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

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Message-ID: <CANk7y0hqnQR6X6rmVgA6O44WCf5QMiKVVJ31txWf-R9HtxhBBg@mail.gmail.com>
Date: Tue, 18 Nov 2025 00:50:09 +0100
From: Puranjay Mohan <puranjay12@...il.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Dylan Hatch <dylanbhatch@...gle.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 Tue, Nov 18, 2025 at 12:06 AM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
>
> 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.
>

BPF programs can sleep, so wouldn't they show up in the stack?
Like if I am tracing a syscall with a bpf program attached using
fentry and the BPF program calls a bpf_arena_alloc_pages(), which can
sleep.