information about the target system and important OS structures.

`info dos sysinfo'
     This command displays assorted information about the underlying
     platform: the CPU type and features, the OS version and flavor, the
     DPMI version, and the available conventional and DPMI memory.

`info dos gdt'
`info dos ldt'
`info dos idt'
     These 3 commands display entries from, respectively, Global, Local,
     and Interrupt Descriptor Tables (GDT, LDT, and IDT).  The
     descriptor tables are data structures which store a descriptor for
     each segment that is currently in use.  The segment's selector is
     an index into a descriptor table; the table entry for that index
     holds the descriptor's base address and limit, and its attributes
     and access rights.

     A typical DJGPP program uses 3 segments: a code segment, a data
     segment (used for both data and the stack), and a DOS segment
     (which allows access to DOS/BIOS data structures and absolute
     addresses in conventional memory).  However, the DPMI host will
     usually define additional segments in order to support the DPMI
     environment.

     These commands allow to display entries from the descriptor tables.
     Without an argument, all entries from the specified table are
     displayed.  An argument, which should be an integer expression,
     means display a single entry whose index is given by the argument.
     For example, here's a convenient way to display information about
     the debugged program's data segment:

     `(gdb) info dos ldt $ds'
     `0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)'


     This comes in handy when you want to see whether a pointer is
     outside the data segment's limit (i.e. "garbled").

`info dos pde'
`info dos pte'
     These two commands display entries from, respectively, the Page
     Directory and the Page Tables.  Page Directories and Page Tables
     are data structures which control how virtual memory addresses are
     mapped into physical addresses.  A Page Table includes an entry
     for every page of memory that is mapped into the program's address
     space; there may be several Page Tables, each one holding up to
     4096 entries.  A Page Directory has up to 4096 entries, one each
     for every Page Table that is currently in use.

     Without an argument, `info dos pde' displays the entire Page
     Directory, and `info dos pte' displays all the entries in all of
     the Page Tables.  An argument, an integer expression, given to the
     `info dos pde' command means display only that entry from the Page
     Directory table.  An argument given to the `info dos pte' command
     means display entries from a single Page Table, the one pointed to
     by the specified entry in the Page Directory.

     These commands are useful when your program uses "DMA" (Direct
     Memory Access), which needs physical addresses to program the DMA
     controller.

     These commands are supported only with some DPMI servers.

`info dos address-pte ADDR'
     This command displays the Page Table entry for a specified linear
     address.  The argument ADDR is a linear address which should
     already have the appropriate segment's base address added to it,
     because this command accepts addresses which may belong to _any_
     segment.  For example, here's how to display the Page Table entry
     for the page where a variable `i' is stored:

     `(gdb) info dos address-pte __djgpp_base_address + (char *)&i'
     `Page Table entry for address 0x11a00d30:'
     `Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30'


     This says that `i' is stored at offset `0xd30' from the page whose
     physical base address is `0x02698000', and shows all the
     attributes of that page.

     Note that you must cast the addresses of variables to a `char *',
     since otherwise the value of `__djgpp_base_address', the base
     address of all variables and functions in a DJGPP program, will be
     added using the rules of C pointer arithmetics: if `i' is declared
     an `int', GDB will add 4 times the value of `__djgpp_base_address'
     to the address of `i'.

     Here's another example, it displays the Page Table entry for the
     transfer buffer:

     `(gdb) info dos address-pte *((unsigned *)&_go32_info_block + 3)'
     `Page Table entry for address 0x29110:'
     `Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110'


     (The `+ 3' offset is because the transfer buffer's address is the
     3rd member of the `_go32_info_block' structure.)  The output
     clearly shows that this DPMI server maps the addresses in
     conventional memory 1:1, i.e. the physical (`0x00029000' +
     `0x110') and linear (`0x29110') addresses are identical.

     This command is supported only with some DPMI servers.

   In addition to native debugging, the DJGPP port supports remote
debugging via a serial data link.  The following commands are specific
to remote serial debugging in the DJGPP port of GDB.

`set com1base ADDR'
     This command sets the base I/O port address of the `COM1' serial
     port.

`set com1irq IRQ'
     This command sets the "Interrupt Request" (`IRQ') line to use for
     the `COM1' serial port.

     There are similar commands `set com2base', `set com3irq', etc. for
     setting the port address and the `IRQ' lines for the other 3 COM
     ports.

     The related commands `show com1base', `show com1irq' etc.  display
     the current settings of the base address and the `IRQ' lines used
     by the COM ports.

`info serial'
     This command prints the status of the 4 DOS serial ports.  For each
     port, it prints whether it's active or not, its I/O base address
     and IRQ number, whether it uses a 16550-style FIFO, its baudrate,
     and the counts of various errors encountered so far.


File: gdb.info,  Node: Cygwin Native,  Next: Hurd Native,  Prev: DJGPP Native,  Up: Native

21.1.5 Features for Debugging MS Windows PE Executables
-------------------------------------------------------

GDB supports native debugging of MS Windows programs, including DLLs
with and without symbolic debugging information.

   MS-Windows programs that call `SetConsoleMode' to switch off the
special meaning of the `Ctrl-C' keystroke cannot be interrupted by
typing `C-c'.  For this reason, GDB on MS-Windows supports `C-<BREAK>'
as an alternative interrupt key sequence, which can be used to
interrupt the debuggee even if it ignores `C-c'.

   There are various additional Cygwin-specific commands, described in
this section.  Working with DLLs that have no debugging symbols is
described in *note Non-debug DLL Symbols::.

`info w32'
     This is a prefix of MS Windows-specific commands which print
     information about the target system and important OS structures.

`info w32 selector'
     This command displays information returned by the Win32 API
     `GetThreadSelectorEntry' function.  It takes an optional argument
     that is evaluated to a long value to give the information about
     this given selector.  Without argument, this command displays
     information about the six segment registers.

`info w32 thread-information-block'
     This command displays thread specific information stored in the
     Thread Information Block (readable on the X86 CPU family using
     `$fs' selector for 32-bit programs and `$gs' for 64-bit programs).

`info dll'
     This is a Cygwin-specific alias of `info shared'.

`dll-symbols'
     This command loads symbols from a dll similarly to add-sym command
     but without the need to specify a base address.

`set cygwin-exceptions MODE'
     If MODE is `on', GDB will break on exceptions that happen inside
     the Cygwin DLL.  If MODE is `off', GDB will delay recognition of
     exceptions, and may ignore some exceptions which seem to be caused
     by internal Cygwin DLL "bookkeeping".  This option is meant
     primarily for debugging the Cygwin DLL itself; the default value
     is `off' to avoid annoying GDB users with false `SIGSEGV' signals.

`show cygwin-exceptions'
     Displays whether GDB will break on exceptions that happen inside
     the Cygwin DLL itself.

`set new-console MODE'
     If MODE is `on' the debuggee will be started in a new console on
     next start.  If MODE is `off', the debuggee will be started in the
     same console as the debugger.

`show new-console'
     Displays whether a new console is used when the debuggee is
     started.

`set new-group MODE'
     This boolean value controls whether the debuggee should start a
     new group or stay in the same group as the debugger.  This affects
     the way the Windows OS handles `Ctrl-C'.

`show new-group'
     Displays current value of new-group boolean.

`set debugevents'
     This boolean value adds debug output concerning kernel events
     related to the debuggee seen by the debugger.  This includes
     events that signal thread and process creation and exit, DLL
     loading and unloading, console interrupts, and debugging messages
     produced by the Windows `OutputDebugString' API call.

`set debugexec'
     This boolean value adds debug output concerning execute events
     (such as resume thread) seen by the debugger.

`set debugexceptions'
     This boolean value adds debug output concerning exceptions in the
     debuggee seen by the debugger.

`set debugmemory'
     This boolean value adds debug output concerning debuggee memory
     reads and writes by the debugger.

`set shell'
     This boolean values specifies whether the debuggee is called via a
     shell or directly (default value is on).

`show shell'
     Displays if the debuggee will be started with a shell.


* Menu:

* Non-debug DLL Symbols::  Support for DLLs without debugging symbols


File: gdb.info,  Node: Non-debug DLL Symbols,  Up: Cygwin Native

21.1.5.1 Support for DLLs without Debugging Symbols
...................................................

Very often on windows, some of the DLLs that your program relies on do
not include symbolic debugging information (for example,
`kernel32.dll').  When GDB doesn't recognize any debugging symbols in a
DLL, it relies on the minimal amount of symbolic information contained
in the DLL's export table.  This section describes working with such
symbols, known internally to GDB as "minimal symbols".

   Note that before the debugged program has started execution, no DLLs
will have been loaded.  The easiest way around this problem is simply to
start the program -- either by setting a breakpoint or letting the
program run once to completion.  It is also possible to force GDB to
load a particular DLL before starting the executable -- see the shared
library information in *note Files::, or the `dll-symbols' command in
*note Cygwin Native::.  Currently, explicitly loading symbols from a
DLL with no debugging information will cause the symbol names to be
duplicated in GDB's lookup table, which may adversely affect symbol
lookup performance.

21.1.5.2 DLL Name Prefixes
..........................

In keeping with the naming conventions used by the Microsoft debugging
tools, DLL export symbols are made available with a prefix based on the
DLL name, for instance `KERNEL32!CreateFileA'.  The plain name is also
entered into the symbol table, so `CreateFileA' is often sufficient.
In some cases there will be name clashes within a program (particularly
if the executable itself includes full debugging symbols) necessitating
the use of the fully qualified name when referring to the contents of
the DLL.  Use single-quotes around the name to avoid the exclamation
mark ("!")  being interpreted as a language operator.

   Note that the internal name of the DLL may be all upper-case, even
though the file name of the DLL is lower-case, or vice-versa.  Since
symbols within GDB are _case-sensitive_ this may cause some confusion.
If in doubt, try the `info functions' and `info variables' commands or
even `maint print msymbols' (*note Symbols::). Here's an example:

     (gdb) info function CreateFileA
     All functions matching regular expression "CreateFileA":

     Non-debugging symbols:
     0x77e885f4  CreateFileA
     0x77e885f4  KERNEL32!CreateFileA

     (gdb) info function !
     All functions matching regular expression "!":

     Non-debugging symbols:
     0x6100114c  cygwin1!__assert
     0x61004034  cygwin1!_dll_crt0@0
     0x61004240  cygwin1!dll_crt0(per_process *)
     [etc...]

21.1.5.3 Working with Minimal Symbols
.....................................

Symbols extracted from a DLL's export table do not contain very much
type information. All that GDB can do is guess whether a symbol refers
to a function or variable depending on the linker section that contains
the symbol. Also note that the actual contents of the memory contained
in a DLL are not available unless the program is running. This means
that you cannot examine the contents of a variable or disassemble a
function within a DLL without a running program.

   Variables are generally treated as pointers and dereferenced
automatically. For this reason, it is often necessary to prefix a
variable name with the address-of operator ("&") and provide explicit
type information in the command. Here's an example of the type of
problem:

     (gdb) print 'cygwin1!__argv'
     $1 = 268572168

     (gdb) x 'cygwin1!__argv'
     0x10021610:      "\230y\""

   And two possible solutions:

     (gdb) print ((char **)'cygwin1!__argv')[0]
     $2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"

     (gdb) x/2x &'cygwin1!__argv'
     0x610c0aa8 <cygwin1!__argv>:    0x10021608      0x00000000
     (gdb) x/x 0x10021608
     0x10021608:     0x0022fd98
     (gdb) x/s 0x0022fd98
     0x22fd98:        "/cygdrive/c/mydirectory/myprogram"

   Setting a break point within a DLL is possible even before the
program starts execution. However, under these circumstances, GDB can't
examine the initial instructions of the function in order to skip the
function's frame set-up code. You can work around this by using "*&" to
set the breakpoint at a raw memory address:

     (gdb) break *&'python22!PyOS_Readline'
     Breakpoint 1 at 0x1e04eff0

   The author of these extensions is not entirely convinced that
setting a break point within a shared DLL like `kernel32.dll' is
completely safe.


File: gdb.info,  Node: Hurd Native,  Next: Darwin,  Prev: Cygwin Native,  Up: Native

21.1.6 Commands Specific to GNU Hurd Systems
--------------------------------------------

This subsection describes GDB commands specific to the GNU Hurd native
debugging.

`set signals'
`set sigs'
     This command toggles the state of inferior signal interception by
     GDB.  Mach exceptions, such as breakpoint traps, are not affected
     by this command.  `sigs' is a shorthand alias for `signals'.

`show signals'
`show sigs'
     Show the current state of intercepting inferior's signals.

`set signal-thread'
`set sigthread'
     This command tells GDB which thread is the `libc' signal thread.
     That thread is run when a signal is delivered to a running
     process.  `set sigthread' is the shorthand alias of `set
     signal-thread'.

`show signal-thread'
`show sigthread'
     These two commands show which thread will run when the inferior is
     delivered a signal.

`set stopped'
     This commands tells GDB that the inferior process is stopped, as
     with the `SIGSTOP' signal.  The stopped process can be continued
     by delivering a signal to it.

`show stopped'
     This command shows whether GDB thinks the debuggee is stopped.

`set exceptions'
     Use this command to turn off trapping of exceptions in the
     inferior.  When exception trapping is off, neither breakpoints nor
     single-stepping will work.  To restore the default, set exception
     trapping on.

`show exceptions'
     Show the current state of trapping exceptions in the inferior.

`set task pause'
     This command toggles task suspension when GDB has control.
     Setting it to on takes effect immediately, and the task is
     suspended whenever GDB gets control.  Setting it to off will take
     effect the next time the inferior is continued.  If this option is
     set to off, you can use `set thread default pause on' or `set
     thread pause on' (see below) to pause individual threads.

`show task pause'
     Show the current state of task suspension.

`set task detach-suspend-count'
     This command sets the suspend count the task will be left with when
     GDB detaches from it.

`show task detach-suspend-count'
     Show the suspend count the task will be left with when detaching.

`set task exception-port'
`set task excp'
     This command sets the task exception port to which GDB will
     forward exceptions.  The argument should be the value of the "send
     rights" of the task.  `set task excp' is a shorthand alias.

`set noninvasive'
     This command switches GDB to a mode that is the least invasive as
     far as interfering with the inferior is concerned.  This is the
     same as using `set task pause', `set exceptions', and `set
     signals' to values opposite to the defaults.

`info send-rights'
`info receive-rights'
`info port-rights'
`info port-sets'
`info dead-names'
`info ports'
`info psets'
     These commands display information about, respectively, send
     rights, receive rights, port rights, port sets, and dead names of
     a task.  There are also shorthand aliases: `info ports' for `info
     port-rights' and `info psets' for `info port-sets'.

`set thread pause'
     This command toggles current thread suspension when GDB has
     control.  Setting it to on takes effect immediately, and the
     current thread is suspended whenever GDB gets control.  Setting it
     to off will take effect the next time the inferior is continued.
     Normally, this command has no effect, since when GDB has control,
     the whole task is suspended.  However, if you used `set task pause
     off' (see above), this command comes in handy to suspend only the
     current thread.

`show thread pause'
     This command shows the state of current thread suspension.

`set thread run'
     This command sets whether the current thread is allowed to run.

`show thread run'
     Show whether the current thread is allowed to run.

`set thread detach-suspend-count'
     This command sets the suspend count GDB will leave on a thread
     when detaching.  This number is relative to the suspend count
     found by GDB when it notices the thread; use `set thread
     takeover-suspend-count' to force it to an absolute value.

`show thread detach-suspend-count'
     Show the suspend count GDB will leave on the thread when detaching.

`set thread exception-port'
`set thread excp'
     Set the thread exception port to which to forward exceptions.  This
     overrides the port set by `set task exception-port' (see above).
     `set thread excp' is the shorthand alias.

`set thread takeover-suspend-count'
     Normally, GDB's thread suspend counts are relative to the value
     GDB finds when it notices each thread.  This command changes the
     suspend counts to be absolute instead.

`set thread default'
`show thread default'
     Each of the above `set thread' commands has a `set thread default'
     counterpart (e.g., `set thread default pause', `set thread default
     exception-port', etc.).  The `thread default' variety of commands
     sets the default thread properties for all threads; you can then
     change the properties of individual threads with the non-default
     commands.


File: gdb.info,  Node: Darwin,  Prev: Hurd Native,  Up: Native

21.1.7 Darwin
-------------

GDB provides the following commands specific to the Darwin target:

`set debug darwin NUM'
     When set to a non zero value, enables debugging messages specific
     to the Darwin support.  Higher values produce more verbose output.

`show debug darwin'
     Show the current state of Darwin messages.

`set debug mach-o NUM'
     When set to a non zero value, enables debugging messages while GDB
     is reading Darwin object files.  ("Mach-O" is the file format used
     on Darwin for object and executable files.)  Higher values produce
     more verbose output.  This is a command to diagnose problems
     internal to GDB and should not be needed in normal usage.

`show debug mach-o'
     Show the current state of Mach-O file messages.

`set mach-exceptions on'
`set mach-exceptions off'
     On Darwin, faults are first reported as a Mach exception and are
     then mapped to a Posix signal.  Use this command to turn on
     trapping of Mach exceptions in the inferior.  This might be
     sometimes useful to better understand the cause of a fault.  The
     default is off.

`show mach-exceptions'
     Show the current state of exceptions trapping.


File: gdb.info,  Node: Embedded OS,  Next: Embedded Processors,  Prev: Native,  Up: Configurations

21.2 Embedded Operating Systems
===============================

This section describes configurations involving the debugging of
embedded operating systems that are available for several different
architectures.

* Menu:

* VxWorks::                     Using GDB with VxWorks

   GDB includes the ability to debug programs running on various
real-time operating systems.


File: gdb.info,  Node: VxWorks,  Up: Embedded OS

21.2.1 Using GDB with VxWorks
-----------------------------

`target vxworks MACHINENAME'
     A VxWorks system, attached via TCP/IP.  The argument MACHINENAME
     is the target system's machine name or IP address.


   On VxWorks, `load' links FILENAME dynamically on the current target
system as well as adding its symbols in GDB.

   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.  (It may be installed with the
name `vxgdb', to distinguish it from a GDB for debugging programs on
the host itself.)

`VxWorks-timeout ARGS'
     All VxWorks-based targets now support the option `vxworks-timeout'.
     This option is set by the user, and  ARGS represents the number of
     seconds GDB waits for responses to rpc's.  You might use this if
     your VxWorks target is a slow software simulator or is on the far
     side of a thin network line.

   The following information on connecting to VxWorks was current when
this manual was produced; newer releases of VxWorks may use revised
procedures.

   To use GDB with VxWorks, you must rebuild your VxWorks kernel to
include the remote debugging interface routines in the VxWorks library
`rdb.a'.  To do this, define `INCLUDE_RDB' in the VxWorks configuration
file `configAll.h' and rebuild your VxWorks kernel.  The resulting
kernel contains `rdb.a', and spawns 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 `rdb.a' 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, run `gdb' (or `vxgdb', depending on your
installation).

   GDB comes up showing the prompt:

     (vxgdb)

* Menu:

* VxWorks Connection::          Connecting to VxWorks
* VxWorks Download::            VxWorks download
* VxWorks Attach::              Running tasks


File: gdb.info,  Node: VxWorks Connection,  Next: VxWorks Download,  Up: VxWorks

21.2.1.1 Connecting to VxWorks
..............................

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:

     (vxgdb) target vxworks tt

   GDB displays messages like these:

     Attaching remote machine across net...
     Connected to tt.

   GDB then attempts 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 (*note Your Program's Environment: Environment.); if it fails to
find an object file, it displays a message such as:

     prog.o: No such file or directory.

   When this happens, add the appropriate directory to the search path
with the GDB command `path', and execute the `target' command again.


File: gdb.info,  Node: VxWorks Download,  Next: VxWorks Attach,  Prev: VxWorks Connection,  Up: VxWorks

21.2.1.2 VxWorks Download
.........................

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.  If both systems
have NFS mounted the same filesystems, you can avoid these problems by
using absolute paths.  Otherwise, 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.
For instance, a program `prog.o' may reside in `VXPATH/vw/demo/rdb' in
VxWorks and in `HOSTPATH/vw/demo/rdb' on the host.  To load this
program, type this on VxWorks:

     -> cd "VXPATH/vw/demo/rdb"

Then, in GDB, type:

     (vxgdb) cd HOSTPATH/vw/demo/rdb
     (vxgdb) load prog.o

   GDB displays a response similar to this:

     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
makes GDB 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's data
structures that reference the target system's symbol table.)


File: gdb.info,  Node: VxWorks Attach,  Prev: VxWorks Download,  Up: VxWorks

21.2.1.3 Running Tasks
......................

You can also attach to an existing task using the `attach' command as
follows:

     (vxgdb) attach TASK

where TASK is the VxWorks hexadecimal task ID.  The task can be running
or suspended when you attach to it.  Running tasks are suspended at the
time of attachment.


File: gdb.info,  Node: Embedded Processors,  Next: Architectures,  Prev: Embedded OS,  Up: Configurations

21.3 Embedded Processors
========================

This section goes into details specific to particular embedded
configurations.

   Whenever a specific embedded processor has a simulator, GDB allows
to send an arbitrary command to the simulator.

`sim COMMAND'
     Send an arbitrary COMMAND string to the simulator.  Consult the
     documentation for the specific simulator in use for information
     about acceptable commands.

* Menu:

* ARM::                         ARM RDI
* M32R/D::                      Renesas M32R/D
* M68K::                        Motorola M68K
* MicroBlaze::			Xilinx MicroBlaze
* MIPS Embedded::               MIPS Embedded
* OpenRISC 1000::               OpenRisc 1000
* PowerPC Embedded::            PowerPC Embedded
* PA::                          HP PA Embedded
* Sparclet::                    Tsqware Sparclet
* Sparclite::                   Fujitsu Sparclite
* Z8000::                       Zilog Z8000
* AVR::                         Atmel AVR
* CRIS::                        CRIS
* Super-H::                     Renesas Super-H


File: gdb.info,  Node: ARM,  Next: M32R/D,  Up: Embedded Processors

21.3.1 ARM
----------

`target rdi DEV'
     ARM Angel monitor, via RDI library interface to ADP protocol.  You
     may use this target to communicate with both boards running the
     Angel monitor, or with the EmbeddedICE JTAG debug device.

`target rdp DEV'
     ARM Demon monitor.


   GDB provides the following ARM-specific commands:

`set arm disassembler'
     This commands selects from a list of disassembly styles.  The
     `"std"' style is the standard style.

`show arm disassembler'
     Show the current disassembly style.

`set arm apcs32'
     This command toggles ARM operation mode between 32-bit and 26-bit.

`show arm apcs32'
     Display the current usage of the ARM 32-bit mode.

`set arm fpu FPUTYPE'
     This command sets the ARM floating-point unit (FPU) type.  The
     argument FPUTYPE can be one of these:

    `auto'
          Determine the FPU type by querying the OS ABI.

    `softfpa'
          Software FPU, with mixed-endian doubles on little-endian ARM
          processors.

