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Re: [PATCH v2] livepatch: apply_alternatives() is only used for livepatch
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 7 Jun 2023 12:15:07 +0200
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Wei Liu <wl@xxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Wed, 07 Jun 2023 10:15:29 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 07.06.2023 11:19, Andrew Cooper wrote:
> On 07/06/2023 10:17 am, Roger Pau Monné wrote:
>> On Wed, Jun 07, 2023 at 11:10:27AM +0200, Jan Beulich wrote:
>>> On 07.06.2023 11:01, Roger Pau Monne wrote:
>>>> Guard it with CONFIG_LIVEPATCH. Note alternatives are applied at boot
>>>> using _apply_alternatives().
>>>>
>>>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>>> Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
>>> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
>>> albeit the implicit ack therein is only on the assumption that (apart
>>> from me) it is generally deemed better ...
>>>
>>>> --- a/xen/arch/x86/alternative.c
>>>> +++ b/xen/arch/x86/alternative.c
>>>> @@ -358,11 +358,12 @@ static void init_or_livepatch
>>>> _apply_alternatives(struct alt_instr *start,
>>>> }
>>>> }
>>>>
>>>> -void init_or_livepatch apply_alternatives(struct alt_instr *start,
>>>> - struct alt_instr *end)
>>>> +#ifdef CONFIG_LIVEPATCH
>>> ... to have the #ifdef than the init_or_livepatch attribute.
>> But the init_or_livepatch attribute doesn't remove the function when
>> !CONFIG_LIVEPATCH, so it's not a replacement for the ifdef.
>>
>> IOW: it's my understanding that the purpose of init_or_livepatch is to
>> add the __init attribute if livepatch is not enabled, but
>> apply_alternatives() should never have the __init attribute because
>> it's solely used by livepatch, it's not used at boot.
>
> For context, Jan you missed the MISRA call yesterday where this was
> identified as an emitted-but-undeferenced function.
Ah, this helps.
Thanks, Jan
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