Path: utzoo!utdoe!generic!pnet91!ericmcg
From: ericmcg@pnet91.cts.com (Eric Mcgillicuddy)
Newsgroups: comp.sys.apple2
Subject: Re: patching toolbox calls
Message-ID: <479@generic.UUCP>
Date: 9 Feb 91 15:21:49 GMT
Sender: root@generic.UUCP
Organization: People-Net [pnet91], Etobicoke, ON
Lines: 20

I use GetTSptr and save the value and then call SetTSptr to add in my
routines. If the initialization fails for some reason (I have a half dozen or
so Memory Manager calls to patch) then it just restores the old ptr and ends. 

Aside from NoewHandle, I just have to do some stuff to update my data and then
JML to the existing routines. I use GetFuncPtr prior to switching TS pointers
and use self modifying (to avoid eating bank $0 memory which is verboten to an
INIT) code. NewHandle is special because I need to do stuff after the call is
completed. Basically I clone the parameters and reissue the call with a JSL
<NewHandle>. I then extract the returned value, do my stuff and return the
value expected. Works fine. CheckHandle also works fine despite the fact I
make a couple of additional MM toolcalls (RestoreHandle mainly) before passing
on control. (also has to restore old PurgeLevel, which I may have altered
previosly)

ViM also includes a new toolcall, DeRefHandle, which Checks, Lockas and
returns a pointer to the memory whose Handle was given. $3002 when installed.

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