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

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Message-ID: <CABCJKuesdSH2xhm_NZOjxHWpt5M866EL_RUBdQNZ54ov7ObH-Q@mail.gmail.com>
Date: Mon, 27 Oct 2025 08:53:49 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Nathan Chancellor <nathan@...nel.org>, Linus Walleij <linus.walleij@...aro.org>
Cc: 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

Hi Nathan,

On Sat, Oct 25, 2025 at 1:53 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> Prior to clang 22.0.0 [1], ARM did not have an architecture specific
> kCFI bundle lowering in the backend, which may cause issues. Select
> CONFIG_ARCH_USES_CFI_GENERIC_LLVM_PASS to enable use of __nocfi_generic.
>
> Link: https://github.com/llvm/llvm-project/commit/d130f402642fba3d065aacb506cb061c899558de [1]
> Link: https://github.com/ClangBuiltLinux/linux/issues/2124
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  arch/arm/Kconfig | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 2e3f93b690f4..4fb985b76e97 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -44,6 +44,8 @@ config ARM
>         select ARCH_USE_BUILTIN_BSWAP
>         select ARCH_USE_CMPXCHG_LOCKREF
>         select ARCH_USE_MEMTEST
> +       # https://github.com/llvm/llvm-project/commit/d130f402642fba3d065aacb506cb061c899558de
> +       select ARCH_USES_CFI_GENERIC_LLVM_PASS if CLANG_VERSION < 220000

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?

Sami