Re: [PATCH 1/4] x86/domain: address Misra rule 11.1 violation in reset_stack_and_call_ind()

[Nicola Vetrini <nicola.vetrini@bugseng.com>]

On 2026-09-03 13:43, Jan Beulich wrote:
> Eclair dislikes both sides of the comparison to differ in noreturn
> attributes, thus deeming this a violation of "Conversions shall not be
> performed between a pointer to a function and any other type". Since 
> gcc
> doesn't permit use of "noreturn" types used in a typecast, resort to
> typeof().
> 
> No functional change intended.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Nicola Vetrini <nicola.vetrini@bugseng.com>

> ---
> Really Eclair's diagnosis is misleading here, and not only because of 
> the
> missing "noreturn" there, making both sides be identical: There are no
> implicit conversions performed on this kind of pointer operands of an
> equality expression. A diagnosis of "comparison of pointers to 
> different
> types", along the lines of what compilers use, would be more to the 
> point.
> 

The point here is that the types are not identical, if you consider 
noreturn as part of the function type (as clang does) or not (as GCC 
does). This is the reason why we err on the side of caution and diagnose 
this, and it's not likely to change in the near future. Perhaps we could 
make the violation message more explicit about the motivation of the 
mismatch.

> --- a/xen/arch/x86/include/asm/current.h
> +++ b/xen/arch/x86/include/asm/current.h
> @@ -208,7 +208,7 @@ unsigned long get_stack_dump_bottom (uns
>  /* The constraint may only specify non-call-clobbered registers. */
>  #define reset_stack_and_call_ind(fn)                                   
>  \
>      ({                                                                 
>  \
> -        (void)((fn) == (void (*)(void))NULL);                          
>  \
> +        (void)((fn) == (typeof(dom_xen->arch.ctxt_switch->tail))NULL); 
>  \
>          switch_stack_and_jump(fn, "INDIRECT_CALL %", "b");             
>  \
>      })

-- 
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253