De-compiler

[Sim085]

Hello, is there a C decompiler for the Amiga? There is a game I wish to decompile in order to see its logic and also just for the fun of it. However I do not know what is the best tool for the job.

[AnimaInCorpore]

I'm afraid there's no such tool.

The best way to understand the logic of a (68k) program is to disassemble it. So assembler knowledge is highly recommended.

Cheers
Sascha

[Sim085]

Originally Posted by AnimaInCorpore

I'm afraid there's no such tool.

The best way to understand the logic of a (68k) program is to disassemble it. So assembler knowledge is highly recommended.

Cheers
Sascha

If you disassemble something then can you make changes and assemble it again?

[AnimaInCorpore]

Originally Posted by Sim085

If you disassemble something then can you make changes and assemble it again?

Well, yes but most likely you have to do some work before.

The best way is trying to rename all the labels with appropriate names like function name or data type, etc. This makes it really easier to understand the code.

Then have a look at the labels and its addresses. Sometimes there are offsets being used in combination with a label so its seems there's something wrong. Then you need to change the label like in the following example from Galaga 88:

MFP_KEY_INTERRUPT_HANDLER:
    movem.l %D0-%D1,-(%A7)

    moveq   #0,%D1
    move.b  L_00E88000+0x2F.l,%D1
    bmi.s   L_0002010E

    move.b  KEY_BIT_TRANSLATION_TABLE(%pc,%D1.w),%D1
    move.w  TRANSLATED_KEY_BITS.l,%D0
    bset    %D1,%D0
    move.w  %D0,TRANSLATED_KEY_BITS.l

    movem.l (%A7)+,%D0-%D1

    rte

L_0002010E:
    move.b  KEY_BIT_TRANSLATION_TABLE-0x80(%pc,%D1.w),%D1
    move.w  TRANSLATED_KEY_BITS.l,%D0
    bclr    %D1,%D0
    move.w  %D0,TRANSLATED_KEY_BITS.l

    movem.l (%A7)+,%D0-%D1

    rte

KEY_BIT_TRANSLATION_TABLE:
    dc.b    0x1F
    dc.b    0x08
    dc.b    0x1F
    dc.b    0x1F
    dc.b    0x1F
    dc.b    0x1F
[...]

Please note the red calculated address which has been an own label after the disassembling process. The label address was 128 bytes below the table pointing to a code address which was strange. Leaving this label unchanged is fatal when you add code within those 128 bytes so you need to change it to a label with offset.

However, there are some more requirements like having a non-modifying code but I think this gives you a good idea on the problems you might face. At least this is what I've learned while porting Galaga 88 and Pacmania from the X68000.

Cheers
Sascha