[lldb] [test/Register] Use initial state for write tests

[mgorny]

Summary

Reset registers to their 'initial' state instead of a semi-random
pattern in write tests. While the latter might have been helpful
while debugging failures (i.e. to distinguish unmodified registers
from mistakenly written zeroes), the former makes it possible to test
whether xstate_bv field is written correctly when using XSAVE.

With this change, the four relevant tests start failing on NetBSD
without D90105.

[labath]

I am somewhat surprised that this is sufficient. IIRC (from the time when I was fixing the same bug on linux) linux will set this bit on ANY modification of these registers, regardless of the value. OTOH, guaranteeing that the process does not touch these registers at all would be pretty tricky, so I guess this is better than nothing.

[mgorny]

Well, NetBSD passes whatever value is in the XSAVE Area, and (according to the Intel manual) XSAVE indicates whether the values match the defaults.

[labath]

In D90114#2353155, @mgorny wrote:

Well, NetBSD passes whatever value is in the XSAVE Area, and (according to the Intel manual) XSAVE indicates whether the values match the defaults.

It seems I was wrong. Disabling the relevant linux code makes your new tests pass. Thanks for figuring how how to test these.

[mgorny]

I've discovered this by accident when I was figuring why fp-write tests started failing.

lldb/test/Shell/Register/Inputs/x86-64-write.cpp

 #include <cinttypes>
 #include <cstdint>
 #include <cstdio>
 
 union alignas(16) xmm_t {
   uint64_t as_uint64[2];
   uint8_t as_uint8[16];
 };
 
 int main() {
   constexpr xmm_t xmm_fill = {
-    .as_uint64 = { 0x0F0F0F0F0F0F0F0F, 0x0F0F0F0F0F0F0F0F }
+    .as_uint64 = { 0, 0 }
   };
 
   uint64_t r64[8];
   xmm_t xmm[8];
 
   asm volatile(
     "movq    %2, %%r8\n\t"
     "movq    %2, %%r9\n\t"

lldb/test/Shell/Register/Inputs/x86-mm-xmm-write.cpp

 #include <cinttypes>
 #include <cstdint>
 #include <cstdio>
 
 union alignas(16) xmm_t {
   uint64_t as_uint64[2];
   uint8_t as_uint8[16];
 };
 
 int main() {
   constexpr xmm_t xmm_fill = {
-    .as_uint64 = { 0x0F0F0F0F0F0F0F0F, 0x0F0F0F0F0F0F0F0F }
+    .as_uint64 = { 0, 0 }
   };
 
   uint64_t mm[8];
   xmm_t xmm[8];
 
   asm volatile(
     "movq    %2, %%mm0\n\t"
     "movq    %2, %%mm1\n\t"

lldb/test/Shell/Register/Inputs/x86-ymm-write.cpp

 #include <cinttypes>
 #include <cstdint>
 #include <cstdio>
 
 union alignas(32) ymm_t {
   uint64_t as_uint64[4];
   uint8_t as_uint8[32];
 };
 
 int main() {
   constexpr ymm_t ymm_fill = {
-    .as_uint64 = { 0x0F0F0F0F0F0F0F0F, 0x0F0F0F0F0F0F0F0F,
-                   0x0F0F0F0F0F0F0F0F, 0x0F0F0F0F0F0F0F0F }
+    .as_uint64 = { 0, 0, 0, 0 }
   };
 
   ymm_t ymm[16];
 
   asm volatile(
     "vmovaps  %1, %%ymm0\n\t"
     "vmovaps  %1, %%ymm1\n\t"
     "vmovaps  %1, %%ymm2\n\t"

lldb/test/Shell/Register/Inputs/x86-zmm-write.cpp

 #include <cinttypes>
 #include <cstdint>
 #include <cstdio>
 
 union alignas(64) zmm_t {
   uint64_t as_uint64[8];
   uint8_t as_uint8[64];
 };
 
 int main() {
   constexpr zmm_t zmm_fill = {
-    .as_uint64 = { 0x0F0F0F0F0F0F0F0F, 0x0F0F0F0F0F0F0F0F,
-                   0x0F0F0F0F0F0F0F0F, 0x0F0F0F0F0F0F0F0F,
-                   0x0F0F0F0F0F0F0F0F, 0x0F0F0F0F0F0F0F0F,
-                   0x0F0F0F0F0F0F0F0F, 0x0F0F0F0F0F0F0F0F }
+    .as_uint64 = { 0, 0, 0, 0, 0, 0, 0, 0 }
   };
 
   zmm_t zmm[32];
 
   asm volatile(
     "vmovaps  %1, %%zmm0\n\t"
     "vmovaps  %1, %%zmm1\n\t"
     "vmovaps  %1, %%zmm2\n\t"