SystemExit#success?

static VALUE
exit_success_p(VALUE exc)
{
    VALUE status_val = rb_attr_get(exc, id_status);
    int status;

    if (NIL_P(status_val))
        return Qtrue;
    status = NUM2INT(status_val);
    return RBOOL(WIFEXITED(status) && WEXITSTATUS(status) == EXIT_SUCCESS);
}