In the May issue of 8/16 Central, there was a message originating from
America Online in which someone said that they had trouble with Aztec C
crashing on the IIgs.  Our User Group also had this problem (our
bulletin board is written in Aztec C (with an accelerator!!!)).

I am posting it on USENET since I don't have access to America Online
from New Zealand.  Could some kind soul please forward this to AOL.

The following solution was discovered by our local guru.

-------------------------------------------------------------------
Patch for Aztec C to prevent crashing on the IIgs

by David Empson
Wellington Apple Users Group of New Zealand

The problem: Aztec C doesn't set the stack pointer.  Ever.  If an interrupt 
occurs on the IIgs and the stack pointer has to wrap around, Aztec C crashes 
into the monitor.

The solution: since Aztec reloads its shell from disk each time a program exits
(including the compiler, linker, etc.), we must patch the shell to reset the
stack pointer.  This patch will work on any Apple II but is only required for
the IIgs (and possibly the enhanced IIe and IIc).

The file to patch is SHELL.SYSTEM.  For Aztec C v1.99j, it is 22049 ($69A4)
bytes long.  If you have a different version of the shell, you will have to
adjust the code to account for any different addresses involved.

As always, make sure you save a copy of the original SHELL.SYSTEM before
modifying it in any way.  Make sure you have backups of any shell programs or
source files you work on until you are satisfied that the new copy of the shell
is safe.

Perform the following steps in BASIC.SYSTEM.

]BLOAD SHELL.SYSTEM,TSYS,A$2000
]CALL-151
*2000L
2000- 4C AF 3C   JMP $3CAF       <- note the JMP address
etc.

If your copy of SHELL.SYSTEM is a different length, you will need to start the
patch at a different location.  Calculate the start address of the patch by
taking the length of the file in hex, and add $2000.  In my case the length is
$69A4, so the patch starts at $89A4.

*89A4:A2 FF 9A A9 AF 8D 01 20 A9 3C 8D 02 20 4C 00 20
*89A4L
89A4- A2 FF      LDX #$FF
89A6- 9A         TXS
89A7- A9 AF      LDA #$AF   <- this is the byte from $2001
89A9- 8D 01 20   STA $2001
89AC- A9 3C      LDA #$3C   <- this is the byte from $2002
89AE- 8D 02 20   STA $2002
89B1- 4C 00 20   JMP $2000
etc.
*2001:A4 89     <- the address of the patch ($89A4)
*BSAVE SHELL.SYSTEM,TSYS,A$2000,L$69B4

The new version of the shell is 16 ($10) bytes longer than the original.  If
your copy of SHELL.SYSTEM was a different length, you will have to adjust the
saved length accordingly.

DISCLAIMER: This patch worked for me, but I make no guarantee that it will for
you.  I will not accept any responsibility for lost data, programs, etc. as a
result of this patch.  Use it at your own risk!

Prior to using this patch, I found Aztec was crashing after every four compiles
or twelve links.  Since I added this patch, Aztec hasn't crashed on me.
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