[PATCH v2] ntdll/tests: Do not write to fs, gs when testing cleared segment regs on x64.

[Paul Gofman]

Fixes the crash in test.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=51152
Signed-off-by: Paul Gofman 
---
v2:
    - fix comment.

dlls/ntdll/tests/exception.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/dlls/ntdll/tests/exception.c b/dlls/ntdll/tests/exception.c
index 328882c1a23..2b18853a72d 100644
--- a/dlls/ntdll/tests/exception.c
+++ b/dlls/ntdll/tests/exception.c
@@ -2908,13 +2908,30 @@ static const struct exception
         0x31, 0xc0, /* xor %eax,%eax */
         0x8e, 0xc0, /* mov %eax,%es */
         0x8e, 0xd8, /* mov %eax,%ds */
+#if 1
+        /* It is observed that fs/gs base is reset
+           on some CPUs on Linux when setting the
+           segment value even to 0 (regardless of CPU spec
+           saying otherwise) and it is not currently
+           handled in Wine.
+           Disable this part to avoid crashing the test. */
         0x8e, 0xe0, /* mov %eax,%fs */
         0x8e, 0xe8, /* mov %eax,%gs */
+#else
+        0x90, 0x90, /* nop */
+        0x90, 0x90, /* nop */
+#endif
         0xfa,       /* cli */
         0x58,       /* pop %rax */
+#if 1
         0x8e, 0xe8, /* mov %eax,%gs */
         0x58,       /* pop %rax */
         0x8e, 0xe0, /* mov %eax,%fs */
+#else
+        0x58,       /* pop %rax */
+        0x90, 0x90, /* nop */
+        0x90, 0x90, /* nop */
+#endif
         0x58,       /* pop %rax */
         0x8e, 0xd8, /* mov %eax,%ds */
         0x58,       /* pop %rax */