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Date:   Sat, 17 Dec 2022 12:44:35 +0800
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Subject: [PATCH 2/3] rust: arch/um: Disable FP/SIMD instruction to match x86
From:   David Gow <davidgow@google.com>
To:     Miguel Ojeda <ojeda@kernel.org>,
        "=?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?=" <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>
Cc:     David Gow <davidgow@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>
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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=53383 )

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 += arch/x86/crypto/
 
+#
+# Disable SSE and other FP/SIMD instructions to match normal x86
+#
+KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx
+KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2
+
 ifeq ($(CONFIG_X86_32),y)
 START := 0x8048000
 
-- 
2.39.0.314.g84b9a713c41-goog