From patchwork Tue Jun 13 23:08:54 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthias Kaehlcke X-Patchwork-Id: 9784919 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 366276038F for ; Tue, 13 Jun 2017 23:10:13 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 28DB02856A for ; Tue, 13 Jun 2017 23:10:13 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 1D110285B1; Tue, 13 Jun 2017 23:10:13 +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 8060C2856A for ; Tue, 13 Jun 2017 23:10:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753961AbdFMXKI (ORCPT ); Tue, 13 Jun 2017 19:10:08 -0400 Received: from mail-pf0-f182.google.com ([209.85.192.182]:36268 "EHLO mail-pf0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753958AbdFMXKH (ORCPT ); Tue, 13 Jun 2017 19:10:07 -0400 Received: by mail-pf0-f182.google.com with SMTP id x63so74453293pff.3 for ; Tue, 13 Jun 2017 16:10:06 -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=ym8UsFcPmaBy8BeypR9/4wZy5W/zXeqXQrsGwvn1jFo=; b=Ah6SvV6C+ZQNRa6wb3LMdf1xoWFTVnSxmVJoFD52DcB7HNHvCAl8BbkgoHtmhFwU2p SFw3YFke3Wg8/6WMAsva4JjY8n75Cm7GoPgNDFxOmMp0qNs8PL9QZ4gl2ZicqmhH5gu4 rQxLiEdWkT7FNEPTqVDCsX5qXiQBqby0Niq1QAl6hBlBqBenm2nHeyfWL7AuZpuHdXB4 EBprBybApYMbKwx9vMfhYIQxZDgy4/Vb14fU4ntIN/SF7BzKThPmNzadALxKKIevAV+V 7tG1c1feblCTm4mJSCOF2z57xym7pKdwBxyrf5O99Gj+/WcINXi2mWYqGJ0KJN7gnLIp jc/w== X-Gm-Message-State: AKS2vOyq6TbVNMHjCSMbI3KYKRzxXIsQWGzDGJnm2+BXKadW3CA1SmBS 9KaAY1jLGCvj5FYY X-Received: by 10.84.224.5 with SMTP id r5mr1796631plj.267.1497395401215; Tue, 13 Jun 2017 16:10:01 -0700 (PDT) Received: from mka.mtv.corp.google.com ([172.22.64.162]) by smtp.gmail.com with ESMTPSA id e18sm29179939pfk.118.2017.06.13.16.10.00 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 13 Jun 2017 16:10:00 -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 v2 4/4] x86/build: Specify stack alignment for clang Date: Tue, 13 Jun 2017 16:08:54 -0700 Message-Id: <20170613230854.112282-5-mka@chromium.org> X-Mailer: git-send-email 2.13.1.518.g3df882009-goog In-Reply-To: <20170613230854.112282-1-mka@chromium.org> References: <20170613230854.112282-1-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 v2: - Changed option name to cc_stack_align_opt - Updated comments about stack alignment arch/x86/Makefile | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 6d3ae4b20a5b..9c3d13999dd3 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-raw, $(CC), $(REALMODE_CFLAGS), -ffreestanding) REALMODE_CFLAGS += $(call cc-option-raw, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector) -REALMODE_CFLAGS += $(call cc-option-raw, $(CC), $(REALMODE_CFLAGS), -mpreferred-stack-boundary=2) +REALMODE_CFLAGS += $(call cc-option-raw, $(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)