How to have gdb exit if program succeeds, break if program crashes?

Question

I seem to have some kind of multithreading bug in my code that makes it crash once every 30 runs of its test suite. The test suite is non-interactive. I want to run my test suite in gdb, and have gdb exit normally if the program exits normally, or break (and show a debugging prompt) if it crashes. This way I can let the test suite run repeatedly, go grab a cup of coffee, come back, and be presented with a nice debugging prompt. How can I do this with gdb?

Answer 1

This is a little hacky but you could do:

gdb -ex='set confirm on' -ex=run -ex=quit --args ./a.out

If a.out terminates normally, it will just drop you out of GDB. But if you crash, the program will still be active, so GDB will typically prompt if you really want to quit with an active inferior:

Program received signal SIGABRT, Aborted.
0x00007ffff72dad05 in raise (sig=...) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
64  ../nptl/sysdeps/unix/sysv/linux/raise.c: No such file or directory.
    in ../nptl/sysdeps/unix/sysv/linux/raise.c
A debugging session is active.

    Inferior 1 [process 15126] will be killed.

Quit anyway? (y or n) 

Like I said, not pretty, but it works, as long as you haven't toggled off the prompt to quit with an active process. There is probably a way to use gdb's quit command too: it takes a numeric argument which is the exit code for the debugging session. So maybe you can use --eval-command="quit stuff", where stuff is some GDB expression that reflects whether the inferior is running or not.

This program can be used to test it out:

#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main() {
    if (time(NULL) % 2) {
        raise(SIGINT);
    }
    puts("no crash");
    return EXIT_SUCCESS;
}

Answer 2

The easiest way is to use the Python API offered by gdb:

 def exit_handler(event):
     gdb.execute("quit")
 
 gdb.events.exited.connect(exit_handler)

You can even do it with one line:

(gdb) python gdb.events.exited.connect(lambda x : gdb.execute("quit"))

You can also examine the return code to ensure it's the "normal" code you expected with event.exit_code.

You can use it in conjuction with --eval-command or --command as mentioned by @acm to register the event handler from the command line, or with a .gdbinit file.