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VGDB

Section: Release 3.12.0 (1)
Updated: 10/21/2016
Index Return to Main Contents

NAME

vgdb - intermediary between Valgrind and GDB or a shell

SYNOPSIS

vgdb [options]

DESCRIPTION

vgdb ("Valgrind to GDB") is used as an intermediary between Valgrind and GDB or a shell. It has two usage modes:

: 1.; As a standalone utility, it is used from a shell command line to send monitor commands to a process running under Valgrind. For this usage, the vgdb OPTION(s) must be followed by the monitor command to send. To send more than one command, separate them with the -c option.

: 2. In combination with GDB "target remote |" command, it is used as the relay application between GDB and the Valgrind gdbserver. For this usage, only OPTION(s) can be given, but no COMMAND can be given.

OPTIONS

--pid=<number>

: Specifies the PID of the process to which vgdb must connect to. This option is useful in case more than one Valgrind gdbserver can be connected to. If the --pid argument is not given and multiple Valgrind gdbserver processes are running, vgdb will report the list of such processes and then exit.

--vgdb-prefix

: Must be given to both Valgrind and vgdb if you want to change the default prefix for the FIFOs (named pipes) used for communication between the Valgrind gdbserver and vgdb.

--wait=<number>

: Instructs vgdb to search for available Valgrind gdbservers for the specified number of seconds. This makes it possible start a vgdb process before starting the Valgrind gdbserver with which you intend the vgdb to communicate. This option is useful when used in conjunction with a --vgdb-prefix that is unique to the process you want to wait for. Also, if you use the --wait argument in the GDB "target remote" command, you must set the GDB remotetimeout to a value bigger than the --wait argument value. See option --max-invoke-ms (just below) for an example of setting the remotetimeout value.

--max-invoke-ms=<number>

Gives the number of milliseconds after which vgdb will force the invocation of gdbserver embedded in Valgrind. The default value is 100 milliseconds. A value of 0 disables forced invocation. The forced invocation is used when vgdb is connected to a Valgrind gdbserver, and the Valgrind process has all its threads blocked in a system call.

If you specify a large value, you might need to increase the GDB "remotetimeout" value from its default value of 2 seconds. You should ensure that the timeout (in seconds) is bigger than the --max-invoke-ms value. For example, for --max-invoke-ms=5000, the following GDB command is suitable:

    (gdb) set remotetimeout 6

--cmd-time-out=<number>

: Instructs a standalone vgdb to exit if the Valgrind gdbserver it is connected to does not process a command in the specified number of seconds. The default value is to never time out.

--port=<portnr>

Instructs vgdb to use tcp/ip and listen for GDB on the specified port nr rather than to use a pipe to communicate with GDB. Using tcp/ip allows to have GDB running on one computer and debugging a Valgrind process running on another target computer. Example:

# On the target computer, start your program under valgrind using
valgrind --vgdb-error=0 prog
# and then in another shell, run:
vgdb --port=1234

On the computer which hosts GDB, execute the command:

gdb prog
(gdb) target remote targetip:1234

where targetip is the ip address or hostname of the target computer.

-c

To give more than one command to a standalone vgdb, separate the commands by an option -c. Example:

vgdb v.set log_output -c leak_check any

-l

: Instructs a standalone vgdb to report the list of the Valgrind gdbserver processes running and then exit.

-D

: Instructs a standalone vgdb to show the state of the shared memory used by the Valgrind gdbserver. vgdb will exit after having shown the Valgrind gdbserver shared memory state.

-d

: Instructs vgdb to produce debugging output. Give multiple -d args to increase the verbosity. When giving -d to a relay vgdb, you better redirect the standard error (stderr) of vgdb to a file to avoid interaction between GDB and vgdb debugging output.