Re: [PATCH v2] misra: add deviation for MISRA C Rule R11.8.

[Jan Beulich <jbeulich@xxxxxxxx>]

On 18.12.2024 15:25, Alessandro Zucchelli wrote:
> Rule 11.8 states as following: "A cast shall not remove any `const' or
> `volatile' qualification from the type pointed to by a pointer".
> 
> Function `__hvm_copy' in `xen/arch/x86/hvm/hvm.c' is a double-use
> function, where the parameter needs to not be const because it can be
> set for write or not. As it was decided a new const-only function will
> lead to more developer confusion than it's worth, this violation is
> addressed by deviating the function.
> All cases of casting away const-ness are accompanied with a comment
> explaining why it is safe given the other flags passed in; such comment is 
> used
> by the deviation in order to match the appropriate function call.
> 
> No functional change.
> 
> Signed-off-by: Alessandro Zucchelli <alessandro.zucchelli@xxxxxxxxxxx>
> ---
> As this patch introduces a deviation for service MC3A2.R11.8, it
> depends on the following patch and shall not be applied prior to its
> application.
> https://lore.kernel.org/xen-devel/cf13be4779f15620e94b99b3b91f9cb040319989.1733826952.git.alessandro.zucchelli@xxxxxxxxxxx/T/#u

This wasn't applicable anymore at the time you posted the patch, I suppose?

> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> @@ -393,6 +393,12 @@ Fixing this violation would require to increase code 
> complexity and lower readab
>  
> -config=MC3R1.R11.8,reports+={safe,"any_area(any_loc(any_exp(macro(^container_of$))))"}
>  -doc_end
>  
> +-doc_begin="Function __hvm_copy in xen/arch/x86/hvm/hvm.c is a double-use
> +function, where the parameter needs to not be const because it can be set for
> +write or not"
> +-config=MC3A2.R11.8,reports+={safe,"any_area(any_loc(text(^.*__hvm_copy.*HVMCOPY_to_guest
>  doesn't modify.*$)))"}

This is probably good enough for now, yet still: It constrains re-formatting
that we may want to do on such function calls. Personally I'd consider it
entirely unexpected if I ended up (re)introducing a violation just by re-
formatting one of those function calls to

    return __hvm_copy(
               (void *)buf /* HVMCOPY_to_guest doesn't modify */,
               addr, size, current, HVMCOPY_to_guest | HVMCOPY_linear,
               PFEC_page_present | PFEC_write_access | pfec, pfinfo);

yet aiui the pattern above would have this effect (I don't think .* matches
newlines; instead I expect such regex-es to be applied to individual lines
only). Thoughts anyone?

Jan