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

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Message-ID: <CAPhsuW6q+yhn0pGQb0K+RhXHYDkjEgomZ2pu3P_MEeX+xNRe0g@mail.gmail.com>
Date: Fri, 14 Feb 2025 14:04:17 -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

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

> BTW, I realized the wrong function size shown in the WARNING stack trace
> is probably just due to a kallsyms quirk.  It calculates a symbol's size
> by subtracting its start address from the next symbol's start address.
> It doesn't actually use the ELF symbol size.  So the next symbol after
> copy_process() in the loaded module's address space might just be far
> away.

Yeah, I also think kallsyms logic was the issue here. So it is not the same
as the gdb-disassembly issue.

> That kallsyms issue has caused other headaches.  It really needs to be
> fixed to use the actual ELF symbol size.

Maybe we should have a "module_text_end" symbol?

Thanks,
Song