Commit b2c51106 authored Jul 21, 2015 by Andy Lutomirski Committed by Ingo Molnar Jul 22, 2015

x86/build: Fix detection of GCC -mpreferred-stack-boundary support

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:

  b96fecbf ("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.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/f5297c192969adfa0d28b84cf8a22d59573db26d.1436126872.git.luto@kernel.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent f2a50f8b

arch/x86/Makefile

+10 −3

Original line number	Diff line number	Diff line
		@@ -39,6 +39,16 @@ ifdef CONFIG_X86_NEED_RELOCS
		LDFLAGS_vmlinux := --emit-relocs
		endif

		#
		# Prevent GCC from generating any FP code by mistake.
		#
		# This must happen before we try the -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 +177,6 @@ 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)

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