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

Song Liu
2025-02-13T07:25:50Z

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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?

Thanks,
Song

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