From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933880AbdGKVaL (ORCPT ); Tue, 11 Jul 2017 17:30:11 -0400 Received: from mail-pg0-f47.google.com ([74.125.83.47]:33077 "EHLO mail-pg0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933513AbdGKVaK (ORCPT ); Tue, 11 Jul 2017 17:30:10 -0400 From: Matthias Kaehlcke To: Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , Masahiro Yamada , Michal Marek Cc: x86@kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, dianders@chromium.org, Michael Davidson , Greg Hackmann , Nick Desaulniers , Stephen Hines , Kees Cook , Arnd Bergmann , Bernhard.Rosenkranzer@linaro.org, Matthias Kaehlcke Subject: [PATCH] x86/build: Fix stack alignment for clang Date: Tue, 11 Jul 2017 14:29:40 -0700 Message-Id: <20170711212940.101416-1-mka@chromium.org> X-Mailer: git-send-email 2.13.2.725.g09c95d1e9-goog Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Signed-off-by: Matthias Kaehlcke --- Apparently I had really bad luck when testing d77698df39a5. It fixed the crash I was investigating and the stack in the debugged function looked good with the patch, so I didn't had any doubt that -mstack-alignment=3 (for x86-64) was the correct solution :( If anyone has suggestions for macro magic to encapsulate the different option name and paramater type I'm happy to adapt the patch. I experimented a bit but didn't find a good solution. arch/x86/Makefile | 15 ++++----------- 1 file changed, 4 insertions(+), 11 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 1e902f926be3..9c6f11ebf288 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -11,14 +11,6 @@ else KBUILD_DEFCONFIG := $(ARCH)_defconfig endif -# For gcc stack alignment is specified with -mpreferred-stack-boundary, -# clang has the option -mstack-alignment for that purpose. -ifneq ($(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 -endif - # How to compile the 16-bit code. Note we always compile for -march=i386; # that way we can complain to the user if the CPU is insufficient. # @@ -36,7 +28,8 @@ 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 += $(call __cc-option, $(CC), $(REALMODE_CFLAGS),\ + -mpreferred-stack-boundary=2,-mstack-alignment=4) export REALMODE_CFLAGS # BITS is used as extension for files which are available in a 32 bit @@ -76,7 +69,7 @@ ifeq ($(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 += $(call cc-option,-mpreferred-stack-boundary=2,-mstack-alignment=4) # 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 +108,7 @@ 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 += $(call cc-option,-mpreferred-stack-boundary=3,-mstack-alignment=8) # Use -mskip-rax-setup if supported. KBUILD_CFLAGS += $(call cc-option,-mskip-rax-setup) -- 2.13.2.725.g09c95d1e9-goog