Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!spool.mu.edu!munnari.oz.au!comp.vuw.ac.nz!canterbury!betelgeux!cree From: cree@elec.canterbury.ac.nz (Michael Cree) Newsgroups: comp.sys.amiga.hardware Subject: Re: Amiga Custom Chips - Mem management and resou Message-ID: <1991Apr5.144106.390@csc.canterbury.ac.nz> Date: 5 Apr 91 02:41:05 GMT Article-I.D.: csc.1991Apr5.144106.390 References: <1991Apr4.034655.3681@uniwa.uwa.oz> Sender: cree@betelgeux (Michael Cree) Followup-To: comp.sys.amiga.hardware Organization: University of Canterbury, Christchurch, New Zealand Lines: 29 Nntp-Posting-Host: betelgeux.elec.canterbury.ac.nz It seems to me that being able to protect unallocated memory in machines with an MMU should be no problem. Here`s roughly how I would see such a an idea being implemented:- First of all, the EXEC recognises which CPU is installed (68000, etc), so it should know about the presence of an MMU. If the MMU is present then link into the AllocMem() call code to mark which memory is used by tasks and which memory is not. This much would be really quite simple. Obviously there are still little points like making sure the 8 bytes of unused (or free) memory is not protected so that the EXEC can maintain its FreeMem list, etc. Now, such an implementation would only protect against accesses to unused memory space. Of course, a task referenceing another task's memory space would still be possible whether it is "valid" or not. Furthermore, task resource tracking is by no means possible under such a sceme (read CBM employee' comments in previous posts to see why). Note also that I havn't addressed what would happen if an illegal memory access happens other than to say it probably implies a GURU. However, I do beleive such a scheme would provide some extra protection against runaway tasks. Certainly not total protection, but a little more than is presently available at little extra coding. Michael Cree "Gold there is cree@elec.canterbury.ac.nz and rubies in abundance; but lips that speak knowledge are a rare jewel." Prov 20:15