Re: [PATCH v3] misra: consider conversion from UL or (void*) to function pointer as safe

[Dmytro Prokopchuk1 <dmytro_prokopchuk1@xxxxxxxx>]

On 10/17/25 10:09, Nicola Vetrini wrote:
> On 2025-10-15 08:20, Jan Beulich wrote:
>> On 14.10.2025 18:16, Dmytro Prokopchuk1 wrote:
>>> --- a/xen/common/version.c
>>> +++ b/xen/common/version.c
>>> @@ -217,6 +217,20 @@ void __init xen_build_init(void)
>>>  #endif /* CONFIG_X86 */
>>>  }
>>>  #endif /* BUILD_ID */
>>> +
>>> +#if defined(__i386__) || defined(__x86_64__) || defined(__arm__) || 
>>> defined(__aarch64__)
>>
>> Why __i386__? Also (nit): Line too long.

Well, I copied this line from Xen codebase,
but yeah, __i386__ is outdated now.
I'll remove it.

>>
>> And why this restriction without any comment here or ...
>>
>>> +static void __init __maybe_unused build_assertions(void)
>>> +{
>>> +    /*
>>> +     * To confirm conversion compatibility between unsigned long, 
>>> (void *)
>>> +     * and function pointers for X86 and ARM architectures only.
>>
>> ... explanation here? More generally - how would people know to update
>> the condition if another port was to be certified?
>>
>> Finally, with the v3 addition here, is Nicola's R-b really still 
>> applicable?
>>
> 
> I agree with the point you make about i386 (e.g., C-language- 
> toolchain.rst may be mentioned to provide some context about the 
> preprocessor guard); that said, my R-by can be retained
> 
>> Jan
>>
>>> +     */
>>> +
>>> +    BUILD_BUG_ON(sizeof(unsigned long) != sizeof(void (*)(void)));
>>> +    BUILD_BUG_ON(sizeof(void *) != sizeof(void (*)(void)));
>>> +}
>>> +#endif
>>> +
>>>  /*
>>>   * Local variables:
>>>   * mode: C
> 

And probably v4 can have the following wording:

/*
  * This assertion checks compatibility between 'unsigned long', 'void *',
  * and function pointers. This is true for X86 (x86_64) and ARM (arm, 
aarch64)
  * architectures, which is why the check is restricted to these.
  *
  * For more context on architecture-specific preprocessor guards, see
  * docs/misc/C-language-toolchain.rst.
  *
  * If Xen is ported to a new architecture, verify that this 
compatibility holds
  * before adding its macro to the condition below. If the compatibility 
does not
  * hold, this assertion may need to be revised or removed for that 
architecture.
  */

BR, Dmytro.