Path: utzoo!mnetor!uunet!cbmvax!snark!eric
From: eric@snark.UUCP (Eric S. Raymond)
Newsgroups: comp.arch
Subject: Re: Is the Intel memory model safe from NO-ONE ?!?
Message-ID: <22830abd:a11@snark.UUCP>
Date: 7 May 88 13:01:14 GMT
References: <1806@obiwan.mips.COM> <2904@omepd> <353@cf-cm.UUCP>
Organization: ill
Lines: 28
Summary: Since when does segmentation = memory protection???

In article <2411@louie.udel.EDU>, rminnich@udel.EDU (Ron Minnich) writes:
>    But having used segmented machines (done right, at Burroughs) and
> non-segmented machines, i can say that i trust programs running
> on segmented machines a whole lot more. And I trust C programs
> running on non-segmented machines not-a-whit- just ask anybody
> who knows about NULL pointers.

Waaaait a second, here. It sounds to me like two very different issues are
being confused. Let's have some definitions:

     Segmented architecture -- one in which the register width is not
         sufficient to address all of memory, so that full addresses must
         be base/offset or segment-descriptor/address pairs.

     Memory protection -- the ability to enforce memory addressing restrictions
         on execution threads so that references outside a 'legal' region are
         detected and trapped (in UNIX terms, raise a SIGSEGV).

These are very different concepts. To trap NULL pointers you want memory
protection. Segmentation implies a crude form of memory protection, with
fixed-sized regions defined by the address span of an offset. But the two
should not be confused.


-- 
      Eric S. Raymond                     (the mad mastermind of TMN-Netnews)
      UUCP: {{uunet,rutgers,ihnp4}!cbmvax,rutgers!vu-vlsi,att}!snark!eric
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