| From foo@baz Wed Nov 21 18:50:25 CET 2018 |
| From: Matthias Kaehlcke <mka@chromium.org> |
| Date: Wed, 16 Aug 2017 17:47:40 -0700 |
| Subject: x86/build: Fix stack alignment for CLang |
| |
| From: Matthias Kaehlcke <mka@chromium.org> |
| |
| commit 8f91869766c00622b2eaa8ee567db4f333b78c1a upstream. |
| |
| 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 += |
| $(call cc-option ...). The reason is that older gcc versions don't |
| support the -mpreferred-stack-boundary option, since cc-option doesn't |
| verify whether the alternative option is valid it would incorrectly |
| select the clang option -mstack-alignment.. |
| |
| Signed-off-by: Matthias Kaehlcke <mka@chromium.org> |
| Cc: Arnd Bergmann <arnd@arndb.de> |
| Cc: Bernhard.Rosenkranzer@linaro.org |
| Cc: Greg Hackmann <ghackmann@google.com> |
| Cc: Kees Cook <keescook@chromium.org> |
| Cc: Linus Torvalds <torvalds@linux-foundation.org> |
| Cc: Masahiro Yamada <yamada.masahiro@socionext.com> |
| Cc: Michael Davidson <md@google.com> |
| Cc: Nick Desaulniers <ndesaulniers@google.com> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Cc: Stephen Hines <srhines@google.com> |
| Cc: Thomas Gleixner <tglx@linutronix.de> |
| Cc: dianders@chromium.org |
| Link: http://lkml.kernel.org/r/20170817004740.170588-1-mka@chromium.org |
| Signed-off-by: Ingo Molnar <mingo@kernel.org> |
| Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| arch/x86/Makefile | 14 ++++++++------ |
| 1 file changed, 8 insertions(+), 6 deletions(-) |
| |
| --- a/arch/x86/Makefile |
| +++ b/arch/x86/Makefile |
| @@ -14,9 +14,11 @@ endif |
| # For gcc stack alignment is specified with -mpreferred-stack-boundary, |
| # clang has the option -mstack-alignment for that purpose. |
| ifneq ($(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 |
| |
| 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) |