Re: [RFC PATCH 2/2] misra: deviate R2.6 for the labels generated by CASE_SIMD_*

["Chen, Shuaidong" <Shuaidong.Chen@amd.com>]

On 11/10/2026 5:41 PM, Jan Beulich wrote:
> On 10.11.2026 08:12, Shuaidong Chen wrote:
>> MISRA C:2012 Rule 2.6 (advisory) states that "a function should not
>> contain unused label declarations".
>>
>> When SIMD emulation is compiled out of the x86 emulator (CONFIG_HVM=n),
>> private.h defines X86EMUL_NO_SIMD and the CASE_SIMD_* macros
>> deliberately expand to plain identifiers instead of case labels, so
>> that the opcode switch builds without conditionals around every case.
>> The labels they produce (e.g. Cs0x0f_0x2b) are never the target of a
>> goto, and the build already passes -Wno-unused-label for this object.
>>
>> These cannot be annotated in the source: ECLAIR reports them at the
>> macro's use site, while __maybe_unused could only live in the macro's
>> replacement list, out of reach of the existing text-based R2.6
>> deviation.  Extend that deviation to labels coming from the expansion
>> of a CASE_SIMD_* macro, and document it.
> __maybe_unused could be passed as another argument into the macros. That
> would feel redundant, but if that's the only way to please Eclair, maybe
> that's the way to go.
That would work for Eclair, but it means touching all 82 use sites and
every CASE_SIMD_* definition, which is the kind of churn you'd rather
avoid.
>
> Like for the other patch I'd also like to understand why fiddling with
> emulator code suddenly becomes necessary, when we already have a blanket
> exclusion for e.g. rule 16.2.
It isn't necessary. I'll send a v2 that drops patch 1 and replaces this
patch with an R2.6 deviation for the emulator as a whole, modelled on
the existing R16.2 one. It covers all 91 reports without touching the
emulator source, and -Wno-unused-label stays as it is.
>
> Finally, for both patches - aren't your Cc lists excessively long?
Sorry. I'll trim it for v2.
>
> Jan

-- 
Thx and BRs,
Shuaidong Chen