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Re: [XEN PATCH v2] xen/hypercalls: address violations of MISRA C:2012 Rule 8.3
- To: Stefano Stabellini <sstabellini@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 29 Aug 2023 08:29:45 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Federico Serafini <federico.serafini@xxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, consulting@xxxxxxxxxxx, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Wei Liu <wl@xxxxxxx>, roger.pau@xxxxxxxxxx
- Delivery-date: Tue, 29 Aug 2023 06:29:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 28.08.2023 23:52, Stefano Stabellini wrote:
> On Mon, 28 Aug 2023, Jan Beulich wrote:
>> On 26.08.2023 00:21, Stefano Stabellini wrote:
>>> Coming to unsigned int, it should be 32-bit on all supported arches,
>>
>> But this isn't a requirement, even if we're using "unsigned int" in the
>> C declarations / definitions: If "unsigned int" was wider, all we'd
>> demand is that hypercall entry code (likely written in assembly anyway)
>> zero-extend incoming values suitably to fit whatever "unsigned int" is.
>> Which is no different to Andrew (aiui) suggesting to use "unsigned
>> long" instead: That'll too require suitable zero-extension up front.
>
> What you wrote assumes that "unsigned int" can only be 32-bit or wider,
> such as 64-bit. However, I think that by the C standard there is no
> guarantee. For instance, it could be smaller, e.g. 16-bit.
Of course, but in Xen (just like e.g. Linux does) we inherently assume
sizeof(int) >= 4.
Jan
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