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From: phil@sequent.UUCP
Newsgroups: comp.arch
Subject: Re: catering to bad code
Message-ID: <2443@sequent.UUCP>
Date: Fri, 20-Feb-87 13:37:23 EST
Article-I.D.: sequent.2443
Posted: Fri Feb 20 13:37:23 1987
Date-Received: Sat, 21-Feb-87 17:41:45 EST
References: <14833@amdcad.UUCP>
Reply-To: phil@sequent.UUCP (Phil Hochstetler)
Organization: Sequent Computer Systems, Beaverton, OR
Lines: 16

In my experience, having a zero of at least 4 bytes at zero is extremely
useful.  I have talked to customers who were very concerned about this.
Apparently, they have fought battles trying to port to machines that
did not have this feature.  For our DYNIX software, we settled on:

	1. an entire readonly page of zeros at zero by default
	2. a loader flag that makes page zero invalid

Using number 2 allows you to create more portable code or fix bugs
in existing code before having to port to a machine without a zero at zero.
NOTE: Having 1 be the default does save lots of headaches.
-- 
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Phil Hochstetler
Sequent Computer Systems
Beaverton, Oregon