Question

Is it possible to control gdb from the debugged program? I’m hoping for a library that can help with this, ideally with an API such as gdb_sendcmd("bt"), but I can live with something like connecting to local gdb via a socket.

Primary use case is programmatically adding a data breakpoint to monitor when a certain memory address next gets modified. Target language is, naturally, C; anything applicable to it can be reused with C++ and Objective-C.

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Answer from Employed Russian has solved my direct problem, but I’d still love to know how I can run GDB commands programmatically from the debugged program. It may speed up some debugging if I could simply add code to the project instead of writing extra startup commands for GDB that would create breakpoints with attached commands.

So if there is a way to run commands programmatically, I’d still love to hear it 😉

Answer 1

The Python interface exported by GDB allows you to do many things. Maybe something like this would fit your requirements:

import gdb

CMD_FCT  = "gdb_run" 
CMD_NAME = "str"

class GdbRunBreakpoint(gdb.Breakpoint):
    def __init__(self):
        gdb.Breakpoint.__init__(self, CMD_FCT, internal=1)
        self.silent = True

    def stop(self):
        cmd = gdb.parse_and_eval(CMD_NAME).string()
        gdb.execute(cmd)
        return False
GdbRunBreakpoint()

(just write than in a file, and source it from your .gdbinit file)

and on the application side:

void gdb_run(char *str) {}


int main () {
    gdb_run("where");
}

I think the code is straight forward, but as I mentioned in https://stackoverflow.com/a/8884512/341106, not everything is allowed in the stop callback, GDB is in an intermediate state, but many things will work as expected.

EDIT: needless to say, this won’t work if you app is not compiled with debug symbols!