Baoquan He <bhe@xxxxxxxxxx> writes:
> 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.
>>
>> 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.
You should be able to trace the conversation back for all of the details
but if you can't here is the summary.
There is a tool that some architectures use called recordmcount. The
recordmcount looks for a symbol in a section, and ignores all weak
symbols. In certain cases sections become so simple there are only weak
symbols. At which point recordmcount fails.
Which means in practice __weak symbols are unreliable and don't work
to add ARCH related functionality.
Given that __weak symbols fail randomly I would much rather have simpler
code that doesn't fail. It has never been the case that __weak symbols
have been very common in the kernel. I expect they are something like
bool that have been gaining traction. Still given that __weak symbols
don't work. I don't want them.
Eric
_______________________________________________
kexec mailing list
kexec@xxxxxxxxxxxxxxxxxxx
http://lists.infradead.org/mailman/listinfo/kexec
