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Subject: Re: [PATCH 00/12] S390: Implement __fentry__
From: Ilya Leoshkevich <iii@linux.ibm.com>
In-Reply-To: <ed187d53-0221-55ab-07a8-161302fd89c0@redhat.com>
Date: Thu, 02 Aug 2018 10:43:00 -0000
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References: <20180802075735.3457-1-iii@linux.ibm.com>
 <ed187d53-0221-55ab-07a8-161302fd89c0@redhat.com>
To: Florian Weimer <fweimer@redhat.com>
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> Am 02.08.2018 um 11:17 schrieb Florian Weimer <fweimer@redhat.com>:
>=20
> 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.
>=20
> Should GCC arrange for suitable ABI markup if -mfentry is used?  I'm worr=
ied that unexpected clobbers of r0 could be quite difficult to figure out o=
therwise.

I don=E2=80=99t 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=E2=80=99 ABI does not change, particula=
rly,
%r0, being a volatile register, used to be clobbered anyway.

Are there other cases that I=E2=80=99m missing?

> Thanks,
> Florian
>=20