linux-kernel - Re: [PATCH 2/3] ARM: Select ARCH_USES_CFI_GENERIC_LLVM

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Message-ID: <CABCJKudsbd6=8B+fkzbw6TkL-dVvSoT3Co=fW+jWOnuBtxsLKg@mail.gmail.com>
Date: Tue, 28 Oct 2025 11:14:35 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Linus Walleij <linus.walleij@...aro.org>, Kees Cook <kees@...nel.org>, 
	Alexander Lobakin <aleksander.lobakin@...el.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Simon Horman <horms@...nel.org>, Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	Russell King <linux@...linux.org.uk>, Tony Nguyen <anthony.l.nguyen@...el.com>, 
	Michal Kubiak <michal.kubiak@...el.com>, linux-kernel@...r.kernel.org, 
	llvm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org
Subject: Re: [PATCH 2/3] ARM: Select ARCH_USES_CFI_GENERIC_LLVM_PASS

On Tue, Oct 28, 2025 at 10:52 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> On Mon, Oct 27, 2025 at 11:56:21PM +0100, Linus Walleij wrote:
> > On Mon, Oct 27, 2025 at 4:54 PM Sami Tolvanen <samitolvanen@...gle.com> wrote:
> > > Instead of working around issues with the generic pass, would it make
> > > more sense to just disable arm32 CFI with older Clang versions
> > > entirely? Linus, any thoughts?
> >
> > We have people using this with the default compilers that come with
> > Debiand and Fedora. I would say as soon as the latest release of
> > the major distributions supports this, we can drop support for older
> > compilers.
>
> Okay, I think that is reasonable enough. This is not a very large
> workaround and I do not expect these type of workarounds to be necessary
> frequently so I think it is worth keeping this working if people are
> actually using it. That means we could mandate the backend version of
> kCFI for ARM with Debian Forky in 2027.

Yeah, it's a bit unfortunate, but I agree that we shouldn't break
existing users until newer Clang is actually available in distros.

Sami