linux-kernel - Re: [PATCH] arm64: rust: clean Rust 1.85.0 warning using softfloat target

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Message-ID: <CAH5fLggGLbL+oTfOPjtCvw1cTLzJU6e+dmZoF1uy1QVTtRq3yQ@mail.gmail.com>
Date: Wed, 12 Feb 2025 10:27:26 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Miguel Ojeda <ojeda@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, 
	moderated for non-subscribers <linux-arm-kernel@...ts.infradead.org>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, patches@...ts.linux.dev, stable@...r.kernel.org, 
	Matthew Maurer <mmaurer@...gle.com>, Ralf Jung <post@...fj.de>, 
	Jubilee Young <workingjubilee@...il.com>
Subject: Re: [PATCH] arm64: rust: clean Rust 1.85.0 warning using softfloat target

On Mon, Feb 10, 2025 at 5:38 PM Miguel Ojeda <ojeda@...nel.org> wrote:
>
> Starting with Rust 1.85.0 (to be released 2025-02-20), `rustc` warns
> [1] about disabling neon in the aarch64 hardfloat target:
>
>     warning: target feature `neon` cannot be toggled with
>              `-Ctarget-feature`: unsound on hard-float targets
>              because it changes float ABI
>       |
>       = note: this was previously accepted by the compiler but
>               is being phased out; it will become a hard error
>               in a future release!
>       = note: for more information, see issue #116344
>               <https://github.com/rust-lang/rust/issues/116344>
>
> Thus, instead, use the softfloat target instead.
>
> While trying it out, I found that the kernel sanitizers were not enabled
> for that built-in target [2]. Upstream Rust agreed to backport
> the enablement for the current beta so that it is ready for
> the 1.85.0 release [3] -- thanks!
>
> However, that still means that before Rust 1.85.0, we cannot switch
> since sanitizers could be in use. Thus conditionally do so.
>
> Cc: <stable@...r.kernel.org> # Needed in 6.12.y and 6.13.y only (Rust is pinned in older LTSs).
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Matthew Maurer <mmaurer@...gle.com>
> Cc: Alice Ryhl <aliceryhl@...gle.com>
> Cc: Ralf Jung <post@...fj.de>
> Cc: Jubilee Young <workingjubilee@...il.com>
> Link: https://github.com/rust-lang/rust/pull/133417 [1]
> Link: https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/arm64.20neon.20.60-Ctarget-feature.60.20warning/near/495358442 [2]
> Link: https://github.com/rust-lang/rust/pull/135905 [3]
> Link: https://github.com/rust-lang/rust/issues/116344
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>

Thanks Matt for boot-testing it.

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>