Date: Wed, 23 Oct 1996 08:59:25 +0200 From: Nadav Eiron <nadav@barcode.co.il> To: johnson@charming.nrtc.northrop.com Cc: questions@FreeBSD.ORG Subject: Re: Virtual memory question: map first page? Message-ID: <326DC24D.5EAA@barcode.co.il> References: <9610230515.AA02752@charming.nrtc.northrop.com>
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johnson@charming.nrtc.northrop.com 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 > johnson@nrtc.northrop.com Nadav
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