From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kjetil Barvik Subject: Re: [PATCH] avoid possible overflow in delta size filtering computation Date: Wed, 25 Mar 2009 17:34:06 +0100 Organization: private Message-ID: <86bprptvcx.fsf@broadpark.no> References: <86hc1hdcj1.fsf@broadpark.no> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7BIT Cc: Junio C Hamano , git@vger.kernel.org To: Nicolas Pitre X-From: git-owner@vger.kernel.org Wed Mar 25 17:35:55 2009 Return-path: Envelope-to: gcvg-git-2@gmane.org Received: from vger.kernel.org ([209.132.176.167]) by lo.gmane.org with esmtp (Exim 4.50) id 1LmW4w-0005B7-F5 for gcvg-git-2@gmane.org; Wed, 25 Mar 2009 17:35:46 +0100 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753259AbZCYQeO (ORCPT ); Wed, 25 Mar 2009 12:34:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1761446AbZCYQeM (ORCPT ); Wed, 25 Mar 2009 12:34:12 -0400 Received: from osl1smout1.broadpark.no ([80.202.4.58]:59860 "EHLO osl1smout1.broadpark.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759685AbZCYQeL (ORCPT ); Wed, 25 Mar 2009 12:34:11 -0400 Received: from osl1sminn1.broadpark.no ([80.202.4.59]) by osl1smout1.broadpark.no (Sun Java(tm) System Messaging Server 6.3-3.01 (built Jul 12 2007; 32bit)) with ESMTP id <0KH200KLBM0WBX80@osl1smout1.broadpark.no> for git@vger.kernel.org; Wed, 25 Mar 2009 17:34:08 +0100 (CET) Received: from localhost ([80.202.166.137]) by osl1sminn1.broadpark.no (Sun Java(tm) System Messaging Server 6.3-3.01 (built Jul 12 2007; 32bit)) with ESMTP id <0KH200JNBM0VKV50@osl1sminn1.broadpark.no> for git@vger.kernel.org; Wed, 25 Mar 2009 17:34:08 +0100 (CET) In-reply-to: User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.3 (gnu/linux) Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Archived-At: Nicolas Pitre writes: > On Wed, 25 Mar 2009, Kjetil Barvik wrote: > >> Nicolas Pitre writes: >> >> > On a 32-bit system, the maximum possible size for an object is less than >> > 4GB, while 64-bit systems may cope with larger objects. Due to this >> > limitation, variables holding object sizes are using an unsigned long >> > type (32 bits on 32-bit systems, or 64 bits on 64-bit systems). >> > >> > When large objects are encountered, and/or people play with large delta >> > depth values, it is possible for the maximum allowed delta size >> > computation to overflow, especially on a 32-bit system. When this >> > occurs, surviving result bits may represent a value much smaller than >> > what it is supposed to be, or even zero. This prevents some objects >> > from being deltified although they do get deltified when a smaller depth >> > limit is used. Fix this by always performing a 64-bit multiplication. >> > >> > Signed-off-by: Nicolas Pitre >> >> I added this patch and rerun the 2 test cases form the table where >> --depth is 20000 and 95000, and got the following result: >> >> --depth=20000 => file size: 19126077 delta: 73814 >> --depth=95000 => file size: 19126087 delta: 73814 >> >> So, it seems that this patch almost fixed the issue. But notice that >> the pack file was 10 bytes larger for the --depth=95000 case. >> >> I made a small perl script to compare the output from 'git verify-pack >> -v' of the 2 idx/pack files, and found the following difference(1) >> (first line from --depth=20000 case, second from --depth=95000): >> >> fe0a6f3e971373590714dbafd087b235ea60ac00 tree 9 19 18921247 731 96a3ec5789504e6d0f90c99fb1937af1ebd58e2d >> fe0a6f3e971373590714dbafd087b235ea60ac00 tree 20 29 18921247 730 12e560f7fb28558b15e3a2008fba860f9a4b2222 > > OK. Apparently, a different base object for that one delta was chosen > between those two runs. > > Is your machine SMP? kjetil ~$ uname -a Linux localhost 2.6.28.4 #26 SMP PREEMPT Tue Feb 10 17:07:14 CET 2009 i686 Intel(R) Core(TM)2 CPU T7200 @ 2.00GHz GenuineIntel GNU/Linux -- kjetil