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Re: [XEN PATCH v2] 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: Wed, 2 Aug 2023 11:47:25 +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: Wed, 02 Aug 2023 09:48:01 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 02.08.2023 10:57, 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."
>
> Given that Xen is using an undocumented GCC extension that specifies the
> behaviour upon defining a struct with no named member, this construct is
> well-defined and thus it is marked as safe.
Especially after realizing that I was wrong here (I was under the wrong
impression that we'd generate a struct without members, when it's one
without named members, yet [to me at least] only the former is a known
gcc extension we use), I've sent an alternative proposal. Let's see
whether in particular Andrew considers this acceptable.
Jan
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