    `fpa'
          GCC-compiled FPA co-processor.

    `softvfp'
          Software FPU with pure-endian doubles.

    `vfp'
          VFP co-processor.

`show arm fpu'
     Show the current type of the FPU.

`set arm abi'
     This command forces GDB to use the specified ABI.

`show arm abi'
     Show the currently used ABI.

`set arm fallback-mode (arm|thumb|auto)'
     GDB uses the symbol table, when available, to determine whether
     instructions are ARM or Thumb.  This command controls GDB's
     default behavior when the symbol table is not available.  The
     default is `auto', which causes GDB to use the current execution
     mode (from the `T' bit in the `CPSR' register).

`show arm fallback-mode'
     Show the current fallback instruction mode.

`set arm force-mode (arm|thumb|auto)'
     This command overrides use of the symbol table to determine whether
     instructions are ARM or Thumb.  The default is `auto', which
     causes GDB to use the symbol table and then the setting of `set
     arm fallback-mode'.

`show arm force-mode'
     Show the current forced instruction mode.

`set debug arm'
     Toggle whether to display ARM-specific debugging messages from the
     ARM target support subsystem.

`show debug arm'
     Show whether ARM-specific debugging messages are enabled.

   The following commands are available when an ARM target is debugged
using the RDI interface:

`rdilogfile [FILE]'
     Set the filename for the ADP (Angel Debugger Protocol) packet log.
     With an argument, sets the log file to the specified FILE.  With
     no argument, show the current log file name.  The default log file
     is `rdi.log'.

`rdilogenable [ARG]'
     Control logging of ADP packets.  With an argument of 1 or `"yes"'
     enables logging, with an argument 0 or `"no"' disables it.  With
     no arguments displays the current setting.  When logging is
     enabled, ADP packets exchanged between GDB and the RDI target
     device are logged to a file.

`set rdiromatzero'
     Tell GDB whether the target has ROM at address 0.  If on, vector
     catching is disabled, so that zero address can be used.  If off
     (the default), vector catching is enabled.  For this command to
     take effect, it needs to be invoked prior to the `target rdi'
     command.

`show rdiromatzero'
     Show the current setting of ROM at zero address.

`set rdiheartbeat'
     Enable or disable RDI heartbeat packets.  It is not recommended to
     turn on this option, since it confuses ARM and EPI JTAG interface,
     as well as the Angel monitor.

`show rdiheartbeat'
     Show the setting of RDI heartbeat packets.

`target sim [SIMARGS] ...'
     The GDB ARM simulator accepts the following optional arguments.

    `--swi-support=TYPE'
          Tell the simulator which SWI interfaces to support.  TYPE may
          be a comma separated list of the following values.  The
          default value is `all'.

         `none'

         `demon'

         `angel'

         `redboot'

         `all'


File: gdb.info,  Node: M32R/D,  Next: M68K,  Prev: ARM,  Up: Embedded Processors

21.3.2 Renesas M32R/D and M32R/SDI
----------------------------------

`target m32r DEV'
     Renesas M32R/D ROM monitor.

`target m32rsdi DEV'
     Renesas M32R SDI server, connected via parallel port to the board.

   The following GDB commands are specific to the M32R monitor:

`set download-path PATH'
     Set the default path for finding downloadable SREC files.

`show download-path'
     Show the default path for downloadable SREC files.

`set board-address ADDR'
     Set the IP address for the M32R-EVA target board.

`show board-address'
     Show the current IP address of the target board.

`set server-address ADDR'
     Set the IP address for the download server, which is the GDB's
     host machine.

`show server-address'
     Display the IP address of the download server.

`upload [FILE]'
     Upload the specified SREC FILE via the monitor's Ethernet upload
     capability.  If no FILE argument is given, the current executable
     file is uploaded.

`tload [FILE]'
     Test the `upload' command.

   The following commands are available for M32R/SDI:

`sdireset'
     This command resets the SDI connection.

`sdistatus'
     This command shows the SDI connection status.

`debug_chaos'
     Instructs the remote that M32R/Chaos debugging is to be used.

`use_debug_dma'
     Instructs the remote to use the DEBUG_DMA method of accessing
     memory.

`use_mon_code'
     Instructs the remote to use the MON_CODE method of accessing
     memory.

`use_ib_break'
     Instructs the remote to set breakpoints by IB break.

`use_dbt_break'
     Instructs the remote to set breakpoints by DBT.


File: gdb.info,  Node: M68K,  Next: MicroBlaze,  Prev: M32R/D,  Up: Embedded Processors

21.3.3 M68k
-----------

The Motorola m68k configuration includes ColdFire support, and a target
command for the following ROM monitor.

`target dbug DEV'
     dBUG ROM monitor for Motorola ColdFire.



File: gdb.info,  Node: MicroBlaze,  Next: MIPS Embedded,  Prev: M68K,  Up: Embedded Processors

21.3.4 MicroBlaze
-----------------

The MicroBlaze is a soft-core processor supported on various Xilinx
FPGAs, such as Spartan or Virtex series.  Boards with these processors
usually have JTAG ports which connect to a host system running the
Xilinx Embedded Development Kit (EDK) or Software Development Kit (SDK).
This host system is used to download the configuration bitstream to the
target FPGA.  The Xilinx Microprocessor Debugger (XMD) program
communicates with the target board using the JTAG interface and
presents a `gdbserver' interface to the board.  By default `xmd' uses
port `1234'.  (While it is possible to change this default port, it
requires the use of undocumented `xmd' commands.  Contact Xilinx
support if you need to do this.)

   Use these GDB commands to connect to the MicroBlaze target processor.

`target remote :1234'
     Use this command to connect to the target if you are running GDB
     on the same system as `xmd'.

`target remote XMD-HOST:1234'
     Use this command to connect to the target if it is connected to
     `xmd' running on a different system named XMD-HOST.

`load'
     Use this command to download a program to the MicroBlaze target.

`set debug microblaze N'
     Enable MicroBlaze-specific debugging messages if non-zero.

`show debug microblaze N'
     Show MicroBlaze-specific debugging level.


File: gdb.info,  Node: MIPS Embedded,  Next: OpenRISC 1000,  Prev: MicroBlaze,  Up: Embedded Processors

21.3.5 MIPS Embedded
--------------------

GDB can use the MIPS remote debugging protocol to talk to a MIPS board
attached to a serial line.  This is available when you configure GDB
with `--target=mips-elf'.

   Use these GDB commands to specify the connection to your target
board:

`target mips PORT'
     To run a program on the board, start up `gdb' with the name of
     your program as the argument.  To connect to the board, use the
     command `target mips PORT', where PORT is the name of the serial
     port connected to the board.  If the program has not already been
     downloaded to the board, you may use the `load' command to
     download it.  You can then use all the usual GDB commands.

     For example, this sequence connects to the target board through a
     serial port, and loads and runs a program called PROG through the
     debugger:

          host$ gdb PROG
          GDB is free software and ...
          (gdb) target mips /dev/ttyb
          (gdb) load PROG
          (gdb) run

`target mips HOSTNAME:PORTNUMBER'
     On some GDB host configurations, you can specify a TCP connection
     (for instance, to a serial line managed by a terminal
     concentrator) instead of a serial port, using the syntax
     `HOSTNAME:PORTNUMBER'.

`target pmon PORT'
     PMON ROM monitor.

`target ddb PORT'
     NEC's DDB variant of PMON for Vr4300.

`target lsi PORT'
     LSI variant of PMON.

`target r3900 DEV'
     Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.

`target array DEV'
     Array Tech LSI33K RAID controller board.


GDB also supports these special commands for MIPS targets:

`set mipsfpu double'
`set mipsfpu single'
`set mipsfpu none'
`set mipsfpu auto'
`show mipsfpu'
     If your target board does not support the MIPS floating point
     coprocessor, you should use the command `set mipsfpu none' (if you
     need this, you may wish to put the command in your GDB init file).
     This tells GDB how to find the return value of functions which
     return floating point values.  It also allows GDB to avoid saving
     the floating point registers when calling functions on the board.
     If you are using a floating point coprocessor with only single
     precision floating point support, as on the R4650 processor, use
     the command `set mipsfpu single'.  The default double precision
     floating point coprocessor may be selected using `set mipsfpu
     double'.

     In previous versions the only choices were double precision or no
     floating point, so `set mipsfpu on' will select double precision
     and `set mipsfpu off' will select no floating point.

     As usual, you can inquire about the `mipsfpu' variable with `show
     mipsfpu'.

`set timeout SECONDS'
`set retransmit-timeout SECONDS'
`show timeout'
`show retransmit-timeout'
     You can control the timeout used while waiting for a packet, in
     the MIPS remote protocol, with the `set timeout SECONDS' command.
     The default is 5 seconds.  Similarly, you can control the timeout
     used while waiting for an acknowledgment of a packet with the `set
     retransmit-timeout SECONDS' command.  The default is 3 seconds.
     You can inspect both values with `show timeout' and `show
     retransmit-timeout'.  (These commands are _only_ available when
     GDB is configured for `--target=mips-elf'.)

     The timeout set by `set timeout' does not apply when GDB is
     waiting for your program to stop.  In that case, GDB waits forever
     because it has no way of knowing how long the program is going to
     run before stopping.

`set syn-garbage-limit NUM'
     Limit the maximum number of characters GDB should ignore when it
     tries to synchronize with the remote target.  The default is 10
     characters.  Setting the limit to -1 means there's no limit.

`show syn-garbage-limit'
     Show the current limit on the number of characters to ignore when
     trying to synchronize with the remote system.

`set monitor-prompt PROMPT'
     Tell GDB to expect the specified PROMPT string from the remote
     monitor.  The default depends on the target:
    pmon target
          `PMON'

    ddb target
          `NEC010'

    lsi target
          `PMON>'

`show monitor-prompt'
     Show the current strings GDB expects as the prompt from the remote
     monitor.

`set monitor-warnings'
     Enable or disable monitor warnings about hardware breakpoints.
     This has effect only for the `lsi' target.  When on, GDB will
     display warning messages whose codes are returned by the `lsi'
     PMON monitor for breakpoint commands.

`show monitor-warnings'
     Show the current setting of printing monitor warnings.

`pmon COMMAND'
     This command allows sending an arbitrary COMMAND string to the
     monitor.  The monitor must be in debug mode for this to work.


File: gdb.info,  Node: OpenRISC 1000,  Next: PowerPC Embedded,  Prev: MIPS Embedded,  Up: Embedded Processors

21.3.6 OpenRISC 1000
--------------------

See OR1k Architecture document (`www.opencores.org') for more
information about platform and commands.

`target jtag jtag://HOST:PORT'
     Connects to remote JTAG server.  JTAG remote server can be either
     an or1ksim or JTAG server, connected via parallel port to the
     board.

     Example: `target jtag jtag://localhost:9999'

`or1ksim COMMAND'
     If connected to `or1ksim' OpenRISC 1000 Architectural Simulator,
     proprietary commands can be executed.

`info or1k spr'
     Displays spr groups.

`info or1k spr GROUP'
`info or1k spr GROUPNO'
     Displays register names in selected group.

`info or1k spr GROUP REGISTER'
`info or1k spr REGISTER'
`info or1k spr GROUPNO REGISTERNO'
`info or1k spr REGISTERNO'
     Shows information about specified spr register.

`spr GROUP REGISTER VALUE'
`spr REGISTER VALUE'
`spr GROUPNO REGISTERNO VALUE'
`spr REGISTERNO VALUE'
     Writes VALUE to specified spr register.

   Some implementations of OpenRISC 1000 Architecture also have
hardware trace.  It is very similar to GDB trace, except it does not
interfere with normal program execution and is thus much faster.
Hardware breakpoints/watchpoint triggers can be set using:
`$LEA/$LDATA'
     Load effective address/data

`$SEA/$SDATA'
     Store effective address/data

`$AEA/$ADATA'
     Access effective address ($SEA or $LEA) or data ($SDATA/$LDATA)

`$FETCH'
     Fetch data

   When triggered, it can capture low level data, like: `PC', `LSEA',
`LDATA', `SDATA', `READSPR', `WRITESPR', `INSTR'.

   `htrace' commands: 
`hwatch CONDITIONAL'
     Set hardware watchpoint on combination of Load/Store Effective
     Address(es) or Data.  For example:

     `hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) &&
     ($SDATA >= 50)'

     `hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) &&
     ($SDATA >= 50)'

`htrace info'
     Display information about current HW trace configuration.

`htrace trigger CONDITIONAL'
     Set starting criteria for HW trace.

`htrace qualifier CONDITIONAL'
     Set acquisition qualifier for HW trace.

`htrace stop CONDITIONAL'
     Set HW trace stopping criteria.

`htrace record [DATA]*'
     Selects the data to be recorded, when qualifier is met and HW
     trace was triggered.

`htrace enable'
`htrace disable'
     Enables/disables the HW trace.

`htrace rewind [FILENAME]'
     Clears currently recorded trace data.

     If filename is specified, new trace file is made and any newly
     collected data will be written there.

`htrace print [START [LEN]]'
     Prints trace buffer, using current record configuration.

`htrace mode continuous'
     Set continuous trace mode.

`htrace mode suspend'
     Set suspend trace mode.



File: gdb.info,  Node: PowerPC Embedded,  Next: PA,  Prev: OpenRISC 1000,  Up: Embedded Processors

21.3.7 PowerPC Embedded
-----------------------

GDB supports using the DVC (Data Value Compare) register to implement
in hardware simple hardware watchpoint conditions of the form:

     (gdb) watch ADDRESS|VARIABLE \
       if  ADDRESS|VARIABLE == CONSTANT EXPRESSION

   The DVC register will be automatically used when GDB detects such
pattern in a condition expression, and the created watchpoint uses one
debug register (either the `exact-watchpoints' option is on and the
variable is scalar, or the variable has a length of one byte).  This
feature is available in native GDB running on a Linux kernel version
2.6.34 or newer.

   When running on PowerPC embedded processors, GDB automatically uses
ranged hardware watchpoints, unless the `exact-watchpoints' option is
on, in which case watchpoints using only one debug register are created
when watching variables of scalar types.

   You can create an artificial array to watch an arbitrary memory
region using one of the following commands (*note Expressions::):

     (gdb) watch *((char *) ADDRESS)@LENGTH
     (gdb) watch {char[LENGTH]} ADDRESS

   PowerPC embedded processors support masked watchpoints.  See the
discussion about the `mask' argument in *note Set Watchpoints::.

   PowerPC embedded processors support hardware accelerated "ranged
breakpoints".  A ranged breakpoint stops execution of the inferior
whenever it executes an instruction at any address within the range it
specifies.  To set a ranged breakpoint in GDB, use the `break-range'
command.

   GDB provides the following PowerPC-specific commands:

`break-range START-LOCATION, END-LOCATION'
     Set a breakpoint for an address range.  START-LOCATION and
     END-LOCATION can specify a function name, a line number, an offset
     of lines from the current line or from the start location, or an
     address of an instruction (see *note Specify Location::, for a
     list of all the possible ways to specify a LOCATION.)  The
     breakpoint will stop execution of the inferior whenever it
     executes an instruction at any address within the specified range,
     (including START-LOCATION and END-LOCATION.)

`set powerpc soft-float'
`show powerpc soft-float'
     Force GDB to use (or not use) a software floating point calling
     convention.  By default, GDB selects the calling convention based
     on the selected architecture and the provided executable file.

`set powerpc vector-abi'
`show powerpc vector-abi'
     Force GDB to use the specified calling convention for vector
     arguments and return values.  The valid options are `auto';
     `generic', to avoid vector registers even if they are present;
     `altivec', to use AltiVec registers; and `spe' to use SPE
     registers.  By default, GDB selects the calling convention based
     on the selected architecture and the provided executable file.

`set powerpc exact-watchpoints'
`show powerpc exact-watchpoints'
     Allow GDB to use only one debug register when watching a variable
     of scalar type, thus assuming that the variable is accessed
     through the address of its first byte.

`target dink32 DEV'
     DINK32 ROM monitor.

`target ppcbug DEV'

`target ppcbug1 DEV'
     PPCBUG ROM monitor for PowerPC.

`target sds DEV'
     SDS monitor, running on a PowerPC board (such as Motorola's ADS).

   The following commands specific to the SDS protocol are supported by
GDB:

`set sdstimeout NSEC'
     Set the timeout for SDS protocol reads to be NSEC seconds.  The
     default is 2 seconds.

`show sdstimeout'
     Show the current value of the SDS timeout.

`sds COMMAND'
     Send the specified COMMAND string to the SDS monitor.


File: gdb.info,  Node: PA,  Next: Sparclet,  Prev: PowerPC Embedded,  Up: Embedded Processors

21.3.8 HP PA Embedded
---------------------

`target op50n DEV'
     OP50N monitor, running on an OKI HPPA board.

`target w89k DEV'
     W89K monitor, running on a Winbond HPPA board.



File: gdb.info,  Node: Sparclet,  Next: Sparclite,  Prev: PA,  Up: Embedded Processors

21.3.9 Tsqware Sparclet
-----------------------

GDB enables developers to debug tasks running on Sparclet targets from
a Unix host.  GDB uses code that runs on both the Unix host and on the
Sparclet target.  The program `gdb' is installed and executed on the
Unix host.

`remotetimeout ARGS'
     GDB supports the option `remotetimeout'.  This option is set by
     the user, and  ARGS represents the number of seconds GDB waits for
     responses.

   When compiling for debugging, include the options `-g' to get debug
information and `-Ttext' to relocate the program to where you wish to
load it on the target.  You may also want to add the options `-n' or
`-N' in order to reduce the size of the sections.  Example:

     sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N

   You can use `objdump' to verify that the addresses are what you
intended:

     sparclet-aout-objdump --headers --syms prog

   Once you have set your Unix execution search path to find GDB, you
are ready to run GDB.  From your Unix host, run `gdb' (or
`sparclet-aout-gdb', depending on your installation).

   GDB comes up showing the prompt:

     (gdbslet)

* Menu:

* Sparclet File::                Setting the file to debug
* Sparclet Connection::          Connecting to Sparclet
* Sparclet Download::            Sparclet download
* Sparclet Execution::           Running and debugging


File: gdb.info,  Node: Sparclet File,  Next: Sparclet Connection,  Up: Sparclet

21.3.9.1 Setting File to Debug
..............................

The GDB command `file' lets you choose with program to debug.

     (gdbslet) file prog

   GDB then attempts to read the symbol table of `prog'.  GDB locates
the file by searching the directories listed in the command search path.
If the file was compiled with debug information (option `-g'), source
files will be searched as well.  GDB locates the source files by
searching the directories listed in the directory search path (*note
Your Program's Environment: Environment.).  If it fails to find a file,
it displays a message such as:

     prog: No such file or directory.

   When this happens, add the appropriate directories to the search
paths with the GDB commands `path' and `dir', and execute the `target'
command again.


File: gdb.info,  Node: Sparclet Connection,  Next: Sparclet Download,  Prev: Sparclet File,  Up: Sparclet

21.3.9.2 Connecting to Sparclet
...............................

The GDB command `target' lets you connect to a Sparclet target.  To
connect to a target on serial port "`ttya'", type:

     (gdbslet) target sparclet /dev/ttya
     Remote target sparclet connected to /dev/ttya
     main () at ../prog.c:3

   GDB displays messages like these:

     Connected to ttya.


File: gdb.info,  Node: Sparclet Download,  Next: Sparclet Execution,  Prev: Sparclet Connection,  Up: Sparclet

21.3.9.3 Sparclet Download
..........................

Once connected to the Sparclet target, you can use the GDB `load'
command to download the file from the host to the target.  The file
name and load offset should be given as arguments to the `load' command.
Since the file format is aout, the program must be loaded to the
starting address.  You can use `objdump' to find out what this value
is.  The load offset is an offset which is added to the VMA (virtual
memory address) of each of the file's sections.  For instance, if the
program `prog' was linked to text address 0x1201000, with data at
0x12010160 and bss at 0x12010170, in GDB, type:

     (gdbslet) load prog 0x12010000
     Loading section .text, size 0xdb0 vma 0x12010000

   If the code is loaded at a different address then what the program
was linked to, you may need to use the `section' and `add-symbol-file'
commands to tell GDB where to map the symbol table.


File: gdb.info,  Node: Sparclet Execution,  Prev: Sparclet Download,  Up: Sparclet

21.3.9.4 Running and Debugging
..............................

You can now begin debugging the task using GDB's execution control
commands, `b', `step', `run', etc.  See the GDB manual for the list of
commands.

     (gdbslet) b main
     Breakpoint 1 at 0x12010000: file prog.c, line 3.
     (gdbslet) run
     Starting program: prog
     Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
     3        char *symarg = 0;
     (gdbslet) step
     4        char *execarg = "hello!";
     (gdbslet)


File: gdb.info,  Node: Sparclite,  Next: Z8000,  Prev: Sparclet,  Up: Embedded Processors

21.3.10 Fujitsu Sparclite
-------------------------

`target sparclite DEV'
     Fujitsu sparclite boards, used only for the purpose of loading.
     You must use an additional command to debug the program.  For
     example: target remote DEV using GDB standard remote protocol.



File: gdb.info,  Node: Z8000,  Next: AVR,  Prev: Sparclite,  Up: Embedded Processors

21.3.11 Zilog Z8000
-------------------

When configured for debugging Zilog Z8000 targets, GDB includes a Z8000
simulator.

   For the Z8000 family, `target sim' simulates either the Z8002 (the
unsegmented variant of the Z8000 architecture) or the Z8001 (the
segmented variant).  The simulator recognizes which architecture is
appropriate by inspecting the object code.

`target sim ARGS'
     Debug programs on a simulated CPU.  If the simulator supports setup
     options, specify them via ARGS.

After specifying this target, you can debug programs for the simulated
CPU in the same style as programs for your host computer; use the
`file' command to load a new program image, the `run' command to run
your program, and so on.

   As well as making available all the usual machine registers (*note
Registers: Registers.), the Z8000 simulator provides three additional
items of information as specially named registers:

`cycles'
     Counts clock-ticks in the simulator.

`insts'
     Counts instructions run in the simulator.

`time'
     Execution time in 60ths of a second.


   You can refer to these values in GDB expressions with the usual
conventions; for example, `b fputc if $cycles>5000' sets a conditional
breakpoint that suspends only after at least 5000 simulated clock ticks.


File: gdb.info,  Node: AVR,  Next: CRIS,  Prev: Z8000,  Up: Embedded Processors

21.3.12 Atmel AVR
-----------------

When configured for debugging the Atmel AVR, GDB supports the following
AVR-specific commands:

`info io_registers'
     This command displays information about the AVR I/O registers.  For
     each register, GDB prints its number and value.


File: gdb.info,  Node: CRIS,  Next: Super-H,  Prev: AVR,  Up: Embedded Processors

21.3.13 CRIS
------------

When configured for debugging CRIS, GDB provides the following
CRIS-specific commands:

`set cris-version VER'
     Set the current CRIS version to VER, either `10' or `32'.  The
     CRIS version affects register names and sizes.  This command is
     useful in case autodetection of the CRIS version fails.

