From mboxrd@z Thu Jan  1 00:00:00 1970
From: forsyth@vitanuova.com
Message-Id: <200008292210.SAA09540@cse.psu.edu>
Date: Tue, 29 Aug 2000 23:08:51 +0100
To: 9fans@cse.psu.edu
Subject: Re: [9fans] Stack initialisation
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>>	Ptab    = 0xbfff5000,    /* Private stack */
>>	Execstk = 0xbf001000,    /* Exec stack linkage area */

the values are related to those of USTKTOP and USTKSIZE
in the  2nd edition kernel, both of which differ in the 3rd edition
kernel, since the arrangement of virtual memory has changed slightly
(on the PC at least).
the exec stack grabs addresses at the low end of the virtual memory
region reserved for the stack, presumably on the grounds that most
Alef processes haven't used the full 16 megabytes.  it is
space that will be reclaimed automatically after the exec.
that's from memory of doing the Alef port to the powerpc
and looking at the various definitions.