REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1303
XCODE disassembly code of InternalSyncDecrement with today's code is:
__asm__ __volatile__ (
"movl $1, %%eax \n\t"
"lock \n\t"
"xadd %%eax, %1 \n\t"
"inc %%eax \n\t"
: "=a" (Result), // %0
"+m" (*Value) // %1
: // no inputs that aren't also outputs
: "memory",
"cc"
);
0: 55 pushl %ebp
1: 89 e5 movl %esp, %ebp
3: 8b 45 08 movl 8(%ebp), %eax
6: b8 01 00 00 00 movl $1, %eax
b: f0 lock
c: 0f c1 00 xaddl %eax, _InternalSyncIncrement(%eax)
f: 40 incl %eax
10: 5d popl %ebp
11: c3 retl
%EAX value retrieved in line #3 is overwritten in line #6.
The patch uses the clobber list to tell GCC that EAX is used in ASM.
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu...@intel.com>
Cc: Liming Gao <liming....@intel.com>
Cc: Michael Kinney <michael.d.kin...@intel.com>
Cc: Laszlo Ersek <ler...@redhat.com>
Cc: Philippe Mathieu-Daudé <phi...@redhat.com>
---
MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
b/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
index af39bdeb51..0a985529fd 100644
--- a/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
+++ b/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
@@ -40,11 +40,13 @@ InternalSyncIncrement (
"lock \n\t"
"xadd %%eax, %1 \n\t"
"inc %%eax \n\t"
- : "=a" (Result), // %0
+ "mov %%eax, %0 \n\t"
+ : "=r" (Result), // %0
"+m" (*Value) // %1
: // no inputs that aren't also outputs
: "memory",
- "cc"
+ "cc",
+ "eax"
);
return Result;
@@ -76,11 +78,13 @@ InternalSyncDecrement (
"lock \n\t"
"xadd %%eax, %1 \n\t"
"dec %%eax \n\t"
- : "=a" (Result), // %0
+ "mov %%eax, %0 \n\t"
+ : "=r" (Result), // %0
"+m" (*Value) // %1
: // no inputs that aren't also outputs
: "memory",
- "cc"
+ "cc",
+ "eax"
);
return Result;
--
2.16.1.windows.1
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