From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:33664 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750826AbdKCM1X (ORCPT ); Fri, 3 Nov 2017 08:27:23 -0400 Received: from pps.filterd (m0098409.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id vA3CK9au029782 for ; Fri, 3 Nov 2017 08:27:22 -0400 Received: from e19.ny.us.ibm.com (e19.ny.us.ibm.com [129.33.205.209]) by mx0a-001b2d01.pphosted.com with ESMTP id 2e0pv764xa-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 03 Nov 2017 08:27:22 -0400 Received: from localhost by e19.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 3 Nov 2017 08:27:21 -0400 Date: Fri, 3 Nov 2017 05:27:19 -0700 From: "Paul E. McKenney" Subject: Re: Invalid compilation without -fno-strict-aliasing Reply-To: paulmck@linux.vnet.ibm.com References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Message-Id: <20171103122719.GH3624@linux.vnet.ibm.com> Sender: perfbook-owner@vger.kernel.org List-ID: To: Yubin Ruan Cc: perfbook@vger.kernel.org On Fri, Nov 03, 2017 at 09:54:15AM +0800, Yubin Ruan wrote: > Does anyone have any idea why this thread > > https://lkml.org/lkml/2003/2/25/270 Hmmm... This is quite the blast from the past. Compilers have changed a bit in the last 14 years. Nevertheles... > is related to strict-aliasing? To me, a compiler barrier like this will fix it: > > if((stream + event_len) < ends) { > iwe->len = event_len; > barrier(); > memcpy(stream, (char *) iwe, event_len); > stream += event_len; > } As with many bugs, there are a number of ways to fix this one. I suggest taking a look at the documentation for -no-strict-alias. This stackoverflow URL might not be a bad place to start: https://stackoverflow.com/questions/23848188/strict-aliasing-rule-and-char-pointers Thanx, Paul