Re: [XEN PATCH] x86/cpu-policy: justify a violation of MISRA C:2012 Rule 1.3

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

On 01/08/2023 15:40, Jan Beulich wrote:
> On 01.08.2023 15:06, Nicola Vetrini wrote:
> > The empty feature set 'str_7c1' in 'tools/misc/xen-cpuid.c' causes the
> > struct declaration to have no named members, hence violating
> > Rule 1.3:
> > "There shall be no occurrence of undefined or critical unspecified 
> > behaviour"
> > because it is forbidden by ISO/IEC 9899:1999(E), Section 6.7.2.1.7:
> > "If the struct-declaration-list contains no named
> > members, the behavior is undefined."
> >
> > It has been assessed that the feature set declaration is intentionally 
> > empty,
> > and that no risk of undesired behaviour stems from it, hence the 
> > struct
> > declaration is marked safe.
> >
> > No functional changes.
> >
> > Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
> > ---
> > As agreed during the MISRA C group meetings, this violation is dealt
> > with by means of a comment deviation, as future changes may eliminate 
> > the
> > root cause, which is the empty feature set.
> > My justification for the claim and the commit message may need some 
> > adjusting.
> A reference to the compiler extension would be nice; the use of 
> extensions
> (which generally are well-defined, even if not always well-documented)
> should eliminate the UB that the standard specifies.
It sure is a good idea to specify this. Since the use of this compiler 
extension is already
documented in 'docs/misra/C-language-toolchain.rst' I can just add a 
reference to that
in the justification.

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