Re: [XEN PATCH][for-next][for-4.19 v2 1/8] xen/include: add macro LOWEST_BIT

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

On 16/10/2023 17:33, Jan Beulich wrote:
> On 12.10.2023 17:28, Nicola Vetrini wrote:
> > --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> > +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> > @@ -274,6 +274,12 @@ still non-negative."
> >  -config=MC3R1.R10.1,etypes+={safe, 
> > "stmt(operator(logical)||node(conditional_operator||binary_conditional_operator))", 
> > "dst_type(ebool||boolean)"}
> >  -doc_end
> >
> > +-doc_begin="The macro LOWEST_BIT encapsulates a well-known pattern to 
> > obtain the value
> > +2^ffs(x) for unsigned integers on two's complement architectures
> > +(all the architectures supported by Xen satisfy this requirement)."
> > +-config=MC3R1.R10.1,reports+={safe, 
> > "any_area(any_loc(any_exp(macro(^LOWEST_BIT$))))"}
> > +-doc_end
> Why is this added here rather than by ...
>
> > --- a/xen/include/xen/macros.h
> > +++ b/xen/include/xen/macros.h
> > @@ -8,8 +8,10 @@
> >  #define DIV_ROUND(n, d) (((n) + (d) / 2) / (d))
> >  #define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
> >
> > -#define MASK_EXTR(v, m) (((v) & (m)) / ((m) & -(m)))
> > -#define MASK_INSR(v, m) (((v) * ((m) & -(m))) & (m))
> a SAF-<n>-safe comment here?
One reason is that now that violations only belonging to tool 
configurations
and similar are documented in docs/misra/deviations.rst (committed in 
Stefano's
branch for-4.19 [1]). Also, there were disagreements on the SAF naming 
scheme, and
patches like those would not be accepted at the moment.

> > +#define LOWEST_BIT(x) ((x) & -(x))
> Personally I consider the name misleading: I'd expect a macro of this
> name to return a bit number, not a mask with a single bit set. No
> good, reasonably short name comes to mind - ISOLATE_LOW_BIT() is too
> long for my taste.
>
> Jan
[1] 
https://gitlab.com/xen-project/people/sstabellini/xen/-/commits/for-4.19
--
Nicola Vetrini, BSc
Software Engineer, BUGSENG srl (https://bugseng.com)