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

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

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@epam.com>
>>>> ---
>>>> Previous discussion thread:
>>>> https://patchew.org/Xen/181a03d5c7625d42c06cf9fa0cf48a9bc6825361.1753647875.git.dmytro._5Fprokopchuk1@epam.com/
>>> 
>>> ... 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