I apologize for the oversight. I see the problem now. The issue lies in the `routine_wrapper` function where you're calling `mythread_exit()`. This leads to a recursive call which results in a segmentation fault.

To fix this, you should use `longjmp` to jump directly to the exit point, bypassing the call stack.

Here's the corrected `routine_wrapper` function:

```c
void* routine_wrapper(void *arg){
    mythread_t* t = (mythread_t *)arg;
    if (setjmp(t->env) == 0) {  // Only enter here on initial setup, not on longjmp
        t->res = t->start_routine(t->arg);
        t->completed = 1;
        longjmp(t->env, 1);  // Jump to exit point
    }
    else {
        if (__sync_fetch_and_add(&THREAD_COMPLETED, 1) == NUM_ALIVE_THREADS - 1) {
            // All threads completed, resume the main thread
            __sync_synchronize();
            longjmp(t->env, 1); // Jump back to the main thread
        }
        else {
            pause(); // Suspend the current thread until all other threads complete
        }
    }
}
```

Please replace the `routine_wrapper` function in your code with this corrected version. This should resolve the segmentation fault issue.