pid_t sys_exec(const char *cmd_line) {
    pid_t child_pid = process_execute(cmd_line);
    if (child_pid != TID_ERROR) {
        sema_down(&thread_current()->child_semaphore);
        bool load_success = thread_current()->child_load_success;
        thread_current()->child_load_success = false;
        if (!load_success)
            return -1;
        else
            insert_into_children(child_pid);
    }
    return child_pid;
}