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[209.132.180.67]) by mx.google.com with ESMTP id y3si11382343plt.68.2019.03.13.13.37.51; Wed, 13 Mar 2019 13:37:51 -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; dkim=pass header.i=@google.com header.s=20161025 header.b=JVx8Cdn4; 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; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727099AbfCMUhv (ORCPT + 14 others); Wed, 13 Mar 2019 16:37:51 -0400 Received: from mail-oi1-f202.google.com ([209.85.167.202]:44437 "EHLO mail-oi1-f202.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727087AbfCMUhu (ORCPT ); Wed, 13 Mar 2019 16:37:50 -0400 Received: by mail-oi1-f202.google.com with SMTP id v74so1352502oia.11 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=I3zrUsUY1m8r4F8OIZl9YkDEMhgzg3oJrAsjgZ1UZPBrLj27aAxvJdgwuoDpvTGXaz R6xKlLJJl89tGpIh+5McV7cprWQsNRsCcc3LkeXx3BKk6B/7fgvXw7jw/3f5yZ8wDSNe 9fKl4Gi/CtRTrQHrm1FpQMkZlpjhb863/1tcz9c4wVZGK2B3zHeftF5Wb4WUPZfKhs/7 L6V+fbS9gxGkIfHs6niH8x990g+WnGKzLuioDIL+Y5sMKmaOIvCT5cZyt+3yIh/wU7AV J1OgkFr6tj04tMrym2elnjuMK40RIb/mAybNOyFNkrWIdpo0+ng87cJ3rStguuKXjz8H mCBQ== X-Gm-Message-State: APjAAAWz21+UeJ+UsqvSKeJA4yNGA7tgaSDzcJhKV6CSb9bJtbO6sAyV WB8jHdbtFMctoZwV6RsRtDrqhC2cRTgeCJBU33A= 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 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@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(+) -- 2.21.0.360.g471c308f928-goog 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.