On 30/09/2018 00:23, Laszlo Ersek wrote:
> The CMPXCHG instruction has the following operands:
> - AX (implicit, CompareValue):input and output
> - destination operand (*Value): input and output
> - source operand (ExchangeValue): input
>
> The IA32 version of InternalSyncCompareExchange16() correctly marks
> CompareValue as input/output, but it marks (*Value) only as input.
>
> The X64 version of InternalSyncCompareExchange16() 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 constraint that can be applied
> to the input instances of I/O operands.
>
> Cc: Liming Gao
> Cc: Michael D Kinney
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1208
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Laszlo Ersek
Reviewed-by: Philippe Mathieu-Daudé
> ---
> MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c | 9 -
> MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c | 10 --
> 2 files changed, 8 insertions(+), 11 deletions(-)
>
> diff --git a/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
> b/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
> index 1976720ac636..bd98a5aebfe7 100644
> --- a/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
> +++ b/MdePkg/Library/BaseSynchronizationLib/Ia32/GccInline.c
> @@ -115,11 +115,10 @@ InternalSyncCompareExchange16 (
> {
>__asm__ __volatile__ (
> "lock \n\t"
> -"cmpxchgw%1, %2 \n\t"
> -: "=a" (CompareValue) // %0
> -: "q" (ExchangeValue), // %1
> - "m" (*Value),// %2
> - "0" (CompareValue) // %3
> +"cmpxchgw%2, %1 \n\t"
> +: "+a" (CompareValue), // %0
> + "+m" (*Value) // %1
> +: "q" (ExchangeValue) // %2
> : "memory",
>"cc"
> );
> diff --git a/MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c
> b/MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c
> index 0212798d7a27..4338fb8e65e8 100644
> --- a/MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c
> +++ b/MdePkg/Library/BaseSynchronizationLib/X64/GccInline.c
> @@ -115,12 +115,10 @@ InternalSyncCompareExchange16 (
> {
>__asm__ __volatile__ (
> "lock \n\t"
> -"cmpxchgw%3, %1 \n\t"
> -: "=a" (CompareValue), // %0
> - "=m" (*Value) // %1
> -: "a" (CompareValue), // %2
> - "r" (ExchangeValue), // %3
> - "m" (*Value) // %4
> +"cmpxchgw%2, %1 \n\t"
> +: "+a" (CompareValue), // %0
> + "+m" (*Value) // %1
> +: "r" (ExchangeValue) // %2
> : "memory",
>"cc"
> );
>
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