Date: Thu, 06 Nov 1997 15:04:48 -0600 From: Tony Overfield <tony@dell.com> To: John-Mark Gurney <gurney_j@resnet.uoregon.edu>, Chuck Robey <chuckr@glue.umd.edu> Cc: Mike Smith <mike@smith.net.au>, Terry Lambert <tlambert@primenet.com>, jamil@trojanhorse.ml.org, hackers@FreeBSD.ORG, Jonathan Mini <j_mini@efn.org> Subject: Re: >64MB Message-ID: <3.0.3.32.19971106150448.006d5438@bugs.us.dell.com> In-Reply-To: <19971106094616.51849@hydrogen.nike.efn.org> References: <Pine.BSF.3.96.971106073452.7018C-100000@picnic.mat.net> <199711061242.XAA00382@word.smith.net.au> <Pine.BSF.3.96.971106073452.7018C-100000@picnic.mat.net>
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At 09:46 AM 11/6/97 -0800, John-Mark Gurney wrote: >Chuck Robey scribbled this message on Nov 6: >> On Thu, 6 Nov 1997, Mike Smith wrote: >> > > >> > > Speaking of vm86(), why not just use real-mode? It's easier and much >> > > better for compatibility while booting. >> > >> > How do you copy the kernel into memory > 1M in real mode? If you could >> > elaborate on this (and how to *stay* in real mode while running over >> > 1M, ie. so that the kzip pass and subsequent real-mode startup >> > requirements could be met), I'd be *very*happy* >> >> Huh? Is that the limitation? I haven't personally used them, but there >> are methods to do this, if you can go into protected mode first, set >> limits, then go back to real mode. Can you do that one? If so, I'll >> personally test such a thing, I can do that here. >> >> The method I'm talking about is commonly known (among those that use it) >> as voodoo memory, I think. The word voodoo is in there somewhere, >> anyways. Some game folks have written programs that run completely in >> such a environment, although that seems really unsafe to me. The limits >> you set in pmode stay active in real-mode. > >yep... I've heard of this (they called it Un-real mode :) )... but >basicly you set your registers to a 4gig limit instead of the 64k limit >that they have normally... I've bounced your message, Mike, to a friend >of mine (Jonathan Mini) who will be able to help with this... Sorry for this useless diversion. It seems my question was ambiguous and that Mike took it the other way. I recommend against using this "unreal" mode trick. >he was quite surprised that we kept flipping between real and protected >mode when he first saw the boot blocks... I wonder why. I don't see anything wrong with flipping into and out of protected and real modes. After all, it needs to be done. My ambiguous question reworded would say... Once you are in the kernel startup code and running in protected mode, why not simply switch back to real mode for BIOS calls and etc. instead of trying to set up a VM86() facility? I think it's easier and much better for compatibility while booting. - Tony
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