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Date:   Tue, 17 May 2022 15:49:41 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [PATCH] kexec_file: Drop pr_err in weak implementations of
 arch_kexec_apply_relocations[_add]
To:     Baoquan He <bhe@redhat.com>
Cc:     Eric Biederman <ebiederm@xmission.com>, kexec@lists.infradead.org,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        Michael Ellerman <mpe@ellerman.id.au>
References: <20220425174128.11455-1-naveen.n.rao@linux.vnet.ibm.com>
        <YoNqJ/MOSIVwKP/o@MiWiFi-R3L-srv>
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Baoquan He wrote:
> On 04/25/22 at 11:11pm, Naveen N. Rao wrote:
>> kexec_load_purgatory() can fail for many reasons - there is no need to
>> print an error when encountering unsupported relocations.
>>=20
>> This solves a build issue on powerpc with binutils v2.36 and newer [1].
>> Since commit d1bcae833b32f1 ("ELF: Don't generate unused section
>> symbols") [2], binutils started dropping section symbols that it thought
>=20
> I am not familiar with binutils, while wondering if this exists in other
> ARCHes except of ppc. Arm64 doesn't have the ARCH override either, do we
> have problem with it?

I'm not aware of this specific file causing a problem on other=20
architectures - perhaps the config options differ enough. There are=20
however more reports of similar issues affecting other architectures=20
with the llvm integrated assembler:
https://github.com/ClangBuiltLinux/linux/issues/981

>=20
>> were unused.  This isn't an issue in general, but with kexec_file.c, gcc
>> is placing kexec_arch_apply_relocations[_add] into a separate
>> .text.unlikely section and the section symbol ".text.unlikely" is being
>> dropped. Due to this, recordmcount is unable to find a non-weak symbol
>=20
> But arch_kexec_apply_relocations_add is weak symbol on ppc.

Yes. Note that it is just the section symbol that gets dropped. The=20
section is still present and will continue to hold the symbols for the=20
functions themselves.

>=20
>> in .text.unlikely to generate a relocation record against. Dropping
>> pr_err() calls results in these functions being left in .text section,
>=20
> Why dropping pr_err() can make arch_kexec_apply_relocations_add put in
> .text?

I'm not actually sure, though Josh suspected that printk() might be=20
cold:
http://lkml.kernel.org/r/20210214155147.3owdimqv2lyhu6by@treble


- Naveen