Re: [PATCH v2 2/3] docs/misra/rules.rst: add rule 5.5

[Jan Beulich <jbeulich@xxxxxxxx>]

On 14.02.2024 12:27, Federico Serafini wrote:
> On 14/02/24 09:28, Jan Beulich wrote:
>> On 13.02.2024 23:33, Stefano Stabellini wrote:
>>> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
>>> ---
>>>   docs/misra/rules.rst | 6 ++++++
>>>   1 file changed, 6 insertions(+)
>>>
>>> diff --git a/docs/misra/rules.rst b/docs/misra/rules.rst
>>> index c185366966..931158b354 100644
>>> --- a/docs/misra/rules.rst
>>> +++ b/docs/misra/rules.rst
>>> @@ -181,6 +181,12 @@ maintainers if you want to suggest a change.
>>>          headers (xen/include/public/) are allowed to retain longer
>>>          identifiers for backward compatibility.
>>>   
>>> +   * - `Rule 5.5 
>>> <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_05_05.c>`_
>>> +     - Required
>>> +     - Identifiers shall be distinct from macro names
>>> +     - Clashes between function-like macros and non-callable entities
>>> +       are allowed. The pattern #define x x is also allowed.
>>
>> Just for me to know what exactly is covered (hence also a question
>> to Roberto as to [to be] implemented Eclair behavior): Even when
>> the above would be sufficient (and imo better) people frequently
>> write
>>
>> #define a(x, y) b(x, y)
>>
>> which, transformed to the specific case here, would then be
>>
>> #define a(x, y) a(x, y)
>>
>> I'd assume such ought to also be covered, but that's not clear
>> from the spelling above.
> 
> I list what happens in some different situations,
> then we can find the right words for the documentation and/or
> refine the configuration:
> 
> If you
> #define x x
> and then use `x' as identifier,
> the resulting violation is deviated (allowed pattern).
> 
> If you
> #define a(x, y) a(x, y)
> and then use `a' as identifier for a non-callable entity,
> the resulting violation is deviated (no clash with non-callable
> entities).
> If you use identifier `a' for a callable entity, the resulting violation
> is reported: the allowed pattern covers only macros expanding to their
> own name, in this case the macro name is considered to be
> `a' only, not a(x, y).
> 
> If you
> #define a(x, y) b(x, y)
> and then use `a' as identifier for a non-callable entity,
> the resulting violation is deviated (no clash with non-callable
> entities).

I'm afraid I don't see what violation there is in this case, to
deviate. As a result I'm also not sure I correctly understand the
rest of your reply.

> If you use `a' as identifier for a callable entity,
> this is not a violation because after the preprocessing phase,
> identifier `a' no longer exists.
> 
> As far as I know, this is what was agreed upon in one of the recent
> MISRA meetings.

That was my fear (of being what I'd call a wrong [insufficient]
interpretation of what was meant).

Jan