Re: x86: Disable SSE4A

[Harry Wentland]

On 2025-10-28 04:32, Christian König wrote:
> Adding AMDs DC people (the component which enables FPU in amdgpu) on CC.
> 
> On 10/28/25 05:19, Arisu Tachibana wrote:
>> On Mon, Oct 27, 2025 at 9:41 PM Borislav Petkov <bp@xxxxxxxxx> wrote:
>>>
>>> On Mon, Oct 27, 2025 at 12:40:59PM +0100, Peter Zijlstra wrote:
>>>> Leyvi Rose reported that his X86_NATIVE_CPU=y build is failing because
>>>> our instruction decoder doesn't support SSE4A and the AMDGPU code seems
>>>> to be generating those with his compiler of choice (CLANG+LTO).
>>>>
>>>> Now, our normal build flags disable SSE MMX SSE2 3DNOW AVX, but then
>>>> CC_FLAGS_FPU re-enable SSE SSE2.
>>>>
>>>> Since nothing mentions SSE3 or SSE4, I'm assuming that -msse (or its
>>>> negative) control all SSE variants -- but why then explicitly enumerate
>>>> SSE2 ?
>>>>
>>>> Anyway, until the instruction decoder gets fixed, explicitly disallow
>>>> SSE4A (an AMD specific SSE4 extension).
>>>>
>>>> Fixes: ea1dcca1de12 ("x86/kbuild/64: Add the CONFIG_X86_NATIVE_CPU option to locally optimize the kernel with '-march=native'")
>>>> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
>>>> ---
>>>>
>>>> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
>>>> index 4db7e4bf69f5..8fbff3106c56 100644
>>>> --- a/arch/x86/Makefile
>>>> +++ b/arch/x86/Makefile
>>>> @@ -75,7 +75,7 @@ export BITS
>>>>  #
>>>>  #    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383
>>>>  #
>>>> -KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx
>>>> +KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -mno-sse4a
>>>>  KBUILD_RUSTFLAGS += --target=$(objtree)/scripts/target.json
>>>>  KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2
>>>
>>> Acked-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
>>>
>>
>>  Acked-by: Arisu Tachibana <arisu.tachibana@xxxxxxxxxxxxxxxx>
> 
> Acked-by: Christian König <christian.koenig@xxxxxxx>
> 

Acked-by: Harry Wentland <harry.wentland@xxxxxxx>

Harry

>>
>>
>> --
>> thanks,
>> arisut
>