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

Indu Bhagat
2025-02-13T23:23:42Z

On 2/12/25 11:25 PM, Song Liu wrote:
> 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.
>
> Indu, does this look like an issue with ld?
>

Sorry for the delay.

Looks like there has been progress since and issue may be elsewhere, but:

FWIW, I looked at the .sframe and .rela.sframe sections here, the data
does look OK. I noted that there is no .sframe for copy_process () in
output.o... I will take a look into it.