linux-kernel - Re: [PATCH] kexec_file: Drop weak attribute from arch_kexec_apply_relocations[

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Message-ID: <YoWySwbszfdZS9LU@MiWiFi-R3L-srv>
Date:   Thu, 19 May 2022 10:58:19 +0800
From:   Baoquan He <bhe@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] kexec_file: Drop weak attribute from
 arch_kexec_apply_relocations[_add]

Hi Eric,

On 05/18/22 at 04:59pm, Eric W. Biederman wrote:
> "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> writes:
> 
> > Since commit d1bcae833b32f1 ("ELF: Don't generate unused section
> > symbols") [1], binutils (v2.36+) started dropping section symbols that
> > it thought 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 in .text.unlikely to generate a relocation record against.
> >
> > Address this by dropping the weak attribute from these functions:
> > - arch_kexec_apply_relocations() is not overridden by any architecture
> >   today, so just drop the weak attribute.
> > - arch_kexec_apply_relocations_add() is only overridden by x86 and s390.
> >   Retain the function prototype for those and move the weak
> >   implementation into the header as a static inline for other
> >   architectures.
> >
> > [1] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=d1bcae833b32f1
> 
> Any chance you can also get machine_kexec_post_load,
> crash_free_reserved_phys_range, arch_kexec_protect_protect_crashkres,
> arch_kexec_unprotect_crashkres, arch_kexec_kernel_image_probe,
> arch_kexec_kernel_image_probe, arch_kimage_file_post_load_cleanup,
> arch_kexec_kernel_verify_sig, and arch_kexec_locate_mem_hole as well.
> 
> That is everything in kexec that uses a __weak symbol.  If we can't
> count on them working we might as well just get rid of the rest
> preemptively.

Is there a new rule that __weak is not suggested in kernel any more?
Please help provide a pointer if yes, so that I can learn that.

In my mind, __weak is very simple and clear as a mechanism to add
ARCH related functionality.

Thanks
Baoquan