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From: Matthias Kaehlcke <mka@chromium.org>
To: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org, dianders@chromium.org,
        Michael Davidson <md@google.com>, Greg Hackmann <ghackmann@google.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Stephen Hines <srhines@google.com>, Kees Cook <keescook@chromium.org>,
        Arnd Bergmann <arnd@arndb.de>, Bernhard.Rosenkranzer@linaro.org,
        Matthias Kaehlcke <mka@chromium.org>
Subject: [PATCH] x86/build: Use cc-option to validate stack alignment parameter
Date: Thu, 17 Aug 2017 11:20:47 -0700
Message-Id: <20170817182047.176752-1-mka@chromium.org>
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With 8f91869766c0 ("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 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.

Fixes: 8f91869766c0 ("x86/build: Fix stack alignment for CLang")
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
 arch/x86/Makefile | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 65ed359eb904..9231bbfae670 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -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 *mis*aligned.
         # 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)
-- 
2.14.1.480.gb18f417b89-goog