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From: m5d@bobkat.UUCP
Newsgroups: comp.os.minix
Subject: Re: MINIX memory management (sort of)
Message-ID: <511@bobkat.UUCP>
Date: Mon, 2-Feb-87 17:23:11 EST
Article-I.D.: bobkat.511
Posted: Mon Feb  2 17:23:11 1987
Date-Received: Wed, 4-Feb-87 07:21:36 EST
References: <252@hqda-ai.UUCP> <1169@steinmetz.steinmetz.UUCP>
Reply-To: m5d@bobkat.UUCP (Mike McNally (dlsh))
Organization: Digital Lynx, Inc; Dallas, TX
Lines: 30
Keywords: shared swapped jobs

In article <1169@steinmetz.steinmetz.UUCP> davidsen@kbsvax.UUCP (william E Davidsen) writes:
>
>If you allocate a full 64k to data, there is hardware protection: you
>can't address more than that. This assures that any program which
>doesn't deliberately set out to cause problems will not modify the
>code. ...

What about a program with a bug in it?  Like "strcpy(a, b)" when "a" is
not quite what I meant?  It's real easy to make this kind of mistake;
how many times while debugging a program on a VAX (or whatever) do you
get SIGBUS or SIGSEGV?

All it takes is a bad value passed to a routine which expects a
pointer.  This won't happen in a finished program, but it's not
unlikely in a program under construction.  To me, the most irritating
thing about non-MMU systems is that a simple bug can cause me to wait 5
(or 10 or more, depending on the system) minutes to re-boot -- not to
mention possible problems with the disk.  For example, let's say I've
got a program that goes a little bonkers and writes into a memory
location that it shouldn't touch.  Let's say (by admittedly slim
chance, though not at all impossible) that the memory my program
attacks happens to contain a block of data in the disk cache waiting to
be written.  When it gets written out, BLAMMO!  My directory structure
may have just bitten the dust.

-- 
Mike McNally, mercifully employed at Digital Lynx ---
    Where Plano Road the Mighty Flood of Forest Lane doth meet,
    And Garland fair, whose perfumed air flows soft about my feet...
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