`show cris-version'
     Show the current CRIS version.

`set cris-dwarf2-cfi'
     Set the usage of DWARF-2 CFI for CRIS debugging.  The default is
     `on'.  Change to `off' when using `gcc-cris' whose version is below
     `R59'.

`show cris-dwarf2-cfi'
     Show the current state of using DWARF-2 CFI.

`set cris-mode MODE'
     Set the current CRIS mode to MODE.  It should only be changed when
     debugging in guru mode, in which case it should be set to `guru'
     (the default is `normal').

`show cris-mode'
     Show the current CRIS mode.


File: gdb.info,  Node: Super-H,  Prev: CRIS,  Up: Embedded Processors

21.3.14 Renesas Super-H
-----------------------

For the Renesas Super-H processor, GDB provides these commands:

`set sh calling-convention CONVENTION'
     Set the calling-convention used when calling functions from GDB.
     Allowed values are `gcc', which is the default setting, and
     `renesas'.  With the `gcc' setting, functions are called using the
     GCC calling convention.  If the DWARF-2 information of the called
     function specifies that the function follows the Renesas calling
     convention, the function is called using the Renesas calling
     convention.  If the calling convention is set to `renesas', the
     Renesas calling convention is always used, regardless of the
     DWARF-2 information.  This can be used to override the default of
     `gcc' if debug information is missing, or the compiler does not
     emit the DWARF-2 calling convention entry for a function.

`show sh calling-convention'
     Show the current calling convention setting.



File: gdb.info,  Node: Architectures,  Prev: Embedded Processors,  Up: Configurations

21.4 Architectures
==================

This section describes characteristics of architectures that affect all
uses of GDB with the architecture, both native and cross.

* Menu:

* AArch64::
* i386::
* Alpha::
* MIPS::
* HPPA::               HP PA architecture
* SPU::                Cell Broadband Engine SPU architecture
* PowerPC::


File: gdb.info,  Node: AArch64,  Next: i386,  Up: Architectures

21.4.1 AArch64
--------------

When GDB is debugging the AArch64 architecture, it provides the
following special commands:

`set debug aarch64'
     This command determines whether AArch64 architecture-specific
     debugging messages are to be displayed.

`show debug aarch64'
     Show whether AArch64 debugging messages are displayed.



File: gdb.info,  Node: i386,  Next: Alpha,  Prev: AArch64,  Up: Architectures

21.4.2 x86 Architecture-specific Issues
---------------------------------------

`set struct-convention MODE'
     Set the convention used by the inferior to return `struct's and
     `union's from functions to MODE.  Possible values of MODE are
     `"pcc"', `"reg"', and `"default"' (the default).  `"default"' or
     `"pcc"' means that `struct's are returned on the stack, while
     `"reg"' means that a `struct' or a `union' whose size is 1, 2, 4,
     or 8 bytes will be returned in a register.

`show struct-convention'
     Show the current setting of the convention to return `struct's
     from functions.


File: gdb.info,  Node: Alpha,  Next: MIPS,  Prev: i386,  Up: Architectures

21.4.3 Alpha
------------

See the following section.


File: gdb.info,  Node: MIPS,  Next: HPPA,  Prev: Alpha,  Up: Architectures

21.4.4 MIPS
-----------

Alpha- and MIPS-based computers use an unusual stack frame, which
sometimes requires GDB to search backward in the object code to find
the beginning of a function.

   To improve response time (especially for embedded applications, where
GDB may be restricted to a slow serial line for this search) you may
want to limit the size of this search, using one of these commands:

`set heuristic-fence-post LIMIT'
     Restrict GDB to examining at most LIMIT bytes in its search for
     the beginning of a function.  A value of 0 (the default) means
     there is no limit.  However, except for 0, the larger the limit
     the more bytes `heuristic-fence-post' must search and therefore
     the longer it takes to run.  You should only need to use this
     command when debugging a stripped executable.

`show heuristic-fence-post'
     Display the current limit.

These commands are available _only_ when GDB is configured for
debugging programs on Alpha or MIPS processors.

   Several MIPS-specific commands are available when debugging MIPS
programs:

`set mips abi ARG'
     Tell GDB which MIPS ABI is used by the inferior.  Possible values
     of ARG are:

    `auto'
          The default ABI associated with the current binary (this is
          the default).

    `o32'

    `o64'

    `n32'

    `n64'

    `eabi32'

    `eabi64'

`show mips abi'
     Show the MIPS ABI used by GDB to debug the inferior.

`set mips compression ARG'
     Tell GDB which MIPS compressed ISA (Instruction Set Architecture)
     encoding is used by the inferior.  GDB uses this for code
     disassembly and other internal interpretation purposes.  This
     setting is only referred to when no executable has been associated
     with the debugging session or the executable does not provide
     information about the encoding it uses.  Otherwise this setting is
     automatically updated from information provided by the executable.

     Possible values of ARG are `mips16' and `micromips'.  The default
     compressed ISA encoding is `mips16', as executables containing
     MIPS16 code frequently are not identified as such.

     This setting is "sticky"; that is, it retains its value across
     debugging sessions until reset either explicitly with this command
     or implicitly from an executable.

     The compiler and/or assembler typically add symbol table
     annotations to identify functions compiled for the MIPS16 or
     microMIPS ISAs.  If these function-scope annotations are present,
     GDB uses them in preference to the global compressed ISA encoding
     setting.

`show mips compression'
     Show the MIPS compressed ISA encoding used by GDB to debug the
     inferior.

`set mipsfpu'
`show mipsfpu'
     *Note set mipsfpu: MIPS Embedded.

`set mips mask-address ARG'
     This command determines whether the most-significant 32 bits of
     64-bit MIPS addresses are masked off.  The argument ARG can be
     `on', `off', or `auto'.  The latter is the default setting, which
     lets GDB determine the correct value.

`show mips mask-address'
     Show whether the upper 32 bits of MIPS addresses are masked off or
     not.

`set remote-mips64-transfers-32bit-regs'
     This command controls compatibility with 64-bit MIPS targets that
     transfer data in 32-bit quantities.  If you have an old MIPS 64
     target that transfers 32 bits for some registers, like SR and FSR,
     and 64 bits for other registers, set this option to `on'.

`show remote-mips64-transfers-32bit-regs'
     Show the current setting of compatibility with older MIPS 64
     targets.

`set debug mips'
     This command turns on and off debugging messages for the
     MIPS-specific target code in GDB.

`show debug mips'
     Show the current setting of MIPS debugging messages.


File: gdb.info,  Node: HPPA,  Next: SPU,  Prev: MIPS,  Up: Architectures

21.4.5 HPPA
-----------

When GDB is debugging the HP PA architecture, it provides the following
special commands:

`set debug hppa'
     This command determines whether HPPA architecture-specific
     debugging messages are to be displayed.

`show debug hppa'
     Show whether HPPA debugging messages are displayed.

`maint print unwind ADDRESS'
     This command displays the contents of the unwind table entry at the
     given ADDRESS.



File: gdb.info,  Node: SPU,  Next: PowerPC,  Prev: HPPA,  Up: Architectures

21.4.6 Cell Broadband Engine SPU architecture
---------------------------------------------

When GDB is debugging the Cell Broadband Engine SPU architecture, it
provides the following special commands:

`info spu event'
     Display SPU event facility status.  Shows current event mask and
     pending event status.

`info spu signal'
     Display SPU signal notification facility status.  Shows pending
     signal-control word and signal notification mode of both signal
     notification channels.

`info spu mailbox'
     Display SPU mailbox facility status.  Shows all pending entries,
     in order of processing, in each of the SPU Write Outbound, SPU
     Write Outbound Interrupt, and SPU Read Inbound mailboxes.

`info spu dma'
     Display MFC DMA status.  Shows all pending commands in the MFC DMA
     queue.  For each entry, opcode, tag, class IDs, effective and
     local store addresses and transfer size are shown.

`info spu proxydma'
     Display MFC Proxy-DMA status.  Shows all pending commands in the
     MFC Proxy-DMA queue.  For each entry, opcode, tag, class IDs,
     effective and local store addresses and transfer size are shown.


   When GDB is debugging a combined PowerPC/SPU application on the Cell
Broadband Engine, it provides in addition the following special
commands:

`set spu stop-on-load ARG'
     Set whether to stop for new SPE threads.  When set to `on', GDB
     will give control to the user when a new SPE thread enters its
     `main' function.  The default is `off'.

`show spu stop-on-load'
     Show whether to stop for new SPE threads.

`set spu auto-flush-cache ARG'
     Set whether to automatically flush the software-managed cache.
     When set to `on', GDB will automatically cause the SPE
     software-managed cache to be flushed whenever SPE execution stops.
     This provides a consistent view of PowerPC memory that is accessed
     via the cache.  If an application does not use the
     software-managed cache, this option has no effect.

`show spu auto-flush-cache'
     Show whether to automatically flush the software-managed cache.



File: gdb.info,  Node: PowerPC,  Prev: SPU,  Up: Architectures

21.4.7 PowerPC
--------------

When GDB is debugging the PowerPC architecture, it provides a set of
pseudo-registers to enable inspection of 128-bit wide Decimal Floating
Point numbers stored in the floating point registers. These values must
be stored in two consecutive registers, always starting at an even
register like `f0' or `f2'.

   The pseudo-registers go from `$dl0' through `$dl15', and are formed
by joining the even/odd register pairs `f0' and `f1' for `$dl0', `f2'
and `f3' for `$dl1' and so on.

   For POWER7 processors, GDB provides a set of pseudo-registers, the
64-bit wide Extended Floating Point Registers (`f32' through `f63').


File: gdb.info,  Node: Controlling GDB,  Next: Extending GDB,  Prev: Configurations,  Up: Top

22 Controlling GDB
******************

You can alter the way GDB interacts with you by using the `set'
command.  For commands controlling how GDB displays data, see *note
Print Settings: Print Settings.  Other settings are described here.

* Menu:

* Prompt::                      Prompt
* Editing::                     Command editing
* Command History::             Command history
* Screen Size::                 Screen size
* Numbers::                     Numbers
* ABI::                         Configuring the current ABI
* Auto-loading::                Automatically loading associated files
* Messages/Warnings::           Optional warnings and messages
* Debugging Output::            Optional messages about internal happenings
* Other Misc Settings::         Other Miscellaneous Settings


File: gdb.info,  Node: Prompt,  Next: Editing,  Up: Controlling GDB

22.1 Prompt
===========

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
GDB sessions so that you can always tell which one you are talking to.

   _Note:_  `set prompt' does not add a space for you after the prompt
you set.  This allows you to set a prompt which ends in a space or a
prompt that does not.

`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'

   Versions of GDB that ship with Python scripting enabled have prompt
extensions.  The commands for interacting with these extensions are:

`set extended-prompt PROMPT'
     Set an extended prompt that allows for substitutions.  *Note
     gdb.prompt::, for a list of escape sequences that can be used for
     substitution.  Any escape sequences specified as part of the prompt
     string are replaced with the corresponding strings each time the
     prompt is displayed.

     For example:

          set extended-prompt Current working directory: \w (gdb)

     Note that when an extended-prompt is set, it takes control of the
     PROMPT_HOOK hook.  *Note prompt_hook::, for further information.

`show extended-prompt'
     Prints the extended prompt.  Any escape sequences specified as
     part of the prompt string with `set extended-prompt', are replaced
     with the corresponding strings each time the prompt is displayed.


File: gdb.info,  Node: Editing,  Next: Command History,  Prev: Prompt,  Up: Controlling GDB

22.2 Command Editing
====================

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 GNU 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.

   *Note Command Line Editing::, for more details about the Readline
interface.  Users unfamiliar with GNU Emacs or `vi' are encouraged to
read that chapter.


File: gdb.info,  Node: Command History,  Next: Screen Size,  Prev: Editing,  Up: Controlling GDB

22.3 Command History
====================

GDB can keep track of the commands you type during your debugging
sessions, so that you can be certain of precisely what happened.  Use
these commands to manage the GDB command history facility.

   GDB uses the GNU History library, a part of the Readline package, to
provide the history facility.  *Note Using History Interactively::, for
the detailed description of the History library.

   To issue a command to GDB without affecting certain aspects of the
state which is seen by users, prefix it with `server ' (*note Server
Prefix::).  This means that this command will not affect the command
history, nor will it affect GDB's notion of which command to repeat if
<RET> is pressed on a line by itself.

   The server prefix does not affect the recording of values into the
value history; to print a value without recording it into the value
history, use the `output' command instead of the `print' command.

   Here is the description of GDB commands related to command history.

`set history filename FNAME'
     Set the name of the GDB command history file to FNAME.  This is
     the file where GDB reads an initial command history list, and
     where it writes the command history from this session when it
     exits.  You can access this list 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' (`./_gdb_history' on MS-DOS)
     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 keeps 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 `!'.
*Note Event Designators::, for more details.

   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 do 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.

`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.


File: gdb.info,  Node: Screen Size,  Next: Numbers,  Prev: Command History,  Up: Controlling GDB

22.4 Screen Size
================

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, or `q' to discard the remaining output.  Also, the
screen width setting determines when to wrap lines of output.
Depending on what is being printed, GDB 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 terminal driver
software.  For example, on Unix GDB uses 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 does not pause during
     output no matter how long the output is.  This is useful if output
     is to a file or to an editor buffer.

     Likewise, you can specify `set width 0' to prevent GDB from
     wrapping its output.

`set pagination on'
`set pagination off'
     Turn the output pagination on or off; the default is on.  Turning
     pagination off is the alternative to `set height 0'.  Note that
     running GDB with the `--batch' option (*note -batch: Mode
     Options.) also automatically disables pagination.

`show pagination'
     Show the current pagination mode.


File: gdb.info,  Node: Numbers,  Next: ABI,  Prev: Screen Size,  Up: Controlling GDB

22.5 Numbers
============

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
neither begin with `0' or `0x', nor end with a `.' 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 commands described below.

`set input-radix BASE'
     Set the default base for numeric input.  Supported choices for
     BASE are decimal 8, 10, or 16.  BASE must itself be specified
     either unambiguously or using the current input radix; for
     example, any of

          set input-radix 012
          set input-radix 10.
          set input-radix 0xa

     sets the input base to decimal.  On the other hand, `set
     input-radix 10' leaves the input radix unchanged, no matter what
     it was, since `10', being without any leading or trailing signs of
     its base, is interpreted in the current radix.  Thus, if the
     current radix is 16, `10' is interpreted in hex, i.e. as 16
     decimal, which doesn't change the radix.

`set output-radix BASE'
     Set the default base for numeric display.  Supported choices for
     BASE are decimal 8, 10, or 16.  BASE must itself be specified
     either unambiguously or using the current input radix.

`show input-radix'
     Display the current default base for numeric input.

`show output-radix'
     Display the current default base for numeric display.

`set radix [BASE]'
`show radix'
     These commands set and show the default base for both input and
     output of numbers.  `set radix' sets the radix of input and output
     to the same base; without an argument, it resets the radix back to
     its default value of 10.



File: gdb.info,  Node: ABI,  Next: Auto-loading,  Prev: Numbers,  Up: Controlling GDB

22.6 Configuring the Current ABI
================================

GDB can determine the "ABI" (Application Binary Interface) of your
application automatically.  However, sometimes you need to override its
conclusions.  Use these commands to manage GDB's view of the current
ABI.

   One GDB configuration can debug binaries for multiple operating
system targets, either via remote debugging or native emulation.  GDB
will autodetect the "OS ABI" (Operating System ABI) in use, but you can
override its conclusion using the `set osabi' command.  One example
where this is useful is in debugging of binaries which use an alternate
C library (e.g. UCLIBC for GNU/Linux) which does not have the same
identifying marks that the standard C library for your platform
provides.

   When GDB is debugging the AArch64 architecture, it provides a
"Newlib" OS ABI.  This is useful for handling `setjmp' and `longjmp'
when debugging binaries that use the NEWLIB C library.  The "Newlib" OS
ABI can be selected by `set osabi Newlib'.

`show osabi'
     Show the OS ABI currently in use.

`set osabi'
     With no argument, show the list of registered available OS ABI's.

`set osabi ABI'
     Set the current OS ABI to ABI.

   Generally, the way that an argument of type `float' is passed to a
function depends on whether the function is prototyped.  For a
prototyped (i.e. ANSI/ISO style) function, `float' arguments are passed
unchanged, according to the architecture's convention for `float'.  For
unprototyped (i.e. K&R style) functions, `float' arguments are first
promoted to type `double' and then passed.

   Unfortunately, some forms of debug information do not reliably
indicate whether a function is prototyped.  If GDB calls a function
that is not marked as prototyped, it consults `set
coerce-float-to-double'.

`set coerce-float-to-double'
`set coerce-float-to-double on'
     Arguments of type `float' will be promoted to `double' when passed
     to an unprototyped function.  This is the default setting.

`set coerce-float-to-double off'
     Arguments of type `float' will be passed directly to unprototyped
     functions.

`show coerce-float-to-double'
     Show the current setting of promoting `float' to `double'.

   GDB needs to know the ABI used for your program's C++ objects.  The
correct C++ ABI depends on which C++ compiler was used to build your
application.  GDB only fully supports programs with a single C++ ABI;
if your program contains code using multiple C++ ABI's or if GDB can
not identify your program's ABI correctly, you can tell GDB which ABI
to use.  Currently supported ABI's include "gnu-v2", for `g++' versions
before 3.0, "gnu-v3", for `g++' versions 3.0 and later, and "hpaCC" for
the HP ANSI C++ compiler.  Other C++ compilers may use the "gnu-v2" or
"gnu-v3" ABI's as well.  The default setting is "auto".

`show cp-abi'
     Show the C++ ABI currently in use.

`set cp-abi'
     With no argument, show the list of supported C++ ABI's.

`set cp-abi ABI'
`set cp-abi auto'
     Set the current C++ ABI to ABI, or return to automatic detection.


File: gdb.info,  Node: Auto-loading,  Next: Messages/Warnings,  Prev: ABI,  Up: Controlling GDB

22.7 Automatically loading associated files
===========================================

GDB sometimes reads files with commands and settings automatically,
without being explicitly told so by the user.  We call this feature
"auto-loading".  While auto-loading is useful for automatically adapting
GDB to the needs of your project, it can sometimes produce unexpected
results or introduce security risks (e.g., if the file comes from
untrusted sources).

   Note that loading of these associated files (including the local
`.gdbinit' file) requires accordingly configured `auto-load safe-path'
(*note Auto-loading safe path::).

   For these reasons, GDB includes commands and options to let you
control when to auto-load files and which files should be auto-loaded.

`set auto-load off'
     Globally disable loading of all auto-loaded files.  You may want
     to use this command with the `-iex' option (*note Option
     -init-eval-command::) such as:
          $ gdb -iex "set auto-load off" untrusted-executable corefile

     Be aware that system init file (*note System-wide configuration::)
     and init files from your home directory (*note Home Directory Init
     File::) still get read (as they come from generally trusted
     directories).  To prevent GDB from auto-loading even those init
     files, use the `-nx' option (*note Mode Options::), in addition to
     `set auto-load no'.

`show auto-load'
     Show whether auto-loading of each specific `auto-load' file(s) is
     enabled or disabled.

          (gdb) show auto-load
          gdb-scripts:  Auto-loading of canned sequences of commands scripts is on.
          libthread-db:  Auto-loading of inferior specific libthread_db is on.
          local-gdbinit:  Auto-loading of .gdbinit script from current directory
                          is on.
          python-scripts:  Auto-loading of Python scripts is on.
          safe-path:  List of directories from which it is safe to auto-load files
                      is $debugdir:$datadir/auto-load.
          scripts-directory:  List of directories from which to load auto-loaded scripts
                              is $debugdir:$datadir/auto-load.

`info auto-load'
     Print whether each specific `auto-load' file(s) have been
     auto-loaded or not.

          (gdb) info auto-load
          gdb-scripts:
          Loaded  Script
          Yes     /home/user/gdb/gdb-gdb.gdb
          libthread-db:  No auto-loaded libthread-db.
          local-gdbinit:  Local .gdbinit file "/home/user/gdb/.gdbinit" has been
                          loaded.
          python-scripts:
          Loaded  Script
          Yes     /home/user/gdb/gdb-gdb.py

   These are various kinds of files GDB can automatically load:

   * *Note objfile-gdb.py file::, controlled by *note set auto-load
     python-scripts::.

   * *Note objfile-gdb.gdb file::, controlled by *note set auto-load
     gdb-scripts::.

   * *Note dotdebug_gdb_scripts section::, controlled by *note set
     auto-load python-scripts::.

   * *Note Init File in the Current Directory::, controlled by *note
     set auto-load local-gdbinit::.

   * *Note libthread_db.so.1 file::, controlled by *note set auto-load
     libthread-db::.

   These are GDB control commands for the auto-loading:

*Note set auto-load off::.           Disable auto-loading globally.
*Note show auto-load::.              Show setting of all kinds of files.
*Note info auto-load::.              Show state of all kinds of files.
*Note set auto-load gdb-scripts::.   Control for GDB command scripts.
*Note show auto-load gdb-scripts::.  Show setting of GDB command scripts.
*Note info auto-load gdb-scripts::.  Show state of GDB command scripts.
*Note set auto-load                  Control for GDB Python scripts.
python-scripts::.                    
*Note show auto-load                 Show setting of GDB Python scripts.
python-scripts::.                    
*Note info auto-load                 Show state of GDB Python scripts.
python-scripts::.                    
*Note set auto-load                  Control for GDB auto-loaded scripts
scripts-directory::.                 location.
*Note show auto-load                 Show GDB auto-loaded scripts
scripts-directory::.                 location.
*Note set auto-load local-gdbinit::. Control for init file in the
                                     current directory.
*Note show auto-load                 Show setting of init file in the
local-gdbinit::.                     current directory.
*Note info auto-load                 Show state of init file in the
local-gdbinit::.                     current directory.
*Note set auto-load libthread-db::.  Control for thread debugging
                                     library.
*Note show auto-load libthread-db::. Show setting of thread debugging
                                     library.
*Note info auto-load libthread-db::. Show state of thread debugging
                                     library.
*Note set auto-load safe-path::.     Control directories trusted for
                                     automatic loading.
*Note show auto-load safe-path::.    Show directories trusted for
                                     automatic loading.
*Note add-auto-load-safe-path::.     Add directory trusted for automatic
                                     loading.

* Menu:

* Init File in the Current Directory:: `set/show/info auto-load local-gdbinit'
* libthread_db.so.1 file::             `set/show/info auto-load libthread-db'
* objfile-gdb.gdb file::               `set/show/info auto-load gdb-script'
* Auto-loading safe path::             `set/show/info auto-load safe-path'
* Auto-loading verbose mode::          `set/show debug auto-load'
*Note Python Auto-loading::.


