Re: [XEN PATCH 04/10] xen/public: address violations of MISRA C Rule 20.7

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

On 2024-02-29 23:49, Stefano Stabellini wrote:
> On Thu, 29 Feb 2024, Nicola Vetrini wrote:
> > On 2024-02-29 17:40, Jan Beulich wrote:
> > > On 29.02.2024 16:27, Nicola Vetrini wrote:
> > > > --- a/xen/include/public/xen.h
> > > > +++ b/xen/include/public/xen.h
> > > > @@ -988,7 +988,7 @@ typedef struct {
> > > >        ((b) >>  8) & 0xFF, ((b) >>  0) & 0xFF,                           \
> > > >        ((c) >>  8) & 0xFF, ((c) >>  0) & 0xFF,                           \
> > > >        ((d) >>  8) & 0xFF, ((d) >>  0) & 0xFF,                           \
> > > > -                e1, e2, e3, e4, e5, e6}}
> > > > +                (e1), (e2), (e3), (e4), (e5), (e6)}}
> > >
> > > Why? Wasn't it agreed already that long macro arguments passed on
> > > (no matter whether to a function, a macro, or like used here) don't
> > > need parenthesizing?
> > >
> >
> > That applies to all outermost macro invocations, but not to the 
> > innermost one.
> I don't understand what you mean. Maybe a couple of trivial examples
> would help.
>
>
> > If you want also aggregate initalizers to be deviated, that could be 
> > done
> > (provided that the macro arg is not included in some expression, such 
> > as
> > "{..., e1 + 1, ...}"
Sorry for the late reply. This is the current state:

#define N(x) somestruct var = {..., x, ...}; // <- not deviated, 
violation here
#define M(x) N(x) // <- deviated, no violation here

...

M(0xff);

The violation is resolved by {..., (x), ...} or by saying that when "x" 
is a whole expression in its fully expanded form, then we allow it not 
to be needlessly parenthesized, as Jan requested (unless I misunderstood 
his reply). In that case, the only this that would still give a 
violation in the above setting is questionable patterns such as
#define Q(x) x, x



> My gut feeling tells me that probably this is what we want but I'd
> rather first understand exactly what you meant above
--
Nicola Vetrini, BSc
Software Engineer, BUGSENG srl (https://bugseng.com)