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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

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.

I think we should take this patch for now and harmonize it once SAF is
improved.