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From: jdb@mordor.UUCP
Newsgroups: net.unix
Subject: Re: need memory syscall
Message-ID: <3018@mordor.UUCP>
Date: Mon, 7-May-84 08:27:35 EDT
Article-I.D.: mordor.3018
Posted: Mon May  7 08:27:35 1984
Date-Received: Fri, 11-May-84 00:12:50 EDT
References: <29300011@uiucuxc.UUCP> <1346@brl-vgr.ARPA>, <477@dual.UUCP>
Organization: S-1 Project, LLNL
Lines: 18

"phys" is certainly a great way to step on yourself.  But then, the
one time that I used it, that was precisely what I intended to do.
I wanted a program which could reboot my V7 PDP-11/45 (and other
local PDP-11's) without tying up kernel I-space.  (I was very
protective of the kernel in those days; I would be today, but on 4.2BSD
it seems hopeless.)  My program just read a disc block, did an spl7(),
copied it to physical location zero, blew away memory management (and
everything else) with a "reset", and jumped to zero.  BLAMMO -- reboot!

Aside from something as inherently machine-dependent as this reboot
program, I was very nervous about programs which referenced memory
directly (or through "/dev/mem").  There are just too many ways to
make mistakes, and UNIX is not very forgiving of accidentally trashed
memory.  (Nor are other users when you cause the machine to crash.)
-- 
  John Bruner (S-1 Project, Lawrence Livermore National Laboratory)
  MILNET: jdb@mordor.ARPA [jdb@s1-c]	(415) 422-0758
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