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Re: [XEN PATCH 11/11] x86/mm: Add assertion to address MISRA C:2012 Rule 2.1
- To: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 3 Aug 2023 17:41:43 +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>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 03 Aug 2023 15:42:18 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 03.08.2023 11:30, Nicola Vetrini wrote:
> On 03/08/2023 11:20, Jan Beulich wrote:
>> On 02.08.2023 16:38, Nicola Vetrini wrote:
>>> --- a/xen/arch/x86/mm/p2m-pod.c
>>> +++ b/xen/arch/x86/mm/p2m-pod.c
>>> @@ -1045,6 +1045,7 @@ p2m_pod_zero_check(struct p2m_domain *p2m, const
>>> gfn_t *gfns, unsigned int count
>>> }
>>>
>>> return;
>>> + ASSERT_UNREACHABLE();
>>>
>>> out_unmap:
>>> /*
>>
>> In the description you say "before", but here you add something _after_
>> "return". What's the deal?
>
> In this case the unreachable part is that after the label (looking at it
> now, I should have
> put the assert after the label to make it clear), because earlier all
> jumps to
> 'out_unmap' are like this:
>
> ASSERT_UNREACHABLE();
> domain_crash(d);
> goto out_unmap;
>
> As I understood it, this is a defensive coding measure, preventing pages
> to remain mapped if,
> for some reason the above code actually executes. Am I correct?
The comment there says "probably". So the label and following code might
be used for another error condition as well. Furthermore both paths
presently using "goto out_unmap" already have ASSERT_UNREACHABLE(), so
it's hard to see why we would need yet one more.
Jan
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