From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751986AbdHCVUp (ORCPT ); Thu, 3 Aug 2017 17:20:45 -0400 Received: from mail-pg0-f44.google.com ([74.125.83.44]:34731 "EHLO mail-pg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751754AbdHCVUo (ORCPT ); Thu, 3 Aug 2017 17:20:44 -0400 From: Matthias Kaehlcke To: zijun_hu , Andrew Morton Cc: linux-kernel@vger.kernel.org, Doug Anderson , Nick Desaulniers , Greg Hackmann , Yury Norov , Ard Biesheuvel , Matthias Kaehlcke Subject: [PATCH v2] bitops: Avoid integer overflow in GENMASK(_ULL) Date: Thu, 3 Aug 2017 14:20:20 -0700 Message-Id: <20170803212020.24939-1-mka@chromium.org> X-Mailer: git-send-email 2.14.0.rc1.383.gd1ce394fe2-goog Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org GENMASK(_ULL) performs a left-shift of ~0UL(L), which technically results in an integer overflow. clang raises a warning if the overflow occurs in a preprocessor expression. Clear the low-order bits through a substraction instead of the left-shift to avoid the overflow. Signed-off-by: Matthias Kaehlcke --- Changes in v2: - use substraction instead of left-shift, get rid off odd right-shift - also change GENMASK - updated commit message include/linux/bitops.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/include/linux/bitops.h b/include/linux/bitops.h index a83c822c35c2..8fbe259b197c 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -19,10 +19,11 @@ * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000. */ #define GENMASK(h, l) \ - (((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h)))) + (((~0UL) - (1UL << (l)) + 1) & (~0UL >> (BITS_PER_LONG - 1 - (h)))) #define GENMASK_ULL(h, l) \ - (((~0ULL) << (l)) & (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h)))) + (((~0ULL) - (1ULL << (l)) + 1) & \ + (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h)))) extern unsigned int __sw_hweight8(unsigned int w); extern unsigned int __sw_hweight16(unsigned int w); -- 2.14.0.rc1.383.gd1ce394fe2-goog