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Subject[PATCH resend] x86: Fix detection of GCC -mpreferred-stack-boundary support
Date
As per https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383, GCC only
allows -mpreferred-stack-boundary=3 on x86_64 if -mno-sse is set.
That means that cc-option will not detect
-mpreferred-stack-boundary=3 support, because we test for it before
setting -mno-sse.

Fix it by reordering the Makefile bits.

Compile-tested only. This should help avoid code generation issues
such as the one that was worked around in b96fecbfa8c8 ("x86/fpu:
Fix boot crash in the early FPU code").

I'm a bit concerned that we could still have problems on older GCC
versions given that our asm code does not respect GCC's idea of the
ABI-required stack alignment.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/Makefile | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 118e6debc483..344dd2110b2a 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -39,6 +39,12 @@ ifdef CONFIG_X86_NEED_RELOCS
LDFLAGS_vmlinux := --emit-relocs
endif

+# prevent gcc from generating any FP code by mistake
+# This must be before we try -mpreferred-stack-boundary -- see
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383
+KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow
+KBUILD_CFLAGS += $(call cc-option,-mno-avx,)
+
ifeq ($(CONFIG_X86_32),y)
BITS := 32
UTS_MACHINE := i386
@@ -167,9 +173,6 @@ KBUILD_CFLAGS += -pipe
KBUILD_CFLAGS += -Wno-sign-compare
#
KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
-# prevent gcc from generating any FP code by mistake
-KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow
-KBUILD_CFLAGS += $(call cc-option,-mno-avx,)

KBUILD_CFLAGS += $(mflags-y)
KBUILD_AFLAGS += $(mflags-y)
--
2.4.3


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