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

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

[Matthias Kaehlcke]

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

Re: [PATCH] x86/build: Use cc-option to validate stack alignment parameter

[Ingo Molnar]

* Matthias Kaehlcke <mka@chromium.org> wrote:

> 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>

I've added the kbuild-bot Reported-by tag to document (and credit) how this bug 
was found.

Thanks,

	Ingo

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

[tip-bot for Matthias Kaehlcke]

Commit-ID:  9e8730b178a2472fca3123e909d6e69cc8127778
Gitweb:     http://git.kernel.org/tip/9e8730b178a2472fca3123e909d6e69cc8127778
Author:     Matthias Kaehlcke <mka@chromium.org>
AuthorDate: Thu, 17 Aug 2017 11:20:47 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 21 Aug 2017 09:53:15 +0200

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

With the following commit:

  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 (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: 8f91869766c0 ("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>
---
 arch/x86/Makefile | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 48f3ae7..6276572 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)