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From: martin@cs.uchicago.edu (Charles Martin)
Newsgroups: comp.sys.mac.programmer
Subject: Re: inits & pascal & variables
Message-ID: <1991Jan31.215826.15554@midway.uchicago.edu>
Date: 31 Jan 91 21:58:26 GMT
References: <1652@n-kulcs.cs.kuleuven.ac.be>
Sender: news@midway.uchicago.edu (News Administrator)
Reply-To: martin@cs.uchicago.edu (Charles Martin)
Organization: University of Chicago
Lines: 45
In-Reply-To: kpottie@icarus.cs.kuleuven.ac.be (Pottie Karl)

kpottie@icarus (Pottie Karl) writes:
>I recently found this file for writing simple inits in Pascal. It worked
>fine till I tried to use variables

How odd, to see one's own code reappear after many months... that bit
of code I wrote before is buggy.  Basically, the offsets were
incorrect, which ended up overwriting the instructions that put the
address of the code into A0 and ToolScratch (which you wouldn't miss
in Pascal).  Probably also overwrote the jump to main, which is why
you crash as soon as you do anything exciting.  Here's another try.

Note: this is meant to be used with THINK Pascal code resources.
THINK Pascal adds a default header that we will mangle to make our
head patch.  All we do is push the real trap address on the stack
before entering our code segment, so the RTS puts us in the real trap
with the same arguments.

Modulo error checking, N...TrapAddress, and etc., here is the installer:

unit install;
interface
procedure main;
implementation
const trap = <...>;
type
    code_hdl = ^code_ptr;
    code_ptr = ^code_t;
    code_t = array [0..0] of integer;
procedure main;
var code: code_hdl;
    addr: longint;
begin
    code := code_hdl (Get1Resource ('CODE',128));
    DetachResource (Handle(code));
    addr := GetTrapAddress (trap);
    code^^ [5] := $2F3C; { MOVE.L #<addr>,-(A7) }
    code^^ [6] := HiWord (addr);
    code^^ [7] := LoWord (addr);
    SetTrapAddress (longint(code^)+10, trap)
end;
end.

Hope this helps!

Charles Martin // martin@cs.uchicago.edu