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                   README for GDBserver & GDBreplay

                    by Stu Grossman and Fred Fish

Introduction:

This is GDBserver, a remote server for Un*x-like systems.  It can be used to

control the execution of a program on a target system from a GDB on a different

host.  GDB and GDBserver communicate using the standard remote serial protocol

implemented in remote.c, and various *-stub.c files.  They communicate via

either a serial line or a TCP connection.

Usage (server (target) side):

First, you need to have a copy of the program you want to debug put onto

the target system.  The program can be stripped to save space if needed, as

GDBserver doesn't care about symbols.  All symbol handling is taken care of by

the GDB running on the host system.

To use the server, you log on to the target system, and run the `gdbserver'

program.  You must tell it (a) how to communicate with GDB, (b) the name of

your program, and (c) its arguments.  The general syntax is:

        target> gdbserver COMM PROGRAM [ARGS ...]

For example, using a serial port, you might say:

        target> gdbserver /dev/com1 emacs foo.txt

This tells gdbserver to debug emacs with an argument of foo.txt, and to

communicate with GDB via /dev/com1.  Gdbserver now waits patiently for the

host GDB to communicate with it.

To use a TCP connection, you could say:

        target> gdbserver host:2345 emacs foo.txt

This says pretty much the same thing as the last example, except that we are

going to communicate with the host GDB via TCP.  The `host:2345' argument means

that we are expecting to see a TCP connection from `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 existing TCP

ports on the target system.  This same port number must be used in the host

GDBs `target remote' command, which will be described shortly.  Note that if

you chose a port number that conflicts with another service, gdbserver will

print an error message and exit.

On some targets, gdbserver can also attach to running programs.  This is

accomplished via the --attach argument.  The syntax is:

        target> gdbserver COMM --attach 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.

Usage (host side):

You need an unstripped copy of the target program on your host system, since

GDB needs to examine it's symbol tables and such.  Start up GDB as you normally

would, with the target program as the first argument.  (You may need to use the

--baud option if the serial line is running at anything except 9600 baud.)

Ie: `gdb TARGET-PROG', or `gdb --baud BAUD TARGET-PROG'.  After that, the only

new command you need to know about is `target remote'.  It's argument is either

a device name (usually a serial device, like `/dev/ttyb'), or a HOST:PORT

descriptor.  For example:

        (gdb) target remote /dev/ttyb

communicates with the server via serial line /dev/ttyb, and:

        (gdb) target remote the-target:2345

communicates via a TCP connection to port 2345 on host `the-target', where

you previously started up gdbserver with the same port number.  Note that for

TCP connections, you must start up gdbserver prior to using the `target remote'

command, otherwise you may get an error that looks something like

`Connection refused'.

Building gdbserver:

The supported targets as of February 2002 are:

        arm-*-linux-gnu

        i386-*-linux-gnu

        ia64-*-linux-gnu

        m68k-*-linux-gnu

        mips-*-linux-gnu

        powerpc-*-linux-gnu

        sh-*-linux-gnu

Configuring gdbserver you should specify the same machine for host and

target (which are the machine that gdbserver is going to run on.  This

is not the same as the machine that gdb is going to run on; building

gdbserver automatically as part of building a whole tree of tools does

not currently work if cross-compilation is involved (we don't get the

right CC in the Makefile, to start with)).

Building gdbserver for your target is very straightforward.  If you build

GDB natively on a target which gdbserver supports, it will be built

automatically when you build GDB.  You can also build just gdbserver:

        % mkdir obj

        % cd obj

        % path-to-gdbserver-sources/configure

        % make

If you prefer to cross-compile to your target, then you can also build

gdbserver that way.  In a Bourne shell, for example:

        % export CC=your-cross-compiler

        % path-to-gdbserver-sources/configure your-target-name

        % make

Using GDBreplay:

A special hacked down version of gdbserver can be used to replay remote

debug log files created by gdb.  Before using the gdb "target" command to

initiate a remote debug session, use "set remotelogfile " to tell

gdb that you want to make a recording of the serial or tcp session.  Note

that when replaying the session, gdb communicates with gdbreplay via tcp,

regardless of whether the original session was via a serial link or tcp.

Once you are done with the remote debug session, start gdbreplay and

tell it the name of the log file and the host and port number that gdb

should connect to (typically the same as the host running gdb):

        $ gdbreplay logfile host:port

Then start gdb (preferably in a different screen or window) and use the

"target" command to connect to gdbreplay:

        (gdb) target remote host:port

Repeat the same sequence of user commands to gdb that you gave in the

original debug session.  Gdb should not be able to tell that it is talking

to gdbreplay rather than a real target, all other things being equal.  Note

that gdbreplay echos the command lines to stderr, as well as the contents of

the packets it sends and receives.  The last command echoed by gdbreplay is

the next command that needs to be typed to gdb to continue the session in

sync with the original session.