Re: [PATCH] misra: deviate explicit cast for Rule 11.1

[Dmytro Prokopchuk1 <dmytro_prokopchuk1@xxxxxxxx>]

On 7/28/25 21:03, Dmytro Prokopchuk wrote:
> 
> 
> On 7/28/25 20:43, Nicola Vetrini wrote:
>> On 2025-07-28 12:49, Andrew Cooper wrote:
>>> On 28/07/2025 10:56 am, Jan Beulich wrote:
>>>> On 27.07.2025 22:27, Dmytro Prokopchuk1 wrote:
>>>>> Explicitly cast 'halt_this_cpu' when passing it
>>>>> to 'smp_call_function' to match the required
>>>>> function pointer type '(void (*)(void *info))'.
>>>>>
>>>>> Document and justify a MISRA C R11.1 deviation
>>>>> (explicit cast).
>>>>>
>>>>> Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@xxxxxxxx>
>>>> All you talk about is the rule that you violate by adding a cast. 
>>>> But what is
>>>> the problem you're actually trying to resolve by adding a cast?
>>>>
>>>>> --- a/xen/arch/arm/shutdown.c
>>>>> +++ b/xen/arch/arm/shutdown.c
>>>>> @@ -25,7 +25,8 @@ void machine_halt(void)
>>>>>      watchdog_disable();
>>>>>      console_start_sync();
>>>>>      local_irq_enable();
>>>>> -    smp_call_function(halt_this_cpu, NULL, 0);
>>>>> +    /* SAF-15-safe */
>>>>> +    smp_call_function((void (*)(void *))halt_this_cpu, NULL, 0);
>>>> Now this is the kind of cast that is very dangerous. The function's 
>>>> signature
>>>> changing will go entirely unnoticed (by the compiler) with such a 
>>>> cast in place.
>>>
>>> I agree.  This code is *far* safer in practice without the cast, than
>>> with it.
>>>
>>>> If Misra / Eclair are unhappy about such an extra (benign here) 
>>>> attribute, I'd
>>>> be interested to know what their suggestion is to deal with the 
>>>> situation
>>>> without making the code worse (as in: more risky). I first thought 
>>>> about having
>>>> a new helper function that then simply chains to halt_this_cpu(), 
>>>> yet that
>>>> would result in a function which can't return, but has no noreturn 
>>>> attribute.
>>>
>>> I guess that Eclair cannot know what an arbitrary attribute does and
>>> whether it impacts the ABI, but it would be lovely if Eclair could be
>>> told "noreturn is a safe attribute to differ on"?
>>>
>>
>> I'm convinced it can do that. Perhaps something like
>>
>> -config=MC3A2.R11.1,casts+={safe, 
>> "kind(bitcast)&&to(type(pointer(inner(return(builtin(void))&&all_param(1, 
>> pointer(builtin(void)))))))&&from(expr(skip(!syntactic(), 
>> ref(property(noreturn)))))"}
>>
>> which is a mess but decodes to that, more or less.
>>
>> I haven't tested it yet, though, but on a toy example [1] it works.
>>
>> [1]
>> void __attribute__((noreturn)) f(void *p) {
>>    __builtin_abort();
>> }
>>
>> void g(int x, void (*fp)(void *p)) {
>>    if (x < 3) {
>>      f((void*)x);
>>    }
>> }
>>
>> int main(int argc, char **argv) {
>>    g(argc, f);
>>    return 0;
>> }
>>
> Thanks, Nicola.
> I will check this.
> 
> Dmytro.
It works.
The violation "non-compliant cast: implicit cast from `void(*)(void*)' 
to `void(*)(void*)'" is gone.

Dmytro