From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751656AbdFIRcW (ORCPT ); Fri, 9 Jun 2017 13:32:22 -0400 Received: from mail-pf0-f175.google.com ([209.85.192.175]:32892 "EHLO mail-pf0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751535AbdFIRcV (ORCPT ); Fri, 9 Jun 2017 13:32:21 -0400 From: Matthias Kaehlcke To: Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , "H . J . Lu" Cc: x86@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] x86/build: Specify stack alignment for clang Date: Fri, 9 Jun 2017 10:31:34 -0700 Message-Id: <20170609173134.181976-1-mka@chromium.org> X-Mailer: git-send-email 2.13.0.506.g27d5fe0cd-goog Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 5851411e60fb..a32badbe87ad 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -27,7 +27,8 @@ REALMODE_CFLAGS := $(M16_CFLAGS) -g -Os -D__KERNEL__ \ -mno-mmx -mno-sse \ $(call cc-option, -ffreestanding) \ $(call cc-option, -fno-stack-protector) \ - $(call cc-option, -mpreferred-stack-boundary=2) + $(call cc-option, -mpreferred-stack-boundary=2) \ + $(call cc-option, -mstack-alignment=2) export REALMODE_CFLAGS # BITS is used as extension for files which are available in a 32 bit @@ -64,8 +65,9 @@ ifeq ($(CONFIG_X86_32),y) # with nonstandard options KBUILD_CFLAGS += -fno-pic - # prevent gcc from keeping the stack 16 byte aligned + # prevent the compiler from keeping the stack 16 byte aligned KBUILD_CFLAGS += $(call cc-option,-mpreferred-stack-boundary=2) + KBUILD_CFLAGS += $(call cc-option,-mstack-alignment=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: @@ -97,8 +99,9 @@ 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. + # Align the stack to 8 bytes if supported. KBUILD_CFLAGS += $(call cc-option,-mpreferred-stack-boundary=3) + KBUILD_CFLAGS += $(call cc-option,-mstack-alignment=3) # Use -mskip-rax-setup if supported. KBUILD_CFLAGS += $(call cc-option,-mskip-rax-setup) -- 2.13.0.506.g27d5fe0cd-goog