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From: Charles Sandmann <sandmann AT clio DOT rice DOT edu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: V2 questions
Date: Tue, 05 Dec 1995 12:21:16 CST
Organization: Rice University, Houston, Texas
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> Thanks. So now, where can I find documentation on how to write such DXE's ??

Well, what little there is is in the info pages for _dxe_load, in the 
tests directory under DXE (an example), and in the source for _dxe_load,
and in the sys/dxe.h include file.  There are certain things (like I/O)
you currently can't do very easily from DXE's, but almost anything else
should be able to be linked in.

> So here is a very technical question about [v2load] :
> 
> I have a 1st program (let us call it S, like Server). I want S to load a 
> second program B, and later a third program C.
> It is possible in B or C to call functions in A ? 

Yes, but this would be a far call (not so easy to do from GCC directly) 
and you would need to realize that the DS/ES/SS still point to the 
image B or C, so you have to either write some wrapper code for the A
routines or write code which only uses automatic variables.  Also be aware
when using v2load that you must hook PM I21, AH=4c to prevent an exit
of the main image (it's not trival to use).

> If yes, how can I manage
> those calls at the linking stage of B or C. Must I provide minimal functions
> with same operands as is A, but which only perform the jump to A services ?
> How can I obtain addresses of functions in A, must I keep a table of 
> functions' offsets in the code ?

It would be much easier to hook a PM software interrupt, which is relatively
easy to call from GCC, and is easy to define your own API.  You can then
either pass argments in registers or on the stack.

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