Re: [PATCH] cpumask: fix integer type in cpumask_first

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 29 Sep 2023, Luca Fancellu wrote:
> > On 29 Sep 2023, at 08:31, Julien Grall <julien@xxxxxxx> wrote:
> > 
> > Hi Stefano,
> > 
> > On 29/09/2023 00:32, Stefano Stabellini wrote:
> >> nr_cpu_ids is unsigned int, but find_first_bit returns unsigned long (at
> >> least on arm).
> > 
> > find_* are meant to be used by common code. So I think the first step is to 
> > correct the return type so it is consistent across all architectures.
> > 
> > I don't have a strong opinion on whether they should all return 'unsigned 
> > long'.
> > 
> > Then we can discuss if the MISRA rule is still violated.
> > 
> >> Use the larger type for min_t to avoid larger-to-smaller
> >> type assignments. This address 141 MISRA C 10.3 violations.
> > 
> > I find interesting you are saying this given that...
> >> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
> >> ---
> >> diff --git a/xen/include/xen/cpumask.h b/xen/include/xen/cpumask.h
> >> index 9826707909..a6ed6a28e8 100644
> >> --- a/xen/include/xen/cpumask.h
> >> +++ b/xen/include/xen/cpumask.h
> >> @@ -208,7 +208,7 @@ static inline void cpumask_copy(cpumask_t *dstp, const 
> >> cpumask_t *srcp)
> >>    static inline int cpumask_first(const cpumask_t *srcp)
> >>  {
> >> - return min_t(int, nr_cpu_ids, find_first_bit(srcp->bits, nr_cpu_ids));
> >> + return min_t(unsigned long, nr_cpu_ids, find_first_bit(srcp->bits, 
> >> nr_cpu_ids));
> > 
> > ... cpumask_first() is return 'int'. So rather than fixing it, you seem to 
> > have just moved the violation.
> > 
> >>  }
> >>    static inline int cpumask_next(int n, const cpumask_t *srcp)
> 
> I’ve also found that find_first_bit returns:
> 
>  - unsigned int on x86
>  - unsigned long on ppc
>  - unsigned long on arm64
>  - int on arm32 (seems that value is always >= 0
> 
> So maybe they can be all unsigned int, and cpumask_first can be as well 
> unsigned int?

I am OK with that. Julien, Shawn do you agree? If so, I can make the
change to find_first_bit so that it returns unsigned int on all arches.