Re: [XEN PATCH][for-4.19 v2 2/2] docs/misra: add deviations.rst to document additional deviations.

[Nicola Vetrini <nicola.vetrini@bugseng.com>]

On 11/10/2023 17:00, Nicola Vetrini wrote:
>>>>>> +
>>>>>> +   * - R2.1
>>>>>> +     - The compiler implementation guarantees that the 
>>>>>> unreachable code
>>>>>> is
>>>>>> +       removed. Constant expressions and unreachable branches of 
>>>>>> if and
>>>>>> switch
>>>>>> +       statements are expected.
>>>>>> +     - Tagged as `safe` for ECLAIR.
>>>>>> +
>>>>>> +   * - R2.1
>>>>>> +     - Some functions are intended not to be referenced.
>>>>>> +     - Tagged as `deliberate` for ECLAIR.
>>>>> 
>>>>> What does it mean "some functions" in this case? Should we list 
>>>>> which
>>>>> functions?
>>>>> 
>>>> 
>>>> Well, there are a lot, typically resulting from build configurations 
>>>> that do
>>>> not
>>>> use them, or because they are used only in asm code. I can mention 
>>>> these
>>>> reasons in the
>>>> document, to make it easier to understand.
>>> 
>>> Yes, I think we need to clarify further this point, because saying 
>>> "Some
>>> functions" doesn't help the reader understand:
>>> - whether all functions can be not referenced
>>> - which subset of functions can be not referenced
>>> 
>>> How to distinguish between? How do we know whether a certain patch is
>>> violating the rule or not?
>>> 
>>> If there is a clear list of functions that can be not referenced, 
>>> then
>>> we should list them here. If there is a methodology we can use to
>>> distinguish between them (e.g. functions called from asm only) then 
>>> we
>>> can write the methodology here. Either way it is fine as long as the
>>> criteria to know if it is OK if a function is not referenced is 
>>> clear.
>> 
>> Aren't they more or less the one we tagged with SAF-1-safe because
>> there were no prototype? If so, we could use the same tags.
>> 
>> We could introduce an extra tags for the others. An alternative would
>> be to add an attribute (e.g. asmcall) to mark each function used by
>> assembly.
>> 
>> Cheers,
> 
> Both suggestion do have some value. As it is, it's not distinguishable
> what causes a
> function to be unreferenced in a certain analysis config. However:
> 
> - functions only used by asm code can be specified in the ECLAIR
> config so that they will
>   have an extra fake reference as far as the checker is concerned. I
> can do that on a
>   separate patch and list them in deviations.rst. An attribute seems a
> good way to signal the
>   intention.
> - Functions that have no reference only in the current analysis should
> have their declaration
>   #ifdef-ed out in the configurations where they are not used, in an
> ideal world.
> - Truly unreferenced functions should be removed, or justified

Especially the last two appear somewhat tricky to disentangle, as they 
do require knowledge of
possible code paths.

-- 
Nicola Vetrini, BSc
Software Engineer, BUGSENG srl (https://bugseng.com)