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um: Only disable SSE on clang to work around old GCC bugs 

commit a3046a618a upstream.

As part of the Rust support for UML, we disable SSE (and similar flags)
to match the normal x86 builds. This both makes sense (we ideally want a
similar configuration to x86), and works around a crash bug with SSE
generation under Rust with LLVM.

However, this breaks compiling stdlib.h under gcc < 11, as the x86_64
ABI requires floating-point return values be stored in an SSE register.
gcc 11 fixes this by only doing register allocation when a function is
actually used, and since we never use atof(), it shouldn't be a problem:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99652

Nevertheless, only disable SSE on clang setups, as that's a simple way
of working around everyone's bugs.

Fixes: 8849818679 ("rust: arch/um: Disable FP/SIMD instruction to match x86")
Reported-by: Roberto Sassu <roberto.sassu@huaweicloud.com>
Link: https://lore.kernel.org/linux-um/6df2ecef9011d85654a82acd607fdcbc93ad593c.camel@huaweicloud.com/
Tested-by: Roberto Sassu <roberto.sassu@huaweicloud.com>
Tested-by: SeongJae Park <sj@kernel.org>
Signed-off-by: David Gow <davidgow@google.com>
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
Tested-by: Arthur Grillo <arthurgrillo@riseup.net>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
David Gow 2023-03-18 12:15:54 +08:00 committed by Greg Kroah-Hartman
parent ca1c9012c9
commit 7d057bf201
1 changed files with 5 additions and 0 deletions
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5
arch/x86/Makefile.um
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@ -3,9 +3,14 @@ core-y += arch/x86/crypto/
# #
# Disable SSE and other FP/SIMD instructions to match normal x86 # Disable SSE and other FP/SIMD instructions to match normal x86
# This is required to work around issues in older LLVM versions, but breaks
# GCC versions < 11. See:
# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99652
# #
ifeq ($(CONFIG_CC_IS_CLANG),y)
KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx
KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2 KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2
endif
ifeq ($(CONFIG_X86_32),y) ifeq ($(CONFIG_X86_32),y)
START := 0x8048000 START := 0x8048000