Path: utzoo!utgpu!water!watmath!clyde!ima!minya!jc
From: jc@minya.UUCP (John Chambers)
Newsgroups: comp.unix.wizards
Subject: Re: Aliasing text and data segments of a process
Summary: ya turkey, ya posted a spoiler!
Message-ID: <459@minya.UUCP>
Date: 28 Jan 88 04:27:04 GMT
References: <11476@brl-adm.ARPA>
Organization: home
Lines: 40

In article <11476@brl-adm.ARPA>, rbj@icst-cmr.arpa (Root Boy Jim) writes:
>  From: Doug Gwyn  <gwyn@brl-smoke.arpa>
>  > This cannot possibly work on an architecture that enforces the
>  > distinction between Instruction and Data spaces.
> While true, most such machines do not *insist* on enforcing the distinction,
> or provide mechanisms around it where appropriate. Thus is is possible to
> build three or four types of executables on a given system:
>
>	[examples deleted]

Jeez, what a turkey!  Here I was enjoying all the flames I was getting from
people telling me what a fool I was thinking that my examples might work on
machines with separate I and D spaces, and you had to go post descriptions
of how it might be implemented.  Now I'm going to have to find some other,
much less entertaining stuff to read.  

At least I have a few good SF books to turn to.

BTW, do you recall back in the early days of the obscure-C contest, there
was a cute entry that started:
	short main[] = {
followed by a jumbled list of numbers in various formats?  It was a program
that ran on PDP-11s and VAXen and did something reasonably silly.  Anyhow,
I tried it out on a PDP-11/75 that I had handy.  The machine definitely had
separate I and D spaces, and the program quite definitely worked.  I didn't
tell the compiler anything special, and I doubt the linker recognized that
_main was special and belonged in I space.  But neither the compiler nor the
linker was fazed by having main as a data array.

So far, I haven't heard from anyone that has claimed to try either of my
posted examples and found them not to work.  I was really hoping I'd get
responses from people telling me where they failed and how.  Well, maybe
if I wait long enough, I'll learn something.  [I do know personally of one
commercial system where breakpoints don't work because I space is unwritable;
I won't let on which one, in hopes I'll learn of more.]

On to the SF books...

-- 
John Chambers <{adelie,ima,maynard,mit-eddie}!minya!{jc,root}> (617/484-6393)