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Mail Archives: djgpp/1999/10/07/20:57:28

From: Nate Eldredge <neldredge AT hmc DOT edu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: far pointers again
Date: Thu, 07 Oct 1999 13:32:24 -0700
Organization: Harvey Mudd College
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Reply-To: djgpp AT delorie DOT com

Fokkema, DBRA, 1043730 wrote:

> I understand all this, but I thought it was nice if you could access all
> memory available. But if gnu cc doesn't support far pointers, and it is,
> as was suggested to me, just a flitch in the early intel processors, does
> this mean that dos c compilers are about the only ones that implement far
> pointers which they invented themselves (i.e. it is not part of the ansi-c
> standard)?

That's correct.

> : I wouldn't support it because I think there are other, better ways to
> : do things (quite apart from anything else, code that was written for
> : a segmented memory model is 100% ugly to port to any other hardware,
> : wheras if you are writing an OS, you can get all the same protection
> : benefits from paging systems which work a similar way on all hardware).
> 
> How exactly do I get the same protection? By paging out all the memory
> belonging to other processes? How many platforms (and which) do support
> segmented memory models? I understand from your '100% ugly to port' statement
> that this aren't many.

Typically you have a separate set of page tables for each process, in
which only the pages belonging to that process are mapped.

And yes, there are very few other architectures that use a segmented
memory model.  In fact, I can't think of any others.

-- 

Nate Eldredge
neldredge AT hmc DOT edu

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