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[209.132.180.67]) by mx.google.com with ESMTP id 140si44519526pga.460.2019.04.15.11.49.51; Mon, 15 Apr 2019 11:50:06 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-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=@kernel.org header.s=default header.b=AfJJwlH6; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729045AbfDOSsD (ORCPT + 99 others); Mon, 15 Apr 2019 14:48:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:51706 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729030AbfDOSsB (ORCPT ); Mon, 15 Apr 2019 14:48:01 -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 52CFD218A1; Mon, 15 Apr 2019 18:47:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555354079; bh=ds/UlyRIcrWH7VpnA/tayigqJ7lXO+usDH9robgy0fE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=AfJJwlH6EB0P9h1JByiuM/3Z9gkqMG/lLkRW0SQOcwhK2TxplUPszOoQyOVNdecvH 7LU4URQppT3OCsEbLG00mN7pyoSHgeywwFuiJz/aBr/BoE2Bfmk1+7pW3DmZfvIp7j GvvUcPpz76yl/4jtpTvI2Rl18hOWx//9CyYNzORw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Arnd Bergmann , Nick Desaulniers , Zhao Qiang , Yalin Wang , Andrew Morton , Linus Torvalds Subject: [PATCH 4.9 65/76] include/linux/bitrev.h: fix constant bitrev Date: Mon, 15 Apr 2019 20:44:29 +0200 Message-Id: <20190415183726.657925107@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190415183707.712011689@linuxfoundation.org> References: <20190415183707.712011689@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 From: Arnd Bergmann commit 6147e136ff5071609b54f18982dea87706288e21 upstream. clang points out with hundreds of warnings that the bitrev macros have a problem with constant input: drivers/hwmon/sht15.c:187:11: error: variable '__x' is uninitialized when used within its own initialization [-Werror,-Wuninitialized] u8 crc = bitrev8(data->val_status & 0x0F); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ include/linux/bitrev.h:102:21: note: expanded from macro 'bitrev8' __constant_bitrev8(__x) : \ ~~~~~~~~~~~~~~~~~~~^~~~ include/linux/bitrev.h:67:11: note: expanded from macro '__constant_bitrev8' u8 __x = x; \ ~~~ ^ Both the bitrev and the __constant_bitrev macros use an internal variable named __x, which goes horribly wrong when passing one to the other. The obvious fix is to rename one of the variables, so this adds an extra '_'. It seems we got away with this because - there are only a few drivers using bitrev macros - usually there are no constant arguments to those - when they are constant, they tend to be either 0 or (unsigned)-1 (drivers/isdn/i4l/isdnhdlc.o, drivers/iio/amplifiers/ad8366.c) and give the correct result by pure chance. In fact, the only driver that I could find that gets different results with this is drivers/net/wan/slic_ds26522.c, which in turn is a driver for fairly rare hardware (adding the maintainer to Cc for testing). Link: http://lkml.kernel.org/r/20190322140503.123580-1-arnd@arndb.de Fixes: 556d2f055bf6 ("ARM: 8187/1: add CONFIG_HAVE_ARCH_BITREVERSE to support rbit instruction") Signed-off-by: Arnd Bergmann Reviewed-by: Nick Desaulniers Cc: Zhao Qiang Cc: Yalin Wang Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- include/linux/bitrev.h | 36 ++++++++++++++++++------------------ 1 file changed, 18 insertions(+), 18 deletions(-) --- a/include/linux/bitrev.h +++ b/include/linux/bitrev.h @@ -31,32 +31,32 @@ static inline u32 __bitrev32(u32 x) #define __constant_bitrev32(x) \ ({ \ - u32 __x = x; \ - __x = (__x >> 16) | (__x << 16); \ - __x = ((__x & (u32)0xFF00FF00UL) >> 8) | ((__x & (u32)0x00FF00FFUL) << 8); \ - __x = ((__x & (u32)0xF0F0F0F0UL) >> 4) | ((__x & (u32)0x0F0F0F0FUL) << 4); \ - __x = ((__x & (u32)0xCCCCCCCCUL) >> 2) | ((__x & (u32)0x33333333UL) << 2); \ - __x = ((__x & (u32)0xAAAAAAAAUL) >> 1) | ((__x & (u32)0x55555555UL) << 1); \ - __x; \ + u32 ___x = x; \ + ___x = (___x >> 16) | (___x << 16); \ + ___x = ((___x & (u32)0xFF00FF00UL) >> 8) | ((___x & (u32)0x00FF00FFUL) << 8); \ + ___x = ((___x & (u32)0xF0F0F0F0UL) >> 4) | ((___x & (u32)0x0F0F0F0FUL) << 4); \ + ___x = ((___x & (u32)0xCCCCCCCCUL) >> 2) | ((___x & (u32)0x33333333UL) << 2); \ + ___x = ((___x & (u32)0xAAAAAAAAUL) >> 1) | ((___x & (u32)0x55555555UL) << 1); \ + ___x; \ }) #define __constant_bitrev16(x) \ ({ \ - u16 __x = x; \ - __x = (__x >> 8) | (__x << 8); \ - __x = ((__x & (u16)0xF0F0U) >> 4) | ((__x & (u16)0x0F0FU) << 4); \ - __x = ((__x & (u16)0xCCCCU) >> 2) | ((__x & (u16)0x3333U) << 2); \ - __x = ((__x & (u16)0xAAAAU) >> 1) | ((__x & (u16)0x5555U) << 1); \ - __x; \ + u16 ___x = x; \ + ___x = (___x >> 8) | (___x << 8); \ + ___x = ((___x & (u16)0xF0F0U) >> 4) | ((___x & (u16)0x0F0FU) << 4); \ + ___x = ((___x & (u16)0xCCCCU) >> 2) | ((___x & (u16)0x3333U) << 2); \ + ___x = ((___x & (u16)0xAAAAU) >> 1) | ((___x & (u16)0x5555U) << 1); \ + ___x; \ }) #define __constant_bitrev8(x) \ ({ \ - u8 __x = x; \ - __x = (__x >> 4) | (__x << 4); \ - __x = ((__x & (u8)0xCCU) >> 2) | ((__x & (u8)0x33U) << 2); \ - __x = ((__x & (u8)0xAAU) >> 1) | ((__x & (u8)0x55U) << 1); \ - __x; \ + u8 ___x = x; \ + ___x = (___x >> 4) | (___x << 4); \ + ___x = ((___x & (u8)0xCCU) >> 2) | ((___x & (u8)0x33U) << 2); \ + ___x = ((___x & (u8)0xAAU) >> 1) | ((___x & (u8)0x55U) << 1); \ + ___x; \ }) #define bitrev32(x) \