Re: [PATCH] misra/eclair: set 'noreturn' attribute as safe during cast

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

On 2025-07-29 12:52, Jan Beulich wrote:
> On 29.07.2025 12:04, Dmytro Prokopchuk1 wrote:
> > On 7/29/25 11:04, Jan Beulich wrote:
> > > On 29.07.2025 00:15, Dmytro Prokopchuk1 wrote:
> > > > ECLAIR reports a non-compliant cast due to the presence
> > > > of the 'noreturn' attribute in the callee function.
> > > Which callee function? Which cast? Please be concrete. You don't need
> > > to enumerate all case, but one specific example wants pointing at.
> > >
> > > > The issue occurs when casting a function pointer with
> > > > the 'noreturn' attribute (void noreturn (*)(void *))
> > > > to a general function pointer type (void (*)(void *)).
> > > And again - why "casting"? As per ...
> > >
> > > > Configure ECLAIR to treat 'noreturn' attributes as safe
> > > > in this conversion.
> > > >
> > > > Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@xxxxxxxx>
> > > > ---
> > > > Previous discussion thread:
> > > > https://patchew.org/Xen/181a03d5c7625d42c06cf9fa0cf48a9bc6825361.1753647875.git.dmytro._5Fprokopchuk1@xxxxxxxx/
> > > ... there was no cast involved, iirc. We specifically rejected your
> > > attempt to add a cast there. It's a conversion the compiler does, 
> > > aiui.
> > Yes, you are right.
> > Word "cast" is not appropriate there.
> >
> > Below is updated text:
> >
> >      misra: allow 'noreturn' as safe for function pointer conversions
> >
> >      The conversion from a function pointer with the
> >      'noreturn' attribute ('void noreturn (*)(void *)')
> >      to a function pointer type ('void (*)(void *)'
> >      causes type incompatibility according to
> >      MISRA C Rule 11.1, which forbids conversions
> >      between incompatible function pointer types.
> >
> >      The violation occurs at the call site
> >          smp_call_function(halt_this_cpu, NULL, 0);
> >      where 'halt_this_cpu' with type 'void noreturn (*)(void *)'
> >      is passed to 'smp_call_function' expecting a function
> >      pointer of type 'void (*)(void *)'.
> >
> >      The 'noreturn' attribute does not change the function
> >      calling convention or parameter handling at runtime,
> >      making the conversion safe.
> Up to here things read much better now, thanks. Just one more request:
> Please make better use of the 72 (or maybe even 75) characters that are
> permitted per line.
>
> >      Configure ECLAIR to treat 'noreturn' attributes as safe.
Configure ECLAIR to treat implicit casts that lose the "noreturn" 
attribute on a function void (*fp)(void*) as safe. This is because the 
deviation actually just deviates void noreturn (*fp)(void*) -> void 
(*fp)(void*)
> This one is still way to imprecise, though. And I hope it's only this
> description, not also the Eclair configuration item that's overly lax.
>
> Jan
--
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253