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Date:      Tue, 22 Oct 1996 22:30:51 -0700
From:      David Greenman <dg@root.com>
To:        johnson@charming.nrtc.northrop.com
Cc:        questions@FreeBSD.ORG
Subject:   Re: Virtual memory question: map first page? 
Message-ID:  <199610230530.WAA02352@root.com>
In-Reply-To: Your message of "Tue, 22 Oct 1996 22:14:59 MDT." <9610230515.AA02752@charming.nrtc.northrop.com> 

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>I noticed that in imgact_aout.c the text segment gets mapped starting at
>linear address 4096.

   Right.

>Is it possible to map the first page of linear memory?  What I would like
>to be able to do is set up a process in which linear addresses starting
>at 0 are mapped.

   Yes, it's possible.

>When I modified imgact_aout.c to map the first linear page of memory as
>an experiment, and then ran a specially cooked executable to exercise that
>code, the machine immediately hung.

   Operator error. :-)

>Is there something special on the first linear page of a user process?

   No. In fact if my memory isn't failing, the original "ZMAGIC" format of
386BSD (which we still support) maps the executable starting at virtual
address 0 (although to skip over the image header, the file offset is 4096).

-DG

David Greenman
Core-team/Principal Architect, The FreeBSD Project



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