Path: utzoo!attcan!uunet!peregrine!elroy!ames!amdahl!nsc!voder!apple!darin
From: darin@Apple.COM (Darin Adler)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Register saving conventions
Message-ID: <15032@apple.Apple.COM>
Date: 1 Aug 88 21:32:38 GMT
References: <664@iraun1.ira.uka.de>
Reply-To: darin@apple.apple.com.UUCP (Darin Adler)
Organization: Apple
Lines: 23

In article <664@iraun1.ira.uka.de> joachim@iraul1.ira.uka.de (Joachim Lindenberg) writes:
> While writing some small patches to toolbox traps, I noticed that
> MultiFinder doesn't conform to the register saving conventions stated
> in Inside Macintosh. Some routines apparently assume, that registers
> are not changed by the trap. The traps I patched are GetResource and
> DrawMenuBar. Both of them work only if I save registers D0-D2/A0-A1.

If you read page I-113 of Inside Macintosh, you will see the following note:

       "Assembly-language note: Except for LoadResource, all Resource
	Manager routine preserve all registers except A0 and D0.
	LoadResource preserves A0 and D0 as well."

Thus, the Resource Manager is an exception to the normal rules for Toolbox
register saving. If you patch a Resource Manager trap, you have to keep this
in mind.

I don't think that this is clear enough in Inside Macintosh, but it is
definitely a documentation problem rather than a MultiFinder problem.
--
Darin Adler					       AppleLink: Adler4
UUCP: {sun,voder,nsc,mtxinu,dual}!apple!darin	  CSNET: darin@Apple.com