Re: [XEN PATCH 7/7] xen/page_alloc: deviate first_valid_mfn for MISRA C Rule 8.4

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Sat, 2 Dec 2023, Julien Grall wrote:
> Hi,
> 
> On 02/12/2023 04:03, Stefano Stabellini wrote:
> > On Fri, 1 Dec 2023, Jan Beulich wrote:
> > > On 01.12.2023 03:47, Stefano Stabellini wrote:
> > > > On Wed, 29 Nov 2023, Nicola Vetrini wrote:
> > > > > No functional change.
> > > > > 
> > > > > Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
> > > > > ---
> > > > > The preferred way to deviate is to use asmlinkage, but this
> > > > > modification is only
> > > > > the consequence of NUMA on ARM (and possibly PPC) being a work in
> > > > > progress.
> > > > > As stated in the comment above the textual deviation, first_valid_mfn
> > > > > will
> > > > > likely then become static and there would be no need for the comment
> > > > > anymore.
> > > > > This works towards having the analysis for this rule clean (i.e. no
> > > > > violations);
> > > > > the interest in having a clean rule is that then it could be used to
> > > > > signal
> > > > > newly introduced violations by making the analysis job fail.
> > > > 
> > > > Please add this text as part of the commit message. It can be done on
> > > > commit.
> > > 
> > > I assume you saw my reply on another of the patches in this series as to
> > > asmlinkage use on variables? IOW I think this paragraph would also need
> > > adjustment to account for that.
> > 
> > I was going to ask you about that: reading your reply
> > https://marc.info/?l=xen-devel&m=170142048615336 it is not clear to me
> > what you are asking or suggesting as next step in regard to asmlinkage
> > use on variables.
> 
> Regardless what Jan wrote there, I think it would be an abuse to add
> asmlinkage for first_valid_mfn because it is not used by assembly code.
> 
> The same goes for the use of SAF-1-safe. This is defined as:
> 
> "Functions and variables used only by asm modules do not need to have a
> visible declaration prior to their definition."
> 
> Now, regarding the violation itself. AFAIU, this would be a violation only on
> x86 because Arm, PPC, RISC-V will all need the declaration as NUMA is not
> supported. For Arm, we may have NUMA support soon, but I doubt this will
> happen in the next couple of years for the others.
> 
> Furthermore, I am sure this is not the only exported variable/function which
> may be used by some archictectures but not others. So I think it would be
> better to declare first_valid_mfn in a common header.

That is true