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=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 03428C43381 for ; Wed, 13 Mar 2019 18:17:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BF2A02075C for ; Wed, 13 Mar 2019 18:17:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="I6Qm7AcN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726922AbfCMSRi (ORCPT ); Wed, 13 Mar 2019 14:17:38 -0400 Received: from mail-vs1-f74.google.com ([209.85.217.74]:43799 "EHLO mail-vs1-f74.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726427AbfCMSRi (ORCPT ); Wed, 13 Mar 2019 14:17:38 -0400 Received: by mail-vs1-f74.google.com with SMTP id y189so654851vsc.10 for ; Wed, 13 Mar 2019 11:17:37 -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=B7yTfa6bCcb9PKaV1iobsmMqwEGi32G0CcJNlnQFP78=; b=I6Qm7AcNBeHZMAsjuo3XWkuLtTJ4JA8+Q0qxlyDLWNkFzprQS2A69hr/ummJwq2QbH xp0gsFaqzX+fQR37P68lR3noqmZ5/xTj+hzOMbFlIT45v+jRAjlOweBXlRawUQVFbu4L 9T/yh1X5JYggBbP+R/dEZt8CluisI6ZAmvOfvdp4ASDBBj5RGEC4P9YS1/pxXZcGGnML pQfP7f3UaG0FZVHp+QK2LA5W0qrTIfoEXEk5nWh3IyUvCGJBU2XIj/lp99ZPjJzQrWXd qCAyTHICvPX8hh3bkTXcN6FkPwOO34DvkucXhUxWNXI65dLjPGk96Kh2uSm6nZ3pqxh5 43tA== 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=B7yTfa6bCcb9PKaV1iobsmMqwEGi32G0CcJNlnQFP78=; b=ggv0H1J72ID6TqqUJ7GGculb6Wc7N8YCPMOHBDqvaGEPEUjKI+u1EthdVD8x289dyC fXdidn98CP+7iSVnS4tSEwkt+1ZmNX3CyppVKpUI2Q9/ArkJvO8HSQJy/OX0eM3+WaTH jplHqD0iAJXN0ZIbQcna2pWhxdj2ORFizb33Q4mQrOuzV4vfOi4xH2lKduo87exT4d0C pO+Rmn1N6iYlke1wKj+45IkVs4vGY7D8iH+N1rGQ/3xg6zN2iKGv8SAxFoWH6Kxq7qyd IAXNq4HoWwUIAyKeyyLivaKHxlrTHbdXVKMKIdQeOGP4qpnjqf2tgnyKdYUeEpPOe35N ohww== X-Gm-Message-State: APjAAAXJcWU5QMY6xrOHtSFgLYTaeKmYYl62sfkfCAFZoQ/0RcgJTr5Y UQtwMJKuMbFTHbBVVUwy/xmzCeH6tbKX67otn+c= X-Google-Smtp-Source: APXvYqz2nsDqUdfhsOtch5ZQiudq9UOD5dUZVG0ip3q2xijQ7cgTgStrIA/vxW5Uvj7iAyAmsArK5wOVgdC3I4I6uOI= X-Received: by 2002:ab0:20d2:: with SMTP id z18mr7508106ual.24.1552501056981; Wed, 13 Mar 2019 11:17:36 -0700 (PDT) Date: Wed, 13 Mar 2019 11:17:15 -0700 In-Reply-To: Message-Id: <20190313181719.87859-1-ndesaulniers@google.com> Mime-Version: 1.0 References: X-Mailer: git-send-email 2.21.0.360.g471c308f928-goog Subject: [PATCH v2] 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 , Alexander Shishkin , Ingo Molnar , "Steven Rostedt (VMware)" , Greg Kroah-Hartman , Dan Williams , Andy Shevchenko , 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 --- 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..b882692bac04 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 - Like memcmp but a non-zero return code simply indicates a non-match. + * @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