File: gdb.info,  Node: Init File in the Current Directory,  Next: libthread_db.so.1 file,  Up: Auto-loading

22.7.1 Automatically loading init file in the current directory
---------------------------------------------------------------

By default, GDB reads and executes the canned sequences of commands
from init file (if any) in the current working directory, see *note
Init File in the Current Directory during Startup::.

   Note that loading of this local `.gdbinit' file also requires
accordingly configured `auto-load safe-path' (*note Auto-loading safe
path::).

`set auto-load local-gdbinit [on|off]'
     Enable or disable the auto-loading of canned sequences of commands
     (*note Sequences::) found in init file in the current directory.

`show auto-load local-gdbinit'
     Show whether auto-loading of canned sequences of commands from
     init file in the current directory is enabled or disabled.

`info auto-load local-gdbinit'
     Print whether canned sequences of commands from init file in the
     current directory have been auto-loaded.


File: gdb.info,  Node: libthread_db.so.1 file,  Next: objfile-gdb.gdb file,  Prev: Init File in the Current Directory,  Up: Auto-loading

22.7.2 Automatically loading thread debugging library
-----------------------------------------------------

This feature is currently present only on GNU/Linux native hosts.

   GDB reads in some cases thread debugging library from places specific
to the inferior (*note set libthread-db-search-path::).

   The special `libthread-db-search-path' entry `$sdir' is processed
without checking this `set auto-load libthread-db' switch as system
libraries have to be trusted in general.  In all other cases of
`libthread-db-search-path' entries GDB checks first if `set auto-load
libthread-db' is enabled before trying to open such thread debugging
library.

   Note that loading of this debugging library also requires
accordingly configured `auto-load safe-path' (*note Auto-loading safe
path::).

`set auto-load libthread-db [on|off]'
     Enable or disable the auto-loading of inferior specific thread
     debugging library.

`show auto-load libthread-db'
     Show whether auto-loading of inferior specific thread debugging
     library is enabled or disabled.

`info auto-load libthread-db'
     Print the list of all loaded inferior specific thread debugging
     libraries and for each such library print list of inferior PIDs
     using it.


File: gdb.info,  Node: objfile-gdb.gdb file,  Next: Auto-loading safe path,  Prev: libthread_db.so.1 file,  Up: Auto-loading

22.7.3 The `OBJFILE-gdb.gdb' file
---------------------------------

GDB tries to load an `OBJFILE-gdb.gdb' file containing canned sequences
of commands (*note Sequences::), as long as `set auto-load gdb-scripts'
is set to `on'.

   Note that loading of this script file also requires accordingly
configured `auto-load safe-path' (*note Auto-loading safe path::).

   For more background refer to the similar Python scripts auto-loading
description (*note objfile-gdb.py file::).

`set auto-load gdb-scripts [on|off]'
     Enable or disable the auto-loading of canned sequences of commands
     scripts.

`show auto-load gdb-scripts'
     Show whether auto-loading of canned sequences of commands scripts
     is enabled or disabled.

`info auto-load gdb-scripts [REGEXP]'
     Print the list of all canned sequences of commands scripts that
     GDB auto-loaded.

   If REGEXP is supplied only canned sequences of commands scripts with
matching names are printed.


File: gdb.info,  Node: Auto-loading safe path,  Next: Auto-loading verbose mode,  Prev: objfile-gdb.gdb file,  Up: Auto-loading

22.7.4 Security restriction for auto-loading
--------------------------------------------

As the files of inferior can come from untrusted source (such as
submitted by an application user) GDB does not always load any files
automatically.  GDB provides the `set auto-load safe-path' setting to
list directories trusted for loading files not explicitly requested by
user.  Each directory can also be a shell wildcard pattern.

   If the path is not set properly you will see a warning and the file
will not get loaded:

     $ ./gdb -q ./gdb
     Reading symbols from /home/user/gdb/gdb...done.
     warning: File "/home/user/gdb/gdb-gdb.gdb" auto-loading has been
              declined by your `auto-load safe-path' set
              to "$debugdir:$datadir/auto-load".
     warning: File "/home/user/gdb/gdb-gdb.py" auto-loading has been
              declined by your `auto-load safe-path' set
              to "$debugdir:$datadir/auto-load".

To instruct GDB to go ahead and use the init files anyway, invoke GDB
like this:

     $ gdb -q -iex "set auto-load safe-path /home/user/gdb" ./gdb

   The list of trusted directories is controlled by the following
commands:

`set auto-load safe-path [DIRECTORIES]'
     Set the list of directories (and their subdirectories) trusted for
     automatic loading and execution of scripts.  You can also enter a
     specific trusted file.  Each directory can also be a shell
     wildcard pattern; wildcards do not match directory separator - see
     `FNM_PATHNAME' for system function `fnmatch' (*note fnmatch:
     (libc)Wildcard Matching.).  If you omit DIRECTORIES, `auto-load
     safe-path' will be reset to its default value as specified during
     GDB compilation.

     The list of directories uses path separator (`:' on GNU and Unix
     systems, `;' on MS-Windows and MS-DOS) to separate directories,
     similarly to the `PATH' environment variable.

`show auto-load safe-path'
     Show the list of directories trusted for automatic loading and
     execution of scripts.

`add-auto-load-safe-path'
     Add an entry (or list of entries) the list of directories trusted
     for automatic loading and execution of scripts.  Multiple entries
     may be delimited by the host platform path separator in use.

   This variable defaults to what `--with-auto-load-dir' has been
configured to (*note with-auto-load-dir::).  `$debugdir' and `$datadir'
substitution applies the same as for *note set auto-load
scripts-directory::.  The default `set auto-load safe-path' value can
be also overriden by GDB configuration option
`--with-auto-load-safe-path'.

   Setting this variable to `/' disables this security protection,
corresponding GDB configuration option is
`--without-auto-load-safe-path'.  This variable is supposed to be set
to the system directories writable by the system superuser only.  Users
can add their source directories in init files in their home
directories (*note Home Directory Init File::).  See also deprecated
init file in the current directory (*note Init File in the Current
Directory during Startup::).

   To force GDB to load the files it declined to load in the previous
example, you could use one of the following ways:

`~/.gdbinit': `add-auto-load-safe-path ~/src/gdb'
     Specify this trusted directory (or a file) as additional component
     of the list.  You have to specify also any existing directories
     displayed by by `show auto-load safe-path' (such as `/usr:/bin' in
     this example).

`gdb -iex "set auto-load safe-path /usr:/bin:~/src/gdb" ...'
     Specify this directory as in the previous case but just for a
     single GDB session.

`gdb -iex "set auto-load safe-path /" ...'
     Disable auto-loading safety for a single GDB session.  This
     assumes all the files you debug during this GDB session will come
     from trusted sources.

`./configure --without-auto-load-safe-path'
     During compilation of GDB you may disable any auto-loading safety.
     This assumes all the files you will ever debug with this GDB come
     from trusted sources.

   On the other hand you can also explicitly forbid automatic files
loading which also suppresses any such warning messages:

`gdb -iex "set auto-load no" ...'
     You can use GDB command-line option for a single GDB session.

`~/.gdbinit': `set auto-load no'
     Disable auto-loading globally for the user (*note Home Directory
     Init File::).  While it is improbable, you could also use system
     init file instead (*note System-wide configuration::).

   This setting applies to the file names as entered by user.  If no
entry matches GDB tries as a last resort to also resolve all the file
names into their canonical form (typically resolving symbolic links)
and compare the entries again.  GDB already canonicalizes most of the
filenames on its own before starting the comparison so a canonical form
of directories is recommended to be entered.


File: gdb.info,  Node: Auto-loading verbose mode,  Prev: Auto-loading safe path,  Up: Auto-loading

22.7.5 Displaying files tried for auto-load
-------------------------------------------

For better visibility of all the file locations where you can place
scripts to be auto-loaded with inferior -- or to protect yourself
against accidental execution of untrusted scripts -- GDB provides a
feature for printing all the files attempted to be loaded.  Both
existing and non-existing files may be printed.

   For example the list of directories from which it is safe to
auto-load files (*note Auto-loading safe path::) applies also to
canonicalized filenames which may not be too obvious while setting it
up.

     (gdb) set debug auto-load on
     (gdb) file ~/src/t/true
     auto-load: Loading canned sequences of commands script "/tmp/true-gdb.gdb"
                for objfile "/tmp/true".
     auto-load: Updating directories of "/usr:/opt".
     auto-load: Using directory "/usr".
     auto-load: Using directory "/opt".
     warning: File "/tmp/true-gdb.gdb" auto-loading has been declined
              by your `auto-load safe-path' set to "/usr:/opt".

`set debug auto-load [on|off]'
     Set whether to print the filenames attempted to be auto-loaded.

`show debug auto-load'
     Show whether printing of the filenames attempted to be auto-loaded
     is turned on or off.


File: gdb.info,  Node: Messages/Warnings,  Next: Debugging Output,  Prev: Auto-loading,  Up: Controlling GDB

22.8 Optional Warnings and Messages
===================================

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.  This
makes 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 *note Commands to Specify Files: Files.

`set verbose on'
     Enables GDB output of certain informational messages.

`set verbose off'
     Disables GDB 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 (*note Errors Reading Symbol Files: Symbol
Errors.).

`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.  Note that running GDB with the
     `--batch' option (*note -batch: Mode Options.) also automatically
     disables confirmation requests.

`set confirm on'
     Enables confirmation requests (the default).

`show confirm'
     Displays state of confirmation requests.


   If you need to debug user-defined commands or sourced files you may
find it useful to enable "command tracing".  In this mode each command
will be printed as it is executed, prefixed with one or more `+'
symbols, the quantity denoting the call depth of each command.

`set trace-commands on'
     Enable command tracing.

`set trace-commands off'
     Disable command tracing.

`show trace-commands'
     Display the current state of command tracing.


File: gdb.info,  Node: Debugging Output,  Next: Other Misc Settings,  Prev: Messages/Warnings,  Up: Controlling GDB

22.9 Optional Messages about Internal Happenings
================================================

GDB has commands that enable optional debugging messages from various
GDB subsystems; normally these commands are of interest to GDB
maintainers, or when reporting a bug.  This section documents those
commands.

`set exec-done-display'
     Turns on or off the notification of asynchronous commands'
     completion.  When on, GDB will print a message when an
     asynchronous command finishes its execution.  The default is off.  

`show exec-done-display'
     Displays the current setting of asynchronous command completion
     notification.  

`set debug aarch64'
     Turns on or off display of debugging messages related to ARM
     AArch64.  The default is off.  

`show debug aarch64'
     Displays the current state of displaying debugging messages
     related to ARM AArch64.  

`set debug arch'
     Turns on or off display of gdbarch debugging info.  The default is
     off

`show debug arch'
     Displays the current state of displaying gdbarch debugging info.

`set debug aix-thread'
     Display debugging messages about inner workings of the AIX thread
     module.

`show debug aix-thread'
     Show the current state of AIX thread debugging info display.

`set debug check-physname'
     Check the results of the "physname" computation.  When reading
     DWARF debugging information for C++, GDB attempts to compute each
     entity's name.  GDB can do this computation in two different ways,
     depending on exactly what information is present.  When enabled,
     this setting causes GDB to compute the names both ways and display
     any discrepancies.

`show debug check-physname'
     Show the current state of "physname" checking.

`set debug coff-pe-read'
     Control display of debugging messages related to reading of COFF/PE
     exported symbols.  The default is off.

`show debug coff-pe-read'
     Displays the current state of displaying debugging messages
     related to reading of COFF/PE exported symbols.

`set debug dwarf2-die'
     Dump DWARF2 DIEs after they are read in.  The value is the number
     of nesting levels to print.  A value of zero turns off the display.

`show debug dwarf2-die'
     Show the current state of DWARF2 DIE debugging.

`set debug dwarf2-read'
     Turns on or off display of debugging messages related to reading
     DWARF debug info.  The default is off.

`show debug dwarf2-read'
     Show the current state of DWARF2 reader debugging.

`set debug displaced'
     Turns on or off display of GDB debugging info for the displaced
     stepping support.  The default is off.

`show debug displaced'
     Displays the current state of displaying GDB debugging info
     related to displaced stepping.

`set debug event'
     Turns on or off display of GDB event debugging info.  The default
     is off.

`show debug event'
     Displays the current state of displaying GDB event debugging info.

`set debug expression'
     Turns on or off display of debugging info about GDB expression
     parsing.  The default is off.

`show debug expression'
     Displays the current state of displaying debugging info about GDB
     expression parsing.

`set debug frame'
     Turns on or off display of GDB frame debugging info.  The default
     is off.

`show debug frame'
     Displays the current state of displaying GDB frame debugging info.

`set debug gnu-nat'
     Turns on or off debugging messages from the GNU/Hurd debug support.

`show debug gnu-nat'
     Show the current state of GNU/Hurd debugging messages.

`set debug infrun'
     Turns on or off display of GDB debugging info for running the
     inferior.  The default is off.  `infrun.c' contains GDB's runtime
     state machine used for implementing operations such as
     single-stepping the inferior.

`show debug infrun'
     Displays the current state of GDB inferior debugging.

`set debug jit'
     Turns on or off debugging messages from JIT debug support.

`show debug jit'
     Displays the current state of GDB JIT debugging.

`set debug lin-lwp'
     Turns on or off debugging messages from the Linux LWP debug
     support.

`show debug lin-lwp'
     Show the current state of Linux LWP debugging messages.

`set debug mach-o'
     Control display of debugging messages related to Mach-O symbols
     processing.  The default is off.

`show debug mach-o'
     Displays the current state of displaying debugging messages
     related to reading of COFF/PE exported symbols.

`set debug notification'
     Turns on or off debugging messages about remote async notification.
     The default is off.

`show debug notification'
     Displays the current state of remote async notification debugging
     messages.

`set debug observer'
     Turns on or off display of GDB observer debugging.  This includes
     info such as the notification of observable events.

`show debug observer'
     Displays the current state of observer debugging.

`set debug overload'
     Turns on or off display of GDB C++ overload debugging info. This
     includes info such as ranking of functions, etc.  The default is
     off.

`show debug overload'
     Displays the current state of displaying GDB C++ overload
     debugging info.  

`set debug parser'
     Turns on or off the display of expression parser debugging output.
     Internally, this sets the `yydebug' variable in the expression
     parser.  *Note Tracing Your Parser: (bison)Tracing, for details.
     The default is off.

`show debug parser'
     Show the current state of expression parser debugging.  

`set debug remote'
     Turns on or off display of reports on all packets sent back and
     forth across the serial line to the remote machine.  The info is
     printed on the GDB standard output stream. The default is off.

`show debug remote'
     Displays the state of display of remote packets.

`set debug serial'
     Turns on or off display of GDB serial debugging info. The default
     is off.

`show debug serial'
     Displays the current state of displaying GDB serial debugging info.

`set debug solib-frv'
     Turns on or off debugging messages for FR-V shared-library code.

`show debug solib-frv'
     Display the current state of FR-V shared-library code debugging
     messages.

`set debug symtab-create'
     Turns on or off display of debugging messages related to symbol
     table creation.  The default is off.

`show debug symtab-create'
     Show the current state of symbol table creation debugging.

`set debug target'
     Turns on or off display of GDB target debugging info. This info
     includes what is going on at the target level of GDB, as it
     happens. The default is 0.  Set it to 1 to track events, and to 2
     to also track the value of large memory transfers.  Changes to
     this flag do not take effect until the next time you connect to a
     target or use the `run' command.

`show debug target'
     Displays the current state of displaying GDB target debugging info.

`set debug timestamp'
     Turns on or off display of timestamps with GDB debugging info.
     When enabled, seconds and microseconds are displayed before each
     debugging message.

`show debug timestamp'
     Displays the current state of displaying timestamps with GDB
     debugging info.

`set debugvarobj'
     Turns on or off display of GDB variable object debugging info. The
     default is off.

`show debugvarobj'
     Displays the current state of displaying GDB variable object
     debugging info.

`set debug xml'
     Turns on or off debugging messages for built-in XML parsers.

`show debug xml'
     Displays the current state of XML debugging messages.


File: gdb.info,  Node: Other Misc Settings,  Prev: Debugging Output,  Up: Controlling GDB

22.10 Other Miscellaneous Settings
==================================

`set interactive-mode'
     If `on', forces GDB to assume that GDB was started in a terminal.
     In practice, this means that GDB should wait for the user to
     answer queries generated by commands entered at the command
     prompt.  If `off', forces GDB to operate in the opposite mode, and
     it uses the default answers to all queries.  If `auto' (the
     default), GDB tries to determine whether its standard input is a
     terminal, and works in interactive-mode if it is,
     non-interactively otherwise.

     In the vast majority of cases, the debugger should be able to guess
     correctly which mode should be used.  But this setting can be
     useful in certain specific cases, such as running a MinGW GDB
     inside a cygwin window.

`show interactive-mode'
     Displays whether the debugger is operating in interactive mode or
     not.


File: gdb.info,  Node: Extending GDB,  Next: Interpreters,  Prev: Controlling GDB,  Up: Top

23 Extending GDB
****************

GDB provides three mechanisms for extension.  The first is based on
composition of GDB commands, the second is based on the Python
scripting language, and the third is for defining new aliases of
existing commands.

   To facilitate the use of the first two extensions, GDB is capable of
evaluating the contents of a file.  When doing so, GDB can recognize
which scripting language is being used by looking at the filename
extension.  Files with an unrecognized filename extension are always
treated as a GDB Command Files.  *Note Command files: Command Files.

   You can control how GDB evaluates these files with the following
setting:

`set script-extension off'
     All scripts are always evaluated as GDB Command Files.

`set script-extension soft'
     The debugger determines the scripting language based on filename
     extension.  If this scripting language is supported, GDB evaluates
     the script using that language.  Otherwise, it evaluates the file
     as a GDB Command File.

`set script-extension strict'
     The debugger determines the scripting language based on filename
     extension, and evaluates the script using that language.  If the
     language is not supported, then the evaluation fails.

`show script-extension'
     Display the current value of the `script-extension' option.


* Menu:

* Sequences::          Canned Sequences of Commands
* Python::             Scripting GDB using Python
* Aliases::            Creating new spellings of existing commands


File: gdb.info,  Node: Sequences,  Next: Python,  Up: Extending GDB

23.1 Canned Sequences of Commands
=================================

Aside from breakpoint commands (*note Breakpoint Command Lists: Break
Commands.), GDB provides two ways to store sequences of commands for
execution as a unit: user-defined commands and command files.

* Menu:

* Define::             How to define your own commands
* Hooks::              Hooks for user-defined commands
* Command Files::      How to write scripts of commands to be stored in a file
* Output::             Commands for controlled output


File: gdb.info,  Node: Define,  Next: Hooks,  Up: Sequences

23.1.1 User-defined Commands
----------------------------

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.  User commands may accept up to 10 arguments separated by
whitespace.  Arguments are accessed within the user command via
`$arg0...$arg9'.  A trivial example:

     define adder
       print $arg0 + $arg1 + $arg2
     end

To execute the command use:

     adder 1 2 3

This defines the command `adder', which prints the sum of its three
arguments.  Note the arguments are text substitutions, so they may
reference variables, use complex expressions, or even perform inferior
functions calls.

   In addition, `$argc' may be used to find out how many arguments have
been passed.  This expands to a number in the range 0...10.

     define adder
       if $argc == 2
         print $arg0 + $arg1
       end
       if $argc == 3
         print $arg0 + $arg1 + $arg2
       end
     end

`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.  COMMANDNAME may be a bare command name consisting of letters,
     numbers, dashes, and underscores.  It may also start with any
     predefined prefix command.  For example, `define target my-target'
     creates a user-defined `target my-target' command.

     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'
     Document the user-defined command COMMANDNAME, so that it can be
     accessed by `help'.  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 displays the documentation you have written.

     You may use the `document' command again to change the
     documentation of a command.  Redefining the command with `define'
     does not change the documentation.

`dont-repeat'
     Used inside a user-defined command, this tells GDB that this
     command should not be repeated when the user hits <RET> (*note
     repeat last command: Command Syntax.).

`help user-defined'
     List all user-defined commands and all python commands defined in
     class COMAND_USER.  The first line of the documentation or
     docstring is included (if any).

`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.  This does not work for
     user-defined python commands.

`show max-user-call-depth'
`set max-user-call-depth'
     The value of `max-user-call-depth' controls how many recursion
     levels are allowed in user-defined commands before GDB suspects an
     infinite recursion and aborts the command.  This does not apply to
     user-defined python commands.

   In addition to the above commands, user-defined commands frequently
use control flow commands, described in *note Command Files::.

   When user-defined commands are executed, the commands of the
definition are not printed.  An error in any command stops execution of
the user-defined command.

   If used interactively, commands that would ask for confirmation
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.


File: gdb.info,  Node: Hooks,  Next: Command Files,  Prev: Define,  Up: Sequences

23.1.2 User-defined Command Hooks
---------------------------------

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.

   A hook may also be defined which is run after the command you
executed.  Whenever you run the command `foo', if the user-defined
command `hookpost-foo' exists, it is executed (with no arguments) after
that command.  Post-execution hooks may exist simultaneously with
pre-execution hooks, for the same command.

   It is valid for a hook to call the command which it hooks.  If this
occurs, the hook is not re-executed, thereby avoiding infinite
recursion.

   In addition, a pseudo-command, `stop' exists.  Defining
(`hook-stop') makes the associated commands execute every time
execution stops in your program: before breakpoint commands are run,
displays are printed, or the stack frame is printed.

   For example, to ignore `SIGALRM' signals while single-stepping, but
treat them normally during normal execution, you could define:

     define hook-stop
     handle SIGALRM nopass
     end

     define hook-run
     handle SIGALRM pass
     end

     define hook-continue
     handle SIGALRM pass
     end

   As a further example, to hook at the beginning and end of the `echo'
command, and to add extra text to the beginning and end of the message,
you could define:

     define hook-echo
     echo <<<---
     end

     define hookpost-echo
     echo --->>>\n
     end

     (gdb) echo Hello World
     <<<---Hello World--->>>
     (gdb)

   You can define a hook for any single-word command in GDB, but not
for command aliases; you should define a hook for the basic command
name, e.g.  `backtrace' rather than `bt'.  You can hook a multi-word
command by adding `hook-' or `hookpost-' to the last word of the
command, e.g.  `define target hook-remote' to add a hook to `target
remote'.

   If an error occurs during the execution of your hook, execution of
GDB commands stops and GDB issues a prompt (before the command that you
actually typed had a chance to run).

   If you try to define a hook which does not match any known command,
you get a warning from the `define' command.


File: gdb.info,  Node: Command Files,  Next: Output,  Prev: Hooks,  Up: Sequences

23.1.3 Command Files
--------------------

A command file for GDB is a text file made 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.

   You can request the execution of a command file with the `source'
command.  Note that the `source' command is also used to evaluate
scripts that are not Command Files.  The exact behavior can be
configured using the `script-extension' setting.  *Note Extending GDB:
Extending GDB.

