132 lines
5.4 KiB
Text
132 lines
5.4 KiB
Text
README for GDBserver & GDBreplay
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by Stu Grossman and Fred Fish
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Introduction:
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This is GDBserver, a remote server for Un*x-like systems. It can be used to
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control the execution of a program on a target system from a GDB on a different
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host. GDB and GDBserver communicate using the standard remote serial protocol.
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They communicate via either a serial line or a TCP connection.
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For more information about GDBserver, see the GDB manual:
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https://sourceware.org/gdb/current/onlinedocs/gdb/Remote-Protocol.html
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Usage (server (target) side):
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First, you need to have a copy of the program you want to debug put onto
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the target system. The program can be stripped to save space if needed, as
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GDBserver doesn't care about symbols. All symbol handling is taken care of by
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the GDB running on the host system.
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To use the server, you log on to the target system, and run the `gdbserver'
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program. You must tell it (a) how to communicate with GDB, (b) the name of
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your program, and (c) its arguments. The general syntax is:
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target> gdbserver COMM PROGRAM [ARGS ...]
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For example, using a serial port, you might say:
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target> gdbserver /dev/com1 emacs foo.txt
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This tells GDBserver to debug emacs with an argument of foo.txt, and to
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communicate with GDB via /dev/com1. GDBserver now waits patiently for the
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host GDB to communicate with it.
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To use a TCP connection, you could say:
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target> gdbserver host:2345 emacs foo.txt
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This says pretty much the same thing as the last example, except that we are
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going to communicate with the host GDB via TCP. The `host:2345' argument means
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that we are expecting to see a TCP connection to local TCP port 2345.
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(Currently, the `host' part is ignored.) You can choose any number you want for
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the port number as long as it does not conflict with any existing TCP ports on
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the target system. This same port number must be used in the host GDB's
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`target remote' command, which will be described shortly. Note that if you chose
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a port number that conflicts with another service, GDBserver will print an error
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message and exit.
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On some targets, GDBserver can also attach to running programs. This is
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accomplished via the --attach argument. The syntax is:
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target> gdbserver --attach COMM PID
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PID is the process ID of a currently running process. It isn't necessary
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to point GDBserver at a binary for the running process.
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Usage (host side):
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You need an unstripped copy of the target program on your host system, since
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GDB needs to examine it's symbol tables and such. Start up GDB as you normally
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would, with the target program as the first argument. (You may need to use the
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--baud option if the serial line is running at anything except 9600 baud.)
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Ie: `gdb TARGET-PROG', or `gdb --baud BAUD TARGET-PROG'. After that, the only
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new command you need to know about is `target remote'. It's argument is either
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a device name (usually a serial device, like `/dev/ttyb'), or a HOST:PORT
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descriptor. For example:
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(gdb) target remote /dev/ttyb
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communicates with the server via serial line /dev/ttyb, and:
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(gdb) target remote the-target:2345
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communicates via a TCP connection to port 2345 on host `the-target', where
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you previously started up GDBserver with the same port number. Note that for
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TCP connections, you must start up GDBserver prior to using the `target remote'
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command, otherwise you may get an error that looks something like
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`Connection refused'.
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Building GDBserver:
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See the `configure.srv` file for the list of host triplets you can build
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GDBserver for.
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Building GDBserver for your host is very straightforward. If you build
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GDB natively on a host which GDBserver supports, it will be built
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automatically when you build GDB. You can also build just GDBserver:
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% mkdir obj
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% cd obj
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% path-to-toplevel-sources/configure --disable-gdb
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% make all-gdbserver
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(If you have a combined binutils+gdb tree, you may want to also
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disable other directories when configuring, e.g., binutils, gas, gold,
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gprof, and ld.)
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If you prefer to cross-compile to your target, then you can also build
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GDBserver that way. For example:
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% export CC=your-cross-compiler
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% path-to-topevel-sources/configure --disable-gdb
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% make all-gdbserver
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Using GDBreplay:
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A special hacked down version of GDBserver can be used to replay remote
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debug log files created by GDB. Before using the GDB "target" command to
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initiate a remote debug session, use "set remotelogfile <filename>" to tell
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GDB that you want to make a recording of the serial or tcp session. Note
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that when replaying the session, GDB communicates with GDBreplay via tcp,
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regardless of whether the original session was via a serial link or tcp.
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Once you are done with the remote debug session, start GDBreplay and
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tell it the name of the log file and the host and port number that GDB
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should connect to (typically the same as the host running GDB):
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$ gdbreplay logfile host:port
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Then start GDB (preferably in a different screen or window) and use the
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"target" command to connect to GDBreplay:
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(gdb) target remote host:port
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Repeat the same sequence of user commands to GDB that you gave in the
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original debug session. GDB should not be able to tell that it is talking
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to GDBreplay rather than a real target, all other things being equal. Note
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that GDBreplay echos the command lines to stderr, as well as the contents of
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the packets it sends and receives. The last command echoed by GDBreplay is
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the next command that needs to be typed to GDB to continue the session in
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sync with the original session.
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