gdb.info: Server

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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.
_On the target machine,_
     you need to have a copy of the program you want to debug.
     `gdbserver' does not need your program's symbol table, so you can
     strip the program if necessary to save space.  GDB on the host
     system does all the symbol handling.
     To use the server, you must tell it how to communicate with GDB;
     the name of your program; and the arguments for your program.  The
     usual syntax is:
          target> gdbserver COMM PROGRAM [ ARGS ... ]
     COMM is either a device name (to use a serial line) or a TCP
     hostname and portnumber.  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.
     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.
     You can debug processes by name instead of process ID if your
     target has the `pidof' utility:
          target> gdbserver COMM --attach `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.
_On the host machine,_
     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'.  You don't need to use
     the `load' command in GDB when using gdbserver, since the program
     is already on the target.

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

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