Hi,
On 09/25/18 21:48, Laszlo Ersek wrote:
> Currently, "gcc-4.8.5-28.el7_5.1.x86_64" generates the following code for
> me, from the XADD inline assembly added to "X64/GccInline.c" in commit
> 17634d026f96:
>
>> 0000000000004383 <InternalSyncIncrement>:
>> UINT32
>> EFIAPI
>> InternalSyncIncrement (
>> IN volatile UINT32 *Value
>> )
>> {
>> 4383: 55 push %rbp
>> 4384: 48 89 e5 mov %rsp,%rbp
>> 4387: 48 83 ec 10 sub $0x10,%rsp
>> 438b: 48 89 4d 10 mov %rcx,0x10(%rbp)
>> UINT32 Result;
>>
>> __asm__ __volatile__ (
>> 438f: 48 8b 55 10 mov 0x10(%rbp),%rdx
>> 4393: 48 8b 45 10 mov 0x10(%rbp),%rax
>> 4397: b8 01 00 00 00 mov $0x1,%eax
>> 439c: f0 0f c1 00 lock xadd %eax,(%rax)
>> 43a0: ff c0 inc %eax
>> 43a2: 89 45 fc mov %eax,-0x4(%rbp)
>> : "m" (*Value) // %2
>> : "memory",
>> "cc"
>> );
>>
>> return Result;
>> 43a5: 8b 45 fc mov -0x4(%rbp),%eax
>> }
>> 43a8: c9 leaveq
>> 43a9: c3 retq
>>
>
> The MOV $0X1,%EAX instruction corrupts the address of Value in %RAX before
> we reach the XADD instruction. In fact, it makes no sense for XADD to use
> %EAX as source operand and (%RAX) as destination operand at the same time.
may I get a fast review for this patch, please? The regression from
commit 17634d026f96 prevents OVMF from booting.
Thanks
Laszlo
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