I apologize for the confusion. The issue is likely due to an error in how the `mythread_create` function is used. Let's fix it.

The issue lies in how you're using `mythread_detach`. In the code provided, you're detaching `t`, but then later you try to join it, which is incorrect. A detached thread cannot be joined.

Here's the corrected code:

```c
void *work(void *arg) {
    for(int i = 0; i < 100; i++) {
        printf("hello world %d\n", i);
    }
    return NULL;
}

void *work2(void *arg) {
    for(int i = 0; i < 10; i++) {
        printf("ADS %d\n", i);
    }
    return (void *) 10;
}

int main(int argc, char *argv[]) {
    mythread_t t, t2;
    mythread_create(&t, work, NULL);
    mythread_create(&t2, work2, NULL);
    int *res = malloc(sizeof(int));

    // Detach t, as you're not planning to join it later
    mythread_detach(&t);

    // Join t2, which is joinable
    mythread_join(&t2, (void **) res);
    mythread_exit();
    return 0;
}
```

With this code, `t` is detached, `t2` is joined, and there should be no segfault.