Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!sri-spam!mordor!lll-lcc!ptsfa!ihnp4!chinet!steinmetz!davidsen
From: davidsen@steinmetz.UUCP
Newsgroups: comp.os.minix
Subject: Re: MINIX memory management/protection
Message-ID: <1199@steinmetz.steinmetz.UUCP>
Date: Wed, 11-Feb-87 14:49:10 EST
Article-I.D.: steinmet.1199
Posted: Wed Feb 11 14:49:10 1987
Date-Received: Thu, 12-Feb-87 22:15:16 EST
References: <252@hqda-ai.UUCP> <1169@steinmetz.steinmetz.UUCP> <511@bobkat.UUCP> <888@cartan.Berkeley.EDU>
Reply-To: davidsen@kbsvax.UUCP (william E Davidsen)
Organization: General Electric CRD, Schenectady, NY
Lines: 36
Keywords: shared swapped jobs

In article <888@cartan.Berkeley.EDU> ballou@brahms.Berkeley.EDU (Kenneth R. Ballou) writes:
$In article <511@bobkat.UUCP> m5d@bobkat.UUCP (Mike McNally (dlsh)) writes:
$>In article <1169@steinmetz.steinmetz.UUCP> davidsen@kbsvax.UUCP (william E Davidsen) writes:
$>>=== what I wrote ===
$>
$>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?
$[Omitted here:  a description of a phenomenon with which I'm sure we are
$ all too painfully familiar -- how wild pointers can crash programs and
$ machines.]
$
$
$	However, this is a blatant lie, and it is possible you are
$vindicated.  For, if auto variables are allocated on the stack, one
$could still easily lose.  Since the stack must lie in the same segment
$as the static data (otherwise, pointers must have segments associated
$with them to distinguish between auto and static variables), it is
$possible to scribble over the stack.  In doing so, one could alter a
$return address and find oneself in another process, or perhaps the
                                    ^^^^^^^^^^^^^^^^
$kernel.  Also, equally likely is that one would try to execute data
 ^^^^^^

NO. You can find yourself somewhere in your own code segment. There
is no way to wind up somewhere else. After you get to your own code
segment there is a posibility of executing a far call, jump, or return.
Since the return is 'under' the auto variables (lower address) and
the most common errors run beyond the end of an array, this is unlikely
but not imposible.
-- 
bill davidsen			sixhub \
      ihnp4!seismo!rochester!steinmetz ->  crdos1!davidsen
				chinet /
ARPA: davidsen%crdos1.uucp@ge-crd.ARPA (or davidsen@ge-crd.ARPA)