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INFO-DIR-SECTION Software development
* Gdb: (gdb). The GNU debugger.
Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996,
1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
2010 2011, 2012 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 7.5.
Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996,
1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
2010 2011, 2012 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:, Node: Symbol Errors, Next: Data Files, Prev: Index Files, Up: GDB Files
18.4 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
`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:
`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:, Node: Data Files, Prev: Symbol Errors, Up: GDB Files
18.5 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
`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:, 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
`show architecture'
Show the current target architecture.
`set 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:, 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:, Node: Target Commands, Next: Byte Order, Prev: Active Targets, Up: Targets
19.2 Commands for Managing Targets
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 BDF target is "auto"'.
Here are some common targets (available, or not, depending on the GDB
`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
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
`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.
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:, 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

File:, 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:, 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
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
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.
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.
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
`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:, 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.
Copy file HOSTFILE from the host system (the machine running GDB)
to TARGETFILE on the target system.
Copy file TARGETFILE from the target system to HOSTFILE on the
host system.
`remote delete TARGETFILE'
Delete TARGETFILE from the target system.

File:, 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
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. 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. 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. TCP port allocation lifecycle of `gdbserver'
This section applies only when `gdbserver' is run to listen on a TCP
`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
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. 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
$ gdbserver --wrapper env -- :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
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, `') 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 `' 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 ("", ...)
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/
(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 `' 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:, 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:
`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
`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
`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
`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
`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
`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'
`get-thread-information-block-address'`qGetTIBAddr' Display
MS-Windows Thread
Information Block.
`search-memory' `qSearch:memory' `find'
`supported-packets' `qSupported' Remote
`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
`osdata' `qXfer:osdata:read' `info os'
`query-attached' `qAttached' Querying remote
process attach
`traceframe-info' `qXfer:traceframe-info:read'Traceframe info
`install-in-trace' `InstallInTrace' Install
tracepoint in
`disable-randomization'`QDisableRandomization' `set
`conditional-breakpoints-packet'`Z0 and Z1' `Support for

File:, 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
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
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
These working remote stubs are distributed with GDB:
For Intel 386 and compatible architectures.
For Motorola 680x0 architectures.
For Renesas SH architectures.
For SPARC architectures.
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:, 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
This routine arranges for `handle_exception' to run when your
program stops. You must call this subroutine explicitly in your
program's startup code.
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.
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:, 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
`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
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
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:, 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
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:
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:, 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:, Node: Native, Next: Embedded OS, Up: Configurations
21.1 Native
This section describes details specific to particular native
* Menu:
* 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
* Neutrino:: Features specific to QNX Neutrino
* Darwin:: Features specific to Darwin

File:, 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:, 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
`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:, 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. `info proc' works only on SVR4 systems
that include the `procfs' code. This includes, as of this writing,
GNU/Linux, OSF/1 (Digital Unix), Solaris, Irix, and Unixware, but not
HP-UX, for example.
`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 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.
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

File:, 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
`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
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
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
`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
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:, 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'.
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
`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:, Node: Non-debug DLL Symbols, Up: Cygwin Native 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. 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...] 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
(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:, Node: Hurd Native, Next: Neutrino, 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
`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
`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

File:, Node: Neutrino, Next: Darwin, Prev: Hurd Native, Up: Native
21.1.7 QNX Neutrino
GDB provides the following commands specific to the QNX Neutrino target:
`set debug nto-debug'
When set to on, enables debugging messages specific to the QNX
Neutrino support.
`show debug nto-debug'
Show the current state of QNX Neutrino messages.

File:, Node: Darwin, Prev: Neutrino, Up: Native
21.1.8 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:, 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
* Menu:
* VxWorks:: Using GDB with VxWorks
GDB includes the ability to debug programs running on various
real-time operating systems.

