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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

> Well, in our case boolean can be used as an array index.
> But index value is limited: 0 or 1.
> I guess MISRA wants to predict such errors related to index limitations.
> And I think fixing the code is easier here, instead of writing a deviation.

It may be easier indeed, but ...

> --- a/xen/common/time.c
> +++ b/xen/common/time.c
> @@ -84,7 +84,7 @@ struct tm gmtime(unsigned long t)
>      }
>      tbuf.tm_year = y - 1900;
>      tbuf.tm_yday = days;
> -    ip = (const unsigned short int *)__mon_lengths[__isleap(y)];
> +    ip = (const unsigned short int *)__mon_lengths[__isleap(y) ? 1 : 0];

... especially as long as it's un-annotated, I'd be very likely to submit
a patch to undo this again, should I ever run across this after having
forgotten about the change here. At least to me, _this_ is the confusing
way to write things.

Once you add a comment though, you can as well leave the code unchanged
and use a SAF comment.

Jan