Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!pacbell!att!ttrdc!ttrde!ttrdf!fjo
From: fjo@ttrdf.UUCP (Frank Owen )
Newsgroups: comp.sys.mac.programmer
Subject: Re: How to do a LEGAL tail-patch
Message-ID: <875@ttrdf.UUCP>
Date: 16 Feb 89 17:17:56 GMT
References: <1272@ccnysci.UUCP>
Organization: AT&T, Skokie, IL
Lines: 22

in article <1272@ccnysci.UUCP>, alexis@ccnysci.UUCP (Alexis Rosen) says:
> 
> Procedure MyPatch
> SetTrapAddress to original trap address
> Trap to original trap using A-line instruction
> SetTrapAddress back to @MyPatch (&MyPatch for C people)
> Fixup stack and return


Nope, Nope, Nope. This won't work. If the trap you are patching looks at
what routine has called it by examining the return address on the stack,
(Multifinder's GetNextEvent does this), it will appear as if only one 
routine (your patch) has ever called it. This may screw up the normal
functioning of the original trap. (It would screw up Multifinder's GNE,
for example.)


-- 
Frank Owen (fjo@ttrdf)  312-982-2182
AT&T Bell Laboratories 
5555 Touhy Ave., Skokie, IL  60077
PATH:  ...!att!ttrdf!fjo