Baoquan He wrote:
Hi Eric,
On 05/18/22 at 04:59pm, Eric W. Biederman wrote:
"Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxxxxxxx> 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.
I've posted a v2 that uses the approach suggested by Michael, and
something that was in use in kexec already. If you are ok with that
approach, I will take a stab at converting the rest of the functions
that are marked __weak.
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.
I'm not aware of a move away from __weak in the kernel, in general.
Steven doesn't prefer it for ftrace, and other maintainers may have a
preference.
In my mind, __weak is very simple and clear as a mechanism to add
ARCH related functionality.
Notwithstanding the ftrace issue, the other caveat with __weak functions
are that they still make it into the final vmlinux even if they are
overridden. That is, you will have instructions from both the __weak
variant as well as from the overridden variant in the final vmlinux,
which can add up if the weak variants are non-trivial.
- Naveen
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