MdePkg/BaseSynchronizationLib GCC: fix X64 InternalSyncCompareExchange64()

(This patch is identical to the X64 half of the last one, except for the
InternalSyncCompareExchange32() -> InternalSyncCompareExchange64() and
"cmpxchgl" -> "cmpxchgq" replacements.)

The CMPXCHG instruction has the following operands:
- AX (implicit, CompareValue):    input and output
- destination operand (*Value):   input and output
- source operand (ExchangeValue): input

The X64 version of InternalSyncCompareExchange64() attempts to mark both
CompareValue and (*Value) as input/output, but it doesn't use the
appropriate constraints for either operand.

Fix these issues. Furthermore, prefer the short "+" constraint for I/O
operands over the <output-operand-number> constraint that can be applied
to the input instances of I/O operands.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1208
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

1 files changed, 4 insertions, 6 deletions

diff --git a/MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c b/MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c
index a85cf0265c..edb904c007 100644
--- a/MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c
+++ b/MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c
@@ -194,12 +194,10 @@ InternalSyncCompareExchange64 (
 {

   __asm__ __volatile__ (

     "lock                 \n\t"

-    "cmpxchgq    %3, %1   \n\t"

-    : "=a" (CompareValue),      // %0

-      "=m" (*Value)             // %1

-    : "a"  (CompareValue),      // %2

-      "r"  (ExchangeValue),     // %3

-      "m"  (*Value)             // %4

+    "cmpxchgq    %2, %1   \n\t"

+    : "+a" (CompareValue),      // %0

+      "+m" (*Value)             // %1

+    : "r"  (ExchangeValue)      // %2

     : "memory",

       "cc"

     );