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Date:      Wed, 23 Oct 1996 08:59:25 +0200
From:      Nadav Eiron <>
Cc:        questions@FreeBSD.ORG
Subject:   Re: Virtual memory question:  map first page?
Message-ID:  <>
References:  <>

Next in thread | Previous in thread | Raw E-Mail | Index | Archive | Help wrote:
> I noticed that in imgact_aout.c the text segment gets mapped starting at
> linear address 4096.
> 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.

Most OS's don't map the first page of memory. The reason is that many
bugs are caught that way. If you dereference a NULL pointer you'll find
yourself  in the first page of memory. Not mapping that would mean that
you'll get a signal for that. Why would you care so much for the first
page of virtual address space?

> 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.

Don't know, but it's not a good idea.

> Is there something special on the first linear page of a user process?
> Thanks,
> Greg Johnson


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