Commit 9e8730b1 authored Aug 17, 2017 by Matthias Kaehlcke Committed by Ingo Molnar Aug 21, 2017

x86/build: Use cc-option to validate stack alignment parameter



With the following commit:

  8f918697 ("x86/build: Fix stack alignment for CLang")

cc-option is only used to determine the name of the stack alignment option
supported by the compiler, but not to verify that the actual parameter
<option>=N is valid in combination with the other CFLAGS.

This causes problems (as reported by the kbuild robot) with older GCC versions
which only support stack alignment on a boundary of 16 bytes or higher.

Also use (__)cc_option to add the stack alignment option to CFLAGS to
make sure only valid options are added.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Bernhard.Rosenkranzer@linaro.org
Cc: Greg Hackmann <ghackmann@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Michael Davidson <md@google.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hines <srhines@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dianders@chromium.org
Fixes: 8f918697 ("x86/build: Fix stack alignment for CLang")
Link: http://lkml.kernel.org/r/20170817182047.176752-1-mka@chromium.org


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

parent 8f918697

arch/x86/Makefile

+3 −3

Original line number	Diff line number	Diff line
		@@ -38,7 +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 += $(cc_stack_align4)
		REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
		export REALMODE_CFLAGS

		# BITS is used as extension for files which are available in a 32 bit
		@@ -78,7 +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 += $(cc_stack_align4)
		KBUILD_CFLAGS += $(call cc-option,$(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:
		@@ -117,7 +117,7 @@ else
		# default alignment which keep the stack misaligned.
		# Furthermore an alignment to the register width reduces stack usage
		# and the number of alignment instructions.
		KBUILD_CFLAGS += $(cc_stack_align8)
		KBUILD_CFLAGS += $(call cc-option,$(cc_stack_align8))

		# Use -mskip-rax-setup if supported.
		KBUILD_CFLAGS += $(call cc-option,-mskip-rax-setup)

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