Date: Tue, 26 Aug 1997 19:15:29 +0300 (IDT)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To: Vik Heyndrickx <Vik DOT Heyndrickx AT rug DOT ac DOT be>
cc: djgpp workers <djgpp-workers AT delorie DOT com>
Subject: Re: _dos_ds segment limit
In-Reply-To: <3402DCDD.6895@rug.ac.be>
Message-ID: <Pine.SUN.3.91.970826190801.6359B-100000@is>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Precedence: bulk


On Tue, 26 Aug 1997, Vik Heyndrickx wrote:

> Wouldn't it be more desirable for debugging purposes to set the segment
> limit of the _dos_ds segment to the range that can be accessed by a
> regular DOS program (1M+64K) instead of 4G.
> And maybe introduce a new selector to access the full flat memory for
> whoever needs it?

This has come up before.  The conclusion was that the current setup is 
wrong, because it makes e.g. farptr functions as dangerous as nearptr, 
only slower.  It also doesn't make much sense since many DPMI hosts won't 
let you access memory-mapped devices above the 1MB mark without 
additional DPMI calls.

Last time we talked about this, DJ replied:

   I'd agree to set it back to 1Mb *if* the documentation for _dos_ds
   tells you why, and how to get to memory above 1Mb.

   Relevent pointers to this in other sections of the manual and FAQ
   would be useful also.

This message is still sitting on my todo list, sigh...  Would you 
consider making this simple docs change?  Please??  (I can dig out 
explanations by Charles about how to access memory-mapped devices above 
1Meg, if you need them.)

As for another selector with 4GB limit: it seems to be unnecessary, since 
people already have nearptrs, and devices mapped to high memory need 
special DPMI calls to map them in anyway.