From 4b09ccd27b935a5cc266d5735a43e1367157c2db Mon Sep 17 00:00:00 2001 From: David Gow Date: Sat, 18 Mar 2023 12:15:54 +0800 Subject: [PATCH] um: Only disable SSE on clang to work around old GCC bugs commit a3046a618a284579d1189af8711765f553eed707 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: 884981867947 ("rust: arch/um: Disable FP/SIMD instruction to match x86") Reported-by: Roberto Sassu Link: https://lore.kernel.org/linux-um/6df2ecef9011d85654a82acd607fdcbc93ad593c.camel@huaweicloud.com/ Tested-by: Roberto Sassu Tested-by: SeongJae Park Signed-off-by: David Gow Reviewed-by: Vincenzo Palazzo Tested-by: Arthur Grillo Signed-off-by: Richard Weinberger Signed-off-by: Greg Kroah-Hartman --- arch/x86/Makefile.um | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/x86/Makefile.um b/arch/x86/Makefile.um index d2e95d1d4db77..1aa64846e5398 100644 --- a/arch/x86/Makefile.um +++ b/arch/x86/Makefile.um @@ -3,9 +3,14 @@ core-y += arch/x86/crypto/ # # 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 ($(CONFIG_CC_IS_CLANG),y) KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2 +endif ifeq ($(CONFIG_X86_32),y) START := 0x8048000 -- 2.47.2