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Re: [XEN PATCH v2 2/7] x86: add deviations for variables only used in asm code
- To: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 18 Oct 2023 16:56:26 +0200
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- Cc: sstabellini@xxxxxxxxxx, michal.orzel@xxxxxxx, xenia.ragiadakou@xxxxxxx, ayan.kumar.halder@xxxxxxx, consulting@xxxxxxxxxxx, andrew.cooper3@xxxxxxxxxx, roger.pau@xxxxxxxxxx, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 18 Oct 2023 14:57:11 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 18.10.2023 16:28, Nicola Vetrini wrote:
> On 16/10/2023 16:58, Jan Beulich wrote:
>> On 09.10.2023 08:54, Nicola Vetrini wrote:
>>> These variables are only used by asm code, and therefore
>>> the lack of a declaration is justified by the corresponding
>>> deviation comment.
>>
>> Hmm, you say "declaration" here, but according to my understanding ...
>>
>>> --- a/xen/arch/x86/include/asm/asm_defns.h
>>> +++ b/xen/arch/x86/include/asm/asm_defns.h
>>> @@ -31,6 +31,7 @@ asm ( "\t.equ CONFIG_INDIRECT_THUNK, "
>>> * gets set up by the containing function.
>>> */
>>> #ifdef CONFIG_FRAME_POINTER
>>> +/* SAF-1-safe */
>>> register unsigned long current_stack_pointer asm("rsp");
>>
>> ... this is a declaration, not a definition.
>>
>
> It has automatic storage duration and it's not defined afterwards
Mind me asking what makes you derive "automatic storage duration"?
I also don't see how "not defined afterwards" matters here. This is
a special construct, not covered by the C standard.
Jan
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