Re: [XEN PATCH][for-4.19 v2 2/2] docs/misra: add deviations.rst to document additional deviations.

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

> > > > > +
> > > > > +   * - R2.1
> > > > > +     - The compiler implementation guarantees that the unreachable 
> > > > > code
> > > > > is
> > > > > +       removed. Constant expressions and unreachable branches of 
> > > > > if and
> > > > > switch
> > > > > +       statements are expected.
> > > > > +     - Tagged as `safe` for ECLAIR.
> > > > > +
> > > > > +   * - R2.1
> > > > > +     - Some functions are intended not to be referenced.
> > > > > +     - Tagged as `deliberate` for ECLAIR.
> > > > What does it mean "some functions" in this case? Should we list 
> > > > which
> > > > functions?
> > > Well, there are a lot, typically resulting from build configurations 
> > > that do
> > > not
> > > use them, or because they are used only in asm code. I can mention 
> > > these
> > > reasons in the
> > > document, to make it easier to understand.
> > Yes, I think we need to clarify further this point, because saying 
> > "Some
> > functions" doesn't help the reader understand:
> > - whether all functions can be not referenced
> > - which subset of functions can be not referenced
> >
> > How to distinguish between? How do we know whether a certain patch is
> > violating the rule or not?
> >
> > If there is a clear list of functions that can be not referenced, then
> > we should list them here. If there is a methodology we can use to
> > distinguish between them (e.g. functions called from asm only) then we
> > can write the methodology here. Either way it is fine as long as the
> > criteria to know if it is OK if a function is not referenced is clear.
> Aren't they more or less the one we tagged with SAF-1-safe because
> there were no prototype? If so, we could use the same tags.
>
> We could introduce an extra tags for the others. An alternative would
> be to add an attribute (e.g. asmcall) to mark each function used by
> assembly.
>
> Cheers,
Both suggestion do have some value. As it is, it's not distinguishable 
what causes a
function to be unreferenced in a certain analysis config. However:

- functions only used by asm code can be specified in the ECLAIR config 
so that they will
  have an extra fake reference as far as the checker is concerned. I can 
do that on a
  separate patch and list them in deviations.rst. An attribute seems a 
good way to signal the
  intention.
- Functions that have no reference only in the current analysis should 
have their declaration
  #ifdef-ed out in the configurations where they are not used, in an 
ideal world.
- Truly unreferenced functions should be removed, or justified

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