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From: erics@eleazar.dartmouth.edu (Eric Schlegel)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Tail patches
Message-ID: <17090@dartvax.Dartmouth.EDU>
Date: 18 Nov 89 18:27:51 GMT
Article-I.D.: dartvax.17090
References: <5249@internal.Apple.COM>
Sender: news@dartvax.Dartmouth.EDU
Reply-To: erics@eleazar.dartmouth.edu (Eric Schlegel)
Organization: Dartmouth College, Hanover, NH
Lines: 39

In article <5249@internal.Apple.COM> chewy@apple.com (Paul Snively) writes:
>In article <1989Nov16.043300.8959@eng.umd.edu> russotto@eng.umd.edu 
>(Matthew T. Russotto) writes:
>> In article <5212@internal.Apple.COM> chewy@apple.com (Paul Snively) writes:
>> >
>> >And I'd be interested in any examples of "something that we have 
>> >decided to break," let alone something that we have decided to break 
>> >and then not fix.
>> Resource Header Application Bytes.  Resource References.  The 'abort event'.
>> 'Launch'  (well, you haven't broken it yet, but you keep promising to do 
>> so). 'Chain'.  JMP 10(ROMBASE) to restart....
>> (and, of course, tail patching-- it did used to work)
>
>* Resource Header Application Bytes
>   What on earth are those?
>
>* JMP 10(ROMBASE) to restart
>   That was never supported; it just happened to work.  Now, of course, we 
>   have a Shutdown Manager that actually does the right things.



Resource Header Application Bytes were 128 bytes of data at the beginning
of a resource file that supposedly were available for application use.
This is documented on pp. 128-9 of IM, volume 1. Tech Note 62, from Jan. 1986,
states that applications should no longer use these bytes as they're 
reserved for future use by the Resource Manager.

On pp. 385-6 of IM, volume 2, is documented the Restart procedure. It's 
marked Not in ROM; assembly-language programmers are advised that "you can
give the following instructions to restart the system:"
     MOVE   ROMBase,A0
     JMP    $0A(A0)

Sorry, Paul. The examples are few, far between, and obscure, but they
do exist.

eric
eric.schlegel@dartmouth.edu