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=-14.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 921BEC10F12 for ; Mon, 15 Apr 2019 19:07:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5334721905 for ; Mon, 15 Apr 2019 19:07:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555355237; bh=Hy425lnHAqhP3mkzcrj7iBQhgNRmuXiyohfhVmq+vNU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=gJTCxsMZPYoaKsqkdKjyq2WX+u5mipc655wlzM5lQUPZXRv9U0AENXIUebc1XREgu Z9bbwAbO3PfmwS/3lKueX0DQ5fCwE9RgAvTMODveP5B0AhK33To4dqvr7lSReKEyVn YCL3g8tIsw7mnRsJpx7v0xqQsmaRJrtnK2HVIeow= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730130AbfDOTHQ (ORCPT ); Mon, 15 Apr 2019 15:07:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:41972 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730110AbfDOTHM (ORCPT ); Mon, 15 Apr 2019 15:07:12 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 89DF12087C; Mon, 15 Apr 2019 19:07:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555355232; bh=Hy425lnHAqhP3mkzcrj7iBQhgNRmuXiyohfhVmq+vNU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=t0UlwLgFsodbQPCgmkRIFKS1VsQvh9ynIZzX6AehM7LMk0OEdHg8A5hLf5THHPCLu LAQr45gJCU5ZjhcH9sy17M26oYqG50XC7Ur6FIUl3SClu50O/0Xx5LJf0Ycd+mlYSn rYeFSoNQTHAzLi3YQoLRyWpkE/GHEsIac9HkCFeU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nick Desaulniers , Nathan Chancellor , Adhemerval Zanella , Arnd Bergmann , James Y Knight , Masahiro Yamada , Rasmus Villemoes , "Steven Rostedt (VMware)" , Andy Shevchenko , David Laight , Namhyung Kim , Alexander Shishkin , Dan Williams , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH 4.19 040/101] lib/string.c: implement a basic bcmp Date: Mon, 15 Apr 2019 20:58:38 +0200 Message-Id: <20190415183742.579457656@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190415183740.341577907@linuxfoundation.org> References: <20190415183740.341577907@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [ Upstream commit 5f074f3e192f10c9fade898b9b3b8812e3d83342 ] 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 Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- include/linux/string.h | 3 +++ lib/string.c | 20 ++++++++++++++++++++ 2 files changed, 23 insertions(+) diff --git a/include/linux/string.h b/include/linux/string.h index 4a5a0eb7df51..f58e1ef76572 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -143,6 +143,9 @@ 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 2c0900a5d51a..72125fd5b4a6 100644 --- a/lib/string.c +++ b/lib/string.c @@ -865,6 +865,26 @@ __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. + * @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. -- 2.19.1