[PATCH] ntdll: NtCurrentTeb: Remove unnecessary use of .byte

[Keno Fischer]

The definitions of `NtCurrentTeb` make use of an inline-assembly .byte
prefix to access the `fs` and `gs` prefixes. Given that the last-modify
date for this file is 23 and 13 years ago for i386 and x86_64
respectively, I assume the reason for this use of `.byte` is that the
assemblers of the time did not understand the %fs and %gs prefixes
in textual assembly. However, this is not the case anymore and modern
assemblers understand these just fine. Further, this doesn't reduce
the set of assembler versions capable of building wine either, since
wine elsewhere uses the `xsavec` instruction, which requires a
relatively recent assembler to assemble correctly. Certainly any
assembler that can assemble `xsavec` can also assemble `%fs` and
`%gs` prefixes properly.

The reason to change this is that gcc/gas generate bad DWARF line
tables for this particular inline assembly. This causes crashes
when debugging wine under GDB and accidentally stepping into a
function that makes use of NtCurrentTeb. Arguably this is a GAS
bug and I have filed an appropriate issue [1], but we might as
well fix this in wine also to make debugging more reliable.

See also [2] where I originally reduced this from the GDB crash.

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=28699
[2] https://github.com/rr-debugger/rr/issues/3009
---
 include/winnt.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/winnt.h b/include/winnt.h
index c80efee077d..365bf2e3cd0 100644
--- a/include/winnt.h
+++ b/include/winnt.h
@@ -2142,7 +2142,7 @@ struct _TEB;
 static FORCEINLINE struct _TEB * WINAPI NtCurrentTeb(void)
 {
     struct _TEB *teb;
-    __asm__(".byte 0x64\n\tmovl (0x18),%0" : "=r" (teb));
+    __asm__("movl %%fs:0x18,%0" : "=r" (teb));
     return teb;
 }
 #elif defined(__i386__) && defined(_MSC_VER)
@@ -2157,7 +2157,7 @@ static FORCEINLINE struct _TEB * WINAPI NtCurrentTeb(void)
 static FORCEINLINE struct _TEB * WINAPI NtCurrentTeb(void)
 {
     struct _TEB *teb;
-    __asm__(".byte 0x65\n\tmovq (0x30),%0" : "=r" (teb));
+    __asm__("movq %%gs:0x30,%0" : "=r" (teb));
     return teb;
 }
 #elif defined(__x86_64__) && defined(_MSC_VER)
-- 
2.25.1