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

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Message-ID: <CAPhsuW48h11yLuU7uHuPgYNCzwaxVKG+TaGOZeT7fR60+brTwA@mail.gmail.com>
Date: Mon, 17 Feb 2025 20:38:22 -0800
From: Song Liu <song@...nel.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Puranjay Mohan <puranjay@...nel.org>, Weinan Liu <wnliu@...gle.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Indu Bhagat <indu.bhagat@...cle.com>, 
	Peter Zijlstra <peterz@...radead.org>, Mark Rutland <mark.rutland@....com>, roman.gushchin@...ux.dev, 
	Will Deacon <will@...nel.org>, Ian Rogers <irogers@...gle.com>, linux-toolchains@...r.kernel.org, 
	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org, 
	joe.lawrence@...hat.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/8] unwind, arm64: add sframe unwinder for kernel

On Fri, Feb 14, 2025 at 3:23 PM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
>
> On Fri, Feb 14, 2025 at 02:04:17PM -0800, Song Liu wrote:
> > Hi Josh,
> >
> > On Fri, Feb 14, 2025 at 11:34 AM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
> > >
> > > On Fri, Feb 14, 2025 at 09:51:41AM -0800, Song Liu wrote:
> > > > > Ignorant arm64 question: is the module's text further away from slab
> > > > > memory than vmlinux text, thus requiring a different instruction (or
> > > > > GOT/TOC) to access memory further away in the address space?
> > > >
> > > > It appears to me the module text is very close to vmlinux text:
> > > >
> > > > vmlinux: ffff8000800b4b68 T copy_process
> > > > module: ffff80007b0f06d0 t copy_process [livepatch_always_inline_special_static]
> > >
> > > Hm... the only other thing I can think of is that the klp relas might be
> > > wrong somewhere.  If you share patched.o and .ko files from the same
> > > build I could take a look.
> >
> > A tarball with these files is available here:
> >
> > https://drive.google.com/file/d/1ONB1tC9oK-Z5ShmSXneqWLTjJgC5Xq-C/view?usp=drive_link
>
> Poking around the arm64 module code, arch/arm64/kernel/module-plts.c
> is looking at all the relocations in order to set up the PLT.  That also
> needs to be done for klp relas, or are your patches already doing that?

I don't think either version (this set and my RFC) added logic for PLT.
There is some rela logic on the kpatch-build side. But I am not sure
whether it is sufficient.

Thanks,
Song