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Re: [PATCH 00/12] S390: Implement __fentry__
On 08/02/2018 12:43 PM, Ilya Leoshkevich wrote:
Am 02.08.2018 um 11:17 schrieb Florian Weimer <email@example.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  and .
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?
Agreed, with the __fentry__ addition in the same release as the
trampoline change, this should be safe and avoid the issue I was worried