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From: res@ihlpl.UUCP
Newsgroups: comp.arch
Subject: Re: Bad Code
Message-ID: <1868@ihlpl.ATT.COM>
Date: Sun, 1-Mar-87 17:52:00 EST
Article-I.D.: ihlpl.1868
Posted: Sun Mar  1 17:52:00 1987
Date-Received: Mon, 2-Mar-87 22:39:25 EST
References: <1733@blia.BLI.COM>
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 21
Keywords: IBM-TSS/360
Summary: Trapping stores into 1st 256 bytes also useful

In response to:

> My opinion of this is that it shouldn't be thought of catering
> to bad code but instead as an excellent way of finding bad code.
> 
> You'd be amazed at the number of bugs
> that I've found due to the fact that VMS protect the first page
> of memory.

When I was involved in developing a large logic simulator written in C
on the IBM TSS/370 system, we routinely set a TRAP on stores into the
first 256 bytes of the virtual memory address spectrum.  It was
amazing, the number of stores done through uninitialized pointers!
Fortunately, the trap indicated where in the many kilobytes the stores
were being done, so debugging was greatly facilitated by this feature.

This was one of many features which "contemporary" operating systems
still lack, as bad-mouthed as TSS was.

					Rich Strebendt
					...!ihnp4!iwsl6!res