Function mutex_gettid

examples/stdlib.c:1479–1487

#ifndef MUTEX_SAFE

static pid_t mutex_gettid(void)
{
    // Warning: this assumes the thread ID is stored at %fs:0x2d0.
    pid_t tid;
    asm volatile (
        "mov %%fs:0x2d0,%0\n" : "=a"(tid)
    );
    return tid;
}

static void mutex_settid(pid_t tid)
{