Path: utzoo!mnetor!tmsoft!torsqnt!jarvis.csri.toronto.edu!rutgers!ucsd!ucbvax!sysc.salford.ac.UK!R.D.Chafer
From: R.D.Chafer@sysc.salford.ac.UK
Newsgroups: comp.sys.atari.st
Subject: Self Modifying code
Message-ID: <15.Nov.89.16:38:32.A10297@UK.AC.SALF.C>
Date: 15 Nov 89 16:38:32 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 44

>Date: 13 Nov 89 01:12:27 GMT
>From: psuvm!sml108@psuvax1.cs.psu.edu
>Subject: Self-Modifying Code
>
>Hi, I am writing an assembly language routine which modifies its own code in
>a tight loop in order to avoid having to do a decision statement at every
>iteration.  Unfortunately, whatever code I am inserting is screwing things up
>royally, and although I have checked it fairly throughly, I cannot figure out
>what is going on.  Question:  Is there something screwy about executable and
>object files that would disallow self modifying.  The block that gets modified
>is this:
>
>         lsr.w   d3
>         bne     cont
>         add.l   #8,a0
>         move.w  #$8000,d3
>  cont:  nop
>
>Since branching is relative, one would think it would work, and a dump of
>the object file indicates this is so.    HELP !!!!
>
>Scott Le Grand
 
I don't know if this has been answered, but could the 68000's instruction
prefetch be causing the problem (The 68010 has a bigger prefetch I believe
which would probably cause problems). Instruction prefetch on a 68000 or
68010 is one good reason NOT to write self modifying code.
 
Robert Chafer
 
 
=========================================================================
From:  Robert Chafer
 
    Computing Centre             Telephone: +44 61 736 5843 x 672 or x7328,
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