linux-kernel - Re: [PATCH v2 0/6] unwind, arm64: add sframe unwinder for kernel

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Message-ID: <nzmtsafrx5vjitgfpducjaa7kq747a3sler2vvyvfbxecutn3v@7ffl2ycnaoo2>
Date: Mon, 17 Nov 2025 15:06:32 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Dylan Hatch <dylanbhatch@...gle.com>
Cc: Puranjay Mohan <puranjay12@...il.com>, Song Liu <song@...nel.org>, 
	Steven Rostedt <rostedt@...dmis.org>, Indu Bhagat <indu.bhagat@...cle.com>, 
	Peter Zijlstra <peterz@...radead.org>, Will Deacon <will@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, Jiri Kosina <jikos@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Weinan Liu <wnliu@...gle.com>, 
	Mark Rutland <mark.rutland@....com>, Ian Rogers <irogers@...gle.com>, 
	linux-toolchains@...r.kernel.org, linux-kernel@...r.kernel.org, live-patching@...r.kernel.org, 
	joe.lawrence@...hat.com, Puranjay Mohan <puranjay@...nel.org>
Subject: Re: [PATCH v2 0/6] unwind, arm64: add sframe unwinder for kernel

On Fri, Nov 14, 2025 at 10:50:16PM -0800, Dylan Hatch wrote:
> On Mon, Sep 29, 2025 at 12:55 PM Puranjay Mohan <puranjay12@...il.com> wrote:
> >
> > I will try to debug this more but am just curious about BPF's
> > interactions with sframe.
> > The sframe data for bpf programs doesn't exist, so we would need to
> > add that support
> > and that wouldn't be trivial, given the BPF programs are JITed.
> >
> > Thanks,
> > Puranjay
> 
> From what I can tell, the ORC unwinder in x86 falls back to using
> frame pointers in cases of generated code, like BPF. Would matching
> this behavior in the sframe unwinder be a reasonable approach, at
> least for the purposes of enabling reliable unwind for livepatch?

The ORC unwinder marks the unwind "unreliable" if it has to fall back to
frame pointers.

But that's not a problem for livepatch because it only[*] unwinds
blocked/sleeping tasks, which shouldn't have BPF on their stack anyway.

[*] with one exception: the task calling into livepatch

-- 
Josh