`source [-s] [-v] FILENAME'
     Execute the command file FILENAME.

   The lines in a command file are generally executed sequentially,
unless the order of execution is changed by one of the _flow-control
commands_ described below.  The commands are not printed as they are
executed.  An error in any command terminates execution of the command
file and control is returned to the console.

   GDB first searches for FILENAME in the current directory.  If the
file is not found there, and FILENAME does not specify a directory,
then GDB also looks for the file on the source search path (specified
with the `directory' command); except that `$cdir' is not searched
because the compilation directory is not relevant to scripts.

   If `-s' is specified, then GDB searches for FILENAME on the search
path even if FILENAME specifies a directory.  The search is done by
appending FILENAME to each element of the search path.  So, for
example, if FILENAME is `mylib/myscript' and the search path contains
`/home/user' then GDB will look for the script
`/home/user/mylib/myscript'.  The search is also done if FILENAME is an
absolute path.  For example, if FILENAME is `/tmp/myscript' and the
search path contains `/home/user' then GDB will look for the script
`/home/user/tmp/myscript'.  For DOS-like systems, if FILENAME contains
a drive specification, it is stripped before concatenation.  For
example, if FILENAME is `d:myscript' and the search path contains
`c:/tmp' then GDB will look for the script `c:/tmp/myscript'.

   If `-v', for verbose mode, is given then GDB displays each command
as it is executed.  The option must be given before FILENAME, and is
interpreted as part of the filename anywhere else.

   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.

   GDB also accepts command input from standard input.  In this mode,
normal output goes to standard output and error output goes to standard
error.  Errors in a command file supplied on standard input do not
terminate execution of the command file--execution continues with the
next command.

     gdb < cmds > log 2>&1

   (The syntax above will vary depending on the shell used.) This
example will execute commands from the file `cmds'. All output and
errors would be directed to `log'.

   Since commands stored on command files tend to be more general than
commands typed interactively, they frequently need to deal with
complicated situations, such as different or unexpected values of
variables and symbols, changes in how the program being debugged is
built, etc.  GDB provides a set of flow-control commands to deal with
these complexities.  Using these commands, you can write complex
scripts that loop over data structures, execute commands conditionally,
etc.

`if'
`else'
     This command allows to include in your script conditionally
     executed commands. The `if' command takes a single argument, which
     is an expression to evaluate.  It is followed by a series of
     commands that are executed only if the expression is true (its
     value is nonzero).  There can then optionally be an `else' line,
     followed by a series of commands that are only executed if the
     expression was false.  The end of the list is marked by a line
     containing `end'.

`while'
     This command allows to write loops.  Its syntax is similar to
     `if': the command takes a single argument, which is an expression
     to evaluate, and must be followed by the commands to execute, one
     per line, terminated by an `end'.  These commands are called the
     "body" of the loop.  The commands in the body of `while' are
     executed repeatedly as long as the expression evaluates to true.

`loop_break'
     This command exits the `while' loop in whose body it is included.
     Execution of the script continues after that `while's `end' line.

`loop_continue'
     This command skips the execution of the rest of the body of
     commands in the `while' loop in whose body it is included.
     Execution branches to the beginning of the `while' loop, where it
     evaluates the controlling expression.

`end'
     Terminate the block of commands that are the body of `if', `else',
     or `while' flow-control commands.


File: gdb.info,  Node: Output,  Prev: Command Files,  Up: Sequences

23.1.4 Commands for Controlled Output
-------------------------------------

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
     is printed unless you specify one.* In addition to the standard C
     escape sequences, a backslash followed by a space stands for a
     space.  This is useful for displaying a string with spaces at the
     beginning or the end, since leading and trailing spaces are
     otherwise trimmed from all arguments.  To print ` 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.  *Note Expressions: 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'.  *Note Output Formats: Output Formats, for
     more information.

`printf TEMPLATE, EXPRESSIONS...'
     Print the values of one or more EXPRESSIONS under the control of
     the string TEMPLATE.  To print several values, make EXPRESSIONS be
     a comma-separated list of individual expressions, which may be
     either numbers or pointers.  Their values are printed as specified
     by TEMPLATE, exactly as a C program would do by executing the code
     below:

          printf (TEMPLATE, EXPRESSIONS...);

     As in `C' `printf', ordinary characters in TEMPLATE are printed
     verbatim, while "conversion specification" introduced by the `%'
     character cause subsequent EXPRESSIONS to be evaluated, their
     values converted and formatted according to type and style
     information encoded in the conversion specifications, and then
     printed.

     For example, you can print two values in hex like this:

          printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo

     `printf' supports all the standard `C' conversion specifications,
     including the flags and modifiers between the `%' character and
     the conversion letter, with the following exceptions:

        * The argument-ordering modifiers, such as `2$', are not
          supported.

        * The modifier `*' is not supported for specifying precision or
          width.

        * The `'' flag (for separation of digits into groups according
          to `LC_NUMERIC'') is not supported.

        * The type modifiers `hh', `j', `t', and `z' are not supported.

        * The conversion letter `n' (as in `%n') is not supported.

        * The conversion letters `a' and `A' are not supported.

     Note that the `ll' type modifier is supported only if the
     underlying `C' implementation used to build GDB supports the `long
     long int' type, and the `L' type modifier is supported only if
     `long double' type is available.

     As in `C', `printf' supports simple backslash-escape sequences,
     such as `\n', `\t', `\\', `\"', `\a', and `\f', that consist of
     backslash followed by a single character.  Octal and hexadecimal
     escape sequences are not supported.

     Additionally, `printf' supports conversion specifications for DFP
     ("Decimal Floating Point") types using the following length
     modifiers together with a floating point specifier.  letters:

        * `H' for printing `Decimal32' types.

        * `D' for printing `Decimal64' types.

        * `DD' for printing `Decimal128' types.

     If the underlying `C' implementation used to build GDB has support
     for the three length modifiers for DFP types, other modifiers such
     as width and precision will also be available for GDB to use.

     In case there is no such `C' support, no additional modifiers will
     be available and the value will be printed in the standard way.

     Here's an example of printing DFP types using the above conversion
     letters:
          printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl

`eval TEMPLATE, EXPRESSIONS...'
     Convert the values of one or more EXPRESSIONS under the control of
     the string TEMPLATE to a command line, and call it.



File: gdb.info,  Node: Python,  Next: Aliases,  Prev: Sequences,  Up: Extending GDB

23.2 Scripting GDB using Python
===============================

You can script GDB using the Python programming language
(http://www.python.org/).  This feature is available only if GDB was
configured using `--with-python'.

   Python scripts used by GDB should be installed in
`DATA-DIRECTORY/python', where DATA-DIRECTORY is the data directory as
determined at GDB startup (*note Data Files::).  This directory, known
as the "python directory", is automatically added to the Python Search
Path in order to allow the Python interpreter to locate all scripts
installed at this location.

   Additionally, GDB commands and convenience functions which are
written in Python and are located in the
`DATA-DIRECTORY/python/gdb/command' or
`DATA-DIRECTORY/python/gdb/function' directories are automatically
imported when GDB starts.

* Menu:

* Python Commands::             Accessing Python from GDB.
* Python API::                  Accessing GDB from Python.
* Python Auto-loading::         Automatically loading Python code.
* Python modules::              Python modules provided by GDB.


File: gdb.info,  Node: Python Commands,  Next: Python API,  Up: Python

23.2.1 Python Commands
----------------------

GDB provides two commands for accessing the Python interpreter, and one
related setting:

`python-interactive [COMMAND]'
`pi [COMMAND]'
     Without an argument, the `python-interactive' command can be used
     to start an interactive Python prompt.  To return to GDB, type the
     `EOF' character (e.g., `Ctrl-D' on an empty prompt).

     Alternatively, a single-line Python command can be given as an
     argument and evaluated.  If the command is an expression, the
     result will be printed; otherwise, nothing will be printed.  For
     example:

          (gdb) python-interactive 2 + 3
          5

`python [COMMAND]'
`py [COMMAND]'
     The `python' command can be used to evaluate Python code.

     If given an argument, the `python' command will evaluate the
     argument as a Python command.  For example:

          (gdb) python print 23
          23

     If you do not provide an argument to `python', it will act as a
     multi-line command, like `define'.  In this case, the Python
     script is made up of subsequent command lines, given after the
     `python' command.  This command list is terminated using a line
     containing `end'.  For example:

          (gdb) python
          Type python script
          End with a line saying just "end".
          >print 23
          >end
          23

`set python print-stack'
     By default, GDB will print only the message component of a Python
     exception when an error occurs in a Python script.  This can be
     controlled using `set python print-stack': if `full', then full
     Python stack printing is enabled; if `none', then Python stack and
     message printing is disabled; if `message', the default, only the
     message component of the error is printed.

   It is also possible to execute a Python script from the GDB
interpreter:

`source `script-name''
     The script name must end with `.py' and GDB must be configured to
     recognize the script language based on filename extension using
     the `script-extension' setting.  *Note Extending GDB: Extending
     GDB.

`python execfile ("script-name")'
     This method is based on the `execfile' Python built-in function,
     and thus is always available.


File: gdb.info,  Node: Python API,  Next: Python Auto-loading,  Prev: Python Commands,  Up: Python

23.2.2 Python API
-----------------

At startup, GDB overrides Python's `sys.stdout' and `sys.stderr' to
print using GDB's output-paging streams.  A Python program which
outputs to one of these streams may have its output interrupted by the
user (*note Screen Size::).  In this situation, a Python
`KeyboardInterrupt' exception is thrown.

* Menu:

* Basic Python::                Basic Python Functions.
* Exception Handling::          How Python exceptions are translated.
* Values From Inferior::        Python representation of values.
* Types In Python::             Python representation of types.
* Pretty Printing API::         Pretty-printing values.
* Selecting Pretty-Printers::   How GDB chooses a pretty-printer.
* Writing a Pretty-Printer::    Writing a Pretty-Printer.
* Type Printing API::		Pretty-printing types.
* Inferiors In Python::         Python representation of inferiors (processes)
* Events In Python::            Listening for events from GDB.
* Threads In Python::           Accessing inferior threads from Python.
* Commands In Python::          Implementing new commands in Python.
* Parameters In Python::        Adding new GDB parameters.
* Functions In Python::         Writing new convenience functions.
* Progspaces In Python::        Program spaces.
* Objfiles In Python::          Object files.
* Frames In Python::            Accessing inferior stack frames from Python.
* Blocks In Python::            Accessing frame blocks from Python.
* Symbols In Python::           Python representation of symbols.
* Symbol Tables In Python::     Python representation of symbol tables.
* Breakpoints In Python::       Manipulating breakpoints using Python.
* Finish Breakpoints in Python:: Setting Breakpoints on function return
                                using Python.
* Lazy Strings In Python::      Python representation of lazy strings.
* Architectures In Python::     Python representation of architectures.


File: gdb.info,  Node: Basic Python,  Next: Exception Handling,  Up: Python API

23.2.2.1 Basic Python
.....................

GDB introduces a new Python module, named `gdb'.  All methods and
classes added by GDB are placed in this module.  GDB automatically
`import's the `gdb' module for use in all scripts evaluated by the
`python' command.

 -- Variable: gdb.PYTHONDIR
     A string containing the python directory (*note Python::).

 -- Function: gdb.execute (command [, from_tty [, to_string]])
     Evaluate COMMAND, a string, as a GDB CLI command.  If a GDB
     exception happens while COMMAND runs, it is translated as
     described in *note Exception Handling: Exception Handling.

     FROM_TTY specifies whether GDB ought to consider this command as
     having originated from the user invoking it interactively.  It
     must be a boolean value.  If omitted, it defaults to `False'.

     By default, any output produced by COMMAND is sent to GDB's
     standard output.  If the TO_STRING parameter is `True', then
     output will be collected by `gdb.execute' and returned as a
     string.  The default is `False', in which case the return value is
     `None'.  If TO_STRING is `True', the GDB virtual terminal will be
     temporarily set to unlimited width and height, and its pagination
     will be disabled; *note Screen Size::.

 -- Function: gdb.breakpoints ()
     Return a sequence holding all of GDB's breakpoints.  *Note
     Breakpoints In Python::, for more information.

 -- Function: gdb.parameter (parameter)
     Return the value of a GDB parameter.  PARAMETER is a string naming
     the parameter to look up; PARAMETER may contain spaces if the
     parameter has a multi-part name.  For example, `print object' is a
     valid parameter name.

     If the named parameter does not exist, this function throws a
     `gdb.error' (*note Exception Handling::).  Otherwise, the
     parameter's value is converted to a Python value of the appropriate
     type, and returned.

 -- Function: gdb.history (number)
     Return a value from GDB's value history (*note Value History::).
     NUMBER indicates which history element to return.  If NUMBER is
     negative, then GDB will take its absolute value and count backward
     from the last element (i.e., the most recent element) to find the
     value to return.  If NUMBER is zero, then GDB will return the most
     recent element.  If the element specified by NUMBER doesn't exist
     in the value history, a `gdb.error' exception will be raised.

     If no exception is raised, the return value is always an instance
     of `gdb.Value' (*note Values From Inferior::).

 -- Function: gdb.parse_and_eval (expression)
     Parse EXPRESSION as an expression in the current language,
     evaluate it, and return the result as a `gdb.Value'.  EXPRESSION
     must be a string.

     This function can be useful when implementing a new command (*note
     Commands In Python::), as it provides a way to parse the command's
     argument as an expression.  It is also useful simply to compute
     values, for example, it is the only way to get the value of a
     convenience variable (*note Convenience Vars::) as a `gdb.Value'.

 -- Function: gdb.find_pc_line (pc)
     Return the `gdb.Symtab_and_line' object corresponding to the PC
     value.  *Note Symbol Tables In Python::.  If an invalid value of
     PC is passed as an argument, then the `symtab' and `line'
     attributes of the returned `gdb.Symtab_and_line' object will be
     `None' and 0 respectively.

 -- Function: gdb.post_event (event)
     Put EVENT, a callable object taking no arguments, into GDB's
     internal event queue.  This callable will be invoked at some later
     point, during GDB's event processing.  Events posted using
     `post_event' will be run in the order in which they were posted;
     however, there is no way to know when they will be processed
     relative to other events inside GDB.

     GDB is not thread-safe.  If your Python program uses multiple
     threads, you must be careful to only call GDB-specific functions
     in the main GDB thread.  `post_event' ensures this.  For example:

          (gdb) python
          >import threading
          >
          >class Writer():
          > def __init__(self, message):
          >        self.message = message;
          > def __call__(self):
          >        gdb.write(self.message)
          >
          >class MyThread1 (threading.Thread):
          > def run (self):
          >        gdb.post_event(Writer("Hello "))
          >
          >class MyThread2 (threading.Thread):
          > def run (self):
          >        gdb.post_event(Writer("World\n"))
          >
          >MyThread1().start()
          >MyThread2().start()
          >end
          (gdb) Hello World

 -- Function: gdb.write (string [, stream])
     Print a string to GDB's paginated output stream.  The optional
     STREAM determines the stream to print to.  The default stream is
     GDB's standard output stream.  Possible stream values are:

    `gdb.STDOUT'
          GDB's standard output stream.

    `gdb.STDERR'
          GDB's standard error stream.

    `gdb.STDLOG'
          GDB's log stream (*note Logging Output::).

     Writing to `sys.stdout' or `sys.stderr' will automatically call
     this function and will automatically direct the output to the
     relevant stream.

 -- Function: gdb.flush ()
     Flush the buffer of a GDB paginated stream so that the contents
     are displayed immediately.  GDB will flush the contents of a
     stream automatically when it encounters a newline in the buffer.
     The optional STREAM determines the stream to flush.  The default
     stream is GDB's standard output stream.  Possible stream values
     are:

    `gdb.STDOUT'
          GDB's standard output stream.

    `gdb.STDERR'
          GDB's standard error stream.

    `gdb.STDLOG'
          GDB's log stream (*note Logging Output::).


     Flushing `sys.stdout' or `sys.stderr' will automatically call this
     function for the relevant stream.

 -- Function: gdb.target_charset ()
     Return the name of the current target character set (*note
     Character Sets::).  This differs from
     `gdb.parameter('target-charset')' in that `auto' is never returned.

 -- Function: gdb.target_wide_charset ()
     Return the name of the current target wide character set (*note
     Character Sets::).  This differs from
     `gdb.parameter('target-wide-charset')' in that `auto' is never
     returned.

 -- Function: gdb.solib_name (address)
     Return the name of the shared library holding the given ADDRESS as
     a string, or `None'.

 -- Function: gdb.decode_line [expression]
     Return locations of the line specified by EXPRESSION, or of the
     current line if no argument was given.  This function returns a
     Python tuple containing two elements.  The first element contains
     a string holding any unparsed section of EXPRESSION (or `None' if
     the expression has been fully parsed).  The second element contains
     either `None' or another tuple that contains all the locations
     that match the expression represented as `gdb.Symtab_and_line'
     objects (*note Symbol Tables In Python::).  If EXPRESSION is
     provided, it is decoded the way that GDB's inbuilt `break' or
     `edit' commands do (*note Specify Location::).

 -- Function: gdb.prompt_hook (current_prompt)
     If PROMPT_HOOK is callable, GDB will call the method assigned to
     this operation before a prompt is displayed by GDB.

     The parameter `current_prompt' contains the current GDB prompt.
     This method must return a Python string, or `None'.  If a string
     is returned, the GDB prompt will be set to that string.  If `None'
     is returned, GDB will continue to use the current prompt.

     Some prompts cannot be substituted in GDB.  Secondary prompts such
     as those used by readline for command input, and annotation
     related prompts are prohibited from being changed.


File: gdb.info,  Node: Exception Handling,  Next: Values From Inferior,  Prev: Basic Python,  Up: Python API

23.2.2.2 Exception Handling
...........................

When executing the `python' command, Python exceptions uncaught within
the Python code are translated to calls to GDB error-reporting
mechanism.  If the command that called `python' does not handle the
error, GDB will terminate it and print an error message containing the
Python exception name, the associated value, and the Python call stack
backtrace at the point where the exception was raised.  Example:

     (gdb) python print foo
     Traceback (most recent call last):
       File "<string>", line 1, in <module>
     NameError: name 'foo' is not defined

   GDB errors that happen in GDB commands invoked by Python code are
converted to Python exceptions.  The type of the Python exception
depends on the error.

`gdb.error'
     This is the base class for most exceptions generated by GDB.  It
     is derived from `RuntimeError', for compatibility with earlier
     versions of GDB.

     If an error occurring in GDB does not fit into some more specific
     category, then the generated exception will have this type.

`gdb.MemoryError'
     This is a subclass of `gdb.error' which is thrown when an
     operation tried to access invalid memory in the inferior.

`KeyboardInterrupt'
     User interrupt (via `C-c' or by typing `q' at a pagination prompt)
     is translated to a Python `KeyboardInterrupt' exception.

   In all cases, your exception handler will see the GDB error message
as its value and the Python call stack backtrace at the Python
statement closest to where the GDB error occured as the traceback.

   When implementing GDB commands in Python via `gdb.Command', it is
useful to be able to throw an exception that doesn't cause a traceback
to be printed.  For example, the user may have invoked the command
incorrectly.  Use the `gdb.GdbError' exception to handle this case.
Example:

     (gdb) python
     >class HelloWorld (gdb.Command):
     >  """Greet the whole world."""
     >  def __init__ (self):
     >    super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
     >  def invoke (self, args, from_tty):
     >    argv = gdb.string_to_argv (args)
     >    if len (argv) != 0:
     >      raise gdb.GdbError ("hello-world takes no arguments")
     >    print "Hello, World!"
     >HelloWorld ()
     >end
     (gdb) hello-world 42
     hello-world takes no arguments


File: gdb.info,  Node: Values From Inferior,  Next: Types In Python,  Prev: Exception Handling,  Up: Python API

23.2.2.3 Values From Inferior
.............................

GDB provides values it obtains from the inferior program in an object
of type `gdb.Value'.  GDB uses this object for its internal bookkeeping
of the inferior's values, and for fetching values when necessary.

   Inferior values that are simple scalars can be used directly in
Python expressions that are valid for the value's data type.  Here's an
example for an integer or floating-point value `some_val':

     bar = some_val + 2

As result of this, `bar' will also be a `gdb.Value' object whose values
are of the same type as those of `some_val'.

   Inferior values that are structures or instances of some class can
be accessed using the Python "dictionary syntax".  For example, if
`some_val' is a `gdb.Value' instance holding a structure, you can
access its `foo' element with:

     bar = some_val['foo']

   Again, `bar' will also be a `gdb.Value' object.

   A `gdb.Value' that represents a function can be executed via
inferior function call.  Any arguments provided to the call must match
the function's prototype, and must be provided in the order specified
by that prototype.

   For example, `some_val' is a `gdb.Value' instance representing a
function that takes two integers as arguments.  To execute this
function, call it like so:

     result = some_val (10,20)

   Any values returned from a function call will be stored as a
`gdb.Value'.

   The following attributes are provided:

 -- Variable: Value.address
     If this object is addressable, this read-only attribute holds a
     `gdb.Value' object representing the address.  Otherwise, this
     attribute holds `None'.

 -- Variable: Value.is_optimized_out
     This read-only boolean attribute is true if the compiler optimized
     out this value, thus it is not available for fetching from the
     inferior.

 -- Variable: Value.type
     The type of this `gdb.Value'.  The value of this attribute is a
     `gdb.Type' object (*note Types In Python::).

 -- Variable: Value.dynamic_type
     The dynamic type of this `gdb.Value'.  This uses C++ run-time type
     information (RTTI) to determine the dynamic type of the value.  If
     this value is of class type, it will return the class in which the
     value is embedded, if any.  If this value is of pointer or
     reference to a class type, it will compute the dynamic type of the
     referenced object, and return a pointer or reference to that type,
     respectively.  In all other cases, it will return the value's
     static type.

     Note that this feature will only work when debugging a C++ program
     that includes RTTI for the object in question.  Otherwise, it will
     just return the static type of the value as in `ptype foo' (*note
     ptype: Symbols.).

 -- Variable: Value.is_lazy
     The value of this read-only boolean attribute is `True' if this
     `gdb.Value' has not yet been fetched from the inferior.  GDB does
     not fetch values until necessary, for efficiency.  For example:

          myval = gdb.parse_and_eval ('somevar')

     The value of `somevar' is not fetched at this time.  It will be
     fetched when the value is needed, or when the `fetch_lazy' method
     is invoked.

   The following methods are provided:

 -- Function: Value.__init__ (VAL)
     Many Python values can be converted directly to a `gdb.Value' via
     this object initializer.  Specifically:

    Python boolean
          A Python boolean is converted to the boolean type from the
          current language.

    Python integer
          A Python integer is converted to the C `long' type for the
          current architecture.

    Python long
          A Python long is converted to the C `long long' type for the
          current architecture.

    Python float
          A Python float is converted to the C `double' type for the
          current architecture.

    Python string
          A Python string is converted to a target string, using the
          current target encoding.

