From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755273Ab2LSOka (ORCPT ); Wed, 19 Dec 2012 09:40:30 -0500 Received: from mail.active-venture.com ([67.228.131.205]:64046 "EHLO mail.active-venture.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751516Ab2LSOkX (ORCPT ); Wed, 19 Dec 2012 09:40:23 -0500 X-Virus-Scan: Scanned by ClamAV 0.97.2 (no viruses); Wed, 19 Dec 2012 08:40:19 -0600 X-Originating-IP: 108.223.40.66 From: Guenter Roeck To: linux-kernel@vger.kernel.org Cc: Andrew Morton , lm-sensors@lm-sensors.org, Juergen Beisert , Guenter Roeck , Jean Delvare Subject: [PATCH v2] linux/kernel.h: Fix DIV_ROUND_CLOSEST with unsigned divisors Date: Wed, 19 Dec 2012 06:40:15 -0800 Message-Id: <1355928015-26212-1-git-send-email-linux@roeck-us.net> X-Mailer: git-send-email 1.7.9.7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit 263a523 fixes a warning seen with W=1 due to change in DIV_ROUND_CLOSEST. Unfortunately, the C compiler converts divide operations with unsigned divisors to unsigned, even if the dividend is signed and negative (for example, -10 / 5U = 858993457). The C standard says "If one operand has unsigned int type, the other operand is converted to unsigned int", so the compiler is not to blame. As a result, DIV_ROUND_CLOSEST(0, 2U) and similar operations now return bad values, since the automatic conversion of expressions such as "0 - 2U/2" to unsigned was not taken into account. Fix by checking for the divisor variable type when deciding which operation to perform. This fixes DIV_ROUND_CLOSEST(0, 2U), but still returns bad values for negative dividends divided by unsigned divisors. Mark the latter case as unsupported. Reported-by: Juergen Beisert Tested-by: Juergen Beisert Cc: Jean Delvare Signed-off-by: Guenter Roeck --- v2: Description update (v1 wasn't supposed to make it to lkml) include/linux/kernel.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/include/linux/kernel.h b/include/linux/kernel.h index d97ed58..45726dc 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -77,13 +77,15 @@ /* * Divide positive or negative dividend by positive divisor and round - * to closest integer. Result is undefined for negative divisors. + * to closest integer. Result is undefined for negative divisors and + * for negative dividends if the divisor variable type is unsigned. */ #define DIV_ROUND_CLOSEST(x, divisor)( \ { \ typeof(x) __x = x; \ typeof(divisor) __d = divisor; \ - (((typeof(x))-1) > 0 || (__x) > 0) ? \ + (((typeof(x))-1) > 0 || \ + ((typeof(divisor))-1) > 0 || (__x) > 0) ? \ (((__x) + ((__d) / 2)) / (__d)) : \ (((__x) - ((__d) / 2)) / (__d)); \ } \ -- 1.7.9.7