Re: [PATCH v2] livepatch: apply_alternatives() is only used for livepatch

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

~Andrew