    `gdb.Value'
          If `val' is a `gdb.Value', then a copy of the value is made.

    `gdb.LazyString'
          If `val' is a `gdb.LazyString' (*note Lazy Strings In
          Python::), then the lazy string's `value' method is called,
          and its result is used.

 -- Function: Value.cast (type)
     Return a new instance of `gdb.Value' that is the result of casting
     this instance to the type described by TYPE, which must be a
     `gdb.Type' object.  If the cast cannot be performed for some
     reason, this method throws an exception.

 -- Function: Value.dereference ()
     For pointer data types, this method returns a new `gdb.Value'
     object whose contents is the object pointed to by the pointer.
     For example, if `foo' is a C pointer to an `int', declared in your
     C program as

          int *foo;

     then you can use the corresponding `gdb.Value' to access what
     `foo' points to like this:

          bar = foo.dereference ()

     The result `bar' will be a `gdb.Value' object holding the value
     pointed to by `foo'.

     A similar function `Value.referenced_value' exists which also
     returns `gdb.Value' objects corresonding to the values pointed to
     by pointer values (and additionally, values referenced by reference
     values).  However, the behavior of `Value.dereference' differs
     from `Value.referenced_value' by the fact that the behavior of
     `Value.dereference' is identical to applying the C unary operator
     `*' on a given value.  For example, consider a reference to a
     pointer `ptrref', declared in your C++ program as

          typedef int *intptr;
          ...
          int val = 10;
          intptr ptr = &val;
          intptr &ptrref = ptr;

     Though `ptrref' is a reference value, one can apply the method
     `Value.dereference' to the `gdb.Value' object corresponding to it
     and obtain a `gdb.Value' which is identical to that corresponding
     to `val'.  However, if you apply the method
     `Value.referenced_value', the result would be a `gdb.Value' object
     identical to that corresponding to `ptr'.

          py_ptrref = gdb.parse_and_eval ("ptrref")
          py_val = py_ptrref.dereference ()
          py_ptr = py_ptrref.referenced_value ()

     The `gdb.Value' object `py_val' is identical to that corresponding
     to `val', and `py_ptr' is identical to that corresponding to
     `ptr'.  In general, `Value.dereference' can be applied whenever
     the C unary operator `*' can be applied to the corresponding C
     value.  For those cases where applying both `Value.dereference'
     and `Value.referenced_value' is allowed, the results obtained need
     not be identical (as we have seen in the above example).  The
     results are however identical when applied on `gdb.Value' objects
     corresponding to pointers (`gdb.Value' objects with type code
     `TYPE_CODE_PTR') in a C/C++ program.

 -- Function: Value.referenced_value ()
     For pointer or reference data types, this method returns a new
     `gdb.Value' object corresponding to the value referenced by the
     pointer/reference value.  For pointer data types,
     `Value.dereference' and `Value.referenced_value' produce identical
     results.  The difference between these methods is that
     `Value.dereference' cannot get the values referenced by reference
     values.  For example, consider a reference to an `int', declared
     in your C++ program as

          int val = 10;
          int &ref = val;

     then applying `Value.dereference' to the `gdb.Value' object
     corresponding to `ref' will result in an error, while applying
     `Value.referenced_value' will result in a `gdb.Value' object
     identical to that corresponding to `val'.

          py_ref = gdb.parse_and_eval ("ref")
          er_ref = py_ref.dereference ()       # Results in error
          py_val = py_ref.referenced_value ()  # Returns the referenced value

     The `gdb.Value' object `py_val' is identical to that corresponding
     to `val'.

 -- Function: Value.dynamic_cast (type)
     Like `Value.cast', but works as if the C++ `dynamic_cast' operator
     were used.  Consult a C++ reference for details.

 -- Function: Value.reinterpret_cast (type)
     Like `Value.cast', but works as if the C++ `reinterpret_cast'
     operator were used.  Consult a C++ reference for details.

 -- Function: Value.string ([encoding[, errors[, length]]])
     If this `gdb.Value' represents a string, then this method converts
     the contents to a Python string.  Otherwise, this method will
     throw an exception.

     Strings are recognized in a language-specific way; whether a given
     `gdb.Value' represents a string is determined by the current
     language.

     For C-like languages, a value is a string if it is a pointer to or
     an array of characters or ints.  The string is assumed to be
     terminated by a zero of the appropriate width.  However if the
     optional length argument is given, the string will be converted to
     that given length, ignoring any embedded zeros that the string may
     contain.

     If the optional ENCODING argument is given, it must be a string
     naming the encoding of the string in the `gdb.Value', such as
     `"ascii"', `"iso-8859-6"' or `"utf-8"'.  It accepts the same
     encodings as the corresponding argument to Python's
     `string.decode' method, and the Python codec machinery will be used
     to convert the string.  If ENCODING is not given, or if ENCODING
     is the empty string, then either the `target-charset' (*note
     Character Sets::) will be used, or a language-specific encoding
     will be used, if the current language is able to supply one.

     The optional ERRORS argument is the same as the corresponding
     argument to Python's `string.decode' method.

     If the optional LENGTH argument is given, the string will be
     fetched and converted to the given length.

 -- Function: Value.lazy_string ([encoding [, length]])
     If this `gdb.Value' represents a string, then this method converts
     the contents to a `gdb.LazyString' (*note Lazy Strings In
     Python::).  Otherwise, this method will throw an exception.

     If the optional ENCODING argument is given, it must be a string
     naming the encoding of the `gdb.LazyString'.  Some examples are:
     `ascii', `iso-8859-6' or `utf-8'.  If the ENCODING argument is an
     encoding that GDB does recognize, GDB will raise an error.

     When a lazy string is printed, the GDB encoding machinery is used
     to convert the string during printing.  If the optional ENCODING
     argument is not provided, or is an empty string, GDB will
     automatically select the encoding most suitable for the string
     type.  For further information on encoding in GDB please see *note
     Character Sets::.

     If the optional LENGTH argument is given, the string will be
     fetched and encoded to the length of characters specified.  If the
     LENGTH argument is not provided, the string will be fetched and
     encoded until a null of appropriate width is found.

 -- Function: Value.fetch_lazy ()
     If the `gdb.Value' object is currently a lazy value
     (`gdb.Value.is_lazy' is `True'), then the value is fetched from
     the inferior.  Any errors that occur in the process will produce a
     Python exception.

     If the `gdb.Value' object is not a lazy value, this method has no
     effect.

     This method does not return a value.


File: gdb.info,  Node: Types In Python,  Next: Pretty Printing API,  Prev: Values From Inferior,  Up: Python API

23.2.2.4 Types In Python
........................

GDB represents types from the inferior using the class `gdb.Type'.

   The following type-related functions are available in the `gdb'
module:

 -- Function: gdb.lookup_type (name [, block])
     This function looks up a type by name.  NAME is the name of the
     type to look up.  It must be a string.

     If BLOCK is given, then NAME is looked up in that scope.
     Otherwise, it is searched for globally.

     Ordinarily, this function will return an instance of `gdb.Type'.
     If the named type cannot be found, it will throw an exception.

   If the type is a structure or class type, or an enum type, the fields
of that type can be accessed using the Python "dictionary syntax".  For
example, if `some_type' is a `gdb.Type' instance holding a structure
type, you can access its `foo' field with:

     bar = some_type['foo']

   `bar' will be a `gdb.Field' object; see below under the description
of the `Type.fields' method for a description of the `gdb.Field' class.

   An instance of `Type' has the following attributes:

 -- Variable: Type.code
     The type code for this type.  The type code will be one of the
     `TYPE_CODE_' constants defined below.

 -- Variable: Type.sizeof
     The size of this type, in target `char' units.  Usually, a
     target's `char' type will be an 8-bit byte.  However, on some
     unusual platforms, this type may have a different size.

 -- Variable: Type.tag
     The tag name for this type.  The tag name is the name after
     `struct', `union', or `enum' in C and C++; not all languages have
     this concept.  If this type has no tag name, then `None' is
     returned.

   The following methods are provided:

 -- Function: Type.fields ()
     For structure and union types, this method returns the fields.
     Range types have two fields, the minimum and maximum values.  Enum
     types have one field per enum constant.  Function and method types
     have one field per parameter.  The base types of C++ classes are
     also represented as fields.  If the type has no fields, or does
     not fit into one of these categories, an empty sequence will be
     returned.

     Each field is a `gdb.Field' object, with some pre-defined
     attributes:
    `bitpos'
          This attribute is not available for `static' fields (as in
          C++ or Java).  For non-`static' fields, the value is the bit
          position of the field.  For `enum' fields, the value is the
          enumeration member's integer representation.

    `name'
          The name of the field, or `None' for anonymous fields.

    `artificial'
          This is `True' if the field is artificial, usually meaning
          that it was provided by the compiler and not the user.  This
          attribute is always provided, and is `False' if the field is
          not artificial.

    `is_base_class'
          This is `True' if the field represents a base class of a C++
          structure.  This attribute is always provided, and is `False'
          if the field is not a base class of the type that is the
          argument of `fields', or if that type was not a C++ class.

    `bitsize'
          If the field is packed, or is a bitfield, then this will have
          a non-zero value, which is the size of the field in bits.
          Otherwise, this will be zero; in this case the field's size
          is given by its type.

    `type'
          The type of the field.  This is usually an instance of `Type',
          but it can be `None' in some situations.

 -- Function: Type.array (N1 [, N2])
     Return a new `gdb.Type' object which represents an array of this
     type.  If one argument is given, it is the inclusive upper bound of
     the array; in this case the lower bound is zero.  If two arguments
     are given, the first argument is the lower bound of the array, and
     the second argument is the upper bound of the array.  An array's
     length must not be negative, but the bounds can be.

 -- Function: Type.vector (N1 [, N2])
     Return a new `gdb.Type' object which represents a vector of this
     type.  If one argument is given, it is the inclusive upper bound of
     the vector; in this case the lower bound is zero.  If two
     arguments are given, the first argument is the lower bound of the
     vector, and the second argument is the upper bound of the vector.
     A vector's length must not be negative, but the bounds can be.

     The difference between an `array' and a `vector' is that arrays
     behave like in C: when used in expressions they decay to a pointer
     to the first element whereas vectors are treated as first class
     values.

 -- Function: Type.const ()
     Return a new `gdb.Type' object which represents a
     `const'-qualified variant of this type.

 -- Function: Type.volatile ()
     Return a new `gdb.Type' object which represents a
     `volatile'-qualified variant of this type.

 -- Function: Type.unqualified ()
     Return a new `gdb.Type' object which represents an unqualified
     variant of this type.  That is, the result is neither `const' nor
     `volatile'.

 -- Function: Type.range ()
     Return a Python `Tuple' object that contains two elements: the low
     bound of the argument type and the high bound of that type.  If
     the type does not have a range, GDB will raise a `gdb.error'
     exception (*note Exception Handling::).

 -- Function: Type.reference ()
     Return a new `gdb.Type' object which represents a reference to this
     type.

 -- Function: Type.pointer ()
     Return a new `gdb.Type' object which represents a pointer to this
     type.

 -- Function: Type.strip_typedefs ()
     Return a new `gdb.Type' that represents the real type, after
     removing all layers of typedefs.

 -- Function: Type.target ()
     Return a new `gdb.Type' object which represents the target type of
     this type.

     For a pointer type, the target type is the type of the pointed-to
     object.  For an array type (meaning C-like arrays), the target
     type is the type of the elements of the array.  For a function or
     method type, the target type is the type of the return value.  For
     a complex type, the target type is the type of the elements.  For
     a typedef, the target type is the aliased type.

     If the type does not have a target, this method will throw an
     exception.

 -- Function: Type.template_argument (n [, block])
     If this `gdb.Type' is an instantiation of a template, this will
     return a new `gdb.Type' which represents the type of the Nth
     template argument.

     If this `gdb.Type' is not a template type, this will throw an
     exception.  Ordinarily, only C++ code will have template types.

     If BLOCK is given, then NAME is looked up in that scope.
     Otherwise, it is searched for globally.

   Each type has a code, which indicates what category this type falls
into.  The available type categories are represented by constants
defined in the `gdb' module:

`gdb.TYPE_CODE_PTR'
     The type is a pointer.

`gdb.TYPE_CODE_ARRAY'
     The type is an array.

`gdb.TYPE_CODE_STRUCT'
     The type is a structure.

`gdb.TYPE_CODE_UNION'
     The type is a union.

`gdb.TYPE_CODE_ENUM'
     The type is an enum.

`gdb.TYPE_CODE_FLAGS'
     A bit flags type, used for things such as status registers.

`gdb.TYPE_CODE_FUNC'
     The type is a function.

`gdb.TYPE_CODE_INT'
     The type is an integer type.

`gdb.TYPE_CODE_FLT'
     A floating point type.

`gdb.TYPE_CODE_VOID'
     The special type `void'.

`gdb.TYPE_CODE_SET'
     A Pascal set type.

`gdb.TYPE_CODE_RANGE'
     A range type, that is, an integer type with bounds.

`gdb.TYPE_CODE_STRING'
     A string type.  Note that this is only used for certain languages
     with language-defined string types; C strings are not represented
     this way.

`gdb.TYPE_CODE_BITSTRING'
     A string of bits.  It is deprecated.

`gdb.TYPE_CODE_ERROR'
     An unknown or erroneous type.

`gdb.TYPE_CODE_METHOD'
     A method type, as found in C++ or Java.

`gdb.TYPE_CODE_METHODPTR'
     A pointer-to-member-function.

`gdb.TYPE_CODE_MEMBERPTR'
     A pointer-to-member.

`gdb.TYPE_CODE_REF'
     A reference type.

`gdb.TYPE_CODE_CHAR'
     A character type.

`gdb.TYPE_CODE_BOOL'
     A boolean type.

`gdb.TYPE_CODE_COMPLEX'
     A complex float type.

`gdb.TYPE_CODE_TYPEDEF'
     A typedef to some other type.

`gdb.TYPE_CODE_NAMESPACE'
     A C++ namespace.

`gdb.TYPE_CODE_DECFLOAT'
     A decimal floating point type.

`gdb.TYPE_CODE_INTERNAL_FUNCTION'
     A function internal to GDB.  This is the type used to represent
     convenience functions.

   Further support for types is provided in the `gdb.types' Python
module (*note gdb.types::).


File: gdb.info,  Node: Pretty Printing API,  Next: Selecting Pretty-Printers,  Prev: Types In Python,  Up: Python API

23.2.2.5 Pretty Printing API
............................

An example output is provided (*note Pretty Printing::).

   A pretty-printer is just an object that holds a value and implements
a specific interface, defined here.

 -- Function: pretty_printer.children (self)
     GDB will call this method on a pretty-printer to compute the
     children of the pretty-printer's value.

     This method must return an object conforming to the Python iterator
     protocol.  Each item returned by the iterator must be a tuple
     holding two elements.  The first element is the "name" of the
     child; the second element is the child's value.  The value can be
     any Python object which is convertible to a GDB value.

     This method is optional.  If it does not exist, GDB will act as
     though the value has no children.

 -- Function: pretty_printer.display_hint (self)
     The CLI may call this method and use its result to change the
     formatting of a value.  The result will also be supplied to an MI
     consumer as a `displayhint' attribute of the variable being
     printed.

     This method is optional.  If it does exist, this method must
     return a string.

     Some display hints are predefined by GDB:

    `array'
          Indicate that the object being printed is "array-like".  The
          CLI uses this to respect parameters such as `set print
          elements' and `set print array'.

    `map'
          Indicate that the object being printed is "map-like", and
          that the children of this value can be assumed to alternate
          between keys and values.

    `string'
          Indicate that the object being printed is "string-like".  If
          the printer's `to_string' method returns a Python string of
          some kind, then GDB will call its internal language-specific
          string-printing function to format the string.  For the CLI
          this means adding quotation marks, possibly escaping some
          characters, respecting `set print elements', and the like.

 -- Function: pretty_printer.to_string (self)
     GDB will call this method to display the string representation of
     the value passed to the object's constructor.

     When printing from the CLI, if the `to_string' method exists, then
     GDB will prepend its result to the values returned by `children'.
     Exactly how this formatting is done is dependent on the display
     hint, and may change as more hints are added.  Also, depending on
     the print settings (*note Print Settings::), the CLI may print
     just the result of `to_string' in a stack trace, omitting the
     result of `children'.

     If this method returns a string, it is printed verbatim.

     Otherwise, if this method returns an instance of `gdb.Value', then
     GDB prints this value.  This may result in a call to another
     pretty-printer.

     If instead the method returns a Python value which is convertible
     to a `gdb.Value', then GDB performs the conversion and prints the
     resulting value.  Again, this may result in a call to another
     pretty-printer.  Python scalars (integers, floats, and booleans)
     and strings are convertible to `gdb.Value'; other types are not.

     Finally, if this method returns `None' then no further operations
     are peformed in this method and nothing is printed.

     If the result is not one of these types, an exception is raised.

   GDB provides a function which can be used to look up the default
pretty-printer for a `gdb.Value':

 -- Function: gdb.default_visualizer (value)
     This function takes a `gdb.Value' object as an argument.  If a
     pretty-printer for this value exists, then it is returned.  If no
     such printer exists, then this returns `None'.


File: gdb.info,  Node: Selecting Pretty-Printers,  Next: Writing a Pretty-Printer,  Prev: Pretty Printing API,  Up: Python API

23.2.2.6 Selecting Pretty-Printers
..................................

The Python list `gdb.pretty_printers' contains an array of functions or
callable objects that have been registered via addition as a
pretty-printer.  Printers in this list are called `global' printers,
they're available when debugging all inferiors.  Each `gdb.Progspace'
contains a `pretty_printers' attribute.  Each `gdb.Objfile' also
contains a `pretty_printers' attribute.

   Each function on these lists is passed a single `gdb.Value' argument
and should return a pretty-printer object conforming to the interface
definition above (*note Pretty Printing API::).  If a function cannot
create a pretty-printer for the value, it should return `None'.

   GDB first checks the `pretty_printers' attribute of each
`gdb.Objfile' in the current program space and iteratively calls each
enabled lookup routine in the list for that `gdb.Objfile' until it
receives a pretty-printer object.  If no pretty-printer is found in the
objfile lists, GDB then searches the pretty-printer list of the current
program space, calling each enabled function until an object is
returned.  After these lists have been exhausted, it tries the global
`gdb.pretty_printers' list, again calling each enabled function until an
object is returned.

   The order in which the objfiles are searched is not specified.  For a
given list, functions are always invoked from the head of the list, and
iterated over sequentially until the end of the list, or a printer
object is returned.

   For various reasons a pretty-printer may not work.  For example, the
underlying data structure may have changed and the pretty-printer is
out of date.

   The consequences of a broken pretty-printer are severe enough that
GDB provides support for enabling and disabling individual printers.
For example, if `print frame-arguments' is on, a backtrace can become
highly illegible if any argument is printed with a broken printer.

   Pretty-printers are enabled and disabled by attaching an `enabled'
attribute to the registered function or callable object.  If this
attribute is present and its value is `False', the printer is disabled,
otherwise the printer is enabled.


File: gdb.info,  Node: Writing a Pretty-Printer,  Next: Type Printing API,  Prev: Selecting Pretty-Printers,  Up: Python API

23.2.2.7 Writing a Pretty-Printer
.................................

A pretty-printer consists of two parts: a lookup function to detect if
the type is supported, and the printer itself.

   Here is an example showing how a `std::string' printer might be
written.  *Note Pretty Printing API::, for details on the API this class
must provide.

     class StdStringPrinter(object):
         "Print a std::string"

         def __init__(self, val):
             self.val = val

         def to_string(self):
             return self.val['_M_dataplus']['_M_p']

         def display_hint(self):
             return 'string'

   And here is an example showing how a lookup function for the printer
example above might be written.

     def str_lookup_function(val):
         lookup_tag = val.type.tag
         if lookup_tag == None:
             return None
         regex = re.compile("^std::basic_string<char,.*>$")
         if regex.match(lookup_tag):
             return StdStringPrinter(val)
         return None

   The example lookup function extracts the value's type, and attempts
to match it to a type that it can pretty-print.  If it is a type the
printer can pretty-print, it will return a printer object.  If not, it
returns `None'.

   We recommend that you put your core pretty-printers into a Python
package.  If your pretty-printers are for use with a library, we
further recommend embedding a version number into the package name.
This practice will enable GDB to load multiple versions of your
pretty-printers at the same time, because they will have different
names.

   You should write auto-loaded code (*note Python Auto-loading::) such
that it can be evaluated multiple times without changing its meaning.
An ideal auto-load file will consist solely of `import's of your
printer modules, followed by a call to a register pretty-printers with
the current objfile.

   Taken as a whole, this approach will scale nicely to multiple
inferiors, each potentially using a different library version.
Embedding a version number in the Python package name will ensure that
GDB is able to load both sets of printers simultaneously.  Then,
because the search for pretty-printers is done by objfile, and because
your auto-loaded code took care to register your library's printers
with a specific objfile, GDB will find the correct printers for the
specific version of the library used by each inferior.

   To continue the `std::string' example (*note Pretty Printing API::),
this code might appear in `gdb.libstdcxx.v6':

     def register_printers(objfile):
         objfile.pretty_printers.append(str_lookup_function)

And then the corresponding contents of the auto-load file would be:

     import gdb.libstdcxx.v6
     gdb.libstdcxx.v6.register_printers(gdb.current_objfile())

   The previous example illustrates a basic pretty-printer.  There are
a few things that can be improved on.  The printer doesn't have a name,
making it hard to identify in a list of installed printers.  The lookup
function has a name, but lookup functions can have arbitrary, even
identical, names.

   Second, the printer only handles one type, whereas a library
typically has several types.  One could install a lookup function for
each desired type in the library, but one could also have a single
lookup function recognize several types.  The latter is the
conventional way this is handled.  If a pretty-printer can handle
multiple data types, then its "subprinters" are the printers for the
individual data types.

   The `gdb.printing' module provides a formal way of solving these
problems (*note gdb.printing::).  Here is another example that handles
multiple types.

   These are the types we are going to pretty-print:

     struct foo { int a, b; };
     struct bar { struct foo x, y; };

   Here are the printers:

     class fooPrinter:
         """Print a foo object."""

         def __init__(self, val):
             self.val = val

         def to_string(self):
             return ("a=<" + str(self.val["a"]) +
                     "> b=<" + str(self.val["b"]) + ">")

     class barPrinter:
         """Print a bar object."""

         def __init__(self, val):
             self.val = val

         def to_string(self):
             return ("x=<" + str(self.val["x"]) +
                     "> y=<" + str(self.val["y"]) + ">")

   This example doesn't need a lookup function, that is handled by the
`gdb.printing' module.  Instead a function is provided to build up the
object that handles the lookup.

     import gdb.printing

     def build_pretty_printer():
         pp = gdb.printing.RegexpCollectionPrettyPrinter(
             "my_library")
         pp.add_printer('foo', '^foo$', fooPrinter)
         pp.add_printer('bar', '^bar$', barPrinter)
         return pp

   And here is the autoload support:

     import gdb.printing
     import my_library
     gdb.printing.register_pretty_printer(
         gdb.current_objfile(),
         my_library.build_pretty_printer())

   Finally, when this printer is loaded into GDB, here is the
corresponding output of `info pretty-printer':

     (gdb) info pretty-printer
     my_library.so:
       my_library
         foo
         bar


File: gdb.info,  Node: Type Printing API,  Next: Inferiors In Python,  Prev: Writing a Pretty-Printer,  Up: Python API

23.2.2.8 Type Printing API
..........................

GDB provides a way for Python code to customize type display.  This is
mainly useful for substituting canonical typedef names for types.

