Re: [Xen-devel] [PATCH 10/27] x86/cpuid: Introduce named feature bitmaps

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.01.17 at 15:53, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 05/01/17 08:27, Jan Beulich wrote:
>>>>> On 04.01.17 at 18:21, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> On 04/01/17 15:44, Jan Beulich wrote:
>>>>>>> On 04.01.17 at 13:39, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>>> Use anonymous unions to access the feature leaves as complete words, and 
>>>>> by
>>>>> named individual feature.
>>>>>
>>>>> A feature name is introduced for every architectural X86_FEATURE_*, other 
>>>>> than
>>>>> the dynamically calculated values such as APIC, OSXSAVE and OSPKE.
>>>> A rationale for this change would be nice to have here, as the
>>>> redundancy with public/arch-x86/cpufeatureset.h means any
>>>> addition will now need to change two places. Would it be possible
>>>> for gen-cpuid.py to generate these bitfield declarations?
>>> Hmm.  I hadn't considered that as an option.
>>>
>>> Thinking about it however, I'd ideally prefer not to hide the
>>> declarations behind a macro.
>> What's wrong with that?
> 
> My specific dislike of hiding code from tools like grep and cscope.
> 
>> It's surely better than having to keep two pieces of code in sync manually.
> 
> True, but that doesn't come with zero cost.
> 
> Thinking about it, the spanner in the works for easily generating this
> in an automatic way is MAWAU in leaf 7, which is the first non-bit thing
> in the feature leaves.

That's a case needing something new anyway, as you can't even
express it using XEN_CPUFEATURE().

Jan


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