Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@cygwin.com Mail-Followup-To: cygwin@cygwin.com Delivered-To: mailing list cygwin@cygwin.com X-Injected-Via-Gmane: http://gmane.org/ To: cygwin@cygwin.com Path: not-for-mail From: Shankar Unni Subject: Re: Repeated gcc yields differing .exe files Date: Fri, 20 Dec 2002 10:27:19 -0800 Lines: 20 Message-ID: <3E036107.9080403@cotagesoft.com> References: <001201c2a820$26daf9a0$6fc82486@medschool.dundee.ac.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Complaints-To: usenet@main.gmane.org User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.0.2) Gecko/20021120 Netscape/7.01 X-Accept-Language: en-us, en fergus@bonhard.uklinux.net wrote: > The fact that hello.exe alters seems a bit non-optimal to me, given that > md5sums are a pretty standard way for people like you and me to check that > we're running the same stuff, intended to do the same thing. Incidentally, > it's always the same two bytes that alter: As egor said: it's the timestamp. Almost every object file format in use today has compilation timestamps to identify when the executable was created; many even have other tagging information identifying the compilation environment. It's a completely invalid assumption that the same source compiled twice will give identical binary files. This is a GOOD thing, because it identifies a *binary* precisely, you know if it has been replaced, even with something "identical". This is especially important when you're installing a full installation of some product with many files - you can take an overall checksum of everything, and verify that nothing has been touched or tampered with. -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Bug reporting: http://cygwin.com/bugs.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/