Path: utzoo!utgpu!attcan!uunet!husc6!lloyd!kent
From: kent@lloyd.camex.uucp (Kent Borg)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Register saving conventions
Message-ID: <130@lloyd.camex.uucp>
Date: 10 Aug 88 20:09:29 GMT
References: <664@iraun1.ira.uka.de> <1133@lzsc.ATT.COM> <15055@santra.UUCP> <6600@umn-cs.cs.umn.edu> <25556@ucbvax.BERKELEY.EDU> <20078@cornell.UUCP>
Reply-To: kent@lloyd.UUCP (Kent Borg)
Organization: Camex, Inc., Boston, Mass USA
Lines: 22

>From: schoaff@gefion.cs.cornell.edu (Peter Schoaff)

>Excuse this basic question, but could someone explain to me what is
>meant by a tail patch on a trap.  

If you want to change the behavior of one the routines in the
Macintosh ROM, you can install your own routine that gets called
first.  You work your special custom magic and then possibly jump back
to the original routine to do what it does.  Because you jumped to the
original routine, when it returns it will return back to the original
calling code, not to your patch.  If, on the misbehaving other hand,
you arrange to have the original routine return control to your patch,
you have installed a tail patch.

I can't remember why tail patches are bad (I've never patched the
Macintosh), but I think it has to do with interference between
multiple patches (and Apple's tail patches?).

Kent Borg
kent@lloyd.uucp
or
hscfvax!lloyd!kent