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Re: [PATCH v2] livepatch: apply_alternatives() is only used for livepatch
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 7 Jun 2023 12:19:06 +0200
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 07 Jun 2023 10:19:43 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 07.06.2023 11:17, 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,
Yes up to here.
> so it's not a replacement for the ifdef.
That depends how you look at it. We don't meaningfully care about a
few extra bytes in .init.text, I think. So it really is the Misra
requirement of not having unreferenced symbols which makes the
difference here.
Jan
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