Re: [PATCH] aarch64: MTE compatible strchrnul

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 03/06/2020 11:24, Florian Weimer via Libc-alpha wrote:
> * Andrea Corallo:
> 
>> Florian Weimer <fweimer@redhat.com> writes:
>>
>>> * Andrea Corallo:
>>>
>>>> Introduce an Arm MTE compatible strchrnul implementation.
>>>>
>>>> Benchmarked on Cortex-A72, Cortex-A53, Neoverse N1 does not show
>>>> performance regressions.
>>>>
>>>> Co-authored-by: Wilco Dijkstra <wilco.dijkstra@arm.com>
>>>
>>> As a very high-level comment, I would expect some sort of markup in the
>>> file that this implementation is now MTE-safe, similar to what we have
>>> for executable stacks.
>>>
>>> Or do you plan to handle that in some other fashion?
>>>
>>> Thanks,
>>> Florian
>>
>> Hi Florian,
>>
>> Now the only markup is the comment on the top of the file stating the
>> MTE compatibility of the routine.
>>
>> I'm not aware of how this marking is done for executable stacks, perhaps
>> could you give an hook on where to look for?
> 
> Typically, the -z noexecstack flag or a special .note.GNU-stack section
> is used for that.
> 
>> Just to make sure we are one the same page wanted to add: these
>> functions are supposed to be backward compatible with what they are
>> replacing, so I'm not sure a marking is necessary.
> 
> It's MTE that isn't backwards-compatible without such markup.

Afaiu there is no need to add any marking for MTE, the main difference
it enforce 16-byte granularity read. I think you are confusing with
BTI, which does require the GNU note.