Re: [XEN PATCH][for-4.19 v5] xen: Add deviations for MISRA C:2012 Rule 7.1

[Luca Fancellu <Luca.Fancellu@xxxxxxx>]

> On 31 Oct 2023, at 15:10, Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx> wrote:
> 
> On 2023-10-31 15:13, Luca Fancellu wrote:
>>> On 31 Oct 2023, at 13:27, Julien Grall <julien@xxxxxxx> wrote:
>>> Hi Stefano,
>>> On 30/10/2023 22:49, Stefano Stabellini wrote:
>>>> On Mon, 30 Oct 2023, Julien Grall wrote:
>>>>> Hi Nicola,
>>>>> On 27/10/2023 16:11, Nicola Vetrini wrote:
>>>>>> diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
>>>>>> index 8511a189253b..8aaaa1473fb4 100644
>>>>>> --- a/docs/misra/deviations.rst
>>>>>> +++ b/docs/misra/deviations.rst
>>>>>> @@ -90,6 +90,13 @@ Deviations related to MISRA C:2012 Rules:
>>>>>>           - __emulate_2op and __emulate_2op_nobyte
>>>>>>           - read_debugreg and write_debugreg
>>>>>>  +   * - R7.1
>>>>>> +     - It is safe to use certain octal constants the way they are 
>>>>>> defined
>>>>>> +       in specifications, manuals, and algorithm descriptions. Such 
>>>>>> places
>>>>>> +       are marked safe with a /\* octal-ok \*/ in-code comment, or with 
>>>>>> a
>>>>>> SAF
>>>>>> +       comment (see safe.json).
>>>>> Reading this, it is unclear to me why we have two ways to deviate the rule
>>>>> r7.1. And more importantely, how would the developper decide which one to 
>>>>> use?
>>>> I agree with you on this and we were discussing this topic just this
>>>> morning in the FUSA community call. I think we need a way to do this
>>>> with the SAF framework:
>>>> if (some code with violation) /* SAF-xx-safe */
>>>> This doesn't work today unfortunately. It can only be done this way:
>>>> /* SAF-xx-safe */
>>>> if (some code with violation)
>>>> Which is not always desirable. octal-ok is just an ad-hoc solution for
>>>> one specific violation but we need a generic way to do this. Luca is
>>>> investigating possible ways to support the previous format in SAF.
>>> Why can't we use octal-ok everywhere for now? My point here is to make 
>>> simple for the developper to know what to use.
>>>> I think we should take this patch for now and harmonize it once SAF is
>>>> improved.
>>> The description of the deviation needs some improvement. To give an 
>>> example, with the current wording, one could they can use octal-ok 
>>> everywhere. But above, you are implying that SAF-xx-safe should be
>>> preferred.
>>> I would still strongly prefer if we use octal-ok everywhere because this is 
>>> simple to remember. But if the other are happy to have both SAF-XX and 
>>> octal-ok, then the description needs to be completely unambiguous and the 
>>> patch should contain some explanation why we have two different ways to 
>>> deviate.
>> Would it be ok to have both, for example: /* SAF-XX-safe octal-ok */
>> So that the suppression engine do what it should (currently it doesn’t 
>> suppress the same line, but we could do something about it) and the developer
>> has a way to understand what is the violation here without going to the 
>> justification database.
> 
> I guess. It could overflow the 80-char limit in xen/arch/x86/hvm/svm/svm.h, 
> though.

Yeah, but we could rule out something in code_style to allow only this kind of 
trailing comments to exceed the 80 chars

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