Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!dogie.macc.wisc.edu!uwvax!rutgers!att!mtuxo!mtgzz!drutx!druco!jon
From: jon@druco.ATT.COM (GotowJK)
Newsgroups: comp.sys.mac.programmer
Subject: Locking executable resources
Keywords: lock init executable patch
Message-ID: <4170@druco.ATT.COM>
Date: 1 May 89 19:29:05 GMT
Distribution: comp
Organization: AT&T, Denver, CO
Lines: 34

The segment loader locks CODE resources into memory before it jumps to 
them.  Why are other executable resources (particularly INIT & cdev) 
not automatically locked?  Sure, you can set the "locked" bit on the 
resource so it loads as a locked handle, but should that really be 
necessary?  Why not make it automatic?  

Here's why this concern arose:

I wrote a quick patch to _InitGraf that simply beeps and then calls the 
real ROM code.  Simple, right?  Except that it crashes on startup when 
other inits load afterwards.  This is because these inits show their 
icons, calling InitGraf in the process, and do not have the "locked" 
bit set on the INIT resources.  When my patch gets called, the INIT 
code gets moved (or purged) because I have a long beep sound installed, 
and the return address from the trap call is no longer valid.  Bingo - 
it executes an empty memory location after it hits the rts.  

The dilemma is that this occurs because _somebody else's_ INIT resource 
is not locked, and I can't control that.  This seems to be major 
problem - or am I missing something?  

I really would like to do much more that just beep in my patch code, 
obviously.  This simple example is good enough to illustrate the point, 
however.  Any comments will be much appreciated.


------------------------------------------------------------------------
Jon Gotow - Physical Designer                             AT&T Bell Labs
General Business Systems Group                         200 Laurel Avenue
ARPA:  jon@druco.att.com                            Middletown, NJ 07748
UUCP:  att!druco!jon

Disclaimer:  As always, the opinions stated here have nothing whatsoever
to do with my employer.