Re: [PATCH 13/22] x86: FRED enumerations

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.08.2025 14:28, Andrew Cooper wrote:
> On 08/08/2025 9:23 pm, Andrew Cooper wrote:
>> diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
>> index a45ce106e210..90cbad13a7c7 100644
>> --- a/xen/arch/x86/Kconfig
>> +++ b/xen/arch/x86/Kconfig
>> @@ -57,6 +57,10 @@ config HAS_CC_CET_IBT
>>      # Retpoline check to work around 
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93654
>>      def_bool $(cc-option,-fcf-protection=branch -mmanual-endbr 
>> -mindirect-branch=thunk-extern) && $(as-instr,endbr64)
>>  
>> +config HAS_AS_FRED
>> +    # binutils >= 2.41 or LLVM >= 19
>> +    def_bool $(as-instr,eretu;lkgs %ax)
>> +
>>  menu "Architecture Features"
>>  
>>  source "arch/x86/Kconfig.cpu"
>> diff --git a/xen/arch/x86/include/asm/asm-defns.h 
>> b/xen/arch/x86/include/asm/asm-defns.h
>> index 61a5faf90446..2e5200b94b82 100644
>> --- a/xen/arch/x86/include/asm/asm-defns.h
>> +++ b/xen/arch/x86/include/asm/asm-defns.h
>> @@ -4,6 +4,15 @@
>>      .byte 0x0f, 0x01, 0xfc
>>  .endm
>>  
>> +#ifndef CONFIG_HAS_AS_FRED
>> +.macro eretu
>> +    .byte 0xf3, 0x0f, 0x01, 0xca
>> +.endm
>> +.macro erets
>> +    .byte 0xf2, 0x0f, 0x01, 0xca
>> +.endm
>> +#endif
> 
> Seeing as I know you are going to be unhappy with the Kconfig...

Well, we've got several, so adding one more isn't going to be the end of
the world. What we really need to do is finally settle for one method,
and then switch everything over to whatever it is going to be. I've
taken note to set up another design session on the topic in San Jose.

> I think I'm dev complete on the PV support now, and there's not an LKGS
> in sight.
> 
> We don't strictly need the conditional in asm-defns.h, and if we don't
> need it in C either then we can drop the Kconfig entirely.

Yeah, might be best for now.

Jan