archive mirror
 help / color / mirror / Atom feed
* [PATCH] arch:um: Only disable SSE on clang to work around old GCC bugs
@ 2023-03-18  4:15 David Gow
  2023-03-20 17:22 ` Vincenzo Palazzo
                   ` (3 more replies)
  0 siblings, 4 replies; 7+ messages in thread
From: David Gow @ 2023-03-18  4:15 UTC (permalink / raw)
  To: Richard Weinberger, Anton Ivanov, Johannes Berg, Thomas Gleixner,
	Ingo Molnar, Nick Desaulniers, Nathan Chancellor, Miguel Ojeda,
	Roberto Sassu, SeongJae Park
  Cc: David Gow, linux-um, x86, llvm, rust-for-linux, kunit-dev, linux-kernel

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:

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 <>
Tested-by: Roberto Sassu <>
Tested-by: SeongJae Park <>
Signed-off-by: David Gow <>
 arch/x86/ | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/ b/arch/x86/
index b70559b821df..2106a2bd152b 100644
--- a/arch/x86/
+++ b/arch/x86/
@@ -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:
+ifeq ($(CONFIG_CC_IS_CLANG),y)
 KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx
 KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2
 ifeq ($(CONFIG_X86_32),y)
 START := 0x8048000

linux-um mailing list

^ permalink raw reply related	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2023-04-04  8:00 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-03-18  4:15 [PATCH] arch:um: Only disable SSE on clang to work around old GCC bugs David Gow
2023-03-20 17:22 ` Vincenzo Palazzo
2023-03-21 20:11 ` Arthur Grillo Queiroz Cabral
2023-03-31  8:25 ` David Gow
2023-03-31  8:37   ` Richard Weinberger
2023-04-04  7:59     ` Richard Weinberger
2023-03-31 13:39 ` Miguel Ojeda

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).