Path: utzoo!utgpu!attcan!uunet!husc6!bloom-beacon!tut.cis.ohio-state.edu!osu-cis!killer!pollux!ti-csl!mips!holland
From: holland@mips.csc.ti.com (Fred Hollander)
Newsgroups: comp.sys.mac.programmer
Subject: How to Patch
Keywords: nothing to do with MF or GNE
Message-ID: <62672@ti-csl.CSNET>
Date: 3 Nov 88 17:07:22 GMT
Sender: news@ti-csl.CSNET
Lines: 42

I would like to patch the Alert trap and I've been having a hard time
finding documentation that spells out the procedure on patches.  I understand
the basic idea: save the existing trap address, set the trap address to point
to your patch, call the old trap, return.  What's missing is how to install
the patch in the first place.  I don't know anything about a PTCH resource.
How do I install the code permanently in the System heap?

Here's a first pass at trying to update the trap dispatch table.  The trap
address for SysBeep seems to have changed while in LSC (by re-executing
GetTrapAddress), but after exiting, the trap address reverts back to the
original address.

#define	trapSysBeep		0xA9C8

long	oldTrapAddress;

newBeep (ignore)
	int	ignore;
	{
		asm{
			move.l	oldTrapAddress,A1
			jsr	(A1)
			rts
		}
	}

main () {
	oldTrapAddress = GetTrapAddress (trapSysBeep);
	SetTrapAddress (newBeep, trapSysBeep);
}

If someone could send me an example, preferrably in LSC, I'd sure appreciate
it.

Thanks,

Fred Hollander
Computer Science Center
Texas Instruments, Inc.
holland%ti-csl@csnet-rela

The above statements are my own and not representative of Texas Instruments.