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

[Julien Grall <julien@xxxxxxx>]

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.
Cheers,

--
Julien Grall