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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 7C1E8C43381 for ; Wed, 13 Mar 2019 13:44:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 480172087C for ; Wed, 13 Mar 2019 13:44:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="JndfyBpO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726686AbfCMNow (ORCPT ); Wed, 13 Mar 2019 09:44:52 -0400 Received: from mail-ed1-f66.google.com ([209.85.208.66]:39531 "EHLO mail-ed1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725832AbfCMNow (ORCPT ); Wed, 13 Mar 2019 09:44:52 -0400 Received: by mail-ed1-f66.google.com with SMTP id p27so1558081edc.6; Wed, 13 Mar 2019 06:44:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=xCrZ11yOtG8QPfE2HPpjToUUNBz0tmsHnDhPpk0RrFw=; b=JndfyBpOpO7mw96jMujoAMZEEmi1z+gnB3Tu8xfWNYjiuLi6MjFevP0MUU6Fz22iz0 t7uTin20+dlrUzw60kmUqtgvhHdAuYfjnFDA05TKwLgvfktlAsZcBNf3R/ZE+whZidF+ VNFH16mwbGgFOWHlkUEDoz3OSJOb3yxrBxn1g3YeAE2UD5kNZ3Qm+jsGfgGuvOmZjipt KTjrTvIuwu62PWE9oAFG1j06AVGJz+y6WPXgJ51Sz58TnEsQJfNEAXz5u6IHKHkxwDOe +tDA0lJvCo4mSIhgQ+oV7pshI4hswOlAEDaCED2d7AipH9GZoDmvHlSKutpTpUngNTvh SsMw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=xCrZ11yOtG8QPfE2HPpjToUUNBz0tmsHnDhPpk0RrFw=; b=hOXjFBbJkZkeXvR8GHUzWvDthzOYAdbwBLert44lK1dh6ZZl+fnUOJd6vjHpkoTHuz BsXhEM0kLSVJR2Fe1hrpJ1eBK9HLV7je0jZv22zk7qEiptg1Ke1LerNnsrsGGQUmL77X XxLdhELnsZHOI3zEAWZqwU4iH2XKW0Y+jgfTUyQoHEwHcmUZfRtoj2Lwt+6hEMY4BKmS S2gOe4UQXZhVWbZQQ3bkrZ3v4rZp7QF8jYH4CfWySvBe8afjM8RDrte/DZh6Vwzl+lp9 AZo0GVraFxxwUVfFhQQBtsMCsqeoouxpZESAY84K9lZWLdrm8eSkDa49CvpSL47dIIJT i84g== X-Gm-Message-State: APjAAAXyVzjFQ5oeSqdh4YwUbdueKzRF+81NGh0PNiLwiPKr2VSmRSeh rACm4ad3zk0xgctRFS+9IOY= X-Google-Smtp-Source: APXvYqxq5cxIArdoYFVirpt+py4JxRmGlbwJk3Vh4/j3HYspiikIEehTkFQikKdYtMP3LXG0Q+Edkg== X-Received: by 2002:a50:b4e6:: with SMTP id x35mr7754879edd.123.1552484689889; Wed, 13 Mar 2019 06:44:49 -0700 (PDT) Received: from archlinux-ryzen ([2a01:4f9:2a:1fae::2]) by smtp.gmail.com with ESMTPSA id b10sm591501edy.80.2019.03.13.06.44.48 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Wed, 13 Mar 2019 06:44:49 -0700 (PDT) Date: Wed, 13 Mar 2019 06:44:47 -0700 From: Nathan Chancellor To: Rasmus Villemoes Cc: Masahiro Yamada , Michal Marek , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, Nick Desaulniers , Arnd Bergmann , James Y Knight , clang-built-linux@googlegroups.com, stable@vger.kernel.org Subject: Re: [PATCH] Makefile: Add '-fno-builtin-bcmp' to CLANG_FLAGS Message-ID: <20190313134447.GA19066@archlinux-ryzen> References: <20190312215203.27643-1-natechancellor@gmail.com> <80fb5b7f-42f9-4fd1-00cf-bfa7965ff8f7@rasmusvillemoes.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <80fb5b7f-42f9-4fd1-00cf-bfa7965ff8f7@rasmusvillemoes.dk> User-Agent: Mutt/1.11.3 (2019-02-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 13, 2019 at 09:13:11AM +0100, Rasmus Villemoes wrote: > On 12/03/2019 22.52, Nathan Chancellor wrote: > > After LLVM revision r355672 [1], all known working kernel configurations > > fail to link [2]: > > > > ld: init/do_mounts.o: in function `prepare_namespace': > > do_mounts.c:(.init.text+0x5ca): undefined reference to `bcmp' > > ld: do_mounts.c:(.init.text+0x5e6): undefined reference to `bcmp' > > ld: init/initramfs.o: in function `do_header': > > initramfs.c:(.init.text+0x6e0): undefined reference to `bcmp' > > ld: initramfs.c:(.init.text+0x6f8): undefined reference to `bcmp' > > ld: arch/x86/kernel/setup.o: in function `setup_arch': > > setup.c:(.init.text+0x21d): undefined reference to `bcmp' > > > > Commit 6edfba1b33c7 ("[PATCH] x86_64: Don't define string functions to > > builtin") removed '-ffreestanding' globally and the kernel doesn't > > provide a bcmp definition so the linker cannot find a reference to it. > > > > > Fix this by explicitly telling LLVM through Clang not to emit bcmp > > references. This flag does not need to be behind 'cc-option' because all > > working versions of Clang support this flag. > > Wouldn't it be better to just define bcmp as an alias for memcmp? They > seem to have compatible prototypes, and then somebody might someday sit > down and implement some word-at-a-time version of bcmp making use of the > weaker guarantees about the return value to gain some performance. But I > suppose that can also be done later. > > Rasmus Hi Rasmus, Thank you much for the review, I didn't even realize this was possible :) I'd certainly like to explore it as that is what glibc does. How would you suggest going about it here? Thanks, Nathan