Re: [PATCH v1] misra: add deviation for rules 21.1 and 21.2

[Jan Beulich <jbeulich@xxxxxxxx>]

On 24.04.2025 23:45, Stefano Stabellini wrote:
> On Thu, 24 Apr 2025, Jan Beulich wrote:
>> On 23.04.2025 19:54, victorm.lira@xxxxxxx wrote:
>>> From: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
>>>
>>> MISRA C Rules 21.1 ("#define and #undef shall not be used on a
>>> reserved identifier or reserved macro name") and R21.2 ("A reserved
>>> identifier or reserved macro name shall not be declared") violations
>>> are not problematic for Xen, as it does not use the C or POSIX
>>> libraries.
>>>
>>> Xen uses -fno-builtin and -nostdinc to ensure this, but there are still
>>> __builtin_* functions from the compiler that are available so
>>> a deviation is formulated for all identifiers not starting with
>>> "__builtin_".
>>>
>>> The missing text of a deviation for Rule 21.2 is added to
>>> docs/misra/deviations.rst.
>>>
>>> To avoid regressions, tag both rules as clean and add them to the
>>> monitored set.
>>>
>>> Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
>>> Signed-off-by: Federico Serafini <federico.serafini@xxxxxxxxxxx>
>>> Signed-off-by: Victor Lira <victorm.lira@xxxxxxx>
>>
>> While the rule is in the library section, ...
>>
>>> --- a/docs/misra/deviations.rst
>>> +++ b/docs/misra/deviations.rst
>>> @@ -587,7 +587,31 @@ Deviations related to MISRA C:2012 Rules:
>>>         construct is deviated only in Translation Units that present a 
>>> violation
>>>         of the Rule due to uses of this macro.
>>>       - Tagged as `deliberate` for ECLAIR.
>>> -
>>> +
>>> +   * - R21.1
>>> +     - Rule 21.1 reports identifiers reserved for the C and POSIX standard
>>> +       libraries. Xen does not use such libraries and all translation units
>>> +       are compiled with option '-nostdinc', therefore there is no reason 
>>> to
>>> +       avoid to use `#define` or `#undef` on such identifiers except for 
>>> those
>>> +       beginning with `__builtin_` for which compilers may perform (wrong)
>>> +       optimizations.
>>> +     - Tagged as `safe` for ECLAIR.
>>
>> ... I'd like to ask that it be explicitly clarified here that it's solely
>> the library (and not e.g. the compiler itself) that are of concern here.
> 
> The language can be clarified:
> 
> - Rule 21.1 reports identifiers reserved for the C and POSIX standard
>   libraries. Xen does not use such libraries and all translation units
>   are compiled with option '-nostdinc', therefore there is no reason to
>   avoid to use `#define` or `#undef` on C and POSIX standard libraries
>   identifiers except for those beginning with `__builtin_` for which
>   compilers may perform (wrong) optimizations.

Which makes it more apparent that there is a gap: What about e.g. __x86_64__?
That falls within what the rules cover, is not a C or POSIX standard library
identifier, yet very clearly must not be fiddled with. Whereas the text
above deviates it.

Jan