Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753326AbdFMA4e (ORCPT ); Mon, 12 Jun 2017 20:56:34 -0400 Received: from mail-pg0-f46.google.com ([74.125.83.46]:36572 "EHLO mail-pg0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753242AbdFMA4E (ORCPT ); Mon, 12 Jun 2017 20:56:04 -0400 From: Matthias Kaehlcke To: Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , "H . J . Lu" , David Woodhouse , Masahiro Yamada , Michal Marek Cc: x86@kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, Michael Davidson , Greg Hackmann , Nick Desaulniers , Stephen Hines , Kees Cook , Arnd Bergmann , Bernhard.Rosenkranzer@linaro.org, Peter Foley , Behan Webster , Douglas Anderson , Matthias Kaehlcke Subject: [PATCH 3/3] x86/build: Specify stack alignment for clang Date: Mon, 12 Jun 2017 17:55:31 -0700 Message-Id: <20170613005531.77656-4-mka@chromium.org> X-Mailer: git-send-email 2.13.1.508.gb3defc5cc-goog In-Reply-To: <20170613005531.77656-1-mka@chromium.org> References: <20170613005531.77656-1-mka@chromium.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2802 Lines: 68 For gcc stack alignment is configured with -mpreferred-stack-boundary=N, clang has the option -mstack-alignment=N for that purpose. Use the same alignment as for gcc. If the alignment is not specified clang assumes an alignment of 16 bytes, as required by the standard ABI. However as mentioned in d9b0cde91c60 ("x86-64, gcc: Use -mpreferred-stack-boundary=3 if supported") the standard kernel entry on x86-64 leaves the stack on an 8-byte boundary, as a consequence clang will keep the stack misaligned. Signed-off-by: Matthias Kaehlcke --- arch/x86/Makefile | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 86b725d69423..7f6c33f4d428 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -11,6 +11,14 @@ else KBUILD_DEFCONFIG := $(ARCH)_defconfig endif +# Handle different option names for specifying stack alignment with gcc and +# clang. +ifeq ($(cc-name),clang) + stack_align_opt := -mstack-alignment +else + stack_align_opt := -mpreferred-stack-boundary +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. # @@ -28,7 +36,7 @@ REALMODE_CFLAGS := $(M16_CFLAGS) -g -Os -D__KERNEL__ \ REALMODE_CFLAGS += $(call cc-option-no-kbuild, $(REALMODE_CFLAGS), -ffreestanding) REALMODE_CFLAGS += $(call cc-option-no-kbuild, $(REALMODE_CFLAGS), -fno-stack-protector) -REALMODE_CFLAGS += $(call cc-option-no-kbuild, $(REALMODE_CFLAGS), -mpreferred-stack-boundary=2) +REALMODE_CFLAGS += $(call cc-option-no-kbuild, $(REALMODE_CFLAGS), $(stack_align_opt)=2) export REALMODE_CFLAGS # BITS is used as extension for files which are available in a 32 bit @@ -65,8 +73,8 @@ ifeq ($(CONFIG_X86_32),y) # with nonstandard options KBUILD_CFLAGS += -fno-pic - # prevent gcc from keeping the stack 16 byte aligned - KBUILD_CFLAGS += $(call cc-option,-mpreferred-stack-boundary=2) + # prevent the compiler from keeping the stack 16 byte aligned + KBUILD_CFLAGS += $(call cc-option,$(stack_align_opt)=2) # 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: @@ -98,8 +106,8 @@ else KBUILD_CFLAGS += $(call cc-option,-mno-80387) KBUILD_CFLAGS += $(call cc-option,-mno-fp-ret-in-387) - # Use -mpreferred-stack-boundary=3 if supported. - KBUILD_CFLAGS += $(call cc-option,-mpreferred-stack-boundary=3) + # Align the stack to 8 bytes if supported. + KBUILD_CFLAGS += $(call cc-option,$(stack_align_opt)=3) # Use -mskip-rax-setup if supported. KBUILD_CFLAGS += $(call cc-option,-mskip-rax-setup) -- 2.13.1.508.gb3defc5cc-goog