Commit-ID: 8f91869766c00622b2eaa8ee567db4f333b78c1a
Gitweb: http://git.kernel.org/tip/8f91869766c00622b2eaa8ee567db4f333b78c1a
Author: Matthias Kaehlcke <m...@chromium.org>
AuthorDate: Wed, 16 Aug 2017 17:47:40 -0700
Committer: Ingo Molnar <mi...@kernel.org>
CommitDate: Thu, 17 Aug 2017 10:27:19 +0200
x86/build: Fix stack alignment for CLang
Commit:
d77698df39a5 ("x86/build: Specify stack alignment for clang")
intended to use the same stack alignment for clang as with gcc.
The two compilers use different options to configure the stack alignment
(gcc: -mpreferred-stack-boundary=n, clang: -mstack-alignment=n).
The above commit assumes that the clang option uses the same parameter
type as gcc, i.e. that the alignment is specified as 2^n. However clang
interprets the value of this option literally to use an alignment of n,
in consequence the stack remains misaligned.
Change the values used with -mstack-alignment to be the actual alignment
instead of a power of two.
cc-option isn't used here with the typical pattern of KBUILD_CFLAGS +=
$(call cc-option ...). The reason is that older gcc versions don't
support the -mpreferred-stack-boundary option, since cc-option doesn't
verify whether the alternative option is valid it would incorrectly
select the clang option -mstack-alignment..
Signed-off-by: Matthias Kaehlcke <m...@chromium.org>
Cc: Arnd Bergmann <a...@arndb.de>
Cc: bernhard.rosenkran...@linaro.org
Cc: Greg Hackmann <ghackm...@google.com>
Cc: Kees Cook <keesc...@chromium.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Masahiro Yamada <yamada.masah...@socionext.com>
Cc: Michael Davidson <m...@google.com>
Cc: Nick Desaulniers <ndesaulni...@google.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Stephen Hines <srhi...@google.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: diand...@chromium.org
Link: http://lkml.kernel.org/r/20170817004740.170588-1-...@chromium.org
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
arch/x86/Makefile | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 70b3aa9..48f3ae7 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -14,9 +14,11 @@ endif
# For gcc stack alignment is specified with -mpreferred-stack-boundary,
# clang has the option -mstack-alignment for that purpose.
ifneq ($(call cc-option, -mpreferred-stack-boundary=4),)
- cc_stack_align_opt := -mpreferred-stack-boundary
-else ifneq ($(call cc-option, -mstack-alignment=4),)
- cc_stack_align_opt := -mstack-alignment
+ cc_stack_align4 := -mpreferred-stack-boundary=2
+ cc_stack_align8 := -mpreferred-stack-boundary=3
+else ifneq ($(call cc-option, -mstack-alignment=16),)
+ cc_stack_align4 := -mstack-alignment=4
+ cc_stack_align8 := -mstack-alignment=8
endif
# How to compile the 16-bit code. Note we always compile for -march=i386;
@@ -36,7 +38,7 @@ REALMODE_CFLAGS := $(M16_CFLAGS) -g -Os -D__KERNEL__ \
REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS),
-ffreestanding)
REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS),
-fno-stack-protector)
-REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS),
$(cc_stack_align_opt)=2)
+REALMODE_CFLAGS += $(cc_stack_align4)
export REALMODE_CFLAGS
# BITS is used as extension for files which are available in a 32 bit
@@ -76,7 +78,7 @@ ifeq ($(CONFIG_X86_32),y)
# Align the stack to the register width instead of using the default
# alignment of 16 bytes. This reduces stack usage and the number of
# alignment instructions.
- KBUILD_CFLAGS += $(call cc-option,$(cc_stack_align_opt)=2)
+ KBUILD_CFLAGS += $(cc_stack_align4)
# Disable unit-at-a-time mode on pre-gcc-4.0 compilers, it makes gcc
use
# a lot more stack due to the lack of sharing of stacklots:
@@ -115,7 +117,7 @@ else
# default alignment which keep the stack *mis*aligned.
# Furthermore an alignment to the register width reduces stack usage
# and the number of alignment instructions.
- KBUILD_CFLAGS += $(call cc-option,$(cc_stack_align_opt)=3)
+ KBUILD_CFLAGS += $(cc_stack_align8)
# Use -mskip-rax-setup if supported.
KBUILD_CFLAGS += $(call cc-option,-mskip-rax-setup)
