linux-kernel - Re: Concerns about SFrame viability for userspace stack walking

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Message-ID: <CAN30aBEVdhju7CG4Tato-D1uof5p+dhTM6nJtjXX_SiYH7fU+Q@mail.gmail.com>
Date: Fri, 31 Oct 2025 01:24:52 -0700
From: Fangrui Song <maskray@...rceware.org>
To: Mark Brown <broonie@...nel.org>
Cc: Andi Kleen <andi@...stfloor.org>, Peter Zijlstra <peterz@...radead.org>, 
	Fangrui Song <maskray@...rceware.org>, linux-toolchains@...r.kernel.org, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Concerns about SFrame viability for userspace stack walking

On Thu, Oct 30, 2025 at 11:45 AM Mark Brown <broonie@...nel.org> wrote:
>
> On Thu, Oct 30, 2025 at 11:31:38AM -0700, Andi Kleen wrote:
> > On Thu, Oct 30, 2025 at 06:07:49PM +0000, Mark Brown wrote:
>
> > > It's going to take a *considerable* time for the hardware support to
> > > become standard.
>
> > Optimizing for the past instead of the future?
>
> On arm64 no currently available hardware has shadow stack support, and
> once systems start becoming available it'll take a very long time for
> that to filter down to even being all newly shipping systems, let alone
> all systems that people care about running new software on.
>
> > Not on x86 at least. All my x86 systems have it, except for a few old
> > skylakes.
>
> My experience trying to find a system to test changes on was somewhat
> different :(  I did eventually get something.

I’ve chatted with mobile toolchain developers at the LLVM Dev Mtg, who
emphasized that size concerns are especially critical for AArch64,
which is heavily deployed on mobile phones.
I think Arm ABI makers are unlikely to want a format known not to work
with mobile Linux to coexist with a future, more widely adopted
compact format with callee-saved register, LSDA, and personality
support. I chatted with Peter Smith, who seems to think so, but I
don't want to put the word into his mouth:)

---

Intel’s 11th Gen and AMD Zen 3 support hardware shadow stack.
A software-only stack walking approach (and remains unvetted for
AArch64-see above) that doesn’t replace .eh_frame would quickly become
obsolete.
Shadow stack can be enabled per process, providing flexibility to
balance performance overhead / memory consumption with profiling
needs, even for users who don’t prioritize the security hardening
aspect.