Re: [RFC/PATCH] New convenience variable $_exitsignal

[Sergio Durigan Junior <sergiodj at redhat dot com>]

On Monday, June 17 2013, Pierre Muller wrote:

>   Hi Sergio,
>
>   Is there a reason why you don't handle
> corelow.c anymore in your new patch?

Hi Pierre,

Yes, corelow.c is not important to this patch because (as Pedro
explained on
<http://sourceware.org/ml/gdb-patches/2013-06/msg00337.html>)
$_exitsignal should not be set for corefiles, because the inferior has
not exited.

corelow.c will be touched in my next patch, which will add $_signo (but
with the modifications proposed by Pedro).

>   Also, I seem to vaguely remember that on
> linux, the signal that generated the program exit is
> finally embedded in the status...
>   See WIFEXITED and WIFSIGNALED macros in linux-nat.c
>
> For instance if I interrupt as (launched without argumrents)
> with Ctrl-C,
> The exit code (at least in bash shell) is 130.
>
>   Is this a shell feature? If not, I am not sure setting $_exitcode 
> variable to zero is the right thing to do.

To the extent of my knowledge, this is a shell feature.  It sets $? (the
variable which contains the exit code of the program) to 128 + signal
number.  However, if you use this simple C program (borrowed from
waitpid's manpage, and modified to print the exit code when the child is
killed by a signal):

    #include <sys/wait.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <stdio.h>

    int
    main(int argc, char *argv[])
    {
        pid_t cpid, w;
        int status;

        cpid = fork();
        if (cpid == -1) {
            perror("fork");
            exit(EXIT_FAILURE);
        }

        if (cpid == 0) {            /* Code executed by child */
            printf("Child PID is %ld\n", (long) getpid());
            if (argc == 1)
                pause();                    /* Wait for signals */
            _exit(atoi(argv[1]));

        } else {                    /* Code executed by parent */
            do {
                w = waitpid(cpid, &status, WUNTRACED | WCONTINUED);
                if (w == -1) {
                    perror("waitpid");
                    exit(EXIT_FAILURE);
                }

                if (WIFEXITED(status)) {
                    printf("exited, status=%d\n", WEXITSTATUS(status));
                } else if (WIFSIGNALED(status)) {
                    printf("killed by signal %d, exit=%d\n", WTERMSIG(status),
                           WEXITSTATUS(status));
                } else if (WIFSTOPPED(status)) {
                    printf("stopped by signal %d\n", WSTOPSIG(status));
                } else if (WIFCONTINUED(status)) {
                    printf("continued\n");
                }
            } while (!WIFEXITED(status) && !WIFSIGNALED(status));
            exit(EXIT_SUCCESS);
        }
    }

And run it:

    $ ./a.out 
    Child PID is 2448

Then, on another terminal:

    $ kill -USR1 2448

You'll see:

    killed by signal 10, exit=0

Thus, it makes sense to unset $_exitcode (note that I am not setting it
to zero, as you said).

>   Sorry to bother you again...

Hey, no problem, your question was actually very pertinent.

Thanks,

-- 
Sergio