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From: Shankar Unni <shankar AT cotagesoft DOT com>
Subject: Re: Repeated gcc yields differing .exe files
Date: Fri, 20 Dec 2002 10:27:19 -0800
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fergus AT bonhard DOT uklinux DOT 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.




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