Self Modifying code

[R.D.C...@sysc.salford.ac.uk]

>Date: 13 Nov 89 01:12:27 GMT
>From: psuvm!sml...@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

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