Re: [PATCH v7 07/11] Arm32: use new-style entry annotations for library code

[Jan Beulich <jbeulich@xxxxxxxx>]

On 25.11.2024 21:15, Julien Grall wrote:
> Hi Jan,
> 
> Sorry for the late answer.
> 
> On 01/10/2024 16:16, Jan Beulich wrote:
>> No functional change, albeit all globals now become hidden, and aliasing
>> symbols (__aeabi_{u,}idiv) as well as __memzero lose their function-ness
>> and size.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> If the function-ness is important, some new construct would need
>> inventing. Not setting size for the aliases may even be desirable, as
>> I'm uncertain whether it is really legal in ELF that two entities
>> overlap in space.
> 
> I can't think of a reason where we would need the "function-ness".

Good, thanks for confirming.

>> I fear I'm breaking __memzero(), as I don't understand the purpose of
>> the ".word 0" next to where the FUNC_LOCAL() appears.
> 
> I am not entirely sure either. AFAIK, "0" is not a valid instruction.
> 
> This code was taken from Linux, the history doesn't give much clue 
> because it seems the ".word 0" was added before Linux used git.

My vague guess is that this is a crude way of arranging for desired
alignment of labels later in the function. That wouldn't require use
of .word (could simply be a nop), yet what specifically is used there
doesn't matter for the patch here.

> However, it looks like Linux replace __memzero with memset() 6 years ago 
> on arm32. So maybe we should get rid of it? This would at least avoid 
> worrying on the purpose of ".word 0".

Certainly an option, yet may I remind you of your replies [1], [2] to
a much older patch of mine, which I still have pending for the
suggested removal never having happened? I fear the patch here may get
stuck over this just like the other one did.

Jan

[1] https://lists.xen.org/archives/html/xen-devel/2022-08/msg01185.html
[2] https://lists.xen.org/archives/html/xen-devel/2022-08/msg01190.html