Re: [XEN PATCH][for-next][for-4.19 v2 1/8] xen/include: add macro LOWEST_BIT

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.10.2023 12:40, Nicola Vetrini wrote:
> On 20/10/2023 08:00, Jan Beulich wrote:
>> On 19.10.2023 21:58, Stefano Stabellini wrote:
>>>>>>>> --- a/xen/include/xen/macros.h
>>>>>>>> +++ b/xen/include/xen/macros.h
>>>>>>>> @@ -8,8 +8,10 @@
>>>>>>>>  #define DIV_ROUND(n, d) (((n) + (d) / 2) / (d))
>>>>>>>>  #define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
>>>>>>>>
>>>>>>>> -#define MASK_EXTR(v, m) (((v) & (m)) / ((m) & -(m)))
>>>>>>>> -#define MASK_INSR(v, m) (((v) * ((m) & -(m))) & (m))
>>>>>>>
>>>>>>> a SAF-<n>-safe comment here?
>>>>>>>
>>>>>>
>>>>>> One reason is that now that violations only belonging to tool
>>>>>> configurations
>>>>>> and similar are documented in docs/misra/deviations.rst (committed 
>>>>>> in
>>>>>> Stefano's
>>>>>> branch for-4.19 [1]).
>>>>>
>>>>> But tool configuration means every analysis tool needs configuring
>>>>> separately. That's why the comment tagging scheme was decided to be
>>>>> preferred, iirc.
>>>>>
>>>>>> Also, there were disagreements on the SAF naming
>>>>>> scheme, and
>>>>>> patches like those would not be accepted at the moment.
>>>>>
>>>>> Well, that needs resolving. The naming there shouldn't lead to 
>>>>> patches
>>>>> being accepted that later may need redoing.
>>>>>
>>>>> Jan
>>>>
>>>> While this is true, in this case I'm not willing to deviate with a 
>>>> SAF, given
>>>> that
>>>> some ECLAIR-specific configuration would be needed anyways, given 
>>>> that I'm
>>>> deviating a macro definition, rather than the line where it's 
>>>> actually used
>>>> (and maybe other tools would need
>>>> that as well).
>>>
>>> Did I get it right that the problem with using SAF in this case is 
>>> that
>>> it wouldn't be sufficient to add a SAF comment on top of the MACRO
>>> definition, but we would need a SAF comment on top of every MACRO
>>> invocation?
>>>
>>> If so, then not just for this MACRO but in general basically we have 
>>> to
>>> use deviations.rst.
>>
>> That would be pretty sad.
> 
> Local deviation comments are for local deviations; deviating patterns is 
> a tool configuration.

That's orthogonal. A deviating comment on a macro definition, when it is
about an aspect that's meaningful only after the macro is expanded (i.e.
not violating some rule concerning macro definitions only), would be
quite helpful to limit the number of such comments that need sprinkling
across the code base.

Jan