   A "type printer" is just a Python object conforming to a certain
protocol.  A simple base class implementing the protocol is provided;
see *note gdb.types::.  A type printer must supply at least:

 -- Instance Variable of type_printer: enabled
     A boolean which is True if the printer is enabled, and False
     otherwise.  This is manipulated by the `enable type-printer' and
     `disable type-printer' commands.

 -- Instance Variable of type_printer: name
     The name of the type printer.  This must be a string.  This is
     used by the `enable type-printer' and `disable type-printer'
     commands.

 -- Method on type_printer: instantiate (self)
     This is called by GDB at the start of type-printing.  It is only
     called if the type printer is enabled.  This method must return a
     new object that supplies a `recognize' method, as described below.

   When displaying a type, say via the `ptype' command, GDB will
compute a list of type recognizers.  This is done by iterating first
over the per-objfile type printers (*note Objfiles In Python::),
followed by the per-progspace type printers (*note Progspaces In
Python::), and finally the global type printers.

   GDB will call the `instantiate' method of each enabled type printer.
If this method returns `None', then the result is ignored; otherwise,
it is appended to the list of recognizers.

   Then, when GDB is going to display a type name, it iterates over the
list of recognizers.  For each one, it calls the recognition function,
stopping if the function returns a non-`None' value.  The recognition
function is defined as:

 -- Method on type_recognizer: recognize (self, type)
     If TYPE is not recognized, return `None'.  Otherwise, return a
     string which is to be printed as the name of TYPE.  TYPE will be
     an instance of `gdb.Type' (*note Types In Python::).

   GDB uses this two-pass approach so that type printers can
efficiently cache information without holding on to it too long.  For
example, it can be convenient to look up type information in a type
printer and hold it for a recognizer's lifetime; if a single pass were
done then type printers would have to make use of the event system in
order to avoid holding information that could become stale as the
inferior changed.


File: gdb.info,  Node: Inferiors In Python,  Next: Events In Python,  Prev: Type Printing API,  Up: Python API

23.2.2.9 Inferiors In Python
............................

Programs which are being run under GDB are called inferiors (*note
Inferiors and Programs::).  Python scripts can access information about
and manipulate inferiors controlled by GDB via objects of the
`gdb.Inferior' class.

   The following inferior-related functions are available in the `gdb'
module:

 -- Function: gdb.inferiors ()
     Return a tuple containing all inferior objects.

 -- Function: gdb.selected_inferior ()
     Return an object representing the current inferior.

   A `gdb.Inferior' object has the following attributes:

 -- Variable: Inferior.num
     ID of inferior, as assigned by GDB.

 -- Variable: Inferior.pid
     Process ID of the inferior, as assigned by the underlying operating
     system.

 -- Variable: Inferior.was_attached
     Boolean signaling whether the inferior was created using `attach',
     or started by GDB itself.

   A `gdb.Inferior' object has the following methods:

 -- Function: Inferior.is_valid ()
     Returns `True' if the `gdb.Inferior' object is valid, `False' if
     not.  A `gdb.Inferior' object will become invalid if the inferior
     no longer exists within GDB.  All other `gdb.Inferior' methods
     will throw an exception if it is invalid at the time the method is
     called.

 -- Function: Inferior.threads ()
     This method returns a tuple holding all the threads which are valid
     when it is called.  If there are no valid threads, the method will
     return an empty tuple.

 -- Function: Inferior.read_memory (address, length)
     Read LENGTH bytes of memory from the inferior, starting at
     ADDRESS.  Returns a buffer object, which behaves much like an array
     or a string.  It can be modified and given to the
     `Inferior.write_memory' function.  In `Python' 3, the return value
     is a `memoryview' object.

 -- Function: Inferior.write_memory (address, buffer [, length])
     Write the contents of BUFFER to the inferior, starting at ADDRESS.
     The BUFFER parameter must be a Python object which supports the
     buffer protocol, i.e., a string, an array or the object returned
     from `Inferior.read_memory'.  If given, LENGTH determines the
     number of bytes from BUFFER to be written.

 -- Function: Inferior.search_memory (address, length, pattern)
     Search a region of the inferior memory starting at ADDRESS with
     the given LENGTH using the search pattern supplied in PATTERN.
     The PATTERN parameter must be a Python object which supports the
     buffer protocol, i.e., a string, an array or the object returned
     from `gdb.read_memory'.  Returns a Python `Long' containing the
     address where the pattern was found, or `None' if the pattern
     could not be found.


File: gdb.info,  Node: Events In Python,  Next: Threads In Python,  Prev: Inferiors In Python,  Up: Python API

23.2.2.10 Events In Python
..........................

GDB provides a general event facility so that Python code can be
notified of various state changes, particularly changes that occur in
the inferior.

   An "event" is just an object that describes some state change.  The
type of the object and its attributes will vary depending on the details
of the change.  All the existing events are described below.

   In order to be notified of an event, you must register an event
handler with an "event registry".  An event registry is an object in the
`gdb.events' module which dispatches particular events.  A registry
provides methods to register and unregister event handlers:

 -- Function: EventRegistry.connect (object)
     Add the given callable OBJECT to the registry.  This object will be
     called when an event corresponding to this registry occurs.

 -- Function: EventRegistry.disconnect (object)
     Remove the given OBJECT from the registry.  Once removed, the
     object will no longer receive notifications of events.

   Here is an example:

     def exit_handler (event):
         print "event type: exit"
         print "exit code: %d" % (event.exit_code)

     gdb.events.exited.connect (exit_handler)

   In the above example we connect our handler `exit_handler' to the
registry `events.exited'.  Once connected, `exit_handler' gets called
when the inferior exits.  The argument "event" in this example is of
type `gdb.ExitedEvent'.  As you can see in the example the
`ExitedEvent' object has an attribute which indicates the exit code of
the inferior.

   The following is a listing of the event registries that are
available and details of the events they emit:

`events.cont'
     Emits `gdb.ThreadEvent'.

     Some events can be thread specific when GDB is running in non-stop
     mode.  When represented in Python, these events all extend
     `gdb.ThreadEvent'.  Note, this event is not emitted directly;
     instead, events which are emitted by this or other modules might
     extend this event.  Examples of these events are
     `gdb.BreakpointEvent' and `gdb.ContinueEvent'.

      -- Variable: ThreadEvent.inferior_thread
          In non-stop mode this attribute will be set to the specific
          thread which was involved in the emitted event. Otherwise, it
          will be set to `None'.

     Emits `gdb.ContinueEvent' which extends `gdb.ThreadEvent'.

     This event indicates that the inferior has been continued after a
     stop. For inherited attribute refer to `gdb.ThreadEvent' above.

`events.exited'
     Emits `events.ExitedEvent' which indicates that the inferior has
     exited.  `events.ExitedEvent' has two attributes:

      -- Variable: ExitedEvent.exit_code
          An integer representing the exit code, if available, which
          the inferior has returned.  (The exit code could be
          unavailable if, for example, GDB detaches from the inferior.)
          If the exit code is unavailable, the attribute does not exist.

      -- Variable: ExitedEvent inferior
          A reference to the inferior which triggered the `exited'
          event.

`events.stop'
     Emits `gdb.StopEvent' which extends `gdb.ThreadEvent'.

     Indicates that the inferior has stopped.  All events emitted by
     this registry extend StopEvent.  As a child of `gdb.ThreadEvent',
     `gdb.StopEvent' will indicate the stopped thread when GDB is
     running in non-stop mode.  Refer to `gdb.ThreadEvent' above for
     more details.

     Emits `gdb.SignalEvent' which extends `gdb.StopEvent'.

     This event indicates that the inferior or one of its threads has
     received as signal.  `gdb.SignalEvent' has the following
     attributes:

      -- Variable: SignalEvent.stop_signal
          A string representing the signal received by the inferior.  A
          list of possible signal values can be obtained by running the
          command `info signals' in the GDB command prompt.

     Also emits  `gdb.BreakpointEvent' which extends `gdb.StopEvent'.

     `gdb.BreakpointEvent' event indicates that one or more breakpoints
     have been hit, and has the following attributes:

      -- Variable: BreakpointEvent.breakpoints
          A sequence containing references to all the breakpoints (type
          `gdb.Breakpoint') that were hit.  *Note Breakpoints In
          Python::, for details of the `gdb.Breakpoint' object.

      -- Variable: BreakpointEvent.breakpoint
          A reference to the first breakpoint that was hit.  This
          function is maintained for backward compatibility and is now
          deprecated in favor of the `gdb.BreakpointEvent.breakpoints'
          attribute.

`events.new_objfile'
     Emits `gdb.NewObjFileEvent' which indicates that a new object file
     has been loaded by GDB.  `gdb.NewObjFileEvent' has one attribute:

      -- Variable: NewObjFileEvent.new_objfile
          A reference to the object file (`gdb.Objfile') which has been
          loaded.  *Note Objfiles In Python::, for details of the
          `gdb.Objfile' object.



File: gdb.info,  Node: Threads In Python,  Next: Commands In Python,  Prev: Events In Python,  Up: Python API

23.2.2.11 Threads In Python
...........................

Python scripts can access information about, and manipulate inferior
threads controlled by GDB, via objects of the `gdb.InferiorThread'
class.

   The following thread-related functions are available in the `gdb'
module:

 -- Function: gdb.selected_thread ()
     This function returns the thread object for the selected thread.
     If there is no selected thread, this will return `None'.

   A `gdb.InferiorThread' object has the following attributes:

 -- Variable: InferiorThread.name
     The name of the thread.  If the user specified a name using
     `thread name', then this returns that name.  Otherwise, if an
     OS-supplied name is available, then it is returned.  Otherwise,
     this returns `None'.

     This attribute can be assigned to.  The new value must be a string
     object, which sets the new name, or `None', which removes any
     user-specified thread name.

 -- Variable: InferiorThread.num
     ID of the thread, as assigned by GDB.

 -- Variable: InferiorThread.ptid
     ID of the thread, as assigned by the operating system.  This
     attribute is a tuple containing three integers.  The first is the
     Process ID (PID); the second is the Lightweight Process ID
     (LWPID), and the third is the Thread ID (TID).  Either the LWPID
     or TID may be 0, which indicates that the operating system does
     not  use that identifier.

   A `gdb.InferiorThread' object has the following methods:

 -- Function: InferiorThread.is_valid ()
     Returns `True' if the `gdb.InferiorThread' object is valid,
     `False' if not.  A `gdb.InferiorThread' object will become invalid
     if the thread exits, or the inferior that the thread belongs is
     deleted.  All other `gdb.InferiorThread' methods will throw an
     exception if it is invalid at the time the method is called.

 -- Function: InferiorThread.switch ()
     This changes GDB's currently selected thread to the one represented
     by this object.

 -- Function: InferiorThread.is_stopped ()
     Return a Boolean indicating whether the thread is stopped.

 -- Function: InferiorThread.is_running ()
     Return a Boolean indicating whether the thread is running.

 -- Function: InferiorThread.is_exited ()
     Return a Boolean indicating whether the thread is exited.


File: gdb.info,  Node: Commands In Python,  Next: Parameters In Python,  Prev: Threads In Python,  Up: Python API

23.2.2.12 Commands In Python
............................

You can implement new GDB CLI commands in Python.  A CLI command is
implemented using an instance of the `gdb.Command' class, most commonly
using a subclass.

 -- Function: Command.__init__ (name, COMMAND_CLASS [, COMPLETER_CLASS
          [, PREFIX]])
     The object initializer for `Command' registers the new command
     with GDB.  This initializer is normally invoked from the subclass'
     own `__init__' method.

     NAME is the name of the command.  If NAME consists of multiple
     words, then the initial words are looked for as prefix commands.
     In this case, if one of the prefix commands does not exist, an
     exception is raised.

     There is no support for multi-line commands.

     COMMAND_CLASS should be one of the `COMMAND_' constants defined
     below.  This argument tells GDB how to categorize the new command
     in the help system.

     COMPLETER_CLASS is an optional argument.  If given, it should be
     one of the `COMPLETE_' constants defined below.  This argument
     tells GDB how to perform completion for this command.  If not
     given, GDB will attempt to complete using the object's `complete'
     method (see below); if no such method is found, an error will
     occur when completion is attempted.

     PREFIX is an optional argument.  If `True', then the new command
     is a prefix command; sub-commands of this command may be
     registered.

     The help text for the new command is taken from the Python
     documentation string for the command's class, if there is one.  If
     no documentation string is provided, the default value "This
     command is not documented." is used.

 -- Function: Command.dont_repeat ()
     By default, a GDB command is repeated when the user enters a blank
     line at the command prompt.  A command can suppress this behavior
     by invoking the `dont_repeat' method.  This is similar to the user
     command `dont-repeat', see *note dont-repeat: Define.

 -- Function: Command.invoke (argument, from_tty)
     This method is called by GDB when this command is invoked.

     ARGUMENT is a string.  It is the argument to the command, after
     leading and trailing whitespace has been stripped.

     FROM_TTY is a boolean argument.  When true, this means that the
     command was entered by the user at the terminal; when false it
     means that the command came from elsewhere.

     If this method throws an exception, it is turned into a GDB
     `error' call.  Otherwise, the return value is ignored.

     To break ARGUMENT up into an argv-like string use
     `gdb.string_to_argv'.  This function behaves identically to GDB's
     internal argument lexer `buildargv'.  It is recommended to use
     this for consistency.  Arguments are separated by spaces and may
     be quoted.  Example:

          print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
          ['1', '2 "3', '4 "5', "6 '7"]


 -- Function: Command.complete (text, word)
     This method is called by GDB when the user attempts completion on
     this command.  All forms of completion are handled by this method,
     that is, the <TAB> and <M-?> key bindings (*note Completion::),
     and the `complete' command (*note complete: Help.).

     The arguments TEXT and WORD are both strings.  TEXT holds the
     complete command line up to the cursor's location.  WORD holds the
     last word of the command line; this is computed using a
     word-breaking heuristic.

     The `complete' method can return several values:
        * If the return value is a sequence, the contents of the
          sequence are used as the completions.  It is up to `complete'
          to ensure that the contents actually do complete the word.  A
          zero-length sequence is allowed, it means that there were no
          completions available.  Only string elements of the sequence
          are used; other elements in the sequence are ignored.

        * If the return value is one of the `COMPLETE_' constants
          defined below, then the corresponding GDB-internal completion
          function is invoked, and its result is used.

        * All other results are treated as though there were no
          available completions.

   When a new command is registered, it must be declared as a member of
some general class of commands.  This is used to classify top-level
commands in the on-line help system; note that prefix commands are not
listed under their own category but rather that of their top-level
command.  The available classifications are represented by constants
defined in the `gdb' module:

`gdb.COMMAND_NONE'
     The command does not belong to any particular class.  A command in
     this category will not be displayed in any of the help categories.

`gdb.COMMAND_RUNNING'
     The command is related to running the inferior.  For example,
     `start', `step', and `continue' are in this category.  Type `help
     running' at the GDB prompt to see a list of commands in this
     category.

`gdb.COMMAND_DATA'
     The command is related to data or variables.  For example, `call',
     `find', and `print' are in this category.  Type `help data' at the
     GDB prompt to see a list of commands in this category.

`gdb.COMMAND_STACK'
     The command has to do with manipulation of the stack.  For example,
     `backtrace', `frame', and `return' are in this category.  Type
     `help stack' at the GDB prompt to see a list of commands in this
     category.

`gdb.COMMAND_FILES'
     This class is used for file-related commands.  For example,
     `file', `list' and `section' are in this category.  Type `help
     files' at the GDB prompt to see a list of commands in this
     category.

`gdb.COMMAND_SUPPORT'
     This should be used for "support facilities", generally meaning
     things that are useful to the user when interacting with GDB, but
     not related to the state of the inferior.  For example, `help',
     `make', and `shell' are in this category.  Type `help support' at
     the GDB prompt to see a list of commands in this category.

`gdb.COMMAND_STATUS'
     The command is an `info'-related command, that is, related to the
     state of GDB itself.  For example, `info', `macro', and `show' are
     in this category.  Type `help status' at the GDB prompt to see a
     list of commands in this category.

`gdb.COMMAND_BREAKPOINTS'
     The command has to do with breakpoints.  For example, `break',
     `clear', and `delete' are in this category.  Type `help
     breakpoints' at the GDB prompt to see a list of commands in this
     category.

`gdb.COMMAND_TRACEPOINTS'
     The command has to do with tracepoints.  For example, `trace',
     `actions', and `tfind' are in this category.  Type `help
     tracepoints' at the GDB prompt to see a list of commands in this
     category.

`gdb.COMMAND_USER'
     The command is a general purpose command for the user, and
     typically does not fit in one of the other categories.  Type `help
     user-defined' at the GDB prompt to see a list of commands in this
     category, as well as the list of gdb macros (*note Sequences::).

`gdb.COMMAND_OBSCURE'
     The command is only used in unusual circumstances, or is not of
     general interest to users.  For example, `checkpoint', `fork', and
     `stop' are in this category.  Type `help obscure' at the GDB
     prompt to see a list of commands in this category.

`gdb.COMMAND_MAINTENANCE'
     The command is only useful to GDB maintainers.  The `maintenance'
     and `flushregs' commands are in this category.  Type `help
     internals' at the GDB prompt to see a list of commands in this
     category.

   A new command can use a predefined completion function, either by
specifying it via an argument at initialization, or by returning it
from the `complete' method.  These predefined completion constants are
all defined in the `gdb' module:

`gdb.COMPLETE_NONE'
     This constant means that no completion should be done.

`gdb.COMPLETE_FILENAME'
     This constant means that filename completion should be performed.

`gdb.COMPLETE_LOCATION'
     This constant means that location completion should be done.
     *Note Specify Location::.

`gdb.COMPLETE_COMMAND'
     This constant means that completion should examine GDB command
     names.

`gdb.COMPLETE_SYMBOL'
     This constant means that completion should be done using symbol
     names as the source.

   The following code snippet shows how a trivial CLI command can be
implemented in Python:

     class HelloWorld (gdb.Command):
       """Greet the whole world."""

       def __init__ (self):
         super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)

       def invoke (self, arg, from_tty):
         print "Hello, World!"

     HelloWorld ()

   The last line instantiates the class, and is necessary to trigger the
registration of the command with GDB.  Depending on how the Python code
is read into GDB, you may need to import the `gdb' module explicitly.


File: gdb.info,  Node: Parameters In Python,  Next: Functions In Python,  Prev: Commands In Python,  Up: Python API

23.2.2.13 Parameters In Python
..............................

You can implement new GDB parameters using Python.  A new parameter is
implemented as an instance of the `gdb.Parameter' class.

   Parameters are exposed to the user via the `set' and `show'
commands.  *Note Help::.

   There are many parameters that already exist and can be set in GDB.
Two examples are: `set follow fork' and `set charset'.  Setting these
parameters influences certain behavior in GDB.  Similarly, you can
define parameters that can be used to influence behavior in custom
Python scripts and commands.

 -- Function: Parameter.__init__ (name, COMMAND-CLASS, PARAMETER-CLASS
          [, ENUM-SEQUENCE])
     The object initializer for `Parameter' registers the new parameter
     with GDB.  This initializer is normally invoked from the subclass'
     own `__init__' method.

     NAME is the name of the new parameter.  If NAME consists of
     multiple words, then the initial words are looked for as prefix
     parameters.  An example of this can be illustrated with the `set
     print' set of parameters.  If NAME is `print foo', then `print'
     will be searched as the prefix parameter.  In this case the
     parameter can subsequently be accessed in GDB as `set print foo'.

     If NAME consists of multiple words, and no prefix parameter group
     can be found, an exception is raised.

     COMMAND-CLASS should be one of the `COMMAND_' constants (*note
     Commands In Python::).  This argument tells GDB how to categorize
     the new parameter in the help system.

     PARAMETER-CLASS should be one of the `PARAM_' constants defined
     below.  This argument tells GDB the type of the new parameter;
     this information is used for input validation and completion.

     If PARAMETER-CLASS is `PARAM_ENUM', then ENUM-SEQUENCE must be a
     sequence of strings.  These strings represent the possible values
     for the parameter.

     If PARAMETER-CLASS is not `PARAM_ENUM', then the presence of a
     fourth argument will cause an exception to be thrown.

     The help text for the new parameter is taken from the Python
     documentation string for the parameter's class, if there is one.
     If there is no documentation string, a default value is used.

 -- Variable: Parameter.set_doc
     If this attribute exists, and is a string, then its value is used
     as the help text for this parameter's `set' command.  The value is
     examined when `Parameter.__init__' is invoked; subsequent changes
     have no effect.

 -- Variable: Parameter.show_doc
     If this attribute exists, and is a string, then its value is used
     as the help text for this parameter's `show' command.  The value is
     examined when `Parameter.__init__' is invoked; subsequent changes
     have no effect.

 -- Variable: Parameter.value
     The `value' attribute holds the underlying value of the parameter.
     It can be read and assigned to just as any other attribute.  GDB
     does validation when assignments are made.

   There are two methods that should be implemented in any `Parameter'
class.  These are:

 -- Function: Parameter.get_set_string (self)
     GDB will call this method when a PARAMETER's value has been
     changed via the `set' API (for example, `set foo off').  The
     `value' attribute has already been populated with the new value
     and may be used in output.  This method must return a string.

 -- Function: Parameter.get_show_string (self, svalue)
     GDB will call this method when a PARAMETER's `show' API has been
     invoked (for example, `show foo').  The argument `svalue' receives
     the string representation of the current value.  This method must
     return a string.

   When a new parameter is defined, its type must be specified.  The
available types are represented by constants defined in the `gdb'
module:

`gdb.PARAM_BOOLEAN'
     The value is a plain boolean.  The Python boolean values, `True'
     and `False' are the only valid values.

`gdb.PARAM_AUTO_BOOLEAN'
     The value has three possible states: true, false, and `auto'.  In
     Python, true and false are represented using boolean constants, and
     `auto' is represented using `None'.

`gdb.PARAM_UINTEGER'
     The value is an unsigned integer.  The value of 0 should be
     interpreted to mean "unlimited".

`gdb.PARAM_INTEGER'
     The value is a signed integer.  The value of 0 should be
     interpreted to mean "unlimited".

`gdb.PARAM_STRING'
     The value is a string.  When the user modifies the string, any
     escape sequences, such as `\t', `\f', and octal escapes, are
     translated into corresponding characters and encoded into the
     current host charset.

