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

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

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