From patchwork Wed Jun 21 23:28:05 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthias Kaehlcke X-Patchwork-Id: 9803157 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 1F8886086C for ; Wed, 21 Jun 2017 23:28:48 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id E9A602785D for ; Wed, 21 Jun 2017 23:28:47 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id CD1CB28415; Wed, 21 Jun 2017 23:28:47 +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=unavailable 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 6A13B2785D for ; Wed, 21 Jun 2017 23:28:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751979AbdFUX2p (ORCPT ); Wed, 21 Jun 2017 19:28:45 -0400 Received: from mail-pg0-f43.google.com ([74.125.83.43]:33760 "EHLO mail-pg0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752171AbdFUX2Z (ORCPT ); Wed, 21 Jun 2017 19:28:25 -0400 Received: by mail-pg0-f43.google.com with SMTP id f127so198898pgc.0 for ; Wed, 21 Jun 2017 16:28:25 -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=huj1Mvg+LiMZNMN2Z1eow6tqOX5b25jMBRMaJ6e/Pi0=; b=Tc8GncoWUPBp3bAKNQT64pxBTnK+q+Gx4wmkl2r0V2+66zOQWc3ZMJzPKoZQ/S2CpJ VBWdRBCMNLevZ7OthtmRJaIbpyXnbQqNcDvmH824MLQ5lrds0UOvwELvzC3kcfM7JKXF ZwOKcrvXtxmHN5KaGEwVffT37Qir3rh5pyrGywXzeDVupWTJrgkknmR6DvaYtxWgcHJ5 PBlZ+Utpm3E9J833QGDhOaLQJNOGSdK6JDJhG3cVYRovFtchotaOCMUOYxrF027GN7Rv M2Iipgt5nTxsYQCQnUB9Md6mKiPvyflzDxPlJ/i3Wd6+w4Jejp36QhhveT/XOrCgXjc9 zF9A== X-Gm-Message-State: AKS2vOyWi/A4GCgsiWyCybzFhVRW8dA48Hbe9I2lqj2Gcx4XCroINOSJ v58JSxqosYpu58y8 X-Received: by 10.84.132.65 with SMTP id 59mr44087512ple.21.1498087704715; Wed, 21 Jun 2017 16:28:24 -0700 (PDT) Received: from mka.mtv.corp.google.com ([172.22.64.162]) by smtp.gmail.com with ESMTPSA id t4sm35618672pfa.68.2017.06.21.16.28.23 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 21 Jun 2017 16:28:24 -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 v5 3/3] x86/build: Specify stack alignment for clang Date: Wed, 21 Jun 2017 16:28:05 -0700 Message-Id: <20170621232805.149448-4-mka@chromium.org> X-Mailer: git-send-email 2.13.1.611.g7e3b11ae1-goog In-Reply-To: <20170621232805.149448-1-mka@chromium.org> References: <20170621232805.149448-1-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 v5: - Use cc-option to probe for a compiler option instead of selecting it based on the compiler name. arch/x86/Makefile | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index b2dae639f778..b32b32b422c2 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -11,6 +11,14 @@ else KBUILD_DEFCONFIG := $(ARCH)_defconfig endif +# For gcc stack alignment is specified with -mpreferred-stack-boundary, +# clang has the option -mstack-alignment for that purpose. +ifneq ($(call cc-option, -mpreferred-stack-boundary=4,),) + cc_stack_align_opt := -mpreferred-stack-boundary +else ifneq ($(call cc-option, -mstack-alignment=4,),) + cc_stack_align_opt := -mstack-alignment +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)