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From: "linkw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/99888] Add powerpc ELFv2 support for
 -fpatchable-function-entry*
Date: Thu, 11 Aug 2022 09:00:35 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99888

--- Comment #6 from Kewen Lin <linkw at gcc dot gnu.org> ---
(In reply to Fangrui Song from comment #5)
> * There is a restriction on the number of instructions between the functi=
on
> label and the .localentry directive.
> * For -fpatchable-function-entry=3DN[,M], M nops must precede the function
> label.
>=20
> On aarch64/x86/etc, these nops are consecutive. Personally I think this
> condition can be lifted for PowerPC ELFv2. The runtime library will need =
to
> check st_other or do some instruction inspection, which may be fine.
>=20=20
>=20=20
>         nop
>         nop
>         nop
> foo:
> .LCF0:
>         .cfi_startproc
>         addis 2,12,.TOC.-.LCF0@ha
>         addi 2,2,.TOC.-.LCF0@l
>         .localentry     foo,.-foo
>         nop
>         nop

Thanks for the input! With your proposal, the nice thing is that we don't n=
eed
to bother the count of NOPs between GEP and LEP. But IMHO it seems confusing
since we take GEP as function entry when patching preceding NOPs while take=
 LEP
as function entry when patching succeeding NOPs. The acceptable counts of N=
OPs
in the proposed patch conforms to ELFv2 ABI, I hope runtime library can sur=
vive
with it.=