From patchwork Sat Apr 6 01:38:45 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 161897 Delivered-To: patch@linaro.org Received: by 2002:a02:c6d8:0:0:0:0:0 with SMTP id r24csp1113047jan; Fri, 5 Apr 2019 18:38:50 -0700 (PDT) X-Google-Smtp-Source: APXvYqzbGCG0Q9ZyExLv78GSxhueFgef7jFs9LRn7pwPlOud1JUtMI4nV8CuonGien7Uvhu1ZhfS X-Received: by 2002:a63:581c:: with SMTP id m28mr15352924pgb.332.1554514730205; Fri, 05 Apr 2019 18:38:50 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1554514730; cv=none; d=google.com; s=arc-20160816; b=kyuLqHG8fxxhNdtGi62+6tuJp9MzGCaCRIxCAQABwiMx3DsKfBRsDnSfgAm/ubEJGN GI3FZGzqxfnw2TkHwYIlQdI0a66h21WgavveCC4GwrKYZ1eA1KLyFA2X3DAouvozYgsS KpvvXK9qxBw3FPNtcmm6v4uo9IDXm7gNG6+R/F0pGkMsfXbZycKDJ5D5q1wAsGX5Vfnk Fo1u8m9PGBvywvvd3ozNbW15OcO1B0G338eky0/tI5IIHW2iD8Vz7u6TQNSFyPUUFanu gHkwACP9EmJLdNu9gdjx7bR1k5hdzokhAdXKaEh9icWJ70oiPHdQAZYwi/HFVkG7M8np WdoA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:user-agent:message-id:subject:to:from :date; bh=V0icJT5hvjHnsSxWT9BGQ1P5B/FKaJlaFyoOaaAm3BM=; b=PKKAG/Ct5HMLQJxJGhhi/HurWrvmS4lgRDImYi3Lu5XFs1o/cSb8aY4QA0caKmYUyd ZaIUMJPf4ZtemYxtLQ6yVLF66RAiAKe5devS0WbzBBJtheAAycwE/wQVris8H9LT6Cdr Yltc3BAvfO6iCm3s3wpnszM2kURr3u3+UQBXRjhiFhoC5vLZYiR/riqXRY3MDRmIA64r 9bmi3cwDWDNBw9fbLRag/QDFiAkddggBq+ymYiVrJpXmreUwTkkOSUAr+w/S2LHnB+Xv xo837As7cnsxKnb1uxmXN3nYnJ9mVcgqs6lqlYBQUKv7YRWv0sv+7KMLFlPm3fK4tvBK eN7Q== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of stable-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=stable-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id a4si20572671pfj.17.2019.04.05.18.38.49; Fri, 05 Apr 2019 18:38:50 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of stable-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of stable-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=stable-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726337AbfDFBit (ORCPT + 14 others); Fri, 5 Apr 2019 21:38:49 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:40968 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725973AbfDFBit (ORCPT ); Fri, 5 Apr 2019 21:38:49 -0400 Received: from localhost.localdomain (c-73-223-200-170.hsd1.ca.comcast.net [73.223.200.170]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id B0AC62537; Sat, 6 Apr 2019 01:38:46 +0000 (UTC) Date: Fri, 05 Apr 2019 18:38:45 -0700 From: akpm@linux-foundation.org To: adhemerval.zanella@linaro.org, akpm@linux-foundation.org, alexander.shishkin@linux.intel.com, andriy.shevchenko@linux.intel.com, arnd@arndb.de, dan.j.williams@intel.com, David.Laight@ACULAB.COM, gregkh@linuxfoundation.org, jyknight@google.com, linux@rasmusvillemoes.dk, mm-commits@vger.kernel.org, namhyung@kernel.org, natechancellor@gmail.com, ndesaulniers@google.com, rostedt@goodmis.org, stable@vger.kernel.org, torvalds@linux-foundation.org, yamada.masahiro@socionext.com Subject: [patch 01/14] lib/string.c: implement a basic bcmp Message-ID: <20190406013845.SWPXm4z6E%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Nick Desaulniers Subject: lib/string.c: implement a basic bcmp 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 Link: http://lkml.kernel.org/r/20190313211335.165605-1-ndesaulniers@google.com Signed-off-by: Nick Desaulniers 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 Acked-by: Steven Rostedt (VMware) Reviewed-by: Nathan Chancellor Tested-by: Nathan Chancellor Reviewed-by: Masahiro Yamada Reviewed-by: Andy Shevchenko Cc: David Laight Cc: Rasmus Villemoes Cc: Namhyung Kim Cc: Greg Kroah-Hartman Cc: Alexander Shishkin Cc: Dan Williams Cc: Signed-off-by: Andrew Morton --- include/linux/string.h | 3 +++ lib/string.c | 20 ++++++++++++++++++++ 2 files changed, 23 insertions(+) --- a/include/linux/string.h~lib-stringc-implement-a-basic-bcmp +++ a/include/linux/string.h @@ -150,6 +150,9 @@ extern void * memscan(void *,int,__kerne #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 --- a/lib/string.c~lib-stringc-implement-a-basic-bcmp +++ a/lib/string.c @@ -866,6 +866,26 @@ __visible int memcmp(const void *cs, con EXPORT_SYMBOL(memcmp); #endif +#ifndef __HAVE_ARCH_BCMP +/** + * bcmp - returns 0 if and only if the buffers have identical contents. + * @a: pointer to first buffer. + * @b: pointer to second buffer. + * @len: size of buffers. + * + * The sign or magnitude of a non-zero return value has no particular + * meaning, and architectures may implement their own more efficient bcmp(). So + * while this particular implementation is a simple (tail) call to memcmp, do + * not rely on anything but whether the return value is zero or non-zero. + */ +#undef bcmp +int bcmp(const void *a, const void *b, size_t len) +{ + return memcmp(a, b, len); +} +EXPORT_SYMBOL(bcmp); +#endif + #ifndef __HAVE_ARCH_MEMSCAN /** * memscan - Find a character in an area of memory.