Re: [XEN PATCH v3] misra: address violation of MISRA C Rule 10.1

[Jan Beulich <jbeulich@xxxxxxxx>]

On 14.07.2025 16:16, Nicola Vetrini wrote:
> On 2025-07-14 15:49, Jan Beulich wrote:
>> On 14.07.2025 15:26, Dmytro Prokopchuk1 wrote:
>>> Rule 10.1: Operands shall not be of an
>>> inappropriate essential type
>>>
>>> The following are non-compliant:
>>> - boolean used as a numeric value.
>>>
>>> The result of the '__isleap' macro is a boolean.
>>> Use a ternary operator to replace it with a numeric value.
>>>
>>> The result of 'NOW() > timeout' is a boolean,
>>> which is compared to a numeric value. Fix this.
>>> Regression was introdiced by commit:
>>> be7f047e08 (xen/arm: smmuv3: Replace linux functions with xen 
>>> functions.)
>>>
>>> Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@xxxxxxxx>
>>> ---
>>> Changes since v2:
>>> - improve the wording
>>> Link to v2: 
>>> https://patchew.org/Xen/41538b6b19811eb74c183051d3e7a4fd216404e6.1752232902.git.dmytro._5Fprokopchuk1@xxxxxxxx/
>>> Link to the deviation of an unary minus: 
>>> https://patchew.org/Xen/7e6263a15c71aafc41fe72cecd1f15c3ce8846f2.1752492180.git.dmytro._5Fprokopchuk1@xxxxxxxx/
>>>
>>> Jan, regarding that:
>>> If an expression is needed here, I'd suggest to use !!, as we have in
>>> (luckily decreasing) number of places elsewhere. Personally I don't
>>> understand though why a boolean cannot be used as an array index.
>>>
>>> The '!!' isn't a solution here, we'll have other violation:
>>> `!' logical negation operator has essential type boolean and standard 
>>> type `int'
>>> (https://saas.eclairit.com:3787/fs/var/local/eclair/xen-project.ecdf/xen-project/people/dimaprkp4k/xen/ECLAIR_normal/deviate_10.1_rule/ARM64/10674114852/PROJECT.ecd;/by_service/MC3A2.R10.1.html#{%22select%22:true,%22selection%22:{%22hiddenAreaKinds%22:[],%22hiddenSubareaKinds%22:[],%22show%22:false,%22selector%22:{%22enabled%22:true,%22negated%22:true,%22kind%22:0,%22domain%22:%22kind%22,%22inputs%22:[{%22enabled%22:true,%22text%22:%22violation%22}]}}})
>>
>> And that doesn't fall under any other of the deviations we already 
>> have?
>> __isleap() is used in another boolean context after all, and apparently
>> there's no issue there.
> 
> I double-checked: there is no specific deviation for using a boolean as 
> an array subscript.
> 
> This is the only problematic use of a macro that returns an essentially 
> boolean expr used as an operand to an operator that expects an integer, 
> which is the reason of the violation:
> xen/common/time.c:#define __isleap(year) \
> xen/common/time.c:    while ( days >= (rem = __isleap(y) ? 366 : 365) )
> xen/common/time.c:        days += __isleap(y) ? 366 : 365;
> xen/common/time.c:    ip = (const unsigned short int 
> *)__mon_lengths[__isleap(y)];

Oh, I see - the !! simply doesn't alter the situation.

Jan