Re: [XEN PATCH v2] x86: p2m-pod: address violation of MISRA C Rule 2.1

[Jan Beulich <jbeulich@xxxxxxxx>]

On 10.09.2024 12:17, Nicola Vetrini wrote:
> On 2024-09-10 12:03, Jan Beulich wrote:
>> On 10.09.2024 11:53, Nicola Vetrini wrote:
>>> On 2024-09-10 11:08, Jan Beulich wrote:
>>>> On 10.09.2024 10:56, Nicola Vetrini wrote:
>>>>> On 2024-07-01 10:36, Jan Beulich wrote:
>>>>>> On 28.06.2024 08:30, Nicola Vetrini wrote:
>>>>>> This being about unreachable code, why are the domain_crash() not 
>>>>>> the
>>>>>> crucial points of "unreachability"? And even if they weren't there,
>>>>>> why
>>>>>> wouldn't it be the goto or ...
>>>>>>
>>>>>>> --- a/xen/arch/x86/mm/p2m-pod.c
>>>>>>> +++ b/xen/arch/x86/mm/p2m-pod.c
>>>>>>> @@ -1040,6 +1040,7 @@ out_unmap:
>>>>>>>       * Something went wrong, probably crashing the domain.  Unmap
>>>>>>>       * everything and return.
>>>>>>>       */
>>>>>>> +    /* SAF-8-safe Rule 2.1: defensive programming */
>>>>>>>      for ( i = 0; i < count; i++ )
>>>>>>>          if ( map[i] )
>>>>>>>              unmap_domain_page(map[i]);
>>>>>>
>>>>>> ... the label (just out of context) where the comment needs to go?
>>>>>
>>>>> Because of the way this rule's configuration work, deviations are
>>>>> placed
>>>>> on the construct that ends up being the target of the 
>>>>> unreachability,
>>>>
>>>> What's "target" here? What if this loop was removed from the 
>>>> function?
>>>> Then both the label and the domain_crash() invocations would still be
>>>> unreachable in debug builds. Are you telling me that this then 
>>>> wouldn't
>>>> be diagnosed by Eclair? Or that it would then consider the closing
>>>> figure brace of the function "the target of the unreachability"?
>>>
>>> Exactly, the end brace is a target to which the "function end" 
>>> construct
>>> is associated.
>>> It would be kind of strange, though: why not just doing 
>>> "domain_crash();
>>> return;" in that case?
>>
>> Sure, the question was theoretical. Now if "return" was used directly
>> there, what would then be the "target"? IOW - the more abstract 
>> question
>> of my earlier reply still wasn't answered.
>>
> 
> The return statement in
> 
> ...
> domain_crash();
> return;
> <~~~~~>
> 
> Whichever statement is found to be unreachable in the current 
> preprocessed code.

Yet then again: Why is it the return statement and not the function call
one (really, it being a macro invocation: the do/while one that the macro
expands to)? That's the first thing that won't be reached.

Jan