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Re: [XEN PATCH] x86/cpu-policy: justify a violation of MISRA C:2012 Rule 1.3
- To: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 1 Aug 2023 15:40:01 +0200
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- Cc: sstabellini@xxxxxxxxxx, michal.orzel@xxxxxxx, xenia.ragiadakou@xxxxxxx, ayan.kumar.halder@xxxxxxx, consulting@xxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 01 Aug 2023 13:40:09 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 01.08.2023 15:06, Nicola Vetrini wrote:
> The empty feature set 'str_7c1' in 'tools/misc/xen-cpuid.c' causes the
> struct declaration to have no named members, hence violating
> Rule 1.3:
> "There shall be no occurrence of undefined or critical unspecified behaviour"
> because it is forbidden by ISO/IEC 9899:1999(E), Section 6.7.2.1.7:
> "If the struct-declaration-list contains no named
> members, the behavior is undefined."
>
> It has been assessed that the feature set declaration is intentionally empty,
> and that no risk of undesired behaviour stems from it, hence the struct
> declaration is marked safe.
>
> No functional changes.
>
> Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
> ---
> As agreed during the MISRA C group meetings, this violation is dealt
> with by means of a comment deviation, as future changes may eliminate the
> root cause, which is the empty feature set.
> My justification for the claim and the commit message may need some adjusting.
A reference to the compiler extension would be nice; the use of extensions
(which generally are well-defined, even if not always well-documented)
should eliminate the UB that the standard specifies.
Jan
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