gistfile1.txt

void* sync_fetch_and_set_ptr(void* volatile* target, void* new_value)
{
    void* previous_value;
    int retry;
    __asm__ volatile(
        "1: ldrex %0, [%1];"
        "   strex %3, %2, [%1];"
        "   teq   %3, #0;"
        "   bne   1b;"
        :"=r"(previous_value)
        :"+r"(target), "r"(new_value), "=&r"(retry)
        :"cc", "memory"
    );
    return previous_value;
}