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

[Julien Grall <julien@xxxxxxx>]

Hi,

On 31/10/2023 15:12, Luca Fancellu wrote:
> > 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
In the past I expressed concerned with this kind of the rule because it 
is not entirely clear how an automatic formatter will be able to check it.
Can you clarify whether clang-format would be able to handle your 
proposed rule?
Cheers,

--
Julien Grall