From patchwork Mon Jun 19 18:37:57 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthias Kaehlcke X-Patchwork-Id: 9797281 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id AC28E600C5 for ; Mon, 19 Jun 2017 18:38:53 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 8EA941FF60 for ; Mon, 19 Jun 2017 18:38:53 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 8383726B39; Mon, 19 Jun 2017 18:38:53 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1AAD61FF60 for ; Mon, 19 Jun 2017 18:38:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753996AbdFSSiu (ORCPT ); Mon, 19 Jun 2017 14:38:50 -0400 Received: from mail-pg0-f54.google.com ([74.125.83.54]:35214 "EHLO mail-pg0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753469AbdFSSir (ORCPT ); Mon, 19 Jun 2017 14:38:47 -0400 Received: by mail-pg0-f54.google.com with SMTP id 132so18186085pgb.2 for ; Mon, 19 Jun 2017 11:38:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=rl3wdcwsZxIg8ex0LAd+QbITC9tQfz+tDc2CG+tFYx0=; b=F9Jsp0BF1Ys3BuTeceMXHk112pLEPEaYsCXmNhphynRt2KU1WTCqhZKC7teT+1EN2N DhjOz80K4X+XcMMtlCIxbS273JfddsmlvH6xzrMyBiOhpbc3QgRgG5W8JcSoRYXO4Jnh 8VkUm1EoYzEblC3oEKbBJuJftbOzx4k4roXwZ5OdFyAYFsqsXcLXfCkWAh0A75/CDF0F M0ZnW9YVGnIvATVbiqOY2DUyM/TvXC5Tg8EI1C2UqqghRuJJsYi3yursDK3UvcgwI4Cj lYhcHffGNtYJ6UWJy3TOyaL3T9UKY78y0DIUp7l7J2g/rX7knaik1X+dyDB/5Q+4Hw9z uYRQ== X-Gm-Message-State: AKS2vOwn8nr8KDQ+rSDIa2G8Mp5D2MlvVgmow6+cBU76wCk/aodNbHV3 nIId+BipkC+uxikE X-Received: by 10.101.73.8 with SMTP id p8mr27990521pgs.0.1497897521914; Mon, 19 Jun 2017 11:38:41 -0700 (PDT) Received: from mka.mtv.corp.google.com ([172.22.64.162]) by smtp.gmail.com with ESMTPSA id a4sm9889673pfc.22.2017.06.19.11.38.40 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 19 Jun 2017 11:38:41 -0700 (PDT) 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 v4 3/3] x86/build: Specify stack alignment for clang Date: Mon, 19 Jun 2017 11:37:57 -0700 Message-Id: <20170619183757.124992-4-mka@chromium.org> X-Mailer: git-send-email 2.13.1.518.g3df882009-goog In-Reply-To: <20170619183757.124992-1-mka@chromium.org> References: <20170619183757.124992-1-mka@chromium.org> Sender: linux-kbuild-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 with 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 | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index b2dae639f778..9406d3670452 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) + cc_stack_align_opt := -mstack-alignment +else + cc_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, $(CC), $(REALMODE_CFLAGS), -ffreestanding) REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector) -REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -mpreferred-stack-boundary=2) +REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align_opt)=2) export REALMODE_CFLAGS # BITS is used as extension for files which are available in a 32 bit @@ -65,8 +73,10 @@ ifeq ($(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) + # 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) # 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 +108,14 @@ 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) + # By default gcc and clang use a stack alignment of 16 bytes for x86. + # However the standard kernel entry on x86-64 leaves the stack on an + # 8-byte boundary. If the compiler isn't informed about the actual + # alignment it will generate extra alignment instructions for the + # 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) # Use -mskip-rax-setup if supported. KBUILD_CFLAGS += $(call cc-option,-mskip-rax-setup)