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From: bryce@hoser.berkeley.edu.UUCP
Newsgroups: comp.sys.amiga
Subject: Kickstart patch to fix the bug in the Alert() function
Message-ID: <21552@ucbvax.BERKELEY.EDU>
Date: Mon, 2-Nov-87 02:38:55 EST
Article-I.D.: ucbvax.21552
Posted: Mon Nov  2 02:38:55 1987
Date-Received: Tue, 3-Nov-87 06:56:46 EST
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: bryce@hoser.berkeley.edu (Bryce Nesbitt)
Organization: Reliable Software, Inc.
Lines: 42
Keywords: bug exec.library hack Alert() A2000 $C00000 memory


Ran across the fix to this bug by accident today.

A long time ago I noticed that recoverable Alert()s did not seem
to be recovering.  Blitzfonts was in my startup-sequence at the time,
so this did not seem too strange.  (Blitzfonts patches graphics.
library without using SetFunction())

Recently on the net someone else mentioned the problem.  I took a
look into it.  If there is autoconfigured memory at $C00000 then
recoverable alerts fail.  None, and they are fine.

While "researching" for my upcoming "Hacking Kickstart" article in
the New Transactor Amiga Magazine I hit it.  Here's the code:

listing of memory contents FC2FF8 to FC3008
FC2FF8    MOVE.L  4,D0
FC2FFC    MOVE.L  D0,D1
FC2FFE    ANDI.L  #$00FF0001,D1
FC3004    BNE.S   *+$5A
FC3006    MOVEA.L D0,A6

This code takes AbsExecBase and does a sanity check.  If it's
insane it branches to *+5A. If execbase is at the location 
were it would be in a CHIP memory only system ($676) then
the AND comes out a zero.  If execbase is at the $C00000
location ($00C00276) then the AND proves fatal.

One would suspect that they meant #$FF000001 instead, though
that would just shift the bug over to some 68020 system at
a future date.

If you don't have the tools to do the patch... sorry!  Or,
better yet, allocate $7.50 and take advantage of the fantastic
introductory bargain Transactor is offering. (-: Oops! 
Commercialism :-)

|\ /|  . Ack! (NAK, SOH, EOT)
{o O} . bryce@hoser.berkeley.EDU -or- ucbvax!hoser!bryce
 (")
  U	"You can count how many seeds are in an Apple, but not how
	 many Apples are in a seed." -Ken Kesey