File:, 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
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
GDB comes up showing the prompt:
* Menu:
* VxWorks Connection:: Connecting to VxWorks
* VxWorks Download:: VxWorks download
* VxWorks Attach:: Running tasks

File:, Node: VxWorks Connection, Next: VxWorks Download, Up: VxWorks 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:, Node: VxWorks Download, Next: VxWorks Attach, Prev: VxWorks Connection, Up: VxWorks 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:, Node: VxWorks Attach, Prev: VxWorks Download, Up: VxWorks Running Tasks
You can also attach to an existing task using the `attach' command as
(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:, Node: Embedded Processors, Next: Architectures, Prev: Embedded OS, Up: Configurations
21.3 Embedded Processors
This section goes into details specific to particular embedded
Whenever a specific embedded processor has a simulator, GDB allows
to send an arbitrary command to the simulator.
Send an arbitrary COMMAND string to the simulator. Consult the
documentation for the specific simulator in use for information
about acceptable commands.
* Menu:
* 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
* Super-H:: Renesas Super-H

File:, 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:
Determine the FPU type by querying the OS ABI.
Software FPU, with mixed-endian doubles on little-endian ARM
GCC-compiled FPA co-processor.
Software FPU with pure-endian doubles.
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'
`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.
Tell the simulator which SWI interfaces to support. TYPE may
be a comma separated list of the following values. The
default value is `all'.

File:, 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:
This command resets the SDI connection.
This command shows the SDI connection status.
Instructs the remote that M32R/Chaos debugging is to be used.
Instructs the remote to use the DEBUG_DMA method of accessing
Instructs the remote to use the MON_CODE method of accessing
Instructs the remote to set breakpoints by IB break.
Instructs the remote to set breakpoints by DBT.

File:, 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:, 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.
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:, 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
`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
host$ gdb PROG
GDB is free software and ...
(gdb) target mips /dev/ttyb
(gdb) load PROG
(gdb) run
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
`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
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
`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
ddb target
lsi target
`show monitor-prompt'
Show the current strings GDB expects as the prompt from the remote
`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:, Node: OpenRISC 1000, Next: PowerPC Embedded, Prev: MIPS Embedded, Up: Embedded Processors
21.3.6 OpenRISC 1000
See OR1k Architecture document (`') 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
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.
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:
Load effective address/data
Store effective address/data
Access effective address ($SEA or $LEA) or data ($SDATA/$LDATA)
Fetch data
When triggered, it can capture low level data, like: `PC', `LSEA',
`htrace' commands:
Set hardware watchpoint on combination of Load/Store Effective
Address(es) or Data. For example:
`hwatch ($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:, 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 \
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'
GDB provides the following PowerPC-specific commands:
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,
`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
`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.
Send the specified COMMAND string to the SDS monitor.

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

File:, Node: Sparclet File, Next: Sparclet Connection, Up: Sparclet 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:, Node: Sparclet Connection, Next: Sparclet Download, Prev: Sparclet File, Up: Sparclet 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:, Node: Sparclet Download, Next: Sparclet Execution, Prev: Sparclet Connection, Up: Sparclet 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:, Node: Sparclet Execution, Prev: Sparclet Download, Up: Sparclet 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
(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!";

File:, 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:, 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
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:
Counts clock-ticks in the simulator.
Counts instructions run in the simulator.
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:, 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:, 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
`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:, Node: Super-H, Prev: CRIS, Up: Embedded Processors
21.3.14 Renesas Super-H
For the Renesas Super-H processor, GDB provides these commands:
This command is deprecated, and `info all-registers' should be
used instead.
Show the values of all Super-H registers.
`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:, 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:
* i386::
* Alpha::
* MIPS::
* HPPA:: HP PA architecture
* SPU:: Cell Broadband Engine SPU architecture
* PowerPC::

File:, Node: i386, Next: Alpha, Up: Architectures
21.4.1 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:, Node: Alpha, Next: MIPS, Prev: i386, Up: Architectures
21.4.2 Alpha
See the following section.

File:, Node: MIPS, Next: HPPA, Prev: Alpha, Up: Architectures
21.4.3 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
`set mips abi ARG'
Tell GDB which MIPS ABI is used by the inferior. Possible values
of ARG are:
The default ABI associated with the current binary (this is
the default).
`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
`show mips compression'
Show the MIPS compressed ISA encoding used by GDB to debug the
`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
`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
`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:, Node: HPPA, Next: SPU, Prev: MIPS, Up: Architectures
21.4.4 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:, Node: SPU, Next: PowerPC, Prev: HPPA, Up: Architectures
21.4.5 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
`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:, Node: PowerPC, Prev: SPU, Up: Architectures
21.4.6 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:, 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:, 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:, 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:, 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
`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:, 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:, 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:, 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
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