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Re: [PATCH 00/12] S390: Implement __fentry__

> Am 02.08.2018 um 11:17 schrieb Florian Weimer <fweimer@redhat.com>:
> 
> On 08/02/2018 09:57 AM, Ilya Leoshkevich wrote:
>> This patch series adds the runtime support in glibc for the -mfentry
>> gcc feature introduced in [1] and [2].
>> Patches 1-9 deal with avoiding clobbering %r0 when calling lazily bound
>> functions, so that the new __fentry__ symbol could be called with return
>> address in that register.
> 
> Should GCC arrange for suitable ABI markup if -mfentry is used?  I'm worried that unexpected clobbers of r0 could be quite difficult to figure out otherwise.

I don’t think we need to do anything ABI-related at this point.

__fentry__ itself is being newly introduced, so there is no old ABI to
comply with. Instrumented functions’ ABI does not change, particularly,
%r0, being a volatile register, used to be clobbered anyway.

Are there other cases that I’m missing?

> Thanks,
> Florian
>
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