From patchwork Thu Jun 15 17:37:15 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthias Kaehlcke X-Patchwork-Id: 9789455 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 D9F2D60325 for ; Thu, 15 Jun 2017 17:43:08 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id CD49F2863A for ; Thu, 15 Jun 2017 17:43:08 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id C1CB828659; Thu, 15 Jun 2017 17:43:08 +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 EA58C28662 for ; Thu, 15 Jun 2017 17:43:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751644AbdFORnB (ORCPT ); Thu, 15 Jun 2017 13:43:01 -0400 Received: from mail-pf0-f177.google.com ([209.85.192.177]:34701 "EHLO mail-pf0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752030AbdFORm7 (ORCPT ); Thu, 15 Jun 2017 13:42:59 -0400 Received: by mail-pf0-f177.google.com with SMTP id s66so10574944pfs.1 for ; Thu, 15 Jun 2017 10:42:59 -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=DMgR2uHdTAcTV0D1lLMwPqzOBpTGigNdZEakcEq51Mo=; b=aZPNuRH36Ew8zjAK9xSzVCJrFcJpyH4rp9jTTldKsTI1LAOYw5DAAtXtLuSJetSzme Gdg6js/Y7c5+nubenQz352zhr0b7+LHK0xB2q0og9a36f9OAepqQyztaj5nUwRxvWKIj BexJTq7XSD5hmXua9ltfw80lxPyR4GTcEdtJZYLBKeQWbzSuKf1WpMfcAOYFWwyDZvjH CPCEmm4dP6YmrHLRdPfAoFb8fzhKbef5Uj9usCSoIXn4/QkIcc+jaf2m+hAAb7xFUwei Q/s5JMXz9jZuOnZlrI6cgrJxnQCp7ObkWEqckVf5fwpItxSRGem9g2fk3eE8wXd8D/bt FYhA== X-Gm-Message-State: AKS2vOzVEKUTW6h0mS7v+Hrk5hEM5gFe0tXoVOmCcf0JenoX66gea7id MElVz97c1kz/s3Q4 X-Received: by 10.98.0.77 with SMTP id 74mr2307490pfa.127.1497548573452; Thu, 15 Jun 2017 10:42:53 -0700 (PDT) Received: from mka.mtv.corp.google.com ([172.22.64.162]) by smtp.gmail.com with ESMTPSA id t2sm1320974pfi.76.2017.06.15.10.42.52 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 15 Jun 2017 10:42:52 -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 v3 3/3] x86/build: Specify stack alignment for clang Date: Thu, 15 Jun 2017 10:37:15 -0700 Message-Id: <20170615173715.40882-4-mka@chromium.org> X-Mailer: git-send-email 2.13.1.518.g3df882009-goog In-Reply-To: <20170615173715.40882-1-mka@chromium.org> References: <20170615173715.40882-1-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 --- Changes in v3: - Use __cc-option instead of cc-option-raw 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)