Message-ID: <36235C46.8C452D20@arx.com>
Date: Tue, 13 Oct 1998 15:57:26 +0200
From: Black Phantom <vadim AT arx DOT com>
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Subject: Re: DOS-based DLL system
References: <3622729c DOT 417426724 AT newshost DOT cc DOT utexas DOT edu>
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To: djgpp AT delorie DOT com
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> 
> I'm interested in creating some sort of DLL (Dynamic Link Library)
> -like ability in a DOS-based program, using DOS-targeting compilers
> (DJGPP, QuickC, or a variety of older assemblers). Is this something
> I'd have to write a library for, like a DLL handler that would load
> the DLL, retrieve function locations, and have a handler function that
> would take the desired DLL function and manually handle the stack and
> IP register to call it? Or is there a simpler way that I'm missing?

More likely it will be harder than you describe: you'll write a TSR that
intercepts DOS program loader, calls the original loader (or loads a
program itself), then checks whether the loaded program contains imports
and resolves the relocations. Alsom you'll it will have to provide with
its own service analogue to "LoadLibrary", to load imports at run-time
rather than at load-time. You will hav to decide: to use DOS 'MZ' EXE
format, extending it to contain import/export tables (say somewhere at
the end of exec. image) or adopt 'NE' format where that tables are
already included; you'll have to write libraries, of course, also.

The whole thing is utterly inefficient since dynamic linking was
designed for sharing one copy of library among different address spaces.
In DOS there is a single-tasking environment so DLL system will eat up a
lot of memory, saving nothing. What do you need it for, what is the
design goal?