From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C332BC0044C for ; Mon, 5 Nov 2018 14:37:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 87F9220819 for ; Mon, 5 Nov 2018 14:37:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 87F9220819 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zytor.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730059AbeKEX5R (ORCPT ); Mon, 5 Nov 2018 18:57:17 -0500 Received: from terminus.zytor.com ([198.137.202.136]:60145 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726255AbeKEX5R (ORCPT ); Mon, 5 Nov 2018 18:57:17 -0500 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id wA5Earep368360 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Mon, 5 Nov 2018 06:36:53 -0800 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id wA5EarhN368357; Mon, 5 Nov 2018 06:36:53 -0800 Date: Mon, 5 Nov 2018 06:36:53 -0800 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Nathan Chancellor Message-ID: Cc: natechancellor@gmail.com, yamada.masahiro@socionext.com, hpa@zytor.com, tglx@linutronix.de, mingo@kernel.org, bp@alien8.de, ndesaulniers@google.com, keescook@chromium.org, namit@vmware.com, linux-kernel@vger.kernel.org Reply-To: yamada.masahiro@socionext.com, natechancellor@gmail.com, hpa@zytor.com, tglx@linutronix.de, bp@alien8.de, mingo@kernel.org, ndesaulniers@google.com, keescook@chromium.org, namit@vmware.com, linux-kernel@vger.kernel.org In-Reply-To: <20181023231125.27976-1-natechancellor@gmail.com> References: <20181023231125.27976-1-natechancellor@gmail.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/urgent] x86/build: Remove -pipe from KBUILD_CFLAGS Git-Commit-ID: f87419e1c9b5d38ea8a81b31e90aefa1be3fde5d X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: f87419e1c9b5d38ea8a81b31e90aefa1be3fde5d Gitweb: https://git.kernel.org/tip/f87419e1c9b5d38ea8a81b31e90aefa1be3fde5d Author: Nathan Chancellor AuthorDate: Tue, 23 Oct 2018 16:11:25 -0700 Committer: Thomas Gleixner CommitDate: Mon, 5 Nov 2018 15:32:40 +0100 x86/build: Remove -pipe from KBUILD_CFLAGS Commit 77b0bf55bc67 ("kbuild/Makefile: Prepare for using macros in inline assembly code to work around asm() related GCC inlining bugs") added -Wa,- to KBUILD_CFLAGS, which breaks compiling with Clang (hangs indefinitely at compiling init/main.o). This happens because while Clang accepts -pipe (and has it documented in its list of supported flags), it silently ignores it after this 2010 commit (thanks to Nick Desaulniers for tracking this down), meaning that gas just infinitely waits for stdin and never receives it. https://github.com/llvm-mirror/clang/commit/c19a12dc3d441bec62eed55e312b76c12d6d9022 Initially, I had suggested just add -Wa,- to KBUILD_CFLAGS when GCC was being used but that was before realizing it is because Clang doesn't do anything with -pipe. H. Peter Anvin suggested checking to see if -pipe gives us any gains out of GCC. Turns out it might actually be hurting: With -pipe: real 3m40.813s real 3m44.449s real 3m39.648s Without -pipe: real 3m38.492s real 3m38.335s real 3m38.975s The issue of -Wa,- being passed along to gas without -pipe being supported should still probably be fixed on the LLVM side (open issue: https://bugs.llvm.org/show_bug.cgi?id=39410) but this is not as much of a workaround anymore since it helps both GCC and Clang. Suggested-by: H. Peter Anvin Signed-off-by: Nathan Chancellor Signed-off-by: Thomas Gleixner Tested-by: Nick Desaulniers Reviewed-by: Nadav Amit Reviewed-by: Nick Desaulniers Cc: Borislav Petkov Cc: Kees Cook Cc: Masahiro Yamada Link: https://github.com/ClangBuiltLinux/linux/issues/213 Link: https://lkml.kernel.org/r/20181023231125.27976-1-natechancellor@gmail.com --- arch/x86/Makefile | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 5b562e464009..88398fdf8129 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -213,8 +213,6 @@ ifdef CONFIG_X86_64 KBUILD_LDFLAGS += $(call ld-option, -z max-page-size=0x200000) endif -# Speed up the build -KBUILD_CFLAGS += -pipe # Workaround for a gcc prelease that unfortunately was shipped in a suse release KBUILD_CFLAGS += -Wno-sign-compare # @@ -239,7 +237,7 @@ archheaders: archmacros: $(Q)$(MAKE) $(build)=arch/x86/kernel arch/x86/kernel/macros.s -ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s -Wa,- +ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s export ASM_MACRO_FLAGS KBUILD_CFLAGS += $(ASM_MACRO_FLAGS)