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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: Ada GC (was Re: Ammo-zilla)
Date: 1999/11/06
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In article <s27tvo5hhpc65@corp.supernews.com>,
  "Vladimir Olensky" <vladimir_olensky@yahoo.com> wrote:
> It just never come to my mind that someone (one the client's
> side) could try to do something (using unchecked conversions )
> for anything that is behind that protection wall  (for me it
> is a crazy idea).

I guess Vladimir that you have solved the problem that has
eluded everyone else in the field, namely how to be absolutely
sure that your program is free of errors. We are not talking
about DELIBERATE errors here, but for instance of a simple
error like using unchecked conversion to do low level buffer
copying, and getting the bounds wrong.

> As a matter of fact  I do not see the way how one can
> penetrate in reality through hardware memory protection wall
> directly using pointer arithmetic.

You are assuming that it is indeed possible to provide the
necessary memory protection between collected and non-collected
domains. First, my point was about systems
where this is not possible. Second: most systems are in practice
in this category!


> Generally there could be many approaches to increase safety.
> One of the nice ones (for me)  is to use notion of safe and
> unsafe modules/packages as in Modula-3 and do not allow any
> unsafe operations in safe packages.

But as we are discussing this segregation in what packages
are allowed to do is not helpful at all in this case in the
absence of the ability to build data allocation firewalls at
the hardware level (something that is often not possible,
both in embedded systems -- which often lack such memory
protection hardware -- and in higher level systems running
on top of standard OS's, which lack this kind of capability).


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