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=-21.6 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable 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 D4B17C4360F for ; Wed, 13 Mar 2019 20:37:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A1DC0213A2 for ; Wed, 13 Mar 2019 20:37:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="JVx8Cdn4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727291AbfCMUhv (ORCPT ); Wed, 13 Mar 2019 16:37:51 -0400 Received: from mail-ot1-f73.google.com ([209.85.210.73]:53858 "EHLO mail-ot1-f73.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726889AbfCMUhu (ORCPT ); Wed, 13 Mar 2019 16:37:50 -0400 Received: by mail-ot1-f73.google.com with SMTP id h10so1354424otl.20 for ; Wed, 13 Mar 2019 13:37:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=8HB51ltATTSFxrkKUn27F32DnBWWX1A5orTg6yCiOwk=; b=JVx8Cdn4Ohqbx6G4FMQBhLTgsdin8muSSnuiMoHKCJBOqYlKSfJF2NuZk4mK4gmjhc OBSTJr2GDoreZ53iauDU9qux56ei152bzSYTX4/hLVQLW8P/S5940Cr+5oS/Qm7UTNSf Jor3ILoCz/hilhwYhHYIwywgaUW3JuTKzygXd+Ote+5NQZMWAvgBI+KDwPbwNPtE2ZOQ 6OG3Bnuz9F5RIwJ/Po8hiilPK1l4zFxrGKN/cpFlPJOJMN0X5GkaXYaFGZLtLpSI3vIg hmJtkvxQ/yTpDMHy9mVI26pysegV5zsuK/r+UuYdrFKIpHIor3ZOOC8XHo8eO8RV4LTG VnoA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=8HB51ltATTSFxrkKUn27F32DnBWWX1A5orTg6yCiOwk=; b=QdXNySf96fnRCzl1anBHodoE/SPAWigRUu08v3+Zfz+4CGI2p6hgRqrZTH6mFcFMcD 3s9kSO36JHSTC4QUk/x1T3X9QzNgy7P2aEgJ6Ack6RmVVSEeERlIudn6INIAeXWqUCLO pUTYrmpTXDgDkxGiz3FBxO5YVHGWtRXm5yDgnxwu2hdf1Vm0uaWkqe5QczWSaCO/R5j0 BqRTOL7iQfmXnRNZK3zlMURNKwBuSK+vRMpzZjWH0UrQ3/4Zowk7pvA3Tn60fCx1uQVH F8r5Q3bHBAGrPdg0nYRMsPaZ/n8oXkVgsCIIfz7fNQR8EUT+9/enCcBfCGjdI+IzOAuk 9rwQ== X-Gm-Message-State: APjAAAWPfpfTTUvvPAXv2bsnNHYYtoXyPgdWPTiXHRkfrgXoi8yBRscC bol9bzvtfsnsAS79DbNfkSWQihAVCyS3B//cjoQ= X-Google-Smtp-Source: APXvYqy8rPYkhjA6+/nL4T7P745g01Bb3rvA7boGj+VCpW2DI1HGxoaUE0Hq2JxQpXPUOWnURu58me69OQPHjqGr7kM= X-Received: by 2002:a9d:77d1:: with SMTP id w17mr24715818otl.65.1552509469760; Wed, 13 Mar 2019 13:37:49 -0700 (PDT) Date: Wed, 13 Mar 2019 13:37:37 -0700 In-Reply-To: <20190313161221.41797313@gandalf.local.home> Message-Id: <20190313203741.142380-1-ndesaulniers@google.com> Mime-Version: 1.0 References: <20190313161221.41797313@gandalf.local.home> X-Mailer: git-send-email 2.21.0.360.g471c308f928-goog Subject: [PATCH v3] lib/string.c: implement a basic bcmp From: Nick Desaulniers To: akpm@linux-foundation.org Cc: clang-built-linux@googlegroups.com, linux-kbuild@vger.kernel.org, Nick Desaulniers , stable@vger.kernel.org, Nathan Chancellor , Adhemerval Zanella , Arnd Bergmann , James Y Knight , Masahiro Yamada , Rasmus Villemoes , Steven Rostedt , Andy Shevchenko , Dan Williams , Namhyung Kim , Alexander Shishkin , Greg Kroah-Hartman , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A recent optimization in Clang (r355672) lowers comparisons of the return value of memcmp against zero to comparisons of the return value of bcmp against zero. This helps some platforms that implement bcmp more efficiently than memcmp. glibc simply aliases bcmp to memcmp, but an optimized implementation is in the works. This results in linkage failures for all targets with Clang due to the undefined symbol. For now, just implement bcmp as a tailcail to memcmp to unbreak the build. This routine can be further optimized in the future. Other ideas discussed: * A weak alias was discussed, but breaks for architectures that define their own implementations of memcmp since aliases to declarations are not permitted (only definitions). Arch-specific memcmp implementations typically declare memcmp in C headers, but implement them in assembly. * -ffreestanding also is used sporadically throughout the kernel. * -fno-builtin-bcmp doesn't work when doing LTO. Link: https://bugs.llvm.org/show_bug.cgi?id=41035 Link: https://code.woboq.org/userspace/glibc/string/memcmp.c.html#bcmp Link: https://github.com/llvm/llvm-project/commit/8e16d73346f8091461319a7dfc4ddd18eedcff13 Link: https://github.com/ClangBuiltLinux/linux/issues/416 Cc: stable@vger.kernel.org Reported-by: Nathan Chancellor Reported-by: Adhemerval Zanella Suggested-by: Arnd Bergmann Suggested-by: James Y Knight Suggested-by: Masahiro Yamada Suggested-by: Nathan Chancellor Suggested-by: Rasmus Villemoes Signed-off-by: Nick Desaulniers Acked-by: Steven Rostedt (VMware) --- Changes V2 -> V3: * Adjust comment as per Steven to Rasmus' sugguestion. * Pick up Steven's Ack. Changes V1 -> V2: * Add declaration to include/linux/string.h. * Reword comment above bcmp. include/linux/string.h | 3 +++ lib/string.c | 15 +++++++++++++++ 2 files changed, 18 insertions(+) diff --git a/include/linux/string.h b/include/linux/string.h index 7927b875f80c..6ab0a6fa512e 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -150,6 +150,9 @@ extern void * memscan(void *,int,__kernel_size_t); #ifndef __HAVE_ARCH_MEMCMP extern int memcmp(const void *,const void *,__kernel_size_t); #endif +#ifndef __HAVE_ARCH_BCMP +extern int bcmp(const void *,const void *,__kernel_size_t); +#endif #ifndef __HAVE_ARCH_MEMCHR extern void * memchr(const void *,int,__kernel_size_t); #endif diff --git a/lib/string.c b/lib/string.c index 38e4ca08e757..48a43a42d3f2 100644 --- a/lib/string.c +++ b/lib/string.c @@ -866,6 +866,21 @@ __visible int memcmp(const void *cs, const void *ct, size_t count) EXPORT_SYMBOL(memcmp); #endif +#ifndef __HAVE_ARCH_BCMP +/** + * bcmp - returns 0 if and only if the buffers have identical contents. + * @cs: One area of memory. + * @ct: Another area of memory. + * @count: The size of the areas. + */ +#undef bcmp +int bcmp(const void *cs, const void *ct, size_t count) +{ + return memcmp(cs, ct, count); +} +EXPORT_SYMBOL(bcmp); +#endif + #ifndef __HAVE_ARCH_MEMSCAN /** * memscan - Find a character in an area of memory. -- 2.21.0.360.g471c308f928-goog