Re: [PATCH 0/8] unwind, arm64: add sframe unwinder for kernel

Puranjay Mohan
2025-02-13T07:46:27Z

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Song Liu <song@kernel.org> writes:

> On Wed, Feb 12, 2025 at 6:45 PM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>>
>> On Wed, Feb 12, 2025 at 06:36:04PM -0800, Song Liu wrote:
>> > > > [ 81.261748] copy_process+0xfdc/0xfd58 [livepatch_special_static]
>> > >
>> > > Does that copy_process+0xfdc/0xfd58 resolve to this line in
>> > > copy_process()?
>> > >
>> > > refcount_inc(&current->signal->sigcnt);
>> > >
>> > > Maybe the klp rela reference to 'current' is bogus, or resolving to the
>> > > wrong address somehow?
>> >
>> > It resolves the following line.
>> >
>> > p->signal->tty = tty_kref_get(current->signal->tty);
>> >
>> > I am not quite sure how 'current' should be resolved.
>>
>> Hm, on arm64 it looks like the value of 'current' is stored in the
>> SP_EL0 register. So I guess that shouldn't need any relocations.
>>
>> > The size of copy_process (0xfd58) is wrong. It is only about
>> > 5.5kB in size. Also, the copy_process function in the .ko file
>> > looks very broken. I will try a few more things.
>
> When I try each step of kpatch-build, the copy_process function
> looks reasonable (according to gdb-disassemble) in fork.o and
> output.o. However, copy_process looks weird in livepatch-special-static.o,
> which is generated by ld:
>
> ld -EL -maarch64linux -z norelro -z noexecstack
> --no-warn-rwx-segments -T ././kpatch.lds -r -o
> livepatch-special-static.o ./patch-hook.o ./output.o
>
> I have attached these files to the email. I am not sure whether
> the email server will let them through.

I think, I am missing something here,

I did :

objdump -Dr livepatch-special-static.o | less

and

objdump -Dr output.o | less

and the disassembly of copy_process() looks exactly same.

> Indu, does this look like an issue with ld?
>
> Thanks,
> Song

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