Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20221217044436.4138642-1-davidgow@google.com> <20221217044436.4138642-3-davidgow@google.com>
In-Reply-To: <20221217044436.4138642-3-davidgow@google.com>
From:   =?UTF-8?Q?Sergio_Gonz=C3=A1lez_Collado?= <sergio.collado@gmail.com>
Date:   Sun, 15 Jan 2023 10:47:39 +0100
Message-ID: <CAA76j91Kn62Rqs9843njNSmuvb2XEyNLnC996Bmmz1obTbCX9w@mail.gmail.com>
Subject: Re: [PATCH 2/3] rust: arch/um: Disable FP/SIMD instruction to match x86
To:     David Gow <davidgow@google.com>
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        Richard Weinberger <richard@nod.at>,
        Anton Ivanov <anton.ivanov@cambridgegreys.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        rust-for-linux@vger.kernel.org, linux-um@lists.infradead.org,
        llvm@lists.linux.dev, linux-doc@vger.kernel.org,
        kunit-dev@googlegroups.com, x86@kernel.org,
        linux-kernel@vger.kernel.org,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Gary Guo <gary@garyguo.net>,
        Brendan Higgins <brendan.higgins@linux.dev>,
        Daniel Latypov <dlatypov@google.com>,
        Jonathan Corbet <corbet@lwn.net>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Sat, 17 Dec 2022 at 05:49, David Gow <davidgow@google.com> wrote:
>
> The kernel disables all SSE and similar FP/SIMD instructions on
> x86-based architectures (partly because we shouldn't be using floats in
> the kernel, and partly to avoid the need for stack alignment, see:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D53383 )
>
> UML does not do the same thing, which isn't in itself a problem, but
> does add to the list of differences between UML and "normal" x86 builds.
>
> In addition, there was a crash bug with LLVM < 15 / rustc < 1.65 when
> building with SSE, so disabling it fixes rust builds with earlier
> compiler versions, see:
> https://github.com/Rust-for-Linux/linux/pull/881
>
> Signed-off-by: David Gow <davidgow@google.com>
> ---
>  arch/x86/Makefile.um | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/arch/x86/Makefile.um b/arch/x86/Makefile.um
> index b3c1ae084180..d2e95d1d4db7 100644
> --- a/arch/x86/Makefile.um
> +++ b/arch/x86/Makefile.um
> @@ -1,6 +1,12 @@
>  # SPDX-License-Identifier: GPL-2.0
>  core-y +=3D arch/x86/crypto/
>
> +#
> +# Disable SSE and other FP/SIMD instructions to match normal x86
> +#
> +KBUILD_CFLAGS +=3D -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx
> +KBUILD_RUSTFLAGS +=3D -Ctarget-feature=3D-sse,-sse2,-sse3,-ssse3,-sse4.1=
,-sse4.2,-avx,-avx2
> +
>  ifeq ($(CONFIG_X86_32),y)
>  START :=3D 0x8048000
>
> --
> 2.39.0.314.g84b9a713c41-goog
>

Reviewed-by: Sergio Gonz=C3=A1lez Collado <sergio.collado@gmail.com>