1 #include <cinttypes>
2 #include <cstdint>
3 #include <cstdio>
4 #include <mutex>
5 #include <thread>
6 
7 std::mutex t1_mutex, t2_mutex;
8 
9 struct test_data {
10   uint32_t eax;
11   uint32_t ebx;
12 
13   struct alignas(16) {
14     uint8_t data[10];
15   } st0;
16 };
17 
18 constexpr test_data filler = {
19   .eax = 0xffffffff,
20   .ebx = 0xffffffff,
21   .st0 = {{0x1f, 0x2f, 0x3f, 0x4f, 0x5f, 0x6f, 0x7f, 0x8f, 0x80, 0x40}},
22 };
23 
24 void t_func(std::mutex &t_mutex) {
25   std::lock_guard<std::mutex> t_lock(t_mutex);
26   test_data out = filler;
27 
28   asm volatile(
29     "finit\t\n"
30     "fldt %2\t\n"
31     "int3\n\t"
32     "fstpt %2\t\n"
33     : "+a"(out.eax), "+b"(out.ebx)
34     : "m"(out.st0)
35     : "memory", "st"
36   );
37 
38   printf("eax = 0x%08" PRIx32 "\n", out.eax);
39   printf("ebx = 0x%08" PRIx32 "\n", out.ebx);
40   printf("st0 = { ");
41   for (int i = 0; i < sizeof(out.st0.data); ++i)
42     printf("0x%02" PRIx8 " ", out.st0.data[i]);
43   printf("}\n");
44 }
45 
46 int main() {
47   // block both threads from proceeding
48   std::unique_lock<std::mutex> m1_lock(t1_mutex);
49   std::unique_lock<std::mutex> m2_lock(t2_mutex);
50 
51   // start both threads
52   std::thread t1(t_func, std::ref(t1_mutex));
53   std::thread t2(t_func, std::ref(t2_mutex));
54 
55   // release lock on thread 1 to make it interrupt the program
56   m1_lock.unlock();
57   // wait for thread 1 to finish
58   t1.join();
59 
60   // release lock on thread 2
61   m2_lock.unlock();
62   // wait for thread 2 to finish
63   t2.join();
64 
65   return 0;
66 }
67