`gdb.PARAM_STRING_NOESCAPE'
     The value is a string.  When the user modifies the string, escapes
     are passed through untranslated.

`gdb.PARAM_OPTIONAL_FILENAME'
     The value is a either a filename (a string), or `None'.

`gdb.PARAM_FILENAME'
     The value is a filename.  This is just like
     `PARAM_STRING_NOESCAPE', but uses file names for completion.

`gdb.PARAM_ZINTEGER'
     The value is an integer.  This is like `PARAM_INTEGER', except 0
     is interpreted as itself.

`gdb.PARAM_ENUM'
     The value is a string, which must be one of a collection string
     constants provided when the parameter is created.


File: gdb.info,  Node: Functions In Python,  Next: Progspaces In Python,  Prev: Parameters In Python,  Up: Python API

23.2.2.14 Writing new convenience functions
...........................................

You can implement new convenience functions (*note Convenience Vars::)
in Python.  A convenience function is an instance of a subclass of the
class `gdb.Function'.

 -- Function: Function.__init__ (name)
     The initializer for `Function' registers the new function with
     GDB.  The argument NAME is the name of the function, a string.
     The function will be visible to the user as a convenience variable
     of type `internal function', whose name is the same as the given
     NAME.

     The documentation for the new function is taken from the
     documentation string for the new class.

 -- Function: Function.invoke (*ARGS)
     When a convenience function is evaluated, its arguments are
     converted to instances of `gdb.Value', and then the function's
     `invoke' method is called.  Note that GDB does not predetermine
     the arity of convenience functions.  Instead, all available
     arguments are passed to `invoke', following the standard Python
     calling convention.  In particular, a convenience function can
     have default values for parameters without ill effect.

     The return value of this method is used as its value in the
     enclosing expression.  If an ordinary Python value is returned, it
     is converted to a `gdb.Value' following the usual rules.

   The following code snippet shows how a trivial convenience function
can be implemented in Python:

     class Greet (gdb.Function):
       """Return string to greet someone.
     Takes a name as argument."""

       def __init__ (self):
         super (Greet, self).__init__ ("greet")

       def invoke (self, name):
         return "Hello, %s!" % name.string ()

     Greet ()

   The last line instantiates the class, and is necessary to trigger the
registration of the function with GDB.  Depending on how the Python
code is read into GDB, you may need to import the `gdb' module
explicitly.

   Now you can use the function in an expression:

     (gdb) print $greet("Bob")
     $1 = "Hello, Bob!"


File: gdb.info,  Node: Progspaces In Python,  Next: Objfiles In Python,  Prev: Functions In Python,  Up: Python API

23.2.2.15 Program Spaces In Python
..................................

A program space, or "progspace", represents a symbolic view of an
address space.  It consists of all of the objfiles of the program.
*Note Objfiles In Python::.  *Note program spaces: Inferiors and
Programs, for more details about program spaces.

   The following progspace-related functions are available in the `gdb'
module:

 -- Function: gdb.current_progspace ()
     This function returns the program space of the currently selected
     inferior.  *Note Inferiors and Programs::.

 -- Function: gdb.progspaces ()
     Return a sequence of all the progspaces currently known to GDB.

   Each progspace is represented by an instance of the `gdb.Progspace'
class.

 -- Variable: Progspace.filename
     The file name of the progspace as a string.

 -- Variable: Progspace.pretty_printers
     The `pretty_printers' attribute is a list of functions.  It is
     used to look up pretty-printers.  A `Value' is passed to each
     function in order; if the function returns `None', then the search
     continues.  Otherwise, the return value should be an object which
     is used to format the value.  *Note Pretty Printing API::, for more
     information.

 -- Variable: Progspace.type_printers
     The `type_printers' attribute is a list of type printer objects.
     *Note Type Printing API::, for more information.


File: gdb.info,  Node: Objfiles In Python,  Next: Frames In Python,  Prev: Progspaces In Python,  Up: Python API

23.2.2.16 Objfiles In Python
............................

GDB loads symbols for an inferior from various symbol-containing files
(*note Files::).  These include the primary executable file, any shared
libraries used by the inferior, and any separate debug info files
(*note Separate Debug Files::).  GDB calls these symbol-containing
files "objfiles".

   The following objfile-related functions are available in the `gdb'
module:

 -- Function: gdb.current_objfile ()
     When auto-loading a Python script (*note Python Auto-loading::),
     GDB sets the "current objfile" to the corresponding objfile.  This
     function returns the current objfile.  If there is no current
     objfile, this function returns `None'.

 -- Function: gdb.objfiles ()
     Return a sequence of all the objfiles current known to GDB.  *Note
     Objfiles In Python::.

   Each objfile is represented by an instance of the `gdb.Objfile'
class.

 -- Variable: Objfile.filename
     The file name of the objfile as a string.

 -- Variable: Objfile.pretty_printers
     The `pretty_printers' attribute is a list of functions.  It is
     used to look up pretty-printers.  A `Value' is passed to each
     function in order; if the function returns `None', then the search
     continues.  Otherwise, the return value should be an object which
     is used to format the value.  *Note Pretty Printing API::, for more
     information.

 -- Variable: Objfile.type_printers
     The `type_printers' attribute is a list of type printer objects.
     *Note Type Printing API::, for more information.

   A `gdb.Objfile' object has the following methods:

 -- Function: Objfile.is_valid ()
     Returns `True' if the `gdb.Objfile' object is valid, `False' if
     not.  A `gdb.Objfile' object can become invalid if the object file
     it refers to is not loaded in GDB any longer.  All other
     `gdb.Objfile' methods will throw an exception if it is invalid at
     the time the method is called.


File: gdb.info,  Node: Frames In Python,  Next: Blocks In Python,  Prev: Objfiles In Python,  Up: Python API

23.2.2.17 Accessing inferior stack frames from Python.
......................................................

When the debugged program stops, GDB is able to analyze its call stack
(*note Stack frames: Frames.).  The `gdb.Frame' class represents a
frame in the stack.  A `gdb.Frame' object is only valid while its
corresponding frame exists in the inferior's stack.  If you try to use
an invalid frame object, GDB will throw a `gdb.error' exception (*note
Exception Handling::).

   Two `gdb.Frame' objects can be compared for equality with the `=='
operator, like:

     (gdb) python print gdb.newest_frame() == gdb.selected_frame ()
     True

   The following frame-related functions are available in the `gdb'
module:

 -- Function: gdb.selected_frame ()
     Return the selected frame object.  (*note Selecting a Frame:
     Selection.).

 -- Function: gdb.newest_frame ()
     Return the newest frame object for the selected thread.

 -- Function: gdb.frame_stop_reason_string (reason)
     Return a string explaining the reason why GDB stopped unwinding
     frames, as expressed by the given REASON code (an integer, see the
     `unwind_stop_reason' method further down in this section).

   A `gdb.Frame' object has the following methods:

 -- Function: Frame.is_valid ()
     Returns true if the `gdb.Frame' object is valid, false if not.  A
     frame object can become invalid if the frame it refers to doesn't
     exist anymore in the inferior.  All `gdb.Frame' methods will throw
     an exception if it is invalid at the time the method is called.

 -- Function: Frame.name ()
     Returns the function name of the frame, or `None' if it can't be
     obtained.

 -- Function: Frame.architecture ()
     Returns the `gdb.Architecture' object corresponding to the frame's
     architecture.  *Note Architectures In Python::.

 -- Function: Frame.type ()
     Returns the type of the frame.  The value can be one of:
    `gdb.NORMAL_FRAME'
          An ordinary stack frame.

    `gdb.DUMMY_FRAME'
          A fake stack frame that was created by GDB when performing an
          inferior function call.

    `gdb.INLINE_FRAME'
          A frame representing an inlined function.  The function was
          inlined into a `gdb.NORMAL_FRAME' that is older than this one.

    `gdb.TAILCALL_FRAME'
          A frame representing a tail call.  *Note Tail Call Frames::.

    `gdb.SIGTRAMP_FRAME'
          A signal trampoline frame.  This is the frame created by the
          OS when it calls into a signal handler.

    `gdb.ARCH_FRAME'
          A fake stack frame representing a cross-architecture call.

    `gdb.SENTINEL_FRAME'
          This is like `gdb.NORMAL_FRAME', but it is only used for the
          newest frame.

 -- Function: Frame.unwind_stop_reason ()
     Return an integer representing the reason why it's not possible to
     find more frames toward the outermost frame.  Use
     `gdb.frame_stop_reason_string' to convert the value returned by
     this function to a string. The value can be one of:

    `gdb.FRAME_UNWIND_NO_REASON'
          No particular reason (older frames should be available).

    `gdb.FRAME_UNWIND_NULL_ID'
          The previous frame's analyzer returns an invalid result.

    `gdb.FRAME_UNWIND_OUTERMOST'
          This frame is the outermost.

    `gdb.FRAME_UNWIND_UNAVAILABLE'
          Cannot unwind further, because that would require knowing the
          values of registers or memory that have not been collected.

    `gdb.FRAME_UNWIND_INNER_ID'
          This frame ID looks like it ought to belong to a NEXT frame,
          but we got it for a PREV frame.  Normally, this is a sign of
          unwinder failure.  It could also indicate stack corruption.

    `gdb.FRAME_UNWIND_SAME_ID'
          This frame has the same ID as the previous one.  That means
          that unwinding further would almost certainly give us another
          frame with exactly the same ID, so break the chain.  Normally,
          this is a sign of unwinder failure.  It could also indicate
          stack corruption.

    `gdb.FRAME_UNWIND_NO_SAVED_PC'
          The frame unwinder did not find any saved PC, but we needed
          one to unwind further.

    `gdb.FRAME_UNWIND_FIRST_ERROR'
          Any stop reason greater or equal to this value indicates some
          kind of error.  This special value facilitates writing code
          that tests for errors in unwinding in a way that will work
          correctly even if the list of the other values is modified in
          future GDB versions.  Using it, you could write:
               reason = gdb.selected_frame().unwind_stop_reason ()
               reason_str =  gdb.frame_stop_reason_string (reason)
               if reason >=  gdb.FRAME_UNWIND_FIRST_ERROR:
                   print "An error occured: %s" % reason_str


 -- Function: Frame.pc ()
     Returns the frame's resume address.

 -- Function: Frame.block ()
     Return the frame's code block.  *Note Blocks In Python::.

 -- Function: Frame.function ()
     Return the symbol for the function corresponding to this frame.
     *Note Symbols In Python::.

 -- Function: Frame.older ()
     Return the frame that called this frame.

 -- Function: Frame.newer ()
     Return the frame called by this frame.

 -- Function: Frame.find_sal ()
     Return the frame's symtab and line object.  *Note Symbol Tables In
     Python::.

 -- Function: Frame.read_var (variable [, block])
     Return the value of VARIABLE in this frame.  If the optional
     argument BLOCK is provided, search for the variable from that
     block; otherwise start at the frame's current block (which is
     determined by the frame's current program counter).  VARIABLE must
     be a string or a `gdb.Symbol' object.  BLOCK must be a `gdb.Block'
     object.

 -- Function: Frame.select ()
     Set this frame to be the selected frame.  *Note Examining the
     Stack: Stack.


File: gdb.info,  Node: Blocks In Python,  Next: Symbols In Python,  Prev: Frames In Python,  Up: Python API

23.2.2.18 Accessing frame blocks from Python.
.............................................

Within each frame, GDB maintains information on each block stored in
that frame.  These blocks are organized hierarchically, and are
represented individually in Python as a `gdb.Block'.  Please see *note
Frames In Python::, for a more in-depth discussion on frames.
Furthermore, see *note Examining the Stack: Stack, for more detailed
technical information on GDB's book-keeping of the stack.

   A `gdb.Block' is iterable.  The iterator returns the symbols (*note
Symbols In Python::) local to the block.  Python programs should not
assume that a specific block object will always contain a given symbol,
since changes in GDB features and infrastructure may cause symbols move
across blocks in a symbol table.

   The following block-related functions are available in the `gdb'
module:

 -- Function: gdb.block_for_pc (pc)
     Return the `gdb.Block' containing the given PC value.  If the
     block cannot be found for the PC value specified, the function
     will return `None'.

   A `gdb.Block' object has the following methods:

 -- Function: Block.is_valid ()
     Returns `True' if the `gdb.Block' object is valid, `False' if not.
     A block object can become invalid if the block it refers to
     doesn't exist anymore in the inferior.  All other `gdb.Block'
     methods will throw an exception if it is invalid at the time the
     method is called.  The block's validity is also checked during
     iteration over symbols of the block.

   A `gdb.Block' object has the following attributes:

 -- Variable: Block.start
     The start address of the block.  This attribute is not writable.

 -- Variable: Block.end
     The end address of the block.  This attribute is not writable.

 -- Variable: Block.function
     The name of the block represented as a `gdb.Symbol'.  If the block
     is not named, then this attribute holds `None'.  This attribute is
     not writable.

 -- Variable: Block.superblock
     The block containing this block.  If this parent block does not
     exist, this attribute holds `None'.  This attribute is not
     writable.

 -- Variable: Block.global_block
     The global block associated with this block.  This attribute is not
     writable.

 -- Variable: Block.static_block
     The static block associated with this block.  This attribute is not
     writable.

 -- Variable: Block.is_global
     `True' if the `gdb.Block' object is a global block, `False' if
     not.  This attribute is not writable.

 -- Variable: Block.is_static
     `True' if the `gdb.Block' object is a static block, `False' if
     not.  This attribute is not writable.


File: gdb.info,  Node: Symbols In Python,  Next: Symbol Tables In Python,  Prev: Blocks In Python,  Up: Python API

23.2.2.19 Python representation of Symbols.
...........................................

GDB represents every variable, function and type as an entry in a
symbol table.  *Note Examining the Symbol Table: Symbols.  Similarly,
Python represents these symbols in GDB with the `gdb.Symbol' object.

   The following symbol-related functions are available in the `gdb'
module:

 -- Function: gdb.lookup_symbol (name [, block [, domain]])
     This function searches for a symbol by name.  The search scope can
     be restricted to the parameters defined in the optional domain and
     block arguments.

     NAME is the name of the symbol.  It must be a string.  The
     optional BLOCK argument restricts the search to symbols visible in
     that BLOCK.  The BLOCK argument must be a `gdb.Block' object.  If
     omitted, the block for the current frame is used.  The optional
     DOMAIN argument restricts the search to the domain type.  The
     DOMAIN argument must be a domain constant defined in the `gdb'
     module and described later in this chapter.

     The result is a tuple of two elements.  The first element is a
     `gdb.Symbol' object or `None' if the symbol is not found.  If the
     symbol is found, the second element is `True' if the symbol is a
     field of a method's object (e.g., `this' in C++), otherwise it is
     `False'.  If the symbol is not found, the second element is
     `False'.

 -- Function: gdb.lookup_global_symbol (name [, domain])
     This function searches for a global symbol by name.  The search
     scope can be restricted to by the domain argument.

     NAME is the name of the symbol.  It must be a string.  The
     optional DOMAIN argument restricts the search to the domain type.
     The DOMAIN argument must be a domain constant defined in the `gdb'
     module and described later in this chapter.

     The result is a `gdb.Symbol' object or `None' if the symbol is not
     found.

   A `gdb.Symbol' object has the following attributes:

 -- Variable: Symbol.type
     The type of the symbol or `None' if no type is recorded.  This
     attribute is represented as a `gdb.Type' object.  *Note Types In
     Python::.  This attribute is not writable.

 -- Variable: Symbol.symtab
     The symbol table in which the symbol appears.  This attribute is
     represented as a `gdb.Symtab' object.  *Note Symbol Tables In
     Python::.  This attribute is not writable.

 -- Variable: Symbol.line
     The line number in the source code at which the symbol was defined.
     This is an integer.

 -- Variable: Symbol.name
     The name of the symbol as a string.  This attribute is not
     writable.

 -- Variable: Symbol.linkage_name
     The name of the symbol, as used by the linker (i.e., may be
     mangled).  This attribute is not writable.

 -- Variable: Symbol.print_name
     The name of the symbol in a form suitable for output.  This is
     either `name' or `linkage_name', depending on whether the user
     asked GDB to display demangled or mangled names.

 -- Variable: Symbol.addr_class
     The address class of the symbol.  This classifies how to find the
     value of a symbol.  Each address class is a constant defined in the
     `gdb' module and described later in this chapter.

 -- Variable: Symbol.needs_frame
     This is `True' if evaluating this symbol's value requires a frame
     (*note Frames In Python::) and `False' otherwise.  Typically,
     local variables will require a frame, but other symbols will not.

 -- Variable: Symbol.is_argument
     `True' if the symbol is an argument of a function.

 -- Variable: Symbol.is_constant
     `True' if the symbol is a constant.

 -- Variable: Symbol.is_function
     `True' if the symbol is a function or a method.

 -- Variable: Symbol.is_variable
     `True' if the symbol is a variable.

   A `gdb.Symbol' object has the following methods:

 -- Function: Symbol.is_valid ()
     Returns `True' if the `gdb.Symbol' object is valid, `False' if
     not.  A `gdb.Symbol' object can become invalid if the symbol it
     refers to does not exist in GDB any longer.  All other
     `gdb.Symbol' methods will throw an exception if it is invalid at
     the time the method is called.

 -- Function: Symbol.value ([frame])
     Compute the value of the symbol, as a `gdb.Value'.  For functions,
     this computes the address of the function, cast to the appropriate
     type.  If the symbol requires a frame in order to compute its
     value, then FRAME must be given.  If FRAME is not given, or if
     FRAME is invalid, then this method will throw an exception.

   The available domain categories in `gdb.Symbol' are represented as
constants in the `gdb' module:

`gdb.SYMBOL_UNDEF_DOMAIN'
     This is used when a domain has not been discovered or none of the
     following domains apply.  This usually indicates an error either
     in the symbol information or in GDB's handling of symbols.  

`gdb.SYMBOL_VAR_DOMAIN'
     This domain contains variables, function names, typedef names and
     enum type values.  

`gdb.SYMBOL_STRUCT_DOMAIN'
     This domain holds struct, union and enum type names.  

`gdb.SYMBOL_LABEL_DOMAIN'
     This domain contains names of labels (for gotos).  

`gdb.SYMBOL_VARIABLES_DOMAIN'
     This domain holds a subset of the `SYMBOLS_VAR_DOMAIN'; it
     contains everything minus functions and types.  

`gdb.SYMBOL_FUNCTION_DOMAIN'
     This domain contains all functions.  

`gdb.SYMBOL_TYPES_DOMAIN'
     This domain contains all types.

   The available address class categories in `gdb.Symbol' are
represented as constants in the `gdb' module:

`gdb.SYMBOL_LOC_UNDEF'
     If this is returned by address class, it indicates an error either
     in the symbol information or in GDB's handling of symbols.  

`gdb.SYMBOL_LOC_CONST'
     Value is constant int.  

`gdb.SYMBOL_LOC_STATIC'
     Value is at a fixed address.  

`gdb.SYMBOL_LOC_REGISTER'
     Value is in a register.  

`gdb.SYMBOL_LOC_ARG'
     Value is an argument.  This value is at the offset stored within
     the symbol inside the frame's argument list.  

`gdb.SYMBOL_LOC_REF_ARG'
     Value address is stored in the frame's argument list.  Just like
     `LOC_ARG' except that the value's address is stored at the offset,
     not the value itself.  

`gdb.SYMBOL_LOC_REGPARM_ADDR'
     Value is a specified register.  Just like `LOC_REGISTER' except
     the register holds the address of the argument instead of the
     argument itself.  

`gdb.SYMBOL_LOC_LOCAL'
     Value is a local variable.  

`gdb.SYMBOL_LOC_TYPEDEF'
     Value not used.  Symbols in the domain `SYMBOL_STRUCT_DOMAIN' all
     have this class.  

`gdb.SYMBOL_LOC_BLOCK'
     Value is a block.  

`gdb.SYMBOL_LOC_CONST_BYTES'
     Value is a byte-sequence.  

`gdb.SYMBOL_LOC_UNRESOLVED'
     Value is at a fixed address, but the address of the variable has
     to be determined from the minimal symbol table whenever the
     variable is referenced.  

`gdb.SYMBOL_LOC_OPTIMIZED_OUT'
     The value does not actually exist in the program.  

`gdb.SYMBOL_LOC_COMPUTED'
     The value's address is a computed location.


File: gdb.info,  Node: Symbol Tables In Python,  Next: Breakpoints In Python,  Prev: Symbols In Python,  Up: Python API

23.2.2.20 Symbol table representation in Python.
................................................

Access to symbol table data maintained by GDB on the inferior is
exposed to Python via two objects: `gdb.Symtab_and_line' and
`gdb.Symtab'.  Symbol table and line data for a frame is returned from
the `find_sal' method in `gdb.Frame' object.  *Note Frames In Python::.

   For more information on GDB's symbol table management, see *note
Examining the Symbol Table: Symbols, for more information.

   A `gdb.Symtab_and_line' object has the following attributes:

 -- Variable: Symtab_and_line.symtab
     The symbol table object (`gdb.Symtab') for this frame.  This
     attribute is not writable.

 -- Variable: Symtab_and_line.pc
     Indicates the start of the address range occupied by code for the
     current source line.  This attribute is not writable.

 -- Variable: Symtab_and_line.last
     Indicates the end of the address range occupied by code for the
     current source line.  This attribute is not writable.

 -- Variable: Symtab_and_line.line
     Indicates the current line number for this object.  This attribute
     is not writable.

   A `gdb.Symtab_and_line' object has the following methods:

 -- Function: Symtab_and_line.is_valid ()
     Returns `True' if the `gdb.Symtab_and_line' object is valid,
     `False' if not.  A `gdb.Symtab_and_line' object can become invalid
     if the Symbol table and line object it refers to does not exist in
     GDB any longer.  All other `gdb.Symtab_and_line' methods will
     throw an exception if it is invalid at the time the method is
     called.

   A `gdb.Symtab' object has the following attributes:

 -- Variable: Symtab.filename
     The symbol table's source filename.  This attribute is not
     writable.

 -- Variable: Symtab.objfile
     The symbol table's backing object file.  *Note Objfiles In
     Python::.  This attribute is not writable.

   A `gdb.Symtab' object has the following methods:

 -- Function: Symtab.is_valid ()
     Returns `True' if the `gdb.Symtab' object is valid, `False' if
     not.  A `gdb.Symtab' object can become invalid if the symbol table
     it refers to does not exist in GDB any longer.  All other
     `gdb.Symtab' methods will throw an exception if it is invalid at
     the time the method is called.

 -- Function: Symtab.fullname ()
     Return the symbol table's source absolute file name.

 -- Function: Symtab.global_block ()
     Return the global block of the underlying symbol table.  *Note
     Blocks In Python::.

 -- Function: Symtab.static_block ()
     Return the static block of the underlying symbol table.  *Note
     Blocks In Python::.

