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From: guy@gorodish.UUCP
Newsgroups: comp.arch
Subject: Re: catering to bad code
Message-ID: <13797@sun.uucp>
Date: Sat, 21-Feb-87 16:43:44 EST
Article-I.D.: sun.13797
Posted: Sat Feb 21 16:43:44 1987
Date-Received: Sun, 22-Feb-87 05:44:32 EST
References: <14833@amdcad.UUCP> <2443@sequent.UUCP>
Sender: news@sun.uucp
Reply-To: guy@sun.UUCP (Guy Harris)
Organization: Sun Microsystems, Mountain View
Lines: 28

>In my experience, having a zero of at least 4 bytes at zero is extremely
>useful.

But is not necessarily possible, convenient, or desirable on all
machines.

>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.

Who's to say they won't fight battles trying to port to machines that
don't have the same byte order, or the same floating-point format, or
the same address space layout, or the same... as the VAX?

>Using number 2 allows you to create more portable code or fix bugs
>in existing code

Bugs is bugs.  If the code has a bug, the fact that it *may* happen
to work on a machine with 0 at location 0 - which is *not*
guaranteed; consider, e.g., that somebody might be treating a null pointer
or a *non*-zero value pointed to by that pointer as a termination
condition.

>NOTE: Having 1 be the default does save lots of headaches.

And creates lots more.  Mapping in page zero is the default on the
3B2's linker; this means *we* get to fix a bunch of bugs that are
*not* our fault, but the fault of programmers at AT&T-IS.