On 15.02.2025 09:59, Nicola Vetrini wrote:
> On 2025-02-15 00:04, Stefano Stabellini wrote:
>> On Fri, 14 Feb 2025, Jan Beulich wrote:
>>>> Would deviating macros "COOKIE2MCTE" and "MCTE2COOKIE" work?
>>>
>>> If it did, COOKIE2ID and ID2COOKIE would likely need including as
>>> well.
>>
>> I wrote this patch. Nicola, can you please check the changes to
>> deviations.ecl, this is the first time I try to write the deviation
>> myself :-)
>>
>> ---
>> misra: add 11.2 deviation for incomplete types
>>
>> struct mctelem_cookie* is used exactly because it is an incomplete type
>> so the pointer cannot be dereferenced. This is deliberate. So add a
>> deviation for it.
>>
>> In deviations.ecl, add the list of macros that do the conversions to
>> and
>> from struct mctelem_cookie*.
>>
>> Signed-off-by: Stefano Stabellini <stefano.stabell...@amd.com>
>>
>> diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl
>> b/automation/eclair_analysis/ECLAIR/deviations.ecl
>> index a28eb0ae76..87bfd2160c 100644
>> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
>> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
>> @@ -366,6 +366,14 @@ constant expressions are required.\""
>> }
>> -doc_end
>>
>> +-doc_begin="Certain pointers point to incomplete types purposely so
>> that they are impossible to dereference."
>> +-config=MC3A2.R11.2,reports+={deliberate,
>> "any_area(any_loc(any_exp(macro(^COOKIE2MCTE$))))"}
>> +-config=MC3A2.R11.2,reports+={deliberate,
>> "any_area(any_loc(any_exp(macro(^MCTE2COOKIE$))))"}
>> +-config=MC3A2.R11.2,reports+={deliberate,
>> "any_area(any_loc(any_exp(macro(^COOKIE2ID$))))"}
>> +-config=MC3A2.R11.2,reports+={deliberate,
>> "any_area(any_loc(any_exp(macro(^ID2COOKIE$))))"}
>> +}
>
> -config=MC3A2.R11.2,reports+={deliberate,
> "any_area(any_loc(any_exp(macro(name(COOKIE2MCTE||MCTE2COOKIE||COOKIE2ID||ID2COOKIE)))))"}
>
> Note however that there is also this deviation in place
>
> -doc_begin="The conversion from a pointer to an incomplete type to
> unsigned long does not lose any information, provided that the target
> type has enough bits to store it."
> -config=MC3A2.R11.2,casts+={safe,
> "from(type(any()))
> &&to(type(canonical(builtin(unsigned long))))
> &&relation(definitely_preserves_value)"
> }
> -doc_end
>
> I was a bit confused by Jan's remark, which seemed correct, but I
> couldn't see any violations in the report, so I dug a bit deeper.
> ID2COOKIE and COOKIE2ID, which operate to/from unsigned long are already
> excluded due to being safe. If you envision those macros to be used with
> other types, then your deviation should mention them, otherwise they are
> already handled.
Yet then can't we leverage that deviation to also make the other two
covered:
#define COOKIE2MCTE(c) ((struct mctelem_ent *)(unsigned long)(c))
#define MCTE2COOKIE(tep) ((mctelem_cookie_t)(unsigned long)(tep))
Arguable that's ...
>> --- a/docs/misra/deviations.rst
>> +++ b/docs/misra/deviations.rst
>> @@ -324,6 +324,12 @@ Deviations related to MISRA C:2012 Rules:
>> semantics that do not lead to unexpected behaviour.
>> - Tagged as `safe` for ECLAIR.
>>
>> + * - R11.2
>> + - Certain pointers point to incomplete types purposely so that
>> they
>> + are impossible to dereference.
>> + - Tagged as `deliberate` for ECLAIR. Such pointer is struct
>> + mctelem_cookie \*.
>> +
>
> I think here (or above in the deviation text) the concern raised by the
> rationale of the rule should be addressed; namely, the rule states:
> "Conversions shall not be performed between a pointer to an incomplete
> type and any other type" because the resulting pointer might be
> misaligned, therefore there should be an argument as to why such thing
> is not possible.
... undermining this rationale of the rule then, though.
Jan
