From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <glibc-bugs-return-19348-listarch-glibc-bugs=sources.redhat.com@sourceware.org>
Received: (qmail 26003 invoked by alias); 19 Aug 2013 23:48:49 -0000
Mailing-List: contact glibc-bugs-help@sourceware.org; run by ezmlm
Precedence: bulk
List-Id: <glibc-bugs.sourceware.org>
List-Subscribe: <mailto:glibc-bugs-subscribe@sourceware.org>
List-Post: <mailto:glibc-bugs@sourceware.org>
List-Help: <mailto:glibc-bugs-help@sourceware.org>, <http://sourceware.org/lists.html#faqs>
Sender: glibc-bugs-owner@sourceware.org
Received: (qmail 25968 invoked by uid 89); 19 Aug 2013 23:48:48 -0000
X-Spam-SWARE-Status: No, score=-0.7 required=5.0 tests=AWL,BAYES_00,FREEMAIL_FROM,SPF_NEUTRAL autolearn=no version=3.3.2
X-Spam-User: qpsmtpd, 2 recipients
Received: from popelka.ms.mff.cuni.cz (HELO popelka.ms.mff.cuni.cz) (195.113.20.131)    by sourceware.org (qpsmtpd/0.84/v0.84-167-ge50287c) with ESMTP; Mon, 19 Aug 2013 23:48:47 +0000
Received: from domone.kolej.mff.cuni.cz (popelka.ms.mff.cuni.cz [195.113.20.131])	by popelka.ms.mff.cuni.cz (Postfix) with ESMTPS id 41D865043F;	Tue, 20 Aug 2013 01:48:43 +0200 (CEST)
Received: by domone.kolej.mff.cuni.cz (Postfix, from userid 1000)	id 196FA60135; Tue, 20 Aug 2013 01:48:42 +0200 (CEST)
Date: Mon, 19 Aug 2013 23:48:00 -0000
From: =?utf-8?B?T25kxZllaiBCw61sa2E=?= <neleai@seznam.cz>
To: tudorb at gmail dot com <sourceware-bugzilla@sourceware.org>
Cc: glibc-bugs@sourceware.org
Subject: Re: [Bug libc/12518] memcpy acts randomly (and differently) with overlapping areas
Message-ID: <20130819234842.GA7823@domone.kolej.mff.cuni.cz>
References: <bug-12518-131@http.sourceware.org/bugzilla/> <bug-12518-131-Bf2M0qA5U8@http.sourceware.org/bugzilla/>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <bug-12518-131-Bf2M0qA5U8@http.sourceware.org/bugzilla/>
User-Agent: Mutt/1.5.20 (2009-06-14)
X-SW-Source: 2013-08/txt/msg00093.txt.bz2

On Mon, Aug 12, 2013 at 05:19:54PM +0000, tudorb at gmail dot com wrote:
> --- Comment #28 from Tudor Bosman <tudorb at gmail dot com> ---
> FYI, this bug has bitten me in a different way: memcpy() copying backwards
> defeats the MADV_SEQUENTIAL flag to madvise(). A trivial file copier
> implementation (mmap source, mmap destination, set MADV_SEQUENTIAL, memcpy from
> source to destination) would perform much worse on machines that support SSSE3
> than on machines that don't because of this bug.
>
Wait, do you have overlapping source and destination areas? If so then a
backward copy is necessary.

Or is backward copy called for not overlapping areas? 
I have a patch that could call backward copy only if src-n < dest < src+n holds.

> (Before anyone tells me that I should copy files using read() and write(), my
> actual usage pattern was more complex, but the details are irrelevant.)
> 
> -- 
> You are receiving this mail because:
> You are on the CC list for the bug.