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From: rouaix@inria.UUCP (Francois Rouaix)
Newsgroups: comp.sys.amiga
Subject: Dos library/SetFunction() question
Message-ID: <455@inria.UUCP>
Date: Thu, 7-May-87 08:21:51 EDT
Article-I.D.: inria.455
Posted: Thu May  7 08:21:51 1987
Date-Received: Sat, 9-May-87 09:45:37 EDT
Organization: INRIA, Rocquencourt. France
Lines: 26

I would like to change some functions in dos.library, adding new features
to CurrentDir() for example.
The best way to do this on a library is:
	- write a piece of code that does what you want, and then call the 
old function.
	- SetFunction() to your new code,  getting the old pointer.

The problem is:
for most libraries, the 'vector table' looks like:
	JMP address1
	JMP address2
	....
LibBase {some code}

I believe the SetFunction() is returning {address1}.

BUT: for dos.library the vector table looks like:
	MOVEQ #x,d0
	BRA entry_point
	(repeated)
where the code at entry_point is doing some standard stack manipulations,
and then computes some address from x and goes to it.
(BTW this reminds me of ProDOS)

My question is: how can you use SetFunction on dos.library ??
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