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From: ephraim@wang.UUCP (pri=8 Ephraim Vishniac x76659 ms1459)
Newsgroups: net.micro.mac
Subject: Re: INIT Resources
Message-ID: <796@wang.UUCP>
Date: Wed, 16-Apr-86 08:32:06 EST
Article-I.D.: wang.796
Posted: Wed Apr 16 08:32:06 1986
Date-Received: Fri, 18-Apr-86 20:52:11 EST
References: <8604110030.AA22220@kim.berkeley.edu>
Organization: Wang Labs, Lowell MA
Lines: 31

Gordon Hamachi asks:
> Can someone explain INIT resources, or say where they are documented?  I
> have not been able to find out anything from Inside Macintosh, except that
> there is a resource type "INIT".  So, how come people are posting INIT
> resource installers?  How do they find out how to write them?

I found out how to write them by calling Stew Rubinstein at Harvard.
He told me that my INITs should start with a BRAnch to the real code,
and that _SizeRsrc was often used to cut back the resource size after
the one-time-only code in them had run.  INITs are loaded, locked, and
invoked with a JSR from the system code.  For reasons I can't imagine,
the system patches two NOPs (4E714E71) over the start of your INIT after
it returns.

INITs are useful for doing anything you want done at system startup, after
PTCH installation.  The INIT number determines the order in which the INITs
are executed.

Detaching or releasing an INIT is a bit tricky.  I got information on how
to do this from Evan Solley of Infosphere, who evidently disassembled the
system code that invokes INITs.  I don't have the details handy, but the
general idea involves knowing that the system leaves a handle to your INIT
in D7 (?), and faking it out when you release your INIT and invalidate the
handle.

Apple is now providing an INIT (#31) which invokes INITs from other files
so that they don't have to live in the system file.  See the December 
supplement for details.

Ephraim Vishniac
decvax!wanginst!wang!ephraim