linux-kernel - Re: [PATCH] rust: x86: remove `-3dnow{,a}` from target features

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CANiq72nH9KZZKtDsMkfosmHpgVjvGM6=yy7fRyNP2NrDFUrkvQ@mail.gmail.com>
Date: Sat, 10 Aug 2024 00:15:50 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Miguel Ojeda <ojeda@...nel.org>
Cc: Alex Gaynor <alex.gaynor@...il.com>, Wedson Almeida Filho <wedsonaf@...il.com>, 
	Nathan Chancellor <nathan@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.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@...sung.com>, 
	Alice Ryhl <aliceryhl@...gle.com>, rust-for-linux@...r.kernel.org, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, llvm@...ts.linux.dev, 
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org, patches@...ts.linux.dev, 
	Nikita Popov <github@...pov.com>
Subject: Re: [PATCH] rust: x86: remove `-3dnow{,a}` from target features

On Tue, Aug 6, 2024 at 4:47 PM Miguel Ojeda <ojeda@...nel.org> wrote:
>
> LLVM 19 is dropping support for 3DNow! in commit f0eb5587ceeb ("Remove
> support for 3DNow!, both intrinsics and builtins. (#96246)"):
>
>     Remove support for 3DNow!, both intrinsics and builtins. (#96246)
>
>     This set of instructions was only supported by AMD chips starting in
>     the K6-2 (introduced 1998), and before the "Bulldozer" family
>     (2011). They were never much used, as they were effectively superseded
>     by the more-widely-implemented SSE (first implemented on the AMD side
>     in Athlon XP in 2001).
>
>     This is being done as a predecessor towards general removal of MMX
>     register usage. Since there is almost no usage of the 3DNow!
>     intrinsics, and no modern hardware even implements them, simple
>     removal seems like the best option.
>
> Thus we should avoid passing these to the backend, since otherwise we
> get a diagnostic about it:
>
>     '-3dnow' is not a recognized feature for this target (ignoring feature)
>     '-3dnowa' is not a recognized feature for this target (ignoring feature)
>
> We could try to disable them only up to LLVM 19 (not the C side one,
> but the one used by `rustc`, which may be built with a range of
> LLVMs). However, to avoid more complexity, we can likely just remove
> them altogether. According to Nikita [2]:
>
> > I don't think it's needed because LLVM should not generate 3dnow
> instructions unless specifically asked to, using intrinsics that Rust
> does not provide in the first place.
>
> Thus do so, like Rust did for one of their builtin targets [3].
>
> For those curious: Clang will warn only about trying to enable them
> (`-m3dnow{,a}`), but not about disabling them (`-mno-3dnow{,a}`), so
> there is no change needed there.
>
> Cc: Nikita Popov <github@...pov.com>
> Cc: Nathan Chancellor <nathan@...nel.org>
> Cc: x86@...nel.org
> Link: https://github.com/llvm/llvm-project/commit/f0eb5587ceeb641445b64cb264c822b4751de04a [1]
> Link: https://github.com/rust-lang/rust/pull/127864#issuecomment-2235898760 [2]
> Link: https://github.com/rust-lang/rust/pull/127864 [3]
> Closes: https://github.com/Rust-for-Linux/linux/issues/1094
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>

Applied to `rust-fixes` -- thanks everyone!

(If someone from x86 still wants to take a look / Ack it, please let me know!)

Cheers,
Miguel