1 #include <cassert>
2 #include <cinttypes>
3 #include <cstdint>
4 #include <cstdio>
5 
6 struct alignas(16) float80_raw {
7   uint8_t data[10];
8 };
9 
10 int main() {
11   float80_raw st[8];
12   uint16_t env[14];
13   union alignas(16) {
14     uint16_t i16[256];
15     uint32_t i32[128];
16     uint64_t i64[64];
17   } fxsave;
18 
19   asm volatile(
20     "finit\n\t"
21     "int3\n\t"
22 #if defined(__x86_64__)
23     "fxsave64 %2\n\t"
24 #else
25     "fxsave %2\n\t"
26 #endif
27     "fnstenv %1\n\t"
28     "fnclex\n\t"
29     "fstpt 0x00(%0)\n\t"
30     "fstpt 0x10(%0)\n\t"
31     "fstpt 0x20(%0)\n\t"
32     "fstpt 0x30(%0)\n\t"
33     "fstpt 0x40(%0)\n\t"
34     "fstpt 0x50(%0)\n\t"
35     "fstpt 0x60(%0)\n\t"
36     "fstpt 0x70(%0)\n\t"
37     :
38     : "a"(st), "m"(env), "m"(fxsave)
39     : "st"
40   );
41 
42   assert(env[0] == fxsave.i16[0]);
43   assert(env[2] == fxsave.i16[1]);
44 
45   printf("fctrl = 0x%04" PRIx16 "\n", env[0]);
46   printf("fstat = 0x%04" PRIx16 "\n", env[2]);
47   printf("ftag = 0x%04" PRIx16 "\n", env[4]);
48   printf("fop = 0x%04" PRIx16 "\n", fxsave.i16[3]);
49 #if defined(__x86_64__)
50   printf("fip = 0x%016" PRIx64 "\n", fxsave.i64[1]);
51   printf("fdp = 0x%016" PRIx64 "\n", fxsave.i64[2]);
52 #else
53   printf("fip = 0x%08" PRIx32 "\n", fxsave.i32[2]);
54   printf("fcs = 0x%04" PRIx16 "\n", fxsave.i16[6]);
55   printf("fdp = 0x%08" PRIx32 "\n", fxsave.i32[4]);
56   printf("fds = 0x%04" PRIx16 "\n", fxsave.i16[10]);
57 #endif
58   printf("mxcsr = 0x%08" PRIx32 "\n", fxsave.i32[6]);
59   printf("mxcsr_mask = 0x%08" PRIx32 "\n", fxsave.i32[7]);
60 
61   for (int i = 0; i < 8; ++i) {
62     printf("st%d = { ", i);
63     for (int j = 0; j < sizeof(st->data); ++j)
64       printf("0x%02" PRIx8 " ", st[i].data[j]);
65     printf("}\n");
66   }
67 
68   return 0;
69 }
70