Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752954AbdLHLl4 (ORCPT ); Fri, 8 Dec 2017 06:41:56 -0500 Received: from mail-he1eur01on0124.outbound.protection.outlook.com ([104.47.0.124]:65271 "EHLO EUR01-HE1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752481AbdLHLlv (ORCPT ); Fri, 8 Dec 2017 06:41:51 -0500 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=aryabinin@virtuozzo.com; Subject: Re: [PATCH v2] ubsan: don't handle misaligned address when support unaligned access To: David Laight , Andrew Morton Cc: Ding Tianhong , "linux-kernel@vger.kernel.org" , LinuxArm References: <5b905d56-609e-3822-096a-3b93b3eb7675@huawei.com> <20171206164916.687d5006b7a49ef1149e7154@linux-foundation.org> <022fdf6b-6e00-fe70-3124-80b8ff50a859@virtuozzo.com> <20171207152453.7aaf8f420ebf69d13c29a761@linux-foundation.org> <8c7cc89e-f976-077b-7b64-1046a1f69569@virtuozzo.com> <168669e65cff4bc1b2fbed842cea5dec@AcuMS.aculab.com> From: Andrey Ryabinin Message-ID: <2b78febd-ff00-0ed1-33fa-8575541a72dc@virtuozzo.com> Date: Fri, 8 Dec 2017 14:45:20 +0300 User-Agent: Mozilla/5.0 (X11; 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>> ... >> x = *ptr; >> ... >> if (ptr & 7) // Compiler can assume that this statement is always false, because 'ptr' was deferenced, so it must be aligned >> do_something(); > > Ugg - shoot the gcc developers :-) The gcc developers must have good self-preservation instinct, that's why they usually provide switch off for optimizations like this.